To over come some of issue with energy losses do to running the heat pump, could it be feasible to have a hot or cold storage. I've heard of building that will cool water overnight while electricity is cheap and the temperature outside is lower and then use it for cooling in the day time. A similar thing could be done with the Volt. That way you're not burning up precious battery stored energy, to convert mechanical energy, only to then conduct heat transfer from cold to hot. I think storing heat energy might be more efficient.