Refrigerating machine having intermediate-pressure receiver

Abstract

A refrigerating machine including a two-stage compressor, a high-pressure gas cooler, a first expansion valve, an intermediate-pressure receiver, a second expansion valve, and an evaporator is further equipped with an intermediate-pressure refrigerant bypass circuit for bypassing gas refrigerant in the intermediate-pressure receiver to an intermediate-pressure portion of the two-stage compressor, a back flow preventing device provided to the intermediate-pressure refrigerant bypass circuit for preventing back flow of refrigerant from the two-stage compressor to the intermediate-pressure receiver, and a refrigerant-pressure control unit for controlling the pressure of the refrigerant in the intermediate-pressure receiver on the basis of the difference between a specific enthalpy of refrigerant discharged from the high-pressure gas cooler and a predetermined reference enthalpy.

1 . A refrigerating machine comprising a two-stage compressor, a high-pressure gas cooler for cooling high-pressure gas refrigerant discharged from the two-stage compressor, a first throttling device for expanding the gas refrigerant from the high-pressure gas cooler, an intermediate-pressure receiver for adjusting a refrigerant circulating amount, a second throttling device for expanding the refrigerant from the intermediate-pressure receiver and an evaporator that are successively connected to one another to form a closed refrigerant circuit, further comprising: 
 an intermediate-pressure refrigerant bypass circuit for bypassing gas refrigerant in the intermediate-pressure receiver to an intermediate-pressure portion of the two-stage compressor;    a back flow preventing device that is provided to the intermediate-pressure refrigerant bypass circuit and prevents back flow of refrigerant from the two-stage compressor to the intermediate-pressure receiver; and    a refrigerant-pressure control unit for controlling the pressure of the refrigerant in the intermediate-pressure receiver on the basis of the difference between a specific enthalpy of refrigerant discharged from the high-pressure gas cooler and a predetermined reference enthalpy.    
   
   
       2 . The refrigerating machine according to  claim 1 , wherein the predetermined reference enthalpy value is set to the enthalpy of saturated liquid corresponding to the pressure of the intermediate-pressure portion of the two-stage compressor.  
   
   
       3 . The refrigerating machine according to  claim 1 , wherein the first throttling device comprises a first expansion valve and the second throttling device comprises a second expansion valve.  
   
   
       4 . The refrigerating machine according to  claim 3 , wherein the refrigerant-pressure control unit controls the valve opening degrees of the first and second expansion values to thereby adjust the pressure of the refrigerant in the intermediate-pressure receiver.  
   
   
       5 . The refrigerating machine according to  claim 1 , wherein the refrigerant-pressure control unit controls at least one of the first throttling device and the second throttling device so that the pressure of the refrigerant in the intermediate-pressure receiver is lower than the pressure of the refrigerant in the intermediate-pressure portion of the two-stage compressor when the specific enthalpy of the refrigerant discharged from the high-pressure gas cooler is not larger than the predetermined reference enthalpy, and also so that the pressure of the refrigerant in the intermediate-pressure receiver is lower than the pressure of saturated liquid whose enthalpy is substantially equal to the specific enthalpy of the refrigerant discharged from the high-pressure gas cooler and also higher than the pressure of the refrigerant in the intermediate-pressure portion of the two-stage compressor when the specific enthalpy of the refrigerant discharged from the high-pressure gas cooler is larger than the predetermined reference enthalpy.  
   
   
       6 . The refrigerating machine according to  claim 5 , wherein the reference predetermined enthalpy value is set to the enthalpy of saturated liquid corresponding to the pressure of the intermediate-pressure portion of the two-stage compressor.  
   
   
       7 . A refrigerating machine comprising: 
 an outdoor unit including a compressor having an intermediate pressure portion into which intermediate-pressure refrigerant having intermediate pressure between refrigerant pressure at a suction port of the compressor and refrigerant pressure at a discharge port of the compressor can be introduced, and an outdoor heat exchanger serving as a heat-source side heat exchanger,    a plurality of indoor units each including an indoor heat exchanger serving as a using side heat exchanger, the plural indoor units carrying out one of cooling operation or heating operation at the same time or carrying out a mixing operation including cooling operation and heating operation at the same time;    an inter-unit pipe for connecting the outdoor unit and each of the indoor units to each other, the inter-unit pipe comprising a high-pressure pipe connected to the refrigerant discharge pipe, a low-pressure pipe connected to the refrigerant suction pipe and an intermediate pressure pipe connected to the other end of the outdoor heat exchanger;    an intermediate-pressure receiver that is disposed between the heat-source side heat exchanger and the using side heat exchanger and separates gas/liquid mixture refrigerant discharged from any one of the heat-source heat exchanger and the using side heat-exchanger into gas refrigerant and liquid refrigerant and supplying the gas refrigerant to the intermediate-pressure portion of the compressor;    a back flow preventing device that is provided between the intermediate-pressure receiver and the intermediate-pressure portion of the compressor and prevents back flow of the gas refrigerant from the compressor to the intermediate-pressure receiver; and    a refrigerant-pressure control unit for controlling the pressure of the refrigerant in the intermediate-pressure receiver on the basis of the difference between a predetermined reference enthalpy and a specific enthalpy of refrigerant discharged from any one of the heat-side heat exchanger and the using side heat exchanger.    
   
   
       8 . The refrigerating machine according to  claim 7 , wherein the refrigerant-pressure control unit comprises a first expansion valve disposed between the heat-source side heat exchanger and the intermediate-pressure receiver and a second expansion valve disposed between the intermediate-pressure receiver and the using side heat exchanger, and a controller for controlling at least one of the valve opening degrees of the first and second expansion valves on the basis of the difference between the predetermined reference enthalpy and the specific enthalpy of the refrigerant discharged from any one of the heat-side heat exchanger and the using side heat exchanger.  
   
   
       9 . The refrigerating machine according to  claim 8 , wherein when any one of the heat-side heat exchanger and the using side heat exchanger operates as a heat-radiation side heat exchanger, the controller controls at least one of the valve opening degrees of the first and second expansion valves so that the pressure of the refrigerant in the intermediate-pressure receiver is lower than the pressure of the refrigerant in the intermediate-pressure portion of the compressor when the specific enthalpy of the refrigerant discharged from the heat-radiation side heat exchanger is not larger than the predetermined reference enthalpy, and also so that the pressure of the refrigerant in the intermediate-pressure receiver is lower than the pressure of saturated liquid whose enthalpy is substantially equal to the specific enthalpy of the refrigerant discharged from the heat-radiation side heat exchanger and also higher than the pressure of the refrigerant in the intermediate-pressure portion of the compressor when the specific enthalpy of the refrigerant discharged from the heat-radiation side heat exchanger is larger than the predetermined reference enthalpy.  
   
   
       10 . The refrigerating machine according to  claim 9 , wherein the predetermined reference enthalpy value is set to the enthalpy of saturated liquid corresponding to the pressure of the intermediate-pressure portion of the compressor.