Abstract: In a conventional heat pump system which has a space heat exchanger, a motor (717) driven compressor (106), a refrigerant, a suction line (104) for feeding refrigerant to the compressor, and a waste heat exchanger (720) for adding or removing heat from the heat pump system, the improvement uses various devices to optimize a temperature of the refrigerant in the suction line (104), where the refrigerant enters the compressor. The preferred device is a Peltier thermocouple (500), which can be controlled by current, in response to a sensor (502) in the suction line, to heat or cool the suction line to minimize the load of incompressible liquid or high gas pressure on the compressor. An improved auxiliary heat exchanger also can improve efficiency.