Optimising Thermal Energy and Comfort in Hot, Humid Tropical Climate

MSc Environmental Design of Buildings Climate Comfort and Energy Dr. Eshrar Latif Mahmoud Bghdadi 21 January 2018

Optimising Thermal Energy and Comfort in Hot, Humid Tropical Climate A study of a Classroom Space in a Primary School
 Kuala Lumpur, Malaysia

Optimising Thermal Energy and Comfort | Mahmoud Bghdadi

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Contents

1. Introduction 1.1 Location and Climate 1.2 Weather Data 1.3 Building and Space Requirements

2.

Methodology 2.1 Calculation of Heat Loss and Heat Gain

3.

Discussion

4.

Typical and Current Practice

5.

Best Practice

6.

Conclusion

7.

References

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1. Introduction The building fabric has a significant impact on the building itself. Not only in aesthetic values and architectural appearance, but it also contributes to improving thermal comfort and optimizing thermal energy consumption for the building. This paper aims to examine the effects of the design or specification of the fabric and services used in the building on indoor thermal comfort in 80 m2 of a classroom of primary school in Kuala Lumpur, Malaysia, involving study activities in that space, and discussing the most suitable practice that would lead to achieving thermal comfort in that specific location.

1.1 Location and Climate The classroom that will be examined in this paper is located in Malaysia, specifically in the capital city Kuala Lumpur. The building is located in a residential zone, surrounded by low rise houses. Trees with less than 3m high can be seen on this site. It is clear that solar radiation has no disturbance that prevents it from penetrating the classroom. According to Koppen Geiger climate classification, Kuala Lumpur has the AF classification which is a tropical rainforest climate. This climate essentially has a rainy sky for the whole year and has no dry season. Generally, it has no winter or summer, it is hot and wet for the whole year.

Figure 2.Location of Kuala Lumpur in Malaysia.Source: Google maps.2017.

Figure 1.Location of Malaysia in the world. time keeper watches. Source: Online. available at http://www.timekeeperwatches.com/world-map-malaysia-177111-00-03-06

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1.2 Weather data

Figure 3. Monthly temperature data for Kuala Lumpur. Source Energy plus 2017 - climate consultant6.0

The average temperature for the whole year in Kuala Lumpur is 27.8°C. (Figure 3) The highest average temperature that can be recorded is in April on average of 28.3°C. and the lowest in average is 26°C in December. 39.4°C is the highest temperature recorded in July. And the lowest temperature was recorded in January with 21°C. (Energy plus, 2017)

Figure4. Monthly Wind speed data for Kuala Lumpur. Source:Energy plus 2017 - Climate consultant6.0

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According to figure 4, The average wind speed for the year in Kuala Lumpur is 1.5m/s. The highest wind speed month, on average, is Dec with an average wind speed of 2m/s. Most of the months have almost the same average record of wind speed in Kuala Lumpur throughout the year.

(Energy plus, 2017) Figure 5 illustrates the annual distribution of wind in Kuala Lumpur. It is clearly shown that there is a variety of distribution from all over the directions. Likewise, most of the wind would flow from the Southeast direction, followed by the northeast and northwest. (Wind finder, 2017)

Figure 5. Yearly Wind distribution data for Kuala Lumpur.

Wind finder.2015

Figure 6. Yearly RH and Cloud coverage data for Kuala Lumpur. World weather online,2015.


 Figure 6 shows that relative humidity percentage is almost the same for all months along the year. The humidity is ranged between 70% to 80%, where it can hit its peak in November and March with around 85%. (world weather online, 2017)

Total horizon solar radiation (W/m2 ) per Hour Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

N

10

20

20

50

100

120

90

50

10

5

6

20

E

90

100

110

100

90

50

20

30

40

110

100

100

S

400

390

250

120

50

50

40

50

170

270

390

420

W

290

310

300

290

210

100

90

100

190

190

240

250




Jan

Table 1. Avg Hourly global horizon radiation in Kuala Lumpur. Source : energy plus 2017 - climate consultant 6.0

From table1, it shows the total horizon solar radiation in Kuala Lumpur from all directions. It is clear that south and west directions have the highest solar radiation among the rest of directions.

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1.3 Building and Space Requirements Teaching will take place in the classroom. A thermal comfort state refers to the metabolism rate of the body as well as the clothing rate of the space users under specific temperature, humidity, wind velocity, and solar radiant temperature. (Fanger, 1982). Body scale, gender, age, food, and indoor thermal comfort expectations are all physical and psychological factors that would affect reaching the thermal comfort zone. (Brager & Dear, 1998).

The classroom is around 80 m2 (Figure 7) and it is considered as high gain space with around 20 kids, 20 PCs, and 5 electrical class lights. These elements would contribute to having more heat gain in the space.

The space has two double glazing windows on the south side. Each window is 10.5 m2 that allows solar radiation to penetrate the space.

Space’s fabric is mainly from 150 mm Thk. Brick wall with 20mm Thk. Plaster paint from the external side. The roof is concrete slab 200mm Thk. With 20mm thick insulation and 20mm The roof tiles on top. North and south walls are exposed to outside. (Table2) According to (BRE,2006) Double glazing (air-filled) has 3.1 W/(m2 k) u-value, 0.4 W/(m2 k) for roof insulation layer, 0.41 W/ (m2 k) for 150 mm Thickness brick wall, 0.15 W/(m2 k) for plaster paint, 0.41W/(m2 k) for roof slap and 0.18 W/(m2 k) for clay roof tiles.

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Figure 7. Classroom plan

Figure 8. Classroom section

Area m2

U-value W/(m2 k)

UA W/K

Brick wall

120

0.41

49.2

Plaster paint

56

0.15

8.4

Concrete roof slap

80

0.4

32

Insulation

80

0.4

32

Roof tiles

80

0.18

14.4

Double glazing

21

3.1

65.1

Fabric

Table 2. U-value and total UA for the material used in that specific class. Total UA= 201.1W/K

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2.

Methodology

2.1 Calculation of heat loss and heat gain This part of the paper will focus on calculating the heat loss and heat gain load by using the heat balance equation in steady state condition where the thermal mass effect for the space was neglected Qf + QV +Qi +Qs +Qh +Qc =0 (CIBSE a, 2015). where: Qf = heat transfer across the envelope due to conduction; QV = heat transfer across the envelope due to ventilation; Qs = heat transfer across the envelope due to solar transmission; Qi = heat input to the interior due to occupancy and equipment; Qh = heat input to the interior due to heating equipment; Qc = heat input to the interior due to cooling equipment.

To perform the heat balance equation, it is required to determine the difference between indoor and outdoor temperature ΔT. Hence, the indoor temperature must be determined firstly.

From Humphreys and Nicol method (Table 3) for spaces in which the occupants had no heating or cooling systems available to them (free-running buildings), it can be predicted what is the thermal comfort indoor temperature in the space with a standard error of 1.0°C for free-running buildings.

The equations for the relationship is: đ?‘‡đ?‘? = 11.9 + 0.534 đ?‘‡đ?‘œ where 
 Tc is comfort temperature (°C). And To is monthly mean outdoor temperature (°C) 


By using the equation đ?‘‡đ?‘? = 11.9 + 0.534 đ?‘‡đ?‘œ, this results would be found for Month

Average external temperature (°C)

Internal comfort temperature (°C)

ΔT (°C)

Jan

26

25.784

-0.22

Feb

27

26.318

-0.68

Mar

28

26.852

-1.15

Apr

28

26.852

-1.15

May

30

27.92

-2.08

June

30

27.92

-2.08

July

29

27.386

-1.61

Aug

28

26.852

-1.15

Sep

28

26.852

-1.15

Oct

27

26.318

-0.68

Nov

26

25.784

-0.22

Dec

26

25.784

-0.22

Table 3.monthly Average external temperature and internal comfort temperature based on Humphreys and Nicol method and difference temperature ΔT Optimising Thermal Energy and Comfort | Mahmoud Bghdadi

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Average external temperature (°C) ΔT (°C)

Internal comfort temperature (°C)

30

22.5

15

7.5

0

-7.5

Jan

Feb

Mar

Apr

May

June

July

Aug

Sep

Oct

Nov

Dec

Figure 9.monthly Average external temperature and internal comfort temperature based on Humphreys and Nicol method and difference temperature ΔT

The line chart illustrates the difference between outdoor and indoor thermal comfort temperatures throughout the year. Since ΔT showed in negative in all months, it means that the space temperature should be cool down in order to reach the thermal comfort zone. So Qh=0 ( no heating load is needed ) along the whole year.

Heat input to the interior due to occupancy and equipment (table 4) (Qi) is determined according to the number of electrical devices and occupants inside the space. The proposed space has 20 PCs and 5 electrical Lights, and 20 students. According to (CIBSE Guide A (2015)). Qi=2250W, Quantity

Value (W) per unit

Totall (W)

PCs

20

55

1100

Human body

20

50

1000

Electrical Lights

5

30

150

Table 4.heat input to the interior due to occupancy and equipment CIBSE Guide A (2006))

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QV = heat transfer across the envelope due to ventilation. QV = NV V/3 (To-Ti) .where : Nv is the infiltration rate, h-1 ;V is the interior volume : m3 Air exchange rate would be determined by (ASHRAE Standard 62.1-2007) as 5 h-1 for classroom space.

Qs = heat transfer across the envelope due to solar transmission; The windows in the proposed classroom are facing south. Area is 10.5 m2 for both openings. (Table5)

Total heat transfer across the envelope (W) Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Window 1

3500 3000

2625

1260

525

525

420

525

1785

2835

3000

3300

Window 2

3500 3000

2625

1260

525

525

420

525

1785

2835

3000

3300

Table 5. Qs : Monthly total heat transfer across the envelope by the windows

According to (table3) Qh=0 ( no heating load is needed ) along the whole year, it is required to determine how much heat gain will be in the space for every month Qc =-[{ UA+nV/3}(To - Ti) +Qs +Qi ].

The space heat balance, average temperature 
 (Energy plus 2017-climate consultant 6.0) 10000

7500

5000

2500

0

Jan

Feb

Mar

Apr

Total Heat gain (Kw/h) Ventilation (W)

May

Jun

Jul

Occupants (W) Solar (W)

Aug

Sep

Oct

Equipment (W)

Nov

Dec

Fabric (W)

Figure 10.monthly Average total heat gain, and heat gain source into the proposed classroom space. average temperature

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The space heat balance, average Highest temperature 
 (Energy plus 2017-climate consultant 6.0) 12000

9000

6000

3000

0

Jan

Feb

Mar

Apr

Total Heat gain (Kw/h) Ventilation (W)

May

Jun

Jul

Aug

Occupants (W) Solar (W)

Sep

Oct

Equipment (W)

Nov

Dec

Fabric (W)

Figure 11.monthly Average total heat gain, and heat gain source into the proposed classroom space. average Highest temperature

The space heat balance, average lowest temperature 
 (Energy plus 2017-climate consultant 6.0) 10000

7500

5000

2500

0

Jan

Feb

Mar

Total Heat gain (Kw/h) Ventilation (W)

Apr

May

Jun

Occupants (W) Solar (W)

Jul

Aug

Sep

Equipment (W)

Oct

Nov

Dec

Fabric (W)

Figure 12.monthly Average total heat gain, and heat gain source into the proposed classroom space. average lowest temperature

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The space heat balance, average temperature after modification 
 (Energy plus 2017-climate consultant 6.0) 5000

3750

2500

1250

0

Jan

Feb

Mar

Apr

Total Heat gain (Kw/h) Ventilation (W)

May

Jun

Jul

Occupants (W) Solar (W)

Aug

Sep

Oct

Equipment (W)

Nov

Dec

Fabric (W)

Figure 13.monthly Average total heat gain, and heat gain source into the proposed classroom space after modification. average temperature

3.

Discussion Due to high occupants and equipment density in that proposed classroom, a high ventilation

rate is required in order to maintain the air quality. According to the figures (10,11,12) and due to the Malaysian climate, net heat gain is shown in the space for the whole year. The most factor that has a significant impact on total heat gain in the space is solar gain due to the position and size of the windows. It is clear that the months September, October, November, December, January, and February have the highest heat gain among the rest of the months due to the high value of solar radiation during that period from the South direction, which the space windows are directed to.

As an improvement for the space, it is suggested to reduce the occupant's density, therefore, less electrical equipment and less heat gain. It is also has been notified that the solar radiation in Kuala Lumpur has its minimum amount from Northside. Hence openings toward the north, with a smaller area of glazing might be the most suitable practice for that space in the specific location.

Figure 13 illustrates the heat gain after improving the classroom, where density and PCs have reduced to the half, windows have directed towards North.

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4.

Typical and Current Practice Passive cooling methods, light structure, and cross ventilation are part of Malaysian

traditional architecture. The current practice that used to meet the cooling requirements in Malaysia is based on an active air conditioning system; such as dry coil air handling units. The current practice in Malaysia would focus on offering methods to control solar gain through windows.

Shading exterior louvers and overhang roofs are common to reduce sunlight on windows(Desa Mahkota School, Kuala Lumpur) (Figures 14 and 15).

Adjusting the glazing area to the wall ratio is another concept practiced to optimize the energy consumption use and thermal comfort for the space. Although the required natural lighting according to Malaysian building standard need to be achieved. For example, if the space depth is 8m or less, the ratio can be 20% in order to optimize thermal comfort and energy (CIBSE B 2012).

Figure 14.Desa Mahkota School. Source: online at:https://www.arthitectural.com/wp-content/uploads/2014/07/Image-4.jpg

Figure 15.Desa Mahkota School. Source: online at:https:// www.designboom.com/wp-content/uploads/2014/01/desa-mahkotaschool-malasya-designboom04.jpg

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5.

Best Practice Figure 16 shows the diamond building in Kuala Lumpur which has the best energy efficiency

concept used in Kuala Lumpur without compromising on the users thermal comfort (Xin, H.Z. & Rao, S., 2013). The aim for this building was to achieve the requirements of low energy building according to the Malaysian standard by using different passive design strategies, such as natural lighting and diagonal facade to minimise the solar radiation. The building aimed for Building Energy Index (BEI) of 85kWh/m2/yr, which consider much lower rate that the other typical office building in Malaysia with has approximately 200 kWh/m2/yr to 300 kWh/m2/yr for their consumption. The Diamond Building has succeed having the Green Mark certification from Singapore as well(Xin, H.Z. & Rao, S., 2013).

Figure 16. The diamond building in Kuala Lumpur. Source: inhabitant.com 2013

Figure 17. The different configurations of the intelligent shading device at the atrium. (Source: Malaysia Energy Commission)

The building designed with glass atrium in the middle (figure 17) to enhance the natural lighting use inside the building , the central atrium has installed with automatic blinds. It has the ability to change the setting for different six times of the day depending on the sun orientation(Xin, H.Z. & Rao, S., 2013). The building also use floor slab cooling system (figure 18), where cold water will be pumped into the pipes to stop the occupants, solar and computers heat gain from disturbing the users (Xin, H.Z. & Rao, S., 2013). A 71.4 kilowatts peak (kWp) photovoltaic (PV) rooftop system have been installed,The solar energy support around 10% of energy consumption in the building (Xin, H.Z. & Rao, S., 2013).

Table 6. Effects of PV on the Diamond Building BEI from October 2010 to February 2011. (Source: Malaysia Energy Commission)

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Figure 18. Floor slab radiant cooling and a mechanical air-side system provide conditioning and ven- tilation. The concrete oors are charged each night, acting as a rechargeable battery as they release cooling throughout the day. Source: Greening Asia–Emerging Principles for Sustainable Architecture

According to the measurements in table 6, the installation of both passive and active energy concept has seen in energy saving for this building of 42% for plug loads, 33% for cooling loads, 18% for lighting and 7% for fans. According to this building design, it is obvious that the strategies used helps to reduce energy consumption and maintain thermal comfort for the users(Xin, H.Z. & Rao, S., 2013).

6.

Conclusion The heat balance calculation illustrates that in hight occupancy density in classroom space in

primary school, specifically in a hot humid climate like Kuala Lumpur, solar heat gain has the significant effect on thermal comfort and energy consumption, while the fabric and ventilation heat gain has the least thermal impact on the space.

As an improvement of the space, and according to some current practices, exterior louvers and overhang roof would protect from sun heat gain. In addition, Passive energy concepts such as cross-ventilation would help to supply fresh air and maintain thermal comfort and energy consumption in the space.

Usage of controlled blind would enhance the building's thermal comfort and natural lighting conditions and provide the ability to control the solar heat gain in the space. Moreover, the implementation of solar panels would help to save energy consumption by at least 10% if it is installed correctly.

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7.

References

• Anderson,B. 2006. Conventions for U-value calculations BRE Report BR 443: BRE 2006. Available at: http://www.bre.co.uk/filelibrary/pdf/rpts BR_443_(2006_Edition).pdf [Accessed 15 January. 2018].

• ASHRAE standard, 2007. Ventilation for acceptable indoor air quality (ANSI approved), Atlanta: American Society of Heating, Refrigerating, and Air Conditioning Engineers.Brager, G.S. & Dear, R.J.D., 1998.

Thermal adaptation in the built environment: a literature review. Energy and Buildings, 27(1), pp.83–96.

• Butcher, K. & Craig, B., 2015. Environmental design: CIBSE guide A, London: Chartered Institution of Building Services Engineers.

• Cheshire, D., 2012. CIBSE Guide F. Energy efficiency in buildings, London: CIBSE. • Chen, T.L. 2013. Malaysia’s green diamond. Malaysia Energy Commission Headquarter (Diamond Building). Available at:http://www.hpbmagazine.org/attachments/article/11746/13F-Malaysia-EnergyCommission-Headquarters-Putrajaya-Malaysia.pdf. [Accessed: 19 January 2018].

• Fanger. 1982. Thermal Comfort Analysis and Applications in Environmental Engineering, Rebert E Krienger Publishing Company, Malabar, Florida • Google maps, 2017. Kuala Lumpur-Malaysia. Available at: https://www.google.co.uk/maps/place/ Kuala+Lumpur. [Accessed: 19 January 2018].

• Köppen, 2017. Classification. Available at: http://hanschen.org/koppen/#contact [Accesed: 10 January 2018].

• Online weather data, Weather Data by Location. Weather Data by Location | EnergyPlus. Available at: https://energyplus.net/weather-location/southwest_pacific_wmo_region_5/MYS//MYS_Kuala.Lumpur.

486470_IWEC [Accessed January 21, 2018].

• Timekeeperwatches, 2017. World map Malaysia. Available at:http://www.timekeeperwatches.com/worldmap-malaysia-177111-00-03-06. [Accessed: 19 January 2018].

• Windfinder.com, Wind and weather statistic Morib/Kuala Lumpur Airport. Windfinder.com. Available at: https://www.windfinder.com/windstatistics/morib_kuala_lumpur [Accessed January 21, 2018].

• World weather online,Kuala Lumpur Weather Forecast. WorldWeatherOnline.com. Available at: https:// www.worldweatheronline.com/kuala-lumpur-weather/kuala-lumpur/my.aspx [Accessed January 21, 2018].

• Xin, H.Z. & Rao, S., 2013. Active Energy Conserving Strategies of the Malaysia Energy Commission Diamond Building. Procedia Environmental Sciences, 17, pp.775–784.

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