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  1. #14
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,765
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    Quote Originally Posted by beenthere View Post
    Is there a frsh air intake connected to the system. If so, it may be bring in too much outside air, and causing the humidity issue.

    Could also be the blower speed/CFM is set too high.
    This is the heart of the problem. How much fresh air infiltration and what is the dew point plus the number of occupants are the sources of moisture.
    The capacity of the a/c sensible and latent system and the hours of run time is how most homes attempt humidity control. Air flow through the cooling coil determines the sensible/latent(dehumidification) ratio.
    The low end of air flow is 275 cfm per ton of total cooling capacity. This is typically 25% latent cooling. This is 3,000 btus per ton of total cooling. A 3 ton a/c would do 9 lbs. (gallon) per hour

    80 cfm of 70^F dew point outdoor air dried down to 50%RH at 75^F is a 55*F dew point. This equates to 3-4 lbs. to moisture per hour plus 2 lbs. from the occupants totals 6 lbs. per hour. A 3 ton a/c cycling +60% of the hour will keep the home <50%RH.
    Works great on a hot day. Not well of warm evening. Impossible during mild humid humid weather.
    The fresh air is important when the home occupied to purge the indoor pollutants and renew oxygen for optimum health.
    A well setup a/c with a 4 lbs. per hour whole house dehumidifier will do maintain fresh air and <50%RH during most normal weather conditions.
    All a/c conditioners in green grass climate have many days when they need a good dehumidifier to keep the home dry.

    The need for oxygen rich air is obvious for resistance to the challanges of threatening home occupants.

    Good discussion.
    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"

  2. #15
    Join Date
    Mar 2020
    Posts
    3
    Post Likes
    Thread Starter
    Thanks again for everyone's responses. Here are some additional answers to questions.

    This is ~30 miles north of Austin.

    There is a fresh air intake for the house, located in the laundry room. It has an on or off switch, and if on, there also has an option with a low speed vent, presumably when doing laundry. We experimented with all settings and did not notice a significant difference (few % relative humidity higher with the fresh air off after a few hours but it stabilizes).

    Just to show we did it based on the 2nd tech recommendation, ran the thermostat at 68F for the weekend (outside temp 67-78F, outside 35-19% red humidity 67-69%).

    Today I requested the commissioning report/checklist and was told they don't give those out. I asked why and got a non-response of nobody requests these.

    We have beautiful weather today 68F, 56% rel humidity and the AC has not run for two days and inside humidity is 58-60% and it is the most comfortable my daughter has been in the 3 weeks she has been in the house.

    We've worked our way to a supervisor coming out next week when it warms up again. How much can an adjustment of the CFM can it make on the rel. humidity?

    Quote Originally Posted by beenthere View Post
    Is there a frsh air intake connected to the system. If so, it may be bring in too much outside air, and causing the humidity issue.

    Could also be the blower speed/CFM is set too high.

  3. #16
    Join Date
    Jan 2004
    Location
    PA
    Posts
    78,516
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    Slowing down the CFM can make a big difference on the indoor RH(5% or more depending on outdoor temp). But only when its warm enough outside for the A/C to need to run.

    Most likely they don't give out the commissioning report. Because like the majority of companies, they don't do commissioning.
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  4. #17
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,196
    Post Likes
    Quote Originally Posted by HumidinTexas View Post
    Thanks again for everyone's responses. Here are some additional answers to questions.

    This is ~30 miles north of Austin.

    There is a fresh air intake for the house, located in the laundry room. It has an on or off switch, and if on, there also has an option with a low speed vent, presumably when doing laundry. We experimented with all settings and did not notice a significant difference (few % relative humidity higher with the fresh air off after a few hours but it stabilizes).

    Just to show we did it based on the 2nd tech recommendation, ran the thermostat at 68F for the weekend (outside temp 67-78F, outside 35-19% red humidity 67-69%).

    Today I requested the commissioning report/checklist and was told they don't give those out. I asked why and got a non-response of nobody requests these.

    We have beautiful weather today 68F, 56% rel humidity and the AC has not run for two days and inside humidity is 58-60% and it is the most comfortable my daughter has been in the 3 weeks she has been in the house.

    We've worked our way to a supervisor coming out next week when it warms up again. How much can an adjustment of the CFM can it make on the rel. humidity?
    It should read "Nobody does those"

    Honestly I would seek another contractor to do a commissioning report along with a Manual "J" load loss calculation. Yes its going to cost but that's the only way to dispute what the contractor and his sub did! (And they will layer it thick)
    Even with it your options are limited.

    Possibly look into a whole house dehumidifier.

  5. #18
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    9,765
    Post Likes
    Quote Originally Posted by HumidinTexas View Post
    Thanks again for everyone's responses. Here are some additional answers to questions.

    This is ~30 miles north of Austin.

    There is a fresh air intake for the house, located in the laundry room. It has an on or off switch, and if on, there also has an option with a low speed vent, presumably when doing laundry. We experimented with all settings and did not notice a significant difference (few % relative humidity higher with the fresh air off after a few hours but it stabilizes).

    Just to show we did it based on the 2nd tech recommendation, ran the thermostat at 68F for the weekend (outside temp 67-78F, outside 35-19% red humidity 67-69%).

    Today I requested the commissioning report/checklist and was told they don't give those out. I asked why and got a non-response of nobody requests these.

    We have beautiful weather today 68F, 56% rel humidity and the AC has not run for two days and inside humidity is 58-60% and it is the most comfortable my daughter has been in the 3 weeks she has been in the house.

    We've worked our way to a supervisor coming out next week when it warms up again. How much can an adjustment of the CFM can it make on the rel. humidity?

    During the high heat of the day while the a/c operates +50% of the time, a well tuned a/c should be able to maintain 50%rH. Evenings and rainy days with very short or no cooling loads, the a/c will not control %RH. If the outdoor dew point is above 50^F and the home is occupied, expect a damp home.

    To make this plain, the a/c will not control the moisture level in the home without significant sensible cooling load.

    The moisture load from adequate fresh air(80 cfm) and occupants is about 4 lbs. of dehumdification per hour, minimum.

    Why is this so difficult to understand in the a/c profession??? Sizing or setup of the a/c will not fix this, please!!!
    Regards Teddy
    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"

  6. #19
    Join Date
    Aug 2002
    Location
    Southold, NY
    Posts
    27,196
    Post Likes
    Quote Originally Posted by teddy bear View Post
    During the high heat of the day while the a/c operates +50% of the time, a well tuned a/c should be able to maintain 50%rH. Evenings and rainy days with very short or no cooling loads, the a/c will not control %RH. If the outdoor dew point is above 50^F and the home is occupied, expect a damp home.

    To make this plain, the a/c will not control the moisture level in the home without significant sensible cooling load.

    The moisture load from adequate fresh air(80 cfm) and occupants is about 4 lbs. of dehumdification per hour, minimum.

    Why is this so difficult to understand in the a/c profession??? Sizing or setup of the a/c will not fix this, please!!!
    Regards Teddy
    Teaching these guys that 500 SqFt per ton is wrong is hard enough!

  7. #20
    Join Date
    Jun 2003
    Location
    Texas
    Posts
    1,513
    Post Likes
    I live about 120 miles north of yall. its that time of year when the ac cant keep the humidity down. ya ether have to have a de-humidifier or deal with it. run the vents when yall shower or cook will help

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