Retrofitting HVAC Systems with UVC to Inactivate Viruses and Other Infectious Pathogens

The big question for specifiers, engineers and HVAC contractors during the COVID-19 pandemic is whether ultraviolet germicidal irradiation (UVGI) can inactivate viruses and other pathogens when installed in HVAC systems or ducts.

The answer is yes. The “SARS-CoV-2 Neutralization by Germicidal UVC Light Systems” study conducted by independent laboratory Innovative Bioanalysis, Costa Mesa, Calif., validated the effectiveness of Fresh-Aire UV ADS disinfection systems. The study validated up to a 4-log, >99.99-percent neutralization of the SARS-CoV-2 virus from .25 to 2 seconds of exposure to Fresh-Aire UV germicidal HVAC UVC 254-nanometer light systems, Jupiter, Fla. The exposure time is comparable to a moving airstream model within a facility’s HVAC or ventilation system. The lab tested Fresh-Aire UV’s ADS airstream and BlueTube XL coil and airstream disinfection systems designed for health-care, education, office and other commercial facility applications. The residential and commercial APCO-X coil and air disinfection system also exhibited similar positive results.

While this was reassuring to the HVAC industry, it was no surprise to UV manufacturers. The 2004 study “Inactivation of the Coronavirus that Induces Severe Acute Respiratory Syndrome, SARS-COV”, published by the National Center for Biotechnology Information (NCBI), had already proven UVC’s success with other related coronaviruses, such as SARS-CoV-1.

Therefore, the question of inactivating SARS-CoV-2, the virus that causes the COVID-19 disease, is more about UV dosage than methodology. Fortunately, the study helped answer the dosage question, too, as well as UVC light irradiance, exposure time and other factors considered for neutralizing the virus.

There are calculation programs, such as BlueCalc, that can help determine a project’s UV output data, such as selected lamp model and parameters, number of lamps, lamp locations, UV power and other considerations.

Prior to the study, the industry had a strong understanding of dosages based on the SARS-CoV-1 study (2004), but another study released in June 2020 conducted by the University of Milano et al confirmed those expectations. The study published on www.medrxiv.org suggested dosages for SARS-CoV-2 are similar to dosages used successfully to inactivate SARS-CoV-1 that appeared in 2004. This is an example of researchers and scientists obtaining a better understanding throughout the first six months of 2020, as to what SARS-CoV-2 dosage is needed in a specified space when installed in a room or HVAC air handler or ventilation duct system. The University of Milano study’s findings revealed a dosage of just 3.7 milijoules/cm2 of UV-C energy was sufficient to achieve a 99.9-percent inactivation. Existing UVC calculation programs, such as Fresh-Aire UV’s BlueCalc software, and their SARS-CoV-1 data parameters for commercial UV-C dosage specifications, have been similar to the study’s dosage requirements data for neutralization of the SARS-CoV-2 virus.

UV-C has also been proven to inactivate viruses, including influenza, smallpox and measles, by scrambling microorganisms’ DNA and RNA to prevent reproduction or infection. It also inactivates non-viral biological contaminants, such as mold, mildew, allergens and bacteria. Dosage specification is critical for engineers because biological contaminants differ in what dosage will inactivate them. For example, viruses are the most susceptible to UV-C exposure, according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Applications Handbook. In order of susceptibility: vegetative bacteria, such as staphylococcus aureus; mycobacteria, such as mycobacterium tuberculosis (TB); bacterial spores, such as bacillus anthracis; and fungal spores, such as apergillus niger are more resistant to germicidal UV light. Therefore, target pathogens all require different dosages. 

Health-care Chaos Amid COVID-19

UVC is a well understood and proven means to disinfect surfaces, especially in the health-care field. Therefore, a desperate health-care industry embraced the technology to treat their personal protective equipment (PPE), particularly N95 respirators, as a result of supply shortages during the first few months of the pandemic. Consequently, first line responders and other health-care workers began designing and building their own UVC disinfection chambers. They were converting refrigerators, toaster-ovens, metal boxes, cabinets and any other enclosure into makeshift disinfection chambers and then installing Fresh-Aire UV lamp systems . Since the chambers are a variety of volumetric sizes, Fresh-Aire UV’s engineers were busy calculating the correct selection and dosages needed for the many requests. 

A desperate health-care industry embraced UVC technology to treat their personal protective equipment, particularly N95 respirators, as a result of supply shortages during the first few months of the pandemic.

Puzzled how a diverse cross section of health-care providers from around North America were making the connection of UVC’s virus inactivation capabilities with PPE disinfection, Fresh-Aire UV soon discovered the U.S. Centers for Disease Control and Prevention (CDC) had issued its guideline document “Crisis Standards of Care Decontamination Recommendations” on April 9, 2020. One CDC recommendation using UVC for disinfecting PPE was a cited study published in the American Journal of Infection Control, “Ultraviolet Germicidal Irradiation of Influenza-Contaminated N95 Filtering Facepiece Respirators (FFR)”, to disinfect PPE for reuse. While the article’s title suggests it was written during the current crisis, the study was ironically published in 2018 under the hypothesis of a future international pandemic. The article’s researchers custom-built a deactivation chamber using high output UVC lamps they had secured from Fresh-Aire UV. The conclusion stated that 60 to 70 seconds of UVC exposures delivered the necessary dosage that was effective in disinfecting N95 respirators for reuse during pandemic shortages.

How Virus Disinfection Studies are Conducted

There are various airborne UVC disinfection studies. Airmid Healthgroup (AHG), Dublin, Ireland, a third-party indoor air cleaning device test facility, proved UVC lights sterilize microorganisms when installed in HVAC systems commonly used in healthcare facilities.

The 2013 study used Fresh-Aire UV’s APCO UV-C light systems to demonstrate airstream microbe inactivation in an ASTM/AHAM style environmental test chamber that simulated a typical building’s indoor environment and HVAC air handler arrangement. A single pass test was also performed on an ASHRAE Standard 52.2 test duct system. 

The test’s single-pass UV light system inactivation results were: Bacteria (S.epidermidis)–98.85-percent; Virus (MS2 coliphage)–99.03-percent; and Mold (A.niger)–78.80-percent.

The test, which simulated the typical indoor HVAC conditions of 73°F (23°C), 55-percent relative humidity and airflow velocity of 492-fpm (0.93m3/sec), was performed on a single pass. IAQ experts claim even higher inactivity rates among the three tested microbes could occur in a multiple pass environment, such as the continual recirculation of air from a typical building HVAC system.

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About the Author

Aaron Engel
Aaron Engel is vice president of business development at Fresh-Aire UV, a North American manufacturer of UV disinfection and carbon/PCO-based indoor air quality products. Fresh-Aire UV offers UVC light systems for virtually every type of HVAC system, ice machine and surface disinfection. Engel can be reached at [email protected] or (800) 741-1195.

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