Heat Pumps and Electric Home Heating - Variable Speed air handler question

Hi,

I am considering a Trane XL14 heat pump, and looking at the air handler alternatives. This would be with electric back-up strip heaters. Could anyone explain how the variable-speed ones work (what controls which speed it runs on), does this take a special thermostat or is it based on temperature difference from the set-point or something? Also I was wondering if the multi-speed work similarly or if they just have different set speeds they use for A/C versus Heat like most furnaces.

And (I have a lot of questions!! :thinker: )... for intermittent fan usage (thermostat Fan switch), what would determine what speed the blower would use?

Referring to the 2/4TEE "variable speed", and alternatively the 2TEH "multi-speed".

Thanks!!

Could anyone explain how the variable-speed ones work (what controls which speed it runs on), does this take a special thermostat or is it based on temperature difference from the set-point or something?

The board in the air handler controls the blower speed, the board will see what the t-stat is telling it to do, and the board will change the blower speed as needed.

I would suggest a good stat with this variable speed and you will be able to stage the electric heat as needed, not all at once. The one I would suggest is the Honeywell IAQ t-stat, That stat can control the heat strip in stages as needed. Wire an outdoor sensor, and lock out the electric heat at a temp that it's not really needed. The IAQ is able to slow down the blower in the summer in A/C mode if the humidity is too high.

With the varlable speed you will have more speed choices, and slow ramping up to speed than sudden start up.

An example, the speed will be.

-Heat Pump speed.
-A/C Normal speed
-A/C dehumidity speed (80% speed)
-50% speed in Fan ON mode.
-Aux heat speed.

Multi Speed,
-Heat
-Cool

Variable speed blower will be cheaper to run, and quieter.

I would suggest a good stat with this variable speed and you will be able to stage the electric heat as needed, not all at once. The one I would suggest is the Honeywell IAQ t-stat, That stat can control the heat strip in stages as needed. Wire an outdoor sensor, and lock out the electric heat at a temp that it's not really needed. The IAQ is able to slow down the blower in the summer in A/C mode if the humidity is too high.


Jay, thanks for the answer. I had assumed the variable speed automatically adjusts based on air temp or something, but now see that it is multiple speed with ramping. My stat does have 2 stage cool and 3 stage heat. Would the heat strips always be setup for separate control on different stages, or would that be something special I would have to have done?

Lets see if I understand this correctly, for example:
1st stage heat could be Heat Pump (above lockout temp)
2nd stage 1 heat strip + low blower speed
3rd stage all heat strips plus medium blower speed

Given a 3-stage thermostat, is the above "setup" based on wiring or is there some sort of pins/switches on the Trane board?

Yes, if your current stat is 2 stage, you can use that, but you won't have the humidity control, but the Comfort-R can help out with that, or a basic humidistat.

What is the make/model of the stat you have now?

The stat I have is a Robertshaw 9725i2, I used it all winter with an oil furnace and I really like it. If I want the furnace to run good long cycles I can adjust it so it doesn't call for heat until there's 2 degrees drop, 1.5 degrees, whatever. For A/C I think that will help with dehumidification (longer less frequent runs). I just wish it had a Usage counter. For usage monitoring I put a couple cheap odometer-type hour meters on the stat wires at the furnace. When heat pump is first stage, it has 2 additional heat stages you can set.The thermostat also has intermittent fan which I can select on the program schedule, to distribute woodstove heat.

I'm not sure what Comfort-R is, it was mentioned in the brochure that it controls humidity better. The Trane brochures could be a lot more detailed I think. Does it basically ramp the fan up extremely slowly, or start out on slow and then go to the std. speed after some time (all with the same thermostat stage signal?)

Yes, if your current stat is 2 stage, you can use that, but you won't have the humidity control, but the Comfort-R can help out with that, or a bic humidistat.

What is the make/model of the stat you have now?

What Comfort-R is, when there is call for cooling, the fan will come on at 50% speed for about a min to allow the coil to get nice and cold to start dehumidifying right away. After a min, the fan the ramps up to 80% speed for 7 min. THen after 7 min, the fan then ramps up to 100% speed of the dip switch settings. If you are in the northern states where summer is not really hot and super humid, the Comfort-R will do fine by itself.

If you go to a new Trane heatpump there . It should come with a Trane tstat XR401 It will do all you have there now. I do like the put the humidifier control and the humidistat control down on the cold air drop or return by the unit. This way you get a better control of what the home needs. Than just where the tstat is at. Up in one place in the home.
You will like the V/S blower for sure. If your not happy with the way a tstat controls the blower. With the V/S you can sure play around with the DIP switch in it and set the blower for what every you want for heat or cool.

You will like the V/S blower for sure. If your not happy with the way a tstat controls the blower. With the V/S you can sure play around with the DIP switch in it and set the blower for what every you want for heat or cool.

The VS fan sounds real nice. Sometimes my furnace fan wakes me up when it kicks on at high speed. So far I have the XL14i (3.5ton) quoted along with new lines and a new coil for on an oil furnace. If I were to go with a VS air handler (get rid of the furnace), can anyone estimate how much more that might cost? Is the coil still installed separately? Thanks!

VS is nice, my gas Trane XV90 is about 10' from me, and I don't hardly hear it.

you will have to get in touch with your dealer to get what the price may be.. Is your electrical service panel large enough to handle the higher AMP for electric back up heat?

VS is nice, my gas Trane XV90 is about 10' from me, and I don't hardly hear it.

you will have to get in touch with your dealer to get what the price may be.. Is your electrical service panel large enough to handle the higher AMP for electric back up heat?

Yes there is room to add breakers, for a feed to a sub-panel at the furnace. I would run that wiring in advance. Hopefully the strips would rarely get used :) Here in southern PA, we don't have too many days below 20 degrees most years.

I take it your home is all electric appliances? If so, check you power company for electric break or Off peek rates.