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  1. #1
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    HVAC, Humidity and ERV for 1000 sq ft tight house!

    Hi everyone, new to this forum. I joined cause Im racking my brain over all the info out there for cooling, dehumidifying and bringing in fresh air for tight built spray foamed houses.

    I'm a general contractor in South Texas and building my first house. Its a small fancy camp house at 1032 sq ft, has 10 ft ceilings with vaulted in the great room/kitchen. The exterior walls are 2x6 and were using open cell foam on exterior walls and the ceiling of the roof for a conditioned attic space. The exterior is being sealed with bottom seal wrap and OSB sheathing taped and caulked for a tight house.

    What I'm looking for is the best HVAC setup to remove humidity and whether I need an ERV to bring in fresh air. Ive read so much about over sizing your HVAC where it does not run long enough to remove humidity. Ive also read about whole home dehumidifiers but all seems to be massively overkill for this size of house. Ive learned about Carrier Infinity two stage for better humidity removal but smallest is 2 ton, I assume I need to be in 1 or 1.5 ton range.



    So pros... how should I proceed?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Simple a/c ducted or mini-split. A small whole house dehumidifier like the Ultra-Aire 70H with fresh make air option when occupied. 1,000 sq.ft. with 3-4 occupants needs 50 cfm of fresh air when occupied to purge indoor pollutants and renew oxygen. When unoccupied, no fresh air is needed.
    A/c off when unoccupied with dehu set at 50%RH will keep it dry for a few bucks a month when the outdoor dew points are high. Will not operate when the outdoor dew points are low. The fresh air needs a manual or electric damper to provide fresh air when occupied and windows closed. Electric switch will activate the damper and fan motor.
    The idea of cooling to dehumidify only works when there is significant sensible cooling load, provided the a/c has minimum of 30^F split and a +30% duty cycle. As the cooling cycle declines, not enough moisture goes down the drain to keep it dry. Over-cooling for humidty control dramitically increases the amount of moisture that most be removed to maintain low indoor humidity. Cooling the structure below the outdoor dew point causes moisture condensation in the structure, as opposed to warming the space and removing moisture with a dehumidifier.
    Simple, reliable, and fool proof.
    I keep my FL. camp dry in this way. No cooling for 7 years when unoccupied and no musty odors.
    Keep us posted.
    Regards Teddy Bear
    Last edited by teddy bear; 04-24-2017 at 12:38 PM.
    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"

  3. #3
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    Thread Starter
    Teddy, thanks for the response and info.

    So basically the Ultra-Aire 70H with the fresh air option is a dehumidifier with ERV all in one? Is that correct? I would have to add an electric damper to the system. Is there a setup for this that includes a controller? Also do you know of anything smaller than the 70H? Still seems overkill but if its the smallest guess thats the option.

  4. #4
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by pearlhomes View Post
    Teddy, thanks for the response and info.

    So basically the Ultra-Aire 70H with the fresh air option is a dehumidifier with ERV all in one? Is that correct? I would have to add an electric damper to the system. Is there a setup for this that includes a controller? Also do you know of anything smaller than the 70H? Still seems overkill but if its the smallest guess thats the option.
    The fresh air supply/filter is built into the Ultra-Aire 70H. There is a controller, DEH3000 that controls fresh air and dehumidification.
    Yes it larger than needed but smallest I know of with all of the features. Over-sizing dehus is not as much of a problem as over-sized a/c. You could build a bigger camp??
    ULtra-Aire.com is a site sponsor also.
    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"

  5. #5
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    Thread Starter
    Makes sense and thanks for the controller info.

    Another HVAC expert here locally is telling me to get the 2 ton Carrier Infinity 21 system which is two stage. He states that this system will take care of all the dehumidifier needs instead of needing a standalone. I would just add an ERV like the smaller Panasonic to it. Whats your thoughts on this take?

  6. #6
    Join Date
    Jun 2003
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    Good, tell him you like the statement of 50%RH during wet cool weather or money back.
    If you trust him go with him. We deal with this all of the time. A/c will control %RH during high cooling loads. During low/no cooling loads, any a/c will not control moisture.
    Keep us posted on how this all works.
    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
    Apr 2017
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    Thread Starter
    Thanks Teddy. Yeah it sounded too good to be true and I feel this contractor although trying to help does not fully understand the spray foam tight house situation. So now what Im looking at is a Goodman 1.5 ton with gas furnace tied to the Ultra Aire 70h with the make fresh air option with damper and DEH controller.

    Thanks again for the advice. Do you know of any of the smart thermos that can connect to Ultra Aire for an all in one?

  8. #8
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    Thread Starter
    Hey Teddy, another question. I was thinking 1.5 ton so it would run longer to assist in dehumidification. But since there is going to be the Ultra Aire 70 in there doing that job anyways should I move up to a 2 ton that will only cycle briefly? If theres little to no savings 1.5 to 2 ton, which would you choose?

    1032 sq ft, spray foam envelope, water and vapor barriers on slab and caulking, etc

  9. #9
    Join Date
    Oct 2012
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    Danville, KY
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    A 2 ton will cost you more money to operate for your cooling needs than a 1.5t.

    Sent from my SM-N910V using Tapatalk

  10. #10
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    Madison, WI/Cape Coral, FL
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    There is no benefit to using a larger unit. Longer runs will do a better job of helping to control the %RH.
    Keep us posted on how this works out.
    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"

  11. #11
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    Apr 2017
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    HVAC systems are capable of regulating humidity. It has an evaporator coil that condenses water vapor from the air. Your air conditioner will be effective at controlling humidity only if it is correctly sized for the amount of work it needs to do. Your professional residential ac repair service NJ specialist will calculate the appropriate size needed for your HVAC system based on the size of your home.

  12. #12
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    Quote Originally Posted by PercyWilliams View Post
    HVAC systems are capable of regulating humidity. It has an evaporator coil that condenses water vapor from the air. Your air conditioner will be effective at controlling humidity only if it is correctly sized for the amount of work it needs to do. Your professional residential ac repair service NJ specialist will calculate the appropriate size needed for your HVAC system based on the size of your home.
    Just to expand my horizons, help me understand how a correctly sized a/c will remove latent load without any sensible cooling load. Like during an extended rainy spell of 70^F, 90%RH outside and several occupants in the home with t-stat set at 75^F, I want 50%RH. The sensible cooling 0 btus and the latent is 4,000 btus per hour from fresh air infiltration and the occupants latent load.
    Looking forward to the 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"

  13. Likes stanbyyourword liked this post
  14. #13
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    Jun 2006
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    I am about to build a home and have a similar situation as the OP. What about winter? How do you address moisture in TX in the winter? In TX a so-called winter can have a 30 or more degree swing. I’m familiar with some foamed homes having heavy window sweating during the winter season. Mine does.

    Does an ERV remedy this? Does a heat-pump do anything for dehumidification in winter?

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