UVC Lights Enhance Indoor-Air Quality at Wastewater-Plant Office Facility

Built in 2002 to accommodate nearly 400 city employees, the Pregerson Building, located at the center of the Hyperion Wastewater Treatment Plant in Los Angeles, quickly became the source of complaints about poor indoor-air quality and odors.

“Our investigation of the complaints found two major problems with the building,” Daniel Strauss, PE, mechanical-engineering manager for the Environmental Engineering Division (EED) of the Bureau of Engineering of the City of Los Angeles Department of Public Works, said. “First, the fresh-air-intake louvers positioned on the face of the building, next to the primary settling tanks, pulled foul air into the building and distributed it via the air-conditioning system. Hydrogen-sulfide (H2S) concentrations of nearly 100 ppb were measured in the office areas.

“Second, the building was under negative pressure, and contaminated air infiltrated into the building through the main entrance doors at ground level.”

To address these problems, the EED selected an odor-control unit that purifies outdoor ventilation air by scrubbing out obnoxious elements. Custom-manufactured by Energy Labs Inc. of San Diego, the equipment contains three banks of activated-carbon filters for H2S removal and two stages of air filtration for particulate capture. A variable-frequency-drive-powered fan, meanwhile, overcomes airflow restrictions and introduces outside air in sufficient quantities to maintain positive pressure in the building.

To provide added insurance against airborne contaminants, the EED specified high-output ultraviolet-C (UVC) lights from Steril-Aire Inc. at cooling coils in air-handling units.

“We had seen presentations about UVC's ability to kill airborne bacteria, as well as surface and airborne fungal contaminants, which are also a cause of widespread discomfort and health problems,” Strauss said. “We believed the addition of UVC lights would allow us to do a complete job and ensure the highest level of indoor-air quality.”

UVC is the most germicidal wave-length in the ultraviolet spectrum. Installed in an air-handling system, UVC lights emit enough of this energy to penetrate — and subsequently kill or deactivate — even the tiniest microbe. In this manner, UVC effectively stops both surface organisms that grow inside of HVAC systems and airborne microbes that circulate through HVAC systems to occupied spaces, including the mold and bacterial contaminants that tend to proliferate in standing water in cooling-coil and drain-pan areas. Additionally, many users of UVC technology report that it generates a “fresh-air” smell in buildings by keeping air-handling systems free of mold and organic buildup.

“Since implementing these improvements in mid-2006, we have eliminated odor problems and the accompanying complaints,” Strauss said. “Presently, the building is under positive pressure, and the ventilation air has less than 2-ppb H2S, making the system at least 98-percent efficient in H2S removal. The UVC lights add an extra dimension of protection, and we believe the benefits exceed the cost.”

The UVC lights require no maintenance, other than periodic changeout (about once a year).

“We believe UVC technology has broad application for all types of buildings and have recommended that it be incorporated into the Bureau of Engineering master specifications for all our HVAC equipment,” Strauss said.

The Pregerson Building air-quality-upgrade project was named a semifinalist in the 2006 Quality and Productivity Awards competition mounted by the city's Quality and Productivity Commission. Based on a rigorous eight-month application and review process, the awards program “recognizes and honors city-employee teams for their initiative, creativity, teamwork, cost-containment efforts, and entrepreneurial spirit in providing a high level of customer service.”

Information and photographs courtesy of Steril-Aire Inc.
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