higher pressures when operating as a turbine a suitable refrigerant is chosen such that the pressures and temperatures are maintained within established limits such an adaptation of existing relatively inexpensive equipment to an application that may be otherwise uneconomical allows for the convenient and economical use of energy that would be otherwise lost by waste heat to the atmosphere application_number US 29372702 A description referring now to fig1 a typical vapor compression cycle is shown as comprising in serial flow relationship a compressor 11 a condenser 12 a throttle valve 13 and an evaporator cooler 14 within this cycle a refrigerant such as r 11 r 22 or r 134a is caused to flow through the system in a counterclockwise direction as indicated by the arrows the compressor 11 which is driven by a motor 16 receives refrigerant vapor from the evaporator cooler 14 and compresses it to a higher temperature and pressure with the relatively hot vapor then passing to the condenser 12 where it is cooled and condensed to a liquid state by a heat exchange relationship with a cooling medium such as air or water the liquid refrigerant then passes from the condenser to a throttle valve wherein the refrigerant is expanded to a low temperature two phase liquid vapor state as it passes to the evaporator cooler 14 the evaporator liquid provides a cooling effect to air or water passing through the evaporator cooler the low pressure vapor then passes to the compressor 11 where the cycle is again commenced depending on the size of the air conditioning system the compressor may be a rotary screw or reciprocating compressor for small systems or a screw compressor or centrifugal compressor for larger systems a typical centrifugal compressor.