CLIMATE RESPONSIVE BUILDING ENVELOPE TO DESIGN ENERGY EFFICIENT BUILDINGS FOR MODERATE CLIMATE

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1 Conference on Sustainable Building South East Asia, 5-7 November 2007, Malaysia CLIMATE RESPONSIVE BUILDING ENVELOPE TO DESIGN ENERGY EFFICIENT BUILDINGS FOR MODERATE CLIMATE VIJAYALAKSHMI AKELLA Faculty, Department of Architecture, BMS College of Engineering, Bangalore, India. ABSTRACT: Buildings are either naturally ventilated or mechanically ventilated to achieve indoor comfort. Indoor conditions in naturally ventilated buildings are dynamic in nature and are static in mechanically ventilated buildings (air conditioned buildings). Selection of right building materials, thickness of, type of roof, orientation, percentage fenestrations, plan form etc are some of the parameters which help in achieving thermal comfort for both types of buildings. An attempt is made in this paper to understand and quantify the effect of different parameters like building materials, orientation, percentage fenestrations, Length/Breadth Ratio, height of the building etc on the building envelope for airconditioned buildings. Heat loads are calculated for volumes ranging from 150cum to 180,000 cum and for two different combinations of materials; Heat loads are calculated for approximately 900 combinations of these parameters. This study led to some interesting conclusions which are useful to the designers. Design charts are developed for two combinations of materials with varying percentage glazing and plan form (L/B Ratio). These charts help the designers to try different combinations of these building parameters to reduce heat loads for a particular building. Design charts sensitize the architect/designer at the planning level as he is able to estimate heat loads. There is also a possibility of earning 10 points which are awarded in LEED rating for green buildings by reducing heat loads and hence an energy efficient building envelope design. Keywords: BUILDING ENVELOPE, INDOOR COMFORT, ENERGY EFFICIENT, GREEN BUILDING, LEED RATING. DESIGN CHARTS 1.0 Introduction: Buildings, as they are designed and used today, contribute to serious environmental problems because of excessive consumption of energy and other natural resources. The close connection between energy use in buildings and environmental damage arises because energy intensive solutions sought to construct a building and meet its demand for heating, cooling, ventilation and lighting cause severe depletion of invaluable environmental resources. As the environmental impact of buildings becomes more apparent, a new field called Green building is gaining momentum. Green or sustainable building is the practice of creating healthier and more resourceefficient models of construction, renovation, operation, maintenance, and demolition. Research and experience increasingly demonstrate that when buildings are designed and operated with their lifecycle impacts in mind, they can provide great environmental, economic, and social benefits. Figure 1.1 approximately shows the energy consumed in buildings. Heating, cooling and lighting consume enormous amount of energy. In tropical climates major amount of energy is consumed in cooling the building. Intelligent use of simple techniques such as orientation, percentage fenestrations, height and volume of the building, materials etc will reduce the energy consumption to considerable amount and improves the performance of the buildings. One-way of assessing the building performance is to study the heat transfer through the building envelope. This paper considers the need to quantify the effect of various parameters like percentage openings, materials used, volume, orientation etc. An attempt is made to quantify the effect of these parameters and optimizing the parameters to design an energy efficient building.

2 Fig 1 Energy Consumption The author currently resides in Bangalore, India, and the work is focused on quantifying the above mentioned parameters at 12 o 58 N latitude, (Bangalore) with moderate climatic conditions. The temperature in peak summer is 38 o c and humidity lies between 50 to 70%. 2.0 HEAT TRANSFER THROUGH BUILDING ENVELOPE : Heat gain or loss in buildings is due to heat transfer through, roof, ceiling, floor, and glazing etc., i.e., the building fabric or envelope. The load due to such heat transfer is often referred to as the envelope heat gain or loss. Majority of Heat transfer takes place in buildings through building envelope. Building envelope consists of, roof, and fenestrations (openings). Heat transfers through and roof is by conduction and is through conduction and radiation in glazing materials. Heat loads are generated through convection which is termed as ventilation load. There are also internal loads inside the building due to occupancy, lighting and heat loads due to air conditioning equipment if any, to maintain indoor comfort. In the present study heat loads due to Conduction, convection, radiation and internal heat load is considered and the method adopted to calculate heat transfer is equivalent temperature differential method. Heat loads due to infiltration, transmission gain through partition, ceiling, floor, etc, are ignored 3.0 PARAMETERS CONSIDERED IN THIS STUDY: The various building elements taken for study which influence the transmission of heat loads are Orientation Building materials used on building envelope Volume Percentage glazing on building envelope Height of the building L/B ratio (length to breadth) This study mainly focusses on the combined as well as the individual influence of these parameters on heat transfer in buildings. These parameters are varied and heat loads are computed to quantify the effect of each of these parameters. Heat loads are computed for North South (NS) and East West orientations (EW). Two combinations of building materials are taken to study the effect of the materials used in building envelope. Combination 1 consists of brick, plate glass for glass area and RCC roof without insulation. Combination 2 consists of Fly ash blocks (Aerocon blocks) for, tinted glass for glass area and insulated with 50mm polystyrene sheets. 455

3 Heat loads are computed for volumes ranging from 150 cum to 180,000 cum i.e., plan area ranging from 10 X 5m to 300 X 200m. 150 cum volume is the smallest possible volume for habitable area and 300 X 200 m plan area is very large and is fixed as upper limit. Percentage glass area is assumed to range from 20% to 80% of the wall area. A maximum of 80% is assumed excluding columns, window frames and also corners of the building. The effect of percentage glazing on heat loads is calculated by assuming different combinations. All the four namely north, south, east and west are assumed to have 20% glass area initially and are increased to 40%, 60% and 80% for both the combinations and orientations. Percentage glass area is kept constant in east and west at 20% and varied in north and south from 20% to 80%. This is done to study the effect of glazing in north and south for both orientations i.e., north south (N-S) and east west (E-W). Similarly the percentage glass area is kept constant in north and south and varied in east and west for both the orientations to study the effect of percentage glazing in east and west. Further, to study the effect of percentage glazing area in each wall, heat loads are computed when percentage glazing area in three is kept constant at 20% in the first simulation and varied in the remaining. For example, to find out the effect of percentage glazing in west wall two simulations are required. In the first simulation, percentage glazing in all is assumed to be 20%. In the second simulation, percentage glazing in west wall is increased to 80% and is kept at 20% for the remaining i.e., north, south and east. Heat loads are also computed when height of the building is assumed to be 3m and 4m for both combinations and orientations. Further, work is carried to study the effect of L/B ratio. The sample volumes of 150cum, 6000cum, 180,000 cum are studied for varying dimensions such that their L/B ratio is 1, 1.25, 1.5, 1.75, and 2.0 for the same plan area. This work is carried out for combination 2 also for both the orientations. 4. Results and discussion: 4.1 Effect of building orientation on heat loads: It is observed from Table 1 that heat loads are lower in case of north south orientation when compared to east west orientation for all volumes. For smaller volumes like 150 cum, the heat load for combination 1 and percentage glass area 20% on all four, is found out to be KW for E-W orientation and found to be KW for N-S orientation. It can be observed that heat loads are less in north-south orientation in comparison to east-west orientation for all volumes. Table 1 shows heat loads for combination 1 and only for 3 volumes. For 150 cum volume and 20% glazing area the reduction is around 10%. As the volume increases to 6000cum the reduction in heat loads for north-south orientation is around 0.78% and is 0.29% for 180,000cum. When the percentage glass area is 80% on all the the heat load for 150 cum is found to be 19.6% less in north-south orientation in comparison to east west orientation. Similar trend was observed for combination 2. The heat loads in north south orientation are reduced by 10% approximately for 150 cum in comparison to east west orientation. For larger volumes the reduction was found to be less than 0.28%. This shows that orientation plays an important role for smaller volumes and almost negligible for larger volumes. The main reason is due to the fact that as volume increases heat transfer through roof is very large when compared to heat transferred through the and subsequently through glazing. 456

4 Table 1 Heat loads in KW (Kilo Watts) for different percentage glazing and orientations Percentage Glazing Area 20% 40% 60% 80% Volume in cum Orientation 150 E-W N-S E-W N-S E-W N-S Effect of building Materials on heat loads: Table 1 and 2 show heat loads in Kilo Watts for combination 1 and combination 2. The following are the observations made: For 150cum volume and 20% percentage glazing area on all, heat loads are KW for combination 1 in E-W orientation. The heat loads are found to be KW for combination 2 when the rest of the parameters are identical. This shows a reduction of 7.85KW (45%) in heat loads when combination 2 is used. The reduction in heat loads is approximately 47% for a volume of 180,000cum (large volume). This trend is observed for all volumes. Table 2 Heat Loads in KW for Combination 2 Percentage Glazing Area 20% 40% 60% 80% Volume Orientation 150 E-W N-S E-W N-S E-W N-S

5 Similarly in N-S orientation for 150 cum volume and 20% glass area in all four for north south orientation the heat loads were found to be KW for combination 1 and KW for combination 2. The percentage reduction in heat loads when combination 2 is used is around 45%, and 47% for 180,000cum volume. This is due to the fact that the U-value for Aerocon block (flyash brick) is around 0.36 and that of brick is 3.2.Similarly roof without insulation has a U-value of and with insulation is This explains the reduction in heat loads by 45 to 47%. It can be stated from the above observations that heat loads reduce by 35 to 45% for combination 2 (low U values) is used, irrespective of orientation, volume and percentage glazing. 4.3 Effect of percentage glazing on heat-loads: Table 3 Shows heat loads in KW for different percentage glazing in east west orientation. As shown in table 3 percentage glazing in east west is kept constant at 20% of the wall area and varied from 20% to 80% in the north south. Similarly the percentage glazing is kept constant at 20% in north south and varied from 20% to 80% in east west. The following are the observations made: Percentage glazing area in east west is very sensitive and contributes significantly to heat loads, larger the glazing area, larger the heat loads. Increasing percentage glazing in north south doesn t contribute significantly to heat loads as it does in east west for both orientations For smaller volumes percentage glazing provided in the cardinal directions is an important design parameter in both NS and EW orientations. For larger volumes varying percentage glazing in east-west or north-south need not be a design parameter in both NS and EW orientations. By minimizing the percentage glazing to 20% in the west wall with 80% percentage fenestrations in the remaining three heat loads can be reduced approximately by 20-40% for small volumes. In N-S orientation north and south are longer than east and west, hence less percentage glazing in east and west. Despite this the percentage glazing in west wall needs to be kept low. However, for smaller volumes, the percentage variation is so high that openings in west wall even for north south orientation, are to be considered an important design parameter even in north south orientation. Table 3 Heat loads in KW for variation in Percentage Glazing for E-W (east west) orientation, combination1 VOLUME cum %GLAZING %GLAZING N-S % VARIATION %GLAZING %GLAZING % VARIATION E-W N-S E-W 20% in north south 80% in north south 20 % in east west 80 % in east west % in east west % in north south % % % %

6 4.4 Effect of increasing the height of the building Heat loads are marginally high when ceiling height is 4m when compared to 3m and hence need not be a design parameter. It was further observed that variation in heat loads for 3m and 4m ceiling height reduces as volume increases. This can be clearly be explained by the fact that as volume increases the major contributor to heat loads is the roof and not the. Hence increasing the height of the building from 3m to 4m increases the heat loads marginally. Table 4 Heat Loads in KW for variations in Heights E-W, Combination 1 Plan area Percenta ge glazing all Height 3m Height 4m %variatio n 50 sqm sqm 60000sq m Effect of L/B (length to breadth) Ratio on heat loads To minimize the heat loads in east west orientation the preferred geometrical shape of the building should be closer to a square. As the L/B ratio increases the east and west dimensions increase too and hence more glazing area. The lesser the L/B ratio the lesser are the heat loads. Table 5 Heat Loads in KW for variations in L/B ratio for E-W orientation Volume Percentage glazing,all The desirable parameters from the above study are: 1) North south orientation,2) Minimum percentage glazing in east west, 3) Height of the building restricted to 3m, 4) Combination 2 which has low U values for building materials L/B ratio closer to 3, which reduces heat loads in north south orientation. 459

7 The undesirable parameters are 1) East west orientation, 2) Maximum percentage glazing in all the,3) 4m height of the building 4) Materials with high U values 5) L/B ratio close to 3(taken as 3 instead of 2 as L/B=2 increases heat loads marginally) 5.0 conclusions: 1. Orientation of the building plays an important role for small buildings. The effect of orientation on large volumes is insignificant. Heat loads are found out to be high in E-W orientation when compared to N-S orientation. From the observations it can be stated that heat loads are reduced by 10 to 20% for buildings of small volume oriented N-S, depending on % glazing over E-W orientation. 2. Heat loads reduce by 35 to 45 % for combination 2 over combination 1 Combination 1 is made of materials with high U values. ( U for is3.2, U for roof is 4.4, U for plate glass is 5.9, solar gain factor is 1) Combination 2 is made of materials with low U values. ( U for is.72, U for roof is.37, U for plate glass is 3.3, solar gain factor is.56) It can be stated that from the study that heat loads are reduced by 35 to 45% for combination 2 in comparison to combination 1 irrespective of orientation of the building, volume and percentage glazing. This conclusion is true for small and large buildings. 3. Heat loads increase as the building volume and percentage glazing area increase. When the building volume increases the heat loads also increase. As the building volume increases percentage glazing area on each of the increases. It is due to the fact that heat transfer by direct radiation through the glazing area is more compared to conduction through. The heat loads are found to be substantially increasing even for large buildings. 4 Percentage glazing area in East and West is very sensitive and contributes significantly to heat loads in East-West orientation, for small volumes 5. Percentage glazing area in East and West is very sensitive and contributes significantly to heat loads in North South orientation, for small volumes. 6. Variation in heat loads is insignificant, in buildings constructed in N-S and E-W orientation, for larger volumes. 7. The percentage increase in heat loads is 35% higher when percentage glazing in west wall is to be considered an important design parameter for small volumes. 8. The percentage increase in heat loads is 11% when percentage glazing in west wall is at 80% with 20% glazing in the remaining. This may be considered as a design parameter for larger volumes. 9. Rating is given to all the based on the percentage glazing. It is based on which wall causes significant effect on heat loads for each of the orientations. The order given below is from high to low. East West orientation West East North South North South orientation West North South East 460

8 10. The heat loads are always more when the height of the ceiling is 4m when compared to 3m for all volumes. 11. To minimize the heat loads in east west orientation the preferred geometrical shape of the building is close to a square. 12. To minimize the heat loads in north south orientation the preferred geometrical shape of the building is a rectangle with a higher L/B ratio. 13. Desirable and some Undesirable parameters are listed based on the study for Bangalore moderate climate. If any proposed building is designed as per the desirable parameters mentioned in this study, that building may earn all 10 points in LEED rating for GREEN buildings. 14. Design charts are developed for small volumes for different L/B ratio and percentage glazing. These charts are prepared for East West and North South orientations. For any particular volume, U value (combination of materials) and L/B ratio these charts help the designer to estimate the heat loads. These parameters have significant effect on small volumes and hence are developed for small volumes only. Graphs 1 to 4 represent heat load variations for combination 1 for 150cum, 600cum, 1800 cum and 6000cum respectively. 6.0 Bibliography: 1. Arora C.P, 2000, Refrigeration and Air conditioning, Tata Mc Graw Hill 2. ASHRAE Standard 55, 1992,Thermal Environment for human comfort, 3. ASHRAE Standard 55 a, 1992,Addendum to Thermal Environment conditions for human occupancy 4. ASHRAE Standard 90.1, 2004,Basic Building Performance, ASHRAE, 5. Givoni B, Man, 1981, climate and Architecture, Applied Science Publishers, 6. Nayak, Anand A, Prajapathi, Hazra, 1999,Empirical validation of the prediction of DOE-2.1 E. Proceedings of National Renewable Energy Convention, Indore, India, 294, 7. Richard J Dear, Gail S Brager, 2000, Thermal Comfort in naturally ventilated buildings, revisions to ASHRAE standard, Energy and buildings, 34, 8.0 Acknowledgements: I would like to thank my father Prof P Venugopala Rao and, Prof P M Damodaran, Prof M.V Seshagiri Rao for their continuous support in carrying out this work 461

9 NSEW20 NS20EW80 NS80EW20 N80SEW20 S80NEW20 E80NSW20 W80NSE80 NSEW80 NSEW20 NS20EW80 NS80EW20 N80SEW20 S80NEW20 E80NSW20 W80NSE20 NSEW Cum, EW Orientation Cum, EW Orientation Heat Loads (KW) L/B Heat Loads (KW) L/B Design chart 1 Design chart 2 NSEW20 NS20EW80 NS80EW20 N80SEW20 S80NEW20 E80NSW20 W80NSE20 NSEW80 NSEW20 NS20EW80 NS80EW20 N80SEW20 S80NEW20 E80NSW20 W80NSE20 NSEW Cum, EW Orientation 6000 Cum, EW Orientation Heat Loads (KW) Heat Loads (KW) L/B L/B Design chart 3 Design chart 4 462

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