UV combats air handler contamination
02/01/2002
Mark A. DeSorbo
TULSA, OK —A research study conducted in a 286,000-square-foot building that houses Public Service Company of Oklahoma indicates that use of ultraviolet radiation within air handling units can drastically reduce microbial contamination.
Mold growth in and around HVAC system coils and drain pans was causing maintenance and management headaches at the energy provider's headquarters, even after cleaning all the air handling units and applying a germicidal agent several times a year.
"In a short while, various odors would signal that the mold and bacteria had returned," reports Tom McKain, building services coordinator.
McKain looked into the use of germicidal ultraviolet light devices that are manufactured specifically for HVAC systems by Steril-Aire Inc. (Cerritos, CA), and installed a few units on the fourth floor of the building.
According to testimony on Steril-Aire's Web site (www.steril-aire-usa.com), the application was a success, and UV emitters were installed throughout the entire 82-year-old building, which was remodeled in 1976. McKain also reports that coil and drain pans are reported free of mold, reducing chances for microbiological problems.
"Cleaner coils also improve heat transfer, and employees are no longer complaining about the odors," he says.
HVAC harboring happens
The situation at Public Service Company of Oklahoma is not uncommon. In fact, fungal contamination is a widespread phenomenon in HVAC systems and a major contributor to building-related illnesses and diseases, says Dr. Estelle Levetin, the mycologist from the University of Tulsa who led the study.
Although research was conducted from 1996 to 1997, a report of the university study wasn't completed until years later, or submitted to the American Society of Microbiology until August 2001.
According to a report, the analysis involved eight of the main air handlers on two floors. One floor with four air handlers was outfitted with UVC emitters from Steril-Aire and designated as the study floor, while the floor without emitters was labeled as the control floor.
Installed within 15 to 20 minutes, Steril-Aire UVC emitters resemble fluorescent lighting tubes, which are positioned downstream, facing the coil of an air handler. While it is obvious what "UV" means, the "C" in UVC refers to the germicidal properties the lamps have once the mercury within the bulbs is vaporized to produce a broadband UVC energy of about 260 nanometers. Each tube produces the specified output at any airflow velocity and air at temperatures of between 35-120 degrees Fahrenheit. Emitters produce no ozone or other secondary contamination, according to Steril-Aire.
The research team took air and surface samples from all air handlers in the spring, before the air conditioning was turned on, and in the fall after cooling season. The objective was to prove that fungal contamination of HVAC systems is a year-round condition that can be effectively reduced through proper application of UVC.
Fighting fungus amongus
Surface samples taken from the air handler insulation prior to cooling season and before the UVC emitters were turned on contained nearly identical concentrations of fungi—approximately 212-213 x 103 colony-forming units (CFU)/cm2, according to the report. The most common contaminants found included penicillium, aspergillus and cladosporium.
After the cooling season, fungal concentrations increased more than tenfold to 2,240 x 103 CFU/cm2 in the untreated air handlers, while concentrations decreased to 30.5 x 103 CFU/cm2 in the UVC-treated air handlers. That's nearly a 99 percent reduction in the contamination of the insulation surfaces, the report indicates.
"Germicidal UV irradiation may be an effective approach for reducing fungal contamination within air handling units," Levetin adds.
Furthermore, the study indicated that there were significantly lower levels of contamination within the fiberglass insulation of air handlers outfitted with UVC emitters. Similar results occurred with the air samples, according to the study.
Sampling in the spring showed microbial concentrations to be similar in the control and test units—about 21-22 x 102 CFU/cm3. After the cooling season, the control units with no UVC experienced a tenfold increase in fungal concentrations to 239.52 x 102 CFU/cm3, while the UVC-treated air handlers experienced nearly a tenfold reduction in fungi (to 2.98 x 102 CFU/cm3). Again, there was a 99 percent reduction in the number of microorganisms circulating through the air handlers from and to the occupied space, the researchers note.
Forrest Fencl, Steri-Aire's president and chief executive, says the study provides "further evidence of the beneficial effects" of the use of ultraviolet radiation.
"Building operators consistently report that the use of UVC yields a noticeable difference in air quality, while enabling them to reduce or eliminate costly cleaning of coils, drain pans and plenums," he adds. "Also, because there is no mold or organic buildup to compromise performance, air handling equipment runs more efficiently and energy costs are reduced."
Applications abound
Fencl contends that Steril-Aire UVC emitters are not only intended for homes and office buildings. Cleanrooms, hospitals, schools, food processing and pharmaceutical plants can also beef up contamination control protocols, he says.
A case study on the company's Web site indicates that The Queen's Medical Center in Honolulu opted for UVC to combat mold, bacteria and airborne pathogens, which thrive in Hawaii's tropical environs.
It cost the hospital about $115,000 to install Steril-Aire's UVC emitters. Typically, UV germicidal irradiation in a 20- to 30-ton air handler would cost $2,000 to $3,000, but in a hospital environment such as Queen's Medical Center, which takes diseases like tuberculosis into account, the cost was $4,000 to $6,000 or more.
Annual maintenance costs, according to the hospital, range from $720 to $1,080, and that upkeep consists of changing the UV tube once a year. Upper air fixtures cost about $3 to $5 per square foot with annual maintenance cost of about $0.50 to $1 per square foot.
Before the UV emitters were installed inside the air handlers, Queen's Medical paid to have air conditioning coils and drain pans cleaned annually. Now, the areas are inspected every three months, but since the installation a year ago, no slime has grown and the system is operating at nearly 100 percent efficiency.
"Staff members and visitors notice that the air is fresher and cleaner—and without the musty odors often found in high-humidity environments," the hospital's testimony indicates.