Secondary refrigeration device
By adjusting the rotation number of the low-level and high-level motors in the secondary refrigeration device, and adjusting the cooling amount and differential pressure of the low-level refrigeration cycle, the problem of the screw low-level compressor bearing with high pressure load is solved, ensuring the bearing Long life and environmental protection and efficiency of the device.
Patent Information
- Application Number
- CN202380044195.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-06-02
- Filing Date
- 2023-05-09
- Publication Date
- 2025-01-10
AI Technical Summary
In a secondary refrigeration device using CO2 as the low-level cooling medium, the bearings of the screw-type low-level compressor are subjected to high pressure loads, making it difficult to guarantee its long life.
The control device is used to measure the suction and discharge pressure difference of the low-level compressor and adjust the rotation number of the low-level and high-level motors to adjust the cooling amount and differential pressure of the low-level refrigeration cycle to ensure that the pressure load of the bearing is within the appropriate range. Use CO2 and R1234yf as cooling medium to ensure stable operation of the screw compressor.
It effectively extends the life of the low-side compressor bearing, reduces the impact on the dry ice degradation of the screw rotor, and improves the environmental protection and efficiency of the device.
Smart Images
Figure CN119301414A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to a two-stage refrigeration device. Background Art
[0002] A two-stage refrigeration device is known that thermally connects a low-stage refrigeration cycle and a high-stage refrigeration cycle by means of a cascade heat exchanger (for example, see Patent Document 1). In the two-stage refrigeration device of Patent Document 1, CO2 (carbon dioxide) is used as a low-stage cooling medium in the low-stage refrigeration cycle, and a scroll-type low-stage compressor is used. Patent Document 1 aims to obtain a two-stage refrigeration device with higher efficiency.
[0003] Prior art literature
[0004] Patent Literature
[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-112615. Summary of the invention
[0006] Technical problem to be solved by the invention
[0007] A rotary low-stage compressor such as a scroll type or a screw type has bearings. If CO2 is used as a low-stage cooling medium and a rotary low-stage compressor is used, a very high pressure load is applied to the bearings. As a result, there is a risk that the bearings cannot be guaranteed to have a long life.
[0008] The technical problem of the present application is to ensure a long life of the bearings of the low-stage compressor in a two-stage refrigeration device using CO2 as a low-stage cooling medium and a screw-type low-stage compressor.
[0009] Means for solving technical problems
[0010] The present application provides a two-stage refrigeration device, comprising:
[0011] A low-stage refrigeration cycle, using CO2 as a low-stage cooling medium, comprising a low-stage compressor, the low-stage compressor being a screw type and compressing the low-stage cooling medium, the low-stage compressor having a screw rotor rotatably supported by a bearing and a low-stage motor driving the screw rotor;
[0012] a high-side refrigeration cycle including a high-side compressor having a high-side motor and compressing a high-side cooling medium;
[0013] A first pressure sensor is used to measure the suction pressure of the low-stage compressor, i.e., the low-stage suction pressure;
[0014] A second pressure sensor measures the discharge pressure of the low-stage compressor, i.e., the low-stage discharge pressure;
[0015] a control device that receives the low-stage side suction pressure from the first pressure sensor and the low-stage side discharge pressure from the second pressure sensor, and calculates a low-stage side differential pressure that is a difference between the low-stage side discharge pressure and the low-stage side suction pressure,
[0016] The low-stage refrigeration cycle and the high-stage refrigeration cycle share a cascade condenser, which functions as a condenser for condensing the low-stage cooling medium in the low-stage refrigeration cycle and as an evaporator for evaporating the high-stage cooling medium in the high-stage refrigeration cycle, and performs heat exchange between the low-stage refrigeration cycle and the high-stage refrigeration cycle.
[0017] The control device is:
[0018] When the low-stage side suction pressure is less than the first lower limit pressure, the number of revolutions of the low-stage side motor is reduced; when the low-stage side suction pressure exceeds the first upper limit pressure, the number of revolutions of the low-stage side motor is increased; when the low-stage side suction pressure is greater than the first lower limit pressure and less than the first upper limit pressure, the number of revolutions of the low-stage side motor is maintained, and the following control corresponding to the low-stage side differential pressure is performed,
[0019] When the low-stage side differential pressure is less than the second lower limit pressure, the speed of the high-stage side motor is reduced; when the low-stage side differential pressure exceeds the second upper limit pressure, the speed of the high-stage side motor is increased; when the low-stage side differential pressure is above the second lower limit pressure and below the second upper limit pressure, the speed of the high-stage side motor is maintained.
[0020] According to this configuration, the low-level side suction pressure can be adjusted to between the first lower limit pressure and the first upper limit pressure, so the cooling amount in the low-level side refrigeration cycle can be adjusted to a suitable range. In addition, the low-level side differential pressure can be adjusted to between the second lower limit pressure and the second upper limit pressure, so the pressure load on the bearing can be adjusted, and the long life of the bearing can be ensured. If the number of revolutions of the low-level side motor is increased, the cooling amount in the low-level side refrigeration cycle increases, and the cooling temperature decreases. Thus, in the low-level side refrigeration cycle, the evaporation temperature decreases, so the evaporation pressure (i.e., the low-level side suction pressure) decreases. On the contrary, if the number of revolutions of the low-level side motor is reduced, the evaporation pressure (i.e., the low-level side suction pressure) rises. In this way, the low-level side suction pressure can be adjusted. In addition, if the number of revolutions of the high-level side motor is increased, the cooling amount in the high-level side refrigeration cycle increases, and the cooling temperature decreases. Thus, the evaporation temperature in the high-level side refrigeration cycle decreases, and the condensation temperature in the low-level side refrigeration cycle thermally connected by the cascade condenser decreases. Therefore, the condensation pressure (i.e., the low-level side discharge pressure) in the low-level side refrigeration cycle decreases. On the contrary, if the number of revolutions of the high-stage side motor is reduced, the condensation pressure (i.e., the low-stage side discharge pressure) in the low-stage side refrigeration cycle will rise. In this way, the low-stage side discharge pressure can be adjusted. Thus, the low-stage side differential pressure that affects the bearing can be adjusted to a suitable range. In addition, the GWP (global warming potential) of CO2 used as a low-stage side cooling medium is 1, and it is environmentally friendly. In addition, the low-stage side compressor is a screw type, so even if CO2 solidifies (dry ice) due to low temperature, it can be crushed with the help of a screw rotor, so there are fewer adverse effects compared to other rotary types such as a scroll type.
[0021] The difference between the second upper limit pressure and the second lower limit pressure may be 0.4 MPa or less. For example, the second lower limit pressure may be 0.6 MPa, and the second upper limit pressure may be 1.0 MPa.
[0022] According to this configuration, the low-stage side differential pressure can be specifically adjusted to be within an appropriate range, and a long life of the bearing can be ensured.
[0023] The high-stage side cooling medium may be R1234yf.
[0024] According to this configuration, R1234yf used as the high-pressure side coolant has a GWP of 1 and is excellent in environmental friendliness.
[0025] The secondary refrigeration device may further include:
[0026] a first temperature sensor, for measuring the temperature of the low-stage motor;
[0027] A second temperature sensor measures the temperature of the high-side motor.
[0028] The control device may receive the temperature of the low-stage motor from the first temperature sensor and the temperature of the high-stage motor from the second temperature sensor,
[0029] The operation of increasing the number of revolutions of the low-stage motor may be put on standby until the temperature of the low-stage motor becomes below an upper limit value.
[0030] The operation of increasing the number of revolutions of the high-stage motor may be performed in a standby state until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
[0031] According to this configuration, the temperatures of the low-stage motor and the high-stage motor can be suppressed to be below the upper limit value, respectively. Therefore, the loads applied to the low-stage motor and the high-stage motor can be suppressed to be below a certain level.
[0032] The secondary refrigeration device may further include:
[0033] a first current sensor, for measuring the current of the low-side motor;
[0034] A second current sensor measures the current of the high-side motor,
[0035] The control device may receive the current of the low-side motor from the first current sensor and receive the current of the high-side motor from the second current sensor,
[0036] The operation of increasing the number of revolutions of the low-stage motor may be put on standby until the current of the low-stage motor becomes below the upper limit value.
[0037] The operation of increasing the number of revolutions of the high-stage motor may be put on standby until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
[0038] According to this configuration, the currents of the low-stage motor and the high-stage motor can be suppressed to be below the upper limit value, respectively. Therefore, the loads applied to the low-stage motor and the high-stage motor can be suppressed to be below a certain level.
[0039] The secondary refrigeration device may further include:
[0040] a first rotation speed sensor for measuring the rotation speed of the low-stage motor;
[0041] A second rotation sensor measures the rotation of the high-speed motor.
[0042] The control device may receive the number of revolutions of the low-stage motor from the first number of revolutions sensor and receive the number of revolutions of the high-stage motor from the second number of revolutions sensor,
[0043] The operation of increasing the rotation speed of the low-stage motor may be put on standby until the rotation speed of the low-stage motor becomes below an upper limit value.
[0044] The operation of increasing the number of revolutions of the high-stage motor may be put on standby until the number of revolutions of the high-stage motor becomes equal to or less than an upper limit value.
[0045] According to this configuration, the rotation speeds of the low-stage motor and the high-stage motor can be suppressed to be below the upper limit value, respectively. Therefore, the loads applied to the low-stage motor and the high-stage motor can be suppressed to be below a certain level.
[0046] Effects of the Invention
[0047] According to the present application, in a two-stage refrigeration device that uses CO 2 as a low-stage cooling medium and employs a screw-type low-stage compressor, a long life of the bearings of the low-stage compressor can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Figure 1 This is a cooling medium circuit diagram of the two-stage refrigeration device according to the first embodiment of the present invention.
[0049] Figure 2 It is a cross-sectional view showing the interior of the low-stage compressor.
[0050] Figure 3 It is a block diagram of the control device in the first embodiment.
[0051] Figure 4 is a flowchart showing control performed by the control device.
[0052] Figure 5 is with Figure 4 This is a flowchart of the rotation speed control of the low-stage motor in the first embodiment corresponding to step S4-3.
[0053] Figure 6 is with Figure 4 Step S4-4 corresponds to a flowchart of the rotation speed control of the high-stage motor in the first embodiment.
[0054] Figure 7 This is a cooling medium circuit diagram of a two-stage refrigeration device according to a second embodiment of the present invention.
[0055] Figure 8 It is a block diagram of the control device in the second embodiment.
[0056] Fig. 9 is with Figure 4 This is a flowchart of the rotation speed control of the low-stage motor in the second embodiment corresponding to step S4-3.
[0057] Fig.10 is with Figure 4 The flowchart of the rotation speed control of the high-stage motor in the second embodiment corresponds to step S4-4.
[0058] Fig.11 is with Figure 4 This is a flowchart of the rotation speed control of the low-stage motor in the first modified example of the second embodiment corresponding to step S4-3.
[0059] Fig.12 is corresponding to Figure 4 This is a flowchart of the rotation speed control of the high-stage motor in the first modified example of the second embodiment of step S4-4.
[0060] Fig.13 is with Figure 4 This is a flowchart of the rotation speed control of the low-stage motor in the second modification of the second embodiment corresponding to step S4-3.
[0061] Fig.14 is with Figure 4 Step S4-4 corresponds to a flowchart of the rotation speed control of the high-stage motor in the second modification of the second embodiment. DETAILED DESCRIPTION
[0062] Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0063] (First Embodiment)
[0064] Reference Figure 1 The two-stage refrigeration device 1 according to the first embodiment includes a low-stage refrigeration cycle 10 , a high-stage refrigeration cycle 20 , and a control device 30 .
[0065] CO 2 (carbon dioxide) is used as a low-pressure side cooling medium in the low-pressure side refrigeration cycle 10 . The low-pressure side refrigeration cycle 10 includes a low-pressure side compressor 11 , an oil recovery device 12 , a cascade condenser 5 , an expansion valve 13 , and an evaporator 14 .
[0066] Refer to Figure 2 The low-stage compressor 11 is a screw type, and compresses the low-stage cooling medium. The low-stage compressor 11 has a screw rotor 11a, a low-stage motor 11b driving the screw rotor 11a, and a housing 11c accommodating them. The screw rotor 11a is rotatably supported by a bearing (rolling bearing) 11d, and is mechanically connected to the low-stage motor 11b via a coupling 11e.
[0067] The low-stage motor 11b includes a stator 11b1 fixed to the housing 11c and a rotor 11b2 disposed inside the stator 11b1 and rotatably supported by a bearing (rolling bearing) 11f. The rotation speed of the low-stage motor 11b can be adjusted via a converter 11g.
[0068] In the present embodiment, the low-pressure side compressor 11 is an oil-cooled type. A shaft sealing device 11h is provided between the screw rotor 11a and the low-pressure side motor 11b, adjacent to the coupling 11e. The shaft sealing device 11h prevents the passage of oil.
[0069] The low-stage compressor 11 sucks the low-stage cooling medium (CO2) from the suction port 11i, compresses it internally, and discharges it from the discharge port 11j. The discharged CO2 contains oil, which is sent to the oil recovery device 12 to recover the oil. The recovered oil is supplied to the low-stage compressor 11, that is, it is recycled. The CO2 separated from the oil in the oil recovery device 12 is sent to the cascade condenser 5.
[0070] The cascade condenser 5 is shared by the low-stage refrigeration cycle 10 and the high-stage refrigeration cycle 20. In the cascade condenser 5, heat exchange is performed between the low-stage refrigeration cycle 10 and the high-stage refrigeration cycle 20. The cascade condenser 5 functions as a condenser in the low-stage refrigeration cycle 10 that cools the low-stage cooling medium and condenses it.
[0071] The low-pressure side refrigerant condensed in the cascade condenser 5 is expanded by passing through the expansion valve 13 and is sent to the evaporator 14. The expansion valve 13 is, for example, a pressure regulating valve.
[0072] In the evaporator 14 , the low-pressure side refrigerant expanded by the expansion valve 13 evaporates, and the evaporated low-pressure side refrigerant is sent to the low-pressure side compressor 11 .
[0073] The low-stage refrigeration cycle 10 is provided with a first pressure sensor 15a for measuring the suction pressure of the low-stage compressor 11, namely the low-stage suction pressure, and a second pressure sensor 15b for measuring the discharge pressure of the low-stage compressor 11, namely the low-stage discharge pressure.
[0074] In the high-side refrigeration cycle 20, for example, HFO (hydrofluoroolefin), HFC (hydrofluorocarbon) or NH3 (ammonia) is used as the high-side cooling medium. In the present embodiment, R1234yf, which is a kind of HFO, is used as the high-side cooling medium. The high-side refrigeration cycle 20 includes a high-side compressor 21, an oil recovery device 22, a condenser 23, an expansion valve 24, and a cascade condenser 5.
[0075] The high-stage compressor 21 compresses the high-stage cooling medium. The high-stage compressor 21 may be, for example, a screw type, a scroll type, or a reciprocating type. The high-stage compressor 21 includes a high-stage motor 21a as a driving source. The high-stage motor 21a can adjust the rotation speed via a converter 21b.
[0076] In the high-stage compressor 21, the high-stage cooling medium is sucked from the suction port 21c, compressed inside, and discharged from the discharge port 21d. The discharged high-stage cooling medium contains oil and is sent to the oil recovery device 22 to recover the oil. The recovered oil is supplied to the high-stage compressor 21, that is, it is recycled. The high-stage cooling medium from which the oil is separated in the oil recovery device 22 is sent to the condenser 23.
[0077] The high-pressure side cooling medium is cooled and condensed in the condenser 23. The high-pressure side cooling medium condensed in the condenser 23 is expanded by passing through the expansion valve 24 and is sent to the cascade condenser 5. The expansion valve 24 is, for example, a pressure regulating valve.
[0078] The cascade condenser 5 functions as an evaporator that heats and evaporates the high-stage refrigerant in the high-stage refrigeration cycle 20. In the cascade condenser 5, the high-stage refrigerant expanded by the expansion valve 24 evaporates, and the evaporated high-stage refrigerant is sent to the high-stage compressor 21.
[0079] The control device 30 performs calculation processing and overall control of the device. The control device 30 includes, for example, a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) that cooperates with software to implement a specified function. The control device 30 can be composed of a hardware circuit such as a dedicated electronic circuit or a reconfigurable electronic circuit designed in a manner to implement a specified function, or it can be composed of various semiconductor integrated circuits. As various semiconductor integrated circuits, in addition to CPUs and MPUs, for example, microcomputers, digital signal processors (DSP: Digital Signal Processor), programmable gate arrays (FPGA: Field Programmable Gate Array), and application-specific integrated circuits (ASIC: Application Specific Integrated Circuit) are listed. In addition, the control device 30 can include storage devices such as random access memory (RAM: Random Access Memory) and read-only memory (ROM: Read Only Memory). Specifically, the control device 30 can be composed of an information processing device such as a desktop personal computer, a notebook personal computer, a workstation, or a tablet terminal, or a printed circuit board with equivalent functions.
[0080] The control device 30 reads the stored data and programs and performs various calculations to realize predetermined functions. The program executed by the control device 30 may be provided from the outside using a communication unit that communicates in accordance with a predetermined communication standard, or may be stored in a removable storage medium.
[0081] Reference Figure 3 The control device 30 has a receiving unit 31, a calculating unit 32, a low-level side rotation number control unit 33, and a high-level side rotation number control unit 34 as functional structures. These are realized by the cooperation of the above-mentioned hardware and software. In addition, these can be respectively understood as corresponding circuits.
[0082] The receiving portion 31 receives the low-stage side suction pressure from the first pressure sensor 15 a and receives the low-stage side discharge pressure from the second pressure sensor 15 b .
[0083] The calculation unit 32 calculates the low-stage differential pressure which is the difference between the low-stage discharge pressure and the low-stage suction pressure.
[0084] The low-side rotation speed control unit 33 is based on Figures 4 to 6 The flowchart of FIG. 1 controls the rotation speed of the low-stage motor 11b via the converter 11g. Similarly, the high-stage rotation speed control unit 34 is based on Figures 4 to 6 The flowchart controls the number of rotations of the high-stage motor 21a via the converter 21b.
[0085] Reference Figure 4 , the control device 30 is, if the operation of the two-stage refrigeration device 1 is started, the high-stage side compressor 21 is started (step S4-1), and the low-stage side compressor 11 is started (step S4-2). After that, the number of revolutions of the low-stage side motor 11b is controlled (step S4-3), and the number of revolutions of the high-stage side motor 21a is controlled (step S4-4). That is, the number of revolutions of the low-stage side motor 11b (step S4-3) and the number of revolutions of the high-stage side motor 21a (step S4-4) are not performed when the high-stage side compressor 21 and the low-stage side compressor 11 are started (i.e., when they are started), but are performed after the high-stage side compressor 21 and the low-stage side compressor 11 are started.
[0086] Reference Figure 5 , in the rotation speed control of the low-stage motor 11b ( Figure 4In step S4-3), a judgment on the low-stage side suction pressure P1 is performed (step S5-1). When the low-stage side suction pressure P1 is less than the first lower limit pressure P11 (A: step S5-1), the number of revolutions of the low-stage side motor 11b is reduced (step S5-2). Then the judgment on the low-stage side suction pressure P1 is performed again (step S5-1). In addition, when the low-stage side suction pressure P1 exceeds the first upper limit pressure P12 (B: step S5-1), the number of revolutions of the low-stage side motor 11b is increased (step S5-3). Then the judgment on the low-stage side suction pressure P1 is performed again (step S5-1). In addition, when the low-stage side suction pressure P1 is greater than the first lower limit pressure P1 and less than the first upper limit pressure P12 (C: step S5-1), the number of revolutions of the low-stage side motor 11b is maintained (step S5-4). Then the number of revolutions control of the low-stage side motor 11b is ended ( Figure 4 Step S4-3).
[0087] Reference Figure 6 , in the rotation speed control of the high-side motor 21a ( Figure 4 In step S4-4), a judgment on the low-stage side differential pressure P2 is performed (step S6-1). When the low-stage side differential pressure P2 is less than the second lower limit pressure P21 (A: step S6-1), the number of revolutions of the high-stage side motor 21a is reduced (step S6-2). Then the judgment on the low-stage side differential pressure P2 is performed again (step S6-1). In addition, when the low-stage side differential pressure P2 exceeds the second upper limit pressure P22 (B: step S6-1), the number of revolutions of the high-stage side motor 21a is increased (step S6-3). Then the judgment on the low-stage side differential pressure P2 is performed again (step S6-1). In addition, when the low-stage side differential pressure P2 is greater than the second lower limit pressure P21 and less than the second upper limit pressure P22 (C: step S6-1), the number of revolutions of the high-stage side motor 21a is maintained (step S6-4). Then the number of revolutions control of the high-stage side motor 21a is ended ( Figure 4 Step S4-4).
[0088] According to the two-stage refrigeration device 1 of the present embodiment, the low-stage side suction pressure P1 can be adjusted to between the first lower limit pressure P11 and the first upper limit pressure P12, so the cooling amount in the low-stage side refrigeration cycle 10 can be adjusted to a suitable range. In addition, the low-stage side differential pressure P2 can be adjusted to between the second lower limit pressure P21 and the second upper limit pressure P22, so the pressure load on the bearing 11d can be adjusted, and the long life of the bearing 11d can be ensured. If the number of revolutions of the low-stage side motor 11b is increased, the cooling amount in the low-stage side refrigeration cycle 10 increases, and the cooling temperature decreases. Thus, in the low-stage side refrigeration cycle 10, the evaporation temperature decreases, so the evaporation pressure (i.e., the low-stage side suction pressure P1) decreases. On the contrary, if the number of revolutions of the low-stage side motor 11b is reduced, the evaporation pressure (i.e., the low-stage side suction pressure P1) increases. In this way, the low-stage side suction pressure P1 is adjustable. In addition, if the number of revolutions of the high-stage side motor 21a is increased, the cooling amount in the high-stage side refrigeration cycle 20 increases, and the cooling temperature decreases. As a result, the evaporation temperature in the high-level refrigeration cycle 20 is reduced, and the condensation temperature in the low-level refrigeration cycle 10 thermally connected by the cascade condenser 5 is reduced. Therefore, the condensation pressure in the low-level refrigeration cycle 10 (i.e., the low-level discharge pressure) is reduced. On the contrary, if the number of revolutions of the high-level motor 21a is reduced, the condensation pressure in the low-level refrigeration cycle 10 (i.e., the low-level discharge pressure) rises. In this way, the low-level discharge pressure is adjustable. Thus, the low-level differential pressure P2 that affects the bearing can be adjusted to a suitable range. In addition, the GWP (global warming potential) of CO2 used as the low-level cooling medium is 1, and it is environmentally friendly. In addition, the low-level compressor 11 is a screw type, so when CO2 solidifies (dry ice) due to low temperature, it can also be crushed by the screw rotor 11a, so it has less adverse effects than other rotary types such as the scroll type.
[0089] In addition, R1234yf used as the high-pressure side coolant has a GWP of 1 and is excellent in environmental friendliness.
[0090] Preferably, the difference between the second upper limit pressure P21 and the second lower limit pressure P22 is less than 0.4MPa. For example, the second lower limit pressure P21 is 0.6MPa, and the second upper limit pressure P22 is 1.0MPa. If the low-stage side differential pressure is above 0.6MPa, it is above the necessary minimum load of the bearing 11d, and the bite failure of the bearing 11d can be avoided to ensure a long life. If the low-stage side differential pressure is within 1.0MPa, overload on the bearing 11d can be avoided to ensure a long life. Thus, the low-stage side differential pressure P2 can be specifically adjusted to an appropriate range, which can ensure a long life of the bearing 11d.
[0091] (Second Embodiment)
[0092] Figure 7In the two-stage refrigeration device 1 described in the second embodiment shown, the configuration of the first temperature sensor 15c, the second temperature sensor 15d, and the control device 30 is different from that of the first embodiment. Except for these parts, it is substantially the same as the first embodiment. Therefore, the description of the parts shown in the first embodiment is sometimes omitted.
[0093] In this embodiment, the low-stage refrigeration cycle 10 is provided with a first temperature sensor 15c for measuring the temperature (eg, coil temperature) of the low-stage motor 11b and a second temperature sensor 15d for measuring the temperature (eg, coil temperature) of the high-stage motor 21a.
[0094] Reference Figure 8 In this embodiment, the receiving unit 31 of the control device 30 not only receives the low-stage side suction pressure and the low-stage side discharge pressure as in the first embodiment, but also receives the temperature of the low-stage side motor 11b from the first temperature sensor 15c and the temperature of the high-stage side motor 21a from the second temperature sensor 15d.
[0095] In this embodiment, the control of the control device 30 is different from that of the first embodiment. Figure 4 is the same as the first embodiment, but Figure 5 , 6 The flowcharts are replaced by Fig. 9 , 10 Flowchart of the process.
[0096] Reference Fig. 9 , in the rotation speed control of the low-stage motor 11b ( Figure 4In step S4-3), a judgment on the low-stage side suction pressure P1 is performed (step S9-1). When the low-stage side suction pressure P1 is less than the first lower limit pressure P11 (A: step S9-1), the number of revolutions of the low-stage side motor 11b is reduced (step S9-2). Then, the judgment on the low-stage side suction pressure P1 is performed again (step S9-1). In addition, when the low-stage side suction pressure P1 exceeds the first upper limit pressure P12 (B: step S9-1), a judgment on the temperature of the low-stage side motor 11b is performed (step S9-3). When the temperature of the low-stage side motor 11b is below the upper limit value (Y: step S9-3), the number of revolutions of the low-stage side motor 11b is increased (step S9-4), and the judgment on the low-stage side suction pressure P1 (step S9-1) is performed again. When the temperature of the low-stage side motor 11b is not below the upper limit value (N: step S9-3), the number of revolutions of the low-stage side motor 11b is reduced (step S9-2), and the judgment on the low-stage side suction pressure P1 is performed again (step S9-1). In addition, when the low-stage side suction pressure P1 is greater than the first lower limit pressure P1 and less than the first upper limit pressure P12 (C: step S9-1), the judgment on the temperature of the low-stage side motor 11b is performed (step S9-5). When the temperature of the low-stage side motor 11b is not less than the upper limit value (N: step S9-5), the number of revolutions of the low-stage side motor 11b is reduced (step S9-2), and the judgment on the low-stage side suction pressure P1 is performed again (step S9-1). When the temperature of the low-stage side motor 11b is less than the upper limit value (Y: step S9-5), the number of revolutions of the low-stage side motor 11b is maintained (step S9-6), and the number of revolutions control of the low-stage side motor 11b is terminated ( Figure 4 Step S4-3).
[0097] That is, in the present embodiment, the control device 30 stands by for increasing the rotation speed of the low-stage motor 11b until the temperature of the low-stage motor 11b becomes equal to or lower than the upper limit value, in addition to the control of the first embodiment.
[0098] Reference Fig.10 , in the rotation speed control of the high-side motor 21a ( Figure 4In step S4-4), a judgment on the low-stage side differential pressure P2 is performed (step S10-1). When the low-stage side differential pressure P2 is less than the second lower limit pressure P21 (A: step S10-1), the number of revolutions of the high-stage side motor 21a is reduced (step S10-2). Then, the judgment on the low-stage side differential pressure P2 is performed again (step S10-1). In addition, when the low-stage side differential pressure P2 exceeds the second upper limit pressure P22 (B: step S10-1), a judgment on the temperature of the high-stage side motor 21a is performed (step S10-3). When the temperature of the high-stage side motor 21a is below the upper limit value (Y: step S10-3), the number of revolutions of the high-stage side motor 21a is increased (step S10-4). Then, the judgment on the low-stage side differential pressure P2 is performed again (step S10-1). When the temperature of the high-stage side motor 21a is not below the upper limit value (N: step S10-3), the number of revolutions of the high-stage side motor 21a is reduced (step S10-2). Then, the judgment on the low-stage side differential pressure P2 is performed again (step S10-1). In addition, when the low-stage side differential pressure P2 is greater than the second lower limit pressure P21 and less than the second upper limit pressure P22 (C: step S10-1), the judgment on the temperature of the high-stage side motor 21a is performed (step S10-4). When the temperature of the high-stage side motor 21a is not below the upper limit value (N: step S10-5), the number of revolutions of the high-stage side motor 21a is reduced (step S10-2). Then, the judgment on the low-stage side differential pressure P2 is performed again (step S10-1). When the temperature of the high-stage side motor 21a is below the upper limit value (Y: step S10-5), the number of revolutions of the high-stage side motor 21a is maintained (step S10-6), and the number of revolutions control of the high-stage side motor 21a is ended ( Figure 4 Step S4-4).
[0099] That is, in this embodiment, in addition to the control of the first embodiment, the control device 30 makes the operation of increasing the rotation speed of the high-stage motor 21a standby until the temperature of the high-stage motor 21a becomes equal to or lower than the upper limit value.
[0100] The upper limit of the temperature of the low-stage motor 11b and the upper limit of the temperature of the high-stage motor 21a may be different depending on the type of motor. For example, the upper limit of the F type may be set to 155°C, the upper limit of the B type may be set to 130°C, and the upper limit of the E type may be set to 120°C.
[0101] According to the present embodiment, the temperatures of the low-stage motor 11b and the high-stage motor 21a can be suppressed to below the upper limit values, respectively. Therefore, the loads applied to the low-stage motor 11b and the high-stage motor 21a can be suppressed to below a certain level.
[0102] Various modifications are conceivable regarding the control corresponding to the temperature of the low-stage motor 11 b and the temperature of the high-stage motor 21 a described above.
[0103] Reference Figure 7 , 8 As a first modification, the first temperature sensor 15c may be changed to a first current sensor 15e for measuring the current of the low-stage motor 11b. Similarly, the second temperature sensor 15d may be changed to a second current sensor 15f for measuring the current of the high-stage motor 21a.
[0104] Reference Fig.11 , 12 , the temperature of the low-level motor 11b can be changed to the current of the low-level motor 11b (steps S11-3, S11-5). Similarly, the temperature of the high-level motor 21a can be changed to the current of the high-level motor 21a (steps S12-3, S12-5). That is, in this modification, the control device 30, in addition to the control of the first embodiment, waits for the action of increasing the number of revolutions of the low-level motor 11b until the current of the low-level motor 11b becomes below the upper limit value, and waits for the action of increasing the number of revolutions of the high-level motor 21a until the current of the high-level motor 21a becomes below the upper limit value.
[0105] The upper limit value of the current of the low-stage motor 11 b and the upper limit value of the current of the high-stage motor 21 a may be set to the rated current values prescribed for the motors.
[0106] According to the first modification, the currents of the low-stage motor 11b and the high-stage motor 21a can be suppressed to be below the upper limit value, respectively. Therefore, the loads applied to the low-stage motor 11b and the high-stage motor 21a can be suppressed to be below a certain level.
[0107] Reference Figure 7 , 8 As a second modification, the first temperature sensor 15c may be replaced by a first rotation sensor 15g for measuring the rotation of the low-stage motor 11b. Similarly, the second temperature sensor 15d may be replaced by a second rotation sensor 15h for measuring the rotation of the high-stage motor 21a.
[0108] Reference Fig.13 , 14, the temperature of the low-level motor 11b can be changed to the number of revolutions of the low-level motor 11b (steps S13-3, S13-5). Similarly, the temperature of the high-level motor 21a can be changed to the number of revolutions of the high-level motor 21a (steps S14-3, S14-5). That is, in this modification, the control device 30, in addition to the control of the first embodiment, waits for the action of increasing the number of revolutions of the low-level motor 11b until the current of the low-level motor 11b becomes below the upper limit value, and waits for the action of increasing the number of revolutions of the high-level motor 21a until the current of the high-level motor 21a becomes below the upper limit value.
[0109] The upper limit of the rotation speed of the low-stage motor 11b and the upper limit of the rotation speed of the high-stage motor 21a can be set in consideration of the allowable rotation speed of the rotating parts and bearings used in the motors. For example, the upper limit can be set to 6000 rpm.
[0110] According to the second modification, the rotation speeds of the low-stage motor 11b and the high-stage motor 21a can be suppressed to be below the upper limit value, respectively. Therefore, the loads applied to the low-stage motor and the high-stage motor can be suppressed to be below a certain level.
[0111] As described above, the specific embodiments of the present invention and its modified examples have been described, but the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications within the scope of the present invention. For example, the contents of each embodiment can be appropriately combined as one embodiment of the present invention.
[0112] This application may include the following solutions.
[0113] (Solution 1)
[0114] A two-stage refrigeration device, comprising:
[0115] A low-stage refrigeration cycle, using CO2 as a low-stage cooling medium, comprising a low-stage compressor, the low-stage compressor being a screw type and compressing the low-stage cooling medium, the low-stage compressor having a screw rotor rotatably supported by a bearing and a low-stage motor driving the screw rotor;
[0116] a high-side refrigeration cycle including a high-side compressor having a high-side motor and compressing a high-side cooling medium;
[0117] A first pressure sensor is used to measure the suction pressure of the low-stage compressor, i.e., the low-stage suction pressure;
[0118] A second pressure sensor measures the discharge pressure of the low-stage compressor, i.e., the low-stage discharge pressure;
[0119] a control device that receives the low-stage side suction pressure from the first pressure sensor and the low-stage side discharge pressure from the second pressure sensor, and calculates a low-stage side differential pressure that is a difference between the low-stage side discharge pressure and the low-stage side suction pressure,
[0120] The low-stage refrigeration cycle and the high-stage refrigeration cycle share a cascade condenser, which functions as a condenser for condensing the low-stage cooling medium in the low-stage refrigeration cycle and as an evaporator for evaporating the high-stage cooling medium in the high-stage refrigeration cycle, and performs heat exchange between the low-stage refrigeration cycle and the high-stage refrigeration cycle.
[0121] The control device is:
[0122] When the low-stage side suction pressure is less than the first lower limit pressure, the number of revolutions of the low-stage side motor is reduced; when the low-stage side suction pressure exceeds the first upper limit pressure, the number of revolutions of the low-stage side motor is increased; when the low-stage side suction pressure is greater than the first lower limit pressure and less than the first upper limit pressure, the number of revolutions of the low-stage side motor is maintained, and the following control corresponding to the low-stage side differential pressure is performed,
[0123] When the low-stage side differential pressure is less than the second lower limit pressure, the speed of the high-stage side motor is reduced; when the low-stage side differential pressure exceeds the second upper limit pressure, the speed of the high-stage side motor is increased; when the low-stage side differential pressure is above the second lower limit pressure and below the second upper limit pressure, the speed of the high-stage side motor is maintained.
[0124] (Solution 2)
[0125] According to the two-stage refrigeration device of claim 1, the difference between the second upper limit pressure and the second lower limit pressure is 0.4 MPa or less.
[0126] (Solution 3)
[0127] According to the two-stage refrigeration device described in Scheme 2,
[0128] The second lower limit pressure is 0.6 MPa,
[0129] The second upper limit pressure is 1.0 MPa.
[0130] (Solution 4)
[0131] According to any one of the two-stage refrigeration devices of Schemes 1 to 3, the high-stage side cooling medium is R1234yf.
[0132] (Scheme 5)
[0133] A two-stage refrigeration device according to any one of schemes 1 to 4,
[0134] Also available:
[0135] a first temperature sensor, for measuring the temperature of the low-stage motor;
[0136] A second temperature sensor measures the temperature of the high-side motor.
[0137] The control device is:
[0138] receiving the temperature of the low-stage motor from the first temperature sensor and receiving the temperature of the high-stage motor from the second temperature sensor,
[0139] The operation of increasing the number of revolutions of the low-stage motor is kept on standby until the temperature of the low-stage motor becomes below the upper limit value.
[0140] The operation of increasing the number of revolutions of the high-stage motor is put on standby until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
[0141] (Scheme 6)
[0142] A two-stage refrigeration device according to any one of schemes 1 to 5,
[0143] Also available:
[0144] a first current sensor, for measuring the current of the low-side motor;
[0145] A second current sensor measures the current of the high-side motor,
[0146] The control device is:
[0147] receiving a current of the low-side motor from the first current sensor and receiving a current of the high-side motor from the second current sensor,
[0148] The operation of increasing the rotation speed of the low-side motor is kept on standby until the current of the low-side motor becomes below the upper limit value.
[0149] The operation of increasing the number of revolutions of the high-stage motor is put on standby until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
[0150] (Scheme 7)
[0151] A two-stage refrigeration device according to any one of schemes 1 to 6,
[0152] Also available:
[0153] a first rotation speed sensor for measuring the rotation speed of the low-stage motor;
[0154] A second rotation sensor measures the rotation of the high-speed motor.
[0155] The control device is:
[0156] receiving the number of revolutions of the low-stage motor from the first number of revolutions sensor and receiving the number of revolutions of the high-stage motor from the second number of revolutions sensor,
[0157] The operation of increasing the rotation speed of the low-stage motor is kept on standby until the rotation speed of the low-stage motor becomes below the upper limit value.
[0158] The operation of increasing the rotation speed of the high-stage motor is put on standby until the rotation speed of the high-stage motor becomes equal to or less than an upper limit value.
[0159] The present application claims priority based on Japanese Patent Application No. 2022-090252 filed on June 2, 2022. The entire disclosure is incorporated herein by reference.
[0160] Description of Reference Numerals
[0161] 1 Secondary refrigeration unit
[0162] 5 Cascade condenser
[0163] 10 Low-side refrigeration cycle
[0164] 11 Low-side compressor
[0165] 11a Screw rotor
[0166] 11b Low-side motor
[0167] 11b1 Fixing parts
[0168] 11b2 Rotating parts
[0169] 11c Housing
[0170] 11d Bearing
[0171] 11e Connector
[0172] 11f Bearing
[0173] 11g Converter
[0174] 11h Shaft sealing device
[0175] 11i Inlet
[0176] 11j Exhaust port
[0177] 12 Oil recovery device
[0178] 13. Expansion valve
[0179] 14 Evaporator
[0180] 15a First pressure sensor
[0181] 15b Second pressure sensor
[0182] 15c First temperature sensor
[0183] 15d Second temperature sensor
[0184] 15e First current sensor
[0185] 15f Second current sensor
[0186] 15g First revolution sensor
[0187] 15h Second speed sensor
[0188] 20 High-side refrigeration cycle
[0189] 21 Advanced Side Compressor
[0190] 21a Advanced side motor
[0191] 21b Converter
[0192] 21c Inlet
[0193] 21d Exhaust port
[0194] 22 Oil recovery device
[0195] 23 Condenser
[0196] 24 Expansion valve
[0197] 30 Control device
[0198] 31 Receiving Department
[0199] 32 Computing Department
[0200] 33 Low-side rotation speed control unit
[0201] 34 Advanced side rotation control unit.
Claims
1. A two-stage refrigeration device, comprising: A low-stage refrigeration cycle, using CO2 as a low-stage cooling medium, comprising a low-stage compressor, the low-stage compressor being a screw type and compressing the low-stage cooling medium, the low-stage compressor having a screw rotor rotatably supported by a bearing and a low-stage motor driving the screw rotor; a high-side refrigeration cycle including a high-side compressor having a high-side motor and compressing a high-side cooling medium; A first pressure sensor is used to measure the suction pressure of the low-stage compressor, i.e., the low-stage suction pressure; A second pressure sensor measures the discharge pressure of the low-stage compressor, i.e., the low-stage discharge pressure; a control device that receives the low-stage side suction pressure from the first pressure sensor and the low-stage side discharge pressure from the second pressure sensor, and calculates a low-stage side differential pressure that is a difference between the low-stage side discharge pressure and the low-stage side suction pressure, The low-stage refrigeration cycle and the high-stage refrigeration cycle share a cascade condenser, which functions as a condenser for condensing the low-stage cooling medium in the low-stage refrigeration cycle and as an evaporator for evaporating the high-stage cooling medium in the high-stage refrigeration cycle, and performs heat exchange between the low-stage refrigeration cycle and the high-stage refrigeration cycle. The control device is: When the low-stage side suction pressure is less than the first lower limit pressure, the number of revolutions of the low-stage side motor is reduced; when the low-stage side suction pressure exceeds the first upper limit pressure, the number of revolutions of the low-stage side motor is increased; when the low-stage side suction pressure is greater than the first lower limit pressure and less than the first upper limit pressure, the number of revolutions of the low-stage side motor is maintained, and the following control corresponding to the low-stage side differential pressure is performed, When the low-stage side differential pressure is less than the second lower limit pressure, the speed of the high-stage side motor is reduced; when the low-stage side differential pressure exceeds the second upper limit pressure, the speed of the high-stage side motor is increased; when the low-stage side differential pressure is above the second lower limit pressure and below the second upper limit pressure, the speed of the high-stage side motor is maintained.
2. The two-stage refrigeration device according to claim 1, characterized in that: The difference between the second upper limit pressure and the second lower limit pressure is 0.4 MPa or less.
3. The two-stage refrigeration device according to claim 2, characterized in that: The second lower limit pressure is 0.6 MPa, The second upper limit pressure is 1.0 MPa.
4. The two-stage refrigeration device according to any one of claims 1 to 3, characterized in that: The high-stage side cooling medium is R1234yf.
5. The two-stage refrigeration device according to any one of claims 1 to 3, characterized in that: Also available: a first temperature sensor, for measuring the temperature of the low-stage motor; A second temperature sensor measures the temperature of the high-side motor. The control device is: receiving the temperature of the low-stage motor from the first temperature sensor and receiving the temperature of the high-stage motor from the second temperature sensor, until the temperature of the low-stage motor becomes below the upper limit value, the operation of increasing the rotation speed of the low-stage motor is put on standby, The operation of increasing the number of revolutions of the high-stage motor is put on standby until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
6. The two-stage refrigeration device according to any one of claims 1 to 3, characterized in that: Also available: a first current sensor, for measuring the current of the low-side motor; A second current sensor measures the current of the high-side motor, The control device is: receiving a current of the low-side motor from the first current sensor and receiving a current of the high-side motor from the second current sensor, until the current of the low-side motor becomes below the upper limit value, the operation of increasing the rotation speed of the low-side motor is put on standby, The operation of increasing the number of revolutions of the high-stage motor is put on standby until the temperature of the high-stage motor becomes equal to or lower than an upper limit value.
7. The two-stage refrigeration device according to any one of claims 1 to 3, characterized in that: Also available: a first rotation speed sensor for measuring the rotation speed of the low-stage motor; A second rotation sensor measures the rotation of the high-speed motor. The control device is: receiving the number of revolutions of the low-stage motor from the first number of revolutions sensor and receiving the number of revolutions of the high-stage motor from the second number of revolutions sensor, until the rotation speed of the low-stage motor becomes below the upper limit value, the operation of increasing the rotation speed of the low-stage motor is put on standby, The operation of increasing the number of revolutions of the high-stage motor is put on standby until the number of revolutions of the high-stage motor becomes equal to or less than an upper limit value.
Citation Information
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