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  1. #1
    Join Date
    Jul 2008
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    26

    Thermostat for Variable-Speed Blower

    I'm thinking of installing a digital programmable heat pump thermostat, but need one that can control a multi-stage compressor as well as a variable-speed blower. Besides the Honeywell VisionPro IAQ (YTH9421), are there any other thermostats that can control humidy by adjusting blower speed?

    In other threads I saw mentioned that there are some other thermostats that compensate for high humidity by overcooling, but which do not actually control blower speed. As my system has a variable speed blower, I am only interested in thermostats that can actually control blower speed.

    Does anyone know if the Carrier Infinity control can be used with non-Carrier systems - like a Lennox?

    BTW: I would have thrown this question out to the "Controls" forum, but the people who frequent that forum seem to be mainly interested in controls for commercial systems.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,874
    No, The Infinity isn't compatable with other brands.
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  3. #3
    Join Date
    Aug 2006
    Location
    Dallas (Plano), TX
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    168
    Quote Originally Posted by wtw View Post
    ... thermostat ... need one that can control a ... variable-speed blower. Besides the Honeywell VisionPro IAQ (YTH9421), are there any other thermostats that can control humidy by adjusting blower speed? ...
    I think there's a prior question that has to be answered before the above question can be answered. And that is, does your Lennox unit have an external and non-proprietary connection for controlling the speed of the variable-speed blower?

    For example, for my HP with variable-speed blower, it has the capability of running at 'normal' or 'dehumidification' speed. Dehumidification speed is 85% of the selected medium and high speeds.

    But, the on/off control for 'normal' vs. 'dehumidification' speed is via a DIP switch setting inside the unit. There's no external, non-proprietary 'access' to hook up a humidity control capable tstat to. I have to decide either to always run in either 'normal' or 'dehumidifaction' mode, or, manually change the DIP switch setting depending on the environment.

    I choose to not mess with the DIP switch setting. But, like you, I wish I could use a humidity control enabled tstat. Perhaps in your case your Lennox 2-stage variable-speed blower unit offers the external, non-proprietary access to slow down a little the blower.

    Best regards,

    Bill

  4. #4
    Join Date
    Jul 2008
    Posts
    26

    What is a "non-proprietary" connection for controlling blower speed?

    Quote Originally Posted by a0128958 View Post
    ...does your Lennox unit have an external and non-proprietary connection for controlling the speed of the variable-speed blower?
    Good question. The blower on my unit is definitely variable. It runs at different speeds under different conditions, and does this without the need for manual intervention (e.g. changing jumpers). But, I am unsure whether or not this control is achieved in a non-prorietary way.

    What is the usual way for thermostats, such as the aforementioned Honeywell VisionPro IAQ, to control variable-speed blowers? Are there extra wires involved to accomplish this? Is the speed of the blower continuously variable, or are there several specific blower speeds from which the thermostat must choose?

  5. #5
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,540
    My preference is to always install whatever brand thermostat the equipment is when you have a variable speed or 2 stage condenser.

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,874
    What brand 2 stage VS system are you getting, or have.
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  7. #7
    Join Date
    Jul 2008
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    26
    Quote Originally Posted by bmathews View Post
    My preference is to always install whatever brand thermostat the equipment is when you have a variable speed or 2 stage condenser.
    Makes sense. However, I was told that the manufacturer's current programmable thermostats might not work as intended if connected to my somewhat older system.

  8. #8
    Join Date
    Jul 2008
    Posts
    26

    Lennox HP21 H.P. with CB21-51/65-1P Air Handler

    Quote Originally Posted by beenthere View Post
    What brand 2 stage VS system are you getting, or have.
    The current system is as follows:
    Outdoor Unit: Lennox HP21-511-3P
    Indoor Unit: Lennox CB21-51/65-1P
    Thermostat: Couldn't find a model on it. (Mechanical)
    Humidistat: Lennox "EfficiencyPlus" (Mechanical)

    It is my understanding that the current humidistat controls blower speed to achieve the desired level of dehumidification. However, it is not infinitely-variable. The "Engineering Data" document (#210055) I have on the air handler explains that the controller on the ECM motor makes available 12 different speeds. From these 12 available speeds, the installer or service technician must field-select three speeds that are actually used:

    1 - Heat
    2 - High Cool
    3 - Low Cool (or continuous fan)

    So, is this how current variable-speed blowers are controlled as well, or is their speed infinitely variable?

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,722
    no v in the blower model# = no v drive blower.

    pretty sure thats just a multi-speed motor.


    hold on waita minute i'll go check...........



    is there a v in the blower model #, i don't see one one davenet that does not have it???
    Last edited by t527ed; 07-09-2008 at 08:03 PM.

  10. #10
    Join Date
    Apr 2007
    Posts
    623
    Why are you shying away from the IAQ, It is a great t-stat, and is the only one I am aware of that does all of the things you are asking for, the de-humidifying feature really sets it apart. What air handler/equipment will you be connecting to?

  11. #11
    Join Date
    Apr 2007
    Posts
    623
    Ignore my post below, you guys swamped this thread while I was typing, All the questions I asked Have pretty much been answered.

  12. #12
    Join Date
    Jul 2008
    Posts
    26
    Quote Originally Posted by aintitfun View Post
    Why are you shying away from the IAQ, It is a great t-stat, and is the only one I am aware of that does all of the things you are asking for, the de-humidifying feature really sets it apart.
    Good question. Consumer Reports recently (Oct., 2007) reviewed programmable thermostats and found that some were much easier to program than others. In their tests, the Honeywell unfortunately did not fare very well in the usability department.

    If the VisionPro IAQ is the only programmable T-stat out there that will control a multi-stage H.P. and a variable-speed blower, then I guess that's what I'll have to get. But, I thought there might be others.

    In fact, I'm told that the current top-of-the-line Lennox control will control a variable-speed blower, but was advised that this might not work with my particular system.

  13. #13
    Join Date
    Jul 2008
    Posts
    26

    Pre-V Model Designation

    Quote Originally Posted by t527ed View Post
    pretty sure thats just a multi-speed motor.
    ...is there a v in the blower model #, i don't see one one davenet that does not have it???
    No "V" in the model name. I am aware that in more recent models, Lennox has added the "V" to designate that it has a variable-speed blower. I guess when they built my particular system they hadn't thought of that yet.

    But you are getting at what may be the crux of the issue - whether the blower in my current system meets the definition of "variable" or "multi-speed." From looking at the engineering doc., it would seem that the motor speed is pretty variable, but it is not continuously variable, and of the 12 available speeds that are possible, only three of these are made available to the thermostat/humidstat. So, does that make it variable or "multi-speed?"

    Are current variable-speed blower motors continuously variable?

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