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.
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
There are three types of UV systems, explains Daniel Jones, president of UV Resources, a UV-C system vendor.
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.
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 lampsare 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.
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.
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.”
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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.
“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.”
“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 even the highest-quality low-pressure mercury vapor lamps will produce ozone if the 185-nanometer wavelengths that produce it aren’t filtered out. “If the lamp tube is made of the right material—e.g. titanium doped quartz—essentially all of the 185-nanometer light is blocked.”
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.”
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.
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, Bahnflethsays. Used properly, a UV system can be a valuable addition to your FM arsenal.
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