Steril-Aire

The Science Behind Steril-Aire: Germicidal UVC Applications for HVAC

In order to understand how Steril-Aire UVC works, it is important to understand the science behind UVC. The C wavelength of the UV spectrum (UVC – 253.7nm) targets the DNA of microorganisms, destroying their cells and making replication impossible. Directed at a cooling coil or drain pan, UVC energy destroys surface biofilm, a gluey matrix of microorganisms that grows in the presence of moisture. Biofilm is prevalent in HVAC systems and leads to a host of indoor air quality (IAQ) and HVAC operational problems. UVC also destroys airborne viruses and bacteria that circulate through an HVAC system.

For the most effective microbial control, Steril-Aire UV germicidal Emitters are installed on the supply side of the system, downstream from the cooling coil and above the drain pan. This location provides more effective biofilm and microbial control than in-duct UVC installations. By irradiating the contaminants at the source – the cooling coils and drains pans – Steril-Aire UVC delivers simultaneous cleaning of surface microorganisms and destruction of airborne microorganisms. Steril-Aire patented this installation configuration in 1998.

Steril-Aire at YNHH

Steril-Aire emitters (white/clear tubes located on the left) after installation at Yale New Haven Hospital, New Haven, CT.

The recirculating air in HVAC systems creates redundancy in exposing microorganisms to UVC, ensuring multiple passes so the light energy is effective against large quantities of airborne microorganisms. Steril-Aire UVC delivers the highest UVC output, driving HVAC system efficiency while improving indoor air quality.

For optimum performance, Steril-Aire UVC is systems engineered to deliver output of nine microwatts per linear inch of glass measured from a distance of one meter, tested at an air velocity of 400 feet per minute at a temperature of 50° F. UVC output declines over time, reaching a half-life after 9,000 operating hours or slightly over one year when running on a 24/7 basis. It is necessary to start at a high enough output, to ensure adequate output will be maintained throughout the service of the device, otherwise, it may not be able to maintain effective micro­bial control.

Steril-Aire in action

Steril-Aire emitters on and in action at Sturdy Memorial Hospital, Attleboro, MA

Steril-Aire’s multi-patented UVC Emitters deliver the longest-lasting UVC performance available. As shown in the comparison graph below, it has been independently tested to deliver up to 6 times the output of other UVC devices under HVAC operating conditions.

Steril-Aire Output

Steril-Aire delivers 6x the output of other devices under HVAC Operating conditions.

UVC use in HVAC systems is now recognized as an important contributor to improved indoor air quality, biofilm control, energy savings, and maintenance reductions in commercial, residential, healthcare and other environments. According to a report issued June 24, 2009, by ASHRAE, airborne transmission of diseases through heating and air conditioning systems may be much more common than previously thought. ASHRAE cites UVC as one of the control strategies that may help avoid transmission.

The ASHRAE HVAC Design Manual for Hospitals and Clinics 2013 – Second Edition identifies the HVAC as a reservoir and source of infections. The Manual further states, “UV radiation can be effective in reducing the virulence of microorganisms and, therefore, in attempting to reduce infection rates.”

The most comprehensive independent source of information for comparing UVC lamp systems is a series of 2006 test reports titled “Biological Inactivation Efficiency of HVAC In-Duct Ultraviolet Light Devices”. This testing was commissioned by the Environmental Protection Agency (EPA) in conjunction with the National Homeland Security Research Center (NHSRC) and conducted by RTI International. This test confirms that, on average, Steril-Aire UVC Emitters are 6 times more effective than tested competitive UV on a Kill/Watt basis.

biological inactivation study

Steril-Aire has developed an Application Standard in order to publish the information necessary for the successful application of UVC germicidal lamps in HVAC systems. It is a compilation of technical data and specifications as well as installation, sizing, dosage and other guidelines necessary to assist readers in proper selection and application techniques of UVC lamp systems.

There is a large body of scientific and anecdotal evidence on HVAC biofilm and establishing the link with poor indoor air quality, hospital-acquired infections and the adverse health effects on occupants.

For more information about Steril-Aire and how we can provide a system for your facility call Tom Proietti, 860.221.0877, email us or visit us on the web. You can always stay up-to-date with all the latest industry news by following us on social media: Twitter, LinkedIn, Google+ and YouTube!

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