GB2585594A

GB2585594A - Refrigerating apparatus

Info

Publication number: GB2585594A
Application number: GB2014309.5A
Authority: GB
Inventors: Ishihara Nobuya; Arii Yusuke; Saikusa Tetsuji
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2018-03-26
Filing date: 2018-03-26
Publication date: 2021-01-13
Anticipated expiration: 2038-03-26
Also published as: WO2019186647A1; JPWO2019186647A1; JP6972304B2; GB2585594B; GB202014309D0

Abstract

Provided is a refrigerating apparatus comprising: a compression system (1) having a first compression device and a second compression device; a cooling circuit having a first heat exchanger (2), a second heat exchanger (3), a first decompression device (4), and a third heat exchanger (5); an intermediate injection circuit (60) that is branched from a downstream side of the second heat exchanger (3), extends through a second decompression device (6) and the second heat exchanger (3), and connected to a medium pressure portion between the first compression device and the second decompression device; and a first by-pass circuit (70) that has a first on-off valve (7), branched from a high-pressure side of the cooling circuit, and connected to an intake side of the compression system. The first on-off valve is opened when a pressure of a refrigerant on an upstream side of the first on-off valve exceeds a first pressure.

Description

DESCRIPTION Title of Invention

REFRIGERATION DEVICE

Technical Field

[0001] The present disclosure relates to a refrigeration device including a plurality of compression mechanisms.

Background Art

[0002] As an example of conventional refrigeration devices including a plurality of compression mechanisms, Patent Literature 1 discloses a refrigeration device including a two-stage compressor including a compression device on a low-pressure side and a compression device on a high-pressure side, and an expansion valve.

Citation List Patent Literature [0003] Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2017-129320

Summary of Invention

Technical Problem [0004] With a refrigeration device including a two-stage compressor as described in Patent Literature 1, when the two-stage compressor is stopped, liquid-phase refrigerant is accumulated in a refrigerant pipe on a high-pressure side connected between a discharge side of the two-stage compressor and a refrigerant inflow side of an expansion valve. In a case where the liquid-phase refrigerant is accumulated in the refrigerant pipe on the high-pressure side, and an outside temperature is high, a saturation pressure of the liquid-phase refrigerant accumulated in the refrigerant pipe on the high-pressure side possibly exceeds a design pressure of the refrigerant pipe on the high-pressure side. With the conventional refrigeration device, to prevent the saturation pressure of the accumulated liquid-phase refrigerant from exceeding the design pressure of the refrigerant pipe on the high-pressure side, an auxiliary heat source such as a cooling device or the like is provided at the refrigerant pipe on the high-pressure side, and the accumulated liquid-phase refrigerant is cooled in the refrigerant pipe on the high-pressure side. However, in the case where the auxiliary heat source is provided, there is a problem that, although safety of the refrigerant pipe on the high-pressure side can be secured, reduction in energy consumption, such as reduction in power consumption, is possibly not achieved.

[0005] The refrigeration device of the present disclosure has been made to overcome the problem described above, and is aimed at providing a refrigeration device with which safety of a refrigerant pipe on a high-pressure side can be secured, and reduction in energy consumption can be achieved.

Solution to Problem [0006] A refrigeration device of an embodiment according to the present disclosure includes: a refrigerant circuit including a compression system including a first compression device, and a second compression device connected to the first compression device, the compression system being configured to compress, at the first compression device and the second compression device, refrigerant that is suctioned in and that is having a low pressure into the refrigerant having a high pressure, and to cause the refrigerant to be discharged, a first heat exchanger connected to a discharge side of the compression system, a second heat exchanger including a first refrigerant passage and a second refrigerant passage, the first refrigerant passage being connected to a downstream side of the first heat exchanger, a first pressure reducing device connected to a downstream side of the first refrigerant passage of the second heat exchanger, and a third heat exchanger connected between a downstream side of the first pressure reducing device and a suction side of the compression system, the refrigerant circuit being configured to cause the refrigerant discharged from the compression system to be circulated; an intermediate injection circuit including a second pressure reducing device connected between the downstream side of the first refrigerant passage of the second heat exchanger and the second refrigerant passage of the second heat exchanger, the intermediate injection circuit branching from the downstream side of the first refrigerant passage of the second heat exchanger, and being connected, via the second pressure reducing device and the second refrigerant passage of the second heat exchanger, to an intermediate-pressure part between the first compression device and the second compression device; and a first bypass including a first opening-and-closing valve, the first bypass branching from a high-pressure side of the refrigerant circuit and being connected to the suction side of the compression system, the high-pressure side of the refrigerant circuit being positioned between the discharge side of the compression system and an upstream side of the first pressure reducing device, wherein the first opening-and-closing valve is in a closed state in a case where a pressure of the refrigerant on an upstream side of the first opening-and-closing valve is at or below a first pressure, and is opened in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve exceeds the first pressure.

Advantageous Effects of Invention [0007] According to the embodiment of the present disclosure, by including the first bypass, the refrigeration device can be configured such that a pressure on the high-pressure side of the refrigerant circuit does not exceed a design pressure of a refrigerant pipe on the high-pressure side of the refrigerant circuit. Furthermore, since the refrigeration device can be configured such that the design pressure of the refrigerant pipe on the high-pressure side of the refrigerant circuit is not exceeded, an auxiliary heat source such as a cooling device does not have to be provided on the high-pressure side of the refrigerant circuit. Accordingly, the present disclosure may provide a refrigeration device with which safety of a refrigerant pipe on a high-pressure side can be secured, and reduction in energy consumption can be achieved.

Brief Description of Drawings

[0008] [Fig. 1] Fig. 1 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit of a refrigerant device according to Embodiment 1 of the present

disclosure.

[Fig. 2] Fig. 2 is a schematic Mollier diagram showing an example of an operation mode of the refrigerant device according to Embodiment 1 of the present disclosure.

[Fig. 3] Fig. 3 is a diagram showing a relationship among refrigerant density, a refrigerant temperature, and a refrigerant pressure, in a case where CO2 refrigerant is used as refrigerant in the refrigeration device according to Embodiment 1 of the present disclosure.

[Fig. 4] Fig. 4 is a schematic refrigerant circuit diagram showing an example modification of the refrigerant circuit in Fig. 1, according to the refrigeration device of

Embodiment 1 of the present disclosure.

[Fig. 5] Fig. 5 is a schematic refrigerant circuit diagram showing another example modification of the refrigerant circuit in Fig. 1, according to the refrigeration device of Embodiment 1 of the present disclosure.

[Fig. 6] Fig. 6 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit of a refrigeration device according to Embodiment 2 of the present

disclosure.

[Fig. 7] Fig. 7 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit of a refrigeration device according to Embodiment 3 of the present disclosure.

[Fig. 8] Fig. 8 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit of a refrigeration device according to Embodiment 4 of the present disclosure.

[Fig. 9] Fig. 9 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit of a refrigeration device according to Embodiment 5 of the present

disclosure.

Description of Embodiments

[0009] Embodiment 1.

A description will be given of a refrigeration device 100 according to Embodiment 1 of the present disclosure. Fig. 1 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 1.

[0010] Note that, in Fig. 1 and subsequent drawings shown below, dimensional relationships and shapes of structural parts may be different from actual dimensional relationships and shapes. Furthermore, in the drawings shown below, a same reference sign is assigned to same or similar structural elements.

[0011] Furthermore, terms "high pressure", "intermediate pressure", and "low pressure" used in the following description each refer to a relative pressure of refrigerant inside the refrigerant circuit 10, and do not refer to an absolute pressure of the refrigerant.

[0012] As shown in Fig. 1, the refrigeration device 100 includes the refrigerant circuit 10, an intermediate injection circuit 60, a first bypass 70, and a second bypass 80.

[0013] The refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 1 of the present disclosure will be described.

[0014] The refrigerant circuit 10 includes a compression system 1, a first heat exchanger 2, a second heat exchanger 3, a first pressure reducing device 4, and a third heat exchanger 5. The refrigerant circuit 10 is configured to cause high-pressure refrigerant discharged from the compression system 1 to be circulated. [0015] The compression system 1 is a fluid system configured to compress low-pressure refrigerant that is suctioned from a suction side of the compression system 1, and to discharge the refrigerant as high-pressure refrigerant. The compression system 1 includes a first compression device 12 disposed on the suction side of the compression system 1, and a second compression device 14 disposed on a discharge side of the compression system 1 and serially connected to the first compression device 12. In other words, a discharge side of the first compression device 12 is connected to a suction side of the second compression device 14. The first compression device 12 is configured to suction low-pressure refrigerant from the suction side of the compression system 1, to compress the refrigerant, and to discharge the refrigerant as intermediate-pressure refrigerant. The second compression device 14 is configured to suction low-pressure refrigerant that is discharged from the first compression device 12, to compress the refrigerant, and to discharge the refrigerant from the compression system 1 as high-pressure refrigerant. Note that the first compression device 12 does not have to be the same as the second compression device 14, and the first compression device 12 may be different from the second compression device 14. Furthermore, depending on a mode of the refrigeration device 100, the first compression device 12 may be referred to as a low-stage compression device, and the second compression device 14 may be referred to as a high-stage compression device.

[0016] With the compression system 1, the first compression device 12 and the second compression device 14 may be separate compressors, and the discharge side of the first compression device 12 and the suction side of the second compression device 14 may be connected by a pipe. In the case where the first compression device 12 and the second compression device 14 are separate compressors, the first compression device 12 and the second compression device 14 may be a reciprocating compressor, a scroll compressor, a rotary compressor, a screw compressor, a centrifugal compressor, or other compressors, depending on the mode of the refrigeration device 100. Note that, in the case where the first compression device 12 and the second compression device 14 are separate compressors, the first compression device 12 and the second compression device 14 do not have to be compressors of a same compression method, but may be compressors of different compression methods. Furthermore, the compression system 1 may further include a separate compression device. Moreover, at least one of the first compression device 12 and the second compression device 14 may be a two-stage compressor or a multi-stage compressor.

[0017] Furthermore, with the compression system 1, the first compression device 12 and the second compression device 14 may be integrated as a two-stage compressor.

In the case where the compression system 1 is a two-stage compressor, the compression system 1 may be a reciprocating two-stage compressor, a scroll two-stage compressor, a rotary two-stage compressor, or other two-stage compressors, depending on the mode of the refrigeration device 100. Furthermore, in the case where the first compression device 12 and the second compression device 14 are integrated, the compression system 1 may be a multi-stage compressor further including a separate compression device.

[0018] The first heat exchanger 2 is a condenser where high-pressure, gas-phase refrigerant discharged from the compression system 1 flows in, and flows out as high-pressure, liquid-phase refrigerant. Note that, depending on the mode of the refrigeration device 100, the first heat exchanger 2 may be referred to as a radiator. Moreover, the first heat exchanger 2 may be a heat exchange device including a plurality of heat exchangers.

[0019] For example, by including a first fan 2a, as shown in Fig. 1, the first heat exchanger 2 may be configured as an air-cooled heat exchanger configured to exchange heat between an air flow induced by the first fan 2a and high-pressure refrigerant passing through the first heat exchanger 2. In the case where the first heat exchanger 2 is of an air-cooled heat exchanger type, the first heat exchanger 2 may be a fin-and-tube heat exchanger, a plate-fin heat exchanger, or other heat exchangers, depending on the mode of the refrigeration device 100. Note that the first fan 2a may be an axial fan such as a propeller fan, a centrifugal fan such as a sirocco fan or a turbo fan, a mixed flow fan, a cross flow fan, or other fans, depending on the mode of the refrigeration device 100.

[0020] Furthermore, depending on the mode of the refrigeration device 100, the first heat exchanger 2 may alternatively be a water-cooled heat exchanger configured to exchange heat between water or brine and the high-pressure refrigerant passing through the first heat exchanger 2. In the case where the first heat exchanger 2 is a water-cooled heat exchanger, the first heat exchanger 2 may be a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger, depending on the mode of the refrigeration device 100.

[0021] The second heat exchanger 3 is a supercooling heat exchanger configured to further cool the liquid-phase refrigerant flowing out of the first heat exchanger 2, to increase a degree of supercooling at a refrigeration cycle of the refrigeration device 100. Note that, depending on the mode of the refrigeration device 100, the second heat exchanger 3 may be a heat exchange device including a plurality of heat exchangers.

[0022] The second heat exchanger 3 includes a first refrigerant passage 3a and a second refrigerant passage 3b, and is an internal heat exchanger configured to exchange heat between high-pressure, liquid-phase refrigerant passing through the first refrigerant passage 3a and intermediate-pressure, liquid-phase refrigerant passing through the second refrigerant passage 3b. The first refrigerant passage 3a forms a part of the refrigerant circuit 10, the first refrigerant passage 3a having one end connected to a downstream side of the first heat exchanger 2 and the other end connected to an upstream side of the first pressure reducing device 4. Although details will be given later, the second refrigerant passage 3b forms a part of the intermediate injection circuit 60. Depending on the mode of the refrigeration device 100, the second heat exchanger 3 may be a shell-and-tube heat exchanger, a plate heat exchanger, a double-tube heat exchanger, or other heat exchangers.

[0023] The first pressure reducing device 4 is connected to a downstream side of the second heat exchanger 3, and is configured to expand and decompress the high-pressure, liquid-phase refrigerant flowing out of the first refrigerant passage 3a of the second heat exchanger 3, and to cause the refrigerant to flow into the third heat exchanger 5. Depending on the mode of the refrigeration device 100, the first pressure reducing device 4 may be an expander, an automatic thermostatic expansion valve, a linear electronic expansion valve, a capillary tube, or the like.

The expander is a mechanical expansion valve adopting a diaphragm in a pressure receiver. The automatic thermostatic expansion valve is an expansion device configured to adjust an amount of refrigerant by a degree of superheat of gas-phase refrigerant on the suction side of the compression system 1. The linear electronic expansion valve is an expansion device, an opening degree of which can be adjusted continuously or in multiple stages, and is abbreviated as LEV.

[0024] The third heat exchanger 5 is an evaporator to which low-pressure, two-phase refrigerant expanded and decompressed by the first pressure reducing device 4 flows in, and from which the refrigerant flows out as low-pressure, gas-phase refrigerant or high-quality, two-phase refrigerant. Note that, depending on the mode of the refrigeration device 100, the third heat exchanger 5 may be referred to as a cooler. Furthermore, the third heat exchanger 5 may be a heat exchange device including a plurality of heat exchangers.

[0025] For example, by the refrigeration device 100 including a second fan 5a, as shown in Fig. 1, the third heat exchanger 5 may be made an air-cooled heat exchanger configured to exchange heat between an air flow induced by the second fan 5a and the low-pressure, two-phase refrigerant passing through the third heat exchanger 5. In the case where the third heat exchanger 5 is of an air-cooled heat exchanger type, the third heat exchanger 5 may be a fin-and-tube heat exchanger, a plate-fin heat exchanger, or other heat exchangers, depending on the mode of the refrigeration device 100. Note that the second fan 5a may be an axial fan such as a propeller fan, a centrifugal fan such as a sirocco fan or a turbo fan, a mixed flow fan, a cross flow fan, or other fans, depending on the mode of the refrigeration device 100.

[0026] Furthermore, depending on the mode of the refrigeration device 100, the third heat exchanger 5 may alternatively be a water-cooled heat exchanger configured to exchange heat between water or brine and the low-pressure, two-phase refrigerant passing through the third heat exchanger 5. In the case where the third heat exchanger 5 is a water-cooled heat exchanger, the third heat exchanger 5 may be a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger, depending on the mode of the refrigeration device 100.

[0027] Next, a description will be given of a first refrigerant pipe 10a, a second refrigerant pipe 10b, a third refrigerant pipe 10c, a fourth refrigerant pipe 10d, and a fifth refrigerant pipe 10e that are refrigerant pipes of the refrigerant circuit 10. [0028] Note that, depending on the mode of the refrigeration device 100, the refrigerant circuit 10 may include an accumulator, an oil separator, or the like.

[0029] The first refrigerant pipe 10a is connected between the discharge side of the compression system 1 and an upstream side of the first heat exchanger 2. The second refrigerant pipe 10b is connected between the downstream side of the first heat exchanger 2 and an upstream side of the first refrigerant passage 3a of the second heat exchanger 3. The third refrigerant pipe 10c is connected between a downstream side of the first refrigerant passage 3a of the second heat exchanger 3 and the upstream side of the first pressure reducing device 4. The fourth refrigerant pipe 10d is connected between a downstream side of the first pressure reducing device 4 and an upstream side of the third heat exchanger 5. The fifth refrigerant pipe 10e is connected between a downstream side of the third heat exchanger 5 and the suction side of the compression system 1. In other words, in the refrigerant circuit 10, the compression system 1, the first heat exchanger 2, the second heat exchanger 3, the first pressure reducing device 4, and the third heat exchanger 5 are sequentially connected by the first refrigerant pipe 10a, the second refrigerant pipe 10b, the third refrigerant pipe 10c, the fourth refrigerant pipe 10d, and the fifth refrigerant pipe 10e.

[0030] In the present disclosure, a part of the refrigerant circuit 10 from the discharge side of the compression system 1 to the upstream side of the first pressure reducing device 4, where the first refrigerant pipe 10a, the first heat exchanger 2, the second refrigerant pipe 10b, the second heat exchanger 3, and the third refrigerant pipe 10c are connected, will be referred to as a high-pressure side of the refrigerant circuit 10. Furthermore, a part of the refrigerant circuit 10 from the downstream side of the third heat exchanger 5 to the suction side of the compression system 1, where the fourth refrigerant pipe 10d, the third heat exchanger 5, and the fifth refrigerant pipe 10e are connected, will be referred to as a low-pressure side of the refrigerant circuit 10. Moreover, an intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14 will be referred to as an intermediate-pressure side of the refrigerant circuit 10.

[0031] Next, a control appliance configured to control the refrigeration device 100 will be described.

[0032] The refrigeration device 100 may include, as a control appliance of the refrigeration device 100, a controller 20 configured to control an operation state of the refrigeration device 100, and a sensor that is connected to the controller 20 in a wired or wireless manner.

[0033] The controller 20 is dedicated hardware, or a microcomputer or a micro-processing unit including a central processing unit, a memory and the like. For example, the controller 20 is a built-in control circuit board, and is accommodated in an electric component box and is disposed inside the refrigeration device 100. Note that Fig. 1 and subsequent drawings do not show an internal structure of the controller 20.

[0034] In the case where the controller 20 is dedicated hardware, the controller 20 may be a single circuit, a combined circuit, an ASIC, an FPGA, or a combination thereof, for example. The controller 20 may implement control processes by respective pieces of hardware, or may implement the control processes by one piece of hardware. Note that "ASIC" is an abbreviation of an application specific integrated circuit, and "FPGA" is an abbreviation of a field programmable gate array.

[0035] In the case where the controller 20 is a microcomputer or a micro-processing unit, control processes to be executed by the controller 20 are implemented by software, firmware, or a combination of software and firmware. The software or the firmware is written as a control program. The memory is a storage unit of the controller 20 storing the control program. For example, the memory may be a nonvolatile or volatile semiconductor memory, such as RAM, ROM, a flash memory, an EPROM, or an EEPROM. The central processing unit is an arithmetic unit configured to implement a control process by reading and executing a control program stored in the memory. Note that the central processing unit is abbreviated as "CPU". Furthermore, the central processing unit may be referred to as a processing device, an arithmetic device, a microprocessor, or a processor.

[0036] Furthermore, the controller 20 may implement some of the control processes by dedicated hardware, and the rest of the control processes by a microcomputer or a micro-processing unit.

[0037] Note that, in Fig. 1, the refrigeration device 100 includes one controller 20, but the refrigeration device 100 may alternatively include a plurality of controllers 20, depending on the mode of the refrigeration device 100. In the case where the refrigeration device 100 includes a plurality of controllers 20, control information may be exchanged among the plurality of controllers 20, depending on the mode of the refrigeration device 100.

[0038] The refrigeration device 100 may include one or more pressure sensors that are connected to the controller 20 in a wired or wireless manner. For example, the pressure sensors may include a piezoelectric pressure sensor, a semiconductor sensor, or a pressure transducer. In the case where the refrigeration device 100 includes a plurality of pressure sensors, the plurality of pressure sensors may be pressure sensors having a same structure or pressure sensors having different structures. Note that Fig. 1 does not show connection lines between the controller 20 and the pressure sensors.

[0039] As shown in Fig. 1, the refrigeration device 100 may include, as the pressure sensors, a first pressure sensor 30a, a second pressure sensor 30b, and a third pressure sensor 30c. Note that, depending on the mode of the refrigeration device 100, some of the pressure sensors may be omitted, or the refrigeration device 100 may include additional pressure sensors.

[0040] The first pressure sensor 30a is a low-pressure sensor disposed on the fifth refrigerant pipe 10e on the low-pressure side of the refrigerant circuit 10, and is configured to detect low pressure on the suction side of the compression system 1.

The second pressure sensor 30b is an intermediate-pressure sensor disposed on the intermediate-pressure side of the refrigerant circuit 10, and is configured to detect pressure at the intermediate-pressure part of the compression system 1. As shown in Fig. 1, the second pressure sensor 30b is disposed between the first compression device 12 and the second compression device 14, such as on the discharge side of the first compression device 12. The third pressure sensor 30c is a high-pressure sensor disposed on the first refrigerant pipe 10a on the high-pressure side of the refrigerant circuit 10, and is configured to detect high pressure on the discharge side of the compression system 1.

[0041] Furthermore, the refrigeration device 100 may include one or more temperature sensors that are connected to the controller 20 in a wired or wireless manner. For example, the temperature sensors may include a thermistor made of a semiconductor material, or a resistance temperature detector of a metal material. In the case where the refrigeration device 100 includes a plurality of temperature sensors, the plurality of temperature sensors may be temperature sensors having a same structure or temperature sensors having different structures. Note that Fig. 1 does not show connection lines between the controller 20 and the pressure sensors, and between the controller 20 and the temperature sensors.

[0042] As shown in Fig. 1, the refrigeration device 100 may include, as the temperature sensors, a first temperature sensor 40a, a second temperature sensor 40b, a third temperature sensor 40c, a fourth temperature sensor 40d, a fifth temperature sensor 40e, a sixth temperature sensor 40f, and a seventh temperature sensor 40g. Note that, depending on the mode of the refrigeration device 100, some of the temperature sensors may be omitted, or the refrigeration device 100 may include additional temperature sensors.

[0043] The first temperature sensor 40a is a temperature sensor disposed on the first refrigerant pipe 10a, and is configured to detect, via the first refrigerant pipe 10a, a temperature of refrigerant flowing on the upstream side of the first heat exchanger 2.

The second temperature sensor 40b is a temperature sensor disposed on the second refrigerant pipe 10b, and is configured to detect, via the second refrigerant pipe 10b, a temperature of refrigerant flowing on the downstream side of the first heat exchanger 2. The third temperature sensor 40c is a temperature sensor disposed on the third refrigerant pipe 10c, and is configured to detect, via the third refrigerant pipe 10c, a temperature of refrigerant flowing on the downstream side of the first refrigerant passage 3a of the second heat exchanger 3. The fourth temperature sensor 40d is a temperature sensor disposed on the fourth refrigerant pipe 10d, and is configured to detect, via the fourth refrigerant pipe 10d, a temperature of refrigerant flowing on the upstream side of the third heat exchanger 5. The fifth temperature sensor 40e is a temperature sensor disposed on the fifth refrigerant pipe 10e, and is configured to detect, via the fifth refrigerant pipe 10e, a temperature of refrigerant flowing on the downstream side of the third heat exchanger 5. The sixth temperature sensor 40f is a temperature sensor disposed at the intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14, and is configured to detect, via a pipe or the like, a temperature of refrigerant flowing through the intermediate-pressure part of the compression system 1. The seventh temperature sensor 40g is an ambient temperature sensor disposed at a certain position around the refrigeration device 100, and is configured to detect an outside temperature.

[0044] Note that, depending on the mode of the refrigeration device 100, the refrigeration device 100 may include sensors other than the pressure sensors and the temperature sensors, such as a refrigerant leakage detection sensor, for example.

[0045] Next, the intermediate injection circuit 60 of the refrigeration device 100 will be described.

[0046] As shown in Fig. 1, the intermediate injection circuit 60 is a bypass branching from the third refrigerant pipe 10c disposed on the downstream side of the first refrigerant passage 3a of the second heat exchanger 3, and is connected to the intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14. The intermediate injection circuit 60 is configured such that refrigerant diverted on the downstream side of the second heat exchanger 3 is injected into the intermediate-pressure part of the compression system 1 as low-temperature, intermediate-pressure refrigerant.

[0047] The intermediate injection circuit 60 is made of the second heat exchanger 3, a second pressure reducing device 6, a first intermediate injection refrigerant pipe 60a, a second intermediate injection refrigerant pipe 60b, and a third intermediate injection refrigerant pipe 60c. Note that a description is already given of a detailed structure of the second heat exchanger 3 as a structural element of the refrigerant circuit 10, and a redundant description will be omitted.

[0048] The second pressure reducing device 6 is configured to expand and decompress high-pressure, liquid-phase refrigerant diverted on the downstream side of the first refrigerant passage 3a of the second heat exchanger 3, and to cause the refrigerant to flow into the second refrigerant passage 3b of the second heat exchanger 3. Depending on the mode of the refrigeration device 100, the second pressure reducing device 6 may be an expander, an automatic thermostatic expansion valve, a linear electronic expansion valve, a capillary tube, or the like. The expander is a mechanical expansion valve adopting a diaphragm in a pressure receiver. The automatic thermostatic expansion valve is an expansion device configured to adjust an amount of refrigerant by a degree of superheat of gas-phase refrigerant on the suction side of the compression system 1. The linear electronic expansion valve is an expansion device, an opening degree of which can be adjusted continuously or in multiple stages, and is abbreviated as LEV. Note that the structure of the second pressure reducing device 6 may be the same or different from the structure of the first pressure reducing device 4.

[0049] The first intermediate injection refrigerant pipe 60a is connected between the third refrigerant pipe 10c and an upstream side of the second pressure reducing device 6. A refrigerant passage of the first intermediate injection refrigerant pipe 60a is connected in a manner branching from a refrigerant passage of the third refrigerant pipe 10c. The second intermediate injection refrigerant pipe 60b is connected between a downstream side of the second pressure reducing device 6 and an upstream side of the second refrigerant passage 3b of the second heat exchanger 3. The third intermediate injection refrigerant pipe 60c is connected between a downstream side of the second refrigerant passage 3b of the second heat exchanger 3 and the intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14. A refrigerant passage of the third intermediate injection refrigerant pipe 60c is connected to merge with a refrigerant passage at the intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14. In other words, the intermediate injection circuit 60 branches from the third refrigerant pipe 10c disposed on the downstream side of the first refrigerant passage 3a of the second heat exchanger 3. Furthermore, the intermediate injection circuit 60 is connected to the intermediate-pressure part between the first compression device and the second compression device, by the second pressure reducing device 6 and the second refrigerant passage 3b of the second heat exchanger 3.

[0050] Next, the first bypass 70 of the refrigeration device 100 will be described.

[0051] The first bypass 70 is a bypass branching from the high-pressure side, of the refrigerant circuit 10, between the discharge side of the compression system 1 and the upstream side of the first pressure reducing device 4, and is connected to the suction side of the compression system 1. For example, in Embodiment 1, as shown in Fig. 1, the first bypass 70 branches from the third refrigerant pipe 10c that is a refrigerant pipe on the high-pressure side of the refrigerant circuit 10 and that is positioned between the downstream side of the second heat exchanger 3 and the upstream side of the first pressure reducing device 4. Moreover, the first bypass 70 is connected to the fifth refrigerant pipe 10e disposed on the suction side of the compression system 1. In other words, the first bypass 70 provides a bypass route through which refrigerant can flow in from the high-pressure side of the refrigerant circuit 10 to the low-pressure side of the refrigerant circuit 10. [0052] The first bypass 70 includes a first opening-and-closing valve 7, a first bypass refrigerant pipe 70a, and a second bypass refrigerant pipe 70b.

[0053] The first opening-and-closing valve 7 is a movable mechanism, an internal passage of which can be opened or closed to release or stop a flow of a fluid. The first opening-and-closing valve 7 is in a closed state in a case where a pressure Ph of refrigerant on an upstream side of the first opening-and-closing valve 7 is at or below a first pressure P1 that is a set pressure of the first opening-and-closing valve 7.

Furthermore, the first opening-and-closing valve 7 is opened in a case where the pressure Ph of the refrigerant on the upstream side of the first opening-and-closing valve 7 exceeds the first pressure P1, to cause the refrigerant to flow to a downstream side of the first opening-and-closing valve 7. In other words, the first opening-and-closing valve 7 is an automatic valve designed such that the set pressure of the first opening-and-closing valve 7 is the first pressure P1.

[0054] The first pressure P1 that is the set pressure of the first opening-and-closing valve 7 is determined based on a design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10, or in other words, the design pressure of the first refrigerant pipe 10a, the second refrigerant pipe 10b, and the third refrigerant pipe 10c. Specifically, with the refrigeration device 100, an allowable pressure on the high-pressure side of the refrigerant circuit 10 set to prevent failure of the refrigerant circuit 10 may be set lower than the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10. In a case where the allowable pressure of the refrigerant circuit 10 is set, the first pressure P1 is set to a pressure higher than a pressure on the high-pressure side of the refrigerant circuit 10 expected at a time of normal operation of the refrigeration device 100 and lower than the allowable pressure of the refrigerant circuit 10.

[0055] For example, the first opening-and-closing valve 7 is a pressure-driven valve that is mechanically opened or closed based on the pressure Ph of the refrigerant on the upstream side of the first opening-and-closing valve 7. In the case where the first opening-and-closing valve 7 is a pressure-driven valve, the first opening-and-closing valve 7 may be a sealed safety valve, for example, depending on the mode of the refrigeration device 100. In the case where the first opening-and-closing valve 7 is a sealed safety valve, the first opening-and-closing valve 7 may be a diaphragm safety valve with which there is a small possibility of fluid leakage from a valve body, for example.

[0056] The first bypass refrigerant pipe 70a is connected between the third refrigerant pipe 10c and the upstream side of the first opening-and-closing valve 7. A refrigerant passage of the first bypass refrigerant pipe 70a is connected in a manner branching from the refrigerant passage of the third refrigerant pipe 10c. The second bypass refrigerant pipe 70b is connected between the downstream side of the first opening-and-closing valve 7 and the fifth refrigerant pipe 10e. A refrigerant passage of the second bypass refrigerant pipe 70b is connected to merge with the refrigerant passage of the fifth refrigerant pipe 10e.

[0057] Next, the second bypass 80 of the refrigeration device 100 will be described.

[0058] The second bypass 80 is a bypass branching from the intermediate-pressure part, of the compression system 1, between the first compression device 12 and the second compression device 14, and is connected to the fifth refrigerant pipe 10e disposed on the suction side of the compression system 1. In other words, the second bypass 80 provides a bypass route through which refrigerant can flow in from the intermediate-pressure side of the refrigerant circuit 10 to the low-pressure side of the refrigerant circuit 10.

[0059] The second bypass 80 includes a second opening-and-closing valve 8, a third bypass refrigerant pipe 80a, and a fourth bypass refrigerant pipe 80b.

[0060] The second opening-and-closing valve 8 is a movable mechanism, an internal passage of which can be opened or closed to release or stop a flow of a fluid. The second opening-and-closing valve 8 is in a closed state in a case where a pressure Pi of refrigerant in the intermediate-pressure part between the first compression device 12 and the second compression device 14 is at or below a second pressure P2 that is a set pressure of the second opening-and-closing valve 8. Furthermore, the second opening-and-closing valve 8 is opened in a case where the pressure Pi of the refrigerant in the intermediate-pressure part between the first compression device 12 and the second compression device 14 exceeds the second pressure P2, to cause the refrigerant to flow to the suction side of the compression system 1. In other words, the second opening-and-closing valve 8 is an automatic valve designed such that the set pressure of the second opening-and-closing valve 8 is the second pressure P2.

[0061] The second pressure P2 that is the set pressure of the second opening-andclosing valve 8 is determined based on the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10, or in other words, the design pressure of the first refrigerant pipe 10a, the second refrigerant pipe 10b, and the third refrigerant pipe 10c. For example, the second pressure P2 is set lower than the first pressure P1 that is the set pressure of the first opening-and-closing valve 7. Specifically, with the refrigeration device 100, an allowable pressure on the intermediate-pressure side of the refrigerant circuit 10 set to prevent failure on the high-pressure side of the refrigerant circuit 10 may be set lower than an intermediate-pressure upper-limit value that is calculated from the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10. In a case where the allowable pressure on the intermediate-pressure side of the refrigerant circuit 10 is set, the second pressure P2 is set to a pressure higher than a pressure on the intermediate-pressure side of the refrigerant circuit 10 expected at the time of normal operation of the refrigeration device 100 and lower than the allowable pressure on the intermediate-pressure side of the refrigerant circuit 10. [0062] For example, the second opening-and-closing valve 8 is a pressure-driven valve that is mechanically opened or closed based on the pressure Pi of the refrigerant in the intermediate-pressure part between the first compression device 12 and the second compression device 14. In the case where the second opening-andclosing valve 8 is a pressure-driven valve, the second opening-and-closing valve 8 may be a sealed safety valve, for example, depending on the mode of the refrigeration device 100. In the case where the second opening-and-closing valve 8 is a sealed safety valve, the second opening-and-closing valve 8 may be a diaphragm safety valve with which there is a small possibility of fluid leakage from a valve body, for example.

[0063] The third bypass refrigerant pipe 80a is connected between the intermediate-pressure part between the first compression device 12 and the second compression device 14, and one end of the second opening-and-closing valve 8. A refrigerant passage of the third bypass refrigerant pipe 80a is connected in a manner branching from the refrigerant passage at the intermediate-pressure part between the first compression device 12 and the second compression device 14. The fourth bypass refrigerant pipe 80b is connected between the other end of the second opening-andclosing valve 8 and the fifth refrigerant pipe 10e. A refrigerant passage of the fourth bypass refrigerant pipe 80b is connected to merge with the refrigerant passage of the fifth refrigerant pipe 10e on the suction side of the compression system 1.

[0064] Next, a description will be given of the refrigerant that is circulated in the refrigeration device 100.

[0065] As the refrigerant in the refrigeration device 100, any type of refrigerant, or mixed refrigerant obtained by mixing two or more types of refrigerant among various types of refrigerant may be selected, depending on use of the refrigeration device 100. As the refrigerant in the refrigeration device 100, a single-component refrigerant, a near-azeotropic refrigerant mixture, a non-azeotropic refrigerant mixture, or refrigerant with low global warming potential is used, for example. As the single-component refrigerant, R22, R134a, R32, HF01234y1, HF01234ze, or HF01123 is used, for example. As the near-azeotropic refrigerant mixture, R410A or R404A is used, for example. As the non-azeotropic refrigerant mixture, R407C is used, for example. As the refrigerant with low global warming potential, those including a double bond in a chemical formula, such as CFsCF=CH2, is used, for example.

[0066] Furthermore, as the refrigerant to be circulated in a refrigeration cycle circuit, natural refrigerant that is advantageous in preventing global warming, such as CO2 or propane, may be used. CO2 refrigerant is natural refrigerant that is advantageous in preventing global warming, but CO2 refrigerant has a disadvantage that CO2 refrigerant has to work under high-temperature, high-pressure conditions. However, since the refrigeration device 100 of the present disclosure includes a plurality of compression devices, refrigerant may be caused to circulate under high-temperature, high-pressure conditions, and CO2 refrigerant is suitably used as working refrigerant. [0067] Next, an operation of the refrigeration device 100 will be described with reference to Fig. 2.

[0068] Fig. 2 is a schematic Mollier diagram showing an example of an operation mode of the refrigeration device 100 according to Embodiment 1. A vertical axis of the Mollier diagram schematically indicates pressure, and a horizontal axis of the Mollier diagram schematically indicates enthalpy. Furthermore, a left side of a protruding curve in the Mollier diagram is a saturated liquid line, and a right side of the protruding curve in the Mollier diagram is a saturated vapor line. Moreover, white circles in the Mollier diagram are provided to describe states of the refrigerant in the operation state of the refrigeration device 100. Moreover, line segments connecting the white circles in the Mollier diagram schematically show changes in the refrigerant during an operation of the refrigeration device 100.

[0069] In Fig. 2, a white circle A indicates a stage when high-temperature, high-pressure, gas-phase refrigerant is discharged from the compression system 1.

[0070] The high-temperature, high-pressure, gas-phase refrigerant discharged from the compression system 1 flows into the first heat exchanger 2 through the first refrigerant pipe 10a. The high-temperature, high-pressure, gas-phase refrigerant flowing into the first heat exchanger 2 flows through the first heat exchanger 2, exchanges heat with an air flow induced by the first fan 2a, and flows out as high-temperature, liquid-phase refrigerant.

[0071] In Fig. 2, a white circle B indicates a stage when the high-pressure, liquid-phase refrigerant flows out from the first heat exchanger 2.

[0072] The high-pressure, liquid-phase refrigerant flowing out of the first heat exchanger 2 flows into the first refrigerant passage 3a of the second heat exchanger 3 through the second refrigerant pipe 10b. The high-pressure, liquid-phase refrigerant flowing into the first refrigerant passage 3a of the second heat exchanger 3 passes through the first refrigerant passage 3a of the second heat exchanger 3, and is supercooled by exchanging heat with intermediate-pressure refrigerant passing through the second refrigerant passage 3b of the second heat exchanger 3. The high-pressure, gas-phase refrigerant supercooled at the second heat exchanger 3 flows out from the first refrigerant passage 3a of the second heat exchanger 3.

[0073] In Fig. 2, a white circle C indicates a stage when the supercooled, high-pressure, gas-phase refrigerant flows out from the first refrigerant passage 3a of the second heat exchanger 3.

[0074] The supercooled, high-pressure, gas-phase refrigerant flowing out of the first refrigerant passage 3a of the second heat exchanger 3 flows into the third refrigerant pipe 10c. At the third refrigerant pipe 10c, a part of the supercooled, high-pressure, gas-phase refrigerant is diverted to flow into the first intermediate injection refrigerant pipe 60a of the intermediate injection circuit 60.

[0075] Another part of the supercooled, high-pressure, gas-phase refrigerant flows into the first pressure reducing device 4 through the third refrigerant pipe 10c. The supercooled, high-pressure, gas-phase refrigerant flowing into the first pressure reducing device 4 is expanded and decompressed at the first pressure reducing device 4, and flows out from the first pressure reducing device 4 as low-temperature, low-pressure, two-phase refrigerant.

[0076] In Fig. 2, a white circle D indicates a stage when the low-temperature, low-pressure, two-phase refrigerant flows out from the first pressure reducing device 4.

[0077] The low-temperature, low-pressure, two-phase refrigerant flowing out of the first pressure reducing device 4 flows into the third heat exchanger 5 through the fourth refrigerant pipe 10d. The low-temperature, low-pressure, two-phase refrigerant flowing into the third heat exchanger 5 passes through the third heat exchanger 5, exchanges heat with an air flow induced by the second fan 5a, and flows out as low-pressure, gas-phase refrigerant. Note that the refrigerant flowing out of the third heat exchanger 5 may possibly be high-quality, two-phase refrigerant. [0078] In Fig. 2, a white circle E indicates a stage when the low-pressure, gas-phase refrigerant flows out from the third heat exchanger 5.

[0079] The low-pressure, gas-phase refrigerant flowing out of the third heat exchanger 5 is suctioned through the fifth refrigerant pipe 10e into the compression system 1 from the suction side. The low-pressure, gas-phase refrigerant suctioned into the compression system 1 is compressed at the first compression device 12, and is discharged into the intermediate-pressure part of the compression system 1 as intermediate-pressure, gas-phase refrigerant.

[0080] In Fig. 2, a white circle F indicates a stage when the intermediate-pressure, gas-phase refrigerant is discharged from the first compression device 12.

[0081] Note that, with the refrigeration device 100, the intermediate-pressure, gas-phase refrigerant discharged from the first compression device 12 may be cooled by heat exchange. A detailed configuration will be described later in Embodiment 2.

In Fig. 2, a white circle G indicates a stage when the intermediate-pressure, gas-phase refrigerant is discharged from the first compression device 12 and is cooled by heat exchange.

[0082] On the other hand, the supercooled, high-pressure, gas-phase refrigerant diverted from the third refrigerant pipe 10c and flowing into the first intermediate injection refrigerant pipe 60a flows into the second pressure reducing device 6 through first intermediate injection refrigerant pipe 60a. The supercooled, high-pressure, gas-phase refrigerant flowing into the second pressure reducing device 6 is expanded and decompressed at the second pressure reducing device 6, and flows out from the second pressure reducing device 6 as intermediate-pressure, liquid-phase refrigerant or highly wet, intermediate-pressure, two-phase refrigerant. [0083] In Fig. 2, a white circle H indicates a stage when the intermediate-pressure, liquid-phase refrigerant or the highly wet, intermediate-pressure, two-phase refrigerant flows out from the second pressure reducing device 6.

[0084] The intermediate-pressure, liquid-phase refrigerant or the highly wet, intermediate-pressure, two-phase refrigerant flowing out of the second pressure reducing device 6 flows into the second refrigerant passage 3b of the second heat exchanger 3 through the second intermediate injection refrigerant pipe 60b. The intermediate-pressure, liquid-phase refrigerant or the highly wet, intermediate-pressure, two-phase refrigerant flowing into the second refrigerant passage 3b of the second heat exchanger 3 passes through the second refrigerant passage 3b of the second heat exchanger 3, and is heated by exchanging heat with the high-pressure, liquid-phase refrigerant passing through the first refrigerant passage 3a of the second heat exchanger 3. The heated, intermediate-pressure refrigerant flows out from the first refrigerant passage 3a of the second heat exchanger 3 as intermediate-pressure, gas-phase refrigerant or high-quality, intermediate-pressure, two-phase refrigerant.

The intermediate-pressure, gas-phase refrigerant or the high-quality, intermediate-pressure, two-phase refrigerant flowing out of the first refrigerant passage 3a of the second heat exchanger 3 flows into the intermediate-pressure part of the compression system 1 through the third intermediate injection refrigerant pipe 60c. [0085] In Fig. 2, a white circle I indicates a stage when the intermediate-pressure, gas-phase refrigerant or the high-quality, intermediate-pressure, two-phase refrigerant flows into the intermediate-pressure part of the compression system 1.

[0086] The intermediate-pressure, gas-phase refrigerant or the high-quality, intermediate-pressure, two-phase refrigerant flowing into the intermediate-pressure part of the compression system 1 through the third intermediate injection refrigerant pipe 60c merges with the intermediate-pressure, gas-phase refrigerant discharged from the first compression device 12. The merged gas-phase refrigerant is intermediate-pressure, gas-phase refrigerant at a lower degree of superheat than the intermediate-pressure, gas-phase refrigerant discharged from the first compression device 12.

[0087] In Fig. 2, a white circle J indicates a stage when the merged, intermediate-pressure, gas-phase refrigerant turns into the intermediate-pressure, gas-phase refrigerant at a lower degree of superheat than the intermediate-pressure, gas-phase refrigerant discharged from the first compression device 12.

[0088] The merged, intermediate-pressure, gas-phase refrigerant is compressed at the second compression device 14, and is discharged from the compression system 1 as high-temperature, high-pressure, gas-phase refrigerant. The cycle described above is repeated at the refrigeration device 100.

[0089] Due to such a configuration described above, the refrigeration device 100 of Embodiment 1 may suppress reduction in refrigeration capacity and superheating of a discharge temperature of the compressor. Accordingly, refrigeration performance may be increased, and energy reduction can be achieved.

[0090] Next, effects of the refrigeration device 100 of Embodiment 1 will be described.

[0091] The refrigeration device 100 of Embodiment 1 includes the first bypass 70 including the first opening-and-closing valve 7, the first bypass 70 branching from the high-pressure side, of the refrigerant circuit 10, positioned between the discharge side of the compression system 1 and the upstream side of the first pressure reducing device 4, and being connected to the suction side of the compression system 1. The first opening-and-closing valve 7 is in the closed state in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 is at or below the first pressure P1, and is opened in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 exceeds the first pressure P1.

[0092] Furthermore, the refrigeration device 100 of Embodiment 1 includes the second bypass 80 including the second opening-and-closing valve 8, the second bypass 80 branching from the intermediate-pressure part between the first compression device 12 and the second compression device 14, and being connected to the suction side of the compression system 1. The second opening-and-closing valve 8 is in the closed state in a case where the pressure of the refrigerant at the intermediate-pressure part between the first compression device 12 and the second compression device 14 is at or below the second pressure P2. Furthermore, the second openingand-closing valve 8 is opened in a case where the pressure of the refrigerant at the intermediate-pressure part between the first compression device 12 and the second compression device 14 exceeds the second pressure P2.

[0093] During an operation of the refrigeration device 100, the controller 20 controls the pressure on the high-pressure side of the refrigerant circuit 10 to not exceed the allowable pressure on the high-pressure side of the refrigerant circuit 10 set to prevent failure of the refrigerant circuit 10. Accordingly, during the operation of the refrigeration device 100, the pressure Ph on the upstream side of the first openingand-closing valve 7 does not exceed the first pressure P1. Furthermore, during the operation of the refrigeration device 100, the pressure at the intermediate-pressure part between the first compression device 12 and the second compression device 14 does not exceed the second pressure P2. Accordingly, during the operation of the refrigeration device 100, the first opening-and-closing valve 7 and the second opening-and-closing valve 8 stay in the closed state, and refrigerant does not flow to either of the first bypass 70 and the second bypass 80.

[0094] In the following, a case where the refrigeration device 100 is switched from the operation state to a stopped state will be considered. Note that the stopped state of the refrigeration device 100 in Embodiment 1 refers not only to a normal operation stop, but also to an operation stop in an abnormal state caused by power outage, for

example.

[0095] In the case where the refrigeration device 100 is switched from the operation state to the stopped state, the first compression device 12 and the second compression device 14 of the compression system 1 are both placed in a stopped state.

[0096] At a time point when the refrigeration device 100 is switched from the operation state to the stopped state, an ambient temperature of the refrigerant circuit 10, such as an outside temperature, is sometimes higher than saturation temperatures of pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 during an operation. When the refrigeration device 100 is placed in the stopped state in a state where the ambient temperature of the refrigerant circuit 10 is higher than the saturation temperatures of the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 during an operation, the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 are increased to a saturation pressure corresponding to the ambient temperature.

[0097] Fig. 3 is a diagram showing a relationship among refrigerant density, a refrigerant temperature, and a refrigerant pressure, in a case where CO2 refrigerant is used as the refrigerant in the refrigeration device 100 according to Embodiment 1. A horizontal axis in Fig. 3 indicates the temperature of the refrigerant in units of degrees C. A vertical axis in Fig. 3 indicates the pressure of the refrigerant in units of Mpa. The refrigerant density takes a numerical value that is obtained by dividing an amount of refrigerant by a volume, and is in units of kg/m3. Note that, in a case where CO2 refrigerant is used as the refrigerant in the refrigeration device 100, it is assumed that the refrigeration device 100 is controlled to perform an operation such that the saturation temperature on the high-pressure side of the refrigerant circuit 10 during an operation is below 31.1 degrees C that is a critical temperature of CO2 refrigerant.

[0098] Furthermore, a straight line L1 in Fig. 3 indicates a relationship between the refrigerant temperature and the pressure when the refrigerant density is 150 [kg/m3]. Furthermore, a straight line L2 in Fig. 3 indicates a relationship between the refrigerant temperature and the pressure when the refrigerant density is 200 [kg/m3].

Furthermore, a straight line L3 in Fig. 3 indicates a relationship between the refrigerant temperature and the pressure when the refrigerant density is 300 [kg/m3]. Still further, a straight line L4 in Fig. 3 indicates a relationship between the refrigerant temperature and the pressure when the refrigerant density is 400 [kg/m3]. Still further, a straight line L5 in Fig. 3 indicates a relationship between the refrigerant temperature and the pressure when the refrigerant density is 500 [kg/m3].

[0099] As shown in Fig. 3, with any of the straight lines L1 to L5, the higher the refrigerant temperature is, the higher the refrigerant pressure is. Furthermore, in the case where the refrigerant temperature is assumed to be constant, the refrigerant pressure is increased as the refrigerant density is increased.

[0100] For example, even when the refrigerant density is 500 [kg/m3], the refrigerant pressure at 31.1 degrees C that is the critical temperature of CO2 refrigerant is lower than 7.5 [MPa]. Accordingly, the refrigeration device 100 can be designed with the design pressure of the refrigerant pipes on the high-pressure side of the refrigeration device 100 at 7.7 [MPa], for example.

[0101] A case of using the refrigeration device 100 in a high-temperature environment, such as an environment where the ambient temperature is 45 degrees C, will be considered. In a case where the ambient temperature is 45 [degrees C], even when the refrigerant density of the refrigeration device 100 is 300 [kg/m3], the refrigerant pressure is increased to 8.68 [MPa] to exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigeration device 100.

[0102] Furthermore, in a case where the refrigeration device 100 is designed with the design pressure of the refrigerant pipes on the high-pressure side at 4.0 [MPa], the saturation pressure may reach 4.0 [MPa] at 6.3 degrees C, when the refrigerant density is at or higher than a specific level. Accordingly, in a case where the ambient temperature of the refrigeration device 100 exceeds 6.3 degrees C, the refrigerant pressure in the refrigerant pipes on the high-pressure side sometimes exceeds the design pressure of the refrigerant pipes on the high-pressure side.

[0103] Furthermore, with the refrigeration device 100 that uses CO2 refrigerant, the refrigeration performance is increased, but because CO2 refrigerant is compressed by the compression system 1 in two or more stages, a discharge pressure from the compression system 1 is higher than in a case where refrigerant other than CO2 refrigerant is used. Accordingly, even in a case where the refrigerant pressure in the refrigerant pipes on the high-pressure side is at or below the design pressure of the refrigerant pipes on the high-pressure side, the refrigerant pressure in the refrigerant pipes on the high-pressure side sometimes exceeds the design pressure of the refrigerant pipes on the high-pressure side at the time of restart.

[0104] Therefore, even in a state where the refrigeration device 100 is stopped, when the ambient temperature of the refrigerant circuit 10 is increased, and the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit are increased, the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 have to be controlled to be at or below the allowable pressure.

[0105] The refrigeration device 100 of Embodiment 1 includes the first bypass 70 including the first opening-and-closing valve 7, the first bypass 70 branching from the high-pressure side, of the refrigerant circuit 10, positioned between the discharge side of the compression system 1 and the upstream side of the first pressure reducing device 4, and being connected to the suction side of the compression system 1. The first opening-and-closing valve 7 is in the closed state in the case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 is at or below the first pressure P1, and is opened in the case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 exceeds the first pressure P1.

[0106] Furthermore, the refrigeration device 100 of Embodiment 1 includes the second bypass 80 including the second opening-and-closing valve 8, the second bypass 80 branching from the intermediate-pressure part between the first compression device 12 and the second compression device 14, and being connected to the suction side of the compression system 1. The second opening-and-closing valve 8 is in the closed state in the case where the pressure of the refrigerant at the intermediate-pressure part between the first compression device 12 and the second compression device 14 is at or below the second pressure P2. Moreover, the second openingand-closing valve 8 is opened in the case where the pressure of the refrigerant at the intermediate-pressure part between the first compression device 12 and the second compression device 14 exceeds the second pressure P2.

[0107] Furthermore, with the refrigeration device 100 of Embodiment 1, the first bypass 70 may branch from the refrigerant pipe on the high-pressure side, of the refrigerant circuit 10, positioned between the downstream side of the first refrigerant passage 3a of the second heat exchanger 3 and the upstream side of the first pressure reducing device 4, or in other words, the third refrigerant pipe 10c.

[0108] According to the configuration described above, in the case where the pressure of refrigerant on the upstream side of the first opening-and-closing valve 7, or in other words, the pressure on the high-pressure side of the refrigerant circuit 10, exceeds the first pressure P1 that is the allowable pressure, the first opening-and-closing valve 7 is opened, and the refrigerant on the high-pressure side of the refrigerant circuit 10 flows into the low-pressure side of the refrigerant circuit 10. When the refrigerant on the high-pressure side of the refrigerant circuit 10 flows into the low-pressure side of the refrigerant circuit 10, the pressure on the high-pressure side of the refrigerant circuit 10 is reduced, and when the pressure falls to or below the first pressure P1, the first opening-and-closing valve 7 is closed. Accordingly, in Embodiment 1, by including the first bypass 70, the refrigeration device 100 can be configured such that the pressure on the high-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10, and safety of the refrigeration device 100 may thus be secured. [0109] Furthermore, in the case where the pressure of refrigerant at the intermediate-pressure part between the first compression device 12 and the second compression device 14, or in other words, the pressure on the intermediate-pressure side of the refrigerant circuit 10, exceeds the second pressure P2 that is the allowable pressure, the second opening-and-closing valve 8 is opened, and the refrigerant on the intermediate-pressure side of the refrigerant circuit 10 flows into the low-pressure side of the refrigerant circuit 10. When the refrigerant on the intermediate-pressure side of the refrigerant circuit 10 flows into the low-pressure side of the refrigerant circuit 10, the pressure on the intermediate-pressure side of the refrigerant circuit 10 is reduced, and when the pressure falls to or below the second pressure P2, the second opening-and-closing valve 8 is closed. In Embodiment 1, by including the second bypass 80, the refrigeration device 100 can be configured such that the pressure on the intermediate-pressure side of the refrigerant circuit 10 does not exceed the allowable pressure on the intermediate-pressure side of the refrigerant circuit 10. By configuring the refrigeration device 100 such that the pressure on the intermediate-pressure side of the refrigerant circuit 10 does not exceed the allowable pressure on the intermediate-pressure side of the refrigerant circuit 10, the refrigerant on the high-pressure side of the refrigerant circuit 10 may be prevented from exceeding the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10 at the time of restart of the refrigeration device 100. Accordingly, in Embodiment 1, by including the second bypass 80, the refrigeration device 100 can be configured such that the pressure on the high-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10, and safety of the refrigeration device 100 may thus be further secured.

[0110] Furthermore, in Embodiment 1, including the first bypass 70 and the second bypass 80 eliminates the need for an auxiliary heat source such as a cooling device on the high-pressure side of the refrigerant circuit 10, and thus, energy consumption may be reduced, and also, the refrigeration device 100 may be made smaller and lighter.

[0111] Moreover, with the refrigeration device 100 of Embodiment 1, the first pressure P1 and the second pressure P2 are determined based on the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10. According to such a configuration, the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 may be prevented from being reduced more than necessary, and reliability of the refrigeration device 100 may be thus increased.

[0112] Moreover, with the refrigeration device 100 of Embodiment 1, the first opening- and-closing valve 7 and the second opening-and-closing valve 8 may be pressure-driven valves. According to such a configuration, the refrigeration device 100 may be configured such that the pressure on the high-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10 even when electricity to the refrigeration device 100 is cut off, and reliability of the refrigeration device 100 may be further increased.

[0113] Furthermore, as described above, the refrigeration device 100 of Embodiment 1 is particularly advantageous when CO2 refrigerant is used as the working refrigerant.

[0114] Fig. 4 is a schematic refrigerant circuit diagram showing an example modification of the refrigerant circuit 10 in Fig. 1, according to the refrigeration device 100 of Embodiment 1. Fig. 4 shows a same structure as that of the refrigeration device 100 in Fig. 1 except that the second bypass 80 is not included. As described below, same effects as those of the refrigeration device 100 in Fig. 1 may be achieved also by a configuration, as shown in Fig. 4, not including the second bypass 80. [0115] As with the refrigeration device 100 in Fig. 1, the first opening-and-closing valve 7 is in the closed state in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 is at or below the first pressure Pl, and is opened in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve 7 exceeds the first pressure P1. With the refrigeration device 100 in Fig. 4, the first opening-and-closing valve 7 is a solenoid valve, such as a bi-directional solenoid valve, opening and closing of which is controlled by the controller 20. Furthermore, with the refrigeration device 100 in Fig. 1, the controller 20 may detect a non-energized state, or in other words, power outage. The first opening-and-closing valve 7 is opened when the controller 20 detects power outage.

[0116] Furthermore, with the refrigeration device 100 in Fig. 4, the second pressure reducing device 6 is an expansion device, opening and closing of which can be controlled by the controller 20. Specifically, depending on the mode of the refrigeration device 100, the second pressure reducing device 6 may be an expander, an automatic thermostatic expansion valve, a linear electronic expansion valve, or the like. Moreover, the second pressure reducing device 6 is opened when the controller 20 detects power outage.

[0117] According to the configuration described above, in a case where power outage is detected by the controller 20, the second pressure reducing device 6 and the first opening-and-closing valve 7 are opened, and the refrigerant on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 flows to the low-pressure side of the refrigerant circuit 10. Accordingly, the refrigeration device 100 may be configured such that, even when the refrigeration device 100 does not include a backup power source, the pressure on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10, and safety of the refrigeration device 100 may be secured.

[0118] Note that the refrigeration device 100 in Fig. 4 may be configured such that power outage is detected by a device other than the controller 20.

[0119] Operations of the second pressure reducing device 6 and the first opening-andclosing valve 7 in a state other than power outage, or in other words, in a case where the refrigeration device 100 in Fig. 4 is stopped in an energized state, will be described.

[0120] With the refrigeration device 100 in Fig. 4, in a case where a high pressure detected by the third pressure sensor 30c exceeds the first pressure P1, the controller 20 performs control to open the first opening-and-closing valve 7. When the first opening-and-closing valve 7 is opened, refrigerant on the high-pressure side of the refrigerant circuit 10 flows to the low-pressure side of the refrigerant circuit 10 through the first bypass 70.

[0121] Furthermore, with the refrigeration device 100 in Fig. 4, in a case where an intermediate pressure detected by the second pressure sensor 30b exceeds the second pressure P2, the controller 20 performs control to open the second pressure reducing device 6 and the first opening-and-closing valve 7. When the second pressure reducing device 6 and the first opening-and-closing valve 7 are opened, refrigerant on the intermediate-pressure side of the refrigerant circuit 10 flows to the low-pressure side of the refrigerant circuit 10 through the intermediate injection circuit and the first bypass 70.

[0122] According to the configuration described above, refrigerant on the high-pressure side or the intermediate-pressure side of the refrigerant circuit 10 may be caused to flow to the low-pressure side of the refrigerant circuit 10, depending on the high pressure or the intermediate pressure at a time when the refrigeration device 100 is stopped. Therefore, according to the configuration described above, the refrigeration device 100 may be configured such that the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 do not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10, and safety of the refrigeration device 100 may be secured. Furthermore, the pressures on the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 may be prevented from being reduced more than necessary, and reliability of the refrigeration device 100 may thus be increased.

[0123] Furthermore, in Embodiment 1, the third heat exchanger 5 may be configured to secure a capacity for temporarily storing refrigerant flowing from the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 to the low-pressure side of the refrigerant circuit 10. Moreover, with the refrigeration device 100, an allowable temperature range may be set for the third heat exchanger 5, such that liquid compression at the first compression device 12 of the compression system 1 due to suction of liquid-phase refrigerant into the first compression device 12 may be prevented at the time of restart of the refrigeration device 100. In a case where a temperature of the third heat exchanger 5 at the time of restart is out of the allowable temperature range of the third heat exchanger 5, control is performed before start of the compression system 1, such that the temperature of the third heat exchanger 5 will be within the allowable temperature range of the third heat exchanger 5. For example, in the case where the refrigeration device 100 includes the second fan 5a, the controller 20 may perform control such that a temperature of refrigerant inside the third heat exchanger 5 will be within the allowable temperature range of the third heat exchanger 5, by adjusting an amount of air sent by the second fan 5a.

[0124] A specific example of control performed to cause the temperature of the refrigerant inside the third heat exchanger 5 to be within the allowable temperature range of the third heat exchanger 5 will be described below with reference to Fig. 5.

[0125] Fig. 5 is a schematic refrigerant circuit diagram showing another example modification of the refrigerant circuit 10 in Fig. 1, according to the refrigeration device 100 of Embodiment 1. Fig. 5 shows a same structure as that of the refrigeration device 100 in Fig. 1 except that a heat source unit 200 and a cooling unit 300 are provided, and that the cooling unit 300 is accommodated in a cooling chamber 400. [0126] The refrigeration device 100 in Fig. 5 is configured with the compression system 1, the first heat exchanger 2, the second heat exchanger 3, and the intermediate injection circuit 60 accommodated in the heat source unit 200.

Furthermore, the refrigeration device 100 in Fig. 5 is configured with the third heat exchanger 5 accommodated in the cooling unit 300. Although not clearly shown in Fig. 5, the heat source unit 200 may be connected by two extension pipes forming parts of the third refrigerant pipe 10c and the fifth refrigerant pipe 10e.

[0127] Note that, in Fig. 5, the first bypass 70 and the first pressure reducing device 4 are accommodated in the cooling unit 300, but the first bypass 70 and the first pressure reducing device 4 may alternatively be accommodated in the heat source unit 200. Furthermore, depending on structures of the first heat exchanger 2 and the third heat exchanger 5, the refrigeration device 100 in Fig. 5 does not have to include the first fan 2a and the second fan 5a. Moreover, as described above, the refrigeration device 100 in Fig. 5 does not have to include the second bypass 80. Moreover, the temperature sensors, the pressure sensors, and the controller 20 may be disposed at positions according to intended uses.

[0128] With the refrigeration device 100 in Fig. 5, the cooling unit 300 is accommodated in the cooling chamber 400. Inside of the cooling chamber 400 is filled with cool air by an operation of the refrigeration device 100. Accordingly, with the configuration described above, when the refrigeration device 100 is stopped, the temperature of refrigerant flowing from the high-pressure side and the intermediate-pressure side of the refrigerant circuit 10 into the third heat exchanger 5 may be reduced by the cool air filling the inside of the cooling chamber 400. For example, in the case where the refrigeration device 100 includes the second fan 5a, the controller 20 may perform control such that a temperature of the refrigerant inside the third heat exchanger 5 will be within the allowable temperature range of the third heat exchanger 5, by adjusting the amount of air sent by the second fan 5a.

[0129] Embodiment 2.

A refrigeration device 100 of Embodiment 2 of the present disclosure will be described with reference to Fig. 6. Fig. 6 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 2.

[0130] As shown in Fig. 6, with the refrigeration device 100 of Embodiment 2, the refrigerant circuit 10 includes a fourth heat exchanger 16. The refrigeration device is otherwise configured in the same manner as in Embodiment 1 described above, and a redundant description will be omitted.

[0131] The fourth heat exchanger 16 is an intermediate cooler where intermediate-pressure, gas-phase refrigerant compressed by the first compression device 12 flows in to be cooled.

As shown in Fig. 6, the fourth heat exchanger 16 is connected to the intermediate-pressure part of the refrigerant circuit 10. Specifically, the fourth heat exchanger 16 is connected between the first compression device 12 and the second compression device 14. Furthermore, the third intermediate injection refrigerant pipe 60c of the intermediate injection circuit 60 is connected between the fourth heat exchanger 16 and the second compression device 14. The refrigerant passage of the third intermediate injection refrigerant pipe 60c is connected to merge with a refrigerant passage between the fourth heat exchanger 16 and the second compression device 14. Furthermore, the sixth temperature sensor 40f is disposed at the intermediate-pressure part between the fourth heat exchanger 16 and the second compression device 14. Note that, depending on the mode of the refrigeration device 100, the fourth heat exchanger 16 may be integrated with the compression system 1, or may be a structure that is separate from the compression system 1 and that is connected by pipes between the first compression device 12 and the second compression device 14. Furthermore, the fourth heat exchanger 16 may be a heat exchange device including a plurality of heat exchangers.

[0132] For example, as shown in Fig. 6, the refrigeration device 100 may include a third fan 16a, in relation to the fourth heat exchanger 16. By the refrigeration device including the third fan 16a, the fourth heat exchanger 16 may be made an air-cooled heat exchanger configured to exchange heat between an air flow induced by the third fan 16a and intermediate-pressure, gas-phase refrigerant passing through the fourth heat exchanger 16. In the case where the fourth heat exchanger 16 is of an air-cooled heat exchanger type, the fourth heat exchanger 16 may be a fin-and-tube heat exchanger, a plate-fin heat exchanger, or other heat exchangers, depending on the mode of the refrigeration device 100. Note that the third fan 16a may be an axial fan such as a propeller fan, a centrifugal fan such as a sirocco fan or a turbo fan, a mixed flow fan, a cross flow fan, or other fans, depending on the mode of the refrigeration device 100.

[0133] Moreover, especially in a case where the fourth heat exchanger 16 is separate from the compression system 1, the fourth heat exchanger 16 may be a water-cooled heat exchanger configured to exchange heat between water or brine and the intermediate-pressure, gas-phase refrigerant passing through the fourth heat exchanger 16, depending on the mode of the refrigeration device 100. In the case where the fourth heat exchanger 16 is a water-cooled heat exchanger, the fourth heat exchanger 16 may be a shell-and-tube heat exchanger, a plate heat exchanger, or a double-tube heat exchanger, depending on the mode of the refrigeration device 100.

[0134] With the refrigeration device 100 of Embodiment 2, since the refrigerant circuit 10 includes the fourth heat exchanger 16, a degree of superheat at the intermediate-pressure part of the refrigerant circuit 10 may be efficiently reduced. To describe in relation to the operation mode of the refrigeration device 100 shown in Fig. 2, an operation of cooling from the white circle F to the white circle H may be efficiently performed with the refrigeration device 100 of Embodiment 2. Therefore, according to the present configuration, performance of the refrigeration device 100 may be increased.

[0135] Furthermore, in Embodiment 2, the fourth heat exchanger 16 may be configured to secure a capacity for temporarily storing refrigerant flowing from the high-pressure side of the refrigerant circuit 10 to the intermediate-pressure side of the refrigerant circuit 10. Moreover, with the refrigeration device 100, an allowable temperature range may be set for the fourth heat exchanger 16, such that liquid compression at the second compression device 14 of the compression system 1 due to suction of liquid-phase refrigerant into the second compression device 14 may be prevented at the time of restart of the refrigeration device 100. In a case where a temperature of the fourth heat exchanger 16 at the time of restart is out of the allowable temperature range of the fourth heat exchanger 16, control is performed before start of the compression system 1, such that the temperature of the fourth heat exchanger 16 will be within the allowable temperature range of the fourth heat exchanger 16. For example, in the case where the refrigeration device 100 includes the third fan 16a, the controller 20 may perform control such that a temperature of refrigerant inside the fourth heat exchanger 16 will be within the allowable temperature range of the fourth heat exchanger 16, by adjusting an amount of air sent by the third fan 16a.

[0136] Embodiment 3.

A refrigeration device 100 of Embodiment 3 of the present disclosure will be described with reference to Fig. 7. Fig. 7 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 3.

[0137] The refrigeration device 100 of Embodiment 3 includes a third bypass 90. The refrigeration device 100 is otherwise configured in the same manner as in Embodiment 1 and Embodiment 2 described above, and a redundant description will be omitted.

[0138] The third bypass 90 of the refrigeration device 100 will be described.

[0139] The third bypass 90 is a bypass branching from the first intermediate injection refrigerant pipe 60a, of the intermediate injection circuit 60, disposed on the upstream side of the second pressure reducing device 6. The third bypass 90 branching from the first intermediate injection refrigerant pipe 60a is connected to the second intermediate injection refrigerant pipe 60b on the downstream side of the second pressure reducing device 6. In other words, the third bypass 90 provides a bypass route through which refrigerant can flow in from the high-pressure side of the refrigerant circuit 10 to the intermediate-pressure side of the refrigerant circuit 10. [0140] The third bypass 90 includes a third opening-and-closing valve 9, a fifth bypass refrigerant pipe 90a, and a sixth bypass refrigerant pipe 90b.

[0141] The third opening-and-closing valve 9 is a movable mechanism, an internal passage of which can be opened or closed to release or stop a flow of a fluid. The third opening-and-closing valve 9 is in a closed state in a case where a pressure Ph of refrigerant on an upstream side of the third opening-and-closing valve 9 is at or below a third pressure P3 that is a set pressure of the third opening-and-closing valve 9. Furthermore, the third opening-and-closing valve 9 is opened in a case where the pressure Ph of the refrigerant on the upstream side of the third opening-and-closing valve 9 exceeds the third pressure P3, to cause the refrigerant to flow to a downstream side of the third opening-and-closing valve 9. In other words, the third opening-and-closing valve 9 is an automatic valve designed such that the set pressure of the third opening-and-closing valve 9 is the third pressure P3.

[0142] As described in Embodiment 1 described above, the third pressure P3 that is the set pressure of the third opening-and-closing valve 9 is determined based on the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10, or in other words, the design pressure of the first refrigerant pipe 10a, the second refrigerant pipe 10b, and the third refrigerant pipe 10c.

Furthermore, the third pressure P3 is set lower than the first pressure P1 that is the set pressure of the first opening-and-closing valve 7, and higher than the second pressure P2 that is the set pressure of the second opening-and-closing valve 8. [0143] For example, the third opening-and-closing valve 9 is a pressure-driven valve that is mechanically opened or closed based on the pressure Ph of the refrigerant on the upstream side of the third opening-and-closing valve 9. In the case where the third opening-and-closing valve 9 is a pressure-driven valve, the third opening-andclosing valve 9 may be a sealed safety valve, for example, depending on the mode of the refrigeration device 100. In the case where the third opening-and-closing valve 9 is a sealed safety valve, the third opening-and-closing valve 9 may be a diaphragm safety valve with which there is a small possibility of fluid leakage from a valve body, for example.

[0144] The fifth bypass refrigerant pipe 90a is connected between the first intermediate injection refrigerant pipe 60a of the intermediate injection circuit 60 and the upstream side of the third opening-and-closing valve 9. A refrigerant passage of the fifth bypass refrigerant pipe 90a is connected in a manner branching from the refrigerant passage of the first intermediate injection refrigerant pipe 60a. The sixth bypass refrigerant pipe 90b is connected between the downstream side of the third opening-and-closing valve 9 and the second intermediate injection refrigerant pipe 60b of the intermediate injection circuit 60. A refrigerant passage of the sixth bypass refrigerant pipe 90b is connected to merge with the refrigerant passage of the second intermediate injection refrigerant pipe 60b.

[0145] As described above, the refrigeration device 100 of Embodiment 3 further includes the third bypass 90 including the third opening-and-closing valve 9, the third bypass 90 branching from the upstream side of the second pressure reducing device 6, and being connected to the downstream side of the second pressure reducing device 6. With the refrigeration device 100 of Embodiment 3, the third opening-and-closing valve 9 is in the closed state in the case where the pressure of the refrigerant on the upstream side of the third opening-and-closing valve 9 is at or below the third pressure P3, and is opened in the case where the pressure of the refrigerant on the upstream side of the third opening-and-closing valve 9 exceeds the third pressure P3. [0146] According to the configuration described above, a route through which refrigerant flows from the high-pressure side of the refrigerant circuit 10 to the intermediate-pressure side of the refrigerant circuit 10 can be secured, and the refrigeration device 100 can be configured such that the pressure on the high-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10. Furthermore, according to the configuration described above, an effective bypass route for reducing the pressure on the high-pressure side of the refrigerant circuit 10 can be secured, in addition to the first bypass 70 that causes refrigerant to flow from the high-pressure side of the refrigerant circuit 10 to the low-pressure side of the refrigerant circuit 10.

Therefore, according to the configuration described above, safety of the refrigeration device 100 may be further increased, and also, reliability of the refrigeration device 100 may be increased.

[0147] Furthermore, with the refrigeration device 100 of Embodiment 3, the third pressure P3 may be determined based on the design pressure of the refrigerant pipes disposed on the high-pressure side of the refrigerant circuit 10, and the third pressure P3 may be made lower than the first pressure P1 and higher than the second pressure P2. According to the present configuration, the pressure on the high-pressure side of the refrigerant circuit 10 may be reduced before the pressure on the high-pressure side of the refrigerant circuit 10 reaches the first pressure P1 that is the allowable pressure. Moreover, according to the present configuration, refrigerant may be caused to move to the intermediate-pressure side of the refrigerant circuit 10 through the third bypass 90, before the refrigerant moves from the high-pressure side of the refrigerant circuit 10 to the low-pressure side of the refrigerant circuit 10 through the first bypass 70. Accordingly, refrigerant may be prevented from moving excessively to the low-pressure side, and liquid compression at the first compression device 12 of the compression system 1 at the time of restart may be prevented. Therefore, according to the present configuration, safety and reliability of the refrigeration device 100 may be further increased.

[0148] Moreover, with the refrigeration device 100 of Embodiment 3, the third openingand-closing valve 9 may be a pressure-driven valve. According to the present configuration, the refrigeration device 100 may be configured such that, even when electricity to the refrigeration device 100 is cut off, the pressure on the high-pressure side of the refrigerant circuit 10 does not exceed the design pressure of the refrigerant pipes on the high-pressure side of the refrigerant circuit 10, and thus, reliability of the refrigeration device 100 may be further increased.

[0149] Note that the fourth heat exchanger 16 is not an essential structural element in Embodiment 3, and depending on the mode of the refrigeration device 100, the refrigeration device 100 does not have to include the fourth heat exchanger 16. [0150] Embodiment 4.

A refrigeration device 100 of Embodiment 4 of the present disclosure will be described with reference to Fig. 8. Fig. 8 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 4.

[0151] The refrigeration device 100 of Embodiment 4 includes a liquid receiver 10b1 on the second refrigerant pipe 10b on the high-pressure side of the refrigerant circuit 10. Furthermore, a first bypass pipe of the first bypass 70 branches from a gas-phase part in the liquid receiver 10b1, and is in communication with the gas-phase part inside the liquid receiver 101)1. The refrigeration device 100 is otherwise configured in the same manner as in Embodiment 1 and Embodiment 2 described above, and a redundant description will be omitted.

[0152] The liquid receiver 10b1 is a storage container having a gas-liquid separation function, the liquid receiver 10b1 being disposed between the first heat exchanger 2 and the first refrigerant passage 3a of the second heat exchanger 3. During an operation of the refrigeration device 100, high-pressure refrigerant flowing out of the first heat exchanger 2 flows into the liquid receiver 10b1, and the liquid receiver 10b1 separates the refrigerant into gas-phase refrigerant and liquid-phase refrigerant, and causes only the high-pressure, liquid-phase refrigerant to flow into the first refrigerant passage 3a of the second heat exchanger 3.

[0153] According to the present configuration, in a case where the pressure on the high-pressure side of the refrigerant circuit 10 exceeds the first pressure P1 that is the allowable pressure, only the gas-phase refrigerant on the high-pressure side of the refrigerant circuit 10 may be caused to flow into the low-pressure side of the refrigerant circuit 10 through the first bypass 70. According to the present configuration, the pressure on the high-pressure side of the refrigerant circuit 10 may be swiftly reduced through the first bypass 70. Moreover, since only the gas-phase refrigerant flows into the low-pressure side of the refrigerant circuit 10, liquid compression at the first compression device 12 of the compression system 1 at the time of restart may be prevented. Therefore, according to the present configuration, safety and reliability of the refrigeration device 100 may be further increased.

[0154] Note that the fourth heat exchanger 16 is not an essential structural element in Embodiment 4, and depending on the mode of the refrigeration device 100, the refrigeration device 100 does not have to include the fourth heat exchanger 16.

[0155] Embodiment 5.

A refrigeration device 100 of Embodiment 5 of the present disclosure will be described with reference to Fig. 9. Fig. 9 is a schematic refrigerant circuit diagram showing an example of a refrigerant circuit 10 of the refrigeration device 100 according to Embodiment 5.

[0156] Embodiment 5 corresponds to Embodiment 4 described above to which the structure of the third bypass 90 of Embodiment 3 described above is added.

According to such a configuration, safety and reliability of the refrigeration device 100 described in Embodiment 3 and Embodiment 4 described above may be further increased.

[0157] Note that the fourth heat exchanger 16 is not an essential structural element in Embodiment 5, and depending on the mode of the refrigeration device 100, the refrigeration device 100 does not have to include the fourth heat exchanger 16. [0158] Other Embodiments.

The present disclosure may be modified in various ways within the scope of the present disclosure, without being limited to the embodiments described above. For example, in a case where the refrigeration device 100 includes a backup power source, one or some or all of the first opening-and-closing valve 7, the second opening-and-closing valve 8, and the third opening-and-closing valve 9 may be a solenoid valve, such as a bi-directional solenoid valve, opening and closing of which is controlled by the controller 20. In the case of adopting the bi-directional solenoid valve as the solenoid valve, a poppet solenoid valve that has a long life and with which refrigerant leakage does not often occur may be adopted. For example, in the case of adopting the solenoid valve, the controller 20 may control opening and closing of the solenoid valve based on information about the intermediate pressure detected by the second pressure sensor 30b and information about the high pressure detected by the third pressure sensor 30c.

[0159] Moreover, the refrigeration device 100 of the present disclosure is applicable mainly to commercial refrigeration devices, and is applicable, for example, to commercial showcases, refrigerators, refrigerating devices, automatic vending machines, or freezers.

Reference Signs List [0160] 1 compression system 2 first heat exchanger 2a first fan 3 second heat exchanger 3a first refrigerant passage 3b second refrigerant passage 4 first pressure reducing device 5 third heat exchanger 5a second fan 6 second pressure reducing device 7 first opening-and-closing valve 8 second opening-and-closing valve 9 third opening-and-closing valve 10 refrigerant circuit 10a first refrigerant pipe10b second refrigerant pipe 10b1 liquid receiver 10c third refrigerant pipe 10d fourth refrigerant pipe 10e fifth refrigerant pipel2 first compression device 14 second compression device 16 fourth heat exchanger 16a third fan 20 controller 30a first pressure sensor 30b second pressure sensor 30c third pressure sensor 40a first temperature sensor 40b second temperature sensor 40c third temperature sensor 40d fourth temperature sensor 40e fifth temperature sensor 40f sixth temperature sensor 40g seventh temperature sensor 60 intermediate injection circuit 60a first intermediate injection refrigerant pipe 60b second intermediate injection refrigerant pipe 60c third intermediate injection refrigerant pipe 70 first bypass 70a first bypass refrigerant pipe 70b second bypass refrigerant pipe 80 second bypass 80a third bypass refrigerant pipe 80b fourth bypass refrigerant pipe 90 third bypass 90a fifth bypass refrigerant pipe 90b sixth bypass refrigerant pipe 100 refrigeration device 200 heat source unit 300 cooling unit 400 cooling chamber.

Claims

CLAIMS [Claim 1] A refrigeration device comprising: a refrigerant circuit including a compression system including a first compression device, and a second compression device connected to the first compression device, the compression system being configured to compress, at the first compression device and the second compression device, refrigerant that is suctioned in and that is having a low pressure into the refrigerant having a high pressure, and to cause the refrigerant to be discharged, a first heat exchanger connected to a discharge side of the compression system, a second heat exchanger including a first refrigerant passage and a second refrigerant passage, the first refrigerant passage being connected to a downstream side of the first heat exchanger, a first pressure reducing device connected to a downstream side of the first refrigerant passage of the second heat exchanger, and a third heat exchanger connected between a downstream side of the first pressure reducing device and a suction side of the compression system, the refrigerant circuit being configured to cause the refrigerant discharged from the compression system to be circulated; an intermediate injection circuit including a second pressure reducing device connected between the downstream side of the first refrigerant passage of the second heat exchanger and the second refrigerant passage of the second heat exchanger, the intermediate injection circuit branching from the downstream side of the first refrigerant passage of the second heat exchanger, and being connected, via the second pressure reducing device and the second refrigerant passage of the second heat exchanger, to an intermediate-pressure part between the first compression device and the second compression device; and a first bypass including a first opening-and-closing valve, the first bypass branching from a high-pressure side of the refrigerant circuit and being connected to the suction side of the compression system, the high-pressure side of the refrigerant circuit being positioned between the discharge side of the compression system and an upstream side of the first pressure reducing device, wherein the first opening-and-closing valve is in a closed state in a case where a pressure of the refrigerant on an upstream side of the first opening-and-closing valve is at or below a first pressure, and is opened in a case where the pressure of the refrigerant on the upstream side of the first opening-and-closing valve exceeds the first pressure.[Claim 2] The refrigeration device of claim 1, wherein the first pressure is determined based on a design pressure of a refrigerant pipe disposed on the high-pressure side of the refrigerant circuit.[Claim 3] The refrigeration device of claim 1 or 2, wherein the first opening-and-closing valve is a pressure-driven valve.[Claim 4] The refrigeration device of any one of claims 1 to 3, wherein the compression system, the first heat exchanger, the second heat exchanger, and the intermediate injection circuit are accommodated in a heat source unit, the third heat exchanger is accommodated in a cooling unit, and the cooling unit is accommodated in a cooling chamber.[Claim 5] The refrigeration device of any one of claim 1 to 4, further comprising a second bypass including a second opening-and-closing valve, the second bypass branching from the intermediate-pressure part between the first compression device and the second compression device and being connected to the suction side of the compression system, wherein the second opening-and-closing valve is in a closed state in a case where the pressure of the refrigerant at the intermediate-pressure part is at or below a second pressure, and is opened in a case where the pressure of the refrigerant at the intermediate-pressure part exceeds the second pressure.[Claim 6] The refrigeration device of claim 5, wherein the second pressure is determined based on a design pressure of a refrigerant pipe disposed on the high-pressure side of the refrigerant circuit.[Claim 7] The refrigeration device of claim 5 or 6, wherein the second opening-andclosing valve is a pressure-driven valve.[Claim 8] The refrigeration device of any one of claims 1 to 7, wherein the first bypass branches from a refrigerant pipe on the high-pressure side of the refrigerant circuit, the high-pressure side of the refrigerant circuit being positioned between the downstream side of the first refrigerant passage of the second heat exchanger and the upstream side of the first pressure reducing device.[Claim 9] The refrigeration device of any one of claims 1 to 7, wherein the refrigerant circuit further includes a liquid receiver connected between the first heat exchanger and the first refrigerant passage of the second heat exchanger, and the first bypass branches from the liquid receiver, and is in communication with a gas-phase part inside the liquid receiver.[Claim 10] The refrigeration device of any one of claims 1 to 9, further comprising a third bypass including a third opening-and-closing valve, the third bypass branching from an upstream side of the second pressure reducing device and being connected to a downstream side of the second pressure reducing device, wherein the third opening-and-closing valve is in a closed state in a case where a pressure of the refrigerant on an upstream side of the third opening-and-closing valve is at or below a third pressure, and is opened in a case where the pressure of the refrigerant on the upstream side of the third opening-and-closing valve exceeds the third pressure.[Claim 11] The refrigeration device of claim 10, wherein the third pressure is determined based on a design pressure of a refrigerant pipe disposed on the high-pressure side of the refrigerant circuit.[Claim 12] The refrigeration device of claim 10 or 11, wherein the third opening-andclosing valve is a pressure-driven valve.[Claim 13] The refrigeration device of any one of claims 1 to 12, wherein the refrigerant is CO2 refrigerant.[Claim 14] The refrigeration device of any one of claim 1 to 13, wherein the refrigerant circuit further includes a fourth heat exchanger connected between the first compression device and the second compression device.