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Parametric equations for energy and load estimations for buildings in India
Applied Thermal Engineering 29 (2009) 3710–3715
Contents lists available at ScienceDirect
Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Parametric equations for energy and load estimations for buildings in India N.K. Bansal a,*, A. Bhattacharya b a b
Shri Mata Vashino Devi University, Katra 182 320, J&K, India Centre for Energy Studies, Indian Institute of Technology, Delhi, New Delhi 110016, India
a r t i c l e
i n f o
Article history: Received 1 April 2009 Accepted 8 July 2009 Available online 15 July 2009 Keywords: Parametric equations Heating and cooling loads Specific energy consumption Insulation thickness Surface to volume ratio (A/V)
a b s t r a c t Detailed simulations have been performed for a single zone building to calculate the maximum heating and cooling loads as well as specific annual energy consumption for a single zone building. Numerical results have been used to derive parametric equations as a function of the thickness of insulation as well as the surface to volume ratio (A/V) taking into account the effect of increasing height as well as increasing length and width. For un-insulated building, the energy consumption increases steeply with increasing height, whereas for an insulated building, the energy consumption decreases slightly. For increasing lengths and widths, the change in energy consumption is a mild positive slope. The optimum thickness of the insulation obtained in the paper corresponds to the recommended U-values of roof and the walls in the building code of India, U being the total heat transfer coefficient. Ó 2009 Published by Elsevier Ltd.
1. Introduction This paper deals with a much studied topic of energy consumption and load calculations in building all over the world. The result are presented usually numerically or graphically to show the effect of increasing insulation, glazing and various other parameters. The studies have been compiled in several books, papers, and manuals [1–7]. The developed mathematical algorithm has been used to develop several building simulation programs that are being used to optimize energy consumption in buildings [8,9]. Studies on energy simulation in buildings, however, continue to draw attention of building physicist, who is trying to find easier and quicker methods to building practitioners to estimate possible energy savings for buildings designed by them. In order to systemize building construction techniques for effective energy saving at nation scales, many building codes are in use in several countries [10–14]. The basis of these codes is extensive building simulation followed by detailed measurements in model building. The two important parameters that effect the energy consumption in a building are the insulation and its shape defined by surface to volume ratio (A/V). Hauser and Maas [15] have developed a graph for the energy consumption in a building as function of A/V. The graph shows a linear trend and for lower values of A/V, energy consumption is also lower. The code prescribes U-values and R-values for thermal insulation in building in different climate zones of India [16]. The architects and building practitioners, however, find it difficult * Corresponding author. Tel.: +91 1991 285686; fax: +91 1991 285694. E-mail address: [email protected] (N.K. Bansal). 1359-4311/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.applthermaleng.2009.07.002
to estimate energy and loads (cooling and heating) for these recommended U-values. It is also found to be difficult to run simulation programs. However, it is possible to develop simplified, easy to use, expressions for annual energy consumption as well as for heating and cooling loads by scientific analysis of detailed simulation results. In this paper, very detailed simulations were performed on a single zone building to evaluate parametric expressions for optimal energy consumption as well as the thermal heating and cooling loads. The results are obtained for composite climatic conditions of India by using DOE2.1E simulation program. The choice of DOE2.1E was due to its use for developing ECBC code for India and because of its capability in calculating the cooling loads and cooling energy in air conditioned buildings. The basis for DOE 2.1 E is the mathematical model of American Society for Heating, Refrigeration and Air Conditioning Engineers, ASHRAE [17], used mostly for calculating air conditioning loads in hot climates. The detailed calculations for a variety of windows and climatic conditions are published elsewhere [18]. Very recently, the Government of India has brought out an energy conservation building code [19,20] in an effort to promote energy efficiency in buildings. A detailed study conducted for Energy Efficient Windows [21] shows that for the composite climatic conditions, a window area of around 10% with respect to the floor area, is the optimum for a single glazed south oriented window. As per air conditioning standard in India, one air change per hour is assumed and the inside air temperature is to be maintained at 24 °C. These are the values used for simulating this single zone building for hourly variation of all the climatic parameters over a statistically averaged year.
N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
3711
Nomenclature A/V d Et Qc
surface to volume ratio (m1) thickness of insulation (m) annual energy consumption (MW h) maximum cooling load (KW)
2. Climatic zones of India Based on statistical analysis of 38 years of meteorological data [16], have divided India into six climatic zones, namely hot and dry, warm and moderate, cold and cloudy, cold and sunny, and composite. Fig. 1 illustrates the variations of climatic parameters in these zones for representative locations i.e. the location where the climate is statistical average of all the parametric variations of metrological parameters of that particular zone. For example, Delhi climate is the representative of the composite climatic conditions in India. Buildings located in these zones would be having
Qh qE R U
maximum heating load (KW) specific energy consumption (MW h/m2 a) resistance of the building component (m2 °C/W) total heat transfer coefficient (W/m2 °C)
different maximum cooling/heating loads (kW) with different peak timings as well as total annual energy demand (measured in MW h, separately for cooling and heating) for the same level of indoor conditions. Delhi has been chosen for this study primarily because of its composite climate, with temperatures ranging from above 40 °C in summer to below 5 °C in winter. Such type of climate is predominant in central part of India. In other climate zones also (accept in North) the conditions are nearly the same [16]. The climate parameters used in this study are based on 30 years of statistical average. For conditioned buildings, therefore, both heating and cooling are
Fig. 1. (a) Climatic zones of India, Ref. [16]. (b) Climatic parameters of India, Ref. [16].
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
Fig. 1 (continued)
required to maintain deserved comfort levels. Its altitude is 216 m, latitude 28°350 N and longitude 77°120 E and annual global radiation is 2476 kWh/m2 a. 3. Building parameters The basic building size has been taken as 15 m (length) 10 m (width) 3 m (height), with a single glazed glass window of the size equaling 10% of the floor area, on the south wall, because for these conditions the energy consumption is least in the composite climates (Fig. 2.6c, in Ref. [21]). It is also seen that in this climate, the use of double glazed windows exhibits a negligible advantage on the overall energy consumption. The wall, under un-insulated condition, has the layers of plaster (0.015 m), brick (0.22 m) and plaster (0.015) the roof having the layers of plaster (0.015 m), Reinforced Cement Concrete (RCC) (0.12 m), Mudphuska (0.08 m) and tiles (0.025 m), and the floor having finish of tiles (0.2 m), RCC (0.1 m), sand (0.15 m) and soil (0.2 m). The inside film resistance for roof, walls, etc. has been taken as of 0.166 m2/kW. Under insulated condition, the layer of expanded polystyrene insulation has been placed after the inside layer of plaster, on the walls and the roof. The thermo-physical properties of used building materials are given in Table 1. The window glass has a wooden frame and a width of 0.10 m with a U-value of 6.31 W/m2 K1 and solar heat gain coefficient (SHGC) of 0.86. Other assumptions made for the conditioned buildings are: inside temperature 24 °C, North wall Azimuth 0°, number of people is nil, no shading on the building and the number of air change per hour is one. The load due to people, lighting, appliances, etc. is an additive term which can be added to the calculated load and the corresponding equations in this paper. The insulation cost varies widely depending on the nature, density and other characteristics of the material being used. In India, market enquiries re-
veal that expanded polystyrene cost varies from Rs. 2500/m3 to Rs. 7000/m3 depending on density and other factors. For the purpose of this study, a value of Rs. 5000/m3 (USD 107.53/m3) has been taken. Similarly, the cost of electric energy varies widely from state to state and within a state from consumer to consumer. Even amongst domestic consumers, say in Delhi, the price, varies between Rs. 2.40 and Rs. 4.60 per kWh, depending on consumption pattern and connected load. Unfortunately, no reliable data of average marginal cost of electricity, at the national or local level is applicable. For the purpose of this study, a conservative marginal cost of Rs. 3.25 (0.07 USD) per kWh has been assumed. (USD 1.0 = INR 46.50, October, 2006). 4. Discussion of results Starting with the basic building dimensions of 15 m 10 m 3 m and the conditions specified earlier, the program was run to obtain the (annual) cooling energy, heating energy and the total energy requirements, as well, as the maximum cooling and the heating loads under un-insulated conditions. Thereafter, the Table 1 Thermo-physical properties of building materials. S. no.
Material
Density (kg/m3)
Th. conductivity (W/m2 K)
Specific Heat (J kg1 K1)
1. 2. 3. 4. 5. 6.
Brick Plaster RCC Mudphuska Tiles Insulationa
1820 1762 2280 1622 1820 34
0.810 0.720 1.580 0.520 0.810 0.035
880.0 840.0 800.0 880.0 880.0 1340.0
a
Expanded polystyrene.
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
ð1Þ
0:35
Q c ¼ 11:97d
ð2Þ
And for maximum heating load 0:47
Q h ¼ 15:09d
ð3Þ
where d is the thickness of the insulation. At this point our effort is to find out the optimum thickness of the insulation, which can be obtained by balancing the cost of adding insulation with the cost of energy saved and the results are plotted in Fig. 4. It can be seen from this figure that the cost of insu-
Annual energy consumption (MW h)
60 50
40
Equation of trend line
Trend line
R2 = 0.99 20
10
1
2
3
4
5
6
7
8
9
10
Insulation thickness (cm) Fig. 2. Total annual energy consumption (MW h) versus insulation thickness (cm).
16 14 Max heating/cooling load (kW)
R2 = 0.99
100
Cost of annual energy savings
80 60 40 20
12 y = 11.97x-0.35
10
R2 = 0.91
Maximum cooling load
8 6 y = 5.09x-0.47 R2 = 0.99
4
Maximum heating load
2 0 1
2
3
4
1
2
3
4
5
6
7
8
9
10
5
6
7
8
9
Fig. 4. Cost of insulation versus cost of annual saving in energy.
lation varies, as expected, linearly with the increasing thickness of the insulation, whereas the annual energy saved and therefore, the reduction in the cost of energy increases logarithmically. The intersection of these two curves provides the optimum thickness of the insulation which is 7.5 cm. This corresponds to a U -value of 0.38 W/m2 K for the wall and for the roof. Very recently, an Energy Conservation Building Code [19] has been made public by the Ministry of Power, Government of India. The prescriptive requirements for roofs and walls for various climatic zones in India are given in Tables 2 and 3, respectively. These values are also obtained from DOE simulation program followed by a complicated life cycle assessment with a pay back period of 7 years and 30 years of life for the building. From the results of ECBC calculations, it is noted that: 1. Except for moderate climates, U-factors for the roof assembly are same for all other climates i.e. a value of U of 0.261 W/ m2 K for 24 h use building and a U-value of 0.409 W/m2 K for day time use building. 2. For the wall assembly, a U-value of 0.44 W/m2 K is prescribed for composite, hot and dry and warm and humid climatic conditions. For moderate and cold climatic conditions, the U-values are taken as 0.431 W/m2 K and 0.369 W/m2 K, respectively.
y = 51.11x0.41
30
0
y = 25259Ln(x) + 55523
120
Insulation thickness (cm)
For the maximum cooling load
0
Cost of Insulation
140
0
0:41
Et ¼ 51:11d
0
160
Cost (Rupees in thousand)
insulation was introduced and its impact on (annual) cooling energy, heating energy and on maximum cooling and heating load requirements has been assessed, by varying the insulation thickness from 0.01 m to 0.10 m. The results of the simulation exercises are shown in Figs. 2 and 3. These figures show that the annual energy consumption, based on the cooling requirements, reduces drastically with the introduction of thermal insulation and then stabilizes gradually. Similar is the scenario for the maximum cooling and heating loads. It has been possible to find trend lines for the cooling/heating loads as well as the corresponding energy consumptions. It is observed that a trend line is fairly fitting the actual data i.e. For the annual energy consumption
10
Insulation thickness (cm)
Fig. 3. Maximum cooling/heating load (kW) as a function of insulation thickness (cm).
Our value of 0.38 W/m2 K for the wall and for the roof therefore is appropriate from practical point of view. In practice, however, one can recommend a value of U = 0.4 W/m2 K. After having fixed the optimum thickness of the insulation, the next study is the effect of building dimensions. The building under consideration of 15 m 10 m 3 m, the dimensions can be increased in the vertical fashion (i.e. increasing the height) and/or in the horizontal direction (i.e. increasing the length and/or the width). It is found convenient to express the results in terms of specific energy consumption is kWh/m2/a1 (i.e. annual energy consumption divided by total carpet area), while in the case of vertical expansion, the normal height for every floor has been taken as of 3 m height. The results are shown in Figs. 5–7, for vertical expansion, for the increased length and for the increased width, respectively. Analysis of Figs. 5–7 yield very interesting results. Fig. 5 shows the specific energy consumption (MW h/m2 a) for the case, when the building height is increased insteps to three meters, thereby changing the ratio of A/V. For the case of an un-insulated building, the specific energy consumption and hence, the total energy consumption increased steeply with increasingly ratio of building surface to volume (A/V). For an insulated building, the energy consumption slightly decreases. It should be mentioned, here, that
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
Table 2 Roof assembly U-factor and insulation R-value requirements. Climate zone
24-h use buildings Hospitals, hotels, call centre, etc.
Composite Hot and dry Warm and humid Moderate Cold
Other buildings types (day time use buildings)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
U-0.261 U-0.261 U-0.261 U-0.409 U-0.261
R-3.5 R-3.5 R-3.5 R-2.1 R-3.5
U-0.409 U-0.409 U-0.409 U-0.409 U-0.409
R-2.1 R-2.1 R-2.1 R-2.1 R-2.1
Table 3 Opaque wall assembly U-factor and insulation R-value requirements. Climate zone
Hospitals, hotels, call centre, etc. (24-h)
Composite Hot and dry Warm and humid Moderate Cold
Other buildings types (day time)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
U-0.440 U-0.440 U-0.440 U-0.431 U-0.369
R-2.10 R-2.10 R-2.10 R-1.80 R-2.20
U-0.440 U-0.440 U-0.440 U-0.397 U-0.352
R-2.10 R-2.10 R-2.10 R-2.00 R-2.35
Annual specific energy consumption (total of heating and cooling MWh/m2
0.40 Annual specific energy consumption (total of 2 cooling and heating) MWh/m
0.40 0.35 0.30
Uninsulated y = 0.47x + 0.05 R2 = 1.00
0.25 0.20
Insulated
y = -0.015x + 0.15
0.15 0.10 0.05 0.00 0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.35 y = 0.30x + 0.16
0.30
Uninsulated
R2= 1.00
0.25 y = 0.075x + 0.094 R2 = 1.00
0.20 0.15 0.10 Insulated 0.05 0.00 0.59
0.60
0.70
0.61
0.62
0.63
0.64
0.65
0.66
0.67
0.68
Surface area/Volume (1/m)
Surface area / Volume (1/m)
Annual specific energy consumption (total of cooling and heating MWh/m2
Fig. 5. Annual specific energy consumption versus A/V ratio with increasing height.
a thickness of 7.5 cm is found to be an optimum one, balancing the cost of insulation with the corresponding energy savings. Figs. 6 and 7 show the variation of specific energy consumption with A/V for the case, i.e. (a) the length of the building is increased and (b) the width of the building is increased. It is observed that, for an insulated building, the energy consumption increased with increasing of A/V, but the rise is much less than corresponding to that of the vertical expansion (increasing height) in both the cases, this is an extremely important result. A least square fit of the curves (lines) from Figs. 5–7, yield algebraic expression for the specific energy consumption as a function of (A/V) for different cases (Table 4).
0.40 0.35 y = 0.40x + 0.09 0.30
Uninsulated
R2= 1.00
0.25 0.20 0.15 y = 0.075x + 0.093 0.10
Insulated
R2 = 1.00
0.05 0.00 0.63
Fig. 7. Annual specific energy consumption versus A/V ratio when only width of building is increased.
5. Conclusions 0.64
0.64
0.65
0.65
0.66
0.66
0.67
0.67
Surface area/Volume (1/m)
Fig. 6. Annual specific energy consumption versus A/V ratio when only length of building is increased.
This paper demonstrate that an interpretation and mathematical synthesis of extensive numerical values of building energy simulation exercise can lead to simple algebraic expressions for heating and cooling loads as well as the annual energy consumption in the
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715 Table 4 Expression for calculating specific energy consumption as a function of A/V. S. no.
Specific energy consumption expression (MW h/m2 a) Vertical expansion (multi-storied)
Un-insulated Insulated
qE = 0.47A/V + 0.05 qE = 0.015A/V + 0.15
building. Besides, the algebraic expressions, the simulations also offer the optimized insulation thickness for composite climatic conditions of India prevailing in the central India as well as the pattern of energy consumption for increasing dimension of a building (changing A/V) for both the cases viz. an un-insulated building as well as an insulated building. The ambient observations are as follows: 1. If the building height increases, the energy consumption increases steeply with increasing surface to volume ratio. For insulated buildings, the increasing height (multistoried) slightly decreases the energy consumptions. 2. If the length of the building is increased, the energy consumption slightly increases with increasing A/V, both for an un-insulated building and an insulated building. The energy consumption for insulated case is obviously lower. 3. If the width of the building is increased, the energy consumption again increases slightly with increasing A/V, for both insulated and un-insulated buildings. The expression derived from this paper can be used for building practitioners to get estimates of energy consumption as well as the maximum cooling and heating loads for varying insulation thickness as well as the building dimensions. It is to be noted that the optimum insulation thickness obtained in this study matches with the corresponding U-values of the ECBC code (2008) recommended for India for majority climatic zones of India.
References [1] F.J. Lotz, S.J, Richards, The influence of ceiling insulation on indoor thermal conditions in olwellirys of heavy weight construction under South African conditions, CSIR Research Report No. 214, Pretoria, South Africa, 1964. [2] B. Givoni, Man Climate and Architecture, Applied Science Publishers, London, 1976. [3] M.S. Sodha, S.C. Kaushik, G.N. Tiwari, et al., Optimum distribution of insulation inside and outside the port, Building and Environment 14 (1979) 47. [4] G. Hauser, Sound and heat insulation in wood construction (in German), Das Banenzentrum 28 (1980) 2–17.
Horizontal expansion Along length
Along width
qE = 0.40A/V + 0.09 qE = 0.075A/V + 0.093
qE = 0.30A/V + 0.16 qE = 0.075A/V + 0.094
[5] G. Hauser, Thermal Energy Consumption in Buildings (in German), Lectures University of Kassel, Kassel, Germany, 1986. [6] G. Hauser, Methods for a Low Energy Hause (in German), in: Proc. 11th International Velta Congress, Tirol, vol. 89, 1989, pp. 9–17. [7] N.K. Bansal, G. Hauser, Passive Building Design: A Handbook of Natural Climate Control, Elsevier, Amsterdam, Netherlands, 1994. [8] DOE2.1, Building energy simulation software Developed by James J. Hirsch and Associates (JJH) in collaboration with Simulation Research Group, Lawrence Berkley Laboratory (reference manual LBL-8706) University of California at Berkley, USA, 1996. [9] TRNSYS, Transient Simulation Program, Solar Energy Laboratory, University of Wisconsin, Madison, WI 53706, USA, 2000. [10] DIN EN 832, Thermal Performance of Buildings: Calculation of energy use for heating residential buildings (Waermetechniques-Verhalten von GebaudenBerechnung des heizenergiebedarfs; ohngebaude), 1998. [11] DIN V 4108-6, Thermal protection and energy economy in buildings, Part 6: Calculation of annual heat and annual energy use (Warmeschutz und Energieeinsparung in Gebauden Teil 6: Berechnung des Jahres Heizwarmeunddes Jahresheizenergie-bedarfs), 2000. [12] DIN V 4701-10, Energy efficiency of heating and ventilation system in buildings, part 10: domestic hot water and ventilation (Energetische Bewertung heiz-undraumluftechnischer Anlagen Teil 10: Heizung, Trinkwassererwarmung, Luftung), 2001. [13] DIN V 4701-12, Energy efficiency of existing heating and ventilation system in buildings, part 12: heating and domestic hot water (Energetische Bewertung heiz-undraumluftechnischer Anlagenim Bestand, Teil 12: Warmeerzeuger and Trinkwassererwarmung), 2004. [14] ASHRAE, Energy Standard for Building except Low-Rise Residential Buildings, ASHRAE Inc., Atlanta, USA, 2004. [15] G. Hauser, A. Mass, Political and technical arrangements for an increase of energy efficiency of buildings in Germany and Europe, in: J. Mathur, H.J. Wanger, N.K. Bansal (Eds.), Energy Security: Climatic Change and Sustainable Development, Anamaya, New Delhi, India, 2007. [16] N.K. Bansal, G. Minke, Climatic Zones and Rural Housing in India, Forschungszentrum Juelich, Germany, 1995. ISBN: 3-89336-162-6. [17] ASHRAE, Handbook Fundamentals, ASHRAE Inc., Atlanta, USA, 1997. [18] I. Singh, Heat transfer in fenestration systems and energy savings in buildings. Ph.D. Thesis, Center for Energy Studies, Indian Institute of Technology, Delhi, India, 2002. [19] ECBC, Energy Conservation Building Code, BEE, Ministry of Power, Government of India, New Delhi, India, 2008. [20] IBC, in: N.K. Bansal, J. Mathur (Eds.), Practical Hand Book on Energy Conservation in Buildings, Indian Building Congress, New Delhi, India, 2008. [21] N.K. Bansal, J. Mathur, Energy Efficient Windows, Anamaya Publishers, New Delhi, India, 2006.
Contents lists available at ScienceDirect
Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng
Parametric equations for energy and load estimations for buildings in India N.K. Bansal a,*, A. Bhattacharya b a b
Shri Mata Vashino Devi University, Katra 182 320, J&K, India Centre for Energy Studies, Indian Institute of Technology, Delhi, New Delhi 110016, India
a r t i c l e
i n f o
Article history: Received 1 April 2009 Accepted 8 July 2009 Available online 15 July 2009 Keywords: Parametric equations Heating and cooling loads Specific energy consumption Insulation thickness Surface to volume ratio (A/V)
a b s t r a c t Detailed simulations have been performed for a single zone building to calculate the maximum heating and cooling loads as well as specific annual energy consumption for a single zone building. Numerical results have been used to derive parametric equations as a function of the thickness of insulation as well as the surface to volume ratio (A/V) taking into account the effect of increasing height as well as increasing length and width. For un-insulated building, the energy consumption increases steeply with increasing height, whereas for an insulated building, the energy consumption decreases slightly. For increasing lengths and widths, the change in energy consumption is a mild positive slope. The optimum thickness of the insulation obtained in the paper corresponds to the recommended U-values of roof and the walls in the building code of India, U being the total heat transfer coefficient. Ó 2009 Published by Elsevier Ltd.
1. Introduction This paper deals with a much studied topic of energy consumption and load calculations in building all over the world. The result are presented usually numerically or graphically to show the effect of increasing insulation, glazing and various other parameters. The studies have been compiled in several books, papers, and manuals [1–7]. The developed mathematical algorithm has been used to develop several building simulation programs that are being used to optimize energy consumption in buildings [8,9]. Studies on energy simulation in buildings, however, continue to draw attention of building physicist, who is trying to find easier and quicker methods to building practitioners to estimate possible energy savings for buildings designed by them. In order to systemize building construction techniques for effective energy saving at nation scales, many building codes are in use in several countries [10–14]. The basis of these codes is extensive building simulation followed by detailed measurements in model building. The two important parameters that effect the energy consumption in a building are the insulation and its shape defined by surface to volume ratio (A/V). Hauser and Maas [15] have developed a graph for the energy consumption in a building as function of A/V. The graph shows a linear trend and for lower values of A/V, energy consumption is also lower. The code prescribes U-values and R-values for thermal insulation in building in different climate zones of India [16]. The architects and building practitioners, however, find it difficult * Corresponding author. Tel.: +91 1991 285686; fax: +91 1991 285694. E-mail address: [email protected] (N.K. Bansal). 1359-4311/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.applthermaleng.2009.07.002
to estimate energy and loads (cooling and heating) for these recommended U-values. It is also found to be difficult to run simulation programs. However, it is possible to develop simplified, easy to use, expressions for annual energy consumption as well as for heating and cooling loads by scientific analysis of detailed simulation results. In this paper, very detailed simulations were performed on a single zone building to evaluate parametric expressions for optimal energy consumption as well as the thermal heating and cooling loads. The results are obtained for composite climatic conditions of India by using DOE2.1E simulation program. The choice of DOE2.1E was due to its use for developing ECBC code for India and because of its capability in calculating the cooling loads and cooling energy in air conditioned buildings. The basis for DOE 2.1 E is the mathematical model of American Society for Heating, Refrigeration and Air Conditioning Engineers, ASHRAE [17], used mostly for calculating air conditioning loads in hot climates. The detailed calculations for a variety of windows and climatic conditions are published elsewhere [18]. Very recently, the Government of India has brought out an energy conservation building code [19,20] in an effort to promote energy efficiency in buildings. A detailed study conducted for Energy Efficient Windows [21] shows that for the composite climatic conditions, a window area of around 10% with respect to the floor area, is the optimum for a single glazed south oriented window. As per air conditioning standard in India, one air change per hour is assumed and the inside air temperature is to be maintained at 24 °C. These are the values used for simulating this single zone building for hourly variation of all the climatic parameters over a statistically averaged year.
N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
3711
Nomenclature A/V d Et Qc
surface to volume ratio (m1) thickness of insulation (m) annual energy consumption (MW h) maximum cooling load (KW)
2. Climatic zones of India Based on statistical analysis of 38 years of meteorological data [16], have divided India into six climatic zones, namely hot and dry, warm and moderate, cold and cloudy, cold and sunny, and composite. Fig. 1 illustrates the variations of climatic parameters in these zones for representative locations i.e. the location where the climate is statistical average of all the parametric variations of metrological parameters of that particular zone. For example, Delhi climate is the representative of the composite climatic conditions in India. Buildings located in these zones would be having
Qh qE R U
maximum heating load (KW) specific energy consumption (MW h/m2 a) resistance of the building component (m2 °C/W) total heat transfer coefficient (W/m2 °C)
different maximum cooling/heating loads (kW) with different peak timings as well as total annual energy demand (measured in MW h, separately for cooling and heating) for the same level of indoor conditions. Delhi has been chosen for this study primarily because of its composite climate, with temperatures ranging from above 40 °C in summer to below 5 °C in winter. Such type of climate is predominant in central part of India. In other climate zones also (accept in North) the conditions are nearly the same [16]. The climate parameters used in this study are based on 30 years of statistical average. For conditioned buildings, therefore, both heating and cooling are
Fig. 1. (a) Climatic zones of India, Ref. [16]. (b) Climatic parameters of India, Ref. [16].
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
Fig. 1 (continued)
required to maintain deserved comfort levels. Its altitude is 216 m, latitude 28°350 N and longitude 77°120 E and annual global radiation is 2476 kWh/m2 a. 3. Building parameters The basic building size has been taken as 15 m (length) 10 m (width) 3 m (height), with a single glazed glass window of the size equaling 10% of the floor area, on the south wall, because for these conditions the energy consumption is least in the composite climates (Fig. 2.6c, in Ref. [21]). It is also seen that in this climate, the use of double glazed windows exhibits a negligible advantage on the overall energy consumption. The wall, under un-insulated condition, has the layers of plaster (0.015 m), brick (0.22 m) and plaster (0.015) the roof having the layers of plaster (0.015 m), Reinforced Cement Concrete (RCC) (0.12 m), Mudphuska (0.08 m) and tiles (0.025 m), and the floor having finish of tiles (0.2 m), RCC (0.1 m), sand (0.15 m) and soil (0.2 m). The inside film resistance for roof, walls, etc. has been taken as of 0.166 m2/kW. Under insulated condition, the layer of expanded polystyrene insulation has been placed after the inside layer of plaster, on the walls and the roof. The thermo-physical properties of used building materials are given in Table 1. The window glass has a wooden frame and a width of 0.10 m with a U-value of 6.31 W/m2 K1 and solar heat gain coefficient (SHGC) of 0.86. Other assumptions made for the conditioned buildings are: inside temperature 24 °C, North wall Azimuth 0°, number of people is nil, no shading on the building and the number of air change per hour is one. The load due to people, lighting, appliances, etc. is an additive term which can be added to the calculated load and the corresponding equations in this paper. The insulation cost varies widely depending on the nature, density and other characteristics of the material being used. In India, market enquiries re-
veal that expanded polystyrene cost varies from Rs. 2500/m3 to Rs. 7000/m3 depending on density and other factors. For the purpose of this study, a value of Rs. 5000/m3 (USD 107.53/m3) has been taken. Similarly, the cost of electric energy varies widely from state to state and within a state from consumer to consumer. Even amongst domestic consumers, say in Delhi, the price, varies between Rs. 2.40 and Rs. 4.60 per kWh, depending on consumption pattern and connected load. Unfortunately, no reliable data of average marginal cost of electricity, at the national or local level is applicable. For the purpose of this study, a conservative marginal cost of Rs. 3.25 (0.07 USD) per kWh has been assumed. (USD 1.0 = INR 46.50, October, 2006). 4. Discussion of results Starting with the basic building dimensions of 15 m 10 m 3 m and the conditions specified earlier, the program was run to obtain the (annual) cooling energy, heating energy and the total energy requirements, as well, as the maximum cooling and the heating loads under un-insulated conditions. Thereafter, the Table 1 Thermo-physical properties of building materials. S. no.
Material
Density (kg/m3)
Th. conductivity (W/m2 K)
Specific Heat (J kg1 K1)
1. 2. 3. 4. 5. 6.
Brick Plaster RCC Mudphuska Tiles Insulationa
1820 1762 2280 1622 1820 34
0.810 0.720 1.580 0.520 0.810 0.035
880.0 840.0 800.0 880.0 880.0 1340.0
a
Expanded polystyrene.
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
ð1Þ
0:35
Q c ¼ 11:97d
ð2Þ
And for maximum heating load 0:47
Q h ¼ 15:09d
ð3Þ
where d is the thickness of the insulation. At this point our effort is to find out the optimum thickness of the insulation, which can be obtained by balancing the cost of adding insulation with the cost of energy saved and the results are plotted in Fig. 4. It can be seen from this figure that the cost of insu-
Annual energy consumption (MW h)
60 50
40
Equation of trend line
Trend line
R2 = 0.99 20
10
1
2
3
4
5
6
7
8
9
10
Insulation thickness (cm) Fig. 2. Total annual energy consumption (MW h) versus insulation thickness (cm).
16 14 Max heating/cooling load (kW)
R2 = 0.99
100
Cost of annual energy savings
80 60 40 20
12 y = 11.97x-0.35
10
R2 = 0.91
Maximum cooling load
8 6 y = 5.09x-0.47 R2 = 0.99
4
Maximum heating load
2 0 1
2
3
4
1
2
3
4
5
6
7
8
9
10
5
6
7
8
9
Fig. 4. Cost of insulation versus cost of annual saving in energy.
lation varies, as expected, linearly with the increasing thickness of the insulation, whereas the annual energy saved and therefore, the reduction in the cost of energy increases logarithmically. The intersection of these two curves provides the optimum thickness of the insulation which is 7.5 cm. This corresponds to a U -value of 0.38 W/m2 K for the wall and for the roof. Very recently, an Energy Conservation Building Code [19] has been made public by the Ministry of Power, Government of India. The prescriptive requirements for roofs and walls for various climatic zones in India are given in Tables 2 and 3, respectively. These values are also obtained from DOE simulation program followed by a complicated life cycle assessment with a pay back period of 7 years and 30 years of life for the building. From the results of ECBC calculations, it is noted that: 1. Except for moderate climates, U-factors for the roof assembly are same for all other climates i.e. a value of U of 0.261 W/ m2 K for 24 h use building and a U-value of 0.409 W/m2 K for day time use building. 2. For the wall assembly, a U-value of 0.44 W/m2 K is prescribed for composite, hot and dry and warm and humid climatic conditions. For moderate and cold climatic conditions, the U-values are taken as 0.431 W/m2 K and 0.369 W/m2 K, respectively.
y = 51.11x0.41
30
0
y = 25259Ln(x) + 55523
120
Insulation thickness (cm)
For the maximum cooling load
0
Cost of Insulation
140
0
0:41
Et ¼ 51:11d
0
160
Cost (Rupees in thousand)
insulation was introduced and its impact on (annual) cooling energy, heating energy and on maximum cooling and heating load requirements has been assessed, by varying the insulation thickness from 0.01 m to 0.10 m. The results of the simulation exercises are shown in Figs. 2 and 3. These figures show that the annual energy consumption, based on the cooling requirements, reduces drastically with the introduction of thermal insulation and then stabilizes gradually. Similar is the scenario for the maximum cooling and heating loads. It has been possible to find trend lines for the cooling/heating loads as well as the corresponding energy consumptions. It is observed that a trend line is fairly fitting the actual data i.e. For the annual energy consumption
10
Insulation thickness (cm)
Fig. 3. Maximum cooling/heating load (kW) as a function of insulation thickness (cm).
Our value of 0.38 W/m2 K for the wall and for the roof therefore is appropriate from practical point of view. In practice, however, one can recommend a value of U = 0.4 W/m2 K. After having fixed the optimum thickness of the insulation, the next study is the effect of building dimensions. The building under consideration of 15 m 10 m 3 m, the dimensions can be increased in the vertical fashion (i.e. increasing the height) and/or in the horizontal direction (i.e. increasing the length and/or the width). It is found convenient to express the results in terms of specific energy consumption is kWh/m2/a1 (i.e. annual energy consumption divided by total carpet area), while in the case of vertical expansion, the normal height for every floor has been taken as of 3 m height. The results are shown in Figs. 5–7, for vertical expansion, for the increased length and for the increased width, respectively. Analysis of Figs. 5–7 yield very interesting results. Fig. 5 shows the specific energy consumption (MW h/m2 a) for the case, when the building height is increased insteps to three meters, thereby changing the ratio of A/V. For the case of an un-insulated building, the specific energy consumption and hence, the total energy consumption increased steeply with increasingly ratio of building surface to volume (A/V). For an insulated building, the energy consumption slightly decreases. It should be mentioned, here, that
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715
Table 2 Roof assembly U-factor and insulation R-value requirements. Climate zone
24-h use buildings Hospitals, hotels, call centre, etc.
Composite Hot and dry Warm and humid Moderate Cold
Other buildings types (day time use buildings)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
U-0.261 U-0.261 U-0.261 U-0.409 U-0.261
R-3.5 R-3.5 R-3.5 R-2.1 R-3.5
U-0.409 U-0.409 U-0.409 U-0.409 U-0.409
R-2.1 R-2.1 R-2.1 R-2.1 R-2.1
Table 3 Opaque wall assembly U-factor and insulation R-value requirements. Climate zone
Hospitals, hotels, call centre, etc. (24-h)
Composite Hot and dry Warm and humid Moderate Cold
Other buildings types (day time)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
Maximum U-factor of the overall assembly (W/m2 °C)
Minimum R-value of insulation alone (m2 °C/W)
U-0.440 U-0.440 U-0.440 U-0.431 U-0.369
R-2.10 R-2.10 R-2.10 R-1.80 R-2.20
U-0.440 U-0.440 U-0.440 U-0.397 U-0.352
R-2.10 R-2.10 R-2.10 R-2.00 R-2.35
Annual specific energy consumption (total of heating and cooling MWh/m2
0.40 Annual specific energy consumption (total of 2 cooling and heating) MWh/m
0.40 0.35 0.30
Uninsulated y = 0.47x + 0.05 R2 = 1.00
0.25 0.20
Insulated
y = -0.015x + 0.15
0.15 0.10 0.05 0.00 0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.35 y = 0.30x + 0.16
0.30
Uninsulated
R2= 1.00
0.25 y = 0.075x + 0.094 R2 = 1.00
0.20 0.15 0.10 Insulated 0.05 0.00 0.59
0.60
0.70
0.61
0.62
0.63
0.64
0.65
0.66
0.67
0.68
Surface area/Volume (1/m)
Surface area / Volume (1/m)
Annual specific energy consumption (total of cooling and heating MWh/m2
Fig. 5. Annual specific energy consumption versus A/V ratio with increasing height.
a thickness of 7.5 cm is found to be an optimum one, balancing the cost of insulation with the corresponding energy savings. Figs. 6 and 7 show the variation of specific energy consumption with A/V for the case, i.e. (a) the length of the building is increased and (b) the width of the building is increased. It is observed that, for an insulated building, the energy consumption increased with increasing of A/V, but the rise is much less than corresponding to that of the vertical expansion (increasing height) in both the cases, this is an extremely important result. A least square fit of the curves (lines) from Figs. 5–7, yield algebraic expression for the specific energy consumption as a function of (A/V) for different cases (Table 4).
0.40 0.35 y = 0.40x + 0.09 0.30
Uninsulated
R2= 1.00
0.25 0.20 0.15 y = 0.075x + 0.093 0.10
Insulated
R2 = 1.00
0.05 0.00 0.63
Fig. 7. Annual specific energy consumption versus A/V ratio when only width of building is increased.
5. Conclusions 0.64
0.64
0.65
0.65
0.66
0.66
0.67
0.67
Surface area/Volume (1/m)
Fig. 6. Annual specific energy consumption versus A/V ratio when only length of building is increased.
This paper demonstrate that an interpretation and mathematical synthesis of extensive numerical values of building energy simulation exercise can lead to simple algebraic expressions for heating and cooling loads as well as the annual energy consumption in the
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N.K. Bansal, A. Bhattacharya / Applied Thermal Engineering 29 (2009) 3710–3715 Table 4 Expression for calculating specific energy consumption as a function of A/V. S. no.
Specific energy consumption expression (MW h/m2 a) Vertical expansion (multi-storied)
Un-insulated Insulated
qE = 0.47A/V + 0.05 qE = 0.015A/V + 0.15
building. Besides, the algebraic expressions, the simulations also offer the optimized insulation thickness for composite climatic conditions of India prevailing in the central India as well as the pattern of energy consumption for increasing dimension of a building (changing A/V) for both the cases viz. an un-insulated building as well as an insulated building. The ambient observations are as follows: 1. If the building height increases, the energy consumption increases steeply with increasing surface to volume ratio. For insulated buildings, the increasing height (multistoried) slightly decreases the energy consumptions. 2. If the length of the building is increased, the energy consumption slightly increases with increasing A/V, both for an un-insulated building and an insulated building. The energy consumption for insulated case is obviously lower. 3. If the width of the building is increased, the energy consumption again increases slightly with increasing A/V, for both insulated and un-insulated buildings. The expression derived from this paper can be used for building practitioners to get estimates of energy consumption as well as the maximum cooling and heating loads for varying insulation thickness as well as the building dimensions. It is to be noted that the optimum insulation thickness obtained in this study matches with the corresponding U-values of the ECBC code (2008) recommended for India for majority climatic zones of India.
References [1] F.J. Lotz, S.J, Richards, The influence of ceiling insulation on indoor thermal conditions in olwellirys of heavy weight construction under South African conditions, CSIR Research Report No. 214, Pretoria, South Africa, 1964. [2] B. Givoni, Man Climate and Architecture, Applied Science Publishers, London, 1976. [3] M.S. Sodha, S.C. Kaushik, G.N. Tiwari, et al., Optimum distribution of insulation inside and outside the port, Building and Environment 14 (1979) 47. [4] G. Hauser, Sound and heat insulation in wood construction (in German), Das Banenzentrum 28 (1980) 2–17.
Horizontal expansion Along length
Along width
qE = 0.40A/V + 0.09 qE = 0.075A/V + 0.093
qE = 0.30A/V + 0.16 qE = 0.075A/V + 0.094
[5] G. Hauser, Thermal Energy Consumption in Buildings (in German), Lectures University of Kassel, Kassel, Germany, 1986. [6] G. Hauser, Methods for a Low Energy Hause (in German), in: Proc. 11th International Velta Congress, Tirol, vol. 89, 1989, pp. 9–17. [7] N.K. Bansal, G. Hauser, Passive Building Design: A Handbook of Natural Climate Control, Elsevier, Amsterdam, Netherlands, 1994. [8] DOE2.1, Building energy simulation software Developed by James J. Hirsch and Associates (JJH) in collaboration with Simulation Research Group, Lawrence Berkley Laboratory (reference manual LBL-8706) University of California at Berkley, USA, 1996. [9] TRNSYS, Transient Simulation Program, Solar Energy Laboratory, University of Wisconsin, Madison, WI 53706, USA, 2000. [10] DIN EN 832, Thermal Performance of Buildings: Calculation of energy use for heating residential buildings (Waermetechniques-Verhalten von GebaudenBerechnung des heizenergiebedarfs; ohngebaude), 1998. [11] DIN V 4108-6, Thermal protection and energy economy in buildings, Part 6: Calculation of annual heat and annual energy use (Warmeschutz und Energieeinsparung in Gebauden Teil 6: Berechnung des Jahres Heizwarmeunddes Jahresheizenergie-bedarfs), 2000. [12] DIN V 4701-10, Energy efficiency of heating and ventilation system in buildings, part 10: domestic hot water and ventilation (Energetische Bewertung heiz-undraumluftechnischer Anlagen Teil 10: Heizung, Trinkwassererwarmung, Luftung), 2001. [13] DIN V 4701-12, Energy efficiency of existing heating and ventilation system in buildings, part 12: heating and domestic hot water (Energetische Bewertung heiz-undraumluftechnischer Anlagenim Bestand, Teil 12: Warmeerzeuger and Trinkwassererwarmung), 2004. [14] ASHRAE, Energy Standard for Building except Low-Rise Residential Buildings, ASHRAE Inc., Atlanta, USA, 2004. [15] G. Hauser, A. Mass, Political and technical arrangements for an increase of energy efficiency of buildings in Germany and Europe, in: J. Mathur, H.J. Wanger, N.K. Bansal (Eds.), Energy Security: Climatic Change and Sustainable Development, Anamaya, New Delhi, India, 2007. [16] N.K. Bansal, G. Minke, Climatic Zones and Rural Housing in India, Forschungszentrum Juelich, Germany, 1995. ISBN: 3-89336-162-6. [17] ASHRAE, Handbook Fundamentals, ASHRAE Inc., Atlanta, USA, 1997. [18] I. Singh, Heat transfer in fenestration systems and energy savings in buildings. Ph.D. Thesis, Center for Energy Studies, Indian Institute of Technology, Delhi, India, 2002. [19] ECBC, Energy Conservation Building Code, BEE, Ministry of Power, Government of India, New Delhi, India, 2008. [20] IBC, in: N.K. Bansal, J. Mathur (Eds.), Practical Hand Book on Energy Conservation in Buildings, Indian Building Congress, New Delhi, India, 2008. [21] N.K. Bansal, J. Mathur, Energy Efficient Windows, Anamaya Publishers, New Delhi, India, 2006.