UVC in AHU at YNHH

4 Factors to Consider When Applying Ultraviolet-C in HVAC Applications

Ultraviolet-C (UVC) applied correctly in air-handling units has been an economically useful tool in sanitizing cooling coils and other HVAC equipment for decades. The many years of research associated with UV-C (200-280 Nanometer) have proven it is also one of the most reliable and widely accepted approaches to non-contact disinfection of viral aerosols.

In short, the COVID-19 pandemic has finally given Ultraviolet Germicidal Irradiation (UVGI) technology the popularity it deserves.

As with all applications, the devil is always in the details so with Flow Tech’s many years of UVC for HVAC applications, we offer some industry “best practices.”

It is important to note, if one is pursuing solutions specific to mitigation of viral aerosols in ventilation systems, ASHRAE, the CDC and others recommend your two best friends in priority order are:

  1. Fresh air – as much outdoor air as your equipment and control sequences can tolerate.
  2. Filtration – as much as the HVAC equipment can handle with specific regard to #1.

Since most existing equipment has been designed to optimize the use of outdoor air for energy/occupancy values, tertiary mitigation technologies like UVC are highly recommended.

L Building AHU
A finished SiteBilt Air Enterprises air-handling unit, complete with Steril-Aire UVC germicidal emitters (what gives it a blue tone)

4 Factors to Consider

Location. Location. Location.

Since UVC lamp energy is affected by area of coverage, air temperature and air speed, the most optimal location for the UV lamps is at the downstream (leaving air) side of the cooling coils. The air in that location is typically much slower than it would be in the ductwork, has been filtered at least once already, and is typically about to speed up as it passes through the blower and into supply ductwork. There are also the many other benefits of the continuous surface sanitization of the coils including better heat transfer, improved fan energy and mitigation of the pathogen reservoir that is a wet cooling coil/drain pan. This is also a very serviceable location, so keeping the lamps updated annually is simplified.

UVC Diagram

How much UVC energy is required?

Since UVC lamp energy is affected by area of coverage, air temperature and air speed, the most optimal location for the UV lamps is at the downstream (leaving air) side of the cooling coils. The air in that location is typically much slower than it would be in the ductwork, has been filtered at least once already, and is typically about to speed up as it passes through the blower and into supply ductwork. There are also the many other benefits of the continuous surface sanitization of the coils including better heat transfer, improved fan energy and mitigation of the pathogen reservoir that is a wet cooling coil/drain pan. This is also a very serviceable location, so keeping the lamps updated annually is simplified.

diagram of UVC light configuration

Safety Precautions and Mechanisms

Direct exposure to UVC is dangerous for all living organisms including humans and warning decals, door safety interlock switches and viewports are commonly used. Again, it is best to consult your experienced local UVC professional prior to installation. Also, some wire coatings and closed cell foam type insulations could be compromised by high intensity UVC. It’s best to cover those materials with something reflective.

Ongoing Maintenance

The lamps typically lose their desired intensity at about 9,000 hours (~ 1 Year). The simplest method is to change them annually to keep the array at optimal intensity.

For more information, we encourage you to download our UVGI Technology Overview, read our previous blog post, or contact us today. You can always visit us on the web and check out our UVC manufacturer webpage. Follow us on social media: FacebookLinkedInTwitter and YouTube, to stay up-to-date on other important Flow Tech news!

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