CFD Analysis of Fixture Output Impact on Upper Room Germicidal Ultraviolet Light System Performance
ASHRAE Journal, Vol. 65, no. 6, June 2023
Kishor Khankari and William Bahnfleth
The wavelength band of 200-280 nm of UV-C radiation can destroy the reproduction ability of microorganisms including viruses, bacteria, and fungi. The UV-C dose, which is the product of the UV-C irradiance and the residence time of the microbes in the UV-C field, is the most crucial factor that affects the efficacy of upper-room UVGI systems. Several factors related to the UV fixtures, HVAC layout, and the resulting airflow flow patterns can affect the performance of upper-room UVGI applications. This study systematically evaluates the impact of UV-C intensities on the effectiveness of an upper room UVGI system using the Computational Fluid Dynamics (CFD) analyses.
It demonstrates that with the addition of a small UV-C output (about 5 mW/m3) the average probability of infection due to airborne pathogens can reduce by 27 percent and limit the spread of infection probability only in the vicinity of an infected individual. Increasing the UV-C output shows a further reduction in the infection probability with a diminishing impact on the survival fraction of the pathogens. Increasing the UV-C input by 54 percent (from 13 to 20 mW/m3 ), the average survival fraction of pathogens reduce by about 20 percent (from 0.56 to 0.45). This study also indicates that increasing the UV-C output can increase the average irradiance in the occupied zone and potentially reach the unsafe limit.
This present study was performed with the same HVAC configuration with a single 4-way supply diffuser and a single return grille which could have limited the residence time of airborne pathogens in the upper room zone of high UV-C intensity. A further investigation is necessary to evaluate the impact of airflow patterns on the performance of UVGI systems. These studies demonstrate that CFD analyses can help optimize the performance of UVGI systems and minimize the probability of infection in indoor spaces.
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