wherein refrigerant that is to be sucked in is supplied to the suction chamber 32 supplied therefrom to the one or the plurality of cylinders 22 and then after being compressed by the cylinders 22 is delivered to the pressure chamber 34 the pressure chamber 34 is provided with a pressure port 38 for compressed refrigerant and a pressure line 42 leads from the pressure port 38 to a condenser 44 which liquefies the pressurised refrigerant in the case of a subcritical mode of operation or cools it in the case of a supercritical mode of operation and then supplies it to a fluid collecting chamber 46 in which a refrigerant reservoir 48 consisting of refrigerant liquid refrigerant in a subcritical mode of operation is formed hereby the fluid collecting chamber 46 can be integrated into the condenser 44 however as illustrated in fig1 the fluid collecting chamber 46 could also be arranged in a collector vessel 52 which forms the fluid collecting chamber and is arranged in the refrigerant circulation path 10 between the condenser 44 and an evaporator 54 however the fluid collecting chamber could also be arranged in a supply line which leads to the evaporator 54 and has been widened out in correspondence with the volume required for example a supply.