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 and costs to implement and operate the system depend greatly on the output of the UV lamps and the exposure time, which are affected by the temperature and the velocity of the air passing through the UVGI device. The type of HVAC system, the installation location of the UVGI device, and the climatic location of the building all have an impact on the air temperature and velocity the device experiences at a given time. The effects of installation location and climate were investigated using simulation of an induct UVGI device installed in a cooling-only VAV system operating in a hypothetical commercial building. The studied device was investigated at locations both upstream and downstream of the cooling coils of the VAV system in three climatically distinct U.S. locations. The results of the six resulting scenarios indicate that UVGI devices installed upstream of the cooling coils provide comparable if not better performance than those installed downstream. The results demonstrate the impact on performance and cost of the dynamic environment that a UVGI device could experience. It can also be observed that the generated heat of UVGI devices has a great impact on cooling and heating loads, and thus affects the overall operating cost. (C) 2013 Elsevier Ltd. All rights reserved.