The building sector is one of the most relevant sectors in terms of environmental impact. Different functional units (FUs) can be used in life cycle assessment (LCA) studies for a variety of purposes. This paper aimed to present different FUs used in the LCA of buildings and evaluate the influence of FU choice and setting in comparative studies.
As an example, we compared the “cradle to grave” environmental performance of four typical Brazilian residential buildings with different construction typologies, i.e., multi-dwelling and single dwelling, each with high and basic standards. We chose three types of FU for comparison: a dwelling with defined lifetime and occupancy parameters, an area of 1 m2 of dwelling over a year period, and the accommodation of an occupant person of the dwelling over a day.
Results and discussion
The FU choice was found to bias the results considerably. As expected, the largest global warming indicator (GWi) values per dwelling unit and occupant were identified for the high standard dwellings. However, when measured per square meter, lower standard dwellings presented the largest GWi values. This was caused by the greater concentration of people per square meter in smaller area dwellings, resulting in larger water and energy consumption per square meter. The sensitivity analysis of FU variables such as lifetime and occupancy showed the GWi contribution of the infrastructure more relevant compared with the operation in high and basic standard dwellings. The definition of lifetime and occupancy parameters is key to avoid bias and to reduce uncertainty of the results when performing a comparison of dwelling environmental performances.
This paper highlights the need for adequate choice and setting of FU to support intended decision-making in LCA studies of the building sector. The use of at least two FUs presented a broader picture of building performance, helping to guide effective environmental optimization efforts from different approaches and levels of analysis. Information regarding space, time, and service dimensions should be either included in the FU setting or provided in the building LCA study to allow adjustment of the results for subsequent comparison.
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One of the authors (HS) wishes to thank the UNESCO Chair in Life Cycle and Climate Change (ESCI-UPF) for hosting him during the 2017 academic year, when part of this research was carried out, as well as the “Inova Talentos” RHAE Trainee Program (Euvaldo Lodi Institute) for the grant. The authors are responsible for the choice and presentation of information contained in this paper as well as for the opinions expressed therein, which are not necessarily those of UNESCO and do not commit this Organization. We thank the Coordination for the Improvement of Higher Education Personnel (CAPES) and the Federal University of Mato Grosso do Sul (UFMS), especially the Environmental Technologies Postgraduate Program (PGTA) at UFMS. We also thank the anonymous reviewers for their comments and suggestions.
This study was financed in part by the Coordination for the Improvement of Higher Education Personnel (CAPES) - Finance Code 001 (grant process number: 88887.466854/2019-00; 88882.453459/2019-01; 1572275) and the National Council for Scientific and Technological Development (CNPq). The funding sources had no involvement with the research.
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de Simone Souza, H.H., de Abreu Evangelista, P.P., Medeiros, D.L. et al. Functional unit influence on building life cycle assessment. Int J Life Cycle Assess (2021). https://doi.org/10.1007/s11367-020-01854-1
- Environmental performance
- Life cycle assessment
- Carbon footprint
- Construction sector
- Functional unit