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  1. #1

    Confused high indoor humidity in summertime

    I have a 1165 sq ft house and just recently replaced an 18 year old HVAC system. We had a 2-ton 14SEER American Standard Allegiance Air conditioner and an American Standard Freedom 90 Contemporary Furnace installed. The problem with it is although it seems to be cooling well, the relative humidity seems still a bit high at around 65% in the daytime. This is not due to short cycling, because during the hottest part of the day when the thermostat is set at 72 F, the air conditioner will run continuously for several hours and while the temp is 72F the relative humidity will only go down to 60%. During Is this normal or shouldn't the AC system be able to bring the RH to 50% or so? I looked at the drain pipe from the condensing coils and there is water trickling out of it. I am going to have the techs come over to look at the system, but any suggestions would be much appreciated.

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,319
    Did your 18 year old system control the humidity satisfactorily?

    Was any ductwork changed/modified when you had the new system installed?

    Could be something as simple as having your installer reduce the indoor blower speed, and if so, adjusting the refrigerant charge concurrently. It also may be the airflow is adequate as is but the refrigerant level is a bit high, which can lead to a cool but clammy feeling in the house.

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,898
    Could be.
    Undercharged.
    Overcharged.
    Too much air flow.
    Leaky return duct.
    Leaky supply duct.
    Humidifier running.
    etc.

    Have them come back ASAP.
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  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,358
    Is it possible to catch a days worth of condensate water? If you are removing 60-70 lbs. of water per day, the home should be dry. If wet after removing that much water, look for air or water leaks. If you are not removing 6 lbs. of water per hour of a/c run, have tech check the previous mentioned items plus temperature drop over the a/c cooling coil. Operate the fan in the "auto" mode to minimize re-evaporation from the coil back to the home during the off cycle. If the a/c is removing enough water everyday, air leakage or water leaking into the crawlspace/basement are next. Also attic exhaust fans suck moist air into the home raising the moisture level. During low/no a/c load conditions, homes with adequate fresh air need supplemental dehumidification to maintain <50%RH. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
    Join Date
    Aug 2004
    Location
    Minnesota
    Posts
    349
    Do you have your indoor fan set to "on"? If so try switching it to "auto". When your air conditioner is not running, a continuous fan will re-evaporate moisture back into your air stream.
    White Bear Township, Minnesota
    www.summitheating.com

  6. #6
    To answer ssome of the posted questions

    (1) I have fan set on auto and not on "on".

    (2) I did not have any ductwork modification done when the HVAC was installed.

    (3) We do not have exhaust attic fans. We do have vents in the attic, but I do not believe we have fans.

    (4) I never looked real carefully, but I believe before the installation of the new HVAC system, the RH was around 60% in the daytime, but never lower. I am not totally sure about this last statement though

    Given statement 4, does this indicate leaky ducts?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,898
    Ducts, excess fresh air from some where. Fan speed too high.
    Just a few possibilities.
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  8. #8
    Quote Originally Posted by edlchiang62 View Post
    I have a 1165 sq ft house and just recently replaced an 18 year old HVAC system. We had a 2-ton 14SEER American Standard Allegiance Air conditioner and an American Standard Freedom 90 Contemporary Furnace installed. The problem with it is although it seems to be cooling well, the relative humidity seems still a bit high at around 65% in the daytime. This is not due to short cycling, because during the hottest part of the day when the thermostat is set at 72 F, the air conditioner will run continuously for several hours and while the temp is 72F the relative humidity will only go down to 60%. During Is this normal or shouldn't the AC system be able to bring the RH to 50% or so? I looked at the drain pipe from the condensing coils and there is water trickling out of it. I am going to have the techs come over to look at the system, but any suggestions would be much appreciated.
    Have you resolved this issue? I have an Allegiance 16 (new system) and have been having humidity problems. I think I've found the reason. I noticed that the system would run for quite a while with the blower running but with the compressor off. This happened particularly after the temp had reached close to the set point, which is when the humidity would rise. Fact is, the fan should only run 3 minutes after compressor shut-off. I found out that the root of the problem is that the compressor is not running in stage 1 mode (but runs in stage 2!), so while the blower runs for 1/2 hour, the compressor is supposed to be in stage 1, but NOT. So the moisture in the coil re-evaporates and humidifies the house. I ran a "System insaller's test" and forced the sytem to operate in stage 1, but the compressor didn't run. PROOF.

    Maybe your situation is the same. I'm waiting for a call back from my contractor so he can trace down why stage 1 doesn't work.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,898
    Except the 14 SEER isn't 2 stage.
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  10. #10
    Quote Originally Posted by jeff_p View Post
    Have you resolved this issue? I have an Allegiance 16 (new system) and have been having humidity problems. I think I've found the reason. I noticed that the system would run for quite a while with the blower running but with the compressor off. This happened particularly after the temp had reached close to the set point, which is when the humidity would rise. Fact is, the fan should only run 3 minutes after compressor shut-off. I found out that the root of the problem is that the compressor is not running in stage 1 mode (but runs in stage 2!), so while the blower runs for 1/2 hour, the compressor is supposed to be in stage 1, but NOT. So the moisture in the coil re-evaporates and humidifies the house. I ran a "System insaller's test" and forced the sytem to operate in stage 1, but the compressor didn't run. PROOF.

    Maybe your situation is the same. I'm waiting for a call back from my contractor so he can trace down why stage 1 doesn't work.

    No I haven't yet...My system is just a single stage system. Yesterday It was seasonably warm and dry outside (temp 80F , dewpoint temp 42F, 31&#37; RH ) and I had the A/C on ad the RH only got down to 54%, I an going on vacation and will have the contractor look at the system when I get back

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,358
    Quote Originally Posted by edlchiang62 View Post
    No I haven't yet...My system is just a single stage system. Yesterday It was seasonably warm and dry outside (temp 80F , dewpoint temp 42F, 31% RH ) and I had the A/C on ad the RH only got down to 54%, I an going on vacation and will have the contractor look at the system when I get back
    What was the temp inside? Sounds like you do not have any real cooling load. Without cooling load, how will your a/c remove moisture? Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Quote Originally Posted by teddy bear View Post
    What was the temp inside? Sounds like you do not have any real cooling load. Without cooling load, how will your a/c remove moisture? Regards TB


    I am not sure what a cooling load is, but the inside temp was 72 F and I had thermostat set at 72F and in the late afternoon when the A/C had been running for half hour continuously (blower fan is set to auto), the RH went down only to 54&#37; which by my calculation is approximately 54F dewpoint temperature. This was occurring when the kitchen was not being used or no one in the house was showering.

    The temp of the air coming out of a register was 57F degrees

  13. #13
    Join Date
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    Location
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    You need several hours of a/c operation to remove enough moistue to provide low %RH. Lower humidity levels without significant cooling requires supplemental dehumidification. Northen green grass climates do not have much of cooling load this year. Hopefully you have some fresh air infiltrating your home to purge indoor pollutants and renew oxygen. The fresh air contains moisture. Typically , removing 30-70 pints of moistue per day maintains <50%RH. On hot days, your a/c removes the moisture. On cool days, a good dehumdifier can do it. More infor to follow from others. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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