A fridge (as I understand it) works by putting out more heat at the back than it removes from its interior, thus conforming to the laws of thermodynamics -- likewise I would assume that the more air-conditioners you install in a given city, the higher the ambient street temperature becomes :-(

I have never really got my head around how air source heat pumps work (and even ground source ones differ fundamentally from geothermal technology), as it seems more akin to the way that an injector somehow uses steam *from* the boiler to accelerate water to a pressure *higher* than that of the boiler in order to squirt it in...!