According to the U.S. EPA, a professionally designed UVGI system “can effectively kill the virus that causes COVID-19 and help protect people from the disease indoors.”[1, 2]
It is important to note that science has not found any microorganism that can withstand the destructive effects of the UV-C germicidal wavelength, including superbugs and other antibiotic-resistant germs. In fact, viruses and bacteria cannot develop a resistance to germicidal UV because it uses energy to kill, rather than synthetic or chemical elements. Today, there are several approaches to using this decades-old technology to reduce microbes in the air and on surfaces, including airstream disinfection (also known as in-duct) and upper-room decontamination.
Germicidal UV-C air disinfection systems are installed in a building’s HVAC ductwork to disinfect moving airstreams before they reach employees. Kill ratios over 99 percent on a first-pass basis have been demonstrated by the Environmental Protection Agency (EPA) and the National Homeland Security Research Center. As air is re-circulated, concentrations of infectious pathogens are further reduced by each subsequent pass (“multiple dosing”).
Upper-room UVC is the oldest disinfection application of the germicidal wavelength for airborne inactivation and is recommended for improved control of highly contagious airborne diseases such as Tuberculosis by the U.S. Centers for Disease Control and Prevention and the National Institute for Occupational Safety and Health.
 National Academies of Sciences, Engineering and Medicine. Does ultraviolet light kill the coronavirus? October 2020. Retrieved from https://sites.nationalacademies.org/BasedOnScience/covid-19-does-ultraviolet-light-kill-the-coronavirus/index.htm
 U.S. Environmental Protection Agency. Frequent Questions about Indoor Air and Coronavirus (COVID-19) What is Upper-Room Ultraviolet Germicidal Irradiation (UVGI)? What is HVAC UVGI? Can either be used to disinfect the air and help protect myself from COVID? Retrieved from
Because most viruses can be transmitted via air and direct contact, it could be presumed that HVAC systems can inadvertently broadcast the infection, increasing its spread. Therefore, facility managers should consider employing both upper-room UVGI and HVAC germicidal fixtures to ensure the greatest mitigation practical for control of microbes and airborne microorganisms in communal spaces.
Airborne droplets containing infectious agents can remain in room air for 6 minutes and longer. Upper-room UVC fixtures can destroy those microbes when they are exposed to the UVC energy in a matter of seconds. Kill ratios up to 99.9 percent on a first-pass basis have been modeled and, as air is recirculated, concentrations are further reduced by each subsequent pass (“multiple dosing”).
Surface-cleaning UV-C systems provide 24/7 irradiation of HVAC/R components to destroy bacteria, viruses and mold that settle and proliferate on HVAC coils, air filters, ducts and drain pans. UVC prevents these areas from becoming microbial reservoirs for pathogen growth that can eventually become airborne and circulated by HVAC systems.
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, along with the primary benefits of restored cleanliness, heat-exchange efficiency and energy use.
While the Ultraviolet spectrum contains four separate wavelengths—UV-A, B, C and Vacuum UV—each operates at different energy levels and only one is capable of producing ozone (Vacuum UV).
As you’ll note in the graphic below, Vacuum UV operates in the 100-200 nm range, where it is capable of producing ozone. UVC, conversely, reaches its optimal germicidal strength near 253.7 nm. Because ozone may only be produced below 200 nm, at 253.7 nm (rounded to 254 nm), the germicidal wavelength does not generate ozone.
In addition to the stronger 254 nm wavelength that does not produce ozone, UVC lamps offer another layer of ozone protection.
Most germicidal lamps, including those from UV Resources, are produced with doped quartz glass, which blocks the transmission of the 185 nm ozone-producing wavelength. The doped quartz glass allows the 253.7 nm radiation to pass through, but it blocks the 185 nm wavelength from escaping. Therefore, germicidal lamps with doped glass CANNOT produce ozone. Learn why UVC cannot produce ozone.
In HVACR equipment, the 254nm germicidal wavelength keeps cooling coil surfaces, drain pans, air filters, and ducts free from organic buildup to maintain original coil-heat transfer efficiency, cooling capacity/airflow levels and IAQ. Because of these benefits, UV‑C systems mounted in air handlers or ducts often run continuously 24/7/365, with only a few systems tied to HVAC operation.
For upper‑room UV‑C applications, industry experts recommend UV‑C fixtures remain operational whenever people are present. For example, in a hospital waiting room, the upper‑room UV‑C fixture would remain active all the time, whereas in a commercial office board room, the fixture could be turned off at night when workers are not present.
Similar to other UV‑C fixtures, lamps in upper‑room emitters should be changed after 9,000 hours of use.
No, a UVC fixture is an air conditioning component that is in addition to other system parts. These include the coil, heating core, fan, dampers, humidifiers, filters, etc. All are designed to do some form of work within the air handler a UVC fixture is just one of these components.
However, UVC and HVAC air filters are a complimentary technology. In such a multi-barrier approach, combining technologies helps ensure that whatever pathogen is not mitigated by one method (say filtering) is inactivated by another (UVC). For example, a MERV 8 filter combined with UVC can yield up to a 78% single-pass removal/inactivation rate for SARS-CoV-2, which is near the 85% removal rate offered by a MERV 13 filter-alone approach. Learn more.
The selection of an air or surface disinfection system is based entirely on the application.
Purpose: Designed to mitigate the spread of infectious diseases in high traffic, communal areas that are ideal for cross-contamination.
Rationale: Because people can be infectious before they are symptomatic, a significant value of UVC technology is the ability to limit the spread of contagious diseases and bacteria 24/7/365.
Purpose: Designed to inactivate microorganisms and disinfect moving airstreams “on-the-fly.”
Rationale: Established means of killing airborne pathogens and mitigating the spread of infectious diseases in ventilation systems, as well as in occupied spaces.
Purpose: Designed to destroy bacteria, viruses and mold that proliferate on HVAC coils, air filters and ducts.
Rationale: UVC removes the biofilm that grows on cooling coil surfaces and improves heat-transfer efficiency and lowers HVAC energy use.
Application: Any building with a HVAC system (stationary AHU, rooftop systems, or individual fan coil units).
For IAQ, improved heat transfer, reduced maintenance and odor, an approach used for well over ten years is to put the lamp row centerlines on 30-inch to 45-inch centerlines. Most highly regarded manufacturers have software that can size these types of installations, and more. Only consult one of these reputable manufacturers when sizing infectious disease agent applications.
Not at all. Simple installation instructions are provided along with layout drawings populated with all the necessary dimensional specifics. Product designs are emerging that allow installation of UV-C in AHU’s in under an hour in many cases. This also includes fan-coil, unitary and rooftop units, the hardest systems to keep clean. Consult a reputable factory and then involve them in any infectious disease application.
There are many different materials found in HVACR systems, from metal to plastic, to glass to synthetic media, and all can be impacted differently by UVC. While metal and glass are impervious to UVC energy (standard glass, in fact, blocks the UVC wavelength), plastic and synthetic media (e.g., air filters) can be affected. Applying aluminum foil tape to plastic and rubber materials (electrical wires) will protect them from direct UVC exposure (and help reflect UVC energy further into the plenum).
Additionally, labeling wires may be wise—as they can deteriorate and become cracked or brittle when exposed to UVC—this will allow you to differentiate the yellow wire from the white. Likewise, you should not install UVC lamps near synthetic air filters typically found in residential and commercial HVACR systems to UVC energy.
We recommend the use of “UV-Safe” or “UV-Resistant” filters, typically “glass” based filters. Finally, fiberglass insulation holds up quite well to UVC. While UVC energy will not affect the “glass” component in the insulation, it can affect the adhesive binders that hold the fiberglass together, but overall the fiberglass insulation will not degrade when left in place due to the glass content. We have had field reports of significant degradation of ArmaFlex™ tube insulation or closed-cell foam insulation when exposed to UVC energy. Some manufacturers provide coatings that act as a sacrificial layer between the UVC energy and the foam material (metal tape can also accomplish the same protection).
UV lamps should be treated the same as other mercury-containing devices, such as fluorescent bulbs, according to local and state regulations. Most lamps must be treated as hazardous waste and cannot be discarded with regular waste. Low-mercury bulbs often can be discarded as regular waste; however, some states and local jurisdictions classify these lamps as hazardous waste. For the purpose of transporting UV lamps to a recycling facility, the U.S. EPA’s universal waste regulations allow users to treat mercury lamps as regular waste. Learn more here.
The National Electrical Manufacturers Association (NEMA) maintains a list of companies claiming to recycle or handle used mercury lamps at www.lamprecycle.org
For infectious disease applications, lamp change-out should be performed using an output measurement device such as a radiometer, while following factory specifications and/or recommendations. For IAQ or mold control, large installs might benefit from a radiometer to preclude premature change-outs. Changing lamps when their output decreases by 20 percent are common, this usually occurs between 12-15 months.
Most lamp manufacturers (Signify, GE, and Sylvania, etc.) recommend replacing UV lamps every 9,000 hours, or, since there are 8,760 hours in a year, most facility managers employ an annual re-lamping / preventative maintenance schedule.
UV light comprises a segment of the electromagnetic spectrum between 100 and 400 nm, corresponding to photon energies from 3 to 124 eV. The UV segment has four wavelengths, labeled: UV-A (400 to 315 nm); UV-B (315 to 280 nm); very high energy and destructive UV-C (280 to 200 nm); and vacuum UV (200 to 100 nm).
UVC’s germicidal or germ-killing effects are well proven. The 253.7 nm electromagnetic waveform is well absorbed by DNA and RNA (the genetic code for all lifeforms), changing its structure. This damage inhibits the ability of the affected cells to reproduce, meaning that they cannot infect and are no longer dangerous.
We’re exposed to parts of the UV spectrum while outdoors. Generally, excessive UV exposure can produce adverse effects depending on wavelength, type and duration, and UV response differences between individuals. The three basic wavelengths:
— UV-C – includes the germicidal wavelength of 253.7nm and is used for air and water disinfection. Human overexposure causes temporary skin redness and harsh eye irritation, but no permanent damage, skin cancer, or cataracts.
— UV-B – is a narrower but more dangerous band of UV. Prolonged exposure has been associated with skin cancer, skin aging, and cataracts (clouding of the lens of the eye).
— UV-A – is more predominant outdoors than the other two. It helps to tan our skin and is used in medicine to treat certain skin disorders. It is generally a harmless wavelength.
UV-A, B and C will damage collagen fibers and accelerate skin aging. Generally, UV-A is the least harmful; UV-B contributes to DNA damage and cancer. It penetrates deeply but does not cause sunburn. Because of no reddening (erythema), it cannot be measured in SPF testing. There is no good clinical measurement of UV-B blocking, but it is important that sunscreens block both UV-A and B. UV-C however, penetrates superficially and has not been associated with long-term tissue effects.
Microorganisms are simple organic structures that readily absorb the UVC wavelength, causing photo-disassociation (destruction). A microbe’s DNA (deoxyribonucleic acid, is first to be adversely affected due to its weaker molecular bonds.
In hundredths of a second, it suffers irreparable damage. The subsequent loss of genetic instructions causes cell death and/or the inability to replicate, rendering them harmless. Continuous exposure causes uninterrupted degradation, such as the sun does, only significantly faster.
Yes, in literally thousands of controlled tests, organic materials build-up on coils was removed with UVC to provide two eventual results: 1. the pressure drop across a coil declines to increase airflow. 2. the leaving air wet-bulb temperature differential increases. Energy savings are therefore through increased heat absorption (transfer), reduced air horsepower (or increased air volume) and/or reduced run time, including at a condenser. These reductions and increases always manifest themselves in some form of energy-saving work.
The CDC [v] and ASHRAE have recommended UVC as one technology that can “reduce the risk of dissemination of infectious aerosols in buildings and transportation environments.” [vi] ASHRAE has recognized that the 253.7 nm germicidal C-band wavelength inactivates virtually all microorganisms living on HVAC/R surfaces with a kill ratio of 90 percent or higher, depending on UV-C intensity, length of exposure, lamp placement, and lamp life cycle. In fact, a CDC-funded study conducted in two hospitals found that UVC reduced the total number of colony-forming units of any pathogen in a room by 91 percent. [vii]
Science has yet to find a microorganism that is immune to the destructive effects of UVC, including superbugs and all other antibiotic-resistant microbes associated with healthcare-associated infections.
[v] CDC. COVID-19 Employer Information for Office Buildings (September 11, 2020). Retrieved from https://www.cdc.gov/coronavirus/2019-ncov/community/office-buildings.html
[vi] ASHRAE Position Document on Infectious Aerosols (April 14, 2020). Retrieved from https://www.ashrae.org/file%20library/about/position%20documents/pd_infectiousaerosols_2020.pdf
[vii] Anderson D. J., et. al. (2013) Decontamination of Targeted Pathogens from Patient Rooms Using an Automated Ultraviolet-C-Emitting Device.” Infection Control & Hospital Epidemiology. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3703853/