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UVC Helps Institute Keep Indoor Air, Cooling-Tower Makeup Water Clean

It is well-known that poor indoor-air quality (IAQ) can be harmful to building occupants. In a biotechnology laboratory, it can be detrimental to the integrity of sensitive research and experiments as well. That is why, after opening a new 72,000-sq-ft facility in Newark, Del., in 2001, the University of Delaware's Delaware Biotechnology Institute (DBI) pressure-washed the coils in two 45,000-cfm air-handling units (AHUs) three or four times a year. Still, Robert Pekala, engineering and operations manager for DBI, was not satisfied.

“In 16 years of dealing with IAQ issues, I have learned that even the most diligently maintained building develops indoor-air-contamination problems within a few years …,” Pekala said. “Though the level of biofilm we measured in the … AHUs was much lower than what you see in most buildings, I knew from experience that it would worsen over time.”

Working with General Aire Systems Inc., a Darby, Pa.-based manufacturer's representative, distributor, and service company specializing in HVAC air-cleaning technologies, Pekala concluded that high-output UVC Emitters manufactured by Steril-Aire Inc. used in combination with high-efficiency air filters would provide the added protection DBI needed.

General Aire performed a life-cycle-cost and energy-savings analysis that projected a six-month payback on the initial investment, followed by $18,000 in savings the remainder of the first year and $36,000 in annual savings thereafter. The estimated savings came from reductions in the electrical energy needed to run the air handlers. By keeping coils free of organic build-up, germicidal ultraviolet-C (UVC) light reduces pressure drop across coils and increases net cooling capacity. Energy savings of 15 to 20 percent and higher have been documented routinely in buildings using the technology. Additionally, Pekala noted, DBI is reaping labor savings from the elimination of coil cleaning, which reduces system downtime and frees in-house crews for other tasks.

General Aire installed the UVC lamps in September 2005. Prior to startup, Rebekah Helton, PhD, a microbiologist and researcher at DBI, sampled the biofilm and condensate in the AHUs. Within a few weeks of the lamps' installation, all visual biofilm had disappeared from both AHUs. Since then, the coils have remained pristine; samples taken one year later revealed no biofilm. Viral abundance within AHU condensate was below detectable limits, and no bacteria were detected.

Except for annual changeout of the bulbs or lamps by a DBI in-house HVAC technician, the UVC devices require no special maintenance.


DBI discovered an unexpected benefit of the UVC devices: Condensate from the coils now is so clean that it can be collected and pumped into the cooling tower as makeup water, substantially reducing water use.

“The biofilm that builds up on coils can contaminate not only the air that circulates through the building, but also the condensate water that is created as the system cools and dehumidifies,” Pekala said. “If you were to take that water from an air handler untreated with UVC and add it to the cooling tower, you would have to increase the use of biocides and chemicals substantially to counteract the added microbial contamination in the cooling tower. With UVC, however, the condensate coming off the air handlers is essentially distilled 55°F water that we can confidently pump into the cooling tower.”

During cooling season, Pekala said, the AHUs produce 2,000 to 5,000 gal. of condensate a day. Added to the cooling tower, this water can replace roughly 30 to 50 percent of the 7,000 to 10,000 gal. that evaporates from the cooling tower every day during hot weather conditions.

Since starting the program in 2005, DBI has experienced a direct savings of $4,000 to $6,000 in water costs during the cooling season.

“We have been able to accomplish these savings with no increase in the level of biocides used in the cooling tower,” Pekala said. “This can be attributed solely to the germicidal effects of the UVC devices.”

Information and photographs courtesy of Steril-Aire Inc.

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