A review on Life Cycle Assessment, Life Cycle Energy ...

Applied Energy 143 (2015) 395–413

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Applied Energy journal homepage: www.elsevier.com/locate/apenergy

Review

A review on Life Cycle Assessment, Life Cycle Energy Assessment and Life Cycle Carbon Emissions Assessment on buildings C.K. Chau ⇑, T.M. Leung, W.Y. Ng Department of Building Services Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong Special Administrative Region

h i g h l i g h t s Three streams of life cycle studies, namely LCA, LCEA and LCCO2A, were compared. Previous findings from the three streams were reviewed. Cases led to discrepancies of results arising from different types of life cycle studies were discussed. Limitations in using life cycle studies as decision tools for building design were identified.

a r t i c l e

i n f o

Article history: Received 20 May 2014 Received in revised form 17 November 2014 Accepted 7 January 2015

Keywords: Life Cycle Assessment Buildings Decision making

a b s t r a c t This paper provides a review on three streams of life cycle studies that have been frequently applied to evaluate the environmental impacts of building construction with a major focus on whether they can be used for decision making. The three streams are Life Cycle Assessment (LCA), Life Cycle Energy Assessment (LCEA) and Life Cycle Carbon Emissions Assessment (LCCO2A). They were compared against their evaluation objectives, methodologies, and findings. Although they share similar objectives in evaluating the environmental impacts over the life cycle of building construction, they show some differences in the major focuses of evaluation and methodologies employed. Generally, it has been revealed that quite consistent results can be derived from the three streams with regard to the relative contribution of different phases of life cycle. However, discrepancies occur among the findings obtained from the three streams when different compositions of fuel mixes are used in power generation, or when the overall impacts are not contributed mostly by greenhouse gases emissions. The use of different functional units in different studies also makes it difficult to compare results with benchmarks or results from previous studies. Besides, there are drawbacks in boundary scoping, methodology framework, data inventory and practices which impair their usefulness as a decision making support tool for sustainable building designs. Ó 2015 Elsevier Ltd. All rights reserved.

Contents 1. 2.

3. 4. 5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scope of the review – Life Cycle Assessment, Life Cycle Energy Assessment, Life Cycle Carbon Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1. Life Cycle Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2. Life Cycle Energy Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1. Methodologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3. Life Cycle Carbon Emission Assessment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1. Fossil carbon emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2. Process carbon emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3. Carbon emissions due to demolition/disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Extended study boundaries to include land footprint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Functional units used for comparing the results from LCA, LCCO2, and LCEA studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summarized findings from previous studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

⇑ Corresponding author. Tel.: +852 2766 7780; fax: +852 2765 7198. E-mail address: [email protected] (C.K. Chau). http://dx.doi.org/10.1016/j.apenergy.2015.01.023 0306-2619/Ó 2015 Elsevier Ltd. All rights reserved.

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6. 7. 8.

9.

C.K. Chau et al. / Applied Energy 143 (2015) 395–413

Other approaches for comparing life cycle study results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discrepancies among different streams of studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Limitations of LCA, LCEA and LCCO2A as decision making support tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1. Boundary scoping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2. Methodology framework. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3. Data inventories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4. Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction The growing environmental awareness has aroused great attention from many governments over the world. Inevitably buildings become a major target for environmental improvement as building sector accounted for nearly 40% of the world’s energy consumption, 30% of raw material use, 25% of solid waste, 25% of water use, 12% of land use, and 33% of the related global greenhouse gas (GHG) emissions [1,2]. Many attempts have been initiated to evaluate the environmental impacts of buildings, their constituent materials, components and systems, and to explore any opportunities to reduce their environmental impacts. Broadly speaking, three major streams of life cycle studies can be classified according to the focus of evaluation of the environmental impacts of buildings. The first stream of studies can be grouped under Life Cycle Assessment (LCA) which focuses on evaluating the total environmental impacts of buildings over their entire life cycles. To be more specific, LCA is an objective process which aims to evaluate the environmental burdens associated with a product, process or an activity by identifying and quantifying the energy and material uses and releases to the environment, and also aims to evaluate and implement opportunities to affect environmental improvements. The assessment includes the entire life cycle of the product, process or activity, encompassing extracting and processing materials; manufacturing, transportation and distribution; use, reuse, maintenance; recycling and final disposal. The International Organization for Standardization (ISO) produced a series of LCA Standards [3–6] focusing on the technical and organizational aspects of an LCA project. The major focus of the second stream of studies grouped under the Life Cycle Energy Assessment (LCEA) is to evaluate the energy use as a resources input to a building over its total life cycle. As LCEA does not take quality of primary energy into account in the assessment, it may not be able to convey a realistic picture on the ultimate environmental impacts. Primary energy generated from fossil fuels produces remarkably higher carbon emissions than those generated from renewable energy like wind and solar. In order to overcome this drawback, a method called Life Cycle Exergy Assessment was developed by De Meester et al. [7] to take into account the difference in quality of energy. Exergy is defined as the amount of useful work extractable from a generic system when it is brought to with its reference environment through a series of reversible processes in which the system can only interact with such environment [8,9]. However, this method has not been frequently used due to its complexity. The third stream of studies grouped under Life Cycle Carbon Emissions Assessment (LCCO2A) focuses on evaluating the CO2 emissions as an output over the whole life cycle of a building. This was possibly conducted in response to the imminently threatening global warming problem caused by greenhouse gas emissions. The Kyoto protocol agreement has set binding targets for 37 industrialized countries and the European community to reduce the green-

405 406 407 407 408 408 408 408 409 409

house gas emissions by an average of 5%, back to 1990 levels within the years of 2008–2012. The launching of the Kyoto Protocol has led to many studies which aimed to evaluate the CO2 emissions from buildings. Kyoto Protocol covers six different types of greenhouse gases and provides CO2-equivalent emission values for individual greenhouse gases. Life cycle carbon emissions consider all the carbon-equivalent emission outputs from a building over different phases of its life cycle. Given a vast amount of studies have been conducted under three different focuses, it is not clear whether their findings are comparable with each other and are useful to inform decision making during building design and assessment. Conceivably, the flexibility of assessment framework, methodology differences, discrepancies in boundary scope or boundary of assessment, data uncertainties, differences in locality and ultimate objectives make it extremely difficult to make a meaningful comparison of their results and thus draw valuable conclusions to inform decision making throughout the life cycle of buildings. Therefore, this review has three major objectives, it attempts (i) to identify the methodology details for estimating the environmental impacts under the three different streams; (ii) to summarize the important findings arising from three streams of studies which can be used to assist decision making in achieving a sustainable or environmental building design, operation and management; and also (iii) to identify the limitations and drawbacks associated with using LCA as a decision-making tool.

2. Scope of the review – Life Cycle Assessment, Life Cycle Energy Assessment, Life Cycle Carbon Assessment Fig. 1 shows the conceptual diagram of LCA. It can be seen that the basic concept of LCA is to evaluate the environmental impacts of a product over different life cycle stages, i.e. ‘‘from cradle to grave’’. LCA evaluates all the resources inputs, including energy, water and materials, and environmental loadings including CO2 emissions, solid wastes and liquid wastes of a product. However, the focuses of the other two variants are different with Life Cycle Energy Assessment (LCEA) being focused on resources input and Life Cycle Carbon Emissions Assessment (LCCO2A) being focused on the CO2 equivalent emissions. 2.1. Life Cycle Assessment Goal and scope definition, Inventory Analysis, Impact Assessment and Interpretation are the four major phases within a LCA (see Fig. 2). The first phase (Goal and Scope) define purpose, objectives, functional and system boundaries. The second phase (Inventory Analysis) consists of collecting all data relating to inputs, processes, emissions, etc. of the whole life cycle. Within the third phase (Impact Assessment), environmental impacts and input resources are quantified based on the inventory analysis. The last phase (Interpretation) is to interpret the results calculated from


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Fig. 1. Basic concepts of LCA, LCEA and LCCO2A.

Fig. 2. Different phases for LCA [6].

Fig. 3. Mandatory and optional elements within the impact assessment phase.

the Impact Assessment phase and to recommend improvement measures as appropriate. As the major focus of this paper is to examine how the methodology details of computing the results, only the Impact Assessment phase will be discussed in details. Fig. 3 shows the mandatory and optional elements within the Impact Assessment phase. This phase, which evaluates the potential environmental impacts and estimates the resources used in the modeled system, consists of three mandatory elements: selection of impact categories, assignment of LCI (Life Cycle Inventory) results (classification), modeling category indicators (characterization) [6,10]. Classification of the LCI results involves assigning the emissions, wastes and resources used to the chosen impact categories. However, it is worth noting that different methods for LCI compilation methods can result in different inventory value even for the same material [11]. The differences or uncertainties in inventory value can lead to difference in study results and conclusions [12,13]. The converted LCI results are aggregated into an indicator result, which is the final result of the mandatory part of an LCA. Broadly speaking, two characterization approaches can be applied to quantify environmental

impacts – the problem-oriented (mid-point) and damage-oriented (endpoints) approach [14]. Under the mid-point approach, use values at the beginning or middle of the environmental mechanism. Impacts are classified on environmental themes such as global warming potential, acidification potential, and ozone depletion potential. This type of method generates a more complete picture of ecological impacts, but requires good knowledge of LCA to interpret the results. In contrast, under the end-point approach, impacts are grouped into general issues of concern such as human health, natural environment and resources, which eventually can be calculated into a single score – which is easier to understand but tend to be less transparent [15,16]. On the contrary, fewer modeling assumptions are needed for mid-point approach [17]. It can also reflect a higher level of societal consensus, and provide more comprehensive results than model coverage for end-point approach [18]. Normalization, grouping, weighting and additional data quality analysis are optional steps [10]. Normalization is the calculation of the magnitude of category indicator results relative to some reference information, for example the average environmental impact of a European citizen in one year [19,20]. Although normalization can help to understand the relative importance of different impact categories in LCA studies, uncertainties in emission data and characterization factors can lead to uncertainties in normalization results [21,22]. Grouping is also a step of impact assessment in which impact categories are aggregated into one or more sets. Weighting is the process of converting indicator results of different impact categories into more global issues of concern or as a single score by using numerical factors based on value-choices, which may be based on policy targets, monetization or panel weighting [19,23,24]. The choice of weighting schemes will significantly affect the conclusions. For example, the weighting schemes significantly affect the conclusions on which substances were most damaging to human and ecosystem health in LCA studies [25]. Hitherto, there is no consensus on the approach or a satisfactory method to guide assignment of weightings [26,27], or objective approach to perform weighting of impact categories [28]. As a result, it is not likely to yield a universal weighting set for the world [29]. Broadly speaking, LCA intends to consider all the environmental impacts, which include both resources input, emissions and wastes output of a building during different phases of the life cycle. It can be represented mathematically by:

I ¼ IExtraction þ IManufacture þ IOnsite þ IOperation þ IDemolition þ IRecycling þ IDisposal

ð1Þ

where I represents the life cycle environmental impact, and Ij represents the environmental impacts of jth building phase. 2.2. Life Cycle Energy Assessment Life Cycle Energy Assessment (LCEA) is a simplified version of LCA which focuses only on the evaluation of energy inputs for

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different phases of the life cycle. Mathematically, the terms ‘I’s in Eq. (1) are replaced by ‘E’s to produce Eq. (2) as shown in the following:

E ¼ EExtraction þ EManufacture þ EOnsite þ EOperation þ EDemolition þ ERecycling þ EDisposal

ð2Þ

where E represents the total energy consumed during the whole life cycle of a building, and Ej represents the energy consumed during jth building phase. LCEA analysis can be performed using either primary or secondary energy (or delivered energy). So it is important to clearly specify the form of energy in focus [30] for facilitating later comparison. Primary energy is the energy extracted from nature (e.g. coal) while secondary energy is the actual energy consumed (e.g. electricity). 2.2.1. Methodologies 2.2.1.1. Embodied energy. Quite often, the first three energy components shown in Eq. (2) are grouped together as embodied energy during the evaluation of energy impacts. Embodied energy is the energy utilized during manufacturing phase of a material. Embodied energy of a building is the energy content of all the materials used in the building and technical installations, and energy consumed at the time of erection/construction and renovation of the building. One of the major objectives of carrying out embodied energy analysis for building construction is to compute the amount of initial and/or recurring energy embodied within building materials and thus to compare the total embodied energy content for different building materials, components, elements and designs. Initial and recurring embodied energy are the two major components of embodied energy. Initial embodied energy is the sum of the energy required for extraction and manufacture of a material together with the energy required for transportation of a material used for the initial building construction. The recurring embodied energy in buildings represents the sum total of the energy embodied in the material use due to maintenance, repair, restoration, refurbishment or replacement during the service life of the building. To estimate the embodied energy content for a building or building design, a vast number of studies have adopted a ‘bottom-up’ technique, sometimes called process-based approach [31–34]. This bottom-up technique relies heavily on the embodied energy databases for construction materials as well as drawings, specifications and/or data from the actual buildings. This technique

Table 1 Embodied energy intensities for different types of building materials.

a

Type of building material

Embodied energy intensitiesa (MJ/kg)

Aluminum Bitumen and asphalt Bricks and blocks Concrete Galvanized steel Glass Stone, gravel and aggregate Purified fly ash (PFA) Paint Plaster, render and screed Plastic, rubber and polymer Plywood Precast concrete element Reinforcing bar and structural steel Stainless steel Thermal and acoustic insulation Ceramic and tile

155.0–227.0 2.6–44.1 0.9–4.6 0.50–1.6 35.8–39 15.0–18.0 0.3–1.0