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  1. #1
    Join Date
    Mar 2017
    Location
    Houston, Tx
    Posts
    47
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    Hmm High Humidity Problem

    Having a really hard time with high humidity levels in a customers home that I'm struggling to resolve.
    Houston, Tx
    High outside temp for the day was 92.
    2 story townhouse, one side of the home is a shared wall with the next unit, the other is an outside wall.
    Home is only about 3 years old
    2 ton unit

    I already installed a Honeywell dehumidfier 90 pint DR90A3000. That unit was installed end of last summer and it seemed to hold up ok. Now it is running non stop and unable to bring the humidity down. Humidity is stuck around 70%.

    Customer's electric bill this past month jumped from $80 to $300.

    • Inspected the duct work for leakage and didn't find anything noticeable.
    • System was overcharged so I recovered some refrigerant to bring it in line with manufacturer specs.
    • Condensate is flowing great from both the system and the dehumidifier.
    • Thought about dropping the fan speed but the blower motor is single speed.
    • Return air temp @furnace was 60.5 DB
    • Supply air temp just after the coil was 82.4 DB
    • Supply temps at grills were 75 DB(this seemed like a pretty drastic loss of supply temp in the duct work)


    Heading back to the customer's tomorrow. Going to recheck all of the duct work and see if I missed something major.

    Any other ideas on what else I should check while I'm there?

  2. #2
    Join Date
    Jul 2010
    Location
    nebraska
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    2,810
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    How is your supply air warmer than return with the AC running? Why is the return 60 degrees?

  3. Likes MPeterson21 liked this post.
  4. #3
    Join Date
    May 2019
    Location
    Jamestown, NY
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    92
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    Quote Originally Posted by martyinlincoln View Post
    How is your supply air warmer than return with the AC running? Why is the return 60 degrees?
    I think it was a typo. I was thinking the same thing.

    Sent from my Pixel 2 XL using Tapatalk

  5. #4
    Join Date
    Dec 2014
    Posts
    3,044
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    Where are you reading your space humidity.? If it's near a supply it's going to read pretty high while the AC is running.

    Sent from my SM-G950U using Tapatalk

  6. #5
    Join Date
    Mar 2017
    Location
    Houston, Tx
    Posts
    47
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    Thread Starter
    Yes that was a typo. Sorry, it was a long day.

    Return air temp @furnace was 82.4 DB
    Supply air temp just after the coil was 60.5DB

  7. #6
    Join Date
    Mar 2017
    Location
    Houston, Tx
    Posts
    47
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    Thread Starter
    Quote Originally Posted by icy78 View Post
    Where are you reading your space humidity.? If it's near a supply it's going to read pretty high while the AC is running.

    Sent from my SM-G950U using Tapatalk
    Reading it next to the upstairs thermostat which is about 4-5 ft from the return. No supply grills nearby.

    You can feel the humidity in the house. Its muggy in there.

  8. #7
    Join Date
    Mar 2010
    Location
    Houston
    Posts
    213
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    Can you toss in a couple other data points?

    Is this a Heat Pump?
    Pressure / temp readings (when you recovered gas?)
    WetBulb reading at return?
    Flex duct? Configuration?
    Attic install?
    Static Pressure across coil?


    A few random thoughts:
    Houston is brutally humid right now, and I’m thinking you may have an infiltration issue on return side or the efficiency has degraded due to one or more airflow anomalies so you’re not really getting 800-1200 cfm in the living space you should be.

    - look for open fresh air vent(s) to outside. Perhaps some appliance exhaust vents ducting failure.

    - Flex can be tough to find failure in attic space. I use a smoke system to find and seal any leaks at connections. Be mindful of restricted return duct too that may have been pinched or collapsed at a support or transition.

    - Make sure the blower wheel is clean. Motor amp draw is normal range for unit.

    - I know you said it was producing lots of condensate, but is it draining enough? Make sure there’s no restrictions in the P-Trap(s) and that the AH is able to push it out completely. If the trap is improperly implemented or a vent cap is left off it won’t be able to drain effectively during operation due to negative pressure.

    That’s all I got at moment... GL

    K

  9. #8
    Join Date
    May 2019
    Location
    Jamestown, NY
    Posts
    92
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    A really good way to find leaks is peppermint oil

    Sent from my Pixel 2 XL using Tapatalk

  10. #9
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,768
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    Quote Originally Posted by JaySWAT View Post
    High outside temp for the day was 92.
    2 story townhouse, one side of the home is a shared wall with the next unit, the other is an outside wall.
    Home is only about 3 years old
    2 ton unit

    I already installed a Honeywell dehumidfier 90 pint DR90A3000. That unit was installed end of last summer and it seemed to hold up ok. Now it is running non stop and unable to bring the humidity down. Humidity is stuck around 70%.

    Customer's electric bill this past month jumped from $80 to $300.

    • Inspected the duct work for leakage and didn't find anything noticeable.
    • System was overcharged so I recovered some refrigerant to bring it in line with manufacturer specs.
    • Condensate is flowing great from both the system and the dehumidifier.
    • Thought about dropping the fan speed but the blower motor is single speed.
    • Return air temp @furnace was 60.5 DB
    • Supply air temp just after the coil was 82.4 DB
    • Supply temps at grills were 75 DB(this seemed like a pretty drastic loss of supply temp in the duct work)


    Heading back to the customer's tomorrow. Going to recheck all of the duct work and see if I missed something major.

    Any other ideas on what else I should check while I'm there?
    You may not want to hear this but. This a classic problem that can teach us lot.

    The a/c must be setup to max the moisture removed on its own during high cooling loads. You mention the most common problem. We need a cold enough cooling coil to get a 75%/25% Sensible Latent cool ratio. This about 3 lbs. of moisture per ton of a/c per hour. A 2 ton a/c should remove 6 lbs. of moisture per hour. This is equal to the moisture 100 cfm of moist air entering the home the moisture from 4 occupants with a 70^F outdoor dew point while maintaining a 55^F dew point inside the home.
    A Honeywell 95 is about 3-4 lbs. per in addition to the a/c if connected properly and functioning.

    First, measure condensate for both units if possible. 10 mins will do with a measuring cup to determine the lbs./pints per hour from each. 6 X actual moisture removed equals one hour of run. 1 pint of water equals 1 lb. of water.
    Then shut off the dehumidifier.
    Now measure the condensate from the a/c only.
    The most common problem is the place the warm, dry air from the dehu is supplied into a/c ducts. The ideal is to suck air from the home open part of the home to the dehu and the warm dry air from the dehu supplied to the a/c supply. Many are connected to the return and warm dry air back to the a/c return which decreases the amount of moisture removed by a/c by about the same amount as the dehu removes.
    If you install is like this it must be change route the dry air from the dehu to the cold a/c supply.
    Measuring the condensate from each unit should confirm this problem.
    Dehu sucking on the return and supply the return requires that the a/c blower be on whenever the dehu is running. If the dehu is sucking from the open part of the home with the warm dry air supply to the cold supply of the a/c, the fan is not needed to circulate the dry air throughout the home. Thus is reduces rapid evaporation of the moisture left on the cooling coil and the electricity used by the dehumidifying process. A/c blowers use almost as much electricity as a dehu.
    Regarding the "Lazy A/C" you must reduce the air flow to get the a/c coil temperature a minimum of 30^F colder than the return air flow. 82^F return should have <52^F coil temperature using the suction pressure to measure. At 75^F, 50%RH, a 55^F dew point, you need 45^F coil temperature. Also a <50^F dew point a/c supply air dew point. With dehu operating alson with the a/c, expect <47^F dew point a/c supply at the grill in the home.
    If unable to reduce the blower speed suggest increasing filter resistance until you get the coil conditions described. For short term testing, add some paper towel to the air filter to slow the air.
    I have learned the above lesson the hard way myself.
    Looking to hear from you about what you find.
    Regards Teddy Bear
    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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  12. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by teddy bear View Post
    You may not want to hear this but. This a classic problem that can teach us lot.

    The a/c must be setup to max the moisture removed on its own during high cooling loads. You mention the most common problem. We need a cold enough cooling coil to get a 75%/25% Sensible Latent cool ratio. This about 3 lbs. of moisture per ton of a/c per hour. A 2 ton a/c should remove 6 lbs. of moisture per hour. This is equal to the moisture 100 cfm of moist air entering the home the moisture from 4 occupants with a 70^F outdoor dew point while maintaining a 55^F dew point inside the home.
    A Honeywell 95 is about 3-4 lbs. per in addition to the a/c if connected properly and functioning.

    First, measure condensate for both units if possible. 10 mins will do with a measuring cup to determine the lbs./pints per hour from each. 6 X actual moisture removed equals one hour of run. 1 pint of water equals 1 lb. of water.
    Then shut off the dehumidifier.
    Now measure the condensate from the a/c only.
    The most common problem is the place the warm, dry air from the dehu is supplied into a/c ducts. The ideal is to suck air from the home open part of the home to the dehu and the warm dry air from the dehu supplied to the a/c supply. Many are connected to the return and warm dry air back to the a/c return which decreases the amount of moisture removed by a/c by about the same amount as the dehu removes.
    If you install is like this it must be change route the dry air from the dehu to the cold a/c supply.
    Measuring the condensate from each unit should confirm this problem.
    Dehu sucking on the return and supply the return requires that the a/c blower be on whenever the dehu is running. If the dehu is sucking from the open part of the home with the warm dry air supply to the cold supply of the a/c, the fan is not needed to circulate the dry air throughout the home. Thus is reduces rapid evaporation of the moisture left on the cooling coil and the electricity used by the dehumidifying process. A/c blowers use almost as much electricity as a dehu.
    Regarding the "Lazy A/C" you must reduce the air flow to get the a/c coil temperature a minimum of 30^F colder than the return air flow. 82^F return should have <52^F coil temperature using the suction pressure to measure. At 75^F, 50%RH, a 55^F dew point, you need 45^F coil temperature. Also a <50^F dew point a/c supply air dew point. With dehu operating alson with the a/c, expect <47^F dew point a/c supply at the grill in the home.
    If unable to reduce the blower speed suggest increasing filter resistance until you get the coil conditions described. For short term testing, add some paper towel to the air filter to slow the air.
    I have learned the above lesson the hard way myself.
    Looking to hear from you about what you find.
    Regards Teddy Bear
    PS. could also be duct leaks as other have said. I am attaching a dew point map. Houston was 76^F, really wet!Name:  Houston dew points 6 7 2019.JPG
Views: 252
Size:  66.9 KB
    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"

  13. #11
    Join Date
    Jun 2019
    Posts
    11
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    The area near the coastline will face high humidity and keeping an AC to run for 15 minutes can dry it off. I am not sure about your exact humidity percent.

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