PURPOSE: To increase the quantity of refrigerant being circulated at cooling and to decrease it heating in a ground source heat pump air conditioning system.

CONSTITUTION: In a closed cycle connecting a compressor 10, a check valve 12, a four-way valve 18, a heat exchanging coil 30 with fan installed in a room 4, heat exchanging coils 40a, 40b, 40c buried in the ground on the outside 2 of the room, a refrigerant circulation regulator 60 and an accumulator 20, automatic expansion valves 34, 44, filter dryers 37, 47, manual expansion valves 39, 42, check valves 38, 48, coil manifolds 35, 45 and distributors 36, 46 are provided in the system. At cooling, refrigerant which is liquefied by discharging heat to the ground is evaporated by absorbing heat on the circumference of an indoor coil and is returned to the compressor. At heating, although a delivery gas from the compressor discharges heat through the an indoor coil 30 and absorbs heat through the underground coil excess refrigerant is stored in a circulation regulator 60 and the underground coil utilizing solenoid valves 50, 51, thus reducing the quantity of refrigerant to be stored and circulated.