Enhancing upper-room UVGI performance through rotating UV source under poorly-mixed ventilation conditions.

Ultraviolet Germicidal Irradiation (UVGI) is an effective and flexible air disinfection method. However, without air mixing, the disinfection efficacy of an upper-room UVGI system is significantly compromised, as bioaerosols can remain in areas not effectively irradiated. Rotating lamps have been reported as an effective enhancement measure, but the underlying mechanism and applicable conditions remain unclear. In this study, bioaerosol decay by Ultraviolet (UV) inactivation alone under non-mixing conditions in a chamber (5.00 m × 2.25 m × 2.30 m) was simulated to investigate the enhancement effect of rotating lamps. Three lamp placements were examined: X-diagonal, X-middle, and Y-middle, which produced chamber-averaged UVGI levels of 0.78, 0.83, and 0.93 μW/cm², respectively. Two bioaerosol distribution patterns were considered by releasing aerosols from different injection locations. Compared with stationary lamps, rotating lamps increased the germicidal irradiance received by indoor bioaerosols under non-mixing conditions, thereby enhancing disinfection performance. Switching from stationary to rotating mode improved the Equivalent Air Change Rate (EACH) from 2.6/h-13.7/h to 9.8/h-17.5/h, corresponding to disinfection enhancements of 27.7-276.9%. When non-UV loss and thermal-plume-induced air mixing were included, the enhancement in EACH provided by rotating lamps diminished but remained appreciable, highlighting that lamp rotation is a reliable enhancement measure in practice.