| 摘要 |
An air conditioning system 10, ideally of a motor vehicle 40, comprises a condenser 14, evaporator 18, compressor 20 and an expansion device 16 connected with one another by a circuit 12 containing a first refrigerant 24. The system includes an exchanging unit 28 operable to remove the first refrigerant from the circuit and replace with a second refrigerant 26 if a predetermined value (50, figure 2) of a boundary condition of the system is reached. Ideally the first refrigerant is carbon dioxide (46, figure 2) and the second refrigerant is R134a (48, figure 2) and the boundary condition corresponds to an ambient temperature (44, figure 2) such that if the ambient temperature exceeds the predetermined value, e.g. 40 degrees centigrade, R134a is used in place of carbon dioxide, thereby increasing the coefficient of performance (COP) of the system. The exchanging unit ideally comprises first and second reservoirs 36,38 containing the refrigerants and first and second valves 32,34 all located between the condenser and the expansion device. A counter-stream heat exchanger 22 and control unit 30 may also be included. A method of operating an air conditioning device is also claimed. |
