Patent ID: 7752857

Claim:
A refrigerator comprising: a first compressor for compressing carbon dioxide as a first coolant; a first radiator for radiating heat from the first coolant; a first flow control valve for regulating flow volume of the first coolant; a first evaporator for evaporating the first coolant; coolant cooling means for cooling the first coolant and including a second compressor for compressing a second coolant, the second coolant having an energy consumption efficiency higher than that of the first coolant, a condenser for radiating heat from the second coolant, a second flow control valve for regulating flow volume of the second coolant, and a second evaporator for evaporating, with heat from the first coolant, the second coolant; heat-exchange-amount control means for controlling quantity of heat exchanged in the coolant cooling means so that a coefficient of performance (COP) value is obtained, in which the difference between the COP value and the maximum COP value obtained when the quantity of heat exchanged in the coolant cooling means is varied under predetermined operational conditions, is within a first predetermined range, wherein the first coolant is circulated through the first compressor, the first radiator, the coolant cooling means, the first flow control valve, and the first evaporator, in that sequence, the second coolant is circulated through the second compressor, the condenser, the second flow control valve, and the second evaporator, in that sequence, and the second coolant, in a second refrigeration cycle, has a cooling capacity in a range of from about one-tenth to about one-fifth of cooling capacity of the first coolant in a first refrigeration cycle.