If nothing else, the temperature range differential needed is very different from cooling in the summer to heating in the winter. Apologies for my Celsius friends. I think most humans consider 70 degrees to be comfortable. If its 80 degrees outside the differential is only 10 degrees (80-70=10). For most people the hottest outside temperature they may have is 100 to 110 degrees. So we’re looking at a differential of 30 to 40 degrees the heat pump would need to keep.

Now lets look at winter during the coldest months where I am 0 degree days are pretty common and -10 to -30 can happen occasionally. So the normal differential is a 70 degrees! And the uncommon differential can be as bad as 100 degrees! Further, I believe heating/cooling follows the inverse square law which means for each degree of temperature change it doesn’t just increase the effort linearly, but rather exponentially. So the farther away the different the harder it is to reach it, and we’ve just seen that winter is much farther away (larger differential) than summer.

I know for my home’s heat pump I use between 2kW and 4kW running for normal cooling (its a variable speed compression in mine) while in the depths of winter it usually is around 4kW and when really cold outside gets as high as 8kW (in pure heat pump mode). Because the differential is so much larger in the winter, I’m asking it to do much more work.