Going Green NRG

Industry News
4.2.2020
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“Anywhere you put thousands of people in close proximity, be it a hospital, airport, large office building or college, it’s advisable to try to eliminate disease transmission as much as possible…”
– Director of Facilities at Schenectady College, Alan Yauney

AIRBORNE VIRUSES
1. Does UV-C kill the COVID-19 Coronavirus?
2. Can UV light mitigate the spread of airborne viruses?
3. Can COVID-19 spread through HVAC ducts?

AIRSTREAM DISINFECTION
4. How does germicidal UV-C “On-The-Fly-Kill” work?

1. Does UV-C kill the COVID-19 Coronavirus?

Researchers don’t yet know if UV-C can kill COVID-19 as this particular strain has not yet been studied. Although the germicidal UV-C waveform (253.7 nm) i s effective in killing other varieties of coronaviruses, such as SARS and MERS, scientists do not yet know about the impact of UV-C on COVID-19.

Research has shown that exposure to UV-C is a practical and cost-effective method of inactivating airborne viruses, mycoplasma, bacteria, and fungi on surfaces*1. Overall, UV-C is a supplemental and extremely effective approach to fighting infectious diseases*2. Predictive-modeling can determine specific dosage rates required to kill individual bacteria, viruses or spores depending on how easily UV-C energy is absorbed by each. For example, viruses are susceptible to UV-C inactivation including Influenza, Measles, SARS and Smallpox.

2. Can UV light mitigate the spread of airborne viruses?

The Ultraviolet Germicidal Wavelength (UV-C or UVGI) kills all known-microorganisms including bacteria, viruses, molds and other pathogens –even antibiotic-resistant superbugs. ASHRAE states that the UV-C wavelength can kill 90% or more of all microorganisms living on HVAC air ducts and evaporator coils, depending on UV-C intensity, length of exposure (aka residence time), UV lamp placement and lamp life cycle.

Operating 24/7/365, upper-room germicidal fixtures can inactivate microbes in under a second including measles, mumps, TB and cold viruses. In fact, ASHRAE’s Position Document on Airborne Infectious Diseases identifies just three proven methods of controlling airborne infection: ventilation, particle filtration and germicidal UV-C energy*3.

Airborne microorganisms exposed to germicidal UV-C undergo an exponential decrease in population similar to that produced by ventilation and other disinfection methods*4.

3. Can COVID-19 (or other viruses) spread through HVAC ducts?

Based on the information available from authorities, coronaviruses can be transmitted via air and direct contact*5. Researchers have found the COVID-19 virus can live in the air for several hours and, on some surfaces, for as long as two to three days*6. Therefore, it could be presumed that HVAC systems can, inadvertently, broadcast the infection and amplify its spread. Facility managers should consider employing both upper-air UVGI and in-duct or coil HVAC germicidal fixtures to ensure the greatest mitigation practical for controlling microbes and airborne microorganisms in communal spaces.

UV-C’s ability to decontaminate the air flowing through a building’s HVAC system can be most beneficial where communicable diseases are more common, such as office buildings, schools, healthcare settings, municipal offices, etc. An improperly maintained HVAC system in these environments can promote disease transmission as it recirculates those same germs throughout the building. Conversely, installing UV lamps, with their ability to destroy airborne viruses, bacteria and mold spores, can prevent disease transmission and/or cross-contamination.

4. How does germicidal UV-C “On-The-Fly-Kill” work?

In-duct germicidal UV-C systems are installed in air-handling units or air distribution systems to inactivate microorganisms and disinfect moving airstreams “on the fly”— as well as on HVAC surfaces. Germicidal UV-C kills 90% or more of all microorganisms living on HVAC air ducts and evaporator coils, depending on the lamp intensity (dose) and the length of exposure.

The operational factors that most directly impact airstream disinfection rates are:

  • Time/Intensity. The volume and velocity of air traveling through an HVAC system significantly impact the length of exposure to the germicidal wavelength (residence time)—a higher volume of air and/or faster-moving air requires greater intensity (more UV-C lamps).
  • Lamp location. Because cold air reduces the output of UV-C lamps and high RH affects pathogen susceptibility to UV-C, on-the-fly airstream disinfection applications are more effective when installed on the upstream side of the coil. In fact, moving UV-C lamps from 55-degree temperatures (typical of downstream) to 75-degree (typical of upstream) can increase a UV-C lamp’s output by 40%. On-the-fly disinfection can be accomplished downstream of the coils; however, this would require an increase in UV-C intensity (i.e. more lamps).
  • Reflectivity. UV-C energy’s effectiveness is multiplied (see chart) as it bounces off of the top, bottom, and sides of a plenum surface. Certain surfaces like aluminum can allow more UV-C energy to reflect and “stay in play” versus being absorbed by the surface. Most cooling coil fins are made from aluminum, which also assists in overall reflectivity.

Upstream/Downstream of Coil
For example, to keep cooling coils free from mold and bacteria, lamps might be installed on the downstream side of a coil surface, spaced every 30- to 40-inches of coil height (this equates to roughly 7.5 lamp watts per square foot). Here, since the coil is stationary, the exposure time to UV-C is 24/7/365, so the UV-C intensity can be lower.

However, for a moving airstream, UV-C intensity must increase significantly due to the decrease in time that the potential pathogen will be exposed to the UV-C energy. Greater UV-C dosage can be achieved by increasing the number of lamp watts per square foot (this equates to roughly 30 lamp watts per square foot on the downstream side of the coil). This can be accomplished by using “fixtureless” UV-C systems for 360-degree irradiation and/or decreasing lamp-row-spacing, for example, to 12-inch centerlines of coil height. When designing an “on-the-fly” kill application, we recommend modeling the intended design to ensure adequate germicidal dosage.

1-https://fas.org/irp/doddir/army/pam385-69.pdf
2-https://www.ncbi.nlm.nih.gov/pubmed/20569852
3-https://www.ashrae.org/File%20Library/About/Position%20Documents/Airborne-Infectious-Diseases.pdf
4-https://www.cdc.gov/niosh/docs/2009-105/pdfs/2009-105.pdf?id=10.26616/NIOSHPUB2009105
5-https://www.researchgate.net/publication/284691618_SARS_Coronavirus_UV_Susceptibility
6-https://www.medrxiv.org/content/10.1101/2020.03.09.20033217v1.full.pdf

HEALTHCARE

● ER Waiting Rooms
● Intensive Care Units
● Operating Rooms
● Urgent Care Clinics
● Doctor and Dental Offices
● Nursing Homes/Extended Care Facilities

MANUFACTURING

● Clean Rooms
● Pharmaceutical Labs
● Bakeries/ Food Manufacturing
● Meat/Dairy Processing

INSTITUTION

● Schools /Universities
● Sports Arenas
● Laboratories
● Prisons/Jails
● Emergency Shelters

BUSINESS

● Daycare
● Veterinary/ Kennels
● Food courts