Refrigerator and method for controlling refrigerator

Abstract

This refrigerator is provided with a refrigeration cycle, a sensor, and a control device. The refrigeration cycle has a circulation line, a first compression part, a middle stage part, a second compression part, an injection pipe, a supercooling heat exchanger, a supercooling expansion valve, a main expansion valve, an evaporator, a bypass pipe, and a bypass valve. The control device has: an acquisition part for acquiring a physical quantity related to the refrigeration cycle; a determination part for determining whether or not a supercooling degree of a refrigerant of the circulation line having passed through the supercooling heat exchanger is lower than a target value, on the basis of the physical quantity related to the refrigeration cycle; and a valve control part for controlling the bypass valve to open the bypass pipe, when the supercooling degree of the refrigerant of the circulation line having passed through the supercooling heat exchanger is lower than the target value.

Description

Technical Field

[0001] The present disclosure relates to a refrigerator and a control method of a refrigerator.

[0002] Priority is claimed on Japanese Patent Application No. 2023-114504, filed July 12, 2023, the content of which is incorporated herein by reference.Background Art

[0003] PTL 1 discloses a two-stage screw refrigerator. The two-stage screw refrigerator is configured to include a refrigerant-oil circulation flow passage and a branch flow passage. The refrigerant-oil circulation flow passage includes a first-stage screw compressor, a second-stage screw compressor, a condenser, a subcooling heat exchanger, a main expansion valve, and an evaporator. The branch flow passage branches from a portion between the condenser and the subcooling heat exchanger in the refrigerant-oil circulation flow passage, passes through a subcooling heat exchanger expansion valve, passes through the subcooling heat exchanger, and then merges with an intermediate stage portion located on a suction side of the second-stage screw compressor on a discharge side of the first-stage screw compressor.

[0004] The subcooling heat exchanger allows a portion of the high-pressure refrigerant discharged from the second-stage screw compressor to bypass and flow into an intermediate-pressure refrigerant that is throttled and expanded to an intermediate pressure by the subcooling heat exchanger expansion valve. The intermediate-pressure refrigerant immediately after the throttling expansion is injected into the intermediate stage portion to increase the subcooling degree of the remaining large amount of high-pressure refrigerant to the main expansion valve.Citation ListPatent Literature

[0005] [PTL 1] Japanese Unexamined Patent Application Publication No. 2005-315506Summary of InventionTechnical Problem

[0006] However, in the refrigerator disclosed in PTL 1, for example, in a low differential pressure condition in which the outside air temperature is low and the evaporation pressure is high, a differential pressure between the high-pressure refrigerant and the intermediate-pressure refrigerant is reduced, and a flow rate of the intermediate-pressure refrigerant that is throttled and expanded to the intermediate pressure is reduced. Therefore, there is a problem that the subcooling degree by the subcooling heat exchanger is reduced and the required subcooling degree cannot be ensured.

[0007] The present disclosure has been made to solve the above-described problem, and an object thereof is to provide a refrigerator and a control method of a refrigerator that can ensure a required subcooling degree.Solution to Problem

[0008] In order to solve the above-described problem, a refrigerator according to the present disclosure includes a refrigeration cycle; a sensor that detects a physical quantity related to the refrigeration cycle; and a control device that controls the refrigeration cycle, in which the refrigeration cycle includes: a circulation line through which a refrigerant circulates; a first compression unit that is provided in the circulation line and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit that is provided in the circulation line and in which the intermediate-pressure refrigerant generated by the first compression unit is discharged; a second compression unit that is provided in the circulation line and that compresses the intermediate-pressure refrigerant in the mid-stage unit to generate a high-pressure refrigerant; a condenser that condenses the high-pressure refrigerant generated by the second compression unit; an injection pipe that branches from a downstream side of the condenser in the circulation line and that returns the refrigerant having passed through the condenser to the mid-stage unit; a subcooling heat exchanger that subcools the refrigerant passing through the condenser and then flowing through the circulation line by heat-exchanging the refrigerant with the refrigerant flowing through the injection pipe; a subcooling expansion valve that is provided on an upstream side of the subcooling heat exchanger in the injection pipe and that expands the refrigerant flowing through the injection pipe before the refrigerant is supplied to the subcooling heat exchanger; a main expansion valve that is provided in the circulation line and that expands the refrigerant having passed through the subcooling heat exchanger; an evaporator that is provided on a downstream side of the main expansion valve in the circulation line and that evaporates the refrigerant having passed through the main expansion valve; a bypass pipe that branches from a downstream side of the subcooling heat exchanger in the injection pipe and that guides the refrigerant flowing through the injection pipe to a position which is provided between the evaporator and the first compression unit in the circulation line and which is provided on an upstream side of the first compression unit; and a bypass valve that is provided in the bypass pipe and that opens and closes the bypass pipe, and the control device includes: an acquisition unit that acquires the physical quantity related to the refrigeration cycle; a determination unit that determines whether or not a subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than a target value based on the physical quantity related to the refrigeration cycle; and a valve control unit that controls the bypass valve to open the bypass pipe in a case where the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than the target value.

[0009] In order to solve the above-described problem, a control method of a refrigerator according to the present disclosure is a control method of a refrigerator including a refrigeration cycle, a sensor that detects a physical quantity related to the refrigeration cycle, and a control device that controls the refrigeration cycle, in which the refrigeration cycle includes: a circulation line through which a refrigerant circulates; a first compression unit that is provided in the circulation line and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit that is provided in the circulation line and in which the intermediate-pressure refrigerant generated by the first compression unit is discharged; a second compression unit that is provided in the circulation line and that compresses the intermediate-pressure refrigerant in the mid-stage unit to generate a high-pressure refrigerant; a condenser that condenses the high-pressure refrigerant generated by the second compression unit; an injection pipe that branches from a downstream side of the condenser in the circulation line and that returns the refrigerant having passed through the condenser to the mid-stage unit; a subcooling heat exchanger that subcools the refrigerant passing through the condenser and then flowing through the circulation line by heat-exchanging the refrigerant with the refrigerant flowing through the injection pipe; a subcooling expansion valve that is provided on an upstream side of the subcooling heat exchanger in the injection pipe and that expands the refrigerant flowing through the injection pipe before the refrigerant is supplied to the subcooling heat exchanger; a main expansion valve that is provided in the circulation line and that expands the refrigerant having passed through the subcooling heat exchanger; an evaporator that is provided on a downstream side of the main expansion valve in the circulation line and that evaporates the refrigerant having passed through the main expansion valve; a bypass pipe that branches from a downstream side of the subcooling heat exchanger in the injection pipe and that guides the refrigerant flowing through the injection pipe to a position between the evaporator and the first compression unit in the circulation line, on an upstream side of the first compression unit; and a bypass valve that is provided in the bypass pipe and that opens and closes the bypass pipe, and the method including: a step of acquiring, by the control device, the physical quantity related to the refrigeration cycle; a step of determining, by the control device, whether or not a subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than a target value based on the physical quantity related to the refrigeration cycle; and a step of controlling, by the control device, the bypass valve to open the bypass pipe in a case where the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than the target value. Advantageous Effects of Invention

[0010] According to a refrigerator and a control method of a refrigerator according to the present disclosure, a required subcooling degree can be ensured.Brief Description of Drawings

[0011] FIG. 1 is a schematic configuration diagram of a refrigerator according to a first embodiment of the present disclosure. FIG. 2 is a functional block diagram of a control device according to the first embodiment of the present disclosure. FIG. 3 is a p-h diagram showing an example of a state change of a refrigerant circulating in the refrigerator according to the first embodiment of the present disclosure. FIG. 4 is a p-h diagram showing an example of a state change of a refrigerant circulating in the refrigerator according to the first embodiment of the present disclosure. FIG. 5 is a p-h diagram showing an example of a state change of a refrigerant circulating in the refrigerator according to the first embodiment of the present disclosure. FIG. 6 is a flowchart showing a procedure of a control method of a refrigerator according to the first embodiment of the present disclosure. FIG. 7 is a graph showing a correlation between an outside air temperature and a subcooling degree according to the first embodiment of the present disclosure. FIG. 8 is a schematic configuration diagram of a refrigerator according to a second embodiment of the present disclosure. FIG. 9 is a functional block diagram of a control device according to the second embodiment of the present disclosure. FIG. 10 is a flowchart showing a procedure of a control method of a refrigerator according to the second embodiment of the present disclosure. FIG. 11 is a schematic configuration diagram of a refrigerator according to a third embodiment of the present disclosure. FIG. 12 is a functional block diagram of a control device according to a third embodiment of the present disclosure. FIG. 13 is a flowchart showing a procedure of a control method of a refrigerator according to the third embodiment of the present disclosure. FIG. 14 is a graph showing a correlation between an outside air temperature and a subcooling degree according to the third embodiment of the present disclosure. FIG. 15 is a schematic configuration diagram of a refrigerator according to a fourth embodiment of the present disclosure. FIG. 16 is a functional block diagram of a control device according to the fourth embodiment of the present disclosure. FIG. 17 is a flowchart showing a procedure of a control method of a refrigerator according to the fourth embodiment of the present disclosure. FIG. 18 is a hardware configuration diagram according to the embodiment of the present disclosure. FIG. 19 is a schematic configuration diagram of a refrigerator according to a modification example of the present disclosure. Description of Embodiments<First Embodiment>(Configuration of Refrigerator)

[0012] Hereinafter, a refrigerator 1 according to the embodiment of the present disclosure will be described with reference to FIGS. 1 to 7.

[0013] As shown in FIG. 1, the refrigerator 1 includes a refrigeration cycle 2, a sensor 50, and a control device 60. The refrigeration cycle 2 includes a refrigerant line 20, a compressor 30, a condenser 3, a subcooling heat exchanger 4, a subcooling expansion valve 5, a check valve 6, a main expansion valve 7, an evaporator 8, an accumulator 9, and a bypass valve 10. The refrigerator 1 uses, for example, CO 2 or the like as a refrigerant. The refrigerant line 20 includes a circulation line 21, an injection pipe 22, and a bypass pipe 23.(Circulation Line)

[0014] The circulation line 21 circulates the refrigerant. The compressor 30, the condenser 3, the subcooling heat exchanger 4, the main expansion valve 7, the evaporator 8, and the accumulator 9 are provided in the circulation line 21 in this order.(Injection Pipe)

[0015] The injection pipe 22 branches from a downstream side of the condenser 3 in the circulation line 21. The injection pipe 22 is connected to the compressor 30 through the subcooling heat exchanger 4. The injection pipe 22 returns the refrigerant that has passed through the condenser 3 to a region (a mid-stage unit 33 described below) in the compressor 30 where an intermediate-pressure refrigerant is discharged.(Bypass Pipe)

[0016] The bypass pipe 23 branches from a downstream side of the subcooling heat exchanger 4 in the injection pipe 22. The bypass pipe 23 guides the refrigerant flowing through the injection pipe 22 to a position between the evaporator 8 and the first compression unit 32 in the circulation line 21, on the upstream side of the first compression unit 32. In the present embodiment, the bypass pipe 23 connects a region between the subcooling heat exchanger 4 and the compressor 30 in the injection pipe 22 and a region between the evaporator 8 and the accumulator 9 in the circulation line 21, on the upstream side of the accumulator 9. The refrigerant flowing in the injection pipe 22 flows into a front side (upstream side) of the accumulator 9 in the circulation line 21 through the bypass pipe 23.(Compressor)

[0017] The compressor 30 includes a casing 31, a first compression unit 32, a mid-stage unit 33, and a second compression unit 34.(First Compression Unit)

[0018] The first compression unit 32 is accommodated in the casing 31. The first compression unit 32 compresses the low-pressure refrigerant supplied from the outside to generate the intermediate-pressure refrigerant.(Mid-Stage Unit)

[0019] The mid-stage unit 33 is a region in the casing 31 where the intermediate-pressure refrigerant generated by the first compression unit 32 is discharged.(Second Compression Unit)

[0020] The second compression unit 34 is accommodated in the casing 31. The second compression unit 34 compresses the intermediate-pressure refrigerant of the mid-stage unit 33 to generate the high-pressure refrigerant.(Condenser)

[0021] The condenser 3 is provided on a downstream side of the second compression unit 34 in the circulation line 21. The condenser 3 condenses the high-pressure refrigerant generated by the second compression unit 34.(Subcooling Heat Exchanger)

[0022] The subcooling heat exchanger 4 is provided on a downstream side of the condenser 3 in the circulation line 21. The subcooling heat exchanger 4 subcools the refrigerant that has passed through the condenser 3 and that flows through the circulation line 21 by heat-exchanging with the refrigerant flowing through the injection pipe 22.(Subcooling Expansion Valve)

[0023] The subcooling expansion valve 5 is provided on an upstream side of the subcooling heat exchanger 4 in the injection pipe 22. The subcooling expansion valve 5 expands the refrigerant flowing through the injection pipe 22 before the refrigerant is supplied to the subcooling heat exchanger 4.(Check Valve)

[0024] The check valve 6 is provided on a downstream side of the subcooling heat exchanger 4 in the injection pipe 22. The check valve 6 prevents the refrigerant from flowing back from the compressor 30 to a low-pressure side (upstream side of the first compression unit 32 in the circulation line 21) through the bypass pipe 23.(Main Expansion Valve)

[0025] The main expansion valve 7 is provided on a downstream side of the subcooling heat exchanger 4 in the circulation line 21. The main expansion valve 7 expands the refrigerant that has passed through the subcooling heat exchanger 4.(Evaporator)

[0026] The evaporator 8 is provided on a downstream side of the main expansion valve 7 in the circulation line 21. The evaporator 8 evaporates the refrigerant that has passed through the main expansion valve 7.(Accumulator)

[0027] The accumulator 9 is provided between the evaporator 8 and the first compression unit 32 in the circulation line 21. The accumulator 9 collects the liquid refrigerant contained in the refrigerant that returns to the compressor 30 from the circulation line 21 and the bypass pipe 23 and prevents the liquid refrigerant from flowing back.(Bypass Valve)

[0028] The bypass valve 10 is provided in the bypass pipe 23. The bypass valve 10 is an electromagnetic valve that is controlled by a control device 60 described below and that opens and closes the bypass pipe 23.(Sensor)

[0029] The sensor 50 detects the physical quantity related to the refrigeration cycle 2. The sensor 50 according to the present embodiment includes an outside air temperature sensor 51.(Outside Air Temperature Sensor)

[0030] The outside air temperature sensor 51 is attached to an outdoor unit or the like (not shown). The outside air temperature sensor 51 detects the outside air temperature.(Control Device)

[0031] The control device 60 controls the refrigeration cycle 2. As shown in FIG. 2, the control device 60 includes functional units of an acquisition unit 61, a determination unit 62, and a valve control unit 63.(Acquisition Unit)

[0032] The acquisition unit 61 acquires the physical quantity related to the refrigeration cycle 2 (for example, the physical quantity detected by the sensor 50).(Determination Unit)

[0033] The determination unit 62 determines whether or not the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value based on the physical quantity related to the refrigeration cycle 2 (for example, the physical quantity detected by the sensor 50). In the following, unless otherwise specified, the "subcooling degree" means the "subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4", and represents a difference between a saturation temperature immediately before passing through the subcooling heat exchanger 4 (position d) and a measured temperature immediately after passing through the subcooling heat exchanger 4 (position f) in the circulation line 21. The determination unit 62 according to the present embodiment includes an evaporation temperature determination unit 62a and an outside air temperature determination unit 62b.(Evaporation Temperature Determination Unit)

[0034] The evaporation temperature determination unit 62a determines whether or not the evaporation temperature of the evaporator 8 is equal to or higher than a threshold value.(Outside Air Temperature Determination Unit)

[0035] The outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than the threshold value.(Valve Control Unit)

[0036] The valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a case where the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value. The valve control unit 63 according to the present embodiment controls the bypass valve 10 to open the bypass pipe 23 in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value. In the present embodiment, the evaporation temperature of the evaporator 8 is set in the control device 60 in advance, for example, in a case of setting an indoor temperature of the refrigerator 1.(Operation of Refrigerator)

[0037] The operation of the refrigerator 1 according to the embodiment of the present disclosure will be described.

[0038] The refrigerant circulates in the circulation line 21 and changes the state as shown in FIGS. 3 and 4. The state of the refrigerant at each position of the alphabets (a to g) in FIGS. 3 and 4 corresponds to the state indicated by the same alphabet in FIG. 1.

[0039] Here, the subcooling heat exchanger 4 allows a portion of the high-pressure refrigerant generated by the second compression unit 34 to bypass via the injection pipe 22 and flow into a refrigerant that is throttled and expanded to the intermediate pressure by the subcooling expansion valve 5. The refrigerant immediately after the throttling expansion is injected into the mid-stage unit 33 of the compressor 30 to increase the subcooling degree of the remaining large amount of high-pressure refrigerant to the main expansion valve 7.

[0040] As shown in FIG. 3, in a condition (high differential pressure condition) in which the outside air temperature is high and the evaporation temperature is low, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the intermediate-pressure refrigerant (position e) is large. As a result, the injection flow rate of the refrigerant into the mid-stage unit 33 increases, the subcooling degree (Δ2) of the high-pressure refrigerant in the subcooling heat exchanger 4 (d → f) increases, and the required subcooling degree is ensured.

[0041] However, as shown in FIG. 4, in a condition (low differential pressure condition) in which the outside air temperature is low and the evaporation temperature is high, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the intermediate-pressure refrigerant (position e) is small. As a result, the injection flow rate of the refrigerant into the mid-stage unit 33 decreases, the subcooling degree (Δ2) of the high-pressure refrigerant in the subcooling heat exchanger 4 (d → f) decreases, and the required subcooling degree may not be ensured.

[0042] As a measure for this, the refrigerator 1 is provided with the bypass pipe 23 and the bypass valve 10 that opens and closes the bypass pipe 23.

[0043] FIG. 5 is a p-h diagram in a case where the bypass pipe 23 is opened in a condition (low differential pressure condition) in which the outside air temperature is low and the evaporation temperature is high. The state of the refrigerant at each position of the alphabets (a to g) in FIG. 5 corresponds to the state indicated by the same alphabet in FIG. 1.

[0044] In a case where the valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a condition (low differential pressure condition) in which the outside air temperature is low and the evaporation temperature is high, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, the high-pressure refrigerant at the position d is throttled and expanded to the low pressure by the subcooling expansion valve 5, so that a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is large. Therefore, even in a condition (low differential pressure condition) in which the outside air temperature is low and the evaporation temperature is high, the flow rate of the throttled and expanded refrigerant (position e) can be ensured, so that the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased and the required subcooling degree can be ensured.(Procedure of Control Method of Refrigerator)

[0045] Subsequently, the control method of the refrigerator 1 that opens the bypass pipe 23 at an appropriate timing will be described.

[0046] The control method of the refrigerator 1 includes a step (step S2 described below in the present embodiment) of the control device 60 acquiring the physical quantity detected by the sensor 50, a step (step S3 described below in the present embodiment) of the control device 60 determining whether or not the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value based on the physical quantity related to the refrigeration cycle 2 (for example, the physical quantity detected by the sensor 50), and a step (step S4 described below in the present embodiment) of the control device 60 controlling the bypass valve 10 to open the bypass pipe 23 in a case where the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value.

[0047] Hereinafter, the control method of the refrigerator 1 according to the present embodiment will be described in detail with reference to FIGS. 6 and 7. Here, the control method of the refrigerator 1 will be described using a case where the target value of the subcooling degree is about 10°C as an example. The actually ensured subcooling degree may slightly deviate from the target value of the subcooling degree. That is, in a case where the target value of the subcooling degree is 10°C, the required subcooling degree of 10°C may be ensured even in a case where the actually ensured subcooling degree is 7°C or 8°C.

[0048] FIG. 6 is a flowchart showing a procedure of the control method according to the present embodiment.

[0049] FIG. 7 is a graph showing a correlation between the outside air temperature and the subcooling degree for each evaporation temperature (ET) band. FIG. 7 shows that the lower the evaporation temperature is, the larger the subcooling degree is. In addition, FIG. 7 shows that, in any evaporation temperature band, the subcooling degree is substantially constant in a region in which the outside air temperature is 0°C or lower, and the subcooling degree gradually increases as the outside air temperature increases in a region in which the outside air temperature is 0°C or higher. In addition, in FIG. 7, a region in which the subcooling degree is 10°C or lower is shown by a broken line.

[0050] As shown in FIG. 7, first, the evaporation temperature determination unit 62a determines whether or not the evaporation temperature of the evaporator 8 set in advance is equal to or higher than a threshold value (in the present embodiment, - 30°C) (step S1). Here, as shown in FIG. 7, in a temperature band in which the evaporation temperature (ET) is -25°C to -30°C or lower, the target subcooling degree of 10°C or higher is ensured regardless of the outside air temperature. On the other hand, in a temperature band in which the evaporation temperature (ET) is -20°C to - 25°C or higher, the target subcooling degree of 10°C is not ensured in a region in which the outside air temperature is 10°C or lower. Therefore, in step S1, the threshold value for determining the evaporation temperature of the evaporator 8 is set to -30°C, and the evaporation temperature determination unit 62a determines whether or not the evaporation temperature of the evaporator 8 is equal to or higher than this threshold value (-30°C), thereby determining whether or not the subcooling degree is less than the target value (10°C). In a case where the evaporation temperature of the evaporator 8 is not equal to or higher than the threshold value (-30°C) (step S1; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value (-30°C) (step S1; YES), the subcooling degree may be less than the target value of 10°C, so that the process proceeds to step S2.

[0051] In step S2, the acquisition unit 61 acquires the outside air temperature from the outside air temperature sensor 51. Thereafter, the outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than the threshold value (step S3). As described above, in a region in which the outside air temperature is 10°C or lower, the target subcooling degree of 10°C is not ensured. Therefore, in step S3, the threshold value for determining the outside air temperature is set to 10°C, and the outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than this threshold value (10°C), thereby determining whether or not the subcooling degree is less than the target value (10°C). In a case where the outside air temperature is not equal to or lower than the threshold value (10°C) (step S3; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the outside air temperature is equal to or lower than the threshold value (10°C) (step S3; YES), the valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 (step S4).

[0052] In step S4, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is large, and the flow rate of the throttle-expanded refrigerant (position e) can be ensured. Therefore, the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased, and the required subcooling degree can be ensured.

[0053] After the above procedure, the control flow of the refrigerator 1 related to the opening of the bypass pipe 23 ends.

[0054] The timing at which the bypass pipe 23 is closed may be, for example, a time at which a predetermined time has elapsed from the opening of the bypass pipe 23 (step S4), or a time at which it is determined that the subcooling degree exceeds the target value from the evaporation temperature or the outside air temperature in the same manner as the above-described procedure.

[0055] In addition, the order of the steps can be appropriately changed. For example, step S2 may be executed before step S3, and may be executed before step S1.(Operations and Effects)

[0056] The refrigerator 1 according to the present embodiment can exhibit the following effects.

[0057] In the present embodiment, the bypass pipe 23 branches from a downstream side of the subcooling heat exchanger 4 in the injection pipe 22 and guides the refrigerant flowing in the injection pipe 22 to a position between the evaporator 8 and the first compression unit 32 in the circulation line 21, on the upstream side of the first compression unit 32. The bypass valve 10 that opens and closes the bypass pipe 23 is provided in the bypass pipe 23. The control device 60 includes the acquisition unit 61, the determination unit 62, and the valve control unit 63. The acquisition unit 61 acquires the physical quantity related to the refrigeration cycle 2. The determination unit 62 determines whether or not the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value based on the physical quantity related to the refrigeration cycle 2. The valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a case where the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 is less than the target value.

[0058] In general, in a condition (low differential pressure condition) in which the outside air temperature is low and the evaporation temperature is high, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is small, and the injection flow rate of the refrigerant into the mid-stage unit 33 decreases. Therefore, the subcooling degree (Δ2) of the high-pressure refrigerant in the subcooling heat exchanger 4 (d → f) is small.

[0059] In the present embodiment, the control device 60 determines whether or not the subcooling degree is less than the target value based on the physical quantity related to the refrigeration cycle 2. In a case where the subcooling degree is less than the target value, the control device 60 can control the bypass valve 10 to open the bypass pipe 23. As a result, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, a differential pressure (Δ1) between the high-pressure refrigerant (position d) that has passed through the circulation line 21 and is supplied to the subcooling heat exchanger 4 and the low-pressure refrigerant (position e) that has passed through the injection pipe 22 and is supplied to the subcooling heat exchanger 4 is large, and the flow rate of the refrigerant (position e) that is throttled and expanded by the subcooling expansion valve 5 can be ensured. Therefore, the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased, and the required subcooling degree can be ensured.

[0060] As described above, according to the present embodiment, the control device 60 can open the bypass pipe 23 at an appropriate timing to ensure the required subcooling degree such that the subcooling degree does not fall below the target value.

[0061] In the present embodiment, the sensor 50 includes the outside air temperature sensor 51. The outside air temperature sensor 51 detects the outside air temperature. The determination unit 62 includes the evaporation temperature determination unit 62a and the outside air temperature determination unit 62b. The evaporation temperature determination unit 62a determines whether or not the evaporation temperature of the evaporator 8 is equal to or higher than a threshold value. The outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than the threshold value. The valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value.

[0062] The subcooling degree tends to be smaller as the evaporation temperature is higher and the outside air temperature is lower. In the present embodiment, first, the control device 60 determines whether or not the evaporation temperature is equal to or higher than the threshold value (-30°C) with respect to the target value (10°C) of the subcooling degree. After it is determined that the evaporation temperature is equal to or higher than the threshold value, the control device 60 determines whether or not the outside air temperature is equal to or lower than the threshold value (10°C). In a case where the outside air temperature is equal to or lower than the threshold value, the subcooling degree may be less than the target value, so that the control device 60 controls the bypass valve 10 to open the bypass pipe 23. As described above, by performing two-stage determination of the determination based on the evaporation temperature and the determination based on the outside air temperature, the control device 60 can open the bypass pipe 23 at a more efficient and appropriate timing.

[0063] In the present embodiment, the evaporation temperature of the evaporator 8 is set in the control device 60 in advance.

[0064] As a result, a step of detecting or calculating the evaporation temperature of the evaporator 8 is not required, so that the control of the refrigerator 1 can be simplified.

[0065] In the present embodiment, the check valve 6 is provided in the bypass pipe 23.

[0066] As a result, even in a case where the bypass pipe 23 is opened, the check valve 6 prevents the refrigerant from flowing back from the compressor 30 to the low-pressure side (upstream side of the first compression unit 32 in the circulation line 21) through the bypass pipe 23.<Second Embodiment>

[0067] Subsequently, a second embodiment will be described with reference to FIGS. 8 to 10. The same configurations as those of the above-described embodiment will be designated by the same reference numerals and names, and will be appropriately omitted from the description. Configurations that will not be described below are the same as those of the above-described embodiment.

[0068] As shown in FIG. 8, in the refrigerator 101 according to the present embodiment, the sensor 150 includes the outside air temperature sensor 51 and a low-pressure side pressure sensor 52.(Low-Pressure Side Pressure Sensor)

[0069] The low-pressure side pressure sensor 52 is provided between the main expansion valve 7 and the first compression unit 32 in the circulation line 21, on an upstream side of the first compression unit 32. More specifically, the low-pressure side pressure sensor 52 is provided between the accumulator 9 and the compressor 30 in the circulation line 21, on an upstream side of the compressor 30. The low-pressure side pressure sensor 52 detects the evaporation pressure (saturation pressure) of the evaporator 8.(Control Device)

[0070] In addition, as shown in FIG. 9, the control device 160 further includes an evaporation temperature calculation unit 64 in addition to the acquisition unit 61, the determination unit 62, and the valve control unit 63.(Evaporation Temperature Calculation Unit)

[0071] The evaporation temperature calculation unit 64 calculates the evaporation temperature (saturation temperature) of the evaporator 8 based on the evaporation pressure (saturation pressure) of the evaporator 8.(Procedure of Control Method of Refrigerator)

[0072] Subsequently, the control method of the refrigerator 101 that opens the bypass pipe 23 at an appropriate timing will be described. In the present embodiment, the control method of the refrigerator 101 will be described using a case where the target value of the subcooling degree is about 10°C as an example.

[0073] FIG. 10 is a flowchart showing a procedure of the control method according to the present embodiment.

[0074] As shown in FIG. 10, first, the acquisition unit 61 acquires the evaporation pressure from the low-pressure side pressure sensor 52 (step S11). Subsequently, the evaporation temperature calculation unit 64 calculates the evaporation temperature (saturation temperature) of the evaporator 8 based on the evaporation pressure (saturation pressure) of the evaporator 8 (step S12). Thereafter, the evaporation temperature determination unit 62a determines whether or not the calculated evaporation temperature of the evaporator 8 is equal to or higher than the threshold value (in the present embodiment, -30°C) (step S13). In a case where the evaporation temperature of the evaporator 8 is not equal to or higher than the threshold value (-30°C) (step S13; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value (-30°C) (step S13; YES), the subcooling degree may be less than the target value of 10°C, so that the process proceeds to step S14.

[0075] In step S14, the acquisition unit 61 acquires the outside air temperature from the outside air temperature sensor 51. Thereafter, the outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than the threshold value (in the present embodiment, 10°C) (step S15). In a case where the outside air temperature is not equal to or lower than the threshold value (10°C) (step S15; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the outside air temperature is equal to or lower than the threshold value (10°C) (step S15; YES), the valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 (step S16).

[0076] In step S16, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, as in the first embodiment, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is large, and the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased. Therefore, the required subcooling degree can be ensured.

[0077] After the above procedure, the control flow of the refrigerator 101 related to the opening of the bypass pipe 23 ends.

[0078] The timing at which the bypass pipe 23 is closed may be, for example, a time at which a predetermined time has elapsed from the opening of the bypass pipe (step S16), or a time at which it is determined that the subcooling degree exceeds the target value from the evaporation temperature or the outside air temperature in the same manner as the above-described procedure.

[0079] In addition, the order of the steps can be appropriately changed. For example, step S14 may be executed before step S15, and may be executed before step S11.(Operations and Effects)

[0080] The refrigerator 101 according to the present embodiment can exhibit the following effects.

[0081] In the present embodiment, the sensor 150 further includes the low-pressure side pressure sensor 52. The low-pressure side pressure sensor 52 is provided between the main expansion valve 7 and the first compression unit 32 in the circulation line 21, on an upstream side of the first compression unit 32, and detects the evaporation pressure of the evaporator 8. The control device 160 further includes the evaporation temperature calculation unit 64. The evaporation temperature calculation unit 64 calculates the evaporation temperature of the evaporator 8 based on the evaporation pressure of the evaporator 8.

[0082] As a result, the control device 160 can calculate the accurate evaporation temperature. Therefore, the control device 160 can perform the determination based on the evaporation temperature with higher accuracy. Therefore, the control device 160 can open the bypass pipe at a more appropriate timing.<Third Embodiment>

[0083] Subsequently, a third embodiment will be described with reference to FIGS. 11 to 14. The same configurations as those of the above-described embodiment will be designated by the same reference numerals and names, and will be appropriately omitted from the description. Configurations that will not be described below are the same as those of the above-described embodiment.

[0084] As shown in FIG. 11, a refrigerator 201 according to the present embodiment includes a control device 260.(Control Device)

[0085] As shown in FIG. 12, the control device 260 further includes an outside air temperature threshold value calculation unit 65 in addition to the acquisition unit 61, the determination unit 62, and the valve control unit 63.(Outside Air Temperature Threshold Value Calculation Unit)

[0086] The outside air temperature threshold value calculation unit 65 calculates a threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator 8.(Procedure of Control Method of Refrigerator)

[0087] Subsequently, the control method of the refrigerator 201 that opens the bypass pipe 23 at an appropriate timing will be described. In the present embodiment, the control method of the refrigerator 201 will be described using a case where the target value of the subcooling degree is about 10°C as an example.

[0088] FIG. 13 is a flowchart showing a procedure of the control method according to the present embodiment.

[0089] As shown in FIG. 13, first, the evaporation temperature determination unit 62a determines whether or not the evaporation temperature of the evaporator 8 set in advance is equal to or higher than a threshold value (in the present embodiment, - 30°C) (step S21). In a case where the evaporation temperature of the evaporator 8 is not equal to or higher than the threshold value (-30°C) (step S21; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value (-30°C) (step S21; YES), the subcooling degree may be less than the target value of 10°C, so that the process proceeds to step S22.

[0090] In step S22, the outside air temperature threshold value calculation unit 65 calculates a threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator 8. For example, the threshold value of the outside air temperature is calculated as follows.

[0091] FIG. 14 is a graph showing a correlation between the outside air temperature and the subcooling degree for each evaporation temperature (ET) band, as in FIG. 7.

[0092] As shown in FIG. 14, in a temperature band in which the evaporation temperature (ET) is -15°C to -20°C and a temperature band in which the evaporation temperature (ET) is -20°C to -25°C, the outside air temperature is around 10°C, and the subcooling degree is less than the target value of 10°C. In step S22, the threshold value of the outside air temperature at which the subcooling degree is 10°C is accurately obtained. For example, in a temperature band in which the evaporation temperature (ET) is -15°C to -20°C, the outside air temperature (about 7°C) at an intersection between a line showing the correlation and a line showing the subcooling degree of 10°C is used as the threshold value for the determination of the outside air temperature. In addition, in a temperature band in which the evaporation temperature (ET) is -20°C to -25°C, the outside air temperature (about 12°C) at an intersection between a line showing the correlation and a line showing the subcooling degree of 10°C is used as the threshold value for the determination of the outside air temperature.

[0093] After step S22, the acquisition unit 61 acquires the outside air temperature from the outside air temperature sensor 51 (step S23). Thereafter, the outside air temperature determination unit 62b determines whether or not the outside air temperature is equal to or lower than the threshold value (step S24). In a case where the outside air temperature is not equal to or lower than the threshold value (10°C) (step S24; NO), the subcooling degree does not fall below the target value of 10°C, so that the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the outside air temperature is equal to or lower than the threshold value (10°C) (step S24; YES), the valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 (step S25).

[0094] In step S25, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, as in the first embodiment, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is large, and the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased. Therefore, the required subcooling degree can be ensured.

[0095] After the above procedure, the control flow of the refrigerator 201 related to the opening of the bypass pipe 23 ends.

[0096] The timing at which the bypass pipe 23 is closed may be, for example, a time at which a predetermined time has elapsed from the opening of the bypass pipe (step S25), or a time at which it is determined that the subcooling degree exceeds the target value from the evaporation temperature or the outside air temperature in the same manner as the above-described procedure.

[0097] In addition, the order of the steps can be appropriately changed. For example, step S23 may be executed before step S24, and may be executed before step S21.

[0098] In addition, the evaporation temperature may not be set in the control device 260 in advance, and may be calculated from the detection value of the evaporation pressure as in the second embodiment.(Operations and Effects)

[0099] The refrigerator 201 according to the present embodiment can exhibit the following effects.

[0100] In the present embodiment, the control device 260 further includes the outside air temperature threshold value calculation unit 65. The outside air temperature threshold value calculation unit 65 calculates a threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator 8.

[0101] As a result, the control device 260 can calculate the accurate threshold value of the outside air temperature. Therefore, the control device 260 can perform the determination based on the outside air temperature with higher accuracy. Therefore, the control device 260 can open the bypass pipe 23 at a more appropriate timing.<Fourth Embodiment>

[0102] Subsequently, a fourth embodiment will be described with reference to FIGS. 15 to 17. The same configurations as those of the above-described embodiment will be designated by the same reference numerals and names, and will be appropriately omitted from the description. Configurations that will not be described below are the same as those of the above-described embodiment.

[0103] As shown in FIG. 15, in a refrigerator 301 according to the present embodiment, a sensor 350 includes a high-pressure side pressure sensor 53 and a line temperature sensor 54.(High-Pressure Side Pressure Sensor)

[0104] The high-pressure side pressure sensor 53 is provided between the second compression unit 34 and the main expansion valve 7 in the circulation line 21, on a downstream side of the second compression unit 34. More specifically, the high-pressure side pressure sensor 53 is provided between a connecting portion (position d) of the condenser 3 and the injection pipe 22 in the circulation line 21, on an upstream side of the position d. The high-pressure side pressure sensor 53 detects the saturation pressure of the circulation line 21.(Line Temperature Sensor)

[0105] The line temperature sensor 54 is provided between the subcooling heat exchanger 4 and the main expansion valve 7 in the circulation line 21 and is provided on an upstream side (position f) of the main expansion valve 7. The line temperature sensor 54 detects the temperature in the circulation line 21.(Control Device)

[0106] In addition, as shown in FIG. 16, the control device 360 further includes a saturation temperature calculation unit 66 and a subcooling degree calculation unit 67 in addition to the acquisition unit 61, the determination unit 62, and the valve control unit 63.(Saturation Temperature Calculation Unit)

[0107] The saturation temperature calculation unit 66 calculates the saturation temperature near the position d based on the saturation pressure near the position d in the circulation line 21.(Subcooling Degree Calculation Unit)

[0108] The subcooling degree calculation unit 67 calculates the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor 54.(Determination Unit)

[0109] The determination unit 62 includes a subcooling degree determination unit 62c and a duration determination unit 62d.(Subcooling Degree Determination Unit)

[0110] The subcooling degree determination unit 62c determines whether or not the calculated subcooling degree is equal to or less than the target value.(Duration Determination Unit)

[0111] The duration determination unit 62d determines whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer.

[0112] The valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer.(Procedure of Control Method of Refrigerator)

[0113] Subsequently, the control method of the refrigerator 301 that opens the bypass pipe 23 at an appropriate timing will be described. In the present embodiment, the control method of the refrigerator 301 will be described using a case where the target value of the subcooling degree is about 10°C as an example.

[0114] FIG. 17 is a flowchart showing a procedure of the control method according to the present embodiment.

[0115] As shown in FIG. 17, first, the acquisition unit 61 acquires the saturation pressure of a connecting portion (position d) of the condenser 3 and the injection pipe 22 in the circulation line 21 from the high-pressure side pressure sensor 53 (step S31). Subsequently, the evaporation temperature calculation unit calculates the saturation temperature based on the acquired saturation pressure of the circulation line 21 (step S32). Thereafter, the acquisition unit 61 acquires the temperature of the refrigerant that is provided between the subcooling heat exchanger 4 and the main expansion valve 7 in the circulation line 21, on an upstream side (position f) of the main expansion valve 7 (step S33). After step S33, the subcooling degree calculation unit 67 calculates the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 from the temperature difference between the calculated saturation temperature and the detection temperature of the line temperature sensor 54 (step S34).

[0116] Thereafter, the subcooling degree determination unit 62c determines whether or not the calculated subcooling degree is equal to or less than the target value (in the present embodiment, 10°C) (step S35). In a case where the calculated subcooling degree is not equal to or less than the target value (10°C) (step S35; NO), the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the calculated subcooling degree is equal to or less than the target value (10°C) (step S35; YES), the process proceeds to step S36.

[0117] In step S36, the duration determination unit 62d determines whether or not the state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer. In a case where the state where the calculated subcooling degree is equal to or less than the target value does not continue for a predetermined time or longer, the control flow ends without opening the bypass pipe 23. On the other hand, in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer (step S36; YES), the valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 (step S37).

[0118] In step S37, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, as in the first embodiment, a differential pressure (Δ1) between the high-pressure refrigerant (position d) and the low-pressure refrigerant (position e) is large, and the subcooling degree (Δ2) obtained by the subcooling expansion valve 5 can be increased. Therefore, the required subcooling degree can be ensured.

[0119] After the above procedure, the control flow of the refrigerator 301 related to the opening of the bypass pipe 23 ends.

[0120] The timing at which the bypass pipe 23 is closed may be, for example, a time at which a predetermined time has elapsed from the opening of the bypass pipe (step S37), or a time at which it is determined that the calculated subcooling degree exceeds the target value in the same manner as the above-described procedure.

[0121] In addition, the order of the steps can be appropriately changed. For example, step S33 may be executed before step S34, and may be executed before step S31.(Operations and Effects)

[0122] The refrigerator 301 according to the present embodiment can exhibit the following effects.

[0123] In the present embodiment, the sensor 350 includes the high-pressure side pressure sensor 53 and the line temperature sensor 54. The high-pressure side pressure sensor 53 is provided between the second compression unit 34 and the main expansion valve 7 in the circulation line 21, on a downstream side of the second compression unit 34, and detects the saturation pressure of the circulation line 21. The line temperature sensor 54 is provided between the subcooling heat exchanger 4 and the main expansion valve 7 in the circulation line 21, on an upstream side of the main expansion valve 7, and detects the temperature in the circulation line 21. The control device 360 includes the saturation temperature calculation unit 66 and the subcooling degree calculation unit 67. The saturation temperature calculation unit 66 calculates the saturation temperature based on the saturation pressure of the circulation line 21. The subcooling degree calculation unit 67 calculates the subcooling degree of the refrigerant in the circulation line 21 that has passed through the subcooling heat exchanger 4 from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor 54. The determination unit 62 includes a subcooling degree determination unit 62c and a duration determination unit 62d. The subcooling degree determination unit 62c determines whether or not the calculated subcooling degree is equal to or less than the target value. The duration determination unit 62d determines whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer. The valve control unit 63 controls the bypass valve 10 to open the bypass pipe 23 in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer.

[0124] In the present embodiment, the control device 360 can calculate the subcooling degree each time from the physical quantity detected by the sensor 350. Therefore, the control device 360 can more accurately determine that the subcooling degree is less than the target value. Therefore, the control device 360 can open the bypass pipe 23 at a more appropriate timing.(Hardware Configuration)

[0125] The control devices 60, 160, 260, and 360 according to the above-described embodiments are mounted on a computer as shown in FIG. 18. FIG. 18 is an example of a schematic block diagram showing a configuration of a computer on which the control devices 60, 160, 260, and 360 according to each embodiment are mounted. The computer 1100 includes a processor 1110, a main memory 1120, a storage 1130, and an interface 1140.

[0126] The operation of each functional unit of the control devices 60, 160, 260, and 360 is stored in the storage 1130 in a form of a program. The processor 1110 reads the program from the storage 1130, loads the read program into the main memory 1120, and executes the above-described processing in accordance with the program. In addition, the processor 1110 ensures a storage area in the main memory 1120 according to the program.

[0127] The program may be a program for implementing some of functions performed by the computer 1100. For example, the program may implement the functions in combination with another program already stored in the storage 1130 or in combination with another program installed on another device. In addition, the computer 1100 may include a custom large scale integrated circuit (LSI) such as a programmable logic device (PLD) in addition to or in place of the above configuration. Examples of the PLD include a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), and a field-programmable gate array (FPGA). In this case, functions that are implemented by the processor 1110 may be partially or entirely implemented by an integrated circuit.

[0128] As an example of the storage 1130, a magnetic disk, a magneto-optical disk, or a semiconductor memory can be used. The storage 1130 may be an internal medium directly connected to a bus of the computer 1100, or may be an external medium connected to the computer 1100 via the interface 1140 or a communication line. In addition, when this program is distributed to the computer 1100 via the communication line, the computer 1100 receiving the distributed program may load the program into the main memory 1120 to execute the above-described processing. The storage 1130 may be a non-transitory tangible storage medium.

[0129] In addition, the program may be a program for implementing some of the above-described functions. In addition, the program may be a so-called difference file (difference program) that implements the above-described functions in combination with another program already stored in the storage 1130.(Other Embodiments)

[0130] The embodiments of the present disclosure have been described in detail with reference to the drawings hereinbefore. However, the specific configuration is not limited to the embodiments, and includes design changes and the like within a scope not departing from the gist of the present disclosure.

[0131] In the above-described embodiment, the target value of the subcooling degree is set to 10°C, the threshold value used for the determination of the evaporation temperature is set to -30°C, and the threshold value used for the determination of the outside air temperature is set to 10°C, but the present disclosure is not limited thereto. These target values and threshold values can be appropriately changed.

[0132] In the above-described embodiment, the configuration of the refrigeration cycle 2 has been described in a simplified manner, but the present disclosure is not limited thereto. Other configurations (not shown) may be provided in the refrigeration cycle 2. For example, a tank may be provided between the compressor 30 and the subcooling heat exchanger 4 in the circulation line 21, on a downstream side of the compressor 30.

[0133] In addition, the above-described embodiment has been described using a case where the number of compressors 30 provided in the refrigerators 1, 101, 201, and 301 is one as an example, but the present disclosure is not limited thereto. As shown in FIG. 19, the refrigerator 1 may include a plurality (two in FIG. 19) of compressors 30. The plurality of compressors 30 are connected in series. In this case, the circulation line 21 includes a connection line 24. For two adjacent compressors 30, the second compression unit 34 of the compressor 30 on the upstream side and the first compression unit 32 of the compressor 30 on the downstream side are connected to each other by the connection line 24. The refrigerant discharged from the second compression unit 34 of the compressor 30 on the most downstream side is sent to the condenser 3. The injection pipe 22 (22a, 22b, 22c) is provided one by one between each compression unit (32, 34). Furthermore, the subcooling heat exchanger 4 (4a, 4b, 4c) is provided for each injection pipe 22 (22a, 22b, 22c). In the example shown in the drawing, on the circulation line 21 connecting the condenser 3 and the main expansion valve 7, a first subcooling heat exchanger 4a, a second subcooling heat exchanger 4b, and a third subcooling heat exchanger 4c are arranged in series from the downstream side. The first injection pipe 22a connected to the compressor 30 on the upstream side is connected to the mid-stage unit 33 of the compressor 30 by passing through the first subcooling heat exchanger 4a. The second injection pipe 22b connected between the compressor 30 on the upstream side and the compressor 30 on the downstream side is connected between the second compression unit 34 of the compressor 30 on the upstream side and the first compression unit 32 of the compressor 30 on the downstream side by passing through the second subcooling heat exchanger 4b. In addition, the third injection pipe 22c connected to the compressor 30 on the downstream side is connected to the mid-stage unit 33 of the compressor 30 on the downstream side by passing through the third subcooling heat exchanger 4c. The bypass pipe 23 and the bypass valve 10 are provided only in the first injection pipe 22a among the plurality of injection pipes 22.

[0134] The modification example can be applied not only to the refrigerator 1 according to the first embodiment but also to the refrigerators 101, 201, and 301 according to the second to fourth embodiments.

[0135] In addition, the third injection pipe 22c sends the gas refrigerant through the subcooling heat exchanger 4c, but a gas-liquid separator (receiver) may be used.

[0136] In the above-described embodiment, the bypass pipe 23 is connected to the upstream side (front side) of the accumulator 9, but the present disclosure is not limited thereto. The bypass pipe 23 may be connected to a downstream side of the accumulator 9 and an upstream side of the first compression unit 32. However, the bypass pipe 23, which is connected to the upstream side (front side) of the accumulator 9, has an advantage in that the liquid refrigerant can be prevented from flowing back by the accumulator 9.<Additional Notes>

[0137] The refrigerators 1, 101, 201, and 301 and the control method of the refrigerator according to each embodiment are understood as follows.

[0138] (1) A refrigerator 1, 101, 201, 301 according to a first aspect includes: a refrigeration cycle 2; a sensor 50, 150, 350 that detects a physical quantity related to the refrigeration cycle 2; and a control device 60, 160, 260, 360 that controls the refrigeration cycle 2, in which the refrigeration cycle 2 includes: a circulation line 21 through which a refrigerant circulates; a first compression unit 32 that is provided in the circulation line 21 and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit 33 that is provided in the circulation line 21 and in which the intermediate-pressure refrigerant generated by the first compression unit 32 is discharged; a second compression unit 34 that is provided in the circulation line 21 and that compresses the intermediate-pressure refrigerant in the mid-stage unit 33 to generate a high-pressure refrigerant; a condenser 3 that condenses the high-pressure refrigerant generated by the second compression unit 34; an injection pipe 22 that branches from a downstream side of the condenser 3 in the circulation line 21 and that returns a refrigerant having passed through the condenser 3 to the mid-stage unit 33; a subcooling heat exchanger 4 that subcools a refrigerant passing through the condenser 3 and then flowing through the circulation line 21 by heat-exchanging the refrigerant with a refrigerant flowing through the injection pipe 22; a subcooling expansion valve 5 that is provided on an upstream side of the subcooling heat exchanger 4 in the injection pipe 22 and that expands the refrigerant flowing through the injection pipe 22 before the refrigerant is supplied to the subcooling heat exchanger 4; a main expansion valve 7 that is provided in the circulation line 21 and that expands a refrigerant having passed through the subcooling heat exchanger 4; an evaporator 8 that is provided on a downstream side of the main expansion valve 7 in the circulation line 21 and that evaporates a refrigerant having passed through the main expansion valve 7; a bypass pipe 23 that branches from a downstream side of the subcooling heat exchanger 4 in the injection pipe 22 and that guides the refrigerant flowing through the injection pipe 22 to a position between the evaporator 8 and the first compression unit 32 in the circulation line 21, on an upstream side of the first compression unit 32; and a bypass valve 10 that is provided in the bypass pipe 23 and that opens and closes the bypass pipe 23, and the control device 60, 160, 260, 360 includes: an acquisition unit 61 that acquires the physical quantity related to the refrigeration cycle 2; a determination unit 62 that determines whether or not a subcooling degree of a refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 is less than a target value based on the physical quantity related to the refrigeration cycle 2; and a valve control unit 63 that controls the bypass valve 10 to open the bypass pipe 23 in a case where the subcooling degree of the refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 is less than the target value.

[0139] In the present aspect, the control device 60, 160, 260, 360 determines whether or not the subcooling degree is less than the target value based on the physical quantity related to the refrigeration cycle 2. In a case where the subcooling degree is less than the target value, the control device 60, 160, 260, 360 can control the bypass valve 10 to open the bypass pipe 23. As a result, the refrigerant that is originally to be injected into the mid-stage unit 33 flows to an upstream side (low-pressure side) of the first compression unit 32. As a result, a differential pressure between the high-pressure refrigerant that has passed through the circulation line 21 and is supplied to the subcooling heat exchanger 4 and the low-pressure refrigerant that has passed through the injection pipe 22 and is supplied to the subcooling heat exchanger 4 is large, and the flow rate of the refrigerant that is throttled and expanded by the subcooling expansion valve 5 can be ensured. Therefore, the subcooling degree obtained by the subcooling expansion valve 5 can be increased, and the required subcooling degree can be ensured.

[0140] (2) The refrigerator 1, 101, 201 according to a second aspect is the refrigerator 1, 101, 201 according to the first aspect, in which the sensor 50, 150 may include an outside air temperature sensor 51 that detects an outside air temperature, the determination unit 62 may include an evaporation temperature determination unit 62a that determines whether or not an evaporation temperature of the evaporator 8 is equal to or higher than a threshold value, and an outside air temperature determination unit 62b that determines whether or not the outside air temperature is equal to or lower than the threshold value, and the valve control unit 63 may control the bypass valve 10 to open the bypass pipe 23 in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value.

[0141] The subcooling degree tends to be smaller as the evaporation temperature is higher and the outside air temperature is lower. In the present aspect, by performing two-stage determination of the determination based on the evaporation temperature and the determination based on the outside air temperature, the control devices 60, 160, 260 can open the bypass pipe 23 at a more efficient and appropriate timing.

[0142] (3) The refrigerator 1, 201 according to a third aspect is the refrigerator 1, 201 according to the second aspect, in which the evaporation temperature of the evaporator 8 may be set in the control device 60, 260 in advance.

[0143] As a result, a step of detecting or calculating the evaporation temperature of the evaporator 8 is not required.

[0144] (4) The refrigerator 101 according to a fourth aspect is the refrigerator 101 according to the second aspect, in which the sensor 150 may further include a low-pressure side pressure sensor 52 that is provided between the main expansion valve 7 and the first compression unit 32 in the circulation line 21 and that is provided on an upstream side of the first compression unit 32, and that detects an evaporation pressure of the evaporator 8, and the control device 160 may further include an evaporation temperature calculation unit 64 that calculates an evaporation temperature of the evaporator 8 based on the evaporation pressure of the evaporator 8.

[0145] As a result, the control device 160 can calculate the accurate evaporation temperature. Therefore, the control device 160 can perform the determination based on the evaporation temperature with higher accuracy.

[0146] (5) The refrigerator 201 according to a fifth aspect is the refrigerator 201 according to any one of the second to fourth aspects, in which the control device 260 may further include an outside air temperature threshold value calculation unit 65 that calculates a threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator 8.

[0147] As a result, the control device 260 can calculate the accurate threshold value of the outside air temperature. Therefore, the control device 260 can perform the determination based on the outside air temperature with higher accuracy.

[0148] (6) The refrigerator 301 according to a sixth aspect is the refrigerator 301 according to the first aspect, in which the sensor 350 includes: a high-pressure side pressure sensor 53 that is provided between the second compression unit 34 and the main expansion valve 7 in the circulation line 21, on a downstream side of the second compression unit 34, and that detects a saturation pressure of the circulation line 21; and a line temperature sensor 54 that is provided between the subcooling heat exchanger 4 and the main expansion valve 7 in the circulation line 21, on an upstream side of the main expansion valve 7, and that detects a temperature in the circulation line 21, the control device 360 includes: a saturation temperature calculation unit 66 that calculates a saturation temperature based on the saturation pressure of the circulation line 21; and a subcooling degree calculation unit 67 that calculates the subcooling degree of the refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor 54, the determination unit 62 includes: a subcooling degree determination unit 62c that determines whether or not the calculated subcooling degree is equal to or less than the target value; and a duration determination unit 62d that determines whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer, and the valve control unit 63 may control the bypass valve 10 to open the bypass pipe 23 in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for the predetermined time or longer.

[0149] In the present aspect, the control device 360 can calculate the subcooling degree each time from the physical quantity detected by the sensor 350. Therefore, the control device 360 can more accurately determine that the subcooling degree is less than the target value.

[0150] (7) A control method of a refrigerator according to a seventh aspect is a control method of a refrigerator 1, 101, 201, 301 including a refrigeration cycle 2, a sensor 50, 150, 350 that detects a physical quantity related to the refrigeration cycle 2, and a control device 60, 160, 260, 360 that controls the refrigeration cycle 2, in which the refrigeration cycle 2 includes: a circulation line 21 through which a refrigerant circulates; a first compression unit 32 that is provided in the circulation line 21 and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit 33 that is provided in the circulation line 21 and in which the intermediate-pressure refrigerant generated by the first compression unit 32 is discharged; a second compression unit 34 that is provided in the circulation line 21 and that compresses the intermediate-pressure refrigerant in the mid-stage unit 33 to generate a high-pressure refrigerant; a condenser 3 that condenses the high-pressure refrigerant generated by the second compression unit 34; an injection pipe 22 that branches from a downstream side of the condenser 3 in the circulation line 21 and that returns the refrigerant having passed through the condenser 3 to the mid-stage unit 33; a subcooling heat exchanger 4 that subcools the refrigerant passing through the condenser 3 and then flowing through the circulation line 21 by heat-exchanging the refrigerant with the refrigerant flowing through the injection pipe 22; a subcooling expansion valve 5 that is provided on an upstream side of the subcooling heat exchanger 4 in the injection pipe 22 and that expands the refrigerant flowing through the injection pipe 22 before the refrigerant is supplied to the subcooling heat exchanger 4; a main expansion valve 7 that is provided in the circulation line 21 and that expands the refrigerant having passed through the subcooling heat exchanger 4; an evaporator 8 that is provided on a downstream side of the main expansion valve 7 in the circulation line 21 and that evaporates the refrigerant having passed through the main expansion valve 7; a bypass pipe 23 that branches from a downstream side of the subcooling heat exchanger 4 in the injection pipe 22 and that guides the refrigerant flowing through the injection pipe 22 to a position between the evaporator 8 and the first compression unit 32 in the circulation line 21, on an upstream side of the first compression unit 32; and a bypass valve 10 that is provided in the bypass pipe 23 and that opens and closes the bypass pipe 23, and the method including: a step of acquiring, by the control device 60, 160, 260, 360, the physical quantity related to the refrigeration cycle 2; a step of determining, by the control device 60, 160, 260, 360, whether or not a subcooling degree of the refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 is less than a target value based on the physical quantity related to the refrigeration cycle 2; and a step of controlling, by the control device 60, 160, 260, 360, the bypass valve 10 to open the bypass pipe 23 in a case where the subcooling degree of the refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 is less than the target value.

[0151] (8) A control method of a refrigerator according to an eighth aspect is the control method of the refrigerator according to the seventh aspect, in which the sensors 50, 150 may include an outside air temperature sensor 51 that detects an outside air temperature, and the control method may further include a step of determining, by the control devices 60, 160, 260, whether or not an evaporation temperature of the evaporator 8 is equal to or higher than a threshold value, a step of determining, by the control devices 60, 160, 260, whether or not the outside air temperature is equal to or lower than the threshold value, and a step of controlling, by the control devices 60, 160, 260, the bypass valve 10 to open the bypass pipe 23 in a case where the evaporation temperature of the evaporator 8 is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value.

[0152] (9) A control method of a refrigerator according to a ninth aspect is the control method of the refrigerator according to the eighth aspect, in which the evaporation temperature of the evaporator 8 may be set in the control device 60, 260 in advance.

[0153] (10) A control method of a refrigerator according to a tenth aspect is the control method of the refrigerator according to the eighth aspect, in which the sensor 150 may further include a low-pressure side pressure sensor 52 that is provided between the main expansion valve 7 and the first compression unit 32 in the circulation line 21 and that is provided on the upstream side of the first compression unit 32, and that detects an evaporation pressure of the evaporator 8, and the control method may further include a step of calculating, by the control device 160, an evaporation temperature of the evaporator 8 based on the evaporation pressure of the evaporator 8.

[0154] (11) A control method of a refrigerator according to an eleventh aspect is the control method of the refrigerator 201 according to any one of the eighth to tenth aspects, in which the control method may further include a step of calculating, by the control device 260, the threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator 8.

[0155] (12) A control method of a refrigerator according to a twelfth aspect is the control method of the refrigerator 301 according to the seventh aspect, in which the sensor 350 may include a high-pressure side pressure sensor 53 that is provided between the second compression unit 34 and the main expansion valve 7 in the circulation line 21, on a downstream side of the second compression unit 34, and that detects a saturation pressure of the circulation line 21, and a line temperature sensor 54 that is provided between the subcooling heat exchanger 4 and the main expansion valve 7 in the circulation line 21 and that is provided on an upstream side of the main expansion valve 7, and that detects a temperature in the circulation line 21, and the control method may further include a step of calculating, by the control device 360, a saturation temperature based on the saturation pressure of the circulation line 21, a step of calculating, by the control device 360, the subcooling degree of the refrigerant in the circulation line 21 having passed through the subcooling heat exchanger 4 from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor 54, a step of determining, by the control device 360, whether or not the calculated subcooling degree is equal to or less than the target value, a step of determining, by the control device 360, whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer, and a step of controlling, by the control device 360, the bypass valve 10 to open the bypass pipe 23 in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for the predetermined time or longer.Industrial Applicability

[0156] According to a refrigerator and a control method of a refrigerator according to the present disclosure, a required subcooling degree can be ensured.Reference Signs List

[0157] 1: refrigerator 2: refrigeration cycle 3: condenser 4: subcooling heat exchanger 5: subcooling expansion valve 6: check valve 7: main expansion valve 8: evaporator 9: accumulator 10: bypass valve 20: refrigerant line 21: circulation line 22: injection pipe 23: bypass pipe 30: compressor 31: casing 32: first compression unit 33: mid-stage unit 34: second compression unit 50: sensor 51: outside air temperature sensor 60: control device 61: acquisition unit 62: determination unit 62a: evaporation temperature determination unit 62b: outside air temperature determination unit 63: valve control unit 101: refrigerator 150: sensor 52: low-pressure side pressure sensor 160: control device 64: evaporation temperature calculation unit 201: refrigerator 260: control device 65: outside air temperature threshold value calculation unit 301: refrigerator 350: sensor 53: high-pressure side pressure sensor 54: line temperature sensor 360: control device 62c: subcooling degree determination unit 62d: duration determination unit 66: saturation temperature calculation unit 67: subcooling degree calculation unit 24: connection line 22a: first injection pipe 22b: second injection pipe 1100: computer 1110: processor 1120: main memory 1130: storage 1140: interface 4a: first subcooling heat exchanger 4b: second subcooling heat exchanger 4c: third subcooling heat exchanger 22a: first injection pipe 22b: second injection pipe 22c: third injection pipe

Claims

1. A refrigerator comprising: a refrigeration cycle; a sensor that detects a physical quantity related to the refrigeration cycle; and a control device that controls the refrigeration cycle, wherein the refrigeration cycle includes: a circulation line through which a refrigerant circulates; a first compression unit that is provided in the circulation line and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit that is provided in the circulation line and in which the intermediate-pressure refrigerant generated by the first compression unit is discharged; a second compression unit that is provided in the circulation line and that compresses the intermediate-pressure refrigerant in the mid-stage unit to generate a high-pressure refrigerant; a condenser that condenses the high-pressure refrigerant generated by the second compression unit; an injection pipe that branches from a downstream side of the condenser in the circulation line and that returns the refrigerant having passed through the condenser to the mid-stage unit; a subcooling heat exchanger that subcools the refrigerant passing through the condenser and then flowing through the circulation line by heat-exchanging the refrigerant with the refrigerant flowing through the injection pipe; a subcooling expansion valve that is provided on an upstream side of the subcooling heat exchanger in the injection pipe and that expands the refrigerant flowing through the injection pipe before the refrigerant is supplied to the subcooling heat exchanger; a main expansion valve that is provided in the circulation line and that expands the refrigerant having passed through the subcooling heat exchanger; an evaporator that is provided on a downstream side of the main expansion valve in the circulation line and that evaporates the refrigerant having passed through the main expansion valve; a bypass pipe that branches from a downstream side of the subcooling heat exchanger in the injection pipe and that guides the refrigerant flowing through the injection pipe to a position which is provided between the evaporator and the first compression unit in the circulation line and which is provided on an upstream side of the first compression unit; and a bypass valve that is provided in the bypass pipe and that opens and closes the bypass pipe, and the control device includes: an acquisition unit that acquires the physical quantity related to the refrigeration cycle; a determination unit that determines whether or not a subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than a target value based on the physical quantity related to the refrigeration cycle; and a valve control unit that controls the bypass valve to open the bypass pipe in a case where the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than the target value.

2. The refrigerator according to claim 1, wherein the sensor includes an outside air temperature sensor that detects an outside air temperature, the determination unit includes: an evaporation temperature determination unit that determines whether or not an evaporation temperature of the evaporator is equal to or higher than a threshold value; and an outside air temperature determination unit that determines whether or not the outside air temperature is equal to or lower than the threshold value, and the valve control unit controls the bypass valve to open the bypass pipe in a case where the evaporation temperature of the evaporator is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value.

3. The refrigerator according to claim 2, wherein the evaporation temperature of the evaporator is set in the control device in advance.

4. The refrigerator according to claim 2, wherein the sensor further includes a low-pressure side pressure sensor that is provided between the main expansion valve and the first compression unit in the circulation line, on the upstream side of the first compression unit, and that detects an evaporation pressure of the evaporator, and the control device further includes an evaporation temperature calculation unit that calculates an evaporation temperature of the evaporator based on the evaporation pressure of the evaporator.

5. The refrigerator according to claim 2, wherein the control device further includes an outside air temperature threshold value calculation unit that calculates the threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator.

6. The refrigerator according to claim 1, wherein the sensor includes: a high-pressure side pressure sensor that is provided between the second compression unit and the main expansion valve in the circulation line, on a downstream side of the second compression unit, and that detects a saturation pressure of the circulation line; and a line temperature sensor that is provided between the subcooling heat exchanger and the main expansion valve in the circulation line, on an upstream side of the main expansion valve, and that detects a temperature in the circulation line, the control device includes: a saturation temperature calculation unit that calculates a saturation temperature based on the saturation pressure of the circulation line; and a subcooling degree calculation unit that calculates the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor, the determination unit includes: a subcooling degree determination unit that determines whether or not the calculated subcooling degree is equal to or less than the target value; and a duration determination unit that determines whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer, and the valve control unit controls the bypass valve to open the bypass pipe in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for the predetermined time or longer.

7. A control method of a refrigerator including a refrigeration cycle, a sensor that detects a physical quantity related to the refrigeration cycle, and a control device that controls the refrigeration cycle, in which the refrigeration cycle includes: a circulation line through which a refrigerant circulates; a first compression unit that is provided in the circulation line and that compresses a low-pressure refrigerant supplied from an outside to generate an intermediate-pressure refrigerant; a mid-stage unit that is provided in the circulation line and in which the intermediate-pressure refrigerant generated by the first compression unit is discharged; a second compression unit that is provided in the circulation line and that compresses the intermediate-pressure refrigerant in the mid-stage unit to generate a high-pressure refrigerant; a condenser that condenses the high-pressure refrigerant generated by the second compression unit; an injection pipe that branches from a downstream side of the condenser in the circulation line and that returns the refrigerant having passed through the condenser to the mid-stage unit; a subcooling heat exchanger that subcools the refrigerant passing through the condenser and then flowing through the circulation line by heat-exchanging the refrigerant with the refrigerant flowing through the injection pipe; a subcooling expansion valve that is provided on an upstream side of the subcooling heat exchanger in the injection pipe and that expands the refrigerant flowing through the injection pipe before the refrigerant is supplied to the subcooling heat exchanger; a main expansion valve that is provided in the circulation line and that expands the refrigerant having passed through the subcooling heat exchanger; an evaporator that is provided on a downstream side of the main expansion valve in the circulation line and that evaporates the refrigerant having passed through the main expansion valve; a bypass pipe that branches from a downstream side of the subcooling heat exchanger in the injection pipe and that guides the refrigerant flowing through the injection pipe to a position between the evaporator and the first compression unit in the circulation line, on an upstream side of the first compression unit; and a bypass valve that is provided in the bypass pipe and that opens and closes the bypass pipe, and the method comprising: a step of acquiring, by the control device, the physical quantity related to the refrigeration cycle; a step of determining, by the control device, whether or not a subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than a target value based on the physical quantity related to the refrigeration cycle; and a step of controlling, by the control device, the bypass valve to open the bypass pipe in a case where the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger is less than the target value.

8. The control method of a refrigerator according to claim 7, wherein the sensor includes an outside air temperature sensor that detects an outside air temperature, the control method further comprises: a step of determining, by the control device, whether or not an evaporation temperature of the evaporator is equal to or higher than a threshold value; a step of determining, by the control device, whether or not the outside air temperature is equal to or lower than the threshold value; and a step of controlling, by the control device, the bypass valve to open the bypass pipe in a case where the evaporation temperature of the evaporator is equal to or higher than the threshold value and the outside air temperature is equal to or lower than the threshold value.

9. The control method of a refrigerator according to claim 8, wherein the evaporation temperature of the evaporator is set in the control device in advance.

10. The control method of a refrigerator according to claim 8, wherein the sensor further includes a low-pressure side pressure sensor that is provided between the main expansion valve and the first compression unit in the circulation line, on the upstream side of the first compression unit, and that detects an evaporation pressure of the evaporator, and the control method further comprises a step of calculating, by the control device, an evaporation temperature of the evaporator based on the evaporation pressure of the evaporator.

11. The control method of a refrigerator according to claim 8, wherein the control method further comprises a step of calculating, by the control device, the threshold value used for the determination of the outside air temperature based on the evaporation temperature of the evaporator.

12. The control method of a refrigerator according to claim 7, wherein the sensor includes: a high-pressure side pressure sensor that is provided between the second compression unit and the main expansion valve in the circulation line, on a downstream side of the second compression unit, and that detects a saturation pressure of the circulation line; and a line temperature sensor that is provided between the subcooling heat exchanger and the main expansion valve in the circulation line, on an upstream side of the main expansion valve, and that detects a temperature in the circulation line, the method further comprises: a step of calculating, by the control device, a saturation temperature based on the saturation pressure of the circulation line; and a step of calculating, by the control device, the subcooling degree of the refrigerant in the circulation line having passed through the subcooling heat exchanger from a temperature difference between the calculated saturation temperature and a detection temperature of the line temperature sensor, a step of determining, by the control device, whether or not the calculated subcooling degree is equal to or less than the target value; and a step of determining, by the control device, whether or not a state where the calculated subcooling degree is equal to or less than the target value continues for a predetermined time or longer, and a step of controlling, by the control device, the bypass valve to open the bypass pipe in a case where the state where the calculated subcooling degree is equal to or less than the target value continues for the predetermined time or longer.

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