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  1. #1
    Join Date
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88

    Evaporator coil bypass for additional humidity control?

    I remember reading about a bypass of the evaporator coil to reduce the tem of the coi, increase run time etc to lower the humidity in the house. my question is how much what are the relative benefits and drawbacks to a system like this?
    I feel certain that a high effiecency dedicated whole house dehumidifier would be more efficient, but they also use power and the additional cost has to be amortized over a period of time.
    My thoughts are that where this might be worthwhile I could add a powered damper for the bypass function.
    My own system has a two stage system, but the airhandler has a PSC motor and the med hi speed is not much different from the high.
    Would there be more advantage in replacing the furnace blower with an Evergreen 6005 to get bettter variable speed control?
    Would the net effect be similar?
    What would the pros and cons be?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,064
    Quote Originally Posted by jbarron4 View Post
    I remember reading about a bypass of the evaporator coil to reduce the tem of the coi, increase run time etc to lower the humidity in the house. my question is how much what are the relative benefits and drawbacks to a system like this?
    I feel certain that a high effiecency dedicated whole house dehumidifier would be more efficient, but they also use power and the additional cost has to be amortized over a period of time.
    My thoughts are that where this might be worthwhile I could add a powered damper for the bypass function.
    My own system has a two stage system, but the airhandler has a PSC motor and the med hi speed is not much different from the high.
    Would there be more advantage in replacing the furnace blower with an Evergreen 6005 to get bettter variable speed control?
    Would the net effect be similar?
    What would the pros and cons be?
    First get your air flow low enough to get a 30^F delta T coil temp to optimized the dehumidification during normal cooling at your t-stat setting. By pass helps reduce duct sweating and fine tuning the air flow to get the ideal coil temp.
    Seldom does over drying with the a/c cause a problem because every evening is a partial load condition that benefits from peak cooling load dry down.
    When there is low cooling loads, bypass or over-cooling is not an acceptable solution to providing <50%RH during low/no cooling loads.
    Even a small whole house dehumidifier like the Ultra-Aire 70H provides <50%RH at fraction of the energy cost of any of the above fixes. These units remove upto 3 lbs. of moisture per hour without any over cooling at a < a kwh. Overcooling with the a/c always leaves a moisture loaded a/c coil which is enough moisture to re-humidify the home 8-10%RH at the end of the cooling cycle. Wlso when the home is unoccupied, the a/c can be setup and the dehu will keep the home <50%RH for minimal energy cost.
    Keep us posted.
    Regards TB
    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
    Apr 2009
    Location
    Mobile, AL.
    Posts
    88
    Thanks.

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