Re: HVAC coil dirty sock syndrome

November 12, 2005

What is a coil?

>

> Our coil keeps developing " dirty sock syndrome " every year around

this

> time. I am so sick we actually have to have the coil removed and

> replaced with a new one. We use good filters, have 3 UV lights

> shining on the coil, no mold visable on our walls, attic is dry,

keep

> the humidity in the house @ 50% but this keeps happening.

>

> Has this happened to anyone else, and if so have there been any

> solutions found?

>

> Lindy

>

November 12, 2005

Lindy,

This is fairly common, though not as gross as in your case. To help

you and the others understand what is happening bear with me for a

short tutorial and then a suggestion.

A/C coils are sometimes called A-coils because they are shaped like

an A-frame house. The are usually at the top of a residential furnace

above the heat exchanger. They are a mass of fins that look a lot

like a car radiator and they are chilled just like in a refrigerator.

If the coil temperature is lower than the dew point of the air

flowing through it (dew point is the combination of temp and humidity

where the air can't hold anymore moisture and it begins to rain) then

the moisture condenses on the coil just as when you set a glass of

ice water on the table and moisture collects on it. In fact, below

the A-coil is a drip pan to collect the water and a hose so it can

flow into a drain opening near the furnace.

The coils and surrounding ducting create a micro-environment that can

create a small location of 100% humidity even if your house is below

50%. Because the coils are wet a lot, normally-occurring bacteria

begin to grow in the film of wetness, creating a biofilm somewhat

similar to plaque on teeth. Very stubborn to remove and providing a

breeding ground for more bacteria and eventually mold. Over time, the

" plaque " gets thicker and begins to fill in the tiny slots between

the fins. Also, more dust - even the stuff too small to be captured

by good filters - collects and builds. Without a decent filter,

bigger dust and even lint, threads and hair from pets and people will

collect. I've seen a layer so thick and strong with fibers you could

almost make a (smelly) sock out of it!

This micro-environment is originally too wet and too clean for mold

to grow first. But as the bacteria grow and die it provides the food

for more bacteria and eventually mold. Also, other " stuff " collects

and begins to rot. As air blows over and through it, any odor and/or

spores generated blows throughout the whole system, which is your

house.

Why don't the UV lights work? Three possible reasons:

1. There was already too much stuff on the coils when the UV was

installed. They don't cure the condition but may be helpful in

preventing it or slowing it down.

2. The UV lamps, no matter how many you have, are typically installed

to shine on the top of the coils but the air comes from below. So the

UV shines on the top but the " plaque " and the dust collect on the

bottom. Another reason I'm not hot on UV in A/C unitsl

3. The moisture may also be wetting the insulation that is inside the

duct walls near the coils. If so, this can be removed and the source

of the odor, etc, is removed. This is often why the odor is like a

dirty sock rather than somethng else.

Suggestion:

Before you pay for the cost of replacement, find out if the

insulation is wet and/or the bottom of the coils can be cleaned. Go

to www.nadca.com the web site for the National Air Duct Cleaners

Assoc and find a NADCA member in your location. Ask if they are

familiar with duct cleaning standard ACR 2005 and the coil cleaning

requirement. If they are, they may be able to remove the wet

insulation and/or clean your coils instead of replace them.

If they aren't, let me know offline and I'll put you in touch with

someone who might be able to help.

Carl Grimes

Healthy Habitats LLC

-----

> Our coil keeps developing " dirty sock syndrome " every year around this

> time. I am so sick we actually have to have the coil removed and

> replaced with a new one. We use good filters, have 3 UV lights

> shining on the coil, no mold visable on our walls, attic is dry, keep

> the humidity in the house @ 50% but this keeps happening.

>

> Has this happened to anyone else, and if so have there been any

> solutions found?

>

> Lindy

>

November 13, 2005

Carl, as usual, has given a very good answer. I would like to make a few

additions. Carl recommends seeing if the insulation is wet. Ken ez of

NIOSH recommended to me that all insulation inside HVAC equipment be

removed, and insulation placed outside the metal ductwork if desired.

Insulation is prime mold growth area. Another unfortunately too common

problem is the use of unlined fiberglass ductboard. This material traps dust

just like filters do, and with the moisture from the HVAC, becomes a mold

garden. If you have this material over your HVAC system, consider replacing

it with sheet metal. It also has the drawback that it cannot be effectively

cleaned without extensive damage.

Another recommendation is to run your fan continuously. If not, in the

cool of the evening, when the system is not running, the moisture in the

drain pan evaporates into the air space inside the HVAC system, creating

100% RH. The temperature in there is no longer the cool air conditioner

temperature, but room temperature, conditions more ideal for mold growth.

Running the fan continuously prevents this situation.

Date: Sat, 12 Nov 2005 15:01:40 -0700

From: " Carl E. Grimes " <grimes@...>

Subject: Re: HVAC Coil Dirty Sock Syndrome