Interplay of ventilation and filtration: Differential analysis of cost function combining energy use and indoor exposure to PM2.5 and ozone

Abstract

This study investigated the effects of ventilation and filtration on building energy consumption and exposure to PM2.5 and ozone in U.S. offices. Energy use and indoor PM2.5 and ozone concentrations were predicted in 15 locations for a typical office with either a constant air volume (CAV) or variable air volume (VAV) mechanical system. For each office and location, annual simulations were performed with combinations of fixed ventilation ranging 20–100 CFM/occ (9.4–47 L/s/occ) and filters ranging in efficiency corresponding to MERV 8–16 and HEPA. Energy use was monetized using historic costs, and PM2.5 and ozone exposures were monetized using incidence valuations and concentration-response functions. These outcomes were combined into a singular cost function, which was characterized empirically as a function of ventilation and filtration. Various partial derivatives of the cost function were calculated to observe trends and interdependencies. Exposure cost was 5.5 times higher than energy cost for cases with common filters (MERV 8–11). Even with high filter efficiency, exposure cost was greater than energy cost on average. Filtration had a much stronger effect than ventilation on indoor contaminant levels and the total cost function. The differential analysis revealed that ventilation and filtration complement each other: Implementing a high efficiency filter can mitigate negative effects of ventilation, and higher ventilation rates can increase the efficacy of filtration (e.g. increasing ventilation from 20 to 60 CFM/occ increased filtration efficacy by 1.2–1.5 for VAV offices).