Location Analysis of Upper-room UVGI on Germicidal Effect in Thermal Plume Dominant Room

A numerical simulation was conducted to evaluate the germicidal effectiveness of an upper-room ultraviolet germicidal irradiation (UVGI) device in a room dominated by thermal plumes. A cylindrical model representing a seated human was used to generate free convection flow. The impact of the relative positions of the dummy and the UVGI device on the germicidal effect was analyzed. To simulate respiratory droplets emitted from the mouth, passive scalar transport was computed. The results indicated that the highest germicidal effect occurred when the dummy was located closest to the direction of UVGI irradiation, with a lateral offset of 0.8 meters. This suggests that germicidal performance is influenced not only by the UV irradiance distribution but also by airflow velocity and exposure time. In particular, when fast-moving air passes through the irradiation zone, effective disinfection may not be realized. Therefore, it is effective to position the irradiation zone further above the main airflow, where the air decelerates after impinging on the ceiling. These findings highlight the importance of strategic placement of UVGI devices to enhance their effectiveness in spaces where thermal plumes dominate air movement.