Multi-stage compression refrigeration cycle device

Abstract

A multi-stage compression refrigeration cycle device includes a controller that controls rotational speeds of a low-stage side compression mechanism and a high-stage side compression mechanism, and a physical quantity sensor that detects a physical quantity correlated with a pressure of a low-pressure refrigerant. The controller is configured to increase a rotational speed ratio of the rotational speed of the low-stage side compression mechanism to the rotational speed of the high-stage side compression mechanism as the pressure of the low-pressure refrigerant becomes higher, based on the physical amount detected by the physical quantity sensor.

1 . A multi-stage compression refrigeration cycle device, comprising:
 a low-stage side compression mechanism that compresses a low-pressure refrigerant to an intermediate-pressure refrigerant and discharges the compressed intermediate-pressure refrigerant;   a high-stage side compression mechanism that compresses the intermediate-pressure refrigerant discharged from the low-stage side compression mechanism to a high-pressure refrigerant and discharges the compressed high-pressure refrigerant;   a heat radiator that exchanges heat between the high-pressure refrigerant discharged from the high-stage side compression mechanism and exterior air to dissipate heat from the high-pressure refrigerant;   an intermediate-pressure expansion valve that decompresses and expands the high-pressure refrigerant flowing out of the heat radiator to an intermediate-pressure refrigerant and then flows out the intermediate-pressure refrigerant to a suction side of the high-stage side compression mechanism;   a low-pressure expansion valve that decompresses and expands the high-pressure refrigerant flowing out of the heat radiator to the low-pressure refrigerant;   an evaporator that exchanges heat between the low-pressure refrigerant decompressed and expanded by the low-pressure expansion valve and ventilation air to be blown into a space to be cooled, causing the refrigerant to evaporate, and then to flow out the refrigerant to a suction side of the low-stage side compression mechanism;   a high-pressure sensor that detects a pressure of the high-pressure refrigerant;   a controller that controls rotational speeds of the low-stage side compression mechanism and the high-stage side compression mechanism; and   a physical quantity sensor that detects a physical quantity correlated with a pressure of the low-pressure refrigerant, wherein   the controller is configured to increase a rotational speed ratio of the rotational speed of the low-stage side compression mechanism to the rotational speed of the high-stage side compression mechanism as the pressure of the low-pressure refrigerant becomes higher, based on the physical amount detected by the physical quantity sensor, and   the controller is configured to increase the rotational speed ratio as the pressure of the low-pressure refrigerant becomes higher, when the pressure of the high-pressure refrigerant detected by the high-pressure sensor is equal to or higher than a predetermined reference value.   
     
     
         2 . The multi-stage compression refrigeration cycle device according to  claim 1 , wherein
 the physical quantity sensor is an in-refrigerator temperature sensor that detects a temperature of the space to be cooled, and   the controller is configured to increase the rotational speed ratio as the temperature of the space to be cooled, detected by the in-refrigerator temperature sensor, becomes higher.   
     
     
         3 . The multi-stage compression refrigeration cycle device according to  claim 1 , further comprising:
 a determination unit that determines whether or not a cool-down operation is necessary to quickly cool the space to be cooled, based on a temperature of the space to be cooled, wherein,   the controller is configured to increase the rotational speed ratio of the rotational speed of the low-stage side compression mechanism to the rotational speed of the high-stage side compression mechanism as the pressure of the low-pressure refrigerant becomes higher, when the determination unit determines that the cool-down operation is to be performed.   
     
     
         4 . The multi-stage compression refrigeration cycle device according to  claim 3 , wherein
 the determination unit determines that the cool-down operation is necessary when the pressure of the high-pressure refrigerant detected by the high-pressure sensor is equal to or higher than a predetermined reference value.   
     
     
         5 . The multi-stage compression refrigeration cycle device according to  claim 1 , further comprising
 a middle-pressure expansion valve that decompresses and expands the high-pressure refrigerant flowing out of the heat radiator to an intermediate-pressure refrigerant, and flows out the intermediate-pressure refrigerant to a suction side of the high-stage side compression mechanism.