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Welcome to the UV Resources "Engineering" page. Here you will find an increasing number of tools that we believe will help you in understanding, sizing and specifying UV-C products on most all of your projects. UV Resources is first to utilize ASHRAE's recommendations in the development of a generic performance specification that most UV manufacturers can bid competitively. The specification also helps to remove the mystery surrounding how much UV-C energy is enough? To do this it calls for "Watts per square foot (W/ft2) of coil surface" instead of the more confusing microwatts per square centimeter (µW/cm2), which is primarily used by researchers and academia, and which UV manufacturers "were" once predisposed to use.

Why Lamp Watts?

UV-C specifications for keeping coils clean and prohibiting microbial growth and transfer, have ranged from 100 to 2500 µW/cm2. Yet one device can meet all of those numbers, which begs the question:

What assures the correct energy and how can a specification be written that everyone can understand and properly bid..... competitively?

Here you'll find an established way to specify UV-C using "Lamp Watts" — the same method used to specify lighting products and purchase replacement lamps. The simpler method applies to all manufacturer's UV-C products, and one that, all can understand, bid to, and verify.

As with all lamps, lamp Watts are printed directly on them and UV-C lamps are no different. Therefore lamp Watts can be incorporated to more simply and correctly calculate what's required in accordance with ASHRAE's recommendations. Like with general lighting it also becomes easier to specify, review submittals and pass the selections on to users for them to purchase the proper replacement lamps.

To enable this easier to understand and specify approach, we have included a simple calculator with sample calculations. This will assist in determining the Watts per square foot needed for any surface irradiance project such as a coil, etc. - which you will need in order to apply UV-C in accordance with ASHRAE's recommendations.

Based on published findings of disinfection and degradation rates of microorganisms and organic debris, combined with past and current work performed by ASHRAE's Technical Committee*, the data demonstrate that the average UV-C lamp Watts per square foot to clean or keep a coil clean is "6" Watts. Using a typical "lamp to coil" distance of 12", this translates to an average > 800 microwatts per square centimeter (µW/cm2) or greater than ASHRAE suggests.

As microwatts are biased by a lamps distance to a surface (inverse square law), lamp Watts become easier to compare submittals to specifications. Microwatts increase as a lamp is moved closer to a surface therefore it's difficult to prove or disprove the number. Lamp Watts is lamp power not influenced by distance and easy to prove!

To use the current method click on the calculator button below. It converts plenum size to lamp Watts and number of lamps needed! "Note" that microwatts produced at one meter by any lamp from all major lamp manufacturers is about three times the lamp Watts, i.e. 145 Watt lamp equals 442 microwatts at one meter.

For your convenience, we have provided the lamp watts for UV Resources lamps within the calculator page. However, you can use any manufacturer’s lamps as long as the lamp Watt data is published and printed on the lamp (just like lamps at Home Depot!). Read ASHRAE’s 2008 and 2011 Handbooks for more information.

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