| 摘要 |
PROBLEM TO BE SOLVED: To provide a dual heat pump system capable of continuing heating of a medium to be heated even during defrosting operation.SOLUTION: In a dual heat pump system, a low stage side heat pump cycle I and a high stage side heat pump cycle II are coupled together through a cascade heat exchanger 3, so that heat is collected from air to heat a medium to be heated. A control means, based on an output signal of a defrost sensor 12, selects one operation mode of a defrost operation mode for defrosting an air heat collection heat exchanger 5 and a normal operation mode. In the defrost operation mode, the control means performs control such that heat exchange with a medium to be heated in a high stage side hot water heating heat exchanger 7 is stopped and a high stage side expansion means 8 is fully opened, and then the heat of a high state side refrigerant is supplied to a low stage side refrigerant through the cascade heat exchanger 3 while the heat of the low stage side refrigerant is supplied to the medium to be heated through a low stage side hot water heating heat exchanger side 2. |
