GB2616806A

GB2616806A - Outdoor unit for refrigeration device and refrigeration device equipped with same

Info

Publication number: GB2616806A
Application number: GB2310202.3A
Authority: GB
Inventors: Egami Makoto; Ishihara Nobuya; Yashiro Takanori
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2021-01-26
Filing date: 2021-01-26
Publication date: 2023-09-20
Also published as: WO2022162730A1; JP7399322B2; GB202310202D0; JPWO2022162730A1

Abstract

A refrigeration device (100) comprises: a first refrigerant circuit (103) in which a first refrigerant circulates; a second refrigerant circuit (104) in which a second refrigerant circulates; and a four-way valve (7) that switches the circulation direction of the first refrigerant between a freezing mode and a defrosting mode. A fourth heat exchanger (214) in the second refrigerant circuit (104) exchanges heat between the second refrigerant, and the first refrigerant flowing between a second heat exchanger (2) and a first expansion valve (3). A liquid receiver (8) is installed between the fourth heat exchanger (214) and the first expansion valve (3) in the first refrigerant circuit (103). A bypass flow path (37) bypasses the liquid receiver (8) in the defrosting mode and allows the first refrigerant to flow from the first expansion valve (3) toward the second heat exchanger (2). In the defrosting mode, a control device (50) controls the second refrigerant circuit (104) to lower the evaporation temperature of the second refrigerant in the fourth heat exchanger (214) in response to the pressure of the first refrigerant circulating in the first refrigerant circuit (103) exceeding a threshold value.

Description

DESCRIPTION

TITLE OF INVENTION: Outdoor Unit for Refrigeration Device and Refrigeration Device Equipped with Same

TECHNICAL FIELD

[0001] The present disclosure relates to an outdoor unit for a refrigeration apparatus and a refrigeration apparatus including the same.

BACKGROUND ART

[0002] A refrigeration apparatus has a defrosting mode for melting frost that forms on a cooler. A known defrosting system is, for example, a reverse hot gas defrosting system that switches a direction of circulation of refrigerant using a four-way valve so as to send high-temperature gas from a compressor to the cooler that normally functions as an evaporator.

[0003] WO 2020/161803 (PTL 1) discloses a refrigeration apparatus that performs defrosting by the reverse hot gas defrosting system in a low-temperature circuit of a dual circuit. In the refrigeration apparatus disclosed in PTL 1, refrigerant is supplied from a liquid receiver to the low-temperature circuit by a refrigerant amount adjustment mechanism, thereby adjusting an amount of refrigerant circulating through the low-temperature circuit to an appropriate amount for defrosting.

CITATION LIST

PATENT LITERATURE

[0004] PTL 1: WO 2020/161803

SUMMARY OF INVENTION

TECHNICAL PROBLEM

[0005] An appropriate amount of refrigerant for defrosting, however, changes depending on the progress of defrosting. Immediately after start of defrosting, a large amount of frost forms on a cooler, leading to a large heat release amount of the refrigerant in the cooler. As defrosting progresses, the amount of frost on the cooler -1 -decreases, and the temperature of the cooler rises, leading to a smaller heat release amount of the refrigerant in the cooler. Thus, even when the amount of refrigerant is appropriate at an early stage of a defrosting period, the amount of refrigerant increases excessively at a final stage of the defrosting period, leading to a higher pressure in the low-temperature circuit. If the pressure in the low-temperature circuit rises to a design pressure, operation may stop automatically for protection, resulting in insufficient defrosting. It is therefore desirable to avoid a situation in which pressure rises excessively during the defrosting operation.

[0006] The present disclosure has been made to solve the above problem, and therefore has an object to provide an outdoor unit for a refrigeration apparatus and a refrigeration apparatus that are able to suppress a rise in refrigerant pressure during a defrosting operation.

SOLUTION TO PROBLEM

[0007] The present disclosure relates to an outdoor unit for a refrigeration apparatus that has a refrigeration mode and a defrosting mode. The outdoor unit includes a first compressor and a second heat exchanger connected such that a first refrigerant circulates between the outdoor unit and an indoor unit including a first expansion valve and a first heat exchanger connected in series. The first compressor, the second heat exchanger, the first expansion valve, and the first heat exchanger constitute a first refrigerant circuit in which the first refrigerant is used. The outdoor unit includes a second refrigerant circuit. The second refrigerant circuit includes a second compressor, a third heat exchanger, a second expansion valve, and a fourth heat exchanger, and causes the second refrigerant to circulate in order of the second compressor, the third heat exchanger, the second expansion valve, and the fourth heat exchanger. The fourth heat exchanger exchanges heat between the second refrigerant and the first refrigerant that flows between the second heat exchanger and the first expansion valve. The outdoor unit further includes a four-way valve, a liquid receiver, a bypass flow path, and a controller. The four-way valve switches a direction of circulation of the first refrigerant in the first refrigerant circuit to a normal -2 -direction in order of the first compressor, the second heat exchanger, the first expansion valve, and the first heat exchanger in the refrigeration mode, and to a reverse direction in order of the first compressor, the first heat exchanger, the first expansion valve, and the second heat exchanger in the defrosting mode. The liquid receiver is located between the fourth heat exchanger and the first expansion valve in the first refrigerant circuit. The bypass flow path causes the first refrigerant to flow from the first expansion valve toward the second heat exchanger while detouring around the liquid receiver in the defrosting mode. In the defrosting mode, the controller controls the second refrigerant circuit to decrease an evaporation temperature of the second refrigerant in the fourth heat exchanger in response to a pressure of the first refrigerant circulating through the first refrigerant circuit exceeding a threshold. ADVANTAGEOUS EFFECTS OF INVENTION [0008] According to the present disclosure, in the defrosting mode, when the pressure of the first refrigerant in the bypass flow path exceeds the threshold, the evaporation temperature of the second refrigerant in the fourth heat exchanger is decreased. This decreases the pressure of the first refrigerant in the fourth heat exchanger, so that part of the refrigerant that has flowed through the bypass flow path flows into the liquid receiver. As a result, in the defrosting mode, an amount of the first refrigerant that circulates through the first refrigerant circuit in the reverse direction decreases, suppressing a pressure rise of the refrigerant during the defrosting operation.

BRIEF DESCRIPTION OF DRAWINGS

[0009] Fig. 1 shows a configuration of a refrigeration apparatus according to Embodiment 1.

Fig. 2 shows a refrigerant flow in a defrosting mode of the refrigeration apparatus of Embodiment 1.

Fig. 3 shows a configuration of a controller that controls the refrigeration apparatus.

Fig. 4 is a flowchart for illustrating control performed by the controller in Embodiment 1. -3 -

Fig. 5 is a flowchart for illustrating control performed by a controller in Embodiment 2.

DESCRIPTION OF EMBODIMENTS

[0010] Embodiments of the present disclosure will be described below in detail with reference to the drawings. Although several embodiments will be described below, an appropriate combination of the configurations described in the respective embodiments has been intended at the time of application. The same or corresponding parts will be designated by the same reference numerals, and description thereof will not be repeated.

[0011] Embodiment 1 Fig. 1 shows a configuration of a refrigeration apparatus according to Embodiment 1. Referring to Fig. 1, a refrigeration apparatus 100 includes an outdoor unit 101, an indoor unit 102, and pipes 27, 31, which connect outdoor unit 101 to indoor unit 102.

[0012] Indoor unit 102 includes a first expansion valve 3 and a first heat exchanger 4.

First expansion valve 3 and first heat exchanger 4 are connected in series. First expansion valve 3 is, for example, a temperature expansion valve controlled based on a temperature at a refrigerant outlet of first heat exchanger 4.

[0013] Outdoor unit 101 includes a first compressor 1 and a second heat exchanger 2.

First compressor 1, second heat exchanger 2, first expansion valve 3, and first heat exchanger 4 constitute a first refrigerant circuit 103 on the low temperature side. A first refrigerant that fills first refrigerant circuit 103 is, for example, CO2.

[0014] Outdoor unit 101 further includes a second refrigerant circuit 104 on the high temperature side, a four-way valve 7, a refrigerant amount adjustment mechanism 10, a bypass flow path 37, check valves 41, 42, a temperature sensor 61, a pressure sensor 62, and a controller 50.

[0015] Second refrigerant circuit 104 includes a second compressor 211, a third heat exchanger 212, a second expansion valve 213, and a fourth heat exchanger 214. Second refrigerant circuit 104 causes a second refrigerant to circulate in order of -4 -second compressor 211, third heat exchanger 212, second expansion valve 213, and fourth heat exchanger 214. The second refrigerant is, for example, HF01234yf, R410A, or CO2.

[0016] Fourth heat exchanger 214 is, for example, a cascade heat exchanger. Fourth heat exchanger 214 exchanges heat between the second refrigerant and the first refrigerant flowing between second heat exchanger 2 and first expansion valve 3. [0017] Refrigeration apparatus 100 has a refrigeration mode and a defrosting mode as operation modes. In the refrigeration mode, refrigerant flows in the direction indicated by the arrows in Fig. 1. Fig. 2 shows a refrigerant flow in the defrosting mode of the refrigeration apparatus of Embodiment 1.

[0018] Four-way valve 7 switches the direction of circulation of the first refrigerant in first refrigerant circuit 103 between the refrigeration mode and the defrosting mode. The four-way valve may be composed of a plurality of valves.

[0019] In the refrigeration mode shown in Fig. 1, four-way valve 7 switches the direction of circulation of the first refrigerant in first refrigerant circuit 103 to a normal direction in order of first compressor 1, second heat exchanger 2, first expansion valve 3, and first heat exchanger 4. In other words, in the refrigeration mode, four-way valve 7 connects a suction port of first compressor 1 to first heat exchanger 4 and connects a discharging port of first compressor 1 to second heat exchanger 2.

[0020] In the defrosting mode shown in Fig. 2, four-way valve 7 switches the direction of circulation of the first refrigerant in first refrigerant circuit 103 to a reverse direction in order of first compressor 1, first heat exchanger 4, first expansion valve 3, and second heat exchanger 2. In other words, in the defrosting mode, four-way valve 7 connects the suction port of first compressor 1 to second heat exchanger 2 and connects the discharging port of first compressor 1 to first heat exchanger 4.

[0021] Refrigerant amount adjustment mechanism 10 (see Fig. 1) is configured to adjust a circulation amount of the first refrigerant in the defrosting mode.

[0022] Refrigerant amount adjustment mechanism 10 includes a liquid receiver 8, a refrigerant exhaust flow path 35, and a flow regulating valve 45. In fast refrigerant -5 -circuit 103, liquid receiver 8 is located between fourth heat exchanger 214 and first expansion valve 3. More specifically, liquid receiver 8 is located between fourth heat exchanger 214 and a first connecting point 23. First connecting point 23 is connected with bypass flow path 37. Refrigerant exhaust flow path 35 connects the outlet of liquid receiver 8 to the suction port of first compressor 1. Flow regulating valve 45 regulates a flow rate of the first refrigerant that flows through refrigerant exhaust flow path 35.

[0023] As shown in Fig. 2, in the defrosting mode, bypass flow path 37 causes the first refrigerant to flow from first expansion valve 3 toward second heat exchanger 2 while detouring around liquid receiver 8. Specifically, bypass flow path 37 connects first connecting point 23 between the outlet of liquid receiver 8 and first expansion valve 3 in first refrigerant circuit 103 to second connecting point 26 between second heat exchanger 2 and fourth heat exchanger 214 in the first refrigerant circuit.

[0024] A third expansion valve 46 is provided in bypass flow path 37. In bypass flow path 37, a check valve 43 is further provided between third expansion valve 46 and second connecting point 26. Check valve 43 assumes the direction from first connecting point 23 toward second connecting point 26 as a forward direction. Accordingly, a refrigerant flow direction of bypass flow path 37 is restricted to the direction from first connecting point 23 toward second connecting point 26 (i.e., the direction from third expansion valve 46 toward second heat exchanger 2).

[0025] Check valve 41 is located between second connecting point 26 and fourth heat exchanger 214 in first refrigerant circuit 103. Check valve 41 assumes the direction from second connecting point 26 toward fourth heat exchanger 214 as a forward direction.

[0026] Check valve 42 is located between the outlet of liquid receiver 8 and first connecting point 23 in first refrigerant circuit 103. Check valve 42 assumes the direction from liquid receiver 8 toward first connecting point 23 as a forward direction. [0027] As four-way valve 7 is switched to the state shown in Fig. 1, check valves 41, 43 allow the first refrigerant that has flowed through second heat exchanger 2 to flow -6 -toward fourth heat exchanger 214 without flowing from second connecting point 26 through bypass flow path 37. In other words, the refrigerant circulates in the direction indicated by the arrows in Fig. 1.

[0028] As four-way valve 7 is switched to the state shown in Fig. 2, check valves 42, 43 allow the first refrigerant that has flowed through first expansion valve 3 to flow through bypass flow path 37 without flowing from first connecting point 23 toward liquid receiver 8. In other words, the refrigerant circulates in the direction indicated by the arrows in Fig. 2.

[0029] Temperature sensor 61 and pressure sensor 62 respectively measure the temperature and pressure of the first refrigerant circulating through first refrigerant circuit 103. Specifically, temperature sensor 61 and pressure sensor 62 respectively measure the temperature and pressure of the first refrigerant in a pipe that is a high-pressure portion in the defrosting mode. The pipe that is the high-pressure portion in the defrosting mode is a pipe between first expansion valve 3 and second heat exchanger 2. In the present embodiment, temperature sensor 61 and pressure sensor 62 respectively measure the temperature and pressure of the first refrigerant in the vicinity of first connecting point 23. Temperature sensor 61 and pressure sensor 62 output measurement results to controller 50.

[0030] Fig. 3 shows a configuration of controller 50 that controls the refrigeration apparatus. As shown in Fig. 3, controller 50 includes a processor 51, a memory 52, and a communication interface (not shown), and the like. Processor 51 controls, for example, an operation frequency of first compressor 1, a connection state of four-way valve 7, second refrigerant circuit 104, and the like in accordance with data stored in memory 52 and information obtained via the communication interface.

[0031] Memory 52 includes, for example, a ROM (Read Only Memory), a RAM (Random Access Memory), and a flash memory. The flash memory stores an operating system, an application program, and various pieces of data. Controller 50 shown in Fig. 1 is implemented by processor 51 executing the operating system and the application program stored in memory 52. The various pieces of data stored in -7 -memory 52 are referred to in the execution of the application program.

[0032] Fig. 4 is a flowchart for illustrating control performed by the controller in Embodiment 1. The process in this flowchart is repeatedly performed every time a certain period of time elapses or every time a predetermined condition is satisfied during operation of refrigeration apparatus 100. For example, in the case where defrosting is performed per certain period of time, controller 50 performs the process of the flowchart in Fig. 4 when a certain period of time elapses from the last defrosting of first heat exchanger 4. Note that this shift to the defrosting mode may be determined based on a refrigerant temperature or a state of formation of frost on first heat exchanger 4, which has been detected.

[0033] As shown in Fig. 4, when the condition for switching to the defrosting mode is satisfied, controller 50 switches four-way valve 7 from the state of Fig. 1 to the state of Fig. 2 at step Si.

[0034] At step S2, controller 50 then monitors an output of pressure sensor 62 and determines whether a pressure P of the first refrigerant circulating through first refrigerant circuit 103 is lower than a threshold Thl. Threshold Thl is determined in advance considering the performance of the pipe of first refrigerant circuit 103, which is a design pressure or a value smaller than the design pressure by a certain value. [0035] When pressure P is smaller than threshold Thl (YES at S2), controller 50 controls the operation of second refrigerant circuit 104 in a normal operation mode (Step S3). In the normal operation mode, operation is performed according to a target evaporation temperature set such that the pressure of the high-pressure portion of first refrigerant circuit 103 does not exceed the design pressure. Specifically, controller 50 controls an operation frequency of second compressor 211 or a degree of opening of second expansion valve 213 such that the evaporation temperature of the second refrigerant in fourth heat exchanger 214 is equal to the target evaporation temperature. [0036] When pressure P is equal to or greater than threshold Thl (NO at S2), at step S4, controller 50 controls second refrigerant circuit 104 to decrease the evaporation temperature of the second refrigerant in fourth heat exchanger 214. Specifically, -8 -controller 50 controls an operation of second refrigerant circuit 104 in an accelerated operation mode. The target evaporation temperature is set lower in the accelerated operation mode than in the normal operation mode. Controller 50 controls the operation frequency of second compressor 211 or the degree of opening of second expansion valve 213 such that the evaporation temperature of the second refrigerant in fourth heat exchanger 214 is equal to the target evaporation temperature. In other words, as the target evaporation temperature is set low, controller 50 performs at least one of control to increase the operation frequency of second compressor 211 and control to increase the degree of opening of second expansion valve 213.

Consequently, the evaporation temperature of the second refrigerant in fourth heat exchanger 214 decreases.

[0037] As the evaporation temperature of the second refrigerant in fourth heat exchanger 214 decreases, in first refrigerant circuit 103, the pressure of the first refrigerant in fourth heat exchanger 214 decreases. This causes a pressure P3 at a point 28 (see Fig. 2) between check valve 41 and fourth heat exchanger 214 to be lower than a pressure P4 at second connecting point 26 in first refrigerant circuit 103. As a result, part of the first refrigerant that has flowed through bypass flow path 37 and reached second connecting point 26 flows into liquid receiver 8 via check valve 41 and fourth heat exchanger 214. As the amount of the refrigerant collected in liquid receiver 8 increases, the circulation amount of the first refrigerant decreases, thus suppressing a rise in the pressure of the first refrigerant circulating through first refrigerant circuit 103.

[0038] The process of steps S2 to S4 is repeated until it is determined at step S5 that defrosting is complete. As a result, a pressure rise attributable to an excessive circulation amount of the first refrigerant is suppressed in the defrosting mode.

[0039] When it is determined that defrosting is complete (YES at 55), at step S6, controller 50 returns four-way valve 7 to the state of the refrigeration mode in Fig. 1. [0040] Embodiment 2 Fig. 5 is a flowchart for illustrating control performed by a controller in -9 -Embodiment 2. The flowchart shown in Fig. 5 is different from the flowchart shown in Fig. 4 in that the former flowchart further includes steps S10 to S14.

[0041] When four-way valve 7 is switched from the state of Fig. 1 to the state of Fig. 2 at step Si, at step S10, controller 50 determines whether determination has been NO at least once at step S2 after shift to the defrosting mode.

[0042] When determination has not been NO even once at step S2 (NO at step S10), controller 50 monitors outputs of temperature sensor 61 and pressure sensor 62 and determines whether a degree of supercooling SC of the first refrigerant in the vicinity of first connecting point 23 is smaller than a threshold Th2 (Step Si!). As threshold Th2, a value of the degree of supercooling when the circulation amount of the first refrigerant is insufficient is set.

[0043] When degree of supercooling SC is lower than threshold Th2 (YES at step S11), controller 50 opens flow regulating valve 45. Thus, the first refrigerant is supplied from liquid receiver 8 to first compressor 1. Consequently, the circulation amount of the first refrigerant increases.

[0044] When degree of supercooling SC is equal to or greater than threshold Th2 (NO at step Si!), the circulation amount of the first refrigerant is sufficient, and thus, controller 50 closes flow regulating valve 45 (step S12).

[0045] Step S2 is performed after steps S11, S12. Also when determination has been NO at least once at step S2 (YES at step S10), step S2 is performed.

[0046] When determination is YES at step S2, controller 50 closes flow regulating valve 45 (step S14). Step S4 is performed after step S14. Steps S10 to S14 and S2 to S4 are performed repeatedly until defrosting is complete.

[0047] According to Embodiment 2, when the circulation amount of the first refrigerant required for defrosting is insufficient, flow regulating valve 45 is opened, thus supplying the first refrigerant from liquid receiver 8 to first compressor 1. Thus, the circulation amount of the first refrigerant is adjusted to be suitable for defrosting. In particular, at the early stage of the defrosting period, a larger amount of frost forms on first heat exchanger 4, leading to a larger heat release amount of the first refrigerant -10 -in first heat exchanger 4. Accordingly, a larger amount of refrigerant is required for defrosting. When the circulation amount of the first refrigerant is insufficient, flow regulating valve 45 is opened, increasing the circulation amount of the first refrigerant. Consequently, defrosting is performed efficiently.

[0048] Contrastingly, at the final stage of the defrosting period, a smaller amount of frost forms on first heat exchanger 4, and the temperature of first heat exchanger 4 rises, leading to a smaller heat release amount of the first refrigerant in first heat exchanger 4. Thus, a smaller amount of refrigerant is required for defrosting. At this time, closing flow regulating valve 45 can prevent supply of the first refrigerant from liquid receiver 8. Further, lowering the evaporation temperature of the second refrigerant in fourth heat exchanger 214 causes pressure P3 at point 28 to be lower than pressure P4 at second connecting point 26 in first refrigerant circuit 103, so that part of the first refrigerant that has flowed through bypass flow path 37 flows into liquid receiver 8. As the amount of the refrigerant collected in liquid receiver 8 increases, the circulation amount of the first refrigerant decreases, thus suppressing a pressure rise.

[0049] Herein, "exceeding" may be relocated by being "equal to or greater than", and being "equal to or less" may be relocated by being "less than". Conversely, being "equal to or greater than" may be relocated by "exceeding", and being "less than" may be relocated by being "equal to or less than".

[0050] It should be understood that the embodiments disclosed herein have been presented for the purpose of illustration and non-restrictive in every respect. It is therefore intended that the scope of the present disclosure is defined by claims, not only by the embodiments described above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.

REFERENCE SIGNS LIST

[0051] 1 first compressor; 2 second heat exchanger; 3 first expansion valve; 4 first heat exchanger; 7 four-way valve; 8 liquid receiver; 10 refrigerant amount adjustment mechanism; 23 first connecting point; 26 second connecting point; 27, 31 pipe; 28 point; 35 refrigerant exhaust flow path; 37 bypass flow path; 41 to 43 check valve; 45 flow regulating valve; 46 third expansion valve; 50 controller; 51 processor; 52 memory; 61 temperature sensor; 62 pressure sensor; 100 refrigeration apparatus; 101 outdoor unit; 102 indoor unit; 103 first refrigerant circuit; 104 second refrigerant circuit; 211 second compressor; 212 third heat exchanger; 213 second expansion valve; 214 fourth heat exchanger.

-12 -

Claims

CLAIMS1. An outdoor unit for a refrigeration apparatus that has a refrigeration mode and a defrosting mode, the outdoor unit comprising: a first compressor and a second heat exchanger connected such that a first refrigerant circulates between the outdoor unit and an indoor unit including a first expansion valve and a first heat exchanger connected in series, the first compressor, the second heat exchanger, the first expansion valve, and the first heat exchanger constituting a first refrigerant circuit in which the first refrigerant is used; a second refrigerant circuit including a second compressor, a third heat exchanger, a second expansion valve, and a fourth heat exchanger, the second refrigerant circuit causing a second refrigerant to circulate in order of the second compressor, the third heat exchanger, the second expansion valve, and the fourth heat exchanger, the fourth heat exchanger exchanging heat between the second refrigerant and the first refrigerant that flows between the second heat exchanger and the first expansion valve; a four-way valve that switches a direction of circulation of the first refrigerant in the first refrigerant circuit to a normal direction in order of the first compressor, the second heat exchanger, the first expansion valve, and the first heat exchanger in the refrigeration mode, and a reverse direction in order of the first compressor, the first heat exchanger, the first expansion valve, and the second heat exchanger in the defrosting mode; a liquid receiver located between the fourth heat exchanger and the first expansion valve in the first refrigerant circuit; a bypass flow path that causes the first refrigerant to flow from the first expansion valve toward the second heat exchanger while detouring around the liquid receiver in the defrosting mode; and a controller, wherein in the defrosting mode, the controller controls the second refrigerant circuit to decrease an evaporation temperature of the second refrigerant in the fourth heat exchanger in response to a pressure of the first refrigerant circulating through the first refrigerant circuit exceeding a threshold.
2. The outdoor unit according to claim 1, wherein in the defrosting mode, the controller causes the second refrigerant circuit to operate in an accelerated operation mode in response to the pressure of the first refrigerant circulating through the first refrigerant circuit exceeding the threshold.
3. The outdoor unit according to claim 1 or 2, further comprising: a refrigerant exhaust flow path connecting an outlet of the liquid receiver to a suction port of the first compressor; and a flow regulating valve that regulates a flow rate of the first refrigerant that flows through the refrigerant exhaust flow path, and in the defrosting mode, the controller closes the flow regulating valve in response to the pressure of the first refrigerant circulating through the first refrigerant circuit exceeding the threshold.
4. The outdoor unit according to any one of claims 1 to 3, wherein the bypass flow path connects a first connecting point to a second connecting point, the first connecting point being located between an outlet of the liquid receiver and the first expansion valve in the first refrigerant circuit, the second connecting point being located between the second heat exchanger and the fourth heat exchanger in the first refrigerant circuit, and the outdoor unit further comprises a first check valve located between the second connecting point and the fourth heat exchanger in the first refrigerant circuit, the first check valve assuming a direction from the second connecting point toward the -14 -fourth heat exchanger as a forward direction.
5. The outdoor unit according to claim 4, further comprising: a second check valve located between the outlet of the liquid receiver and the first connecting point, the second check valve assuming a direction from the liquid receiver toward the first connecting point as a forward direction; and a third check valve located in the bypass flow path, the third check valve assuming a direction from the first connecting point toward the second connecting point as a forward direction.
6. A refrigeration apparatus comprising: the outdoor unit according to any one of claims 1 to 5; and the indoor unit.-15 -