An experimental study and model analysis were performed to assess the effectiveness of commercially available in-room air cleaners in minimizing the impact of a hazardous aerosol released in a building. Two air cleaners were evaluated: a HEPA-type air cleaner and an electrostatic precipitator.

The effectiveness of a stand-alone room air cleaner depends on three principal characteristics: single-pass filtration efficiency, air flow rate, and the airflow pattern that the cleaner induces in the room. Accordingly, the air cleaners were first experimentally evaluated for their single-pass filtration efficiencies, which were determined for aerosol particle ranging in diameter from 0.03 to 10 µm under different airflow rates. A series of test chamber experiments was then performed in which concentration decay rates were determined from continuously monitoring aerosol concentration at a particular location in the room. The degree of variability in the cumulative exposure dosages occurring in the room was considered using filter samples taken at several different locations.

Additionally, model analyses were performed using computational fluid dynamics (CFD) calculations, which suggested that CFD methodology can offer a viable alternative to field testing. The model was reasonably effective at predicting trends in the relative variability of contaminant concentration in the test chamber, but overestimated the concentration decay rate. Challenges associated with performing CFD calculations for flow configurations encountered under such conditions are discussed.

As a general finding of this work, room air cleaners can offer a noticeable threat reduction potential by reducing both the peak concentration of aerosolized pollutant in the room and the overall level of occupants’ exposure. Consequently, the room air cleaner can increase the time it takes to reach a particular level of threshold concentration in the room, or even prevent it. However, the extent of the threat reduction potential may depend greatly on many factors, including those related to the pathogen aerosolization scenario and room configuration.

Units: I-P