Refrigerating apparatus

Abstract

In a heat-source unit ( 15 ) which heats heating-medium water inside of a heat storage tank ( 16 ), a refrigerant circuit ( 30 ) is provided with a low-stage compressor ( 52 ), a high-stage compressor ( 62 ) and an expander ( 65 ) for power recovery. The low-stage compressor ( 52 ) is rotated by an electric motor ( 54 ) connected to a drive shaft ( 53 ) thereof. The high-stage compressor ( 62 ) is rotated by an electric motor ( 64 ) and the expander ( 65 ) connected to a drive shaft ( 63 ) thereof. A high-stage control section of a controller ( 90 ) adjusts the rotational speed of the high-stage compressor ( 62 ) in such a way that a value measured by an outlet water-temperature sensor ( 77 ) becomes a target temperature. A low-stage control section adjusts the rotational speed of the low-stage compressor ( 52 ) in such a way that a value measured by a discharge pressure sensor ( 74 ) becomes a target high pressure.

1 . A refrigerating apparatus which conducts a two-stage compression refrigeration cycle by circulating a refrigerant through a refrigerant circuit, the refrigerant circuit being formed by connecting: a low-stage compressor and a high-stage compressor each rotating to compress a refrigerant; an expander connected to a drive shaft of the high-stage compressor and driving the high-stage compressor with power generated by the expansion of a high-pressure refrigerant; a gas-liquid separator separating an intermediate-pressure refrigerant flowing from the expander into a liquid refrigerant and a gas refrigerant and supplying the gas refrigerant to the suction side of the high-stage compressor; a low-stage expansion mechanism expanding a liquid refrigerant flowing from the gas-liquid separator; a utilization-side heat exchanger; and a heat-source-side heat exchanger,
 wherein a control means is provided which executes: a first control operation for adjusting the rotational speed of the high-stage compressor in such a way that a heating capacity or a cooling capacity obtained in the utilization-side heat exchanger becomes a predetermined target capacity; and a second control operation for adjusting the rotational speed of the low-stage compressor in such a way that a high pressure in the refrigeration cycle conducted through the refrigerant circuit becomes a predetermined target high pressure.   
     
     
         2 . The refrigerating apparatus according to  claim 1 , wherein:
 the utilization-side heat exchanger works as a radiator and the heat-source-side heat exchanger works as an evaporator to thereby conduct a heating operation; and   in the first control operation during the heating operation, the control means uses the temperature of a heating fluid after passing the utilization-side heat exchanger as a physical quantity indicating a heating capacity obtained in the utilization-side heat exchanger and adjusts the rotational speed of the high-stage compressor in such a way that the temperature of the heating fluid after passing the utilization-side heat exchanger becomes a predetermined target temperature.   
     
     
         3 . The refrigerating apparatus according to  claim 1 , wherein:
 the utilization-side heat exchanger works as a radiator and the heat-source-side heat exchanger works as an evaporator to thereby conduct a heating operation; and   during the heating operation, the control means sets the target high pressure based on the temperature of a refrigerant flowing from the utilization-side heat exchanger and the temperature of a heating fluid flowing into the utilization-side heat exchanger.   
     
     
         4 . The refrigerating apparatus according to  claim 1 , wherein:
 the refrigerant circuit is provided with an opening-variable expansion valve as the low-stage expansion mechanism; and   the control means executes a third control operation for adjusting the opening of the expansion valve in such a way that the superheat of a refrigerant sucked into the low-stage compressor becomes a predetermined target value of superheat.   
     
     
         5 . The refrigerating apparatus according to  claim 4 , wherein:
 the utilization-side heat exchanger works as a radiator and the heat-source-side heat exchanger works as an evaporator to thereby conduct a heating operation; and   the control means sets the target value of superheat based on the temperature of a refrigerant discharged from the high-stage compressor during the heating operation.   
     
     
         6 . The refrigerating apparatus according to  claim 1 , wherein the utilization-side heat exchanger works as a radiator and the heat-source-side heat exchanger works as an evaporator to thereby conduct a heating operation for heating water through a heat exchange with a refrigerant in the utilization-side heat exchanger. 
     
     
         7 . The refrigerating apparatus according to  claim 1 , wherein the refrigerant circuit is provided with an internal heat exchanger making a heat exchange between a refrigerant sent to the low-stage expansion mechanism from the gas-liquid separator and a refrigerant sucked into the low-stage compressor.