Refrigeration cycle apparatus

Abstract

A refrigeration cycle apparatus includes an expander-compressor unit ( 1 ) having a first motor ( 12 ), a second compressor ( 2 ) having a second motor ( 22 ), and a controller ( 7 ). The controller ( 7 ) determines the target rotational frequency F 1 of the first motor ( 12 ) and the target rotational frequency F 2 of the second motor ( 22 ) for a start-up operation, and determines whether the opening X of an injection valve ( 61 ) should be in a fully opened state or in a fully closed state during the start-up operation, based on an outside air temperature and other factors. Then, the controller ( 7 ) performs the start-up operation by controlling the rotational frequencies f 1 and f 2 of the first motor and the second motor to be the determined target rotational frequencies F 1 and F 2 while maintaining the opening X of the injection valve in the fully opened state or in the fully closed state.

1 . A refrigeration cycle apparatus comprising:
 a first compressor including a first compression mechanism for compressing a refrigerant, an expansion mechanism for recovering power from an expanding refrigerant, a first motor coupled to the first compression mechanism and the expansion mechanism by a shaft, and a first closed casing for accommodating the first compression mechanism, the expansion mechanism and the first motor;   a second compressor including a second compression mechanism for compressing the refrigerant, the second compression mechanism being connected in parallel with the first compression mechanism in a refrigerant circuit, a second motor coupled to the second compression mechanism by a shaft, and a second closed casing for accommodating the second compression mechanism and the second motor;   a radiator for radiating heat from the refrigerant discharged from the first compression mechanism and the second compression mechanism;   an evaporator for evaporating the refrigerant discharged from the expansion mechanism;   a first pipe for guiding the refrigerant from the first compression mechanism and the second compression mechanism to the radiator;   a second pipe for guiding the refrigerant from the radiator to the expansion mechanism;   a third pipe for guiding the refrigerant from the expansion mechanism to the evaporator;   a fourth pipe for guiding the refrigerant from the evaporator to the first compression mechanism and the second compression mechanism;   an injection passage, branched from the second pipe, for supplying the refrigerant additionally to the expansion mechanism during an expansion process;   an opening-adjustable injection valve provided in the injection passage;   an outside air temperature sensor for detecting an outside air temperature; and   a controller for determining a target rotational frequency of the first motor and a target rotational frequency of the second motor for a start-up operation based on the outside air temperature detected by the outside air temperature sensor in such a manner that the relationship between the target rotational frequency of the first motor and the target rotational frequency of the second motor is reversed at a threshold temperature predetermined for the outside air temperature and determining that an opening of the injection valve should be in a fully closed state during the start-up operation when the detected outside air temperature is lower than or equal to the threshold temperature and that the opening of the injection valve should be in a fully opened state during the start-up operation when the detected outside air temperature is higher than the threshold temperature, and performing the start-up operation by controlling rotational frequencies of the first motor and the second motor to be the determined target rotational frequencies while maintaining the opening of the injection valve in the fully opened state or in the fully closed state.   
     
     
         2 . The refrigeration cycle apparatus according to  claim 1 , wherein
 the radiator is a heat exchanger for heating a fluid by the refrigerant, and includes a refrigerant passage through which the refrigerant flows and a fluid passage through which the fluid flows, and   the controller determines the target rotational frequencies of the first motor and the second motor for the start-up operation and determines whether the opening of the injection valve should be in the fully opened state or in the fully closed state during the start-up operation, based on either a target temperature of the fluid to be heated in the radiator or a preset discharge temperature of the refrigerant to be guided to the radiator through the first pipe, and the outside air temperature detected by the outside air temperature sensor, and performs the start-up operation by controlling the rotational frequencies of the first motor and the second motor to be the determined target rotational frequencies while maintaining the opening of the injection valve in the fully opened state or in the fully closed state.   
     
     
         3 . (canceled) 
     
     
         4 . The refrigeration cycle apparatus according to  claim 2 , further comprising: a supply pipe for supplying the fluid to the fluid passage; and a fluid temperature sensor for detecting a temperature of the fluid that flows through the supply pipe,
 wherein the controller determines the target rotational frequencies of the first motor and the second motor for the start-up operation and determines whether the opening of the injection valve should be in the fully opened state or in the fully closed state during the start-up operation, based on the preset discharge temperature, the outside air temperature detected by the outside air temperature sensor, and the fluid temperature detected by the fluid temperature sensor, and performs the start-up operation by controlling the rotational frequencies of the first motor and the second motor to be the determined target rotational frequencies while maintaining the opening of the injection valve in the fully opened state or in the fully closed state.   
     
     
         5 . The refrigeration cycle apparatus according to  claim 4 , wherein
 tables are stored in the controller, the tables having target rotational frequencies of the first motor and the second motor and openings of the injection valve in association with preset discharge temperatures, outside air temperatures and fluid temperatures, and   the controller determines the target rotational frequencies of the first motor and the second motor for the start-up operation and determines whether the opening of the injection valve should be in the fully opened state or in the fully closed state during the start-up operation, based on the preset discharge temperature, the outside air temperature detected by the outside air temperature sensor, and the fluid temperature detected by the fluid temperature sensor, by using the tables.   
     
     
         6 . The refrigeration cycle apparatus according to  claim 5 , wherein each of the target rotational frequencies of the second motor in the tables is higher than a corresponding rotational frequency of the second motor in a steady operation table for an ideal steady operation derived from a preset discharge temperature, an outside air temperature and a fluid temperature. 
     
     
         7 . The refrigeration cycle apparatus according to  claim 6 , wherein a ratio of each of the target rotational frequencies of the first motor to a counterpart target rotational frequency of the second motor in the tables is lower than a corresponding ratio of a rotational frequency of the first motor to a rotational frequency of the second motor in the steady operation table. 
     
     
         8 . The refrigeration cycle apparatus according to  claim 5 , wherein a difference between each of the target rotational frequencies of the first motor and a counterpart target rotational frequency of the second motor in the tables is smaller than an upper limit value of an allowable driving range. 
     
     
         9 . The refrigeration cycle apparatus according to  claim 5 , wherein a ratio of each of the target rotational frequencies of the first motor to a counterpart target rotational frequency of the second motor in the tables is in a range between an upper limit value and a lower limit value of an allowable driving range. 
     
     
         10 . The refrigeration cycle apparatus according to  claim 2 , wherein the controller divides a time period of the start-up operation into time-based control sections, and brings a sum of the rotational frequencies of the first motor and the second motor closer to a sum of the determined target rotational frequencies of the first motor and the second motor step by step as the control section shifts from one to another during the start-up operation. 
     
     
         11 . The refrigeration cycle apparatus according to  claim 10 , further comprising a refrigerant temperature sensor for detecting a temperature of the refrigerant guided to the radiator through the first pipe,
 wherein the controller calculates a difference between the preset discharge temperature and the refrigerant temperature detected by the refrigerant temperature sensor every time the control section shifts from one to another, and when the difference is a relatively large value, increases relatively significantly the sum of the rotational frequencies of the first motor and the second motor.   
     
     
         12 . The refrigeration cycle apparatus according to  claim 2 , wherein the controller divides a time period of the start-up operation into time-based control sections, and sets a ratio of the rotational frequency of the first motor to the rotational frequency of the second motor lower than a determination ratio that is a ratio of the determined target rotational frequency of the first motor to the determined target rotational frequency of the second motor in an earliest control section of the control sections, and brings the ratio closer to the determination ratio step by step as the control section shifts from one to another in the control sections following the earliest section during the start-up operation. 
     
     
         13 . The refrigeration cycle apparatus according to  claim 12 , further comprising a refrigerant temperature sensor for detecting a temperature of the refrigerant guided to the radiator through the first pipe,
 wherein the controller calculates a difference between the preset discharge temperature and the refrigerant temperature detected by the refrigerant temperature sensor every time the control section shifts from one to another, and when the difference is a relatively large value, increases the ratio of the rotational frequency of the first motor to the rotational frequency of the second motor at a slow rate.   
     
     
         14 . The refrigeration cycle apparatus according to  claim 10 , wherein the controller increases both the rotational frequencies of the first motor and the second motor as the control section shifts from one to another. 
     
     
         15 . The refrigeration cycle apparatus according to  claim 1 , wherein when determining that the opening of the injection valve should be in the fully opened state, the controller controls the opening of the injection valve to be in the fully closed state for a predetermined period of time after the start-up operation starts and then switched to the fully opened state. 
     
     
         16 . The refrigeration cycle apparatus according to  claim 11 , wherein the controller adjusts the opening of the injection valve as well as the rotation frequencies of the first motor and the second motor so that the refrigerant temperature detected by the refrigerant temperature sensor becomes equal to the preset discharge temperature after the start-up operation is completed. 
     
     
         17 . The refrigeration cycle apparatus according to  claim 12 , wherein the controller increases both the rotational frequencies of the first motor and the second motor as the control section shifts from one to another. 
     
     
         18 . The refrigeration cycle apparatus according to  claim 13 , wherein the controller adjusts the opening of the injection valve as well as the rotation frequencies of the first motor and the second motor so that the refrigerant temperature detected by the refrigerant temperature sensor becomes equal to the preset discharge temperature after the start-up operation is completed.