Compression system

Abstract

To provide a compression system capable of reducing restrictions on design.SOLUTION: A compression system comprises: 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 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 provided in the first bypass pipe; and a control device that opens the first valve to make the first bypass pipe open when the first compressor and the second compressor start operating.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to compression systems. [Background technology]

[0002] Patent Document 1 discloses a multi-stage compression compressor having first and second rotary compression elements. In this compressor, the refrigerant compressed and discharged by the first rotary compression element is sucked into the second rotary compression element, compressed, and discharged to a gas cooler. Furthermore, this compressor is provided with a bypass circuit that supplies the refrigerant discharged from the first rotary element to an evaporator without reducing the pressure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-108334 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the compressor described in Patent Document 1, the intermediate pressure in the compressor increases due to the difference in the displacement between the first and second rotary compression elements at the start of operation. When the intermediate pressure increases, the high pressure on the discharge side of the second rotary compression element becomes excessively high, which requires an increase in the thickness of the piping on the high pressure side, resulting in a problem of increased design constraints.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide a compression system that can reduce design constraints. [Means for solving the problem]

[0006] In order to solve the above problems, a compression system according to the present disclosure includes 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 connecting 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 connecting pipe and the suction pipe and returns the refrigerant flowing through the connecting pipe to the suction pipe, a first valve provided in the first bypass pipe, and a control device that opens the first valve to open the first bypass pipe when the first compressor and the second compressor start operating. Effect of the Invention

[0007] The compression system of the present disclosure allows for reduced design constraints. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a compression system according to a first embodiment of the present disclosure. [Diagram 2] FIG. 2 is a functional block diagram of a control device according to the first embodiment of the present disclosure. [Diagram 3] 4 is a flow diagram showing a procedure for opening and closing a first bypass pipe according to the first embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating a case where a first bypass pipe according to the first embodiment of the present disclosure is in an open state. [Diagram 5] FIG. 4 is a diagram illustrating a case where a first bypass pipe according to the first embodiment of the present disclosure is in a closed state. [Figure 6] FIG. 4 is a schematic diagram of a compression system according to a second embodiment of the present disclosure. [Figure 7] 13 is a flow diagram showing a procedure for opening and closing a first bypass pipe, a second bypass pipe, and a third bypass pipe according to a second embodiment of the present disclosure. [Figure 8] FIG. 11 is a diagram illustrating a case where a first bypass pipe, a second bypass pipe, and a third bypass pipe are in an open state according to a second embodiment of the present disclosure. [Figure 9]FIG. 11 is a diagram illustrating a case where a first bypass pipe and a second bypass pipe are in an open state and a third bypass pipe is in a closed state according to a second embodiment of the present disclosure. [Figure 10] FIG. 11 is a diagram illustrating a case where a second bypass pipe according to a second embodiment of the present disclosure is in an open state, and a first bypass pipe and a third bypass pipe are in a closed state. [Figure 11] FIG. 11 is a diagram illustrating a case where a first bypass pipe, a second bypass pipe, and a third bypass pipe are in a closed state according to a second embodiment of the present disclosure. [Figure 12] FIG. 2 is a hardware configuration diagram according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] First Embodiment (Compression system configuration) Hereinafter, a compression system 1 according to a first embodiment of the present disclosure will be described with reference to FIGS. The compression system 1 shown in FIG. 1 is used in, for example, an air conditioner for refrigeration and freezing. The compression system 1 compresses a refrigerant, which is a gas such as carbon dioxide. The compression system 1 includes a refrigerant pipe 20 that is a pipe for distributing and circulating the refrigerant, a first compressor 30 arranged on the refrigerant pipe 20, an intercooler 2, a second compressor 40, a condenser 3, an expansion valve 4, an evaporator 5, 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. During operation of the compression system 1, the refrigerant also passes through each device in this order.

[0010] (First compressor) The first compressor 30 compresses the refrigerant in the refrigerant pipe 20. As a result, the pressure and temperature of the refrigerant after passing through the first compressor 30 are increased compared to the refrigerant before passing through. The first compressor 30 discharges the compressed refrigerant and pressure-feeds it toward the intercooler 2.

[0011] (Intercooler) The intercooler 2 cools the refrigerant discharged from the first compressor 30 .

[0012] (Second compressor) The second compressor 40 further compresses the refrigerant compressed by the first compressor 30 and cooled by the intercooler 2. As a result, the pressure and temperature of the refrigerant after passing through the second compressor 40 are further increased compared to the refrigerant before passing through. In addition, the displacement of the second compressor 40 is smaller than the displacement of the first compressor 30.

[0013] (Condenser) The condenser 3 exchanges heat between the refrigerant that has flowed into the condenser 3 and a heat medium that is supplied from the outside.

[0014] (Expansion valve) The expansion valve 4 reduces the pressure of the refrigerant passing through the expansion valve 4, thereby rapidly reducing the temperature.

[0015] (Evaporator) The evaporator 5 evaporates the refrigerant that has passed through the first compressor 30 and the second compressor 40. In this embodiment, the above-mentioned condenser 3 and expansion valve 4 are provided between the evaporator 5 and the compressor, so the refrigerant that has passed through these devices flows into the evaporator 5. The evaporator 5 exchanges heat between the refrigerant that has flowed into the evaporator 5 and a heat medium supplied from the outside. This causes the refrigerant that has flowed into the evaporator 5 to evaporate. The refrigerant that has passed through the evaporator 5 is supplied to the accumulator 6 and the sub-accumulator 7 in this order.

[0016] (accumulator) The accumulator 6 is provided between the evaporator 5 and the first compressor 30 on the refrigerant pipe 20, and is capable of temporarily storing the refrigerant.

[0017] (Sub-accumulator) The sub-accumulator 7 is provided between the accumulator 6 and the first compressor 30 on the refrigerant pipe 20, and is capable of temporarily storing the refrigerant, similar to the accumulator 6. The capacity of the sub-accumulator 7 is smaller than the capacity of the accumulator 6. The sub-accumulator 7 is disposed at a position close to the first compressor 30.

[0018] (Refrigerant piping) The refrigerant piping 20 includes a suction pipe 21 , a connecting pipe 22 , a discharge pipe 23 , an intermediate pipe 24 , and a first bypass pipe 25 .

[0019] (Suction pipe) The suction pipe 21 connects the evaporator 5 and the first compressor 30. The suction pipe 21 supplies refrigerant to the first compressor 30. The suction pipe 21 is provided with the above-mentioned accumulator 6 and sub-accumulator 7. The accumulator 6 is provided on the suction pipe 21 between the evaporator 5 and the first compressor 30, and the sub-accumulator 7 is provided on the suction pipe 21 between the accumulator 6 and the first compressor 30.

[0020] (Connecting pipe) The connecting pipe 22 connects the first compressor 30 and the second compressor 40. The connecting pipe 22 supplies the refrigerant compressed by the first compressor 30 to the second compressor 40. The connecting pipe 22 is provided with the above-mentioned intercooler 2.

[0021] (discharge pipe) 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.

[0022] (Intermediate piping) 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 intermediate pipe 24 is provided with an expansion valve 4.

[0023] (First bypass pipe) The first bypass pipe 25 connects the connecting pipe 22 and the suction pipe 21. In this embodiment, the first bypass pipe 25 connects a portion of the connecting pipe 22 between the intercooler 2 and the second compressor 40 and a portion of the suction pipe 21 between the accumulator 6 and the sub-accumulator 7. The first bypass pipe 25 returns the refrigerant flowing through the connecting pipe 22 to the suction pipe 21.

[0024] (First Valve) The first bypass pipe 25 is provided with a first valve 8 that opens and closes the first bypass pipe 25. The first valve 8 is a so-called electromagnetic valve, and is controlled by a control device 50, which will be described later.

[0025] (Sensor) The sensor 9 detects the 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 the pressure of the low-pressure refrigerant supplied to the first compressor 30, and transmits the pressure to the control device 50.

[0026] (Control device) The control device 50 controls each device constituting the compression system 1 described above. As shown in FIG. 2, the control device 50 has various functional units, such as a receiving unit 51, a pressure determining unit 52, and a valve control unit 53. The receiving unit 51 receives information including the pressure value of the low-pressure refrigerant flowing through the suction pipe 21, which is transmitted from the sensor 9. The pressure determination unit 52 determines whether the pressure detected by the sensor 9 (the pressure of the refrigerant flowing through the suction pipe 21) is equal to or lower than a threshold value. 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 open the first bypass pipe 25 when the first compressor 30 and the second compressor 40 start operating, and closes the first valve 8 to close the first bypass pipe 25 when the first compressor 30 and the second compressor 40 enter steady operation.

[0027] The time when the first compressor 30 and the second compressor 40 start operating here includes not only the moment when the first compressor 30 and the second compressor 40 start operating, but also a predetermined time before the first compressor 30 and the second compressor 40 start operating, and a predetermined time after the first compressor 30 and the second compressor 40 start operating.

[0028] (Bypass pipe opening and closing procedure) The first bypass pipe 25 is opened and closed at the start of operation of the compression system 1. The procedure for opening and closing the first bypass pipe 25 will be described with reference to the flow chart of FIG. First, before the compression system 1 starts operating, the valve control unit 53 opens the first valve 8 and opens the first bypass pipe 25 (step S10). In this state, the compression system 1 operates. Then, as shown in Fig. 4, the refrigerant flows through the refrigerant pipe 20 and starts circulating within the compression system 1. In the following, the refrigerant pipe 20 in the open state is illustrated by a solid line, and the refrigerant pipe 20 in the closed state is illustrated by a dashed line. Furthermore, the direction of refrigerant flow is illustrated by an arrow.

[0029] Since the first bypass pipe 25 is in an open state, the pressure difference between the suction pipe 21 and the connecting pipe 22 is small. Usually, immediately after starting operation, there is a risk that the pressure in the connecting pipe 22 and the discharge pipe 23 may exceed the limit pressure (design pressure), and complicated operation control is required, but in this embodiment, by opening the first bypass pipe 25, the increased pressure is reduced, and the pressure in the connecting pipe 22 and the discharge pipe 23 can be kept within the limit pressure with simple operation control.

[0030] At this time, the sensor 9 detects the pressure in the suction pipe 21, through which the low-pressure refrigerant supplied to the first compressor 30 flows, and transmits information including the pressure in the suction pipe 21 to the control device 50. The pressure detection and information transmission by the sensor 9 are performed periodically, for example, at regular time intervals. Then, the receiving unit 51 of the control device 50 receives the transmitted pressure in the suction pipe 21 (step S11).

[0031] After step S11, the pressure determination unit 52 determines whether the pressure in the suction pipe 21 is equal to or lower than a preset threshold value (step S12). If the pressure in the suction pipe 21 is not equal to or lower than the threshold value (step S12; NO), the process returns to step S11. If the pressure in the suction pipe 21 is equal to or lower than the threshold value (step S12; YES), the valve control unit 53 closes the first valve 8 and closes the first bypass pipe 25 as shown in FIG. 5 (step S13).

[0032] Here, there is a correlation between the pressure in the suction pipe 21, the pressure in the connecting pipe 22, and the pressure in the discharge pipe 23, and the higher the pressure in the suction pipe 21, the higher the pressure in the connecting pipe 22 and the discharge pipe 23. This preset threshold is a pressure value in the suction pipe 21 at which the pressure in the connecting pipe 22 and the discharge pipe 23 becomes the limit pressure. When the pressure in the suction pipe 21 is lower than this threshold (step S12; YES), the pressures in both the connecting pipe 22 and the discharge pipe 23 become equal to or lower than the limit pressure, and the compression system 1 can operate stably. In this manner, the first bypass pipe 25 is opened and closed.

[0033] (Action and effect) The compression system 1 of the present embodiment can provide the following advantageous effects.

[0034] In this embodiment, the first bypass pipe 25 connects the connecting pipe 22 and the suction pipe 21, and returns the refrigerant flowing through the connecting 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 open the first bypass pipe 25 when the first compressor 30 and the second compressor 40 start operating.

[0035] Usually, at the start of operation, the pressure in the connecting pipe 22 rises suddenly due to the difference in the displacement between the first compressor 30 and the second compressor 40, and there is a risk that the pressure in the connecting pipe 22 will exceed the limit pressure (design pressure), requiring complex operation control. In this embodiment, when the first compressor 30 and the second compressor 40 start operation, the first valve 8 is opened to open the first bypass pipe 25, so that the pressure in the connecting pipe 22 is released to the suction pipe 21. This reduces the pressure difference between the connecting pipe 22 and the suction pipe 21, and the pressure rise in the connecting pipe 22 can be reduced. In addition, by reducing the pressure in the connecting pipe 22 between the first compressor 30 and the second compressor 40, the pressure in the discharge pipe 23 on the high-pressure side of the second compressor 40 is also reduced. Therefore, it is possible to easily prevent the internal pressure of the connecting 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 connecting pipe 22 and the discharge pipe 23 to ensure pressure resistance. This reduces design constraints.

[0036] In this embodiment, the control device 50 closes the first valve 8 to close the first bypass pipe 25 when the first compressor 30 and the second compressor 40 are in steady operation.

[0037] The pressures of the first compressor 30 and the second compressor 40 become stable after a predetermined time has elapsed (steady operation). In the steady operation, the pressure in the connecting pipe 22 becomes stable at a state lower than the limit pressure, and therefore it becomes unnecessary to release the pressure in the connecting pipe 22 from the first bypass pipe 25. The control device 50 closes the first bypass pipe 25 when the first compressor 30 and the second compressor 40 enter the steady operation. This makes it possible to suppress a decrease in compression efficiency.

[0038] Second Embodiment Next, a second embodiment will be described with reference to Fig. 6 to Fig. 11. The same components as those in the above embodiment will be denoted by the same reference numerals and names, and the description will be omitted as appropriate. The components not described below are assumed to be the same as those in the above embodiment.

[0039] As shown in FIG. 6, the compression system 101 of this embodiment includes a refrigerant piping 120, a first compressor 30 arranged on the refrigerant piping 120, an intercooler 2, a second compressor 40, a condenser 3, an expansion valve 4, an evaporator 5, an accumulator 6, a sub-accumulator 7, a first valve 8, a second valve 10, a third valve 11, a sensor 9, and a control device 50.

[0040] (First compressor) The first compressor 30 includes a first casing 31 , a first compression section 32 , and a second compression section 33 .

[0041] (First casing) The first casing 31 is disposed so as to extend in the vertical direction. The first casing 31 seals the internal space. The suction pipe 21 and the connection pipe 22 are connected to the first casing 31. The refrigerant is introduced into the first casing 31 from the outside through the suction pipe 21.

[0042] (First compression section) The first compression section 32 is provided in the first casing 31 and compresses the refrigerant supplied from the suction pipe 21. The first compression section 32 in this embodiment is a so-called rotary compression section, and is disposed in an oil sump (not shown) at the lower part of the first casing 31. The first compression section 32 is provided with a discharge hole (not shown). Through this discharge hole, the refrigerant compressed in the first compression section 32 is discharged into the upper internal space of the first casing 31, which is kept at intermediate pressure.

[0043] (Second compression section) The second compression section 33 is provided in the first casing 31, and further compresses the refrigerant compressed to an intermediate pressure in the first compression section 32. The second compression section 33 in this embodiment is a so-called scroll compression section, and is disposed in an upper portion in the first casing 31. The displacement of the second compression section 33 is smaller than the displacement of the first compression section 32. The refrigerant compressed in the second compression section 33 is pumped to the connecting pipe 22 and supplied to the second compressor 40 downstream.

[0044] (Second compressor) The second compressor 40 includes a second casing 41 , a third compression section 42 , and a fourth compression section 43 .

[0045] (Second casing) The second casing 41 is disposed so as to extend in the vertical direction. The second casing 41 seals the internal space. The connecting pipe 22 and the discharge pipe 23 are connected to the second casing 41. The refrigerant is introduced into the second casing 41 from the outside through the connecting pipe 22.

[0046] (Third compression section) The third compression section 42 is provided in the second casing 41 and compresses the refrigerant supplied from the connecting pipe 22. The third compression section 42 in this embodiment is a so-called rotary compression section, and is disposed in an oil sump (not shown) at the lower part of the second casing 41. The third compression section 42 is provided with a discharge hole (not shown). Through this discharge hole, the refrigerant compressed in the third compression section 42 is discharged into the upper internal space of the casing, which is kept at intermediate pressure.

[0047] (Fourth compression section) The fourth compression section 43 is provided in the second casing 41, and further compresses the refrigerant compressed to an intermediate pressure in the third compression section 42. The fourth compression section 43 in this embodiment is a so-called scroll compression section, and is disposed in an upper portion in the second casing 41. The displacement of the fourth compression section 43 is smaller than the displacement of the third compression section 42. The refrigerant compressed in the fourth compression section 43 is pumped to the discharge pipe 23 and supplied to the condenser 3 downstream.

[0048] (Refrigerant piping) The refrigerant piping 120 of this embodiment has a suction pipe 21, a connecting pipe 22, a discharge pipe 23, an intermediate pipe 24, a first bypass pipe 25, as well as a second bypass pipe 26 and a third bypass pipe 27.

[0049] (Second bypass pipe) The second bypass pipe 26 connects the first compressor 30 and the suction pipe 21. In this embodiment, the second bypass pipe 26 connects the first casing 31 of the first compressor 30 and a portion of the suction pipe 21 between the accumulator 6 and the sub-accumulator 7. In addition, the second bypass pipe 26 is connected to the downstream side of the suction pipe 21 relative to the first bypass pipe 25. The second bypass pipe 26 returns the intermediate-pressure refrigerant compressed in the first compression section 32 in the first casing 31 to the suction pipe 21.

[0050] (Second valve) The second bypass pipe 26 is provided with a second valve 10 that opens and closes the second bypass pipe 26. The second valve 10 is a so-called electromagnetic valve, and is controlled by the controller 50, which will be described later, in the same manner as the first valve 8.

[0051] (Third bypass pipe) The third bypass pipe 27 connects the second compressor 40 and the connecting pipe 22. In this embodiment, the third bypass pipe 27 connects the second casing 41 of the second compressor 40 and a portion of the connecting pipe 22 downstream of the intercooler 2. In addition, the third bypass pipe 27 is connected to the connecting pipe 22 downstream of the first bypass pipe 25. The third bypass pipe 27 returns the intermediate-pressure refrigerant compressed in the third compression section 42 in the second casing 41 to the connecting pipe 22.

[0052] (Third valve) The third bypass pipe 27 is provided with a third valve 11 that opens and closes the third bypass pipe 27. The third valve 11 is a so-called electromagnetic valve, and is controlled by the control device 50, which will be described later, in the same manner as the first valve 8.

[0053] (Control device) The control device 50 has, for example, functional units such as a receiving unit 51, a pressure determining unit 52, and a valve control unit 53, similarly to the first embodiment. The valve control unit 53 controls the first valve 8, the second valve 10, and the third valve 11 to open and close the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27, respectively. More specifically, when the first compressor 30 and the second compressor 40 start operating, the valve control unit 53 opens the first valve 8, the second valve 10, and the third valve 11 to open the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27, and when the first compressor 30 and the second compressor 40 enter a steady operation, the valve control unit 53 closes the third valve 11, the first valve 8, and the second valve 10 to close the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in this order.

[0054] In this embodiment, similarly to the first embodiment, a sensor 9 is provided for detecting the pressure in the suction pipe 21. 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 the detection value of the sensor 9. More specifically, the valve control unit 53 closes the third valve 11 to close the third bypass pipe 27 when the pressure in the suction pipe 21 is lower than a first threshold value, closes the first valve 8 to close the first bypass pipe 25 when the pressure in the suction pipe 21 is lower than a second threshold value that is lower than the first threshold value, and closes the second valve 10 to close the second bypass pipe 26 when the pressure in the suction pipe 21 is lower than a third threshold value that is lower than the second threshold value.

[0055] (Bypass pipe opening and closing procedure) The opening and closing operations of the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are performed at the start of operation of the compression system 101. The procedure for opening and closing the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 will be described with reference to the flow of FIG. 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, and opens the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 (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 circulating in the cooling system. In the following, the refrigerant pipe 120 in the open state is illustrated by a solid line, and the refrigerant pipe 120 in the closed state is illustrated by a dashed line. Furthermore, the flow direction of the refrigerant is illustrated by an arrow.

[0056] Since the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are in the open state, the boost pressure in the connecting pipe 22 and the discharge pipe 23 is small, and the pressure in the first compressor 30 and the second compressor 40 can be kept within the limit pressure.

[0057] At this time, the sensor 9 detects the pressure in the suction pipe 21, through which the refrigerant supplied to the first compressor 30 flows, and transmits information including the pressure in the suction pipe 21 to the control device 50. The pressure detection and information transmission by the sensor 9 are performed periodically, for example, at regular time intervals. Then, the receiving unit 51 of the control device 50 receives the transmitted pressure in the suction pipe 21 (step S21).

[0058] After step S21, the pressure determination unit 52 determines whether the pressure in the suction pipe 21 is equal to or lower than a preset first threshold value (step S22). If the pressure in the suction pipe 21 is not equal to or lower than the first threshold value (step S22; NO), the process returns to step S21. If the pressure in the suction pipe 21 is equal to or lower than the first threshold value (step S22; YES), the valve control unit 53 closes the third valve 11 and closes the third bypass pipe 27 as shown in FIG. 9 (step S23).

[0059] After step S23, the receiving unit 51 of the control device 50 again receives the pressure in the suction pipe 21 transmitted from the sensor 9 (step S24).

[0060] After step S24, the pressure determination unit 52 determines whether the pressure in the suction pipe 21 is equal to or lower than a preset second threshold value (step S25). If the pressure in the suction pipe 21 is not equal to or lower than the second threshold value (step S25; NO), the process returns to step S24. If the pressure in the suction pipe 21 is equal to or lower than the second threshold value (step S25; YES), the valve control unit 53 closes the first valve 8 and closes the first bypass pipe 25 as shown in FIG. 10 (step S26).

[0061] After step S26, the receiving unit 51 of the control device 50 again receives the pressure in the suction pipe 21 transmitted from the sensor 9 (step S27).

[0062] After step S27, the pressure determination unit 52 determines whether the pressure in the suction pipe 21 is equal to or lower than a preset third threshold value (step S28). If the pressure in the suction pipe 21 is not equal to or lower than the third threshold value (step S28; NO), the process returns to step S27. If the pressure in the suction pipe 21 is equal to or lower than the third threshold value (step S28; YES), the valve control unit 53 closes the second valve 10 and closes the second bypass pipe 26 as shown in FIG. 10 (step S29).

[0063] In this manner, the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27 are opened and closed. After step S29, the compression system 101 is able to operate stably (steady operation).

[0064] (Action and effect) The compression system 101 of this embodiment can provide the following advantageous effects.

[0065] In this embodiment, the first compressor 30 includes a first casing 31, a first compression section 32, and a second compression section 33. The first casing 31 is connected to the suction pipe 21 and the connecting pipe 22. The first compression section 32 is provided in the first casing 31 and compresses the refrigerant supplied from the suction pipe 21. The second compression section 33 is provided in the first casing 31 and has a smaller displacement than the first compression section 32, and further compresses the intermediate-pressure refrigerant compressed in the first compression section 32 and sends it to the connecting pipe 22. The second compressor 40 includes a second casing 41, a third compression section 42, and a fourth compression section 43. The second casing 41 is connected to the connecting pipe 22 and the discharge pipe 23. The third compression section 42 is provided in the second casing 41 and compresses the refrigerant supplied from the connecting pipe 22. The fourth compression section 43 is provided in the second casing 41, has a smaller displacement than the third compression section 42, and further compresses the intermediate-pressure refrigerant compressed in the third compression section 42 and pumps it to the discharge pipe 23. The compression system 101 further includes a second bypass pipe 26, a second valve 10, a third bypass pipe 27, and a third valve 11. The second bypass pipe 26 returns the intermediate-pressure refrigerant compressed in the first compression section 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 in the third compression section 42 in the second casing 41 to the connecting pipe 22. The third valve 11 is provided in the third bypass pipe 27. When the first compressor 30 and the second compressor 40 start operating, the control device 50 opens the first valve 8, the second valve 10, and the third valve 11 to open the first bypass pipe 25, the second bypass pipe 26, and the third bypass pipe 27.

[0066] According to the above configuration, the compression system 101 can compress the refrigerant in four stages using the first compression section 32, the second compression section 33, the third compression section 42, and the fourth compression section 43. Furthermore, when the first compressor 30 starts operation, the second valve 10 is opened to open the second bypass pipe 26, so that the intermediate pressure in the first casing 31 is released to the suction pipe 21. This reduces the pressure difference between the low pressure side and the intermediate pressure side of the first casing 31, and suppresses an overall pressure rise in the first casing 31. Therefore, since the pressure rise on the high pressure side in the first casing 31 is suppressed, it is possible to more reliably prevent the internal pressure of the connecting pipe 22 from exceeding the limit pressure. In addition, when the second compressor 40 starts operation, the third valve 11 is opened to open the third bypass pipe 27, so that the intermediate pressure in the second casing 41 is released to the connecting pipe 22. This reduces the pressure difference between the low pressure side and the intermediate pressure side of the second casing 41, and suppresses the overall pressure increase in the second casing 41. Therefore, the pressure increase on the high pressure side in the second casing 41 is suppressed, so that the internal pressure of the discharge pipe 23 can be more reliably prevented from exceeding the limit pressure. In addition, when the second compressor 40 starts operation, the first valve 8 is opened to open the first bypass pipe 25, so that the pressure in the connecting pipe 22 is released to the suction pipe 21, and the internal pressure of the connecting pipe 22 does not exceed the limit pressure due to the intermediate pressure in the second casing 41. Therefore, according to this embodiment, the increased pressure of the refrigerant can be suppressed, thereby reducing design constraints.

[0067] In this embodiment, when the first compressor 30 and the second compressor 40 are in steady operation, the control device 50 closes the third valve 11, the first valve 8, and the second valve 10 to close the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in this order. When the first compressor 30 and the second compressor 40 are in steady operation, the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 are closed in this order, so that the bypass pipes can be closed in order from the high pressure side. This makes it possible to suppress a pressure rise in the connecting pipe 22 and the discharge pipe 23.

[0068] In this embodiment, the compression system 101 further includes a sensor 9 that detects the pressure in the suction pipe 21. The control device 50 closes the third valve 11 to close the third bypass pipe 27 when the pressure in the suction pipe 21 is lower than a first threshold value, closes the first valve 8 to close the first bypass pipe 25 when the pressure in the suction pipe 21 is lower than a second threshold value that is lower than the first threshold value, and closes the second valve 10 to close the second bypass pipe 26 when the pressure in the suction pipe 21 is lower than a third threshold value that is lower than the second threshold value.

[0069] As a result, the control device 50 switches the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 from an open state to a closed state in a stepwise manner in that order based on the pressure in the suction pipe 21, making it possible to transition to steady operation while reliably suppressing pressure increases in each bypass pipe. This further prevents the thickness of the connection pipe 22 and the discharge pipe 23 from increasing in order to ensure pressure resistance. This further alleviates design constraints.

[0070] (Hardware configuration) The control device 50 of the above-described embodiments is implemented in a computer as shown in Fig. 12. Fig. 12 is an example of a schematic block diagram showing the configuration of a computer in which the control device 50 according to each embodiment is implemented. The computer 1100 includes a processor 1110, a main memory 1120, a storage 1130, and an interface 1140.

[0071] The operation of each functional unit of the control device 50 is stored in the form of a program in the storage 1130. The processor 1110 reads the program from the storage 1130, loads it in the main memory 1120, and executes the above-mentioned processing in accordance with the program. The processor 1110 also secures a storage area in the main memory 1120 in accordance with the program.

[0072] The program may be for realizing a part of the functions to be performed by the computer 1100. For example, the program may be for realizing the functions by combining with other programs already stored in the storage 1130 or by combining with other programs implemented in other devices. The computer 1100 may also include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions to be realized by the processor 1110 may be realized by the integrated circuit.

[0073] Examples of storage 1130 include a magnetic disk, a magneto-optical disk, and a semiconductor memory. Storage 1130 may be an internal medium directly connected to the bus of computer 1100, or an external medium connected to computer 1100 via interface 1140 or a communication line. In addition, when this program is distributed to computer 1100 via a communication line, computer 1100 that receives the program may load the program in main memory 1120 and execute the above-mentioned processing. Storage 1130 may be a non-transitory tangible storage medium.

[0074] The program may be for implementing part of the above-mentioned functions. Furthermore, the program may be a so-called differential file (differential program) that implements the above-mentioned functions in combination with other programs already stored in the storage 1130.

[0075] (Other embodiments) Although the embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not depart from the gist of the present disclosure are also included.

[0076] In the above embodiment, the first compression section 32 is a rotary compression section and the second compression section 33 is a scroll compression section, but this is not limited thereto. For example, the first compression section 32 may be a scroll compression section and the second compression section 33 may be a rotary compression section. In addition, both the first compression section 32 and the second compression section 33 may be rotary compression sections. In addition, both the first compression section 32 and the second compression section 33 may be scroll compression sections.

[0077] In addition, although the third compression section 42 is a rotary compression section and the fourth compression section 43 is a scroll compression section, the present invention is not limited thereto. For example, the third compression section 42 may be a scroll compression section and the fourth compression section 43 may be a rotary compression section. Furthermore, both the third compression section 42 and the fourth compression section 43 may be rotary compression sections. Furthermore, both the third compression section 42 and the fourth compression section 43 may be scroll compression sections.

[0078] 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 low-pressure side suction pipe 21 in the above description, but the present invention is not limited to this. For example, the opening and closing of only the third bypass pipe 27 may be controlled based on the elapsed time from the start of operation, and the first bypass pipe 25 and the second bypass pipe 26 may be opened and closed based on the pressure of the low-pressure side suction pipe 21.

[0079] In addition, although the first compression section 32 and the second compression section 33 are provided in the same first casing 31, this is not limited thereto. For example, the first compression section 32 and the second compression section 33 may be provided in separate casings. Similarly, the third compression section 42 and the fourth compression section 43 may be provided in separate casings. Furthermore, the number of compression sections in compression system 101 may be other than four. For example, three or five or more compression sections may be connected in series, and a bypass pipe and a valve may be provided in the discharge pipe of each compression section except for the highest stage (most downstream side), and the return destination of each bypass pipe may be connected to the suction pipe of the respective compression section or the suction pipe 21 of compression system 101.

[0080] <Additional Notes> The compression systems 1 and 101 described in the respective embodiments can be understood, for example, as follows.

[0081] (1) A compression system 1, 101 according to a first aspect includes a 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 connecting pipe 22 that connects the first compressor 30 and the second compressor 40 and 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 connecting pipe 22 and the suction pipe 21 and returns the refrigerant flowing through the connecting pipe 22 to the suction pipe 21, a first valve 8 provided in the first bypass pipe 25, and a control device 50 that opens the first valve 8 to open the first bypass pipe 25 when the first compressor 30 and the second compressor 40 start operating.

[0082] Usually, at the start of operation, the pressure in the connecting pipe 22 rises suddenly due to the difference in the displacement between the first compressor 30 and the second compressor 40, and there is a risk that the pressure in the connecting pipe 22 will exceed the limit pressure (design pressure), requiring complex control. In this embodiment, when the first compressor 30 and the second compressor 40 start operation, the first valve 8 is opened to open the first bypass pipe 25, so that the pressure in the connecting pipe 22 is released to the suction pipe 21. This reduces the pressure difference between the connecting pipe 22 and the suction pipe 21, and the pressure rise in the connecting pipe 22 can be reduced. In addition, by reducing the pressure in the connecting pipe 22 between the first compressor 30 and the second compressor 40, the pressure in the discharge pipe 23 on the high-pressure side of the second compressor 40 is also reduced. Therefore, it is possible to easily prevent the internal pressure of the connecting pipe 22 and the discharge pipe 23 from exceeding the limit pressure (design pressure). This eliminates the need to increase the thickness of the connecting pipe 22 and the discharge pipe 23 to ensure pressure resistance.

[0083] (2) The compression system 1, 101 of the second aspect is the compression system 1, 101 of the first aspect, and the control device 50 may close the first valve 8 to close the first bypass pipe 25 when the first compressor 30 and the second compressor 40 are in steady operation.

[0084] The pressures of the first compressor 30 and the second compressor 40 become stable after a predetermined time has elapsed (steady operation). In the steady operation, the pressure in the connecting pipe 22 becomes stable at a state lower than the limit pressure, and therefore it is not necessary to release the pressure in the connecting pipe 22 from the first bypass pipe 25. The control device 50 closes the first bypass pipe 25 when the first compressor 30 and the second compressor 40 enter steady operation.

[0085] (3) A compression system 101 of a third aspect is the compression system 101 of the first aspect, wherein the first compressor 30 includes a first casing 31 to which the suction pipe 21 and the connecting pipe 22 are connected, a first compression section 32 provided in the first casing 31 and compressing the refrigerant supplied from the suction pipe 21, and a second compression section 33 provided in the first casing 31 and having a smaller displacement than the first compression section 32, and further compressing the intermediate-pressure refrigerant compressed in the first compression section 32 and pumping it to the connecting pipe 22; and the second compressor 40 includes a second casing 41 to which the connecting pipe 22 and the discharge pipe 23 are connected, a third compression section 42 provided in the second casing 41 and compressing the refrigerant supplied from the connecting pipe 22, and a second compression section 33 provided in the second casing 41 and compressing the refrigerant from the third compression section 42. the third compression section 42 further compresses the intermediate-pressure refrigerant compressed in the first compression section 32 in the first casing 31 to the suction pipe 21, a second valve 10 provided in the second bypass pipe 26, a third bypass pipe 27 returning the intermediate-pressure refrigerant compressed in the third compression section 42 in the second casing 41 to the connecting pipe 22, and a third valve 11 provided in the third bypass pipe 27, and when the first compressor 30 and the second compressor 40 start operating, the control device 50 may open 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.

[0086] According to the above configuration, the compression system 101 can compress the refrigerant in four stages using the first compression section 32, the second compression section 33, the third compression section 42, and the fourth compression section 43. Furthermore, when the first compressor 30 starts operation, the second valve 10 is opened to open the second bypass pipe 26, so that the intermediate pressure in the first casing 31 is released to the suction pipe 21. This reduces the pressure difference between the low pressure side and the intermediate pressure side of the first casing 31, and suppresses an overall pressure rise in the first casing 31. Therefore, since the pressure rise on the high pressure side in the first casing 31 is suppressed, it is possible to more reliably prevent the internal pressure of the connecting pipe 22 from exceeding the limit pressure. In addition, when the second compressor 40 starts operation, the third valve 11 is opened to open the third bypass pipe 27, so that the intermediate pressure in the second casing 41 is released to the connecting pipe 22. This reduces the pressure difference between the low pressure side and the intermediate pressure side of the second casing 41, and suppresses the overall pressure increase in the second casing 41. Therefore, the pressure increase on the high pressure side in the second casing 41 is suppressed, so that the internal pressure of the discharge pipe 23 can be more reliably prevented from exceeding the limit pressure. In addition, when the second compressor 40 starts operation, the first valve 8 is opened to open the first bypass pipe 25, so that the pressure in the connecting pipe 22 is released to the suction pipe 21, and the internal pressure of the connecting pipe 22 does not exceed the limit pressure due to the intermediate pressure in the second casing 41.

[0087] (4) The compression system 101 of a fourth aspect is the compression system 101 of the third aspect, and the control device 50 may close the third valve 11, the first valve 8, and the second valve 10 when the first compressor 30 and the second compressor 40 are in steady operation, to close the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 in this order.

[0088] When the first compressor 30 and the second compressor 40 are in steady operation, the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 are closed in this order, so that the bypass pipes can be closed in order from the high pressure side. This makes it possible to suppress a pressure rise in the connecting pipe 22 and the discharge pipe 23.

[0089] (5) A fifth aspect of the compression system 101 is the compression system 101 of the fourth aspect, further including a sensor 9 for detecting the pressure in the suction pipe 21, and the control device 50 may close the third valve 11 to close the third bypass pipe 27 when the pressure in the suction pipe 21 is lower than a first threshold value, close the first valve 8 to close the first bypass pipe 25 when the pressure in the suction pipe 21 is lower than a second threshold value that is lower than the first threshold value, and close the second valve 10 to close the second bypass pipe 26 when the pressure in the suction pipe 21 is lower than a third threshold value that is lower than the second threshold value.

[0090] As a result, the control device 50 gradually switches the third bypass pipe 27, the first bypass pipe 25, and the second bypass pipe 26 from an open state to a closed state in that order based on the pressure in the suction pipe 21, making it possible to transition to steady operation while reliably suppressing pressure increases in each bypass pipe. [Explanation of symbols]

[0091] REFERENCE SIGNS LIST 1... compression system 2... intercooler 3... condenser 4... expansion valve 5... evaporator 6... accumulator 7... sub-accumulator 8... first valve 9... sensor 20... refrigerant piping 21... suction pipe 22... connecting pipe 23... discharge pipe 24... intermediate pipe 25... first bypass pipe 30... first compressor 40... second compressor 50... control device 51... receiving unit 52... pressure determination unit 53... valve control unit 101... compression system 10... second valve 11... third valve 120... refrigerant piping 26... second bypass pipe 27... third bypass pipe 31... first casing 32... first compression section 33... second compression section 41... second casing 42... third compression section 43... fourth compression section 1100... computer 1110... processor 1120... main memory 1130... storage 1140... interface

Claims

1. A first compressor; A second compressor having a smaller displacement than the first compressor; a suction pipe for supplying a refrigerant to the first compressor; a connecting pipe connecting the first compressor and the second compressor and supplying a refrigerant compressed by the first compressor to the second compressor; a discharge pipe through which the refrigerant compressed by the second compressor is discharged; a first bypass pipe connecting the connecting pipe and the suction pipe and returning the refrigerant flowing through the connecting pipe to the suction pipe; a first valve provided in the first bypass pipe; a control device that opens the first valve to open the first bypass pipe when the first compressor and the second compressor start operating; A compression system comprising:

2. The compression system according to claim 1 , wherein the control device closes the first valve to close the first bypass pipe when the first compressor and the second compressor are in steady operation.

3. The first compressor is a first casing to which the suction pipe and the connecting pipe are connected; a first compression section provided in the first casing and configured to compress a refrigerant supplied from the suction pipe; a second compression section provided in the first casing, having a smaller displacement than the first compression section, further compressing the intermediate-pressure refrigerant compressed by the first compression section and pumping the intermediate-pressure refrigerant to the connecting pipe; Equipped with The second compressor is a second casing to which the connecting pipe and the discharge pipe are connected; a third compression section provided in the second casing and configured to compress the refrigerant supplied from the connecting pipe; a fourth compression section provided in the second casing, having a smaller displacement than the third compression section, further compressing the intermediate-pressure refrigerant compressed in the third compression section and pumping the intermediate-pressure refrigerant to the discharge pipe; Equipped with a second bypass pipe for returning the intermediate-pressure refrigerant compressed in the first compression section in the first casing to the suction pipe; a second valve provided in the second bypass pipe; a third bypass pipe for returning the intermediate-pressure refrigerant compressed in the third compression section in the second casing to the connecting pipe; a third valve provided in the third bypass pipe; Further equipped with 2. The compression system according to claim 1, wherein the control device opens the first valve, the second valve, and the third valve to open the first bypass pipe, the second bypass pipe, and the third bypass pipe when the first compressor and the second compressor start operating.

4. 4. The compression system according to claim 3, wherein the control device closes the third valve, the first valve, and the second valve when the first compressor and the second compressor are in steady operation, to close the third bypass pipe, the first bypass pipe, and the second bypass pipe in this order.

5. A sensor for detecting the pressure of the suction pipe is further provided.

5. The compression system of claim 4, wherein the control device closes the third valve to close the third bypass pipe when the pressure in the suction pipe is lower than a first threshold value, closes the first valve to close the first bypass pipe when the pressure in the suction pipe is lower than a second threshold value that is lower than the first threshold value, and closes the second valve to close the second bypass pipe when the pressure in the suction pipe is lower than a third threshold value that is lower than the second threshold value.

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