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

Refrigeration device and control method

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

[0002] Refrigeration systems equipped with multiple compressors and oil separators are known. For example, Patent Document 1 discloses a technology for configuring a large-capacity multi-refrigeration system by combining and connecting multiple refrigerators, each of which has a compressor, an oil separator, and a condenser. Also, Patent Document 2 discloses a refrigeration system incorporating multiple compressors and oil separators.

[0003] JP-A No. 2-217763 JP-A No. 11-173686

[0004] In refrigeration systems equipped with multiple oil separators, slight pressure differences can occur within each oil separator, causing the amount of oil contained in the multiple oil separators to become uneven. In this case, the amount of oil returned from the oil separator to the compressor can become insufficient, causing malfunctions in the operation of the refrigeration system, and therefore improvements are needed.

[0005] An object of the present disclosure is to provide a refrigeration apparatus having a plurality of oil separators, which is capable of adjusting the amount of oil contained in the plurality of oil separators, and a control method thereof.

[0006] The refrigeration system of the present disclosure includes N (N is an integer of 2 or greater) refrigeration units, each having a compressor, an oil separator, and an oil return pipe that returns oil separated from the refrigerant by the oil separator to the compressor; an oil supply pipe connecting the oil return pipes of the N refrigeration units; N oil supply valves that are arranged in the oil supply pipe between the oil return pipes of adjacent refrigeration units and control the flow of oil in the oil supply pipe; and a control unit that controls to open all N oil supply valves when it is determined that the amount of oil in the oil separator of at least any of the N refrigeration units is less than a predetermined threshold.

[0007] The control method disclosed herein is a control method for a refrigeration system including: N (N is an integer of 2 or greater) refrigeration units, each having a compressor, an oil separator, and an oil return pipe that returns oil separated from the refrigerant by the oil separator to the compressor; a supply oil pipe connecting the oil return pipes of the N refrigeration units; N supply oil valves that are arranged in the supply oil pipe between the oil return pipes of adjacent refrigeration units and control the flow of oil in the supply oil pipe; and a control unit, wherein the control method determines whether the amount of oil in the oil separator of at least any of the N refrigeration units is less than a predetermined threshold, and opens all of the N supply oil valves when it is determined that the amount of oil in the oil separator of at least any of the refrigeration units is less than the predetermined threshold.

[0008] According to the refrigeration apparatus of the present disclosure, in a refrigeration apparatus including a plurality of oil separators, the amount of oil contained in the plurality of oil separators can be adjusted.

[0009] FIG. 1 is a diagram showing a schematic configuration of a refrigeration device according to an embodiment of the present disclosure; FIG. 2 is a diagram showing a schematic configuration of a refrigeration unit; FIG. 3 is a block diagram showing a control system of the refrigeration device; FIG. 4 is a diagram for explaining first control; FIG. 5 is a diagram for explaining second control;

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] <Configuration of Refrigeration Apparatus 1> First, the configuration of the refrigeration apparatus will be described. Fig. 1 is a diagram showing a schematic configuration of a refrigeration apparatus 1 according to an embodiment of the present disclosure. Fig. 2 is a diagram showing a schematic configuration of a refrigeration unit 20.

[0012] As shown in FIG. 1, a refrigeration device 1 according to an embodiment of the present disclosure includes four refrigeration units 20_1 to 20_4, a cooling unit 50, a connection unit 60, and a control unit .

[0013] The four freezer units 20_1 to 20_4 are arranged in parallel in the refrigeration cycle. Note that, although the present embodiment describes an example in which the refrigeration device 1 includes four freezer units 20_1 to 20_4, the refrigeration device of the present disclosure may include a plurality of freezer units (N units). In other words, the number of freezer units included in the refrigeration device may be two, three, five or more.

[0014] In the following explanation, one of the four freezer units will be referred to as 20_1, the freezer unit arranged adjacent to freezer unit 20_1 will be referred to as 20_2, the freezer unit arranged further adjacent to freezer unit 20_2 will be referred to as 20_3, and the freezer unit arranged further adjacent to freezer unit 20_3 will be referred to as 20_4.

[0015] The four freezer units 20_1 to 20_4 each have the same configuration. In this specification, when there is no need to distinguish between the four freezer units, the suffixes "1," "2," "3," and "4" may be omitted. For this reason, in FIG. 2 , which describes the configuration common to the four freezer units 20_1 to 20_4, the suffixes are omitted.

[0016] 2 , the refrigeration unit 20 includes a compression section 21, a heat dissipation heat exchanger 22, an oil separator 23, a pressure reducing valve 41, an intercooler 42, and a split heat exchanger 43. That is, the refrigeration apparatus 1 includes four pressure reducing valves, which is the same number as the number of the refrigeration units.

[0017] The 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 a refrigeration cycle. The compression unit 21 may include one compressor or three or more compressors. When the compression unit 21 includes three or more compressors, the three or more compressors are arranged in parallel in a refrigeration cycle. Because the first compressor 211 and the second compressor 212 have a similar configuration, the first compressor 211 will be described in detail, and the second compressor 212 will be described briefly.

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

[0019] A first low-stage compression element, a first high-stage compression element, and a first motor (not shown) are arranged in a sealed container of the first compressor 211. 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 pressurizes the low-pressure refrigerant drawn from the evaporator of the cooling unit 50 via the pipe P1 and the first low-stage suction port 211A to an intermediate pressure. The first low-stage compression element discharges the refrigerant, which has been pressurized to the intermediate pressure, to the intercooler 222 via the first low-stage discharge port 211B and the pipe P2. The first high-stage compression element pressurizes the intermediate-pressure refrigerant drawn from the intercooler 222 to a high pressure via the first high-stage suction port 211C and the pipe P3. The first high-stage compression element discharges the refrigerant, which has been pressurized to the high pressure, to the oil separator 23 via the first high-stage discharge port 211D and the pipe P4. In this way, the first compressor 211 compresses the refrigerant in two stages.

[0021] The second compressor 212 includes a sealed container having a second low-stage intake port 212A, a second low-stage discharge port 212B, a second high-stage intake port 212C, and a second high-stage discharge port 212D. The second low-stage intake port 212A is connected to the evaporator of the cooling unit 50 via a pipe P5 branching from the pipe P1. The second low-stage discharge port 212B is connected to an intercooler 222 via a pipe P6 branching from the pipe P2. The second high-stage intake port 212C is connected to the intercooler 222 via a pipe P7 branching from the pipe P3. The second high-stage discharge port 212D is connected to the oil separator 23 via a pipe P8 branching from the pipe P4. A check valve CV2 is disposed in the pipe P8.

[0022] A second low-stage compression element, a second high-stage compression element, and a second motor (not shown) are arranged in a sealed container of the second compressor 212. Similar to the first compressor 211, the second compressor 212 compresses the refrigerant in two stages by the second low-stage compression element and the second high-stage compression element rotating in synchronization with the rotation of the second motor.

[0023] A first oil level detection unit 211E that detects the amount of oil remaining in the sealed container is disposed in the sealed container of the first compressor 211. A second oil level detection unit 212E that detects the amount of oil remaining in the sealed container is disposed in the sealed container of the second compressor 212. The first and second oil level detection units 211E, 212E are each formed of, for example, an oil level switch, and output a signal corresponding to the detected remaining amount to the control unit 70.

[0024] The heat-dissipating heat exchanger 22 includes a heat-dissipating fan 221 , an intercooler 222 , and a gas cooler 223 .

[0025] The heat-dissipating fan 221 cools the intercooler 222 and the gas cooler 223 .

[0026] The 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 the refrigerant to the first and second high-stage compression elements.

[0027] The gas cooler 223 is connected to the oil separator 23 via a pipe P9. The gas cooler 223 is connected to the economizer 42 via a pipe P10. The gas cooler 223 cools the high-pressure refrigerant discharged from the oil separator 23 and discharges the refrigerant to the economizer 42.

[0028] An outside air temperature sensor 224 is disposed near the heat-dissipating heat exchanger 22. The outside air temperature sensor 224 outputs a signal corresponding to the result of detecting the outside air temperature to the control unit 70.

[0029] The oil separator 23 is connected to the respective sealed containers of the first compressor 211 and the second compressor 212 via an oil return pipe Q1. The oil return pipe Q1 includes a main pipe Q10 having one end connected to the oil separator 23, a first branch pipe Q11 connecting the other end of the main pipe Q10 to the sealed container of the first compressor 211, and a second branch pipe Q12 connecting the other end of the main pipe Q10 to the sealed container of the second compressor 212. A connecting pipe Q13, which is connected to the connecting unit 60, is connected to the main pipe Q10 between the oil separator 23 and the branch point of the first branch pipe Q11 and the second branch pipe Q12.

[0030] The oil separator 23 separates and stores 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 oil separator 23 returns the stored oil to the first and second compressors 211 and 212 via an oil return pipe Q1.

[0031] A first oil valve V1 is disposed in the first branch pipe Q11. A second oil valve V2 is disposed in the second branch pipe Q12. A return valve V3 is disposed in the main pipe Q10. The first oil valve V1, the second oil valve V2, and the return valve V3 are each constituted by, for example, an electric valve, and are opened and closed under the control of the control unit 70. The first oil valve V1, the second oil valve V2, and the return valve V3 may be valves whose opening degrees can be controlled in multiple stages under the control of the control unit 70.

[0032] The first oil valve V1, the second oil valve V2, and the return valve V3 are opened and closed to control the destination of the oil returned from the oil separator 23. In particular, opening and closing the return valve V3 prevents gas from flowing from the oil separator 23 into the oil return pipe Q1 when, for example, the oil separator 23 is low in oil.

[0033] A high-pressure sensor H1 is disposed in the pipe P10. The high-pressure sensor H1 outputs a signal corresponding to the pressure in the pipe P10 to the control unit 70. The pressure detected by the high-pressure sensor H1 is approximately the same as the pressure in the gas cooler 223 and the oil separator 23.

[0034] The pressure reducing valve 41 is configured by, for example, an electric valve. The pressure reducing valve 41 is disposed closer to the economizer 42 than the high-pressure sensor H1 is disposed in the pipe P10. The pressure reducing valve 41 reduces the pressure of the high-pressure refrigerant discharged from the gas cooler 223, and discharges the refrigerant into an upper portion of the economizer 42.

[0035] A lower part of the economizer 42 is connected to one end of a first flow path 431 of the split heat exchanger 43 via a pipe P41. An upper part of the economizer 42 is connected to one end of a second flow path 432 of the split heat exchanger 43 via a pipe P42. A gas return motor-operated valve V11 is disposed on the pipe P42. The economizer 42 cools the refrigerant decompressed by the pressure reducing valve 41. The refrigerant liquefied by cooling (liquid refrigerant) is discharged to the first flow path 431 of the split heat exchanger 43 via the pipe P41. The refrigerant not liquefied by cooling (gas refrigerant) is discharged to the second flow path 432 of the split heat exchanger 43 via the pipe P42.

[0036] The other end of the first flow path 431 of the split heat exchanger 43 is connected to the cooling unit 50 via a pipe P43. A pipe P44 branching from the pipe P42 is connected to the middle of the pipe P43. A liquid return motor-operated valve V12 is disposed in the pipe P44. The other end of the second flow path 432 of the split heat exchanger 43 is connected to the pipe P3 via a pipe P45.

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

[0038] The cooling unit 50 is disposed in, for example, a showcase that is the cooling target of the refrigeration device 1. Pipes P43_1 to P43_4 extending from the refrigeration units 20_1 to 20_4, respectively, are connected to the cooling unit 50. Although not shown in the figure, the cooling unit 50 includes one or more pressure reducing valves and the same number of evaporators as the pressure reducing valves.

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

[0040] The evaporator of the cooling unit 50 exchanges heat between the liquid refrigerant flowing in from the pressure reducing valve and the air surrounding the evaporator to generate cooled air for cooling an object to be cooled. The refrigerant after heat exchange passes through pipes P1_1 to P1_4 and P5_1 to P5_4 and is returned to the first and second low-stage compression elements of the freezing units 20_1 to 20_4.

[0041] The connection unit 60 connects the oil separators 23_1 to 23_4 of the four refrigeration units 20_1 to 20_4 to each other. The connection unit 60 has a loop-shaped oil supply pipe 61, four oil supply valves 62_1 to 62_4, and four check valves 63_1 to 63_4.

[0042] The oil supply pipe 61 connects the oil return pipes Q1_1 to Q1_4 of the refrigeration units 20_1 to 20_4 via the connecting pipes Q13_1 to Q13_4. As described above, the oil return pipes Q1_1 to Q1_4 are connected to the oil separators 23_1 to 23_4, respectively, so the oil supply pipe 61 connects the oil separators 23_1 to 23_4 of the four refrigeration units 20_1 to 20_4 in parallel.

[0043] Four oil supply valves 62_1 to 62_4 are provided in the same number as the four refrigeration units 20_1 to 20_4. The four oil supply valves 62_1 to 62_4 are provided on an oil supply pipe 61. The oil supply valves 62 are arranged between the oil return pipes Q1 of the adjacent refrigeration units 20. That is, the oil supply valve 62_1 is arranged between the oil return pipe Q1_1 of the refrigeration unit 20_1 and the oil return pipe Q1_2 of the refrigeration unit 20_2. The oil supply valve 62_2 is arranged between the oil return pipe Q1_2 of the refrigeration unit 20_2 and the oil return pipe Q1_3 of the refrigeration unit 20_3. The oil supply valve 62_3 is arranged between the oil return pipe Q1_3 of the refrigeration unit 20_3 and the oil return pipe Q1_4 of the refrigeration unit 20_4. Further, the oil supply valve 62_4 is disposed between the oil return pipe Q1_4 of the refrigeration unit 20_4 and the oil return pipe Q1_1 of the refrigeration unit 20_1.

[0044] The oil supply valve 62 is, for example, an electrically operated valve. Each of the four oil supply valves 62_1 to 62_4 controls the flow of oil in the oil supply pipe 61 by opening and closing based on the control of a control unit 70, which will be described later.

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

[0046] The check valve 63 allows oil to flow in either direction through the oil supply pipe 61. In the example shown in Figure 1, oil flows only clockwise through the oil supply pipe 61, but in the present disclosure, oil may also flow in the opposite direction (counterclockwise) through the oil supply pipe.

[0047] The control unit 70 controls the controllable components of the refrigeration device 1, thereby controlling the overall operation of the refrigeration device 1. The control unit 70 is configured by, for example, a processor or microcontroller having a CPU (Central Processing Unit).

[0048] 1, the refrigeration device 1 includes one control unit 70, but the present disclosure is not limited to this. For example, a control unit that controls the refrigeration unit 20_1, a control unit that controls the refrigeration unit 20_2, a control unit that controls the refrigeration unit 20_3, and a control unit that controls the refrigeration unit 20_4 may be provided separately.

[0049] In this case, the four control units may cooperate with each other to operate the entire refrigeration system 1. The oil supply valve 62_1 arranged between the freezing unit 20_1 and the freezing unit 20_2 may be controlled by the control unit that controls the freezing unit 20_1. The oil supply valve 62_2 arranged between the freezing unit 20_2 and the freezing unit 20_3 may be controlled by the control unit that controls the freezing unit 20_2. The oil supply valve 62_3 arranged between the freezing unit 20_3 and the freezing unit 20_4 may be controlled by the control unit that controls the freezing unit 20_3. The oil supply valve 62_4 arranged between the freezing unit 20_4 and the freezing unit 20_1 may be controlled by the control unit that controls the freezing unit 20_4.

[0050] <Control System of Refrigeration Apparatus 1> The following describes the control system of the refrigeration apparatus 1, including the control unit 70. Fig. 3 is a block diagram showing the control system of the refrigeration apparatus 1.

[0051] As shown in FIG. 3, the control unit 70 is configured to be able to send and receive various signals between the high-pressure sensors H1_1 to H1_4, the outside air temperature sensors 224_1 to 224_4, the first oil valves V1_1 to V1_4, the second oil valves V2_1 to V2_4, the return valves V3_1 to V3_4, the pressure reducing valves 41_1 to 41_4, the oil supply valves 62_1 to 62_4, the first oil amount detection units 211E_1 to 211E_4, and the second oil amount detection units 212E_1 to 212E_4.

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

[0053] The first threshold is an example of a predetermined threshold in the present disclosure. The first threshold is the minimum amount of oil required for the amount of oil in the oil separator 23 to supply sufficient oil to the first and second compressors 211, 212. The first threshold is determined in advance based on the capacities of the first and second compressors 211, 212, etc. Alternatively, the first threshold may be determined in advance based on the initial values ​​of the oil retention amounts of the first and second compressors 211, 212, the initial values ​​of the oil level positions, etc.

[0054] In a typical refrigeration system, an oil level detection unit such as an oil level switch is provided in the compressor, but in the refrigeration system 1 of the present disclosure, the oil level in the oil separator 23 is determined using the first and second oil level detection units 211E, 212E that are generally provided, so there is no need to provide the refrigeration system 1 with a new configuration for determining the oil level in the oil separator 23. Therefore, the oil level in the oil separator 23 can be determined at relatively low cost.

[0055] In addition, the control unit 70 selectively controls the return valve V3 and oil supply valve 62 of each refrigeration unit 20 to perform a first control of circulating oil within each refrigeration unit 20, and a second control of supplying oil from one of the refrigeration units to another refrigeration unit.

[0056] Fig. 4 is a diagram for explaining the first control. For simplification, Fig. 4 and Fig. 5 described later show only the main components, and the arrangement of piping may differ from the example shown in Fig. 2. Furthermore, in Fig. 4 and Fig. 5 described later, the suffixes "_1" to "_4" are omitted for the internal configurations of the refrigeration units 20_1 to 20_4.

[0057] In Fig. 4 and Fig. 5 (described later), the pipes shown with solid lines are pipes through which oil, refrigerant, or a mixture thereof flows. The pipes shown with dashed lines are pipes through which oil, refrigerant, or a mixture thereof does not flow. In Fig. 4 and Fig. 5 (described later), when the figure showing the oil supply valve 62 is filled in, it indicates that the valve is open, and when it is filled in, it indicates that the valve is closed.

[0058] 4 and 5, the pipe P1 through which the refrigerant returning from the cooling unit 50 passes is not shown.

[0059] 4, when performing the first control, the control unit 70 opens the return valves V3 of all the refrigeration units 20 and closes all the oil supply valves 62 to drive the compression units 21. As a result, in each of the refrigeration units 20, oil circulates between the first and second compressors 211, 212 and the oil separator 23, and the movement of oil between the plurality of refrigeration units 20 via the oil supply pipes 61 is restricted.

[0060] Fig. 5 is a diagram for explaining the second control. The second control is a control for supplying oil from another freezer unit to a freezer unit whose oil in the oil separator 23 has fallen below the first threshold. In the following description, a freezer unit whose oil in the oil separator 23 has fallen below the first threshold and that is the target of oil supply will be referred to as a target unit. Fig. 5 shows an example of the second control when the freezer unit 20_3 is the target unit.

[0061] 5 shows a case in which only one freezer unit 20_3 is the target unit among the four freezer units 20_1 to 20_4, but the present disclosure is not limited to this. In the present disclosure, a plurality of units (e.g., two or three) among the N (e.g., four) freezer units may be the target units.

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

[0063] As described above, the check valves 63_1 to 63_4 allow oil to flow in one direction through the oil supply pipe 61. Therefore, oil that has flowed into the oil supply pipe 61 from a refrigeration unit 20 other than the target unit flows in one direction (clockwise in the example shown in FIG. 5) through the oil supply pipe 61 and flows out from the oil supply valve 62 connected to the oil return pipe Q1 of the target unit.

[0064] Here, the reason for performing the second control will be explained. When the compression unit 21 is driven to perform the first control, the refrigerant containing oil (hereinafter sometimes referred to as "oil-containing refrigerant") passes from the compression unit 21 of each freezing unit 20 through the oil separator 23, the gas cooler 223, and the pressure reducing valve 41, is supplied to the cooling unit 50, and then returns to the compression unit 21 of each freezing unit 20. In this case, if the amount of oil-containing refrigerant returning to the compression unit 21 of each freezing unit 20 is approximately the same, the amount of oil circulating through each freezing unit 20 in the first control will be approximately the same. In other words, the amount of oil separated by the oil separator 23 of each freezing unit 20 will be approximately the same. As a result, the amount of oil in the oil separator 23 of each freezing unit 20 will all be equal to or greater than the first threshold.

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

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

[0067] However, in the cases of (1) to (3) below, for example, an imbalance may occur in the amount of oil circulating through any of the refrigeration units 20 in the first control.

[0068] (1) When the amount of oil-containing refrigerant returning to each compression section 21 differs due to the degree of diversion when the oil-containing refrigerant returns from the evaporator of the cooling unit 50 to the compression section 21 of each freezing unit 20.

[0069] (2) Due to the difference between the intermediate pressure and the high pressure in each refrigeration unit 20 being different, the speed at which oil returns from the oil separator 23 to the compression section 21 differs for each refrigeration unit 20, and the speed at which oil disappears from the oil separator 23 differs.

[0070] (3) When the operating frequencies of the first and second compressors 211 and 212 constituting the compression section 21 are different for each refrigeration unit 20.

[0071] In the cases of (1) to (3), for example, the amount of oil in the oil separator 23 may become less than the first threshold value, and the refrigeration unit 20 may become unable to increase the amount of oil in at least one of the first and second compressors 211, 212 to equal to or greater than the second threshold value. The second control is performed to prevent such malfunctions from occurring.

[0072] Next, the operation of the refrigeration device 1 will be described with reference to Fig. 6. Fig. 6 is a flowchart for explaining an example of the operation of the refrigeration device 1.

[0073] The operation of the refrigeration device 1 illustrated in Fig. 6 is an operation of cooling an object to be cooled using a refrigerant compressed in two stages by the first and second compressors 211 and 212. Fig. 6 is a flowchart showing the operation of the refrigeration device.

[0074] In step S1, the control unit 70 starts the first control based on, for example, a user operation (step S1). When starting the first control, the control unit 70 opens the return valves V3 of all the refrigeration units 20, closes all the oil supply valves 62, and starts the operation of the compression units 21 of each refrigeration unit 20, as described above (see FIG. 4).

[0075] When the operation of the compression section 21 starts, the refrigerant compressed in two stages by the compression section 21 flows into the oil separator 23 .

[0076] The oil separated from the refrigerant by the oil separator 23 is stored in the oil separator 23. Based on the detection results of the first and second oil amount detection units 211E and 212E, the control unit 70 supplies oil from the oil separator 23 to the first and second compressors 211 and 212 so that the amounts of oil in both the first and second compressors 211 and 212 are equal to or greater than a second threshold. For example, the control unit 70 keeps the first oil valve V1 open (maximum opening) until the amount of oil in the first compressor 211 is equal to or greater than the second threshold, and closes the first oil valve V1 (reducing the opening to zero) when the amount of oil in the first compressor 211 is equal to or greater than the second threshold. At this time, the pressure in the oil separator 23 is higher than the pressure at the portion of the first compressor 211 into which the oil flows, and the oil in the oil separator 23 is supplied to the first compressor 211 due to this pressure difference.

[0077] On the other hand, the refrigerant that has passed through the oil separator 23 is decompressed by the pressure reducing valve 41 and is used to generate cooling air in the cooling unit 50 .

[0078] Furthermore, while performing the first control, the control unit 70 controls the pressure reducing valve 41 so that the pressure inside the oil separator 23 becomes a target high pressure value based on the outside air temperature, based on the detection result of the outside air temperature sensor 224. Specifically, the control unit 70 controls the pressure reducing valve 41 so that the pressure detected by the high-pressure sensor H1 becomes higher as the outside air temperature becomes higher.

[0079] In step S2, the control unit 70 determines whether the amount of oil in the oil separator 23 of any of the four refrigeration units 20 is less than the first threshold value. As described above, the control unit 70 estimates (determines) that the amount of oil in the oil separator 23 is less than the first threshold value, for example, if the state in which the amount of oil in at least one of the first compressor 211 and the second compressor 212 is less than the second threshold value continues for a predetermined time or longer.

[0080] When it is determined that there is a refrigeration unit 20 (target unit) in which the amount of oil in the oil separator 23 is less than the first threshold (step S2: YES), the control unit 70 starts the second control in step S3. When starting the second control, as described above, the control unit 70 closes the return valve V3 of the target unit, opens the return valves V3 of the refrigeration units 20 other than the target unit, and opens all the oil supply valves 62_1 to 62_4.

[0081] By opening all of the oil supply valves 62_1 to 62_4, oil is supplied to the target unit from the refrigeration units 20 other than the target unit, as shown in Figure 5. This prevents a situation in which oil runs short in the first and second compressors 211, 212 of each refrigeration unit 20.

[0082] In the target unit, the amount of oil in the oil separator 23 decreases below the first threshold, which may cause gaseous refrigerant to flow through the oil return pipe Q1 into the compression unit 21. In the second control, the return valve V3 provided in the oil return pipe Q1 is closed to prevent the refrigerant from flowing into the compression unit 21.

[0083] In the second control, if the pressure in the oil separator 23 of the target unit is higher than the pressure in the oil separators 23 of the units other than the target unit, it may be difficult for oil from units other than the target unit to flow into the target unit even if all of the oil supply valves 62_1 to 62_4 are opened. For this reason, in the second control, in addition to the above control, the control unit 70 may control the pressure reducing valves 41 of each refrigeration unit 20 so that the pressure in the oil separator 23 of the target unit is lower than the pressure in the oil separators 23 of the units other than the target unit. Here, the control of the pressure reducing valves 41 in the second control may be performed only on the pressure reducing valves 41 of the target unit, or on the pressure reducing valves 41 of refrigeration units 20 other than the target unit whose oil separator 23 pressure is higher than that of the target unit, or on both.

[0084] Furthermore, in the refrigeration units 20 other than the target unit during the second control, it may be better to prioritize supplying oil to the target unit rather than supplying oil from the oil separator 23 to the first and second compressors 211, 212. For such cases, in the second control, the control unit 70 may further perform control to reduce the opening degrees of the first oil valve V1 and the second oil valve V2 in the refrigeration units 20 other than the target unit compared to the opening degrees in the first control.

[0085] A specific example will be described below. For example, assume that the opening degrees of the first oil valve V1 and the second oil valve V2 can be controlled to three levels: "100" (opening degree when the valves are fully opened), "0" (opening degree when the valves are closed), and "50" (opening degree intermediate between fully opened and closed). In this case, the control unit 70 controls the opening degrees of the first oil valve V1 and the second oil valve V2 to "100" during the first control, and controls the opening degrees of the first oil valve V1 and the second oil valve V2 to "50" in the refrigeration units 20 other than the target unit during the second control. Note that it is desirable to maintain the opening degrees of the first oil valve V1 and the second oil valve V2 of the target unit at "100."

[0086] By such control, in the refrigeration units 20 other than the target unit, the oil supplied from the oil separator 23 can be made to flow more easily to the target unit 20 than to the compression section 21 of the unit.

[0087] Returning to the description of Fig. 6, in step S4, the control unit 70 determines whether the amount of oil in all of the compressors (first and second compressors 211, 212) of all of the refrigeration units 20 has become equal to or greater than the second threshold value, based on the detection results of the first and second oil amount detection units 211E, 212E of each refrigeration unit 20.

[0088] If the control unit 70 determines that the amount of oil in all compressors of all refrigeration units 20 is not greater than the second threshold value (step S4: NO), it performs the process of step S4 again after a predetermined period of time has elapsed.

[0089] On the other hand, if the control unit 70 determines that the amount of oil in all compressors of all refrigeration units 20 has reached or exceeded the second threshold (step S4: YES), it terminates the second control, returns operation to step S1, and resumes the first control.

[0090] If the control unit 70 determines that there are no target units in which the amount of oil in the oil separator 23 is less than the first threshold value (step S2: NO), the control unit 70 returns operation to step S1 and continues the first control.

[0091] The operations of steps S1 to S4 described above are executed until, for example, a user performs an operation to terminate the operation of the refrigeration device 1.

[0092] As described above, the refrigeration device 1 according to the embodiment of the present disclosure includes N (N is an integer of 3 or more) refrigeration units 20 each having a compressor (first compressor 211, second compressor 212), an oil separator 23, and an oil return pipe Q1 that returns oil separated from the refrigerant by the oil separator 23 to the first compressor 211 and the second compressor 212; an oil supply pipe 61 that connects the oil return pipes Q1 of the N refrigeration units 20; N oil supply valves 62 that are arranged in the oil supply pipe 61 between the oil return pipes Q1 of adjacent refrigeration units 20 and control the flow of oil in the oil supply pipe 61; and a control unit 70 that controls to open all N oil supply valves 62 when it is determined that the amount of oil in the oil separator 23 of at least any of the N refrigeration units 20 is less than a first threshold value.

[0093] With this configuration, in the refrigeration system 1 according to the embodiment of the present disclosure, if there is a target unit among the N refrigeration units 20 in which the amount of oil in the oil separator 23 is less than the amount (first threshold) sufficient to supply oil to the first and second compressors 211, 212, the target unit can be replenished with oil from units other than the target unit via the oil supply pipe 61 and oil supply valve 62. This prevents problems (such as breakdowns) that may occur due to a lack of oil in the first and second compressors 211, 212 of the target unit. When replenishing oil, the control unit 70 only needs to open all oil supply valves 62 at once, eliminating the need to individually control multiple oil supply valves 62. This reduces the control cost of the control unit 70.

[0094] Furthermore, in the refrigeration device 1 according to the embodiment of the present disclosure, each refrigeration unit 20 further has a return valve V3 provided in the oil return pipe Q1, and the control unit 70 controls the refrigeration unit 20 (target unit) to close the return valve V3 when the amount of oil in the oil separator 23 is determined to be less than the first threshold value.

[0095] This prevents refrigerant gas from flowing from the oil separator 23 into the oil return pipe Q1 in the target unit.

[0096] In addition, in the refrigeration device 1 according to the embodiment of the present disclosure, each refrigeration unit 20 further has a pressure reducing valve 41 that reduces the pressure of the refrigerant separated by the oil separator 23, and the control unit 70 controls the pressure reducing valve 41 of each refrigeration unit 20 so that the pressure inside the oil separator 23 of the target unit is lower than the pressure inside the oil separator 23 of the refrigeration units 20 other than the target unit.

[0097] This reduces the pressure in the oil separator 23 of the target unit, making it easier for oil from refrigeration units 20 other than the target unit to flow into the oil separator 23 of the target unit. This prevents a situation in which oil from refrigeration units 20 other than the target unit flows into other refrigeration units 20 other than the target unit, preventing the target unit from being replenished with oil.

[0098] [Modifications] The present disclosure is not limited to the embodiments described above. Various modifications can be made to the present disclosure without departing from the spirit of the disclosure. Furthermore, the above embodiments and the modifications shown below can be combined in any way as long as they function properly.

[0099] For example, the oil supply pipe 61 does not need to be provided with a plurality of check valves 63. For example, the oil supply valve 62 may be configured as a directional control valve, and may be controlled by the control unit 70, so that the direction of the oil flowing through the oil supply pipe 61 can be arbitrarily controlled.

[0100] Furthermore, the oil supply pipe 61 does not have to be a looped pipe. The oil supply pipe of the present disclosure may be, for example, a straight pipe. Even in such a case, the control unit opens an oil supply valve provided on the oil supply pipe, so that oil is supplied from another refrigeration unit to a refrigeration unit having a small amount of oil in the oil separator and low pressure inside the oil separator. In this case, by configuring the oil supply valve as a directional control valve, oil can be supplied more efficiently.

[0101] Furthermore, in the above-described embodiment, the control unit 70 estimates (determines) the amount of oil in the oil separator 23 based on the detection results of the first and second oil amount detection units 211E, 212E provided in the first and second compressors 211, 212. However, in the present disclosure, for example, a detection unit that detects the amount of oil in each oil separator 23 may be provided for each oil separator 23, and the control unit 70 may determine whether the amount of oil in each oil separator 23 is less than the first threshold value based on the detection results of the detection unit.

[0102] In the above-described embodiment, an example was described in which the connecting unit 60 has an oil supply pipe 61, an oil supply valve 62, and a check valve 63, but at least one of the oil supply valve 62 and the check valve 63 may be included in any of the N refrigeration units 20.

[0103] In the above-described embodiment, a control unit 70 is provided to control the operation of the entire refrigeration apparatus 1. In the present disclosure, an independent control unit may be provided for each of the N refrigeration units 20, for example. In this case, the control units provided for each of the N refrigeration units 20 communicate with each other and operate in cooperation with each other, or one of the control units mainly controls the other control units, thereby achieving the same operation as in the above-described embodiment. In this case, the oil supply valve 62_1 provided between the refrigeration unit 20_1 and the refrigeration unit 20_2 may be controlled by, for example, a control unit provided in the refrigeration unit 20_1 or a control unit provided in the refrigeration unit 20_2.

[0104] In the above-described embodiment, the four refrigeration units 20 each have a split heat exchanger 43. In the present disclosure, for example, only one split heat exchanger may be provided for multiple refrigeration units. In this case, the piping extending from the gas cooler of each refrigeration unit may be connected to one split heat exchanger.

[0105] The disclosures of the specification, drawings and abstract contained in Japanese Patent Application No. 2023-127063, filed on August 3, 2023, are incorporated herein by reference in their entirety.

[0106] The present disclosure is applicable to refrigeration devices.

[0107] REFRIGERATION SYSTEM 20 REFRIGERATION UNIT 21 COMPRESSION SECTION 22 RADIATION HEAT EXCHANGER 23 OIL SEPARATOR 41 PRESSURE REDUCE VALVE 42 INTERCOOLER 43 SPLIT HEAT EXCHANGER 50 COOLING UNIT 60 CONNECTION UNIT 61 OIL SUPPLY 62 OIL SUPPLY VALVE 63 CHECK VALVE 70 CONTROL UNIT 211 SECOND COMPRESSOR 211A FIRST LOW STAGE SUCTION PORT 211B FIRST LOW STAGE DISCHARGE PORT 211C FIRST HIGH STAGE SUCTION PORT 211D FIRST HIGH STAGE DISCHARGE PORT 211E FIRST OIL AMOUNT DETECTION SECTION 212 SECOND COMPRESSOR 212A SECOND LOW STAGE SUCTION PORT 212B SECOND LOW STAGE DISCHARGE PORT 212C SECOND HIGH STAGE SUCTION PORT 212D SECOND HIGH STAGE DISCHARGE PORT 212E SECOND OIL AMOUNT DETECTION SECTION 221 RADIATION BLOWER 222 Intercooler 223 Gas cooler 224 Outside air temperature sensor 431 First flow path 432 Second flow path 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 Piping Q1 Oil return pipe Q10 Main pipe Q11 First branch pipe Q12 Second branch pipe Q13 Connecting pipe V1 First oil valve V11 Gas return motorized valve V12 Liquid return motorized valve V2 Second oil valve V3 Return valve

Claims

1. A refrigeration system comprising: N (N is an integer of 2 or greater) refrigeration units, each having a compressor, an oil separator, and an oil return pipe for returning oil separated from a refrigerant by the oil separator to the compressor; an oil supply pipe connecting the oil return pipes of each of the N refrigeration units; N oil supply valves disposed in the oil supply pipe between the oil return pipes of adjacent refrigeration units and controlling the flow of oil in the oil supply pipe; and a control unit that controls the opening of all N oil supply valves when it is determined that the amount of oil in the oil separator of at least any of the N refrigeration units is less than a predetermined threshold value.

2. The refrigeration device according to claim 1, wherein the refrigeration unit further has a return valve provided in the oil return pipe, and the control unit controls to close the return valve of the refrigeration unit when it is determined that the amount of oil in the oil separator is less than the predetermined threshold value.

3. The refrigeration system according to claim 1, wherein the oil supply pipe has a loop-shaped pipe.

4. The refrigeration system according to claim 1, wherein the N oil valves are directional control valves capable of controlling a flow direction of the oil in the oil supply pipe.

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

6. The refrigeration device of claim 1, wherein the refrigeration units further have pressure reducing valves for reducing the pressure of the refrigerant separated by the oil separator, and the control unit controls the pressure reducing valves of each refrigeration unit so that the pressure within the oil separator of the refrigeration unit in which it has been determined that the amount of oil in the oil separator is less than a predetermined threshold value is lower than the pressure within the oil separator of the refrigeration unit in which it has not been determined that the amount of oil in the oil separator is less than the predetermined threshold value.

7. A control method for a refrigeration system comprising: N (N is an integer of 2 or more) refrigeration units, each having a compressor, an oil separator, and an oil return pipe that returns oil separated from the refrigerant by the oil separator to the compressor; an oil supply pipe connecting the oil return pipes of each of the N refrigeration units; N oil supply valves arranged in the oil supply pipe between the oil return pipes of adjacent refrigeration units and controlling the flow of oil in the oil supply pipe; and a control unit, comprising: determining whether the amount of oil in the oil separator of at least any of the N refrigeration units is less than a predetermined threshold; and opening all of the N oil supply valves when it is determined that the amount of oil in the oil separator of at least any of the refrigeration units is less than the predetermined threshold.

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