I have a post & beam SIP house that incorporates 10" of white "bead-board" styrofoam between exterior sheathing and interior T&G pine board or 5/8" sheetrock. It came with a 2-ton water-source (what we used to call them) hand-made heat pump, using a closed-loop system down the well hole. That unit finally died after 23 years, and we replaced it with a 2-1/2 ton Water Furnace unit.
I haven't done power calculations for quite some time, but my house is only around 1800 sq ft, with open stairs and a non-ducted return; last time I checked, however, my heating costs were running between one-half and one-third of folks who heat with oil or propane.
Unit is located in the basement (concrete), which has blue-board styrofoam of 2" on the upper half, 1" down to the footings, and I believe 2" under the floor slab. Many windows have already been replaced, but I currently have no storms on the outside of the south & west-facing double-hungs (need to rectify that soon!); windows that face east and north are low-E casements, and there are two Velux skylights in the downstairs and three in the loft peak, plus one in a bedroom. Several of those have also been replaced; house is now 28 years old.
We had some problems with critters getting into the styrofoam at the roof peaks, so I know the insulation isn't as good as it used to be, and most likely the house isn't as tight as it was when it was built. The house also came with a HRV (heat recovery ventilator), which works very well.
My old unit, on a good day, would have a 16 degree delta T across the air coil. It also had both a desuperheater as well as a refrigerant-to-water condensing unit, so it would make some hot water no matter what it was doing, but could also function as a hot water generator on its own. It actually took heat from the house and put it into DHW during AC, a real plus.
The new Water Furnace has a desuperheater (but no electric back-up heat resistance coils), but cannot make hot water on its own. It also has decided that, during AC mode, there isn't sufficient head pressure to make hot water using the desuperheater. Bummer. It also has a manual lockout on the freeze-stat in the water coil, so if the loop gets too cold, the ^%$ thing shuts off -- and stays off. Not sure whose brain fart that was. (My old one was auto-reset.) As a result, when temps get below +10 and it runs quite a bit, I fire up my wood stove, which is located near the heat pump in the basement, to give the heat pump a break and make sure the water loop doesn't get too cold. I generally run 71F on the t-stat year round; I don't like the cold much, either.
Currently, all "hidden" charges included, we're paying around 16 cents per KWH (and it's going up).
What I do know, however, is:
1) the Water Furnace heat pump generally runs a 20+ degree delta T across the air coil
2) basement temps settle, without wood stove, around 68F; old one would see 62-65F
3) the WF heat pump uses under 10 amps as opposed to my old one which was 12+ amps (and that was for a 2-ton unit vs. current 2-1/2 ton)
4) the WF heat pump is HUGELY quieter than my old one
So, overall, I like it, with some reservations. It's certainly far more efficient than my old one (which had a COP of approx. 3.25, new one is around 4.5) Guess one of these days I should look at energy use again. Our house is also all-electric- stove, washer/dryer, etc. Use no oil and no gas.
ijk
