Heat Pumps and Electric Heating - Do "intelligent recovery" thermostats work efficiently for multi-stage heat pump

Some say yes, some say no. Anyone know where I can look at some data/read some published results and get the real story?:coffee:

Pretty vague question. You need to be more specific about what kind of situation you are wanting to know about. It also depends on equipment.

If you want to freeze use if not dont........................................

My personal opinion ................................

Hi n, yes a few more details would help. Not a pro in this area, but I like some applications of intelligent boxes. When done right I believe they do save on energy. But, just wiring up a programmable stat to a heat pump can end up going the wrong way.

Air source heat pumps have their negative side. As the temp outside goes down and the need for heat goes up, they become less effective. So during a cold spell, a simple setback can result in the heat pump not being able to catch up, thus switching to auxiliary power, which if all electric can be expensive.

Any smart box should match the equipment and the design.
Bud

I'm beginning to think that maybe 2° is the largest set back that 2 stage heat pumps should be programmed to in the winter... I've a newbie with a Honeywell TH6220

See my other post regarding Trane XE1000 thermostats for more details. Don't want to reinvent the wheel by having two strings talking about the same thing. Sorry 'bout that and thanks for the advice given.

nrusinak

I am not able to point you to any specific data/information on this subject. I can give you my experience though.

First I will assume you have a modern type heat pump, not a goldie oldie.


There is nothing wrong with these so called "adaptive intelligence" thermostats as long as common sense and good judgement are used.

For modern heat pumps, I would not use a large setback more than four degrees. I would lock out the backup heat strips or if dual fuel at/around 32-35 degrees.

This morning it was in the high 30s here in my area. I have my programmable HW thermostat setback to 65 degrees sleeping and 68 degrees at 6 AM. It works like a charm. I was up early around 5:30 this morning-dog was barking. I heard my stat "click" and knew recovery was operating. It is a slow recovery and usually takes several cycles to bring home up to temp. But this is a nice feature if you want to use setback/recovery.

an energy saver? I really think it's not much-certainly not as much as advertised by stat makers or electric utilities.

IMO
TD
:)

There is energy to be saved because it requires less energy to maintain smaller temperature differentials. You just have to make sure that auxiliary heat isn't used during recovery or the savings get washed out. For heat pumps, this means when it gets cold enough you'll want to set it at one temp and leave it so it doesn't have to try and recover when it doesn't have the capacity for it.

I have three heat pumps, two of them have dual-stage compressors, all have electric backup. I use the Honeywell TH8320U thermostats on all of them. I use a setback on all of them for some period of the day, and if it's not so cold that the heat pump can't recover, they don't appear to turn on the electric backup. Honeywell is very close-mouthed about the exact algorythm used in these units, so it's hard to know under what conditions they'll kick in the electric backup.

I have them programmed to inhibit the electric backup above 40F, it's below that where the question mark lies.

I do it for energy savings and also because I like to sleep when it's cooler. I have it come back to my normal 68F before it's time to get up, and again in the evening, but during the day and the middle of the night, I drop back to 64F.

If it's really cold (which it rarely gets), I suspect the electric heat will come on, but for normal winter weather here, I'm hoping that it's just running the heat pump.

I'm planning on connecting a relay and a running time meter on the electric backup connection to see when and how long it runs on at least one of the units. It's too bad that Motorola didn't see fit to keep track of this value, it would have been trivial.

Here's the deal. The intelegent recovery remembers how long it takes to get to a set temp. If you set the temp back to 60 from 68 (picking numbers) at 10 pm and want it to be 68 at 7 am, the stat will remember how long it takes to get from 60 to 68. So if the stat realizes it took 2 hours to get from 60 to 68 it will start 2 hours early. Meaning if you set back to 60 and want the temp back to 68 at 7 am the stat will start the system at 5 am to ensure the temp is 68 at 7 am. The stat keeps keeping track of this time and will adjust itself as needed. If it sees the time needed changes from 2 hours to 1 hour then it start 1 hour early rather than 2.

That's how that works.

If you have an air to air heat pump, set the temp and leave it. Any other type of heat use the setback. Set back on air to air cost more than set it and forget it. A/C mode yes use setback.

Good discussion! Exactly the kind that may help me figure this thing out. I have an older (13yr) air-to-air heat pump that utilizes electric backup heat. I currently use an inexpensive programmable thermostat "RiteTemp" 8022C. My wife and I keep it at 68 degrees during the day and night time. Someone, a while ago, told me that once you begin "playing with in-home temps such that there is more than 2 degree difference, (setback at 66 recover to 68, for example) backup heaters will come: these "kill" you on the bill :(

That is why we've been pretty much keeping our temp at a constant 68 with rare exceptions when we are out of the house for vacation or 2-3 days.

What I've been recommended today by a professional AC/Heating Co., is to buy a thermostat with adoptive intelligence recovery feature to save money. What I do not get is how this thermostat actually "knows" NOT to turn on backup heat. If I inderstand correctly, this type of thermostat turns on reg. heat, locks out backup heat, unless it's lower than 40F outside, supposedly providng savings this way. Isn't it more cost-efficient to keep temp at a more or less lower constant temp, say 67 or 68 - as supposed to playing this setback / recovery "game"?

Well, the normal temperature I keep my house at is 68F, but I want to save energy when nobody is there. :)

I personally don't believe that if the thermostat indeed correctly computes the recovery time that it's less efficient setback for a period of time and let it recover.

I did a test last night, the temperature this morning was 33F, so it was colder than the 40F backup heat limit lockout allowed by my thermostat. My thermostat is a Honeywell TH8320U, and it's been running the same program for several weeks, hopefully enough time to have adapted to the recovery times. My normal temperature in the bedrooms is 68F, and I have a setback to 64F, and a recovery in the morning to 68F again. I connected a latching relay to the aux heat terminal of the heatpump to see if the aux heat ever came on during the recovery period. The answer was no, the relay never latched. However, when I got up to go to the bathroom at around 4:00, the temperature was indeed at 64F, so it had to do the full recovery.

I'm planning on repeating this test when the temperature gets even colder to see what results I get, but so far I disagree that a setback doesn't save energy. I'm going to see if I can find an A/C running time meter to check how long the backup heat runs in total as well.

The published specifications for my heat pumps show them running well over 1:1 efficiency well below 0F. Since the lowest average temperature in this area is 30F for January, I suspect much of the time the aux heat won't be required, except for defrost mode.

I've search extensively on this topic and as can be expected, conflicting information abounds. However, an almost general consensus seems to be that there is a potential for saving energy using a modern thermostat with adaptive recovery. That obviously also depends on a host of factors for the individual installation. YMMV

gunrunnerjohn and stant_98 I, and others, say with air to air set it and forget it. Try installing a KW meter and testing usage with and without setback.

Gunner, what is your make and model? 1:1 below zero? I'd like to look at those specs.

Well, I hear you saying that, that doesn't necessarily make me believe it. :) I doubt I'm going to try to do as controlled a test as would be necessary to actualy verify this with a KW meter, not to mention the expense of buying and installing it. Do you actually think that's a practical suggestion?

This is one of my heat pumps, the other is a 16 SEER unit from the same family, and it has very similar heating specifications. The third heat pump is an older HEIL unit that will be replaced in a few years I suspect, but it's working fine now.

Outside Unit: Amana ASZ180361A (http://www.amana-hac.com/Portals/1/pdf/SS-2/SS-ASZ18.pdf)
Air Handler: Amana AEPF (http://www.amana-hac.com/Portals/1/pdf/SS-2/SS-AAEPF.pdf)


The columns don't line up, but this is from page 17 of the outside unit specification above. The COP is 2.07 at 0F.

ASZ180361A* / CA*F3642C6A*+TXV/ MBE1600**-1
Outdoor Ambient Temperature
65 60 55 50 47 45 40 35 30 25 20 17 15 10 5 0 -5 -10
COP 4.64 4.49 4.32 4.12 3.99 3.90 3.71 3.50 3.30 3.13 2.95 2.83 2.75 2.54 2.31 2.07 1.82 1.53

Obviously, I realize that in the real world I might get somewhat less, but I doubt I'm getting half. Of course, with the reduced heat output of the unit, I may also not be getting enough heat out of the unit to actually maintain the temperature, though at more seasonable temperatures here I'm pretty sure I will. This unit heats/cools four large rooms and two baths, two of the rooms have vaulted ceilings.

I honestly do not believe these charts. Amana expects a 3 ton heat Pump to deliver almost 4 tons heating at 65 degrees. At 0 degrees I might believe it 14000 BTU, just over a ton, But the latter, no way.

Well, what can I say. First off, I doubt many people are heating with outside temperatures at 65F, so I suspect that specification is somewhat moot. :) As I understand it, the three ton rating is made at a lower temperature, 45-50F? Who am I to believe? It difficult for me to believe that Amana can publish specifications that are wildly inaccurate. As I previously mentioned, I suspect that the ratings are done in lab conditions, and probably will not be realized out here in the real world. However, since single digits are very unusual for our area, I don't have too much trouble believing that the heat pump will be more efficient than resistance heat at say 10F, which is about the minimum I ever expect to see in a winter, and that's only one or two days a year. Average low temperatures around here are in the mid 20's.

From the same chart, I get 18440 BTU at 10F, let's say really 15000 BTU in the real world. At those low temperatures, I'd probably dip into the backup heat. The old two ton unit could keep up without the backup heat at 30F for the same space, and after 20 years, I suspect it was not running at peak efficiency. I expect this unit to maintain the 68F temperature down to around 20F without assistance from the backup.

FWIW, We had a fan failure a couple of years ago in January with the old unit, and two 1500 watt space heaters managed to heat half the space to the mid 60's with the outside air temperatures in the low 20's overnight and high 30's daytime for several days waiting on the parts to fix it. That would be about 10,000 BTU carrying the load.

Well, the normal temperature I keep my house at is 68F, but I want to save energy when nobody is there. :)

I personally don't believe that if the thermostat indeed correctly computes the recovery time that it's less efficient setback for a period of time and let it recover.
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You would be correct. As long as Aux. heat isn't used, PHYSICS defines and requires the energy savings from using a setback. if the outside temp is 30 degrees, it takes less energy to maintain a 64 degree inside temp than 68 degrees. Pure physics.

The added run time to recover from 64 to 68 is washed out from the lack of runtime during the drop from 64 to 68 assuming outside temp stays constant.

All the savings is accrued from the time spent at the lower setting. The more time you can spend at a lower setting, the more you save.

That would be my reading as well. Of course, this analysis does indeed depend on the ability of the thermostat to inhibit running the resistance backup during the recovery period. My old Hunter thermostats actually stated they tried not to run the backup, but the new Motorola VisionPro ones are very tight-lipped about the algorythm used during the recovery period.