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  1. #14
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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?

  2. #15
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by dannyb View Post
    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?
    First, you need a fresh air change in 4-5 hours to purge indoor pollutants and renew oxygen whenever the home is occupied. The dew point of the outdoor air plus moisture from the occupants determines the moisture level or dew point of the air in the home.
    We have focused on the moisture level in the high moisture seasons and removing moisture with an a/c and a dehumidifier maintaining 50%RH.
    Ok, next comes the cold time of the year when the outdoor temperatures are low enough to make windows condense moisture on the inside. This means the sweating surface is below the indoor air dew point.
    First comes the problem that the tons of material inside the home is at summer moisture levels. The window surfaces suddenly goes to <45^F while the home is 68^F, 50%RH, a 48^F indoor dew point. The windows are covered with moisture.
    Even with a fresh air change in 4-5 hours of dry outside air the home is slow to dry down. The occupants are adding 1-2 lbs. moisture per hour plus the home may be adding several lbs. of moisture per hour, resulting in air above many of the surface of the home.
    Now, simply, cracking in a window or/and operating exhaust fans will quickly lower the indoor dew point, stopping the sweating in a couple hours. With low outdoor dew point air, increasing the ventilation rate is more practical than operating a dehumidifier which will have difficulty to get the indoor dew point down 40^F that may be needed to stop poor windows.
    Moisture on winter windows is a sign of inadequate fresh air ventilation, very poor windows, excessive temperature setback, or drape covering.
    Keep in mind after the home dries down in fall, the main moisture is from the occupants. One person adds <.5 lbs. per hour. 2-3 occupants in a small home with an air change in 4-5 hours may need slightly more fresh air change to keep the windows dry. A large home with an air change in an air change in 4-5 hours and the same number of occupants will need humidification to maintain 35%RH during the coldest low dew points of winter to be comfortable inside.
    Generally, adequate air changes with a make-up air from a whole house ventilating dehumidifier will keep the home comfortable and good windows dry. Also the exhaust devices like the clothes drier, bath fans, and kitchen hood need the make-up air from the fresh air ventilation to exhaust indoor pollutants.
    Long story for a simple problem.
    Post any questions and 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"

  3. #16
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Sorry about the long previous post.
    The short answer is that during high outdoor dew points with low sensible cooling loads, a small whole house dehumidifier like the Ultra-Aire 70H with fresh air ventilation option keeps the home <50%RH.
    During the cold times of the year, the adequate fresh air ventilation will keep the home dry. If any inside surface including windows sweat, increase the fresh air ventilation rate.
    Much better right?
    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. #17
    Join Date
    Jun 2006
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    I think I have a better understanding. I kind of think some of these local HVAC guys are doing the "same old same old" with their system configurations.

    I appreciate the feedback!!!!!

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