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Physical filtration, ultraviolet light, and increased outdoor air ventilation continue to be three high-profile elements of the conversation surrounding how to kill the novel coronavirus. Physical filtration had a head start of sorts, enjoying more clarity about exactly what a certain type of filter could accomplish with regard to the virus. Outdoor air has the frequent advantage of requiring system adjustments (and not purchases) in order to introduce more, along with the easily understandable benefits of dilution.

However, ultraviolet light has several things going for it that position it for long-term success in the COVID era and beyond. Ultraviolet is not a new concept to the general public, thanks to bug zappers and other products. It has an established role in the HVAC community as a tool for coil cleanliness inside HVAC systems.

For contractors, UV encompasses more than one type of light, multiple strategies for neutralizing indoor air contaminants, and increasing options. In a wave of expanded consumer interest toward any effective IAQ tool, UV may represent a substantial opportunity for contractors who are willing to expand their relationship beyond the ductwork or air handler.


Upper Room UV-C & Far UV

The COVID-19 pandemic has pushed some existing but lower-profile solutions toward the forefront. One of these is upper room UV-C.

In this aptly named approach, the UV fixtures install at a height of at least 7 feet in the room, facing upwards to avoid direct exposure for any occupants.

Ashish Mathur, Ph.D., is vice president, innovation and technology, for UltraViolet Devices Inc. He said that sufficient airflow is necessary in the room for this strategy to be effective, as it kills contaminants in the course of ordinary circulation closer to the ceiling.

“Upper room UV-C had its roots historically for use in controlling the transmission of tuberculosis dating to the early 20th century,” Mathur explained.

How well does it work?

“’Kill’ or inactivation rates of up to 99.9 percent on a first-pass basis have been modeled,” Jones said, with a virus’ presence reduced by each subsequent pass of recirculated air.

Daniel Jones, president of UV Resources in Santa Clarita, California, said that airborne droplets or aerosols containing infectious agents can remain in room air for six minutes or longer. Harkening back to its origins, a 24/7 upper-room system “can inactivate microbes in seconds, including measles, mumps, TB, and cold viruses,” he said.

Elsewhere beyond the ductwork, Dave Ogle, BEAP, president and founder at Tech-UV, refers to another approach, known as far UV, as “promising, and development is currently happening.”

Differences between high-room UV-C and far UV are worth emphasizing. Far UV light has a different wavelength than the more common UV-C. As a result, its characteristics are different. Research has found it to be effective against H1N1 influenza and other viruses.

However, Mathur noted, because of its higher intensity, “ACGIH safety guidelines do not support the use of Far-UV in occupied spaces for prolonged exposure,” adding a layer of complexity to indoor usage.

Portable air purifiers represent yet another category that some may come across in COVID-related searches. These manufacturers warn against hurrying into an investment for virus-related purposes.

“Most portable units do not have the UV-C wattage needed to kill D90 single pass,” said Ogle.

Mathur echoed that while they are designed specifically to deal with things like pollen, allergens, and odors, “many” are not designed or proven to work against pathogens like a coronavirus. It becomes especially important to make sure the technical information and evidence aligns with the user’s objective.

Ultraviolet options.

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IN-DUCT OPTIONS: Ultraviolet options beyond the duct and air handler may be on the rise, but the traditional system still offers different opportunities for different objectives. Image courtesy UV Resources.


Surface Concerns

Outside of radiant systems, the world of HVAC doesn’t really concern intersect much with surfaces in a room. That may be ready to change a little, thanks to COVID’s characteristics and UV-C’s abilities.

UV-C has a track record in institutional settings for disinfecting common surfaces, and current condition make it easier to see room for growth.

“Based on the emerging research demonstrating the persistence of coronavirus on surfaces for up to nine days,” Mathur said, “we are also seeing broader interest in mobile whole room UV-C disinfection devices, such as those typically used in health care facilities to disinfect patient rooms and operating rooms.”

Mobile units are not the only option, increasing the potential for HVAC contractors.

“A system installed for HVAC surface irradiation, while not specifically designed for it, can also provide first-pass kill ratios of airborne pathogens of up to 30 percent,” said Jones, “along with the primary benefits of restored cleanliness, heat-exchange efficiency, and energy use.”


No Plug-And-Play

Not much is worse for the contractor, customer, and manufacturer than an improper selection or installation of “new” technology that winds up making the customer unhappy and giving the technology a worse name than it deserved. So it goes with UV and its expanding possibilities.

Mathur encourages contractors to proactively engage with facility management to identify key areas and analyze where is the best candidate for what.

“While a broader portfolio can be alluring, it is important to ensure any technologies implemented are evidenced-based and scientifically proven,” he said.

Ogle seconded the need for contractors to do their homework.

“Most in-duct systems do not have the wattage or contact time for a virus kill,” he emphasized.

Ogle added a recent example that his company is currently custom-building three systems for 10-ton rooftop units that will have 860 watts of UV in each supply duct, aided by white Teflon reflectivity.

Jones noted that “a higher volume of air and/or faster-moving airstream require greater intensity” of the germicidal wavelength to achieve the desired effect.

Similarly, he said, cold reduces the output of UV-C lamps, humidity affects pathogen susceptibility to UV-C, and duct reflectivity also plays a role.

As a result, UV-C can be and often is done well, but it is definitely not a “one size fits all” situation. Differences in objectives and effective doses mean that “Oh, I already have UV in the ducts” will not be a lucky shortcut for anyone looking to fight COVID-19.

Of course, that inconvenient truth may also leave the door (and the customer) open to the prepared contractor, either for adding UV presence or for modifying existing in-duct systems.


Niche No More

Yearly combat against the flu is nothing new in residential or commercial settings. With the pandemic’s arrival, nonresidential spaces seem primed to adopt or expand UV-based strategies.

Ogle sees adding UV-C to air circulation as “the primary step to remediating viruses,” adding that it needs to be building code in every occupied public building.

Jones notes that UV Resources has seen interest spike four-fold from managers in settings from schools and restaurants to airports and museums, military bases, offices, health clubs, and some residential.

Moreover, growing scientific sentiment that COVID can transmit via aerosol (i.e., can linger “airborne” and is not only dependent on the heavier droplets) may increase the risks for common spaces and the urgency to take countermeasures.

“Almost overnight,” Jones said, “UV-C systems have transformed from an HVAC accessory to a health and safety necessity.”

The temporary downside? In his experience, deliveries have gone from one to two weeks’ lead time to eight weeks or more as the supply chain works to catch up to the shift from niche to mainstream.


The Next Normal

What could the daily UV use of tomorrow look like?

“I anticipate we will see more-and-more autonomous devices for environmental or surface hygiene,” Mathur said. “Just as our homes are becoming increasingly filled with Internet of Things devices, I expect we may see truly robotic cleaning and disinfecting products in professional settings.”

Ogle can envision new strategies becoming the norm.

“Added light fixtures in public/private occupied rooms that come on when the room is unoccupied,” he cited as one example. “Like a 10-minute safety stop between classes, of 5000+ Watt of UV-C in the classroom without students. Close the door and hit a button. Something like that.”

Ogle added that LED UV-C “will naturally come, but cost is an issue. Heat dissipation is another issue. UV-C LED’s run hot.”

For now, COVID risks have piled atop traditional seasonal concerns like the flu. As much as people miss old routines, public willingness to inhabit work- or leisure-related spaces does not seem likely to return to previous levels anytime soon.

That is why, in Mathur’s estimation, “proactive measures deploying UV technologies to provide continuously disinfected air — along with high visibility messaging assuring consumers, guests and employees that they are entering a protected space — will be key to getting America back on its feet and [can be] a winning approach for contractors.”


Research Update: The Dose Is Close

UV-C light may be headed toward making an airtight case as a coronavirus killer, but it isn’t there quite yet.

“There are currently no peer-reviewed, published studies regarding SARS-CoV-2 relative to UV-C susceptibility,” said Daniel Jones of UV Resources, referring to the gold standard of scientific evidence.

In the meantime, relevant previous and recent science in the form of other studies or research does exist to support the idea.

UVDI’s Mathur mentioned one recently published study at Italy’s University of Milano “specifying the appropriate UV-C dose for SARS-CoV-2.”

Dave Ogle, BEAP, president and founder at Tech-UV, pointed to “Bouri-Kowalski dosage calculations for D90 deactivation” from March of this year, referring to the dose of UV light needed to kill 90 percent of a given virus.

Mathur and Jones agreed that all indications so far suggest that the dose of UV-C required to kill the current virus will not be all that different than the doses confirmed as effective against previously researched similar viruses.

Jones noted one 2007 study seen as a rough approximation for the moment. Obtaining D90 and D99 results against a previous coronavirus in that study required UV doses of 700 and 1,300 μW-sec/cm2 (microwatt-seconds per square centimeter), respectively.

Germicidal Engineering Control Recommended Application/Rule of Thumb
  • Goal >50 microwatts seconds per-square-centimeter (µW-s/cm2)
  • Wall-mounted
  • >7-feet high in occupied spaces
Airstream Disinfection*
  • Lamps spaced every 14-inches of coil height
  • Duct run-length >24-inches
  • Air Velocity <500 fpm
  • Minimum Exposure Time > 0.24 seconds
  • Upstream of coil (where warmer air increases UV-C output)
Coil-Surface Cleaning
  • Downstream of coil
  • lamps spaced every 30-40 inches of coil height
*Consult with UV fixture manufacturer for modeling of specific application.