Compression system

Abstract

A compression system according to the present disclosure comprises a first compressor, a second compressor that has a smaller amount of displacement than the first compressor, a suction pipe that supplies refrigerant to the first compressor, a connection pipe that connects the first compressor and the second compressor and supplies the refrigerant compressed by the first compressor to the second compressor, a discharge pipe that discharges the refrigerant compressed by the second compressor, a first bypass pipe that connects the connection pipe and the suction pipe and returns the refrigerant flowing through the connection pipe to the suction pipe, a first valve that is provided to the first bypass pipe, and a control device that opens the first valve to configure the first bypass pipe in an open state when the first compressor and the second compressor start an operation.

Description

Technical Field

[0001] The present disclosure relates to a compression system.

[0002] Priority is claimed on Japanese Patent Application No. 2023-113280, filed July 10, 2023, the content of which is incorporated herein by reference.Background Art

[0003] PTL 1 discloses a multistage compression type compressor comprising a first rotation compression element and a second rotation compression element. The compressor sucks a refrigerant compressed and discharged by the first rotation compression element into the second rotation compression element, compresses, and discharges the refrigerant to a gas cooler. Further, the compressor is provided with a bypass circuit that supplies the refrigerant discharged from a first rotation element to an evaporator without decompression.Citation ListPatent Literature

[0004] [PTL 1] Japanese Unexamined Patent Application Publication No. 2004-108334Summary of InventionTechnical Problem

[0005] However, in the compressor disclosed in PTL 1, an intermediate pressure in the compressor is increased due to a difference in displacement between the first rotation compression element and the second rotation compression element at a time of start of operation. When the intermediate pressure is increased, a high pressure on a discharge side of the second rotation compression element is excessively increased, and a thickness of a pipe on a high-pressure side needs to be increased, which causes a problem in that a design constraint is increased.

[0006] The present disclosure is made to solve the above-described problem, and an object of the present disclosure is to provide a compression system capable of reducing a design constraint.Solution to Problem

[0007] In order to solve the above-described problem, according to an embodiment of the present disclosure, there is provided a compression system including a first compressor, a second compressor having a smaller displacement than the first compressor, a suction pipe that supplies a refrigerant to the first compressor, a connection pipe that connects the first compressor and the second compressor and that supplies the refrigerant compressed by the first compressor to the second compressor, a discharge pipe that discharges the refrigerant compressed by the second compressor, a first bypass pipe that connects the connection pipe and the suction pipe and that returns the refrigerant flowing through the connection pipe to the suction pipe, a first valve that is provided in the first bypass pipe, and a control device that opens the first valve to put the first bypass pipe in an open state when the first compressor and the second compressor start an operation.Advantageous Effects of Invention

[0008] According to the compression system of the present disclosure, a design constraint can be reduced.Brief Description of Drawings

[0009] FIG. 1 is a schematic diagram of a compression system 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 flowchart showing an open and close procedure of a first bypass pipe according to the first embodiment of the present disclosure. FIG. 4 is a diagram showing a case in which the first bypass pipe according to the first embodiment of the present disclosure is in an open state. FIG. 5 is a diagram showing a case in which the first bypass pipe according to the first embodiment of the present disclosure is in a closed state. FIG. 6 is a schematic diagram of a compression system according to a second embodiment of the present disclosure. FIG. 7 is a flowchart showing an open and close procedure of a first bypass pipe, a second bypass pipe, and a third bypass pipe according to the second embodiment of the present disclosure. FIG. 8 is a diagram showing a case in which the first bypass pipe, the second bypass pipe, and the third bypass pipe according to the second embodiment of the present disclosure are in an open state. FIG. 9 is a diagram showing a case in which the first bypass pipe and the second bypass pipe according to the second embodiment of the present disclosure are in an open state, and the third bypass pipe according to the second embodiment of the present disclosure is in a closed state. FIG. 10 is a diagram showing a case in which the second bypass pipe according to the second embodiment of the present disclosure is in an open state, and the first bypass pipe and the third bypass pipe according to the second embodiment of the present disclosure are in a closed state. FIG. 11 is a diagram showing a case in which the first bypass pipe, the second bypass pipe, and the third bypass pipe according to the second embodiment of the present disclosure are in a closed state. FIG. 12 is a hardware configuration diagram according to the embodiment of the present disclosure. Description of Embodiments<First Embodiment>(Configuration of Compression System)

[0010] Hereinafter, a compression system 1 according to a first embodiment of the present disclosure will be described with reference to FIGS. 1 to 5.

[0011] The compression system 1 shown in FIG. 1 is used, for example, in an air conditioner for refrigeration and freezing. The compression system 1 compresses a refrigerant that is a gas, such as carbon dioxide. The compression system 1 includes a refrigerant pipe 20 that is a pipe through which a refrigerant flows and circulates, a first compressor 30 disposed on the refrigerant pipe 20, an intercooler 2, a second compressor 40, a condenser 3, an expansion valve 4, an evaporator 5 (evaporator), an accumulator 6, a sub-accumulator 7, a first valve 8, a sensor 9, and a control device 50. The first compressor 30, the intercooler 2, the second compressor 40, the condenser 3, the expansion valve 4, the evaporator 5, the accumulator 6, and the sub-accumulator 7 are arranged in this order on the refrigerant pipe 20. In addition, during operation of the compression system 1, the refrigerant also passes through each device in this order.(First Compressor)

[0012] The first compressor 30 compresses a refrigerant in the refrigerant pipe 20. As a result, a pressure and a temperature of the refrigerant after passing through the compressor 30 are increased as compared with the refrigerant before passing through the first compressor 30. The first compressor 30 discharges the compressed refrigerant and pumps the refrigerant toward the intercooler 2.(Intercooler)

[0013] The intercooler 2 cools the refrigerant discharged from the first compressor 30.(Second Compressor)

[0014] The second compressor 40 further compresses the refrigerant compressed by the first compressor 30 and cooled by the intercooler 2. As a result, a pressure and a temperature of the refrigerant after passing through the second compressor 40 are further increased as compared with the refrigerant before passing through the second compressor 40. In addition, a displacement of the second compressor 40 is smaller than a displacement of the first compressor 30.(Condenser)

[0015] The condenser 3 performs heat exchange between the refrigerant flowing into the condenser 3 and a heat medium supplied from the outside.(Expansion Valve)

[0016] The expansion valve 4 rapidly lowers a temperature by reducing the pressure of the refrigerant passing through the expansion valve 4.(Evaporator)

[0017] The evaporator 5 evaporates the refrigerant passing through the first compressor 30 and the second compressor 40. In the present embodiment, since the condenser 3 and the expansion valve 4 are provided between the evaporator 5 and the compressor, the refrigerant after passing through these devices flows into the evaporator 5. The evaporator 5 performs heat exchange between the refrigerant flowing into the evaporator 5 and the heat medium supplied from the outside. As a result, the refrigerant flowing into the evaporator 5 evaporates. The refrigerant passing through the evaporator 5 is supplied to the accumulator 6 and the sub-accumulator 7 in this order.(Accumulator)

[0018] The accumulator 6 is provided between the evaporator 5 and the first compressor 30 on the refrigerant pipe 20 and can temporarily store the refrigerant.(Sub-accumulator)

[0019] The sub-accumulator 7 is provided between the accumulator 6 and the first compressor 30 on the refrigerant pipe 20 and can temporarily store the refrigerant, in the same manner as the accumulator 6. A capacity of the sub-accumulator 7 is smaller than a capacity of the accumulator 6. The sub-accumulator 7 is disposed at a position close to the first compressor 30.(Refrigerant Pipe)

[0020] The refrigerant pipe 20 includes a suction pipe 21, a connection pipe 22, a discharge pipe 23, an intermediate pipe 24, and a first bypass pipe 25.(Suction Pipe)

[0021] The suction pipe 21 connects the evaporator 5 and the first compressor 30. The suction pipe 21 supplies the refrigerant to the first compressor 30. The suction pipe 21 is provided with the accumulator 6 and the sub-accumulator 7 described above. The accumulator 6 is provided between the evaporator 5 and the first compressor 30 on the suction pipe 21, and the sub-accumulator 7 is provided between the accumulator 6 and the first compressor 30 on the suction pipe 21.(Connection Pipe)

[0022] The connection pipe 22 connects the first compressor 30 and the second compressor 40. The connection pipe 22 supplies the refrigerant compressed by the first compressor 30 to the second compressor 40. The intercooler 2 described above is provided in the connection pipe 22.(Discharge Pipe)

[0023] The discharge pipe 23 connects the second compressor 40 and the condenser 3. The discharge pipe 23 discharges the refrigerant compressed by the second compressor 40. The refrigerant discharged from the second compressor 40 is supplied to the condenser 3 through the discharge pipe 23.(Intermediate Pipe)

[0024] The intermediate pipe 24 connects the condenser 3 and the evaporator 5. The intermediate pipe 24 sends the refrigerant condensed in the condenser 3 to the evaporator 5. The expansion valve 4 is provided in the intermediate pipe 24.(First Bypass Pipe)

[0025] The first bypass pipe 25 connects the connection pipe 22 and the suction pipe 21. In the present embodiment, the first bypass pipe 25 connects a portion between the intercooler 2 and the second compressor 40 on the connection pipe 22 and a portion between the accumulator 6 and the sub-accumulator 7 on the suction pipe 21. The first bypass pipe 25 returns the refrigerant flowing through the connection pipe 22 to the suction pipe 21.(First Valve)

[0026] The first valve 8 that opens and closes the first bypass pipe 25 is provided in the first bypass pipe 25. The first valve 8 is a so-called solenoid valve, and is controlled by a control device 50 described below.(Sensor)

[0027] The sensor 9 detects a pressure when the refrigerant is supplied to the first compressor 30. The sensor 9 is provided in the suction pipe 21. The sensor 9 detects a pressure of the low-pressure refrigerant supplied to the first compressor 30 and transmits the detected pressure to the control device 50.(Control Device)

[0028] The control device 50 controls each device constituting the compression system 1 described above.

[0029] As shown in FIG. 2, the control device 50 includes, for example, each functional unit of a reception unit 51, a pressure determination unit 52, and a valve control unit 53.

[0030] The reception unit 51 receives information including a pressure value of the low-pressure refrigerant flowing through the suction pipe 21, which is transmitted from the sensor 9.

[0031] The pressure determination unit 52 determines whether or not the pressure (pressure of the refrigerant flowing through the suction pipe 21) detected by the sensor 9 is equal to or less than a threshold value.

[0032] The valve control unit 53 controls the first valve 8 to open and close the first bypass pipe 25. More specifically, the valve control unit 53 opens the first valve 8 to put the first bypass pipe 25 in the open state when the first compressor 30 and the second compressor 40 start an operation, and closes the first valve 8 to put the first bypass pipe 25 in the closed state when the first compressor 30 and the second compressor 40 reach a steady operation.

[0033] The time when the first compressor 30 and the second compressor 40 start an operation means not only a moment when the first compressor 30 and the second compressor 40 start an operation but also a predetermined time before the first compressor 30 and the second compressor 40 start an operation and a predetermined time after the first compressor 30 and the second compressor 40 start an operation.(Open and Close Procedure of Bypass Pipe)

[0034] The first bypass pipe 25 is opened and closed at the start of operation of the compression system 1. The open and close procedure of the first bypass pipe 25 will be described with reference to the flowchart of FIG. 3.

[0035] First, before the compression system 1 is operated, the valve control unit 53 opens the first valve 8 to put the first bypass pipe 25 in the open state (step S10). In this state, the compression system 1 is operated. Then, as shown in FIG. 4, the refrigerant flows through the refrigerant pipe 20 and starts to circulate in the compression system 1. Hereinafter, the refrigerant pipe 20 in the open state is shown by a solid line, and the refrigerant pipe 20 in the closed state is shown by a broken line. Further, a direction in which the refrigerant flows is shown by an arrow.

[0036] Since the first bypass pipe 25 is in the open state, a pressure difference between the suction pipe 21 and the connection pipe 22 becomes small. Usually, immediately after the start of operation, pressures of the connection pipe 22 and the discharge pipe 23 may exceed a limit pressure (design pressure) and complicated operation control is required. However, in the present embodiment, by putting the first bypass pipe 25 in the open state, a pressure rise is reduced, and the pressures of the connection pipe 22 and the discharge pipe 23 can be limited within a limit pressure by simple operation control.

[0037] In addition, at this time, the sensor 9 detects a pressure of the suction pipe 21 through which the low-pressure refrigerant supplied to the first compressor 30 flows, and transmits information including the pressure of the suction pipe 21 to the control device 50. The pressure detection and the information transmission by the sensor 9 are performed periodically, for example, at certain time intervals. Then, the reception unit 51 of the control device 50 receives the transmitted pressure in the suction pipe 21 (step S11).

[0038] After step S 11, the pressure determination unit 52 determines whether or not the pressure of the suction pipe 21 is equal to or less than a preset threshold value (step S12). When the pressure of the suction pipe 21 is not equal to or less than the threshold value (step S12; NO), the process returns to step S11. When the pressure of the suction pipe 21 is equal to or less than the threshold value (step S12; YES), the valve control unit 53 closes the first valve 8 to put the first bypass pipe 25 in the closed state as shown in FIG. 5 (step S13).

[0039] Here, there is a correlation between the pressure of the suction pipe 21, the pressure of the connection pipe 22, and the pressure of the discharge pipe 23, and the higher the pressure of the suction pipe 21, the higher the pressures of the connection pipe 22 and the discharge pipe 23. The preset threshold value is a pressure value of the suction pipe 21 at which the pressures of the connection pipe 22 and the discharge pipe 23 reach the limit pressure. When the pressure of the suction pipe 21 is a value lower than the threshold value (step S12; YES), both the pressure of the connection pipe 22 and the pressure of the discharge pipe 23 become equal to or less than the limit pressure, and the compression system 1 can stably operate.

[0040] In this manner, the first bypass pipe 25 is opened and closed.(Operations and Effects)

[0041] The compression system 1 according to the present embodiment can exhibit the following effects.

[0042] In the present embodiment, the first bypass pipe 25 connects the connection pipe 22 and the suction pipe 21 and returns the refrigerant flowing through the connection pipe 22 to the suction pipe 21. The first valve 8 is provided in the first bypass pipe 25. The control device 50 opens the first valve 8 to put the first bypass pipe 25 in the open state when the first compressor 30 and the second compressor 40 start an operation.

[0043] Usually, at the start of operation, the pressure of the connection pipe 22 is rapidly increased due to the difference in displacement between the first compressor 30 and the second compressor 40, and the pressure of the connection pipe 22 may exceed a limit pressure (design pressure) of the connection pipe 22, which requires complicated operation control. In the present embodiment, when the first compressor 30 and the second compressor 40 start an operation, the first valve 8 is opened to put the first bypass pipe 25 in the open state, so that the pressure in the connection pipe 22 is released to the suction pipe 21. As a result, the pressure difference between the connection pipe 22 and the suction pipe 21 is reduced, and the increase in the pressure of the connection pipe 22 can be reduced. In addition, by reducing the pressure of the connection pipe 22 between the first compressor 30 and the second compressor 40, the pressure of the discharge pipe 23 on the high-pressure side of the second compressor 40 is also reduced. Therefore, it is possible to easily prevent an internal pressure of the connection pipe 22 and the discharge pipe 23 from exceeding the limit pressure (design pressure). Therefore, it is not necessary to increase the thickness of the connection pipe 22 and the discharge pipe 23 in order to ensure pressure resistance. Therefore, a design constraint can be reduced.

[0044] In the present embodiment, the control device 50 closes the first valve 8 to put the first bypass pipe 25 in the closed state when the first compressor 30 and the second compressor 40 reach a steady operation.

[0045] When a predetermined time elapses, the pressures of the first compressor 30 and the second compressor 40 are stabilized (steady operation). In the steady operation, since the pressure of the connection pipe 22 is stabilized at a state lower than the limit pressure, it is not necessary to release the pressure of the connection pipe 22 from the first bypass pipe 25. The control device 50 puts the first bypass pipe 25 in the closed state when the first compressor 30 and the second compressor 40 reach the steady operation. Therefore, the deterioration in the compression efficiency can be suppressed.<Second Embodiment>

[0046] Subsequently, a second embodiment will be described with reference to FIGS. 6 to 11. The same configurations as those in the above-described embodiment will be appropriately omitted by assigning the same names and the same reference numerals. Configurations not described below are the same as those in the above-described embodiment.

[0047] As shown in FIG. 6, a compression system 101 according to the present embodiment includes a refrigerant pipe 120, the first compressor 30 disposed on the refrigerant pipe 120, the intercooler 2, the second compressor 40, the condenser 3, the expansion valve 4, the evaporator 5, the accumulator 6, the sub-accumulator 7, the first valve 8, a second valve 10, a third valve 11, the sensor 9, and the control device 50.(First Compressor)

[0048] The first compressor 30 includes a first casing 31, a first compression portion 32, and a second compression portion 33.(First Casing)

[0049] The first casing 31 is disposed to extend in the up-down direction. The first casing 31 seals an internal space. The suction pipe 21 and the connection pipe 22 are connected to the first casing 31. The refrigerant is introduced from the outside into the first casing 31 through the suction pipe 21.(First Compression Portion)

[0050] The first compression portion 32 is provided in the first casing 31 and compresses the refrigerant supplied from the suction pipe 21. The first compression portion 32 according to the present embodiment is a so-called rotary compression portion and is disposed in an oil sump (not shown) in a lower portion of the first casing 31. A discharge hole (not shown) is provided in the first compression portion 32. The refrigerant compressed by the first compression portion 32 is discharged to an upper internal space of the first casing 31 that is set to an intermediate pressure through the discharge hole.(Second Compression Portion)

[0051] The second compression portion 33 is provided in the first casing 31 and further compresses the refrigerant compressed by the first compression portion 32 and set to the intermediate pressure. The second compression portion 33 according to the present embodiment is a so-called scroll compression portion and is disposed in an upper portion of the first casing 31. A displacement of the second compression portion 33 is smaller than a displacement of the first compression portion 32. The refrigerant compressed by the second compression portion 33 is pumped to the connection pipe 22 and is supplied to the second compressor 40 downstream.(Second Compressor)

[0052] The second compressor 40 includes a second casing 41, a third compression portion 42, and a fourth compression portion 43.(Second Casing)

[0053] The second casing 41 is disposed to extend in the up-down direction. The second casing 41 seals an internal space. The connection pipe 22 and the discharge pipe 23 are connected to the second casing 41. The refrigerant is introduced from the outside into the second casing 41 through the connection pipe 22.(Third Compression Portion)

[0054] The third compression portion 42 is provided in the second casing 41 and compresses the refrigerant supplied from the connection pipe 22. The third compression portion 42 according to the present embodiment is a so-called rotary compression portion and is disposed in an oil sump (not shown) in a lower portion of the second casing 41. A discharge hole (not shown) is provided in the third compression portion 42. The refrigerant compressed by the third compression portion 42 is discharged to an upper internal space of the casing that is set to an intermediate pressure through the discharge hole.(Fourth Compression Portion)

[0055] The fourth compression portion 43 is provided in the second casing 41 and further compresses the refrigerant compressed by the third compression portion 42 and set to the intermediate pressure. The fourth compression portion 43 according to the present embodiment is a so-called scroll compression portion and is disposed in an upper portion of the second casing 41. A displacement of the fourth compression portion 43 is smaller than a displacement of the third compression portion 42. The refrigerant compressed by the fourth compression portion 43 is pumped to the discharge pipe 23 and is supplied to the condenser 3 downstream.(Refrigerant Pipe)

[0056] The refrigerant pipe 120 according to the present embodiment includes a second bypass pipe 26 and a third bypass pipe 27, in addition to the suction pipe 21, the connection pipe 22, the discharge pipe 23, the intermediate pipe 24, and the first bypass pipe 25.(Second Bypass Pipe)

[0057] The second bypass pipe 26 connects the first compressor 30 and the suction pipe 21. In the present embodiment, the second bypass pipe 26 connects the first casing 31 of the first compressor 30 and a portion between the accumulator 6 and the sub-accumulator 7 of the suction pipe 21. In addition, the second bypass pipe 26 is connected to the suction pipe 21 on a downstream side of the first bypass pipe 25. The second bypass pipe 26 returns the intermediate-pressure refrigerant compressed by the first compression portion 32 in the first casing 31 to the suction pipe 21.(Second Valve)

[0058] The second valve 10 that opens and closes the second bypass pipe 26 is provided in the second bypass pipe 26. The second valve 10 is a so-called solenoid valve, and is controlled by the control device 50 described below, in the same manner as the first valve 8.(Third Bypass Pipe)

[0059] The third bypass pipe 27 connects the second compressor 40 and the connection pipe 22. In the present embodiment, the third bypass pipe 27 connects the second casing 41 of the second compressor 40 and a portion of the connection pipe 22 on a downstream side of the intercooler 2. In addition, the third bypass pipe 27 is connected to the connection pipe 22 on a downstream side of the first bypass pipe 25. The third bypass pipe 27 returns the intermediate-pressure refrigerant compressed by the third compression portion 42 in the second casing 41 to the connection pipe 22.(Third valve)

[0060] A third valve 11 that opens and closes the third bypass pipe 27 is provided in the third bypass pipe 27. The third valve 11 is a so-called solenoid valve, and is controlled by the control device 50 described below, in the same manner as the first valve 8.(Control Device)

[0061] The control device 50 has, for example, each functional unit of the reception unit 51, the pressure determination unit 52, and the valve control unit 53, similar to the first embodiment.

[0062] The valve control unit 53 controls the first valve 8, the second valve 10, and the third valve 11 to open and close each of the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27. More specifically, the valve control unit 53 opens the first valve 8, the second valve 10, and the third valve 11 to put the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 in the open state when the first compressor 30 and the second compressor 40 start an operation, and closes the third valve 11, the first valve 8, and the second valve 10 to put the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in the closed state in this order when the first compressor 30 and the second compressor 40 reach a steady operation.

[0063] In the present embodiment as well, the sensor 9 that detects the pressure of the suction pipe 21 is provided, as in the first embodiment. The valve control unit 53 controls the opening and closing of the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 based on a detection value of the sensor 9. More specifically, the valve control unit 53 closes the third valve 11 to put the third bypass pipe 27 in the closed state when the pressure of the suction pipe 21 is smaller than a first threshold value, closes the first valve 8 to put the first bypass pipe 25 in the closed state when the pressure of the suction pipe 21 is smaller than a second threshold value smaller than the first threshold value, and closes the second valve 10 to put the second bypass pipe 26 in the closed state when the pressure of the suction pipe 21 is smaller than a third threshold value smaller than the second threshold value.(Open and Close Procedure of Bypass Pipe)

[0064] The first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are opened and closed at the start of operation of the compression system 101. The open and close procedure of the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 will be described with reference to the flowchart of FIG. 7.

[0065] First, before the compression system 101 is operated, the valve control unit 53 controls the first valve 8, the second valve 10, and the third valve 11 to open each valve to put the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 in the open state (step S20). In this state, the compression system 101 is operated. Then, as shown in FIG. 8, the refrigerant flows through the refrigerant pipe 120 and starts to circulate in a cooling system. Hereinafter, the refrigerant pipe 120 in the open state is shown by a solid line, and the refrigerant pipe 120 in the closed state is shown by a broken line. Further, a direction in which the refrigerant flows is shown by an arrow.

[0066] Since the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are in the open state, a pressure rise in the connection pipe 22 and the discharge pipe 23 is reduced, and the pressures of the first compressor 30 and the second compressor 40 can be limited within the limit pressure.

[0067] In addition, at this time, the sensor 9 detects a pressure of the suction pipe 21 through which the refrigerant supplied to the first compressor 30 flows, and transmits information including the pressure of the suction pipe 21 to the control device 50. The pressure detection and the information transmission by the sensor 9 are performed periodically, for example, at certain time intervals. Then, the reception unit 51 of the control device 50 receives the transmitted pressure in the suction pipe 21 (step S21).

[0068] After step S21, the pressure determination unit 52 determines whether or not the pressure of the suction pipe 21 is equal to or less than the preset first threshold value (step S22). When the pressure of the suction pipe 21 is not equal to or less than the first threshold value (step S22; NO), the process returns to step S21. When the pressure of the suction pipe 21 is equal to or less than the first threshold value (step S22; YES), the valve control unit 53 closes the third valve 11 to put the third bypass pipe 27 in the closed state as shown in FIG. 9 (step S23).

[0069] After step S23, the reception unit 51 of the control device 50 receives the pressure in the suction pipe 21 transmitted from the sensor 9 again (step S24).

[0070] After step S24, the pressure determination unit 52 determines whether or not the pressure of the suction pipe 21 is equal to or less than the preset second threshold value (step S25). When the pressure of the suction pipe 21 is not equal to or less than the second threshold value (step S25; NO), the process returns to step S24. When the pressure of the suction pipe 21 is equal to or less than the second threshold value (step S25; YES), the valve control unit 53 closes the first valve 8 to put the first bypass pipe 25 in the closed state as shown in FIG. 10 (step S26).

[0071] After step S26, the reception unit 51 of the control device 50 receives the pressure in the suction pipe 21 transmitted from the sensor 9 again (step S27).

[0072] After step S27, the pressure determination unit 52 determines whether or not the pressure of the suction pipe 21 is equal to or less than the preset third threshold value (step S28). When the pressure of the suction pipe 21 is not equal to or less than the third threshold value (step S28; NO), the process returns to step S27. When the pressure of the suction pipe 21 is equal to or less than the third threshold value (step S28; YES), the valve control unit 53 closes the second valve 10 to put the second bypass pipe 26 in the closed state as shown in FIG. 10 (step S29).

[0073] In this manner, the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are opened and closed.

[0074] After step S29, the compression system 101 can be stably operated (steady operation).(Operations and Effects)

[0075] The compression system 101 according to the present embodiment can exhibit the following effects.

[0076] In the present embodiment, the first compressor 30 includes the first casing 31, the first compression portion 32, and the second compression portion 33. The suction pipe 21 and the connection pipe 22 are connected to the first casing 31. The first compression portion 32 is provided in the first casing 31 and compresses the refrigerant supplied from the suction pipe 21. The second compression portion 33 is provided in the first casing 31, has a smaller displacement than the first compression portion 32, and further compresses the intermediate-pressure refrigerant compressed by the first compression portion 32 and pumps the refrigerant to the connection pipe 22. The second compressor 40 includes the second casing 41, the third compression portion 42, and the fourth compression portion 43. The connection pipe 22 and the discharge pipe 23 are connected to the second casing 41. The third compression portion 42 is provided in the second casing 41 and compresses the refrigerant supplied from the connection pipe 22. The fourth compression portion 43 is provided in the second casing 41, has a smaller displacement than the third compression portion 42, and further compresses the intermediate-pressure refrigerant compressed by the third compression portion 42 and pumps the refrigerant to the discharge pipe 23. In addition, the compression system 101 further includes the second bypass pipe 26, the second valve 10, the third bypass pipe 27, and the third valve 11. The second bypass pipe 26 returns the intermediate-pressure refrigerant compressed by the first compression portion 32 in the first casing 31 to the suction pipe 21. The second valve 10 is provided in the second bypass pipe 26. The third bypass pipe 27 returns the intermediate-pressure refrigerant compressed by the third compression portion 42 in the second casing 41 to the connection pipe 22. The third valve 11 is provided in the third bypass pipe 27. The control device 50 opens the first valve 8, the second valve 10, and the third valve 11 to put the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 in the open state when the first compressor 30 and the second compressor 40 start an operation.

[0077] According to the above configuration, the compression system 101 can compress the refrigerant in four stages using the first compression portion 32, the second compression portion 33, the third compression portion 42, and the fourth compression portion 43.

[0078] Further, when the first compressor 30 starts an operation, the second valve 10 is opened to put the second bypass pipe 26 in the open state, so that the intermediate pressure in the first casing 31 is released to the suction pipe 21. As a result, a pressure difference between the low-pressure side and the intermediate-pressure side of the first casing 31 can be reduced, and the overall pressure increase in the first casing 31 can be suppressed. Therefore, since an increase in the pressure on the high-pressure side in the first casing 31 is suppressed, it is possible to more reliably prevent the internal pressure of the connection pipe 22 from exceeding the limit pressure.

[0079] In addition, when the second compressor 40 starts an operation, the third valve 11 is opened to put the third bypass pipe 27 in the open state, so that the intermediate pressure in the second casing 41 is released to the connection pipe 22. As a result, a pressure difference between the low-pressure side and the intermediate pressure side of the second casing 41 can be reduced, and the overall pressure increase in the second casing 41 can be suppressed. Therefore, since an increase in the pressure on the high-pressure side in the second casing 41 is suppressed, it is possible to more reliably prevent the internal pressure of the discharge pipe 23 from exceeding the limit pressure. When the second compressor 40 starts an operation, the first valve 8 is opened and the first bypass pipe 25 is put in the open state, so that the pressure of the connection pipe 22 is released to the suction pipe 21, and the internal pressure of the connection pipe 22 does not exceed the limit pressure due to the intermediate pressure in the second casing 41.

[0080] Therefore, according to the present embodiment, the design constraint can be reduced by suppressing the pressure rise in the refrigerant.

[0081] In the present embodiment, the control device 50 closes the third valve 11, the first valve 8, and the second valve 10 to put the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in the closed state in this order when the first compressor 30 and the second compressor 40 reach the steady operation.

[0082] When the first compressor 30 and the second compressor 40 reach the steady operation, the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 are put in the closed state in this order, so that each bypass pipe can be put in the closed state in order from the high-pressure side. As a result, the pressure increase of the connection pipe 22 and the discharge pipe 23 can be suppressed.

[0083] In the present embodiment, the compression system 101 further includes the sensor 9 that detects a pressure of the suction pipe 21. The control device 50 closes the third valve 11 to put the third bypass pipe 27 in the closed state when the pressure of the suction pipe 21 is smaller than the first threshold value, closes the first valve 8 to put the first bypass pipe 25 in the closed state when the pressure of the suction pipe 21 is smaller than the second threshold value smaller than the first threshold value, and closes the second valve 10 to put the second bypass pipe 26 in the closed state when the pressure of the suction pipe 21 is smaller than the third threshold value smaller than the second threshold value.

[0084] As a result, based on the pressure of the suction pipe 21, the control device 50 sequentially switches the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 from the open state to the closed state, thereby enabling transition to steady operation while reliably suppressing a pressure increase in each bypass pipe. Therefore, it is possible to further suppress an increase in the thickness of the connection pipe 22 and the discharge pipe 23 in order to ensure the pressure resistance. Therefore, the design constraint can be further reduced.(Hardware Configuration)

[0085] The control device 50 according to the above-described embodiment is mounted in a computer as shown in FIG. 12. FIG. 12 is an example of a schematic block diagram showing a configuration of a computer in which the control device 50 according to each embodiment is mounted. The computer 1100 includes a processor 1110, a main memory 1120, a storage 1130, and an interface 1140.

[0086] Then, the operations of the respective functional units of the control device 50 are stored in the storage 1130 in the form of a program. The processor 1110 reads the program from the storage 1130, develops the read program in the main memory 1120, and executes the above-described process in accordance with the program. In addition, the processor 1110 secures a storage area in the main memory 1120 according to the program.

[0087] The program may be intended to realize some of functions fulfilled by the computer 1100. For example, the program may fulfill a function in combination with another program previously stored in the storage 1130, or in combination with another program installed in 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 realized by the processor 1110 may be partially or entirely realized by the integrated circuit.

[0088] 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 develop the program in the main memory 1120 to execute the above-described process. The storage 1130 may be a non-transitory tangible storage medium.

[0089] In addition, the program may be used to partially realize the above-described functions. In addition, the program may be a so-called difference file (difference program) that realizes the above-described functions in combination with another program previously stored in the storage 1130.(Other Embodiments)

[0090] 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.

[0091] In the above-described embodiment, the first compression portion 32 is the rotary compression portion and the second compression portion 33 is the scroll compression portion, but the present disclosure is not limited to this. For example, the first compression portion 32 may be the scroll compression portion and the second compression portion 33 may be the rotary compression portion. In addition, both the first compression portion 32 and the second compression portion 33 may be the rotary compression portions. In addition, both the first compression portion 32 and the second compression portion 33 may be the scroll compression portions.

[0092] In addition, the third compression portion 42 is the rotary compression portion and the fourth compression portion 43 is the scroll compression portion, but the present disclosure is not limited to this. For example, the third compression portion 42 may be the scroll compression portion and the fourth compression portion 43 may be the rotary compression portion. In addition, both the third compression portion 42 and the fourth compression portion 43 may be the rotary compression portions. In addition, both the third compression portion 42 and the fourth compression portion 43 may be the scroll compression portions.

[0093] In addition, all of the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are opened and closed based on the pressure of the suction pipe 21 on the low-pressure side, but the present disclosure is not limited to this. For example, the third bypass pipe 27 may be controlled to be opened and closed based on the elapsed time from the start of an operation, and the first bypass pipe 25 and the second bypass pipe 26 may be controlled to be opened and closed based on the pressure of the suction pipe 21 on the low-pressure side.

[0094] In addition, the first compression portion 32 and the second compression portion 33 are provided in the same first casing 31, but the present disclosure is not limited to this. For example, the first compression portion 32 and the second compression portion 33 may be provided in separate casings. The third compression portion 42 and the fourth compression portion 43 may also be provided in separate casings.

[0095] In addition, the number of compression portions in the compression system 101 may be other than 4. For example, three or five or more compression portions may be connected in series, and a bypass pipe and a valve may be provided in each discharge pipe of each compression portion excluding the highest stage (most downstream side), and a return destination of each bypass pipe may be connected to the suction pipe of each compression portion or the suction pipe 21 of the compression system 101.<Additional Notes>

[0096] The compression system 1, 101 described in each embodiment is understood as follows, for example. (1) A compression system 1, 101 according to a first aspect includes the first compressor 30, a second compressor 40 having a smaller displacement than the first compressor 30, a suction pipe 21 that supplies a refrigerant to the first compressor 30, a connection pipe 22 that connects the first compressor 30 and the second compressor 40 and that supplies the refrigerant compressed by the first compressor 30 to the second compressor 40, a discharge pipe 23 that discharges the refrigerant compressed by the second compressor 40, a first bypass pipe 25 that connects the connection pipe 22 and the suction pipe 21 and that returns the refrigerant flowing through the connection pipe 22 to the suction pipe 21, a first valve 8 that is provided in the first bypass pipe 25, and a control device 50 that opens the first valve 8 to put the first bypass pipe 25 in an open state when the first compressor 30 and the second compressor start 40 an operation. Usually, at the start of an operation, the pressure of the connection pipe 22 is rapidly increased due to a difference in displacement between the first compressor 30 and the second compressor 40, and a pressure of the connection pipe 22 may exceed a limit pressure (design pressure) of the connection pipe 22, which requires complicated control. In the present aspect, when the first compressor 30 and the second compressor 40 start an operation, the first valve 8 is opened to put the first bypass pipe 25 in the open state, so that the pressure in the connection pipe 22 is released to the suction pipe 21. As a result, the pressure difference between the connection pipe 22 and the suction pipe 21 is reduced, and the increase in the pressure of the connection pipe 22 can be reduced. In addition, by reducing the pressure of the connection pipe 22 between the first compressor 30 and the second compressor 40, the pressure of the discharge pipe 23 on the high-pressure side of the second compressor 40 is also reduced. Therefore, it is possible to easily prevent an internal pressure of the connection pipe 22 and the discharge pipe 23 from exceeding the limit pressure (design pressure). Therefore, it is not necessary to increase the thickness of the connection pipe 22 and the discharge pipe 23 in order to ensure pressure resistance. (2) In a compression system 1, 101 according to a second aspect, in the compression system 1, 101 according to the first aspect, the control device 50 may close the first valve 8 to put the first bypass pipe 25 in a closed state when the first compressor 30 and the second compressor 40 reach a steady operation. When a predetermined time elapses, the pressures of the first compressor 30 and the second compressor 40 are stabilized (steady operation). In the steady operation, since the pressure of the connection pipe 22 is stabilized at a state lower than the limit pressure, it is not necessary to release the pressure of the connection pipe 22 from the first bypass pipe 25. The control device 50 puts the first bypass pipe 25 in the closed state when the first compressor 30 and the second compressor 40 reach the steady operation. (3) In a compression system 101 according to a third aspect in the compression system 101 according to the first aspect, the first compressor 30 includes a first casing 31 to which the suction pipe 21 and the connection pipe 22 are connected, a first compression portion 32 that is provided in the first casing 31 and that compresses the refrigerant supplied from the suction pipe 21, and a second compression portion 33 that is provided in the first casing 31, that has a smaller displacement than the first compression portion 32, that further compresses an intermediate-pressure refrigerant compressed by the first compression portion 32 and pumps the refrigerant to the connection pipe 22, the second compressor 40 includes a second casing 41 to which the connection pipe 22 and the discharge pipe 23 are connected, a third compression portion 42 that is provided in the second casing 41 and that compresses the refrigerant supplied from the connection pipe 22, and a fourth compression portion 43 that is provided in the second casing 41, that has a smaller displacement than the third compression portion 42, that further compresses an intermediate-pressure refrigerant compressed by the third compression portion 42 and pumps the refrigerant to the discharge pipe 23, the compression system 101 further includes a second bypass pipe 26 that returns the intermediate-pressure refrigerant compressed by the first compression portion 32 in the first casing 31 to the suction pipe 21, a second valve 10 that is provided in the second bypass pipe 26, a third bypass pipe 27 that returns the intermediate-pressure refrigerant compressed by the third compression portion 42 in the second casing 41 to the connection pipe 22, and a third valve 11 that is provided in the third bypass pipe 27, and the control device 50 opens the first valve 8, the second valve 10, and the third valve 11 to put the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 in an open state when the first compressor 30 and the second compressor 40 start an operation.

[0097] According to the above configuration, the compression system 101 can compress the refrigerant in four stages using the first compression portion 32, the second compression portion 33, the third compression portion 42, and the fourth compression portion 43.

[0098] Further, when the first compressor 30 starts an operation, the second valve 10 is opened to put the second bypass pipe 26 in the open state, so that the intermediate pressure in the first casing 31 is released to the suction pipe 21. As a result, a pressure difference between the low-pressure side and the intermediate-pressure side of the first casing 31 can be reduced, and the overall pressure increase in the first casing 31 can be suppressed. Therefore, since an increase in the pressure on the high-pressure side in the first casing 31 is suppressed, it is possible to more reliably prevent the internal pressure of the connection pipe 22 from exceeding the limit pressure.

[0099] In addition, when the second compressor 40 starts an operation, the third valve 11 is opened to put the third bypass pipe 27 in the open state, so that the intermediate pressure in the second casing 41 is released to the connection pipe 22. As a result, a pressure difference between the low-pressure side and the intermediate pressure side of the second casing 41 can be reduced, and the overall pressure increase in the second casing 41 can be suppressed. Therefore, since an increase in the pressure on the high-pressure side in the second casing 41 is suppressed, it is possible to more reliably prevent the internal pressure of the discharge pipe 23 from exceeding the limit pressure. When the second compressor 40 starts an operation, the first valve 8 is opened and the first bypass pipe 25 is put in the open state, so that the pressure of the connection pipe 22 is released to the suction pipe 21, and the internal pressure of the connection pipe 22 does not exceed the limit pressure due to the intermediate pressure in the second casing 41.

[0100] (4) In a compression system 101 according to a fourth aspect, in the compression system 101 according to the third aspect, the control device 50 closes the third valve 11, the first valve 8, and the second valve 10 to put the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in a closed state in this order when the first compressor 30 and the second compressor 40 reach a steady operation.

[0101] When the first compressor 30 and the second compressor 40 reach the steady operation, the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 are put in the closed state in this order, so that each bypass pipe can be put in the closed state in order from the high-pressure side. As a result, the pressure increase of the connection pipe 22 and the discharge pipe 23 can be suppressed.

[0102] (5) In a compression system 101 according to a fifth aspect, in the compression system 101 according to the fourth aspect, the compression system 101 further includes a sensor 9 that detects a pressure of the suction pipe 21, in which the control device 50 closes the third valve 11 to put the third bypass pipe 27 in a closed state when the pressure of the suction pipe 21 is smaller than a first threshold value, closes the first valve 8 to put the first bypass pipe 25 in a closed state when the pressure of the suction pipe 21 is smaller than a second threshold value smaller than the first threshold value, and closes the second valve 10 to put the second bypass pipe 26 in a closed state when the pressure of the suction pipe 21 is smaller than a third threshold value smaller than the second threshold value.

[0103] As a result, based on the pressure of the suction pipe 21, the control device 50 sequentially switches the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 from the open state to the closed state, thereby enabling transition to steady operation while reliably suppressing a pressure increase in each bypass pipe.Industrial Applicability

[0104] According to the compression system of the present disclosure, a design constraint can be reduced.Reference Signs List

[0105] 1: compression system 2: intercooler 3: condenser 4: expansion valve 5: evaporator 6: accumulator 7: sub-accumulator 8: first valve 9: sensor 20: refrigerant pipe 21: suction pipe 22: connection pipe 23: discharge pipe 24: intermediate pipe 25: first bypass pipe 30: first compressor 40: second compressor 50: control device 51: reception unit 52: pressure determination unit 53: valve control unit 101: compression system 10: second valve 11: third valve 120: refrigerant pipe 26: second bypass pipe 27: third bypass pipe 31: first casing 32: first compression portion 33: second compression portion 41: second casing 42: third compression portion 43: fourth compression portion 1100: computer 1110: processor 1120: main memory 1130: storage 1140: interface

Claims

1. A compression system comprising: a first compressor; a second compressor having a smaller displacement than the first compressor; a suction pipe that supplies a refrigerant to the first compressor; a connection pipe that connects the first compressor and the second compressor and that supplies the refrigerant compressed by the first compressor to the second compressor; a discharge pipe that discharges the refrigerant compressed by the second compressor; a first bypass pipe that connects the connection pipe and the suction pipe and that returns the refrigerant flowing through the connection pipe to the suction pipe; a first valve that is provided in the first bypass pipe; and a control device that opens the first valve to put the first bypass pipe in an open state when the first compressor and the second compressor start an operation.

2. The compression system according to Claim 1, wherein the control device closes the first valve to put the first bypass pipe in a closed state when the first compressor and the second compressor reach a steady operation.

3. The compression system according to Claim 1, wherein the first compressor includes a first casing to which the suction pipe and the connection pipe are connected, a first compression portion that is provided in the first casing and that compresses the refrigerant supplied from the suction pipe, and a second compression portion that is provided in the first casing, that has a smaller displacement than the first compression portion, that further compresses an intermediate-pressure refrigerant compressed by the first compression portion and pumps the refrigerant to the connection pipe, the second compressor includes a second casing to which the connection pipe and the discharge pipe are connected, a third compression portion that is provided in the second casing and that compresses the refrigerant supplied from the connection pipe, and a fourth compression portion that is provided in the second casing, that has a smaller displacement than the third compression portion, that further compresses an intermediate-pressure refrigerant compressed by the third compression portion and pumps the refrigerant to the discharge pipe, the compression system further comprises a second bypass pipe that returns the intermediate-pressure refrigerant compressed by the first compression portion in the first casing to the suction pipe, a second valve that is provided in the second bypass pipe, a third bypass pipe that returns the intermediate-pressure refrigerant compressed by the third compression portion in the second casing to the connection pipe, and a third valve that is provided in the third bypass pipe, and the control device opens the first valve, the second valve, and the third valve to put the first bypass pipe, the second bypass pipe, and the third bypass pipe in an open state when the first compressor and the second compressor start an operation.

4. The compression system according to Claim 3, wherein the control device closes the third valve, the first valve, and the second valve to put the third bypass pipe, the first bypass pipe, and the second bypass pipe in a closed state in this order when the first compressor and the second compressor reach a steady operation.

5. The compression system according to claim 4, further comprising: a sensor that detects a pressure of the suction pipe, wherein the control device closes the third valve to put the third bypass pipe in a closed state when the pressure of the suction pipe is smaller than a first threshold value, closes the first valve to put the first bypass pipe in a closed state when the pressure of the suction pipe is smaller than a second threshold value smaller than the first threshold value, and closes the second valve to put the second bypass pipe in a closed state when the pressure of the suction pipe is smaller than a third threshold value smaller than the second threshold value.

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