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Ultra violet lights

Wayco Wayne_2Wayco Wayne_2 Member Posts: 2,472
on these ultra violet lights that are installed in ducts. I've seen them made to be mounted in the return duct with a turbulator to increase air exposure so it can kill germs that fly by, and I've seen them made to be mounted in the supply plenum with a bulb over each side of the evaporator coil drain pan to kill mold in the drain pan. What is the reality of these appliances. Where should they be mounted and what is their real benefit? I have a customer asking about them. (She saw them for sale in Home Depot. Arrrrrgh!) Thanks in advance WW

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  • Paul Bock_2Paul Bock_2 Member Posts: 40
    UV lights

    I'd start with a search of The News website. I think they've had some recent articles.

    I'll foment rebellion with my Opinion that UV lighting isn't the solution to our problem, it only prolongs the demise of airside systems.

    Contractors who want to get ahead of the curve will start talking about Radiant Cooling, with dedicated makeup Air Systems.

  • lchmblchmb Member Posts: 2,989

    I have installed a number of these and depending on the make depend's where they want them. They need to be in the plenum generally on the supply side so that most large airborn particles are first caught in the filter. As to performance, I honestly have no idea. Most of them are required to be on 24/7. I have seen a few wired in to the fan and limit to activate only with the blower, this seem's to me to be self defeating..
  • Ken D.Ken D. Member Posts: 836

    We have installed a number of them. We use Field Controls units. UV light does kill germs and molds. I have seen in the installed units a decrease or absence of mold. As for as hard science- how effective they are in the duct- I'll have to defer to the manufacture's literature and trade publications. Those say that they are effective. Perhaps Consumer Reports will test them soon. The best way- according to Field- to install them is to mount them as close to the outlet and/or inlet as possible before take offs and mount the light at a 45 degree angle so as to expose the maximum air to the light. The longer it is exposed, the more micro-organisms are killed. Ask your local supplier for the tech sheets.
  • Jack_21Jack_21 Member Posts: 99

    As UV is a very specific part of the light spectrum they all work the same. I think the best are those that project into the RA plenum. Be careful with plastic filters and some humidifiers as the UV may deteriorate the plastic. UV's kill zone is within 2" of the bulb. UV can sterilize up to 24" away. If it cannot reproduce it cannot grow.

    There is one unit that puts the bulb in a 4" pipe and puts it parallel to the air flow and claims higher kill rates. Whatever goes thru the pipe is killed. Look at the cross section of 4" (+/-12.5") vs the average RA duct (8-12x24) and figure how many times the air has to circulate to get thru that pipe. But...they claim higher kill rates. They all work the same if they are in the right lite spectrum.

    As to the supply side location, UV is temperature sensitive. it works best between 55 and 90 (I think those are the right #'s). Those temps are exceeded in a both H&C. Also, How much of the coil can a unit really "see". My opinion is RA is best.

    Start with a very thorough cleaning, add merv 11 air filtration, the UV lite and keep the system clean. UV is no magic bullet for less cleaning. It does what it does very well but...

    One other thing. There is a definite life to a UV bulb. They may light up but it is the "Solarization" on the inside of the bulb which decreases its output. Check the numbers and compare. I cannot remember the hr life of a bulb.

    And perhaps most important. Don't look at the damned thing while it is lit. Welders burn...and you don't want it!
  • GMcDGMcD Member Posts: 477
    My kind of thinking!

    As a somewhat "experienced" designer/specifier of medical isolation room systems and Level 3 Containment labs (as well as radiant cooling systems with DOAS), and based on my own research over the last 10 years since these things started making an appearance- yes, UV lamps will work as long as it's the right type of UV light, and the air passes over the lamp or is irradiated with enough intensity, it'll kill pretty well all the bugs. Try searching for the Saunuvox website- some good case studies there.
  • jerry scharf_2jerry scharf_2 Member Posts: 414
    watch out for ozone


    UV is high energy light, and it can break down many organic compounds. It can be effective against germs, but I'm not sure at the power and air velocities of a typical duct unit, it will get them all. Once you don't get them all, you have just created a natural selection agent to breed more resistant bugs. (This is why I hate antibacterial soap and the like.) Thinks like mold spores don't really get touched. Another benefit of UV lamps is that they can break down volatile organics such as formaldehyde. One of their best uses IMO is for mold control in A/C DX coils.

    (my ozone rant...)
    Not all UV lamps are created equal, and though it seems counterintuitive, you need to make sure you don't get a lamp that has high enough energy to produce ozone. Ozone is a seriously active chemical agent, and the EPA considers it one of the most critical forms of air polution. It's just as bad for you inside a house as it is in the smog outside (the EPA clearly says this on it's IAQ web site.) The problem with ozone as compared to the things that lower energy UV lamps produce is the half-life. Whereas the half-life of agents produced by 200+nm light is a few seconds, the half-life of ozone is about 20 minutes. Ozone is especially bad for those with respiratory problems and infants, and they stay inside the house more than active adults. The science and medicine on this is conclusive, despite what marketing people may say to the contrary.

    If the lamp doesn't explicitly say that it produces no ozone, I wouldn't put it in any house ever!

    (this rant is up there with the UL approved CO detector ones.)


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