Heat Pump Function/Operation

[TarpleyG]

I have a heat pump setup for one zone of my house.  It has an "emergency" or "auxiliary" heating system so in the event that the outside coils freeze up, it can continue to provide heat by blowing air across electric heat coils built-in to the air handler.  With me so far?

I installed a programmable thermostat because I need to get my daytime temps down since we aren't here all day.  Simple enough.  I bought a 7-day programmable thermostat that supports my heat pump configuration and installed it per the instructions and triple-checked my work.

Here's the tricky part--it was 60+ F here yesterday when I was testing all this.  When I turn on the heat, the main (heat pump) unit shows as heating on the thermostat for a while and then it switches to auxiliary.  It hasn't been cold enough for me to really rule out the outside temperature having an effect on my system either using the outside coil unit or the electric coils.

My question is this--how does a normally operating heat pump w/ auxiliary heat function during a normal on/off cycle?  All this might be ordinary but my old thermostat did not indicate anything was going on out of the ordinary.

Greg

[280plus]

Well, NORMALLY, in normal operation, you would have a 2 stage t'stat on the wall. When t'stat stage #1 calls for heat it turns on the heat pump. If the heat pump can't keep up because it's too cold out the t'stat will sense the continued drop in room temp and call in 2nd stage heat which turns on the electric. It SOUNDS (without actually looking at it) like your heat pump proper is not doing the trick (even at 60* ODT) and thereby calling in 2nd stage. This could be for any number of reasons. Most heat pumps these days will also sense the fact that they are not working correctly, shut themselves down and energize 2nd stage which now becomes considered "emergency" heat. Most will also let you switch to emergency heat manually at the T'stat. Regardless of what you call it it is still usiong the same electric heat strips for auxiliary/supplemental/ emergency heat.

I'll be around today so feel free to pick me brain if you have to.

[Unisaw]

How big was the difference between the room air temperature and the temperature setting on the thermostat?  If the difference is large, the heat pump may switch to emergency heat to close the gap faster.

[280plus]

Yep. that's true as well, meaning second stage would call in. It's possible your initial setting was say 4* or more higher than room temp and possibly there is a delay function that is turning on aux heat after so many minutes to help it catch up faster. Question is, when the aux heat comes on does the outside unit shut off? It shouldn't. While it's running outside try and feel an uninsulated area of the fat tube coming out of the outside unit. Does it feel good and hot? Touch it lightly first, don't just grab it. It could be pretty hot if it's working right.

[280plus]

BTW, This is why you should not set your heat back more than 4* maximum at night. If you set back too far you end up turning on electric heat in the morning to catch up. This is a bad thing. If I were you I wouldn't set back more than 3* at night. If you see yur aux heat coming on when it comes out of setback you know you're set back too far.

[Mabs2]

Auxilliary heat comes on when the actual tempurature is more than 2 degrees below the set tempurature.
So if you let it get 60 degrees and you suddenly bump it up to 75, of course it's going to come on.
But once it gets to 75 it'll cut on when the temp drops to 74 or 73 or so and the aux heat wont kick in.
Eddited to add:  Usually heat pumps will have two electric heating elements as backup.  In aux heat mode, the heat pump and one electric strip will run to give it a boost.  In emergency heat, the heat pump will not run and both strips will run.  During defrost, the heat pump will start up in air conditioner mode (causing the outdoor coils to warm up) and the heat strips will come on to heat the house.

[TarpleyG]

Thanks for the input guys.  Yes, I was just testing it so I had set the temp up 4 or 5 degrees.  I looked at it again later this morning and it seemed to be functioning correctly.

My thought was to turn down the temp to 62* during the day and have it return to 68* by the time we get home.  For the time when we are sleeping, I was going to set it to 65* and go back to 68* in the AM.  Sound like a good plan or am I wasting money here?

Greg

[280plus]

Yup, no more than 4* setback day or night or you'll end up spending more than you saved. With a heatpump I might even limit it to 3*. You DON'T want that electric heat coming on to catch you back up after set back. VERY important if you want to save a little $.

[K Frame]

Heat pumps really fly in the face of the entire set back scenario simply because they will switch over to the toaster so quickly.

I normally set mine at 68 and keep it there the entire winter.

[TarpleyG]

Let me ask this...this thermostat has what they coin "Smart Response Technology" to supposedly overcome this instant demand for heat.  It is supposed to "learn" how long it takes for your system to reach a desired preset temperature and gradually heat until it reaches that temperature at the time you designated in the schedule.  Will this negate the issue or is it hype?

Greg

[TarpleyG]

Oh, and I found this while browsing around for more info:

From a post at http://www.selfhelpforums.com/printthread.php?t=2308&pp=40

From a manufacturer regarding the setback "ramping" stats:
"# Programmable setback thermostats - specially designed heat pump thermostats with an adaptive-recovery or "ramping" feature allow the thermostat to be programmed for one or more "setback" periods per day without relying on the more expensive supplemental heating to bring the temperature back up. Their microprocessor unit senses the temperature difference to be overcome when bringing the space temperature back up, and brings the temperature up gradually over a longer period of time. This allows the heat pump alone to provide the temperature increase and minimizes the use of the more costly electric resistance auxiliary heat."

[K Frame]

I have an older Honeywell thermostat that supposedly ramps the heat up.

I don't know if I never got it programmed correctly (I sort of doubt that, as it's pretty simple), but it never effectively ramped.

I have an all-electric house, and only in the coldest winters does my electric bill go over $125 for the month.

[280plus]

Sounds good to me as long as it works. 

I STILL think I'd stick with no more than a 3-4* setback though.