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CFD Analysis of Room Air Distribution: Effect On Upper-Room UVGI System Performance

ASHRAE Journal, Vol. 65, no. 11, November 2023


Kishor Khankari and William Bahnfleth


The UV-C dose, which is the product of UV-C fluence and the residence time of microbes in the UV-C field, is a key factor in determining the efficacy of upper-room UVGI systems. Indoor airflow patterns carry 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 using CFD simulations systematically evaluated the impact of locations and number of supply diffusers and return grilles (HVAC layout) on the airflow patterns in a representative office space with cubicles. The analyses indicate that the addition of UVGI reduces the average probability of infection at the breathing zone of occupants by 39% and the zone of the probability of infection, Spread Index (SI)10, by 79%.

The room airflow patterns resulting from the variations in the number and locations of four-way diffusers and returns show 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, the aerodynamic containment layout with the distributed supply and distributed returns may 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 optimize HVAC layout and strategic placement of UV-C fixtures to reduce the probability of infection in indoor spaces.

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    About the author

    Dr. Kishor Khankari

    ASHRAE Fellow, ASHRAE Distinguished Lecturer

    Dr Kishor Khankari is the founder of AnSight LLC. As a specialist in Computational Fluid Dynamics (CFD), his passion for solving engineering problems and providing sound scientific solutions has led to innovations and optimized designs in the industry.

    A noted expert in his field, he has a Ph.D. from the University of Minnesota and has published in several technical journals and trade magazines. As a well sought-after speaker Dr. Khankari makes regular presentations in various technical conferences and professional meetings worldwide.

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