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Thread: sweating AHU

  1. #1
    Join Date
    May 2005
    Location
    Pasco County Fl
    Posts
    6
    Hey, heres one for you all! Can anyone give me a clue as to why 12 seer and higher units tend to sweat profusely when installed with existing ductwork! This has become a very serious problem for the company I work for, even to the point of changing out AHUs due to the fact they are saturated with moisture! Everyone seems to think increasing return size is the answer, but I tend to disagree, as I believe it will throw the balance of the entire system off, and cause even more sweating to take place! If anyone has a cure for this situation, I would really appreciate any advice you could give me! I am at my wits end with this one! Thanks, Ron!

  2. #2
    Join Date
    Jul 2004
    Location
    Poughkeepsie, Ny
    Posts
    631
    Originally posted by bucmarc
    Hey, heres one for you all! Can anyone give me a clue as to why 12 seer and higher units tend to sweat profusely when installed with existing ductwork! This has become a very serious problem for the company I work for, even to the point of changing out AHUs due to the fact they are saturated with moisture! Everyone seems to think increasing return size is the answer, but I tend to disagree, as I believe it will throw the balance of the entire system off, and cause even more sweating to take place! If anyone has a cure for this situation, I would really appreciate any advice you could give me! I am at my wits end with this one! Thanks, Ron!
    My guess would be are the condenser and air hander matched? We had a run of sweating duct work because someone was mismatching components. "In the name of SEER!"

    We also ran into a problem where we had to replace tin that was insulated on the outside and replaced with tin that was insulated on the inside. There was also air leakage problems and the insulation was insuffecient. We checked back for water and there was none.

    That is what I have found with the problem that you describle. Providing that the A/H is draining properly and the correct TXV is installed and you did a subcooling.

    [Edited by atufano on 07-21-2005 at 08:28 PM]
    Happiness is the only good. The time to be happy is now. The place to be happy is here. The way to be happy is to make others so.
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  3. #3
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Higher static pressures are common in the duct systems in your area.Certain brands have low static capabilities,and a media or worse yat 3M filter,and problems occur.

    Horizontial air handlers need relatively low static on the return to allow proper drainage,deep trap helps,plus they can "pull/blow" water off the coil,at higher statics.

    have you checked the static,does your company provide a manometer,or magnahelic to test it with?


    Use the search function on this site "static or ESP" to read more.

  4. #4
    Join Date
    Nov 2004
    Location
    CA
    Posts
    238
    "....Use the search function on this site "static or ESP" to read more....."


    I can not find the "Search" function, can you help ?

  5. #5
    Join Date
    Feb 2005
    Location
    Richmond
    Posts
    480

  6. #6
    Join Date
    Jul 2005
    Posts
    14
    You have mentioned 12 seer, but there is no example of tonage. Is it possible that (for EXAMPLE), an older 2 ton system was removed (which could be an unknown if all the original equipment tags had been removed, or fallen off), and a 3 ton was installed with all existing ductwork left the same? Undersized ductwork could be a cause, but this goes back to knowing what the static pressure is, in a specific example, of a system installed.

    I have no reason to question your salespeople (I don't know them), but sizing, and existing ductwork evaluation, is still a problem, even in this day-and-age.

    More info (and specific install info, e.g. installed in crawlspaces?) would be needed to "guess".

  7. #7
    Join Date
    Jul 2005
    Posts
    37
    Higher static pressures are common in the duct systems in your area.Certain brands have low static capabilities,and a media or worse yat 3M filter,and problems occur.




    Just curious..as I just put a new "High Efficiancy" 3M Filtrete filter in on my new system. What is the problem with them and what should homeowners use??

    Thanks

  8. #8
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    3M filters are usually to restrictive.Feel the air flow at the farthest register,with the 3M in place,then with a regular filter.If it's too much for your system you'll feel a dramatic differenc.


    They alosa "load up" fast,meaning when clean they may allow enough air flow,but not after a week or two.



    The ESP,resistance of your ducts versus the fan speed being used,should be checked by a Pro,to see what "better " filter your system can handle without reducing air flow to a point of equipment damage resulting.If it's too high they can tell you what duct modifications need to be made.

    Be aware that not all techs or companies can or will do this ,so ask before wasting your time and theirs.

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