Thermostat for Variable-Speed Blower

[aintitfun]

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.

[beenthere]

The IAQ is pretty easy to program.
Problem with CR. Is how many of the people that had problems programing it. Never got a good explanation of how to program it from the installer.

[aintitfun]

Go to the link below, go to page 11, and notice at the top of this page it says OLD RESIDENTIAL NOMENCLATURE. This shows that the model # you gave is not a variable speed. And this is going off the supposed "pre-V" Nomenclature. MV, would be a variable speed blower.



http://www.lennox.com/pdfs/Lennox%20...menclature.pdf

[a0128958]

"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

[wtw]

Go to the link below, go to page 11, and notice at the top of this page it says OLD RESIDENTIAL NOMENCLATURE. This shows that the model # you gave is not a variable speed. And this is going off the supposed "pre-V" Nomenclature. MV, would be a variable speed blower.

http://www.lennox.com/pdfs/Lennox%20...menclature.pdf

Hmmm... Earlier this week, I called Lennox and gave them the model # that appears on the label on my unit (CB21-51/65-1P). They sent me an "Engineering Data" doc. (doc# 210055 / filename: ehb_cb21_0494), that they said covers my unit. When I opened the document, I noticed that the title said it was for model "CB21V/CBH21V." Thinking they might have sent the wrong document, I called them back. They told me that the doc. they sent was from April, 1994, and was the earliest they could find for my system. They told me that the "V" designation was added after my system was made (1992). So, I don't know - perhaps my system uses an even older nomenclature than it discussed in the document to which you refer??

In any case the document they sent would appear to describe my system. Here's what it says about the variable speed blower:

"Units are equipped with a variable speed motor (VSM) which maintains a specified air volume throughout the external static range. The motor is controlled by the BDC2 blower drive control. This electronic control allows the blower to operate at three of the twelve air volumes or speeds available. The three speeds may be field selected on the BDC2 control depending on on the blower coil unit size and air volume desired. See blower performance tables."

...and on the following page:

"BDC2 Blower Control — Blower control interfaces the VSM motor with the thermostat and optional CCB1 humidity control. Solid-state board controls the evaporator humidity by controlling the blower speed and the compressor speed on two speed outdoor units. ... The three speeds, heating, high speed cooling and low speed (cooling or continuous fan) are made by simple jumper pins on the board."

The kind of "variable speed" they are referring to in these passages is not what I would have thought of as "variable speed." And, I take it from the comments I have seen here that others would agree with that assessment. Yet, when I spoke with a Lennox dealer I understood him to say that that is how their "variable-speed" blowers work even today.

Are most modern "variable-speed" blower motors continuously variable, and if so, how is this accomplished?

[t527ed]

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?

i'm not sure what you have...

Davenet only shows the cb21 as a v drive blower but it has a v in the model #......

wiring diagram for the cbv21 shows the same terminal as current models for slowing down the blower.

forget what CR says, the IAQ is the best stat out there for what you want to do.

i am a lennox dealer and we use the iaq over lennox's comfortsense on all of our high end units.

best thing you could do is get a lennox dealer that knows v drive units to see exactly what you have and go from there.

[wtw]

...wiring diagram for the cbv21 shows the same terminal as current models for slowing down the blower ... i am a lennox dealer and we use the iaq over lennox's comfortsense on all of our high end units...

Couple of questions for you:

1 - Are Lennox's current "variable-speed" blowers continuously variable, or are they variable in the same way as my current system - where the motor controller offers a number (12) of possible speeds, from which a lesser number (3) must be field-selected? (If the latter is true, then I would think I should probably be able to use the same thermostat for mine as you use when installing a new system.)

2 - Do you recommend the Honeywell VisionPro IAQ over Lennox's own "ComfortSense™ 7000 Series Touchscreen Thermostat," and if so, why? Doesn't the 7000 also control humidity by controlling blower speed?

Thanks much...

[t527ed]

not real familiar with the older v drive systems but what you are describing pretty much sounds like the newer ones.

we can now pick
low speed heat cfm's
high speed heat cfm's
low spped cool cfm's
high speed cool cfm's
fan on cfm's

the blower will ramp up and down to and from the selected speeds depending on what ramping profile is selected by the installer.

blower will vary the actual speed to deliver the cfm's selected to allow for a filter getting dirty.

its not really an infinately variable motor.

3 main reasons we use the iaq thermostats are #1 we only need 3 wires between stat and module mounted at furnace, means we don't have to run new wire. #2 the relays for the iaq are in the module instead of the stat so the customer will never complain about the stat "clicking" every time it goes on and off.#3 i have always liked honeywell stats over lennox's "who's gonna make it this time" stats. when they do use rebranded honeywell stats thats what we use.

[wtw]

...the blower will ramp up and down to and from the selected speeds depending on what ramping profile is selected by the installer. blower will vary the actual speed to deliver the cfm's selected to allow for a filter getting dirty. its not really an infinately variable motor.

3 main reasons we use the iaq thermostats are #1 we only need 3 wires between stat and module mounted at furnace, means we don't have to run new wire. #2 the relays for the iaq are in the module instead of the stat so the customer will never complain about the stat "clicking" every time it goes on and off...

Thanks for the clarification...

So, in summary, it seems that the motor itself is variable-speed, but the thermostat does not control that speed directly. I wonder if other manufacturers "variable-speed" blowers operate in a similar fashion, or if their speed is under the direct control of the thermostat.

[beenthere]

Most VS motors operate that way.
With one or 2 exceptions.

[wtw]

Most VS motors operate that way.
With one or 2 exceptions.

Do you mean that the speed of most VS motors is under direct control of the thermostat/humidistat, or that their speed is not under direct control of the thermostat/humidistat?

What are the one or two exceptions?

[beenthere]

The thermostat can only slow it down through teh dehum terminal, what ever that brand allows in percent. The stat has no other blower speed control.

Carrier Infinity control, on the Infinity line.
And I think Lennox has a model furnace and special stat that has more blower control.

[wtw]

The thermostat can only slow it down through teh dehum terminal, what ever that brand allows in percent. The stat has no other blower speed control.

Carrier Infinity control, on the Infinity line.
And I think Lennox has a model furnace and special stat that has more blower control.

So (other than the two cases you mentioned) the VisionPro IAQ dehumidifies by slowing the blower down to whatever speed has been field-selected on the control module for that blower motor?