Life cycle energy analysis of buildings: An overview

Life cycle energy analysis of buildings: An overview

Energy and Buildings 42 (2010) 1592–1600 Contents lists available at ScienceDirect Energy and Buildings journal homepage: www.elsevier.com/locate/en...

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Energy and Buildings 42 (2010) 1592–1600

Contents lists available at ScienceDirect

Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild

Review

Life cycle energy analysis of buildings: An overview T. Ramesh a , Ravi Prakash a,∗ , K.K. Shukla b a b

Department of Mechanical Engineering, Motilal Nehru National Institute of Technology, Allahabad, UP, India Department of Civil Engineering, Motilal Nehru National Institute of Technology, Allahabad, UP, India

a r t i c l e

i n f o

Article history: Received 19 September 2009 Received in revised form 28 April 2010 Accepted 13 May 2010 Keywords: Life cycle energy Embodied energy Operating energy Life cycle assessment Building

a b s t r a c t Buildings demand energy in their life cycle right from its construction to demolition. Studies on the total energy use during the life cycle are desirable to identify phases of largest energy use and to develop strategies for its reduction. In the present paper, a critical review of the life cycle energy analyses of buildings resulting from 73 cases across 13 countries is presented. The study includes both residential and office buildings. Results show that operating (80–90%) and embodied (10–20%) phases of energy use are significant contributors to building’s life cycle energy demand. Life cycle energy (primary) requirement of conventional residential buildings falls in the range of 150–400 kWh/m2 per year and that of office buildings in the range of 250–550 kWh/m2 per year. Building’s life cycle energy demand can be reduced by reducing its operating energy significantly through use of passive and active technologies even if it leads to a slight increase in embodied energy. However, an excessive use of passive and active features in a building may be counterproductive. It is observed that low energy buildings perform better than self-sufficient (zero operating energy) buildings in the life cycle context. Since, most of the case studies available in open literature pertain to developed and/or cold countries; hence, energy indicative figures for developing and/or non-cold countries need to be evaluated and compared with the results presented in this paper. © 2010 Elsevier B.V. All rights reserved.

Contents 1. 2.

3. 4. 5. 6. 7.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Life cycle energy analysis (LCEA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Embodied energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1. Initial embodied energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.2. Recurring embodied energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Operating energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Demolition energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4. Life cycle energy (LCE) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Life cycle assessment (LCA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Literature review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Low energy buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction

∗ Corresponding author. Tel.: +91 9336668662; fax: +91 532 2545341. E-mail address: [email protected] (R. Prakash). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.05.007

Buildings are constructed for residential, office and commercial purposes all over the world. They are major contributors to socio-economic development of a nation and also utilize a large

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proportion of energy and available natural resources. Worldwide, 30–40% of all primary energy is used for buildings and they are held responsible for 40–50% of green house gas emissions [1]. It is therefore essential for the building construction industry to achieve sustainable development in the society. Sustainable development is viewed as development with low environmental impact, and high economical and social gains. To achieve the goals of sustainability it is required to adopt a multi-disciplinary approach covering a number of features such as energy saving, improved use of materials including water, reuse and recycling of materials and emissions control. Life cycle energy analysis of buildings assumes greater significance for formulating strategies to achieve reduction in primary energy use of the buildings and control emissions. 2. Life cycle energy analysis (LCEA) Life cycle energy analysis is an approach that accounts for all energy inputs to a building in its life cycle. The system boundaries of this analysis (Fig. 1) include the energy use of the following phases: manufacture, use, and demolition. Manufacture phase includes manufacturing and transportation of building materials and technical installations used in erection and renovation of the buildings. Operation phase encompasses all activities related to the use of the buildings, over its life span. These activities include maintaining comfort condition inside the buildings, water use and powering appliances. Finally, demolition phase includes destruction of the building and transportation of dismantled materials to landfill sites and/or recycling plants. Energy use in each phase is discussed below. 2.1. Embodied energy Embodied energy is the energy utilized during manufacturing phase of the building. It is the energy content of all the materials used in the building and technical installations, and energy incurred at the time of erection/construction and renovation of the building. Energy content of materials refers to the energy used to acquire raw materials (excavation), manufacture and transport to

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the building site. Embodied energy is divided in two parts: initial embodied energy and recurring embodied energy. 2.1.1. Initial embodied energy Initial embodied energy of a building is the energy incurred for initial construction of the building. It is expressed as: EEi =



mi Mi + Ec

(1)

where EEi = initial embodied energy of the building; mi = quantity of building material (i); Mi = energy content of material (i) per unit quantity; Ec = energy used at site for erection/construction of the building. 2.1.2. Recurring embodied energy A large variety of materials are being used in building construction. Some of them may have a life span less than that of the building. As a result, they are replaced to rehabilitate the building. In addition to this, buildings require some regular annual maintenance. The energy incurred for such repair and replacement (rehabilitation) needs to be accounted during the entire life of the buildings. The sum of the energy embodied in the material, used in the rehabilitation and maintenance is called recurring embodied energy and can be expressed as: EEr =



mi Mi [(Lb /Lmi ) − 1]

(2)

where EEr = recurring embodied energy of the building; Lb = life span of the building; Lmi = life span of the material (i). Embodied energy largely depends on the type of the materials used, primary energy sources, and efficiency of conversion processes in making building materials and products. 2.2. Operating energy It is the energy required for maintaining comfort conditions and day-to-day maintenance of the buildings. It is the energy for HVAC (heating, ventilation and air conditioning), domestic hot water, lighting, and for running appliances. Operational energy largely varies on the level of comfort required, climatic conditions and operating schedules. Operating energy in the life span of the building is expressed as: OE = EOA Lb

(3)

where OE = operating energy in the life span of the building; EOA = annual operating energy; Lb = life span of the building. 2.3. Demolition energy At the end of buildings’ service life, energy is required to demolish the building and transporting the waste material to landfill sites and/or recycling plants. This energy is termed as demolition energy and expressed as: DE = ED + ET

(4)

where DE = demolition energy; ED = energy incurred for destruction of the building; ET = energy used for transporting the waste materials. 2.4. Life cycle energy (LCE) Life cycle energy of the building is the sum of the all the energies incurred in its life cycle. It is thus expressed as: Fig. 1. System boundaries for life cycle energy analysis.

LCE = EEi + EEr + OE + DE

(5)

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Energy savings from recycling or reusing the demolished building materials is not considered in the life cycle energy estimation of the buildings. This is primarily due to the fact that there is no common agreement over attributing this saved energy to the demolished building. However, it would be more appropriate if this energy from recycling or reusing is incorporated in the life cycle energy estimation in overall sense. Studies on the life cycle energy use of the building are desirable, to evaluate strategies for reduction in energy requirement of the buildings. By performing life cycle energy analysis, the phases that have highest energy demand can be identified and targeted for improvement. Life cycle energy, if quantified in terms of primary energy can give a useful indication of the greenhouse gas emissions attributable to buildings and therefore its impact on the environment. However, for broader environmental impact analysis, life cycle assessment (LCA) of buildings is useful. 3. Life cycle assessment (LCA) LCA is a process whereby the material and energy flows of a system are quantified and evaluated. Typically, upstream (extraction, production, transportation and construction), use, and downstream (deconstruction and disposal) flows of a product or service system are inventoried first. Subsequently, global and/or regional impacts (e.g. global warming, ozone depletion, eutrophication and acidification) are calculated; based on energy consumption, waste generation, etc. LCA allows for an evaluation of impacts of different processes and life cycle stages on the environment. As per international organisation for standardisation [2], LCA studies generally consist of four phases: goal and scope definition, life cycle inventory (LCI), impact assessment and interpretation of results. The goal and scope defines the purposes, audiences, and system boundaries. The LCI involves data collection and calculations to quantify material and energy inputs and outputs of a system, and the impact assessment evaluates the significance of potential environmental impacts based on the LCI. In other industrial sectors, life cycle analysis is currently widely used to assess the life cycle environmental impact of products. In order to use LCA methods to assess the environmental impact, it is necessary to perform an inventory analysis. However, in the construction industry, the materials used in construction, operation, and demolition are varied and the range of environmental criteria that are relevant to buildings is potentially enormous. This may serve as a severe limitation to the use of LCA methods in the building industry. Modern day buildings are typically largescale projects utilizing different kinds of building materials, so their constructions have a great impact on many other industrial sectors. Building materials production processes are much less standardized than most manufactured goods because of the unique character of each building. There is limited quantitative information about the environmental impacts of the production and manufacturing of construction materials, or the actual process of construction and demolition. All these factors make environmental assessments of the building industry a challenging task. 4. Literature review Buildings consume energy directly or indirectly in all phases of their life cycle right from the cradle to the grave and there is interplay between phases of energy use (embodied and operating energy). Hence, they need to be analysed from life cycle point of view. Bekker [3] highlighted that in the building sector a life cycle approach is an appropriate method for analysis of energy and use of other natural resources as well as the impact on the environment.

Later on Adalberth [4] presented a method describing the calculation of the energy use during the life cycle of a building. The method is applied to gain insight into the total energy use of dwellings in its life cycle in his companion paper [5]. The paper presented case studies of the total energy use for three single-unit dwellings built in Sweden wherein, it was reported that 85% of the total energy usage was required during the operation phase and energy used in manufacturing all the construction materials employed in construction with the erection and renovation amounts approximately to 15% of the total energy use. The transportation and process energy used during erection and demolition of the dwellings comprises approximately 1% of the total energy requirement. Several other similar studies are reported in the open literature for residential buildings [6–9] and office buildings [10–12]. Table 1 shows an abstract of data sources adopted by different authors to evaluate life cycle analysis of buildings. It is concluded from these case studies that operating energy has major share (80–90%) in life cycle energy use of buildings followed by embodied energy (10–20%), whereas demolition and other process energy has negligible or little share. Since operating energy of the buildings has largest share in life cycle energy distribution, reducing it appears to be the most important aspect for the design of buildings which demand less energy throughout their life cycle. Embodied energy should then be addressed in second instance. In order to reduce operational energy demand of the buildings, passive and active measures such as providing higher insulation on external walls and roof, using gas filled multiple pane windows with low emissivity (LE) coatings, ventilation air heat recovery from exhaust air, heat pumps coupled with air or ground/water heat sources, solar thermal collectors and building integrated solar photovoltaic panels, etc. were examined in life cycle perspective by many researchers. Mithraratne and Vale [13] recommended provision of higher insulation to a timber framed house situated in New Zealand as an energy saving strategy. Different versions of the same building with varying active and passive measures were also analysed [14–16]. It is observed that reductions in life cycle energy of the buildings over their conventional ones are proportional to the degree and number of energy saving measures used in the building. Conventional building refers to a building built according to the common practice of a specific country. However, reduced demand for operating and life cycle energy is achieved by a little increase in embodied energy of the building due to the energy intensive materials used in technical and other installations. Thormark [17] reported that embodied energy and its share in the life cycle energy for low energy building is higher than conventional ones. Though embodied energy constitutes only 10–20% to life cycle energy, opportunity for its reduction should not be ignored. There is a potential for reducing embodied energy requirements through use of materials in the construction that requires less energy during manufacturing [18]. While using low energy materials, attention must be focussed on their thermal properties and longevity as they have impact on energy use in other phases of a building’s life cycle. Oka et al. [19] quantified energy consumption and environmental pollution caused by construction in Japan. Buchanan and Honey [20] made a detailed study on embodied energy of buildings and resulting carbon dioxide emissions with wood, concrete, and steel structures for office and residential purposes in New Zealand and concluded that wood constructions have less embodied energy than concrete and steel structures. Venkatarama Reddy and Jagadish [21] estimated the embodied energy of residential buildings using different construction techniques and low energy materials and obtained 30–45% reduction in embodied energy. Shukla et al. [22] evaluated embodied energy of an adobe house in Indian context. The house was constructed using low energy intensive materials like soil, sand, cow dung, etc. For the adobe house [22], about 50% reduction in embodied energy was observed

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Table 1 Data sources for life cycle analysis. Life cycle phase

Activity

Possible sources of data

(a) Manufacturing phase

Building material Production

Manufacturing energy data of the building materials from literature, economic input and output tables, process analysis, hybrid analysis. Quantities estimated from building drawings, bill of materials and from interviews with building designer, contractor/owner Average distances for material transport. Energy data for transport operations Energy use from site visit

Transport Building construction including refurbishment (b) Use phase

Use of electricity and fuels for heating, sanitary water and lighting

Simulation software-ENERGY-PLUS, VISUAL DOE, E-QUEST, DESIGN BUILDER, ENORM, TRNSYS, ECOTECT, SUNCODE, etc., annual electricity bills, house hold survey on energy use. Inventory data for fuel production. Electricity mix data

(c) Demolition phase

Building demolition

Recycling

Demolition operations and quantities from specific measured data. Use of equipment and explosives from data base Average distances for material transport energy data for transport operations Specific measured data

(d) Life cycle energy

Total energy use of the building in its life cycle

Phase a + b + c

(e) Life cycle assessment

Life cycle material and energy flow estimation Impact assessment that building makes on the environment

Phase a + b + c Greenhouse effect or global warming, ozone depletion, acidification, eutrophication, photochemical smog, etc. estimated using software – SIMAPRO, ECOBAT, LEGEP, BEES, ATHENA, etc.

Transport

compared to a conventional concrete house. This reduction was achieved due to the use of low energy intensive and locally available materials (e.g. soil, sand, cow dung, etc.) compared to burnt clay bricks, concrete, cement, etc., in the concrete house. Another opportunity for reducing embodied energy is through use of recycling materials in the construction. Thormark [23] studied two cases: (i) the building which was built with a large proportion of reused materials and components; (ii) the building in which all materials and components had been new. The results showed that about 55% of energy could be saved with reused materials and components. Thus, it can be observed from the reported results that buildings can be made to demand low energy in their life cycle with passive and active measures as well as using low energy materials in the construction. Low energy buildings become sustainable constructions, provided most of its energy use for operation (electricity) is derived largely from renewable or low CO2 resources [24]. In order to directly address a set of specific environmental loads caused by buildings and their operation, researchers have increased the scope of analysis beyond pure energy accounting and applied a full life cycle assessment analysis in their studies [25–28]. Environmental impacts like global warming potential, acidification potential, and photo-oxidant formation potential are considered in these studies. Seo and Hwang [29] examined and estimated CO2 emissions in the entire life cycle of buildings. From these studies, it may be observed that the impact of different phases of the building on environment is similar to energy share of these phases in the life cycle energy of the buildings. LCA is much dependent on the primary sources of the energy of a particular place and conversion efficiency of materials production processes. If energy source is changed from fossil to renewable, environmental impact drastically changes. Also, it can be seen that the renewable sources of energy have less impact on the environment. There are also comparative life cycle assessment studies in the open literature; Marceau and VanGeem [30] presented life cycle assessment of a single-family house modelled with two types of exterior walls: wood framed and insulating concrete form (ICF). The house was modelled in five cities of different climates in US. The results showed that in almost all cases, for a given climate,

the impact indicators are greater for the wood house than for the ICF house. Xing et al. [31] presented the life cycle assessment of office buildings constructed in China using steel and concrete. They observed that embodied energy and environmental emissions of steel framed building was superior to the concrete framed one. However, energy use and associated emissions were larger for steel framed building due to the higher thermal conductivity of steel than concrete. As a result life cycle energy consumption and environmental emissions of steel framed building were slightly higher. From the LCA studies of the buildings presented in the literature it can be concluded that impacts on the environment correlate closely with primary energy demand of the buildings in their life cycle.

5. Methodology A literature survey on buildings’ life cycle energy use was performed resulting in 73 case studies from 13 countries. Survey included both office and residential buildings. An attempt is made in this paper to find the normal range of life cycle energy values (energy indicative figures) for conventional office and residential buildings and to distinguish low energy buildings from conventional ones based on the life cycle energy use. Data is collected for wood, steel, concrete and other structured buildings. Progressive numbers were assigned for case studies according to their source and they are presented graphically by their number. Case study no. 1–46 is assigned for residential buildings and 47–73 for office buildings. Exclusive embodied energy cases were exempted from the analysis as they were not holistic in building energy evaluation process. Similarly, life cycle assessment case studies in which data on life cycle energy use of the buildings was not available were also exempted. Different versions of the same building presented in source were also considered as case studies. An overview of case studies found in literature is presented in Table 2. In some of the literature, data were presented in tables in text form; while in others through graphs. In the latter case,

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Table 2 Overview of literature, general information. Reference

Case study no.

Country

Adalberth [14] Adalberth [5] Adalberth et al. [28] Asif et al. [1] Buchanan and Honey [20] Citherlet and Defaux [15] Cole and Kernan [11] Fay et al. [8] Junnila et al. [26] Kofoworola and Gheewala [12] Kofoworola and Gheewala [25] Medgar and VanGeem [30] Mithraratne and Vale [13] Oka et al. [19] Peuportier [27] Venkatarama Reddy and Jagadish [21] Sartori and Hestnes [32] Shukla et al. [22] Suzuki and Oka [10] Thormark [17] Treloar et al. [7] Utama and Gheewala [9] Winther and Hestnes [16] Xing et al. [31] Zimmermann et al. [24]

1–13 14–16 17–20 – – 26–28 59–70 36–37 47–48 73 –

Sweden Sweden Sweden Scotland New Zealand Switzerland Canada Australia US and Europe Thailand Thailand US New Zealand Japan France India Germany India Japan Sweden Australia Indonesia Norway China Switzerland

32–34 – – – 41–46 31 49–58 38 35 39–40 21–25 71–72 29–30

Embodied energy only

Life cycle energy √ √ √

Life cycle assessment



√ √ √ √ √ √ √



√ √ √ √

√ √ √ √ √ √ √ √ √ √ √ √

CO2



Type of building

Data

Res Res Res Res Off Res Off Res Off Off Off Res Res Off Res Res Res Res Off Res Res Res Res Off Res

T T G – – G T T T T – G G, T T – – G T G T T T G, T T T

Res: residential; Off: office; G: graph; T: table and/or text.

numerical values have been read from the graphs, thus they might be subjected to slight imprecision. The form of energy presented in case studies was either end use or primary. End use energy is the energy measured at final use level. It is also called as delivered energy. Primary energy is the energy used to produce the end use energy, including extraction, transformation and distribution losses. Concerning operating energy of residential buildings, some sources expressed it as primary, others as end use. In case of embodied energy, no clear statement about primary/end-use was found. It was assumed that data were expressed as primary energy, as this is the common practice in LCA analysis of products according to Sartori and Hestnes [32]. The form of energy used for construction, demolition and transportation is also considered as primary energy. In order to present life cycle energy of the buildings in primary units, operating energy in end-use of case studies in Refs. [5,12,14,28] from Sweden, and Thailand has been converted into primary units using approximate conversion factors. Based on the information in Refs. [17,25] about sources of electricity in above countries, it is considered that electricity (indigenous/imported) derived mostly from thermal sources (>75%) is used in the above case studies. Country specific data for oil and gas is difficult to obtain as the oil/gas industry is international in character controlled by multinational companies. In view of the above, a conversion factor of 3.4 for electricity and 1.4 for oil/gas is used as reported in Ref. [8], a case study from Australia, where majority of electricity (more than 75%) comes from thermal sources.

operating energy and life cycle energy of the buildings is almost linear despite climatic and other differences. Life cycle energy of case study no. 35–37 in Refs. [7,8] is higher for that particular operating energy due to the wider system boundaries adopted in evaluating building’s embodied energy. This is due to the fact that energy content of appliances, roads and footpaths, boundary walls, land scaping, etc. is included in the buildings’ embodied energy which was out of the scope in other studies. There is also a clear distinction between the life cycle energy use of residential and office buildings due to the higher embodied and operating energy of office buildings as compared to residential ones. It may be attributed to the fact that office buildings are generally multi-storey concrete or steel structures, requiring high embodied energy than wood structures of residential buildings. Operating energy is also more due to high occupancy, requiring more energy to maintain comfort conditions

6. Results and discussions Life cycle energy, operating and embodied energy use of residential and office buildings were calculated and normalised to kWh/m2 per year to neutralize the differences in building parameters like floor area and life span and are shown in Tables A.1 and B.1 in Appendix A. Fig. 2 depicts the relation between life cycle energy and operating energy for 73 cases. It can be seen that the relationship between

Fig. 2. Relation between operating and life cycle energy for 73 cases.

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Fig. 5. Interplay between operating and embodied energy for case studies [16]. Fig. 3. Normalized life cycle energy for conventional residential buildings (primary).

inside the building. In addition to this, electrical energy required for lighting and to power appliances is also large because they exist in large numbers compared to residential houses. All these factors contribute to higher life cycle energy of the office buildings as compared to residential ones. Further, it can also be observed from Fig. 2 that life cycle and operating energy of case study no.73 from Thailand [12], is falling quite away from other case studies from cold countries. This is due to the fact that in tropical and developing countries like Thailand, electricity derived mostly from fossil fuels is being used for all activities during operation phase, which when converted to primary energy (using conversion factor 3.4) results in higher values. But, in case of cold countries, though they are using electricity for lighting and other purposes, its share in operating phase is very small as most of the energy is consumed in the form of oil/gas (conversion factor 1.4) for space heating. Hence, they have lesser energy figures during operation phase. This indicates that there is distinct difference in energy use of buildings for cold and tropical countries; hence, they need to be analysed separately. Figs. 3 and 4 present bar chart showing the life cycle energy use of conventional residential and office buildings, respectively from cold countries. Wood, concrete and steel structured buildings are considered. Cases have been sorted in ascending order of their normalized life cycle energy. To fix life cycle energy range, lower and upper limits of energy use are rounded off to nearest whole numbers allowing a little margin. Normalised life cycle

Fig. 4. Normalized life cycle energy for conventional office buildings (primary).

energy use for conventional residential buildings is falling in the range of 150–400 kWh/m2 per year and that of office buildings in the range of 250–550 kWh/m2 per year. Wide variation in the life cycle energy use of residential as well as office buildings is mainly due to the differences in climatic conditions of the places where these buildings are located. Moreover, as operating energy is expressed in primary energy terms, energy conversion factors from end use to primary (particularly in case of electricity) also have role in this variation. Countries which have clean sources of energy (hydro, wind, solar) have low energy figures than other countries with fossil fuel energy sources. Another reason for this variation, which may contribute a little, is energy content of materials used in the building construction, which again depends on energy carriers and efficiency of processes of one country in making building products. 6.1. Low energy buildings Low energy buildings are the buildings having specific design that demand less operating and life cycle energy than if built according to conventional criteria with parity of all other conditions [32]. Design of low energy building is achieved by reducing its operating energy through active and passive technologies. But, reduction in operating energy is generally accompanied by little increase in embodied energy of the building due to energy intensive materials used in the energy saving measures (Fig. 5). Table 3 shows the life cycle energy savings through operating energy reduction by installing passive and active measures for the case studies mentioned in Refs. [14–16]. It shows that life cycle energy savings are in accordance with reduction in operating energy which in turn is proportional to the degree and number of passive and active energy saving measures used in the building. This indicates that one can go on reducing energy use for operation of the building in order to produce low energy buildings by increased use of passive and active energy saving measures and at one stage operating energy can be made zero and thus produce zero energy buildings (self-sufficient). A zero energy building requires neither fuels nor electricity for its operation as all the energy it needs is locally produced (utilizing solar and wind sources) and stored. Sartori and Hestnes [32] reviewed life cycle energy consumption of conventional, low energy and zero energy buildings. Six versions of the building (one conventional, four low energy, and one self-sufficient) are analysed in German context. Results show that life cycle energy of the self-sufficient building is more than some of its low energy versions (Fig. 6). This is due to the fact that, in case of low energy buildings, increase in embodied energy because of energy saving measures is little compared to decrease

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T. Ramesh et al. / Energy and Buildings 42 (2010) 1592–1600

Table 3 Energy savings with active and passive measures over conventional constructions. Case study no. 7 8



24 23

22

25

26 27

28

Energy saving measures (passive and active)

Reduction in operating energy %

Life cycle energy saving%

Reference

Conventional. Ventilation: mechanical supply and exhaust system with plate heat exchanger to recover heat. Ventilation: mechanical supply and exhaust system with plate heat exchanger and windows: single pane and a sealed argon filled unit with low emission coatings. Conventional. Exhaust air heat pump preheats ventilation air and hot water. Solar collectors preheat hot water and air heat recovery unit efficiency 70%. Ground coil and heat pump system for space and water heating, PV system and air heat recovery unit efficiency 85%. Conventional. Increased insulation on facades, roof and slab, heat pump coupled to ground, 55% heat recovery from exhaust air. Super insulation on fac¸ade, roof and slab, 3 pane windows with two low e-coatings, heat pump coupled to ground, 55% heat recovery from exhaust air, solar thermal collectors for hot water, PV panels to generate half of the electricity required.

– 15

– 14

Adalberth [14]



18

– 21

– 19

30

26

62

50

20

– 16

54

49

in its operating energy; hence, their life cycle energy comes down significantly. But, in case of self-sufficient house, though its operating energy is zero, its embodied energy is so high that it exceeded life cycle energy of some of the low energy cases. This indicates that self-sufficient house is not the lowest life cycle energy consumer among all versions of a building and there is a limit for life cycle energy savings through reduction in operating energy by installing complex and energy intensive technical installations. Similarly, in Ref. [16], author compared self-sufficient house in Freiburg with energy use of the five versions of the row houses at Hamar. Embodied energy of self-sufficient house was larger than highest energy user of five versions. Author expressed a view that

Winther and Hestnes [16]

Citherlet and Defaux [15]

there is a limit to reduction in energy use for operation by energy intensive domestic engineering systems. But these studies did not tell how much the energy use for operation can be reduced before the embodied energy will be so high that the total energy use during the life time will start to increase again. This limit varies from one study to another and will not be unique even for particular studies as it depends on the type and mix of active and passive measures used, climatic conditions of the place, and materials used in the construction. This requires more detailed study. But, conclusion that can be drawn at this stage is that, carefully designed low energy buildings perform better than self-sufficient houses in life cycle context. Too many technical installations in order to make building self-sufficient are not desirable. 7. Conclusions

Fig. 6. Life cycle versus embodied energy for case studies reviewed [32].

The analysis of cases found in literature showed that life cycle energy use of buildings depends on the operating (80–90%) and embodied (10–20%) energy of the buildings. Normalised life cycle energy use of conventional residential buildings falls in the range of 150–400 kWh/m2 per year (primary) and office buildings in the range of 250–550 kWh/m2 per year (primary). Building’s life cycle energy demand can be reduced by reducing its operating energy significantly through use of passive and active technologies even if it leads to a slight increase in embodied energy. However, an excessive use of passive and active features in a building may be counterproductive. It is further observed that low energy buildings perform better than self-sufficient building in life cycle context. Most of the case studies found in literature are from cold countries where oil/gas is used for larger part of the operation phase, i.e., for space heating. However, in non-cold and developing countries like India, Thailand, etc. electricity derived mostly from fossil

T. Ramesh et al. / Energy and Buildings 42 (2010) 1592–1600

fuels (coal) is being used in operation phase for space cooling, lighting, and other purposes. In addition, construction of buildings may involve usage of indigenous building materials and architectural techniques. Hence, a difference in the total life cycle energy of the buildings in non-cold developing countries is expected. For example, life cycle energy indicative figure for office building for Thailand is coming around 850 kWh/m2 per year (primary). This is quite

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high compared to office buildings in cold countries. Hence, energy indicative figures for non cold countries need to be evaluated separately. Appendix A. Tables A.1 and B.1

Table A.1 Energy data related to residential buildings in kWh/m2 per year (primary). Case study no.

Size (m2 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

1190 1190 1190 1190 1190 1190 1190 1190 700 1160 1190 1520 1190 130 129 138 700 1160 1190 1520 110 110 110 110 110 266 266 266 N.A. N.A. 100 94 94 94 123 128 128 120 50 50 156 156 156 156 156 156

Life span 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50 40 100 100 100 30 100 100 50 40 40 80 80 80 80 80 80

Principal structure Wood Wood Wood Wood Wood Wood Wood Wood Concrete Concrete Wood SCC Concrete Wood Wood Wood Concrete Concrete Wood SCC Wood Wood Wood Wood Wood Wood Wood Wood Wood Wood Adobe Wood Concrete Wood Brick veneer Brick veneer Brick veneer Wood Clay Cement Wood Wood Wood Wood Wood Wood

Embodied 32 33 33 33 34 33 33 33 25 26 33 24 30 28 27 23 27 24 35 22 14 13 12 9 25 27 31 25 20 28 37 12 13 14 143 101 98 39 13 7 19 20 20 29 107 22

Operating 330 323 314 323 299 296 323 274 234 251 322 265 320 260 273 243 234 251 322 265 151 119 133 169 65 188 151 86 311 309 24 23 21 12 233 267 292 120 84 95 259 202 148 64 0 49

Life cycle 350 344 335 344 320 318 344 295 257 276 343 288 344 288 301 268 261 276 357 288 165 132 145 178 90 215 182 111 331 337 61 47 45 33 376 368 390 144 97 102 278 222 168 93 107 71

Reference [14] [14] [14] [14] [14] [14] [14] [14] [14] [14] [14] [14] [14] [5] [5] [5] [28] [28] [28] [28] [16] [16] [16] [16] [16] [15] [15] [15] [24] [24] [22] [13] [13] [13] [7] [8] [8] [17] [9] [9] [32] [32] [32] [32] [32] [32]

SCC: steel column and concrete; N.A.: national average.

Table B.1 Energy data related to office buildings in kWh/m2 per year (primary). Case study no. 47 48 49 50 51 52 53 54 55

Size (m2 ) 4400 4400 1879 1404 1857 1340 1328 1253 1291

Life span

Principal structure

Embodied

Operating

Life cycle

Reference

50 50 40 40 40 40 40 40 40

SRC SRC RC RC RC RC RC RC RC/S

40 73 56 69 69 83 111 83 125

261 376 313 299 236 285 340 444 326

301 453 382 368 306 368 451 528 451

[26] [26] [10] [10] [10] [10] [10] [10] [10]

1600

T. Ramesh et al. / Energy and Buildings 42 (2010) 1592–1600

Table B.1 (Continued ) Case study no. 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

Size (m2 ) 1358 8458 22,982 4620 4620 4620 4620 4620 4620 4620 4620 4620 4620 4620 4620 46,240 34,620 60,000

Life span

Principal structure

Embodied

Operating

Life cycle

Reference

40 40 40 50 50 50 50 50 50 50 50 50 50 50 50 50 50 50

RC/S SRC Steel Wood Steel Concrete Wood Steel Concrete Wood Steel Concrete Wood Steel Concrete Steel Concrete Concrete

139 90 69 60 65 62 59 64 60 60 65 62 59 64 61 33 44 38

333 257 389 292 292 292 266 266 261 489 489 489 454 454 454 249 218 812

472 347 472 352 357 354 325 330 320 550 554 552 513 518 515 282 262 850

[10] [10] [10] [11] [11] [11] [11] [11] [11] [11] [11] [11] [11] [11] [11] [31] [31] [12]

SRC: steel reinforced concrete; RC: reinforced concrete; RC/S: reinforced concrete/steel.

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