Natural Ventilation for High-Rise Residential Buildings in Tropics
Debarpita Mohapatra Student ID: 4114654 K14 DTM (Advanced Tall Building Studio)
Contents 1.
Abstract ................................................................................................................................................. 1
2.
Introduction .......................................................................................................................................... 1
3.
World Climate Zones............................................................................................................................. 1
4.
Tropical Climate .................................................................................................................................... 2
5.
Ventilation and Natural Ventilation ...................................................................................................... 4 5.1
Ventilation..................................................................................................................................... 4
5.2
Natural Ventilation........................................................................................................................ 4
6.
Natural Ventilation in Tropical Climate................................................................................................. 4 6.1
Historical Overview ....................................................................................................................... 5
6.2
Natural Ventilation for Residential High-Rise Buildings................................................................ 6
7.
Natural Ventilation Principles and Strategies ....................................................................................... 7 7.1
Single sided Ventilation................................................................................................................. 7
7.2
Cross Ventilation ........................................................................................................................... 7
7.3
Stack Ventilation (Cross Ventilation with central atrium) ............................................................ 8
7.4
Double Skin Facade System .......................................................................................................... 8
7.5
Wind wing-wall Device.................................................................................................................. 9
8.
Factors affecting Natural Ventilation in Tropical Climate ..................................................................... 9
9.
Design Factors for Natural Ventilation ............................................................................................... 10 9.1
Building Orientation and Form ................................................................................................... 10
9.2
Position of Openings ................................................................................................................... 10
9.3
Size of Openings .......................................................................................................................... 10
9.4
Internal Arrangement ................................................................................................................. 10
10.
Case Study ....................................................................................................................................... 11
10.1
1 Moulmein Rise, Singapore ....................................................................................................... 11
10.1.1 10.2
Newton Suites, Singapore ........................................................................................................... 14
10.2.1 11.
Natural Ventilation Strategy ............................................................................................... 11
Natural Ventilation Strategy ............................................................................................... 14
Conclusion ....................................................................................................................................... 15 Bibliography .................................................................................................................................... 17
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Images: Figure 3-1 The world climate pattern according to Koppen (Source: NOAA, National Oceanic and Atmospheric Administration) ........................................................................................................................ 2 Figure 4-1 Tropical climate zone (Source: http://en.wikipedia.org/wiki/File:Koppen_World_Map_Af_Am_Aw.png) .................................................. 3 Figure 4-2 Few important cities in the Climatic Zone (Source: http://kantan-net.main.jp/, Modified)....... 3 Figure 5-1 Natural Ventilation (Source: http://www.squidoo.com/passivebuildingcooling) ...................... 4 Figure 6-2 Natural Ventilation strategy in traditional Malay House (Source: Yuan, L J The Malay House) .. 5 Figure 6-1 Airflow Strategy in traditional Malay House (Source: Yuan, L J The Malay House) .................... 5 Figure 6-3 The Equitable Building (Source: http://www.nyc-architecture.com).......................................... 6 Figure 7-1 Single Sided Ventilation (Source: http://www.dyerenvironmental.co.uk) ................................. 7 Figure 7-2 Double Sided Ventilation (Source: http://www.dyerenvironmental.co.uk) ............................... 7 Figure 7-3 Stack Ventilation (Source: http://www.dyerenvironmental.co.uk) ............................................ 8 Figure 7-4 Cross Ventilation with Double Skin Facade (Source: sauerbruch hutton architects) .................. 9 Figure 7-5 Wind wing wall (Source: http://passivesolar.sustainablesources.com/) .................................... 9 Figure 10-1 Moulmein Rise (Source: http://singaporearchitecture.wordpress.com) ................................ 11 Figure 10-2 Architect's sketch of Monsoon window (Source: WOHA Architects) ...................................... 12 Figure 10-3 Section through Moulmein Rise (Source: WOHA Architects) .................................................. 13 Figure 10-4, The shading device integrated with facade (Source: WOHA Architects) ............................... 13 Figure 10-5 Moulmein Rise typical floor Plan (Source: WOHA Architects) ................................................ 13
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1. Abstract The aim of the research is to investigate possible ways and designs to achieve natural ventilation in tall buildings for tropical climate, where mechanical ventilation (Air-conditioning) is highly used for desired thermal comfort. The research is carried out by studying existing tall buildings from tropical region namely Moulmein Rise, Singapore MBF Tower, Penang, to draw some valuable conclusions.
2. Introduction In tall Buildings, it is difficult to achieve required thermal comfort with less energy consumption by using Natural ventilation systems. This is due to some factors, which are related with personal variables like clothing, activities etc. Wind induced natural ventilation is the result of local wind velocity and the direction of the wind. However design of the tall buildings is also influential. According to survey ‘ building industry consumes 40% of world’s energy from which 50% are only due to mechanical ventilation, more over survey also shows that mechanical ventilation system consume more energy in Tropical region because of hot and humid weather (1). The tropical climate is characterized by relatively high temperature and humidity usually required both cooling and dehumidification and the problems lead to most of high-rise buildings relying on mechanical ventilation. Nevertheless, design principles such as orientation, spatial organization, shading devices, Cross ventilation, use of smart material, thermal mass, evaporative cooling, use of colour and texture, roof gardens, strategic plantation etc. may be addressed together to avoid or minimize this reliance. According to Dr. Ken Yeang, well known architect for Tall buildings in Tropical region, 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. (1)
3. World Climate Zones The most accepted 'Koppen System' divides the world climate into five regions. a. Tropical Climate b. Dry Climate c. Temperate Climate d. Continental Climate e. Polar Climate
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Figure 3-1 The world climate pattern according to Koppen (Source: NOAA, National Oceanic and Atmospheric Administration)
4. Tropical Climate According to Koppen Climate Classification, it is the non-arid climate where an average monthly temperature is always more than 18° C throughout the year. The tropical climate is further subdivided in to:
Tropical Rainforest Climate
The region within 5°-10° latitude of both side of Equator having monthly average rainfall more than 60mm and with no natural seasons are Tropical Rainforest Climate.
Tropical Monsoon Climate
The region experiences monthly mean temperatures more than 18° C throughout the year, features wet and dry seasons, occasionally also known as tropical wet or tropical monsoon and trade wind littoral climate.
Tropical Wet & Dry (Savanna) Climate
A tropical savanna climate either experiences less rainfall than a tropical monsoon climate or have more pronounced dry seasons than a tropical monsoon climate.
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Figure 4-1 Tropical climate zone (Source: http://en.wikipedia.org/wiki/File:Koppen_World_Map_Af_Am_Aw.png)
So precisely the climatic factors dominated in tropical region are – 1. Constant High temperature 2. Amount of precipitation in air, which influences the architecture of the region.
Figure 4-2 Few important cities in the Climatic Zone (Source: http://kantan-net.main.jp/, Modified)
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5. Ventilation and Natural Ventilation 5.1 Ventilation Ventilation is the process of air circulation of a space (especially enclosed) maintaining the required air quality. This is not only exchange of inside air with outside but the control over moisture, temperature, odour, smoke, dust etc. as well as circulation of air throughout the space or building. The invention of air-conditioning system by Willis H. Carrier in the year 1902, subdivided the ventilation strategies in buildings in to Natural Ventilation and Mechanical Ventilation. All the historical buildings were naturally ventilated using the natural forces, orientation, opening strategies and even buoyancy, though it has some limitations which differ in different climatic zones. In particular, the supply of fresh air into the building was most important in historical buildings. The limitation of natural ventilation stands out when it comes to humidity control in humid climates.
5.2 Natural Ventilation In simple words, Ventilation without any mechanical system is called Natural Ventilation. The climatic factors, wind speed and pressure in the region, outside and inside temperature, controllable openings as well as strategic positions and buoyancy are few natural forces to make the outside air flow and distribution of fresh air throughout a space. Natural ventilation can be either controlled by wind speed or wind pressure, technically termed as wind driven Figure 5-1 Natural Ventilation (Source: http://www.squidoo.com/passivebuildingcooling) or buoyancy driven ventilation.
6. Natural Ventilation in Tropical Climate Natural ventilation system uses the natural forces of wind to supply fresh air without using mechanical devices like fans, which consumes energy. This fresh air achieves the level of thermal comfort but in tropical region, it is difficult to control the humidity level in the air, which is more than 65%. For the comfort there should be thermal balance between the body and surrounding environment but again it depends on physical factors like activity, clothing, acclimatization etc and environmental factors like humidity, air temperature etc. Particularly in tropical climate, the air movement near the body helps in fast swear evaporation and this provides thermal comfort. With proper orientation of the building in consideration of prevailing winds and controllable openings, the desired air movement can be achieved in humid climates. Still it is very challenging to dehumidify the incoming air.
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6.1 Historical Overview Traditional society gives us data about the relation between buildings physical performance and climatic conditions. 100 years ago, all the buildings were naturally ventilated. Looking in to traditional Malaya houses in Malaysia, Javanese architecture in Indonesia and traditional Vietnamese architecture we can notice that, - Building form accelerates air into the building for ventilation. - Strategic positioning of openings to allow the airflow at body level. - Open interior spaces for proper ventilation. - Elevated floor level to catch the wind of higher velocity.
- Strategic plantation to allow wind flow through the building. - Light weight construction material.
Figure 6-1 Airflow Strategy in traditional Malay House (Source: Yuan, L J The Malay House)
Figure 6-2 Natural Ventilation strategy in traditional Malay House (Source: Yuan, L J The Malay House)
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In 19th century Chicago evolved with first generation of high-rise structures which were mainly office buildings. Until the invention of air-conditioning system in 20th century, passive system was only adopted by designers. Features like limited depth of floor plate, open court yard and large open able windows were only meant for natural ventilation.
Figure 6-3 The Equitable Building (Source: http://www.nyc-architecture.com)
The Equitable Building, built in 1915 in New York has a H shape plan for passive ventilation strategies with less deeper floor plans. The shape allowed for proper air circulation and natural illumination.
6.2 Natural Ventilation for Residential High-Rise Buildings 17% of the total energy of China is consumed by buildings only (Q. Chen, 2001) and the household usage of air-conditioners has increased significantly from 7.8% in 1978 to 57.7% in 1998 in Singapore (N. H. Wong, 2001). It shows buildings consume more energy and became the major source of green house gas emissions around all over the world. Natural ventilation is perfect answer for these problems which has been approved by tenants in Singapore where most of the population of the country is living in HDB (Housing development Board), where apartments are designed to be naturally ventilated (Wong Nyuk Hien, 2006).
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7. Natural Ventilation Principles and Strategies Minimization of cooling requirement with design principles such as orientation, spatial organization, shading devices, Cross ventilation, use of smart material, thermal mass, evaporative cooling, use of colour and texture, roof gardens, strategic plantation etc. are some of the strategies to achieve the thermal comfort level of the interior, maintaining a humidity level of 60-65% and a temperature range of 22-27° C. ‘Ventilation strategy’ is the allowing fresh air to enter inside the enclosed space and taking it out. There are three different categories of natural ventilation systems. Namely – a. Single sided ventilation b. Cross ventilation c. Stack ventilation.
7.1 Single sided Ventilation In this type the inlet and outlet openings (windows) are provided only on one side (as shown in the figure 7-1). Here wind is the main driving force with desired temperature difference between inside and outside the openings. This can be used only if the depth of the room is less than or equal to the 2.5 times the height.
Figure 7-1 Single Sided Ventilation (Source: http://www.dyerenvironmental.co.uk)
7.2 Cross Ventilation In this method, the significant pressure difference between two adjacent sided of the building facades makes the airflow through the interior space. Here inlet and outlets are provided on both sides of the enclosed space. This is effective when the depth of the room is less than 5 times height of the room.
Figure 7-2 Double Sided Ventilation (Source: http://www.dyerenvironmental.co.uk)
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7.3 Stack Ventilation (Cross Ventilation with central atrium) In buildings having large footprint, the centrally positioned atriums can enhance the natural ventilation process. In this case, air flows inside the building and extracted out through atriums. Here the thermal buoyancy created in atrium drives the air movement throughout the building.
Figure 7-3 Stack Ventilation (Source: http://www.dyerenvironmental.co.uk)
7.4 Double Skin Facade System Double skin façade in tall building can be treated as one of the best possible buoyancy induced natural ventilation strategy, which is proven and more effective in cold climate than the hot and humid climate; however, few studies investigated on ventilated double skin façade in tall building in hot and humid climate and finding shows: Since the intense solar gain on building façade is, an endemic factor in tropical climate the amount of heat gain on the same can be reduced significantly by designing a ventilated double skin façade where outdoor air uses natural ventilation in the cavity to reject heat gain. (2) A south facing double skin façade system would be the most efficient for annual saving and has produced an 80% acceptability limit for the cavity of 300mm at external temperatures between 26 ° C and 28 ° C. (3) The present investigation on HDB Flat, Singapore stated that the active stack through booster fans could be used to enhance the ventilation rate with compared to the passive one and could be powered by solar energy thus making the whole system more energy efficient as compared to the air conditioning system. (4)
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Figure 7-4 Cross Ventilation with Double Skin Facade (Source: sauerbruch hutton architects)
7.5 Wind wing-wall Device Malaysian Architect, Dr. Ken Yeang is known for his principles for bioclimatic towers in Tropical Climate. In his high-rise buildings he extensively used this innovative ventilation strategy for natural ventilation by manipulating the flow of prevailing wind And the wind wing wall is the most interesting building element designed by him.
set
The 'wind wing wall' is simply a short wall placed perpendicular to an opening in an building, used in combination with the orifice as a device like a pocket to collect or direct the prevailing winds into the insides of the building. The design of the device depends on local wind conditions, Figure 7-5 Wind wing wall (Source: http://passivesolar.sustainablesources.com/) the plan depth and built form. Computational Fluid Dynamic (CFD) simulation ascertains the effectiveness, size of opening, wing-wall shape, size, orientation and location in relation to the built form (5).
8. Factors affecting Natural Ventilation in Tropical Climate Acclimatization is an important factor in the process of natural ventilation. Person staying in natural ventilated designed buildings usually adopt a wider temperature range as compared to the one staying in mechanically ventilated (Air- conditioned) buildings. Occupants in hot and humid climate usually accept high temperature and humidity level. Therefore, building should be designed to full fill the requirement of ventilation along with the protection from sun and wind.
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Physical factors like, surrounding land use, nearby building geometry and street pattern influences the ventilation strategy.
9. Design Factors for Natural Ventilation 9.1 Building Orientation and Form Building orientation mainly helps in taking maximum advantage in utilizing the prevailing winds and to minimize the solar gains. According to the study, the building face facing perpendicular to the wind direction is not so favourable. The building face of the windward side inclined at an angle between 3045째 allows more airflow to the interior. Moreover, building orientation depends on physical factors like, site orientation, access point to site, view from site etc. Shading devices, overhangs, louvers, verandahs etc also affect the solar heat gain and air circulation in the space.
9.2 Position of Openings To achieve more indoor airflow, inlet openings should be facing inward wind direction. However according to research, the inlet openings should keep at an angle of 45 degrees for more airflow (6). This is more effective than inlet facing inward wind direction. To get better result openings should designed adjacent to each other. Here wind is incident at a right angle than the one at oblique angle.
9.3 Size of Openings In single sided ventilation, the window size has very less impact on internal air velocity when compared with cross ventilation strategy. The opening ratio should be adjustable to control the internal wind velocity. Along with this, the flexibility to control the opening of window also accelerates the air-driven ventilation. Size of opening always has minimal effect on the overall ventilation condition and internal air velocity where windows on one wall as compared to a room with windows on opposite walls.
9.4 Internal Arrangement The layout of residential floor plan should emphasize the usability and ventilation requirement of the space. A good ventilation condition can be obtained where air can flow from one place to the other without any internal obstructions. Moreover, better conditions in airflow rate can be obtained where partitions are nearer to outlet when compared to a room where partitions are nearer to inlet.
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10. Case Study 10.1 1 Moulmein Rise, Singapore Information Project:
Moulmein Rise
Architect:
WOHA Architects Pte Ltd
Client:
United Land Overseas Pte Ltd
Year:
2003
Building type: Residential Footprint:
230 Sq M
Built Area:
6491 Sq M
Height:
102 M
No. of Floors:
28 Storey
No. of Apps.:
50
Location:
1.18째N & 103.5째E, Singapore
Climate:
Tropical Warm & Humid
Vegetation:
Rainforest
Figure 10-1 Moulmein Rise (Source: http://singaporearchitecture.wordpress.com)
Munn Sum Wong and Richard Hassel of WOHA Architects are well known for innovative strategies for tropical tall buildings.Their award winning project, 1 Moulmein Rise in Singapore incorporate simple features from traditional dwellings to create a permeative skin for the purpose of Natural Ventilation with innovative details.
10.1.1 Natural Ventilation Strategy With two apartments per floor, the slender tower designed properly to allow cross ventilation as well as single sided ventilation. The building is oriented North-South for optimized environmental performance with minimum solar gain and maximum cooling potential. The north facade is cladded with sliding perforated panels to maximise the solar shading as well as natural ventilation. 'Monsoon Window' is the most innovative feature of this building. Monsoon window is basically a bay window incorporating a sliding aluminium shelf to allow the natural breeze from outside during rain, which are mainly on the southern facade of the building. This is the common feature of Malay, Vietnamese and Indonesian vernacular houses. These were incorporated in few houses in Singapore 11 | P a g e
during 1970s and 1980s and also appeared in a hall of residence at the National Technical University in late 1980s (7). Architects have used a horizontal steel grill maintenance ledge between the timber louvers and windows, set flush with internal floor. When the louvers are shut and windows are open the cool air comes in. Horizontal openings keep the rain out without interrupting the air movement of cool breeze. A winder operates the panel and the perforated metal shelf above the opening prevents things to fall through (7).
Figure 10-2 Architect's sketch of Monsoon window (Source: WOHA Architects)
The 'Monsoon Window' also helps to air the apartments even when it is not occupied which is quite important for the tropical warm and humid climate. The monsoon windows are kept to the south side where normal windows are facing to the north side, which helps for very good cross ventilation. The device is well used and the occupancy survey says many sleep without air-conditioning, where as in climate like Singapore where mechanical ventilation (Air conditioning) is must for thermal comfort.
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Figure 10-4, The shading device integrated with facade (Source: WOHA Architects)
Figure 10-3 Section through Moulmein Rise (Source: WOHA Architects)
Figure 10-5 Moulmein Rise typical floor Plan (Source: WOHA Architects)
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10.2 Newton Suites, Singapore Project:
Newton Suites
Architect:
WOHA Architects Pte Ltd
Client:
United Land Overseas Pte Ltd
Year:
2007
Building type: Residential Height:
120 M
No. of Floors:
36 Storey
No. of Apps.:
118
Location:
1.18째N & 103.5째E, Singapore
Climate:
Tropical Warm & Humid
Vegetation:
Rainforest
Figure 10-6 Newton Suites (Source: http://singaporearchitecture.wordpress.com)
Newton Suites is another exemplary environment friendly skyscraper designed by Munn Sum Wong and Richard Hassel of WOHA Architects well known for its full-height green wall (the tallest continual green wall in the world).
10.2.1 Natural Ventilation Strategy The unique and extraordinary residential high-rise tower stands amongst most successful projects of the architect. The architect uses the principles of natural ventilation to achieve indoor thermal comfort in various possible ways where the use of air-conditioning in most of buildings in tropical climate is very much essential for thermal comfort of the occupants. The building is oriented North-South for optimized environmental performance with minimum solar gain and maximum cooling potential. Extensive use of sunshades and protruding balconies adapt the tropical climate responsive strategies helps in minimizing the energy demand. An expanded steel mesh louver (a 3 dimensional section) is used around the building facade by appearing transparent when looking down while blocking sunlight by appearing solid from the angle of the sun (Fig 10.7, 10.8, 10.9). Creeper vines cover the blank facade and sheltered sky gardens with overhang trees at every four levels on the southeast facade, which help in minimizing the intense solar gain and maximizing the natural ventilation in the building.
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11.
Figure 12-7, Unified Facade of Screens & protruding balconies. (Source: CTBUH Journal, 2009, Issue lll)
Figure 12-8, Repetitive Sunshading screens of angled mesh (Source: CTBUH Journal, 2009, Issue lll)
Figure 11-9, Repetitive Sunshade mesh screen detail (Source: CTBUH Journal, 2009, Issue lll)
12. Conclusion The present investigation has pointed out that the natural ventilation in tall building is depended on the holistic design approach and various findings show occupants are naturally acclimatized and natural ventilation is the most effective cooling strategy for whole year-round in hot humid climate. (Arens et al, 1984) Some Findings to be considered from the starting of the design procedure, which can protect against the adverse climatic factors of tropical climate to enhance natural ventilation and reducing the solar gain These issues should be notice at one time instead of noticing individually.
Building forms and configuration: small or narrow footprint along with west and east direction. Internal layout plan: Open plan with high ceiling. Building details to enhance cross ventilation: dynamic building façade.
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Balconies or verandas should be shaded for the protection against rain and sun. Use of tree canopy for sun protection in summer to shade building but allow breeze for ventilation since deep recessions with plantings influences the air movement. Ventilation/airflow is important during the rain. Special architectural features: Wind wing wall, Monsoon window etc. enhance this.
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