Weighing the benefits of UV disinfection for HVAC 

While ultraviolet (UV) radiation is not a new tool for disinfection, the COVID-19 pandemic has brought it to the forefront of discussions again. UV radiation, with sufficient intensity and contact time, can inactivate viruses and bacteria through three main approaches: air, water and surface. One of the applications for UV lamps includes inside HVAC systems. 

Within the electromagnetic spectrum of UV, UVC (200 nm to 280 nm) falls in the range that is useful for maintaining HVAC systems. Following are two areas where UVC can be utilized in HVAC applications: 

Coil cleaning. A time-tested and proven use of UVC lamps is to use them to disinfect coils by installing downstream of the coils in an air-handling unit (AHU). The radiation reduces organic growth and improves coil performance. While this can be easily accomplished on larger AHUs, smaller AHUs or prepackaged equipment may have issues with the space requirements needed for the installation of UVC lamps in the unit. UVC lamps are more efficient at higher temperatures, so installations in front of the cooling coil will require fewer lamps where air cleaning is the primary objective. Each situation will require specific calculations for UVC lamp quantity to provide the required intensity. While the germicidal system is designed to keep the coil clean, it will have minimal impact on any viruses or bacteria within the airstream due to the higher intensity and contact time requirements. UVC lamps must deactivate whenever the doors to the AHU open for the safety of any worker entering the unit. Lastly, monitoring the system is necessary to identify when the lamp’s intensity starts to drop and replacement bulbs should be installed.

Air disinfection. A designer or manufacturer must understand which virus or bacteria is being targeted as well as the desired rate of disinfection. Factors impacting this selection include air velocity through the kill zone, length of the tunnel (intensity versus time) and temperature of the airstream. UVC can be used in lieu of higher-level filtration due to the lower air pressure drop compared to filtration with similar effectiveness. UVC light efficiency will reduce over time unlike filters; however, it may be less costly in the long term when fan energy is considered. UVC systems will require exponentially higher lamp intensity as the desired kill rate increases. With a properly designed system, the kill rate can be similar to HEPA filters, but lifetime cost of the system must be evaluated.

American Society for Health Care Engineering members can visit the ASHE Resources link under above to learn whether UVC could be a useful tool for their facilities.