There is a renewed interest in the application of UV to the treatment of indoor air and heating, ventilating and air conditioning (HVAC) equipment. UV treatment of air was popular in the 1950s and was utilized in areas such as food preparation and medical facilities. It was particularly popular in the control of tuberculosis.

Recently there has been a renewed interest in improving indoor air quality (IAQ) with UV. As with water, the public has become more concerned with the quality of its air. Many factors in our environment have put pressure on our air quality.

• Tighter homes and buildings (i.e., less fresh air and ventilation).
• Energy saving measures.
• Decrease in the quality of outdoor air.
• Substantial increases in the incidence of asthma.
• Sick building syndrome.
• The realization that mold (fungi) in the air can cause serious health problems within a building.

Basically two applications of UV are becoming common. In one, the moving air stream is disinfected in much the same manner as with a water system. In the other application, stationary components of the system such as air conditioning coils, drain pans and filter surfaces are exposed to help prevent mold and bacteria growth or to disinfect the filter to aid in handling.

The transmissibility of UV in air is far better than in water and, therefore, the number of lamps required in a large duct is quite reasonable. Common airborne virus and bacteria are readily deactivated with UV. Fungi (molds and spores) require much higher doses. Usually only the 254 nm wavelength UV is used in air as 185 nm produces ozone, which is undesirable in indoor air applications.

In the moving air stream, high wattage lamps are used, usually without a quartz sleeve. Proper system design accounts for the cooling effect of the air stream, the reflectivity of the ductwork and proper geometry. As a large portion of the air in a room generally is recirculated, air quality can be improved with each pass.

In the treatment of stationary components (AC coils, filters, etc.), UV wattage can be quite low as residence times often are up to 24 hours per day. UV lamp fixtures are placed in such a manner as to completely irradiate surfaces where bacteria and mold might collect and grow.

Math modeling (software) and bioassay testing have been developed, to allow efficient design and validation of these system.3

Applications utilizing UV for disinfection and removal of certain contaminants are becoming more and more popular. Low operating costs and reasonable equipment costs can make UV very cost effective. Since UV disinfects without the addition of chemicals, it often is a preferred treatment where clean water, taste and clean air are required.

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