remote diagnose HVAC humidity

Thought I might pick your brains.

Every summer at the theater, the A/C sucks.  It will cool everything down to whatever temp I want.  We have two 10-ton and one 20-ton rooftop units and they make it plenty cold.  But they make it ridiculously humid.  I was guessing 70%, but I brought in a hygrometer and it said 77%.  Paint won't dry.  The masonite floor has become so damp that it is swelling up and turning into cardboard.  Water drips from the vents.  The curtains are so damp I'm getting crystals forming in the fire retardant.

Over the last three summers I have had two different HVAC companies come look at it a total of 4 times and they say everything is tip top shape.  Last summer we had one compressor seize and when it got replaced under warranty I thought maybe all would be right with the world.  It wasn't.

I just went through today and sliced through the buckled parts of the masonite floor with a circular saw so I could screw it back down... only to realize that the screws go right through the masonite because it has become that damp.  I realized that all the layers of paint on the floor are just more or less "floating" on it because there is nothing for it to stick to.  The only thing really holding the floor in place is the 1/16" of latex paint covering it.

I crawled under the floor to look in the air return expecting to see something wet, but nothing.

I'm stumped, two HVAC companies are stumped.  Any ideas?

I have trouble controlling the humidity in my house, but nothing like what you're describing.

I'm no expert in this, but I wonder if the units that you have cool so efficiently that they don't run long enough to pull the humidity down.

It sounds like you need dehumidifiers, not more air conditioning / cooling.

That is typically true - if the units are oversized, they will short cycle and not pull the humidity out.

Another reason that you're having issues is that (I assume) your fresh air supply is not decoupled from the units - you probably have big RTUs that are drawing in lots of fresh air, cooling it, and dumping it into the space full of moisture.  It's best if that is handled by a separate system, and the HVAC is actually just recirculating and conditioning the pre-tempered fresh air.  But if you can't decouple them then you at least need terminal reheating where your air is cooled way past the set point to expunge excess moisture, and then reheated back up to the comfort level.

Call Gipe Associates in Easton, MD and ask for Dave Hoffman.  Tell him Duke sent you.  He is a mechanical engineer and he knows his, umm, stuff.  He'll chat with you for a little and offer advice.

What Duke said.

Also, try running only one system for the whole theater, so it has to run a lot longer on the way to cool.. to soak up some of the humidity  

Is your stage over a dirt floor crawl space by any chance?

Well, the units have been up there for 10 years and the last three summers were the only problem.  It isn't a short-cycle issue.  I have paid attention to it and they seem to be cycling just fine.  The volume of air they have to move means that the cycles come in hours, not minutes.  The three units control three separate "wings" of the building that are only connected by 36" doors, so running one to cool the whole place won't really demonstrate much.

This is something that was a non-issue for 7 years, then suddenly became an issue for the last three.  There have been no changes to the A/C system (other than the compression replacement under warranty in the middle of the humidity issue and one fan belt replacement.)

The issue is in the main theater 20-ton unit.  The 10- ton for the costume shop/storage is fine.  The 10-ton for the office wing seems to be fine.  But walk from the offices into the theater, and your glasses sometimes fog up.

OHSCrifle said:

 

Is your stage over a dirt floor crawl space by any chance?

 

No.  Concrete.  difficult to explain all the intricacies, but it is a sprung-wood floor about 3' above a concrete floor.  No water, and even so, that wouldn't explain why it hasn't been an issue for so many years and suddenly the last three it's like a swamp. 

Check your water bill. Leak somewhere?

Shouldn't there be drains for the condensate that comes off of the coils?  Where do the drains go and are they clear of mold and other debris?

I think Duke nailed it on the first try. Assuming the main system had one.. I suspect a reheat coil has failed. 

In reply to OHSCrifle :

Reheat coil. Is that something that would normally be found in a home unit? 

I rarely can get my house below 63%. With some of the windows boarded up, it's at 71 right now, and shows a maximum of 81.

If I had room for one, I'd have a dehumidifier in the house. The HVAC is in the attic. The drain pan is fine.

Dirt crawl space, wood floors, sixty year old block house, Central Florida. I have had some interior paint buckle.

I think I'll first put a fan in one of the crawl space vents.

If the units are running ok, then there could be a building envelope problem. It could be a gap in the wall or an open window. Or maybe the hvac system is no longer balanced in terms of air in and out of the building. Has an exhaust fan recently installed or an old one recently turned back on? Those could cause infiltration of raw wet air rather than the RTUs conditioning the air first.

In reply to Floating Doc :

No, reheat is not typical in residential HVAC.  At least not around the northeast quadrant of the country.

CJ said:

Shouldn't there be drains for the condensate that comes off of the coils?  Where do the drains go and are they clear of mold and other debris?

Drains are clear and the pans drain well.  They drain out of the evaporator unit onto the roof.

Duke said:

That is typically true - if the units are oversized, they will short cycle and not pull the humidity out.

Another reason that you're having issues is that (I assume) your fresh air supply is not decoupled from the units - you probably have big RTUs that are drawing in lots of fresh air, cooling it, and dumping it into the space full of moisture.  It's best if that is handled by a separate system, and the HVAC is actually just recirculating and conditioning the pre-tempered fresh air.  But if you can't decouple them then you at least need terminal reheating where your air is cooled way past the set point to expunge excess moisture, and then reheated back up to the comfort level.

Call Gipe Associates in Easton, MD and ask for Dave Hoffman.  Tell him Duke sent you.  He is a mechanical engineer and he knows his, umm, stuff.  He'll chat with you for a little and offer advice.

 

I will give him a call.  Thank you.

The fresh air doors have been disconnected, screwed shut, and taped with butyl tape.  That was last year's attempted fix.

Don't tell anyone.  I'm not supposed to close them.

Quick math.  The 20-ton unit is cooling a volume that is about 1.5M cuft.  That's a 50x60 theater with 27' high ceilings, a 30x70 lobby with 22' ceilings, and a shop the same size as the lobby.  Insulation is mostly non-existent and it's a black rubber roof.  I paid closer attention to the cycles yesterday.  It was about 88 outside and very humid.  Typical cycle was about 2 hours on, 45 min off.  I was in there painting the floor all day so it was pretty easy to follow.  (and today the paint is still tacky.  Grrrr)

RossD said:

If the units are running ok, then there could be a building envelope problem. It could be a gap in the wall or an open window. Or maybe the hvac system is no longer balanced in terms of air in and out of the building. Has an exhaust fan recently installed or an old one recently turned back on? Those could cause infiltration of raw wet air rather than the RTUs conditioning the air first.

I don't think there is.  I think I would notice a gap.  The only exhaust fan is located in the boiler room which is a sequestered room on the other side of the building in the shop, and that exhaust fan isn't even wired.  Just has a pigtail hanging off of it.

The other thing that confuses the heck out of me is that even on a dry day outside (relative humidity in the 40s) it is still swampy inside.  That makes no sense to me.  I could understand if it took a while to remove the moisture from the air on a dry day, but it never really does.  I go up to the roof and the drains are flowing.  Open the side panel and the pan is draining just fine.

So, I'm definitely thinking on the same lines... .moisture is coming in somewhere.  Given that a dry day doesn't seem to help, it must be ground water, liquid water, or something not from outside air.

The fun part is I have to get this done asap.  In about a week I'll probably be turning off the HVAC and the problem will completely disappear until May when I turn it back on.

Also, I snapped this picture for you.  I pulled these black cotton curtains out of an open-top tote sitting in the theater.  What you're seeing is where the top fold was sticking out of the top of the tote.  They're so damp, they are darker there.  These have been hanging for 18 hours and I just took this photo 2 minutes ago.

Curtis said:

Duke said:

Call Gipe Associates in Easton, MD and ask for Dave Hoffman.  Tell him Duke sent you.  He is a mechanical engineer and he knows his, umm, stuff.  He'll chat with you for a little and offer advice.

I will give him a call.  Thank you.

I was just with Dave this morning and I told him I referred you.  I think they have a Harrisburg office as well, but start with Dave in Easton and he'll point you in the right direction.

Curtis said:

OHSCrifle said:

 

Is your stage over a dirt floor crawl space by any chance?

 

No.  Concrete.  difficult to explain all the intricacies, but it is a sprung-wood floor about 3' above a concrete floor.  No water, and even so, that wouldn't explain why it hasn't been an issue for so many years and suddenly the last three it's like a swamp. 

What's the humidity in this 3' space?  If the A/C system is working properly, you're getting moisture infiltrating from somewhere.  How's the roof?

When was the last time the coils were correctly cleaned, and if not was refrigerant added by the professionals? There is a way to determine how much heat the units are removing to tell of they are working properly. Do you know if they tried it? You could probably do it yourself. 

1988RedT2 said:

Curtis said:

OHSCrifle said:

 

Is your stage over a dirt floor crawl space by any chance?

 

No.  Concrete.  difficult to explain all the intricacies, but it is a sprung-wood floor about 3' above a concrete floor.  No water, and even so, that wouldn't explain why it hasn't been an issue for so many years and suddenly the last three it's like a swamp. 

What's the humidity in this 3' space?  If the A/C system is working properly, you're getting moisture infiltrating from somewhere.  How's the roof?

The space is under the theater floor and it is the air return.  The suspended wood floor has 12 air grates in it around the perimeter.  Return air goes down there, through a hole in the wall, and up through a big duct to the RTU.  So, that air is constantly recycled... and therefore the same humidity as the rest.

To expand on that... The theater is a black box.  The theater space is what used to be the audience.  It was a raked floor that started at grade on one end and sloped down 3' toward the old stage.  In 99 we put in a bunch of stud walls down there and joists with a plywood floor to raise it up to grade.  Never had any water trouble down there.  Never standing water.  Even if I had standing water somewhere, I couldn't imagine it being as humid as it is.  If I had a lake in there, I could imagine 60%, but no standing water and 75% or more?

tooms351 said:

When was the last time the coils were correctly cleaned, and if not was refrigerant added by the professionals? There is a way to determine how much heat the units are removing to tell of they are working properly. Do you know if they tried it? You could probably do it yourself. 

 

We have a contract with an HVAC company and they come every spring.  They spray the coil cleaner on, pressure wash it off, test refrigerant, change filters, inspect belts, grease fan bearings, etc.  The 20-ton unit got a new compressor last year under warranty.  (sidenote... it was the 70% compressor that died leaving us with just the 30% compressor.  It struggled to keep up with temps, but it did it, and you would think with the increased duty cycle it would have helped humidity, but it didn't.)

But the point is, the system was recharged last year with the new compressor installation, and then checked again this spring.  According to two different companies, everything about the RTUs is 100%

How about a non-working exhaust fan?

The medical facility I used to manage had a recurring problem. It had 18 large bathroom exhaust fans on the roof which ran continuously. We always knew when we blew a belt, because water would leak into the ceiling on the lower level- 3 stories down. (It happened every other month)

It turned out the building was designed to have that much loss through the exhaust fans continuously. When the fans were not functioning, the negative pressure in the building would suck air DOWN the exhaust ducting (drafting through other exhaust fans).  Exhaust ducting is not insulated, and ran through the return air plenum. The unconditioned air in the uninsulated duct would condensate on the inside of the cold duct in the conditioned plenum, and water would chase the exhaust ducting to it’s lowest point before leaking out and damaging the ceiling. 

What’s your average relative humidity outside?  If it’s LOWER than the 77% you are measuring in the building, then sealing your fresh air intake doors is not helping you, it’s hurting you. 

I would think it is not normally that high in your part of the country. 

Sounds like the maintenance is being done, but since the building hasn't really changed I  would suspect the units. See if you can get them to check the units efficiency, heres one of the problems we were doing in school. It should tell you if the units are working up to their stated capacity.

You don’t have a problem with building envelope or your HVAC system. 

You have a problem with your 20 ton unit. More specifically, the system attached to your 20 ton unit. 

The HVAC contractors have checked the functionality of the unit, but they have not checked the integrity of the SYSTEM. 

You said you had water dripping from the vents. I am going to speculate that you have compromised insulation and duct sealing on the ductwork for the 20 ton system, probably in a concealed area.  The system is condensating, creating it’s own water, and circulating it through the space it supplies. 

And open those fresh air doors.  With 40% relative humidity outside, you are recirculating wetter and wetter air with every cycle. If the insulation is compromised, you are just adding fuel to the fire. You are pre-charging the air with excessive humidity before pumping  it through an oversized condensing unit. 

SVreX said:

How about a non-working exhaust fan?

 

Interesting thought. The exhaust fan in the boiler room is pretty isolated (and has always been there) behind an overhead door and two fire doors with minimal air exchange.  The only other vents are the two bathrooms and they have residential style 3" bathroom fans.