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Air handler condensation

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zepfan
zepfan Member Posts: 474
in A-C, Heat Pumps & Refrigeration

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

  • HVACNUT
    HVACNUT Member Posts: 7,608

    Is the return insulated and sealed?

    zepfan
  • mattmia2
    mattmia2 Member Posts: 17,889
    edited 1:30AM

    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.

    zepfan
  • zepfan
    zepfan Member Posts: 474

    The job is in Maryland. Not quite as high as Florida or Louisiana, but close

  • zepfan
    zepfan Member Posts: 474

    the return air is sound lined on the inside, sealed, but not insulated on the outside

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 20,811

    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.

    mattmia2
  • Kaos
    Kaos Member Posts: 957

    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.

  • mattmia2
    mattmia2 Member Posts: 17,889

    if the insulation in the air handler is fiberglass and wet it won' be insulation anymore

  • ratio
    ratio Member Posts: 4,290

    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.

  • pecmsg
    pecmsg Member Posts: 7,431

    Why is there no overflow pan below the unit?

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