DUALITY COLD CYCLE OF HEAT PUMP SYSTEM WITH CASCADE HEAT EXCHANGER

The present invention relates to a cascade heat exchanger for a binary refrigeration cycle heat pump system. More specifically, according to the present invention, a cascade heat exchanger for a binary refrigeration cycle heat pump system allows heat exchange to be performed between the refrigerant of a high-temperature cycle and the refrigerant of a low-temperature cycle, or between the refrigerant of the low-temperature cycle and the hot water of the source of demand according to the predetermined hot-water temperature of the source of demand so that the system can be prevented from being down; and efficiency in a refrigeration cycle can be improved as the hot water can be directly produced from the refrigerant of the low-temperature cycle, wherein the system can be down by a high-pressure state when overheating occurs in an existing binary refrigeration cycle. In addition, according to the present invention, three-way valves are installed on pipes of which each is branched to be connected to the low-temperature first inlet/outlet of a first plate-type heat exchanger and the low-temperature second inlet/outlet of a second plate-type heat exchanger respectively so that the refrigerant of the low-temperature cycle can be transferred to improve the efficiency of the heat exchange according to the predetermined hot-water temperature of the source of demand.