Localized air-conditioning with upper-room UVGI to reduce airborne bacteria cross-infection
Localized airflow can result in both temperature and pollutant concentration segregations with limited mixing between adjacent environmental zones. However, when the bacteria source is within the environmental zone, it becomes important to look for effective methods to disinfect the localized air and prevent cross-infection among occupants in the same zone. This work investigates the effectiveness of upper-room ultraviolet germicidal irradiation (UVGI) in reducing airborne bacteria transmission within a zone conditioned by localized ceiling-mounted airconditioning system that recirculates return air. A computational fluid dynamics (CFD) model was developed to simulate the transport and inactivation by UV of Serratia marcescens, an extremely UV-susceptible microorganism. The CFD–UV model was validated using measurements of airflow, temperature, and UV irradiance. Numerous CFD simulations were performed for a case study to determine the maximal fraction of return air that can be recirculated for energy conservation without violating the indoor air quality standards for CO2 and bacteria concentrations. Results revealed that a maximum of 23% return air can be tolerated when minimal UV output of 15 W is delivered to the space. The use of the optimal setting reduced the energy consumption of the system by 15% compared to 100% fresh air case without UVGI.