Appliance Design - May 2008 - (Page 37)

UV essentially infinite. In these cases, therefore, only low levels of UV intensity are required to destroy microbes. INDoor AIr QuAlIty Installation of uV systems for a large hospital in Florida. This installation is typical of the configured approach embraced by OEM customers. Why uV? The concept of using UV to destroy microbes (such as bacteria and mold or fungi) has been understood for more than a century. UV has been utilized to disinfect both water and air. Thousands of municipal water treatment plants and wastewater treatment plants throughout the world utilize UV as a primary disinfectant. In air, UV has been used to deactivate microbes for many decades. In addition, UV has been used to irradiate the upper air in rooms and also to disinfect moving air streams in duct systems. The ability of UV to serve these applications is well understood and has led to its wide deployment. More recently, however, UV has been integrated into HVAC/R systems, on air-conditioning coils and drains pans for economic and air quality reasons. Coils and drain pans provide ideal environments for the capture and growth of bacteria and mold. Moisture from the condensate and nutrients supplied from the air stream nourish the growth of bacteria and www.applianceDESIGN.com mold and eventually the equipment can become significantly fouled with organic matter. This fouling has many detrimental effects on the proper operation of the HVAC system. As the space between fins becomes fouled, the pressure drop increases across the coil. In addition, heat transfer from the coils is decreased. Maintenance and cleaning costs increase, or if maintenance is not performed, system performance deteriorates. Indoor air quality is degraded as the fouled coils can become a source of airborne organic matter and odors. Applying UV light can provide many benefits, including reducing or eliminating the need for coil cleaning, saving energy (through improved heat transfer and lower pressure drop), and, most importantly, improving indoor air quality. Market drivers in the HVAC/R market seem to be helping the rapid growth of UV technology. Important drivers include reducing energy costs and improving life cycle operating costs. One driver encouraging OEMs to consider factory installations is the GSA specification now in effect for new building construction of government facilities. This specification requires the instal- lation of UV to irradiate the coil and drain pan. In addition, architects and engineers are beginning to specify UV in new equipment installations. Even commercial refrigeration manufacturers and manufacturers of food preparation and display coolers now find themselves exploring the benefits of UV. Design considerations There are many variables that affect the output of a UV lamp and its performance in a system. Working with an experienced UV component manufacturer can make the job of designing the system and providing a proper UV dose much simpler. Some of the key considerations are: 4UV output. The amount of UVC generated by a specific lamp. 4Air velocity and temperature. This affects the output of the lamp. 4Exposure time. In a moving air stream, this depends on the duct length and air velocity. On surfaces, this may be infinite. 4Reflectivity of system materials. Microbes must be hit by the light via direct line of sight or indirectly by reflection. It should be noted that UVC is reflected differently than visible light. (See Table 1.) applianceDESIGN May 2008 37 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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