"Dirty Sock Syndrome" in an air/water coil

[Mikeylikesit]

Anybody ever heard of it?

I have 5 seperate air handlers with hot and cold water coils. The coils (and control components) are about 10 years new, the rest of the system is almost 50 years. About 2 years ago, one of my buildings began reporting a "musty" odor......but sporadically and not constantly. Sometimes in the morning, sometimes in the afternoon, sometimes strong, sometimes not.
The only factual correlation I can draw is that it always happens while the chillers are running.

Does not happen at all during the heating season. (this interests me, because in my limited knowledge of biology, HEAT tends to activate bacteria or mold spores, not COLD!)

So, we began inspecting. We took tape samples from all surfaces for our risk mgmnt folks to assess. (all negative other than common mold spores, and not in any quantity which would cause problems, according to the industrial hygienist. The inside surfaces (lagging) were pretty dirty, especially just after the coils, so we removed it. We steam cleaned the coils from both directions. We used several coil cleaning solutions, per directions, then steam cleaned again. This would cause abatement of symptoms.....sometimes for as long as 3 or 4 months.

(BTW, we do treat our condensate pans properly.......kind of rules the pans out as a source......I THINK!)

Now, last week, a different building is experiencing the same problem. Same smell. What is strange is that the smell seems to come in "waves", meaning it will present itself for a few minutes, or an hour, and then disappear.....with no rhyme or reason that I can tell.

What a great wealth of knowledge here on HVAC.com, Im hoping maybe some of you will point me in the right direction. I appreciate your taking the time to read this.........

signed, a frustrated operating engineer.

[bodeen]

Is the building(s) in question under a positive pressure in relationship to the outside? This is the first thing to look at. If the building is in a negative pressure then the smells could be coming from all kinds of places.

Bodeen

[Mikeylikesit]

Yes, my VFD's maintain 1" of static pressure.

[jayhawker]

I am currently working on the same problem. The odor comes back every time the cooling starts up but never in heat. What was recomended the company I work for was using a UV C system to decontaminate the evaporator coil.
http://www.ultravation.com/si_series.html

[Mikeylikesit]

jayhawker,
I have been researching this for about a year. The bottom line, as I understand it, is that the UV systems will maintain the evap coil sterility, (or close to it); they will not, however, get rid of an existing problem. As I say, this is my understanding........if I had a concrete answer, I might be retiring waaay early!

Anyway, the battle goes on.......I too have applied for Professional Member status so I can see the "secret" stuff......

[caddy]

Have found in some units with dirty sock smell to come from mold in ductwork. As I understand it the mold spores tend to "stink" when running in cool mode. This mold growth have found to come from improper cfm causing sweating of ductwork and mold growth. Usually washing coils "evap", drain pan, spraying bleach+water mixture on mold growth and checking for proper cfm has solved odor problem.

[orion242]

>Yes, my VFD's maintain 1" of static pressure.

You’re talking supply duct static pressure not building pressure. 1" of building pressure would something to see. Opening a door would take out your teeth, membrane roof would be a balloon, etc.

[Mikeylikesit]

>Yes, my VFD's maintain 1" of static pressure.

You’re talking supply duct static pressure not building pressure. 1" of building pressure would something to see. Opening a door would take out your teeth, membrane roof would be a balloon, etc.

ah, yes......got me there!


When we commissioned the EMS and new controls in the plant, I happened to ask the guy programming where the 1" SP setpoint came from. He replied that the 1" SP would maintain positive pressure in the building. Went right over my head then, but thinking about it now, how would you ensure positive pressure in the building using only a single fan unit?


At any rate, I think this is moot, because the smell is coming from the air handler, no bout a doubt it.

[bodeen]

If your building is under a negative pressure the AHU is just distributing the smells coming from who knows where. The old stand by way to quickly check takes a very special piece of equipment. Get a piece of toilet paper two feet long, go to the exterior door and with all other exterior doors shut, hold the toilet paper next to the crack of the door next to the frame. Slowly open door and see which way she blows. I do this first thing on strange odor, excessive humidity, condensation issues.

Bodeen

[Mikeylikesit]

OK I just used the "hi-tech device" and have proved that the building in positively pressurized. I should have know that, as we have "relief grilles" in some of the office spaces which allow excess air pressure in the building to vent thru spring loaded dampers on the roof....

Steam cleaned and bio-treated the coils yesterday, we will see how long it takes to re-appear.

on a related topic, is the surface rust which delvlops on the condensate pans inside the air handler an issue? If so, how do you prevent it? Again, we use treatment in the pans, but sometimes there is not enough condensate to activate the "sweet tarts" (large tablets).
Im really grasping at straws here to figure this out, but I guess if this is the worst problem I have then life could be alot worse......

Thanks all for the replies and comments, keep them coming!

[mw17]

Have found in some units with dirty sock smell to come from mold in ductwork. As I understand it the mold spores tend to "stink" when running in cool mode. This mold growth have found to come from improper cfm causing sweating of ductwork and mold growth. Usually washing coils "evap", drain pan, spraying bleach+water mixture on mold growth and checking for proper cfm has solved odor problem.

i am researching a problem i have and this was the closest discussion to my problem....

I have a flat roof with ducting sitting on top. The day after I run AC my vents will sweat steamy air into the house. Need help fast. Is is a unit/furnace problem or a duct problem.

thanks!!!!!!!!!!!!!!!!!

[nchvac]

I have to wonder if you dehuming with your units. Is there any chance that the hot coil has flow or if some strips are on in the unit. Does this odor appear all of the time, or just when the unit comes on in the cool mode?

[duke of earl]

I think some joker comes back after a good ole mexican lunch and is sticking his butt in the returns. I actually did this one time with a friend and we couldn't stop laughing from the comments in the space being served.