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  1. #1
    Join Date
    Jul 2004
    Location
    Nashville TN.
    Posts
    44
    I'm building a new house with WaterFurnace model-E36 Premier E system with dehumidify mode. Will it be more energy efficient than the Therma-Stor model 135 dehumidification system. I don't know if I can disable the option on main unit.
    I'm not a HVAC person, just would like to know what the pro's think. Thanks

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,588
    Originally posted by ac4me
    I'm building a new house with WaterFurnace model-E36 Premier E system with dehumidify mode. Will it be more energy efficient than the Therma-Stor model 135 dehumidification system. I don't know if I can disable the option on main unit.
    I'm not a HVAC person, just would like to know what the pro's think. Thanks
    My estimate, 13 SEER ARI a/c @75^F,50%RH 85^F outside temp. est. 10 btus/watt, 8 sensible, 2 latent,-- 2,100 buts latent removal or 2 pints per KWH requires 325 cfm of 52^F, 95%RH cold air supply per ton of a/c.

    Ultra-Aire 135H removes 5,250 btus, 5 pints of dehumidification per KWH and returns 8,600 btus of free reheat.

    Typical latent load from 4 occupants, 50 cfm of 70^F dew point of fresh air infiltration/ventilation, and moisture diffusion throught the structure is 80,000-110,000 btus latent load /day or 70-100 pints moisture load per day.
    A 3 ton a/c removes 6,300 btus of latent or 6 pints per hour of cooling or 6 pints. 12-14 hours of cooling will remove the latent moisture load and provide <50% RH inside the home. On a cool rainy day like 70-75^F, the a/c will not run but the same latent load will build causing high indoor %RH. On these days, the UA 135H set @ 50%RH operates 14-18 hours to remove the 70-100 pints of latent moisture load. The reheat from the UA 135H may cause the a/c to operate which also removes some latent load.

    IN summary, I suggest setting up the a/c to remove enough moisture to maintain <50%RH on hot days of significant load. During days of minimal or no a/c load, the UA135H operates when the indoor %RH exceeds 50%RH. To conserve energy, when the house is unoccupied for the extended hours, the a/c t-stat should be set up or a/c turned off, allowing the UA135h control %RH at a fraction of the operating cost of a/c.
    Using the deep dehumidification mode of an a/c over-cools the home which is uncomfortable, waste energy, and causes condesation in walls, on a/c ducts and grills. Days of high moisture on these cold surfaces grows mold. Thanks for the tug on my chain.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,461
    Nice post Ted.

    Our local utility's moisture guru would agree. He maintains all the fancy controls & 2 stage A/Cs alone isn't going to maintain a dry house, especially on days like you point out, mild & rainy, when the A/C doesn't run or has to overcool.

    The Aprilaire or Thermastor dehumidifiers are the answer.

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,588
    Dehumidifiers are also rated for pints or liters of dehumidification per kwh . The residential dehus remove 1-2 pints per kwh, similar to a/cs. The best residential dehus are listed with EPAs "Energy Star" @ http://www.energystar.gov/ia/product..._prod_list.xls
    The Aprilaire is 3.3 pints per kwh. Ultra-Aires are 5 pints per kwh.

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