Ozone interactions with HVAC filters

by 1980- Zhao, Ping

Residential and commercial HVAC filters that have been loaded with particles during operation in the field can remove ozone from intake or re-circulated air. However, knowledge of the relative importance of HVAC filters as a removal mechanism for ozone in residential and commercial buildings is incomplete. We measured the ozone removal efficiencies of clean (unused) fiberglass, clean synthetic filters, and field-loaded residential and commercial filters in a controlled laboratory setting. For most filters, the ozone removal efficiency declined rapidly but converged to a non-zero (steady-state) value. This steady-state ozone removal efficiency varied from 0% to 9% for clean filters. The mean steady-state ozone removal efficiencies for loaded residential and commercial filters were 10% and 41%, respectively. Repeated exposure of filters to ozone following a 24-hour period of no exposure led to a regeneration of ozone removal efficiency. Based on a theoretical scaling analysis of mechanisms that are involved in the ozone removal process, we speculate that the steady-state ozone removal efficiency is limited by reactant diffusion out of particles, and that re-generation is due to internal diffusion of reactive species to sites available to ozone for reaction. Finally, by applying our results to a screening model for typical residential and commercial buildings, HVAC filters were estimated to contribute 22% and 95%, respectively, of total ozone removal in HVAC systems. 143