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  1. #1
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    Sep 2012
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    HRV versus Whole house dehumidifer versus fresh air damper

    I've got a client that has a house built about 5 years ago, 2000 s.f., full unfinished basement, with a ground source heat pump for heating/cooling. Has 5 kids in the house (high humidity load due to showering). Entire house has been insulated with open cell. Cincinnati area. Complaint is high humidity in winter. It was around 60% this week and at the same time, my house was 31%. I had him turn his 3 bath fans on and it has dropped to 45% in 48 hours, which I believe is indicating lack of ventilation/low ACH.

    Three options I am considering are an HRV, whole house dehum, or a simple fresh air damper. Obviously, the damper is the least efficient, but lowest cost. The dehum would offer the benefit of additional latent capacity in winter. I am unsure whether the HRV or dehum would result in the best energy effciency and I'm looking for opinions on how to best determine that. Thank you.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Most IAQ experts suggest an air change in 4-5 hour to purge indoor pollutants and renew oxygen. This would be 100 cfm when occupied. Three good bath fans may be 200 cfm plus drier/kitchen hood action. You reduced to 45% in 2 days. My guess is that the big pull down is a sign excess air change.
    Probably 100 cfm will control the moisture that the windows do not sweat, indoor pollutants will be controlled, and oxygen renewed.
    Consider that during winter with full measure of stack effect and winds, the home has much more natural air change than than during the milder seasons of the year. In other words, winter air change in this home is inadequate. During the milder seasons of the year when the windows are closed, this home is unhealthy.
    My point is that you need a small amount of fresh air during winter, but the rest of the year you need full measure of the suggested 100 cfm of fresh air. With the moisture from the 100 cfm of fresh outdoor air plus the moisture from 5 occupants, and controlling a basement, you need a whole house dehumidifier to maintain <50%RH to avoid possible mold and dust mites growing in the home. My bet is there are dust mites in the home already.
    If you can recognize the fact that maintain 50%RH should be necessary for health and comfort, the whole house dehumidifier is critical long term. Next it is most practical to use the fresh air option of a dehumidifier like the Ultra-Aire, a site sponsor.
    Consider that the clothes drier, kitchen hood, bath fans all need make-up air function, the additional fresh air is not worth going after in a mild climate like yours. I expect that all things considered, <$100 of energy would be saved per year. A good install of an HRV is 2,000 D.
    Get a good whole house like a Ultra-Aire 70H or 98H and install it ideally. Also make the a/c is capable of maintain 50%RH during peak cooling loads with fresh air operating. This means a cooling coil that is 30^F colder than the return air temperature to remove enough moisture contribute properly to maintain <50%RH throughout the mild seasons. Also critical is to route the dehumidifier air to the cold air supply duct and connect the fresh air and a return from the open part of the home to the dehu return.
    These are small critical parts of a good install.
    We will be glad to assist in details.
    Keep us posted and than you for your concern.
    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. #3
    Join Date
    Sep 2012
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    Thread Starter
    Thank for the write up, TB.

    One lingering question - if the house doesn't have humidity issues in the summer, what would the advantage be of the dehumidifier over the HRV? Wouldn't it's operating cost be higher? I'd imagine the install cost to be the same.

    Also, do you have distributors in Cincinnati, or do you sell direct to the contractor?

    Thanks again!

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by ckelley3 View Post
    Thank for the write up, TB.

    One lingering question - if the house doesn't have humidity issues in the summer, what would the advantage be of the dehumidifier over the HRV? Wouldn't it's operating cost be higher? I'd imagine the install cost to be the same.

    Also, do you have distributors in Cincinnati, or do you sell direct to the contractor?

    Thanks again!
    Of course, the answer is not simple. A home is located in a climate that determines the needs of conditioning equipment. Also occupants add heat and moisture. Start with outdoor conditions, If the outdoor dew point is always below 50^F, ventilation will keep a heated to 70^F +-50%RH. No need for a dehumidifier.
    As the outdoor moisture content or dew point rises above 55^F or as the inside temperatures are <70^F, the need for dehumidification increases.
    Green grass climates typically need dehumidification much of the time during the mild seasons of the year.
    Dehumidification benefits the home to maintain 50%RH. If large quanitities of fresh hot or cold air is needed while maintaining a specific temperature, there may be enough of a benefit to justify a HRV/ERV.
    Typically, homes get enough fresh air during winter, windy weather to not need supplemental mechanical fresh air. During mild seasons with the windows closed and low winds, most home need mechanical filtered fresh air ventilation.
    In green grass climates, adding a small whole house to simple well setup a/c provides fresh filtered air when needed and supplements the a/c to maintain temperature and %RH desire good air quality and comfort for a reasonable investment and operating cost.
    Any time there is market for a product, a/c wholesalers will stock a product. Therma-Stor Madison WI sells direct to contractors or distributors. They also manufacture private labeled dehu for many.
    800 533 7533 and talk to Justin.
    Thank you for a great question and 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"

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