The Evolving Carbon Balance of High-Performance Buildings

Abstract

Highly operationally-efficient buildings typically require significant embodied flows to guarantee low energy consumption. To highlight this tension, an operational energy simulation of a prototypical mid-rise apartment was equipped with all-electric heating, ventilation, and air conditioning (HVAC) systems. The building was then upgraded from the comparatively under-performing ASHRAE 90.1-2004 standard to the higher-performing PHIUS 2021 certification, while the grid that supplied the building was simulated with aggressive, moderate, and business-as-usual emissions intensity scenarios. To assess life-cycle impacts, changes to the building’s structure, foundation, enclosure, and mechanical equipment were evaluated using life-cycle assessment (LCA), and refrigerant impacts were calculated separately using a range of 100-year global warming potentials (GWP) and leakage assumptions. In the end, the ranking of optimal high-performance building strategies is sensitive to different combinations of grid, refrigerant, and carbon accounting assumptions. As an example, the results suggest that, given a rapidly decarbonized grid, operationally-inefficient buildings with low-embodied-carbon materials will emit less life-cycle carbon than certain low-energy buildings with standard materials.