Here's an interesting bit of information I learned about my reversible heat pump. Well, I guess it is logical when you think about how engines work.
Anyway, what I learned is that the thermal efficiency of my heat pump is greater when the unit is heating the house than the thermal efficiency is when the unit is cooling the same space. This is because of the heat generated by the compressor.
When heating, the unit can use the heat created by the compressor to heat the house. The compressor creates the same heat when cooling and that heat has to be removed. Thus that process uses more energy.