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  1. #1
    Join Date
    Nov 2011
    Posts
    32

    Reducing humidity with variable speed blower

    Hi, I'm in a new home with a variable speed furnace but builder grade AC compressor. I'm the southeast, so the humidity is high right now on the outside and I'm not seeing the humidity in the home ever drop below 50% even with the AC running. Any advice on how to get better dehumidification or what to check for? From a quick internet search, I am able to glean that possible issues could be (1) poor seals in ductwork where outdoor air is being pulled in or (2) blower speed needs to be reduced to allow air to move more slowly over coils. Does this sound right and is there anything else I could look for?

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,260
    the 50%RH is pretty good for most homes. The fun starts during low/no cooling load conditions when this not enough cooling load for the a/c to remove the moisture. Your will rise depending on the outside dew points, occupants, and limited a/c operation.
    A dehumidifier is good solution to the problem of maintaining <50%RH during the rest of the year.
    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
    Mar 2012
    Location
    West Chester, PA
    Posts
    511
    most variable speed motors have a delay profile which allows them to ramp up slowly, to address high humidity. Look in the OEM literature for this setting. You may also consider reducing airflow (slightly!) for better dehumidification but i wouldn't go below 350cfm per ton

  4. #4
    Join Date
    Aug 2003
    Posts
    906
    Make sure the thermostat fan setting is on "auto" and not "on" (always running)

  5. #5
    Join Date
    Sep 2012
    Posts
    24
    reducing the fan speed will also reduce the static and it could affect your air quantity which in turn reducing your cooling capacity.

  6. #6
    Join Date
    Jul 2011
    Location
    East coast USA
    Posts
    955
    if your maintaining a comfortable temp and have 50% humidity. whats the problem?

  7. #7
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,137
    sealing ductwork is always a good investment.
    make sure that mastics are used and not duct or foil tapes.

    less than 50% RH..dehumidifier.
    I find my VS ahu can keep the house between 50-55% RH
    lower than that..turn on whole house dehumidifier..45% RH.

    good investment for me.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #8
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,699
    Quote Originally Posted by energy_rater_La View Post
    sealing ductwork is always a good investment.
    make sure that mastics are used and not duct or foil tapes.

    less than 50% RH..dehumidifier.
    I find my VS ahu can keep the house between 50-55% RH
    lower than that..turn on whole house dehumidifier..45% RH.

    good investment for me.

    best of luck.
    Yes.

    Be careful about sealing supplies and not returns.

    In fact, if you have natural draft appliances it might not be a great idea to seal the supplies unless you know how to perform worst case combustion appliance zone testing. For example, you don't want to turn the dryer on, have the furnace fire, then have the water heater backdraft and kill the baby.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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