@bikepedantic best explanation I have heard (seriously) was from the children's TV presenter Maddie Moate. Basically, think of it as a reverse fridge.
@PipGowenlock maybe that’s all a testament to how cool heat pumps are.
@bikepedantic best not to share my description of mechanical heat recovery being an achievable form of Maxwell's Demon.
@bikepedantic @PipGowenlock It's like, thermodynamics, man.