How To Calculate Energy From A Building

Transcription

1 Life cycle energy of steel and concrete framed commercial buildings Tuan Ngo 1, Ali Mirza 1, Ranjith Gammampila 1, Lu Aye 1*, Robert Crawford 2 and Priyan Mendis 1 1 Department of Civil and Environmental Engineering 2 Faculty of Architecture Building and Planning The University of Melbourne, AUSTRALIA Vic 3010 * lua@unimelb.edu.au ABSTRACT The construction and operation of buildings are vastly responsible for significant environmental impacts, predominantly through resource consumption, waste production and greenhouse gas emission. Environmental issues continue to become increasingly significant and hence the building operational energy efficiency and the energy required for construction and consequently, for the material production, are getting greater importance. The commercial buildings in general consumes significant amount of materials in construction and consumes significant amount of energy during operation. Therefore it is essential to determine both embodied energy and operational energy. This paper quantifies and compares the embodied energy and operational energy of concrete and steel framed structures, which are commonly used in commercial buildings. A typical high rise office building in Melbourne has been chosen for this exercise. The studied building is a fifty storey with a flat roof and the total net-lettable area of square meters. The embodied energy contribution of the substructure, the super structure with the structural elements namely foundation, beams, columns roof, facades and stairs are investigated. The results shown that the structural building materials, concrete (with steel reinforcement) represents the largest component of embodied energy for concrete frame structure while the steel framed structure examined showed the beams represent the largest component of embodied energy. It was fond that there is no significant difference in operational energy. Keywords Concrete framed buildings, Life cycle energy, Steel framed buildings INTRODUCTION The buildings are one of the largest energy consumers in any industrialised country and the commercial buildings carry a significant share. The construction and operation of buildings requires energy, and the production of that energy emits greenhouse gases (GHG). While there has been much research into the possibilities of reducing

2 operational energy consumption, there has been very little investigation into reducing the whole life cycle energy required for the buildings. The aim of this paper is to quantify the life cycle energy and the GHG emissions during the construction phase and the operational phase of two typical office buildings, one with structural steel frame and the other one with cast in place concrete frame. The analysis also identifies the contribution of the different building elements and materials on the overall life cycle energy to explore the potential to minimize them. Life cycle greenhouse gas emission analysis can be used as a decision making tool for the selection of a better alternative for the reduction of GHG. It gives information about GHG emissions during various stages of a building and helps in their comparison. For the calculation of GHG emissions, the life cycle energy analysis (LCEA) needs to be performed. Life cycle energy analysis of the building consists of its initial embodied energy, recurrent embodied energy, operational energy and demolition energy over its lifetime (Fay et al. 2000). The LCEA is a decision making tool which can aid developers in examining different alternatives. It uses energy as a measure of environmental impact which helps in a detailed energy analysis (Fay et al. 2000). Several case studies have been done using LCEA for buildings as it helps in comparing different energy types of the building and aid in identifying the aspects, which can be modified to reduce the energy consumption. Life cycle stages of a building are most commonly categorized as - resource extraction stage, design stage, construction stage, operational stage, demolition stage. Initial embodied energy refers to the energy required to acquire raw materials for the building, their transportation and their installation in the building during construction process. Embodied energy of the building is the energy required to acquire raw materials and manufacture, transport and install building products in the construction of the building (Cole and Kernan 1996). It is categorized into two types: the initial embodied energy and the recurrent embodied energy. The energy required to refurbish and maintain the goods and services in the building is called recurrent embodied energy (Fay, Treloar et al. 2000). Based upon the measurability and definability of the energy process, embodied energy is either a direct embodied energy or indirect embodied energy. The energy used directly at each stage is direct energy as it is measurable and is comprised of energy for construction, pre fabrication and transport activities. However, the energy required indirectly to support the main process is not obvious and difficult to measure, such as embodied energy in the building materials (Fay, Treloar et al. 2000). To get a holistic understanding of energy consumption and its associated GHG emissions, embodied energy must also be taken into account. There are several reasons for the increasing significance of embodied energy; 1) Modern day buildings are relatively larger in sizes thus require more building material and equipment, 2) Modern day construction processes require extensive machine operations rather than labour, thus using more and more energy, 3) Technological advancements are reducing the consumption of operational energy, 2

3 4) Use of more energy intensive material such as aluminium, stainless steel glass etc. has increased the proportion of embodied energy, 5) Transportation distance of building materials have increased in the recent times thus increasing the embodied energy (Australian Greenhouse Office 1999). There have been numerous methodologies and tools developed across a range of disciplines for embodied energy analysis and life cycle inventories, namely the process analysis, input output analysis, Hybrid analysis and the variation has been described by Menzies et al. (2007) and Crawford (2007). A variation of a hybrid life cycle inventory analysis was investigated by Crawford (2007) and the author concluded that the Inputoutput based hybrid analysis is the preferred method for life cycle inventory of Australian building and building related products due to superior level of completeness. The input-output based hybrid analysis generally shows an increase in embodied energy as much as 45% have shown in a comprehensive study on commercial buildings (Crawford et al 2005 & Menzies et al 2007). A few life cycle energy studies have being conducted during on office buildings. Aye et al. (1999) have studied the correlation between embodied energy and height for low rise commercial buildings. Treloar et al (2001) have completed a detail study to compare the embodied energy in office buildings with varying heights and investigated the embodied energy in substructure, super structure and finished elements. This study revealed that the high rise building requires more energy intensive materials to meet structural requirements as compared to low rise office buildings. Operational energy is the energy required for heating, cooling, ventilation, lighting and running other appliances in the building (Cole and Kernan 1996). It varies with the building use, occupancy hours, number of employees, climate, efficiency of the building equipments etc. Therefore, it becomes important to distinguish between those aspects of operational energy which depend upon building and its system design (insulation standards, efficiency of lighting system, efficiency of HVAC system etc.) and the ones which depend upon use of building (occupancy hours, number of employees, building use, control strategies etc.) (Cole and Kernan 1996). The selection of building envelope materials affects not only the structural strength of the building but also the indoor environmental quality, the operational energy use and consequently environmental impacts. It should be noted that the operational energy consumption also depends on other factors such as the climate zone, building orientation, glazing, passive and active type cooling and heating systems, lighting systems, appliances, usage and occupancy factor. A number of studies have been conducted to estimate the operational energy of commercial buildings. According to Treloar et al. (2001), embodied energy represents 20 to 50 times the annual operational energy of most Australian residential, commercial, institutional and educational buildings. Life Cycle Assessment The assessment of environmental impacts of products, buildings or other services throughout their life time is known as lifecycle assessment (LCA) (ISO standard). The assessment includes the entire life cycle of a product encompassing the 3

4 extraction and processing of raw materials, manufacturing, transportation and distribution, use, reuse, maintenance, recycling and final disposal. There are several factors that influence the life cycle assessment such as boundary definitions, completeness of the study, energy supply, energy source assumption, product specifications, manufacturing differences, complication of economic activities and data quality and characteristics (Menzies et al. 2007). In order to determine the primary energy inputs required to produce a product, it is necessary to trace the flow of energy through the relevant industrial sector. Several different methods of energy analysis are available, principle once been the statistical analysis, input output analysis and the process analysis (Hammond et al. 2008). The statistical analysis often provides a reasonable estimate of the primary energy; however it cannot account for indirect requirements. Most widely used methods are the process analysis and the input - output analysis. The process analysis involves the evaluation of direct and indirect energy inputs of each product process. As this methodology is likely to ignore some process such as banking, finance, insurance and other ancillary activities, the net process analysis could be strongly under estimated. The input output analysis uses the entire economic activities and hence have a great advantage (Menzies et al. 2007). However the input-output analysis can be subjected to many uncertainties due to high level of aggregation of products. The disadvantage of the previous methods can be reduced to a certain extent by using a hybrid method combining both process based and input output based LCA. This has evolved as two separate categories of hybrid energy analysis, process based hybrid analysis and the input output based hybrid analysis (Menzies et al. 2007).The hybrid LCA method potentially enables a large increase in framework completeness and hence increase the overall reliability and the environmental impact (Treloar et al 1999).The variation of a hybrid life cycle inventory analysis has been investigated by Crawford (2007) and recommended that the Input-output based hybrid analysis is the preferred method for life cycle inventory of Australian building and building related products due to superior level of completeness. Case study building This research considers the life cycle analysis approach to estimate and compare the embodied and operational GHG emissions of concrete and steel framed commercial buildings. Both concrete and steel framed structures are commonly used in commercial buildings. A typical multi storey office building in Melbourne has been selected to compare the GHG emissions of concrete and steel frames. The building is a fifty storey office building, with a flat roof and a total usable gross floor area of m 2 and a structural system consisting of beams, columns and slab, with a core area as shown in Figure 1. Forty grade concrete has been selected for foundation and columns and a thirty grade for the rest of the concrete elements. The steel framed building consists of steel columns and beams and concrete slabs. The building cladding consists of double glazed panels with aluminium mullions and the roof of the building consists of reinforced concrete slab in both cases. 4

5 RESULTS & DISCUSSION Figure 1: Plan view of the building Embodied Energy Analysis Input-output based hybrid analysis has been used for this life cycle GHG emission analysis and the GHG coefficients are shown in Table 1. The embodied energy and GHG coefficients used for glass & aluminium have been taken from The Centre for Building Performance Research of New Zealand and they are based on process based hybrid analysis. Table 1: Embodied energy (EE) and embodied GHG Coefficients Material Density (kg/m3) EE Coefficient (MJ/kg) EGHG Coefficient (kg CO2-e/kg) Reference Concrete -Grade Crawford (2009) Concrete -Grade Crawford (2009) Steel reinforcement- Grade Crawford (2009) Structural steel- Grade Crawford (2009) Glass tinted (4mm float glass) CBPR NZ (2009) Aluminium extruded CBPR NZ (2009) The construction materials for both buildings have been analysed to compare the embodied energy and GHG emissions. Only the major construction elements have been selected for this exercise which are - foundation, reinforcement, beams, columns, slabs, roof, stairways and the facades. Comparison of Building Material in Steel and Concrete Framed Building The volumes and weights of the building elements are presented in Table 2. The analysis revealed that the steel building has a significant advantage on quantity of material used by weight and volume against concrete as a building material. The 5

6 concrete framed building required 24% and 20% more volume and weight respectively than the steel option. The weight per total floor area was 1.29 & 1.04 t per m 2 for concrete and steel respectively. Table 2: Embodied energy (EE) and embodied GHG emissions (NLA = m 2 ) Element Total Volume (m 3 ) Total Weight (t) EE (GJ) EGHG (t CO 2-e ) C S C S C S C S Foundation Beam Column Slabs Shear Walls Staircase Roof slab Façade Total C = Concrete frame building, S = Steel frame building Figure 2: The weight distribution between concrete and steel buildings Comparison of Embodied Energy The comparative values of embodied energy are presented in Table 2 and in Figure 3. The analysis shows that the embodied energy of the steel building is 70% more than that of the concrete framed building. The embodied energy per total floor area was and 6.71 GJ/m 2 for concrete and steel frames respectively. The foundation contributed to the highest embodied energy of 24.5% in case of the concrete building, whereas for the steel building, beams had the highest embodied energy of 36.9% of the total. Comparison of Embodied GHG The comparative values of embodied GHG emissions for each building are presented in Table 2 and in Figure 4. It can be seen that the steel framed building has 68% more 6

7 embodied GHG emissions as compared to the concrete framed one. The embodied GHG emissions per total floor area was 470 and 780 kg per square meter for concrete and steel respectively. Among the building elements, the foundation contributed to highest GHG emissions (23.8%) for concrete framed building and beams for steel framed buildings (36%). Figure 3: The Embodied Energy distribution between concrete and steel buildings Figure 4: Embodied GHG distribution between concrete and steel buildings Operational Energy To compare the energy consumption and GHG emissions for both concrete and steel framed buildings during user phase, chillers with a COP of 3.4 and a boiler with an 7

8 efficiency of 85% have been assumed for air conditioning and heating purposes respectively. The occupancy, lighting and equipment profile has is according to the Building Code of Australia 2009 (BCA 2009). The U values of various building elements are also according to BCA 2009 minimum requirements and are listed as follows: Roof = 1.56 W/m 2 K Ceiling = 0.44 W/m 2 K Window (double glazed) = 2.4 W/m 2 K and shading coefficient = 0.8 Wall = 0.65 W/m 2 K Floor = 0.68 W/m 2 K In this study, the operational energy has been calculated based on primary energy factors. This concept of primary energy has been discussed by Treloar et al. (2000) who stated that the operational energy calculation should be carried out in terms of primary energy and not in delivered energy. Delivered energy is the metered energy that is supplied to the building. It can be in the form of electricity or gas. A considerable amount of primary energy is required to produce that metered energy. It can vary depending upon the energy source and conversion technology such as coal fired power plant, hydro power plant or wind power plant etc. Table 3 shows the primary energy required to provide one unit of delivered energy. These primary factors have been applied in the analyses. Table 3: Primary energy factors for Victoria Coal, oil and gas Petroleum, coal products Electricity Gas The GHG factors for electricity and gas have been taken from National Australian Built Environment Rating System (NABERS) resource, which are 1.34 and 0.32 respectively. Table 4 presents the operational energy consumption of user phase for both concrete and steel framed buildings. The simulated operational energy is based on an efficient HVAC system with minimum losses and a controlled building behaviour in terms of hours of occupancy and equipment profile. Thus, this operational energy figure would change if the hours of occupancy and equipment profile are changed or some other system is used for HVAC. Simulation results indicate that the operational energy and GHG emissions are the same for both concrete and steel framed structures. The literature suggests that concrete structured buildings carry a higher thermal mass, which is effective in reducing the HVAC energy consumption. However, in this case study, both buildings have thermal masses inside the building envelope therefore the difference in the operational energy consumption is negligible. Table 4: Operational energy & GHG emissions Structure Type Operational Energy (kwh/m 2 /yr) Operational Energy (GJ/yr) Operational GHG (kg CO 2eq /yr) Concrete Steel

9 Table 5 shows the comparison between embodied and operational energy and GHG emissions. It can be seen that the operational GHG emissions over a 50-year life of the building is higher as compared to embodied GHG emissions. The operational energy in case of concrete building is comparable to embodied energy but in case of steel building, it is 31% less than embodied energy. Table 5: Comparison of embodied and operational energy and GHG over 50 years Structure Type Embodied Energy (GJ/m 2 ) Operational Energy (GJ/m 2 ) Embodied GHG (ton CO 2eq ) Operational GHG (ton CO 2eq ) Concrete Steel CONCLUSIONS The study has shown that the steel framed building has higher embodied energy and associated GHG emissions than concrete framed building. The embodied energy of steel framed building is 70% more than that of concrete framed building. The main contributor towards embodied energy in case of concrete building was foundation whereas for the steel framed building, beams had the highest embodied energy. Both steel and concrete framed buildings have same operational energy. No thermal mass effect was observed, which could be due to the fact that the main thermal mass elements such as beams and columns of the buildings are inside the building envelop. Over a span of 50 years, the operational GHG emission is significantly more than that of embodied GHG emission which points towards the need to reduce the operational energy consumption in the buildings through efficient HVAC system and better building façade and insulation. It is clearly evident that the material choice in the construction of building has an important effect on the GHG emissions. The study has a limitation on the embodied energy calculation via recycling of both concrete and steel. It requires extensive and reliable data and is beyond the scope of this paper. Based on this study, it can be concluded that the concrete framed buildings have less GHG emissions than steel framed buildings. REFERENCES Australian Greenhouse Office (1999). Australian commercial building sector greenhouse gas emissions , Australian Greenhouse Office. Aye, L., Bamford, N., Charters, W.W.S. & Robinson, J. (1999). Optimising embodied energy in commercial office development, The Challenge of Change: Construction and Building for the New Milennium, Salford, The University of Salford, 1-2 September City of Melbourne (2003). Zero Net Emissions by A Roadmap to a Climate Neutral City. Melbourne. Cole, R. J. and P. C. Kernan (1996). Life-cycle energy use in office buildings. Building and Environment 31(4):

10 Cole, R. J. and P. C. Kernan (1996). Life-cycle energy use in office buildings. Building and Environment 31(4): Crawford, R. (2008) Validation of a hybrid life-cycle inventory analysis method, Journal of Environmental Management, 88: Dimoudi, A. and C. Tompa (2008). Energy and environmental indicators related to construction of office buildings. Resources, Conservation and Recycling 53: Edwards, B. and P. Hyett (2002). Rough Guide to Sustainability. London, ECIY 8NA, RIBA Publications. Energy Victoria (1994). Energy Efficient Housing Manual: Design Guidelines and Case Studies. East Melbourne, Victoria, Renewable Energy Authority Victoria. Evans, M. (1980). Housing, Climate and Comfort. London, Architectural Press. Fay, M. R. (1999). Comparative Life Cycle Energy Studies of Typical Australian Suburban Dwellings, PhD thesis, Faculty of Architecture, Building and Planning, The University of Melbourne. Fay, MR and Treloar, G and Iyer-Raniga, U (2000). Life-cycle energy analysis of buildings: a case study. Building Research & Information 28(1): Guggemos, A. A. and A. Horvath (2005). Comparison of environmental effects of steel and concrete framed buildings. Journal of Infrastructure Systems: Hammond, G. P. and Jones, C. I. (2008) Embodied energy and carbon in construction materials, Proceedings of the Institution of Civil Engineers, Energy 161, Menzies, G.F., Turan, S. and Banfill, P.F.G. (2007) Life-cycle assessment and embodied energy: a review, Proceedings of the Institution of Civil Engineers, Construction Materials 160, O Sullivan, P. (1994). Energy and Architectural Form. Global warming and the built environment. R. Samuels and D. Prasad, E & FN Spon: Steel, M. and R. Heath (1998). Energy Efficient Building Use. Oxford, England, Chandos Publishing Limited. Szokolay, S. (1988). Climatic Data and Its Use in Design. Canberra, RAIA Education Division. Treloar, G., Fay, R., Ilozor, B. and Love, P. (2001). Building materials selection: greenhouse strategies for built facilities. Facilities 3/4: Treloar, G. J. (1997). Extracting embodied energy paths from input-output tables: towards an input-output-based hybrid energy analysis method. Economic Systems Research 9(4): 375. Xing, S., Xu, Z. and Jun, G. (2008). Inventory analysis of LCA on steel and concrete construction office buildings. Energy and Buildings 40: