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Thread: Dripping Ducts

  1. #1

    Dripping Ducts

    Hello and thanks in advance for any help you can offer. I will do my best to explain my problem. I have attached 3 pictures which will probably explain my situation better than I can.

    *10 ton package HVAC sitting on flat roof
    *Ductwork is suspended in dining room about 15 feet high
    *Several doors in restaurant that allow heat and humidity in the room which all rises (naturally) to ceiling - where ducts are.
    *Cold air being forced into warm duct work creates a drip of varying severity depending on weather / humidity.
    *Most times it's right where the cold air comes in the duct and extends about 3 to 4 feet on each side (above dining room tables)
    *On really humid days it can extend 10-15 feet down the ductwork

    Questions:

    1. I know I could insulate but as the picture shows these are exposed ducts so wrapping them with traditional insulation would look like crap?

    2. Is there another kind of insulation / tape with insulating qualities that would provide enough insulation to fix the problem without looking bad?

    3. Any other solutions?

    The unit has two stages. The second stage kicks in when the temperature dips 2 degrees above set point. I can alleviate the problem somewhat by increasing thermostat to stay out of 2nd stage but then of course the temperature in the room increases and on really hot days that's not an option.

    Hope this is enough info. Appreciate any help you can give me.
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  2. #2
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    Let's start by ruling out a few things before we take the step of insulating the ducts.

    I see exposed, uninsulated ductwork all the time in commercial buildings and rarely see condensation problems.

    #1. You need to have a technician verify that the unit is moving the correct amount of air. Low airflow can lead to low duct temps and, consequently, to condensation.

    #2 What is the humidity in the room, and are you using any strategy to control it?

  3. #3
    1. Unit is only 18 months old. We've had this problem for years (previous unit and new unit). It is a York Model # DM090N15N2AAA4B (attached). And it's 7.5 tons, we have two other 10 ton units - got confused.

    So I have to assume the airflow is what it should be for that model.

    2. Humidity is bad. Restaurant does 2500 dinners nightly with seats indoor and out. So doors are constantly swinging, impossible to keep them closed. We have an air door on the main entrance which helps keep the lobby somewhat cool and flies down but all other doors are open / closed hundreds of times a night.
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  4. #4
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    Quote Originally Posted by harpoonhannas View Post
    1. Unit is only 18 months old. We've had this problem for years (previous unit and new unit). It is a York Model # DM090N15N2AAA4B (attached). And it's 7.5 tons, we have two other 10 ton units - got confused.

    So I have to assume the airflow is what it should be for that model.

    2. Humidity is bad. Restaurant does 2500 dinners nightly with seats indoor and out. So doors are constantly swinging, impossible to keep them closed. We have an air door on the main entrance which helps keep the lobby somewhat cool and flies down but all other doors are open / closed hundreds of times a night.
    ASSUME nothing.

    Airflow can be tested, measured, adjusted and balanced by a qualified technician.

  5. #5
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    Where is the return located?

    Is the fan running the whole time the room is use, or only when the stat calls for cooling?

    Is here any fresh air on that unit?
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  6. #6
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    Just a thought, but I'd expect that the Exhaust for the Kitchen isn't up to speed. That would cause the ventilation from the Kitchen to force high amounts of hot/moist air into the dinning room.

    Like I said, it's just a thought. Hard to tell from where I'm sitting.

  7. #7
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    With the "people load" and the moisture from cooking even before you consider the outside conditions makes the decission to not insulate (internal) the duct look even more short sighted and foolish. You will never have bare duct not sweat until you insert the new notched board into the system to fix the problem.
    But you already know that.
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  8. #8
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    I cant think of the name of the small entrance area that isolates the conditioned space from the outdoor air using two seperate doors.

    A foyer ? Vestibule ? Its basically a airlock and they're pretty common on high traffic applications like restaurants.

    Either that or revolving doors !!!

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  10. #10
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    It appears that the spiral duct is not reduced after the registers. This will cause low static and make the supply air extremely slow, cold and cause unwanted condensation.

    It's hard to tell from the pictures but that's what I see.
    You're only as good as your customer will allow you to be.........If they want junk, sell them junk, but make your junk look neat!!!

  11. #11
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    No economizer? Does it have a manual fresh air intake?
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  12. #12
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    I know you have multiple doors that open and close often, but I would look at making sure you have positive air pressure. If you can't get positive air pressure with your doors closed you will always have infiltration allowing the humidity and outside air to just come right in.

    Second, I would never have installed that kind of duct work in a ring around the outside wall. I am willing to bet if it had been installed center building out you would loose the majority of your condensation from outside air humidity.
    If you're too "open" minded, your brains will fall out.
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  13. #13
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    I see where you are going

    Quote Originally Posted by superd77 View Post
    It appears that the spiral duct is not reduced after the registers. This will cause low static and make the supply air extremely slow, cold and cause unwanted condensation.

    It's hard to tell from the pictures but that's what I see.
    But I don't think this is the Main Problem, just non insulated duct with a surface that reached dewpoint. the velocity probably wouldn't affect it that much more IMO
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

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