Embodied Energy of Building Envelopes and its Influence on Cooling Load in Typical Indonesian Middle Class Houses

Transcription

1 Embodied Energy of Building Envelopes and its Influence on Cooling Load in Typical Indonesian Middle Class Houses Agya Utama and Shabbir H. Gheewala The Joint Graduate School of Energy and Environment, King Mongkut s University of Technology Thonburi, Bangkok, Thailand Abstract: Energy demands on residential in Indonesia counted almost 50%, the material enclosure on this sector plays an important role for reducing the cooling load. Air conditioner (A/C) as the major contributor for the electricity bill should be reduced, more than 50% of the electricity bill in residential sector resulted from this appliances. To reduce cooling load by using the correct and low U- value local materials can reduce more than 350 MJ per month. Concrete based material for building enclosure in single houses seems to be not only higher emergy during production and its transportation also contributes to the cooling load (perimeter load). The perimeter load of which has big contribution in the tropical countries cooling load, also has significant impact towards its energy consumption during operational phase. Low R-value material, such as local clay material proved significantly reduce the thermal load caused by solar radiation Keywords: LCA, Emergy, Residential, House, Material 1. INTRODUCTION More than 35% of the total electricity demand in the US [1] and almost 50% in Indonesia are from residential houses [2]. In terms of cost, building envelopes contribute major percentage of material used in the residential building, walls contributing 46% and roofs, 16% [3]. For the overall energy usage during the life cycle of the building, the operation phase constitutes more than 80% of the demand. Thus, the energy use during the occupation phase needs to be analyzed. Heat gain through building envelopes (perimeter load) approximately contribute percent of the total heat gain in the building [3]. Construction materials have already consumed intensive energy before they reach the construction site. The energy during material production is called 'embodied energy' (emergy). Embodied energy is a measure of the quantity of the energy bound into a product due to raw material extraction and manufacturing process required to produce a finished product. Also included is the energy associated with transportation of raw materials to the factory and of finished products to the customer [4]. Java is selected as the focus of research since 85% of the total population in Indonesia lives on this island and along with Bali, it contributes to 80% of the electricity demand [2]. Semarang has been selected as a representative city for analyzing the operational energy demand in the residential sector. The middle class houses have been selected due to the enormous percentage of houses from this class. 2. METHODOLOGY 2.1 Embodied energy Embodied energy in a product comprise the energy to extract, transport and refine the raw materials and then to manufacture the components and assemble the product [5]. The energy consumed directly at each phase is clearly definable and measurable; this paper measures the direct energy consumed by residential building materials. Though the study site for the buildings is selected as Semarang city, the data collection for the enclosure materials has been conducted throughout Java island as not all the material is manufactured locally. The emergy in single houses envelopes material from its extraction to the construction phase (cradle to gate) had been assessed. Moreover the energy during occupation phase is assessed as cooling load using CLTD (Cooling Load Temperature Different) method. The method combines the temperature difference between indoor and outdoor, solar radiation and considers thermal capacity of the enclosure. 2.1 Case study Middle class residential houses were used in this study; the typical materials that are currently used have been chosen along with typical floor area and occupancy rate. The studied houses are air conditioned and having similar occupant behaviors. The research focused on a single house type 55 (area ~55 m 2 ), typical gable roof, 2 rooms and 1 living room. The air conditioned room has an average volume of 21 m 3, is used by three occupants and has a life span of 50 years. As the heat gain in this typical single house is mostly through the roof, walls and windows, the cooling load effects will be considered using the static calculation, and the cooling load (sensible) calculated by means of putting external sensible load factors as main consideration in the calculation. The operational energy demand during occupation phase has been collected in Semarang city, two single house types in Semarang had been selected, namely House 1 and House 2. House 1 uses concrete block as its walls material, and concrete roof as its roof enclosure. On the other hand, the House 2 uses bricks as main component of its walls and clay tile roof as roof enclosure. Both houses use the same material for roof frame, ceiling and window glass; namely steel, gypsum and clear glass, respectively. Based on observations, the study considers that only the two main bedrooms are air conditioned, the appliances are assumed to be the same in every bed room and the occupant rate for using the rooms is also similar. The total number of persons staying in the bed rooms during night time is three. Corresponding author: shabbir_g@jgsee.kmutt.ac.th 1

2 2.2 Process analysis and operational energy As the simplest energy analysis, process analysis focused on the energy required for each particular material production. The calculation was done measuring the energy content based on its primary energy input, the results being expressed. per m 2 concrete block, per unit clay tile etc. The energy comparison between theory using CLTD method and the real condition energy demand will be delivered as well. The approximate calculation before the actual survey was conducted will be compared to the survey result for the particular house and the same occupation behavior. Totally 50 houses with similar main enclosure material except the material for roof and walls had been selected and surveyed, one house with concrete roof and wall and one house with clay roof with bricks wall had been chosen for this study. The information about electricity bills, appliances, air conditioners and occupants' behavior were recorded. The cooling loads were calculated from these data. 2.3 Life-cycle energy analysis Life cycle energy analysis was used in this study to calculate the embodied energy of enclosure material and the energy use during occupation caused by the thermal properties of the enclosure. Life-cycle energy comprises the operational energy of the building and its initial and recurrent embodied energy, over its life time. This study only comprised the life-cycle energy until the end of its life time; the disposal phase is not included. Life-cycle energy was calculated using the equitation: LCE = EEi + EErec + ( OE * year) (1) where: LCE = the life-cycle energy; EEi = the initial embodied energy of material EErec = the recurrent embodied energy (maintenance) OE = the total annual operational energy (cooling load) Year = Building lifetime The life-cycle energy here compares two building types with different enclosure materials. First building (House 1) using concrete roof and concrete block as their main material and the second building (House 2) using roof tile and bricks as their main material for enclosure. The rest of the supported material using the same material, namely: steel for its roof frame, gypsum for ceiling material, single window glass and aluminum window frame. The assessment does not includes the end of life of the materials. The survey revealed that there is no recycling industry in this city. Most of the materials are dumped or sent to the municipal landfill without any further processing. Only some of the material is reused (i.e. aluminum and steel frame); however, the reuse processed are not inlcuded in this study. For simplicity of calculations, the annual operational energy consumption was assumed to remain constant throughout the lifecycle of the house. However, it is obvious that the energy consumed during occupation phase is difficult to be constant due to various factors such as occupant monthly income, appliances quantity (internal load), appliances efficiency over time, etc. Therefore this limitation should be addressed in future research. 3. RESULTS AND DISCUSSION 3.1 Building materials and embodied energy The embodied energy, operational energy (cooling load) and life-cycle energy are shown per square meter rate based on the building envelope areas. The life-cycle energy is calculated based on embodied energy for materials as the enclosure or supporting material for building envelopes along with the operational energy caused by the effect of enclosure material. The U-value or R-value will significantly influence the energy use during occupation phase. Table 1 presents the embodied energy of building materials for typical middle class residential houses in Semarang city. The study reported that more than 75% houses in Semarang, chose concrete roof as their main material for roof enclosure, only less than 25% chose the clay tile roof. This is due to the economic considerations; the concrete roofs work out to be cheaper than the clay ones. The R-values of the typical envelopes material in Semarang are presented in Table 2. The R-value of clay is much higher than concrete leading to a higher overall value for the roof. It is thus anticipated that the House 2 will have a lower cooling requirement, and consequently a lower life-cycle energy, than House 1. This issue will be analyzed further in the later sections along with quantitative results. 2

3 Table 1 Embodied energy for enclosure materials in single houses Material Embodied energy Common Steel MJ/kg [1] Gypsum (3 mm) 2.69 MJ/kg Single glass (clear 2 mm) 13 MJ/kg [6] Aluminum frame (1 mm) 232 MJ/kg Mold (m 2 ) Cement Sand House 1 Concrete roof (2 mm) (18 pcs/m 2 ) Concrete block (100 mm) (24 pcs/m 2 ) Mold (1 PC : 5 sand) House 2 Clay roof (2 mm) (18 pcs/m 2 ) Bricks wall (100 mm) (60 pcs/m 2 ) Mold (1 PC : 5 sand) MJ/kg 0.6 MJ/kg MJ/kg MJ/kg MJ/m MJ/kg 1.3 MJ/kg MJ/m 2 Table 2 Building envelope material R-value House 1 R-value House 2 R-value Concrete (2 mm) 0.3 Clay (2 mm) 2.39 Dead air space 1.01 Dead air space 1.01 Gypsum (3 mm) 0.58 Gypsum (3 mm) 0.58 Total R-value for roof 1.89 Total R-value for roof 3.98 Concrete block (10 mm) 1.11 Bricks (10 mm) 1.90 Clear glass 0.22 Clear glass Embodied energy The initial energy for building envelopes material in the middle class houses accounting for concrete and clay roof, steel frame, gypsum ceiling, concrete block and bricks walls, aluminum windows frame and clear glass have been studied. Material Table 3 The building envelopes emergy Emergy per Emergy Construction Volume/mass/area unit [MJ] [MJ] Common Steel kg MJ/kg 15, Gypsum (3 mm) 55 m MJ/m 2 1, Single glass (clear 2 mm) 4.8 m MJ/m 2 3, Aluminum frame (1 x 5) m 3 353,104 MJ/m 3 1, House 1 Concrete roof (2 mm) (18 pcs/m 2 ) 55 m MJ/pcs 14, concrete block (100 mm) (24 pcs/m 2 ) 90 m MJ/pcs 14, Walls mold 90 m MJ/m House 2 Clay roof (2 mm) (18 pcs/m2) 55 m MJ/pcs 5, Bricks wall (100 mm) (60 pcs/m2) 90 m MJ/pcs 16, Walls mold 90 m MJ/m Table 3 shows the embodied energy for building envelopes material during its raw material excavation, production and its transportation. It also shows the energy used during construction process which is less than 0.5% for both houses. The total embodied energy for House 1 works out to a little over 50,000 MJ and is considerably higher than for House 2 which is only about 43,700 MJ. From the Table 3, it can be seen that the biggest contributor for the first house is the initial energy for concrete roof which is much higher than the clay roof in House 2. The high emergy of concrete roof is due to the high percentage of the cement ingredients. Moreover the biggest contributor for the second house is coming from bricks walls which accounted almost 17,000 MJ. This is due to the amount of bricks in every square meter of walls (60 pcs/m 2 ). 3.3 CLTD method result The thermal energy result based on Cooling Load Temperature Difference calculation for the building enclosures of the two selected house are calculated. The theoretical calculation for cooling load is divided into three categories, first is the latent load, second is the internal load (appliances) and third is the perimeter load (load influenced by its enclosure). Houses 1 and 2 have the same occupancy rate and occupant behavior, as well as the number of occupants staying in the air conditioned rooms is the same. The internal load is also the same as every room has one electronic appliance which is the source of internal heat. The total internal load and latent heat caused by occupants accounted 206 kwh on a monthly basis for both houses. The perimeter load for House 1 was calculated to be kwh, this value is considerably higher than the perimeter load at 3

4 House 2 (accounted kwh). The differences are due to the R-value or U-value for the roof enclosure material, the R-value for House 1 at 1.89 is much lower than that for House 2 which is The walls material R-value seems to have little influences on the perimeter load, as shown in Table 2 where the House 1 walls concrete block has 1.11 compared to bricks walls (1.90) on House 2. The total cooling load for House 1 was accounted kwh/month or MJ/month. Moreover, the total cooling load for House 2 seems to be lower than House 1, the load accounted for kwh/month or MJ/month. 3.4 Case study result Two houses have been selected out of 50 surveyed houses in Semarang. Both houses have similar condition, orientation, occupant behavior and material as the theoretical assumption. The total area for both is also 55 m 2, each one has two main bed rooms with air conditioning system. Three occupants stay at the bed rooms during evening and night time. The average usage for these rooms is 10 hours and was occupied by 3 person (2 main bed room and 1 on the other room). The operational energy result for cooling load for House 1 accounted for kwh on a monthly basis, which is very similar to the result from the CLTD calculation. This figure is also considerably higher than House 2 which accounted only kwh per month. The energy value for House 1 accounted for MJ per month and House 2 was accounted for MJ per month. These two figures resulted from the actual calculation have similar result with the CLTD calculation (table 4). Table 4 Cooling load comparison between CLTD and Real on yearly basis House 1 House 2 [MJ/year] [MJ/m 2 /year] [MJ/year] [MJ/m 2 /year] CLTD 23, , Actual 23, , Thus, it seems that the CLTD method gives fairly similar results to the actual measurements and can be used for calculating the cooling load during the occupation phase to measure the energy consumed caused by perimeter load for different house models and type, and also for different location and area and therefore for different enclosure materials. 3.5 Life-cycle energy Life-cycle energy analyses over 30 and 50 years' life time were carried out for the middle class single housing in Semarang city. The calculations and results are presented in Tables 5 and 6. The material replacement for most of the materials are not accounted, due to the material durability. However the clay tile roof seems to be less durable, therefore the clay roof is considered to be replaced after 30 years' occupation. Table 5 House 1 Life-cycle energy Years Emergy Replacement Operational Total [MJ] [MJ] [MJ/year] [MJ] 30 50, , , , , ,232, Table 5 shows the total life-cycle energy of House 1 which has concrete base material as the main enclosure. The concrete provides a relatively high emergy value especially in the roof and a low R-value which creates high thermal load during occupation phase, therefore increasing the cooling load through its perimeter. Table 6 House 2 Life-cycle energy Years Emergy Replacement Operational Total [MJ] [MJ] [MJ/year] [MJ] 30 43, , , , , , , Table 6 shows the Life-cycle energy of House 2, where the replacement is considered to account for the lower durability of the clay roof material. Even so, the lower embodied energy of the clay roof and the high R-value result in a much lower life-cycle energy as compared to House 1 both for 30 as well as 50 years. The emergy of the building materials for both the houses are in the range of 4-7% of the life-cycle energy requirements. These values are actually lower than those reported in other studies though the order of magnitude is similar. 4. CONCLUSION The concrete based material is preferred to clay due to its more competitive price. However, the study showed that it consumes more energy during the operation (use) phase. This is due to the higher R-value of clay roof which leads to a reduced cooling requirement (air-conditioning) and consequently lower life-cycle energy. The results hold for both 30 and 50 years life time even though the clay material is less durable and has to be replaced. The general conclusions from this study are: - High thermal resistance material is more preferable for tropical weather - Cement based material consumes more energy during production compared to the clay based material - Clay based material have higher R-value than concrete based material and therefore more thermal resistance - Reduction in cooling load has a more significant effect on the overall energy requirement as compared to internal and latent load 4

5 5. ACKNOWLEDGMENTS The authors gratefully acknowledge the contribution of all plant managers at Gresik cement Plc, Boral Gypsum Plc, Bluescoop Plc, Krakatau Steel Plc, and all the medium and small enterprise for concrete roof, concrete block, clay roof, and bricks production throughout the city of Semarang, Indonesia. The financial support of the Joint Graduate School of Energy and Environment is also acknowledged. 6. REFERENCES [1] S. Blanchard, P. Reppe, 1998, LCA of a residential home in Michigan, MSc Report University of Michigan, October 1998 [2] National Electricity Company (PLN), 2004, Java and Bali grid efficiency [in Bahasa], Available online: surf on April 22 nd 2006 [3] P. Tiwari, J. Parikh, 1994, Cost of CO 2 reduction in building construction. Energy, 20, pp, [4] U.G. Yasantha, S. Babel, S. Gheewala, A. Sharp, 2006, Environmental, economic and social analysis of material for doors and windows in Sri Lanka. Building and Environment, article in press. [5] R. Fay, G. Treloar, 1998, Life-cycle energy analysis A measure of the environmental impact of buildings. Environment design guide, 22, November 1998 [6] M. Asif, T. Muneer, R. Kelle, 2005, Life cycle assessment: A case study of a dwelling home in Scotland, Building and Environment, article in press. 5