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  1. #1
    Join Date
    Aug 2010
    Location
    Houston, TX
    Posts
    8

    Dehumidifier control with thermostats

    Hello,

    I have Honeywell TruDry whole house dehumidifier installed and being controlled with a simple separate mechanical(dial) control. It is plumbed separately with its own return and outs. I want to upgrade my thermostat and might as well combine the two controls. I would also like to use the non variable speed HVAC blower motor to circulate more air than this dehumidifier will currently move(and get rid of the extra duct work in the attic). Can these humidity controlling thermostats work the HVAC and dehumidifier separately, yet run the fan only if dehumidification is only needed? I don't want a controller that will call for A/C and dehumidifier to get the job done. I've been told if I want one thermostat to control everything, I have to get a new HVAC system with variable speed...which I find hard to swallow, and very expensive.

    Thanks
    Wheeler
    Houston, TX

  2. #2
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    1,755
    The Honeywell Prestige will do that. While you don't NEED a variable speed blower for de-humidifying, it will work better with one. There will be more over-cooling with a conventional 3-speed blower motor. The thermostat has several choices for the method of de-humidification. The Prestige 2.0 is the current version but a new version is right around the corner.

  3. #3
    Join Date
    Aug 2010
    Location
    Houston, TX
    Posts
    8
    Thanks for the reply. Do you know if the prestige unit will run just the fan and dehumidifier without running the A/C compressor?

  4. #4
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,341
    Quote Originally Posted by wheelerjb View Post
    Thanks for the reply. Do you know if the prestige unit will run just the fan and dehumidifier without running the A/C compressor?
    Running a conventional fan motor uses as much electricity as the dehumidifier. If your dehumidifier keeps your home <50%RH, forget about running the a/c blower when run only the dehumidifier. also operating the a/c fan will quickly evaporate any moisture on the cooling coil. This will increase your dehumidifers load.
    What is to be gained by operating the a/c fan while dehumidifying?
    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"

  5. #5
    Join Date
    Aug 2010
    Location
    Houston, TX
    Posts
    8
    Teddy Bear, that makes sense too and therefore may be asking for trouble. I noticed in the manual there are other ways to connect the dehumidifier to the system, one being the dry air going into the return pre blower. Obviously the fan has to be running for this to work and then dry air goes all over the house, plus wet air gets filtered by the regular A/C filters. I'd like to upgrade to a better single filter system as well. Better distribution was my goal...

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,341
    Quote Originally Posted by wheelerjb View Post
    Teddy Bear, that makes sense too and therefore may be asking for trouble. I noticed in the manual there are other ways to connect the dehumidifier to the system, one being the dry air going into the return pre blower. Obviously the fan has to be running for this to work and then dry air goes all over the house, plus wet air gets filtered by the regular A/C filters. I'd like to upgrade to a better single filter system as well. Better distribution was my goal...
    Yes there are many ways to connect dehumidifiers to the home/a/c. Suck air from the home and blow the dry air into the ducts of a/c, return or supply will cause circulation without the fan of a/c operating. This is the most effective way of causing circulation throughout the home without operating the a/c blower. The blower in a Honeywell dehu is strong enough to move air on either the return or supply of most a/cs. Occasionally, the supply side of the a/c may be +.4" WG. If so, blow the dry air into the return side of the a/c system.
    Keep us posted. Does the dehu maintain <50%RH during high outdoor dew points?
    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"

  7. #7
    Join Date
    Aug 2010
    Location
    Houston, TX
    Posts
    8
    I don't have an outside sensor, but my house is leaky and the digital sensor I have says it is less than 50 depending on placement. I like it dry, so i keep the controller at 35-40. It works great...want it to work better . Thanks for the info, I have a better understanding of it now.

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