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1. A cascade refrigeration cycle apparatus comprising:
a high-temperature-side refrigeration circuit including:
a high-temperature-side compressor,a high-temperature-side four-way selector valve,a high-temperature-side condenser,a high-temperature-side expander, anda primary-side channel of a cascade heat exchanger, wherein said high-temperature-side compressor, said high-temperature-side four-way selector valve, said high-temperature-side condenser, said high-temperature-side expander and said primary-side channel are in communication with one another via high-temperature-side refrigerant piping, and wherein in a refrigeration cycle operation, the high-temperature-side refrigeration circuit circulates a first refrigerant in a first direction, the first direction being a direction in which the first refrigerant circulates sequentially from the high-temperature-side compressor through the high-temperature-side four-way selector valve, the high-temperature-side condenser, the high-temperature-side expander, and the primary-side channel of the cascade heat exchanger and back to the high-temperature-side compressor; a low-temperature-side refrigeration circuit including:
a low-temperature-side compressor,a low-temperature-side four-way selector valve,a secondary-side channel of the cascade heat exchanger,a low-temperature-side expander, andan air-heat exchanger; wherein said low-temperature-side compressor, said low-temperature-side four-way selector valve, said secondary-side channel of the cascade heat exchanger, said low-temperature-side expander and said air-heat exchanger are in communication with one another via low-temperature-side refrigerant piping, wherein in the refrigeration cycle operation, the low-temperature-side refrigeration circuit circulates a second refrigerant in a second direction, the second direction being a direction in which the second refrigerant circulates sequentially from the low-temperature-side compressor through the low-temperature-side four-way selector valve, the secondary-side channel in the cascade heat exchanger, the low-temperature-side expander, and the air-heat exchanger and back to the low-temperature-side compressor; wherein in the refrigeration cycle operation, the high-temperature-side four-way selector valve and the low-temperature-side four-way selector valve are in a first state position, wherein the apparatus further comprises: an inverter connected to at least one of the high-temperature-side compressor of the high-temperature-side refrigeration circuit and the low-temperature-side compressor of the low-temperature-side refrigeration circuit; a bypass pipe provided in the high-temperature-side refrigeration circuit which enables communication between:
the high-temperature-side refrigerant piping at a first point between the high-temperature-side four-way selector valve and the high-temperature-side condenser, andthe high-temperature-side refrigerant piping at a second point between the primary-side channel of the cascade heat exchanger and the high-temperature-side four-way selector valve; a flow control device provided in the bypass pipe; and a controller which controls the inverter so that a set operating frequency for the high-temperature-side compressor is higher than a set operating frequency for the low-temperature-side compressor when the control section starts the refrigeration cycle operation; wherein the controller operates the apparatus in a defrosting operation, wherein in the defrosting operation, the high-temperature side four-way selector valve and the low-temperature-side four-way selector valve are switched from said first state position to a second state position, to thereby reverse the first refrigerant and the second refrigerant in directions opposite to the first and second direction, respectively, and wherein when the control section ends the defrosting operation, the controller opens the flow control device to allow the first refrigerant to flow through the bypass pipe, switches the high-temperature side four-way selector valve and the low-temperature-side four-way selector valve back to the first state position, starts operating the low-temperature-side compressor, closes the flow control device, and starts operating the high-temperature-side compressor, in this order. |
