Development and experimental validation of a mathematical model for the irradiance of in-duct ultraviolet germicidal lamps

An ultraviolet (UV) germicidal lamp installed in a ventilation duct (in-duct) is one of the most effective means for disinfecting pathogens circulated inside ventilation duct. We presented a new mathematical model based on the view factor approach, which was first developed to calculate the irradiance (I _r ) of a typical in-duct UV lamp consisting of short and double luminous tubes within a full-scale ventilation duct system. The model predicted both of the emissive irradiance (I _re ) of in-duct UV lamp and the diffuse reflection from the ventilation duct wall. Validation experiments were conducted by measuring I _re for 1/4, 1/2 and full UV lamp luminous length in a full-scale ventilation system. The efficacy (η) of the in-duct 1/2 luminous length UV lamp in disinfecting Escherichia coli (E. coli) was also experimentally and numerically studied. The results showed that the predicted I _re matched the measurement data well. The irradiance decreased accordingly as the luminous length of the UV lamp shrank. The disinfection efficacy declined as the air supply velocity increased and the highest measured η was 67.1% for a 1/2 luminous length in-duct UV lamp on E. coli, with 3 m/s air supply velocity. The results suggested that in-duct UV lamp is an efficient way to inactivate the airborne E. coli. The developed model facilitates the prediction of the irradiance including the diffuse reflection and can prompt the application for in-duct UV disinfection systems.