Air handler condensation
we have a job that has a five ton Bryant air handler installed horizontally above an acoustical ceiling. The unit was installed by others in 2021.
The unit is installed in the ceiling of what was a warehouse that was converted into office space. Ceiling height is about 9’ the distance from the drop ceiling to the concrete deck is about 7 feet.
the issue is the entire bottom of the air handler has condensation on it. The unit has a ducted return that is large enough for 2000 cfm. The unit is trapped and is draining properly. The condensation goes right out the back of the building, and there is a steady stream of water coming out of the line while the unit is running. The charge in the unit is good, good super heat and sub cooling.
the only solution I see would be to insulate the bottom of the air handler to stop this condensation? While above the ceiling is a non conditioned area, I have seen air handlers installed in tightly insulated attics that have not sweat like this one is. It just appears that the internal insulation in the air handler is not a high enough R value to overcome the heat above the ceiling? I was above the ceiling and only measured a temperature of around 85, while the room temperature the unit was maintaining was 73. 85 doesn’t seem that warm to me. Has anyone else experienced this type of issue and if so, what was the solution? Thanks to all
Comments
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Is the return insulated and sealed?
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you need to use a psychometer to measure the wet bulb temp. the dewpoint has to be crazy high up there for some reason.
maybe they are trying to use a lot of setback. maybe there is a roof or plumbing leak that is making it extra humid up there. unless it is just plain open to the outside conditioning the space should bring the humidity up there down too.
if the wet bulb above the ceiling is more than outside someone needs to figure out why. you are in a midwest or east coast climate, not like florida or louisiana, right?
that also is why putting the coil at the inlet isn't a great idea.
maybe look at airflow and delta t too.
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The job is in Maryland. Not quite as high as Florida or Louisiana, but close
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the return air is sound lined on the inside, sealed, but not insulated on the outside
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Check the return air temp and RH versus the space temp and RH. If the temp and humidity in the RA duct at the AHu is higher than the space then the ductwork needs sealing and insulation. You could be leaking in RH
Questions
What is the evap temp?
Should be about 40 if lower that could be the issue
does it sweat before it gets to the coil or after?
I would cap the condensate drain pan and fill it with water and let it sit without running to make sure the pan isn't leaking.
Check the insulation inside is it wet or dry?
Check the blower compartment to make sure the velocity is not pulling condensate off the coil past the drain pan. Anything over 500fpm or so will pull water off the coil.
Check the AHU instructions and find out if it is as it was shipped. Did they convert it from LH to RH air flow or vise versa and forget something or tear the insulation up?
You could probably glue Armaflex sheet on the bottom if all else fails.
Put an aux drain pan under it, but the condensation needs to be fixed so the unit doesn't rot out.
My attic in my house was well over 100 deg and never had an issue except when the condensate pipe froze up one winter.
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That gap between the acoustic ceiling and roof is an in-between space currently. It is neither inside or outside the building envelope which can create these types of issues.
Concrete roof decks (espacially if there are roof leaks) can also hold a lot of moisture and when the sun hits it, it pushes this moisture into the building. This moisture is now stuck in this in-between space and that is most likely why you have problems.
The best solution is to condition this space which will reduce the RH there and prevent the condensation you see. This generally means putting a supply and return register up there with sufficient flow to keep the RH in check.1 -
if the insulation in the air handler is fiberglass and wet it won' be insulation anymore
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I've seen this too, when the unit is hung in an unconditioned space above the offices in a warehouse. It's not quite the same as in an unconditioned attic space. Warehouses generally have lots more moisture in the air from various sources like cardboard, fuel-burning equipment, direct fired makeup air, & if it's less than a few years old, green concrete. This all works to drive the dew point up, so when it gets warm out and the unit starts running long cooling cycles it starts to condense on all sorts of surfaces that normally don't.
I'm not sure what the eventual solution was, ISTR that they ended up running the sheetrock to the deck & maybe added a moisture barrier to it as well. A drip pan with an overflow drain might be a pragmatic solution.
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Why is there no overflow pan below the unit?
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you could also put a piece of plastic a couple feet square over the floor in a couple places and see if it gets wet after a few days to see if water is coming up through the floor. the building might be kinda getting saturated with water from poor drainage.
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thanks to all that commented. I don’t know why the original installer did not put an emergency pan under the AHU, but I installed one today to at least temporarily prevent any more ceiling tiles from being ruined.
Upon further checking it appears it may be more of condensation being pulled off the evaporator coil, then an air properties issue. The blower housing even at the top is wet. The air handler a Carrier
M# FB4CNP061 is in its factory horizontal left configuration. So the coil wasn’t removed and re configured. The blower is on medium speed, but it appears water is being pulled from the coil. The evaporator coil is clean, and the unit is definitely draining
Thanks to all
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We installed a Carrier AHU once in a paper mill. They had to have very strict humidity control for the paper and in the winter the air was too dry.
They had us install spray nozzles in the AHu. Just copper tubes with pressurized water with nozzles on the end (like oil burner nozzles) position to spray against the air flow.
The theory is that the entering dry return air will absorb all the water by the time the air reaches the fan. It didn't work at first.
So then the battle started everyone is monkeying around with this until I measured the air velocity and it was too high they had about 750 fpm.
500-550 is the max fpm so you don't pull water off the coil.
But they argued with me for months and even installed some drip baffles to help the water absorb better. "Carrier said it will work" was all I herd for 6 months. I even put my foot down and said if you not going to listen to me don't send me back there.
This is simple physics. It doesn't matter whose ahu it is or anything else 500-550fpm is all you can do. that is how the MFgs size ahus. Doesn't matter if it is 5 tons or 100 tons.
With a 5 ton unit they build a tin box that will allow 2000 cfm to flow with a velocity of 500-550. Its as simple as that. That's why I mentioned velocity in my first post.
I would make sure the return air plenum approach is attached full size to the ahu. if they ran a duct sized for 2000 cfm right up to the ahu and attached it with no plenum thats no good. The velocity may not drop off fast enough.
Maybe you can slow down the fan
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the ducting may be shaped such that the airflow isn't even across the coil too so maybe one part is 300 fpm and another part is 800 fpm.
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I found the manual. Your going to have to do some reading and testing.
In one place they talk about the addition of a 'Water Management kit" and on the last page in the notes they mention a Minimum discharge static as well as mentioning if the return static is excessive you may pull water in
This typical Carrier Blue Oval crap.
They don't want to build the unit right so they give you the info to make it work in the field.
On top of that i guess this thing is discontinued. See the attached. Good Luck
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I've run into coils shedding water into the air stream due to excessive velocity. It's a real thing, but uncommon enough that it isn't often the first thing checked.
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This is a late post. In Maryland this situation is not uncommon. I once had a system that took three days to remove the humidity and finally reach set temp during 100F days from a house that sat unconditioned for two months while occupants vacationed. I have designed ac systems for Maryland and Florida, and they are almost identical due to our high humidity. It's just that Maryland's season is shorter than FA. Still, a great install would include a drain pan. Just remember not all residential designed units work everywhere without extras. When latent load is a factor for any reason you have to design for it. I had an extremely tight and insulated house in a forest next to a stream. He wanted two ac systems. His total load was 2 ton. Yet he had requirements for fresh air heat exchangers and kitchen exhaust and a smoking room that required differential pressure negative compared to the main house. Sensible stat control would not do the job by itself. I had to add a humiditrol to keep the AC running until latent load was satisfied. Not to mention air balance the whole house.
One of the weakest part of our hvac industry is ductwork design and proper application selection for various installations.
We cannot keep installing AC systems like putting in window units and walk away. And Forbid we run into old systems that were always wrong in the first place. A system designed to maintain is not the same as a system designed to do a 1/4 mi drag race. Until indoor conditions match equipment design it will struggle or fail. Don't forget the operator may be part of the problem. Leaves that door open, misuses it.
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I agree uncommon but it can happen. Also cleaning the coil even if it doesn't look dirty may help.
The other thing that can happen (not in this case) is with a two stage system with two circuits first stage is always the lower coil. You don't want the wet coil on top draining water over the dry coil below if possible.
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