Question on E heat control thermostat.

[600SL]

Hello

I just put in a heat pump system and am very happy with the way it works with on exception. The thermostat I have Pro1 721 will turn on the heating coils at 2 x the swing temperature setting which is limited to at most 2° meaning my coils will come on until at most 4° of set point.

Since this is a garage and temperature does not need to be controlled as precisely as my living room, I would prefer to have the coils only come on below say 55° F, or maybe 10° F of the set point.

Is there a there an alternative thermostat that will accommodate more latitude as to when backup heat comes on. I really would like to avoid the electric heat every time I open an overhead door.

 

[Milton Shaw]

You can put an outside thermostat on the outdoor unit that will open the circuit to the backup heat so that it will not come on until say 25 degrees outside then the circuit is complete. Your heat pump originally was designed to be able to maintain a certain temp without the emergency heat coming on(this varies by house design ). That temp should be what the outdoor thermostat is set too.

 

[bazar01]

Hello

Is there a there an alternative thermostat that will accommodate more latitude as to when backup heat comes on. I really would like to avoid the electric heat every time I open an overhead door.

Find a thermostat that has a program for two modes of operation.
1. Comfort mode - will turn on aux heat at 1 degree below set point
2. Economy mode - will delay aux heat turning on by about 2-3 degrees below set point

 

[600SL]

You can put an outside thermostat on the outdoor unit that will open the circuit to the backup heat so that it will not come on until say 25 degrees outside then the circuit is complete. Your heat pump originally was designed to be able to maintain a certain temp without the emergency heat coming on(this varies by house design ). That temp should be what the outdoor thermostat is set too.

Kind of what I was thinking as a work around. Only I was thinking about it on the inside with a thermostat that leaves the W2 wire open above 50° indoor temp. But I would think there should already be a system that allows a little more independent control of the aux heater.

Outside temp might be better for the case where I really need aux heat to get the temp above say 50° indoor temp.

 

[600SL]

Find a thermostat that has a program for two modes of operation.
1. Comfort mode - will turn on aux heat at 1 degree below set point
2. Economy mode - will delay aux heat turning on by about 2-3 degrees below set point

The one I have can already do 4°. Maybe that's just fine. I will have the opportunity to try it this week end. It getting down to the 20s. Lets see what happens when I open the garage door and pull out a car.

 

[Ohmthis]

Milton nailed it. I like the OT1860 outdoor lock out relay (about $30). It lets you take the aux wire from the Tstat and breaks the connection (locked out) to the aux strip heat. When the temp gets down to a certain temp (it's fully adjustable) it makes and lets the aux strip heat kick in. They are very easy to use. It will usually fit inside the electrical compartment in the heat pump. BTW, if you haven't already I'd recommend a 5-2-1 hard start if you are using a TXV.

 

[bazar01]

The one I have can already do 4°. Maybe that's just fine. I will have the opportunity to try it this week end. It getting down to the 20s. Lets see what happens when I open the garage door and pull out a car.

Do you leave the thermostat ON and at a set temp like 63F?
The issue here is most of us don't leave the thermostat on in the shop and set at a certain comfort temp. Whenever you turn ON the thermostat or there is a sudden rush of very cold air and causes the actual temp to jump more than 4 degrees below set point , it will always turn on the aux heat.

A work around is a toggle switch mounted beside the thermostat that will open the W2 signal wire from thermostat if you only want the heat pump to run and not the aux electric heat.

 

[600SL]

A lot of good ideas here. I appreciate the comments. I guess garages that don't maintain heating at all times have this issue. There are a couple of scenarios to consider.

Typical 20°F day I would want aux heat all the time because that would be required to bring temp up to 65° and maintain it.

Typical 45° day and I have not been in the shop for a week. I would want aux heat to come on the first time to bring temp up to set point as quickly as possible get the interior heated up but never come on again.

Seems like it all requires a manual switch on the aux heat signal. Or a computer program that senses both outside air and inside air and keeps track of when the system was last activated for the day.

I came into the shop this morning it was 52 degrees in the shop and the aux heater is pumping gigawatts.

For the moment I'm going to try to program a 2° swing which will give me a 4° aux heat cutoff below set point. Seams a reasonable compromise.

 

[bazar01]

A lot of good ideas here. I appreciate the comments. I guess garages that don't maintain heating at all times have this issue. There are a couple of scenarios to consider.

Typical 20°F day I would want aux heat all the time because that would be required to bring temp up to 65° and maintain it.

Typical 45° day and I have not been in the shop for a week. I would want aux heat to come on the first time to bring temp up to set point as quickly as possible get the interior heated up but never come on again.

Seems like it all requires a manual switch on the aux heat signal. Or a computer program that senses both outside air and inside air and keeps track of when the system was last activated for the day.

I came into the shop this morning it was 52 degrees in the shop and the aux heater is pumping gigawatts.

For the moment I'm going to try to program a 2° swing which will give me a 4° aux heat cutoff below set point. Seams a reasonable compromise.

Let me know if you were able to write a program to control the aux heat.

For me, when outside temp is above 35F, I let the heat pump do the heating. It runs a lot longer with no short cycling. I turn off the electric aux heat. Saves a lot on power bill.
When outside temp drops below 35F, I turn off the heat pump condenser circuit breaker inside and let the electric aux heat do the job. Saves power with no compressor and fan running.
Nothing complicated.

 

[600SL]

Let me know if you were able to write a program to control the aux heat.

For me, when outside temp is above 35F, I let the heat pump do the heating. It runs a lot longer with no short cycling. I turn off the electric aux heat. Saves a lot on power bill.
When outside temp drops below 35F, I turn off the heat pump condenser circuit breaker inside and let the electric aux heat do the job. Saves power with no compressor and fan running.
Nothing complicated.

Simple enough approach. But I would think letting the compressor run in the winter would save over pure aux heat. My system still produces 20,000 BTU at 20°. Not enough to do the whole job on its own but my understanding is that even though the output is low at low temperature the current going to the compressor also is low.

 

[bazar01]

If you have the high efficiency newer heat pump unit, yes, it can still extract heat outside below 32F.
I have a 15 year old Rheem high efficiency with TXV and I can probably still push it to 32F, but I want it to last a little longer though.

 

[Ohmthis]

Let me know if you were able to write a program to control the aux heat.

For me, when outside temp is above 35F, I let the heat pump do the heating. It runs a lot longer with no short cycling. I turn off the electric aux heat. Saves a lot on power bill.
When outside temp drops below 35F, I turn off the heat pump condenser circuit breaker inside and let the electric aux heat do the job. Saves power with no compressor and fan running.
Nothing complicated.

The outdoor relay does this without having to physically turn the power. With the relay that I mentioned, you can lock out the electric strips and then lock out the heat pump as well if you choose. Saving money when you don't need the aux heat, but when you do, you can lock out the heat pump when it can't make useful heat. Both ways save $$$.

 

[600SL]

Got to try it out today and this seams like a non issue. It was 43° out, not the coldest day I expect to see but cold enough to get the general idea. Inside was at 69° with a set point of 68°. The pump had just cycled off. I opened the garage door an pulled out a car. When I got back inside and closed the garage door, temp was still at 69° and the unit did not come on for another 10 minutes when the temp dropped to 67°. Aux heat never came on.

Of course there was no wind and it really wasn't that cold but but I got the feeling this was not going to be an issue especially if I change my swing temp to 2° which will hold the heat coils off until 4° below set point.

 

[Ohmthis]

Glad you are happy with your setup.

 

[600SL]

Glad you are happy with your setup.

Thanks and pretty much the same results today with a lower 35° day.