Method Proposal for Location Determination of Single Ultraviolet Lamp in Air-Conditioning System to Improve Sterilization Effect on Airflow

<p>Ultraviolet germicidal irradiation (UVGI) is employed to purify the microbes in airflows and on solid surfaces. When air containing bacilli moves through an air-conditioning system with UVGI, the airflow is exposed to radiation during its residence time. The radiation is affected by the location of the UV lamp in the airflow. To determine better installation conditions, the dependence of the sterilization effect on such installation conditions needs to be analyzed. In the present study, guidelines are proposed to determine the installation location based on the concept of the age of air. A numerical simulation is performed to validate the guidelines. In general, the airflow inside the air-conditioning system is not uniform although a heat exchanger equalizes the pressure. Hence, the residence time of the air varies depending on the stream lines. If the UV lamp is installed on a stream line that has a long residence time, the airflow on the stream line can be exposed to more UV intensity; however, the airflow on other stream lines with shorter residence times will accordingly be at a disadvantage. Therefore, the lamp needs to be installed on the stream line with the shortest residence time inside the system to increase the level of sterilization. Even if the average amount of UV dose of the entire airflow is high, the minimum value may be low depending on the non-uniformity of the airflow. The minimum value should be increased to assure a good sterilization effect. A numerical simulation of UV radiation coupled with fluid dynamics was performed for a simplified model of a fan-coil unit and two realistic models. The residence time was analyzed to determine the location of the lamp installation. The results of the UV dose D were compared between the proposed and conventional lamp locations. The proposed lamp location resulted in a D value that is 10–100% higher than that for the conventional lamp location. This indicates the validity of the proposed guideline to determine the UV lamp location.</p>