A "DX" heat pump is provided herein which is based on the principle of providing optimal heat exchange in the heating mode through three parallel ground loops, two of which can be cut off from the system and evacuated of refrigerant in the cooling mode. The loops are designed in terms of volume so that the refrigerant charge is correct in the heating mode when split in three loops and also correct in the cooling mode when only one loop is used, but it contains the full system refrigerant charge. The loops are provided with "TX" metering valves which can be individually operated to provide a staged cooling system.