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  1. #1
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    Jul 2008
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    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
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    No, The Infinity isn't compatable with other brands.
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  3. #3
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    Aug 2006
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    Dallas (Plano), TX
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    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
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    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
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    Round Rock
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    My preference is to always install whatever brand thermostat the equipment is when you have a variable speed or 2 stage condenser.

  6. #6
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    What brand 2 stage VS system are you getting, or have.
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  7. #7
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    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?

  8. #8
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    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.

  9. #9
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    Dallas (Plano), TX
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    "external and non-proprietary connection for controlling blower speed"

    said another way:

    a pair of contacts associated with the air handler, that wires can be connected to, that when closed/opened cause the blower to reduce speed x% amount.

    The IAQ's control unit has corresponding contacts, for 'slow down the blower mode,' that wire to the air handler's 'external and non-proprietary connection for controlling blower speed.'

    My point was that without the air handler having slow-down-the-blower functionality, and without it being installer 'connectable,' having an IAQ tstat won't provide humidity control to the point of slowing down the blower. The IAQ works fine as a temp tstat, and works fine reducing RH via running the A/C farther past the tstat's setpoint, but, the IAQ's slow-down-the-blower capability is simply not used.

    Best regards,

    Bill

  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
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    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
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    Jul 2008
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    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
    Apr 2007
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    623
    Quote Originally Posted by wtw View Post
    Good question. Consumer Reports recently (Oct., 2007) reviewed programmable thermostats and found that some were much easier to program than others. Unfortunately, in their tests, the Honeywell 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.
    No, that is not what I said, many stats will control a multi-stage heat pump, and the variable speed is not an issue, the air handler controls that, it just needs a signal from the stat, and it will decide what to do with it. The de-humidifying option, is where the IAQ comes in, So in short, to get all the features you asked for in one stat , this is the only one I know of,. By the way you fan is NOT VARIABLE SPEED, I looked up your model number online. It is a standard motor that probably has 3 speeds, and utilizes one for cool, one for heat, and possibly a third for continous fan. And also the IAQ can be programmed by a baboon.

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