Annual simulation of in-duct ultraviolet germicidal irradiation system performance

In-duct ultraviolet germicidal irradiation (UVGI) systems treat moving air streams in heating, ventilation, and air-conditioning (HVAC) systems to inactivate airborne microorganisms. UVGI system performance depends on air temperature, velocity, cumulative operating time, variations in exposure time and other factors. Annual simulations of UVGI efficiency and space concentration that accounted for these effects were performed for a hypothetical building served by a VAV system.  The UVGI device was assumed to be located in the supply air stream and exposed to a near constant temperature, but variable flow. UVGI performance was compared with enhanced ventilation and infiltration. Large seasonal variations in UVC dose due mainly to the effect of airflow variation on residence time were observed.  UVGI air treatment resulted in much lower predicted space concentrations of Staphylococcus aureus than ventilation according to ASHRAE Standard 62.1 and levels comparable to those achieved by high efficiency, but sub-HEPA, particulate filtration.  Transient variations in space concentration due to lamp output variation were small, but adjustment of lamp output to the design operating condition was very important for modeling accuracy.