UVC Technology
Despite growing acceptance, UVC devices for HVAC systems are not yet governed by an official standard. Until a UVC standard is published, there is useful independent information available from a series of test reports commissioned by the U.S. Environmental Protection Agency (EPA)
The reports compare nine leading UVC devices. The testing provides a benchmark for comparing performance of various UVC devices. (Research highlights can be accessed at www.epa.gov/NHSRC/news/news100406a.html.)
When researching UVC Germicidal Fixtures, you may come across several different types of lamp technologies.
All UVC lamps essentially consist of a quartz envelope containing mercury and other gases and electrodes. When the lamp is struck, the energy between the electrodes excites the mercury into a vapor, which produces C-band ultraviolet energy. Almost all germicidal lamps currently being used in mainstream HVAC applications have been low-pressure lamps, although High Output lamps are now often recommended. Following is information about some of the more common UVC lamps:
- Hot Cathode low-pressure lamps - this older technology, which is not very common today, uses a soft glass envelope (which devitrifies faster) and small electrodes (which put out less intensity and doesn't last as long as other lamps). They are rather inexpensive when compared to Slimline or High Output lamps.
- Slimline low-pressure lamps- these have been the most commonly used germicidal ultraviolet lamps. They utilize a much harder quartz envelope and bigger electrodes than hot cathode lamps. They can have a useful life of up to 15,000 hours and produce almost two times the intensity of a hot cathode lamp of the same size.
- High-output lamps- essentially Slimline lamps, these high-output lamps use a heavy-duty electrode and slightly different gas mixture to produce 100% more UV intensity than an equal length Slimline lamp, while still maintaining an effective life of up to 15,000 hours. The majority of American Ultraviolet UVC Germicidal Fixtures for HVAC applications use an even more efficient High Output ultraviolet lamp, and have an effective life of up to 17,000 hours (two years)
When considering UVC, be prepared to ask educated questions of potential suppliers.
What is the output of the device? Devices marketed for commercial HVAC applications fall into two basic categories—those with new generation, high output lamps introduced in the 1990s and those using conventional, older style UVC lamps not engineered for HVAC use. The germicidal output of these devices will vary widely, especially when exposed to HVAC operating conditions.
For optimum performance, the device should be manufactured to deliver output of nine microwatts per linear inch of glass measured from a distance of one meter, tested at an air velocity of 400 fpm (feet per minute), and situated in a temperature of 50°F. This information is critical because UVC output declines over time, reaching a half-life after 9,000 operating hours or slightly over one year when running on a 24/7 basis. It is necessary to start at a high enough output, based on microwatts per linear inch of glass, to ensure adequate output will be maintained throughout the service life of the device. Otherwise, the device may not be able to maintain effective microbial control.
Has the device been independently tested under HVAC conditions? Some devices are tested in warm, still air instead of cold, moving air conditions. Some are tested at closer distances than one meter (or with insulating sleeves), and such conditions can yield higher output results that are deceiving.
Where will the device be installed? For the most effective microbial control, UVC devices should be installed on the supply side of the system downstream from the cooling coil and above the drain pan. This location provides more effective control than in-duct UVC installations, because it attacks contaminants at the source to deliver simultaneous cleaning of surface and airborne microbes.
What is the dose (defined as output x exposure time to UVC) per watt? This is a measure of the energy needed for microbial control. It is a useful measure of performance, because it not only considers output but it also weighs the energy used by the device to deliver that output.
Once installed, UVC devices can serve fms as an effective way to keep the interiors of HVAC equipment free from biofilm, mold, and other types of build up.
