High-Intensity UVC Irradiation of Air Handling Units for Enhanced Energy Efficiency Under Varying Biofouling Risks

Ultraviolet germicidal irradiation (UVGI) is widely used to inactivate microorganisms on air-handling unit (AHU) cooling coils; however, its impact on energy performance under real-world operating conditions remains insufficiently quantified, particularly with respect to initial coil biofouling severity. The thermal performance response of two operational AHUs with similar capacities but distinct levels of coil biofouling was evaluated under high-intensity UVC irradiation. Field measurements were conducted in a healthcare facility located in a cool-humid climate during the cooling season. Baseline operation was monitored for eight weeks, followed by seven weeks of continuous high-intensity UVC operation. The installed UVC systems delivered surface irradiation intensities exceeding 1000 μW/cm2. Thermal performance was assessed using enthalpy-based heat-transfer conductance (UA) calculated at reference conditions, while fan power was continuously monitored. Results indicate that high-intensity UVC irradiation significantly improved coil thermal performance in both AHUs. Mean UA increased by 14.7% for the moderately fouled coil and by 18.4% for the heavily fouled coil, indicating greater absolute performance recovery at higher initial biofouling levels. In contrast, no measurable reduction in fan energy consumption was observed due to residual non-biological particulate accumulation caused by upstream filter bypass. Overall, the findings demonstrate that UVC irradiation is effective in restoring cooling coil heat-transfer performance across varying fouling conditions, while highlighting the importance of filtration integrity in realizing airflow-related energy savings. The results provide field-based evidence to support more accurate estimation of UVC-related energy benefits in building applications.