Effective mitigation of cross-contamination in classroom conditioned by intermittent air jet cooling with use of portable air cleaners

Abstract

This work investigated the effect of using portable air cleaners (PACs) in a classroom ventilated by an intermittent air jet system (IAJS) for reducing the risk of cross-contamination. The classroom had two student groups separated by an aisle where the PACs were placed and operated continuously. A 3-D computational fluid dynamic (CFD) model was developed and validated experimentally to predict the complex transient flow field. The spread of contaminants from one group to another (scenario 1) and from one row to another within one group (scenario 2) was evaluated in terms of reaching concentration levels similar to the case implementing the 2-m distancing between students. Two indicators were used; the intake fraction index (iF) and an exposure reduction index (ER) that compared the proposed system to a reference case when the PAC is not used (“No-PAC”).It was found that a PAC flowrate of 350 m3/h was able to fulfill the aforementioned criteria for typical IAJS flow rate of 294 l/s and a period of 4.5 min. The proposed system reduced the exposure by 67% for the students sitting in the same group of the infected student and by 87% for the students sitting in the neighboring group compared to the “No-PAC” case. The maximum exposure level of IJAS-PAC system was lower than that obtained with seating distance of 2 m. Furthermore, it was found that operating the PAC at 350 m3/h resulted in 3% increase of the energy compared to operation of the IAJS alone.