heat pumps don't work in subfreezing conditions. Not with the refrigerants used in retail AC units, which are sub-optimal even for that use when compared with

heat pumps don't work in subfreezing conditions. Not with the refrigerants used in retail AC units, which are sub-optimal even for that use when compared with some of the older HCFC's and CFC's. A lot of the current designs also likely ice up, so you need much larger evaporator coils/fields. Then there ends up being the question of what the efficiency looks like. Anyway, I'm just trying to say, that there is still heat in the air/etc below the freezing point of water, the science says it can work, and if you do a bit of googling you can even find vendors advertising fairly cold weather devices (-27C). https://daikinatlantic.ca/2019/11/03/what-are-the-best-heat-pumps-for-cold-weather/ https://daikinatlantic.ca/2019/11/03/what-are-the-best-heat-... So, making better ones is an engineering problem.