minus 20 deg. celcius

[eledille]

VolkerP:

Yes, but you must be careful... as you say, the COP number depends on other factors, it's meaningless without context. Also, a larger model with a poorer COP can perform better in real life than a smaller, more heavily loaded pump with a better COP, and the COP number says nothing about partial load performance.

dpeilow:

Re heat storage: That's becoming very popular here in larger installations like schools and office buildings. If there is moving ground water, you have to seal that off first. Expensive, but can pay off in five years.

Re COP > 5: Yes, I do I tend to believe it's true too, at least it performs very well, much better than I expected. Another data point: Mitsubishi Electric claims it delivers 3.2 kW at -15 outside and +20 inside temperature. "Nominal power consumption" from the spec sheet is 600 W. This would seem to yield a COP of 5.33 at -15/+20, which is astonishingly good if correct.

 

[neroden]

I believe the recent performance increase is due to inverter controlled brushless pump motors, digitally controlled release valves which allow precise control of pressure in both halves of the loop and new, better refrigerant (R410A).

This doesn't mean that Model S' HVAC can do the same, of course, only that it's possible. Also, there are much tighter space constraints in a car. This is the model we bought.

Thanks for the masses of detail. I appreciate it a lot! I think my home's Mitsubishi heat pump (circa 2005) is new enough to have inverter controlled brushless pump motors and digitally controlled release valves, but I think it uses an older refrigerant. This was the one rated to be 'worse than resistive heating' (COP<1) at -20C outdoor temperature but better (COP>1) above that temperature, though they may have been rating conservatively.

You can get far better numbers with geothermal, of course, not that that's an option for a car.