One such solution is the use of ultraviolet (UV) light as a method of fighting microbiological contaminants in HVAC systems. By definition, UV represents the frequency of light between 200 nanometers (nm) and 400 nm and cannot be seen with the naked eye. Within this spectrum lies a germicidal UV light (200 nm to 280 nm) or UVC, which is known for its effectiveness in controlling microbial growth.
“Most UVC light systems operate seamlessly with both existing or newly installed HVAC systems,” said Gregg Burnett, vice president and general manager of Dust Free Inc., Royse City, TX. “Recent advancements in UVC light technology have led to the introduction of increasingly powerful, safer, and easier-to-install units than previous models.
“By increasing the microbial damaging capability against surface and airstream contaminants such as molds, bacteria, and viruses, and promoting better coil efficiency, the goal of creating a higher quality of supply air can be achieved.”
HOW UVC SYSTEMS WORKBurnett explained that UVC light “can penetrate the thin cellular wall of a microbe and damage its DNA. UVC renders microbes harmless, sterile, or unable to spread. Time and microbial resistance to UVC energy determines how effective UVC light will be against a specific pathogen.
“This becomes critically important when looking at surface vs. airstream microorganism control.”
Burnett added that laboratory testing involving the application of UVC technology onto surfaces “clearly demonstrates its effectiveness on both coils and filter media.”
“One test was designed to replicate the deployment of a UVC light array upstream, or prior to, a bank of pleated filters that had been inoculated with viable Bacillus thuringiensis (Bt) spores. Bt was chosen as the surrogate challenge since the DNA of Bt is virtually the same as the DNA of Bacillus anthracis, commonly referred to as anthrax.
“Application of the UVC light from the 16-inch high-output lamp at a distance of 12 inches for 15 minutes resulted in a 74 percent spore count reduction as compared to the control sample.”
INSTALLATION, MAINTENANCEBurnett said that the location of the UVC in a given system can affect “optimal microbial control.” He used the example of locating UVC light near a cooling coil.
“In order to achieve the maximum amount of eradication of both surface and airborne microorganisms, place the unit above the cooling coil. In a heat- only application, or where space prohibits installation downstream of the coil, the UVC light should be installed in front of the air filter.”
Burnett added, “Other installation locations to consider involve the proximity of the light to UVC-sensitive materials such as plastic and rubber. Such components are not always resistant to UVC and may deteriorate over time by becoming cracked or brittle. If cause for concern exists, shield the component(s) with aluminum foil tape.
“To eliminate the risk of inadvertent human-exposure to UVC, do not place the unit in a closet/hallway return grill. Always follow practical electrical guidelines to avoid the possibility of an electrical fault by avoiding the placement of an indoor unit in an outdoor area or beneath any source of water.”
Burnett said that maintenance of a UVC light system should always include annual bulb replacements. “Remember, UVC bulbs may still be brightly lit and appear fully functional after a year’s time, but the actual UVC energy will have diminished to the point of being less effective, particularly in the area of airborne application,” he said.
When installing UVC light in a dusty environment, Burnett said it is necessary to wipe down the bulbs with a clean cotton cloth every six months to ensure maximum UVC output. Dirt and/or debris on bulbs can shield microbes from exposure to UVC light.
“Another aid in keeping the bulb(s) clean and the coils free of residue would be the installation of a high-efficiency air filter up- stream of the fixture,” Burnett added.
AN EYE TOWARD SAFETYBurnett stressed the importance of eye safety when working with UVC light fixtures. He listed some precautions which should be followed to ensure that neither the consumer nor the technician’s eyes become irritated or burned. These include:
Publication date: 07/22/2002