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  1. #1
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    Aug 2018
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    Humidity Issues in TN

    I live in Nashville TN with its hot and humid summers. We are having high humidity levels in our house, up to 75%, lowest noted recently was 59%. (we have had condensation on the vents) We built this new house 3 years ago, and upgraded to 16 SEER Units expecting less energy usage and comfort. The house is Energy Star Certified with a HERS index of 66. The contractors just replaced the TXV yesterday on the package 5 ton unit that serves my downstairs, approximately 3000 SF, and I hope that will help. Upstairs is a split 2 ton unit serving less than 1000 SF. Also, we have a crawl space that has been completely sealed and an industrial dehumidifier installed that maintains humidity around 45-50%. Also, I bought a portable dehumidifier which is running constantly but maybe that will change now. We set the units at 74 in the day, down to 68 at night. I also run the fans constantly as that seems to balance out the temperatures in the house…although I have seen comments saying this will increase humidity but others that say this is not true and increase is minimal.

    I found out my thermostats are not 2 stage and was told the stages were controlled by boards in each unit. I asked contractor to replace but they do not want to unless I pay, of course. I have confirmed that both stages do operate. Would a 2 Stage thermostat be appropriate; I called Honeywell and they said my TH810R1008 is not compatible with the units and should be replaced with TH8300R…but of course they would want me to buy an upgrade.

    I feel like I am getting the run around so I would like any help on the following questions?

    1. What should I expect my humidity level to be? (was told 50 is the target)
    2. Should my AC units manage humidity or do I need separate dehumidifiers? I am hoping the TXV will take care of this problem but the verdict is still out.
    3. Any other suggestions to control humidity.
    4. Is there a benefit to replacing thermostats?
    5. Fans “on” or “auto”?

    I look forward to any comments or ideas or additional questions. Thank you!

  2. #2
    Join Date
    Jan 2004
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    PA
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    A 3 year old house shouldn't need 5 tons for a 3000 sq ft first sfoor. So over sizing may be part of the problem.

    Doubt a board in the unit is controlling staging of the A/C. You should upgrade to a thermostat that can control 2 stages of cooling.

    And yes, continuous fan will raise the indoor humidity by 3 to 5 percent. When you get the new thermostat, you might want to use circ instead of fan on.

    55% or lower.

    Post brand and model number of first floor unit.
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  3. #3
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    During the hottest part of the day, a slightly oversized a/c should keep the home in the 48-52%RH range. The a/c must be functioning well with the air flow through the cooling coil adjusted to have a 30^F split between the return air temperature and the a/c coil temperature. The results will be 5-8^F dew point reduction as the air is cooled by the a/c.
    75^F, 50%RH, a 55^F dew point entering a 45^F cooling coil will leave with a 6-7^F dew point reduction. This setup will remove 3 lbs. of moisture per hour per ton. 5 ton a/c should remove 15lbs. of moisture per hour.
    During evening and rainy days, when there is low/no sensible cooling loads, the a/c will not remove enough moisture to maintain 50%RH. Supplemental dehumidification will be required during evenings and rainy days and high outdoor dew points, +65^F.
    Yes fan "on" will quickly re-evaporate the moisture left on the cooling coil at the end of the cooling cycle.
    Sounds like your a/c is either not working or has excess air flowing through the cooling during peak cooling hours plus needs a properly installed whole house dehumidifier.
    Consider Ultra-Aire XT155H paired with the 5 ton after the a/c are checked for function and correct air.
    New homes like this also should some fresh air ventilation when the home is occupied. This could be done by using the fresh air option on the dehumidifier.
    Keep us posted.
    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"

  4. #4
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    Aug 2018
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    Thread Starter
    Thanks for your response.

    It is a Goodman GPC156014041CA, I took a picture of the unit tag but I could not figure out how to attach a picture to this.

    So, I have witnessed that the units will switch from Stage 1 to Stage 2 so there must be something (the contractor called it a board) that is controlling this. But if I changed the thermostat is to would be the thermostat that controls switching between stages, correct?

  5. #5
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    Aug 2018
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    Thread Starter
    The differential of temperature between the vents and return air is 28 for the downstairs unit (including the new TXV) and 25 for the upstairs unit). Is that appropriate?

    This is the first summer we have had this problem so I hope the issue was the TXV, not that I will need to add a whole house dehumidifier. If I went the route to add a dehumidifier would one on the larger downstairs unit suffice?

    Did you have thoughts on the thermostats?

    thanks for your responses!

  6. #6
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by kevdanc View Post
    The differential of temperature between the vents and return air is 28 for the downstairs unit (including the new TXV) and 25 for the upstairs unit). Is that appropriate?
    We need the temp/%RH in the room and the temp/%RH on the supply to comment on the wether this adequate

    This is the first summer we have had this problem so I hope the issue was the TXV, not that I will need to add a whole house dehumidifier. If I went the route to add a dehumidifier would one on the larger downstairs unit suffice?

    Did you have thoughts on the thermostats?

    thanks for your responses!
    It the top flow open to the lower level.
    If open stairwell and mostly open door on the top floor. On whole house should do the job. I am assuming that the a/c on the top also will be setup to maintain 50%RH during high cooling loads.
    Keep posted.
    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"

  7. #7
    Join Date
    Nov 2004
    Location
    SW FL
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    Quote Originally Posted by kevdanc View Post
    The differential of temperature between the vents and return air is 28 for the downstairs unit (including the new TXV) and 25 for the upstairs unit). Is that appropriate?

    This is the first summer we have had this problem so I hope the issue was the TXV,
    not that I will need to add a whole house dehumidifier.

    If I went the route to add a dehumidifier would one on the larger downstairs unit suffice?

    Did you have thoughts on the thermostats?

    thanks for your responses!
    So when the t-stat is reading 68'F in the morning, you have a DIRECT Measurement of 40'F Supply Air at the diffusers.

    Therefore, you cannot have humidity issues unless your runtimes are at < 30% of the time
    (or a few windows are open).

    When were your hygrometers ( i.e. humidity meter) last tested and certified.?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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