Appliance Design - May 2008 - (Page 36)

INDoor AIr QuAlIty USING HVAC/R systems clean up with ultraviolet light. he integration of ultraviolet energy systems into HVAC/R equipment is rapidly growing. UV has been used for many years to disinfect air and in recent years has seen increasing growth in applications to irradiate air-conditioning coils and drain pans. Initially, most of the installations of UV equipment were done in the aftermarket as retrofits. Recently, however, HVAC/R OEMs have begun to offer UV equipment as a standard or factory-installed option. The wavelength of ultraviolet light is at the low end of the light spectrum, and below the visible light range. UV light is further classified into three wavelength ranges: 4UVA (300 to 380 nanometer). 4UVB (279 to 320 nanometer). 4UVC (220 to 280 nanometer). UVA is generally used for sun tanning, and “black lights.” UVB has some medical uses, but it is UVC that is generally used for disinfection, as its wavelength range possesses germicidal properties. All microorganisms are susceptible to UVC irradiation. A microorganism’s DNA is damaged by wavelengths between about 230 and 290 nanometer, with about 260 nanometer considered ideal for that purpose. uV system specifically designed for residential HVAC systems. t by david l. witham David L. Witham is vice president of technology at UltraViolet Devices, Valencia, Calif. 36 applianceDESIGN May 2008 Certain types of mercury fluorescent lamps, designed specifically for UVC emission, produce most of their light energy at 254 nanometers so they are ideal for germicidal applications. While all microbes are sensitive to UVC irradiation, their sensitivity varies. Generally, airborne viruses and bacteria can be readily destroyed with UVC. Fungi (including molds) are much more difficult to disable and the amount of UVC needed is higher. Research in this area has been performed for decades, leading to some well-established figures for the approximate dosages required to disable different types of microbes. These figures are readily available in the scientific literature. When UV is used to disinfect an airstream, the UV levels must be high enough to supply an adequate dosage when exposure times are short, typically a fraction of a second. When trying to disable fungi in a moving air stream, it may be necessary to combine filtration and UV in order to effectively contain the microbes. When UV is used to irradiate a surface, such as a coil, filter, drain pan or duct wall, the UV lamps are typically operated continuously, making exposure time extremely long, www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - May 2008 Contents Editorial Shipments/Forecasts News Watch New and Notable Displays & Indicators Elastomers Quality & Standards Indoor Air Quality IHHS Highlights New Products Classifieds Design Marts Advertiser’s Index Association Report: PSMA

Appliance Design - May 2008

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