Refrigeration equipment

Abstract

To provide a refrigerating device that can appropriately supply oil separated by oil separators to compressors depending on a situation.SOLUTION: A refrigerating device comprises: N refrigerating units each comprising a compressor, an oil separator, an oil return pipe, and a heat dissipation heat exchanger; N pressure reducing valves connected to the heat dissipation heat exchangers of the N refrigerating units respectively; and an oil return control mechanism for controlling a return destination of oil separated by the oil separators of the N refrigerating units. The oil return control mechanism comprises: an oil supply pipe connecting the oil return pipes of the N refrigerating units; and a flow control mechanism arranged in the oil supply pipe, and for controlling a state in which the oil in the oil supply pipe flows.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a refrigeration device.

Background Art

[0002] Conventionally, a configuration including a mechanism for separating oil from refrigerant compressed by a compressor and a mechanism for returning the oil separated from the refrigerant to the compressor is known (see, for example, Patent Document 1).

[0003] The configuration of Patent Document 1 includes two compressors and two oil separators respectively arranged in parallel in a refrigeration cycle, and one oil tank. Each compressor is connected to one oil separator. Each compressor is connected to the oil tank via a first oil flow pipe provided with a first solenoid valve. Each oil separator is connected to the oil tank via one return oil pipe provided with a second solenoid valve. The bottom of the oil tank is connected to each compressor via a second oil flow pipe.

[0004] During the operation of the refrigeration device, an operation of closing the first solenoid valve while opening the second solenoid valve (hereinafter referred to as "first operation") and an operation of opening the first solenoid valve while closing the second solenoid valve (hereinafter referred to as "second operation") are repeated every predetermined time. When the first operation is performed, the oil separated by each oil separator is returned to the oil tank, and then the internal pressure of the oil tank rises due to the internal pressure of the oil separator, so that it is supplied from the oil tank to each compressor. On the other hand, when the second operation is performed, since the internal pressure of the oil tank and the internal pressure of each compressor become equal, if the oil level in the compressor is higher than the oil extraction port, the oil in the compressor flows into the oil tank through the oil extraction port. By repeating such first operation and second operation, the position of the oil level in each compressor is adjusted to a predetermined position.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] In a configuration like that described in Patent Document 1, if there is a pressure difference between one compressor and one oil separator and between the other compressor and the other oil separator, a difference will occur in the amount of oil separated by each oil separator, and in some cases, almost no oil may be separated by one of the oil separators. Even in such a case, in a configuration like that described in Patent Document 1, an unnecessary first operation is performed in which oil is returned to the oil tank from the oil separator in question.

[0007] The present disclosure aims to provide a refrigeration system that can appropriately supply oil separated by an oil separator to a compressor depending on the circumstances. [Means for solving the problem]

[0008] The refrigeration apparatus of the present disclosure comprises N refrigeration units (where N is a natural number of 2 or more) each having a compressor, an oil separator, an oil return pipe for returning oil separated from the refrigerant by the oil separator to the compressor, and a heat exchanger for cooling the refrigerant from which the oil has been separated; N pressure reducing valves, one of which is connected to each of the heat exchangers for the heat dissipation of the N refrigeration units; and an oil return control mechanism for controlling the return destination of the oil separated by the oil separator of the N refrigeration units, wherein the oil return control mechanism comprises an oil replenishment pipe connecting the oil return pipes of the N refrigeration units to each other, and a flow control mechanism disposed in the oil replenishment pipe for controlling the state of oil flow in the oil replenishment pipe. [Effects of the Invention]

[0009] According to the refrigeration apparatus of this disclosure, the oil separated by the oil separator can be appropriately supplied to the compressor depending on the situation. [Brief explanation of the drawing]

[0010] [Figure 1] Block diagram showing the schematic configuration of a refrigeration system. [Figure 2] Block diagram showing the control system of a refrigeration unit. [Figure 3] Diagram illustrating the first control. [Figure 4] Diagram illustrating the first oil replenishment control. [Figure 5] Diagram illustrating the second oil replenishment control system. [Figure 6] Flowchart showing the operation of a refrigeration system [Modes for carrying out the invention]

[0011] [Embodiment] Embodiments of this disclosure will be described below.

[0012] <Configuration of the refrigeration system> First, let's explain the configuration of the refrigeration system. Figure 1 is a block diagram showing the schematic configuration of the refrigeration system. Figure 2 is a block diagram showing the control system of the refrigeration system. Figure 3 is an explanatory diagram of the first control. Figure 4 is an explanatory diagram of the first oil replenishment control. Figure 5 is an explanatory diagram of the second oil replenishment control.

[0013] The refrigeration system 1 shown in Figure 1 comprises a refrigerator 1A and a cooling unit 1B.

[0014] The refrigerator 1A comprises a first refrigeration unit 2, a second refrigeration unit 3, a first supercooling mechanism 4A, a second supercooling mechanism 4B, and an oil return control mechanism 5. In other words, the refrigeration device 1 comprises N refrigeration units (where N is a natural number greater than or equal to 2). The first refrigeration unit 2 and the second refrigeration unit 3 are arranged in parallel in the refrigeration cycle. Since the first refrigeration unit 2 and the second refrigeration unit 3 have similar configurations, the first refrigeration unit 2 will be described in detail, and the second refrigeration unit 3 will be described briefly.

[0015] The first refrigeration unit 2 comprises a first compression section 21, a first heat exchanger 22 for heat dissipation, and a first oil separator 23.

[0016] The first compression unit 21 includes a first compressor 211 and a second compressor 212. The first compressor 211 and the second compressor 212 are arranged in parallel in the refrigeration cycle. Note that the first compression unit 21 may include one or three or more compressors. When the first compression unit 21 includes three or more compressors, the three or more compressors are arranged in parallel in the refrigeration cycle. Since the first compressor 211 and the second compressor 212 have the same configuration, the first compressor 211 will be described in detail, and the second compressor 212 will be briefly described.

[0017] The first compressor 211 includes a sealed container. In the sealed container, a first low-stage suction port 211A, a first low-stage discharge port 211B, a first high-stage suction port 211C, and a first high-stage discharge port 211D are formed. The first low-stage suction port 211A is connected to a pair of evaporators 48 of the cooling unit 1B via a pipe P1. The first low-stage discharge port 211B is connected to a first intercooler 222 of the first heat exchanger 22 for heat dissipation via a pipe P2. The first high-stage suction port 211C is connected to the first intercooler 222 via a pipe P3. The first high-stage discharge port 211D is connected to a first oil separator 23 via a pipe P4. A check valve CV1 for preventing the refrigerant discharged from the first high-stage discharge port 211D from flowing back to the first high-stage discharge port 211D is arranged in the pipe P4.

[0018] Inside the sealed container of the first compressor 211, a first low-stage compression element, a first high-stage compression element, and a first motor (not shown respectively) are arranged. The first low-stage compression element and the first high-stage compression element rotate in synchronization with the rotation of the first motor.

[0019] When the first motor rotates, the first low-stage compression element boosts the pressure of the low-pressure refrigerant inhaled from the pair of evaporators 48 to the intermediate pressure through the pipe P1 and the first low-stage suction port 211A. The first low-stage compression element discharges the refrigerant whose pressure has been boosted to the intermediate pressure to the first intercooler 222 through the first low-stage discharge port 211B and the pipe P2. The first high-stage compression element boosts the pressure of the intermediate-pressure refrigerant inhaled from the first intercooler 222 to the high pressure through the first high-stage suction port 211C and the pipe P3. The first high-stage compression element discharges the refrigerant whose pressure has been boosted to the high pressure to the first oil separator 23 through the first high-stage discharge port 211D and the pipe P4. Thus, the first compressor 211 compresses the refrigerant in two stages.

[0020] The second compressor 212 includes a sealed container in which a second low-stage suction port 212A, a second low-stage discharge port 212B, a second high-stage suction port 212C, and a second high-stage discharge port 212D are formed. A pair of evaporators 48 are connected to the second low-stage suction port 212A through a pipe P5 branched from the pipe P1. The first intercooler 222 is connected to the second low-stage discharge port 212B through a pipe P6 branched from the pipe P2. The first intercooler 222 is connected to the second high-stage suction port 212C through a pipe P7 branched from the pipe P3. The second high-stage discharge port 212D is connected to the first oil separator 23 through a pipe P8 branched from the pipe P4. A check valve CV2 is arranged in the pipe P8.

[0021] Inside the sealed container of the second compressor 212, a second low-stage compression element, a second high-stage compression element, and a second motor (not shown respectively) are arranged. Similar to the first compressor 211, the second compressor 212 compresses the refrigerant in two stages by the rotation of the second low-stage compression element and the second high-stage compression element synchronously with the rotation of the second motor.

[0022] The sealed container of the first compressor 211 is equipped with a first oil quantity detection unit 211E that detects the remaining amount of oil in the sealed container. The sealed container of the second compressor 212 is equipped with a second oil quantity detection unit 212E that detects the remaining amount of oil in the sealed container. The first and second oil quantity detection units 211E and 212E are configured, for example, with oil level switches and output a signal corresponding to the detected remaining amount to the control device 6 shown in Figure 2.

[0023] The first heat exchanger 22 comprises a first heat dissipation fan 221, a first intercooler 222, and a first gas cooler 223.

[0024] The first heat dissipation fan 221 cools the first intercooler 222 and the first gas cooler 223.

[0025] The first intercooler 222 cools the intermediate-pressure refrigerant discharged from the first and second low-stage compression elements of the first and second compressors 211 and 212, and discharges it to the first and second high-stage compression elements.

[0026] The first gas cooler 223 is connected to the first oil separator 23 via piping P9. The first gas cooler 223 is connected to the first intercooler 42 of the first subcooling mechanism 4A via piping P10. The first gas cooler 223 cools the high-pressure refrigerant discharged from the first oil separator 23 and discharges it to the first intercooler 42.

[0027] A first ambient temperature sensor 224 is located near the first heat exchanger 22. The first ambient temperature sensor 224 outputs a signal corresponding to the detected ambient temperature to the control device 6.

[0028] The first oil separator 23 is connected to the respective sealed containers of the first compressor 211 and the second compressor 212 via the first oil return pipe Q1. The first oil return pipe Q1 comprises a first base pipe Q10 with one end connected to the first oil separator 23, a first branch pipe Q11 connecting the other end of the first base pipe Q10 to the sealed container of the first compressor 211, and a second branch pipe Q12 connecting the other end of the first base pipe Q10 to the sealed container of the second compressor 212. The first oil separator 23 separates and stores the oil contained in the high-pressure refrigerant discharged from the first and second high-stage compression elements of the first and second compressors 211 and 212. The first oil separator 23 returns the stored oil to the first and second compressors 211 and 212 via the first oil return pipe Q1.

[0029] A first oil valve V1 is located in the first branch pipe Q11. A second oil valve V2 is located in the second branch pipe Q12. The first oil valve V1 and the second oil valve V2 are each, for example, electrically operated valves and are opened and closed by control of the control device 6. The opening and closing of the first oil valve V1 and the second oil valve V2 controls the return destination of the oil from the first oil separator 23.

[0030] The second refrigeration unit 3 comprises a second compression section 31, a second heat exchanger 32 for heat dissipation, and a second oil separator 33.

[0031] The second compression unit 31 comprises a third compressor 311 and a fourth compressor 312.

[0032] A pair of evaporators 48 are connected to the third low-stage suction port 311A ​​of the third compressor 311 via piping P21, which is branched from piping P1. The second intercooler 322 of the second heat exchanger 32 is connected to the third low-stage discharge port 311B of the third compressor 311 via piping P22. The second intercooler 322 is connected to the third high-stage suction port 311C of the third compressor 311 via piping P23. The second oil separator 33 is connected to the third high-stage discharge port 311D of the third compressor 311 via piping P24. A check valve CV11 is located on piping P24.

[0033] Inside the sealed container of the third compressor 311 are a third low-stage compression element (not shown), a third high-stage compression element, and a third motor. Similar to the first compressor 211, the third compressor 311 compresses the refrigerant in two stages by the rotation of the third low-stage compression element and the third high-stage compression element in sync with the rotation of the third motor.

[0034] A pair of evaporators 48 are connected to the fourth low-stage suction port 312A of the fourth compressor 312 via pipe P25, which branches off from pipe P21. A second intercooler 322 is connected to the fourth low-stage discharge port 312B of the fourth compressor 312 via pipe P26, which branches off from pipe P22. A second intercooler 322 is connected to the fourth high-stage suction port 312C of the fourth compressor 312 via pipe P27, which branches off from pipe P23. A second oil separator 33 is connected to the fourth high-stage discharge port 312D of the fourth compressor 312 via pipe P28, which branches off from pipe P24. A check valve CV12 is located on pipe P28.

[0035] Inside the sealed container of the fourth compressor 312 are a fourth low-stage compression element (not shown), a fourth high-stage compression element, and a fourth motor. Similar to the third compressor 311, the fourth compressor 312 compresses the refrigerant in two stages by the rotation of the fourth low-stage compression element and the fourth high-stage compression element in sync with the rotation of the fourth motor.

[0036] A third oil level detection unit 311E is located in the sealed container of the third compressor 311. A fourth oil level detection unit 312E is located in the sealed container of the fourth compressor 312. The third and fourth oil level detection units 311E and 312E are configured, for example, with oil level switches and output signals to the control device 6 corresponding to the remaining amount of oil in the sealed containers of the third and fourth compressors 311 and 312.

[0037] The second heat exchanger 32 comprises a second heat blower 321, a second intercooler 322, and a second gas cooler 323. The second gas cooler 323 is connected to the second oil separator 33 via piping P29. The second gas cooler 323 is connected to the second intermediate cooler 45 of the second supercooling mechanism 4B via piping P30. A second ambient temperature sensor 324 is located near the second heat exchanger 32, which outputs a signal corresponding to the detection result of the ambient temperature to the control device 6.

[0038] The second oil separator 33 is connected to the respective sealed containers of the third compressor 311 and the fourth compressor 312 via a second oil return pipe Q2 having a second base pipe Q20, a third branch pipe Q21, and a fourth branch pipe Q22. The second oil separator 33 separates the oil contained in the high-pressure refrigerant discharged from the third and fourth compressors 311 and 312 from the refrigerant and returns the separated oil to the third and fourth compressors 311 and 312. The third branch pipe Q21 and the fourth branch pipe Q22 are equipped with a third oil valve V3 and a fourth oil valve V4, respectively, which are opened and closed by control of the control device 6. The third oil valve V3 and the fourth oil valve V4 are configured, for example, as electrically operated valves.

[0039] A first high-pressure sensor H1 is located in piping P10. A second high-pressure sensor H2 is located in piping P30. The first and second high-pressure sensors H1 and H2 output signals corresponding to the pressures in piping P10 and P30, respectively, to the control device 6. The pressure detected by the first high-pressure sensor H1 is approximately the same as the pressure in the first gas cooler 223 and the first oil separator 23. The pressure detected by the second high-pressure sensor H2 is approximately the same as the pressure in the second gas cooler 323 and the second oil separator 33.

[0040] The first supercooling mechanism 4A comprises a first pressure reducing valve 41, a first intercooler 42, and a first split heat exchanger 43. The second supercooling mechanism 4B comprises a second pressure reducing valve 44, a second intercooler 45, and a second split heat exchanger 46. In other words, the refrigeration system 1 is equipped with N pressure reducing valves, the same number as the refrigeration unit. Since the first pressure reducing valve 41 and the second pressure reducing valve 44, the first intercooler 42 and the second intercooler 45, and the first split heat exchanger 43 and the second split heat exchanger 46 each have similar configurations, the first pressure reducing valve 41, the first intercooler 42, and the first split heat exchanger 43 will be described in detail, while the second pressure reducing valve 44, the second intercooler 45, and the second split heat exchanger 46 will be described briefly.

[0041] The first pressure reducing valve 41 is configured, for example, by an electric valve. The first pressure reducing valve 41 is positioned on the side of the first intercooler 42 that is positioned at the location of the first high-pressure sensor H1 in the piping P10. The first pressure reducing valve 41 reduces the pressure of the high-pressure refrigerant discharged from the first gas cooler 223 and discharges it to the top of the first intercooler 42.

[0042] The lower part of the first intercooler 42 is connected to one end of the first flow path 431 of the first split heat exchanger 43 via piping P41. The upper part of the first intercooler 42 is connected to one end of the second flow path 432 of the first split heat exchanger 43 via piping P42. A first gas return electric valve V11 is located in piping P42. The first intercooler 42 cools the refrigerant that has been depressurized by the first pressure reducing valve 41. The refrigerant liquefied by cooling (liquid refrigerant) is discharged through piping P41 into the first flow path 431 of the first split heat exchanger 43. The refrigerant that has not been liquefied by cooling (gas refrigerant) is discharged through piping P42 into the second flow path 432 of the first split heat exchanger 43.

[0043] The other end of the first flow path 431 of the first split heat exchanger 43 is connected to a pair of evaporators 48 via piping P43. Piping P44, which branches off from piping P42, is connected to piping P43. A first liquid return electric valve V12 is located in piping P44. The other end of the second flow path 432 of the first split heat exchanger 43 is connected to piping P3 via piping P45.

[0044] In the first split heat exchanger 43 having this configuration, when the first liquid return electric valve V12 is open, most of the liquid refrigerant discharged from the first intercooler 42 flows into the evaporator 48 through the first flow path 431 and piping P43, while the remainder flows into the second flow path 432 through piping P44 and P42. This inflow of the remaining liquid refrigerant into the second flow path 432 causes the refrigerant passing through the first flow path 431 toward the evaporator 48 to be supercooled. The gaseous refrigerant discharged from the first intercooler 42 is returned to the first and second high-stage compression elements of the first and second compressors 211 and 212 by passing through piping P42, the second flow path 432, and piping P45, P3, and P7.

[0045] The second pressure reducing valve 44 is, for example, an electric valve and is located on the second intercooler 45 side of the location of the second high-pressure sensor H2 in the piping P30.

[0046] The lower part of the second intercooler 45 is connected to one end of the third flow path 461 of the second split heat exchanger 46 via piping P46. The upper part of the second intercooler 45 is connected to one end of the fourth flow path 462 of the second split heat exchanger 46 via piping P47, in which the second gas return electric valve V13 is located.

[0047] The other end of the third channel 461 of the second split heat exchanger 46 is connected to the evaporator 48 via pipe P48, which branches off from pipe P43. Pipe P49, which branches off from pipe P47, is connected to pipe P48. The second liquid return electric valve V14 is located in pipe P49. The other end of the fourth channel 462 of the second split heat exchanger 46 is connected to pipe P23 via pipe P50.

[0048] The second split heat exchanger 46, having this configuration, supercools the refrigerant passing through the third flow path 461 toward the evaporator 48. The gaseous refrigerant discharged from the second intercooler 45 passes through piping P47, the fourth flow path 462, and piping P50, P23, and P27, and is returned to the third and fourth high-stage compression elements of the third and fourth compressors 311 and 312.

[0049] The cooling unit 1B is located, for example, in a showcase. The cooling unit 1B comprises a pair of third pressure reducing valves 47 and a pair of evaporators 48.

[0050] From the point where piping P43 connects to piping P48, the section on the evaporator 48 side branches into two. One third pressure reducing valve 47 is located at each of these two branched sections. In addition, one evaporator 48 is connected to the end of each of these two branched sections. From the point where piping P1 connects to piping P21, the section on the evaporator 48 side branches into two. One evaporator 48 is connected to the end of each of these two branched sections.

[0051] Each third pressure reducing valve 47 is configured, for example, by an electric valve. Each third pressure reducing valve 47 reduces the pressure of the refrigerant discharged from the first and second split heat exchangers 43 and 46 and discharges it to each evaporator 48.

[0052] Each evaporator 48 generates cooling air for cooling the object to be cooled by exchanging heat between the liquid refrigerant flowing in from each third pressure reducing valve 47 and the air surrounding the evaporator 48. The refrigerant after this heat exchange passes through piping P1, P5, P21, and P25 and is returned to the first, second, third, and fourth low-stage compression elements of the first, second, third, and fourth compressors 211, 212, 311, and 312.

[0053] The oil return control mechanism 5 controls the return destination of the oil separated by the first and second oil separators 23 and 33 of the first and second refrigeration units 2 and 3.

[0054] The oil return control mechanism 5 includes an oil supply pipe 51 and a flow control mechanism 52.

[0055] The oil supply pipe 51 connects the first base pipe Q10 of the first oil return pipe Q1, which is connected to the first oil separator 23, and the second base pipe Q20 of the second oil return pipe Q2, which is connected to the second oil separator 33. The oil supply pipe 51 comprises a first oil supply base pipe 511, a second oil supply base pipe 512, a first oil supply branch pipe 513, and a second oil supply branch pipe 514. One end of the first oil supply base pipe 511 is connected to the first base pipe Q10 of the first oil return pipe Q1. The other end of the first oil supply base pipe 511 is connected to one end each of the first oil supply branch pipe 513 and the second oil supply branch pipe 514. One end of the second oil supply base pipe 512 is connected to the second base pipe Q20 of the second oil return pipe Q2. The other end of the second oil supply base pipe 512 is connected to the other ends of the first oil supply branch pipe 513 and the second oil supply branch pipe 514, respectively.

[0056] The flow control mechanism 52 is located in the oil supply pipe 51 and controls the state of oil flow in the oil supply pipe 51. The flow control mechanism 52 includes a first regulating mechanism 521 and a second regulating mechanism 522, which are arranged in parallel with the oil supply pipe 51.

[0057] The first regulating mechanism 521 is located in the first oil supply branch pipe 513. The first regulating mechanism 521 comprises a first oil supply valve 523 and a first oil supply check valve 524 arranged in series. The second regulating mechanism 522 is located in the second oil supply branch pipe 514. The second regulating mechanism 522 comprises a second oil supply valve 525 and a second oil supply check valve 526 arranged in series. The first oil supply valve 523 and the second oil supply valve 525 are each composed of, for example, solenoid valves and are opened and closed by control of the control device 6. The first oil supply check valve 524 is located on the second refrigeration unit 3 side of the first oil supply valve 523 and is positioned to prevent oil flowing from the first oil supply valve 523 toward the second refrigeration unit 3 from flowing back into the first oil supply valve 523. The second oil check valve 526 is positioned closer to the first refrigeration unit 2 than the second oil valve 525, and is positioned to prevent oil flowing from the second oil valve 525 toward the first refrigeration unit 2 from flowing back into the second oil valve 525. In other words, the first oil check valve 524 and the second oil check valve 526 are positioned to allow oil to flow in only different directions from each other.

[0058] The control device 6 shown in Figure 2 controls the operation of the entire refrigeration system 1. The control device 6 is configured to send and receive various signals between the first and second high-pressure sensors H1 and H2, the first and second ambient temperature sensors 224 and 324, the first to fourth oil valves V1 to V4, the first, second and third pressure reducing valves 41, 44 and 47, the first and second oil replenishment valves 523 and 525, and the first, second, third and fourth oil quantity detection units 211E, 212E, 311E and 312E. The control device 6 includes an oil quantity estimation unit 61 and a control unit 62.

[0059] The oil quantity estimation unit 61 determines whether the amount of oil in the first and second oil separators 23 and 33 is less than a first threshold, based on the detection results from the first, second, third, and fourth oil quantity detection units 211E, 212E, 311E, and 312E. In this way, by estimating the amount of oil in the first and second oil separators 23 and 33 using an oil quantity detection unit that is generally located in the compressor, it becomes unnecessary to provide a new configuration in the refrigeration system 1 for detecting the amount of oil in the first and second oil separators 23 and 33.

[0060] The control unit 62 controls the oil return control mechanism 5 and the first and second pressure reducing valves 41 and 44 to perform a first control, as shown in Figure 3, to circulate oil within the first refrigeration unit 2 and the second refrigeration unit 3, respectively, and a second control, to supply oil from one refrigeration unit to a predetermined refrigeration unit. The second control includes a first oil replenishment control, as shown in Figure 4, to supply oil separated by the second oil separator 33 of the second refrigeration unit 3 to the second compression unit 31 and the first compression unit 21, and a second oil replenishment control, as shown in Figure 5, to supply oil separated by the first oil separator 23 of the first refrigeration unit 2 to the first compression unit 21 of the first refrigeration unit 2 and the second compression unit 31 of the second refrigeration unit 3. The control unit 62 performs the first control when the oil amount estimation unit 61 estimates that the amount of oil in the first and second oil separators 23 and 33 is equal to or greater than a first threshold. On the other hand, the control unit 62 performs a first oil replenishment control if the oil quantity estimation unit 61 estimates that the oil quantity in the first oil separator 23 is less than a first threshold. Furthermore, the control unit 62 performs a second oil replenishment control if the oil quantity estimation unit 61 estimates that the oil quantity in the second oil separator 33 is less than a first threshold.

[0061] Here, we will explain the reason for performing the second control. When the first control is performed by driving the first and second compression units 21 and 31, the refrigerant containing oil (hereinafter sometimes referred to as "oil-containing refrigerant") may pass through the first and second oil separators 23 and 33 and return to the first and second compression units 21 and 31 via the first and second gas coolers 223 and 323, the first, second and third pressure reducing valves 41, 44 and 47, and the evaporator 48. In this case, if the amount of oil-containing refrigerant returning to the first and second compression units 21 and 31 is approximately the same, then in the first control, the amount of oil circulating in the first and second refrigeration units 2 and 3 will be approximately the same. And the amount of oil separated by the first and second oil separators 23 and 33 will be approximately the same. As a result, the amount of oil in the first and second oil separators 23 and 33 will both be above the first threshold. The first threshold is set to a value that allows the amount of oil in the first, second, third, and fourth compressors 211, 212, 311, and 312 to be equal to or greater than the second threshold by returning the oil stored in the first oil separator 23 to the first and second compressors 211 and 212, or by returning the oil stored in the second oil separator 33 to the third and fourth compressors 311 and 312.

[0062] However, in the following case, for example, the amount of oil circulating in the first and second refrigeration units 2 and 3 will be different in the first control. (1) When the amount of oil-containing refrigerant returning to the 1st, 2nd, 3rd, and 4th compressors 211, 212, 311, and 312 differs due to the way the flow is divided when the oil-containing refrigerant returns from the evaporator 48 to the 1st, 2nd, 3rd, and 4th compressors 211, 212, 311, and 312 (2) When the difference between the intermediate pressure and high pressure in the first and second refrigeration units 2 and 3 is different, causing the oil to return from the first and second oil separators 23 and 33 to the first and second compression units 21 and 31 at different rates, resulting in different rates at which oil is removed from the first and second oil separators 23 and 33. (3) When the operating frequencies of the first and second compressors 211 and 212 constituting the first compression section 21 are different from the operating frequencies of the third and fourth compressors 311 and 312 constituting the second compression section 31. In these cases, for example, the amount of oil in the first oil separator 23 falls below the first threshold, making it impossible to maintain the oil level of at least one of the first and second compressors 211 and 212 above the second threshold. A second control is performed to suppress the occurrence of such malfunctions.

[0063] The specific processing of the oil quantity estimation unit 61 and the control unit 62 will be described later.

[0064] Next, the operation of the refrigeration system 1 will be explained using Figures 3 to 6. The following examples illustrate the operation of cooling an object using refrigerant compressed in two stages by the first, second, third, and fourth compressors 211, 212, 311, and 312. Note that the operation is similar to that described below when cooling an object using refrigerant compressed in two stages by at least one compressor each constituting the first compression section 21 and the second compression section 31. Also, in Figures 3 to 5, when the figures representing the first and second oil valves 523 and 525 are filled in black, it indicates that the valves 523 and 525 are open; when they are outlined in white, it indicates that the valves 523 and 525 are closed. Figure 6 is a flowchart showing the operation of the refrigeration system.

[0065] When a user operates an operating unit (not shown) to issue a command to start the operation of the refrigeration unit 1, the control unit 62 starts the first control (step S1). When the control unit 62 starts the first control, it closes the first and second oil valves 523 and 525 of the oil return control mechanism 5, as shown in Figure 3. Then, the control unit 62 starts the operation of the first and second compression units 21 and 31. When the operation of the first and second compression units 21 and 31 starts, the refrigerant compressed in two stages by the first compression unit 21 flows into the first oil separator 23, and the refrigerant compressed in two stages by the second compression unit 31 flows into the second oil separator 33.

[0066] The oil separated from the refrigerant by the first oil separator 23 is stored in the first oil separator 23. Similarly, the oil separated from the refrigerant by the second oil separator 33 is stored in the second oil separator 33. Based on the detection results of the first and second oil quantity detection units 211E and 212E, the control unit 62 supplies oil L from the first oil separator 23 to the first and second compressors 211 and 212 so that the amount of oil L in both the first and second compressors 211 and 212 is equal to or greater than the second threshold. For example, the control unit 62 keeps the first oil valve V1 open until the amount of oil L in the first compressor 211 is equal to or greater than the second threshold, at which point it closes the first oil valve V1. At this time, the pressure inside the first oil separator 23 is higher than the pressure at the point where oil L flows into the first compressor 211. Due to this pressure difference, oil L in the first oil separator 23 is supplied to the first compressor 211. Furthermore, based on the detection results of the third and fourth oil quantity detection units 311E and 312E, the control unit 62 supplies oil L in the second oil separator 33 to the third and fourth compressors 311 and 312 so that the amount of oil L in both the third and fourth compressors 311 and 312 is equal to or greater than the second threshold.

[0067] Meanwhile, the refrigerant that has passed through the first and second oil separators 23 and 33 is depressurized by the first, second, and third pressure reducing valves 41, 44, and 47 and used to generate cooling air in the evaporator 48.

[0068] Furthermore, while performing the first control, the control unit 62 controls the first and second pressure reducing valves 41 and 44 based on the detection results from the first and second ambient temperature sensors 224 and 324 so that the pressure inside the first and second oil separators 23 and 33 becomes a target high-pressure value based on the ambient temperature. Specifically, the control unit 62 controls the first and second pressure reducing valves 41 and 44 so that the higher the ambient temperature, the higher the pressure detected by the first and second high-pressure sensors H1 and H2.

[0069] Next, the oil quantity estimation unit 61 estimates whether the amount of oil L in the first oil separator 23 is less than a first threshold (step S2). For example, if the amount of oil L in at least one of the first compressor 211 and the second compressor 212 remains below a second threshold for a predetermined period of time or longer, the oil quantity estimation unit 61 estimates that the amount of oil L in the first oil separator 23 is less than the first threshold.

[0070] For example, as shown in Figure 4, if the amount of oil L in the first oil separator 23 is estimated to be less than the first threshold because the amount of oil L in the second compressor 212 is less than the second threshold (step S2: YES), the control unit 62 starts the first oil replenishment control (step S3). When the control unit 62 starts the first oil replenishment control, it opens the second oil replenishment valve 525 of the second regulating mechanism 522. This control maintains the state in which oil L in the second oil separator 33 is supplied to the third and fourth compressors 311 and 312. Furthermore, because the pressure in the second oil separator 33 is higher than the pressure at the point in the first compression section 21 where oil L flows in, the oil L in the second oil separator 33 is supplied via the second regulating mechanism 522 to the compressor among the first compressor 211 and the second compressor 212 whose amount of oil L is less than the second threshold.

[0071] Furthermore, the control unit 62 controls the first and second pressure reducing valves 41 and 44 so that the pressure in the second oil separator 33 detected by the second high-pressure sensor H2 is higher than the pressure in the first oil separator 23 detected by the first high-pressure sensor H1. Due to this pressure difference, for example, the oil L in the second oil separator 33 can be forcibly supplied to the first compression unit 21 without having to place a discharge valve that restricts the discharge of oil L from the first oil separator 23 on the first oil separator 23 side of the connection point with the oil supply pipe 51 in the first base pipe Q10.

[0072] The control unit 62 determines, based on the detection results of the first and second oil quantity detection units 211E and 212E, whether the amount of oil L in all the compressors (first and second compressors 211 and 212) of the first compression unit 21 is equal to or greater than the second threshold (step S4). If the control unit 62 determines that the amount of oil L in all the compressors of the first compression unit 21 is not equal to or greater than the second threshold (step S4: NO), it performs the process of step S4 after a predetermined period of time has elapsed. On the other hand, if the control unit 62 determines that the amount of oil L in all the compressors of the first compression unit 21 is equal to or greater than the second threshold (step S4: YES), it closes the second oil supply valve 525 of the second regulating mechanism 522, while restarting control of the first and second pressure reducing valves 41 and 44 based on the ambient temperature detection result, thereby ending the first oil supply control (step S5) and starting the first control (step S1).

[0073] On the other hand, if the oil quantity estimation unit 61 estimates that the amount of oil L in the first oil separator 23 is not less than the first threshold (step S2: NO), it estimates whether the amount of oil L in the second oil separator 33 is less than the first threshold using the same method as in step S2 (step S6). If the oil quantity estimation unit 61 estimates that the amount of oil L in the second oil separator 33 is not less than the first threshold (step S6: NO), it estimates whether the amount of oil L in the first oil separator 23 is less than the first threshold after a predetermined period of time has elapsed (step S2).

[0074] On the other hand, for example, as shown in Figure 5, if it is estimated that the amount of oil L in the second oil separator 33 is less than the first threshold because the amount of oil L in the fourth compressor 312 is less than the second threshold (step S6: YES), the control unit 62 starts the second oil replenishment control (step S7). When the control unit 62 starts the second oil replenishment control, it opens the first oil replenishment valve 523 of the first regulating mechanism 521. With this control, the state in which oil L in the first oil separator 23 is supplied to the first and second compressors 211 and 212 is maintained by the same phenomenon as during the first oil replenishment control, and the oil L in the first oil separator 23 is supplied to the compressor among the third compressor 311 and the fourth compressor 312 whose amount of oil L is less than the second threshold. Furthermore, the control unit 62 can forcibly supply the oil L in the first oil separator 23 to the second compression unit 31 by controlling the first and second pressure reducing valves 41 and 44 so that the pressure in the first oil separator 23 becomes higher than the pressure in the second oil separator 33.

[0075] The control unit 62 determines, based on the detection results of the third and fourth oil quantity detection units 311E and 312E, whether the amount of oil L in all the compressors (third and fourth compressors 311 and 312) of the second compression unit 31 is equal to or greater than the second threshold (step S8). If the control unit 62 determines that the amount of oil L in all the compressors of the second compression unit 31 is not equal to or greater than the second threshold (step S8: NO), it performs the process of step S8 after a predetermined period of time has elapsed. On the other hand, if the control unit 62 determines that the amount of oil L in all the compressors of the second compression unit 31 is equal to or greater than the second threshold (step S8: YES), it closes the first oil supply valve 523 of the first regulating mechanism 521, while restarting the control of the first and second pressure reducing valves 41 and 44 that set the pressure in the first and second oil separators 23 and 33 to the target high pressure value, thereby ending the second oil supply control (step S9) and starting the first control (step S1). The processes described in steps S1 to S9 above are carried out until the user issues a command to terminate the operation of the refrigeration unit 1.

[0076] As explained above, the refrigeration device 1 performs a first control to circulate oil L within each refrigeration unit 2 and 3 if the amount of oil L in the first and second oil separators 23 and 33 is equal to or greater than a first threshold, that is, if the amount of oil L in all the compressors of the first and second compression units 21 and 31 can be increased to equal to or greater than a second threshold by supplying oil L circulating within each refrigeration unit 2 and 3. On the other hand, the refrigeration device 1 performs a first oil replenishment control to supply oil L from the second refrigeration unit to the first compression unit 21 of the first refrigeration unit 2 if, for example, the amount of oil L in the first oil separator 23 is less than a first threshold, that is, if the amount of oil L in all the compressors of the first compression unit 21 cannot be increased to equal to or greater than a second threshold by supplying oil L circulating within the first refrigeration unit 2. In this way, the refrigeration device 1 can appropriately supply the oil L separated by the first and second oil separators 23 and 33 to the first and second compression units 21 and 31 according to the situation.

[0077] [Modified examples of embodiments] This disclosure is not limited to the embodiments described herein, and various modifications can be made without departing from its spirit. Furthermore, the embodiments described above and the modifications shown below may be combined in any way, as long as they function properly.

[0078] For example, the first and second regulating mechanisms 521 and 522 do not necessarily have to include the first and second oil supply check valves 524 and 526. Although a flow control mechanism 52 equipped with the first and second regulating mechanisms 521 and 522 has been illustrated, the oil supply pipe 51 may be composed of only one pipe, and the flow control mechanism may be composed of a single solenoid valve or electric valve placed in that pipe. If the oil supply pipe 51 is composed of only one pipe, the flow control mechanism may be composed of a tube pump placed in that pipe, and the direction in which the oil L flows may be controlled by rotating the rotating body of the tube pump in the forward or reverse direction.

[0079] Although the configuration exemplified shows the control unit 62 switching between the first control, the first oil replenishment control, and the second oil replenishment control based on the estimation results from the oil quantity estimation unit 61, the control unit may also switch the oil return destination based on the user's operation of the operation unit for switching between the first control, the first oil replenishment control, and the second oil replenishment control. Alternatively, the user may manually switch the first and second oil replenishment valves 523 and 525 to switch the oil return destination without using the control unit.

[0080] A detection unit may be placed in each oil separator 23, 33 to detect the amount of oil L in each oil separator 23, 33, and based on the detection result from the detection unit, the oil amount estimation unit 61 may estimate whether or not the amount of oil L in each oil separator 23, 33 is less than a first threshold.

[0081] In the first oil replenishment control, the control unit 62 controlled each pressure reducing valve 41, 44 so that the pressure in the second oil separator 33 becomes higher than the pressure in the first oil separator 23. However, it may also control each pressure reducing valve 41, 44 to set the pressure in each oil separator 23, 33 to the target high pressure value, as in the first control. Similarly, in the second oil replenishment control, it may also control each pressure reducing valve 41, 44 to set the pressure in each oil separator 23, 33 to the target high pressure value.

[0082] The refrigeration system 1 may include three or more refrigeration units arranged in parallel in the refrigeration cycle. In this case, multiple oil return pipes should be provided to connect the oil return pipes of each refrigeration unit, and a flow control mechanism should be placed in each oil return pipe. [Industrial applicability]

[0083] This disclosure is applicable to refrigeration equipment. [Explanation of Symbols]

[0084] 1. Refrigeration equipment 1A Refrigeration Unit 1B Cooling Unit 2 (1st) Refrigeration Unit 3 (2nd) Refrigeration Unit 4A 1st supercooling mechanism 4B 2nd supercooling mechanism 5. Oil return control mechanism 6. Control device 21,31 First and second compression sections 22,32 1st and 2nd heat exchanger 23,33 First and second oil separators 41. First pressure reducing valve 42 First Intercooler 43. First Split Heat Exchanger 44. Second pressure reducing valve 45. Second Intercooler 46. ​​Second Split Heat Exchanger 47. Third pressure reducing valve 48 Evaporator 51 Oil bunker pipe 52 Flow control mechanism 61 Oil volume estimation unit 62 Control Unit 211, 212, 311, 312 Compressors 1, 2, 3, and 4 211A, 212A, 311A, 312A 1st, 2nd, 3rd, 4th low-stage intake ports 211B, 212B, 311B, 312B 1st, 2nd, 3rd, 4th low stage discharge port 211C, 212C, 311C, 312C 1st, 2nd, 3rd, 4th high-stage suction port 211D, 212D, 311D, 312D: 1st, 2nd, 3rd, and 4th high-stage side discharge ports 211E, 212E, 311E, 312E 1st, 2nd, 3rd, 4th oil level detection unit 221,321 1st and 2nd heat radiation blower 222,322 First and second intercoolers 223,323 First and second gas coolers 224,324 First and second ambient temperature sensors 431, 432, 461, 462 1st, 2nd, 3rd, 4th channels 511,512 1st and 2nd bunkering main pipe 513, 514 First and second oil supply branch pipes 521, 522 First and Second Regulatory Organizations 523, 525 First and second oil valves 524, 526 First and second oil supply check valves CV1, CV2, CV11, CV12 Check valves H1, H2 First and second high-voltage sensors P1,P2,P3,P4,P5,P6,P7,P8,P9,P10,P21,P22,P23,P24,P25,P26,P27,P28,P29,P30,P41,P42,P43,P44,P45,P46,P47,P48,P49,P50,Q1,Q2 plumbing Q10,Q20 1st, 2nd base pipe Q11, Q12, Q21, Q22: 1st, 2nd, 3rd, and 4th branch pipes V1, V2, V3, V4: 1st, 2nd, 3rd, and 4th oil valves V11, V13 1st and 2nd Gas Return Electric Valves V12, V14 1st and 2nd liquid return electric valves

Claims

1. N refrigeration units (N being a natural number of 2 or more) each having a compressor, an oil separator, an oil return pipe for returning the oil separated from the refrigerant by the oil separator to the compressor, and a heat dissipation heat exchanger for cooling the refrigerant from which the oil has been separated; N pressure reducing valves connected to the heat dissipation heat exchangers of the N refrigeration units, respectively; an oil return control mechanism for controlling a return destination of the oil separated by the oil separator of the N refrigeration units, The oil return control mechanism includes: an oil supply pipe connecting the oil return pipes of the N refrigeration units; a flow control mechanism disposed in the oil supply pipe and controlling the state of oil flow in the oil supply pipe; Refrigeration equipment.

2. The flow control mechanism includes a pair of restriction mechanisms arranged in parallel on the fuel oil pipe, The pair of restriction mechanisms each include a refueling valve and a refueling check valve arranged in series, The pair of bunker check valves are arranged to allow oil to flow only in directions different from each other. The refrigeration system of claim 1.

3. Further, a control unit for controlling the oil return control mechanism is provided. The control unit a first control for circulating oil in each refrigeration unit by closing all of the oil supply valves; and a second control for supplying oil from another refrigeration unit to the compressor of the specified refrigeration unit by opening the oil supply valve of the regulating mechanism that can flow oil into the specified refrigeration unit, out of the pair of regulating mechanisms of the oil supply pipe connected to the oil return pipe of the specified refrigeration unit.

3. The refrigeration system of claim 2.

4. Each refrigeration unit further includes an outside air temperature detection unit that detects an outside air temperature, The control unit When the first control is performed, the N pressure reducing valves are controlled so that the pressure in each oil separator becomes a target high pressure value based on an outside air temperature. When the second control is performed, the N pressure reducing valves are controlled so that the pressure in the oil separator of the other refrigeration unit is higher than the pressure in the oil separator of the predetermined refrigeration unit.

4. The refrigeration system of claim 3.

5. an oil amount estimating unit that estimates the amount of oil in each oil separator; The control unit When the oil amount estimation unit estimates that the amount of oil in the oil separators of all the refrigeration units is equal to or greater than a threshold, the first control is performed; When the oil amount estimation unit estimates that the amount of oil in the oil separator of the other refrigeration unit is less than the threshold value, the second control is performed.

5. The refrigeration system according to claim 3 or 4.

6. Each compressor is provided with an oil amount detector that detects the amount of oil in the compressor, the oil amount estimation unit determines whether the amount of oil in the oil separator is less than the threshold value based on the detection result of the oil amount detection unit.

6. The refrigeration system of claim 5.

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