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  1. #1
    Join Date
    Jun 2006
    Location
    New Jersey
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    4,330

    McQuay RTU Sweat

    The other day I had to look at a 80ton McQuay RPS for a refrigerant leak. Noticed upon shutting down, that the electrical section was sweating. Later in the day I started it back up to checked temps and all, no sweating. So I tell them I need to get back when it's cold.

    So I get there this morning. Open up the electrical, full of sweat again. It coming from the seams of the interior paneling. This includes inside the unit, too.

    Return is 70 degrees 50%RH. Supply was 60 degrees 72%RH. No heat or cooling running. Fixed 33% OA.

    Was thinking the only solution was to seal the panel joints inside the unit and install a electrical cabinet heater (like the air cooled chillers).

    Anyone else run into this? I never have and I have work on quite a few RPS's.

  2. #2
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    Based on 70 Fdb 50% RH and 33% OA damper position (I'm assuming you don't actually have an OA flow station on this unit and you're actually getting 50% OA flow) and 60 Fdb 72% RH SA you've got saturated OA at about 55 Fdb . That's cold enough to cause condensation of 70 Fdb 50% RH or 60 Fdb 72% RH air if your electric compartment is getting pressurized with a small amount of return or supply air. Can you verify what the outside air conditions were at the time of your visit? Also verify no cooling operation. Your SA condition is consistent with cooling coil operation or the conditions I described above.

  3. #3
    Join Date
    Jun 2006
    Location
    New Jersey
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    4,330
    Quote Originally Posted by 19characterusername View Post
    Based on 70 Fdb 50% RH and 33% OA damper position (I'm assuming you don't actually have an OA flow station on this unit and you're actually getting 50% OA flow) and 60 Fdb 72% RH SA you've got saturated OA at about 55 Fdb . That's cold enough to cause condensation of 70 Fdb 50% RH or 60 Fdb 72% RH air if your electric compartment is getting pressurized with a small amount of return or supply air. Can you verify what the outside air conditions were at the time of your visit? Also verify no cooling operation. Your SA condition is consistent with cooling coil operation or the conditions I described above.
    It was about 37 degrees 68%RH OA. Don't have flow stations, but the unit was balanced 3 months ago. Balancing sheet shows 18532cfm supply and 10643cfm return.

  4. #4
    Join Date
    Mar 2003
    Posts
    7,321
    This is the second one I heard about recently. On the first one, they had the vfd mounted INSIDE the supply plenum, and it was getting drippies. It has since been relocated outside of the air tunnel at no charge to the end user by the factory. The problem continues, but at least now it isnt getting in the drive.

  5. #5
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    It's just a POS unit. Those doors don't seal well and the way they construct the cabinet leaves gaps for air leakage.

    We have a bunch of OAH's, those things have great doors and the interior structure is tight. No problems.

  6. #6
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    Were the OAHU McQuay as well? Also how old is thr unit? I was considering their indoor modular product on a job.

  7. #7
    Join Date
    Mar 2003
    Posts
    7,321
    If I were looking at buying air handlers right now, depending upon application, I might look elsewhere. We see a lot of new air handlers and quality is not comparable these days. some are comparably priced, but dont come close in quality.

  8. #8
    Join Date
    Feb 2012
    Location
    New York City
    Posts
    106
    yeah my boss and I like the support the mcquay rep is giving the office and the client will accept the units for indoor low pressure applications, but I keep hearing so many issues about quality. OTOH I had an SWP substituted in for a v-cube a few years back and that unit seemed fine. Anyway I think the thread is done...

  9. #9
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    Quote Originally Posted by 19characterusername View Post
    Were the OAHU McQuay as well? Also how old is thr unit? I was considering their indoor modular product on a job.
    The RPS RTU is only one year old.

    As far as the OAHU's, yes they are McQuays.

    Actually was on a site today with some.
    Attached Images Attached Images   

  10. #10
    Join Date
    Apr 2012
    Location
    So. Fl.
    Posts
    57
    MCQUAY has had issues with condensation, what about the cond.drain
    Lines? Are they of a sufficient pitch? Didn't see any on unit externally, we've had to actually go in and spray foam all gaps around inside of several ahu's. Once done problem went away,that was down here in so. Florida.

  11. #11
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,330
    Quote Originally Posted by Bklyntek View Post
    MCQUAY has had issues with condensation, what about the cond.drain
    Lines? Are they of a sufficient pitch? Didn't see any on unit externally, we've had to actually go in and spray foam all gaps around inside of several ahu's. Once done problem went away,that was down here in so. Florida.
    I should have updated. Those pics are of McQuay AHU's I don't have issues with.

    My main gripe is with the RPS's and the like. There are gaps in the internal panels and with crappy doors, it leads to sweating in areas. Most importantly, the main controls area.

    What we have be doing to control this, is we go in with rope armaflex and stuff it all the interior gaps. Then we mastic all interior joints. Also, the bigger tonage units, the bottom of the electrical panel is not insulated and it hangs over the curb. We insulate it with sheet armaflex.

    So far, no more sweating of electrical controls. I would love for these companies to buy something else or really just go with chw, but we are stuck with it and have to deal with it.

  12. #12
    Join Date
    Jul 2013
    Posts
    1
    ACSJ - I just sent you an email. Hoping you have a picture of that unit sweating

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