Apr 29, 2020 UV-C Lamps: Installed, Yet Not Forgotten
You’re sitting at a desk and above you a fluorescent lamp is flickering or has gone out. Your immediate reaction is to get that lamp replaced with a new lamp! A UV-C lamp on the other hand is the fluorescent lamps first cousin, and it can and will suffer a similar demise! The difference is that it’s not above your desk in plain sight, rather its hidden away somewhere keeping the plenum and/or air microbially clean while it maintains the coils heat exchange efficiency, keeping energy use at a minimum! Therefore a UV-C lamp is much more important to replace.
UV-C lamps, while typically thought of as mysterious, are in fact manufactured on the same types of machines as fluorescent lamps and operate identically. However, UV-C lamps use an expensive type of glass that does not include the internal phosphor that makes fluorescent lamps “glow” to produce visible light. In other words, the UV-C wavelength (253.7 nm) is invisible to the eye, the blue light that one sees represents only 5% of the total output of the lamps. So unlike the unlit or flickering lamp above the desk or in the conference room, the visible light emitted from a UV-C lamp is not an indicator of its performance. UV lamps will continue to emit the blue light long after the UV-C output has decreased, even by more than 50%!
UV fixture design, while similar to fluorescent fixtures, is different in a number of ways. One of the primary differences is the environment in which these HVAC type fixtures are meant to operate. Its stainless steel construction is one of the main differentiators; however, the functional life difference has to be its electronic ballast design. Being in a cold, damp environment requires a robust ballast that can withstand the fluctuating electrical demands of the lamp as its surrounding air cools, warms and moves. Also, the damp environment provides an additional challenge for the electronic components and necessitates the use of a complete waterproofing… or, that it be mounted remotely outside of the plenum.
The applications of UV-C lamps are many, as mentioned, they are used in virtually all building types for HVAC surface irradiation to keep cooling coils and plenums clean, along with air filters – disinfected for “capture & kill”, and for infection control (i.e. the “on-the-fly” killing of pathogens). Another popular use since the 1940’s is upper air UVGI systems for in-room killing of airborne pathogens. In all cases, maintaining the lamps so that the installed systems are emitting the proper amount of UV-C energy to accomplish the applications goal, is of course imperative.
Most lamp manufacturers (Phillips, GE, and Sylvania, etc.) recommend removing and replacing UV lamps every 9,000 hours or 1 year (annual PM). Most quality lamps will emit better than 80% of their original UV-C output at the end of one year. In “remote” systems (mechanical rooms, interstitial spaces), there are accessories available for continuous monitoring of lamp-ballast functionality (UV-Com™) that communicate with building management systems. Monitoring of critical environments (hospital isolation rooms, etc.) for whole system performance and lamp-on hour meters (UVReport™ stationary radiometer) can be provided as well.
The locations where UV-C fixtures are typically applied has unfortunately created a situation where the lamps are “installed and often forgotten”. This has led a few users to believe they don’t work when in actuality, the lamps useful life has simply past. Whether UV-C is installed at the air handler manufacturer’s factory (common today) or retrofitted into an existing system, or even installed in the upper air of a room, UV-C should be installed, and immediately added to the building PM programs. This way it’s not forgotten and its many benefits can be enjoyed for many years to come.