Specifying antimicrobial coating for ductwork

[mrev23]

Are the benefits of using an antimicrobial coating on ductwork justified by the added cost?

It is not mentioned in the VA's specs here:

http://www.wbdg.org/ccb/VA/VAASC/VA 23 31 00.pdf

My read is that the colloidal silver coating:
[ol ]
[li]Is activated by moisture; If the inside of the duct is dry, as it should be, the product remains dormant.[/li]
[li]Is inhibited by dust between the coating and the contaminant; If the duct has a thin layer of dust, as it probably will, the product may be prevented from acting on the organisms.[/li]
[/ol]

One supplier cites a study comparing counts of microorganisms ten years after a remodeling project where the antimicrobial coating was used on new ducts. There is galvanized duct without the coating in the same project. I didn't find mention of how long the galvanized duct was in service prior to the remodeling project. The old ductwork may have been gathering contaminants for several decades. So the comparison may not be between ducts with and without the coating that were comparably clean ten years ago.

I am skeptical that the antimicrobial coating is worth the extra cost.

Has anyone found this coating to be necessary (possibly to appease lawyers or LEED) or beneficial?

 

[EnergyProfessional]

I didn't know the effect is limited to moisture. i wonder at what RH level, or only on wet surfaces? the reason is that micrbiological growth happens before you actually have moisture (RH 100%). So in a suppplyduct with air leaving the cooling coil you have above RH 60% = growth.

I think if you silver-coat the coil (this is done in some premium car AC to prevent the musty smell when starting the AC) and make sure no organic material (duct liner etc.) is in the downstream side and filter the air going to CC (use MERV 13 or higher) you should be more than safe if the VA is concerned about microbiological growth.

silver-coating the entire ductwork seems a waste. Do the above if you want to go above and beyond or the client wants it.

For growth you need three things: moisture (even when not liquid), organic material, and acceptable temperature. With temp you don't have much of a choice since other factors dictate your supply temp.

As far as dust goes, if it settled and is dormant, then it doesn't go into the space. Like asbestos, only an issue if you stir it up.

 

[Drazen]

coil coating is anti-fungal, which is different from anti-microbes, as whatever kills microbes would hurt yourself much as well, whatever sellers say.

anti-fungal serves to prevent fungus growth on wet surfaces, which has little to do with normal use of ventilation ducts.

in reality nothing but regular and proper cleaning can keep your ducts healthy. special coatings are used for chemical resistance against special conditions of atmosphere, but that only applies to exhaust ducts, supply ducts bring what you breath and no any experiments are acceptable in that domain.

 

[urgross]

They may have concerns on Legionella. If you have access to VA Directive 1061, you may agree that the VA can go overboard follwing an event of legionella. For potable water systems, this will be hundreds of millions of dollars over many years to implement. They may have concerns over MRSA or aspergillus (a boogie man for Infection Control) as MEDICARE/MEDICAID will not pay for hospital acquired infections, which might be a large part of their cusomters.

Duct work is already specified to be mold resistant by reference to ASHRAE 62.1. Only problem I see is continuously wetted areas of the duct, such as at the cooling coil or in duct mounted humidifiers, such as with OR and SPS. I've seen some severe problems with duct mounted humidifiers when they go out of control. Typically, OR doctors and ORN's prefer a higher humidity level, 50 to 60%. Ionic silver coatings may be an alternative to using UV at problem areas such as at the cooling coil.

From my experience, Drazen is corrent. That is why OR and SPS ductwork is cleaned on an annaul basis. Funny thing, the O&M requirement does not mention NADCA por any other standard or accreditation.

NIH issued a paper on this, which an overzealous IC might have read. Ionic silver dramatically reduces legionella at 37*C. When is your duct work in a hosptial going to be at 37*C? The VA already requires complaince with ASHRAE 55, so it should be rare to see tmperatures higher than 95*F.

I think coating the entire duct with product would be an extravagant waste, but might be acceptable for areas where UV might otherwise be applied. You might want to discuss concerns with their Infection Control. If you say "legionella" they might even defecate in their shorts for you.

 

[mrev23]

Thank you for the replies. To clarify: this is not a VA project. I looked at the VA spec because I thought "if anyone wants silver-coated ductwork to control the growth of microorganisms, it would be the VA." But it does not seem that they require it anywhere.

 

[EnergyProfessional]

since urgross mentioned humidifiers: whatever "doctor" requires a humidifier should open one up and see how much growth is in there (and consequently in the air). Yes they may add UV light, but that only kills so much and also is not always maintained. and having 50-60RH in winter will cause mold growth in the entire perimeter wall. Our daughter's doctor always suggests to my wife we get a humidifier. He doesn't know buildings, he doesn't know how high humidity is in our house (over 30% in winter...) - but he says we need a humidifier. Next time I will advice one of his patients what medicine to take without knowing medicine and without ever seeing that patient...

and those "doctors" requiring 50-60% RH should look up in a biology book at what RH levels microbes like to live....

If they are really concerned about growth on the coil (hard to imagine if it has filters and gets maintained/cleaned) you can have it silver-coated. If they are concerned about microbes traveling around (return air), a UV chamber may help. anything else seems to be snake oil.