Computational Fluid Dynamics (CFD) Analysis of HVAC Layout on the Performance of Ultraviolet Germicidal (UV-C) to Control the Probability of Infection Due to Transmission of Airborne Pathogens
ASHRAE Annual Conference Toronto, Canada, 2022
Kishor Khankari and William Bahnfleth
The UV-C dose which is a product of UV-C irradiance and the residence time of microbes in the UV-C field is one of the important factors that affect the efficacy of upper-room UVGI systems. The indoor airflow patterns help carry the infectious aerosols from the breathing zone of occupants into the upper room UV-C radiation field. The number and locations of air supply diffusers and return are among several factors that affect the indoor airflow patterns and the resulting flow path of airborne aerosols in indoor spaces. This study with the help of CFD simulations systematically evaluates the impact of locations and number of supply diffusers and return grilles (HVAC layout) on the airflow patterns in a typical office space with cubicles.
The analyses indicate that addition of upper room UV-C radiation reduces the average probability of infection at the breathing plane of occupants by 39 percent and the zone of the probability of infection (Spread Index (SI)10) by 79 percent. The room airflow patterns resulting from the variations in the number and locations of 4-way diffusers and returns show a little impact on the overall effectiveness of UV-C. However, these analyses show subtle differences in the nature of airflow patterns and their impact on UV-C effectiveness. It indicates that a formation of stagnant zones with recirculating airflow patterns in the vicinity of an infected individual and under the high UV-C intensity zone can be most effective in reducing the zone of a high probability of infection. Since a location of an infected individual is not known a priori, the aerodynamic containment layout with the distributed supply and distributed returns can be the most promising design layout to attain both ventilation effectiveness as well as UV-C effectiveness. These studies demonstrate that CFD analyses if performed with adequate expertise, can help in optimizing HVAC layout and strategic placement of UV-C fixtures to reduce the probability of infection in indoor spaces.