CFD Evaluation of Far-UVCand Air Cleaning Technologies in Classrooms without Mechanical Ventilation

Far-UVC systems and air cleaners are effective strategies for controlling airborne pathogen transmission, particularly in densely occupied spaces with insufficient ventilation, such as school classrooms. This study evaluates the disinfection performance and ozone (O₃) formation of different far-UVC systems and air cleaners in a standard-sized classroom using computational fluid dynamics (CFD) simulation. Results show that ceiling-mounted far-UVC systems reduce airborne pathogen exposure by up to 30 % more than upper-room and wall-mounted configurations, based on intake fractions and room-average concentrations. However, they also increase breathing zone O₃ concentrations by approximately 0.1 - 0.6 ppb due to photolytic O₃ production. Among air cleaners evaluated, ceiling-mounted units demonstrated the highest removal efficiency for airborne pathogens. Ceiling-mounted air cleaners reduce breathing zone exposure by up to 20 % more than units placed at central and rear locations, primarily due to improved room air mixing. Results further show that to achieve more than 50 % reduction in exposure, air cleaners require a clean air delivery rate (CADR) of at least 1020 m³∙h^-1, comparable to far-UVC systems operating at a room-average UV fluence rate of 0.5 μW∙cm^-2. The study also reveals the spatial distribution of O₃ and effects of carbon filters on O₃ removal, showing that such filters can lower O₃ exposure by up to 30 %, depending on their placement and efficiency. These findings highlight the need to balance disinfection performance with indoor air quality when implementing UV-based systems in occupied classrooms.