Numerical Investigation of Upper‐Room UVGI Disinfection Efficacy in an Environmental Chamber with a Ceiling Fan

This study investigated the disinfection efficacy of the upper‐room ultraviolet germicidal irradiation ( UR ‐ UVGI ) system with ceiling fans. The investigation used the steady‐state computational fluid dynamics ( CFD ) simulations to solve the rotation of ceiling fan with a rotating reference frame. Two ambient air exchange rates, 2 and 6 air changes per hour (ACH), and four downward fan rotational speeds, 0, 80, 150 and 235 rpm were considered. In addition, the passive scalar concentration simulations incorporated ultraviolet ( UV ) dose by two methods: one based on the total exposure time and average UV fluence rate, and another based on SVE 3* (New Scale for Ventilation Efficiency 3), originally defined to evaluate the mean age of the air from an air supply opening. Overall, the CFD results enabled the evaluation of UR ‐ UVGI disinfection efficacy using different indices, including the fraction of remaining microorganisms, equivalent air exchange rate, UR ‐ UVGI effectiveness and tuberculosis infection probability by the Wells–Riley equation. The results indicated that air exchange rate was the decisive factor for determining UR ‐ UVGI performance in disinfecting indoor air. Using a ceiling fan could also improve the performance in general. Furthermore, the results clarified the mechanism for the ceiling fan to influence UR ‐ UVGI disinfection efficacy.