Effectiveness of the In-duct Ultraviolet Germicidal Irradiation Devices with Two Modeled Lamp Configurations PDF

Airborne infectious diseases have been a concern in buildings for many years, even more so now with recent serious health threats such as H1N1, SARS, the Avian Flu and others. In-duct ultraviolet germicidal irradiation (UVGI) is currently being used to help control infectious airborne diseases in many buildings such as healthcare facilities. Many factors play into the effectiveness of these systems including the air and lamp properties.

This study uses the Lighting Technologies Inc.'s ray-tracing (Monte Carlo Method) software, Photopia v3.0, to simulate two in-duct UVGI devices. The use of ray-tracing software is proposed because the software is capable of predicting spherical irradiance values. With the prediction of the spherical irradiance, dose received by microorganisms could be more accurately estimated and the prediction of the survival rate of the microorganisms would also be improved. Four identical ultraviolet (UVC) lamps are modeled inside a rectangular HVAC duct with dimensions of 2'x2'x9' (0.6m x 0.6m x 2.7m). The lamps are either arranged in parallel or cross-flow as these are the two most common configurations in the industry. This modelling approach for the UVC lamps adopted in this study was previously validated with experimental measurements. The simulated material of the duct surface and the supporting rods in the parallel flow configuration is perfectly diffuse aluminum. Spherical irradiance values in five locations along the length of the duct, before, between, and after the lamps, can be compared between the two configurations.

The lamp configuration with higher average irradiance was identified and was used to indicate a more effective lamp configuration for in-duct UVGI systems under different thermal conditions.

In conclusion, without accounting for the thermal effect on lamp output, a UVGI device placed in a cross flow would give a higher average UV irradiance for both centerline and edge flow paths that are considered in this study. This benefit would be practical when sufficient straight run is provided for the UVGI devices in ventilation systems. However, lamps in parallel flow would produce a more uniform UV irradiance field near the center for both paths. When considering the impacts due to the thermal condition, arranging lamps in parallel flow would provide a higher average irradiance at high velocity and low temperature conditions.