Electric heat pumps lose efficiency whenever they cycle off upon meeting the building heating or cooling load. Refrigerant
pressures equalize throughout the system and heat exchanger temperatures return to the indoor and outdoor ambient temperatures.
When the heat pump comes back on, the compressor has to re-establish the pressure difference between the "high" and "low" sides
and the heat exchangers have to be brought back to the operating temperatures. All of this requires energy without providing
much in the way of heating or cooling the home. Variable-capacity heat pumps try to reduce or eliminating these cycling
losses by following the building load either "continuously" using variable-speed motors or through step changes in capacity
with two- or three-speed motors or through creative design of the compressor drive mechanism.
Links to Publications:
Efficiency Characteristics of Speed-Modulated Drives at Predicted Torque Conditions for Air-to-Air Heat Pumps
Field Monitoring of a Variable-Speed Integrated Heat Pump/Water Heating Appliance
An Initial Laboratory Evaluation of a Single Solution Circuit Cycle for Use with Nonazeotropic Refrigerants
Laboratory Efficiency Comparisons of Modulating Heat Pump Components Using Adjustable Speed Drives
Laboratory Examination and Seasonal Analysis of the Dynamic Losses for a Continuously Variable-Speed Heat Pump
Steady-State Refrigerant Flow and Airflow Control Experiments for a Continuously Variable Speed Air-to-Air Heat Pump
- Westinghouse Advanced Electric Heat Pump