Functional unit choice in space conditioning life cycle assessment: Review and recommendations

Space cooling through air conditioners and electric fans, which already accounts for 10% of global energy consumption, is expected to increase as temperatures rise under climate change and as air conditioning becomes more accessible. The life cycle greenhouse gas (GHG) emissions of this energy-intensive activity are concerning in their potential to create a positive feedback loop for climate change. There is thus a growing need for life cycle assessments (LCAs) on space conditioning systems to be designed to facilitate comparison for climate change mitigation efforts, with similar standardization as has developed in the electricity LCA field, in which the vast majority of LCAs conform to a specific system boundary and functional unit. We present the first study that assesses the uniformity and identifies discrepancies in methodology between space conditioning LCAs. We analyzed the goals, system boundaries, and chosen functional units of 33 peer-reviewed LCAs on single-structure space conditioning systems published between 2000 and 2020. The findings indicate that the stated goals of these studies were mostly aligned, but there was a lack of consensus on functional unit definition, with multiple different types of units used across studies. This lack of consistency in functional units complicates and may even prevent the comparison of life cycle environmental impacts of technologies and methods of space conditioning, which is necessary to make decisions towards increased sustainability in space conditioning. Consequently, we recommend that a standard functional unit for space conditioning systems be defined as 1 MJ of heat added to or removed from conditioned space to ensure future studies are comparable. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).