Originally Posted by
Michael Vasquez
(some units located in the attic and some in hall or garage closets)
Originally Posted by
Ted Menelly
or insulation is missing in the cabinet. It shouldn't be sweating.
If the AHU is in a hall closet, that would be within the conditioned space, no sweating should be expected there.
If the AHU is in an attic or in a garage, in unconditioned space, many times there is enough humidity in the air and enough temperature difference to cause a high dew point at the surface of the cabinet.
I've seen - in new construction - units in a garage or attic, all sealed up, no air leakage, yet lots of sweating. These are brand new units with the insulation intact, no time yet for the insulation to have become wet or damaged.
One of the problems is the R-value of the insulation inside the cabinet may not be sufficient to keep the cabinet below the dew point under those hot and high humidity conditions.
Years ago (maybe 10 or so) in talking with one of the manufacturers they stated their units should not be installed in unconditioned space. When I called back later to get that in an e-mail or fax as they has said they would send me (but never did) I was told that their units could be installed in unconditioned space.
I don't know if it was just me or not, but I suspect the builder told their HVAC contractor who told the factory representative who told everyone at the factory that if they say that, they will no longer be selling any AHU in Florida (because they were all being installed in unconditioned garages). I think the idea of losing all of those sales resulted in a change in their position regarding installation in unconditioned spaces.
In my second call to them, they said that 'no we did not say our units *SHOULD NOT BE* installed in unconditioned space ... we said we *recommend* that our units be installed in conditioned space, ... but that *it is okay* to install our units in unconditioned space' ... yeah, right, I bet the first person I talked to was right.
If you see horizontally installed AHU in attics (unconditioned space) sweating along the bottom and only a couple of inches up the sides, that's a pretty good indication that the condensate pan in the unit overflow inside the unit and soaked the insulation on the bottom and the lower part of the side insulation, making it almost useless. When you see that, you will not see a secondary condensate drain line installed draining into the auxiliary drain pan - because the HVAC installer said 'I don't need to install a secondary condensate drain line to drain into the auxiliary pan, when the primary condensate pan overflow all of that is going to run out the seam in the AHU cabinet and drain down to the auxiliary pan anyway'.
Hey, HVAC tech ... why do you think the manufacturer installs that secondary condensate drain line?
Yeah, to avoid ruining the friggin' insulation in the AHU when it overflows!
Crimeny, those HVAC techs should have to pay to replace each and every single unit damaged by them not installing the secondary condensate drain line. If they were to pay for even one, they would likely never leave that secondary drain line off ever again.
