Heat pump apparatus

A heat pump apparatus, comprising a basic refrigeration circuit including a main refrigerant line consisting of a first refrigerant pipe extending from a compressor to a four-way valve, second and third refrigerant pipes sequentially connecting the four-way valve, an indoor heat exchanger, a cooling-mode expansion valve, a heating-mode expansion valve and an outdoor heat exchanger to each other, and a fourth refrigerant pipe extending from the outdoor heat exchanger to said four-way valve;

• and a refrigerant suction line extending from said four-way valve to the compressor, further comprising:
• a main bypass line extending from the main refrigerant line at a position between the cooling-mode expansion valve and the heating-mode expansion valve installed on the third refrigerant pipe to the refrigerant suction line, with a liquid refrigerant tank installed on said main bypass line;
• a pressure control valve and a solenoid valve installed on said main bypass line at positions around inlet and outlet ports of the liquid refrigerant tank, respectively;
• a second bypass line extending from the second refrigerant pipe at a position between the four-way valve and the indoor heat exchanger to the fourth refrigerant pipe;
• and
• a plurality of capillary tubes installed in said liquid refrigerant tank and connected to both the second bypass line and a branch line branching from the main bypass line at a position around an inlet port of the pressure control valve.