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  1. #53
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    Sep 2008
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    Western PA
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    25,567

  2. #54
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    Quote Originally Posted by Cap'n Preshoot View Post
    Unfortunately 10 hrs later there's no improvement in RH. Still hanging in there, drifting between 57 and 62%
    That is too high a humidity% variation...

    Something else was overlooked & is wrong; it would be unusual for it to be drifting from 57% up to 62%.

    Does the condensate drain off the coil & down the drain properly?

    Does the indoor blower (on auto) cycle off with the condenser?

    Is there a source of humidity entering the conditioned space or the return air?

    How long are the runtimes?

    Was the heatload slacking off too much - so that it reduced runtime too much?

    How tight is your home & Return Air situation?
    Last edited by udarrell; 08-27-2012 at 10:11 PM. Reason: How tight is your home...?

  3. #55
    Join Date
    Apr 2012
    Location
    Louisiana
    Posts
    660
    I'm with darrel, make sure your fan is on auto. Did you reconnect the fresh air damper?

  4. #56
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    I would still look to see if any return ducting was kicked loose by the alarm guy in the attic. Paper test not good enough. Have tech inspect all return ducts for signs of damage. Should not be too hard to spot.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #57
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    Quote Originally Posted by Sicofthis View Post
    I'm with darrel, make sure your fan is on auto. Did you reconnect the fresh air damper?
    Fresh air damper remains disconnected. Fan is on 'auto'. RH is showing 55% this morning (5:30 AM)

  6. #58
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    4,975
    Hot attic air contains a lot more grains of moisture, even at the same %RH as the much cooler room air, those extra grains of moisture have to be removed; - many times when there are shorter runtimes.

    Going into the evening hours before midnight, the attic air is still quite warm to hot, while the conditioned space load (especially on the first floor) is lower which results in shorter runtimes with much less length of runtime to condense moisture from the air.

    That scenario could contribute to the %RH fluctuation the system experienced. It doesn't take a very big attic leak into the Return Air to put an extra latent load on the cooling coil.

    By morning with shorter & fewer runtimes, a 55%RH may not be too bad.

    Keep close track of specifically what time periods the %RH changes happen...those guys in the attic, as we discussed before, could have caused a RA duct leak...

    I also sure wish you had a 3-Ton cooling coil instead of the 4-Ton.
    IMO, one of the mistakes that is being made in an effort to get another point higher imaginary SEER Rating has nearly everyone going to the up-sized tonnage coil, which only works well in dry climate zones.

    I remember the good old days when compressor BTUs were equal to or greater than the condenser's Rating.

    Back in the early to mid-1970's, with those larger capacity compressors & no oversized coils, those babies, with a coil operating just a few degrees above the freezing point, when not oversized too much, would flat-out pull the humidity down.

    Indoor temp-splits, depending on indoor humidity levels, which got low in a hurry, were like +26 degrees...

    Our govt has gone too far trying to reduce the peak-load so electrical power companies wouldn't have to spend money building more power capacity; they have compromised comfort levels for paperwork numbers that don't pan out & are NOT realized in non-laboratory field conditions.

  7. #59
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    Quote Originally Posted by Shophound View Post
    I would still look to see if any return ducting was kicked loose by the alarm guy in the attic. Paper test not good enough. Have tech inspect all return ducts for signs of damage. Should not be too hard to spot.
    With 18" of blown-in insulation it's awfully hard to go trapesing through it without causing as much damage as you set out to cure (or search for). Believe me, I was not at all happy that the the alarm guy had to go through it, so much so that I came very close to cancelling the glass-break sensors (and sorely wish now that I had cancelled). I really don't want anyone else breaching the insulation to go on a fishing expedition.

    If there was some way to conduct a definitive test and first verify there's a problem in the RA vents, THEN I might be more receptive (tho nonetheless upset) to have the leak found and fixed. With all due respect guys, right now an RA leak is only a hypothesis. Help me out here - how can we be 99.9% certain before making an exploratory trip?

    thx

  8. #60
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
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    Duct leakage test (blower door, duct blaster, home energy audit) are the only ways to definitively test for duct leakage

  9. #61
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,325
    After I posted my last it occurred to me that there is a test that's not difficult to do, but requires a little conversion work to make any sense.

    It involves measuring the dew point of the air entering the return right before the air goes into the ducts in the attic. A second measurement is then made right at the inlet to the air handler or furnace. If there is a noticeable difference between dew point temperatures measured at the return inlet and the air handler inlet, you may have significant return air duct leakage. An instrument that measures temperature and relative humidity can be used for this test, with the readings from each point converted to dew point.

    Being that you're in Katy, Texas, it is safe to assume you live in a humid climate. Meaning if you or your tech were to conduct this test, the dew point difference behavior between the return inlet and the air handler inlet would be a higher dew point temperature at the air handler if your attic return air ducts have significant leakage. You will probably also notice a regular temperature difference at the air handler vs. the inlet, but this is normal due to the ducts being in a hot attic. However, if the difference is stark, that could also indicate leakage, along with an elevated dew point temperature.

    This test is far less invasive than plowing through a blizzard of insulation to find a leak. That said, if the alarm tech was the culprit, where he trod through the insulation in the attic will still be evident, and it is those paths I would explore first for problems.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  10. #62
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    Quote Originally Posted by Shophound View Post
    After I posted my last it occurred to me that there is a test that's not difficult to do, but requires a little conversion work to make any sense.

    It involves measuring the dew point of the air entering the return right before the air goes into the ducts in the attic. A second measurement is then made right at the inlet to the air handler or furnace. If there is a noticeable difference between dew point temperatures measured at the return inlet and the air handler inlet, you may have significant return air duct leakage. An instrument that measures temperature and relative humidity can be used for this test, with the readings from each point converted to dew point.

    Being that you're in Katy, Texas, it is safe to assume you live in a humid climate. Meaning if you or your tech were to conduct this test, the dew point difference behavior between the return inlet and the air handler inlet would be a higher dew point temperature at the air handler if your attic return air ducts have significant leakage. You will probably also notice a regular temperature difference at the air handler vs. the inlet, but this is normal due to the ducts being in a hot attic. However, if the difference is stark, that could also indicate leakage, along with an elevated dew point temperature.

    This test is far less invasive than plowing through a blizzard of insulation to find a leak. That said, if the alarm tech was the culprit, where he trod through the insulation in the attic will still be evident, and it is those paths I would explore first for problems.
    Thanks. Great idea!!

    I just happen to have a combo Temp/RH gauge which also includes DP display as well. It's an ExTech #445814 "Psychrometer". It's been recently calibrated, so should be close. There's no external probe on it, but I certainly could pull the media filter and rig something up to hold it in place w/the access door closed so it didn't get sucked into the fan. Project for the weekend perhaps

    A bit unusual considering the past couple weeks, but right now (8 PM) we're in good shape. Here in the study it's reading exactly 50% RH with a temperature of 75.9 and a DP of 55.9 (outside temp is 89.8, RH 45%, DP 65.5)

    You're correct about the climate. Katy is a western suburb of Houston

  11. #63
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50

    Mystery solved

    Okay, you guys get another star >sheepish grin<

    There indeed was a leak in the RA ducting, of all places right at the base of the RA plenum where the large (20") round duct attaches to the collar. The strap was in place & tight but there was about a 5" gap large enough to put your hand through where the duct was not completely seated on the coller. I really can't fault either tech, as you literally had to get down on your hands & knees and feel all around it. Right at the very bottom, hardest to get to, of course, the collar was bent and duct was not completely seated on it. I'm of the opinion this has likely been like that from day-one and we only recently began noticing the humidity

    Perhaps of some interest, Shophound's idea paid off, using a RH meter & thermometer at the RA grille, though the reading took about 15 minutes to settle. At the RA grille the RH was 56%. Measured again at the plenum (pulled the filter & tied the meter in place with a coat hanger. closed the access door then waited another 15 mins w/system running, RH there was 60% and the RA temperture was 5 deg warmer than at the RA grille downstairs. We never saw this much difference in RA temp previously because we were inserting the probe into the duct, about 15 inches or so ahead of the leak, not realizing where the leak was. (Duhh..)

    I spent almost an hour in the attic looking for the leak, never found it until I got all the way back to the plenum. I could have saved myself an hour and a gallon of perspiration and not had to venture out into the 'blizzard' if I'd started there first. Another one of life's ongoing lessons. 75 for a new nylon tie-wrap & we're good to go. Thanks again for y'alls patience & suggestions. Indoor RH 51% (also now 21deg. split between RA plenum and first supply duct (at the coil). Wheee! (tail is wagging) Seriously, I really appreciate the many suggestions & assist.

  12. #64
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    6,811
    Glad you were able to get it fixed

  13. #65
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,975

    Witnessed an HVAC user with the persistence to follow through with Shophound's advice

    Quote Originally Posted by Cap'n Preshoot View Post
    Okay, you guys get another star >sheepish grin<

    There indeed was a leak in the RA ducting, of all places right at the base of the RA plenum where the large (20") round duct attaches to the collar. The strap was in place & tight but there was about a 5" gap large enough to put your hand through where the duct was not completely seated on the collar. I really can't fault either tech, as you literally had to get down on your hands & knees and feel all around it. Right at the very bottom, hardest to get to, of course, the collar was bent and duct was not completely seated on it. I'm of the opinion this has likely been like that from day-one and we only recently began noticing the humidity

    Perhaps of some interest, Shophound's idea paid off, using a RH meter & thermometer at the RA grille, though the reading took about 15 minutes to settle. At the RA grille the RH was 56%. Measured again at the plenum (pulled the filter & tied the meter in place with a coat hanger. closed the access door then waited another 15 mins w/system running, RH there was 60% and the RA temperature was 5 deg warmer than at the RA grille downstairs. We never saw this much difference in RA temp previously because we were inserting the probe into the duct, about 15 inches or so ahead of the leak, not realizing where the leak was. (Duhh..)

    I spent almost an hour in the attic looking for the leak, never found it until I got all the way back to the plenum. I could have saved myself an hour and a gallon of perspiration and not had to venture out into the 'blizzard' if I'd started there first. Another one of life's ongoing lessons. 75 for a new nylon tie-wrap & we're good to go. Thanks again for y'alls patience & suggestions. Indoor RH 51% (also now 21deg. split between RA plenum and first supply duct (at the coil). Wheee! (tail is wagging) Seriously, I really appreciate the many suggestions & assist.
    Shophound is a real treasure, he understands the physics of the air's properties & how important those properties are when you're trouble shooting humidity problems in the conditioned space.

    That was the logical check because with the air handler & ducts in a hot attic there would be some temp rise in the air return from the RA grille(s); however, with that sensible temp-rise the percent of RH should be lower, NOT higher.

    If you took the wet bulb at the return air & then knew the CFM air flow you could also run the Enthalpy numbers & realize that There was an excessive load being introduced elsewhere into the duct system increasing the load on the evaporator.

    Using an easy to use enthalpy chart & modern test instruments, it only takes a few minutes to get the, close enough, ballpark DELIVERED Btuh of the system. It is critically IMPORTANT to know the Btuh the SYSTEM is ACTUALLY DELIVERING to the rooms; far too many systems are operating way to far below their Ratings.

    Three cheers for an HVAC user that listened to what we (so-called PROs) were telling him & who followed through using our shophound's methodical advice to locate & fix the problem, - at virtually no cost to him...you just witnessed the difference between a Tech that knows how to troubleshoot every kind of problem & others that don't know how to do it, - a night & day difference...
    Last edited by udarrell; 09-07-2012 at 07:44 AM. Reason: Typos etc...

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