uv lights

Craig R. Bergman_4

If you have a permanent filter make sure the filter is shaded from the UV. The filter WILL get trashed by the UV.

A little school of hard knocks there!

Bergy

seabee570

uv lights for forced air

are any of the uv lights effective in eliminating pet dander,pollutants etc,or is it ok to use just a better standard filter.wife has allergy problems.does the size of the bulb,or multiple bulbs make it more effective?
thanks

Brad White_192

You Vee, if I may

UV lamps (usually the UV-C part of the spectrum) do not remove particulates (that is for the filters to do).

What UV-C does is to maintain a level of sterility (as opposed to "cleaning" a fouled area).

Where I apply them: Downstream of the cooling coil to irradiate the coil face and drain pan. My second choice is on the upstream side of the cooling coil where they might irradiate the downstream filter face for what that is worth- less value than upstream of the filter.

Once a bio-film is established, clean it first, then maintain.

What is key is coverage and distance. Most of my AHU's with UV-C lamps have one full-width lamp set about a foot off the surface. Effectiveness with any radiation decreases with the square of the distance.
Any reputable manufacturer has literature with perhaps some white paper research to share. This technology was used in the 1940's in hospitals (with UV-A at best) along ceilings and around doors.


Bulbs are effective for about a year and I just manually switch them and leave them on. Only an automatic door kill switch to shut it off. Higher-end installations have a tinted view-port to see if it is on. (Shades of "the refrigerator light! How would you know?)

(EDIT: I came across an ASHRAE IAQ article on UV lights and the damage they cause to synthetics, plastic and rubber materials. I was also reminded that Unico, for one, tells you not to use UV within their units because of damage to the internal cabinet insulation. Caveat!)


My $0.02 anyway

Unknown

Great answer, Brad!

Brad is right. Adding a UV won't "cure" anything. If you have a condensate pan that is heavily contaminated with algae or mold, it must be cleaned thoroughly before you install the light. There are two locations where UV's are used. The more important one is over the AC coil, to minimize bio-fouling(algae growth) promoted by the damp enviroment. Heat pump coils are more susecptible than conventional units. The other location is in the return, when the UV zaps any passing airborne "bad actors", either killing them or scrambling their DNA so they can't reproduce. They don't get everything, however.

Allegies are triggered by many things, and UV's aren't going to have any effect on particles like pollen or pet dander, as Brad said. Particles and vapors generally trigger allergies. Have your wife's Doctor tell you what she is allergic to, and develop a plan from there. HEPA filters and electronic air cleaners do a good job removing particles. Vapors and gases need to be diluted and removed, either with an energy recovery ventilator, or by removing the source. Let me know if you need more info.

Dave Yates (GrandPAH)_11

extension of question

GSHP estimate yesterday. Damp concrete floor basement leads to a damp dirt-tunneled crawl space. Suggested to owner we UV both the coil and return due to the excessive humidity and that he will need to run dehumidifiers in order to prevent mold growth (already has a mold issue).

One thing I am finding to be nearly a constant: solar and GSHP requests are coming in fast-n-furious from the outer reaches of populated areas from people I might best describe as being from the fringes of society. Interesting folks who have done well at avoiding utilizing anything conventional!

Josh M.

Question Brad, where would you place the bulbs in a conventional residential application where the HP coil is upstream of the blower?

Jeff Lawrence_25

Brad,

Doesn't the contaminants have to be exposed to the light for more than a second to do any good?

Brad White_193

Hi Josh

I have most often seen them placed in the return, upstream of the filters. Most of my jobs have air handlers moving between 3,000 and 50,000 cfm so there are a few more options

But the key area is the drain pan. Not sure if an A-coil unit has a shot.

Brad White_193

Hi Jeff

Distance and time are both factors which another reason why we place them by the cooling coils and drain pans. The moisture which stays in place is the other.

I have heard from 0.5 to 1.0 seconds (500 to 1,000 milliseconds sound so much more technical, no?)

But intensity and distance vary by the square so not sure how to assess the time in those examples.

Keep in mind that you are not trying to fry particles as they move on by- (oh, you may zap a mere few and you could never cover that well, practically speaking).

Instead you are striving for surface coverage at a reasonable distance to maintain sterility in the exposed field. Keep things from getting a toe-hold in the first place!

Unknown

Dwell time...

is what we are talking here. In regular speak, that means how much time a bioaerosol is exposed to the UV. Some are killed outright, some are totally uneffected in the few milliseconds they are exposed in the return. The light over the A coil keeps the condensate pan and coil cleaner by preventing any biofilm growth and buildup. The one in the return doesn't get everything, but gets enough of the bad stuff to make it worthwhile.