Thermostat for Variable-Speed Blower

[wtw]

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.

[beenthere]

No, The Infinity isn't compatable with other brands.

[a0128958]

... 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

[wtw]

...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?

[bmathews]

My preference is to always install whatever brand thermostat the equipment is when you have a variable speed or 2 stage condenser.

[beenthere]

What brand 2 stage VS system are you getting, or have.

[wtw]

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.

[wtw]

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?

[t527ed]

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???

[aintitfun]

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?

[aintitfun]

Ignore my post below, you guys swamped this thread while I was typing, All the questions I asked Have pretty much been answered.

[wtw]

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.

[wtw]

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?