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  1. #27
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,535
    Quote Originally Posted by squirrel71477 View Post
    Valid points indeed T.Bear but down here in the south where we have RH of 70-85% most of the time that theory doesn't work so good. Most of the time down here we need to get the humidity out, not in. Didn't work when I lived in Western N.C. either where it rained all the time. All depends on your climate.
    I feel that with the right equipment and strategies you can have fresh air and maintain low humidity throughout the summer. We have several hundred a/c contractors that do this in the SE U.S.. There are a couple critical factors.
    1. Limit the fresh air ventilation to times of people occupancy. The quantity of fresh air should be setup to avoid over ventilation. ASHRAE's 7 cfm per person + .1 cu.ft. per 100 sqft. of space the minimum amount. This amounts to 50-75 cfm of fresh air when people are in the home. During your extreme humidity, this is 3-4 lbs. of moisture per hour removal while maintaining 75^F, 50%RH. A properly setup a/c will remove the moisture during the heat of the day. During the evening hours when the a/c load is low, a good whole house dehumidifier is needed to remove the 2-4 lbs. of moisture per hour to maintain <50%RH.

    2. During the days of setting the a/c up to +80^F(no people), no fresh air ventilation is used. There is some infiltration, but because of no cooling, there much less dehumidification needed to maintain <50%RH. Roughly 2 lb./hour of dehumidification or half of moisture removal. When homes are cooled below the outside dew point, more moisture condenses on the exterior surfaces. The condensed moisture moves through the wall to the inside of the home increasing the moisture load.

    3. Cooling the home down 10^F prior to the poeple coming provide a long run to efficiently remove a lot of moisture. Also critical to operate the a/c with a very cold coil. Freeze-up and duct sweating determine the minimal coil temperature.
    Using the above points will reduce operating cost maintaining the summer temperature in the home. The cost of single speed a/c and a whole house ventilating dehumidifier is competitive to the full featured 2 speed a/c. Inculding the dehumidifier provides humidity control without any a/c operation. This works well. 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"

  2. #28
    Join Date
    Jul 2003
    Location
    Philadelphia Pa.
    Posts
    461
    so we should have a indoor relative humidity of 50% in the summer?

  3. #29
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    Quote Originally Posted by jerrod6 View Post
    In past years I would keep the stat set to 76 during the days, and then 73 for a return and night time temperature. 73 all weekends

    ....

    Now I am thinking about running it 76 during the day starting at 7:30am, 75 for a return temp at 5:30pm and 74 during the night starting at 11:30pm. 74 during the weekends. I am just going to sit at home during the day with little to no clothes on. Do you think I will realize any savings from these temps or would some other pattern be better?
    Might as well set it for 73 at night if that's what you like, A/C is very efficient at night (assuming it's in good order). It'll also start the day off 1 degree cooler and a little less humid.

    -HF

  4. #30
    Join Date
    Jul 2006
    Posts
    14
    maybe im wrong but according to the law that heat moves to cold and a 5 degree coil would heat up 100 degree air faster than a 65 degree coil vs the same air. i think of my home the same. If it gets up to 85 degrees then a 55 degree coil can exchange more btus that a 55 coil vs 60 degree coil. just my thoughts.

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