UC Berkeley

The environmental impacts of mechanical, electrical and plumbing (MEP) systems have been largely overlooked and are commonly excluded from building-scale life cycle assessments (LCAs). Understanding the impacts and reduction potential of these systems is crucial for decarbonizing retrofits and new buildings. Therefore, we have conducted a critical review of LCA studies on MEP systems in buildings, selected using a systematic method, to identify: 1) estimates for upfront embodied [A1-A5] and replacement [B4] carbon impacts; 2) LCA reporting fundamentals needed to ensure transparency and interpretability of results; 3) future research directions. Since 2016, 54 studies presented sufficient information to investigate presented methodologies and LCA results of MEP systems. The review reinforces the need to report environmental impacts by individual life cycle stages and building or system elements to interpret influencing factors and enable further utility of results. Two studies did not report the impact assessment method nor background dataset used for the assessment rendering their results incomparable with others and are excluded from analysis. Based on the median (and mean) of the reviewed studies, estimates for A1-A3 and A1-A5 of the MEP systems are 40 (49) and 49 (61) kgCO2e/m², respectively. Additionally, based on reviewed studies, the systems will be replaced at least twice throughout a 60-year reference study period leading to approximately 100 kgCO2e/m² for B4. These values almost certainly underestimate actual impacts due to the incomplete physical scopes spanned by the studies. Studies with more complete scopes generally reported higher values. The variability in scopes covered, reporting practices, and values reported, and the relatively small number of studies found, highlight the need for further investigation and improvement. Ten key research needs are identified, including the impact reduction potential of MEP systems and the influence of system layout and typology on the reported impacts. Additionally, future research should develop system specific benchmarks and reduction strategies while moving away from purely descriptive studies that report environmental impacts using single-point values.