Heat pump system and control method thereof

A heat pump system comprising:

• a compressor configured to compress a refrigerant;
• a water heat exchanger configured to exchange heat between the compressed refrigerant and input water to condense the refrigerant;
• an expansion valve configured to expand the refrigerant after the refrigerant has been condensed in the water heat exchanger;
• an outdoor heat exchanger configured to exchange heat between the refrigerant expanded in the expansion valve and outdoor air;
• a high-pressure pressure sensor configured to detect a pressure of the refrigerant discharged by the compressor;
• a water output temperature sensor configured to detect a temperature of water having undergone heat exchange in the water heat exchanger;
• and
• a controller including at least one processor, comprising processing circuitry, and the at least one processor being individually and/or collectively configured to:
• determine a target condensation temperature of the refrigerant based on a result of detecting of the water output temperature sensor,
• determine a current condensation temperature by converting the pressure detected by the high-pressure pressure sensor into a saturation temperature,
• compare the target condensation temperature with the current condensation temperature, and
• control an opening degree of the expansion valve based on a result of comparing the target condensation temperature with the current condensation temperature.