(Photo: Upper-air or upper-room UV systems use convection or mechanical air currents to lift air to the ceiling, where UV fixtures destroy infectious agents that may be carried in droplets suspended in the air. Credit: UV Resources)
The COVID-19 pandemic has renewed interest in the role HVAC technologies play in mitigating the spread of infectious disease.
One such technology, UV irradiation, works by using light in the 253.7-nanometer wavelength to damage the DNA or RNA of microorganisms, ultimately killing them. Here are the key considerations to know about UV germicidal irradiation.
Types of UV Systems and How They Work
There are three types of UV systems, explains Daniel Jones, president of UV Resources, a UV-C system vendor.
1. Upper-room or upper-air UV
These fixtures use the natural rise and fall of convection or mechanical air currents to lift air up to the ceiling, where UV fixtures destroy infectious agents suspended in the air. These systems are most often used in high-traffic communal areas like waiting rooms, cafeterias or sports facilities. They’re typically combined with airflow management to ensure that air is passed over the UV-C fixtures, explains Dr. Jeffrey Siegel, a professor in the Department of Civil and Mineral Engineering at the University of Toronto.
(Photo: This corporate child care center uses an upper-room UV system. Credit: UV Resources)
2. HVAC airstream disinfection
UV air disinfection systems are installed in the ducts of HVAC systems, air handling units or air distribution systems. They can “inactivate microorganisms and disinfect moving airstreams on the fly,” Jones explains. The intensity of the UV lamps are calibrated to target specific microbes, depending on that microbe’s susceptibility to UV-C and how long the microbe will be exposed to UV-C energy.
3. Coil or surface irradiation
These are also installed in air-handling units, but their main function is to destroy the bacteria, viruses and mold that collect on HVAC coils, air filters, ducts and drain pans. Keeping these areas clean means the HVAC system works more efficiently, so the heat exchange process doesn’t require quite as much energy as a system with dirty coils would. However, it’s not specifically designed for airstream disinfection.
Can UV-C Lamps Solve COVID-19?
The FDA is currently weighing the benefits of far-UVC systems with a wavelength of 222 nanometers, saying “UV-C radiation has been shown to destroy the outer protein coating of the SARS-coronavirus, which is a different virus from the current SARS-CoV-2 virus.”
The Illuminating Engineering Society notes that conventional 254-nanometer UVC can inactivate SARS-CoV-2 by damaging its DNA or RNA “if the virus is directly illuminated by UV-C at the effective dose level.”
How to Specify UV Fixtures
Interested in installing a UV system? Ask vendors these five questions to ensure you’re getting a system that functions properly and meets your needs.
1. How long have you been in business?
“Understand the reputation of the vendor,” Siegel recommends. “You want someone who has a long track record in the type of system you’re looking at.”
2. Does your product generate ozone?
“UV can generate ozone, which is a respiratory hazard we don’t want in buildings,” Siegel says.
Dr. William P. Bahnfleth, professor of architectural engineering at The Pennsylvania State University, notes that some lamp types, such as low-pressure mercury vapor lamps, will produce ozone if they produce 185-nanometer wavelengths. It's crucial to make sure the lamps produce the correct wavelengths and are made of material that shields users from ozone, such as titanium doped quartz.
3. How do you do your sizing calculations?
Software tools simplify the sizing process for in-duct systems, Bahnfleth explains. “That’s better than a guess or a rule of thumb about how many lamps you need.”
4. What are your product’s credentials?
The manufacturer should be registered with the EPA as a pesticide device producing establishment, Jones says. The product should also meet all applicable safety standards and certifications, such as UL 2998, Environmental Claim Validation Procedure (ECVP) for Zero Ozone Emissions from Air Cleaners.
[Read also: The Emerging Role of Luminaire Embedded Controls]
5. What would it cost for me to achieve my goal with filtration or ventilation instead of with UV?
Understand what your goals are, then determine which technology (or technologies) you need to achieve it, Siegel recommends.
“Talk to someone who can provide an alternate system that would achieve the same thing and make an informed decision,” Siegel says. “They might tell you you’ve got no ability to put in filters because you have a small ventilation system and you’re heating the building with radiators. You might hear ‘Sure, we could put in filtration, but you’re going to have this problem with noise.’ Get a sense of the tradeoffs. Your goal is risk reduction, and you want to get a sense of what the alternative is to achieve the same amount of risk reduction.”
Proper design and maintenance are the key to UV success. To achieve any risk reduction, you need a system that’s designed well, and you need to perform maintenance (including changing out older lamps that have lost their effectiveness) on a regular basis, Bahnfleth says. Used properly, a UV system can be a valuable addition to your FM arsenal.