Refrigeration device and control method

Abstract

A refrigeration device according to the present disclosure comprises: N (N is an integer of 2 or more) refrigeration units; an oil replenishment pipe which connects oil return pipes of each of the N refrigeration units together; N oil replenishment valves which are disposed in the oil replenishment pipe between the oil return pipes of the refrigeration units that are adjacent to each other, and which control the flow of oil in the oil replenishment pipe; and a control unit which performs control to open all the N oil replenishment valves if it is determined that the amount of oil in an oil separator of at least any one of the N refrigeration units is less than a predetermined threshold.

Description

Technical Field

[0001] The present disclosure relates to a refrigeration apparatus and a control method thereof.Background Art

[0002] A refrigeration apparatus including a plurality of compressors and a plurality of oil separators has been known. For example, Patent Literature (hereinafter, referred to as PTL) 1 discloses a technique of combining and connecting a plurality of refrigerators that each include a compressor, an oil separator, and a condenser, and configuring a large-capacity multi-unit refrigerator. In addition, PTL 2 discloses a refrigeration apparatus that includes a plurality of compressors and a plurality of oil separators.Citation ListPatent Literature

[0003] PTL 1 Japanese Patent Application Laid-Open No. H2-217763 PTL 2 Japanese Patent Application Laid-Open No. H11-173686 Summary of InventionTechnical Problem

[0004] In the refrigeration apparatus including a plurality of oil separators, a minute pressure difference occurs between the oil separators, and the amount of oil stored in the plurality of oil separators possibly becomes uneven due to the pressure difference. In this case, the amount of oil returned from the oil separator to the compressor may become insufficient, and thus a malfunction possibly occurs in the operation of the refrigeration apparatus. Thus, improvement is desired.

[0005] An object of the present disclosure is to provide a refrigeration apparatus including a plurality of oil separators, and a method for controlling the refrigeration apparatus, each capable of adjusting the amount of oil stored in the plurality of oil separators.Solution to Problem

[0006] A refrigeration apparatus according to the present disclosure includes: refrigeration units that each include a compressor, an oil separator, and an oil return pipe for returning, to the compressor, oil separated from a refrigerant by the oil separator, the refrigeration units being N (N is an integer of 2 or more) refrigeration units; an oil replenishing pipe that connects a plurality of the oil return pipes of the N refrigeration units to each other; replenishing valves that are each disposed in the oil replenishing pipe between the oil return pipes of the refrigeration units adjacent to each other and control flow of oil in the oil replenishing pipe, the oil replenishing valves being N oil replenishing valves; and a controller that opens all of the N oil replenishing valves when an oil amount in the oil separator of at least one of the refrigeration units is determined to be less than a predetermined threshold value.

[0007] A control method according to the present disclosure is for a refrigeration apparatus that includes: refrigeration units each including: a compressor, an oil separator, and an oil return pipe for returning, to the compressor, oil separated from a refrigerant by the oil separator, the refrigeration units being N (N is an integer of 2 or more) refrigeration units; an oil replenishing pipe connecting a plurality of the oil return pipes of the N refrigeration units to each other; oil replenishing valves each disposed in the oil replenishing pipe between the oil return pipes of the refrigeration units adjacent to each other, and controlling flow of oil in the oil replenishing pipe, the oil replenishing valves being N oil replenishing valves; and a controller, and the method includes: determining whether an oil amount in the oil separator of at least one of the refrigeration units is less than a predetermined threshold value; and opening all of the N oil replenishing valves when the oil amount in the oil separator of the at least one of the refrigeration units is determined to be less than the predetermined threshold value.Advantageous Effects of Invention

[0008] According to the refrigeration apparatus according to the present disclosure, in the refrigeration apparatus including a plurality of oil separators, the amount of oil stored in the plurality of oil separators can be adjusted.Brief Description of Drawings

[0009] FIG. 1 is a diagram illustrating a schematic configuration of a refrigeration apparatus according to an embodiment of the present disclosure; FIG. 2 is a diagram illustrating a schematic configuration of a refrigeration unit; FIG. 3 is a block diagram illustrating a control system of the refrigeration apparatus; FIG. 4 is a diagram for describing first control; FIG. 5 is a diagram for describing second control; and FIG. 6 is a flowchart for describing an operation example of the refrigeration apparatus. Description of Embodiments

[0010] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings.<Configuration of Refrigeration Apparatus 1>

[0011] First, a configuration of the refrigeration apparatus will be described. FIG. 1 is a diagram illustrating a schematic configuration of refrigeration apparatus 1 according to the embodiment of the present disclosure. FIG. 2 is a diagram illustrating a schematic configuration of refrigeration unit 20.

[0012] As illustrated in FIG. 1, refrigeration apparatus 1 according to the embodiment of the present disclosure includes four refrigeration units 20_1 to 20_4, cooling unit 50, connecting unit 60, and controller 70.

[0013] Four refrigeration units 20_1 to 20_4 are disposed in parallel in the refrigeration cycle. In the present embodiment, an example in which refrigeration apparatus 1 includes four refrigeration units 20_1 to 20_4 will be described. However, the refrigeration apparatus according to the present disclosure may include a plurality (N) of refrigeration units. That is, the number of refrigeration units included in the refrigeration apparatus may be two, three, five, or more.

[0014] In the following description, one of the four refrigeration units will be referred to as refrigeration unit 20_1, a refrigeration unit disposed adjacent to refrigeration unit 20_1 will be referred to as refrigeration unit 20_2, a refrigeration unit disposed adjacent to refrigeration unit 20_2 will be referred to as refrigeration unit 20_3, and a refrigeration unit disposed adjacent to refrigeration unit 20_3 will be referred to as refrigeration unit 20_4.

[0015] Four refrigeration units 20_1 to 20_4 have the same configuration. In the present specification, when the four refrigeration units need not be distinguished, the suffixes "_1," "_2," "_3," and "_4" may be omitted. Thus, in FIG. 2 illustrating the common configuration of four refrigeration units 20_1 to 20_4, the suffixes are omitted.

[0016] As illustrated in FIG. 2, refrigeration unit 20 includes compressor section 21, heat exchanger for heat dissipation (hereinafter, referred to as heat dissipation heat exchanger) 22, oil separator 23, pressure reducing valve 41, intermediate cooler 42, and split heat exchanger 43. That is, refrigeration apparatus 1 includes four pressure reducing valves equal in number to the refrigeration units.

[0017] Compressor section 21 includes first compressor 211 and second compressor 212. First compressor 211 and second compressor 212 are disposed in parallel in the refrigeration cycle. Note that compressor section 21 may include one, three, or more compressors. In a case where compressor section 21 includes three or more compressors, the three or more compressors are disposed in parallel in the refrigeration cycle. Since first compressor 211 and second compressor 212 have the same configuration, first compressor 211 will be described in detail, and second compressor 212 will be described briefly.

[0018] First compressor 211 includes a sealed container. The sealed container is formed with first low-stage-side suction port 211A, first low-stage-side discharge port 211B, first high-stage-side suction port 211C, and first high-stage-side discharge port 211D. The evaporator of cooling unit 50 is connected to first low-stage-side suction port 211A via pipe P1. Intercooler 222 of heat dissipation heat exchanger 22 is connected to first low-stage-side discharge port 211B via pipe P2. Intercooler 222 is connected to first high-stage-side suction port 211C via pipe P3. Oil separator 23 is connected to first high-stage-side discharge port 211D via pipe P4. Check valve CV1 that prevents the refrigerant discharged from first high-stage-side discharge port 211D from flowing back to first high-stage-side discharge port 211D is disposed in pipe P4.

[0019] In the sealed container of first compressor 211, a first low-stage compression element, a first high-stage compression element, and a first motor, which are not illustrated, are disposed. The first low-stage compression element and the first high-stage compression element rotate in synchronization with the rotation of the first motor.

[0020] When the first motor rotates, the first low-stage compression element increases the pressure of the low-pressure refrigerant drawn from the evaporator of cooling unit 50 via pipe P1 and first low-stage-side suction port 211A to an intermediate pressure. The first low-stage compression element discharges the refrigerant that has been increased in pressure to the intermediate pressure to intercooler 222 via first low-stage-side discharge port 211B and pipe P2. The first high-stage compression element increases the pressure of the intermediate-pressure refrigerant drawn from intercooler 222 via first high-stage-side suction port 211C and pipe P3 to a high pressure. The first high-stage compression element discharges the refrigerant that has been increased in pressure to a high pressure to oil separator 23 via first high-stage-side discharge port 211D and pipe P4. As described above, first compressor 211 performs two-stage compression of the refrigerant.

[0021] Second compressor 212 includes a sealed container formed with second low-stage-side suction port 212A, second low-stage-side discharge port 212B, second high-stage-side suction port 212C, and second high-stage-side discharge port 212D. The evaporator of cooling unit 50 is connected to second low-stage-side suction port 212A via pipe P5 branched from pipe P1. Intercooler 222 is connected to second low-stage-side discharge port 212B via pipe P6 branched from pipe P2. Intercooler 222 is connected to second high-stage-side suction port 212C via pipe P7 branched from pipe P3. Oil separator 23 is connected to second high-stage-side discharge port 212D via pipe P8 branched from pipe P4. Check valve CV2 is disposed in pipe P8.

[0022] In the sealed container of second compressor 212, a second low-stage compression element, a second high-stage compression element, and a second motor, which are not illustrated, are disposed. As in first compressor 211, second compressor 212 performs two-stage compression of the refrigerant by rotating the second low-stage compression element and the second high-stage compression element in synchronization with the rotation of the second motor.

[0023] First oil amount detector 211E that detects the remaining amount of oil in the sealed container is disposed in the sealed container of first compressor 211. Second oil amount detector 212E that detects the remaining amount of oil in the sealed container is disposed in the sealed container of second compressor 212. First and second oil amount detectors 211E and 212E are each configured by, for example, an oil level switch, and output a signal corresponding to the detected remaining amount to controller 70.

[0024] Heat dissipation heat exchanger 22 includes heat dissipation blower 221, intercooler 222, and gas cooler 223.

[0025] Heat dissipation blower 221 cools intercooler 222 and gas cooler 223.

[0026] Intercooler 222 cools the intermediate-pressure refrigerant discharged from the first and second low-stage compression elements of first and second compressors 211 and 212, and discharges the cooled refrigerant to the first and second high-stage compression elements.

[0027] Gas cooler 223 is connected to oil separator 23 via pipe P9. Gas cooler 223 is also connected to intermediate cooler 42 via pipe P10. Gas cooler 223 cools the high-pressure refrigerant discharged from oil separator 23 and discharges the cooled refrigerant to intermediate cooler 42.

[0028] Outdoor air temperature sensor 224 is disposed in the vicinity of heat dissipation heat exchanger 22. Outdoor air temperature sensor 224 outputs a signal corresponding to the detection result of the outdoor air temperature to controller 70.

[0029] Oil separator 23 is connected to each of the sealed containers of first compressor 211 and second compressor 212 via oil return pipe Q1. Oil return pipe Q1 includes base pipe Q10 having one end connected to oil separator 23, first branch pipe Q11 that connects the other end of base pipe Q10 and the sealed container of first compressor 211, and second branch pipe Q12 that connects the other end of base pipe Q10 and the sealed container of second compressor 212. Between oil separator 23 and a branch portion of first branch pipe Q11 and second branch pipe Q12 in base pipe Q10, connection pipe Q13 connected to connecting unit 60 is connected.

[0030] Oil separator 23 separates oil contained in the high-pressure refrigerant discharged from the first and second high-stage compression elements of first and second compressors 211 and 212 from the refrigerant, and stores the oil. Oil separator 23 returns the stored oil to first and second compressors 211 and 212 via oil return pipe Q1.

[0031] First oil valve V1 is disposed in first branch pipe Q11. Second oil valve V2 is disposed in second branch pipe Q12. Return valve V3 is disposed in base pipe Q10. First oil valve V1, second oil valve V2, and return valve V3 are each configured by, for example, an electric valve, and are opened and closed under the control of controller 70. First oil valve V1, second oil valve V2, and return valve V3 may be valves of which the opening degree can be controlled in a plurality of stages under the control of controller 70.

[0032] The return destination of the oil from oil separator 23 is controlled by opening and closing first oil valve V1, second oil valve V2, and return valve V3. In particular, the opening and closing of return valve V3 prevents gas from flowing into oil return pipe Q1 from oil separator 23 when oil separator 23 is short of oil, for example.

[0033] High-pressure sensor H1 is attached to pipe P10. High-pressure sensor H1 outputs a signal corresponding to the pressure in pipe P10 to controller 70. The pressure detected by high-pressure sensor H1 is substantially the same as the pressure in gas cooler 223 and oil separator 23.

[0034] Pressure reducing valve 41 is configured by, for example, an electric valve. Pressure reducing valve 41 is disposed on the side of intermediate cooler 42 with respect to the position where high-pressure sensor H1 is attached to pipe P10. Pressure reducing valve 41 reduces the pressure of the high-pressure refrigerant discharged from gas cooler 223 and discharges the refrigerant to an upper portion of intermediate cooler 42.

[0035] The lower portion of intermediate cooler 42 is connected to one end of first flow passage 431 of split heat exchanger 43 via pipe P41. The upper portion of intermediate cooler 42 is connected to one end of second flow passage 432 of split heat exchanger 43 via pipe P42. Gas return electric valve V11 is disposed in pipe P42. Intermediate cooler 42 cools the refrigerant that is reduced in pressure by pressure reducing valve 41. The refrigerant (liquid refrigerant) that has been liquefied by cooling is discharged to first flow passage 431 of split heat exchanger 43 via pipe P41. The refrigerant (gas refrigerant) that is not liquefied by cooling is discharged to second flow passage 432 of split heat exchanger 43 via pipe P42.

[0036] The other end of first flow passage 431 of split heat exchanger 43 is connected to cooling unit 50 via pipe P43. Pipe P44 branched from pipe P42 is connected to a middle portion of pipe P43. Liquid return electric valve V12 is disposed in pipe P44. The other end of second flow passage 432 of split heat exchanger 43 is connected to pipe P3 via pipe P45.

[0037] In split heat exchanger 43 having such a configuration, when liquid return electric valve V12 is open, most of the liquid refrigerant discharged from intermediate cooler 42 flows into cooling unit 50 by passing through first flow passage 431 and pipe P43, while the remaining liquid refrigerant flows into second flow passage 432 by passing through pipes P44 and P42. The inflow of the remaining liquid refrigerant into second flow passage 432 subcools the refrigerant that passes through first flow passage 431 toward the evaporator of cooling unit 50. The gas refrigerant discharged from intermediate cooler 42 is returned to the first and second high-stage compression elements of first and second compressors 211 and 212 by passing through pipe P42, second flow passage 432, and pipes P45, P3, and P7.

[0038] Cooling unit 50 is disposed in, for example, a showcase that is a cooling target of refrigeration apparatus 1. Pipes P43_1 to P43_4 respectively extending from refrigeration units 20_1 to 20_4 are connected to cooling unit 50. Although not illustrated, cooling unit 50 includes one or a plurality of pressure reducing valves and one or a plurality of evaporators equal in number to the pressure reducing valves.

[0039] The pressure reducing valve of cooling unit 50 is configured by, for example, an electric valve. The pressure reducing valve of cooling unit 50 reduces the pressure of the refrigerant discharged from split heat exchanger 43 of refrigeration unit 20 and discharges the refrigerant to the evaporator.

[0040] The evaporator of cooling unit 50 generates cooling air for cooling the cooling target by performing heat exchange between the liquid refrigerant flowing in from the pressure reducing valve and air around the evaporator. The refrigerant after the heat exchange is returned to the first and second low-stage compression elements of refrigeration units 20_1 to 20_4 by passing through pipes P1_1 to P1_4 and P5_1 to P5_4.

[0041] Connecting unit 60 connects oil separators 23_1 to 23_4 respectively included in four refrigeration units 20_1 to 20_4 to each other. Connecting unit 60 includes oil replenishing pipe 61 having a loop shape, four oil replenishing valves 62_1 to 62_4, and four check valves 63_1 to 63_4.

[0042] Oil replenishing pipe 61 connects oil return pipes Q1_1 to Q1_4 respectively included in refrigeration units 20_1 to 20_4 to each other via connection pipes Q13_1 to Q13_4. Oil return pipes Q1_1 to Q1_4 are connected to oil separators 23_1 to 23_4, respectively, as described above, and thus oil replenishing pipe 61 connects oil separators 23_1 to 23_4 of four refrigeration units 20_1 to 20_4 in parallel.

[0043] Four oil replenishing valves 62_1 to 62_4 are provided in the same number as four refrigeration units 20_1 to 20_4. Four oil replenishing valves 62_1 to 62_4 are provided in oil replenishing pipe 61. Oil replenishing valves 62 are each disposed between oil return pipes Q1 of refrigeration units 20 adjacent to each other. That is, oil replenishing valve 62_1 is disposed between oil return pipe Q1_1 of refrigeration unit 20_1 and oil return pipe Q1_2 of refrigeration unit 20_2. In addition, oil replenishing valve 62_2 is disposed between oil return pipe Q1_2 of refrigeration unit 20_2 and oil return pipe Q1_3 of refrigeration unit 20_3. Oil replenishing valve 62_3 is disposed between oil return pipe Q1_3 of refrigeration unit 20_3 and oil return pipe Q1_4 of refrigeration unit 20_4. In addition, oil replenishing valve 62_4 is disposed between oil return pipe Q1_4 of refrigeration unit 20_4 and oil return pipe Q1_1 of refrigeration unit 20_1.

[0044] Oil replenishing valves 62 are, for example, electric valves. Each of four oil replenishing valves 62_1 to 62_4 performs an opening and closing operation based on the control of controller 70 described below to control the flow of oil in oil replenishing pipe 61.

[0045] Four check valves 63_1 to 63_4 are provided in the same number as four refrigeration units 20_1 to 20_4. Four check valves 63_1 to 63_4 are provided in oil replenishing pipe 61. Check valves 63 are disposed in series with oil replenishing valves 62 between oil return pipes Q1 of refrigeration units 20 adjacent to each other. Check valve 63_1 is disposed between oil return pipe Q1_1 of refrigeration unit 20_1 and oil return pipe Q1_2 of refrigeration unit 20_2. In addition, check valve 63_2 is disposed between oil return pipe Q1_2 of refrigeration unit 20_2 and oil return pipe Q1_3 of refrigeration unit 20_3. Check valve 63_3 is disposed between oil return pipe Q1_3 of refrigeration unit 20_3 and oil return pipe Q1_4 of refrigeration unit 20_4. In addition, check valve 63_4 is disposed between oil return pipe Q1_4 of refrigeration unit 20_4 and oil return pipe Q1_1 of refrigeration unit 20_1.

[0046] Oil replenishing pipe 61 allows oil to flow in any one direction by check valves 63. In the example illustrated in FIG. 1, the oil flows only in the clockwise direction in oil replenishing pipe 61, but in the present disclosure, the oil may flow in oil replenishing pipe in the opposite direction (counterclockwise direction).

[0047] Controller 70 controls the operation of the entire refrigeration apparatus 1 by controlling the controllable configuration of refrigeration apparatus 1. Controller 70 is configured by, for example, a processor or a microcontroller including a central processing unit (CPU).

[0048] In the example illustrated in FIG. 1, refrigeration apparatus 1 includes one controller 70, but the present disclosure is not limited thereto. For example, a controller that controls refrigeration unit 20_1, a controller that controls refrigeration unit 20_2, a controller that controls refrigeration unit 20_3, and a controller that controls refrigeration unit 20_4 may be provided separately.

[0049] In this case, the four controllers may operate in cooperation with each other to operate entire refrigeration apparatus 1. Oil replenishing valve 62_1 disposed between refrigeration unit 20_1 and refrigeration unit 20_2 may be controlled by the controller that controls refrigeration unit 20_1. Oil replenishing valve 62_2 disposed between refrigeration unit 20_2 and refrigeration unit 20_3 may be controlled by the controller that controls refrigeration unit 20_2. Oil replenishing valve 62_3 disposed between refrigeration unit 20_3 and refrigeration unit 20_4 may be controlled by the controller that controls refrigeration unit 20_3. Oil replenishing valve 62_4 disposed between refrigeration unit 20_4 and refrigeration unit 20_1 may be controlled by the controller that controls refrigeration unit 20_4.<Control System of Refrigeration Apparatus 1>

[0050] Hereinafter, a control system of refrigeration apparatus 1 including controller 70 will be described. FIG. 3 is a block diagram illustrating the control system of refrigeration apparatus 1.

[0051] As illustrated in FIG. 3, controller 70 is configured to transmit and receive various signals to and from high-pressure sensors H1_1 to H1_4, outdoor air temperature sensors 224_1 to 224_4, first oil valves V1_1 to V1_4, second oil valves V2_1 to V2_4, return valves V3_1 to V3_4, pressure reducing valves 41_1 to 41_4, oil replenishing valves 62_1 to 62_4, first oil amount detectors 211E_1 to 211E_4, and second oil amount detectors 212E_1 to 212E_4.

[0052] Controller 70 determines whether the amount of oil in oil separator 23 is less than a first threshold value, based on the detection results of first oil amount detector 211E and second oil amount detector 212E in each refrigeration unit 20.

[0053] The first threshold value is an example of a predetermined threshold value of the present disclosure. The first threshold value is a minimum value of the amount of oil in oil separator 23 required to supply sufficient oil to first and second compressors 211 and 212. The first threshold value is determined in advance according to the capacity and the like of each of first and second compressors 211 and 212. In addition, the first threshold value may be determined in advance based on an initial value of the oil retention amount in each of first and second compressors 211 and 212, an initial value of an oil surface position, or the like.

[0054] In a general refrigeration apparatus, an oil amount detector such as an oil level switch is disposed in the compressor, but in refrigeration apparatus 1 of the present disclosure, the amount of oil in oil separator 23 is determined using first and second oil amount detectors 211E and 212E generally provided, so that it is not necessary to provide a new configuration in refrigeration apparatus 1 to determine the amount of oil in oil separator 23. Therefore, the oil amount in oil separator 23 can be determined at a relatively low cost.

[0055] In addition, controller 70 performs first control of selectively controlling return valve V3 and oil replenishing valve 62 of each refrigeration unit 20 to circulate the oil in each refrigeration unit 20, and second control of supplying, to any one of the refrigeration units, the oil in another refrigeration unit.

[0056] FIG. 4 is a diagram for describing the first control. In FIGS. 4 and FIG. 5 described below, for simplification, only the main configurations are illustrated, and the disposition of the pipes may be different from the example illustrated in FIG. 2. In addition, in FIG. 4 and FIG. 5 described below, the descriptions of the suffixes "_1" to "_4" are omitted for the internal configurations of refrigeration units 20_1 to 20_4.

[0057] In FIG. 4 and FIG. 5 described below, the pipes illustrated by the solid lines are pipes through which oil, refrigerant, or a mixture thereof flows. The pipes illustrated by the broken lines are pipes through which oil, refrigerant, or a mixture thereof does not flow. In addition, in FIG. 4 and FIG. 5 described below, when a figure indicating oil replenishing valve 62 is filled in black, the valve is in an open state, and when the figure is unfilled, the valve is in a closed state.

[0058] In addition, in FIGS. 4 and 5, pipe P1 through which the refrigerant returning from cooling unit 50 passes is not illustrated.

[0059] As illustrated in FIG. 4, when the first control is performed, controller 70 opens return valves V3 of all refrigeration units 20, closes all oil replenishing valves 62, and drives compressor section 21. Accordingly, in each refrigeration unit 20, oil circulates between first and second compressors 211 and 212 and oil separator 23, and the movement of oil between the plurality of refrigeration units 20 via oil replenishing pipe 61 is restricted.

[0060] FIG. 5 is a diagram for describing the second control. The second control is control of supplying, to the refrigeration unit in which the amount of oil in oil separator 23 is less than the first threshold value, the oil in another refrigeration unit. In the following description, the refrigeration unit in which the amount of oil in oil separator 23 is less than the first threshold value and which becomes a target of the oil supply is referred to as a target unit. FIG. 5 illustrates an example of the second control in a case where refrigeration unit 20_3 becomes the target unit.

[0061] Note that, in FIG. 5, a case where only one refrigeration unit 20_3 among four refrigeration units 20_1 to 20_4 becomes the target unit is illustrated, but the present disclosure is not limited thereto. In the present disclosure, a plurality of units (for example, two or three units) among the N refrigeration units (for example, four units) may become the target units.

[0062] As illustrated in FIG. 5, when performing the second control, controller 70 closes return valve V3 of the target unit and opens return valves V3 of refrigeration units 20 other than the target unit. Then, controller 70 opens all oil replenishing valves 62_1 to 62_4. As a result, oil flows from oil separators 23 of refrigeration units 20 other than the target unit to oil replenishing pipe 61 through oil return pipe Q1, base pipe Q10, and connection pipe Q13. Then, the oil is supplied to first compressor 211 and second compressor 212 of the target unit through connection pipe Q13 and oil return pipe Q1 of the target unit. Consequently, oil is replenished to the target unit.

[0063] Here, as described above, oil replenishing pipe 61 allows oil to flow in any one direction by check valves 63_1 to 63_4. Therefore, the oil flowing into oil replenishing pipe 61 from refrigeration units 20 other than the target unit flows in one direction (clockwise direction in the example illustrated in FIG. 5) in oil replenishing pipe 61, and then flows out from oil replenishing valve 62 connected to oil return pipe Q1 of the target unit.

[0064] Here, a reason for performing the second control will be described. In a case where the first control is performed by driving compressor section 21, the refrigerant that contains oil (hereinafter, sometimes referred to as "oil-containing refrigerant") is supplied to cooling unit 50 from compressor section 21 of each refrigeration unit 20 through oil separator 23, gas cooler 223, and pressure reducing valve 41, and then returns to compressor section 21 of each refrigeration unit 20. In this case, when the amount of the oil-containing refrigerant returning to compressor section 21 of each refrigeration unit 20 is substantially the same, the amount of oil circulating in each refrigeration unit 20 in the first control is substantially the same. That is, the amount of oil separated by oil separator 23 of each refrigeration unit 20 is substantially the same. As a result, the amount of oil in oil separator 23 of each refrigeration unit 20 is equal to or greater than the first threshold value.

[0065] The first threshold value is set to a value at which the amount of oil in first and second compressors 211 and 212 can be set to be equal to or greater than a second threshold value by returning the oil stored in oil separator 23 to first and second compressors 211 and 212.

[0066] The second threshold value is the minimum amount of oil required in first and second compressors 211 and 212.

[0067] However, for example, in the following cases (1) to (3), in the first control, the amount of oil circulating in any refrigeration unit 20 may become imbalanced. (1) In a case where the amounts of oil-containing refrigerant returning to compressor sections 21 differ due to the degree of division of the oil-containing refrigerant returning to compressor section 21 of each refrigeration unit 20 from the evaporator of cooling unit 50. (2) In a case where the speed at which the oil returns from oil separator 23 to compressor section 21 differs between refrigeration units 20 because the difference between the intermediate pressure and the high pressure differs between refrigeration units 20, resulting in the difference in the speed at which the oil is depleted from oil separator 23. (3) In a case where the operation frequencies of first and second compressors 211 and 212 constituting compressor section 21 are different for each refrigeration unit 20.

[0068] In these cases (1) to (3), for example, refrigeration unit 20 in which the amount of oil in oil separator 23 is less than the first threshold value and the amount of oil in at least one of first and second compressors 211 and 212 cannot be set to be equal to or greater than the second threshold value may occur. The second control is performed to suppress the occurrence of such a malfunction.

[0069] Next, the operation of refrigeration apparatus 1 will be described with reference to FIG. 6. FIG. 6 is a flowchart for describing the operation example of refrigeration apparatus 1.

[0070] The operation of refrigeration apparatus 1 illustrated in FIG. 6 is an operation of cooling a cooling target using a refrigerant that is two-stage compressed by first and second compressors 211 and 212. FIG. 6 is a flowchart illustrating the operation of the refrigeration apparatus.

[0071] In Step S1, for example, controller 70 starts the first control based on an operation of the user or the like (Step S1). When the first control is started, as described above, controller 70 opens return valves V3 of all refrigeration units 20, closes all oil replenishing valves 62, and starts the operation of compressor section 21 of each refrigeration unit 20 (see FIG. 4).

[0072] When the operation of compressor section 21 is started, the refrigerant that has been two-stage compressed by compressor section 21 flows into oil separator 23.

[0073] The oil separated from the refrigerant by oil separator 23 is stored in oil separator 23. Based on the detection results of first and second oil amount detectors 211E and 212E, controller 70 supplies the oil in oil separator 23 to first and second compressors 211 and 212 such that the amounts of oil in both first and second compressors 211 and 212 are equal to or greater than the second threshold value. For example, controller 70 maintains first oil valve V1 in an open state (in which the opening degree is maximum) until the amount of oil in first compressor 211 is equal to or greater than the second threshold value, and closes first oil valve V1 (sets the opening degree to 0) when the amount of oil in first compressor 211 becomes equal to or greater than the second threshold value. At this time, because the pressure in oil separator 23 is higher than the pressure at the portion in first compressor 211 where the oil flows, the oil in oil separator 23 is supplied to first compressor 211 by the pressure difference.

[0074] Meanwhile, the refrigerant that has passed through oil separator 23 is reduced in pressure by pressure reducing valve 41 and is used to generate cooling air in cooling unit 50.

[0075] In addition, during the first control, controller 70 controls, based on the detection result of outdoor air temperature sensor 224, pressure reducing valve 41 such that the pressure in oil separator 23 reaches a target high pressure value based on the outdoor air temperature. Specifically, controller 70 controls pressure reducing valve 41 such that the pressure detected by high-pressure sensor H1 increases as the outdoor air temperature increases.

[0076] In Step S2, controller 70 determines whether, among four refrigeration units 20, there is any refrigeration unit in which the amount of oil in oil separator 23 is less than the first threshold value. As described above, controller 70 estimates (determines) that the amount of oil in oil separator 23 is less than the first threshold value in the case where a state in which the amount of oil in at least one of first compressor 211 or second compressor 212 is less than the second threshold value continues for a predetermined time or longer.

[0077] In a case where it is determined that there is refrigeration unit 20 (target unit) in which the amount of oil in oil separator 23 is less than the first threshold value (Step S2: YES), in Step S3, controller 70 starts the second control. When the second control is started, as described above, controller 70 closes return valve V3 of the target unit, opens return valves V3 of refrigeration units 20 other than the target unit, and opens all oil replenishing valves 62_1 to 62_4.

[0078] By opening all oil replenishing valves 62_1 to 62_4, as illustrated in FIG. 5, oil is replenished to the target unit from refrigeration units 20 other than the target unit. Thus, it is possible to prevent a situation in which oil is insufficient in first and second compressors 211 and 212 of each refrigeration unit 20.

[0079] In the target unit, the amount of oil in oil separator 23 is reduced to less than the first threshold value, and thus the gaseous refrigerant may flow into the side of compressor section 21 through oil return pipe Q1. In the second control, closing return valve V3 provided in oil return pipe Q1 can prevent the inflow of the refrigerant into the side of compressor section 21.

[0080] Note that, in the second control, in a case where the pressure in oil separator 23 of the target unit is higher than the pressure in oil separators 23 of refrigeration units 20 other than the target unit, even when all oil replenishing valves 62_1 to 62_4 are opened, oil from refrigeration units other than the target unit possibly not easily flows into the target unit. For this reason, in the second control, in addition to the above control, controller 70 may control pressure reducing valve 41 of each refrigeration unit 20 such that the pressure in oil separator 23 of the target unit becomes lower than the pressure in oil separators 23 of refrigeration units 20 other than the target unit. Here, the control of pressure reducing valve 41 in the second control may be performed only on pressure reducing valve 41 of the target unit, may be performed on pressure reducing valve 41 of refrigeration unit 20 other than the target unit in which the pressure in oil separator 23 is higher than that in the target unit, or may be performed on both.

[0081] In addition, in refrigeration units 20 other than the target unit during the second control, it may be preferred to prioritize the supply of oil to the target unit over the supply of oil from oil separator 23 to first and second compressors 211 and 212. For this case, in the second control, controller 70 may further perform control of making the opening degrees of first oil valve V1 and second oil valve V2 in refrigeration units 20 other than the target unit lower than the opening degrees in the first control.

[0082] Hereinafter, a specific example will be described. It is assumed, for example, that the opening degrees of first oil valve V1 and second oil valve V2 can be controlled in three stages of "100" (opening degree when the valve is fully opened), "0" (opening degree when the valve is closed), and "50" (intermediate opening degree between when the valve is fully opened and when the valve is closed). In this case, in the first control, controller 70 controls the opening degrees of first oil valve V1 and second oil valve V2 to "100," and in refrigeration units 20 other than the target unit during the second control, controller 70 controls the opening degrees of first oil valve V1 and second oil valve V2 to "50." Note that, it is desired that the opening degrees of first oil valve V1 and second oil valve V2 of the target unit be maintained at "100."

[0083] With such control, in refrigeration units 20 other than the target unit, the oil supplied from oil separator 23 can be made to flow more easily to target unit 20 than to compressor section 21 of the unit.

[0084] Returning to the description of FIG. 6. In Step S4, controller 70 determines whether the amounts of oil in all the compressors (first and second compressors 211 and 212) of all refrigeration units 20 are equal to or greater than the second threshold value, based on the detection results of first and second oil amount detectors 211E and 212E of each refrigeration unit 20.

[0085] In a case where the amount of oil in at least one compressor of all refrigeration units 20 is determined to be not equal to or greater than the second threshold value (Step S4: NO), controller 70 performs the process of Step S4 again after a predetermined period elapses.

[0086] On the other hand, in a case where it is determined that the amounts of oil in all the compressors of all refrigeration units 20 are equal to or greater than the second threshold value (Step S4: YES), controller 70 ends the second control, returns the operation to Step S1, and resumes the first control.

[0087] In addition, in a case where it is determined that there is no target unit in which the amount of oil in oil separator 23 is less than the first threshold value (Step S2: NO), controller 70 returns the operation to Step S1 and continues the first control.

[0088] The operations of Steps S1 to S4 are executed, for example, until the user performs an operation to end the operation of refrigeration apparatus 1.

[0089] As described above, refrigeration apparatus 1 according to the embodiment of the present disclosure includes: N (N is an integer of 3 or more) refrigeration units 20 that each includes a compressor (first compressor 211 and second compressor 212), oil separator 23, and oil return pipe Q1 for returning oil separated from the refrigerant by oil separator 23 to first compressor 211 and second compressor 212; oil replenishing pipe 61 that connects oil return pipes Q1 of the N refrigeration units 20 to each other; N oil replenishing valves 62 that are disposed in oil replenishing pipe 61 between oil return pipes Q1 of refrigeration units 20 adjacent to each other and control the flow of oil in oil replenishing pipe 61; and controller 70 that performs control of opening all of N oil replenishing valves 62 when the amount of oil in oil separator 23 of at least any one of N refrigeration units 20 is determined to be less than a first threshold value.

[0090] With such a configuration, in refrigeration apparatus 1 according to the embodiment of the present disclosure, in a case where, among N refrigeration units 20, there is a target unit in which the amount of oil in oil separator 23 is less than the amount (first threshold value) of oil capable of supplying sufficient oil to first and second compressors 211 and 212, oil can be replenished to the target unit from units other than the target unit via oil replenishing pipe 61 and oil replenishing valves 62. This makes it possible to avoid a malfunction (failure or the like) caused by the shortage of oil in first and second compressors 211 and 212 of the target unit. When replenishing oil, controller 70 only needs to open all oil replenishing valves 62 collectively, and thus there is no need to individually control the plurality of oil replenishing valves 62. Therefore, the control cost of controller 70 can be reduced.

[0091] In addition, in refrigeration apparatus 1 according to the embodiment of the present disclosure, each refrigeration unit 20 further includes return valve V3 provided in oil return pipe Q1, and controller 70 performs control of closing return valve V3 of refrigeration unit 20 (target unit) determined to have the amount of oil in oil separator 23 less than the first threshold value.

[0092] This can prevent, in the target unit, the refrigerant gas from flowing from oil separator 23 to oil return pipe Q1.

[0093] In addition, in refrigeration apparatus 1 according to the embodiment of the present disclosure, each refrigeration unit 20 further includes pressure reducing valve 41 that reduces the pressure of the refrigerant separated by oil separator 23, and controller 70 controls pressure reducing valve 41 of each refrigeration unit 20 such that the pressure in oil separator 23 of the target unit becomes lower than the pressure in oil separators 23 of refrigeration units 20 other than the target unit.

[0094] This reduces the pressure in oil separator 23 of the target unit, causing the oil from refrigeration units 20 other than the target unit to easily flow into oil separator 23 of the target unit. Therefore, it is possible to prevent a situation in which, for example, oil from refrigeration units 20 other than the target unit flows into other refrigeration units 20 other than the target unit, and oil is not replenished to the target unit.[Variation]

[0095] The present disclosure is not limited to the embodiment described above. Various modifications can be made to the present disclosure without departing from the spirit thereof. In addition, the embodiment and the variations illustrated below may be combined as long as they function properly.

[0096] For example, oil replenishing pipe 61 need not be provided with a plurality of check valves 63. For example, oil replenishing valves 62 may be configured by directional control valves, and the direction of the oil flowing through oil replenishing pipe 61 may be arbitrarily controllable by being controlled by controller 70.

[0097] In addition, oil replenishing pipe 61 need not be a loop-shaped pipe. The oil replenishing pipe of the present disclosure may be, for example, a linear pipe. Even in such a case, by the controller opening the oil replenishing valve provided in the oil replenishing pipe, oil is replenished from other refrigeration units to a refrigeration unit in which the amount of oil in the oil separator is small and the pressure in the oil separator is low. In this case, by configuring the oil replenishing valve with a directional control valve, oil can be replenished more preferably.

[0098] In addition, in the embodiment described above, controller 70 estimates (determines) the amount of oil in oil separator 23 based on the detection results of first and second oil amount detectors 211E and 212E provided in first and second compressors 211 and 212, respectively. However, in the present disclosure, for example, a detector that detects the amount of oil in oil separator 23 may be disposed for each oil separator 23, and controller 70 may determine whether the amount of oil in each oil separator 23 is less than the first threshold value, based on the detection result of the detector.

[0099] In the embodiment described above, the example has been described in which connecting unit 60 includes oil replenishing pipe 61, oil replenishing valve 62, and check valve 63, but at least one of oil replenishing valve 62 or check valve 63 may be included in any of N refrigeration units 20.

[0100] In the embodiment described above, controller 70 that controls the operation of the entire refrigeration apparatus 1 is provided. In the present disclosure, for example, an independent controller may be provided for each of N refrigeration units 20. In this case, the controllers respectively provided in N refrigeration units 20 communicate with each other and operate in cooperation with each other, or any one controller controls the other controllers, whereby the same operation as that of the embodiment described above can be performed. In addition, in this case, the control of oil replenishing valve 62_1 provided between refrigeration unit 20_1 and refrigeration unit 20_2 may be performed by, for example, the controller provided in refrigeration unit 20_1 or the controller provided in refrigeration unit 20_2.

[0101] In the embodiment described above, the case has been described in which each of four refrigeration units 20 includes split heat exchanger 43. In the present disclosure, for example, only one split heat exchanger may be provided for the plurality of refrigeration units. In this case, the pipes extending from the gas coolers of the refrigeration units may be connected to one split heat exchanger.

[0102] The disclosure of Japanese Patent Application No. 2023-127063, filed on August 3, 2023, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.Industrial Applicability

[0103] The present disclosure can be applied to a refrigeration apparatus.Reference Signs List

[0104] 1 Refrigeration apparatus 20 Refrigeration unit 21 Compressor section 22 Heat dissipation heat exchanger 23 Oil separator 41 Pressure reducing valve 42 Intermediate cooler 43 Split heat exchanger 50 Cooling unit 60 Connecting unit 61 Oil replenishing pipe 62 Oil replenishing valve 63 Check valve 70 Controller 211 Second compressor 211A First low-stage-side suction port 211B First low-stage-side discharge port 211C First high-stage-side suction port 211D First high-stage-side discharge port 211E First oil amount detector 212 Second compressor 212A Second low-stage-side suction port 212B Second low-stage-side discharge port 212C Second high-stage-side suction port 212D Second high-stage-side discharge port 212E Second oil amount detector 221 Heat dissipation blower 222 Intercooler 223 Gas cooler 224 Outdoor air temperature sensor 431 First flow passage 432 Second flow passage CV1 Check valve CV2 Check valve H1 High-pressure sensor P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P41, P42, P43, P44, P45 Pipe Q1 Oil return pipe Q10 Base pipe Q11 First branch pipe Q12 Second branch pipe Q13 Connection pipe V1 First oil valve V11 Gas return electric valve V12 Liquid return electric valve V2 Second oil valve V3 Return valve

Claims

1. A refrigeration apparatus, comprising: refrigeration units that each include a compressor, an oil separator, and an oil return pipe for returning, to the compressor, oil separated from a refrigerant by the oil separator, the refrigeration units being N (N is an integer of 2 or more) refrigeration units; an oil replenishing pipe that connects a plurality of the oil return pipes of the N refrigeration units to each other; replenishing valves that are each disposed in the oil replenishing pipe between the oil return pipes of the refrigeration units adjacent to each other and control flow of oil in the oil replenishing pipe, the oil replenishing valves being N oil replenishing valves; and a controller that opens all of the N oil replenishing valves when an oil amount in the oil separator of at least one of the refrigeration units is determined to be less than a predetermined threshold value.

2. The refrigeration apparatus according to claim 1, wherein each of the refrigeration units further includes a return valve provided in the oil return pipe, and the controller performs control of closing the return valve of the at least one of the refrigeration units determined to have the oil amount in the oil separator less than the predetermined threshold value.

3. The refrigeration apparatus according to claim 1, wherein the oil replenishing pipe has a loop shape.

4. The refrigeration apparatus according to claim 1, wherein each of the N oil replenishing valves is a directional control valves capable of controlling a direction of the flow of the oil in the oil replenishing pipe.

5. The refrigeration apparatus according to claim 1, wherein the oil replenishing pipe further includes a check valve for restricting the flow of the oil in any one direction.

6. The refrigeration apparatus according to claim 1, wherein each of the refrigeration units further includes a pressure reducing valve for reducing a pressure of the refrigerant separated by the oil separator, and the controller controls the pressure reducing valve of each of the refrigeration units such that a pressure in the oil separator of the at least one of the refrigeration units determined to have the oil amount less than the predetermined threshold value becomes lower than a pressure in the oil separator of at least one of the refrigeration units not determined to have the oil amount less than the predetermined threshold value.

7. A control method for a refrigeration apparatus that includes: refrigeration units each including: a compressor, an oil separator, and an oil return pipe for returning, to the compressor, oil separated from a refrigerant by the oil separator, the refrigeration units being N (N is an integer of 2 or more) refrigeration units; an oil replenishing pipe connecting a plurality of the oil return pipes of the N refrigeration units to each other; oil replenishing valves each disposed in the oil replenishing pipe between the oil return pipes of the refrigeration units adjacent to each other, and controlling flow of oil in the oil replenishing pipe, the oil replenishing valves being N oil replenishing valves; and a controller, the method comprising: determining whether an oil amount in the oil separator of at least one of the refrigeration units is less than a predetermined threshold value; and opening all of the N oil replenishing valves when the oil amount in the oil separator of the at least one of the refrigeration units is determined to be less than the predetermined threshold value.

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