Abstract: A heat exchange apparatus including an external rotor. An internal stator is hermetically sealed within the rotor. An inertia device, attached to the stator, is able to resist movement of the stator so that a difference in speed between the stator and the rotor can be maintained on rotation of the rotor. A refrigerant is present. A rotary compressor for the refrigerant comprises a core attached to the stator. A wheel surrounds the stator. Vanes are mounted on the wheel and are able to move with the rotor and there is a cylinder, eccentric to the vanes and attached to the stator. Oil is able to form a liquid piston on rotation. Thus relative rotation of the vanes and the cylinder compresses refrigerant as the volume between the wheel and the liquid piston decreases. There is a condenser for the compressed refrigerant. An evaporator evaporates condensed refrigerant and evaporated refrigerant is returned to the compressor. The oil can be separated and its level required for the liquid piston can be maintained.