Thoughts on UV light system in HVAC ?

[Perry Holbrook]

I met with the HVAC contractor for the new house this week. Unusual design of the house is creating a few challenges but he seems to have a handle on that. In my past life I dealt with many companies in that trade and know they live on up selling to customers that are uninformed. He does not seem to be in that category. I'm wanting to do a few things that seem to be out of the ordinary although he has done before. I want thermostats that will control humidity as well as temp and a fresh air damper with enthalpy control. During our discussions he mentioned installing UV light systems in each system. We are not germaphobes at all but after the last couple of years experiences it's worth taking a look.

Anyone have experiences with these UV systems?

Thanks,
Perry

[Malcolm McLeod]

No experience on HVAC-UV, but general impression I've gotten from reading is that HEPA filters will get you most of the way 'there'. I'd assume the CapEx for UV is certainly higher, but (replacement) filter's OpEx will eventually catch up (UV will have some OpEx too).

[Ole Anderson]

We installed three of those systems in our air handlers at church. One more item to check off on the Covid 19 list. Not just UV light, the LED UV light hits a catalytic-like converter, generating "hydro-peroxides" that are circulated by the air handler "destroying harmful microbials in the air and on surfaces" according to the brochure. My son, who is in the HVAC supply industry, says they have been selling these to contractors like crazy for commercial and institutional installs. Many schools are installing them before opening up. The brand we got was Reme-Halo. https://www.rgf.com/products/air/reme-halo/

[Curt Harms]

I wonder what the required exposure time is for UV to kill most pathogens. I have zero knowledge of such things but gut says air passing through some sort of chamber isn't going to be there long enough to do much.

[roger wiegand]

My experience with UV sterilization in the lab suggests that it would either be extraordinarily expensive and complicated or ineffective window dressing. To kill bacteria and viruses you need very powerful short wavelength lamps (quite dangerous and expensive to buy and run), typically with pretty long exposure to get a few logs of killing. To treat a moving air stream you'd either have to have a large apparatus with many lamps or extremely powerful lamps. The lamps also only last ~6 months in use before UV production falls too far to be useful, so a regular ongoing expense that could run many hundreds of dollars a couple times a year.

Alternately, they sell you a box that makes some bluish light and does essentially nothing. Unfortunately, unless you are dealing with someone who makes systems for BL3/4 biocontainment labs, this is what your local HVAC provider is likely trying to sell you.

HEPA filtration is a far less expensive and more effective route to a microbe-free air flow (well, ~99% reduction). HEPA filters aren't cheap, however and also require regular replacement to maintain efficacy. You'll want a pre-filter system to try to keep your expensive HEPA filter clean. I'm not sure any of it is worth the trouble in a home environment; wearing a good surgical mask when you have visitors will accomplish more for a much lower cost and hassle factor.

[John K Jordan]

I have no experience other than having a high-intensity UV lamp for treating small items. A quick google search gave a lot of information from people wanting to sell UV systems, often not reliable sources.

I found an page by the FDA that includes some information about UV systems in HVAC ducts and compares it to other options. This is page is primarily concerned with the coronovirus but has other perhaps useful information. A lot of reading.

https://www.fda.gov/medical-devices/...nd-coronavirus
Some appropriate links in the Q&A section, such as:
Q: Where can I read more about UV radiation and disinfection?

I also see a paper by the EPA that might be interesting but I didn't skim through it:
https://cfpub.epa.gov/si/si_public_f...load_id=459522
Technology evaluation report
Biological Inactivation Efficiency by HVAC
In-Duct Ultraviolet Light Systems

JKJ

I met with the HVAC contractor for the new house this week. Unusual design of the house is creating a few challenges but he seems to have a handle on that. In my past life I dealt with many companies in that trade and know they live on up selling to customers that are uninformed. He does not seem to be in that category. I'm wanting to do a few things that seem to be out of the ordinary although he has done before. I want thermostats that will control humidity as well as temp and a fresh air damper with enthalpy control. During our discussions he mentioned installing UV light systems in each system. We are not germaphobes at all but after the last couple of years experiences it's worth taking a look.

Anyone have experiences with these UV systems?

Thanks,
Perry

[George Yetka]

Uv lights are ineffective in most cases.
They work best in a situation where a room is used for a couple hours and not used for a long while after. (churches for example)
-In most commercial situations the velocity in the ductwork is fairly high usually just under the noise threshold. UV lights work better at low velocity giving the UV a chance to work.
-For them to be effective even at a lower velocity would require multiple air changes. Many commercial spaces wont give them a chance to work.(Places that close and keep the circulation going may benefit but after a bunch of employees and customers are there it has to start the process over again.)

Residentialy they may be more effective the units are relatively small and the air velocity not too high plus you will have much fewer amount of people.

I feel they are capitalizing on fear. They dont do nothing but they arent going to do as much as people expect.(expect annual bulb changes)

I do have one on my well water it is an oversized commercial unit and has been effective. So im not a complete hater. I just dont think they do enough in the commercial HVAC realm

[Jack Frederick]

When I was in my business I represented a manuf who offered UV lights. Now, this was 15 yrs or so ago. They decline in effectiveness over time. I believe it is called solarization. How often they need to be replaced and the performance curve over time would be useful in making a decision. I think you would be best with one of Trion’s Air Bear 5” MERV 12-13 pleated filters. Adding that to existing duct work and equipment has to be calc’d out as the resistance to air flow through the tighter filter can screw up the systems static pressure.

[Stan Calow]

I wonder what the required exposure time is for UV to kill most pathogens. I have zero knowledge of such things but gut says air passing through some sort of chamber isn't going to be there long enough to do much.

Agree. UV needs exposure time to kill things.

[Brian Elfert]

Many HVAC guys will recommend a cheap filter as a better filter can restrict air flow. Air conditioning needs good air flow to work properly and not ice up the coil. I would think a system specifically designed for a HEPA filter or other more restrictive filter would be fine.

[Alan Rutherford]

Funny you should ask. Yesterday we had our system cleaned for the first time since it was installed, about 5 years ago. It's a relatively modern 2-ton sytem with a heat pump outside and air handler inside. A friend who knows what he was taking about convinced me to get a UV light in the air handler. When the HVAC guy opened up the air handler yesterday, it barely needed cleaning and there was no hint of mold or mildew. He thought that was largely due to the UV light.

If what you want is sterile air, I don't think this is the way to do it, but it can help keep stuff from growing inside the air handler. If you clean the system more often than I do, it might not make any difference but in this case I think it paid for itself. BTW, the packaging urged me to replace it every year. I haven't and it still seems to be working.

[Curt Harms]

Funny you should ask. Yesterday we had our system cleaned for the first time since it was installed, about 5 years ago. It's a relatively modern 2-ton sytem with a heat pump outside and air handler inside. A friend who knows what he was taking about convinced me to get a UV light in the air handler. When the HVAC guy opened up the air handler yesterday, it barely needed cleaning and there was no hint of mold or mildew. He thought that was largely due to the UV light.

If what you want is sterile air, I don't think this is the way to do it, but it can help keep stuff from growing inside the air handler. If you clean the system more often than I do, it might not make any difference but in this case I think it paid for itself. BTW, the packaging urged me to replace it every year. I haven't and it still seems to be working.

I can believe that would work. The air handler surfaces are exposed to UV whenever the UV source is on, they aren't exposed for a few seconds on the way through.

[Ole Anderson]

Seems to be some confusion here. There are (at least) two UV systems. Those that rely solely on UV radiation to kill bad stuff and those that use UV light to create an oxidizer that are dispersed via the HVAC system. The latter use a UV sensitive catalyst to generate H2O2 ions.

[John K Jordan]

Seems to be some confusion here. There are (at least) two UV systems. Those that rely solely on UV radiation to kill bad stuff and those that use UV light to create an oxidizer that are dispersed via the HVAC system. The latter use a UV sensitive catalyst to generate H2O2 ions.

Just curious, what levels of hydrogen peroxide are released into the room air? What does that do to lungs?

[Myk Rian]

Getting off the UV question, how many hvac systems are being installed?
How many zones for each?

Humidity is best read and controlled by the return air readings. If several zones are involved, controlling them individually would be a nightmare.

I have a skuttle feeding outside air to the return duct. We close it during the summer to prevent the Michigan humidity from invading.