ED Masters Dissertation by Pattnaik Mohanty

Effectiveness of Natural Ventilation in Tall Residential Building in Tropical Climate - A critical analysis of Kanchanjunga Apartment, Mumbai; MBF Tower, Penang; 1- Moulmein Rise, Singapore and Design a conceptual naturally ventilated tall residential tower in Tropical Climate -

By Pattnaik Ompriya Mohanty A dissertation submitted in partial fulfillment of the regulations for the Degree of Masters in Architecture (Environmental Design) in the University of Nottingham, 2010. i

Acknowledgement: I would like to give my sincere obligation to “Lord Jagannath” & many thanks and regards to my supervisor Professor Michael Stacey, for the inspiration and for his continuous support during the entire duration of my dissertation. I am also very grateful to Professor Brian Ford, Professor David Etheridge, and Associate Professor Guohui Gan, for their guidance and personal assistance. I would like to thanks my tutors in ‘The School of the Built Environment’, particularly Professor Benson Lau, my personal tutor Dr. Lucélia Taranto Rodrigues and Dr. Philip Oldfield who are sincerely dedicated to the enhancement of the students ‘educational experience. I would like to give my special thanks to Liu Pei-Chun and Dr. Naghman Khan for providing me with useful information. I am also thankful to ‘WOHA Architects’ for responding to my numerous e-mails and for providing me with the information about the Moulmein Rise Tower, Singapore. Sincere thanks to my parents, brother, brother in law & sister for their love, encouragement and continuous support. Also I wish to express my appreciation to my friends Luca & Apeksha to help me to do CFD whenever required. Many thanks to my friend Tushar, for his advice and assistance throughout the year. Finally I would like to thank my all the friends and well-wishers.

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Abstract: Natural Ventilation is the form of ventilating system where natural forces of wind and buoyancy are utilized for the supply of fresh air unlike fan-forced or mechanical ventilation. There is a lack of rigorous studies on implications of more intuitive approach towards passive cooling technique in tall residential building in tropical climate. The situation is more vulnerable in the case of tall buildings as people are getting more affluent; air conditioning is becoming more popular to achieve desired thermal comfort. Moreover, natural ventilation in tall building to achieve acceptable thermal comfort and low energy consumption is not an easy task. However, the interconnectedness of various design issues is addressed at one time rather individually to achieve wind induced natural ventilation in buildings. Since wind-driven natural ventilation works best in tropical climate, in this dissertation, the study is carried out by analyzing relevant case studies. In addition, the effectiveness of natural ventilation performance is interpreted in relation to various survey and testing results and adaptive thermal comfort theory using â&#x20AC;&#x153;Building bioclimatic Chartâ&#x20AC;? for developing and developed country. The aim is to analyze the climate interactive design based on natural ventilation performance in different tropical cities and cultural context by taking Kanchanjunga apartment, Mumbai, India by Charles Correa; MBF Tower, Penang, Malaysia by Ken Yeang and 1 Moulmein Rise, Singapore by WOHA Architects. Using simulation based programs like CFD (Gambit & fluent) and TAS, it is found that the residents are naturally acclimatized to the local climate conditions and the effectiveness of natural ventilation in tall building is not merely dependent on wind force but also the strong correlation between the thermal comfort perception and wind sensation which reveals that design considerations that are more critical should be given to the building layout, orientation to prevailing wind with less exposure to solar radiation and window positioning & opening area of the building design with respect to its climatic conditions. This can create the preferred higher indoor airflow and thus enhance the thermal comfort of the residents. Furthermore, this dissertation also concludes with a conceptual tall residential building by mapping solar radiation and wind speed on facades using programs like Rhinoceros and Geco (Grasshopper & Ecotect), which can rely on wind induced natural ventilation in tropical climate.

Table of Contents 1

Introduction .................................................. Error! Bookmark not defined. 1.1

Motivation of Research: ....................................................... Error! Bookmark not defined.

1.2

Ventilation: ........................................................................... Error! Bookmark not defined.

1.3

Natural ventilation: ............................................................... Error! Bookmark not defined.

1.3.1

Need of Natural Ventilation .......................................... Error! Bookmark not defined.

1.3.2

Effectiveness of Natural Ventilation in different climatic zonesError! Bookmark not defined.

1.4

1.4.1

Natural Ventilation in Tall Office Building: ................. Error! Bookmark not defined.

1.4.2

Natural Ventilation in Tall Residential Building: ......... Error! Bookmark not defined.

1.5

Natural Ventilation in Tropical Climate: .............................. Error! Bookmark not defined.

Aim and objective ................................................................. Error! Bookmark not defined.

1.5.1

Research Questions ....................................................... Error! Bookmark not defined.

1.5.2

Focus ............................................................................. Error! Bookmark not defined.

1.5.3

Structure of the thesis .................................................... Error! Bookmark not defined.

1.5.4

Outline of Dissertation .................................................. Error! Bookmark not defined.

1.6

References: ........................................................................... Error! Bookmark not defined.

1.7

Bibliography ......................................................................... Error! Bookmark not defined.

Literature Review ......................................... Error! Bookmark not defined. 2.1

Introduction .......................................................................... Error! Bookmark not defined.

2.1.1

Passive and active means of ventilation ........................ Error! Bookmark not defined.

2.1.2

Ventilation functions and requirements ........................ Error! Bookmark not defined.

2.1.3

Benefits of Natural Ventilation ..................................... Error! Bookmark not defined.

2.1.4

Historical overview on the development of natural ventilation in tall buildingsError! Bookmark not defi

2.2

Natural Ventilation Strategies............................................... Error! Bookmark not defined.

2.2.1

The Physical mechanism (the driving forces for natural ventilation) in tall buildingError! Bookmark not

2.2.2

Natural ventilation principles ........................................ Error! Bookmark not defined.

2.3

Adaptive thermal comfort in Tropical climate ..................... Error! Bookmark not defined.

2.3.1

Heat discomfort and adaptive thermal comfort ............. Error! Bookmark not defined.

2.3.2

Thermal requirements in Tropics .................................. Error! Bookmark not defined.

2.4

Potential, Challenges and risks associated with natural ventilation in Tall buildingError! Bookmark not defin

2.5

Basic Principles and design factors affecting natural ventilation in tropical climateError! Bookmark not defin

2.5.1

Comfort ventilation ....................................................... Error! Bookmark not defined.

2.5.2

Applicability of comfort ventilation ............................. Error! Bookmark not defined.

2.5.3

Enhancement of daytime comfort ventilation ............... Error! Bookmark not defined. v

2.5.4

Continuous ventilation with passive solar use of thermal massError! Bookmark not defined.

2.5.5

Design factors affecting natural ventilation .................. Error! Bookmark not defined.

2.6

Selection of comparative study............................................. Error! Bookmark not defined.

2.7

Analysis of earlier studies simulated in TAS and CFD ........ Error! Bookmark not defined.

2.8

Concluding Summary ........................................................... Error! Bookmark not defined.

2.9

References: ........................................................................... Error! Bookmark not defined.

2.10

Bibliography ......................................................................... Error! Bookmark not defined.

Methodology.................................................. Error! Bookmark not defined. 3.1

Introduction .......................................................................... Error! Bookmark not defined.

3.2

Process: ................................................................................. Error! Bookmark not defined.

3.3

Qualitative Analysis: ............................................................ Error! Bookmark not defined.

3.3.1

Case- 1 (Kanchanjunga Apartment, Mumbai) .............. Error! Bookmark not defined.

3.3.2

Case- 2 (Moulmein Rise, Singapore.) ........................... Error! Bookmark not defined.

3.4

Quantitative analysis............................................................. Error! Bookmark not defined.

3.4.1

Quantitative analysis through TAS ............................... Error! Bookmark not defined.

3.4.2

Quantitative analysis through CFD ............................... Error! Bookmark not defined.

3.5

Reference .............................................................................. Error! Bookmark not defined.

4 Critical Analysis of Case-studies, Results and Discussion: .............. Error! Bookmark not defined. 4.1

Case study 1 - Kanchenjunga apartment, Mumbai, India ..... Error! Bookmark not defined.

4.1.1

Key information ............................................................ Error! Bookmark not defined.

4.1.2

Introduction ................................................................... Error! Bookmark not defined.

4.1.3

Site micro climate analysis ........................................... Error! Bookmark not defined.

4.1.3.3 Precipitation .................................................................. Error! Bookmark not defined. 4.1.4

Built form and orientation ............................................. Error! Bookmark not defined.

4.1.5

Spatial Configuration .................................................... Error! Bookmark not defined.

4.1.6

Natural Ventilation Strategy ......................................... Error! Bookmark not defined.

4.1.7

Qualitative Analysis ...................................................... Error! Bookmark not defined.

4.1.8

Quantitative Analysis .................................................... Error! Bookmark not defined.

4.1.9

Concluding Summary ................................................... Error! Bookmark not defined.

4.2

Case study 3 - MBF Tower, Penang, Malaysia .................... Error! Bookmark not defined.

4.2.1

Introduction ................................................................... Error! Bookmark not defined.

4.2.2

Site micro climate analysis ........................................... Error! Bookmark not defined.

4.2.2.1 Temperature variation: .................................................. Error! Bookmark not defined. vi

4.2.3

Built Form and Orientation ........................................... Error! Bookmark not defined.

4.2.4

Natural Ventilation Strategy ......................................... Error! Bookmark not defined.

4.2.5

Quantitative Analysis .................................................... Error! Bookmark not defined.

4.2.6

Concluding Summary ................................................... Error! Bookmark not defined.

4.3

Case study 3- Moulmein Rise, Singapore............................. Error! Bookmark not defined.

4.3.1

Introduction ................................................................... Error! Bookmark not defined.

4.3.2

Site micro climate analysis ........................................... Error! Bookmark not defined.

4.3.3

Built form and orientation ............................................. Error! Bookmark not defined.

4.3.4

Spatial Configuration .................................................... Error! Bookmark not defined.

4.3.5

Natural Ventilation Strategy ......................................... Error! Bookmark not defined.

4.3.6

Qualitative Analysis ...................................................... Error! Bookmark not defined.

4.3.7

Quantitative Analysis .................................................... Error! Bookmark not defined.

4.3.8

Concluding Summary ................................................... Error! Bookmark not defined.

4.4

Concluding Summary of the chapter: ................................... Error! Bookmark not defined.

4.5

Reference: ............................................................................. Error! Bookmark not defined.

Comparative Analysis & Discussion:........... Error! Bookmark not defined. 5.1

Overviewing the Results:...................................................... Error! Bookmark not defined.

5.2

Critical Approach: ................................................................ Error! Bookmark not defined.

5.3

Potential of the Process:........................................................ Error! Bookmark not defined.

5.3.1

Answer to research questions ........................................ Error! Bookmark not defined.

5.4

Future scope of the Research: ............................................... Error! Bookmark not defined.

5.5

References: ........................................................................... Error! Bookmark not defined.

Conclusion ..................................................... Error! Bookmark not defined. 6.1

Overview .............................................................................. Error! Bookmark not defined.

6.2

Basic parameters ................................................................... Error! Bookmark not defined.

6.3

Inspiration ............................................................................. Error! Bookmark not defined.

6.3.1

Control on intense solar gain and high wind force ....... Error! Bookmark not defined.

6.3.2

Control on high wind force. .......................................... Error! Bookmark not defined.

6.3.3

Vertical scape (a living wall) ........................................ Error! Bookmark not defined.

6.4

Conceptual design................................................................. Error! Bookmark not defined.

6.5

Reference : ............................................................................ Error! Bookmark not defined.

Appendix ....................................................... Error! Bookmark not defined.

vii

Table of Illustrations: Figure 1.1 1, Rate of Urbanization in the tropics (Source: Adapted from Emmanuel, 2005:6) 1 Figure 1.1 2, Annual energy consumption by end use in the tropics, Source: Nyuk Hien Wong, 2009

Figure 1.1 3, Graph showing contribution of various greenhouse gases to global warming, Source http://www.ace.mmu.ac.uk

Figure 1.3 1, Schematic representation of various approaches for expressing ventilation needs. (Source: Peter Wouters, Christophe Delmotte, N. Heijmans, Building ventilation, p 283).

Figure 1.4 1, 1: Plaza IBM (left) and Menara Mesiniaga (right) The peripheral service cores tested are single sided East, West and two double- sided core positions.( Source: [18])12 Figure 1.5 1, Showing five factors affecting Natural ventilation. (Source: Abdul Razak Sapian modified by author [19])

Figure 2.1 1, The passive and active building models showing the effects of energy consumption for the three types of climate responses strategies available: - Site and climate related, building form and fabric, mechanical plant and services. Ref: Climate responsive design, Richard Hyde) 22 Figure 2.1 2, Combined evolution of pollution level and energy demand, (Source: Allard, 1998, Natural ventilation in buildings; A design handbook p. 4)

Figure 2.1 3, Home Insurance Building Chicago, 1885, (Source: Rise of the New York skyscraper, 1865-1913 Carl W Condit) 29 Figure 2.1 4, Bird’s-eye view of Chicago Board of Trade district (1898) showing the ‘Chicago Quarter Block’ and the central open courts. Source: (Chicago's 'loop' in 1893, as seen by Rand McNally's artists). Figure

2.1

29 LA

Salle

street,

North

Adams

Street,

Chicago

(Source:

http://chicagopc.info/Chicago%20postcards/) 29 Figure 2.1 6: The Wainwright Building (1981) second floor plan and exterior view. LHS: (Source:

Arnold,

Sullivanesque.htm

1999a).

RHS:

http://www.essential-architecture.com/STYLE/STY-

viii

Figure 2.1 7: The Strauss Building Fourteenth floor plan and exterior view. LHS (Source: Arnold, 1999a), RHS; http;//67.73.47/public/zecom/museum/ghostowers/index.htm Figure

2.1

Equitable

building

showing

H-shaped

plan

(Source:

http;//67.73.47/public/zecom/museum/ghostowers/index.htm 31 Figure 2.1 9, Marshall Field and Company Store, Chicago, 1914, Daniel Burnham & Co. (Source: http;//67.73.47/public/zecom/museum/ghostowers/index.htm) 31 Figure below demonstrates cross-section of one such design by Italian designer and architect from Portland, Ore., Pietro Belluschi (Figure 2.1 10) 32 Figure 2.1 11, LHS: Milan Building (First fully air conditioning used) RHS: Fully glazed curtain wall,

Lake

shore

Drive

Apartment,

Multifamily

housing,

1951

(Source:

http;//67.73.47/public/zecom/museum/ghostowers/index.htm) 32 Figure 2.1 12, Belluschi.s 1943 design study for an office building in .194X (Source: ASHRAE JOURNAL, JULY 1999By David Arnold, F.R.Eng. Member ASHRAE

Figure 2.2 1, Schematic distribution of pressure around a building, based on result by Irminger and Nokkentved. (Source: Givoni, 1976, p 286)

Figure 2.2 2, Thermal buoyancy in a space with two openings. (Source: Kleiven 2003)

Figure 2.2 3, Single sided ventilation. Source: Environmental Design Guide 36 Figure 2.2 4, Double sided ventilation. (Source: Environmental Design Guide)

Figure 2.2 5, Internal air speeds in models with vertical projections of varying depths, compared with values in models without projection. Window width is 1/3 of wall width. Source (Givoni, 1976) 38 Figure 2.2 6, Cross ventilation with central Atrium. Source: Environmental Design Guide

Figure 2.2 7, LHS: Diagrammatic plan showing perimeter conservatories and central core. RHS: Swiss re Tower floor plan, London (Source: Foster & Partners) Figure

2.2

Vertical

wing-walls

protruding

from the

40 Southwest

elevations.(Source: Left (Richards, 2001); Right (Powell, 1999)

Figure 2.2 9 Seasonal strategy for building with wind scoop [9]

and

Northeast

Figure 2.2 10, showing stack ventilation, (Source: Environmental Design Guide) Figure

2.3

showing

world

map

with

Tropical

region

http://commons.wikimedia.org/wiki/File:Koppen_classification_worldmap_A.png

(Source: 43

Figure 2.3 2 Bioclimatic chart modified for hot humid climates (adapted from Olgyay following Jitkhajornwanich), Source: Torwong Chenvidyakarn 45 Figure 2.3 3, the comfort temperature of naturally ventilated buildings in Hong Kong, (Source: Pei-chun (Ingrid) Liu, 2010)

Figure 2.3 4, Psychrometric chart showing boundary of different passive cooling approach for Hot developing Countries (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 2.3 5 Psychrometric chart showing boundary of different passive cooling approach for Developed Countries (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 2.3 6,shows the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved by natural ventilation in day, with indoor air speed of 0.25 and 2 m/s for Hot developing countries. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.) 48 Figure 2.3 7, shows the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved by natural ventilation in day, with indoor air speed of 0.25 and 2 m/s for developed countries. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 2.3 8, Air speeds yelding E/Emax ratios 0.1, 0.2 and 0.3 of resting people at different air temperature and vapour pressure. (Source: Givoni, 1976)

Figure 2.4 1a Wind Speed near ground level in front of a high rise building is increased, Givoni, 1998) 49 Figure 2.4 2, Variations in air velocity according to thr ground roughness (Source: Boutet, 1987) 50 Figure 2.4 3, Different sizes of openings adjoining the atrium at each level (Source: Ford and Etheridge, 2008, modified by Author) 51

Figure 2.4 4, Illustration of segmentation of tall building. LHS: Segmented (MBF Tower, Penang), RHS: Unsegmented (1 Moulmein Rise, Singapore). (Source: Author)

Under still air, the simplest strategy to improve comfort is day time ventilation by providing high indoor airspeed. Figure 2.5 1, 7 show the boundaries within which indoor comfort can be achieved by daytime ventilation with a very light breeze about 2m/s (Givoni 1976, 1998).

Figure 2.5 2, Moulmein Rise “Monsoon window” detail inspired from vernacular design (Source: Tim Giffith)

Figure 2.5 3, Effect of sub-division of internal space on distribution of internal air speeds. (Source: Givoni, 1976) 56 Figure 2.5 4, Flow pattern in models with different patterns of internal sub-division.(Source: Givoni,1976) 56 Figure 2.6 1, Location of Kanchanjunga Apt. Mumbai (Source: Google map) 58 Figure 2.6 2, Location of MBF Tower, Penang (Source: Google map) 58 Figure 2.6 3, Moulmein Rise, Singapore. Mumbai (Source: Google map)

Figure 2.6 4, Site plan (Source: Hakki Can Özkan, 2009 modified by Author) 58 Figure 2.6 5, Site Plan, (Source: Source: T. R. Hamzah and Yeang: Ecology of the Sky) Figure 2.6 6, Site Plan. (Source: WOHA Architects)

Figure 2.6 7, view of Kanchanjunga Apartment (Source: CTBUH) Figure 2.6 8, view of MBF Tower (Source: Jeremy Lee)

Figure 2.6 9, view of 1 Moulmein Rise (Source: WOHA Architects) 58 Figure 3.1 1, Showing typical section and yearly wind direction LHS: Kanchanjunga Apt, Mumbai, Centre: MBF Tower, Penang RHS: Moulmein Rise, Singapore (Source: Ecotect, Modified by Author) 69 Figure 3.3 1, Showing Section of Kanchanjunga (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 3.3 2, Different Types of flats in Kanchanjunga Apartment Mumbai (Source: Hakki Can Özkan, 2009 modified by Author)

71 xi

Figure 3.4 1, TAS model of Kanchanjanga Apartment, Mumbai (Source: Author) Figure 3.4 2, CFD testing: 3D model of Kanchanjunga (Source: Author)

Figure 3.4 3, Showing CFD model of Kanchanjunga Apt., Mumbai (Source: Author) 83 Figure 3.4 4, Showing CFD model of MBF Tower, Penang (Source: Author) 83 Figure 3.4 5, Showing CFD model of Moulmein Rise, Singapore (Source: Author)

Figure 3.4 6 Gambit model showing boundary conditions given for one of the tower. (Source: Author)

Figure 3.4 7, showing boundary conditions used for all simulations (Source: Author) 84 Figure 3.4 8, CFD graph showing obtained scaled residuals for one of simulation, (Source: Author)

Figure 3.4 9, Showing CFD model of Kanchanjunga Apartment.Type A plan, (Source: Author) 87 Figure 4.1 1, Kanchanjunga Apt. Mumbai (Source: CTBUH Mumbai, 2010) 89 Figure 4.1 2, Showing the skyline of the Mumbai (Source: unknown ) 90 Figure 4.1 3, showing location of Kanchanjunga Apt. with respect to Arabian Sea.

Figure 4.1 4, showing Average Temp (Source: Ecotect modified by Author) 91 Figure 4.1 5, Showing LHS: WBT and DBT variation. RHS: Solar Radiation (Source: climate consultant Modified by Author)

Figure 4.1 6, Showing Avg. Temp & Rel. Humidity (Source: Ecotect and Modified by Author) 92 Figure 4.1 7, Showing Rainfall (Source: http://www.windfinder.com/windstats, Modified by Author)

Figure 4.1 8, showing Pre-dominant Prevailing wind directions in summer months. (Source: Ecotect weather tool modified by Author)

Figure 4.1 9, showing yearly wind directions. (Source: Ecotect weather tool modified by Author) 93

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figure 4.1 10, Psychrometric chart showing the boundaries of outdoor temperature and humidity wi4.1 11indoor air speed of 0.25 and 2 m/s for Mumbai, (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.) 94 Figure 4.1 12, Sun Path over Kanchenjunga Apt. (Source: Ecotect weather tool Modified by Author)

Figure 4.1 13, Showing LHS: Winter Solstice, Center: Equinox and RHS: Summer Solstice sun path (Source: Ecotect and Modified by Author)

Figure 4.1 14, Sectional View. (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 4.1 15, Typical Floor plan and Views of individual Bungalows of the Apartment (Source: Hakki Can Özkan, 2009 modified by Author) 96 Figure 4.1 16, (Source: Hakki Can Özkan , 2009 modified by Author) 97 Figure 4.1 17, Showing structural system (Source: (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 4.1 18, View from Terrace Garden (Source: Charles Correa, 1987, Modified by Author 97 Figure 4.1 19, showing South, West, and East & North Elevation (Source: Hakki Can Özkan, 2009, modified by Author)

Figure 4.1 20, Section showing wind induced cross ventilation in different type of flats at each level. (Source: Author) 98 Figure 4.1 21, showing ventilation strategies for different types of Flats, (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 4.1 22, Design features and elements help to enhance cross ventilation. (Source: CTBUH Mumbai, 2010) 100 Figure 4.1 23, Occupant’s survey Results, Source: Author

101

Figure 4.1 24, LHS: CFD Testing of block plan with SW wind & RHS: with NW Wind (Source: Author)

103

Figure 4.1 25, CFD Testing of block plan (Source: Author)

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104

Figure 4.1 26, Type A Lower floor plan, Source Author

105

Figure 4.1 27, CFD Testing of Type A, lower floor showing the velocity vector and static pressure, (Source: Author)

105

Figure 4.1 28, CFD Testing of Type A, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

106

Figure 4.1 29: CFD Testing of Type A, Upper floor showing the velocity vector and static pressure, (Source: Author)

106

Figure 4.1 30, CFD Testing of Type A, Upper floor showing path lines (airflow pattern in the flat) (Source: Author) 107 Figure 4.1 31, RECOMMENDED VENTILATED RATES FOR FRESH AIR, Source: Natural ventilation in non-domestic buildings-Applications Manual AM10, 2005, CIBSE

107

Assuming the ventilation rate as 100 l/s per person. (Refer figure 4.1 32 and Section 2.1.2 and table 2.1)

107

Figure 4.1 33 CFD Testing of Type B, lower floor showing the velocity vector and static pressure, (Source: Author)

108

Figure 4.1 34, CFD Testing of Type B, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

109

Figure 4.1 35, CFD Testing of Type B, Upper floor showing the velocity vector and static pressure, (Source: Author)

109

Figure 4.1 36, CFD Testing of Type B, Upper floor showing path lines (airflow pattern in the flat) (Source: Author)

110

Figure 4.1 37, CFD Testing of Type C, lower floor showing the velocity vector and static pressure, (Source: Author)

110

Figure 4.1 38, CFD Testing of Type C, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

111

Figure 4.1 39, CFD Testing of Type C, Upper floor showing the velocity vector and static pressure, (Source: Author)

111

xiv

Figure 4.1 40, CFD Testing of Type C, Upper floor showing path lines (airflow pattern in the flat) (Source: Author)

112

Figure 4.1 41, CFD Testing of Type D, lower floor showing the velocity vector, (Source: Author) 112 Figure 4.1 42, CFD Testing of Type D, lower floor showing static pressure & path lines (airflow pattern in the flat) (Source: Author)

113

Figure 4.1 43, CFD Testing of Type D, Upper floor showing the velocity vector, (Source: Author) 113 Figure 4.1 44, CFD Testing of Type D, Upper floor showing static pressure & path lines (airflow pattern in the flat) (Source: Author)

114

Figure 4.1 45 Upper figure showing plan with section lines and lower figure showing CFD testing of 3D model of the Tower, (Source: Author) 115 Figure 4.1 46 showing CFD testing of 2D sections of the Tower, (Source: Author) Figure 4.1 47, CFD Testing of Detail section of tower (Source: Author)

116

117

Figure 4.1 48, CFD Testing showing static pressure and path lines (Source: Author) 118 Figure 4.1 49, CFD Testing (Source: Author) 120 Figure 4.1 50, TAS Model of Building (Source: Author)

121

Figure 4.1 51,TAS Model: Lower. Fl. Type A, (Source: Author) Figure 4.1 52, Interior View Of type A (Source: Author)

121

Figure 4.1 53, TAS Model: Upper Fl., Type A, (Source: Author)

121

Figure 4.1 54, 3D model showing different zones selected for simulations. (Source: Author) 122 Figure 4.1 55, View showing double heighted spaces of Type A flat. LHS: Lower Level and RHS: Upper Level. (Source: Author) 122 Figure 4.1 56, Graph showing Temp on Hottest day 95, (Source: Ecotect modified by Author) 122 Figure 4.1 57, 3D- view showing North-east living Room Zone, (Source: Author)

123

Figure 4.1 58, Graph showing Indoor Temp. Variation due to 24 hr. and Night Ventilation. (Source: Author)

123

Figure 4.1 59, Graph showing Indoor Temp. Variation on in North east living room on hottest day 95 (Source: Author)

124

Figure 4.1 60, Graph showing Indoor Temp. Variation due to 24 hr. and Night Ventilation (Source: Author)

125

Figure 4.1 61, Graph showing Indoor Temp. Variation on the hottest day 95 (Source: Author) 126 Figure 4.1 62, Graph showing Indoor Temp. Variation in Northeast room, Comparison between test 5& 3 (Source: Author)

127

Figure 4.1 63, Graph showing Indoor Temp. Variation in North east room, Comparison between test 5& 6 (Source: Author)

128

Figure 4.1 64, Graph showing Temp. Variation in North East living room of different Fl. (Source: Author)

129

Figure 4.1 65, Graph showing variation in air change per hour in different floors (Source: Author) 129 Figure 4.1 66, Graph showing Indoor temp. and RH in N-E living room of 24th Flr.

130

Figure 4.1 67, Graph showing temp difference between N-E living room and S-W living room (Source; Author)

130

Figure 4.1 68, Plan showing N-E and S-W Living room. (Source: Author)

130

Figure 4.1 69, LHS: View showing West Bedroom on Lower fl. and RHS: East bedroom on Upper fl. of 24th Floor flat. (Source: Author) 131 Figure 4.1 70, Graph showing temp. Variation in West bedroom and East Bedroom. (Source: Author)

131

Figure 4.1 71, CFD model showing airflow pattern LHS: Lower Flr, RHS: Upper Flr. 131 Figure 4.1 72, Graph showing Temperature variation in east and west side bedroom of different floors, (Source: Author)

132

Figure 4.1 73, Temperature variation in east and west side bedroom of different floors132

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Figure 4.2 1, Showing MBF Tower, Penang (Source:http://realestate.net.)

134

Figure 4.2 2, showing skyline of the Malaysia (Source: Richards, Ivor)

134

Figure 4.2 3, Architects Design Idea for MBF Tower, (Source: Ken Yeang, 2001)

135

Figure 4.2 4, Showing Location of MBF Tower (Source: Google map)136 Figure 4.2 5, Graph showing monthly Average Temp. (Source: Weather Tool, modified by Author)

136

Figure 4.2 6, WBT and DBT variation, (Source: Climate consultant and Modified by Author) 137 Figure 4.2 7, Showing radiation range (Source: Climate consultant and modified by Author) 137 Figure 4.2 8, Graph showing temperature on Peak hottest day (Source: weather tool and modified by Author)

137

Figure 4.2 9, Graph showing Relative Humidity variation (Source: Weather Tool modified by Author)

138

Figure 4.2 10, Graph showing Avg. Rainfall. (Source: http://insurance.essentialtravel.co.uk/tgasia/malaysia/penang-weather.asp modified by Author)

138

Figure 4.2 11, Showing Yearly pre dominant wind directions. (Source: Ecotect and modified by Author)

138

Figure 4.2 12, Psychrometric chart showing boundary of different passive cooling approach for Penang (Source: Climate consultant, boundary drawn by Author with respect to building bioclimatic chart, Givoni , 1998.) 139 Figure 4.2 13, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Penang, (Source: Climate consultant, boundary drawn by Author with respect to building bioclimatic chart, Givoni , 1998.) 139 Figure 4.2 14, Showing Sun-Path diagram over MBF Tower. (Source: Ecotect and modified by Author)

139

Figure 4.2 15, Showing sun path diagram LHS: winter solstice, Centre: Equinox and RHS: Summer solstice. (Source: Ecotect and modified by Author)

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140

Figure 4.2 16, Figure showing a.: Ground Level Plan 140 Figure 4.2 17, Showing Typical Residential Floor Plan, (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

141

Figure 4.2 18, showing front annd side elevation of the MBF Tower. (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

141

Figure 4.2 19, showing the sky court (Source: Author) 142 Figure 4.2 20, showing Northeast pre dominant wind direction with respect to tower (Source: Author)

142

Figure 4.2 21, Internal Images of MBF Tower (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

143

Figure 4.2 22 , Section showing natural ventilation Strategy in the tower. (Source: Author) Figure 4.2 23, showing velocity vector by X-velocity m/sec. (Source: Author)

143

144

Figure 4.2 24, Defining Boundary Conditions, NĂ&#x2030; wind direction (Source: CFD for ventilation design handouts, Guohui Gan, University of Nottingham)

144

Figure 4.2 25, CFD Testing showing block plan (Source: Author)

145

Figure 4.2 26, CFD Testing (Source: Author) 146 Figure 4.2 27, CFD Testing (Source: Author) 146 Figure 4.2 28, CFD Testing (Source: Author) 147 Figure 4.2 29, RECOMMENDED VENTILATED RATES FOR FRESH AIR, Source: Natural ventilation in non-domestic buildings-Applications Manual AM10, 2005, p 1197, CIBSE Figure 4.2 30, CFD Testing, (Source: Author) 150 Figure 4.2 31, CFD Testing, (Source: Author) 150 Figure 4.2 32, CFD Testing, (Author) 151 Figure 4.2 33, CFD Testing (Source: Author) 152 Figure 4.2 34, Plan showing North Facing Living room (Source: Author)

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154

148

Figure 4.2 35, View showing North facing living room. (Source: Author) Figure 4.2 36, (Source: Author)

155

Figure 4.2 37, (Source: Author)

155

154

Figure 4.2 38 shows indoor temperatures of (ground,12th and 24th floor) are similar to the outdoor temperature during night time.

156

Figure 4.2 39, (Source: Author)

156

Figure 4.2 40, (Source: Author)

157

Figure 4.2 41, showing temperature variation due to change in orientation (Source: Author) 158 Figure 4.2 42, (Source: Author)

158

Figure 4.2 43, Showing indoor wind speed on 7th and 24th Fl. (Source: Author)

159

Figure 4.2 44, showing variation in indoor and outdoor Temperature and RH (Source: Author) 159 Figure 4.2 45, Architects Design Idea for MBF Tower, (Source: Ken Yeang, 2001)

160

Figure 4.2 46,LHS showing N-E prevailing wind and RHS showing S-W prevailing wind

160

Figure 4.2 47, Showing Vertical Landscape (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

161

Figure 4.2 48, Sky Court, Source: Author

161

Figure 4.2 49, showing the central core of the tower (Source: Author) 161 Figure 4.3 1, Moulmein rise, (Source:http://propertyhighlights.blogspot.com) 162 Figure 4.3 2, Sky line of the Singapore, (Source: Dr. Dickie Hertweck)

162

Figure 4.3 3, showing location of Moulmein Rise Building (Source: Google Map)

163

Figure 4.3 4, Showing wind distribution, Sun path diagram, Yearly temperature Graph, Rainfall and Humidity for Singapore, (Source: Ecotect and Modified by Author)

164

Figure 4.3 5, Showing WBT and DBT variation, (Source: Climate consultant and Modified by Author)

165

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Figure 4.3 6, Showing Solar radiation range, (Source: Climate consultant and Modified by Author)

165

Figure 4.3 7, Psychrometric chart showing boundary of different passive cooling approach for Singapore (Source: Climate consultant, boundary drawn by Author with respect to building bioclimatic chart, Givoni , 1998.) 166 Figure 4.3 8, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore, (Source: Climate consultant, boundary drawn by Author with respect to building bioclimatic chart, Givoni , 1998.) 166 Figure 4.3 9, showing yearly wind directions. (Source: Ecotect and modified by Author)

167

figure 4.3 10: Showing sun path diagram LHS: winter solstice, Centre: Equinox and RHS: Summer solstice. (Source: Ecotect and modified by Author)

167

Figure 4.3 11, Annual Sun-path over Singapore, (Source: Ecotect and modified by Author) Figure 4.3 12, showing East Elevation of the Tower. (Source: WOHA Architects)

168

Figure 4.3 13, Typical Floor Plan of Moulmein Rise, (Source: WOHA Architects)

169

168

Figure 4.3 14, Showing, LHS: North Elevation and RHS: South Elevation (Source: WOHA Architects)

169

Figure 4.3 15, showing window with shading device on external facades of the Tower. (Source: WOHA Architects)

170

Figure 4.3 16, showing Monsoon window, (Source:WOHA Architects)

170

Figure 4.3 17, Showing Plan and Section, LHS: Single sided Ventilation, RHS: Cross Ventilation strategies in the Building (Source: WOHA Architects modified by Author)

171

Figure 4.3 18: Design features and elements involve enhancing natural ventilation. (Source: http://www.h88.com.sg/article/Architecture+Feature+-+1+Moulmein+Rise/) 172 Figure 4.3 19, showing the results of the occupant survey (Source: Author)

173

Figure 4.3 20 & 4.3 21,CFD Testing showing velocity vector by X-velocity m/sec due to SW wind (Source: Author) 174

Figure 4.3 22, CFD Testing showing static pressure and path lines (Source: Author) 175 Figure 4.3 23, CFD Testing showing velocity and pressure due to North wind (Source: Author) 176 Figure 4.3 24, CFD Testing showing detail plan (Source: Author)

176

Figure 4.3 25, CFD Testing (Source: Author) 177 Figure 4.3 26, CFD Testing (Source: Author) 178 Figure 4.3 27, CFD Testing of detail section (Source: Author) 179 Figure 4.3 28, CFD Testing (Source: Author) 180 Figure 4.3 29, CFD Testing (Source: Author) 181 Figure 4.3 30, Plan showing the south east living room, (Source: Author)

183

Figure 4.3 31, Temp variation graph for 24 hr. Ventilation (Source: Author) 183 Figure 4.3 32, Temp. variation graph for 24 hr. Ventilation and Night time ventilation (Source: Author)

184

Figure 4.3 33, Temp variation graph for 24 hr. Ventilation and Night time ventilation (Source: Author)

184

Figure 4.3 34, showing temp variation (Source: Author)

185

Figure 4.3 35, Facade of the Tower with sun screen, (Source: WOHA Architects) Figure 4.3 36, Faรงade of the Tower, (Source: WOHA Architects)

186

Figure 4.3 37, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore, (Source: Climate consultant, boundary drawn by Author with respect to building bioclimatic chart, Givoni , 1998.) 187 Figure 4.3 38,Modified Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore according to above analysis and developing country chart. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.) 187 xxi

Figure 4.3 39,CFD Testing showing detail designed section (Source: Author) 188 Figure 4.3 40, CFD Testing (Source: Author) 189 Figure 5.2 1 Showing five factors affecting Natural ventilation. (Source: Abdul Razak Sapian modified by author) [1]

192

Figure 5.3 1showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Mumbai) Source: Author

193

Figure 5.3 2 showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Penang) Source: Author

194

Figure 5.3 3 showing Comparative Temperature variation in living room of 24th fl in three Cities, Source: Author 194 Figure 5.3 4 showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Singapore) Source: Author

194

Figure 5.3 5, LHS Showing Kanchanjunga Apt with NW wind, Center Showing MBF Tower with NE wind & RHS Showing 1 Moulmein Rise with South & SW prevailing wind during peak summer period 195 figure 5.3 6:CFD Testing : LHS Showing Terrace gardens and typical detail section of Kanchanjunga Apt., Center Showing sky courts and typical detail Section of MBF Tower & RHS Showing Block and typical detail section through 1 Moulmein Rise

196

Figure 6.1 1, Residential building model with a void ratio of 0% (with 6 apartments), Source: [3] 198 figure 6.1 2,, Residential building with void ratio of 50% (with 6 apartments), Source: [3]

198

Figure 6.2 1, LHS : the optimum aspect ratio of towers in tropical region, which is 1:3. Centre and RHS: showing Split cores. Source: Author 200 Figure 6.2 2 showing different building forms with less exposed peripheral area to external air, Source: Author 201 figure 6.2 3 showing best building orientation, Source Author 201 Figure 6.2 4 showing void in ground help in free airflow, source Author

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201

figure 6.2 5 shows 100% solar shading requirement in Tropics, Source: Author

202

Figure 6.2 6 , LHS: Sun path over Singapore, Source: Ecotect modified by Author, Central : Airflow around sky courts, Source: Milind, 2007 RHS: Airflow around commerz bank, (Source: Milind, 2007 )

202

Figure 6.2 7, CFD simulation of wind environment around a 30-story high-rise block with a sky garden in the middle [7].

203

Figure 6.2 8, LHS: Internal air speeds in models with vertical projections of varying depths, compared with values in models without projection. Window width is 1/3 of wall width. (Source: Givoni, 1976) RHS: wind wing wall diagram 3, 4, and 5 illustrate the effect of a wing wall on a façade of a building (Source: Yeang, 1999, 2008)

204

Figure 6.3 1, Sino steel Tower, (Source: MAD Architects)

204

figure 6.3 2, LHS Showing Façade pattern developed by mapping solar radiation and wind speed and RHS showing four different façade pattern205 Figure 6.3 3, LHS: Swiss re Tower, London, and RHS: Wind pattern around Aerodynamic Form. (Foster and Partners, 2005)

205

Figure 6.3 4, Showing living wall in 40 storeyed tower, Antelia residence, Mumbai.Source [10] 206 Figure 6.4 1, Showing Total radiation on LHS: Circular form. RHS: Square form for High rise Building: source: (GECO) (Grasshopper + Ecotect), modified by Author

206

Figure 6.4 2, Total radiation on, LHS: Rectangular form. RHS: Elliptical form for High rise Building source: (GECO) (Grasshopper + Ecotect), modified by Author

207

Figure 6.4 3, Elliptical plan and Concave facade generated using Rhinoceros programme. (Source: Author)

207

Figure 6.4 4, Fig. 1 Showing Radiation on SE & SW façade, Fig.2 showing Radiation on East façade, Fig.3 showing Radiation on NE façade: Radiation is calculated on Façade using Rhino (3D Modelling) + GECO (Grasshopper + Ecotect) (Source: Author). 208 Figure 6.4 5, smaller opening at upper part for balanced indoor airflow and high radiation receiving part to minimize solar gain, Source: Author 209

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Figure 6.4 6, Larger openings at lower part for balanced indoor airflow and low radiation receiving part on faรงade, Source: Author

209

Figure 6.4 7, Showing recessed balcony with wing wall, Source: Author

209

figure 6.4 8 showing variable openings used on facade: openings are modeled through mapping the solar radiation on different point by using GECO (Grasshopper + Ecotect) (Source: Author). 209 Figure 6.4 9 Upper figures, showing variable openings with radiation on the tower, lower RHS showing wind flow around and through sky courts, lower LHS showing vertical green with wind flow pattern. (Source: Author) 210

xxiv

List of Tables: Table 2 1, Required Ventilation rate for different functions, (Source, S Willis, 1995) 24 Table 2 2, Wind speeds: Beaufort scale and its effect, (Source: Ken Yeang, 2008,)

Table 2 3, Minimum ventilation rates in breathing zones: (Source: Lewis G Harriman, 2009) 26 Table 2 4: Effect of cross-ventilation on indoor average air velocity

Table 2 5, Average indoor air velocity in rooms with a single exposure with different number & arrangement of the windows. 39 Table 2 6: The usage of AC in house during different time of the day, Source: (N.H. Wong, 2000) 61 Table 2 7: The usage of fan, Source: (N.H. Wong, 2000)

Table 2 8, the usage of bedroom window, Source: (N.H. Wong, 2000) 62 Table 3 1, Terrain coefficients for wind speed Calculation, (Source: CIBSE guide A, 2006)

Table 3 2, Vr calculation for the simulation, (Source: Author) 86 Table 3 3, Vr calculation for the simulation, (Source: Author) 86 Table 4 1 shows Wind Speed and Direction

Table 4 2, Flow rates for the inlets and ACH-1 Achieved

107

Table 4 3, Flow rates for the inlets and ACH-1 Achieved, (Source: Author)

148

Table 4 4, Flow rates for the inlets and ACH Achieved, (Source: Author)

149

Table 4 5, Flow rates for the inlets and ACH Achieved, (Source: Author)

153

Table 6 1 Showing Adverse climatic elements with response strategies

199

Table 6 2, Energy saving measures by Tropical region, (Source: Lloyds Jones, D., 1998

xxv

Introduction

The surviving archeological evidence indicates that man can exist, unassisted, on practically those parts of the world that are at present inhabited, except for the most arid and cold regions. The operative word is ‘existence’; a naked man appears to be a viable organism everywhere on land, except in extreme climates. Only in order to flourish, rather than merely survive, mankind needs more ease and leisure than a bare-fisted and barebacked human. In order to control the immediate environment : to get adaptive thermal comfort by cooling in heat, heating in cold, dryness in rainstorms and to enjoy acoustic and visual privacy , apparently massive and permanent structures has been built by deployment of technical resources and social organization which gave birth to the today’s technical world. (Reyner Banham, 1969, p 18) [1] The words like air pollution, sick building syndrome, global warming, energy crisis that circulate all over the world are blamed on to automobiles in mid twentieth century, on the railways, factory system in nineteenth century. However, the fact that is ignored is that the main root of these evils is the crowding of men in restricted spaces. It was necessary for men, “to come together in cities in order to lead a good life”, (Aristotle). By virtue of coming together, these became places of pollution and congestion and the working and living conditions of men gave birth to the myriad environmental problems, which leads to a change in climate.

Figure 1.1-1, Rate of Urbanization in the tropics (Source: Adapted from Emmanuel, 2005:6)

Climate Change means erratic and extreme weather conditions resulting in heavier rainfall, more snow in some places, longer periods of drought, more storms and hurricanes, and more frequent heat waves. Climate forcing factors are being created by the human and there are few processes impacted by these such as variations in solar radiation, deviations in the Earth’s orbit, mountain building and continental drift and changes in greenhouse gas concentrations. There are varieties of climate change Page | 1

feedbacks that can either amplify or diminish the initial forcing. Some parts of climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcing because of their large mass. Therefore, the climate system can take centuries or longer to respond fully but due to various factors. Change of urban climate is the major after-effect of the rapid urbanization. The threat from globalwarming is that there may not be enough time left for human and other species to protect themselves from its detrimental effects. Through enhanced greenhouse forcing, we may be pushing the climate system towards a point, where climatic responses may become highly non-linear through complex feedback processes, driving the system to a completely different and inhospitable state for human kind.[2].One such example is the emergence of the urban heat island (UHI) effect in the tropical cities which creates hazards of thermal discomfort, air and water pollution. â&#x20AC;&#x153;I only wish that the first really worthwhile discovery of science would be that it recognized that the unmeasurable is what they are really fighting to understand, that the measurable is only the servant of unmeasurable; that everything that man makes must be fundamentally unmeasurableâ&#x20AC;? (Louis kahn)[3]. The author tried to make us understand about the nature, utility of science and technology and their relationship with architecture, but at the same time new technologies and science have invented concepts like air conditioning in building, which has a great impact on energy consumption. The big question is whether we can stop this global warming or not! The answer is always in front of us and it says, there are many ways we individually or together can solve the problem by using less electricity, gas and oil, turning off unnecessary lights and relying on natural ventilation than go for air conditioning, all together by reducing our carbon foot print. Looking back at the past 25 years, there has always been a need of thermal comfort through all the western countries especially Europe. Until 1973, there was no real policy on usage of building energy but after the oil crisis of 1973; those countries became conscious about the scarce amount of energy available. Therefore, main result in terms of building activity is to reduce the global energy consumption used for air conditioning and heating purposes. It is believed that 40% of all energy consumption in the world is done by buildings, from which 50% are only because of air conditioning and study shows that air conditioning systems are the main consumer of energy in tropical climate. Co2 emissions from air conditioning worldwide make a significant contribution of green house gas emission.

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Electr ic C onsum p tion (Mwh ) Area Lighting

Ve ntilation

Msc. Equipme nt

Space Cooling 33 %

4 4% 15 %

Figure 1.1-2, Annual energy consumption by end use in the tropics, Source: Nyuk Hien Wong, 2009

Contribution of Greenhouse Gases to Global Warming Carbon Dioxide

Methane

CFCs

HCFCs and HFCs 12%

Nitrous Oxide

4% 20%

62%

Figure 1.1-3, Graph showing contribution of various greenhouse gases to global warming, Source http://www.ace.mmu.ac.uk

The use of air conditioning is so pervasive that it has resulted in drastic increment of electricity consumption by building industry. The situation is more vulnerable in the case of tall buildings as people are getting more affluent; air conditioning is becoming more popular to achieve desired thermal comfort. Study shows the percentage of households in Singapore who are using air conditioning has increased significantly in the past 20 years from only 7.8% in 1978 to 57.7% in 1998. [4] According to Huang and Lin (2007), in Taiwan, peak power demand and power shortages are due to the cooling load. In a typical office building, on a daily basis, the air-conditioning load accounts for around 45% of the total energy consumption. [5] With the advancement of building technology during the early twentieth century, Skyscrapers established as an alternative to traditional buildings in urban areas, particularly in USA and East Asia. However, older cities like London have only started following the same recently as a potential model for future development. Tall buildings have a number of advantages over traditional forms of low-rise building, particularly for the need of sustainable development. The major advantage is the optimized use of land within cities and it helps in the expansion of urban sprawl to the green-field Page | 3

sites. Another advantage is the reduction in amount of transport required within cities reducing energy consumption. The skyscraper is considered unecological as compared to other building types as it uses one third more amount of energy and material resources to build, maintain and demolish. However, in urban areas because of land scarcity, skyscraper is a viable option and will be continued to be built. Hence, designers should apply thought on reducing its negative environmental impact and making it more ecofriendly rather than just rejecting the concept of skyscrapers (Yeang, 2008). He emphasizes that, indoor spaces of a tall structure need not to be totally enclosed. Instead, spaces should be created where cross ventilation and daylight, are welcome into the building, providing cooling and desired thermal comfort that relates to its tropical location. However, there are specific problems associated with tall buildings and it is not universally agreed that they are the best approach to sustainable urban development. Roaf (2005) argues:

“…the higher the building, the more it costs to run because of the increased need to raise people (lifts), goods and services and also, importantly, because the more exposed the building is to the elements the more it costs to heat and cool.” [6] A recent report to the Corporation of London (2002) states: “The primary design concern for many tall buildings is their operational efficiency rather than their environmental impact. A new balance needs to be struck between these two factors. Inefficient energy use is a particular concern.” [7] Natural ventilation in a tall building to achieve acceptable thermal comfort and low energy consumption is not an easy task, particularly due to those factors associated with human behavior such as when to open windows and close blinds with respect to desired thermal comfort level. The specific context of this investigation, therefore, is the need to reduce the energy consumption of tall buildings through natural ventilation. Mechanical ventilation systems often account for a significant proportion of the total energy consumption and therefore natural ventilation strategies would appear to be a favorable solution to minimize the energy consumption. Until start of twentieth century, natural ventilation was in vogue for high-rise structures and again after almost a century of usage of mechanical means of ventilation using air conditioning, the focus shifted back again to natural ventilation owing to the growing concern for global warming. [8]

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This chapter describes why and how this study has been conducted and the major driving forces for the dissertation. It starts by describing the research on 1.1 Motivation of research, 1.2 Ventilation, 1.3 Need and effectiveness of natural ventilation in different climatic zones, 1.4 Natural Ventilation In Office and residential building in tropics, 1.5 the main aim and objective of the study with explanation of how the research questions will be answered and the chapter ends with an outline of the research.

1.1 Motivation of Research: According to The World Business Council for sustainable Development (WBCSD), building sector use 40% of the world energy with carbon emission more than transport sector. A new study on energy efficiency in building (EEB) states those global building sectors need to rethink its energy consumption and cut it down to 60% by 2050, in order to achieve global climate change targets. According to WBCSD, the building sector must achieve energy efficiency through technological innovations. (Environmental leader, 2009). [9] Insulation, Natural Ventilation, thermal mass and renewable energy sources are the various ways of energy conservation in recent times. This dissertation focuses on Natural ventilation and puts forth few suggestions/tips to incorporate in todayâ&#x20AC;&#x2122;s building industry.

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1.2 Ventilation: For a nonprofessional, the definition of ventilation can be the process of replacing air in one place to provide the same but with better quality. However, for an architect the word air includes moisture, odor, smoke, heat, dust and so on. Ventilation neither means the supply of Oxygen nor to get rid of Carbon dioxide to the occupants in the building. The two primary reasons for ventilation of occupied spaces in buildings are to provide acceptable IAQ (Indoor Air Quality) and based on supply of fresh air and removal of indoor pollution concentration and to provide thermal comfort to the occupants in the building. ISO 7730 states, “Thermal comfort is that condition of mind that expresses satisfaction with the thermal environment”. When the term ‘Ventilation’ is used for a building then there are two options for the same. One is Natural Ventilation and the other is Mechanical Ventilation. If we peep in to the history of Architecture, we will never find the presence of any mechanical system for the purpose of ventilation in Historic Buildings. They were naturally ventilated before the invention of air conditioning in 1902.Natural Ventilation, unlike fan-forced ventilation, uses the natural forces of wind and buoyancy to deliver fresh air in to buildings. However, unlike true air-conditioning, natural ventilation is ineffective at reducing the humidity of incoming air. This places a limit on the application of natural ventilation in humid climates (Andy Walker, 2010). With the invention of machines, the forced way of ventilation (Air conditioning) became a common practice during the 20th century. These technologies have developed in to systems of great complexity with an increasing number of components, need for space and use of electricity.[10],[11] Furthermore, natural ventilation seems to provide an answer to many complaints from the users of air conditioning which appears to be noisy and creation of many health problem like sick building syndrome (SBS). [12], [13], [14]. Despite of all these, many systems do not manage to deliver the desired indoor climate. It also has been claimed that mechanical ventilation systems and their components are significant source of pollution. Mechanical ventilation has been commonly used during the last half of the 20th century. There is more than 240 million of air conditioning that has already been installed worldwide and 15% of worldwide electricity consumption is due to air conditioning and refrigeration [15]. In contrast natural ventilation is preferred by the occupants though it can be easily installed and provides more comfortable and healthier environment if correctly integrated (Liddament, M., 1996).As a strategy to achieve acceptable indoor air quality which is based on the supply of fresh air to the space and dilution of the indoor pollution and odor concentration (Liddament, M., 1990). By using natural ventilation, fluctuations in indoor temperature and air quality may be experienced but satisfactory control and prediction of airflow in natural ventilation can be achieved through various

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design elements. Moreover, the combination of natural and mechanical ventilation named as hybrid ventilation or mixed-mode ventilation systems is evolved in 20th century, which tries to utilize advantages and eliminate drawbacks from both natural and mechanical ventilation process.

1.3 Natural ventilation: Natural ventilation is the intentional flow of outdoor air through an enclosure under the influence of wind and thermal pressure through controllable openings. It can effectively control both temperature and contaminants, particularly in mild climates. Temperature control by natural ventilation is often the only means of providing cooling when mechanical air-conditioning is not available. The arrangement, location and control of ventilation openings should combine the driving forces of wind and temperature to achieve desired ventilation rate and good distribution of fresh air through the building. Natural ventilation is driven by pressure differences across the openings caused by ambient pressure and temperature differences between different openings within a unit. 1.3.1

Need of Natural Ventilation

Natural ventilation has emerged as the cost-effective and energy efficient approach to provide a healthy indoor environment in recent times as compared to high-cost and energy consuming mechanical means. However, owing to the unpredictable nature of its driving forces, it remains less controllable and manageable as compared to mechanical ventilation. Research by Von Pettenkofer (1860) Yaglou

Pollution related to

Limit values of IAQ

human bodies. (CO2

Expression of need

level. (Large variations)

as marker)

concerning ventilation for

Use of Default values

Project specific

acceptable IAQ Pollution related to

Limited on conditions of

other sources

unacceptable IAQ conditions

values

Databases on pollution sources

Research by Fanger

Progress in simulation tools

Allows performance based

for prediction of airflow and

natural and Hybrid ventilation

pollution concentrations

concepts.

Figure 1.3-1, Schematic representation of various approaches for expressing ventilation needs. (Source: Peter Wouters, Christophe Delmotte, N. Heijmans, Building ventilation, p 283).

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Natural ventilation includes many ways in which external air can be used for occupantâ&#x20AC;&#x2122;s benefit of buildings. It can be used to enhance the comfort level of occupants, for a healthy atmosphere and even for building cooling. All these can be achieved from air change (high ACH-1), air movement, airflow rate and wind velocity. Same as ventilation it has two needs, to increase the level of thermal comfort and removal of moisture and contaminated air. Reasonable organization of Natural Ventilation is both energy and cost effective. Research says that the energy consumption can be reduced by almost 50%, if air-conditioning is replaced by natural ventilation as well as it also reduces the emission of carbon dioxide and other harmful gases used in mechanical ventilation system. Meanwhile, it decreases the dependency of those equipment, which use by mechanical ventilation and air-conditioning to ensure a healthy building environment. High-rise building has a much longer vertical distance and much bigger volume when compared to other type of structures. Thus, the organization of natural ventilation in high-rise building is more difficult and challenging. [16] However, looking towards Energy issues, it is wiser to go with green architecture as well as maximum use of renewable energies like solar energy, wind power, daylight etc. These are most efficient ways to save energy. So properly designed and constructed passive buildings offer benefits like year round low energy bills, high economical return on a life cycle cost basis, greater independence in energy crisis in future, greater thermal comfort, less reliance on noisy mechanical systems, reduced cost of maintenance of the building, increased daylight or higher quality lighting system which enhances environmental sanitation as well as reduced energy usage. [17] Keeping the indoor temperature at a constant value with high investment cost and environmental impact is not only one solution rather we can save energy by designing a building which can have a wider range in which it can run freely, in fact many field studies shows that people accept a wider range of temperature in a naturally ventilated building than an air conditioning one (de Dear et al, 1997; Brager and de Dear, 1998, 2000). [15]

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1.3.2

Effectiveness of Natural Ventilation in different climatic zones

“As the location is the most endemic factor, climate provides the designer with a legitimate starting point for architectural expression in the endeavors to design in relation to place, because climate is one of the dominant determents of the local inhabitant’s lifestyle and the landscapes ecology” (Yeang, 1996). Natural ventilation is mainly influenced by macro or micro wind climate and weather. However, architectural factors and design elements are also influential (Cook. 1985). Architectural factors will determine the capability of wind to facilitate Natural Ventilation, which can examine the actual effectiveness of a building design for a particular climate. After consideration of temperature, humidity, solar radiation, vapour pressure and all climatic factors Miller classified the climate in to 4 types (Givoni, 1976, p. 341) and such as: •

Hot climates : Hot dry ( hot deserts), warm-wet (equatorial and tropical marine), hot dry and warm – wet (tropical and continental ) , monsoon

•

Warm temperate climates (western margin type and eastern margin type)

•

Cool temperate climate

•

Cold climate

There are three global wind belts in each hemisphere such as trade wind, the westerlies and the polar winds and the monsoon, which mostly formed due to annual differences in heating of land and sea areas whose effect is the greatest in the region of the Indian Ocean surrounded by south Asia, Australia and east Africa. In all climatic regions of the world when the outdoor temperature is pleasant and the natural ventilation is the most effective and simplest method to provide indoor thermal comfort, even in most hot climate for some specific period when the natural ventilation could be a favorable option to achieve thermal comfort, however in warm-humid climate natural ventilation is an effective cooling strategy year round. (Givoni, 1997 p.88). Based on microclimatic analysis in different climatic conditions it can infer that the effectiveness of natural ventilation varies from place to place and according to the building bioclimatic chart (BBCC) by Givoni, there are many ways by which one can avail thermal comfort in hot climates without air conditioning and the options include: comfort (day time) ventilation, Nocturnal ventilative cooling, radiant cooling, direct and indirect evaporative cooling and earth cooling system. The Building bioclimatic chart is developed by Givoni (1976) to address the problems associated with Olgyay’s chart, which represents boundaries of various passive cooling strategies for developed and hot developing countries, which will be discussed in detail in next chapter.

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Especially in hot – humid climate, humidity comfort limit affects the amount of energy use for dehumidification. The body evaporates & produces more sweat than in lower humidity to obtain the required amount of physiological cooling where the latent heat of vaporization is taken from ambient air instead of from the body when the cooling efficiency of sweat evaporation decreases at high humidity (Givoni and Belding, 1962; Givoni, 1976) .To compensate for the reduced cooling efficiency the evaporation and rate of sweat exceed the need for evaporation cooling. Body feels discomfort and excessive heat due to low humidity and high temperature in desert climate but alleviation can be achieved by lowering the ambient temperature and wind speed at body level by closing the window openings but in contrast to desert climate, in warm-humid climate the discomfort is mainly due to still air conditions and excessive skin wetness. Therefore thermal discomfort results from the combination of heat sensation and sensible perspiration hence the higher indoor air velocity would be an effective solution especially when the air temperature is below 33°c. Study shows people living in hot climate prefer higher temperature and suffer less during hot period than people living in cold climate due to body acclimatization for prevailing thermal environment. High-rise buildings are always subjected to high wind loads, which can be compensated in various ways. They may have some forms of innovative envelope due to its challenges, which are more than low-rise structures, primarily because the potential magnitudes of the driving forces become greater and their relative magnitudes can vary over a wider range while designing the envelope and opening. Segmentation offers the least risky approach for envelope design of non-residential tall buildings (Etheridge and Ford, 2008). Study shows for a high-rise building situated in cool climate, double-skin glass or double glazed unit would be a better solution for natural ventilation where as for tropical climate, the ‘wing-wall’ device used in The Menara UMNO and isolated open block plan in MBF Tower, Penang could be regarded as some of suitable characteristic design elements to enhance the effectiveness of natural ventilation.

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1.4 Natural Ventilation in Tropical Climate: Natural Ventilation is the form of ventilating system where natural forces of wind and buoyancy are utilized for the supply of fresh air unlike fan-forced or mechanical ventilation. The requirement of fresh air is to increase the level of thermal comfort as well as to alleviate odors. The interior temperature can be reduced as low as 5Â° C at an indoor air velocity of 160 FPM (Feet per Minute). However, natural ventilation is ineffective at reducing the humidity of incoming air unlike mechanical ventilation system. Moreover, this stands as a challenge and places a limit on the application of natural ventilation in humid climates. One of the primary requirements for human health and comfort is to maintain the thermal balance between the human body and its environment, which depends on individualâ&#x20AC;&#x2122;s activity, acclimatization, clothing and some environmental factors such as air temperature, humidity and air movement. Main cause of discomfort in humid climate is feeling of skin wetness all year round for which ventilation should ensure sweat evaporation rate sufficient not only to make possible for thermal equilibrium but also to enable sweat evaporation as the sweat emerges from the pores, without accumulating on the skin. Minimum and optimum ventilation requirements depend on type of climate and seasons and maintenance of minimum ventilation rate is more challenging in humid climates. In hot humid region, main function of ventilation is to provide thermal comfort by air movement near the body for fast sweat evaporation. Desired air movement can be achieved by adjusting design details or orienting the building towards the direction of prevailing wind. Moreover, the provision should be made to get indoor air velocity of up to 2m/sec to achieve thermal comfort (Givoni, 1976). However, ventilation in a hot and humid climate is seen as expensive and tricky which costs a considerable amount to clean and dry incoming air to achieve fresh and dehumidified air. 1.4.1

Natural Ventilation in Tall Office Building:

Carrol et al (1982) states that if natural ventilation in office bldg. in USA is properly designed then energy saving could be estimated up to 25% in humid climate up to 50% in warm climates. [15] Similar studies in Taiwan by Huang and Lin (2007) demonstrated that heavy cooling load resulted in peak power shortage on a daily basis; around 45% of the energy consumed in a typical office building is due to air-conditioning. Since the overheating risk of double facades in this climate is evident but it can be minimized with well-designed and well-positioned openings with shading device and by maintaining an optimized space between the facades (Schittich, 2001; Gratia and

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Herde, 2004). Plazas IBM, Menara Mesiniaga are some of influential tall buildings designed with passive cooling strategies for humid climate by Ken Yeang and some points are discussed below.

The impact of core positioning – Plaza IBM Cores if positioned on the periphery of the building then the area of glazed surface can be reduced minimizing solar gain.

Figure 1.4-1, 1: Plaza IBM (left) and Menara Mesiniaga (right) The peripheral service cores tested are single sided East, West and two double- sided core positions.( Source: [18])

Impact of Sky-courts – Sky-courts are located on all floors except 1st, 2nd, 11th and 12th floor modeled as ‘incisions’ into the basic cylindrical model to enhance high indoor airflow. 1.4.2

Natural Ventilation in Tall Residential Building:

Throughout the entire world, major sources of green house gas emissions and major consumer of energy are buildings. In China, 17% of total energy of the country is consumed by the buildings only (Q.Chen, 2001). The percentage of households in Singapore who are using air conditioning has increased significantly in the past 20 years from only 7.8% in 1978 to 57.7% in 1998 (N.H.Wong, 2001). Without any doubts, natural ventilation can be an appropriate solution for these deteriorating problems. In fact, the idea of natural ventilation has already been accepted by occupants in Singapore since 86% of the population is living in Housing Development Board (HDB) flats, which are designed to be naturally ventilated (Wong Nyuk Hien, 2006). Although the concept of natural ventilation is not complicated, it is a challenge to design naturally ventilated buildings since it is difficult to control.

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1.5 Aim and objective In general, there is a lack of rigorous studies on implications of more intuitive approaches towards passive cooling technique in high-rise residential building in tropical climate. The interconnectedness of various design issues should be addressed at one time rather individually to achieve sustainability in a building. â&#x20AC;&#x2DC;It is the very interconnectedness of all these factors which are the essence of the design problems rather than the isolated factors themselvesâ&#x20AC;Śâ&#x20AC;&#x2122; (Lawson, 1990). [18] Minimizing cooling needs in hot humid climate is a significant step towards energy conservation and the appropriate passive design strategy could able to provide desired thermal comfort. Despite the benefits with air conditioning, natural ventilation has experienced a strongly growing interest, even a renaissance, in the late 1990s. Design of ventilation for indoor air quality control and design of ventilation as a natural cooling strategy are two different aspects of natural ventilation design. (Heiselberg, 2004). In general, to minimize the cooling needs, solar and conductive heat gains should be contained, and natural ventilation should be promoted for cooling and humidity removal. Some of the key strategies for minimizing cooling needs involve appropriate orientation and spatial organization, horizontal and vertical Segmentation, appropriate designed envelope and strategically placed opening with shading devices, and appropriate use of materials, colors, textures and vegetation. This study will focus on the method of minimum required fresh airflow rate for ventilated cooling in terms of indoor thermal comfort for a tropical building by evaluating its climate suitability for natural ventilation. There are many ways through which one can have thermal comfort in hot and humid climate without air conditioning and the best option can be identified by studying the building bioclimatic chart (BBCC) by Givoni. The primary objective of this study is to identify the key parameters, which determine whether a high-rise residential building can be entirely dependent on natural ventilation and for how many days it could rely on natural ventilation based on its local climatic condition. The second is to achieve a natural system that could ensure the required flow rates and air flow distribution and to give as much control as possible through various design elements. The last but not the least is to assess whether the natural ventilation strategy adopted for each of the selected case studies could provide some design guidelines for new high-rise residential buildings. The aim is to analyze the climate interactive design based on natural ventilation performance in different tropical cities and cultural context by taking some of key works by Charles Correa, Ken Yeang and WOHA Architects. In addition, this dissertation will develop a conceptual tall residential building, which could rely on wind induced natural ventilation in tropical climate.

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1.5.1

•

Research Questions From the description of the research field, the basic questions of this Dissertation can be formulated as follows:

•

How natural ventilation is depended upon global and local climate?

•

Evaluation of Importance of natural ventilation in tall residential building especially in tropical climate.

•

The importance of adaptive thermal comfort of the occupants to be considered while designing passive cooling strategy for a local climate.

•

How can wind induced natural ventilation be utilized effectively in tall residential building?

•

How do the basic building design parameters affect the natural ventilation in tall residential building typology?

•

How wind microclimate study, especially on the modern cities having tall buildings should be taken in to consideration strongly?

•

How far the occupant survey and study through various simulation tools like CFD and TAS are relevance while analyzing the design issue?

•

How does an aerodynamic form affect wind-induced ventilation in tall building?

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1.5.2

Focus

The scope of this study is limited to residential tall buildings in tropical climate. The endeavor of studying residential tall building is driven by the fact that, the present scenario of urbanization is highly dependent on environmental per formative tower. This research will focus on effectiveness of natural ventilation in tall residential building typology through the selection of several case studies such as MBF Tower, Penang, Malaysia; Kanchanjunga apartment, Mumbai, India and Moulmein rise, Singapore. Though the potential of wind driven natural ventilation depends on the wind speed and direction, natural ventilation takes place mostly through the window opening so the building design for natural ventilation means, to a greater extent, designing with respect to orientation, number, sizes, types and some design elements which totally dependent on designerâ&#x20AC;&#x2122;s decision for making a building purely naturally ventilated. Five main design factors affecting natural ventilation came about from the literature review. They are types of building (Givoni,1998), building forms and configuration(Givoni, 1994; Boutet, 1987; Abdul Majid, 1996; Malsiah, 2001), internal layout plan (Boutet, 1987; Givoni, 1981; Awbi, 1994), building details (Givoni, 1981; Boutet, 1987; Melargno, 1982) and special architectural features (Abdul Majid, 1996; Yeang, 1996; Powell, 1999; McCarthy,1999) as summarized in figure 1.5-1[19] Since wind-driven natural ventilation works best in tropical climate, in this dissertation, the study is carried out by analyzing relevant case studies.

Figure 1.5-1, Showing five factors affecting Natural ventilation. (Source: Abdul Razak Sapian modified by author [19])

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1.5.3

Structure of the thesis

The main aim of the chapter 2 (Literature review) is to analyze the effectiveness of natural ventilation. Hence, it discusses about the passive and active means of ventilation with purposes and benefits. It also explains historical background of tall buildings, evolved in terms of their ventilating systems. As per the aim, it includes various natural ventilation strategies with sub sections discussing the driving forces and principles, the adaptive thermal comfort and basic principles of passive design for tropical climate. It also discusses the potential and challenges associated with natural ventilation in tall buildings in tropics. In addition to that, it will provide some information about the chosen case studies from the tropical region and some relevant concluding summary as a whole from the chapter. In chapter 3, various quantitative (CFD and TAS simulations) and qualitative (Occupant’s survey) methods are applied on the case studies to analyze the performance of the buildings in terms of Natural ventilation. The chapter 4, ‘Critical analysis, results and discussion,’ contain discussions about the results obtained from the applied methods in chapter 3. The chapter 5, ‘Comparative analysis’ compares the performance of the above mentioned 3 different case studies with respect to their locations. Chapter 6, ‘Conclusion’ partially fulfills the main aim of the dissertation.

1.5.4

Outline of Dissertation

Refer Flow Chart:

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1.6 References:

[1] Banham, R. (1969). The architecture of the well tempered environment. London: William Clowes and sons. [2] Aruna Murthy, Vikram Aditya: Teachers guide on Climate Change & Energy,WWF for living planet. http://assets.wwfindia.org. (Accessed: 14.08.2010) [3] Hawkes, D. (2008). The Environmental Imagination, technique and poetics of the architectural environment. Oxon: Taylor & Francis. [4] Singapore Statistic Bureau. Key indicators of the household expenditure survey, 1978â&#x20AC;&#x201C;1998, 2000.) [5] Pei-Chun, Liu1,*, David W. Etheridge1 and Brian Ford , Buoyancy-driven Ventilation in respect of Tall Office Buildings in a Hot and Humid Climate, 1Department of Built Environment, University of Nottingham, UK. [6] Roaf. S. et al, Adapting Buildings and Cities for Climate Change: A 21st Century Survival Guide, Oxford: Architectural Press, 2005, pp.247-248. [7] Pank, W. et al, Tall Buildings and Sustainability, Report to the Corporation of London, London, March 2002, p.5. [8] A performance specification for the energy efficient office of the future, DOEâ&#x20AC;&#x2122;s EOF, Report 30, 1995. [9] Leader, E. (2009, April 27). Building sector Needs to Reduce Energy Use 60% by 2050. Retrieved August Saturday, 2010, from Energy and Environmental News for Business: http://www.environmentalleader.com/2009/04/27/building-sector-needs-to-reduce-energy-use-60-by2050/?

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[10] Søgnen, O. G. et al. (1999) Bygningsnettverkets energistatistikk, årsrapport 1999. NVE’s byggoperatør, Bergen. [11] Tokle, T. et al. (1999) Status for energibruk, energibærere og CO2-utslipp for den norske bygningsmassen. SINTEF Energiforskning rapport (TR A4887), Trondheim. [12] Seppänen, O. and Fisk, J. (2002) Association of ventilation system type with SBS symptoms in office workers, Indoor Air 2002; 12: pp 98-112. [13] Fisk, W. J., Mendell, M. J., Daisey, J. M., Faulkner, D., Hodgson, A. T., Nematollahi, M., and Macher, J. M. (1993) Phase 1 of the California Healthy Building Study: a Summary, Indoor Air 1993; 3: pp 246-254. [14] Zweers, T., Preller, L., Brunekreef, B., and Boleij, J. S. M. (1992) Health and Indoor Climate Complaints of 7043 Office Workers in 61 Buildings in the Netherlands, Indoor Air 1992; 2: pp 127-136. [15] Mat Santamouris, 2006, Building Ventilation, the state of the art. Statistics from IIR 2002, Earthsacn, London. [16] Xu, F., Zhang, G.Q. and Xie, M.J. (2006). The emphasis on Ecological Design for High-rise Buildings, Renewable Energy Resources and a Greener Future. Vol. VIII-4-4, Shenzhen, China. [17] Le Thi Hong Na* and Jin-Ho Park**.Emphasis on Passive Design for Tropical High-rise Housing in Vietnam, [18] Linking bioclimatic theory and environmental performance in its climatic and cultural context – an analysis into the tropical high-rises of Ken Yeang, Puteri Shireen Jahnkassim1 and Kenneth Ip2, PLEA2006 - The 23rd Conference on Passive and Low Energy Architecture, Geneva, Switzerland, 6-8 September 2006.

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[19] Abdul Razak Sapian, The effect of High rise open ground floor to wind flowand Natural Ventilation, (Ph.D.) Department of Architecture Kulliyyah of Architecture & Environmental Design, International Islamic University Malaysia.

1.7 Bibliography N.H. Wong ∗, H. Feriadi, P.Y. Lim, K.W. Tham, C. Sekhar, K.W. Cheong, Thermal comfort evaluation of naturally ventilated public housing in Singapore, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore Received 9 April 2001 By Tommy Kleiven, Natural Ventilation in Buildings, Architectural concepts, consequences and possibilities, Norwegian University of Science and Technology, Faculty of Architecture and Fine Art, Ruba Salib, 2008, Natural Ventilation in High Rise Office Buildings, University of Nottingham, 2008 J. P. Davey May 2006. Natural Ventilation Strategies for Tall Buildings, University of Nottingham, 2006 Natural Ventilation in Buildings by Tony Rofail, Director, WINDTECH Consultants Pty Ltd. NEERG Seminar Thursday 31 August 2006 N.H. Wong ∗, H. Feriadi, P.Y. Lim, K.W. Tham, C. Sekhar, K.W. Cheong, 2002, Thermal comfort evaluation of naturally ventilated public housing in Singapore, , Building and Environment 37 (2002) 1267 – 1277, Allard, F. ( 1998 ). Natural Ventilation in Buildings. London: James and James.

Brian Ford, Rosa Schiand-Phan, Elizabeth Francis. (2010). The Architecture & Engineering of Downdrought Cooling A design source book. UK: PHDC Press. Page | 19

Givoni, B. (1997). Climte considerations in building and urban design. New York: John Wiley & sons, Inc. Nyuk Hien Wong, Yu Chen. (2009). Tropical Urban Heat Islands, Climate, buildings and greenery. Oxon: Taylor & Francis.

Websites: http://www.wbdg.org/resources/naturalventilation.php http://www.ace.mmu.ac.uk/resources/teaching_packs/key_stage_4/climate_change/01p.html http://en.wikipedia.org http://en.wikipedia.org/wiki/Air_conditioning http://www.wbdg.org/resources/naturalventilation.php

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Literature Review

2.1 Introduction “Mainstream contemporary Architecture” has been unable to relate resources with design and consequently with environmental impact. Hence, the foremost aspect of green design is concerned with resource utilization. Energy consumption is a big challenge in present building industry with the increasing concern of ‘Global Warming’. Building sector consumes 40-50% of the total delivered energy in countries like UK and US [1] [2], out of which 70% is consumed in mechanical ventilation, climate control systems, cooling and heating system [3]. The percentage of households in Singapore who are using air conditioning has increased in the past 20 years from only 7.8% in 1978 to 57.7% in 1998(N.H.Wong, 2001). Use of passive environmental solutions instead of mechanical ventilation system can significantly reduce the energy usage. For example, a well-designed naturally ventilated building can consume only a third of the energy consumed by an air-conditioned building [3] along with a compared level of comfort. Design considerations and implementations of passive design principles like adaptation of local climates, better utilization of natural energy resources like wind and thermal buoyancy help to prove comfortable, pleasant and healthier interior environment for the occupants, when compared with the one with mechanical ventilation exclusively with sick building syndrome [4]. 2.1.1 Passive and active means of ventilation ‘Passive System’ often proves heat, light and ventilation free, whereas energy is consumed in ‘Active System’. Both have their own advantages and disadvantages. Being an essential part in the building design, ventilation in the form of ‘Change of Air’ is required to prevent the deterioration and to prevent health problems such as SBS (Sick Building Syndrome).

Passive means of ventilation: The most natural way ‘Passive Stack Ventilation’ (PSV) system, uses the hot air inside the building. As the hot air rises out, it sucks fresh air inside from the surroundings. This is a noise free process and no mechanical devices are included. It reduces the energy requirement of the building. Wind based Ventilation systems are more powerful than the PSV systems. It is implemented in a building in such a way that the external air pressure on one side of the building is lower than the side Page | 21

that facing the wind. Wind is then channeled through the building replacing old rot air and drawing it out towards the low-pressure zone of the leeward side. These are cheap and effective but the quality of air is related to external conditions. They can pull pollution from exteriors. It is difficult to control precisely pollutants. In ideal conditions, Wind and PSV systems are combined together for a full phase natural ventilation system to work round the clock. The Passive Building Model: Here the change in buildingâ&#x20AC;&#x2122;s inside climate is achieved without any use of mechanical equipment. The highest level of achievement could be the internal temperature similar to the external shade temperature. In this case, the characteristic of performance is variable.

Figure 2.1-1, The passive and active building models showing the effects of energy consumption for the three types of climate responses strategies available: - Site and climate related, building form and fabric, mechanical plant and services. Ref: Climate responsive design, Richard Hyde)

Active means of ventilation: Active ventilation system is wasteful, requires harmful chemicals and consumes power to make the air to flow in to the buildings. However, it has the advantage of filterization, control on the level of humidity and the ability to recover some heat from the air to be pumped outside with the use of heat exchangers. These can capture up to 80% of the exhaust ventâ&#x20AC;&#x2122;s heat and distributes it back to the Page | 22

building. However, the energy gained with this recovery is not effective in consumption of power and neither prevents fuel from burning. The Active Building Model: Being opposite to passive model, active model uses plants or mechanical equipments for the internal climate change, other-wisely known as air-conditioning and provides a proper level of thermal comfort. However, this is related with local thermal comfort conditions and energy efficiency. (Refer Appendix 7.1) Without any use of electromechanical systems, the comfort conditions can be improved in Passive mode. Adopting appropriate building configurations and orientation related to the local climate and suitable faĂ§ade design are few examples of design strategies for passive mode. For a building designed with principles of passive system, mixed-mode or productive mode devices should be the last option for creating optimal comfort levels inside. Passive mode not just synchronizes the built formâ&#x20AC;&#x2122;s design considering the local meteorological information, but also optimizes the ambient local energy for improvement in thermal condition. The comfort level remains better during power failure with an optimized passive mode design. [5]

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2.1.2 Ventilation functions and requirements Ventilation serves three distinct functions, such as: Health ventilation in all climatic conditions maintain the quality of the indoor air above a certain minimum level by replacing indoor air, vitiated in the process of living and occupancy, by outdoor fresh air. It is to provide the necessary amount of oxygen for breathing, cooking etc to prevent the unduly high levels of carbon dioxide and odors (Givoni, 1976, p 260) Thermal comfort ventilation is to provide thermal comfort by increasing the heat loss from the human body and preventing discomfort due to feelings of warmth and skin wetness. High speed of indoor air movement in the occupied area would be the best solution to provide thermal comfort.

Table 2-1, Required Ventilation rate for different functions, (Source, S Willis, 1995)

Structural cooling ventilation cools the thermal mass when the indoor temperature is above its outdoor temperature. Air has a very low heat capacity and in an unventilated space, indoor air temperature attains its outdoor surrounding temperature and fluctuates about the average outdoor surface temperature. Comfortable temperature can be achieved by permanent ventilation or night ventilation. The relative importance of each function depends on different climatic conditions in different places in different seasons. The three major functions dependent on different levels of airflow through building in relation to climate:

â&#x20AC;˘

Maintain acceptable indoor air quality by replacing the outdoor fresh air, which is needed for every climate but it is of interest in cold climate and in air conditioning buildings in all climates.

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•

By providing high rate of airspeed over the body, thermal comfort can be achieved by increasing convective heat loss from the body and prevents discomfort from excessively moist skin in a humid climate.

•

Cooling the building mass during night through night ventilation and utilizing it as a “heat sink” during the following daytime in order to achieve thermal comfort, this is mostly for desert climate.

The most important and universal thing is to maintain air quality through ventilation, which depends on the number of people per unit volume in a habitable place, their lifestyle and sensitivity. So a ventilation rate of 0.5 air change per hour (ACH) can be suggested as the minimum health ventilation rate for an occupied residential building. Minimum and optimum ventilation requirements depend on type of climate and seasons. Maintenance of minimum ventilation rate is more challenging in humid climates. In hot humid region, main function of ventilation is to provide thermal comfort by air movement near the body for fast sweat evaporation. Air movement can be achieved by adjusting design details, and the provision should be made to get indoor air velocity of up to 2m/sec to achieve thermal comfort (Givoni, 1976).

Type of wind 8

Wind speed

Effect

Name

More than 24.4

Damage building and tress

7 Wind

17.1 -24.4

speed

People over

blown Strong gale by gusts,

cause damages or

generally

problems

impedes progress,

great

difficulty

with

balance in gusts 6

13.8-17.1

Inconvenience felt

Near gale

when

walking 5

10.7-13.8

Umbrellas with

used Strong breeze.

difficulty,

difficulty to walk Page | 25

Tormenting wind

steadily,

Wind

speed

noise on ears can unpleasant. 4

5.4-10.7

Raise soil

dust,dry Moderate and

and

loose fresh breeze.

paper,

hair

disarranged, force of wind felt on body, limit of agreeable

wind

on land 3

3.3-5.4

Wind

extends Gentle breeze

light flag, hair is disturbed, Acceptable wind speed

clothing flaps 2

1.5-3.3

Wind felt on face

Less than 1.5

Calm,

Light breeze

no Calm

noticeable wind. Table 2-2, Wind speeds: Beaufort scale and its effect, (Source: Ken Yeang, 2008,1) Table 2-3, Minimum ventilation rates in breathing zones: (Source: Lewis G Harriman, 20092)

Residential MUM VENTILATION RATES IN BREATHING ZONES Occupancy Outdoor category

air

per Outdoor

occupant, plus cfm/person L/s.

Air

per unit of

Occupants Combined

floor area.

per

Cfm/ft2 L/s.

1000ft2 or Cfm/person L/s.person

2.5

0.06

0.3

0.06

0.3

minimum class

outdoor air

100m2

person Dwelling

air Notes Default assumptions

F,G

unit corridors

Ken Yeang,2008, Eco design, a manual for ecological Design, Great Britain, John Wiley & sons, Ltd Lewis G. Harriman, 2009, The ASHRAE Guide for buildings in Hot & Humid climates, Atlanta, W. Stephen Comstock

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F: Default occupancy for dwelling units shall be two people for studio and one-bedroom units, with one additional person for each additional bedroom G: Air from one residential dwelling unit not shall be recirculated or transferred to any other space outside of that dwelling unit. K: ASHRAE standard 62.1-2007 has not provided a minimum assumed occupancy for this space. However, outdoor air remains requirement, in order to dilute contaminants generated by the building itself and its contents. Refer to the columns labeled. â&#x20AC;Ś Outdoor air per unit of floor area to calculate the minimum outdoor air requirement for this space.

2.1.3 Benefits of Natural Ventilation Comfortable thermal condition for occupants and good indoor air quality are among the other advantages of a well integrated natural ventilation system apart from energy saving and positive impact on environment. In addition, problems associated with mechanical HVAC systems like noise and health problems like sick building syndromes are unemployed, providing a healthier and more comfortable environment, which enhances the productivity of occupants. The use of natural ventilation reduces the capital, maintenance and operational costs of mechanical equipments and the space requirement for them (Allard, 1998). HVAC systems can take up to 2 to 3 intermediate floors in tall buildings to house mechanical plant equipments (Arnold, 1999b). Each building type requires a specific amount of fresh air to dilute the internal pollution to achieve a good indoor air quality. According to Allard, the air that is free of pollutants that cause irritation, discomfort or ill health in the occupants is optimum quality of air. He also states that the pollution level decreases with the increase in airflow rate and at the same time the occupantâ&#x20AC;&#x2122;s behavior like opening and closing of windows and doors has a great impact on the energy consumption in a building (Allard, 1998, p3,4).

Figure 2.1-2, Combined evolution of pollution level and energy demand, (Source: Allard, 1998, Natural ventilation in buildings; A design handbook p. 4)

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Figure 2.1-2 shows effectiveness of airflow rate on pollution level and the energy demand. In the other hand, high airflow rate may affect the comfort level of occupants, the thermal performance of building and energy requirement in winters to heat the large amount of incoming fresh air in cold climate and cool the air during summer in hot climates. There are hardly any tall building (25 storey or more), solely dependent on Natural Ventilation. Potential energy saving and other benefits of natural ventilation are equivalently valid for low-rise non-domestic buildings and tall buildings. There are several notable buildings designed with natural ventilation system but they also have some form of mechanical system. These are mixed mode or hybrid designs reducing the risks associated with a completely natural ventilation system (Etheridge and Ford, 2008). 2.1.4 Historical overview on the development of natural ventilation in tall buildings Climate and surroundings have shaped the way human beings choose and design their habitat through ages. From pre-historic men living in caves to modern housing- the focus is to get protection from natureâ&#x20AC;&#x2122;s climatic changes and get indoor comfort. 19th century saw the emergence of tall buildings and the indoor environment control in these buildings was mostly done by passive means like openable windows for air circulation and use of radiator or stove for heating. Throughout this century, the focus was on natural lighting and air circulation. In 20th century, mechanical ventilation and air conditioning techniques played the central role in maintaining a comfortable thermal environment and air quality. But these technologies, however complex and intricate could not result in the desired level of indoor climatic experience and became a major cause of energy consumption leading to global warming. This shifted the focus on naturally ventilated designs, which endeavored the designers to rethink about the natural ventilation in high-rise buildings. The focus shifted to an energy efficient, robust yet simpler design solution. By integrating old and classic styles with natural ventilation, techniques and passive heating and cooling strategies gave rise to a new era in building design by end of 20th century. Since the advent of tall buildings in 1885 till present day, ventilation strategies have undergone a multitude of changes. In late 19th century natural ventilation and reducing humidity was a major concern for architects (Arnold, 1999 a). Many buildings during this period were influenced by classical architecture styles â&#x20AC;&#x201C; which meant use of open courts and limited plan depths to enable natural light and air ventilation.

Page | 28

Figure 2.1-3 shows, the world’s first skyscraper The Home Insurance Building (naturally ventilated).

Figure 2.1-3, Home Insurance Building Chicago, 1885, (Source: Rise of the New York skyscraper, 1865-1913 Carl W Condit)

This style was imminent in Chicago and popularly known as “Chicago Quarter Block” (figure 2.1-4) owing to the fact that the design involves open courts and filled blocks between streets.

Figure 2.1-5, LA Salle street, North of Adams Street, Chicago (Source: http://chicagopc.info/Chicago%20postcard s/)

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Figure 2.1-4, Bird’s-eye view of Chicago Board of Trade district (1898) showing the ‘Chicago Quarter Block’ and the central open courts. Source: (Chicago's 'loop' in 1893, as seen by Rand McNally's artists).

Figure 2.1-6: The Wainwright Building (1981) second floor plan and exterior view. LHS: (Source: Arnold, 1999a). RHS: http://www.essential-architecture.com/STYLE/STY-Sullivanesque.htm

This was followed by similar design pattern being adopted in many US cities- light courts integrated into building designs in E, H (Equitable Building refer figure 2.1-8) and U plan forms. An example is Wainwright Building (Louis Sullivan) in St. Louis.

It has the classical style based on Uffizi

Building, Florence (Refer Fig 2.1-6) in a U shaped plan, which facilitates air and light to the office, along with use of external sunshades to provide thermal comfort. (Arnold, 1999 a) Another building demonstrating the classical style with open courts is the Strauss Building and Marshall Field and Company Store, Chicago (Refer 2.1-7, 9)

Figure 2.1-7: The Strauss Building Fourteenth floor plan and exterior view. LHS (Source: Arnold, 1999a), RHS; http;//67.73.47/public/zecom/museum/ghostowers/index.htm

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Figure 2.1-8, Equitable building showing H-shaped plan (Source: http;//67.73.47/public/zecom/museum/ghostowers/index.htm

Figure 2.1-9, Marshall Field and Company Store, Chicago, 1914, Daniel Burnham & Co. (Source: http;//67.73.47/public/zecom/museum/ghostowers/index.htm)

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This trend continued in 20th century in the US with classical buildings like the Woolsworth , the Chrysler(1930) and the Empire State Building (1931) relying heavily on natural ventilation and lighting with no specific emphasis given to natural ventilation strategy. (Arnold, 1999 a). With the US economy, recovering from depression in late 1930s, air conditioning equipment sales saw a deep rise. This had a major impact in the design of tall buildings where passive means of air control were no longer a concern and the mechanical means to control temperature and humidity meant there was more freedom with respect to plan depth, plan form and window fenestrations. Transparent and deepplanned Buildings with curtain-walled windows became the order of the day.

Figure below

demonstrates cross-section of one such design by Italian designer and architect from Portland, Ore., Pietro Belluschi (Figure 2.1-10)

Figure 2.1-11, LHS: Milan Building (First fully air conditioning used) RHS: Fully glazed curtain wall, Lake shore Drive Apartment, Multifamily housing, 1951 (Source: http;//67.73.47/public/zecom/museum/ghostowers/index.htm)

Figure 2.1-12, Belluschi.s 1943 design study for an office building in .194X (Source: ASHRAE JOURNAL, JULY 1999By David Arnold, F.R.Eng. Member ASHRAE

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However, in these designs, increased transparency and no consideration to solar shading meant heavy pressure on the air-conditioning devices to maintain thermal comfort in the interiors coupled with a higher rate of energy consumption. After the oil crisis in 1973, such designs heavily dependent on air-conditioning slowly began to lose their efficacy. The focus shifted to conservation of fuel by diminishing heat loss through ventilation (Ugursal, 2003). This was achieved by sealing the buildings to increase insulation levels and reduce air filtration levels. This approach however had no consideration of the occupant’s comfort and well-being. This led to unhygienic indoor air, mould growth and spread of diseases due to humidity condensation – Sick Building Syndrome was prevalent. (Allard, 1998) To overcome this scenario more stress was put by the architects and engineers on occupant comfort by designing for a healthy and environment friendly interior. According to Allard, this started the era of “energy efficiency”, in the 1980’s and 1990’s, when architects focused on natural ventilation strategies and passive heating and cooling techniques. (Allard, 1998)

2.2

Natural Ventilation Strategies

Design for minimizing cooling requirement such as by orientation and spatial organization, use of shading devices, ventilative cooling by wind or buoyancy or both wind and buoyancy, material, color and texture, thermal mass, radiant cooling, indirect evaporative cooling such as use of roof pond, roof spray and roof garden and dehumidification technique especially in humid climate are some of strategies could be used to achieve indoor thermal comfort. (Refer Appendix 7-2) 2.2.1 The Physical mechanism (the driving forces for natural ventilation) in tall building Pressure difference across a building’s interior and exterior induce airflow through the building by wind force and thermal force or by both (Givoni, 1976, Ford and Etheridge, 2008)

2.2.1.1 Wind induced ventilation Pressure differences are created across a building when wind blows against it – the pressure on walls facing the wind is elevated where as the pressure on the leeward side is reduced which induced air flow from high pressure to low pressure zone (Givoni, 1976, Kleiven, 2003) These zones are also known as pressure zone and suction zone respectively. When wind direction is at right angles to a Page | 33

rectangular building, front wall acts as pressure zone and the sides and rear act as suction zones. When the direction is oblique, two upwind sides are pressure zone and the rest sides are suction zones. Roof in all cases acts as a suction zone. From the center of pressure zone the pressure diminishes outwards on the windward surfaces. For a perpendicularly blowing wind, the pressure variation across the walls is smaller as compared to a wind blowing in an oblique direction. There is a drastic drop in pressure from windward to leeward corners in case of oblique wind. At a 450 incidence angle, pressure on the downward corners is almost zero where as at a lesser angle, a suction zone develops. An air pressure variation in suction zones is greater as compared to that in the pressure zones. For instance, with a perpendicular wind, on the sidewalls, the suction is greater upwind and at the rear wall, it reduces from center to peripheral zone. With an oblique wind the suction magnitude on the sides and the roof is diminishes downwind. (Givoni, 1976, Man, climate and architecture, p 286). (Refer Appendix 7-3)

Figure 2.2-1, Schematic distribution of pressure around a building, based on result by Irminger and Nokkentved. (Source: Givoni, 1976, p 286)

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2.2.1.2 Buoyancy induced ventilation Changes in average air temperature inside and outside a building create a difference in air density and vertical pressure gradients on the inside and outside of doors. If there’s a single aperture at a certain level in a building, air pressure on either side of it equalizes with time and there’s no air flow after this even though there may be thermal differences. at a certain height of the building, the indoor pressure and the outdoor pressure are equal to each other, causing air stagnation known as the ‘neutral plane’. (Givoni, 1976, p 282; Kleiven, 2003) (For details, refer Appendix 7-4)

Figure 2.2-2, Thermal buoyancy in a space with two openings. (Source: Kleiven 2003)

2.2.1.3 The combined effect of wind and thermal force The combined effect of wind and thermal forces result in the effective airflow in a building. For a given opening, the gradient is a sum of pressure differences by each force separately. The resultant airflow is proportional to the square root of combined pressure gradients. Thus, even when both the forces work in the same direction, the resultant airflow will be only slightly higher (by 40% maximum) than it would be with the greater force alone. Thermal force of ventilation is dependent on temperature gradient and height of opening, it is important only when either of these have a high value. For residential buildings the height of ventilation path is very small so the deciding factor becomes temperature difference in interior and exterior, which is only existent in cold regions in winter where as wind will typically be the dominating driving force on a windy hot day (Kleiven, 2003) In summer hence, thermal force has little application except for kitchens, bathrooms and W.C where ventilation is through vertical pipes which can go up to multiple storey and here the resultant Page | 35

thermal force can aid in natural ventilation. The thermal force however can induce airflow only by pressure difference. Therefore, if two rows of openings are placed on a wall at different heights and airflow is induced by thermal force only, air will enter through the lower set of openings and leave through the upper set of openings in case indoor temperature is higher. However in case of air flow induced by wind pressure can result in air flow across the whole room , whose pattern is determined by inertial force of the incoming air mass, hence can be controlled by detailed design of the inlet openings. For same quantity of air moved, such airflow may produce higher velocity owing to turbulence than the one induced by thermal pressure. (Givoni, 1976, p 288) 2.2.2 Natural ventilation principles The introduction of air into a building and the extraction of the same out of the building is ‘Ventilation Strategy’. There are three main categories of ventilating strategies; single-sided ventilation, cross and stack ventilation (Kleiven, 2003). Location of openings for ventilation and the shape of the building together act as controller for natural ventilation and it can be differentiated by three different principles: •

Single-sided ventilation

•

Cross ventilation

•

Stack ventilation

2.2.2.1 Single-sided ventilation Here only one side of the building is used as the inlet and outlet of air. Openings are in one side only. This is an effective way for summers for a room of depth at least 2.5 times of the height (refer to Figure 2.2-3). Wind is the main driving force in this case. If there is a significant difference between the inside and outside temperature and/or the openings are on different heights for ventilation then buoyancy effect can also aid single-sided ventilation (Kleiven, 2003).

Figure 2.2-3, Single sided Environmental Design Guide

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ventilation.

Source:

2.2.2.2 Cross ventilation: This depends on flow of air between two sides of a buildingâ&#x20AC;&#x2122;s envelope due to difference in pressure as air moves from windward to leeward side (Kleiven, 2003). Cross ventilation is effective for a room of depth, maximum five times of the height.

Figure 2.2-4, Double sided ventilation. (Source: Environmental Design Guide)

Cross-ventilation is facilitated when a room has apertures at both pressure and suction zones. Below table illustrates the finding of a study on average air velocity in a square room model with a constant total number of openings. Table 2-4: Effect of cross-ventilation on indoor average air velocity

Effect of cross-ventilation on indoor average air velocity (% of external air velocity) Location of openings

Total width of openings

Cross

Direction

ventilation

wind

of 2/3 of wall Av.

Max.

3/3 of wall Av.

Max .

None

Single

opening

pressure zone Single

opening

in perpendicular

Oblique

in Oblique

in perpendicular

103

Oblique

118

110

in perpendicular

102

Oblique

suction zone Two

openings

suction zone Provided

Two

openings

adjacent walls Two

openings

opposite walls

For obliquely incident wind on external wall, there is a flow of air along and parallel to the length of the wall resulting in pressure gradient and inducing airflow from high and low pressure area. This Page | 37

pressure difference can be used to better the ventilation condition in a room by providing two lateral windows at upwind and downwind sides as compared to a single window of the same area. However, since pressure gradients are not that significant, the resultant airflow may not be high. However, according to experiments at B.R.S. in Haifa, it was demonstrated that by creating â&#x20AC;&#x153;artificialâ&#x20AC;? pressure and suction zones along the external wall, ventilation conditions could be improved to a good extent in case of rooms with a single external window. Such pressure differences are provided by providing each of the two windows a single vertical projection from the internal side. (Refer Figure 2.2-5)

Figure 2.2-5, Internal air speeds in models with vertical projections of varying depths, compared with values in models without projection. Window width is 1/3 of wall width. Source (Givoni, 1976)

As shown in above picture a pressure zone is created in front of the foremost window and a suction zone is created at the front of the rear window. This results in air entering through front window and leaving through the second.

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Table 2-5, Average indoor air velocity in rooms with a single exposure with different number & arrangement of the windows.

Average indoor air velocity in rooms with a single exposure Window/wall Number and type Wind direction total area

of windows

Perpendi Oblique cular

Oblique

Obliqu

at 22.50 at 450 - at 67.50 e from - front

front

- front

the rear

2/9

One central

10.4

Two lateral

11.8

16.8

17.5

8.9

5.4

38.4

36.2

8.1

Two at side with 16 projections 1/9

One central

4.7

3.6

3.3

3.8

3.6

Two lateral

6.5

11.4

15.7

8.0

3.4

30.8

36.0

35.0

4.9

20.8

Two lateral with 11.4 vertical projections Two lateral with 17.3 balconies

As can be seen from above table with single central window average velocity is as low as 4% of outdoor speed in case of a smaller window and 10% in case of a larger window. The indoor velocity almost becomes double when there are two windows at side of the wall, of same area as single central window. With two windows with vertical projections the indoor velocity rose to an extent where it is comparable with that in rooms with good cross-ventilation, when wind is incident oblique to the wall, in particular. It seemed balconies were not as effective as vertical projections in terms of creating a gradient but had some considerable effect. Conclusion from above study can be summarized as with buildings with a single external wall exposed to wind, best indoor ventilation conditions can be achieved when wind direction is oblique to the wall at an angle from 20 to 70 degrees. Driving force for ventilation is greatly reduced if projection is provided with the windows on both sides. The depth of projection for a building with multiple rooms should not be great enough to interfere with the ventilation of adjacent rooms. (Givoni, 1976, P 294)

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2.2.2.2.1 Cross Ventilation with Central Atrium: In large buildings, with the use of central atrium, the principle of buoyancy can be applied for ventilation process (Figure 2.2-6). Fresh air flows throughout the building and later exhausts out via openings at high level of atrium. With this configuration, the primary driving force at low wind speed is the thermal buoyancy generated in the atrium by virtue of its height with some assistance from the wind. (Behr et al, 1995) [6] (Refer Appendix 7-5)

Figure 2.2-6, Cross ventilation with central Atrium. Source: Environmental Design Guide

2.2.2.2.2

Cross ventilation with Perimeter Conservatories

Architect Christopher Ingenhoven, who got the second position in the design competition for the Commerzbank also proposed cross ventilation in his design. He got a cross-shaped floor plan (Figure 2.2-7) with the use of perimeter conservatories instead of central atrium. (Further details refer Appendix 7-6)

Figure 2.2-7, LHS: Diagrammatic plan showing perimeter conservatories and central core. RHS: Swiss re Tower floor plan, London (Source: Foster & Partners)

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2.2.2.2.3

The Wind wing-wall

Buildings in hot and humid climates have a higher cooling requirement throughout the year as compared to other climates and it is a challenge for designers because of the outer air condition and requirement of sheer volume to provide adequate cooling. Malaysian Architect, Dr. Ken Yeang has used extensively an innovative wind-driven ventilation strategy in his high-rise buildings to avoid air-conditioning systems.

Figure 2.2-8, Vertical wing-walls protruding from the Southwest and Northeast elevations.(Source: Left (Richards, 2001); Right (Powell, 1999)

â&#x20AC;&#x2DC;Wing-wall Conceptâ&#x20AC;&#x2122; perhaps is the most interesting innovation by him, which is essentially a vertical fin fixed to the faĂ§ade of the building, perpendicular and adjacent to the openings. These are used in the combination of separately ventilated floor and cross ventilation system, helping in increase the airflow through an opening. Wing-walls enhances the effectiveness of wind-driven cross ventilation by increasing the wind pressure coefficients across openings and are designed to suit the wind pattern of a particular site. However, it is less effective with low wind speed.

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2.2.2.2.4

The Wind Scoop

The ancient approach for wind-driven natural ventilation in Egypt and other hot-arid climates during 1300 BC [7] has been developed by Ken Yeang in conjunction with Battle McCarthy Consulting Engineers for tall buildings. Shanghai Armoury Tower (1997) is the example to use this ‘Wind Scoop’. In this principle, the air is drawn through a central atrium and exhausted through the façade (Figure 2.2-9). The wind scoops should be Omni directional for effective operation. A building with wind scoop will still be naturally ventilated for a short period during the year, as mechanical ventilation is needed during extreme conditions of winter and summer to provide comfortable conditions [8]. In addition, it might be ineffective at low wind speed and certain wind directions.

Figure 2.2-9 Seasonal strategy for building with wind scoop [9]

2.2.2.3 Stack ventilation: In this type of ventilation, fresh air is allowed to enter the building at a lower level and exhausts out from the building at a opening in higher level. Buildings with central atriums, chimneys and elevated parts often use stack ventilation. (Kleiven, 2003)

Figure 2.2-10, showing stack ventilation, (Source: Environmental Design Guide)

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2.3 Adaptive thermal comfort in Tropical climate Two climatic types as suggested by Miller â&#x20AC;&#x201C; such as equatorial and tropical marine regions. The equatorial region extends along a strip of up to 10 to 15 degree on either side of the equator according to building design aspect, which is warm all year round, and the other is regions with hot humid summers with cool and cold winter (Givoni, 1976).

Figure 2.3-1, showing world map with Tropical region (Source: http://commons.wikimedia.org/wiki/File:Koppen_classification_worldmap_A.png

Equatorial climate is spread on either side of the equator along a thin strip, going into Africa and South America. It is characterized by high temperature and relative constancy of the annual average temperature and humidity with little variation in diurnal temperature range and average monthly temperature range. The annual mean temperature is 270C and the range of monthly average temperature is minimal at the range of 1 to 3 0C. The diurnal range however is about 80C. Maximum temperatures range around 320C and it can reach to an extreme of 380C. During most times of the year, the humidity and rainfall are at their peak at most of the time. The specific humidity (amount of water vapor in an unit mass of dry air) is about 20gr/kg which sometime rises up to 25gr/kg with relative humidity around 90% and rainfalls occurring mostly in the afternoons. These are caused when trade winds from northern and southern hemisphere converge in the equatorial zone, expanding and cooling at the same time. Though the regions on tropic have similar temperature, rainfall and humidity conditions, the local climate has a great impact on building design alike their wind Page | 43

condition may vary from one place to another. In coastal areas, regular land and sea breezes are created by the constant heating and cooling patterns of land and sea respectively providing regular wind flow mainly during the afternoon time with windless night. 2.3.1

Heat discomfort and adaptive thermal comfort

It is mainly related with the air temperature and the air velocity over the body but the most complex on comfort and human thermal balance is the effect of humidity. In 1958-59, Givoni concluded that up to about 25°c, one sedentary body could not experience any difference in thermal sensation, skin wetness, body temperature and sweat rate between 30 to 80% relative humidity (Givoni, 1998). According to Allard (1998, p.4) human thermal comfort is ‘the condition in which a person would prefer neither warmer nor cooler surroundings’. He further defines human thermal comfort in terms of psychological parameters (age, sex etc.), external parameters (activity and clothing) and physical parameters. Air temperature, relative humidity, light intensity and air velocity are the main physical parameters to affect human thermal comfort (Allard, 1998). Theoretical comfort models or standards, such as Fanger’s PMV widely accepted method (1972) and its derivatives like ISO 7730 and most versions of ASHRAE Standard 55 were developed based on those above factors. [10] Some of field studies show the comfort is experienced at a temperature as high as 320C at over 85% RH in Bangladesh [11], and in Thailand , higher ranges of temperatures 25-31.5๐C and RH of 62.2-90% [12] where as ASHRAE Standard 55-1992 Addenda 1995 [13] suggests that the summertime comfort zone ranges from about 23.5๐C at 25% RH to about 26๐C at 60% RH, which states that the theoretical models predict comfort zones which are independent of local thermal conditions which neglect the impact of acclimatization of occupants in hot humid climates [14,15]. Indeed, thermal comfort expectation is influenced by degree of adaptive opportunity: as people have more control over the environment in their home as compared to office, they tend to accept warmer environments more readily in their homes than in offices [16]. It can be concluded that that passive design strategy probably has greater potential to provide thermal comfort in hot humid climates than is generally believed thus thermal preferences extend to a wider range of airflow speed and temperature (Humphreys, 1975; De Dear, 1998, 2000).thus various field surveys done by (Klitsikas, 1995; Lin Borong et al, 2004; Hien, 2002) in Athens, China and Singapore respectively stated PMV model need to be corrected while evaluating thermal sensation in the natural thermal environment. In addition, the PMV model is fitted for the air conditioning building where as the occupants in a

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naturally ventilated building prefer a wider range, which is not satisfying the PMV model. (De Dear & Brager, 2002; Mat Santamouris, 2006, Building Ventilation, p 221, 222). However (Olgay,1963) first stated the Bioclimatic chart with the comfort range , bounded with the lower fixed temperature at 21Â°c and upper comfort temperature is 27.8Â°c when relative humidity is below 50% but with increase of relative humidity above 50% ,upper temperature limit drops down gradually until it touches the lower limit at 90% relative humidity. After a study, Jitkhajornwanich modifies Olgyayâ&#x20AC;&#x2122;s bioclimatic chart to take into account the acceptance of higher temperature and humidity in hot humid climates [17] but the timetable, proved inappropriate for hot-arid regions (Givoni, 1998, p 26, 28) which was again modified.

Figure 2.3-2 Bioclimatic chart modified for hot humid climates (adapted from Olgyay following Jitkhajornwanich), Source: Torwong Chenvidyakarn

Moreover De Dear and Brager proposed an adaptive thermal-comfort standard for naturally ventilated buildings with the comfort range varies from 23-280C at a monthly mean outdoor temperature of 250C and 26-310C for mean monthly temperatures above 330C (de Dear 1998, de Dear and Brager 1998, Brager and de Dear 2000) which shows the indoor comfort temperature increased with outdoor temperature and incorporated in the ASHRAE thermal-comfort standard (ASHRAE_55 2004). Furthermore, Ng et al. (2004) stated the comfortable thermal environment in the summer months of Hong Kong could be achieved with a steady indoor air movement of around 1m/s across the occupant space. Page | 45

Figure 2.3-3, the comfort temperature of naturally ventilated buildings in Hong Kong, (Source: Pei-chun (Ingrid) Liu, 2010)

However the building bioclimatic chart (BBCC) by Givoni (1994) preserves all the psychometric relationships which defined the boundaries of climatic conditions within which various building design strategies and natural cooling systems can provide indoor thermal comfort (Givoni 1998). Hence, in this dissertation, it is used to interpret the overall effectiveness of natural ventilation.

Figure 2.3-4, Psychrometric chart showing boundary of different passive cooling approach for Hot developing Countries (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

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Figure 2.3-5 Psychrometric chart showing boundary of different passive cooling approach for Developed Countries (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

According to Yeang (1999), direct and indirect physiological effects are the two ways to enhance the level of human comfort in natural ventilation. He termed it as ‘Comfort Ventilation’, which involves more wind through openings to increase the indoor airflow and this results the occupants feel cooler. Moreover, Givoni (1998) stated the comfort ventilation is applicable mainly to regions and seasons when outdoor maximum air temperature does not exceed 28-320C with diurnal temperature range less than 100C. According to Yeang (1999) a physiological cooling effect can be achieved even when the humidity level and indoor air temperatures are high. The rate of evaporation of sweat from skin increases with the increase in velocity of indoor air (1-2 m/sec) and it minimizes the discomfort occupant’s feel as compared to when their skin is wet (Yeang, 1999). Allard (1998) also argues that with the change of air movement around the body, the thermal comfort level can be controlled. (Givoni, 1994) presented the boundaries of outdoor temperature and humidity within which indoor comfort can be provided by natural ventilation during the day with indoor airspeed of 2 m/s. However, in office space upper limit of indoor air speed is about 0.8m/s by ASHRAE Guide (1985) presumably to prevent paper flying where as in residential building it depends on the temperature. Secondly, indirect approach is to improve the level of comfort by ventilating the building at night to cool down the interior, which is termed as ‘Nocturnal Ventilative Cooling’. This allows the building to absorb the heat during the day and to flush it away during night (Givoni, 1998; Yeang, 1999). Indirect method to improve comfort level and to reduce the internal temperature gain requires large window openings and increased rate of airflow, to wash away the excess heat gained during summer, though it might be impractical during occupancy (Allard, 1998). Page | 47

In addition, the BBCCs for hot-developing countries offer thermal comfort boundary for two conditions: ‘still air’ (less than 0.25 m/s), which lies between 18◦C (winter) and 29◦C (summer) and for ‘a very light breeze’ (2.0 m/s), which extends the envelope to 32◦C where as for developed countries the range varies from 18◦C to 25◦C (winter) and 20◦C to 27◦C (summer) in ‘still air’ and for ‘a very light breeze’ (2.0 m/s), which extends the envelope to 30◦C during summer. The upper (summer time) temperature limits decrease above 50% relative humidity and upper limits are placed on RH of 80% for still air and 90% for a very light breeze. (Givoni 1998) More recently, Lomas et al. (2004) tested and suggested that the BBCCs can be used for the buildings, which are cooled by different ventilation strategies in developed countries. Hence, in this dissertation, it is used to interpret the overall effectiveness of natural ventilation in the selected case study buildings.

Figure 2.3-6,shows the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved by natural ventilation in day, with indoor air speed of 0.25 and 2 m/s for Hot developing countries. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 2.3-7, shows the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved by natural ventilation in day, with indoor air speed of 0.25 and 2 m/s for developed countries. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

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2.3.2

Thermal requirements in Tropics

In tropical climates, the primary concern is continuous ventilation for comfort requirements and it impacts all aspects of building design. Proper care must be taken in such climates to protect from sun and rain without compromising on ventilation conditions. (Further detail, Refer Appendix 7-7)

Figure 2.3-8, Air speeds yelding E/Emax ratios 0.1, 0.2 and 0.3 of resting people at different air temperature and vapour pressure. (Source: Givoni, 1976)

2.4 Potential, Challenges and risks associated with natural ventilation in Tall building The urban land has seen a slurge of tall buildings over a period of time, leading to a greater change in urban land vicinity. In the city free airflow above the building and restricted air velocity in built up zone are quite different due to densely placed tall buildings cause low airflow rate. However, at

Figure 2.4-1a Wind Speed near ground level in front of a high rise building is increased, Givoni, 1998)

street level some time it increases the turbulence and wind speed around high-rise buildings by up to 300% (Givoni, 1998, p 231). Specific location experiencing low wind speed, this effect can be highly welcome and in cities with excessive wind, the effect may react adversely. The urban wind speed decreased with increase of concentration of air pollutants (Zhang X.et.al., 2007). Thus, there are local problems related to excessive airflow near the buildings or the strong formation of turbulence arises enormously in some situations (Katarzyna, 2007). As most high-rise buildings are located in dense area, due to which air pollution and noise create obstruction to the natural ventilation (Allard, 1998). There are higher numbers of risks and challenges involved in design of naturally ventilated high-rise buildings than low-rise structures. The important one is change in airflow pattern at higher level,

Page | 49

which is not suitable for ventilation. (Boutet, 1987). The upper stories of the tall buildings are more vulnerable to high wind speed & solar exposure, exposures to storms and wind driven rain mostly in tropics, in contrast, the occupants of the high stories enjoy lower humidity and temperature due to the vapor generation by evaporation from vegetation and moist soil occurs at ground level. Natural ventilation in tall building is not that common as like in the non-domestic buildings, designed with pure natural ventilation strategies. “This is not surprising in view of the potential risks to a successful design”. (Ford and Etheridge, 2008) It is more difficult to control the air temperature and predict airflow patterns, inside and outside of the high-rise buildings. (Ugursal, 2003) This creates difficulties in calculation of the surface heat transfer between air and the walls. (Allard, 1998) According to Ford and Etheridge (2008) ‘Challenges in designing façade and openings in tall buildings are more, because the potential magnitudes of the two driving forces (pressures due to wind and buoyancy), become greater and their relative magnitudes can vary over a wider range’. The first physical mechanism for natural ventilation; the pressure difference generated by the wind (∆p) can be expressed as follows: ∆p=0.5ρU2∆Cp, where •

U denotes the wind speed measure at the height of the building.

•

∆Cp is the pressure coefficient, which depends on factors such as the building’s shape, the wind direction, and the influence of the surroundings.

At ground, surface air velocity is low as compare the higher level. Since the wind speeds increase at higher altitudes, the increased value of ‘U’ implies that the wind pressure on tall buildings can be relatively large.

Figure 2.4-2, Variations in air velocity according to thr ground roughness (Source: Boutet, 1987)

In addition, the exposed nature of high-rise buildings at top-level increase the value of the pressure coefficient Cp, and the wind pressure difference ∆p (Ford and Etheridge, 2008). It represents that the wind pressure difference at top level is significantly higher than lower level therefore the façade should have different opening sizes at every level. It can be concluded that the need to formulate a

Page | 50

natural ventilation concept that can operate under a wide range of wind pressures can generate control difficulties in high-rise buildings. (Ford and Etheridge, 2008) The second mechanism for natural ventilation; the difference in buoyancy pressure (∆p), ∆p=∆T ρgh, where, •

∆T denotes the temperature difference

•

g is the gravitational constant and h is the height over which the temperature difference acts

This equation shows the buoyancy pressure will be more if there is a temperature difference over the entire height of the building, which is higher at ground stories than top stories if there is any atrium used as stack chimney. (Ford and Etheridge, 1998) This will form various thermal pressure differences at the openings around the shaft. Same sizes of all these openings will result better ventilation at lower level than top levels. Therefore, it is necessary to calculate the sizes of the openings around the shaft, which will be more at top level and less at ground level. (Oesterle, 2001) According

Ford

and

Etheridge

dividing building into segments by open spaces offers the least risky approach for envelope design of tall buildings, which will minimize the aerodynamic effects. These segments can be the sky courts (Figure 2.4-4). This will help to calculate the required airflow directions and magnitudes

for

each

section

independently.

Figure 2.4-4, Illustration of segmentation of tall building. LHS: Segmented (MBF Tower, Penang), RHS: Unsegmented (1 Moulmein Rise, Singapore). (Source: Author)

Page | 51

Figure 2.4-3, Different sizes of openings adjoining the atrium at each level (Source: Ford and Etheridge, 2008, modified by Author)

When the buildings are having large horizontal dimension they divert the airflow to upward direction and create wind shadow behind them and in other hand, buildings having small ground footprint than the surrounding low-rise building create turbulence and pressure difference that improve the ventilation condition of those low-rise buildings. However, wind speed above the bulk of low-rise buildings are quite high which helps those tall building to have a greater airflow speed especially in Tropics, Wise et al. and Givoni. In tropical region during rainy season, gusty winds along with rain results start affecting the occupants. To overcome these gusty winds, WOHA Architects developed a strategy of projecting bay windows “monsoon window” with sliding ledge, which maximize the airflow without letting the rain to come in.

2.5 Basic Principles and design factors affecting natural ventilation in tropical climate People stay in naturally ventilated building usually accepts a wider range of temperature difference than in an air-conditioned space. Hence it can be assumed that the inhabitants of developing country and acclimatized to hot – humid climate would have acceptance of higher temperature and humidity level. Hence, the design and construction of a building in needs the following requirements to be satisfied – provision of continuous and efficient ventilation, protection from sun & rain. (Refer Appendix 7-8) 2.5.1

Comfort ventilation

There are two ways to improve ventilation such as direct effect through enhancing the cooling sensation of the inhabitants by providing a higher indoor airspeed known as “comfort ventilation”. Other is an indirect method, nocturnal ventilative cooling (convective cooling) which is mostly applicable in arid and desert region where the diurnal temperature swing is more than about 15°c with high day time temperature more than 36°c . (Givoni 1998) 2.5.2

Applicability of comfort ventilation

The regions which come under hot climate with maximum outdoor temperature does not exceed 28°c-32°c and particularly in regions where the diurnal temperature range is less than about 10°c. For e.g. the climate in Singapore, Penang and Mumbai, applicability of comfort ventilation is quite high. Whereas the night ventilation could be more effective for the region where the maximum Page | 52

temperature is similar with above but with a higher diurnal range. The comfort ventilation can be applied for every types of building with high or moderate amount of wind speed, it is possible with an exhaust fan for indoor air circulation in case of low wind or where the effective cross ventilation is not possible. (Givoni 1998) 2.5.3

Enhancement of daytime comfort ventilation

Under still air, the simplest strategy to improve comfort is day time ventilation by providing high indoor airspeed. Figure 2.5-1, 7 show the boundaries within which indoor comfort can be achieved by daytime ventilation with a very light breeze about 2m/s (Givoni 1976, 1998). 2.5.4

Continuous ventilation with passive solar use of thermal mass

Givoni experimented on the building mass to control the thermal comfort of occupied space applying continuous ventilation. Even when buildings are cross ventilated , in a well-insulated high mass building the indoor maximum temperature can be reduced by 2-3째c below its outdoor temperature whereas the indoor maximum temperature is close to the outdoor temperature in a low mass building. It means thermal mass can reduce the indoor daytime temperature and improve the comfort of the occupants through day and night ventilation, provided that the night ventilation must have the capacity to maintain the indoor minimum temperature close to the outdoor minimum temperature. On the other hand, in a naturally ventilated low mass building fan assisted night ventilation could not reduce the indoor daytime temperatures significantly (Givoni, 1994).(Refer Appendix 7-8a) The usage of airflow through the building in warmer climates can enhance night cooling of internal mass (Li & Xu, 2006). Diurnal temperature variation is reduced by 15% by providing lower indoor daytime temperatures (Cook, 1989). In warm humid climates, humidity reduces much of impact of this additional cooling. It is difficult to moderate such climates using passive solar techniques. During warmest periods, solar shading needs to be in place on exteriors of large buildings to avoid heat gain. Masonry walls, concrete floor slabs etc. can be used as airflow channels to speed the night cooling process (Fairey et al, 1985).

Page | 53

2.5.5

Design factors affecting natural ventilation

In hot climate of lower latitude; verandahs, overhangs work well with movable horizontal louvers. However, in extremely hot low latitude climates, east and west should completely be window less due to intense solar gain. (Givoni, 1976, P 208)To overcome this extreme situation, the Ideas and examples for natural ventilation and passive cooling strategy should be taken from the Vernacular architecture (Fathey, 1986). Figure shows “Monsoon window” of 1 Moulmein Rise, Singapore is designed by WOHA Architects by taking inspiration from vernacular housing of Indonesia.

Figure 2.5-2, Moulmein Rise “Monsoon window” detail inspired from vernacular design (Source: Tim Giffith)

2.5.5.1 Built form and orientation For ventilation , favorable condition is not only perpendicular wind direction but when wind is incident at an angle 30° to 120° and 45° to 105° to the wall and especially if the openings in windward and leeward side can provide effective amount of airflow in to the spaces. Orientation of a room is the direction to which its external elevation faces and the main problem of building orientation is primarily related to long block. The choice of the orientation is subject to much consideration such as nature of climate, topography, accessible roads to the site and view in different directions. Based on climatic consideration it affects the indoor climate in two different aspects & such as: •

Heating effect of solar radiation on different facades of the building.

•

Ventilation problem associated with the direction of the prevailing wind with respect to its orientation.

Considering these two factors the design may lead to a contradictory condition but finding an optimum solution for any particular situation can be possible with a proper design consideration

Page | 54

based on microclimatic conditions (Givoni, 1976, P 214). Airflow pattern in a room is affected by pressure distribution around the building and the inertial force of the moving air. Irrespective of window positions in either windward or leeward walls, average indoor pressure always equals itself to the outdoor pressure. When windows are positioned both on the windward and leeward walls, airflow continues from the windward window and due to its inertial flow, it flows undeflected through the leeward window. If the position of leeward window doesn’t fall in the wind direction, the airflow suffers friction and is directed towards a low-pressure opening.

2.5.5.1.1

Window opening orientation with respect to prevailing wind

Contrary to the assumption that inlet window should directly face the inward window to provide maximum indoor air flow, recent studies have demonstrated that when inlet windows are positioned at an oblique angle to incoming wind (around 45 degrees) more air flow and circulation occur inside the room all across as compared to a situation when the inlet window is placed directly at the wind in which case air just passes through the inlet and outlet with little or no impact on the side walls. However when the windows are placed adjacent to each other better results are obtained at the window where wind is incident at a right angle than the one where wind hits at an oblique angle. Such patterns are demonstrated in the table: (Refer Appendix: 7-9) (Givoni, 1976, P 290). 2.5.5.1.2

Window size

In a room where windows are positioned on only one wall, size of window will have minimal effect on the overall ventilation condition and internal air velocity as compared to a room with windows on opposite walls. Below table illustrates average internal velocity in a model room with single window with the dimension varying as per the table (Refer Appendix 7-10) (Givoni, 1976, P 292). •

Vertical location of windows, Windows – positions and methods of opening. (Refer Appendix 7-10)

2.5.5.1.3

Sub-division of the internal space

Impact of sub-dividing the internal space into two unequal parts was experimented. Figure 2.5-3 shows the results.

Page | 55

Figure 2.5-3, Effect of sub-division of internal space on distribution of internal air speeds. (Source: Givoni, 1976)

In the above experiment, wind direction was perpendicular to the walls and measurements were taken at the level of window center. It was observed that with different arrangements, the air flowed from inlet to outlet or was made to change direction four times in the room before leaving. In addition, it can be seen from the figure above that subdivision did reduce the internal velocities overall, the highest

reduction

being

44.5%

30.5%.

Velocities were lowest when partitions were nearer to inlet but when partition was nearer to outlet, better conditions were obtained. Hence, it can be concluded that good ventilation conditions can be obtained in apartments where air can pass from one room to the other as long as connections between rooms are kept open during ventilation. Below figure depicts airflow patterns with different types of subdivision of the internal

Figure 2.5-4, Flow pattern in models with different patterns of internal sub-division.(Source: Givoni,1976)

space. 2.5.5.1.4

Page | 56

Effect of fly-screens. (Refer Appendix 7.11)

2.5.5.1.5

Concluding Summary of effectiveness of orientation

particularly in humid climate where the primary physiological comfort requirement is for air motion under all suitable condition like light color insulated walls and shaded windows, the indoor climate is dependent on ventilation which states that orientation is more important with respect to prevailing wind than in relation to the patterns of solar irradiation even when the inlet wall need not be oriented towards the prevailing wind; satisfactory ventilation can be achieved with wind incident to the wall at up to an angle of 45° to possible range of 90°. 2.5.5.2 Effects of verandahs, balconies and terrace gardens, Choice of materials (Wall and roof) •

Porches, verandahs, and balconies should be placed in between rooms, especially in east and west façade. (Refer Appendix 7.12)

•

Choice of materials (Refer Appendix 7.12)

•

Wall (Refer Appendix 7.12)

•

Roof (Refer Appendix 7.12)

2.5.5.3 Relationship of the building to the ground (vertical green) In urban city where high-rise buildings are predominant, vertical landscaping can reduce the solar gain and provide indoor thermal comfort to the occupants living in higher floors. Experiment shows a vertical greenery system can provide excellent thermal protection to the wall and the surface temperature of hard surfaces can be reduced up to about 15°c especially on east and west façade, which are protected by dense trees (Nyuk Hien wong and Yu Chen, 2009, Tropical Urban Heat Islands, p 226)

2.6 Selection of comparative study Based on the research framework developed through the initial studies of natural ventilation in tall building in tropics (Chapter 1 & 2), three case studies are used to identify effectiveness of natural ventilation in tropical climate. Consequences that related to the generic building type and consequences that are common for all the three generic types are identified with respect to the natural ventilation strategies.

Page | 57

Kanchanjunga Apt, Mumbai

Figure 2.6-1, Location of Kanchanjunga Apt. Mumbai (Source: Google map)

Figure 2.6-4, Site plan (Source: Hakki Can Ă&#x2013;zkan, 2009 modified by Author)

Figure 2.6-7, view of Kanchanjunga Apartment (Source: CTBUH)

Page | 58

MBF Tower, Penang

Moulmein Rise, Singapore

Figure 2.6-2, Location of MBF Tower, Penang (Source: Google map)

Figure 2.6-3, Moulmein Rise, Singapore. Mumbai (Source: Google

Figure 2.6-5, Site Plan, (Source: Source: T. R. Hamzah and Yeang: Ecology of the Sky)

Figure 2.6-6, Site Plan. (Source: WOHA Architects)

Figure 2.6-8, view of MBF Tower (Source: Jeremy Lee)

Figure 2.6-9, view of 1 Moulmein Rise (Source: WOHA Architects)

2.7 Analysis of earlier studies simulated in TAS and CFD Many studies report that the high probability of achieving comfort can be relied on natural ventilation in Singapore.[17] The impacts of various ventilation strategies on indoor thermal environment for naturally ventilated residential buildings in Singapore has studied by Wong Nyuk Hien and Wang Liping and they tested four ventilation strategies such as night time-only ventilation, daytime-only ventilation, full-day ventilation and no ventilation according to the number of thermal discomfort hours in the whole typical year on the basis of TAS simulations and also Parametric studies of faรงade designs on orientations, window to wall ratios and shading devices were tested through TAS, ESP-r and CFD (FLUENT).[18,19] The results indicate that full-day ventilation for indoor thermal comfort is better than the others and it was found that north and south facing facades can provide much comfortable indoor environment than east and west facades in Singapore. However, for naturally ventilated buildings there are no clear facade design guidelines in Singapore, India and Penang. Building regulations in Singapore only specify that the U-value of any external wall in non-air conditioned building should not be more than 3.5W/m2 K. [20, 21], however there is no such regulation for India. After various simulation and study, Wong Nyuk Hien and Wang Liping recommended that U-value for the east and west facing facade should not be more than 2W/m2K and for north and south should be no more than 2.5W/m2 K [22] and optimum window to wall ratio 0.24 can improve indoor thermal comfort for full-day ventilation with minimum of 600mm horizontal shading devices. [19] The study through the Questionnaire survey investigated the impact of different sessions of the day, building heights and flat types on thermal perception. From comparative analysis of thermal sensation and thermal comfort votes, it was seen that a high proportion of people found the conditions to be comfortable. The adaptive behavior of the occupants in the usage of climatic control such as windows, fans and air-conditioning to modify the indoor environment has also studied.(N.H. Wong, 2000) [23]

Page | 59

The assessment was based on the occupantâ&#x20AC;&#x2122;s votes on thermal sensation. In naturally ventilated buildings when air temperature and humidity of indoor air is almost impossible to be modified, it is believed that only higher wind speed can create higher thermal comfort satisfaction. [23] The high percentage acceptability (i.e. 82.6%) suggests that the occupants feel comfortable. However, the higher wind speed required for creating the cooling effect is not sufficient to increase the occupantâ&#x20AC;&#x2122;s thermal acceptability in the hot afternoon. Despite the temperature drop in the evening, a lower 41% feel satisfied as compared to the 49% in the afternoon hours. The results show that people feel more comfortable in the afternoon than in the evening even though the weather is warmer in the afternoon. Air-conditioned office buildings offer a minimal range of thermal conditions as compared to a naturally ventilated building and hence such people when return back home after work will have some expectation from the home in terms of environment conditions. Thermal condition is acceptable within the comfort limits, with 82.3%, 77.9 %, 88.1% expressing satisfaction from low, middle and high floor levels, respectively. This suggests that the air movement might have an influence over the respondentsâ&#x20AC;&#x2122; comfort sensation. Hence, the higher comfort votes in the maisonette units are probably due to the higher air movement within the house, which alleviates the effects of high temperature and improves the comfort sensation of the occupants. [23]

Behavioral adaptation As can be seen from Fig 8, 84% occupants prefer switching on the fan, 70% prefer opening windows followed by 54% who prefer switching on AC and getting more drink. Doing clothing adjustments and taking more frequent bath constitutes 45% and the least preferred at 15% was going to cooler places. It is confirmed by the finding that 98.9% of the AC owners installed the AC in their bedroom (Table 2-6), The usage of fan is much higher in the afternoon and evening with the percentage as high as 88.8% and 75.6%, respectively (Table 2-7). Compared to AC usage, the fan is less preferred at night (51.2%). The percentage of people who open their window at least 12 hr a day is 87.9%. At night, the occupants like to close their window, which could be due to privacy or security reasons or because of AC being switched on. (Refer table 2-8) [23]

Page | 60

Table 2-6: The usage of AC in house during different time of the day, Source: (N.H. Wong, 2000) (a) AIR CONDITIONER USAGE MORNING

NOON

EVENING

NIGHT

(%) 0.6 4.2 3 44.6 1.2 25.9 1.8 0.6 3 0.6 1.2

5.4

9.6

35.5

74.4

(%)

DINING

STUDY

(%)

(b) AC INSTALLATION BED

LIVING

57.3 1.2 9 23 6.2 3.4 98.9

13.5

9.6

32.9

(%)

NIGHT

(%)

Table 2-7: The usage of fan, Source: (N.H. Wong, 2000)

USAGE OF FAN MORNING

NOON

EVENING

0.8 10.8 0.8 4.4 1.2 0.4 19.2 6.8 4.8

Page | 61

16 14.8 20 38.4

88.8

75.6

51.2

(%)

NIGHT

(%)

Table 2-8, the usage of bedroom window, Source: (N.H. Wong, 2000) WINDOW USAGE OF BEDROOM MORNING

NOON

EVENING

4.7 5.9 1.6 12.9 0.4 0.8 6.7 1.2 14.5 1.2 50.2 84.7

90.2

78.6

53.4

(%)

This adaptive behavior contributes in a positive way to the higher-level satisfaction over the environment. When the thermal acceptability is low in the afternoon session, the action of opening the window and switching on the fan reach the highest frequency of choice. However, during nighttime, which has a higher thermal acceptability, usage of AC shows a higher frequency. In terms of the use of climatic control to modify the indoor environment, it is found that the opening of windows and usage of fans are high in both the afternoon and evening. The high usage of airconditioning for night hours is observed and It indicates that the differences in the thermal comfort perceptions between types and floor levels are minimal (less than 10% in most cases). However, the strong correlation between the thermal comfort perception and wind sensation reveals that considerations that are more critical should be given to the layout and window opening area of the building design, which can create the preferred higher air movement (wind) and thus increase the thermal comfort of the residents. Findings show evidence that occupants are naturally acclimatized to the local hot and humid climate conditions. [23]

Page | 62

Neutral temperatures and comfort ranges of subjects in the hot and humid region, Source: (N.H. Wong, 2000) Researcher

Time

Time of Study

Country

Webb

1950

Field Study

Singapore

Ellis

1952

Field Study

Journey between

Number of SubjectsTemperature of Comfort (째C) 16

26.2 ET

Singapore-Hong Kong

5211

26.1 ET

1853

Field Study

Singapore

118

22-25.5 ET

Busch

1990

Field Study

Bangkok, Thailand

1100

28.5 ET (NV)

De Dear

1990

Thermal Chamber Singapore

25.4 Ta

1990

Thermal Chamber Singapore

25.4 Ta (70%)

1990

Field Study

583

28.5 (NV)

235

24.2 (AC)

596

26.7 To (NV+AC)

27.9 Ta (35%)

Karyono

1994

Field Study

Singapore Jakarta, Indonesia

2.8 Concluding Summary Most of the modern lightweight and highly glazed structures after the 1950s started adopting mechanical ventilation, particularly air conditioning system to compensate the excess heat gain. While this facilitated freedom and flexibility of design, it also increased the cost with higher energy consumption. This triggered designers to reevaluate the role of natural ventilation in buildings and to become familiar with the basic principles. Consumption of energy and more user control over the immediate environment were main concerns. With minimal use of energy and reliance on mechanical systems, a building with passive design principles always take the advantage of natural renewable energy resources such as daylight, wind and thermal buoyancy, to achieve a comfortable internal environment to live in. Thus, the building design should adapt to climatic considerations by means of natural ventilation and sunlight shading etc. As high-rise housing consumes more energy, there is an important significance of passive design. It means environment; geography and climate should be considered by the architects and designers during the design process. In tropical region, natural ventilation is the most effective cooling strategy for whole year-round and natural ventilation using wind pressure is widely applicable for achieving airflow for indoor thermal comfort. (Arens et al, 1984) However changing modern lifestyle leads to higher electricity Page | 63

consumption. For the residential buildings in Singapore, the energy consumption has increased almost 100% during the past 10 years from 950.8 KWh/resident in 1991 to 1803 KWh/resident in 2001. Moreover, as the economies of certain parts in hot humid regions grow peoplesâ&#x20AC;&#x2122; tolerance to higher temperature and humidity may diminish due to increased expectations [25]. In this Dissertation, the natural ventilation performance will be interpreted in relation to various survey and testing results and adaptive thermal comfort theory using BBCCs, which described in literature review. Though the BBCCs boundaries are considerable to evaluate adaptive comfort theory for a hot and humid climate (Busch, 2000; de Dear, 1998, 2002; Jitkhajornwanich et al., 1998; Wong et al., 2002; Ng et al., 2007; van Hoof, 2008; Moujalled, 2008) and thus will be used as assessment criteria for the performance of wind induced ventilation for the chosen case studies.

2.9 References: [1] Department of Trade and Industry (DTI). (2003). Renewables innovation review. Retrieved May 1, 2007, from http://www.berr.gov.uk/files/file21955.pdf. (Accessed 11.07.2010) [2] U.S. Environmental Protection Agency (EPA). (2004). Buildings and the environment: A statistical summary. September 1, 2007, from http://www.epa.gov/greenbuilding/pubs/gbstats.pdf. (Accessed 17.07.2010) [3] Building Research Establishment, Sustainable Construction Unit (BRESCU). (2000). Energy consumption guide 19: Energy use in offices. Watford, UK: Energy Efficient Best Practice Programme, BRE.

Page | 64

[4] Baker, N. V., & Steemers, K. (2000). Energy and environment in architecture: A technical design guide. London: E & FN Spon. Review Article: Passive Design for Thermal Comfort in Hot Humid Climates Torwong Chenvidyakarn, University of Cambridge, UK. [5] Yeang, K. (2007). Designing The Eco skyscraper: Premises for Tall Building Design, The Structural Design of Tall and Special Buildings, Wiley Inter science, vol. 16, pp. 411-42. [6] Behr, E. et al, â&#x20AC;&#x153;The Skyscraper-Naturally Ventilated? New Responses to Ecology in High-Rise Buildingsâ&#x20AC;?, 5th CTBUH World Congress, Amsterdam, Holland, May 1995, pp.739-774. [7]. Battle McCarthy Consulting Engineers, Wind Towers, Chichester: Wiley-Academy, 1999, pp.24-26. [8],[9] Richards, I. et al, T.R. Hamzah and Yeang: Ecology of the Sky, Australia:Images Publishing, 2001, p.128-129 [10] Fanger, P.O. (1970). Thermal comfort, analysis and application in environment engineering. Copenhagen, Denmark: Danish Technical Press. [11] Mallick, F. H. (1996). Thermal comfort and building design in the tropical climates. Energy and Buildings, pp. 23, 161-167. [12] Jitkhajornwanich, K. (2006). Thermal comfort and adaptation for thermal comfort of local populations. The 2006 National Research Council of Thailand Award. Bangkok, Thailand, 117-120. [13] American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). (1995). ASHRAE standard 55-1992, addenda 1995: Thermal environmental conditions for human occupancy, including ANSI/ASHRAE addendum 55a-1995. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers. [14] Zhang, G., Zheng, C., Yang, W., Zhang, Q., & Moschandreas, D. J. (2007). Thermal comfort investigation of naturally ventilated classrooms in a subtropical region. Indoor and Built Environment, 16(2), pp. 148-158. Page | 65

[15] Wong, N. H., Feriadi, H., Lim, P. Y., Tham, K. W., Sekhar, C., & Cheong, K. W. (2002). Thermal comfort evaluation of naturally ventilated public housing in Singapore. Building and Environment, pp. 37, 1267-1277. [17] Khedari, J., Yamtraipat, N., Pratintong, N., & Hirunlabh, J. (2000). Thailand ventilation comfort chart. Energy and Buildings, pp. 32, 245-249. [16] Feriadi, H., & Wong, N. H. (2004). Thermal comfort for naturally ventilated houses in Indonesia. Energy and Buildings, pp. 36, 614-626.

[17] Wang L, Wong NH. Thermal analysis of climate environments based on weather data in Singapore for naturally ventilated buildings. Indoor air 2005. [18] Wang Liping, Wong Nyuk Hien, (2006) The impacts of ventilation strategies and facade on indoor thermal environment for naturally ventilated residential buildings in Singapore, Department of Building, School of Design and Environment, National University of Singapore, [19] Wong Nyuk Hien, Li Shuo, Wang Liping, (2006) Facade design optimization for naturally ventilated residential buildings in Singapore *, Department of Building, School of Design and Environment, National University of Singapore, Singapore 117566, Singapore [20] The development &building control division (P.W.D.) Singapore. Handbook on energy conservation in building and building services. Singapore: The division; 1979. [21]

http://goliath.ecnext.com/coms2/gi_0199-5592331/Determination-of-acceptable-U-

values.html. (Accessed: 14.07.2010) [22] Wong NH. Thermal performance of facade materials and design and the impacts on indoor and outdoor environment. Technical report, National University of Singapore, 2004. [23] N.H. Wong â&#x2C6;&#x2014;, H. Feriadi, P.Y. Lim, K.W. Tham, C. Sekhar, K.W. Cheong, (2001) Thermal comfort evaluation of naturally ventilated public housing in Singapore Department of Page | 66

Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore Received 9 April 2001; received in revised form 2 August 2001; accepted 12 November 2001 [24] http://goliath.ecnext.com/coms2/gi_0199-5592331/Determination-of-acceptable-U-values.html.

(Accessed: 20.07.2010) [25] de Dear, R. J., Leow, K. G., & Foo, S. C. (1991). Thermal comfort in the humid tropics: Field experiments in air conditioned and naturally ventilated buildings in Singapore. International Journal of Biometeorology, 34, 259-265.

2.10 Bibliography B. Givoni, (1976) Man, climate and architecture, London: Applied Science Publishers, ISBN 085334678x Baruch Givoni (1994) Passive and low energy cooling of buildings /. New York; Chichester: John Wiley. ISBN 0471284734 Baruch Givoni. (1998). Climate considerations in building and urban design New York; Chichester : Van Nostrand Reinhold Torwong Chenvidyakarn, 2007, Passive Design for Thermal Comfort in Hot Humid Climates, Department of Architecture, University of Cambridge, Ph.D. Ruba Salib, 2008, Natural Ventilation in High Rise Office Buildings, University of Nottingham, Master Thesis.

J. P. Davey May 2006, Natural Ventilation Strategies for Tall Buildings, University of Nottingham, School of Built Environment, Master Thesis. Kleiven, T. (2003), Natural Ventilation in Buildings: Architectural concepts, consequences, and possibilities, Norwegian University of Science and Technology, Thesis submitted upon the partial

Page | 67

fulfillment of the requirements for the degree of Doktor Ingenirّ at the Faculty of Architecture and Fine Art, pp. 1-305. Le Thi Hong Na, Jin-Ho Park. Emphasis on Passive Design for Tropical High-rise Housing in Vietnam Richard Aynsley, (2001) Natural Ventilation in Passive Design. Torwong Chenvidyakarn, Ph.D. Passive Design for Thermal Comfort in Hot Humid Climates Review Article: Etheridge D.W. and Ford B.H. Natural ventilation of tall buildings – options and limitations. CTBUH 8th World Congress, Dubai. 3-5 March 2008.

J.L. Niu, J. Burnett, (2001) Setting up the criteria and credit-awarding scheme for building interior material selection to achieve better indoor air quality, Environment International. pp. 26 (7–8) 573– 580. Jianlei Niu, (2003) Some significant environmental issues in high-rise residential building design in urban areas Department of Building Services Engineering, The Hong Kong Polytechnic University,Hunghom, Kowloon, Hong Kong, China. Allard, F. (1998) Natural Ventilation in Buildings, James and James, London. David Rennie and Foroutan Parand, Environmental Design Guide for naturally ventilated and daylit offices, 1998, BRE, London, BR 345 ISBN 1 860812279. Journal of Architectural/ Planning Research and Studies, Volume 5, Issue 1. 2007 Faculty of Architecture and Planning, Thammasat University Natural Ventilation by Andy Walker, National Renewable Energy Laboratory 06-15-2010 http://www.wbdg.org/resources/naturalventilation.php. (Accessed: 25.07.2010)

http://tigger.uic.edu/depts/ahaa/imagebase/intranet/chiviews/page197.gif. (Accessed: 25.07.2010) Page | 68

Methodology

3.1 Introduction Generally intuitive design process marks the start of any project, which also facilitates consideration of environmental performance aspect in the design ; however usage of environmental simulation programs like Ecotect, TAS and CFD, designer can predict the preliminary design outcome. In this research approach, programmes like Ecotect, TAS and CFD (Gambit and Fluent) will be used for evaluation of natural ventilation performance on tall residential buildings. The aim is to ensure the airflow rates and the flow pattern in the building envelope by using CFD. In addition, the dynamic thermal simulation program (TAS) will be used to evaluate the thermal performance of the examined buildings at different locations. More over the overall ventilation performance is interpreted in relation to adaptive thermal comfort theory, which discussed earlier in (section 2.3.1).

Page | 69 Figure 3.1-1, Showing typical section and yearly wind direction LHS: Kanchanjunga Apt, Mumbai, Centre: MBF Tower, Penang RHS: Moulmein Rise, Singapore (Source: Ecotect, Modified by Author)

3.2 Process: In tropics, tall buildings are more vulnerable to high wind speed, high solar exposure, exposures to storms and wind driven rain, which draw certain limitation in designing of a natural ventilated tall building. Hence, the thorough study of site microclimate has been analyzed by calculating diurnal, monthly and yearly temperature, relative humidity, solar radiation; wind speed and rain fall for each case study, which helps to analyze the buildings through TAS and CFD. The detail microclimate analysis will be discussed in next chapter. The main objective of this report is to analyze the

efficiency of the natural ventilation and this is undertaken using two different methods: Qualitative and Quantitative Analysis. The process involves following steps: a. Detail Study of the macro & microclimate. b. Understand the adaptive thermal comfort. c. Analyzing the building design and its passive strategies. d. Performance evaluation by using digital technologies. e. Analyzing the performance.

3.3 Qualitative Analysis: Qualitative analysis, which includes a post occupancy evaluation conducted to assess the adaptive thermal comfort of the occupants staying in the particular building. The occupant survey has done for the old building: Kanchanjunga Apartment, Mumbai (1970 â&#x20AC;&#x201C; 1983) and the new building Moulmein Rise, Singapore (2003) for a comparative and detail analysis. A questionnaire with 15 questions was given to the occupants of Kanchanjunga Apartment, Mumbai and Moulmein Rise, Singapore. 3.3.1

Case- 1 (Kanchanjunga Apartment, Mumbai)

The Condominium of 32 luxury duplex apartments of four different types, two flats on each floor. Hence different rooms on different flat types of different orientation like the living room at the center and North west bed room on lower floor and south east bed room on upper floor has chosen in each apartment unit

Page | 70

Figure 3.3-1, Showing Section of Kanchanjunga (Source: Hakki Can Ă&#x2013;zkan, 2009 modified by Author)

for the survey since east- and west-facing facade receive much more solar radiation than north and south facing facades in the tropical region. Refer the sample questionnaire prepared for the occupant survey and the answers filled up by one of the resident.

Figure 3.3-2, Different Types of flats in Kanchanjunga Apartment Mumbai (Source: Hakki Can Ă&#x2013;zkan, 2009 modified by Author)

Page | 71

TYPE â&#x20AC;&#x201C; A, floor_ _11

_ _ _, flat no. _NE side_ _ _

Occupants Satisfaction Survey â&#x20AC;&#x201C;University of Nottingham This questionnaire is taken as part of research to investigate Thermal comfort in Kanchanjunga apartment, Mumbai

In summer How would you describe typical thermal conditions SUMMER?

In Living and dining space. 1.

Temperature in summer.

Uncomfortably warm

How do you feel about

Air Circulation

Uncomfortably cold

Still

Draughty

Air Quality of the space

Stuffy

Fresh

In BEDROOM 1.

Temperature in Summer

Uncomfortably warm

2. Page | 72

How do you feel about

Uncomfortably cold

Air Circulation

Still

Draughty

Air Quality of the space

Stuffy

Fresh

In Master Bed room 1. Temperature in summer

Uncomfortably warm

Uncomfortably cold

2. How do you feel about Air Circulation

Still

Draughty

Air Quality of the space

Stuffy

Fresh

In winter (Entire house) 1. How would you describe typical thermal conditions in WINTER? Temperature in winter

Uncomfortably warm 2. How do you feel about?

Page | 73

4 Uncomfortably cold

a. Air Circulation

Still

Draughty

b. Air Quality of the space

Stuffy

Fresh

In Monsoon (Entire house) How would you describe typical thermal conditions in MONSOON? 1. Temperature in Monsoon

Uncomfortably warm

Uncomfortably cold

2. How do you feel about? a. Air Circulation

Still

Draughty

b. Air Quality of the space

Stuffy

Fresh

Overall Year. 1. Freedom to Control your environment

1 None

Full Control

2. To what extent do you recommend mechanical ventilation (A.C.) to replace the current system? Page | 74

Not at all

Highly recommend

Reasons : The natural ventilation system in effect currently works well during most part of the year. A slight stuffy feeling is observed during the monsoons due a high humidity and generally low wind speed during this season. Mechanical ventilation may be useful for summer time but is not required during the winter months. 3. in which rooms, you are using Air conditioning and what time do you use (afternoon / nighttime)? AC is used mainly in the smaller rooms with less ventilation. Mainly in the bedrooms, the need for AC is felt during the summer at afternoon and night times. In addition, bedrooms facing west or south have more need for AC. Also during monsoon, AC is used sometimes during the night. 4. Any other recommendations to improve the natural ventilation in the building. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 5. Which room works best in summer with Natural ventilation without A.C.? Bigger areas like living and dining rooms work best.

Page | 75

3.3.2

Case- 2 (Moulmein Rise, Singapore.)

The Condominium of 50 luxury apartments (48 simplex and two duplex at the top floor) of two different types, two flats on each floor.50 questionnaires were prepared and given to the each flats in the building. Refer the sample questionnaire prepared for the occupant survey and the answers filled up by one of the resident.

Occupants Satisfaction Survey â&#x20AC;&#x201C;University of Nottingham This questionnaire is taken as part of research to investigate Thermal comfort in Moulmein rise, Singapore Please feel free to fill up this questionnaire which will take few minutes and we will collect it on next weekend, thanks

1. Which Flat are you in? Type A _ _ _

Type B_ _ _

2. Which floor are you in? _13_____

In Summer - Southwest Monsoon (April â&#x20AC;&#x201C; August) 1. How would you describe typical thermal conditions in SUMMER? Temperature in Summer

Uncomfortably warm

Page | 76

4 Uncomfortably cold

2. How do you feel about? a. Air Circulation

Still

Draughty

b. Air Quality of the space

Stuffy

Fresh

In winter (September - November) 1. How would you describe typical thermal conditions in WINTER? Temperature in Winter

Uncomfortably warm

Uncomfortably cold

2. How do you feel about a. Air Circulation

Still

Draughty

b. Air Quality of the space

Stuffy

Fresh

In Northeast Monsoon (December â&#x20AC;&#x201C; March) How would you describe typical thermal conditions in NE MONSOON? 1. Temperature in NE Monsoon

Uncomfortably warm

Page | 77

4 Uncomfortably cold

2. How do you feel about? a. Air Circulation

Still

Draughty

b. Air Quality of the space

Stuffy

Fresh

Overall Year. 1. Freedom to Control your environment

None

Full Control

2. To what extent do you recommend mechanical ventilation (A.C.) to replace the current system? 1

Not at all

Highly recommend

Reasons: only if uncomfortably warm in the afternoon 3. in which rooms, you are using Air conditioning and what time do you use(afternoon / night time) ? Bed room (Afternoon sun) 4. Any other recommendations to improve the natural ventilation in the building. ______________________________________________________________________________ ______________________________________________________________________________ 5. Which room works best in summer with Natural ventilation without A.C.? Living Room.

Page | 78

3.4 Quantitative analysis Quantitative analysis through TAS and CFD simulation has carried out to study the effectiveness of natural ventilation on each case study. 3.4.1

Quantitative analysis through TAS

The simulation is carried out in order to find out the effectiveness of natural ventilation in hot-humid climate through the dynamic simulation tool TAS that includes TAS Building Designer, system and Ambiens, which helps to simulate the thermal performance of the building. Four different ventilation strategies with the combination of various construction materials for naturally ventilated buildings for tropical climate are investigated in Singapore through TAS [1].After analyzing

the literature review this simulation is

carried out for two different ventilation strategies including 24 hours ventilation and night time only ventilation. Considering the solar radiation, outdoor temperature profile and the occupancy period, the night ventilation is scheduled from 6pm

Figure 3.4-1, TAS model of Kanchanjanga Apartment, Mumbai (Source: Author)

to 10 am. 3.4.1.1 Case- 1 (Kanchanjunga Apartment, Mumbai) The Kanchanjunga Apartment comprises of 32 luxury duplex apartments of four different types, two flats on each floor. Alike the survey, the similar rooms such as living room at the center and North west bed room on lower floor and southeast bed room on upper floor has been chosen for study since east and west facing facade receive much more solar radiation than north and south facing facades in the tropical regions. The residential tower is 28-storeys with 2 units per floor having different orientations. The geometric model of the Kanchanjunga Apartment (Fig.3.4-1) has been built in TAS to carry out the parametric simulations based on the previous study and the occupantâ&#x20AC;&#x2122;s perception for the whole typical year of Mumbai. Due to the time constraint three rooms has simulated for a relevant output. Page | 79

Below criteria/steps are followed at the time of selection of the rooms to be simulated: •

The highest solar gain receiving rooms are selected. The rooms, which are used most of the time by the occupants (by interviewing the occupants).

•

To check the variation in airflow rate with respect to height, the living and dining space and North west bed room (as they receive high solar gain) of ground floor, 12th floor and 24th floor has selected for the simulation.

•

To check the variation in airflow rates according to change in orientation, both the living and dining space in each flats on ground floor, 12th floor and 24th floor (since two flats in one floor are facing opposite to each other) has also selected.

•

Southeast bedroom on upper floors such as 1st, 4th, 7th, 10th, 13th, 16th, 19th, 22nd and 25th floors has simulated.

Consideration taken at the time of simulation Weather File:

Mumbai Weather file from Energy PLus

Analyisis Period :

Average monthly, Summerperiod : March and April (wind direction from Northwest) & May (wind direction from Northwest and Southwest)

No. of floors:

Floor height:

Window to Wall ratio :

The living and dining space – 48%, North West bedroom – 34% and South East Master bed room – 45%

Shading devices :

Each openings are well shaded with balcony and terrace gardens.

Building Materials and Construction: As per base condition and earlier study (U value of external facade ranges from 0.3 W/m2 0C to 3.6 W/m2 0C)

Roof:

150mm Reinforced Cement Concrete (U=7.45 W/m20C), Floor/Ceiling: 150mm R. C. C + tiles (U=3.07 W/m2 0C),

Page | 80

Additional construction materials, plaster, white paint etc. are also taken in to consideration

(refer

section 2.7 for detail)

Occupancy pattern, Planning and Program:

By interviewing the occupants.

The living and dining space:

Occupied period (morning - 7 AM to 10 AM) And evening (6 PM to11 PM) North West bedroom: Occupied period (11 PM to 07 AM) at nighttime only.

South East Master bed room:

Occupied period (11 PM to 07 AM) at night time only

Internal Conditions:

As per occupantâ&#x20AC;&#x2122;s Use (Refer Appendix 7-13)

The living and dining space:

Three occupants

North West bedroom: one occupant:

South East Master bedroom: two occupants

Schedule of opening: Full day ventilation:

Doors and window openings are 50% open 24 hours

Nighttime only ventilation:

Doors and window openings are 50% open during nighttime i.e. from evening 6 PM to morning 10 AM

Nighttime only ventilation:

Doors and window openings are increased from 50% to 75% open during nighttime i.e. from evening 6 PM to morning 10AM

Schedule and Aperture Type:

(Refer Appendix 7-14)

As per base condition and earlier study, various systematic testing is carried out by changing the U value of external wall ranges from 0.5 W/m2 0C to 3.6 W/m2 0C to analyze the performance of the building. (Refer Chapter 4) 3.4.1.2 Case- 2 (MBF Tower, Penang, Malaysia) and Case- 3 (Moulmein Rise, Singapore) Due to time constraint, to get the result from case 2 and case 3: case 1 building model is simulated by placing it on different climatic conditions such as in Singapore and Penang. Case 1 building is tested for case 2 in Penang and case 3 in Singapore to check the building performance for the particular

Page | 81

local climate by changing the building orientation with respect to the prevailing wind direction on summer. Various systematic testing is carried out by changing the orientation. (Refer Chapter 4) 3.4.2

Quantitative analysis through CFD

Thermal comfort and neutral temperature of the naturally ventilated building can be increased by increasing the indoor air velocity [2]. According to several investigators Irminger and Nokkentved, Smith, Wannenburgh and Vanstraaten (unknown year) the flow pattern is independent to the Raynolds number and wide variation in air velocity do not affect the flow rate and pressure distribution over the surfaces therefore the normal wind speed is used during the investigation of building ventilation associated problems.(Givoni, 1976). The CFD (Gambit & Fluent) is employed to assess the performance of the wind driven natural ventilation of the chosen case studies. Fluent is the most dynamic and widely used tool for modeling fluid flows. Its robustness and accuracy that employs a body-fitted coordinate system produce accurate representation of a flow domain with irregular geometries. This study of airflow is carried out for better understanding of the effectiveness of natural ventilation and to create some pictorial image of airflow pattern. How effective the sky courts, terrace gardens are on a tall building is also answered by some basic comparative analysis. More over a comparative study is carried out by analyzing the natural ventilation strategies followed on different floor plans with respect to the wind direction on different cases. At the end, CFD result is compared with the TAS result for calculation of the airflow rate and air change rate (ACH-1) for the simulated building.

Figure 3.4-2, CFD testing: 3D model of Kanchanjunga (Source: Author)

Questions to be answered â&#x20AC;˘

Effect of orientation of the building block with respect to the prevailing wind direction?

â&#x20AC;˘

Effect of sky court and terrace gardens?

â&#x20AC;˘

Effect of open layout plan for free indoor air circulation and appropriate opening to let outdoor air in to the space?

Page | 82

3.4.2.1 Testing of Case 1, Case 2 and Case 3 Case- 1 (Kanchanjunga Apartment, Mumbai)

Figure 3.4-3, Showing CFD model of Kanchanjunga Apt., Mumbai (Source: Author)

•

The building block plan

•

Internal layout plan with openings of four types of plan

•

Building block section showing terrace gardens

•

Detail building section showing internal walls with openings of four types of modules i.e. Type A,B,C and D

Case- 2 (MBF Tower, Penang, Malaysia)

Figure 3.4-4, Showing CFD model of MBF Tower, Penang (Source: Author)

•

The building block plan

•

Internal layout plan with openings

•

Building block section showing sky courts

•

Detail building section showing internal walls with openings

Page | 83

Case- 3 (Moulmein Rise, Singapore)

Figure 3.4-5, Showing CFD model of Moulmein Rise, Singapore (Source: Author)

•

The building block plan

•

Internal layout plan with openings

•

Building block section

•

Detail building section showing internal walls with openings

3.4.2.2 Process Since the airflow modeling is for wind driven natural ventilation, a computational domain would be required around the building for the mesh to be created for studying the effect of the surroundings on the natural ventilation of the building. However, there are no surrounding buildings within a range of 500 m, which could block the airflow to the chosen tall building to be simulated. The chosen case study buildings are free from obstructions on the prevailing wind direction. Fig 3.4:7 shows the width and height of the computational domain used for analysis. Since air movements are considered as the natural cooling resource, the computations are carried out for isothermal conditions. Standard k- є model is used. (Refer Appendix 7-15 for the detail procedure)

Figure 3.4-7, showing boundary conditions used for all simulations (Source: Author)

Page | 84

Figure 3.4-6 Gambit model showing boundary conditions given for one of the tower. (Source: Author)

Data Input for the simulation: Size of openings are provided as per the building Drawings. Avg. wind speed: 2m/s has been taken by comparing the result from both Ecotect and climate consultant software according to the Weather file of the each case studies. (Refer, detail microclimatic study on chapter 4) Since the velocity magnitude changes at different height, to provide accurate wind speed at different height, the domain is divided in to several parts at an interval of 3m for calculation of Vr at each 3m level. Wind speed Consideration: Wind within the lower regions of the earth’s atmosphere is characterized by random fluctuations in velocity which when averaged over a fixed period of time, yields mean values of speed and direction. Wind data are generally obtained from a meteorological station located away from an urban environment. In general, this wind speed must be corrected for terrain conditions and for the height of the building relative to the height of wind measurement (usually 10 m). An approximate correction is proposed in BS 5925 and is given as: Vr = vm k za [Environmental Design, CIBSE guide A, 2006, p 157]

Where Vr is the wind speed at the building height (m·s–1), vm is the wind speed measures in open country at a height of 10 m (m·s–1), z is the building height (m), k and a are constants dependent on the terrain. Terrain coefficients for wind speed Calculation: Table 3-1, Terrain coefficients for wind speed Calculation, (Source: CIBSE guide A, 2006)

Terrain

Open, flat country

0.68

0.17

Country with scattered wind 0.52

0.20

breaks Urban

0.35

0.25

City

0.21

0.33

Context: City: Wind Velocity (V) = 2m/sec, K = 0.21, A =0.33, Floor height (H) =3 m, Vr = 2 x

0.31 x 30.21= 0.603531 m/s

Page | 85

Table 3-2, Vr calculation for the simulation, (Source: Author)

Hei

12m

15m

18m

21m

24m

27m

30m

33m

36m

39m

0.6035

0.7586

0.867

0.953

1.026

1.090

1.147

1.198

1.246

1.290

1.331

1.370

1.407

ght Vr

Height

10m

20m

30m

40m

50m

60m

70m

80m

90m

100m

110m

0.897944

1.128728

1.290326

1.527247

1.621957

1.7066

1.783483

1.854169

1.91977

1.981111

2.0

Table 3-3, Vr calculation for the simulation, (Source: Author)

Boundary conditions given for the simulations, specified as follows: Left edge of domain- Velocity inlet Right and top edge of domain- Pressure outlet Since the ground as well as at the inner or outer building surface are constant, stress layers are assumed to exist and the wall function is used in order to avoid the need for large number of nodal points usually required for a region with large velocity gradients. Hence, Building and ground line- Walls Results: The refinement has been performed until the solution reaches convergence to give a more accurate and consistent result in each case, only the final product is published on the result (Refer Appendix for the detail procedure). After one boundary, one region and 2 boundary adaptations the following residuals were obtained.

Figure 3.4-8, CFD graph showing obtained scaled residuals for one of simulation, (Source: Author)

The graph shows the solution has almost reached convergence and the errors are less than 1%

Page | 86

Case- 1 (Kanchanjunga Apartment, Mumbai) The Kanchanjunga Apartment comprises of 32 luxury duplex apartments of four different types, two flats on each floor. Alike the TAS simulation, the 3D geometric model of the Kanchanjunga Apartment has built in Gambit to carry out the parametric simulations on Fluent.

Figure 3.4-9, Showing CFD model of Kanchanjunga Apartment.Type A plan, (Source: Author)

Based on the above questions, simulation has taken place through various testing by inputting different values of Vr for different tests. The refinement of each testing has been performed until the solution reaches convergence, which produces more accurate and consistent result. (Refer chapter 4 for detail analysis)

Case- 2 (Moulmein Rise, Singapore) and Case- 3 (MBF Tower, Penang, Malaysia)

As in case 1, similar procedure is carried out for the simulation of case 2 and case 3 buildings. (Refer chapter 4)

Figure 3.4-10, LHS: Showing CFD model of Moulmein Rise Plan, RHS: Showing CFD model of MBF Tower Plan (Source: Author)

Page | 87

3.5 Reference [1] EDSL Ltd. TAS, Software package for the thermal analysis of buildings. Stony Stratford, Milton Keynes, UK, 2000 /http://www.edsl.net/S. (Accessed : 21.07.2010) [2] Feriadi H, Thermal comfort for natural ventilated residential buildings in the tropical climate. PhD. dissertation, National University of Singapore, Singapore, 2003. [3] Environmental Design, CIBSE guide A, 2006, p 157

Page | 88

Critical Analysis of Case-studies, Results and Discussion:

The intention of selecting these buildings for study is to address the importance of natural ventilation to minimize the load on mechanical cooling. The aim of the research is based on analysis of the effectiveness of natural ventilation in tall residential building in tropics; therefore, the study is focused on the ‘wind driven cross ventilation’, which is the most dominant strategy use in tropical climate. Here the intention is to find out the potential and risk of natural ventilation strategies incorporated in the existing buildings based on microclimatic considerations. To achieve an architectural design that effectively responds to the diverse and often conflicting requirements of a tropical climatic context is indeed a challenge. An attempt has been made in this study to develop a realistic natural ventilation strategy that responds to the wind force in its complete three-dimensional configuration and enables cooling. Air has been proposed as a medium to create a naturally cooled environment in all chosen case studies. Different and unique systems have been designed to allow free and quick movement of air. These strategies are reflected in the building’s architectural configuration, which will be discussed in this chapter.

4.1 4.1.1

Case study 1 - Kanchenjunga apartment, Mumbai, India Key information

Project:

Kanchanjunga apartment

Year of completion:

1983.

Location:

Latitude of 18.54° N and Longitude of 72.49° E,

Altitude:

11m above the sea level

Climate:

Tropical wet & Dry

Architect:

Charles Correa

Building foot print:

441 SQ.M

Site and situation:

City landscape surrounded by mid-rise and high-rise structures.

Prevailing wind direction:

From S-W and N-W

Type:

Residential

Height:

85 M.

Number of Floors:

Page | 89

Figure 4.1-1, Kanchanjunga Apt. Mumbai (Source: CTBUH Mumbai, 2010)

4.1.2

Introduction

The ‘Kanchanjunga Apartment’ was Architect’s inception which was completed after some fifteen years of time based on his own several housing experiments and Corbusier’s skip level sections, ‘Safdie’s Montreals Habitat’. Charles Correa’s 28 storeyed ‘Kanchanjunga Apartment’ in Mumbai elaborates his penchant for sectional displacement appropriately accompanied by changes in floor surface. Here he pushed his capacity for ingenious cellular planning to the limit. A great combination of interlocking one and a half storey, split-level, 3 and 4 bedroom units with the two and half storey 5 and 6 bedroom units can be seen successfully attempted in a high rise building creating 32 luxurious apartments. The main ideas behind: •

The apartment himself is a direct response to the present society, the

Figure 4.1-2, Showing the skyline of the Mumbai (Source: unknown )

escalating urbanization, and the climatic conditions for the region. •

Distinctive in Mumbai’s urban landscape.

•

Well ventilated and appear to suit the contemporary life style.

•

One and two floor height terrace gardens in each flat.

•

The typical open floor plans with double heighted living room for cross-ventilation.

•

Best views of Arabian Sea on west and the harbour on the east.

•

Use of terrace gardens alike to the protective verandas in bungalow.

4.1.3

Site micro climate analysis

Architectural design needs to respond to the hot humid climatic context of the site. The Kanchanjunga apartment is located in south-west of downtown Mumbai in an upscale suburban

Arabian Sea

Figure 4.1-3, showing location of Kanchanjunga Apt. with respect to Arabian Sea.

Page | 90

(Source: Google Map, modified by Author)

setting. The final solution needs to satisfy the diverse and often conflicting conditions of hot summer, monsoon and cold period. Cooling remains as the predominant requirement due to the tropical climate. The Kanchanjunga tower of total 441 m2 of floor area is located on Peddar road, Mumbai, India. The site is situated in a medium-density area from the town center and surrounded by the Arabian Sea on west just 500 m distant and the harbor on the east (Figure 4.1.3) As per the Climate Classification chart, the site falls in the tropical climate and due to the

moderating influence of the sea, the temperature in Bombay undergoes little seasonal fluctuation; the monsoons bringing about the only significant change.The city experiences wet and dry climate with 7 months dryness along with high rainfall especially during the south west monsoon from midJune to September with the highest of rains in July. Cold season is from December to February followed by Summer Season from March to June.

INDOOR COMFORT ZONE

4.1.3.1 Temperature Variation: The average annual temperature in Mumbai is 27.2°C. The daily mean maximum temperature ranges from 29.1 °C to 33.3 °C while the daily mean minimum temperature ranges from 16.3 °C to 26.2 °C The hotter months are between March and mid of June with mean temperatures ranging

Figure 4.1-4, showing Average Temp (Source: Ecotect modified by Author)

between 27 and 30°C with hottest month April, while the cooler months are between December to

February with mean temperatures ranging between 24 and 27°C. The day time temperature fluctuates between 27°C-35°C, and night time fluctuates between 20°C-25°C in summer with low diurnal temperature difference of 7 0C to 10 0C.

Figure 4.1-5, Showing LHS: WBT and DBT variation. RHS: Solar Radiation (Source: climate consultant Modified by Author)

Page | 91

4.1.3.2 Relative Humidity: The average relative humidity fluctuates between 60% 85% during summer and monsoon period with minimum in the month of November to march. 4.1.3.3 Precipitation: Mumbai lies in a zone of high monsoon downpour and it afflicts its residents. However, it brings the

Figure 4.1-6, Showing Avg. Temp & Rel. Humidity (Source: Ecotect and Modified by Author)

temperature down, but the clamminess in the air worsens the situation. Precipitation occurs during the southwest

monsoon

period

(from

mid-June

September).The lowest precipitation occurs in the months of December to March. However, the mean annual precipitation is 2167mm. 3

Figure 4.1-7, Showing Rainfall (Source: http://www.windfinder.com/windstats, Modified by Author)

4.1.3.4 Wind The prevailing wind direction varies during all seasons. Mostly the summer months, March and April avail northwest prevailing wind whereas May and June avail southwest, west and northwest prevailing wind. The mean surface winds over Mumbai city are generally mild, with an average wind speed of 3.4 m/s, and a maximum speed of 5.4 m/s.4 4-1 shows Wind Speed and Direction4

Nature of Wind Prevailing

March, April wind NW

May, June

Aug

Nov

NW/SW/W

W/S

E/NE

10.78

15.93

10.14

direction Mean Monthly Wind 10.62 to 10.78 Speed (km/hr)

http://en.wikipedia.org/wiki/File:India_mumbai_temperature_precipitation_averages_chart.svg (Accessed 01.08.2010).

http://www.windfinder.com/windstats ((Accessed 01.08.2010).

Page | 92

March- N-W Prevailing Wind

May- S-W Prevailing Wind

April- N-W Prevailing Wind

June- W/S-W Prevailing Wind

Figure 4.1-8, showing Pre-dominant Prevailing wind directions in summer months. (Source: Ecotect weather tool modified by Author)

Page | 93

Figure 4.1-9, showing yearly wind directions. (Source: Ecotect weather tool modified by Author)

Figure 4.1-10, Psychrometric chart showing boundary of different passive cooling approach for Mumbai (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 4.1:10 Shows boundary of various passive cooling strategies. Figure (4.1:11) shows indoor thermal comfort can be achieved during most of the time of the summer months with indoor air velocity of 2m/s.

figure 4.1-10, Psychrometric chart showing the boundaries of outdoor temperature and humidity wi4.1-11indoor air speed of 0.25 and 2 m/s for Mumbai, (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Page | 94

4.1.4

Built form and orientation

Buildings oriented east to west in Mumbai get the best view of Arabian Sea on one side and harbor on the other as well as catch the prevailing sea breeze. In the other hand East-West is also the direction of the hot Sun and heavy monsoon rains. Therefore, in the ancient practice of Architecture, the bungalows solved the issue of Sun and monsoon rain with the provision of Verandah around the main living areas to act as a protective layer. Combining all these considerations, the square form is having two interlocking units facing east and west. The building is facing towards sea on west and northwest.

Figure 4.1-12, Sun Path over Kanchenjunga Apt. (Source: Ecotect weather tool Modified by Author)

Optimum orientation of each space to prevailing breeze and strong linkage between leeward and windward sides strengthen the utilization of the pressure difference to facilitate wind induced cross ventilation.

Figure 4.1-13, Showing LHS: Winter Solstice, Center: Equinox and RHS: Summer Solstice sun path (Source: Ecotect and Modified by Author)

Page | 95

4.1.5

Spatial Configuration

Kanchanjunga is a condominium of 32 luxury apartments of four different types, varying from three to six bedrooms each. The tower has a proportion of 1:4 (being 21 meters square and 84 meters high).

•

Type A (10 number of Flats): Lower floor Area – 210.4 Sq.m , Upper floor Area- 118 Sq.m

•

Type B (12 number of Flats): Lower floor Area – 210.4 Sq.m , Upper floor Area- 48.9 Sq.m

•

Type C (8 number of Flats): Lower floor Area - 210.4 Sq.m , Upper floor Area- 188 Sq.m

•

Type D (4 number of Flats): Lower floor Area - 210.4 Sq.m , Upper floor Area- 170 Sq.m

Figure 4.1-14, Sectional View. (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 4.1-15, Typical Floor plan and Views of individual Bungalows of the Apartment (Source: Hakki Can Özkan, 2009 modified by Author)

Page | 96

The complex spatial organization of living spaces within the tower can be guessed from the minimum unbroken surfaces and the double height terrace gardens at corners. Cantilevers, the result of variations and interlocking are hold up by shear end walls.

Figure 4.1-16, (Source: Hakki Can Özkan , 2009 modified by Author)

Figure 4.1-17, Showing structural system (Source: (Source: Hakki Can Özkan, 2009 modified by Author)

Figure 4.1-18, View from Terrace Garden (Source: Charles Correa, 1987, Modified by Author

The plan has four units at each floor. Each set is separated from the lift core. The building is in the form of single square towers connected by the central service core. The typical floors are designed to be column free. Toilets and Kitchen areas are looking inwards while the Living Areas, Study rooms and Bedrooms have outer views. Deeper terrace gardens are provided to minimize the solar gain.

Figure 4.1-19, showing South, West, and East & North Elevation (Source: Hakki Can Özkan, 2009, modified by Author)

Page | 97

The building is a 32-storeyed reinforced concrete structure with 6.3m cantilevered open terraces. The central core houses lifts and other services provide the main structural element for resisting lateral loads. With its concrete construction and large areas of white panels, bears a strong resemblance to modern apartment buildings in the West. 4.1.6

Natural Ventilation Strategy

Type D Type C Type B Type A

Figure 4.1-20, Section showing wind induced cross ventilation in different type of flats at each level. (Source: Author)

Page | 98

The external earth filled terraces and internal elevated spaces were critical being a smaller displacement of levels. Correa also managed to shield these High-rise units from both Sun and monsoon rains effectively. The deep terrace gardens, garden verandahs suspended in air are protective, working as a protector from rain and Sun. Corbusierâ&#x20AC;&#x2122;s Unit Habitat built at Marseilles in 1952 had similar configuration. The terrace gardens at Kanchanjunga Apartments are actually a modern interpretation for the future of traditional Indian Bungalowâ&#x20AC;&#x2122;s. In Kanchenjunga there was a successful attempt made to maintain the privacy and transparency of the occupants. The plan is oriented in such way; both flats facing North West get maximum benefits from northwesterly prevailing wind in the hottest period of the year. Though the each flat are having different planning approach, they all are benefitted by wind induced cross ventilation for the whole year. Wisely, placed terrace gardens and double heighted living room enhance the cooling effect during the summer period. The cut out shapes of these two green terraces on two facades strongly minimize the solar gain in to the space while maximize the cooling effect.

Figure 4.1-21, showing ventilation strategies for different types of Flats, (Source: Hakki Can Ă&#x2013;zkan, 2009 modified by Author)

Page | 99

Shaded double Storeyed Terrace Garden

Double storeyed Living Room

Larger openings

Terrace Garden

Figure 4.1-22, Design features and elements help to enhance cross ventilation. (Source: CTBUH Mumbai, 2010)

Page | 100

4.1.7

Qualitative Analysis

Qualitative analysis, which includes a post occupancy evaluation, conducted to assess the adaptive thermal comfort of the occupants staying in the Kanchanjunga Apartment. Finding (08 filled up questionnaire out of 34) shows most of the occupants are naturally acclimatized to the local hot and humid climate. In terms to modify the indoor environment, it is found that the occupants open and close the windows during nighttime and afternoon time respectively as per their requirement to control their indoor environment.

Satisfaction Chart Upper floors

Satisfaction level in Living room

Midddle floors

Comfortable

Lower floors

Neutral

20%

35% 40%

80%

25%

Satisfaction Level in Peak Summer period (Comparision between Southeast and Northwest bed room)

The most comfortable room during Summer Living room

Northwest Bed room

Southeast Bed room 10%

Northwest Bed room 30%

90%

70%

Usage of Air Conditioning Living room

Bed room

20% 80%

Figure 4.1-23, Occupantâ&#x20AC;&#x2122;s survey Results, Source: Author

Page | 101

The result indicates, the differences in the thermal comfort perceptions between A, B, C and D types and floor levels are minimal. More occupants are finding comfort in living room, which works best during the summer period. The high usage of air-conditioning for night hours especially in bedroom is observed. More over the northwest bedrooms are more comfortable than the southeast bedroom. Since building needs to respond its extreme climatic condition hence to reach a conclusion, the testing is carried out for the hottest day of the year through various simulation programs like CFD and TAS.

Page | 102

4.1.8

Quantitative Analysis

Both the analysis is based on the occupant survey and previous study (Refer section 2.3 & 2.7).

4.1.8.1 Analysis through CFD Questions to be answered: â&#x20AC;&#x153;Effect of orientation of the building block with respect to the prevailing wind direction.â&#x20AC;?

4.1.8.1.1 Testing 1: During both the northwest and southwest prevailing wind. The building block plan: The building facades having larger openings are facing towards the Northwest and southeast. The summer months are from March to mid-June and during these months, March and the hottest month April experience the northwest prevailing wind whereas May and June experience the southwest, northwest and west wind. Just to compare the impact of NW and SW wind on the building, testing 1 is carried out for both the northwest and southwest wind. Figure showing the top-level plan of the tower and data input for the testing: At velocity inlet (Vr = 2m/s) is given for the calculation. (Refer detail calculation on section 3.2.2).

Figure 4.1-24, LHS: CFD Testing of block plan with SW wind & RHS: with NW Wind (Source: Author)

Building is situated at 450 m away from the sea and the southwest and northwest wind hits the building face at an angle of 900, Openings are perpendicular to the prevailing wind.

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Figure 4.1-25, CFD Testing of block plan (Source: Author)

Above analysis shows, the wind hits the building face and is deflected to both sides. Since there is a low pressure created at the back of the tower, the velocity at the front varies from 1.39m/s to 1.74m/s and velocity at the back varies from 0.2 to 0.17 m/s. In both the condition SW and NW wind having similar magnitude, however due to SW wind, the flat in southwest side experiencing greater air flow whereas the northeast side flat experiencing very low airflow rate, But in the other case both the two flats experiencing 1.56 to 1.74 m/s air velocity, though both the flats have their openings on northwest faรงade which help for better indoor air flow during peak summer period. The negative pressure (suction effect) at the leeward side of 45ยบ wind direction is the highest compared with the negative pressure effect at 0ยบ wind direction ( Abdul Razak Sapian, Unknown year) which concludes, the airflow could be much better if the openings would have experienced oblique prevailing wind. (For more detail, refer 2.5.5.1, 5)

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Question

â&#x20AC;&#x153;Effect of open layout plan for free indoor air circulation and appropriate opening to let outdoor air in to the indoor space.â&#x20AC;? 4.1.8.1.2 Testing 2: During northwest prevailing wind.

Internal layout plan with openings, of four types of plan: Different Vr for different floor levels of the building hence Vr is calculated for each floor levels and the values are put in the velocity inlet edge, (Refer section 3.2.2)

Figure 4.1-26, Type A Lower floor plan, Source Author

Type A Flat, 11th floor having lower and upper floor (Lower Floor, height - 39m from ground), Vr = 1.14070 m/s

Rake 1 Rake 2

Figure 4.1-27, CFD Testing of Type A, lower floor showing the velocity vector and static pressure, (Source: Author)

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Figure 4.1-28, CFD Testing of Type A, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

â&#x20AC;˘

Type A Flat , upper floor (upper Floor, 42m from ground)Vr = 1.4418m/s

Figure 4.1-29: CFD Testing of Type A, Upper floor showing the velocity vector and static pressure, (Source: Author)

Page | 106

Figure 4.1-30, CFD Testing of Type A, Upper floor showing path lines (airflow pattern in the flat) (Source: Author)

ANALYSIS OF VENTILATION RATE & AIRCHANGES PER HOUR IN LOWER FLOOR: 4-2, Flow rates for the inlets and ACH-1 Achieved

Area Surface

Flow rate

the

Area weighted

opening

average X

velocity

m3/s

(m/s)

Rake 1

1.44

0.383

0.552

Rake 2

1.2

0.300

0.3605

Ventilation rate

0.9125

Volume of the lower floor of flat A

225m2

ACH-1

14.6

Figure 4.1-31, RECOMMENDED VENTILATED RATES FOR FRESH AIR, Source: Natural ventilation in non-domestic buildings-Applications Manual AM10, 2005, CIBSE

Required Air change per hour (ACH-1) Assuming the ventilation rate as 100 l/s per person. (Refer figure 4.1-32 and Section 2.1.2 and table 2.1) For 5 person occupancy in the flat, Ventilation rate = 0.1 * 5= 0.5 m3/s ACH-1 = 0.5*3600/225 = 9 ACH-1 Page | 107

Above results, (Refer Table 4-2) conclude the achieved air change per hour for lower floor is 14.6, which is sufficient for five occupants in the flat with respect to the required ACH-1. However, the airflow is not uniformly distributed since all the openings are open during the time of simulation, which can be controlled by closing the window as per occupantâ&#x20AC;&#x2122;s requirement. There is no air movement in the habitable area of the living room due to the obstructing partition wall between living and study room, which does not allow the air to come in. However, the partition wall is

provided with ventilator at upper level which enables the air enters in to the living room at a height of 2.2m level. Hence the air comes through the upper level openings in to the living area and gets diverted towards upper floor through the cut out provided in the living room. Figure shows the air funneling is created in the corridor space however, no negative effects created in the habitable area due to high wind velocity. In other hand, the upper floor is having no airflow though there is no opening in the northwest faĂ§ade. Due to the interlocking deign planning between two level flats the air flow in the upper floor achieved indoor velocity of only 0.2 to 0.3m/s. However due to the double heighted living room, upper floor rooms are getting some amount of airflow. The result can be compared with the section 2.5.5.1.3 on literature review. Type B Flat, 10th floor with lower and upper floor (Lower Floor, height - 33m from ground), Vr = 1.33155 m/s.

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Figure 4.1-33 CFD Testing of Type B, lower floor showing the velocity vector and static pressure, (Source: Author)

Figure 4.1-34, CFD Testing of Type B, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

Type B Flat, Upper floor (Upper Floor, 36m height from ground)Vr = 1.3703m/s

Figure 4.1-35, CFD Testing of Type B, Upper floor showing the velocity vector and static pressure, (Source: Author)

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Figure 4.1-36, CFD Testing of Type B, Upper floor showing path lines (airflow pattern in the flat) (Source: Author)

The result shows, airflow is uniformly distributed to all its internal spaces since the living room is fully open to the northwest wind without any obstruction, which can be compared with the lower floor of type A. The upper floor is also having good amount of air circulation in to its habitable area as it is facing towards the NW prevailing wind during summer period. Type C Flat, 8th floor with Lower and Upper floor (Lower Floor, height - 27m from ground), Vr = 1.246233 m/s.

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Figure 4.1-37, CFD Testing of Type C, lower floor showing the velocity vector and static pressure, (Source: Author)

Figure 4.1-38, CFD Testing of Type C, lower floor showing path lines (airflow pattern in the flat) (Source: Author)

Type C Flat, Upper floor (Upper Floor, 30m from ground)Vr = 1.290326 m/s

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Figure 4.1-39, CFD Testing of Type C, Upper floor showing the velocity vector and static pressure, (Source: Author)

Figure 4.1-40, CFD Testing of Type C, Upper floor showing path lines (airflow pattern in the flat) (Source: Author)

Hence, from the result, with compared to flat A and B, it gets more and uniform air flow in to the space as this type has got more floor area in the upper floor which enhance the indoor air flow rate due to the large pressure difference in the wind ward and lee ward side .Though it’s getting the similar effect in lower floor living room alike to flat A due to the similar floor plan however due to the bigger upper floor plan and double heighted living space the airflow rate and pattern is balanced in between two floors. •

Type D Flat, 6th floor with lower and upper floor

•

(Lower Floor, height 21m from ground), Vr = 1.147048 m/s.

Figure 4.1-41, CFD Testing of Type D, lower floor showing the velocity vector, (Source: Author)

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Figure 4.1-42, CFD Testing of Type D, lower floor showing static pressure & path lines (airflow pattern in the flat) (Source: Author)

Type D Flat, Upper floor (Height - 24m from ground)Vr = 1.198723 m/s

Figure 4.1-43, CFD Testing of Type D, Upper floor showing the velocity vector, (Source: Author)

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Figure 4.1-44, CFD Testing of Type D, Upper floor showing static pressure & path lines (airflow pattern in the flat) (Source: Author)

Hence, with compared to flat A, B and C it gets more and uniform air flow in to the space as this type has got full upper floor as flat C but the living room on lower floor is fully open to the terrace garden without any obstructing walls which enhance the indoor air flow rate especially when compared to flat C. It concludes that the southeast side bedroom is also having good amount of indoor air velocity of 0.7m/s due to the large pressure difference in the windward and leeward side.

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Question: “Effect of Terrace gardens in each level of a tall building.”

4.1.8.1.3 Testing 3: During northwest prevailing wind.

Building block section showing terrace gardens. (Various sections cut from the 3D Model) The domain is divided in to several parts at an interval of

3m height up to the height of 130 m, which is more than the building height. Then Vr at each 3m level is calculated for each floor levels and the values were put in the velocity inlet face (Refer calculation “section 3.2.2”).Northwest prevailing wind is perpendicular to the northwest façade of the tower.

Figure 4.1-45 Upper figure showing plan with section lines and lower figure showing CFD testing of 3D model of the Tower, (Source: Author)

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Figure 4.1-46 showing CFD testing of 2D sections of the Tower, (Source: Author)

Above analysis concludes the double storeyed terrace gardens are acting as wind trapping zone

and help to channel the air in to the apartment units. It also enhances building permeability to wind. It shows the wind velocity is high at the edge of the building. The three vertical sections showing different air pressure with different air velocity at every point. In the first and third section, the terrace gardens enhance the free air movement in to the interior instead of creating stagnation point on the faรงade which is opposite in case of the second section, high pressure is created in the plain facade. The tower views are representing how the northwest wind hits the building at the center and create stagnation point where as at the edge of the tower, air is diverted towards the indoor space through the large terrace gardens.

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4.1.8.1.4 Testing 4: During northwest prevailing wind.

Detail building section with openings of four types of modules i.e. Type A, B, C and D The domain is divided in to several parts at an interval of 3m height up to the height of 130 m. Then Vr at each 3m level is calculated for each floor levels and the values are put in the velocity inlet edge. The figures showing Internal section of Type A - 11th floor, Type B - 10th floor, Type C - 8th floor, Type D â&#x20AC;&#x201C; 6th floor from top to bottom have stimulated by providing different Vr values. Type A (Vr = 1.290326m/s) and for other types refer (section 3.2.2).

Type A Type B Type C Type D

Figure 4.1-47, CFD Testing of Detail section of tower (Source: Author)

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Q Type A

Type B Type C

1 Type D

If P1 > P2, Pin will lie between P1 & P2. If P1 = P2, Pin = P1 & P2.Hence Q is low

Figure 4.1-48, CFD Testing showing static pressure and path lines (Source: Author)

Above analysis concludes all the floors are having indoor air velocity of nearly 2m/s, which seems it can be possible to achieve indoor thermal comfort during daytime. (Refer figure 4.1.11 & section 2.3) In case of flat A, airflow is happening through smaller inlet in the windward side and going out through the larger outlet in the leeward side and distributed to both the lower and upper floors. In Page | 118

case of flat B, airflow is happening exactly opposite to type A, High pressure is created at the double storeyed terrace garden, which enables the air to flow towards the leeward side. In case of type C little variation is happening due to the study room in the windward side, which is having no indoor airflow since the windward side wall is having similar size openings which create no pressure difference.(Refer 1) In case of Type D, more airflow is happening with compared to other types due to the larger opening at both windward and leeward side but air funneling is created in the lower floor, which can be solved by closing the some window openings. It concludes that there are no major changes of air velocity within a 10m height (Refer section 3.2.2). In addition, it shows the upper floor is not having uniform airflow in the habitable area however, in the actual case due to the double heighted living room in the lower floor, the upper floors get airflow in their habitable area.

4.1.8.1.5 Testing 5: During northwest prevailing wind.

Building block (sectional plans showing terrace gardens) The figures (4.1:49) showing the different level plans (2nd floor, 3rd floor, 13th floor and 25th floor).

Page | 119

Figure 4.1-49, CFD Testing (Source: Author)

Each floor levels are having different wind speed and flow pattern in the tower. In addition, the exposed nature of tall buildings at top-level increase the value of the pressure coefficient Cp, and the wind pressure difference â&#x2C6;&#x2020;p (Ford and Etheridge, 2008). It represents that the wind pressure difference at top level is significantly higher than lower level therefore the faĂ§ade should have different opening sizes at every level. It concludes that the need to formulate a natural ventilation concept that can operate under a wide range of wind pressures can generate control difficulties in tall buildings. (Refer section 2.4) To overcome this situation, tall buildings should have terrace gardens or sky courts at different level for air permeability and to balance the air pressure on the tower.

Page | 120

4.1.8.2 Analysis through TAS Since building needs to respond its extreme climatic condition hence to reach a conclusion, the testing is carried out for the hottest day of the year: day 95: 5th of April. Zones created for the simulation NDZG – Northeast living room SDZG – Southwest living room West side bedroom (Northwest bedroom)

Figure 4.1-50, TAS Model of Building (Source: Author)

Figure 4.1-51,TAS Model: Lower. Fl. Type A, (Source: Author)

Zones created for the simulation: EB1 – Southeast Bedroom

Figure 4.1-52, Interior View Of type A (Source: Author)

Figure 4.1-53, TAS Model: Upper Fl., Type A, (Source: Author)

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Figure 4.1-55, View showing double heighted spaces of Type A flat. LHS: Lower Level and RHS: Upper Level. (Source: Author)

Figure 4.1-56, Graph showing Temp on Hottest day 95, (Source: Ecotect modified by Author)

Figure 4.1-54, 3D model showing different zones selected for simulations. (Source: Author)

Page | 122

4.1.8.2.1 •

Testing 1: The hottest day 95 20

U Value of External facades – 3.6 W/m

C (refer Chapter 2, section 2.7 for detail) and doors &

window openings - 50%, two testing - full day (24 hours ventilation) and night time only ventilation.

NDZG- North East Living room

Figure 4.1-57, 3D- view showing North-east living Room Zone, (Source: Author)

INDOOR COMFORT ZONE

Figure 4.1-58, Graph showing Indoor Temp. Variation due to 24 hr. and Night Ventilation. (Source: Author)

Page | 123

Above result shows, on the hottest day the northeast living room is having maximum indoor temperature of 370c with 24hr ventilation whereas the indoor maximum goes above 350c only at 6 pm with nighttime ventilation. However, in both the cases the whole daytime period from 8am to 7pm is not under comfort zone.

4.1.8.2.2 Testing 2: 20

U Value of External North and South facades â&#x20AC;&#x201C; 2.7 W/m C and external East and West facades â&#x20AC;&#x201C; 2.2 W/m C

(refer Chapter 2, section 2.7 for detail) and doors & window openings - 50%, two testing - full day (24 hours ventilation) and Night time only ventilation.

Figure 4.1-59, Graph showing Indoor Temp. Variation on in North east living room on hottest day 95 (Source: Author)

Above result shows, there is no change in indoor temperature while compared to test one. Moreover, the maximum temperature increased from 36.58 to 37.20c at 6 pm with nighttime ventilation with compared to test one. Page | 124

4.1.8.2.3

Testing 3: According to the Actual construction materials, which was used at the time of construction of the Building.

â&#x20AC;˘

U Value of External facades â&#x20AC;&#x201C; 2.4 W/m

C and doors & window openings - 50%, two testing -

full day (24 hours ventilation) and Nighttime only ventilation.

Figure 4.1-60, Graph showing Indoor Temp. Variation due to 24 hr. and Night Ventilation (Source: Author)

Above result shows, there is a vast change in indoor temperature while compared to test one and test two. Moreover, the maximum temperature decreased from 36.58 to 360c at 6 pm with nighttime ventilation with compared to test one. However, in this test with both the cases the whole daytime period from 9am to 7pm is not under comfort zone. Hence, nighttime ventilation could be a better ventilation strategy to achieve indoor thermal comfort.

Page | 125

4.1.8.2.4 •

Testing 4: 2 0

U Value of External North and South facades – 2.4 W/m

C and external East and West facades – 2

W/m2 0C (Refer Chapter 2, section 2.7 for detail) and doors & window openings - 50% open, Nighttime only ventilation.

Figure 4.1-61, Graph showing Indoor Temp. Variation on the hottest day 95 (Source: Author)

Above result shows, there is no change in indoor temperature while compared to test three. Moreover, the indoor temperature in every hour of the day is increased by a range of 0.20c to 0.50c while compared to test three. Hence, test three will be tested again on the next step by changing some parameters.

Page | 126

4.1.8.2.5 Testing 5: Same as Testing 3 however the aperture-opening percentage increased from 50% to 75% (Windows and doors opened 75% of their total size during night time) U Value of External facades â&#x20AC;&#x201C; 2.4 W/m2 0C and doors & window openings increased from â&#x20AC;&#x201C; 50% to 75%, Nighttime only ventilation.

Figure 4.1-62, Graph showing Indoor Temp. Variation in Northeast room, Comparison between test 5& 3 (Source: Author)

Result shows, the indoor condition is improving by increasing the aperture opening from 50% to 75%. Moreover, the indoor temperature in every hour of the day is decreased by a range of 0.50c to 0.80c while compared to test three.

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4.1.8.2.6 â&#x20AC;˘

Testing 6: 20

U Value of External facades â&#x20AC;&#x201C; 0.5 W/m

C having insulation and doors & window openings -

50% open, two testing done - full day (24 hours ventilation) and Night time only ventilation.

Figure 4.1-63, Graph showing Indoor Temp. Variation in North east room, Comparison between test 5& 6 (Source: Author)

Above result shows, there is no change in indoor temperature while compared to test five. Moreover, the indoor temperature in every hour of the day is increased by a range of 0.10c to 0.90c while compared to test five. Hence, U Value of 2.4 W/m2 0C for external facades with doors & window openings of 75% and nighttime ventilation could be a better option.

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4.1.8.2.7 Result (Detail Analysis of Testing 5)

Question: â&#x20AC;&#x153;Which floor works best with wind induced ventilation?â&#x20AC;?

Figure 4.1-64, Graph showing Temp. Variation in North East living room of different Fl. (Source: Author)

Openings

are

closed

during

unoccupied hours.

Figure 4.1-65, Graph showing variation in air change per hour in different floors (Source: Author)

Above result shows, from 9 am to 7pm the indoor temperatures of ground, 12th and 24th floor are above comfort zone. Moreover, indoor temperature of 24th floor is always lower than the other two floors which means the higher floors in a tall tower is having lower temperature with compared to others due to higher airflow in to the indoor space. It can also be identified that the more ACH is achieved in the 24th floor among others. Achieved ACH varies from 4.5 to 16, which is sufficient for 5 occupants and can be compared to the CFD result (Refer table 4-2)

Page | 129

24th Flr.

Figure 4.1-66, Graph showing Indoor temp. and RH in N-E living room of 24th Flr.

Question: “Which Orientation works best?” Comparision between Southwest and northeast living room. S-W

N-E Figure 4.1-67, Graph showing temp difference between N-E living room and S-W living Figure 4.1-68, Plan showing N-E and Sroom (Source; Author) W Living room. (Source: Author)

Above result shows, the indoor temperature of southwest living room is always higher than the northeast living room. Since all the inputs are same for both the rooms it can be concluded that, due to intense solar radiation on west façade, the southwest living room is having more indoor temperature. Hence, west façade of tall building should be carefully designed by minimizing solar exposure to achieve lower indoor temperature.

Page | 130

Question: â&#x20AC;&#x153;Which Orientation works best?â&#x20AC;? (Comparision between west bedroom in lower floor and east bedroom in upper floor of 24th floor flat ) West Bedroom

East Bedroom Figure 4.1-69, LHS: View showing West Bedroom on Lower fl. and RHS: East bedroom on Upper fl. of 24th Floor flat. (Source: Author)

Figure 4.1-70, Graph showing temp. Variation in West bedroom and East Bedroom. (Source: Author)

Figure 4.1-71, CFD model showing airflow pattern LHS: Lower Flr, RHS: Upper Flr.

Above result shows, the indoor temperature of east bedroom is always higher than the west bedroom during daytime. Though west side bed room is more sensitive to solar exposure but due to high air flow rate in the west bedroom of lower floor ,the indoor temperature is lower than the upper floor east bedroom which is having no indoor airflow during day time

Page | 131

Temperature variation in east and west side bedroom of different floors

Figure 4.1-72, Graph showing Temperature variation in east and west side bedroom of different floors, (Source: Author)

Figure 4.1-73, Temperature variation in east and west side bedroom of different floors

Above result shows the indoor temperature increases from lower to higher floors in a tall building. In both the graphs, the indoor temperature of east and west bedroom is decreased gradually from ground floor to top floors

Page | 132

4.1.9

Concluding Summary

The overall performance of the building according to the adaptive thermal comfort theory, BBCC (section 2.3) and the above analysis reveals that the residents are naturally acclimatized to the local climate conditions and building’s natural ventilation strategy is generally successful in relation to its form, orientation, solar exposure and the prevailing wind directions. The double storeyed terrace gardens enhance the indoor airflow and double heighted living room enhances the indoor airflow of the upper level of the flat. Variable openings in the façade due to the interlocking planning approach help to create pressure difference, which enhance airflow rate, however the high airflow rate due to high wind speeds at high altitudes might cause discomfort for the residents. The central core is consuming more energy as it is absolutely devoid of any natural light and ventilation. The buoyancy driven natural ventilation strategy generated by the stack effect, which is inherently present in tall building has not taken in to consideration. Since cross ventilation strategy mainly occurs due to wind force, the rooms in the leeward side are devoid of any indoor airflow during calm or no wind day. Due to the interlocking planning approach the upper level rooms especially in the type A flat does not have any airflow due to northwest prevailing wind during hottest month.

4.1.9.1Further investigation and suggestions The effectiveness of wind induced natural ventilation strategy applied in the tower can be highly reliable during the summer period except between mid of March to April, as external temperature goes higher than 320c,comfort daytime ventilation is not applicable (Refer Section 2.3). Study shows the wind induced cross ventilation is not possible during hot afternoon and evening time on the month of March. (Figure 4.1:63 and 4.1:65) Hence, an alternative method of conventional airconditioning “Downdraught cooling” system can be used to cool the building. Since a Passive downdraught cooling can be achieved through the evaporation of water within an air-stream in hot dry conditions when the external wet bulb temperature goes below 24°C. [1] It might not be possible to apply PDEC system during the whole summer period as Mumbai lies in tropical climate. However, according to micro climatic analysis, the WBT goes below 24°C only during the month of March “the hottest month of the year” (Figure 4.1:5). Hence, PDEC can be applied during the month of March, which is energy efficient, cost effective and environmental friendly system alternative to airconditioning system. Further investigation is needed before coming to a conclusion.

Page | 133

4.2 Case study 3 - MBF Tower, Penang, Malaysia Key information Project:

MBF Tower

Year of completion:

1994.

Location:

Latitude of 5.2° N and Longitude of 100.2° E, Penang, Malaysia

Climate:

Tropical warm & humid

Architect:

T.R Hamzah and Yeang

Client:

M B F HOLDINGS BERHAD

Site Area:

7482.39 Sq. mt

Site and situation:

City landscape surrounded by low rise and high rise structures.

Prevailing wind direction:

from south-west and northeast

Type:

Mixed (office & Residential)

Building height:

111.1 meters.

Number of storey:

31 (Till six stories building is occupied

Figure 4.2-1, Showing MBF Tower, Penang (Source:http://realestate.net.)

With conditioned office, space and rest are naturally ventilated residential flats) Structure:

4.2.1

Reinforced Concrete

Introduction

T.R.Hamzah & Yeang is an international renowned Architect, best known for his innovative signature green buildings and master plans. Much of his early work pioneers the passive low-energy design of skyscrapers, as the 'bioclimatic skyscraper' and MBF tower “an image with overtones of the spirit of Arch gram” (Robert Powell, 1999) is one among them. The predominant and potential for openness and separation in design of the tower has resulted the architect’s idea of “places in the sky” and direct expressive idea of the principle of natural ventilation and vertical landscaping.

Page | 134

Figure 4.2-2, showing skyline of the Malaysia (Source: Richards, Ivor)

Architect’s design ideas: •

Tropical high-rise design ideas:

•

Cut outs in the building acting as Sky Courts.

•

Units are separated from the lift core for all-round cross-ventilation.

•

The typical open floor plans are designed to be column free and cross ventilated.

•

Stepped planters on the facade of the building.

•

Units are seaward facing on western edge.

Figure 4.2-3, Architects Design Idea for MBF Tower, (Source: Ken Yeang, 2001)

4.2.2

Site micro climate analysis

Architectural design needs to respond to the warm humid climatic context of the site. The final solution needs to satisfy the diverse and often conflicting conditions of warm-humid and monsoon period. Cooling remains as the predominant requirement due to the equatorial climate. The MBF tower, of total 17538 sq.m. built up area is located on the Jalan Sultan Ahmad Shah road, Penang, Malaysia.The site is situated in a low-density area just 2 miles from the town center and surrounded by the sea on north east, low rise structures in the south west and two high rise structures sri pardana condominium and The Northam all suite on the east and west respectively. (Figure 4.2:4)

Page | 135

Figure 4.2-4, Showing Location of MBF Tower (Source: Google map)

As per the Climate Classification chart, the site falls in the tropical climate, which is warm, sunny and humid, along with high rainfall especially during the southwest monsoon from April to September. The climate shows no distinct hot or cold seasons with a little seasonal and diurnal temperature variations. 4.2.2.1 Temperature variation: The average annual temperature in Penang is 27°C. The hotter months are between December and April with mean temperatures ranging between 26.2 and 27.6°C with hottest month march, while the coolest months are between June and October with mean temperatures ranging between 26.2 and 27.3. The day time temperature fluctuates between 27°C-30°C, and night time fluctuates between 22°C-24°C with low diurnal temperature difference of 5 0C to 6 0C.5

Figure 4.2-5, Graph showing monthly Average Temp. (Source: Weather Tool, modified by Author)

Essential Travel, Penang Weather. WWW at the Essential Travel WWW page at: <http://insurance.essentialtravel.co.uk/tg-asia/malaysia/penang-weather.asp.

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Figure 4.2-6, WBT and DBT variation, (Source: Climate consultant and Modified by Author)

Figure 4.2-7, Showing radiation range (Source: Climate consultant and modified by Author)

Figure 4.2-8, Graph showing temperature on Peak hottest day (Source: weather tool and modified by Author)

Page | 137

4.2.2.2 Relative Humidity: The average relative humidity fluctuates between 70% - 90% with minimum in the month of December to march.

Figure 4.2-9, Graph showing Relative Humidity variation (Source: Weather Tool modified by Author)

4.2.2.3 Precipitation: Precipitation occurs in the form of rainfall whole year around with highest during the southwest monsoon period (from April to September).The lowest precipitation occurs in the months of December to March. However, the mean annual precipitation is 2670 mm.

Figure 4.2-10, Graph showing Avg. Rainfall. (Source: http://insurance.essential travel.co.uk/tgasia/malaysia/penangweather.asp modified by Author)

Average rainfall

Rainfall 400 300 200 100 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Months

4.2.2.4 Wind The prevailing wind direction is from southwest and northeast. Mostly December to march avail northeast prevailing wind whereas April to September avail southwesterly prevailing wind. The mean surface wind over Penang city is generally mild, with an average wind speed of 1.5 m/s, and a maximum speed of 8 m/s.

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Figure 4.2-11, Showing Yearly pre dominant wind directions. (Source: Ecotect and modified by Author)

Figure 4.2-12, Psychrometric chart showing boundary of different passive cooling approach for Penang (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 4.2-13, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Penang, (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

4.2.3

Built Form and Orientation

Muscular rectangular form with four blocks in one floor and exposed column holding the gigantic built structure is oriented approximately north south, facing towards sea on northeast. Optimum orientation of each space to prevailing breeze and strong linkage between leeward and windward sides strengthen the utilization of the pressure difference to facilitate cross ventilation. Figure 4.2-14, Showing Sun-Path diagram over MBF Tower. (Source: Ecotect and modified by Author)

Page | 139

Figure 4.2-15, Showing sun path diagram LHS: winter solstice, Centre: Equinox and RHS: Summer solstice. (Source: Ecotect and modified by Author)

The project consists of a six-storeyed podium of a banking and office hall at the base with an open terrace having swimming pool and an upper apartment block of 68 units. Parking is in the basement as well as around the structure. Two cores are for the offices where one with separate entrance goes throughout the structure. The office floors are intended to be cooled with central water-cooled package air-conditioning system where as the apartments blocks are depended on natural ventilation.

North Figure 4.2-16, Figure showing a.: Ground Level Plan b.: Podium Level, c: Podium roof plan. (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

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4.2.3.1 Typical residential plan: Triple banded plan has four units at each floor. Each one of them is separated from the lift core for all-round cross-ventilation with terraces and sky courts in-between as gardens-

in-the-sky. The building is in the form of two separate rectangular towers with curved ends connected by the central service core. The typical floors are designed to be column free. Toilets and Kitchen areas are looking inwards while the Living Areas and Bedroom have outer views. Planter boxes provided along the

Figure 4.2-17, Showing Typical Residential Floor Plan, (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

stepped terraces and sky courts to minimize solar gain. The plan is oriented in such way; both sides i.e. north east and north side walls of the flat get maximum benefits from northeasterly prevailing wind and vice versa for southwesterly wind. The width and depth of each flat is at 1:2 ratios. The north east facing flats are having floor area of 74.4 sq.m and southwest facing flats has area of 69 sq.m with width and depth aspect ratio of 1:2 with maximum width of 5.22m.

Figure 4.2-18, showing front annd side elevation of the MBF Tower. (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

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4.2.4

Natural Ventilation Strategy

In all of Yeang’s work till date, this residential highrise tower stands amongst his most successful projects for its heroic futurist, in use for his unique and extraordinary design. Though the use of airconditioning in most of buildings in warm and humid climate is very much essential for thermal comfort of the occupants, the architect uses the principles of natural ventilation to achieve indoor thermal comfort in various ways. The main objective of the wind induced natural ventilation principle was to generate

Figure 4.2-20, showing Northeast pre dominant wind direction with respect to tower (Source: Author)

high air-changes to achieve comfort conditions by controlling indoor temperature and airflow rate. Minimum use of internal partitions and maximum number of (single, double and three sided) openings in each room facilitate the wind induced cross ventilation. Window Openings are placed with respect to windward and leeward side of the building, which enhance the airflow rate in the habitable spaces. In this regard, the exposed ‘mega structure’ is the first building of its own kind that exploits wind-induced natural ventilation not only for the purpose of air-displacement and fresh air supply but also to create indoor thermal comfort for the residents. To achieve comfort ventilation (Refer section 2.3, 5) which is considerably more difficult endeavor, the higher air-changes per hour is facilitated with both horizontal and vertical floor slots and gaps. Air is funneled into the building from the windward side to the central part (the central core) space between the two blocks and then directed to both side flats. In addition, the two storey sky courts at two levels and the dramatically inclined northeastern façade with terraces and planter boxes which step back to half way up the building further strengthen the ventilation strategy. The intensification of articulation of all above design elements in both horizontal and vertical section enhance the cross ventilation throughout the building and creates a three dimensional inner volume flow Figure 4.2-19, showing the sky court (Source: Author)

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by lowering the thermal load.

Figure 4.2-21, Internal Images of MBF Tower (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

Figure 4.2-22 , Section showing natural ventilation Strategy in the tower. (Source: Author)

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4.2.5

Quantitative Analysis

4.2.5.1 Analysis through CFD Question to be answered: “Effect of orientation of the building block with respect to the prevailing wind direction.” 4.2.5.1.1

Testing 1:

The building block plan: The building is facing towards the southwest and northeast prevailing wind direction. The hotter months are between December and April and during these months northeasterly prevailing wind is dominant hence testing is carried out for the northeast wind. Figure showing the top-level plan of the tower and data input for the testing: At velocity inlet (Vr = 2m/s) is given for the calculation. (Refer detail calculation on Chapter 3, section 3.2.2).

Figure 4.2-23, showing velocity vector by X-velocity m/sec. (Source: Author)

Building is situated at 250m away from the sea and the northeast wind hits the building front face at an angle of 750

Figure 4.2-24, Defining Boundary Conditions, NÉ wind direction (Source: CFD for ventilation design handouts, Guohui Gan, University of Nottingham)

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Figure 4.2-25, CFD Testing showing block plan (Source: Author)

Above analysis shows the wind hits the front block and gets deflected to both sides. At the passage, it creates funneling effect on both sides of the core then diverted to the left in between two blocks. Since there is a low pressure created at the back of the two blocks and core, the velocity at the front varies from 2.05m/s to 2.4m/s and velocity at the back varies from 0.8 to 0.4 m/s Page | 145

Question: â&#x20AC;&#x153;Effect of open layout plan for uniform indoor airflow and appropriate opening to let

outdoor air come in to the indoor space.â&#x20AC;? 4.2.5.1.2 Testing 2: Internal layout plan of 23rd floor: (Vr = 1.621957m/s) is taken in to consideration for the simulation (Refer section 3.2.2). Type B Rake 3

Type A

Rake 2 Rake 1 Rake 4

Rake 1 Rake 2

Rake 3

Figure 4.2-26, CFD Testing (Source: Author)

Figure 4.2-27, CFD Testing (Source: Author)

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Figure 4.2-28, CFD Testing (Source: Author)

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ANALYSIS OF VENTILATION RATE & AIRCHANGES PER HOUR IN TYPE A FLOOR: 4-3, Flow rates for the inlets and ACH-1 Achieved, (Source: Author)

Area Surface

Flow rate

the

Area weighted

opening

average X

velocity

m3/s

(m/s)

rake 1

1.87

0.16

0.272

rake 2

1.8

0.23

0.4

rake 3

2.3

0.03

0-08

rake 4

1.95

0.07

0.15

Ventilation rate

0.902

Volume of flat A

223m2

ACH-1

14.5

Figure 4.2-29, RECOMMENDED VENTILATED RATES FOR FRESH AIR, Source: Natural ventilation in non-domestic buildings-Applications Manual AM10, 2005, p 1197, CIBSE

Required Air change per hour (ACH) Assuming the ventilation rate as 100 l/s per person. (Refer figure 4.2-29 and Section 2.1.2 and table 2.1) For 5 person occupancy in the flat Ventilation rate = 0.1 * 5= 0.5 m3/s ACH-1 = 0.5*3600/223.2= 8 ACH-1

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ANALYSIS OF VENTILATION RATE & AIRCHANGES PER HOUR IN TYPE B FLOOR: 4-4, Flow rates for the inlets and ACH Achieved, (Source: Author)

Area Surface

Flow rate

the

Area weighted

opening

average X

velocity

m3/s

(m/s)

rake 1

2.3

0.2

0.4

rake 2

2.2

0.1

0.132

rake 3

2.8

0.9

0.25

Ventilation rate

0.9125

Volume of flat B

207m2

ACH-1

12.1

Required Air change per hour (ACH) Assuming the ventilation rate as 100 l/s per person. For 5 person occupancy in the flat Ventilation rate = 0.1 * 5= 0.5 m3/s ACH-1 = 0.5*3600/207= 8.6 ACH

Hence, table 4.3,4 shows the air changes per hour is sufficient for five occupants However; the fresh air is not uniformly distributed since all the openings are open during the time of simulation, which can be controlled by closing the window as per occupantâ&#x20AC;&#x2122;s requirement. Achieved ACH for flat A and B is 14.5 and 12.1 respectively. There is minimal air movement in some part of the flat. Air funneling has created in the corridor zone due to the narrow width. However, no negative effects in the habitable space are experiencing.

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Question: â&#x20AC;&#x153;Effect of sky court.â&#x20AC;? 4.2.5.1.3

Testing 3:

Building block section showing Sky courts at different level. The domain is divided in to several parts at an interval of 3m height up to the height of 130 m, which is more than the building height. Then Vr at each 3m level is calculated for each floor levels and the values were put in the velocity inlet face (Refer section 3.2.2).

Figure 4.2-30, CFD Testing, (Source: Author)

Figure 4.2-31, CFD Testing, (Source: Author)

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Figure 4.2-32, CFD Testing, (Author)

Above analysis shows sky courts act as wind trapping zone and channel the airflow in to the spaces. It also increases building permeability to wind. It shows the wind flow is high at the sky court and enhances the airflow in to the other side of the building. Rate of airflow is also increasing in the core due to the sky court. Above figures (4.2:32) showing the change of airflow pattern in case of sky court and without the sky court. Instead of creating stagnation point on the faรงade, it enhances free air movement by minimizing the stagnant areas on leeward side.

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4.2.5.1.4

Testing 4: Detail building section with openings

Internal section of 29th floor to 32th floor: (Vr = 1.7066m/s) is taken in to consideration for 29th floor, rest Vr calculation (Refer detail calculation on Chapter 3, section 3.2.2).

Rake C Rake B

Figure 4.2-33, CFD Testing (Source: Author)

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Rake A

ANALYSIS OF VENTILATION RATE & AIRCHANGES PER HOUR 4-5, Flow rates for the inlets and ACH Achieved, (Source: Author)

Area Surface

Flow

Volume of ACH-1

the

Area weighted

rate/Ventilation floor

opening

average

rate

m3/s

velocity

(m/s)

rake A

3.15

0.12

0.378

223

17.2

rake B

3.15

0.09

0.28

223

rake C

3.15

0.13

0.4095

223

18.6

Table 4-5 shows the air changes per hour is sufficient for five occupants However; the fresh air is uniformly distributed in the habitable area. Achieved ACH for flat A and B is 17.2 and 13.79 respectively. Though both the flats are in same floor, since flat A is at windward it gets more ACH whereas the other having little less air movement. Whereas achieved ACH for flat A and C is 17.2 and 18.6 respectively due to the height difference between 2 flats. Hence, the airflow rate increases with increase of height.

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4.2.5.2 Analysis through TAS The analysis is undertaken on the hottest day 73: 14th of March. The simulation is carried out in order to find the effectiveness of natural ventilation in Penang climate.

North

Figure 4.2-34, Plan showing North Facing Living room (Source: Author)

•

Weather File: George Town Weather file from Energy Plus

•

All other inputs are similar to the Case 1 Kanchanjunga Building.

4.2.5.2.1 Testing 1: Building orientation is changed to northeast and southwest direction; the openings are perpendicular to the Northeast prevailing wind. (Similar to MBF Tower plan). U Value of External North and South facades – 2.4 W/m2 0C and external East and West facades – 2 W/m2 0C (refer Chapter 2, section 2.7 for detail) and doors & window openings (Aperture – 75 % open), two testing done - full day (24 hours ventilation) and Night time only ventilation.

Figure 4.2-35, View showing North facing living room. (Source: Author)

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Living room with maximum openings facing Northeast prevailing wind is simulated for analyzing the indoor temperature variation in the hottest day: 14th of March.

Figure 4.2-36, (Source: Author)

Figure 4.2:36 shows indoor temperatures of (ground,12th and 24th floor) are 20C higher than outdoor temperature during night time i.e. 18 to 10â&#x20AC;&#x2122;o clock in the morning then it become similar to the outdoor temperature from 10 to 18 in the evening.

Figure 4.2-37, (Source: Author)

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Figure 4.2-38 shows indoor temperatures of (ground,12th and 24th floor) are similar to the outdoor temperature during night time i.e. 22 to 10’o clock in the morning. Between 10 to 12’o clock and 18 to 22’o clock indoor temp. is higher than outdoor temp. where as during afternoon indoor temperature is 20C lower than out side temperature since the windows are closed during the day time and opened in night time (from 18 to 10’o clock in the morning).Moreover it shows the highest floor (24th fl.) is having lower temperature and the middle floor (12th fl) is having higher temperature.

Figure 4.2-39, (Source: Author)

Figure 4.2:38 shows the diffrence of indoor temperature of 24th floor with night ventilation and full day ventilation. Due to night ventilation strategy, indoor environment is experiencing lower temperature than full day ventilation for almost 20 hours of the day. Night ventilation is more preferable than full day ventilation.

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4.2.5.2.2

Testing 2:

Question : “To check whether U value of north and south facades make any difference in Penang Climate to achieve comfort” Similar to the Testing one but the U Value of External North and South facades change from 2.4 W/m2 0C to 2 W/m2 0C. From various testing with U value 2 W/m2 0C, night ventilation is more preferable than full day ventilation.

Figure 4.2-40, (Source: Author)

Figure 4.2:39 shows the indoor temperature is almost similar for U value of 2 W/m2 0C and 2.4 W/m2 0C .Hence U Value of 2.4 W/m2 0C with night time ventilation is more preferable since indoor temperature does not change by changing the U Value of 2 W/m2 0C .Rather it shows the indoor temperature increased by 0.1 to 0.50C at some period by changing the U Value from 2.4 W/m2 0C to 2 W/m2 0C.

4.2.5.2.3

Testing 3:

Question : “Effect of orientation” Simulation is carried out by changing the orientation of the building from (North: 240 0 to 450) the facade which having less openings orientated towards Northeast prevailing wind.

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Input given for the simulation: U Value of External North and South facades – 2.4 W/m2 0C and external East and West facades – 2.2 W/m2 0C with night ventilation.

Figure 4.2-41, showing temperature variation due to change in orientation (Source: Author)

Figure 4.2:40 shows indoor temperatures of (ground,12th and 24th floor) are always 20C higher than outdoor temperature only except the period of 13 to 16’o clock in the afternoon when temperature drops by 1.50C from the outdoor temperature.

Figure 4.2-42, (Source: Author)

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Figure 4.2:41 shows indoor temperatures of 24th floor in testing 3 is always 10C to 1.50C higher than the testing 1 result.which proved that the larger openings should be provided in the prevailing wind direction to maximize indoor cooling . 4.2.5.2.4

Final Result

U Value of External North and South facades – 2.4 W/m2 0C and external East and West facades – 2.2 W/m2 0C. Doors & window openings (Aperture – 75 % open) with nighttime only ventilation works best in the hottest day: 14th of March.

Figure 4.2-43, Showing indoor wind speed on 7th and 24th Fl. (Source: Author)

Figure shows ACH varies from 6.5 to 16 for 7th floor and 6.5 to 17 for 24th floor, it can be concluded that the upper floors are having more airflow with compared to lower floors which make the upper floors more cooler than the lower ones.

Figure 4.2-44, showing variation in indoor and outdoor Temperature and RH (Source: Author)

Figure 4.2:43 shows variation of outdoor and indoor temperature and relative humidity on 24th floor.

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4.2.6

Concluding Summary

Above analysis concluded that the building’s natural ventilation strategy is generally successful in relation to its form, orientation and the prevailing wind directions. The double storey sky courts at three levels enhance the indoor airflow rate. The tower is getting more benefit from the location, as seashore areas get benefit from the daytime sea breeze, which usually reaches its maximum speed in the afternoon, and nighttime land breeze, which provides thermal comfort of low temperature and higher wind speed. Insertion of transitional spaces at the upper parts of the tower acts like “isolated bungalows” in the sky. The orientation of the tower enhance the effectiveness of wind induced cross ventilation during both southwest and northeast

Figure 4.2-45, Architects Design Idea for MBF Tower, (Source: Ken Yeang, 2001)

prevailing wind as the tower is having openings towards the prevailing wind direction. Oblique wind enhances the indoor airflow rate which concept was strictly followed in the MBF Tower for enhance the effectiveness of natural ventilation. When the wind changes direction from northeast to southwest for example, wind would still hit the southwestern building blocks at an oblique angle of 75o, hence ensuring the effectiveness of wind driven ventilation.

Figure 4.2-46,LHS showing N-E prevailing wind and RHS showing S-W prevailing wind

Moreover, the higher air-changes per hour are facilitated with both horizontal and vertical floor slots and gaps. On the other hand, only two out of the four flats in each floor have a good sea view and direct sea breezes. Green terrace gardens are not maintained as intended, which might help to cool the tower during afternoon time. Each apartment blocks are intended to rely on cross ventilation, but the apartment blocks do have the option for air-conditioning. (Robert Powell, 1999)

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4.2.6.1 Further investigation and suggestions The effectiveness of wind induced natural ventilation strategy applied in the tower can be highly reliable mainly due to its form, orientation and location. Stepped terrace gardens could enhance the effectiveness of natural ventilation if properly maintained as intended earlier. The central core could be utilized as a wind-trapping zone, which can enhance the indoor airflow rate instead of letting the air to go out through back of the tower and â&#x20AC;&#x153;in betweenâ&#x20AC;? space of two flats. Further investigation is needed to explore about horizontal and vertical wing wall for further improvement of natural ventilation.

Figure 4.2-49, showing the central core of the tower (Source: Author)

Page | 161

Figure 4.2-47, Showing Vertical Landscape (Source: T. R. Hamzah and Yeang: Ecology of the Sky)

Figure 4.2-48, Sky Court, Source: Author

4.3 Case study 3- Moulmein Rise, Singapore Key information Project:

Moulmein Rise

Year of completion:

2003

Location:

Latitude of 1.18° N and Longitude of

103.5° E, Singapore Climate:

Tropical warm & humid

Vegetation:

Rainforest

Architect:

WOHA Architects

Client:

UOL Development Pvt Ltd

Building footprint:

230 SQ.M

Site and situation:

City landscape surrounded by low rise and high rise structures.

Prevailing wind direction:

South west, northeast

Type:

Residential

Height:

102 m

Number of storeys:

4.3.1

Introduction

Figure 4.3-1, Moulmein rise, (Source:http://propertyhighlights.blog spot.com)

“Much of the developing world is located around the equatorial belt, and it is vital that tropical design research addresses the important questions of how we can live well and sustainably with our climate and with the densities projected for the rapidly growing region.”

Figure 4.3-2, Sky line of the Singapore, (Source: Dr. Dickie Hertweck)

Page | 162

(Mun Summ Wong and Richard Hassell, 2009). Their innovative design approach for tropical highrise could be considered as an environmental per formative design, which can be clearly identified in 1 Moulmein Rise, Singapore. Its varied yet simple façade incorporates features from vernacular housing of Indonesia. The award-winning tower is not only planned to suit its naturally sloping site but all of its facades are also designed according to the direction they face. This holistic approach in planning, smart and innovative details is what makes this aesthetically pleasing building a model for the future residential projects in the city. Architect’s most innovative design ideas: • Implementation of tropical vernacular ideas • Climate responsive façades • Slender building form to maximize cross-ventilation 4.3.2

Site micro climate analysis

Architectural design needs to respond to the tropical rainforest climatic context of the site. Cooling remains as the predominant requirement due to the equatorial climate. The ‘1 Moulmein Rise’, footprint of 230 sq.m. is located on the edge of a conservation area, among a stretch of greenery, the Moulmein Rise tower sets an example for the residential high rise in the tropics situated on the Moulmein road, Singapore. The site is situated in a low-density area surrounded by low rise and two tall structures in the west (Figure 4.3-3)

Figure 4.3-3, showing location of Moulmein Rise Building (Source: Google Map)

Singapore is located at latitude of 1.180 N and longitude of 103.50 E, which comes under equatorial region, possesses uniformly high temperatures, humidity with high rainfall throughout the year.

Page | 163

4.3.2.1 Temperature variation: The temperature is uniform throughout the year. The average monthly temperature is 270C where in summer temperature reaches to 350C. Due to high humidity in air, temperature is relatively moderate. With hottest month march minimum diurnal temperature range fluctuates from 23 to 27â&#x2014;ŚC and maximum 30 to 34â&#x2014;ŚC with low diurnal temperature difference of 7 0C.

Figure 4.3-4, Showing wind distribution, Sun path diagram, Yearly temperature Graph, Rainfall and Humidity for Singapore, (Source: Ecotect and Modified by Author)

Page | 164

Figure 4.3-5, Showing WBT and DBT variation, (Source: Climate consultant and Modified by Author)

Figure 4.3-6, Showing Solar radiation range, (Source: Climate consultant and Modified by Author)

4.3.2.2 Relative Humidity: The average relative humidity fluctuates between 75% - 80% with minimum in the month of March. Mean annual RH value of 84%. 4.3.2.3 Precipitation: Due to high amount of rainfall, the seasons are defined by the monsoon. The northeast monsoon (Novemberâ&#x20AC;&#x201C;March) is the wettest and windiest period with rainfall reaching an average monthly more than 250 mm in December and the southwest monsoon period (Mayâ&#x20AC;&#x201C;September) are having least amount of rainfall and the lightest winds with rainfall dropping to a monthly less than 7 inches in July. Sluggish air movements and afternoon showers and thunderstorms are characterize intermonsoonal periods of April and October. However, the mean annual precipitation is 2342.2 mm.

Page | 165

Figure 4.3-7, Psychrometric chart showing boundary of different passive cooling approach for Singapore (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 4.3-8, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore, (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Page | 166

4.3.2.4 Wind: Mostly December to march avail north and northeast prevailing wind whereas April (South west), may, October and November having variable wind direction. June to September avail south and southeast prevailing wind. The mean wind speed range varies from 1.4 m/s the lowest on November and the highest 2.8m/s on February.6 Figure 4.3-9, showing yearly wind directions. (Source: Ecotect and modified by Author)

4.3.2.5 Sun-path over Singapore: Sun path over Singapore is relatively unchanged. The sun is straight overhead most of the time in year. In December (During Winter Solstice), sun angle is 670 (when the sun is inclined towards South Direction) and in March (During Summer solstice), it again makes an angle of 670 towards North direction.

figure 4.3-10: Showing sun path diagram LHS: winter solstice, Centre: Equinox and RHS: Summer solstice. (Source: Ecotect and modified by Author) 6

Guide to Singaporeâ&#x20AC;&#x2122;s Weather, http://app2.nea.gov.sg/index.aspx Page | 167

NEA

Meteorological

Services,

National

Environment

Agency,

4.3.3

Built form and orientation

Slender rectangular form with two flats in one floor is oriented north and south to minimize the intense solar gain and maximize airflow circulation. The optimum orientation of each room to prevailing breeze facilitate through and through cross ventilation all year round.

4.3.4

Spatial Configuration

Originally, the tower was planned to be much lower in

Figure 4.3-11, Annual Sun-path over Singapore, (Source: Ecotect and modified by Author)

height and wider in plan. However, the architects were keen on implementing passive environmental strategies and therefore suggested the current design of a much slender and taller tower. This allowed for deeper light penetration and natural ventilation between facades. The building is oriented North-South and has deep overhangs to minimize heat gain. The north facade overhang is about 1000mm while that on the south is 600mm. The former comprises of a perforated sunscreen, which staggers along the height of the building in order to allow natural light and ventilation in but keep the rain out; while the latter, is a composition of traditional balcony spaces. This interesting composition is achieved by a nonregular arrangement of balconies, planters, overhangs and bay windows. Such a variation represents the individuality and flexibility that the apartments provide to its residents. [2],[3].With a plot ratio of 2:1 and 102m of height, the

Figure 4.3-12, showing East Elevation of the Tower. (Source: WOHA Architects)

slender tower having 50 flats in 28 storeyed was designed to achieve the maximum occupant comfort through various design elements. The tower is having

Page | 168

Figure 4.3-13, Typical Floor Plan of Moulmein Rise, (Source: WOHA Architects)

two units having floor area of 95m2 each with the lift and stair core at the center. The living and dining space is facing towards south whereas bedrooms and kitchen are facing towards north.

Figure 4.3-14, Showing, LHS: North Elevation and RHS: South Elevation (Source: WOHA Architects)

Page | 169

4.3.5

Natural Ventilation Strategy

Architect’s main concept was to minimize the solar gain and maximize cooling potential of the tower through wind induced single sided and cross ventilation strategy. The most innovative feature of this tower is its modern interpretation of a ‘monsoon window’. The manner

which

the

architects

have

incorporated them in the facade is highly commendable. Installed bay window in the form of a sliding aluminum panel, this horizontal window keeps the rain out, while

Figure 4.3-16, showing Monsoon window, (Source:WOHA Architects)

allowing continuous cool breeze in to the space. “A winder operates the panel, and a perforated metal shelf above the opening prevents objects from falling through. The device is well used, and many occupants sleep without air-conditioning.”[2] The tower is having a slender form, which helps to minimize the intense solar gain in west and east façade and maximize the airflow through cross ventilation strategy almost during the summer months. Different natural ventilation strategies are applied in the tower such as single sided and cross ventilation, which is fully dependent on the occupants how, they control their indoor environment. Each facade is designed in relation to the local climatic condition, which acted as climate responsive façade. The choice of materials used in the tower is equally smart and compliments the design well. The exposed concrete surface is coated with textured paint that hides dust and damage. The climatic responsive facade comprises of tempered glass, aluminum, steel, timber clad steel and wood, which helps the Figure 4.3-15, showing window with shading device on external facades of the Tower. (Source: WOHA Architects)

Page | 170

building to be cooled.[2][3].

Figure 4.3-17, Showing Plan and Section, LHS: Single sided Ventilation, RHS: Cross Ventilation strategies in the Building (Source: WOHA Architects modified by Author)

Page | 171

South living room

Vernacular window Detail

South living room

Monsoon window

Core

having

perforated

sun

screen

Figure 4.3-18: Design features and elements involve enhancing natural http://www.h88.com.sg/article/Architecture+Feature+-+1+Moulmein+Rise/)

Page | 172

ventilation. (Source:

4.3.6

Qualitative Analysis

Qualitative analysis, which includes a post occupancy evaluation, conducted to assess the adaptive thermal comfort of the occupants staying in the 1 Moulmein Rise. The survey analysis of 07 filled up questionnaires out of 50 and previous study (Refer Section 2.7) shows most of the

occupants are naturally acclimatized to the local hot and humid climate. In terms to modify the indoor environment, it is found that the occupants use full day (24hour) ventilation strategy to control their indoor environment. Usage of A.C.

Satisfaction level in Living room Comfortable

Neutral

Living room in the afternoon Bed room in the afternoon and night

20%

20% 80%

80%

% of residents who want the current system to be replaced with mechanical ventilation Neutral

Not highly but recommended

Not at all

10% 30% 60%

Figure 4.3-19, showing the results of the occupant survey (Source: Author)

The result indicates that the differences in the thermal comfort perceptions as 30% of residents want the current system should change whereas 60% are in neutral position. More occupants are finding comfort in living room, which works best during the summer period. The high usage of airconditioning for afternoon and night hours especially in bedroom is observed which is quite similar to the previous study.(Refer table 2.6,8) To reach a conclusion, the study is carried out for the hottest day of the year through various simulation programmes like CFD and TAS.

Page | 173

4.3.7

Quantitative Analysis

Both the analysis is based on the occupant survey and previous study (Refer section 2.7 & table 2). 4.3.7.1 Analysis through CFD Question to be answered: “Effect of orientation of the building block with respect to the prevailing wind direction.” 4.3.7.1.1

Testing 1: During both the north (December to march) and southwest prevailing wind (‘April’ having the hottest day of the year).

The building block plan: The building is facing towards north and south prevailing wind direction. Figure showing the top-level plan of the tower and data input for the testing: At velocity inlet (Vr = 2m/s) is given for the calculation. (Refer section 3.2.2) The impact due to southwest wind: southwest wind hits the building’s south face at an angle of 450

Figure 4.3-20 & 4.3-21,CFD Testing showing velocity vector by X-velocity m/sec due to SW wind (Source: Author)

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Figure 4.3-22, CFD Testing showing static pressure and path lines (Source: Author)

The above analysis shows the wind hits the corner edge of the block and is deflected to both sides. The north face is devoid of any airflow as the wind shadow is created .turbulence is created at three corners of the building, which may not allow the air to letting in to the indoor space. Since low pressure is created at the east side, south faรงade is having a good amount of airflow as wind is moving from high to low pressure zone which result of a range of wind velocity of about 1.4 to 2.4m/s at the south and west faรงade of the tower.

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The impact due to north prevailing wind: North wind hits the building’s north facade at an angle of 900

Figure 4.3-23, CFD Testing showing velocity and pressure due to North wind (Source: Author)

The above analysis shows the wind hits the north facade of the tower and is deflected to both sides. As prevailing wind is perpendicular to one façade, three facades of the tower are devoid of any airflow. Again high pressure (8.25 pas) is created on the north façade while compared to the previous case (4.1 pas). Question “Effect of open layout plan for free indoor air circulation and appropriate opening to let

outdoor air in to the indoor space.” 4.3.7.1.2

Testing 2:Internal layout plan of 13th floor: (Vr = 1.4188258m/s) is taken in to consideration for the calculation. (Refer section 3.2.2)

Type A

Northwest bedroom

Type B

Northeast bedroom

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Figure 4.3-24, CFD Testing showing detail plan (Source: Author)

Southwest living room

Southeast living room

Figure 4.3-25, CFD Testing (Source: Author)

Above results show the achieved air change per hour for Type A is 17.2, which is sufficient for

occupants in the flat with compared to the required ACH. However, the achieved air change per hour for Type B is 12.2 lower than the type A. Figure 4.3:24 shows there is no air movement in the northwest bedroom of type A and northeast bedroom of type B since the air funnel is created

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in the narrow passage and going out through the neighboring bedroom. Figure 1.3:25 shows southwest living room of flat A is having uniform airflow pattern due to the proper arrangement of window openings whereas the fresh air is not uniformly distributed in the southeast living room of flat B. 4.3.7.1.3

Testing 3: During south prevailing wind (June to September) Building block section.

The domain is divided in to several parts at an interval of 3m height up to the height of 130 m, which is more than the building height. Then Vr at each 3m level is calculated for each floor levels and the values are put in the velocity inlet face.

Figure 4.3-26, CFD Testing (Source: Author)

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The above analysis shows the faรงade is having high pressure at the bottom and low pressure at the top part of the tower. The previous analysis showed in the (section 4.2.5.1.3), the wind speeds are much amplified on the sky court, which is lacking in this present case. Due to lack in air permeability, stagnant areas are created on leeward side. Hence, the leeward side of the tower is lack of any airflow. 4.3.7.1.4

Testing 4: During north prevailing wind (December to march) Detail building section with openings

Internal section of 13th floor to 17th floor: (Vr = 1.4188258m/s) is taken in to consideration for 13th floor, rest Vr calculation (Refer section 3.2.2).

Type A

Type B

Figure 4.3-27, CFD Testing of detail section (Source: Author)

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Southfacing

North facing bedroom

living room

Figure 4.3-28, CFD Testing (Source: Author)

The result shows indoor wind velocity varies from 0.5 m/s to 2.2m/s in different flats, as the openings are different in each flat, specifically there is more airflow in type A than the type B due to different opening sizes. Path lines figure shows the habitable level in bedroom is not having any airflow whereas the living room is having uniform airflow in the habitable level. Hence, it can be concluded that the shape, size and location of external openings on the windward and leeward side play a vital role for wind induced cross ventilation in a tall building.

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4.3.7.1.5

Test 5: During South prevailing wind (June to September) Detail building section with openings

Internal section of 13th floor to 17th floor: (Vr = 1.4188258m/s) is taken in to consideration for 13th floor.

Figure 4.3-29, CFD Testing (Source: Author)

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Southfacing living room North facing bedroom

The result shows indoor wind velocity varies from 0.5 m/s to 3m/s in different flats, Path lines figure shows the habitable level in living room is not having any airflow whereas the living room is having uniform airflow in the habitable level. Hence, it can be concluded that the occupants must have control over their indoor environment like opening of windows and doors to achieve indoor thermal comfort as per their requirement.

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4.3.7.2 Analysis through TAS The analysis is undertaken on the hottest day 113: 23rd of April. The simulation is carried out in order to find the effectiveness of natural ventilation in Singapore climate.

Figure 4.3-30, Plan showing the south east living room, (Source: Author)

Weather File: Singapore Weather file from Energy Plus, All other inputs are similar to the Case 1 building except the Weather file.

4.3.7.2.1

Testing 1: Building orientation is changed to north south direction; the openings are perpendicular to the South prevailing wind for maximum airflow similar to Moulmein rise plan.

U Value of External North and South facades â&#x20AC;&#x201C; 2.4 W/m2 0C and external East and West facades â&#x20AC;&#x201C; 2 W/m2 0C (refer Chapter 2, section 2.7 for detail) and doors & window openings - 50% open, full day (24 hours ventilation) and nighttime ventilation only.

Figure 4.3-31, Temp variation graph for 24 hr. Ventilation (Source: Author)

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Figure 4.3-32, Temp. variation graph for 24 hr. Ventilation and Night time ventilation (Source: Author)

Figure 4.3:31 shows with 24hr ventilation, indoor temperature flactuates 280c to 340c during the full day, however during night time indoor temperature always lies below 300c within comfort zone where as indoor temperature is similar to the outdoor temperature during daytime.figure 4.3:32 shows with night time ventilation indoor temperature increased to 360c above the out door temperature during day time which is extremely uncomfortable.hence for indoor cooling 24 hr ventilation is always the best option in Singapore climate.the result shows similar to the previous study by Wong Nyuk Hien (Refer section 2.7) 4.3.7.2.2

Testing 2: Same as Testing 1 however the aperture opening % increases from 50% to 75% 20

U Value of External North and South facades â&#x20AC;&#x201C; 2.3 W/m

C and external East and West facades â&#x20AC;&#x201C; 2 W/m2 0C

(refer Chapter 2, section 2.7 for detail) and doors & window openings - 75% open, full day (24 hours ventilation) only.

Figure 4.3-33, Temp variation graph for 24 hr. Ventilation and Night time ventilation (Source: Author)

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Figure 4.3-34, showing temp variation (Source: Author)

Figure 4.3:33 shows, with 24hr ventilation indoor temperature remain samillar to the outdoor temperature during daytime.How ever with increased in aperture opening from 50% to 75% indoor temperature decreased by 0.5 to 0.8 0c during night time while compared to the 24hr ventilation having 50% aperture opening.Hence nighttime indoor temperture could be decreased with increase in aperture opening but there is no change in daytime temperature.hence in the next simulation(figure 4.3:34) the aperture opening kept constant without changing from 50% to 75% in daytime but during night time it was increased from 50% to 75% and the result shows the indoor tempertaure slightly decreased during daytime without any change in night time temperature with compared to the previous one.Hence by aperture opening of 50% during daytime and 75% during night time the comfort range can be achieved during night time.

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4.3.8

Concluding Summary

The overall performance of the building according to the previous study by Wong Nyuk Hien and Wang Liping in Singapore (Refer section 2.7) and the above analysis reveals

that the residents are naturally acclimatized to the local climate conditions and building’s wind induced natural ventilation strategy is generally successful in relation to its form, orientation, solar exposure and the prevailing wind directions. However, the psychrometric chart for developed country (Figure 4.3.37) shows the natural ventilation strategy could not be applied to achieve indoor thermal comfort for Singapore climate for most of the period. Nevertheless, according to various thermal comfort studies

Figure 4.3-36, Façade of the Tower, (Source: WOHA Architects)

in Singapore and above analysis results shows it is possible to have indoor thermal comfort with indoor air speed of 2 m/s for Singapore during most of the time. (Figure 4.3.38) (Refer section 2.3

and 2.7) Variable openings in the façade help the occupants to control their indoor environment as per their requirement. Due to large opening in the south living room, it enhance indoor airflow rate, however the high airflow rate due to high wind speeds at high altitudes might cause discomfort for the residents. The central core is also naturally cross ventilated which consumes less energy .The horizontal “monsoon window” designed by taking inspiration from vernacular design ideas keeps the rain out, while allowing continuous cool breeze in to the indoor space. The choice of materials used in the tower is equally Figure 4.3-35, Facade of the Tower with sun screen, (Source: WOHA Architects)

smart especially the perforated sunscreen, which allows indoor airflow by keeping the rain out. Since the cross ventilation strategy mainly

done by wind force, the rooms in the leeward side are devoid of any indoor airflow during calm or no wind. Since wind speeds are much amplified on the sky garden in a tall building, which enhance indoor airflow as well as air permeability is lack in the Moulmein Rise tower.

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Figure 4.3-37, Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore, (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

Figure 4.3-38,Modified Psychrometric chart showing the boundaries of outdoor temperature and humidity within which the indoor comfort can be achieved, with indoor air speed of 0.25 and 2 m/s for Singapore according to above analysis and developing country chart. (Source: Climate consultant, boundary drawn by Author with respect to building bio-climatic chart, Givoni , 1998.)

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4.3.8.1 Further investigations and suggestions The effectiveness of wind induced natural ventilation strategy applied in the tower can be highly reliable for the full year except certain time especially during the afternoon and evening time of the summer months. Microclimatic study shows during high humidity period dehumidification might help to get indoor thermal comfort. Hence, maximizing the opening in the prevailing wind direction (Test 6) and minimizing the solar radiation especially in the west and east faรงade might improve the effectiveness of wind-induced ventilation in the tower, however further analysis is needed for a concrete solution. 4.3.8.1.1

Test 6: During South prevailing wind (June to September)

Detail building section with openings Internal section of 13th floor to 17th floor: (Vr = 1.4188258m/s) is taken in to consideration for 13th floor.

Southfacing living room

Figure 4.3-39,CFD Testing showing detail designed section (Source: Author)

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Southfacing living room

Figure 4.3-40, CFD Testing (Source: Author)

The result shows indoor velocity varies same as test 5, However Path lines figure shows the habitable level in living room and bedroom, both are having uniform airflow .As in this case one extra window opening is added below the horizontal â&#x20AC;&#x153;monsoon window â&#x20AC;&#x153;which helps the indoor air to flow in the lower level of the room instead of going up as shown in test 5.

4.4 Concluding Summary of the chapter: Above analysis concludes that the residents are naturally acclimatized to the local hot and humid climatic conditions of tropics. The effectiveness of natural ventilation in a tall building is not merely dependent on wind force but also the strong correlation between the thermal comfort perception and wind sensation, which reveals that design considerations that are more critical should be given to the building layout, orientation to prevailing wind with less exposure to solar radiation and window opening area of the building design, which can create the preferred higher indoor air flow and thus increase the thermal comfort of the residents.

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4.5 Reference: [1] Brian Ford, Rosa Schiano-Phan, Elizabeth Francis, (2010) The architecture & engineering of Downdraught cooling A design Sourcebook, 2010, p 34 [2] Aga Khan Award for Architecture, 2007, http://78.136.16.169/pages/p03291.html (Accessed:

15.08.2010) [3] CTBUH Journal Issue 3, 2009, p 25 [4] Hasan-Uddin Khan, Charles Correa, Architect in India, Butterworth Architecture, 1984. Isbn 0-408-50043-3. [5] Robert Powell (1999), Rethinking The Skyscraper, The complete architecture of Ken Yeang, 1999, Thames and Hudson, ISBN 0-500-28155-6. [6] Richards, Ivor , T. R. Hamzah and Yeang: Ecology of the Sky,2001 [7] CIBSE, Natural ventilation in non-domestic buildings-Applications Manual, AM10, 2005, p 1197

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Comparative Analysis & Discussion:

5.1 Overviewing the Results: (Refer Comparative Table) The process and the results studied in the research shows, it is possible to use wind induced natural ventilation in tall building in tropical climate for the whole year with little limitation (Refer figure 4.1-10, 4.2-13, 4.3-38) which can be resolved by application of some basic design principles. Following the tests and experiments carried out at different locations, the extent to which the methodology has achieved its goal is evident. From the results obtained from TAS simulation (particularly for the hottest day of the year) and CFD simulation(for a calm day) and further analysis, it has been observed that the wind induced ventilation strategy can be adapted for other time of the year by controlling some of the parameters like window to wall ratio, aperture opening % during day and night for existing building (selected case study buildings) and applying some design principles like appropriate orientation, building form, spatial organization, opening with shading devices and spread out planning, sky courts and terrace gardens and living wall for new buildings. The study shows integration of natural ventilation in high-rise buildings especially in tropical climate, in terms of performance and the process will give a better, energy efficient and sustainable solution to overcome the energy crisis.

5.2 Critical Approach: One of the important part of the developed performance evaluation process is the use of different parameters like changing of U value of external walls, by increasing the aperture opening percentage for high airflow rate, by providing shading devices to control the high solar radiation and application of 24 hour or nighttime only ventilation as per the climatic conditions to evaluate the effectiveness of natural ventilation. Using modeling process in CFD and TAS, valuable simulation analysis is obtained which is based on bottom up approach of the growth process. Even if the results of the simulations like (Indoor temperatures obtained from TAS and ACH-1 obtained from CFD) are accurate as per the standard, adaptive thermal comfort theory and the Building bioclimatic chart, more simulation is needed before coming to a conclusion.

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Figure 5.2-1 Showing five factors affecting Natural ventilation. (Source: Abdul Razak Sapian modified by author) [1]

Here author wants to say that, effectiveness of natural ventilation in a tall building especially in tropical climate does not depend only on wind and buoyancy force but also depends on adaptive thermal comfort of occupants and many architectural design elements(Refer figure). Enhancement of effectiveness of natural ventilation depends upon the designer to decide which strategy and design elements would be ideal with respect to micro climatic conditions which is explained in (section), by testing the Kanchanjunga apartment in different climatic condition and by changing the building orientation alike to MBF Tower and Moulmein Rise in Penang and Singapore. Based on this the author derived the â&#x20AC;&#x153;impact of opening orientation, ventilation strategy like 24hr and night ventilation and local climatic conditionâ&#x20AC;? on natural ventilation in a tall building . The conclusion is, environmental constraints will not derive the form and design elements, but it is the vision and the expertise of the designers to interpret the results of building performance simulations.

5.3 Potential of the Process: Wind induced natural ventilation in tall building in tropical climate could be the optimum solution to achieve indoor thermal comfort by passive strategy. This is due to its effectiveness and performance with respect to the most diverse and conflicting condition of high temperature and high humidity. The natural ventilation strategy in tall residential building will add new potential to their existence. In this study the process has achieved its effective performance by controlling some parameters like percentage of openings with 24hr or night ventilation, orientation to prevailing wind, by providing sky court and terrace gardens and incorporating climate responsive facades to minimize intense solar Page | 192

gain. Wind induced ventilation strategy might provide some adverse impact on tall building due to its high speed, which creates high-pressure difference current (high wind speed) which is not discussed in this research. The study focuses on maximum airflow rate and airflow pattern to achieve indoor thermal comfort based on BBCC by Givoni. (Refer figure 4.1-10, 4.2-13, and 4.3-38) 5.3.1

Answer to research questions

5.3.1.1 How the occupant survey and study through various simulation tools like CFD and TAS are relevant while analyzing the design issue? Conducting CFD and TAS simulations can improve the potential success of natural ventilation in tall buildings. These studies can help to obtain surface pressures at each window openings, sky courts and terrace gardens, so that the facade openings can be shaped and sized accordingly throughout the tower (in relation to the desired airflow rate) and also to predict the indoor and outdoor airflow pattern in the tower .In addition, TAS simulation could be used to analyze the thermal performance of the building with natural ventilation which can reduce the risks associated with natural ventilation in tall buildings. Through these simulation tools, it becomes easy to check and reuse the performance of the design. In this research, the author correlates the result obtained from both the simulation tools to get some effective findings. (Refer Table 4.2 & figure 4.1.47 and 4.1.64) 5.3.1.2 How â&#x20AC;&#x2DC;effectiveness of natural ventilationâ&#x20AC;&#x2122; is dependent on global and local climate? (Effectiveness of natural ventilation in different climatic zones of tropics) This study stresses the effectiveness of natural ventilation in tropical climate and how it gets affected by different micro climate, which is proved by the author by making critical changes in Kanchanjunga apartment (like making the opening orientation towards the prevailing wind direction with respect to other case study buildings of Penang & Singapore and testing the tower in Penang and Singapore climate) and thus receiving desired positive results.

Figure 5.3-1showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Mumbai) Source: Author

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Figure 5.3-2 showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Penang) Source: Author

Figure 5.3-4 showing Temperature variation in living room of 24th fl (Kanchanjunga Apt., Singapore) Source: Author

Figure 5.3-3 showing Comparative Temperature variation in living room of 24th fl in three Cities, Source: Author

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Above result concludes that same tower is tested in different locations with its best possible orientation i.e. the openings are orientated towards the prevailing wind as per the micro climate of each location and result shows wind induced natural ventilation can effectively work in all locations however it depends on some specific considerations.

Figure 5.3-5, LHS Showing Kanchanjunga Apt with NW wind, Center Showing MBF Tower with NE wind & RHS Showing 1 Moulmein Rise with South & SW prevailing wind during peak summer period

5.3.1.3 How do the basic building design parameters affect the natural ventilation in tall residential building?

Mumbai Climate The best possible way to get indoor thermal comfort and required ACH-1 during summer in Kanchanjunga Apartment Inlet openings should orient towards Northwest, U Value of External facades – 2.4 W/m2 0C , doors & window openings open 75% with shading devices, Night-time only ventilation.

Singapore Climate The best possible way to get indoor thermal comfort and required ACH-1 during summer Inlet openings should orient towards South, U Value of External North and South Walls – 2.3 W/m2 0

C and external East and West Walls – 2 W/m2 0C and doors & window openings - 50% open during

daytime and 75% open during night time with shading devices, full day (24 hours ventilation) only.

Penang Climate The best possible way to get indoor thermal comfort and required ACH-1 during summer

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Inlet openings should orient towards Northeast, U Value of External North and South walls – 2.4 W/m2 0C and external East and West walls – 2.2 W/m2 0C. Doors & window openings (Aperture – 75 % open) with shading devices with night time only ventilation.

5.3.1.4 How would wind induced natural ventilation be utilized effectively in tall residential building? This study stresses the effectiveness of natural ventilation in tropical climate and how it get affected by sky court, terrace garden, internal planning & (inlet and outlet opening placements, shapes and sizes) which is proved by the author by providing similar wind speed of 2m/s considering a calm day for all locations (for detail Vr calculation, refer table 3.1) and thus receiving desired positive results.(For detail result refer section 4.1.8, 4.2.5, 4.2.5)

figure 5.3-6:CFD Testing : LHS Showing Terrace gardens and typical detail section of Kanchanjunga Apt., Center Showing sky courts and typical detail Section of MBF Tower & RHS Showing Block and typical detail section through 1 Moulmein Rise

With best possible orientation in all climates, achieved average indoor temperature in Mumbai is 31.010C on hottest day (day 95) with night ventilation, in Penang 29.240C on hottest day (day 73) with night ventilation and in Singapore 30.050C on hottest day (day 113) with full day ventilation, with wind induced natural ventilation having indoor air velocity of 2m/s. It concludes, indoor thermal comfort can be achieved during summer period in tropical climate through full day ventilation having indoor air velocity of 2m/s. Some variations like, in Kanchanjunga Apartment, night ventilation strategy can be applied during month of March and April to cool down the space during nighttime, as occupants are more affluent to air-conditioning during nighttime. During the hottest month of March

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in Penang, again, night ventilation can be used however; it cannot be applied in Singapore as full daytime ventilation has the capacity to cool down the interior all round the year.

5.4 Future scope of the Research: The main research subject of the thesis is to develop a naturally ventilated tall residential building in tropical climate, which can completely rely on wind induced natural ventilation. Following the testing of the case study, few solutions came forth. However, the whole potential and effectiveness of natural ventilation is not tested in this research. Further investigation in this subject will enable to find the real time potential and effectiveness of wind induced natural ventilation, in terms of indoor thermal comfort. As per the main aim, this research will only develop a conceptual tall residential building, which can rely on wind induced natural ventilation in tropical climate. However, the author is aware about the role of other architectural and climatic factors, which is not discussed in this dissertation. Advanced research in developing natural ventilation in tall building by using the performance evaluating process is possible, which will create more advanced, and energy efficient designs.

5.5 References:

[1] Abdul Razak Sapian, The effect of High rise open ground floor to wind flowand Natural Ventilation, (Ph.D.) Department of Architecture Kulliyyah of Architecture & Environmental Design, International Islamic University Malaysia.

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Conclusion

6.1 Overview Tall buildings are more vulnerable to wind and solar radiation. However architectural design process explores the use of aerodynamic form, specifically its adaptability characteristics combined with wind and solar energy from sustainability point of view. The performance considered here is the passive relation between building form with wind, solar radiation and vertical scape. The effectiveness of wind induced natural ventilation in different buildings in different locations is analyzed and the parameters are assigned to produce a conceptual design. As discussed in the literature review, thermal comfort expectation is influenced by degree of adaptive opportunity: as people have more control over their environment in home as compared to office, they tend to accept warmer environment more readily in their homes than in offices [1]. Various findings show occupants are naturally acclimatized [2] and wind induced natural ventilation is the most effective cooling strategy for whole year-round and wind pressure is applicable for achieving airflow for indoor thermal comfort in hot humid climate (Arens et al, 1984). In addition, it has greater potential to provide thermal comfort in tropical climate than is generally believed thus thermal preferences extend to a wider range of airflow speed and temperature (Humphreys, 1975; De Dear, 1998, 2000). The primary objective of this study is to identify the key parameters, which determine whether a tall residential building can be entirely dependent on natural ventilation in tropical climate thus some of the parameters are pointed out (Refer table 6.1) which can fight with the adverse climatic factors of hot humid climate and one of primary and initial step could be building permeability to enhance the effectiveness of natural ventilation and minimizing solar gain. (Refer figure 6.1-1, 2)[3]

figure 6.1-2,, Residential building with void ratio of 50% (with 6 apartments), Source: [3]

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Figure 6.1-1, Residential building model with a void ratio of 0% (with 6 apartments), Source: [3]

Table 6-1 Showing Adverse climatic elements with response strategies

Adverse elements of climate

method

Response strategies

Humidity

Minimize heat gain

Narrow plan with east and west

High heat

Maximize ventilation

Insolation

and

Rain

shading in openings

Minimum diurnal variation

axis High ceiling Cross ventilation Shaded veranda for rain and sun protection to external spaces Shading over openings all year -round Use of tree canopy for sun protection in summer to shade building but allow breeze for ventilation

From The quantitative and qualitative analysis, it can be concluded that, the residents are naturally acclimatized to the local hot and humid climate and the effectiveness of natural ventilation in a tall building is not merely dependent on wind force but also the strong correlation between the thermal comfort perception and wind sensation, which reveals that critical design guidelines should be applied to the building layout, opening orientation to prevailing wind with less exposure to solar radiation and shape, size and positioning of window openings, which can create the preferred and adequate higher indoor air flow and thus increase the thermal comfort of the residents. (Refer Figure 5.2-1) The present study suggests some specific design parameters to develop a conceptual design, which can rely on wind induced natural ventilation in tropical climate.

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6.2 Basic parameters Range of opportunity with respect to the climatic condition and the figure shows the optimum energy saving measures for tropical climate. Hence, natural ventilation and solar shading are the two major factors should be taken in to consideration while designing. Table 6-2, Energy saving measures by Tropical region, (Source: Lloyds Jones, D., 1998)

Passive comfort Measures

Tropical

Natural ventilation

Solar control and Shading

No Importance

Very Important

Figure 6.2-1, LHS : the optimum aspect ratio of towers in tropical region, which is 1:3. Centre and RHS: showing Split cores. Source: Author

1. Survey results from Singapore and Mumbai show afternoon and evening periods are the most uncomfortable time of the day during summer, which insists them to use A.C and mechanical cooling system (Refer section 2.7, table 2.6, 8). Finding shows especially in the context of Singapore, North / south orientation can reduce cooling load by 8.5 â&#x20AC;&#x201C;11.5% compared to an east /west orientation building. [4] Hence one way to reduce solar gain, Cores can be placed on east and west sides of the tower â&#x20AC;&#x153;split core systemâ&#x20AC;? which will help to provide shades from the low angle sun during morning and evening. Hence, this position of the core prevents high heat gain into the internal habitable space.

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2. Building orientation should take an advantage from the solar energy in terms of heat and light. With respect to the sun path in tropics, the building shape should be rectangular along the east-west axis. However square floor plan has less peripheral area and is less exposed to the external air than any other form, which results in minimizing air conditioning load. Moreover, the circular and rectangular form also helps to reduce intense solar radiation and acted as better solar controller. (Refer fig.6.2-2)

Figure 6.2-2 showing different building forms with less exposed peripheral area to external air, Source: Author

3. To minimize solar exposure, for bioclimatic planning, orientation is an important factor, therefore for tropical buildings, the main orientation should be on an axis 5o north of east and the directional emphasis should be North-south. figure 6.2-3 showing best building orientation, Source Author

4. Along with the orientation faรงade design also have great priority in designing of high-rise. Wind effects around the building can be controlled by shelterbelt planting or with permeable combination

walling with

can

compatible

used

devices.

Introduction of void or open ground floor in tall building enhances indoor airflow, which affects the natural ventilation performance in a greater range at windward and leeward facades of the tower. [5] (Refer fig. 6.2-4)

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Figure 6.2-4 showing void in ground help in free airflow, source Author

The permeability of the faรงade should be controllable for heat, light, air and visual transparency. The location of Transitional spaces in towers plays important role, it can be located in such a way that, it will protect hot sides of the tower. These transitional spaces might need sliding ventilated shutters to protect from the high wind speed. In addition, in tropical region 100% solar shading is required. (Refer Fig. 6.2-5)

figure 6.2-5 shows 100% solar shading requirement in Tropics, Source: Author

5. In tropics, external faรงades should allow natural ventilation and protect solar radiation. The most of the heat gain by the towers in tropical region can be possible to reduce, by using sunshade, balconies, deep recesses and sky courts or terrace gardens. Study shows natural ventilation in tall buildings can be improved with the use of skycourt by virtue of its form and placement in tall building. skycourt acts as wind trapping zone and channel the airflow into the interior spaces. Plantation in the skycourt filters and conditions the air (Refer section 5.3.1.4). CFD study on

airflow around skycourts revealed that the skycourt enhances

building permeability to wind (Yau, 2002) (Fig. 6.2.5 center). The effectiveness of natural ventilation reduces when the window openings are facing stagnant area. But Skycourts are effective in minimizing the stagnant areas on leeward side which enhance performance of natural ventilation in adjacent regions. Yau, 2002 revealed in case of the tower having skycourt, the mean ventilation coefficient was increased by about 43.0% as compared to the tower without skycourt. In addition,the best example could be the Commerz Bank where skycourts facilitate natural ventilation into the interiors through BMS controlled openings (Fig.6.2.5 RHS).[6]

Figure 6.2-6 , LHS: Sun path over Singapore, Source: Ecotect modified by Author, Central : Airflow around sky courts, Source: Milind, 2007 RHS: Airflow around commerz bank, (Source: Milind, 2007 )

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In Fig. 6.2-7, the CFD simulation results indicate that the wind speeds are much amplified on the sky garden in the middle of a 30-story high-rise tower. [7] Moreover tall buildings stand as an obstacle to the wind and redirect air along various streams creating strong current and pressure difference on the surface due to its high speed, hence to counteract such extreme risks some mitigating measures need to be enforced into sky court or terrace

garden

design

for

controlled

optimum

natural

ventilation. Figure 6.2-7, CFD simulation of wind environment around a 30-story highrise block with a sky garden in the middle [7].

6. There are two ways to achieve natural ventilation in high-rise and bring about the desired indoor comfort. The first one has direct physiological effect; this can be achieved by allowing more wind inside the space by using window openings to increase the indoor air speed, which will make the residents feel cooler. Since relative humidity is very high. As ‘air speed’ is directly proportional to the ‘rate of sweat evaporation’ from the skin. It minimizes the discomfort of the residents (when their skin is wet). Generally, air movement between 0.4 m and 3.0 m/s can generate cooling effects for occupants (Refer section 2.1.2, 2.3 and 2.7) again which is proved by the author in the research process (Refer section 4.1,4.2 and 4.3).Moreover in tropical regions it is easy to achieve comfortable air flow rate with wind pressure than buoyancy force, hence to achieve effective wind induced ventilation within a height of 2 m from the floor level (habitable level), different opening sizes and venting devices are needed at different height zones since the wind pressure difference at top level is significantly higher than lower level therefore the façade should have different opening sizes at every level. It concludes that the need to formulate a natural ventilation concept that can operate under a wide range of wind pressures can generate control difficulties in tall buildings (Refer section 2.3, 4.2.5.1.3) which would be more effective by using wing walls with controllable shutters. (Refer fig.6.2.8)

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Figure 6.2-8, LHS: Internal air speeds in models with vertical projections of varying depths, compared with values in models without projection. Window width is 1/3 of wall width. (Source: Givoni, 1976) RHS: wind wing wall diagram 3, 4, and 5 illustrate the effect of a wing wall on a façade of a building (Source: Yeang, 1999, 2008)

Another way is through indirect ventilation, which would be possible by ventilating the building only at night and use this air to cool the building in daytime. The cooled air mass minimizes the heat buildup rate during daytime which is possible in case of Mumbai and Penang during peak summer period. (Refer TAS result in section 4.1.8.2.7 & 4.2.5.2.4)

6.3 Inspiration 6.3.1

Control on intense solar gain and high wind force

“Sino steel plaza” a contemporary organic landmark in Tianjin, China whose façade is consisting of five different sizes of the hexagonal patterns around the building in irregular patterns like cells organization in living body. The pattern makes the building alive, by changing the looks from different perspectives. The tower is a perfect example of the parametric design and the most attractive pattern that appears irregular on the façade is designed to respond the building against intense solar radiation and high wind speed. The random pattern of the facade with variable window opening Size are decided by mapping different airflow pattern and solar radiation on the site to control the indoor environment of the tower during different seasons. [8] (Refer Fig. 6.3-2)

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Figure 6.3-1, Sino steel Tower, (Source: MAD Architects)

figure 6.3-2, LHS Showing Façade pattern developed by mapping solar radiation and wind speed and RHS showing four different façade pattern

6.3.2

Control on high wind force.

The curve shape of the building control the air around its base and inside circulate air allowing it to rise as it became hot by passing through the peripheral atriums which resulted of less space heating requirement and saving energy [9].

Figure 6.3-3, LHS: Swiss re Tower, London, and RHS: Wind pattern around Aerodynamic Form. (Foster and Partners, 2005)

6.3.3

Vertical scape (a living wall)

In urban city where high-rise buildings are predominant, vertical landscaping can reduce the solar gain and provide indoor thermal comfort to the occupants living in higher floors. Experiment shows a vertical greenery system can provide excellent thermal protection to the wall and the surface temperature of hard surfaces can be reduced up to about 15°c especially on east and west façade, which are protected by dense trees (Nyuk Hien wong and Yu Chen, 2009, Tropical Urban Heat Page | 205

Islands, p 226)The best example would be the Residence Antilia, Mumbai, India which is having a living wall with entwined plants running up to the top floor (40th floor) of the tower. After completion, this can be treated as the worldâ&#x20AC;&#x2122;s tallest continuous living organism having massive terrace gardens and waterfalls & green vertical wall [10]

Figure 6.3-4, Showing living wall in 40 storeyed tower, Antelia residence, Mumbai.Source [10]

6.4 Conceptual design Above design parameters and inspiration concludes with a solution for the main research subject of the thesis â&#x20AC;&#x153;A conceptual naturally ventilated tall residential building in tropical climate, which can completely rely on wind induced ventilation. After the form findings, (Fig. 6.4-1, 2) the design gave birth an elliptical per formative tower, which can rely on natural ventilation.

Figure 6.4-1, Showing Total radiation on LHS: Circular form. RHS: Square form for High rise Building: source: (GECO) (Grasshopper + Ecotect), modified by Author

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Figure 6.4-2, Total radiation on, LHS: Rectangular form. RHS: Elliptical form for High rise Building source: (GECO) (Grasshopper + Ecotect), modified by Author

Due to concave shape of the Tower, Different faรงades will receive different amount of solar radiation at different time. The part of the faรงade, which is receiving more solar radiation (on average) throughout the day, is having small openings to avoid unnecessary heating due to solar radiations. The part of the faรงade under low radiation is having comparatively large openings. The recessed balconies are acted as different projected wing walls to ensure the high amount of airflow to the internal space. The varying opening sizes can respond to high wind flow on different height and this is modeled by mapping the wind flow around the building at different levels of the tower.

Figure 6.4-3, Elliptical plan and Concave facade generated using Rhinoceros programme. (Source: Author)

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Steps followed at the time of design: (Weather file used for simulation – Mumbai, India)

3 Figure 6.4-4, Fig. 1 Showing Radiation on SE & SW façade, Fig.2 showing Radiation on East façade, Fig.3 showing Radiation on NE façade: Radiation is calculated on Façade using Rhino (3D Modelling) + GECO (Grasshopper + Ecotect) (Source: Author).

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Figure 6.4-7, Showing recessed balcony with wing wall, Source: Author

Figure 6.4-6, Larger openings at lower part for balanced indoor airflow and low radiation receiving part on faรงade, Source: Author

Figure 6.4-5, smaller opening at upper part for balanced indoor airflow and high radiation receiving part to minimize solar gain, Source: Author

After calculating the solar radiation on the building faรงade, openings are assigned as required performance. Like the part of the faรงade receiving more solar radiation throughout the day, are provided with smaller openings and more depth as compare to the other parts of the faรงade. This will enhance the natural ventilative cooling performance by minimizing the intense solar gain. These variable openings can be controlled by mapping different wind velocity at different points like those that smaller openings can be arranged at upper parts while larger openings at lower part to maintain required indoor airflow.

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figure 6.4-8 showing variable openings used on facade: openings are modeled through mapping the solar radiation on different point by using GECO (Grasshopper + Ecotect) (Source: Author).

Figure 6.4-9 Upper figures, showing variable openings with radiation on the tower, lower RHS showing wind flow around and through sky courts, lower LHS showing vertical green with wind flow pattern. (Source: Author)

The integration of Simulation based programs like Rhinoceros with Geco (Grasshopper & Ecotect), CFD and TAS shows immense potential for the bottom-up design process. However, the whole potential and effectiveness of natural ventilation is not tested in this research. Further investigation in this subject will able to find the real time potential and effectiveness of wind induced natural ventilation, in terms of indoor thermal comfort. However, these findings can be useful for the future planning of naturally ventilated tall residential buildings in tropical climate.

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6.5 References : [1] Feriadi, H., & Wong, N. H. (2004). Thermal comfort for naturally ventilated houses in Indonesia. Energy and Buildings, pp 36, 614-626. [2] N.H. Wong ∗, H. Feriadi, P.Y. Lim, K.W. Tham, C. Sekhar, K.W. Cheong, (2001), Thermal comfort evaluation of naturally ventilated public housing in Singapore, Department of Building, School of Design and Environment, National University of Singapore, 4 Architecture Drive, Singapore 117566, Singapore, [3] Hirano et al. (2006). A study on a porous residential building model in hot and humid regions: Part 1—the natural ventilation performance and the cooling load reduction effect of the building model. Building and Environment, 41. pp. 21 – 32. [4] Wong, N. H. & Li, S. (2007). A study of the effectiveness of passive climate control in naturally ventilated residential buildings in Singapore. Building and Environment, 42 (2007). pp. 1395 – 1405. [5] Abdul Razak Sapian, The effect of High rise open ground floor to wind flowand Natural Ventilation, (Ph.D.) Department of Architecture Kulliyyah of Architecture & Environmental Design International Islamic University Malaysia, Jalan Gombak, 53100 Kuala Lumpur. [7] J.L. Niu, J. Burnett, (2001) Setting up the criteria and credit-awarding scheme for building interior material selection to achieve better indoor air quality, Environment International 26 (7–8) pp. 573–580. [8] Magzine, dezeen Design. Sinosteel International Plaza by MAD. dezeen Design Magzine. Toy library, 30 July 2008. http://www.dezeen.com/2008/07/30/sinosteel-international-plaza-by-mad/. (Accessed 18.07.2010.) [9] Foster and Partners. Modelling the Swiss Re. Architecture week. [Online] 4 May 2005. [Cited: 5 June 2010.] http://www.architectureweek.com/2005/0504/tools_1-1.html. (Accessed 12.07.2010.)

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[10] Huge Hanging Gardens Going Up In Mumbai India (2007) by

Skyscrapernews.com

http://www.skyscrapernews.com/news.php?ref=93 Huge Hanging Gardens Going Up In Mumbai India. Copyright Holder - Reliance Industries, (Accessed 15.08.2010.

6.6 Bibliography:

Khade Milind, 2007, Benefits of Skycourt in High-Rise Buildings, University of Nottingham. Master Thesis Peter Clegg, (2007) Feilden Clegg Bradley: the environmental handbook, edited by Ian Latham and Mark Swenarton. London: Right Angle Publishing, ISBN 0953284859 Johann Eisele, Ellen Kloft. (2003) High-rise manual: typology and design, construction and technology. Basel: Birkhauser-Publishers for Architecture, ISBN 3764302747. Mat Santamouris and Peter Wouters, (2006) Building ventilation: the state of the art. London: Earthscan, 2006. George Baird, (2001) the architectural expression of environmental control systems, London: Spon Press, ISBN 0419244301. Ken Yeang., (2002).Reinventing the skyscraper: a vertical theory of urban design. Chichester: Wiley-Academy. ISBN 0470843551. Ken Yeang. Ecodesign: a manual for ecological design, Hoboken, N.J.: Wiley, 2008. ISBN 9780470997789/ 0470997788. Ivor Richards. (2001) T.R, Hamzah & Yeang: ecology of the sky, Mulgrave, Vic. Ken Yeang. (1992) the architecture of Malaysia. Amsterdam: Pepin Press, ISBN 9054960019. Francis Allard (1998) Natural ventilation in buildings: a design handbook, London: James & James, 1998. ISBN 1873936729 / 1873936729. Leon Van Schaik (2010) Vertical ecoinfrastructure: the work of T.R. Hamzah & Yeang, Mulgrave. ISBN 9781864703863 / 1864703865.

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Steven V. Szokolay. (2005), Introduction to architectural science: the basis of sustainable design, Oxford: Elsevier Architectural Press, c2008. ISBN 0750658495. Ken Yeang. (1999) the green skyscraper: the basis for designing sustainable intensive buildings. Munich: Prestel, ISBN 3791319930 B. Givoni, (1976) Man, climate and architecture, London: Applied Science Publishers, ISBN 085334678x Baruch Givoni (1994) Passive and low energy cooling of buildings /. New York; Chichester: John Wiley. ISBN 0471284734 Baruch Givoni. (1998). Climate considerations in building and urban design New York; Chichester : Van Nostrand Reinhold Alison G. Kwok and Walter T. Grondzik. (2007) The green studio handbook: environmental strategies for schematic design, Oxford: Architectural Press, ISBN 0750680229 (pbk.) 9780750680226 (pbk.) G.Z. Brown, Mark DeKay (2001); illustrations Virginia Cartwright Sun, wind & light: architectural design strategies / New York; Chichester: Wiley, ISBN 0471348775 / 9780471348771. Richard Hyde (2000), Climate responsive design: a study of buildings in moderate and hot humid climates / London: E & FN Spon, ISBN: 0419209700 Busch F. (1992).,A tale of two populations: thermal comfort in air-conditioned and naturally ventilated offices in Thailand. Energy and Buildings, 18, pp.235-49. CIBSE. (2005), Application Manual 10: Natural ventilation in non-domestic buildings. The Chartered Institution of Building Services Engineers, London, UK. De Dear R. (1998). A Global Database of Thermal Comfort Field Experiments. American Society of Heating, Refrigerating and Air-Conditioning Engineers Transactions, 104(1B), pp.1141-52. De Dear R. and Brager G. (2002), Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55, Energy and Buildings, 34(6), pp.549â&#x20AC;&#x201C;61.

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Baird, G. (2001) The Architectural Expression of Environmental Control Systems, Spon Press, London. Boutet, T. S. (1987) Controlling Air Movement, Mc Graw-Hill, New York. Canizares, A. G. (2005) Great New Buildings of the World, Harper Design, New York. Eisele, J., Kloft, E. (2003) High Rise Manual: Typology and Design, Construction and Technology, Birkhauser, Basel. Harris, J., Wigginton, M. (2006), Intelligent Skins, Architectural Press, UK. Oesterle, E. (2001), Double-Skin Facades: Integrated Planning, Prestel, New York. Wells, M. (2005), Skyscrapers: Structure and Design, King, London. Davi Rennie, Foroutan Parand (1998), Environmental design guide for naturally ventilated and daylit offices. Watford : Construction Research Communications, Lewis G. Harriman III .[et al.] (2009). The ASHRAE guide for buildings in hot and humid climates, Atlanta, GA : American Society of Heating, Refrigerating, and Air-Conditioning Engineers, ISBN: 9781933742434 1933742437 Nyuk Hien Wong and Yu Chen. Abingdon (2009), Tropical urban heat islands : climate, buildings and greenery / Taylor & Francis,. ISBN : 9780415411042 Jianlei Niu, 2003, Some significant environmental issues in high-rise residential building design in urban areas, Department of Building Services Engineering, The Hong Kong Polytechnic University, Hunghom, Kowloon, Hong Kong, China

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Appendix

1. Active means of Ventilation Both active and passive heating, lighting and ventilation systems have their own uses for the green building. The result can be stunning with careful consideration while constructing a new build. Various buildings in Middle East use solar energy to ventilate the hot dessert air and to provide warm water. German passive style of building in UK consumes less than 15KWh/m² instead of an average of 55 KWh/m² with the incorporation of passive solar design, a combination of mechanical and natural ventilation, efficient insulation and various forms of heating etc.

2. Natural Ventilation Strategies Building form and site layout should take the design advantage from ‘Summer Winds’. Building orientation should have the maximum exposure to the prevailing wind. •

Narrow plan shape of buildings to allow air through the building.

•

Wall openings to facilitate the passage of air through the building to be located.

•

Use of water feature to add a sense of coolness and passive evaporative cooling method in hot and dry climates.

•

Use of vegetation to enhance ventilation, cool incoming air and also to divert wind direction.

•

Use of ceiling fans to reduce the load on air conditioning.

3. Wind Induced Ventilation This experimental approach was taken by Irminger and Nokkentved in Denmark and at the N.B.R.I in Pretoria where impact of wind direction, building shape and external obstruction on the pressure ratio was investigated. They conducted their experiment in a medium speed wind tunnel with velocity of about 20m/sec with variety of different building models of different shapes and varying roof slopes. They found that when wind was incident normal to the building, elevated pressure was recorded at the windward walls , averaging 76% of the velocity pressure and diminishing slightly from the center of the wall (+95%) to the roof (+85%) and sides (60%). The suction average on the side walls was at an average -62%, which was highest at upwind section of the walls (-70%) and Page | 215

diminishing to -30% at the corners. At the leeward wall the suction was more or less evenly distributed , averaging -28.5% and average on roof was -65%, decreasing from -70% on upwind section to -50% downwind. When the wind was oblique the upwind corner recorded the highest pressure, diminishing downwards resulting in a pressure gradient being maintained along the windward walls. The leeward walls recorded a uniform suction which was directly proportional to the angle between the wind and the wall. In this experiment, when the wind was incident on the wall at an angle of 60 degrees, the pressure on the wall was +95% of the velocity head at the upwind corner, reducing to zero downwind while on another windward wall where the angle of incidence was 30 degrees, pressure ranged from ± 30 % upwind to -10% downwind. Average suction on the wall opposite that with wind angle60% was -34.5% and on the other leeward wall it was -50.3%.The roof, under all circumstances remained under suction with little variance in magnitude.

The scale is of ∆P/

Richard and other at N.I.B.R carried out another experimental investigation in a low-speed wind tunnel on the impact of wind direction on the pressure ratio. As per their findings: “ … in the case of single-roomed building with windows in two opposite walls …changes in wind direction upto 30 degrees either side of the perpendicular have little influence on the value of pressure ratio.” For all wind directions within these limits a value of 1 – 2 was suggested and for all others the pressure ratio was found to be directly proportional to and angle between the wind and the wall. This analysis produced the following formula to predict the pressure ratio (p.r) as a function of angle between wind direction and wall with the inlet window (α) for range 0° to 60° : p.r = 0.1 + 0.0183 α The expected value of p.r remains between 1-2 for angle between 60° to 90°. The investigations on pressure distribution on thatched roofs at N.I.B.R showed that if air hits the wall at an angle of 18° to 25° depending on wall height, both the windward and leeward sides turn into suction zones, in case of low-pitched roof. In case of a high-pitched roof, the windward side is on pressure and leeward side is under suction.

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According to C.S.T.B, there are two different schematic pressure distribution assumptions over a rectangular building: - For wind blowing perpendicular to one of the walls pressure on the windward side equals the dynamic pressure (∆p) and suction on the rest three sides is -0.3 ∆p - For wind blowing at an angle of 45°, pressure on two windward walls at upwind corner equals to the dynamic pressure diminishing to zero at the downwind corners and the suction over two leeward walls is -0.5∆p.Pressure distribution techniques can be used to determine pressure ratio across any two points in a building envelope. The greater the pressure difference between any two points, the higher is the rate of air flow through the building. Even when the windows are closed the rate of infiltration is also dependent on the pressure difference and also on the permeability of the openings. Thus the estimation of rate of air flow through a building is heavily impacted by pressure ratio which also plays a pivotal role in determining air change rates and infiltration heat gain or loss. In case of comfort ventilation however this concept must be carefully applied as there velocity over the occupied space has more importance than rate of air change. For example, as per C.S.T.B pressure ratio in a building with two windows in the center of opposite walls and where wind is hitting perpendicularly is 1.3 and when wind blows obliquely at 45° angle the pressure ratio is only 1.0 . However, practically a higher average internal velocity will be obtained in the second case because of better air flow distribution despite the lower pressure difference (Givoni, 1976, Man, climate and architecture, p 286).

4. Buoyancy induced Ventilation The rate of air pressure variation above and below the aperture is directly proportional to the air density above and below the opening. If indoor is warmer than outdoors, indoor air is less dense and vertical pressure gradient is less than outdoors. There is excess pressure built up indoors at any level above the aperture and a depression below it which again increases as we move away from the aperture. There is however, no air flow to outdoors as no aperture exists where there’s a pressure gradient. In case there are two apertures at different heights and a thermal difference exist as above, excess pressure is built up in the indoors at the upper aperture resulting in air flowing outwards and a depression is formed at the lower aperture resulting in air from outside flowing in. If indoor

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temperature is lower than the outdoors, air flow direction is reversed. The total volumetric weight difference between the indoor and outdoor columns of air is directly proportional to the height difference between both the apertures, denoted by h and the ratio ∆t/T, where ∆t is the thermal difference between indoors-outdoors and T the average absolute temperature(°K = °C+273) At ordinary temperature and pressure levels, average weight of a 1 cm column of water equals to 8.5 meters of air column. The total pressure head or ∆P is given by the below formula –

∆P =

(Cm of H2O)

With the above formula, as an example if the average indoor temperature is 30°C and outdoor temperature is 35°C with the height difference between the apertures being 5 m, the pressure head can be computed as below:

∆P =

= 0.0096 (Cm of H2O)

Air flow (Q) induced by temperature difference is proportional to square root of pressure head and free area of the aperture: Q = kA (h∆t) 0.5 Where k is a constant depending on the resistance given by the openings. For standard openings the ASHVE guide suggests the value of k = 9.4 (British units) Q = 9.4 A (h∆t) 0.5 (ft3/min/ft2) In Metric units Q = 7A (h∆t) 0.5 (m3/min/m2) (Givoni, 1976, Man, climate and architecture, p 282)

5. Cross Ventilation with Central Atrium In this proposal, the depth of office space should be limited to 5.5 meter to allow all areas to be ventilated properly through open-able windows and the contaminated air is exhausted with the vertical shaft which runs the entire height of the building. Page | 218

But it has few design problems. Firstly, there should be right balance between daylight and solar gain factor. Overheating because of large surface of glazing may resist sufficient airflow to offset the heat gain. Secondly, as there is no provision of treatment at the inlet, no tempering of air can occur in winter conditions. Thirdly, unpredictability in the airflow may occur in case of multiple stacks or atriums. Fourthly, it is not possible to achieve a uniform flow of air throughout. There are also potential problems with high wind pressure generated across internal doors, estimated to be between 200 and 600Pa [Ibid, p.761.]. In case of fire, smoke could reenter from the leeward side, into the building through windows due to the formation of eddy currents at the façade [Ibid, p.771.]. A built example of this approach is the Commerzbank Building, Frankfurt, designed by Foster and Partners (1991-1997). Here, central atrium and open-able windows are used for natural ventilation scheme and each of segregated unit includes a garden area and it is connected to outside atrium for exhaust of air. Double façade technology was used to control the airflow and solar gain [1].

[1] Pepchinski, M., ‘Commerzbank Reinvents the Skyscraper’, Architectural Record, No. 1, Vol. 186, January 1998, pp.68-79.

6. Cross Ventilation with Perimeter Conservatories All offices have windows that open to the conservatories allowing air to be tempered in winter conditions. The conservatory was extended the full height of each section of smaller zones of around six floors. And the central core was utilized as smoke extractor [5]. The overheating can occur during summers as conservatories temper the air. In a recent Swiss Re-Building, 30 St Mary Axe, London, by Foster and Partners (2000-2004) has six triangular conservatories around the floor plate which extend up to either two or six floors. For this circular tower, it was anticipated to use mixed mode of ventilation only for 40% time of the year [6].

7. Thermal requirements in Tropics The major cause of discomfort in such a climate is excessive sweating. Good ventilation design in such cases should ensure a greater sweat evaporation rate to maintain thermal equilibrium and also

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ensure that sweat evaporates as it generates from the pores and not given a chance to deposit on the skin causing discomfort.

As seen from above picture, the wetness of skin depends on the ratio between heat stress on the body and the evaporative capacity of the air (E/Emax). If this ratio is kept under 0.1, dry skin conditions can be ensured and to prevent skin clammy but no moisture condition this ratio must be below 0.2 â&#x20AC;&#x201C; a condition only achievable by air conditioning. In warm-wet climates with air-conditioning the acceptable ratio is taken as 0.3. Above picture shows the air velocities required to produce the required ratio of 0.1, 0.2 and 0.3.

8. Basic Principles and Design Factors Raising the building on stilts is an efficient design in warm-wet climates. It helps better ventilation by positioning the windows above the zone of maximum wind damping by surrounding vegetation. It also enables cooling the temperature from below, protects from termites and insects and helps avoid flood water corrode the building.

Positioning of windows also plays a major role in ensuring proper indoor ventilation.

In the bedrooms, maximum air concentration can be achieved by providing smaller inlets as compared to outlets where as in living rooms it is preferred to have both inlet and outlet windows of same size.

Large doors and windows are beneficial in warm-wet climates provided that there is adequate protection mechanism available for solar heat. Large openings provide better ventilation and aid in cooling down the indoors at night.

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The effective height of windows in buildings in warm-wet climate is about 0.5 to 1.5 meters above the occupied zone. It is important to bring window sills the closer possible in bedrooms, this helps adequate air flow around the sleeping area. If upper windows are used, care should be taken to design in such a way that when they are open, air flow is directed downwards.

Fly screens are a necessity in warm-wet climates, the efficient way is to position fly screens on the widest possible area such as balcony rather than putting them on the windows there by ensuring a greater volume of air could pass through onto the windows.

Large openings in buildings in this climate require adequate shading measures otherwise the internal temperature may rise to an uncomfortable level. Solar protection may be combined with rain protection as well, not only for the windows but for all the walls. This is done by extending the roof beyond the floor area which helps prevent the walls from corrosion by heavy rains which are characteristics of warm-wet climate. Planning is also required to provide a way of disposal of run-off rain water which may cause soil erosion around the base of the walls. 9. Window Opening Orientation with respect to Prevailing Wind 7-1 Effect of window location and wind direction on average air velocities

Effect of window location and wind direction on average air velocities (% of external velocity) Inlet

width Outlet width Windows in opposite walls

Windows in adjacent walls

Wind perpendicular Wind oblique Wind perpendicular Wind oblique 1/3

1/3

2/3

1/3

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2/3

1/3

3/3

1/3

2/3

3/3

2/3

3/3

From the results above it is evident that ventilation conditions are better when air has to change direction inside the room rather than just pass from inlet to outlet. This finding is critical, especially for regions with westerly or easterly wind as buildings with such orientation are difficult for shading. Especially in long building blocks where windows are placed in opposite walls in one room or two rooms connected by a hall. Required orientation for ventilation and solar shading aspects can be conflicting in such scenarios.

However in regions with westerly winds, good ventilation conditions can be possible even when to make shading easier the long faรงade is turned 45 degrees to north-west or south-west. The long faรงade can be oriented towards north or south depending on the wind direction resulting in optimal ventilation and good solar shading (Givoni, 1976, P 290) 10. Window Size 10. Table 7-2 Effect of window size in room without cross-ventilation on average air velocities (% of external wind velocity)

Effect of window size in room without cross-ventilation on average air velocities (% of external wind velocity) Direction of wind

Perpendicular to window

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Width of window 1/3

2/3

3/3

Oblique in front

Oblique from rear

As can be seen from table above, only when the wind is oblique to the window, thereâ&#x20AC;&#x2122;s a considerable rise in velocity when window size is increased as compared to wind blowing perpendicular or blowing from rear.

Below table shows variation in average and maximum air velocity with different size of inlet and outlet window sizes, windows on opposite walls.

Table 7-3, Effect of inlet and outlet width on average and maximum velocities

Effect of inlet and outlet width on average and maximum velocities (% of external wind speed) Wind direction

Inlet size Outlet size

Perpendicula r

Oblique

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1/3

2/3

3/3

Aver

Maximu

Averag

Maximu

Averag

Maximu

age

1/3

2/3

131

3/3

137

1/3

2/3

133

131

3/3

152

137

115

As can be seen from the table above the air velocity is affected to a considerable extent, when the room is cross-ventilated and the size of both inlet and outlet windows are increased simultaneously. Increasing any one of them has slight impact on the air velocity. Also when the outlet is larger than the inlet then much higher maximum velocity and little higher average velocity are obtained. The above experimental results of Givoni were analyzed mathematically in India and the following relationship has been found between average indoor velocity and size of windows (inlet and outlet assumed equal sizes): _ V(i) =0.45 (1 â&#x20AC;&#x201C; e -3.84X) V(o)

Where _ V(i) is average indoor velocity, X is ratio of window area to wall area and V(o) is outdoor wind speed (Applicable for a square room with windows on opposite walls)

Below table shows internal air velocity in models with different ratios of inlet to outlet size As can be seen from above the average indoor velocity is dependent on size of the smaller opening, either inlet or outlet. The maximum velocity however sees an increase with increase in ratio between outlet and inlet size. (Givoni, 1976, P 292).

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Vertical location of windows Free wind above the level of buildings has a more constant direction vertically than horizontally; hence vertical distribution of air velocities is much more a constant factor and by controlling height and design of inlet openings, it is possible to have greater control on the velocity distribution. Because of inertia, flow pattern of air mass inside a room is primarily determined by the direction air enters the room. This means the location and design of inlet openings have more significance than that of outlet openings. The velocity sees a drastic drop below the window sill area of an inlet window to an extent of 25% of main stream velocity in a cross-ventilated room. However the average air flow inside the room is slightly affected. In warm regions bedroom window sill heights are important as during night time maximum use should be made of the night time reduced air velocity.

Windows – positions and methods of opening In Texas a study was carried out by Holleman to understand internal air flow patter using different types of windows. This suggested incoming wind blows horizontally and in its original direction in case of double-hung and horizontally sliding windows. In such windows the maximum free opening is about half of the total area. In vertical pivoted windows it was possible to control the wind direction and air mass. In case of casement windows opening outside, this control is implemented by opening one sash against the wind and the other with it or opening both the sashes. In horizontal projected windows as per the study it was found that air flow direction was upwards with any angle of opening of windows other than horizontally fully open position. Hence the best suited position for the windows is below the required level of wind movement. By using jalousie windows and controlling the angle of glass louvres, the air direction can be changed either upward or downwards In another study by van Straten and others in South Africa it was shown that “…the horizontal centre-pivot-hung sash window is the most suitable for directing the incoming air towards any desired level within the room, particularly if the sashes can be made to open downwards on the room side to 10 degrees below the horizontal. Louvre type windows serve the same purpose.” As per this

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study, it was also found that side-hung windows were less effective in air pattern and speed of indoor air movement. Another study in Israel showed that the angle to which a window opens and any alteration there in has impact on the flow pattern and velocity distribution inside the room and not significant effect on average velocity. In all the above studies and research done, what comes as an important aspect is for any window arrangements tested in different experiments, the air velocity close to the floor was higher compared to levels near the windows. This is due to the two major air streams formed â&#x20AC;&#x201C; one from inlet and the second one along the roomâ&#x20AC;&#x2122;s surface, wall and ceiling. In office and classroom based scenarios, it is desirable to have a drastic drop in air velocity below a certain level, which otherwise can be a distraction to work, i.e. lifting papers from desk etc. The ideal solution in such cases would be to design in such a way so as to have a high velocity at head level at around 120 cm and sharp decrease in the velocity at the desk level at around 70 cm.

11. Effect of fly-screens Particularly in the tropics, fly screens are essential. These reduce the air flow through the windows to a considerable extent when external force is slow. According to van Straaten, the decrease in total air flow caused by a 16 mesh , 30 gauge wire screen is about 60% and 50% when wind speeds are 1.5 and 2 mph and its is about 25% when wind speed is 10mph. As per a wind tunnel study at B.R.S. in Haifa, effect of fly screens is dependent on a combination of air direction and number and position of inlet windows. Reduction in air speed due to screens over a single central window was more in case of wind incident obliquely (the wind seemed to slip over the window)

compared

wind

incident

perpendicularly.

When screens are applied to the balcony instead of the inlet windows, it provided better results and air gets a larger area to pass through with some resistance and then can pass through the inlet window without any obstructions.

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It can hence be concluded that fly screens provide resistance to incident air flow, reduce internal speed and it causes wind to slip over it. 12. Choice of materials The choice of materials in building design in warm-wet climates is driven by factors such as prevention of daytime temperature rise and minimization of temperature in the nighttime, weathering quality of material in damp and moist conditions, and insect and fungi infection. The heat capacity of the building should be as low as possible to prevent heat accumulation during daytime which would also elevate the temperature in night times. Non-determinant building material, lightweight is preferred for quick response due to little variation in diurnal temperature. Wall The external walls with adequate thermal resistance help minimizing heat flow from outdoors. Modern insulating materials with low weight and heat capacity provide high thermal resistance and a better indoor atmosphere; however such materials should also be insect-proof and fire-proof. When heavy-weight materials are used for the structures, care must be taken to provide adequate insulation. For instance in concrete multistoried buildings insulating material must be used in ceilings to provide heat insulation and help reduce temperature at night. Placing aluminium foil beneath the roof can reduce radiant heat flow from roof to ceiling. This can be supplemented by placing another insulating layer above or below the ceiling and by ventilation of the attic space. Roof Light color to reflect solar radiation, parasol type to maximize ventilation, reflecting foil laminate under roof to reflect radiation, minimal use of roof lights with minimal area. Double roofs with air flow between them provide solar-protecting quality and protection from rain as well. Appropriate care however must be taken to ensure these withstand heavy winds.

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12. TAS Simulation: Internal Conditions

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13 & 14. TAS Simulation: Schedule and Aperture Types

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15. CFD Simulation: Procedure

CFD CODES: CFD codes are structured around numerical algorithms that can tackle fluid flow problems. All codes contain three main elements: 1. Pre-processor

Solver

Postprocessor

1. PrepocessorPre-processing consists of an input of a flow problem to a CFD program by means of an operator friendly interface and the subsequent transformation of this input into a form suitable use by the solver. The user activities at the pre-processing stage involve: • Definition of the geometry of the region of interest – the computational domain • Grid generation- the subdivision of the domain into a number of smaller, non overlapping sub domains; a grid (or mesh) of cells(or control volumes or elements). • Selection of the physical and chemical phenomena that need to be modelled • Definition of fluid properties • Specification of appropriate boundary conditions at cells which coincide with or touch the domain boundary The solution to a flow problem (velocity, pressure, temperature, etc.) is defined at nodes inside each cell. The accuracy of the CFD solution is governed by the number of cells in the grid. In general, the Page | 230

larger the number of cells, the better the solution accuracy. The number of cells can also be increased before or after achieving converge through mesh refinement.

2. Solver Out of the three distinct streams of numerical solution techniques; finite difference, finite element and spectral methods; only the finite volume method (a special finite difference formulation) id considered. In outline the numerical algorithm consists of the following steps: • Integration of the governing equations of fluid flow over all the finite control volumes of the domain • Discretisation- conversion of the resulting equations into a system of algebraic equations • Solution of the algebraic equations by an iterative method. 3. Post Processor The post processor includes: • Domain geometry and grid display • Vector plots • Line and shaded contour plots • 2D and 3D surface plots • Particle tracking • View manipulation (translation, rotation, scaling, etc.) • Colour Post Script output The postprocessor has the graphics output capabilities that communicate the solution of the CFD problem or related ideas to a non-specialist. [Reference: An introduction to computational fluid dynamics-The finite volume method Author- HK Versteeg , W Malalaskera, 1995, pg.2-3]

MESH REFINEMENTS: Need of a Mesh: The governing partial differential equations of fluid flow can be discretized using the following techniques to produce algebraic equations: • The finite difference method • The finite element method • The finite volume method Page | 231

Regardless of which of the three discretisation techniques is used, a mesh of points has to be produced within the volume of the fluid. This can be considered as the discretisation of space in which the flow takes place. If the finite difference method is used then the values of the variables at the points are used to produce equations for the variables that enable a solution to be determined. This involves a grid of points. If the finite volume method is used then the points are arranged so that they can be grouped into a set of volumes and the partial differential equations can be solved by equating various flux terms through the faces of the volumes. If the finite element method is used then the points are grouped to define elements within which the numerical analogue to the partial differential equations can be setup. In both the latter cases the structure of the mesh does not depend on the discretisation method.

Purpose of mesh refinement: Once a mesh has been built it is possible to modify it in such a way that the CFD solution that is produced on the modified mesh is better and more accurate. This modification can take place either before a solution to the flow problem is found or afterwards. Some CFD pre-processors can take a mesh with a regular structure and smoothen it, such that the cells form an orthogonal mesh. This can reduce the computing effort required to produce a solution and increase the accuracy of the solution. These smoothing routines are based on the solution of a series of partial differential equations that describe the variation in the grid coordinates (Thompson, et al., 1982). In this process the original mesh is used as the first guess in an iterative solution procedure. Other mesh modification techniques can be applied after a CFD solution has been produced on an initial mesh. These techniques are used to modify the mesh in the light of the results achieved on it, and so the dependence of the quality of the results on the users experience is reduced. These modification procedures require that an initial analysis is made using a crude but realistic mesh of points in the flow domain. From the results of this initial analysis the mesh is recreated such that the density of the mesh points is greatest in areas of the domain where the fluid variables change rapidly or where the error in the numerical equations is found to be large (Zienkiewicz abd Taylor,1989) the mesh is said to be adapted to take account of the results generated. The following two types of mesh modification are used:

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Mesh enrichment: Additional points are placed within the domain at the locations where they are needed. The original mesh of triangles has a regular spacing but the enriched mesh has additional nodes and elements in it so that there are more elements near the solid surface. This technique is applied to meshes that consist of triangular cells or elements in 2-D and tetrahedral cells in 3-D. Such meshes allow to be created in the mesh and then Delaunay triangulation method can be used to create a new set of elements. Mesh adaptation- where the topology of the mesh stays the same but the mesh points are moved so that the density of the points increases where required. Here a boundary layer is again modelled. The number of nodes or elements remains the same in the adapted mesh. Only the node positions are changed. By using these smoothing or adaptation techniques the accuracy of the solution can be increased, but extra computational effort is required to find the solution. (REFERENCE: Using Computational Fluid Dynamics- Author CT Shaw, 1992, pg. 110-111) Fig. shows the series of mesh refinements performed in this case (any wall-floor/ceiling junction)

BEFORE REFINEMENT 14253 CELLS

ADAPT 2: 240744 CELLS

ADAPT 1: 36483 CELLS

ADAPT 3: 162204 CELLS Mesh refinements during simulation

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