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  1. #1
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    I would like to ask the people on this board a little more about adding a humidistat to a single stage AC with variable speed (VS) air handler. That is what I have, the brand is Trane/A.Standard.

    Specifically, I have heard that one can have a humidistat modify the airflow when the AC is running. During periods of high humidity, the fan can be slowed with the resultant shift from sensible to latent capacity. And I suppose during periods of highest sensible need, can the airflow be speeded up to maximize sensible capacity (and latent be damned for the moment)? I wonder what parts would be needed if this can be done?

    I have absolutely no intention of this being a DIY project, just need to learn to communicate better with the men selling me this stuff. If I don't know what to ask for, I often don't get the sales pitch for what I truly want to buy. I have tried to learn about this before, it seems my learning process is not as quick as it could be, and I might need to be reminded of what's already been said on this board<g>.

    Thanks very much -- Pstu



  2. #2
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,305
    I have a Trane XV90 w/ XR11 2 ton A/C, and I was thinking of adding a humidistat (or is dehumidstat?) to my set up to control the humidity.

    I have found out that with the Comfort-R turned on, it does a pretty good job of keeping the house around 45%, some times 40% humidity.

    I know Minnesota summer is not as extream as the south, but we do get our days where it's very humid and high dew point. So the humidistat may work best for people down the south.

    I think the key thig is the equipement being sized right for the home, and dip switches set up right for tonnage and CFM per ton.

  3. #3
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,784
    Humidistats work well for aiding humidity control.

    When the humidity is high in the house it will keep the fan speed slower, when the humidity is below set point, it will let the fan speed increase, and do more sensible work.
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  4. #4
    Join Date
    Jan 2005
    Posts
    27
    the carrier thermidistat will work ,this will control dehumidification and humidification robert shaw also makes athermostat with the same features ,not sure of model number. i have atrane system the thermidistat works great with it

  5. #5
    Join Date
    Mar 2004
    Posts
    1,042
    This can be retrofitted on a shoestring budget with an ordinary humidistat (same as the ones used with humidifiers), installed either in the living space or on the return duct. With most modern variable speed furnace/air handlers, no additional parts are required.

    It's better to get a humidity-controlling thermostat like the Thermidistat, but this setup is still an improvement over the most basic control schemes. A Thermidistat can also start a call for cooling solely because of a need for dehumidification, and back off on dehumidification during times of great sensible demand. It's beneficial to be able to run the system when there is demand for dehumidification but not for cooling, because those are typically the times when indoor humidity gets the highest.

    The only caveat is that the system will run the lower blower speed if there is demand for extra dehumidification, and the higher blower speed otherwise. It will not back off on dehumidifying during a time of great demand for sensible cooling, though; there's not any brains in this type of system to make that kind of decision. A savvy contractor could achieve that effect with a two-stage thermostat and a relay, but if you don't already have the two stage thermostat, for about the same money you might as well just get a Thermidistat.

  6. #6
    Join Date
    Apr 2005
    Location
    illinois
    Posts
    257
    wyounger
    Do you know of any compatability issues with Tranes/ American Standard's Comfort R and the Thermidistat?

  7. #7
    Join Date
    Mar 2004
    Posts
    1,042
    I'm not aware of any such problems. Comfort-R all happens in the furnace/air handler; those don't know what kind of thermostat you have, really. The Thermidistat is unusually clever, but in the end it should be about as close as anything out there to being universally compatible.

    Keep in mind, of course, that I'm an overeducated consumer, not a pro.

  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304

    New words for my vocabulary

    The word "humidistat" is a new one for me. Believe I understand its meaning OK.

    The word "thermidistat", is that a Carrier copyright? Is it unique to Carrier, or are there other brands (besides Bryant of course)?

    This is great info. I am getting hot to trot with either or both of these. I've been wanting to control my humidity more closely for over 2 years!

    Thanks much -- Pstu

  9. #9
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,516
    you can have your contractor install a honeywell vision pro and set up the v drive blower. as long as the system is sized right and set up correctly you will be very content with it

  10. #10
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Tinknocker, I apologize for putting you on the spot but I will do it anyway.

    Will the VisionPro actually cause the CFM to be altered in response to humidity conditons?

    Thank you -- Pstu

  11. #11
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,516
    not on the spot
    yes it can ramp the blower down to a certain cfm and pull out more humidity with out over cooling the house. when the stat calls for cooling it will ramp the blower back up to the needed cfm to cool the house down to the set point. if the humidity level is still higher the set point on the stat it will ramp the blower back down till the humisity level reaches

    it is important to have a tech set the system up for best results

  12. #12
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    That sounds like the control I want. One more question: will the VisionPro also initiate a cooling call just for humidity reasons, when the temperature is at or very close to setpoint?

    I understand that you can easily get too much overcooling in pursuit of humidity control. But when it's humid outside and not really warm, I always find myself wanting to move the thermostat setpoint down for comfort reasons. In my mind it would be no sin for a machine to do the same, within reason. So does the VisionPro do that too?

    Most definitely I would plan to have a pro install it and set it up the right way!

    Best wishes -- Pstu

  13. #13
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,305
    Originally posted by tinknocker service tech
    not on the spot
    yes it can ramp the blower down to a certain cfm and pull out more humidity with out over cooling the house. when the stat calls for cooling it will ramp the blower back up to the needed cfm to cool the house down to the set point. if the humidity level is still higher the set point on the stat it will ramp the blower back down till the humisity level reaches

    it is important to have a tech set the system up for best results
    Tin, Vision Pro only had three lines,

    -Single stage heat/cool
    -3 stage heat/2 cool
    -3 stage heat/2 cool, with humidity control.

    The last one only "cool to dehumidfy", it dose not control the fan speed. Unless they just came out with something???

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