2022 Design Studies Thesis Prize: Allison Hyatt’s “Priorities in Building Decarbonization: Accounting for total carbon and the time value of carbon in cost-benefit analyses of residential retrofits”

by Allison Hyatt (MDes ’22) — Recipient of the Design Studies Thesis Prize.

Energy consumption in new construction is decreasing thanks to stricter building codes, but few codes limit emissions from existing buildings, particularly from existing homes. This study investigates the carbon- and cost-effectiveness of three decarbonization strategies in residential retrofits: electrifying buildings, upgrading envelopes, and adding renewable energy. Each strategy is further divided into distinct retrofit interventions to guide homeowners and policymakers in prioritizing energy upgrades. Focusing on pre-1980’s single-family homes in Houston, Los Angeles, and Chicago, the study analyzes homes in cities with distinct climates and grid emission rates. Many studies on building performance upgrades have investigated the operational carbon reductions associated with different retrofit strategies, but embodied carbon, grid decarbonization, and the time value of carbon (TVC) are often omitted. And if those subjects are addressed, they are rarely analyzed all together.

Using energy simulation and life cycle assessment, we quantified the total carbon reduction and life cycle cost associated with each retrofit, ranked the interventions accordingly, and calculated how the rankings would change if electricity grid emission rates decreased or if we accounted for the TVC. Assuming current grid emission rates, envelope retrofits tended to rank better than renewable energy and electrification upgrades in terms of carbon reduction per dollar spent. However, as anticipated emission rates decreased, electrification upgrades improved in rank, while renewable energy upgrades declined. Including the TVC generally caused retrofits with high initial carbon investments to drop in ranking. The results illustrate that considering total carbon and the TVC has important implications on decarbonization recommendations.