Framework for assessing collection-based photocatalytic oxidation systems in HVAC applications for bioaerosol control

Abstract

We use a non-dimensional framework to examine the applicability of photocatalytic oxidation (PCO) to reduce bioaerosol concentration in heating, ventilation, and air conditioning (HVAC) systems. Two non-dimensional parameters: collection efficiency and dimensionless photon flux were used to evaluate the performance of two PCO reactor geometries: 1) honeycomb (HC) and 2) parallel plate (PP) since bioaerosol deposition and photon utilization are prerequisites for effective inactivation in collection based PCO systems. Collection efficiencies of the HC for bioaerosols (0.01–10 μm) were modeled by varying aspect ratios from 25 to 100, air velocities from 0.5 to 2 m/s, and charge numbers from 10 to 10000. The collection efficiencies and the photon fluxes of HC and PP were compared using prior literature studies. The modeling results show that larger bioaerosols (5–10 μm) have a higher collection efficiency than other aerosols for low velocities and longer channels. Larger aspect ratios (channels that are longer for a given diameter) are needed than those found in most commercial HC products, since the effects of gravitational settling and diffusion are inadequate for bioaerosol collection. Furthermore, using ionizers to increase the collection efficiency of PCO systems proved ineffective. The efficiency only increased 2 to 5 times for 0.01–1 μm bioaerosols for charge numbers on the order of 1000. These charge numbers may be impractical to obtain for this size range. PP requires longer channel lengths than HC to achieve the same collection efficiencies. However, the PP configuration has better photon utilization characteristics than HC.