Welcome
to the April edition of Steril-Aire's UVC E-Newsletter. In each issue, we will
address an important question about ultraviolet C or "UVC" devices for
building HVAC systems. Steril-Aire
will also be happy to provide you with a free on-site evaluation on how to equip
your building(s) for energy, mold, IAQ and infection control using UVC technology.
If you would like to know more, contact
us today. Q.
Why is output so important with UVC devices? Is there such a thing as too much
output? A.
The UVC devices used in HVAC applications fall into two basic categories: those
with the new generation "high output" lamps introduced by Steril-Aire
in the 1990s, and those with conventional older-style lamps that were not engineered
specifically for HVAC use. The germicidal output delivered by these devices varies
widely. Output
is critical because it affects a UVC lamp's ability to perform as expected - i.e..,
to kill or inactivate microbial contaminants. Do high-output lamps deliver
too much output? Is there such a thing as overkill? Misconceptions on this topic
abound. Some
suppliers use confusing mathematical calculations to suggest that a UVC device
constantly "doses" the space with germicidal energy, an action which
adds up to thousands and thousands of doses over time. Using this logic, even
the lowest-priced, lowest output device should be adequate. But this argument
ignores two critical facts: (1) UVC output declines over time, and (2) the dosing
effect is not cumulative. To
clean coils effectively, a UVC lamp should provide output measuring 9 µWatts/cm2
per inch of glass from a distance of 1 meter, when tested in a 500 fpm airstream
of 50 °F. By definition, this requires the use of a high-output lamp. Conventional-style
lamps simply do not provide enough intensity to deliver the needed germicidal
energy over time. The comparison graph shows the dramatic difference between
the two styles of devices:
All
UVC lamps lose output on a linear basis over time, reaching their half-life after
about one year or 9,000 operating hours. For a high output UVC device, 12-month
changeout is recommended. Such lamps may continue to deliver germicidal energy
for months more, causing some suppliers to promote extended two-year service life.
However, insufficient output over the full time span is a very real risk, so annual
changeout is considered to be the best practice. To
learn more about output and other critical issues in UVC selection, click on the
link to read a newly published article, "Putting
UVC Under a New Light".
Sincerely,
Robert
Scheir, Ph.D. President
and Chairman
Steril-Aire,
Inc.
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