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Chandra Sekhar, Ph.D., National University of Singapore
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Li Ting Soh, Environmental Health Institute, National Environmental Agency
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Vivien Goh, Environmental Health Institute, National Environmental Agency
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Hooi Ming Yap, Environmental Health Institute, National Environmental Agency
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Yi Wang, National University of Singapore
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Ramona A Gutiérrez, Environmental Health Institute, National Environmental Agency
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Lee Ching Ng, Environmental Health Institute, National Environmental Agency
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Kok Wai Cheong, Ph.D., National University of Singapore
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William P. Bahnfleth, PhD, P.E., FASHRAE, FASME, Pennsylvania State University
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In a hot and humid climate, the year-round wetting of cooling coils and drain pans make them ideal breeding grounds for microorganisms, which may have adverse effects on indoor air quality. Ultraviolet coil irradiation systems are marketed on the basis of claims that they will improve coil performance and save energy. The disinfection performance of a coil irradiation system was investigated via a field study. A commercially available coil irradiation system was installed on the downstream side of a cooling coil in a variable air volume (VAV) air handling unit (AHU) serving a library building. The disinfection performance was assessed by a “before” and “after” irradiation comparison of bio-contamination level on coil surfaces and in condensate water. Surface biological samples were collected from both upstream and downstream side coil fin surfaces based on a 2 × 3 sampling grid using spear-shaped absorbent swabs. Water samples were collected from condensate drain pan. Seven samplings were conducted (two before irradiation and five after irradiation) throughout the study. The measurements taken showed that 1) bio-contamination on the surfaces of this coil was mainly fungi contamination; 2) neither bacteria nor fungi could be isolated from downstream surface samples after four weeks of irradiation, except for those collected when the outdoor air bio-contamination level was high; 3) neither bacteria nor fungi could be isolated from water samples after six weeks of irradiation. The above observations suggest that coil irradiation systems may be effective in disinfecting coil surfaces and drain pans in a hot and humid climate.
