Heat Pumps and Electric Heating - Restricting backup heat operation

I have three heat pumps, one that's a few years old, and two that are recently installed.

I live in SE-PA, and I'd like to try to determine if I can increase the efficiency of operation by using the outside temperature sensor to limit the backup heat operation to when it's really required.

The units involved are:

Main Floor
Heil HHP436AKA1 (3 ton)
Single Speed air handler (Lennox from old system with new coil)

Second Floor
Goodman ASZ180361AB (dual-speed 2.5 ton)
Goodman AEPF426016CA (variable speed air handler)

Office Area
Goodman ASZ160241AD (dual-speed 2 ton)
Goodman AEPF313716AA (variable speed air handler)

All are using the Honeywell TH832U VisionPRO thermostats.


I'd like to configure the thermostats to restrict the backup heat until a fixed temperature, say 30F. One issue is trying to find out exactly what the efficiency curves for these units are to determine what temperature limit makes sense. That seems to be somewhat of a "black art" and not readily available. I'm not sure what temperature I should configure the backup limiting for. Note that I use the setback feature to turn down the temperature when the areas are not being used, one of the reasons I want to limit the backup heat.

I'd also like to know what the lower limit is where I should configure them for strictly backup heat and not run the heat pump. Is that 5F, 10F, what? At what temperature do the heat pumps cross the 1.0 efficiency and start using more energy than plain resistance heat?

I believe those Goodman's were made for Amana, so the correct Goodman model number is a little different.

What you ideally want are the Coefficient of Performance (COP) charts for these units.

So from the Goodman site I get
DSZ180361A* / CA*F3642C6A*+TXV/ MBE1600**-1
Temperature 65.0 60.0 55.0 50.0 47.0 45.0 40.0 35.0 30.0 25.0 20.0 17.0 15.0 10.0 5.00 0.00 -5.0 -10.0
Coff. of Perf. 4.54 4.39 4.23 4.04 3.91 3.83 3.64 3.44 2.96 2.81 2.65 2.54 2.48 2.28 2.08 1.87 1.64 1.39

DSZ160241A* / CA*F3636C6C* + TXV / MBE1600**-1B* High
Temperature 65.0 60.0 55.0 50.0 47.0 45.0 40.0 35.0 30.0 25.0 20.0 17.0 15.0 10.0 5.00 0.00 -5.0 -10.0
Coff. of Perf. 4.74 4.58 4.40 4.20 4.06 3.97 3.77 3.55 3.18 3.01 2.84 2.72 2.65 2.44 2.22 1.99 1.74 1.47

So for both units it appears you are well above COP of 1 all the way. Since these numbers do not include defrost you can monitor your system to get a sense of how long defrost takes at these lower numbers and reduce these COP numbers accordingly.

This does not consider your comfort, nor does it say if this is more economical than a fossil fuel backup.

Thanks, I couldn't find those on the Amana site, I guess I should have gone to Goodman's site. :)

I have electric backup, so the fossil fuel issue is moot, my backup has a COP of 1.0.

I guess I'll start at around 30F to allow the backup to run and see where that gets me. It's REALLY unusual for us to see temperatures below 0F here, so I guess the low end isn't an issue.

I went and picked up the specifications that match my two units, nice to have the additional data... :)