Study the HVAC system photodegradation caused by the low level UVC light irradiance used for coil maintenance and air stream disinfection

Abstract

This paper studied the detrimental effects of low (50–750 µW/cm2) level ultraviolet C (UVC) irradiation used for coil maintenance and air stream disinfection on the surfaces of different HVAC materials and components. Photoreactors were initially used to study low level UVC photodegradation of materials with the highest UVC susceptibilities and demonstrated that the rates/mechanisms of surface damage are highly dependent on the material processing history as well as polymer structure. Due to the low levels of damage after months of exposure (UVC damage equal in magnitude to surface roughness of polished surfaces), the low level UVC photoreactor results described herein were unable to establish a mathematical relationship between UVC irradiation level and photodegradation rate, especially for the less susceptible materials. However, the results did indicate that the UVC susceptibility rankings were unaffected by UVC irradiation levels, which indicated that high UVC irradiation levels are suitable for shortening the test times required to obtain sufficient surface photodegradation to rank the UVC susceptibilities of polymers/materials used in HVAC systems. To make the UVC susceptibility testing suitable for nonlaboratory settings, a test cell fixture designed to house a single sample, a variable power UVC LED, and an optical photodegradation measuring device was constructed and evaluated. The ability to run each test cell at a different UVC level by simply adjusting the LED input power level allowed multiple samples to be run simultaneously under a wide range of UVC levels/environmental conditions.