Heat source unit and refrigeration device

Abstract

A heat source unit (10) includes a heat source side circuit (11) and a controller (101). In the heat source side circuit (11), an expansion valve (14a) is arranged between a heat source side heat exchanger (13) and an accumulator (15). In a state where a compression component (C) of the heat source side circuit (11) has stopped, the controller (101) controls the expansion valve (14a) based on one or both of a refrigerant pressure of the accumulator (15) and a refrigerant pressure of the heat source side heat exchanger (13).

Description

Technical Field

[0001] This disclosure relates to a heat source unit and a refrigeration device. Background Technology

[0002] Patent document 1 discloses a heat source unit for a refrigeration device. The heat source unit is connected to a user-side unit to perform a refrigeration cycle. The heat source unit includes equipment such as a compressor, an outdoor heat exchanger, and a liquid receiver.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2022-152437 Summary of the Invention

[0006] -The technical problem the invention aims to solve-

[0007] Liquid refrigerant is stored in the receiver of the heat source unit. Therefore, under conditions of high outdoor air temperature, such as in summer, the following situation occurs: during periods when the heat source unit is not in operation, heat is transferred from the outdoor air to the liquid refrigerant in the receiver, causing some of the liquid refrigerant to evaporate and the refrigerant pressure in the receiver to rise. Furthermore, when the refrigerant pressure in the receiver exceeds its design pressure (the upper limit of the design pressure), the receiver may be damaged.

[0008] The purpose of this disclosure is to prevent damage to the liquid storage tank in advance, thereby ensuring the reliability of the heat source unit.

[0009] - Technical solutions for solving technical problems -

[0010] The first aspect of this disclosure pertains to a heat source unit 10 connected to a heat source unit 50, 60 for a refrigeration cycle. The heat source unit 10 includes a heat source side loop 11 and a controller 101. The heat source side loop 11 has a compression component C, a heat source side heat exchanger 13, an expansion valve 14a, and a receiver 15. The compression component C has one or more compressors 21, 22, 23. The controller 101 controls the expansion valve 14a. In the heat source side loop 11, the expansion valve 14a is arranged between the heat source side heat exchanger 13 and the receiver 15. During periods when the compression component C is stopped, the controller 101 controls the expansion valve 14a based on either the refrigerant pressure of the receiver 15 or the refrigerant pressure of the heat source side heat exchanger 13, or both.

[0011] In the heat source side circuit 11 of the first aspect, an expansion valve 14a is provided between the heat source side heat exchanger 13 and the liquid receiver 15. When the expansion valve 14a is open, the heat source side heat exchanger 13 and the liquid receiver 15 are in communication with each other. When the expansion valve 14a is closed, the connection between the heat source side heat exchanger 13 and the liquid receiver 15 is cut off. Therefore, by controlling the expansion valve 14a, the flow state of the refrigerant between the heat source side heat exchanger 13 and the liquid receiver 15 can be changed.

[0012] In the first aspect, the controller 101 controls the expansion valve 14a during the shutdown of the compression component C. Even during the shutdown of the compression component C, if the controller 101 controls the expansion valve 14a, the flow state of the refrigerant between the heat exchanger 13 on the heat source side and the receiver 15 will change. As a result, the refrigerant pressure in the receiver 15 and the refrigerant pressure in the heat exchanger 13 on the heat source side change. In this aspect, the controller 101 controls the expansion valve 14a during the shutdown of the compression component C based on either the refrigerant pressure in the receiver 15 or the refrigerant pressure in the heat exchanger 13 on the heat source side, or both. Therefore, according to this aspect, the refrigerant pressure in the receiver 15 during the shutdown of the compression component C can be controlled, thereby suppressing excessive rise in the refrigerant pressure in the receiver 15.

[0013] The second aspect of this disclosure, based on the first aspect described above, involves the controller 101 performing a first action after switching the expansion valve 14a to a closed state along with the cessation of the compression component C. In this first action, the expansion valve 14a is opened when the refrigerant pressure of the heat exchanger 13 on the heat source side is lower than a first pressure.

[0014] In the second aspect, the controller 101 closes the expansion valve 14a as the compression component C stops. The stopping of the compression component C and the closing of the expansion valve 14a do not need to occur simultaneously. Even when the expansion valve 14a is closed, refrigerant in the heat source-side heat exchanger 13 flows out gradually through the compression component C, causing the refrigerant pressure in the heat source-side heat exchanger 13 to gradually decrease. Therefore, the controller 101 of the second aspect performs a first action after closing the expansion valve 14a as the compression component C stops. The first action is to open the expansion valve 14a when the refrigerant pressure in the heat source-side heat exchanger 13 is lower than a first pressure. When the expansion valve 14a is open, the refrigerant in the receiver 15 can move towards the heat source-side heat exchanger 13 through the expansion valve 14a. Therefore, the rise in refrigerant pressure in the receiver 15 can be suppressed.

[0015] The third aspect of this disclosure is based on the second aspect described above, wherein after the controller 101 performs the first action, it performs a second action, in which the expansion valve 14a is closed when the refrigerant pressure of the liquid receiver 15 is higher than the second pressure.

[0016] In the third aspect, after executing the first action, the controller 101 performs a second action. The second action is to close the expansion valve 14a when the refrigerant pressure in the receiver 15 is higher than the second pressure. When the refrigerant pressure in the receiver 15 is higher than the second pressure, the outdoor air temperature is more likely to be higher. Under conditions of higher outdoor air temperature, the liquid refrigerant remaining in the heat exchanger 13 on the heat source side evaporates, and the refrigerant pressure in the heat exchanger 13 on the heat source side increases.

[0017] Therefore, the controller 101 of the third aspect performs a second action to close the expansion valve 14a. When the expansion valve 14a is closed, the flow of refrigerant from the heat source side heat exchanger 13 to the receiver 15 is cut off by the expansion valve 14a. Therefore, even if the refrigerant pressure in the heat source side heat exchanger 13 rises, the resulting rise in the refrigerant pressure in the receiver 15 can be suppressed.

[0018] The fourth aspect of this disclosure, based on the third aspect described above, involves the heat source-side circuit 11 having a venting passage 37 for delivering gaseous refrigerant from the reservoir 15 to the compression unit C. After performing the second action, the controller 101 performs a third action, in which, when the refrigerant pressure in the reservoir 15 is higher than a third pressure, the compression unit C is activated, thereby drawing in gaseous refrigerant from the reservoir 15 via the venting passage 37.

[0019] If the refrigerant pressure in the receiver 15 continues to rise after the expansion valve 14a is closed by the second action, the controller 101 of the fourth aspect performs a third action. The third action involves activating the compressor C when the refrigerant pressure Prv in the receiver 15 is higher than the third pressure P3, thereby causing the compressor C to draw gaseous refrigerant into the receiver 15 via the venting passage 37. When the compressor C draws gaseous refrigerant out of the receiver 15, the refrigerant pressure in the receiver 15 decreases.

[0020] The fifth aspect of this disclosure, based on any one of the first to fourth aspects described above, involves filling the heat source side circuit 11 with carbon dioxide as a refrigerant.

[0021] In the fifth aspect, carbon dioxide is used as the refrigerant in the heat source side circuit 11.

[0022] The sixth aspect of this disclosure is a refrigeration apparatus comprising a heat source unit 10 according to any one of the first to fifth aspects described above, and a utilization side unit 50, 60 connected to the heat source unit 10.

[0023] In the sixth aspect, the refrigeration unit 1 is composed of the heat source unit 10 and the utilization side units 50 and 60. Attached Figure Description

[0024] Figure 1 This is a piping system diagram showing the structure of the refrigeration device according to the first embodiment;

[0025] Figure 2 This is a block diagram showing the structure of the controller of the heat source unit according to the first embodiment;

[0026] Figure 3 This is equivalent to showing the flow of refrigerant during refrigeration operation. Figure 1 The image;

[0027] Figure 4 This shows the flow of refrigerant under the first heating operation, equivalent to Figure 1 The image;

[0028] Figure 5 This shows the flow of refrigerant under the second heating operation, equivalent to Figure 1 The image;

[0029] Figure 6 This is equivalent to showing the flow of refrigerant under the third heating operation. Figure 1 The image;

[0030] Figure 7 This shows the flow of refrigerant under reduced pressure operation, equivalent to Figure 1 The image;

[0031] Figure 8 This is a flowchart illustrating the operation of the controller according to the first embodiment;

[0032] Figure 9 This is a piping system diagram showing the structure of the refrigeration device according to the second embodiment. Detailed Implementation

[0033] The embodiments will be described with reference to the accompanying drawings. It should be noted that the following embodiments are merely preferred examples and are not intended to limit the invention, its application, or its scope of use.

[0034] (First Implementation)

[0035] The first embodiment will be described. The refrigeration device 1 of this embodiment is capable of cooling the object being cooled and conditioning the indoor air. The object being cooled here includes the air inside equipment such as cold storage rooms, freezers, and display cases.

[0036] - Overall structure of the refrigeration unit -

[0037] like Figure 1 As shown, the refrigeration unit 1 includes an outdoor heat source unit 10, an air conditioning unit 50 for conditioning the indoor air, and a cooling unit 60 for cooling the air inside the storage room. In this embodiment, the refrigeration unit 1 includes one heat source unit 10, multiple cooling units 60, and multiple air conditioning units 50. It should be noted that the number of cooling units 60 or air conditioning units 50 included in the refrigeration unit 1 can also be one.

[0038] In the refrigeration unit 1, the refrigerant circuit 6 is composed of the heat source unit 10, the cooling unit 60, the air conditioning unit 50, and the connecting pipes 2, 3, 4, and 5 that connect these units 10, 50, and 60.

[0039] In refrigerant circuit 6, the refrigerant circulates, thereby performing a refrigeration cycle. In this embodiment, the refrigerant in refrigerant circuit 6 is carbon dioxide. Refrigerant circuit 6 is configured to perform a refrigeration cycle with high pressure reaching or exceeding the critical pressure of the refrigerant.

[0040] It should be noted that the refrigerant filled in refrigerant circuit 6 is not limited to carbon dioxide. Refrigerant circuit 6 can also be filled with so-called Freon refrigerant.

[0041] In the refrigerant circuit 6, multiple air conditioning units 50 are connected to the heat source unit 10 via a first liquid connection pipe 2 and a first gas connection pipe 3. In the refrigerant circuit 6, the multiple air conditioning units 50 are connected in parallel to each other.

[0042] In the refrigerant circuit 6, multiple cooling units 60 are connected to the heat source unit 10 via a second liquid connection pipe 4 and a second gas connection pipe 5. In the refrigerant circuit 6, multiple cooling units 60 are connected in parallel to each other.

[0043] -Heat source unit-

[0044] The heat source unit 10 has an outdoor fan 12 and an outdoor circuit 11. The outdoor circuit 11 includes a compression component C, a flow path switching mechanism 30, an outdoor heat exchanger 13, a first outdoor expansion valve 14a, a liquid receiver 15, a subcooled heat exchanger 16, an intercooler 17, and a bypass pipe 85. The outdoor circuit 11 is a heat source side circuit. In addition, the heat source unit 10 has a controller 101.

[0045] <Compression Components>

[0046] Compression unit C compresses the refrigerant. Compression unit C includes a high-pressure stage compressor 21, a first low-pressure stage compressor 23, and a second low-pressure stage compressor 22. The high-pressure stage compressor 21, the first low-pressure stage compressor 23, and the second low-pressure stage compressor 22 are rotary compressors whose compression mechanisms are driven by an electric motor. These compressors 21, 22, and 23 are, for example, hermetic scroll compressors. The high-pressure stage compressor 21, the first low-pressure stage compressor 23, and the second low-pressure stage compressor 22 are configured as variable-capacity compressors capable of changing the rotational speed of the compression mechanism.

[0047] Compression unit C performs two-stage compression. The first low-pressure stage compressor 23 compresses the refrigerant already drawn from the air conditioning unit 50 or the outdoor heat exchanger 13. The second low-pressure stage compressor 22 compresses the refrigerant already drawn from the cooling unit 60. The high-pressure stage compressor 21 draws in and compresses the refrigerant already injected by the first low-pressure stage compressor 23 and the refrigerant already injected by the second low-pressure stage compressor 22.

[0048] A high-pressure stage suction pipe 21a and a high-pressure stage discharge pipe 21b are connected to the high-pressure stage compressor 21. The high-pressure stage discharge pipe 21b is a discharge pipe for the refrigerant that has been discharged from the high-pressure stage compressor 21. A first low-pressure stage suction pipe 23a and a first low-pressure stage discharge pipe 23b are connected to the first low-pressure stage compressor 23. The first low-pressure stage suction pipe 23a is a suction pipe for the refrigerant to be drawn into the first low-pressure stage compressor 23. A second low-pressure stage suction pipe 22a and a second low-pressure stage discharge pipe 22b are connected to the second low-pressure stage compressor 22. In the compression unit C, both the first low-pressure stage discharge pipe 23b and the second low-pressure stage discharge pipe 22b are connected to the high-pressure stage suction pipe 21a.

[0049] The second low-pressure stage suction pipe 22a is connected to the second gas connection pipe 5. The second low-pressure stage compressor 22 is connected to the cooling unit 60 via the second gas connection pipe 5. The first low-pressure stage suction pipe 23a is connected to the air conditioning unit 50 via the flow path switching mechanism 30 and the first gas connection pipe 3.

[0050] The compression component C includes a first low-pressure stage pipe 24c and a second low-pressure stage pipe 24b. The first low-pressure stage pipe 24c is a pipe through which refrigerant flows, bypassing the first low-pressure stage compressor 23. One end of the first low-pressure stage pipe 24c is connected to a first low-pressure stage suction pipe 23a, and the other end is connected to a first low-pressure stage discharge pipe 23b. The first low-pressure stage pipe 24c is arranged parallel to the first low-pressure stage compressor 23. The second low-pressure stage pipe 24b is a pipe through which refrigerant flows, bypassing the second low-pressure stage compressor 22. One end of the second low-pressure stage pipe 24b is connected to a second low-pressure stage suction pipe 22a, and the other end is connected to a second low-pressure stage discharge pipe 22b. The second low-pressure stage pipe 24b is arranged parallel to the second low-pressure stage compressor 22.

[0051] <Flow path switching mechanism>

[0052] The flow path switching mechanism 30 is a mechanism for switching the flow path of the refrigerant in the refrigerant circuit 6. The flow path switching mechanism 30 has a first pipe 31, a second pipe 32, a third pipe 33, a fourth pipe 34, a first switching valve 81, and a second switching valve 82.

[0053] The inflow ends of the first pipe 31 and the second pipe 32 are connected to the high-pressure stage discharge pipe 21b. The outflow ends of the third pipe 33 and the fourth pipe 34 are connected to the first low-pressure stage suction pipe 23a.

[0054] The first switching valve 81 and the second switching valve 82 respectively switch the flow path of the refrigerant to be drawn into the first low-pressure stage compressor 23 and the flow path of the refrigerant already sprayed from the high-pressure stage compressor 21. The first switching valve 81 and the second switching valve 82 are both four-way reversing valves with four valve ports.

[0055] The first valve port of the first switching valve 81 is connected to the outflow end of the first pipeline 31. The second valve port of the first switching valve 81 is connected to the inflow end of the third pipeline 33. The third valve port of the first switching valve 81 is closed. The fourth valve port of the first switching valve 81 is connected to one end of the first outdoor gas pipe 35. The other end of the first outdoor gas pipe 35 is connected to the first gas connection pipeline 3.

[0056] The first port of the second switching valve 82 is connected to the outflow end of the second pipe 32. The second port of the second switching valve 82 is connected to the inflow end of the fourth pipe 34. The third port of the second switching valve 82 is connected to the second outdoor gas pipe 36. The fourth port of the second switching valve 82 is closed.

[0057] The first switching valve 81 and the second switching valve 82 are respectively in the first state ( Figure 1 The state shown by the solid line) and the second state ( Figure 1Switching is performed between the states indicated by the dashed lines. In each switching valve 81 and 82 in the first state, the first valve port is connected to the third valve port, and the second valve port is connected to the fourth valve port. In each switching valve 81 and 82 in the second state, the first valve port is connected to the fourth valve port, and the second valve port is connected to the third valve port.

[0058] It should be noted that in the flow path switching mechanism 30, the first switching valve 81 and the second switching valve 82 can also be three-way valves with three valve ports.

[0059] <First Outdoor Heat Exchanger>

[0060] The outdoor heat exchanger 13 constitutes a heat source-side heat exchanger. The outdoor heat exchanger 13 is a finned-tube air heat exchanger. An outdoor fan 12 is arranged near the outdoor heat exchanger 13. The outdoor fan 12 delivers outdoor air. The outdoor heat exchanger 13 allows the refrigerant flowing within it to exchange heat with the outdoor air delivered by the outdoor fan 12.

[0061] A second outdoor gas pipe 36 is connected to the gas end of the outdoor heat exchanger 13. An outdoor flow path O is connected to the liquid end of the outdoor heat exchanger 13.

[0062] <Outdoor Flow Path>

[0063] The outdoor flow path O includes: outdoor first pipe O1, outdoor second pipe O2, outdoor third pipe O3, outdoor fourth pipe O4, outdoor fifth pipe O5, outdoor sixth pipe O6, outdoor seventh pipe O7, and outdoor eighth pipe O8.

[0064] One end of the outdoor first pipe O1 is connected to the liquid end of the outdoor heat exchanger 13. One end of the outdoor second pipe O2 and one end of the outdoor third pipe O3 are respectively connected to the other end of the outdoor first pipe O1. The other end of the outdoor second pipe O2 is connected to the top of the liquid reservoir 15.

[0065] One end of the outdoor fourth pipe O4 is connected to the bottom of the reservoir 15. One end of the outdoor fifth pipe O5 and the other end of the outdoor third pipe O3 are respectively connected to the other end of the outdoor fourth pipe O4. One end of the outdoor sixth pipe O6 and one end of the outdoor eighth pipe O8 are respectively connected to the other end of the outdoor fifth pipe O5.

[0066] The other end of the outdoor eighth pipe O8 is connected to the first liquid-side main pipe 4a of the second liquid connection pipe 4. The outdoor eighth pipe O8 is a liquid pipe for supplying liquid refrigerant downstream of the liquid receiver 15. The other end of the outdoor sixth pipe O6 is connected to the first liquid connection pipe 2. One end of the outdoor seventh pipe O7 is connected midway through the outdoor sixth pipe O6. The other end of the outdoor seventh pipe O7 is connected midway through the outdoor second pipe O2.

[0067] <Outdoor Expansion Valve>

[0068] A first outdoor expansion valve 14a is installed on the first outdoor pipe o1 of the outdoor circuit 11. Additionally, a second outdoor expansion valve 14b is installed on the third outdoor pipe o3 of the outdoor circuit 11. Both the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are electronic expansion valves capable of adjusting their opening degree. Both the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are expansion valves installed on the outdoor circuit 11, which serves as the heat source side circuit.

[0069] <Liquid Storage>

[0070] The receiver 15 constitutes a container for storing refrigerant. The receiver 15 is located downstream of the first outdoor expansion valve 14a. In the receiver 15, the refrigerant is separated into gaseous refrigerant and liquid refrigerant. The other end of the outdoor second pipe O2 and one end of the vent pipe 37 (described later) are connected to the top of the receiver 15.

[0071] The receiver 15 is covered with insulation material 15a. Glass wool can be cited as an example of insulation material 15a. By covering the receiver 15 with insulation material 15a, the amount of heat transferred from the outdoor air to the refrigerant in the receiver 15 is reduced under conditions of high outdoor air temperature, such as in summer.

[0072] Intermediate Injection Circuit

[0073] The outdoor circuit 11 includes an intermediate injection circuit 49. The intermediate injection circuit 49 is a circuit that supplies refrigerant, after being depressurized by the first outdoor expansion valve 14a, to the high-pressure stage suction pipe 21a. The intermediate injection circuit 49 includes a vent pipe 37 and an injection pipe 38.

[0074] One end of the injection pipe 38 is connected to the middle of the fifth outdoor pipe o5. The other end of the injection pipe 38 is connected to the high-pressure stage suction pipe 21a. A pressure reducing valve 40 is installed on the injection pipe 38. The pressure reducing valve 40 is an expansion valve with a variable opening degree.

[0075] The vent pipe 37 is a conduit used to deliver gaseous refrigerant from the receiver 15 to the high-pressure stage suction pipe 21a. The vent pipe 37 forms a venting passage. Specifically, one end of the vent pipe 37 is connected to the top of the receiver 15. The other end of the vent pipe 37 is connected midway to the injection pipe 38. A vent valve 39 is connected to the vent pipe 37. The vent valve 39 is an electronically adjustable expansion valve.

[0076] <Subcooled heat exchanger>

[0077] The outdoor circuit 11 includes a subcooled heat exchanger 16. The subcooled heat exchanger 16 is a heat exchanger that cools the refrigerant (mainly liquid refrigerant) separated from the receiver 15. The subcooled heat exchanger 16 is located downstream of the receiver 15. The subcooled heat exchanger 16 has a first flow path 16a and a second flow path 16b. The subcooled heat exchanger 16 allows heat exchange between the refrigerant flowing in the first flow path 16a and the refrigerant flowing in the second flow path 16b.

[0078] In the subcooled heat exchanger 16, the refrigerant flowing in the first flow path 16a is cooled. The first flow path 16a is connected midway to the outdoor fourth pipe o4, which is a liquid pipe for supplying liquid refrigerant in the outdoor circuit 11.

[0079] The second flow path 16b is included in the intermediate injection circuit 49. Specifically, the second flow path 16b is connected downstream of the pressure reducing valve 40 in the injection pipe 38. The second flow path 16b supplies the refrigerant flow after its pressure is reduced by the pressure reducing valve 40.

[0080] Intercooler

[0081] Intercooler 17 is connected to intermediate flow path 41. One end of intermediate flow path 41 is connected to both the first low-pressure stage ejector pipe 23b and the second low-pressure stage ejector pipe 22b. The other end of intermediate flow path 41 is connected to high-pressure stage suction pipe 21a.

[0082] Intercooler 17 is a finned tube air heat exchanger. A blower fan 17a is arranged near intercooler 17. Intercooler 17 allows the refrigerant flowing inside it to exchange heat with outdoor air supplied by blower fan 17a.

[0083] <Check valve>

[0084] The outdoor circuit 11 includes: a first check valve CV1, a second check valve CV2, a third check valve CV3, a fourth check valve CV4, a fifth check valve CV5, a sixth check valve CV6, a seventh check valve CV7, an eighth check valve CV8, and a ninth check valve CV9. These check valves CV1 to CV9 allow refrigerant to flow towards... Figure 1 The refrigerant should flow in the direction indicated by the arrow; refrigerant should not flow in the opposite direction of the arrow.

[0085] The first check valve CV1 is connected to the high-pressure stage outlet pipe 21b. The second check valve CV2 is connected to the second low-pressure stage outlet pipe 22b. The third check valve CV3 is connected to the first low-pressure stage outlet pipe 23b. The fourth check valve CV4 is connected to the outdoor second pipe O2. The fifth check valve CV5 is connected to the outdoor third pipe O3. The sixth check valve CV6 is connected to the outdoor sixth pipe O6. The seventh check valve CV7 is connected to the outdoor seventh pipe O7. The eighth check valve CV8 is connected to the second low-pressure stage pipe 24b. The ninth check valve CV9 is connected to the first low-pressure stage pipe 24c.

[0086] <sensor>

[0087] The heat source unit 10 has various sensors. These sensors include: a high-pressure sensor 71, an intermediate-pressure sensor 72, a first low-pressure sensor 73, a second low-pressure sensor 74, a liquid refrigerant pressure sensor 75, and a high-pressure stage suction temperature sensor 77.

[0088] The high-pressure sensor 71 is connected to the high-pressure stage discharge pipe 21b. The high-pressure sensor 71 detects the pressure of the refrigerant (high-pressure refrigerant pressure HP) that has been discharged by the high-pressure stage compressor 21.

[0089] Intermediate pressure sensor 72 is connected downstream of intercooler 17 in intermediate flow path 41. Intermediate pressure sensor 72 detects the pressure of the refrigerant in intermediate flow path 41. In other words, intermediate pressure sensor 72 detects the pressure of the refrigerant (intermediate pressure refrigerant MP) between high-pressure stage compressor 21, second low-pressure stage compressor 22, and first low-pressure stage compressor 23.

[0090] The first low-pressure sensor 73 is connected to the second low-pressure stage suction pipe 22a. The first low-pressure sensor 73 detects the pressure of the suction refrigerant (the pressure LP1 of the first low-pressure refrigerant) to be drawn into the second low-pressure stage compressor 22.

[0091] The second low-pressure sensor 74 is connected to the first low-pressure stage suction pipe 23a. The second low-pressure sensor 74 detects the pressure of the suction refrigerant (the pressure LP2 of the second low-pressure refrigerant) to be drawn into the first low-pressure stage compressor 23.

[0092] A liquid refrigerant pressure sensor 75 is connected to the outdoor fourth pipe O4. The liquid refrigerant pressure sensor 75 detects the pressure of the refrigerant flowing in the outdoor fourth pipe O4. In other words, the liquid refrigerant pressure sensor 75 detects the pressure of the liquid refrigerant in the receiver 15.

[0093] A high-pressure stage suction temperature sensor 77 is installed on the high-pressure stage suction pipe 21a. The high-pressure stage suction temperature sensor 77 detects the temperature of the refrigerant flowing in the high-pressure stage suction pipe 21a. In other words, the high-pressure stage suction temperature sensor 77 detects the temperature of the refrigerant to be drawn into the high-pressure stage compressor 21.

[0094] <Design pressure of outdoor circuit>

[0095] In the outdoor circuit 11, there is a portion with a design upper limit pressure of the first design pressure Pu1 and a portion with a design upper limit pressure of the second design pressure Pu2.

[0096] Specifically, the upper limit pressure of the first outdoor gas pipe 35, the second outdoor gas pipe 36, the flow path switching mechanism 30, the outdoor heat exchanger 13, and the first outdoor expansion valve 14a is the first design pressure Pu1. On the other hand, the upper limit pressure of the outdoor flow path O, the liquid reservoir 15, the subcooled heat exchanger 16, the vent pipe 37, the injection pipe 38, the vent valve 39, the pressure reducing valve 40, the intermediate flow path 41, and the intercooler 17 is the second design pressure Pu2.

[0097] The first design pressure Pu1 is higher than the second design pressure Pu2. The first design pressure Pu1 is, for example, 12 MPa. The second design pressure Pu2 is, for example, 9 MPa.

[0098] <Controller>

[0099] like Figure 2 As shown, the controller 101 includes a microcomputer 102 and a storage device 105. The microcomputer 102 is mounted on a control board, and the storage device 105 stores software for operating the microcomputer 102. The storage device 105 is a semiconductor memory. The controller 101 controls the components of the heat source unit 10.

[0100] The microcomputer 102 of the controller 101 functions as the reservoir pressure control unit 103 by executing a program stored in the storage device 105. The reservoir pressure control unit 103 performs actions to maintain the refrigerant pressure in the reservoir 15 at a level lower than the second design pressure Pu2 during the shutdown of the compression component C.

[0101] -Air conditioning unit-

[0102] Air conditioning unit 50 is the first-use unit installed in the room. Air conditioning unit 50 regulates the air in the indoor space. Air conditioning unit 50 has an indoor fan 52 and an indoor circuit 51. A first liquid connection pipe 2 is connected to the liquid end of the indoor circuit 51. A first gas connection pipe 3 is connected to the gas end of the indoor circuit 51.

[0103] In the indoor circuit 51, an indoor expansion valve 53 and an indoor heat exchanger 54 are arranged sequentially from the liquid end to the gas end. The indoor expansion valve 53 is an electronic expansion valve with variable opening. The indoor heat exchanger 54 is a finned tube air heat exchanger. An indoor fan 52 is arranged near the indoor heat exchanger 54. The indoor fan 52 delivers indoor air. The indoor heat exchanger 54 facilitates heat exchange between the refrigerant flowing within it and the indoor air delivered by the indoor fan 52.

[0104] - Cooling Unit -

[0105] Cooling unit 60 is a second-use unit installed within the room. Cooling unit 60 is, for example, a refrigerated display case installed in a convenience store or similar store. It should be noted that cooling unit 60 can also be a unit cooler used to cool the air inside a cold storage room.

[0106] The cooling unit 60 has a cooling fan 62 and a cooling circuit 61. A liquid-side branch pipe 4c of a second liquid connection pipe 4 is connected to the liquid end of the cooling circuit 61. A gas-side branch pipe 5c of a second gas connection pipe 5 is connected to the gas end of the cooling circuit 61.

[0107] In the cooling circuit 61, a cooling expansion valve 63 and a cooling heat exchanger 64 are arranged sequentially from the liquid end to the gas end. The cooling expansion valve 63 is an electronically controlled expansion valve with a variable opening. The cooling heat exchanger 64 is a finned tube air heat exchanger. A cooling fan 62 is arranged near the cooling heat exchanger 64. The cooling fan 62 delivers air from the storage chamber. The cooling heat exchanger 64 allows the refrigerant flowing inside it to exchange heat with the air delivered by the cooling fan 62.

[0108] - Operation of the refrigeration unit -

[0109] The operation of the refrigeration unit 1 will be described. The refrigeration unit 1 performs refrigeration operation, first heating operation, second heating operation, and third heating operation. In addition, the refrigeration unit 1 also performs defrosting operation and pressure reduction operation. The defrosting operation melts the frost attached to the outdoor heat exchanger 13, and the pressure reduction operation is used to reduce the refrigerant pressure in the liquid receiver 15.

[0110] <Refrigeration Operation>

[0111] Reference Figure 3 The refrigeration operation of refrigeration unit 1 will be explained. Refrigeration operation refers to the operation of air conditioning unit 50 to cool the indoor space.

[0112] During refrigeration operation, the first switching valve 81 and the second switching valve 82 are set to the first state, and the second outdoor expansion valve 14b is kept closed. Additionally, during refrigeration operation, the first low-pressure stage compressor 23, the second low-pressure stage compressor 22, and the high-pressure stage compressor 21 operate. During refrigeration operation, the refrigerant circulates in the refrigerant circuit 6, thereby performing a refrigeration cycle. The outdoor heat exchanger 13 functions as a heat exchanger (gas cooler), while the cooling heat exchanger 64 and the indoor heat exchanger 54 function as evaporators.

[0113] Refrigerant ejected from the high-pressure stage compressor 21 flows into the outdoor heat exchanger 13 through the second switching valve 82, releasing heat to the outdoor air. The refrigerant that has passed through the outdoor heat exchanger 13 is depressurized upon passing through the first outdoor expansion valve 14a, then passes through the receiver 15, and is subsequently cooled during its passage through the first flow path 16a of the subcooled heat exchanger 16. A portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows through the injection pipe 38 into the second flow path 16b of the subcooled heat exchanger 16, evaporates after absorbing heat, and then flows into the high-pressure stage suction pipe 21a. The remaining portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows separately into the first liquid connection pipe 2 and the second liquid connection pipe 4.

[0114] The refrigerant flowing in the first liquid connection pipe 2 is distributed to multiple air conditioning units 50. In each air conditioning unit 50, the refrigerant that has flowed into the indoor circuit 51 is depressurized as it passes through the indoor expansion valve 53, and then evaporates by absorbing heat from the indoor air in the indoor heat exchanger 54. Each air conditioning unit 50 blows the air that has been cooled in the indoor heat exchanger 54 into the indoor space.

[0115] The refrigerant that has flowed out of the indoor heat exchanger 54 of each air conditioning unit 50 flows into the first gas connection pipe 3 and merges with it, then flows into the first outdoor gas pipe 35 of the outdoor circuit 11, and then flows into the first low-pressure stage suction pipe 23a through the first switching valve 81, and is then sucked in and compressed by the first low-pressure stage compressor 23.

[0116] The refrigerant flowing in the second liquid connection pipe 4 is distributed to multiple cooling units 60. In each cooling unit 60, the refrigerant that has flowed into the cooling circuit 61 is depressurized as it passes through the cooling expansion valve 63, and then evaporates by absorbing heat from the air inside the storage unit in the cooling heat exchanger 64. Each cooling unit 60 blows the air that has been cooled in the cooling heat exchanger 64 toward the storage space.

[0117] The refrigerant that has flowed out of the cooling heat exchanger 64 of each cooling unit 60 flows into the second gas connection pipe 5 and merges with it, then flows into the second low-pressure stage suction pipe 22a of the outdoor circuit 11, and is then sucked in and compressed by the second low-pressure stage compressor 22.

[0118] The refrigerant, compressed in the first low-pressure stage compressor 23 and the second low-pressure stage compressor 22 respectively, releases heat to the outside air in the intercooler 17, and then merges with the refrigerant flowing in the injection pipe 38 before being drawn into the high-pressure stage compressor 21. The high-pressure stage compressor 21 compresses the drawn-in refrigerant and then sprays it out.

[0119] <First Heating Operation>

[0120] Reference Figure 4 The first heating operation of the refrigeration unit 1 will be explained. The first heating operation is the operation in which the air conditioning unit 50 heats the room. The first heating operation is carried out under the condition that the heat released by the refrigerant in the air conditioning unit 50 is less than the heat absorbed by the refrigerant in the cooling unit 60.

[0121] During the first heating operation, the first switching valve 81 is set to the second state, the second switching valve 82 is set to the first state, and the second outdoor expansion valve 14b is kept closed. Additionally, during the first heating operation, the first low-pressure stage compressor 23 is off, while the second low-pressure stage compressor 22 and the high-pressure stage compressor 21 operate. During the first heating operation, the refrigerant circulates in the refrigerant circuit 6, thereby performing a refrigeration cycle. The indoor heat exchanger 54 and the outdoor heat exchanger 13 function as heat exchangers (gas coolers), and the cooling heat exchanger 64 functions as an evaporator.

[0122] A portion of the refrigerant that has been injected from the high-pressure stage compressor 21 flows into the first outdoor gas pipe 35 through the first switching valve 81, and the remaining portion flows into the second outdoor gas pipe 36 through the second switching valve 82.

[0123] Refrigerant flowing in the first outdoor gas pipe 35 is distributed to multiple air conditioning units 50 via the first gas connection pipe 3. In each air conditioning unit 50, the refrigerant that has flowed into the indoor circuit 51 releases heat towards the indoor air in the indoor heat exchanger 54, and then, after being depressurized by the indoor expansion valve 53, flows into the first liquid connection pipe 2. The refrigerant that has flowed from each air conditioning unit 50 into the first liquid connection pipe 2 flows into the liquid receiver 15 of the outdoor circuit 11. Each air conditioning unit 50 blows air that has been heated in the indoor heat exchanger 54 into the indoor space.

[0124] The refrigerant flowing in the second outdoor gas pipe 36 flows into the outdoor heat exchanger 13 and releases heat to the outdoor air. The refrigerant that has passed through the outdoor heat exchanger 13 is depressurized when it passes through the first outdoor expansion valve 14a and then flows into the liquid receiver 15.

[0125] The refrigerant flowing out of the receiver 15 is cooled during its passage through the first flow path 16a of the subcooled heat exchanger 16. A portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows through the injection pipe 38 into the second flow path 16b of the subcooled heat exchanger 16, and after absorbing heat and evaporating, flows into the high-pressure stage suction pipe 21a. The remaining portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows into the second liquid connection pipe 4.

[0126] The refrigerant flowing in the second liquid connection pipe 4 is distributed to multiple cooling units 60. In each cooling unit 60, the refrigerant that has flowed into the cooling circuit 61 is depressurized as it passes through the cooling expansion valve 63, and then evaporates by absorbing heat from the air inside the storage unit in the cooling heat exchanger 64. Each cooling unit 60 blows the air that has been cooled in the cooling heat exchanger 64 toward the storage space.

[0127] The refrigerant that has flowed out of the cooling heat exchanger 64 of each cooling unit 60 flows into the second gas connection pipe 5 and merges with it, then flows into the second low-pressure stage suction pipe 22a of the outdoor circuit 11, and is then sucked in and compressed by the second low-pressure stage compressor 22.

[0128] The refrigerant, already compressed in the second low-pressure stage compressor 22, releases heat to the outside air in the intercooler 17. After merging with the refrigerant flowing in the injection pipe 38, it is drawn into the high-pressure stage compressor 21. The high-pressure stage compressor 21 compresses the drawn-in refrigerant and then ejects it.

[0129] <Second Heating Operation>

[0130] Reference Figure 5 The second heating operation of the refrigeration unit 1 will be explained. The second heating operation is the operation in which the air conditioning unit 50 heats the room. The second heating operation is carried out under the condition that the heat released by the refrigerant in the air conditioning unit 50 and the heat absorbed by the refrigerant in the cooling unit 60 are in balance.

[0131] In the second heating operation, the first switching valve 81 and the second switching valve 82 are set to the second state, and the second outdoor expansion valve 14b is kept closed. Additionally, in the second heating operation, the first low-pressure stage compressor 23 is off, while the second low-pressure stage compressor 22 and the high-pressure stage compressor 21 are operating. In the second heating operation, a refrigeration cycle is performed by circulating refrigerant in the refrigerant circuit 6. The indoor heat exchanger 54 functions as a heat exchanger (gas cooler), the cooling heat exchanger 64 functions as an evaporator, and the outdoor heat exchanger 13 is off.

[0132] Refrigerant injected from the high-pressure stage compressor 21 flows into the first outdoor gas pipe 35 through the first switching valve 81, and is then distributed to multiple air conditioning units 50 through the first gas connection pipe 3. In each air conditioning unit 50, the refrigerant that has flowed into the indoor circuit 51 releases heat towards the indoor air in the indoor heat exchanger 54, and then, after being depressurized by the indoor expansion valve 53, flows into the first liquid connection pipe 2. The refrigerant that has flowed from each air conditioning unit 50 into the first liquid connection pipe 2 flows into the liquid receiver 15 of the outdoor circuit 11. Each air conditioning unit 50 blows the air that has been heated in the indoor heat exchanger 54 into the indoor space.

[0133] The refrigerant flowing out of the receiver 15 is cooled during its passage through the first flow path 16a of the subcooled heat exchanger 16. A portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows through the injection pipe 38 into the second flow path 16b of the subcooled heat exchanger 16, and after absorbing heat and evaporating, flows into the high-pressure stage suction pipe 21a. The remaining portion of the refrigerant that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows into the second liquid connection pipe 4.

[0134] The refrigerant flowing in the second liquid connection pipe 4 is distributed to multiple cooling units 60. In each cooling unit 60, the refrigerant that has flowed into the cooling circuit 61 is depressurized as it passes through the cooling expansion valve 63, and then evaporates by absorbing heat from the air inside the storage unit in the cooling heat exchanger 64. Each cooling unit 60 blows the air that has been cooled in the cooling heat exchanger 64 toward the storage space.

[0135] The refrigerant that has flowed out of the cooling heat exchanger 64 of each cooling unit 60 flows into the second gas connection pipe 5 and merges with it, then flows into the second low-pressure stage suction pipe 22a of the outdoor circuit 11, and is then sucked in and compressed by the second low-pressure stage compressor 22.

[0136] The refrigerant, already compressed in the second low-pressure stage compressor 22, releases heat to the outside air in the intercooler 17. After merging with the refrigerant flowing in the injection pipe 38, it is drawn into the high-pressure stage compressor 21. The high-pressure stage compressor 21 compresses the drawn-in refrigerant and then ejects it.

[0137] <Third Heating Operation>

[0138] Reference Figure 6 The third heating operation of the refrigeration unit 1 will be explained. The third heating operation is the operation in which the air conditioning unit 50 heats the room. The third heating operation is carried out when the heat released by the refrigerant in the air conditioning unit 50 is greater than the heat absorbed by the refrigerant in the cooling unit 60.

[0139] In the third heating operation, the first switching valve 81 and the second switching valve 82 are set to the second state, and the first outdoor expansion valve 14a is kept fully open. Additionally, in the third heating operation, the first low-pressure stage compressor 23, the second low-pressure stage compressor 22, and the high-pressure stage compressor 21 operate. In the third heating operation, the refrigerant circulates in the refrigerant circuit 6, thereby performing a refrigeration cycle. The indoor heat exchanger 54 functions as a heat exchanger (gas cooler), and the cooling heat exchanger 64 and the outdoor heat exchanger 13 function as evaporators.

[0140] Refrigerant injected from the high-pressure stage compressor 21 flows into the first outdoor gas pipe 35 through the first switching valve 81, and is then distributed to multiple air conditioning units 50 through the first gas connection pipe 3. In each air conditioning unit 50, the refrigerant that has flowed into the indoor circuit 51 releases heat towards the indoor air in the indoor heat exchanger 54, and then, after being depressurized by the indoor expansion valve 53, flows into the first liquid connection pipe 2. The refrigerant that has flowed from each air conditioning unit 50 into the first liquid connection pipe 2 flows into the liquid receiver 15 of the outdoor circuit 11. Each air conditioning unit 50 blows the air that has been heated in the indoor heat exchanger 54 into the indoor space.

[0141] The refrigerant that has flowed out of the receiver 15 is cooled during its passage through the first flow path 16a of the subcooled heat exchanger 16. The refrigerant branch that has passed through the first flow path 16a of the subcooled heat exchanger 16 flows into the outdoor fifth pipe O5 and the outdoor third pipe O3.

[0142] A portion of the refrigerant flowing in the fifth outdoor pipe O5 flows into the injection pipe 38, and the remainder flows into the eighth outdoor pipe O8. The refrigerant flowing in the injection pipe 38 flows into the second flow path 16b of the supercooled heat exchanger 16, and after absorbing heat and evaporating, flows into the high-pressure stage suction pipe 21a.

[0143] The refrigerant flowing in the outdoor eighth pipe 08 is distributed to multiple cooling units 60 via the second liquid connection pipe 4. In each cooling unit 60, the refrigerant that has flowed into the cooling circuit 61 is depressurized as it passes through the cooling expansion valve 63, and then evaporates by absorbing heat from the air inside the storage unit in the cooling heat exchanger 64. Each cooling unit 60 blows the air that has been cooled in the cooling heat exchanger 64 toward the storage space.

[0144] The refrigerant that has flowed out of the cooling heat exchanger 64 of each cooling unit 60 flows into the second gas connection pipe 5 and merges with it, then flows into the second low-pressure stage suction pipe 22a of the outdoor circuit 11, and is then sucked in and compressed by the second low-pressure stage compressor 22.

[0145] The refrigerant flowing in the outdoor third pipe o3 is depressurized when passing through the second outdoor expansion valve 14 and then flows into the outdoor heat exchanger 13, where it absorbs heat from the outdoor air and evaporates. The refrigerant that has passed through the outdoor heat exchanger 13 flows into the first low-pressure stage suction pipe 23a through the second switching valve 82, and is then drawn in and compressed by the first low-pressure stage compressor 23.

[0146] The refrigerant, compressed in the first low-pressure stage compressor 23 and the second low-pressure stage compressor 22 respectively, releases heat to the outside air in the intercooler 17, and then merges with the refrigerant flowing in the injection pipe 38 before being drawn into the high-pressure stage compressor 21. The high-pressure stage compressor 21 compresses the drawn-in refrigerant and then sprays it out.

[0147] <Defrosting Operation>

[0148] The defrosting operation of the refrigeration unit 1 will be explained. The defrosting operation is for melting the frost adhering to the outdoor heat exchanger 13. During the third heating operation, when the frost adhering to the outdoor heat exchanger 13 reaches a certain level, the refrigeration unit 1 temporarily stops the third heating operation and performs the defrosting operation.

[0149] During defrosting operation, the refrigerant flows in the refrigerant circuit 6 in the same manner as during the first heating operation. Specifically, the second switching valve 82 is set to the first state, and the outdoor heat exchanger 13 functions as a heat exchanger (gas cooler). The frost adhering to the outdoor heat exchanger 13 is melted by the refrigerant heating.

[0150] <Reduced Pressure Operation>

[0151] In summer or other conditions with high outdoor air temperatures, the following situation occurs: during the shutdown of the refrigeration unit 1, heat is transferred from the outdoor air to the refrigerant in the receiver 15, causing the refrigerant pressure in the receiver 15 to rise. In this situation, the refrigeration unit 1 operates in pressure reduction mode to lower the refrigerant pressure in the receiver 15.

[0152] Reference Figure 7 The pressure reduction operation of refrigeration unit 1 will be explained.

[0153] During pressure reduction operation, the first switching valve 81 and the second switching valve 82 are set to the first state, the first outdoor expansion valve 14a and the vent valve 39 are kept in the open state, and the second outdoor expansion valve 14b and the pressure reducing valve 40 are kept in the closed state. During pressure reduction operation, the opening degree of the first outdoor expansion valve 14a and the vent valve 39 is appropriately adjusted.

[0154] During pressure reduction operation, the first low-pressure stage compressor 23 and the second low-pressure stage compressor 22 are kept in a stopped state, while the high-pressure stage compressor 21 operates. Additionally, during pressure reduction operation, the outdoor fan 12 operates, while the supply fan 17a is kept in a stopped state.

[0155] The high-pressure stage compressor 21 draws in refrigerant from the receiver 15 via the injection pipe 38 and the vent pipe 37. The high-pressure stage compressor 21 compresses the drawn-in refrigerant and then ejects it. The refrigerant ejected from the high-pressure stage compressor 21 flows into the outdoor heat exchanger 13 and releases heat to the outdoor air, then passes through the first outdoor expansion valve 14a. The refrigerant, depressurized upon passing through the first outdoor expansion valve 14a, flows into the receiver 15.

[0156] Thus, during pressure reduction operation, gaseous refrigerant is drawn from the receiver 15 by the high-pressure stage compressor 21, and the refrigerant, after being depressurized as it passes through the first outdoor expansion valve 14a, flows into the receiver 15. Therefore, the refrigerant pressure in the receiver 15 decreases due to the pressure reduction operation of the refrigeration unit 1.

[0157] - Controller Actions -

[0158] As described above, during the shutdown period of the refrigeration unit 1 (in other words, during the shutdown period of the compressor unit C), there is a possibility that the refrigerant pressure in the receiver 15 may rise. When the refrigerant pressure in the receiver 15 exceeds the second design pressure Pu2, the receiver 15 may be damaged, and the refrigerant may leak into the atmosphere. Therefore, the receiver pressure control unit 103 of the controller 101 operates to maintain the refrigerant pressure in the receiver 15 at a level lower than the second design pressure Pu2 during the shutdown period of the compressor unit C.

[0159] Here, during the shutdown of the compression component C, the refrigerant pressure in the receiver 15 rises, which is due to high outdoor air temperatures, such as in summer. When the outdoor air temperature is high, the refrigeration unit 1 operates in cooling mode. During the cooling operation of the refrigeration unit 1, the first switching valve 81 and the second switching valve 82 of the flow path switching mechanism 30 are in their first state.

[0160] Reference Figure 8 The flowchart below explains the operations performed by the reservoir pressure control unit 103 of the controller 101. It should be noted that the operations performed by the reservoir pressure control unit 103 are... Figure 8 The actions from step ST3 to step ST8.

[0161] <Step ST1>

[0162] When an operator inputs a signal to the controller 101 to stop the refrigeration unit 1, the controller 101 performs step ST1. In step ST1, the controller 101 stops the compression component C. Specifically, the controller 101 stops all compressors 21, 22, and 23 that constitute the compression component C. The state where the compression component C is stopped means that all compressors 21, 22, and 23 that constitute the compression component C have stopped.

[0163] <Step ST2>

[0164] Next, the controller 101 performs step ST2. In step ST2, the controller 101 closes the first outdoor expansion valve 14a and the second outdoor expansion valve 14b as the compression component C stops. For example, if the second outdoor expansion valve 14b is already closed, the controller 101 switches the first outdoor expansion valve 14a from the open state to the closed state and keeps the second outdoor expansion valve 14b closed. When the controller 101 performs step ST2, the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are both fully closed.

[0165] It should be noted that the moment when the controller 101 stops the compression component C may be the same as or different from the moment when the controller 101 closes the first outdoor expansion valve 14a and the second outdoor expansion valve 14b.

[0166] <Step ST3>

[0167] When step ST2 ends, the receiver pressure control unit 103 of controller 101 performs step ST3. During step ST3, the receiver pressure control unit 103 acquires the measured value from the high-pressure sensor 71 as the refrigerant pressure Phx of the outdoor heat exchanger 13. With the second switching valve 82 of the flow path switching mechanism 30 in the first state and the compression component C stopped, the measured value from the high-pressure sensor 71 represents the refrigerant pressure Phx of the outdoor heat exchanger 13.

[0168] The first outdoor expansion valve 14a is closed by the controller 101 performing step ST2. Even though the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are closed, the refrigerant in the outdoor heat exchanger 13 will flow out little by little through the compressors 21, 22, and 23 that constitute the compression component C, so the refrigerant pressure Phx of the outdoor heat exchanger 13 will gradually decrease.

[0169] In step ST3, the receiver pressure control unit 103 determines whether the condition "the acquired refrigerant pressure Phx of the outdoor heat exchanger 13 is lower than the predetermined first pressure P1 (Phx < P1)" is met. If the condition is not met, the receiver pressure control unit 103 performs step ST3 again. On the other hand, if the condition is met, the receiver pressure control unit 103 performs step ST4.

[0170] The first pressure P1 is lower than the upper limit of the design pressure of the reservoir 15, i.e., the second design pressure Pu2 (9 MPa in this embodiment). In this embodiment, the first pressure P1 is, for example, 5 MPa.

[0171] It should be noted that during the operation of step ST3, the receiver pressure control unit 103 can also determine whether the condition "the acquired refrigerant pressure Phx of the outdoor heat exchanger 13 is lower than the first pressure P1 (Phx≤P1)" is met. In this case, the receiver pressure control unit 103 essentially determines whether the condition "the acquired refrigerant pressure Phx of the outdoor heat exchanger 13 is lower than the first pressure P1 (Phx<P1)" is met, and whether the condition "the acquired refrigerant pressure Phx of the outdoor heat exchanger 13 is equal to the first pressure P1 (Phx=P1)" is met.

[0172] <Step ST4>

[0173] In step ST4, the reservoir pressure control unit 103 switches the first outdoor expansion valve 14a from a closed state to an open state. Specifically, the reservoir pressure control unit 103 increases the opening degree of both the first outdoor expansion valve 14a and the second outdoor expansion valve 14b from zero to a predetermined opening degree. This predetermined opening degree can be fully open or a degree smaller than fully open.

[0174] Steps ST3 and ST4 are the first actions performed by the liquid receiver pressure control unit 103. The first action is to open the first outdoor expansion valve 14a and the second outdoor expansion valve 14b when the refrigerant pressure Phx of the outdoor heat exchanger 13 is lower than the first pressure P1.

[0175] When the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are open, the receiver 15 and the outdoor heat exchanger 13 are connected to each other via the fourth outdoor pipe o4, the third outdoor pipe o3, and the first outdoor pipe o1. As a result, the refrigerant pressure of the receiver 15 is substantially equal to the refrigerant pressure Phx of the outdoor heat exchanger 13. Therefore, if the refrigerant pressure Phx of the outdoor heat exchanger 13 is lower than the specified first pressure P1, the refrigerant pressure of the receiver 15 is also lower than the first pressure P1.

[0176] Here, when the outdoor air temperature is high, heat is transferred from the outdoor air to the refrigerant in the receiver 15. As a result, the liquid refrigerant in the receiver 15 evaporates, and the refrigerant pressure in the receiver 15 increases.

[0177] When the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are closed, almost all the gaseous refrigerant generated from the evaporation of the liquid refrigerant in the receiver 15 remains in the receiver 15. On the other hand, when the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are open, if the refrigerant pressure in the receiver 15 rises due to the evaporation of the liquid refrigerant in the receiver 15, a portion of the refrigerant in the receiver 15 will flow out of the receiver 15 and sequentially through the second outdoor expansion valve 14b and the first outdoor expansion valve 14a to the outdoor heat exchanger 13 side. Therefore, compared to the case where the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are closed, the case where the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are open can suppress the rise in refrigerant pressure in the receiver 15.

[0178] <Step ST5>

[0179] When step ST4 ends, the receiver pressure control unit 103 proceeds to step ST5. In step ST5, the receiver pressure control unit 103 acquires the measured value from the liquid refrigerant pressure sensor 75 as the refrigerant pressure Prv of the receiver 15. As described above, the measured value from the liquid refrigerant pressure sensor 75 is substantially equal to the pressure of the liquid refrigerant within the receiver 15. Therefore, the measured value from the liquid refrigerant pressure sensor 75 represents the refrigerant pressure Prv of the receiver 15.

[0180] If the outdoor air temperature is high during the period when the refrigeration unit 1 is stopped, the temperature of the outdoor heat exchanger 13 will rise, and the refrigerant pressure of the outdoor heat exchanger 13 will rise accordingly. When the refrigerant pressure Phx of the outdoor heat exchanger 13 increases, the refrigerant pressure Prv of the liquid receiver 15 connected to the outdoor heat exchanger 13 will also increase.

[0181] Therefore, in step ST5, the receiver pressure control unit 103 determines whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is higher than the predetermined second pressure P2 (Prv > P2)" is met. If the condition is not met, the receiver pressure control unit 103 performs step ST5 again. On the other hand, if the condition is met, the receiver pressure control unit 103 performs step ST6.

[0182] The second pressure P2 is lower than the upper limit design pressure of the receiver 15, i.e., the second design pressure Pu2 (9 MPa in this embodiment). Furthermore, the second pressure P2 is higher than the first pressure P1 (5 MPa in this embodiment). In this embodiment, the second pressure P2 is, for example, 7 MPa. The second pressure P2 in this embodiment is lower than the critical pressure of carbon dioxide as a refrigerant (7.38 MPa).

[0183] It should be noted that during the operation of step ST5, the receiver pressure control unit 103 can also determine whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is greater than or equal to the second pressure P2 (Prv≥P2)" is met. In this case, the receiver pressure control unit 103 essentially determines whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is higher than the second pressure P2 (Prv>P2)" and whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is equal to the second pressure P2 (Prv=P2)" is met.

[0184] <Step ST6>

[0185] In step ST6, the reservoir pressure control unit 103 switches the first outdoor expansion valve 14a from the open state to the closed state. In other words, the reservoir pressure control unit 103 makes the first outdoor expansion valve 14a fully closed. When the first outdoor expansion valve 14a is closed, the connection between the reservoir 15 and the outdoor heat exchanger 13 is cut off by the first outdoor expansion valve 14a. It should be noted that in step ST6, the reservoir pressure control unit 103 can switch the second outdoor expansion valve 14b from the open state to the closed state, or it can keep the second outdoor expansion valve 14b open.

[0186] Steps ST5 and ST6 are the second actions performed by the receiver pressure control unit 103. The second action is to close the first outdoor expansion valve 14a when the refrigerant pressure Prv of the receiver 15 is higher than the second pressure P2.

[0187] The outdoor heat exchanger 13 is a heat exchanger that facilitates heat exchange between the refrigerant and the outdoor air, and it has fins to promote heat exchange between the refrigerant and the outdoor air. That is, the area of ​​the portion of the outdoor heat exchanger 13 in contact with the outdoor air is relatively large. Therefore, the refrigerant pressure Phx of the outdoor heat exchanger 13 is easily affected by the outdoor air temperature.

[0188] On the other hand, the receiver 15 is covered by insulation material 15a. Insulation material 15a prevents heat from moving from the outside air into the refrigerant inside the receiver 15. Therefore, the refrigerant pressure Prv of the receiver 15 is less affected by the outside air temperature than the refrigerant pressure Phx of the outdoor heat exchanger 13.

[0189] However, when the first outdoor expansion valve 14a is open, since the liquid receiver 15 is connected to the outdoor heat exchanger 13, the refrigerant pressure Prv of the liquid receiver 15 is substantially equal to the refrigerant pressure Phx of the outdoor heat exchanger 13.

[0190] Therefore, in the operation of step ST6, in order to suppress the rise of refrigerant pressure Prv in the liquid receiver 15, the liquid receiver pressure control unit 103 switches the first outdoor expansion valve 14a to the closed state, thereby cutting off the connection between the liquid receiver 15 and the outdoor heat exchanger 13.

[0191] The operation performed by the receiver pressure control unit 103 in steps ST5 and ST6 is the second operation. The second operation is to close the first outdoor expansion valve 14a when the refrigerant pressure Prv of the receiver 15 is higher than the second pressure P2.

[0192] <Step ST7>

[0193] When step ST6 is completed, the receiver pressure control unit 103 proceeds to step ST7. In step ST7, the receiver pressure control unit 103 acquires the measured value from the liquid refrigerant pressure sensor 75 as the refrigerant pressure Prv of the receiver 15. As described above, the measured value from the liquid refrigerant pressure sensor 75 represents the refrigerant pressure Prv of the receiver 15.

[0194] As described above, the receiver 15 is covered by insulation material 15a. Therefore, the refrigerant pressure Prv of the receiver 15 is less affected by the outdoor air temperature. However, when the outdoor air temperature becomes very high (e.g., exceeding 35°C), the refrigerant pressure Prv of the receiver 15 will rise due to the evaporation of liquid refrigerant within the receiver 15.

[0195] Therefore, in step ST7, the receiver pressure control unit 103 determines whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is higher than the predetermined third pressure P3 (Prv > P3)" is met. If the condition is not met, the receiver pressure control unit 103 performs step ST3 again. On the other hand, if the condition is met, the receiver pressure control unit 103 performs step ST8.

[0196] The third pressure P3 is lower than the upper limit design pressure of the reservoir 15, i.e., the second design pressure Pu2 (9 MPa in this embodiment). Furthermore, the third pressure P3 is higher than the second pressure P2 (7 MPa in this embodiment). For example, the third pressure P3 in this embodiment is 7.5 MPa.

[0197] It should be noted that during the operation of step ST7, the receiver pressure control unit 103 can also determine whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is greater than or equal to the third pressure P3 (Prv≥P3)" is met. In this case, the receiver pressure control unit 103 essentially determines whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is higher than the third pressure P3 (Prv>P3)" and whether the condition "the acquired refrigerant pressure Prv of the receiver 15 is equal to the third pressure P3 (Prv=P3)" is met.

[0198] <Step ST8>

[0199] In step ST8, the reservoir pressure control unit 103 causes the refrigeration unit 1 to perform a pressure reduction operation. In other words, the reservoir pressure control unit 103 controls the components of the heat source unit 10 to cause the refrigeration unit 1 to perform a pressure reduction operation.

[0200] As described above, during the pressure reduction operation of the refrigeration unit 1, the high-pressure stage compressor 21 draws in refrigerant from the receiver 15 via the injection pipe 38 and the vent pipe 37. In other words, the gaseous refrigerant in the receiver 15 is drawn out of the receiver 15 by the high-pressure stage compressor 21.

[0201] Steps ST7 and ST8 are the third actions performed by the receiver pressure control unit 103. The third action is to activate the compression unit C when the refrigerant pressure Prv of the receiver 15 is higher than the third pressure P3, thereby causing the compression unit C to draw gaseous refrigerant into the receiver 15 through the vent pipe 37.

[0202] When the refrigeration unit 1 operates under pressure reduction, gaseous refrigerant is discharged from the receiver 15, and the refrigerant pressure Prv of the receiver 15 decreases. When the refrigerant pressure Prv of the receiver 15 becomes sufficiently low (e.g., below 5 MPa), the receiver pressure control unit 103 stops the high-pressure stage compressor 21, thereby ending the pressure reduction operation of the refrigeration unit 1.

[0203] -Features of the first embodiment (1)-

[0204] In the refrigeration apparatus 1 of this embodiment, after the liquid receiver pressure control unit 103 of the controller 101 switches the first outdoor expansion valve 14a and the second outdoor expansion valve 14b to the closed state along with the stopping of the compression component C, it performs a first operation. The first operation is to open the first outdoor expansion valve 14a and the second outdoor expansion valve 14b when the refrigerant pressure of the outdoor heat exchanger 13 is lower than the first pressure.

[0205] When the first outdoor expansion valve 14a and the second outdoor expansion valve 14b are open, the liquid receiver 15 is connected to the outdoor heat exchanger 13 via the first outdoor expansion valve 14a and the second outdoor expansion valve 14b. Therefore, even if the liquid refrigerant in the liquid receiver 15 evaporates due to factors such as an increase in outdoor air temperature, causing an increase in refrigerant pressure in the liquid receiver 15, the refrigerant in the liquid receiver 15 can still move towards the outdoor heat exchanger 13 through the first outdoor expansion valve 14a and the second outdoor expansion valve 14b. As a result, the increase in refrigerant pressure in the liquid receiver 15 can be suppressed.

[0206] In this way, according to this embodiment, the rise in refrigerant pressure in the receiver 15 can be suppressed during the shutdown of the refrigeration device 1, thereby preventing damage to the receiver 15 in advance and ensuring the reliability of the refrigeration device 1.

[0207] -Features of the first embodiment (2)-

[0208] In the refrigeration apparatus 1 of this embodiment, the liquid receiver pressure control unit 103 of the controller 101 performs a second operation after completing the first operation. The second operation is to close the first outdoor expansion valve 14a when the refrigerant pressure in the liquid receiver 15 is higher than the second pressure.

[0209] As described above, the receiver 15 is covered by insulation material 15a. Therefore, compared to the refrigerant pressure of the outdoor heat exchanger 13, the refrigerant pressure of the receiver 15 is less affected by the outdoor air temperature. Therefore, in order to suppress the rise in refrigerant pressure of the receiver 15, the receiver pressure control unit 103 switches the first outdoor expansion valve 14a to the closed state, thereby disconnecting the receiver 15 from the outdoor heat exchanger 13. As a result, even when the outdoor air temperature is high, the rise in refrigerant pressure of the receiver 15 can be suppressed.

[0210] Therefore, according to this embodiment, the refrigerant pressure rise in the receiver 15 can be suppressed during the shutdown of the refrigeration device 1, thereby preventing damage to the receiver 15 in advance and ensuring the reliability of the refrigeration device 1.

[0211] -Features of the first embodiment (3)-

[0212] In the refrigeration apparatus 1 of this embodiment, the liquid receiver pressure control unit 103 of the controller 101 performs a third operation after completing the second operation. The third operation is to operate the high-pressure stage compressor 21 when the refrigerant pressure in the liquid receiver 15 is higher than the third pressure, thereby causing the high-pressure stage compressor 21 to draw gaseous refrigerant into the liquid receiver 15 through the vent pipe 37.

[0213] When the receiver pressure control unit 103 performs its third operation, gaseous refrigerant is discharged from the receiver 15, and the refrigerant pressure in the receiver 15 decreases. Therefore, according to this embodiment, the rise in refrigerant pressure in the receiver 15 during the shutdown period of the refrigeration device 1 can be suppressed, thereby preventing damage to the receiver 15 in advance and ensuring the reliability of the refrigeration device 1.

[0214] -Features of the first embodiment (4)-

[0215] In the refrigeration apparatus 1 of this embodiment, the receiver pressure control unit 103 of the controller 101 controls the first outdoor expansion valve 14a and the second outdoor expansion valve 14b during the first and second operations. If the refrigerant pressure rise in the receiver 15 cannot be suppressed even when the first and second operations are performed, the receiver pressure control unit 103 of the controller 101 causes the refrigeration apparatus 1 to perform pressure reduction operation. Therefore, compared to the case where the receiver pressure control unit 103 does not perform the first and second operations, the frequency of pressure reduction operation of the refrigeration apparatus 1 can be reduced.

[0216] During the pressure reduction operation of the refrigeration unit 1, power is consumed because the high-pressure stage compressor 21 operates. On the other hand, in this embodiment, the frequency of pressure reduction operation of the refrigeration unit 1 is reduced compared to the case where the liquid receiver pressure control unit 103 does not perform the first and second operations. Therefore, according to this embodiment, the frequency of power-consuming pressure reduction operation can be reduced, thereby reducing the power consumption of the refrigeration unit 1.

[0217] (Second Implementation)

[0218] The second embodiment will be described. Here, the differences between the refrigeration device 1 of this embodiment and the refrigeration device 1 of the first embodiment will be explained.

[0219] -Structure of the Refrigeration Unit-

[0220] like Figure 9 As shown, in the refrigeration device 1 of this embodiment, the cooling unit 60 of the first embodiment is omitted. In the refrigerant circuit 6 of the refrigeration device 1 of this embodiment, one heat source unit 10 and multiple air conditioning units 50 are connected through a first liquid connection pipe 2 and a second gas connection pipe 5.

[0221] In the heat source unit 10 of this embodiment, the second low-pressure stage compressor 22, the second low-pressure stage suction pipe 22a, and the second low-pressure stage discharge pipe 22b of the first embodiment are omitted. The compression component C of this embodiment includes the first low-pressure stage compressor 23 and the high-pressure stage compressor 21, but does not include the second low-pressure stage compressor 22.

[0222] The heat source unit 10 in this embodiment includes a switching valve 80 instead of the flow path switching mechanism 30 in the first embodiment. Similar to the first switching valve 81 and the second switching valve 82 in the first embodiment, the switching valve 80 is composed of a four-way directional valve 150. The first valve port of the switching valve 80 is connected to the high-pressure stage outlet pipe 21b, the second valve port is connected to the first low-pressure stage intake pipe 23a, the third valve port is connected to the second outdoor gas pipe 36, and the fourth valve port is connected to the first outdoor gas pipe 35.

[0223] Switching valve 80 in the first state ( Figure 9 The state shown by the solid line) and the second state ( Figure 9 Switching between states (shown by the dashed line). In the first state, the first valve port is connected to the third valve port, and the second valve port is connected to the fourth valve port. In the second state, the first valve port is connected to the fourth valve port, and the second valve port is connected to the third valve port.

[0224] - Operation of the refrigeration unit -

[0225] The refrigeration device 1 in this embodiment performs refrigeration operation, heating operation, defrosting operation, and pressure reduction operation.

[0226] During refrigeration operation, the switching valve 80 is set to the first state. In the refrigerant circuit 6 during refrigeration operation, the first low-pressure stage compressor 23 and the high-pressure stage compressor 21 are working, the outdoor heat exchanger 13 functions as a heat exchanger (gas cooler), and the indoor heat exchangers 54 of each air conditioning unit 50 function as evaporators.

[0227] During heating operation, the switching valve 80 is set to the second state. In the refrigerant circuit 6 during heating operation, the first low-pressure stage compressor 23 and the high-pressure stage compressor 21 are working, the indoor heat exchanger 54 of each air conditioning unit 50 functions as a heat exchanger (gas cooler), and the outdoor heat exchanger 13 functions as an evaporator.

[0228] The defrosting operation is for melting the frost adhering to the outdoor heat exchanger 13. During heating operation, when the frost adhering to the outdoor heat exchanger 13 reaches a certain level, the refrigeration unit 1 temporarily stops the heating operation and performs the defrosting operation.

[0229] During defrosting operation, the refrigerant flows in the refrigerant circuit 6 in the same manner as during refrigeration operation. Specifically, the switching valve 80 is set to the first state, and the outdoor heat exchanger 13 functions as a heat exchanger (gas cooler). The frost adhering to the outdoor heat exchanger 13 is melted by the refrigerant heating.

[0230] During pressure reduction operation, the switching valve 80 is set to the first state. Similar to the first embodiment, during pressure reduction operation, the first outdoor expansion valve 14a and the vent valve 39 are kept open, while the second outdoor expansion valve 14b and the pressure reducing valve 40 are kept closed. Furthermore, during pressure reduction operation, the first low-pressure stage compressor 23 is kept stopped, the high-pressure stage compressor 21 operates, the outdoor fan 12 operates, and the blower fan 17a is kept stopped.

[0231] - Controller Actions -

[0232] If both the high-pressure stage compressor 21 and the first low-pressure stage compressor 23 constituting the compression component C stop, the reservoir pressure control unit 103 of the controller 101 performs the same operation as in the first embodiment.

[0233] Specifically, if the compressor C stops, the receiver pressure control unit 103 performs a first operation and a second operation. In the first and second operations, the receiver pressure control unit 103 controls the first outdoor expansion valve 14a and the second outdoor expansion valve 14b to suppress the rise in refrigerant pressure in the receiver 15. If the rise in refrigerant pressure in the receiver 15 cannot be suppressed by the first and second operations, the receiver pressure control unit 103 performs a third operation. In the third operation, the receiver pressure control unit 103 causes the refrigeration unit 1 to operate in a pressure-reducing mode.

[0234] (Other implementation methods)

[0235] - First variation -

[0236] In the receiver pressure control unit 103 of the controller 101 in the first and second embodiments, the second pressure used to determine whether to close the first outdoor expansion valve 14a during the second operation is set to a value lower than the critical pressure of carbon dioxide, which is the refrigerant. This second pressure can also be set to a value higher than the critical pressure of carbon dioxide. However, the second pressure must be lower than the third pressure.

[0237] When the second pressure is lower than the critical pressure of carbon dioxide, the difference between the second and third pressures becomes relatively large. Therefore, the time required for the refrigerant pressure in the receiver 15 to rise from the second pressure to the third pressure becomes longer, thereby suppressing the frequency of pressure-reducing operation of the refrigeration unit 1 to be lower.

[0238] On the other hand, when the second pressure is higher than the critical pressure of carbon dioxide, at the moment when the liquid receiver pressure control unit 103 closes the first outdoor expansion valve 14a during the second operation, the refrigerant pressure of the outdoor heat exchanger 13 is higher than the critical pressure of carbon dioxide, and the refrigerant present in the outdoor heat exchanger 13 becomes supercritical. Therefore, even if the outdoor air temperature rises afterward, refrigerant evaporation will not occur in the outdoor heat exchanger 13, thereby preventing a sharp rise in the refrigerant pressure of the outdoor heat exchanger 13.

[0239] - Second variation -

[0240] In the heat source unit 10 of the first and second embodiments, the compression component C may also be configured to perform single-stage compression. In this variation, the compression component C includes a single compressor or multiple compressors connected in parallel with each other.

[0241] In the outdoor circuit 11 of this modification, the vent pipe 37 is connected to either the inlet or the suction port of the compressor constituting the compression component C. The inlet is the port through which refrigerant is introduced into the compression chamber of the compressor during the compression process. The suction port is the port through which refrigerant is introduced into the compression chamber of the compressor during the suction process.

[0242] The embodiments and modifications have been described above; however, it should be understood that various changes can be made to their form and specific details without departing from the spirit and scope of the claims. Furthermore, the above embodiments and modifications can be appropriately combined or substituted as long as the function of the object of this disclosure is not affected. Additionally, the terms "first," "second," "third," etc., used in the specification and claims are only used to distinguish statements containing these terms and are not intended to limit the number or order of the statements.

[0243] -Industry Applicability-

[0244] In summary, this disclosure is useful for heat source units and refrigeration equipment.

[0245] - Symbol Explanation -

[0246] 1. Refrigeration unit

[0247] 10 Heat source units

[0248] 11. Outdoor circuit (heat source side circuit)

[0249] 13 Outdoor heat exchanger (heat source side heat exchanger)

[0250] 14a First outdoor expansion valve (expansion valve)

[0251] 15. Liquid reservoir

[0252] C Compression component

[0253] 21. High-pressure stage compressor (compressor)

[0254] 22 Second low-pressure stage compressor (compressor)

[0255] 23 First low-pressure stage compressor (compressor)

[0256] 37. Venting pipe (venting passage)

[0257] 50 Air conditioning units (using side units)

[0258] 60 Cooling Unit (Utilizing Side Unit)

[0259] 101 Controller

Claims

1. A heat source unit (10), said heat source unit (10) being connected to a side unit (50, 60) for a refrigeration cycle, characterized in that: The heat source unit (10) includes a heat source side circuit (11) and a controller (101). The heat source side circuit (11) has a compression component (C), a heat source side heat exchanger (13), an expansion valve (14a), and a liquid reservoir (15), wherein the compression component (C) has one or more compressors (21, 22, 23). The controller (101) controls the expansion valve (14a). In the heat source side circuit (11), the expansion valve (14a) is arranged between the heat source side heat exchanger (13) and the liquid reservoir (15). During the shutdown of the compression component (C), the controller (101) controls the expansion valve (14a) based on either the refrigerant pressure of the reservoir (15) or the refrigerant pressure of the heat source-side heat exchanger (13), or both. After switching the expansion valve (14a) to a closed state along with the shutdown of the compression component (C), the controller (101) performs a first action in which the expansion valve (14a) is opened when the refrigerant pressure of the heat source-side heat exchanger (13) is lower than a first pressure. The first pressure is lower than the upper limit pressure designed for the reservoir (15).

2. The heat source unit according to claim 1, characterized in that: After performing the first action, the controller (101) performs a second action. In the second action, when the refrigerant pressure in the liquid receiver (15) is higher than the second pressure, the expansion valve (14a) is closed. The second pressure is lower than the upper limit pressure and higher than the first pressure.

3. The heat source unit according to claim 2, characterized in that: The heat source side circuit (11) has a venting passage (37) for sending the gaseous refrigerant in the reservoir (15) to the compression component (C). After performing the second action, the controller (101) performs a third action. In the third action, when the refrigerant pressure in the reservoir (15) is higher than the third pressure, the compressor (C) is activated, thereby causing the compressor (C) to draw in gaseous refrigerant from the reservoir (15) through the venting passage (37). The third pressure is lower than the upper limit pressure and higher than the second pressure.

4. The heat source unit according to any one of claims 1 to 3, characterized in that: Carbon dioxide is filled in the heat source side circuit (11) as a refrigerant.

5. A refrigeration device, characterized in that: The refrigeration device includes a heat source unit (10) as described in any one of claims 1 to 3, and a utilization side unit (50, 60) connected to the heat source unit (10).

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