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  1. #1
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    Feb 2006
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    Dehumidify control for central AC

    A means of reheating the air is necessary and a good condenser pressure control must be used on the outdoor unit. By running the cooling coil and ringing the moisture out of the air, you may subcool the space so bring on some reheat and that heat will actually lower the relative humidity.A dehumidistat is necessary also.
    It might get loud!

  2. #2
    Join Date
    Apr 2006
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    Midwest
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    Check out the Lennox Himiditrol system. Seems to work ok, but it will cost you some doe. Not only to buy but also to run. Good Luck
    He never hit the brakes and was shifting gears!! GB

  3. #3
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    Jul 2007
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    Mount Airy, MD
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    This post should be posted in the residential section, this section is for commercial/industrial building controls

  4. #4
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    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    I have a comment but will wait for the reposting in the residiental a/c section. 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
    Mar 2005
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    Illinois
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    Quote Originally Posted by Chris_Worthingt View Post
    This post should be posted in the residential section, this section is for commercial/industrial building controls
    I dont get a chance to visit this forum often, but from the title I would think this post would be OK for a HVAC controls forum.

  6. #6
    Join Date
    Jun 2001
    Location
    Louisville, KY
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    12,189
    Well, I moved it.

    However, I really don't understand the purpose of the OP. Seems to be more of a statement rather than a question for discussion.
    Perhaps you should have read the instructions before calling.

  7. #7
    Join Date
    Jun 2008
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    100
    Quote Originally Posted by jrbenny View Post
    Well, I moved it.

    However, I really don't understand the purpose of the OP. Seems to be more of a statement rather than a question for discussion.
    Where did my original post go to?
    It's definitely a question. I'm trying to find out what kind of control will do what I describe, dehumidifying overnight and in the fall/spring, whether it will do it ok, whether it can work on any central AC's.
    I saw something saying that the IQ Drive central AC's only take their own controls. But other than that?
    I don't mind being a bit chilly from AC running to dehumidify, or a bit warm because of heat running to dehumidify, as long as it's dehumidified below 50&#37;.
    Laura

  8. #8
    Join Date
    Jun 2008
    Posts
    100
    Quote Originally Posted by steward View Post
    Check out the Lennox Himiditrol system. Seems to work ok, but it will cost you some doe. Not only to buy but also to run. Good Luck
    That's actually a whole-house dehumidifier. I was wondering about controlling a central AC unit to dehumidify overnight - even though it might keep on cooling the house down. Maybe with a heating element to keep it from icing up.
    I can imagine, with the right control, keeping the house during the day below 78F and 50% rh. Then in the evening, I would reset it so that it would be in dehumidification mode. So it would keep on running slowly overnight, slowly cooling things down and dehumidifying to stay below 50% rh. When it gets over 78F, it would go back into cooling mode.
    So my question is what kind of control can do this, and can it run on various central AC's?
    Also I would like to know if you think this wouldn't be needed to keep it dehumidified overnight, for some reason. It probably does need dehumidifying overnight, at least I've noticed the humidity goes up at lot in a room just from me sleeping in it overnight.
    My house was built in 1955. It's wood frame construction with 4" insulation in the walls. So that should give you an idea of the leakiness of it.
    Laura

  9. #9
    Join Date
    Jun 2008
    Posts
    100
    Quote Originally Posted by steward View Post
    Check out the Lennox Himiditrol system. Seems to work ok, but it will cost you some doe. Not only to buy but also to run. Good Luck
    That's actually a whole-house dehumidifier. I was wondering about controlling a central AC unit to dehumidify overnight - even though it might keep on cooling the house down. Maybe with a heating element to keep it from icing up.
    I can imagine, with the right control, keeping the house during the day below 78F and 50% rh. Then in the evening, I would reset it so that it would be in dehumidification mode. So it would keep on running slowly overnight, slowly cooling things down and dehumidifying to stay below 50% rh. When it gets over 78F, it would go back into cooling mode.
    Or maybe it could do all this automatically.
    So my question is what kind of control can do this, and can it run on various central AC's?
    Also I would like to know if you think this wouldn't be needed to keep it dehumidified overnight, for some reason. It probably does need dehumidifying overnight, at least I've noticed the humidity goes up at lot in a room just from me sleeping in it overnight.
    My house was built in 1955. It's wood frame construction with 4" insulation in the walls. So that should give you an idea of the leakiness of it.
    Laura

  10. #10
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    6,638
    Quote Originally Posted by plarian View Post
    Where did my original post go to?
    It's definitely a question. I'm trying to find out what kind of control will do what I describe, dehumidifying overnight and in the fall/spring, whether it will do it ok, whether it can work on any central AC's.
    I saw something saying that the IQ Drive central AC's only take their own controls. But other than that?
    I don't mind being a bit chilly from AC running to dehumidify, or a bit warm because of heat running to dehumidify, as long as it's dehumidified below 50%.
    Laura
    A/c removes 3X more sensible heat (cooling) than latent (dehumidification). Cooling is more pronounce than drying. The Humiditrol concept adds heat while removing moisture but expensive to operate.
    A dehumidifier is the simplest solution. Get a whole house dehu that can connect to the a/c ducts. The dehu maintains 50%RH regardless what the cooling load is. If you want the best of indoor air quality, consider a small amount of fresh air to consistantly purge the indoor pollutants and renew the oxygen. High efficiency dehus like Santa Fe/Ultra-Air operate for much less than typical residential dehus. They also will provide fresh air if desired. 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"

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Reduce infiltration of humid outdoor air into the structure. It will reduce the need for dehumidification. Teddy Bear lives in a climate subject to many days of cool, wet weather, which makes dehumidification via central a/c only to be challenging. For hot, humid climates, central a/c dehumidification can occur satisfactorily for most of the cooling season, with only shoulder seaons possibly being problematic (multi-stage equipment may help there, along with a more airtight building). TIghter homes may require more deliberate introduction of fresh air to make up for reduced introduction via infiltration. That can work to one's advantage by requiring this fresh air be conditioned, which is not possible with infiltration.

    Commercial HVAC is a different animal than residential, so the controls are different. Unless the residence is quite large and has extensive mechanical systems, the standard method of controlling residential interior environments is still largely accomplished via sensible temperature, with the system configured to handle design levels of temperature and humidity. It is when a residential system is below design conditions that temperature/humidity control may become problematic, but with intelligence in system design, control, and building envelope configuration, central a/c can manage interior comfort requirements for a good part of the year. One should carefully analyse all factors before considering supplemental dehumidification; there are instances where it may be required in spite of all other efforts.

  12. #12
    Join Date
    Jun 2008
    Posts
    100
    Quote Originally Posted by duke of earl View Post
    A means of reheating the air is necessary and a good condenser pressure control must be used on the outdoor unit.
    Do you mean something like that idea of having heat strips on the outdoor unit so it doesn't ice up?
    Would it have to be warmed up somehow to dehumidify overnight?
    Laura

  13. #13
    Join Date
    Jun 2008
    Posts
    100
    Quote Originally Posted by teddy bear View Post
    A/c removes 3X more sensible heat (cooling) than latent (dehumidification). Cooling is more pronounce than drying. The Humiditrol concept adds heat while removing moisture but expensive to operate.
    A dehumidifier is the simplest solution. Get a whole house dehu that can connect to the a/c ducts. The dehu maintains 50%RH regardless what the cooling load is.
    It seems like the AC might dehumidify a lot, if I can get it to do what I described: keep the house say 78F and <50% RH during the day when cooling is needed; and at night run AC slowly to keep on removing humidity while cooling the house. Because it could remove a lot of humidity while cooling the house slowly from 78F to 68F, couldn't it?
    Is this the kind of thing the "dehumidify" setting on a minisplit does?
    Is such a control is available for central AC's?
    I'm trying to find out how to do as much as possible (reasonable) with AC, then maybe do more dehumidifying if needed later.

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