Center for the Built Environment

The use of life cycle assessment (LCA) to evaluate the environmental impacts of buildings has largely ignored the embodied impacts of mechanical, electrical and plumbing (MEP) systems that rely on significant proportions of metals and contain a multitude of complex components. A better understanding of the environmental impacts of MEP systems is needed to achieve a net-zero carbon future. The study serves as an initial step in developing benchmarks and impact reduction strategies for MEP systems. It considers the material substitution from standard practice to PEX pipe throughout (Radiant: PEX in slab, copper and steel elsewhere; VAV: steel and copper) and for both typical single-riser pipe layout and multi-riser layout for both HVAC system types. When assessed for a four-story office building, the A1-A4 GWP100 impacts for the pipe in the standard layout for the radiant and VAV systems are 1.1 kgCO2e/m2 and 0.8 kgCO2e/m2, respectively. Implementing a like-for-like material substitution to PEX with a single-riser layout led to 41% reduction for the pipe impacts in the radiant system and a 64% reduction for the VAV system. Employing a multi-riser layout with standard materials reduced the pipe impacts by 30% for the radiant system and 66% for the VAV system. The embodied impacts for the ductwork in the radiant and VAV systems in this building were 5.8 and 7.7 kgCO2e/m2, respectively. The use of PEX and/or a multi-riser layout represent relatively easy changes that lead to measurable GWP100 reductions for MEP systems.