Heat pump system and method for controlling the same

A heat pump system, comprising:

• a refrigerant compressor;
• a high-pressure refrigerant pipe connected with a discharge port of the refrigerant compressor;
• a low-pressure refrigerant pipe connected with a suction port of the refrigerant compressor;
• a heat-source side heat exchanger connected to either one of the high-pressure refrigerant pipe and the low-pressure refrigerant pipe, and configured to cause a heat-exchange between refrigerant flowing therein and fluid passing therethrough;
• a liquid refrigerant pipe connected with the heat-source side heat exchanger, and configured to be connected to a utilization side heat exchanger which is configured to cause a heat-exchange between refrigerant flowing therein and fluid passing therethrough;
• a gas refrigerant pipe connected to another one of the high-pressure refrigerant pipe and the low-pressure refrigerant pipe, and configured to be connected to the utilization side heat exchanger;
• a main expansion mechanism disposed in the liquid refrigerant pipe;
• a first bypass pipe connected with the liquid refrigerant pipe at a point between the main expansion mechanism and the refrigerant heat exchanger, and connected with the low-pressure refrigerant pipe or an injection port of the compressor;
• a refrigerant heat exchanger configured to cause a heat-exchange between refrigerant flowing in the liquid refrigerant pipe and refrigerant flowing in first bypass pipe;
• a first bypass valve disposed in the first bypass pipe at a point between the liquid refrigerant pipe and the refrigerant heat exchanger;
• a second bypass pipe connected with the liquid refrigerant pipe at a point between the main expansion mechanism and the utilization side heat exchanger, and connected with the low-pressure refrigerant pipe;
• a second bypass valve disposed in the second bypass pipe;
• a superheated temperature detector configured to detect parameters indicating superheated temperature of refrigerant flowing in the first bypass pipe;
• a discharge side sensor configured to detect, as discharge temperature, temperature of refrigerant flowing in the high-pressure refrigerant pipe between the refrigerant compressor and the either one of the heat-source side heat exchanger and the utilization side heat exchanger;
• and
• a controller configured to control opening degree of the first bypass valve based on the superheated temperature indicated by the detected parameters and discharge temperature, and control opening degree of the second bypass valve based on the discharge temperature.