A burner-assisted heat pump system was developed to overcome the disadvantages of the conventional. heat pump system. The new system is equipped with a burner in the outdoor unit that transmits, in the heating mode, the heat of combustion indoors through the refrigerant circuit. It was confirmed, experimentally, that the heating capacity of the system is not influenced at all by the outdoor temperature. Thus, the use of a new refrigerant circuit reduces the compressor input and results in a high level of heating efficiency.

When the outdoor temperature is above a certain level, the refrigerant circuit is changed to the heat pump cycle. Therefore, this system can be operated stably with high efficiency throughout the year, ensuring comfortable indoor conditions.