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A Comparative Review of existing data and methodologies for calculating embodied energy and carbon of buildings

Moncaster, A. M. and Song, J-Y. (2012). A Comparative Review of existing data and methodologies for calculating embodied energy and carbon of buildings. International Journal of Sustainable Building Technology and Urban Development, 3(1)

DOI (Digital Object Identifier) Link: https://doi.org/10.1080/2093761X.2012.673915
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Abstract

In the Climate Change Act of 2008 the UK Government pledged to reduce carbon emissions by 80% by 2050. As one step towards this, regulations are being introduced requiring all new buildings to be ‘zero carbon’ by 2019. These are defined as buildings which emit net zero carbon during their operational lifetime. However, in order to meet the 80% target it is necessary to reduce the carbon emitted during the whole life-cycle of buildings, including that emitted during the manufacture of materials and components, and during the processes of construction, refurbishment and demolition. These elements make up the ‘embodied carbon’ of the building. This paper reviews the existing European and UK standards, methodologies, databases and software tools for the estimation of embodied energy and carbon of buildings.

While there is currently no legislation requiring the calculation of embodied energy in buildings, voluntary standards are being developed by the European Committee for Standardisation Technical Committee 350 (CEN/TC 350). Based on BS EN ISO 14040 and BS EN ISO 14044, these define a four stage process-based life cycle assessment method to calculate the embodied energy in construction, with a compulsory ‘product’ stage and optional further stages for ‘construction’, ‘use’ and ‘end of life’. A further voluntary specification for the assessment of the life-cycle greenhouse gas emissions of goods and services, PAS2050, was introduced in the UK in 2008. It too uses a process-based assessment the environmental impact of a building calculated through this method can therefore be seen as the sum of the environmental impacts of the products and processes that have created the building.

Other Life Cycle Assessment methodologies have been developed in this area, including input-output (I-O) and hybrids of process and input-output. The environmental impact of a building defined by an input-output based assessment in contrast to that by a process-based method, is seen as a proportion of the total impacts of the different economic sectors which have created the building. The I-O approach therefore inherently assigns responsibility for environmental impacts to a particular industrial sector. Process-based methods are more specific to the construction product, and more accurate within the limited boundaries used. However they omit the supporting services necessary for construction, including finance, insurance, government and organisational administration and all related office buildings. While I-O assessment overcomes the problems with process assessment by considering a complete system boundary, the assumptions of homogeneity and proportionality in particular limit its use for comparison of impacts from individual products. For the purposes of designing a low embodied energy building, the I-O approach is too broad-brushed and generic to be helpful. The hybrid approaches attempt to overcome the limitations of both the process and the I-O methods.

There is some existing embodied carbon and embodied energy data. However, due to the lack of current regulations and the inherent complexity and diversity of the area, the available data are varied in scope and application. There are three main sources of data:

1. There are several databases which include embodied energy and carbon of standard building materials and components. Some of these are construction sector-specific, while others contain more general product data. These provide data for the ‘cradle to factory gate’ phase of the embodied energy. Manufacturers are also starting to develop their own Environmental Product Declarations (EPDs) which include this data, and several of these are publicly available.
2. Both commercial and in-house software tools have been developed to calculate whole life-cycle embodied energy for buildings and infrastructure projects. This is known as ‘cradle to grave’ assessment.
3. Detailed life cycle assessments of specific buildings, including housing developments and individual dwellings, have also been carried out by academic researchers.

A review of the research literature shows a wide range for the calculated embodied energy. This range in reported figures is due to the use of diverse product data arrived at through different LCA methodologies, different boundaries and often for specific manufacturers, which are therefore non-comparable; different calculation methodologies for the LCA of the whole building; and different building construction and designs. Perhaps most crucially, in spite of the likelihood of an underestimation by current analysis methods, the results show that embodied energy and carbon of buildings can be a very significant absolute value, as well as an increasingly high proportion of the whole life energy and carbon.

The existing databases and much of the literature provide data for the product stage (stage 1) of the process – that is for the embodied energy and carbon in the building materials. However there is less, very limited, data available for composite components such as windows, for services components and for innovative materials and products. There is also a particular shortage of data across the construction sector in the energy used and carbon emitted during transport to site (part of stage 1 in prEN 15804), stages 2 (construction), 3 (in use) and 4 (end of life). The commercial and in-house analysis tools also vary in the databases they use, in their LCA methods and in the boundaries assumed in analysis.

Taking each of the missing calculations in turn, the calculation of the reduced impacts of transport to site of local construction materials will inform and support the European standard BS EN 15643 parts 3 and 4, which considers the social and economic sustainability of construction works.

Some construction projects last for several years and have hundreds of workers on site carrying out energy intensive activities. The accurate prediction of energy use and carbon emissions during standard site operations for stage 2 of the life cycle is therefore a fundamental part of the calculation for whole life embodied energy. Separately the development of off-site construction systems has been heralded as a ‘sustainable’ solution; this can only be verified with the development of an accurate ‘carbon costing’ method for both on-site and off-site construction activities, enabling the accurate comparison of different techniques and materials. Furthermore there is a lack of general data on the carbon and energy savings to be made by site management operations such as reuse of subgrade rather than the import of new materials.

While ongoing maintenance and repair can be considered as part of the operational energy requirements, as suggested by the Strategic Forum for Construction (SFfC) [15], the impacts of major retrofit and refurbishment works form part of stage 3 of the whole life embodied impacts of a building. A clear understanding of the service life of individual components is necessary for these to be calculated.

Finally there is limited data on the energy used by demolition, reuse and recycling processes at the end of life of a building. While these may be less important for building types with a long expected lifetime such as UK housing, it is a key element of short expected lifespans such as stadia, where design approaches are often required to consider deconstruction and reuse of components.

In conclusion, it is essential to measure the whole life embodied energy and carbon of buildings, as well as their operational energy and carbon emissions. The comprehensive development of a robust methodology, and a deeper understanding of its limitations, is a necessary prerequisite for this. Various initiatives to develop and collate data and tools and make them freely available are still in their infancy, and these should be encouraged by the construction industry. It is hoped that the forthcoming standardisation of EPDs should ensure that all manufacturers produce equivalent information for their products within a few years. However the diversity of products used within construction will mean that the LCA of individual buildings will remain complex.

This review will guide the future development of a consistent and transparent database and software tool to calculate the embodied energy and carbon of buildings within the specific context of the UK. The research is being carried out as part of a project led by BLP Insurance, and with the support of the Technology Strategy Board and the Engineering and Physical Sciences Research Council (EPSRC).

In the Climate Change Act of 2008 the UK Government pledged to reduce carbon emissions by 80% by 2050. As one step towards this, regulations are being introduced requiring all new buildings to be ‘zero carbon’ by 2019. These are defined as buildings which emit net zero carbon during their operational lifetime. However, in order to meet the 80% target it is necessary to reduce the carbon emitted during the whole life-cycle of buildings, including that emitted during the processes of construction. These elements make up the ‘embodied carbon’ of the building. While there are no regulations yet in place to restrict embodied carbon, a number of different approaches have been made. There are several existing databases of embodied carbon and embodied energy. Most provide data for the material extraction and manufacturing only, the ‘cradle to factory gate’ phase. In addition to the databases, various software tools have been developed to calculate embodied energy and carbon of individual buildings. A third source of data comes from the research literature, in which individual life cycle analyses of buildings are reported. This paper provides a comprehensive review, comparing and assessing data sources, boundaries and methodologies. The paper concludes that the wide variations in these aspects produce incomparable results. It highlights the areas where existing data is reliable, and where new data and more precise methods are needed. This comprehensive review will guide the future development of a consistent and transparent database and software tool to calculate the embodied energy and carbon of buildings.

Item Type: Journal Item
Academic Unit/School: Faculty of Science, Technology, Engineering and Mathematics (STEM) > Engineering and Innovation
Faculty of Science, Technology, Engineering and Mathematics (STEM)
Item ID: 49695
Depositing User: Alice Moncaster
Date Deposited: 22 Jun 2017 13:50
Last Modified: 10 Jul 2017 10:07
URI: http://oro.open.ac.uk/id/eprint/49695
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