At low speeds, the efficiency of the compressor used in this unit is outstanding.

The VSGSHP can attain greater efficiencies than either a single-speed GSHP or variable-speed air heat pumps.

Microprocessor-based control is necessary to realize the full benefits of this concept.

The thermostatic expansion valves tested to date can be improved.

Low-cost speed controllers for wet rotor pumps can be used, and either microprocessor or relay-type control is possible.

Heating and cooling demand can be significantly reduced by lowering the maximum acceptable compressor speed. In order to counteract the loss in capacity, a compressor with a larger displacement must be substituted.

Future testing of VSGSHPs should focus on the control logic, more performance testing with larger, slower compressors and improved TEVs, and field tests.

Based on the cost of the VS air heat pump, it is apparent that the brushless DC motor and drive are expensive. A possible alternative is the substitution of a conventional motor (three-phase) and speed controller with a 230 VAC single-phase input and a variable-frequency three-phase output. This type of speed control is available up to 5 kW.