Refrigerator

Abstract

To solve a problem that in a refrigerator to which a two-stage compression mechanism comprising a low-stage side compressor and a high-stage side compressor is applied, when a size of a casing is limited, a size of a gas cooler for cooling a refrigerant discharged from the high-stage side compressor is restricted by an intercooler and thus there is the possibility that performance of the gas cooler might become insufficient.SOLUTION: A refrigerator 100 includes a refrigerant circuit 10 in which a first compressor 21, a second compressor 22, a heat source side heat exchanger 23, a first heat source side expansion valve 25a, a second heat source side expansion valve 25b and a utilization side heat exchanger 31 are sequentially connected. The heat source side heat exchanger 23 functions as a radiator for a refrigerant. The utilization side heat exchanger 31 functions as a heat absorber for the refrigerant. A difference between a first temperature that is a temperature of the refrigerant at an inlet of the heat source side heat exchanger 23 and a second temperature that is a temperature of air of which heat is exchanged with the refrigerant in the heat source side heat exchanger 23 is controlled to a first value or larger. The first temperature is controlled to a second value or smaller. The refrigerant flowing in the refrigerant circuit 10 is carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Regarding refrigeration equipment. [Background technology]

[0002] As described in Patent Document 1 (JP 2016-128734 A), a refrigeration system is known that uses carbon dioxide as a refrigerant and employs a two-stage compression mechanism consisting of a low-stage compressor and a high-stage compressor. This refrigeration system uses an intercooler to cool the refrigerant discharged from the low-stage compressor, thereby lowering the temperature of the refrigerant sucked into the high-stage compressor and suppressing an increase in the temperature of the refrigerant discharged from the high-stage compressor. Summary of the Invention [Problem to be solved by the invention]

[0003] In such a refrigeration system, if the size of the housing is restricted, the size of the gas cooler that cools the refrigerant discharged from the high-stage compressor is restricted by the intercooler, and the performance of the gas cooler may be insufficient. Also, if such a refrigeration system is used in an environment where the outside air temperature is high, the dryness of the refrigerant at the inlet of the gas-liquid separator may increase, and the degree of superheat of the refrigerant sucked into the high-stage compressor may decrease. As a result, the temperature of the refrigerant discharged from the high-stage compressor may decrease, and the performance of the gas cooler may decrease. [Means for solving the problem]

[0004] A refrigeration device according to a first aspect includes a refrigerant circuit in which a compression mechanism, a first heat exchanger, an expansion mechanism, and a second heat exchanger are connected in sequence. The first heat exchanger functions as a heat radiator for refrigerant compressed by the compression mechanism. The second heat exchanger functions as a heat absorber for refrigerant decompressed by the expansion mechanism. The refrigerant circuit has a first mechanism. The first mechanism controls a difference between a first temperature, which is the temperature of the refrigerant at the inlet of the first heat exchanger, and a second temperature, which is the temperature of air exchanging heat with the refrigerant in the first heat exchanger, to a first value or more. The first mechanism controls the first temperature to a second value or less. The refrigerant flowing through the refrigerant circuit is carbon dioxide.

[0005] The refrigeration apparatus of the first aspect increases the difference between the temperature of the first heat exchanger and the outside air temperature to improve the performance of the first heat exchanger, while suppressing overheating of the first heat exchanger and suppressing deterioration of the refrigeration oil. Therefore, the refrigeration apparatus of the first aspect can suppress deterioration of the reliability of the compressor while maintaining high performance of the radiator.

[0006] A refrigeration apparatus of a second aspect is the refrigeration apparatus of the first aspect, wherein the compression mechanism has a first compressor that compresses the refrigerant that has absorbed heat in the second heat exchanger, and a second compressor that compresses the refrigerant discharged from the first compressor.

[0007] The refrigeration apparatus of the second aspect has a two-stage compression mechanism using a first compressor on the low stage side and a second compressor on the high stage side. Therefore, the refrigeration apparatus of the second aspect can increase the temperature of the refrigerant undergoing heat exchange in the radiator, thereby maintaining high performance of the radiator.

[0008] A refrigeration apparatus of a third aspect is the refrigeration apparatus of the second aspect, wherein the first mechanism heats the refrigerant before being sucked into the second compressor by heating gas refrigerant contained in the refrigerant decompressed by the expansion mechanism through heat exchange with refrigerant that has dissipated heat in the first heat exchanger and mixing the gas refrigerant with the refrigerant before being sucked into the second compressor, in order to control the difference between the first temperature and the second temperature to be equal to or greater than a first value.

[0009] A refrigeration apparatus according to a third aspect heats, by heat exchange, a gas refrigerant contained in the refrigerant decompressed by the expansion mechanism, and mixes the gas refrigerant with the refrigerant before being drawn into the second compressor. This increases the degree of superheat of the refrigerant drawn into the second compressor, and increases the difference between the temperature of the first heat exchanger and the outside air temperature. Therefore, the refrigeration apparatus according to the third aspect can maintain high performance of the radiator. Furthermore, the refrigeration apparatus according to the third aspect cools the outlet refrigerant of the first heat exchanger by heat exchange, thereby reducing the dryness of the refrigerant decompressed by the expansion mechanism. Therefore, the refrigeration apparatus according to the third aspect can suppress a shortage of refrigerant drawn into the low-stage compressor, and suppress a decrease in the reliability of the compressor.

[0010] A refrigeration device of a fourth aspect is the refrigeration device of the second aspect, wherein the first mechanism cools the refrigerant before it is sucked into the second compressor by mixing liquid refrigerant contained in the refrigerant decompressed by the expansion mechanism with the refrigerant before it is sucked into the second compressor, in order to control the first temperature to be equal to or lower than a second value.

[0011] The refrigeration apparatus of the fourth aspect cools the refrigerant before it is drawn into the second compressor by using liquid refrigerant contained in the refrigerant decompressed by the expansion mechanism. Therefore, the refrigeration apparatus of the fourth aspect can suppress overheating of the refrigerant at the inlet of the radiator, and suppress deterioration of the reliability of the compressor.

[0012] A refrigeration apparatus according to a fifth aspect is the refrigeration apparatus according to the second aspect, in which the first mechanism includes a gas-liquid separator, a third heat exchanger, a first flow path, a second flow path, and an adjustment mechanism. The gas-liquid separator separates the refrigerant in a gas-liquid two-phase state decompressed by the expansion mechanism into a liquid refrigerant and a gas refrigerant. The third heat exchanger heats the gas refrigerant in the gas-liquid separator by exchanging heat with the refrigerant after heat dissipation in the first heat exchanger and before decompression by the expansion mechanism. The first flow path mixes the gas refrigerant heated in the third heat exchanger with the refrigerant before being sucked into the second compressor in order to heat the refrigerant before being sucked into the second compressor. The second flow path mixes the liquid refrigerant in the gas-liquid separator with the refrigerant before being sucked into the second compressor in order to cool the refrigerant before being sucked into the second compressor. The adjustment mechanism adjusts the amount of gas refrigerant flowing through the first flow path and the amount of liquid refrigerant flowing through the second flow path.

[0013] A refrigeration apparatus according to a fifth aspect uses the gas refrigerant in the gas-liquid separator to heat the refrigerant before it is drawn into the second compressor, and uses the liquid refrigerant in the gas-liquid separator to cool the refrigerant before it is drawn into the second compressor. Therefore, the refrigeration apparatus according to the fifth aspect can suppress a decrease in the reliability of the compressor while maintaining high performance of the radiator.

[0014] A refrigeration apparatus according to a sixth aspect is the refrigeration apparatus according to any one of the second to fifth aspects, wherein the compression mechanism has a second mechanism. The second mechanism suppresses a decrease in temperature of the refrigerant after it is discharged from the first compressor and before it is drawn into the second compressor, due to heat exchange.

[0015] The refrigeration apparatus of the sixth aspect can maintain high performance of the radiator by increasing the temperature of the refrigerant undergoing heat exchange in the radiator. Also, the refrigeration apparatus of the sixth aspect does not require a heat exchanger for cooling the refrigerant discharged from the low-stage compressor, so that the size of the radiator can be sufficiently ensured.

[0016] A refrigeration apparatus according to a seventh aspect is the refrigeration apparatus according to any one of the first to sixth aspects, wherein the first mechanism controls the first temperature to be equal to or higher than 90°C and equal to or lower than 120°C.

[0017] The refrigeration apparatus of the seventh aspect can maintain high performance of the radiator even when the outside air temperature is high by setting the temperature of the refrigerant that exchanges heat in the radiator to a predetermined value or higher. Also, the refrigeration apparatus of the seventh aspect can suppress deterioration of the refrigeration oil and suppress deterioration of the reliability of the compressor by setting the temperature of the refrigerant that exchanges heat in the radiator to a predetermined value or lower. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing an example of an overall configuration of a refrigeration device 100 of a first embodiment. [Diagram 2] FIG. 2 is a block diagram of a control unit 70 according to the first embodiment. [Diagram 3] FIG. 2 is a Mollier diagram of the first embodiment. [Figure 4]FIG. 1 is a diagram showing an example of an overall configuration of a refrigeration device 200 according to a second embodiment. [Diagram 5] FIG. 11 is a block diagram of a control unit 70 according to a second embodiment. [Figure 6] FIG. 11 is a Mollier diagram of the second embodiment. [Figure 7] FIG. 11 is a diagram showing an example of an overall configuration of a refrigeration device 300 according to a third embodiment. [Figure 8] FIG. 11 is a block diagram of a control unit 70 according to a third embodiment. [Figure 9] FIG. 11 is a Mollier diagram of the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] -First embodiment- (1) Configuration of Refrigeration Device 100 1, the refrigeration system 100 includes a heat source unit 2, a utilization unit 3, a liquid side refrigerant connection pipe 6, a gas side refrigerant connection pipe 7, a remote control 8, and a control unit 70. In the refrigeration system 100, the heat source unit 2 and the utilization unit 3 are connected via the liquid side refrigerant connection pipe 6 and the gas side refrigerant connection pipe 7 to form a refrigerant circuit 10 in which the refrigerant circulates.

[0020] The refrigeration system 100 performs a vapor compression refrigeration cycle in which the refrigerant sealed in the refrigerant circuit 10 is compressed, condensed, depressurized, evaporated, and then compressed again. The refrigeration system 100 cools the air in a target space by evaporation of the refrigerant circulating through the refrigeration cycle. The refrigeration system 100 is attached to, for example, a shipping container, and cools the air in the target space inside the container.

[0021] The refrigeration device 100 may include a plurality of utilization units 3. In this case, a refrigerant circuit 10 is configured by connecting a plurality of utilization units 3 in parallel to one heat source unit 2.

[0022] The refrigerant sealed in the refrigerant circuit 10 is carbon dioxide (R744). Carbon dioxide is a non-flammable natural refrigerant with a smaller global warming potential (GWP) than fluorine-containing refrigerants. In the refrigerant circuit 10, the high-pressure refrigerant in the refrigeration cycle is in a supercritical state, where the pressure is higher than the critical pressure.

[0023] (1-1) Heat source unit 2 The heat source unit 2 is installed in a space outside the target space. The heat source unit 2 is installed, for example, outdoors. As shown in Fig. 1, the heat source unit 2 has a first compressor 21, a first accumulator 21b, a second compressor 22, a second accumulator 22b, a heat source side heat exchanger 23, a heat source side fan 24, a first heat source side expansion valve 25a, a second heat source side expansion valve 25b, a gas-liquid separator 26, an intermediate heat exchanger 27, a liquid side shutoff valve 28, a gas side shutoff valve 29, and a gas vent valve 41.

[0024] The heat source unit 2 has a first pipe 51 to a sixth pipe 56, which are pipes through which the refrigerant circulating in the refrigerant circuit 10 flows. The first pipe 51 connects the gas side shutoff valve 29 and the suction side of the first compressor 21. The second pipe 52 connects the discharge side of the first compressor 21 and the suction side of the second compressor 22. The third pipe 53 connects the discharge side of the second compressor 22 and the inlet side of the heat source side heat exchanger 23. The fourth pipe 54 connects the outlet side of the heat source side heat exchanger 23 and the inlet side of the gas-liquid separator 26. The fifth pipe 55 connects the liquid outlet side of the gas-liquid separator 26 and the liquid side shutoff valve 28. The sixth pipe 56 connects the gas outlet side of the gas-liquid separator 26 and the second pipe 52.

[0025] The first compressor 21 and the second compressor 22 constitute a compression mechanism of the refrigeration device 100, and compress a low-pressure refrigerant in the refrigeration cycle until it becomes a high-pressure refrigerant. The low-pressure refrigerant in the refrigeration cycle is compressed by the first compressor 21 to become an intermediate-pressure refrigerant. The intermediate-pressure refrigerant is compressed by the second compressor 22 to become a high-pressure refrigerant. The intermediate pressure in the refrigeration cycle is a pressure between the low pressure and the high pressure. The intermediate-pressure refrigerant in the refrigeration cycle is in a state in which its pressure is lower than the critical pressure. The first compressor 21 and the second compressor 22 have a sealed structure in which a volume-variable compression element such as a rotary type or a scroll type is rotated by the first compressor motor 21a and the second compressor motor 22a, respectively. The first compressor motor 21a and the second compressor motor 22a can control the operating frequency (the rotation speed of the first compressor 21 and the second compressor 22) by an inverter.

[0026] The first accumulator 21b is provided in the first pipe 51. The second accumulator 22b is provided in the second pipe 52. The first accumulator 21b and the second accumulator 22b are refrigerant containers capable of temporarily storing surplus refrigerant in the refrigerant circuit 10 as liquid refrigerant.

[0027] The heat source side heat exchanger 23 is a gas cooler that functions as a radiator (condenser) of high-pressure refrigerant in the refrigeration cycle.

[0028] The heat source-side fan 24 supplies air outside the target space (external air, etc.) to the heat source-side heat exchanger 23, exchanges heat with the refrigerant in the heat source-side heat exchanger 23, and then generates an air flow for discharging the air to the outside of the heat source unit 2. The heat source-side fan 24 is rotationally driven by a heat source-side fan motor 24a.

[0029] The first heat source side expansion valve 25a is provided on the fourth pipe 54. The second heat source side expansion valve 25b is provided on the fifth pipe 55. The first heat source side expansion valve 25a and the second heat source side expansion valve 25b constitute an expansion mechanism of the refrigeration device 100, and reduce the pressure of the high-pressure refrigerant in the refrigeration cycle to a low-pressure refrigerant. The high-pressure refrigerant in the refrigeration cycle is reduced in pressure by the first heat source side expansion valve 25a to an intermediate-pressure refrigerant. The intermediate-pressure refrigerant is reduced in pressure by the second heat source side expansion valve 25b to a low-pressure refrigerant. The first heat source side expansion valve 25a and the second heat source side expansion valve 25b are electric expansion valves whose opening can be adjusted by control of the control unit 70.

[0030] The gas-liquid separator 26 is a container for separating the refrigerant, which has been reduced in pressure by the first heat source side expansion valve 25a and is in a two-phase gas-liquid state, into liquid refrigerant and gas refrigerant. The two-phase gas-liquid refrigerant that has passed through the first heat source side expansion valve 25a flows into the gas-liquid separator 26 from the inlet side of the gas-liquid separator 26. The gas refrigerant separated in the gas-liquid separator 26 flows out from the gas outlet side of the gas-liquid separator 26. The liquid refrigerant separated in the gas-liquid separator 26 flows out from the liquid outlet side of the gas-liquid separator 26.

[0031] The intermediate heat exchanger 27 exchanges heat between the refrigerant after heat dissipation in the heat source side heat exchanger 23 and before being depressurized by the first heat source side expansion valve 25a, and the gas refrigerant flowing out from the gas outlet side of the gas-liquid separator 26. The refrigerant before being depressurized by the first heat source side expansion valve 25a dissipates heat through heat exchange in the intermediate heat exchanger 27. The gas refrigerant flowing out from the gas outlet side of the gas-liquid separator 26 is heated through heat exchange in the intermediate heat exchanger 27.

[0032] The liquid side shutoff valve 28 is a manual valve disposed at the connection portion with the liquid side refrigerant connection pipe 6.

[0033] The gas side shutoff valve 29 is a manual valve disposed at the connection portion with the gas side refrigerant connection pipe 7 .

[0034] The gas vent valve 41 is provided in the sixth piping 56. The gas vent valve 41 is provided between the gas-liquid separator 26 and the intermediate heat exchanger 27. The gas vent valve 41 adjusts the amount of gas refrigerant flowing through the sixth piping 56. The gas vent valve 41 is an electric expansion valve whose opening degree can be adjusted by control by the control unit 70.

[0035] The heat source unit 2 has a heat source unit control unit 20 that controls the operation of each component that constitutes the heat source unit 2. The heat source unit control unit 20 constitutes a control unit 70. The heat source unit control unit 20 is, for example, a microcomputer including a CPU, a memory, etc. The heat source unit control unit 20 is connected to the utilization unit control unit 30 of the utilization unit 3 via a communication line, and transmits and receives control signals, etc.

[0036] The heat source unit 2 further includes a first temperature sensor 61 and a second temperature sensor 62.

[0037] The first temperature sensor 61 is attached to the third pipe 53. The first temperature sensor 61 is attached, for example, near the inlet of the heat source side heat exchanger 23. The first temperature sensor 61 measures a first temperature, which is the temperature of the refrigerant at the inlet of the heat source side heat exchanger 23. The first temperature is substantially equal to the temperature of the refrigerant before it flows into the heat source side heat exchanger 23 and is subjected to heat exchange in the heat source side heat exchanger 23.

[0038] The second temperature sensor 62 is installed outdoors. The second temperature sensor 62 is attached to, for example, the outer surface of the casing of the heat source unit 2. The second temperature sensor 62 measures a second temperature, which is the temperature of the air undergoing heat exchange with the refrigerant in the heat source side heat exchanger 23. The second temperature is substantially equal to the outside air temperature.

[0039] (1-2) Unit 3 The utilization unit 3 is installed in the target space. As shown in FIG.

[0040] The utilization side heat exchanger 31 functions as a heat absorber (evaporator) of low pressure refrigerant in the refrigeration cycle. A pipe extending from the inlet side of the utilization side heat exchanger 31 is connected to the liquid side refrigerant connection pipe 6. A pipe extending from the outlet side of the utilization side heat exchanger 31 is connected to the gas side refrigerant connection pipe 7. As a result, in the refrigerant circuit 10, the first compressor 21, the second compressor 22, the heat source side heat exchanger 23, the first heat source side expansion valve 25a, the second heat source side expansion valve 25b, and the utilization side heat exchanger 31 are connected in sequence to form a refrigerant circulation flow path.

[0041] The usage-side fan 32 supplies air in the target space to the usage-side heat exchanger 31, and generates an air flow for discharging the air into the target space after heat exchange with the refrigerant in the usage-side heat exchanger 31. The usage-side fan 32 is rotationally driven by a usage-side fan motor 32a.

[0042] The utilization unit 3 has a utilization unit control unit 30 that controls the operation of each component that constitutes the utilization unit 3. The utilization unit control unit 30 constitutes a control unit 70. The utilization unit control unit 30 is, for example, a microcomputer including a CPU, a memory, etc. The utilization unit control unit 30 is connected to the heat source unit control unit 20 of the heat source unit 2 via a communication line, and transmits and receives control signals, etc.

[0043] (1-3) Remote Control 8 The remote control 8 functions as an input device for a user of the refrigeration apparatus 100 to input various instructions to the refrigeration apparatus 100. For example, the user operates the remote control 8 to adjust the set temperature and set humidity of the target space. The remote control 8 also functions as a display device for displaying the operating state of the refrigeration apparatus 100 and predetermined notification information. The remote control 8 is connected to the heat source unit control unit 20 and the utilization unit control unit 30 via communication lines, and transmits and receives signals to and from each other.

[0044] (1-4) Control unit 70 In the refrigeration device 100, the heat source unit control unit 20 and the utilization unit control unit 30 are connected via a communication line to configure a control unit 70, which is hardware that controls the operation of the refrigeration device 100. The control by the control unit 70 is realized by the heat source unit control unit 20 and the utilization unit control unit 30 operating together.

[0045] 2, the control unit 70 is electrically connected to the actuators included in the heat source unit 2. Specifically, the actuators included in the heat source unit 2 are the first compressor motor 21a, the second compressor motor 22a, the heat source side fan motor 24a, the first heat source side expansion valve 25a, the second heat source side expansion valve 25b, and the gas vent valve 41. The control unit 70 is also electrically connected to the first temperature sensor 61, the second temperature sensor 62, the remote control 8, and the actuators included in the utilization unit 3. Specifically, the actuator included in the utilization unit 3 is the utilization side fan motor 32a.

[0046] 2, the control unit 70 has a storage unit 71, a communication unit 72, an actuator control unit 74, and a display control unit 75. Each of these elements realizes a specific function of the control unit 70. The control unit 70 executes these functions by executing control programs stored in a ROM, a RAM, a flash memory, or the like.

[0047] The storage unit 71 stores predetermined information in a predetermined storage area upon request from other elements of the control unit 70. The predetermined information is, for example, the result of a calculation executed by the control unit 70 and a command input to the remote control 8.

[0048] The communication unit 72 functions as a communication interface for transmitting and receiving signals to and from each device connected to the control unit 70. Upon receiving a request from the actuator control unit 74, the communication unit 72 transmits a predetermined signal to a specified actuator. The communication unit 72 receives a signal output from the remote control 8 or the like, and requests the storage unit 71 to store the signal in a predetermined storage area. The communication unit 72 also receives the temperatures measured by the first temperature sensor 61 and the second temperature sensor 62 from the first temperature sensor 61 and the second temperature sensor 62.

[0049] The actuator control unit 74 controls the operation of each actuator included in the refrigeration apparatus 100 based on a control program. Specifically, the actuator control unit 74 has a function of controlling the rotation speed of the first compressor 21, the rotation speed of the second compressor 22, the rotation speed of the heat source side fan 24, the opening degree of the first heat source side expansion valve 25a, the opening degree of the second heat source side expansion valve 25b, the rotation speed of the utilization side fan 32, and the opening degree of the gas vent valve 41 in real time.

[0050] The display control unit 75 is a functional unit that controls the operation of the remote control 8 as a display device. The display control unit 75 causes the remote control 8 to output predetermined information in order to notify the user of information related to the operating state and status of the refrigeration apparatus 100. For example, the display control unit 75 causes the display of the remote control 8 to display the set temperature, etc.

[0051] (2) Operation of the Refrigeration Device 100 Next, a change in the state of the refrigerant circulating through the refrigerant circuit 10 of the refrigeration device 100 will be described using the Mollier diagram shown in Fig. 3. Fig. 3 shows the saturated liquid line L1, dry saturated vapor line L2, and critical point CP of the refrigerant. The critical point CP is the high-pressure side end point of the saturated liquid line L1 and the dry saturated vapor line L2. Refrigerant at a pressure higher than the critical point CP is in a supercritical state.

[0052] During operation of the refrigeration apparatus 100, the refrigerant circuit 10 is in either a first state or a second state. In the first state, the gas vent valve 41 is closed. In the second state, the gas vent valve 41 is open. In Fig. 3, the parts of the refrigeration cycle representing the second state that differ from the refrigeration cycle representing the first state are indicated by dotted lines.

[0053] (2-1) Change in state of refrigerant in the first state In the heat source unit 2, the low-pressure refrigerant flowing through the refrigerant circuit 10 is compressed in the first compressor 21 to become an intermediate-pressure refrigerant (P1 → P2). The intermediate-pressure refrigerant discharged from the first compressor 21 releases a small amount of heat when passing through the second piping 52 (P2 → P3). The intermediate-pressure refrigerant is then compressed in the second compressor 22 to become a high-pressure refrigerant (P3 → P4). The high-pressure refrigerant discharged from the second compressor 22 flows into the heat source side heat exchanger 23. The high-pressure refrigerant that has flowed into the heat source side heat exchanger 23 exchanges heat with the outside air and releases heat (P4 → P5).

[0054] The refrigerant that has released heat in the heat source side heat exchanger 23 is depressurized by the first heat source side expansion valve 25a to become an intermediate pressure refrigerant (P5→P6). The refrigerant that has been depressurized by the first heat source side expansion valve 25a to become a gas-liquid two-phase state flows into the gas-liquid separator 26 and is separated into a liquid refrigerant and a gas refrigerant (P6→P7, P8). The liquid refrigerant separated in the gas-liquid separator 26 is further depressurized by the second heat source side expansion valve 25b to become a low pressure refrigerant (P7→P9). The liquid refrigerant depressurized by the second heat source side expansion valve 25b passes through the liquid side stop valve 28 and the liquid side refrigerant connection pipe 6 to flow into the utilization unit 3, and then flows into the utilization side heat exchanger 31. The low pressure liquid refrigerant that has flowed into the utilization side heat exchanger 31 exchanges heat with the air in the target space in which the utilization unit 3 is installed, absorbs heat, and becomes a gas refrigerant (P9→P1). The refrigerant that has absorbed heat in the utilization side heat exchanger 31 passes through the gas side refrigerant communication pipe 7 and flows into the heat source unit 2 from the gas side shutoff valve 29. The low-pressure refrigerant that has flowed into the heat source unit 2 is sucked into the first compressor 21.

[0055] (2-2) Change in state of refrigerant in the second state In the heat source unit 2, the low-pressure refrigerant flowing through the refrigerant circuit 10 is compressed in the first compressor 21 to become an intermediate-pressure refrigerant (P1 → P2). The intermediate-pressure refrigerant discharged from the first compressor 21 is separated in the gas-liquid separator 26 and merges with the gas refrigerant heated in the intermediate heat exchanger 27 (P2 → P10). The intermediate-pressure refrigerant is then compressed in the second compressor 22 to become a high-pressure refrigerant (P10 → P11). The high-pressure refrigerant discharged from the second compressor 22 flows into the heat source side heat exchanger 23. The high-pressure refrigerant that has flowed into the heat source side heat exchanger 23 exchanges heat with the outside air and releases heat (P11 → P5).

[0056] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 exchanges heat with the gas refrigerant separated in the gas-liquid separator 26 in the intermediate heat exchanger 27 and further dissipates heat (P5 → P12). After that, the refrigerant that has dissipated heat in the intermediate heat exchanger 27 is depressurized by the first heat source side expansion valve 25a to become an intermediate pressure refrigerant (P12 → P13). The refrigerant that has been depressurized in the first heat source side expansion valve 25a to become a gas-liquid two-phase state flows into the gas-liquid separator 26 and is separated into a liquid refrigerant and a gas refrigerant (P13 → P7, P8). The liquid refrigerant separated in the gas-liquid separator 26 is further depressurized by the second heat source side expansion valve 25b to become a low pressure refrigerant (P7 → P9). The liquid refrigerant that has been depressurized by the second heat source side expansion valve 25b flows into the utilization unit 3 through the liquid side stop valve 28 and the liquid side refrigerant connection pipe 6, and then flows into the utilization side heat exchanger 31. The low-pressure liquid refrigerant that flows into the utilization side heat exchanger 31 exchanges heat with the air in the target space in which the utilization unit 3 is installed, absorbing heat and becoming a gas refrigerant (P9 → P1). The refrigerant that has absorbed heat in the utilization side heat exchanger 31 passes through the gas side refrigerant connection pipe 7 and flows into the heat source unit 2 from the gas side shut-off valve 29. The low-pressure refrigerant that flows into the heat source unit 2 is sucked into the first compressor 21.

[0057] The gas refrigerant separated in the gas-liquid separator 26 flows through the sixth pipe 56, and is slightly depressurized when passing through the gas vent valve 41 (P8 → P14). The depressurized gas refrigerant is heated in the intermediate heat exchanger 27 by heat exchange with the refrigerant before being depressurized by the first heat source side expansion valve 25a, and merges with the intermediate-pressure refrigerant discharged from the first compressor 21 (P14 → P10).

[0058] (3) Control of the refrigeration device 100 As described below, while the refrigeration device 100 is operating, the control unit 70 controls the state of the refrigerant circuit 10 in real time based on the first temperature obtained from the first temperature sensor 61 and the second temperature obtained from the second temperature sensor 62.

[0059] The control unit 70 controls the aperture of the gas vent valve 41 so that the difference between the first temperature and the second temperature is equal to or greater than a first value during operation of the refrigeration apparatus 100. Specifically, when the difference between the first temperature and the second temperature is less than the first value, the control unit 70 increases the aperture of the gas vent valve 41. This increases the amount of gas refrigerant separated in the gas-liquid separator 26 and heated in the intermediate heat exchanger 27, and increases the degree of superheat of the refrigerant drawn into the second compressor 22. As a result, the temperature of the refrigerant discharged from the second compressor 22 increases, and the difference between the first temperature and the second temperature increases.

[0060] Moreover, during operation of the refrigeration device 100, the control unit 70 controls the opening degree of the gas vent valve 41 so that the first temperature is equal to or less than the second value. Specifically, when the first temperature is greater than the second value, the control unit 70 sets the opening degree of the gas vent valve 41 to a predetermined value or greater or to the maximum. This increases the amount of gas refrigerant flowing from the gas-liquid separator 26 into the intermediate heat exchanger 27. Therefore, the gas refrigerant separated in the gas-liquid separator 26 is not sufficiently heat exchanged in the intermediate heat exchanger 27 and merges with the refrigerant sucked into the second compressor 22, so that the first temperature decreases. Furthermore, when the first temperature is greater than the second value, the control unit 70 may increase the opening degree of the first heat source side expansion valve 25a. In this case, the pressure of the refrigerant in the heat source side heat exchanger 23 decreases, the compression ratio of the second compressor 22 decreases, and the first temperature decreases.

[0061] (4) Effects of the refrigeration device 100 (4-1) The refrigeration device 100 includes a two-stage compression mechanism consisting of a first compressor 21 and a second compressor 22 in order to increase the difference between a first temperature, which is the temperature of the refrigerant at the inlet of the heat source side heat exchanger 23, and a second temperature, which is the outside air temperature, and thereby maintain the performance of the heat source side heat exchanger 23. In the refrigeration device 100, the gas refrigerant separated in the gas-liquid separator 26 and heated in the intermediate heat exchanger 27 is sucked into the second compressor 22 on the high stage side. As a result, the degree of superheat of the refrigerant sucked into the second compressor 22 increases, and the first temperature increases.

[0062] However, when the refrigeration apparatus 100 is used in an environment where the second temperature is high, the specific enthalpy of the refrigerant at the outlet of the heat source side heat exchanger 23 is high, and the dryness of the refrigerant at the inlet of the gas-liquid separator 26 is high. As a result, the degree of superheat of the refrigerant sucked into the second compressor 22 decreases, and the first temperature decreases, which may degrade the performance of the heat source side heat exchanger 23.

[0063] The control unit 70 of the refrigeration device 100 controls the refrigerant circuit 10 so that the difference between the first temperature and the second temperature becomes equal to or greater than a first value, thereby suppressing a decrease in the degree of superheat of the refrigerant sucked into the second compressor 22. This suppresses a decrease in the first temperature and a decrease in the performance of the heat source side heat exchanger 23.

[0064] Furthermore, the control unit 70 controls the refrigerant circuit 10 so that the first temperature becomes equal to or lower than the second value, thereby suppressing deterioration of the refrigerating machine oil due to overheating of the heat source side heat exchanger 23.

[0065] Therefore, the refrigeration apparatus 100 can suppress a decrease in the reliability of the first compressor 21 and the second compressor 22 while maintaining high performance of the heat source side heat exchanger 23 which is a radiator.

[0066] (4-2) Conventionally, refrigeration devices equipped with an intercooler are known. The intercooler is installed between a low-stage compressor and a high-stage compressor, and cools the refrigerant discharged from the low-stage compressor to lower the temperature of the refrigerant drawn into the high-stage compressor. This suppresses an increase in the temperature of the refrigerant discharged from the high-stage compressor. However, if there is a restriction on the size of the casing of the refrigeration device, the size of a gas cooler that cools the refrigerant discharged from the high-stage compressor is restricted by the intercooler, and the performance of the gas cooler may be insufficient.

[0067] Since the refrigeration device 100 does not include an intercooler, it is possible to ensure a sufficient size of the heat source side heat exchanger 23 equivalent to a gas cooler. As a result, the refrigeration device 100 can maximize the size of the heat source side heat exchanger 23, thereby maintaining high performance of the heat source side heat exchanger 23.

[0068] Furthermore, in the refrigeration device 100, the refrigerant discharged from the first compressor 21 is drawn into the second compressor 22 without being cooled by an intercooler, so the first temperature is more likely to rise than in a configuration including an intercooler. Therefore, the refrigeration device 100 can increase the difference between the first temperature and the second temperature and maintain high performance of the heat source side heat exchanger 23.

[0069] (4-3) The refrigeration apparatus 100 heats the gas refrigerant separated in the gas-liquid separator 26 in the intermediate heat exchanger 27 by heat exchange with the refrigerant at the outlet of the heat source side heat exchanger 23. The refrigerant heated in the intermediate heat exchanger 27 is mixed with the refrigerant before being sucked into the second compressor 22, and the degree of superheat of the refrigerant sucked into the second compressor 22 increases. Therefore, the refrigeration apparatus 100 can increase the difference between the first temperature and the second temperature and maintain high performance of the heat source side heat exchanger 23.

[0070] (4-4) In the refrigeration apparatus 100, the intermediate heat exchanger 27 cools the refrigerant at the outlet of the heat source side heat exchanger 23 by heat exchange with the gas refrigerant separated in the gas-liquid separator 26. This reduces the dryness of the refrigerant that has passed through the first heat source side expansion valve 25a and has been decompressed. Therefore, the refrigeration apparatus 100 can suppress a shortage of the refrigerant drawn into the first compressor 21.

[0071] Furthermore, since the amount of gas refrigerant separated in the gas-liquid separator 26 decreases, the gas refrigerant separated in the gas-liquid separator 26 is more likely to be heated by heat exchange in the intermediate heat exchanger 27. This increases the degree of superheat of the refrigerant sucked into the second compressor 22, making it easier to increase the first temperature. Therefore, the refrigeration apparatus 100 can increase the difference between the first temperature and the second temperature, thereby maintaining high performance of the heat source side heat exchanger 23.

[0072] -Second embodiment- The basic configuration and operation of the refrigeration device 200 of this embodiment are the same as those of the refrigeration device 100 of the first embodiment. The following description will focus on the differences between the refrigeration device 200 of this embodiment and the refrigeration device 100 of the first embodiment.

[0073] (1) Configuration of Refrigeration Device 200 The main differences between the refrigeration apparatus 200 and the refrigeration apparatus 100 of the first embodiment are the heat source unit 2 and the control unit 70.

[0074] 4, the heat source unit 2 of the refrigeration apparatus 200 has a configuration similar to that of the heat source unit 2 of the refrigeration apparatus 100 of the first embodiment, with a liquid injection valve 42 and a seventh pipe 57 further added. The seventh pipe 57 is a pipe through which the refrigerant circulating in the refrigerant circuit 10 flows. The seventh pipe 57 connects the fifth pipe 55 and the sixth pipe 56. One end of the seventh pipe 57 is connected to the fifth pipe 55 between the gas-liquid separator 26 and the second heat source side expansion valve 25b. The other end of the seventh pipe 57 is connected to the sixth pipe 56 between the intermediate heat exchanger 27 and the second pipe 52.

[0075] The liquid injection valve 42 is provided in the seventh pipe 57. The liquid injection valve 42 adjusts the amount of liquid refrigerant flowing through the seventh pipe 57. The liquid injection valve 42 is an electric expansion valve whose opening degree can be adjusted by control by the control unit 70.

[0076] As shown in FIG. 5, the actuator control unit 74 of the control unit 70 has the function of controlling in real time the rotation speed of the first compressor 21, the rotation speed of the second compressor 22, the rotation speed of the heat source side fan 24, the opening degree of the first heat source side expansion valve 25a, the opening degree of the second heat source side expansion valve 25b, the rotation speed of the utilization side fan 32, the opening degree of the gas vent valve 41, and the opening degree of the liquid injection valve 42.

[0077] (2) Operation of the Refrigeration Device 200 Next, the change in state of the refrigerant circulating through the refrigerant circuit 10 of the refrigeration device 200 will be described using the Mollier diagram shown in Fig. 6. Fig. 6 shows the saturated liquid line L1, dry saturated vapor line L2, and critical point CP of the refrigerant. The critical point CP is the high-pressure side end point of the saturated liquid line L1 and the dry saturated vapor line L2. The refrigerant at a pressure higher than the critical point CP is in a supercritical state.

[0078] During operation of the refrigeration device 200, the refrigerant circuit 10 is in one of a first state, a second state, and a third state. In the first state, the gas vent valve 41 and the liquid injection valve 42 are closed. In the second state, the gas vent valve 41 is opened, and the liquid injection valve 42 is closed. In the third state, the gas vent valve 41 and the liquid injection valve 42 are opened. The first and second states operate in the same manner as in the first embodiment, and therefore will not be described. In FIG. 6, the parts of the refrigeration cycle representing the third state that are different from the refrigeration cycle representing the first state are indicated by dotted lines. The change in the state of the refrigerant in the third state will be described below.

[0079] In the heat source unit 2, the low-pressure refrigerant flowing through the refrigerant circuit 10 is compressed in the first compressor 21 to become an intermediate-pressure refrigerant (P1→P2). The intermediate-pressure refrigerant discharged from the first compressor 21 merges with the gas refrigerant separated in the gas-liquid separator 26 and heated in the intermediate heat exchanger 27, and the liquid refrigerant separated in the gas-liquid separator 26 (P2→P10a). Thereafter, the intermediate-pressure refrigerant is compressed in the second compressor 22 to become a high-pressure refrigerant (P10a→P11a). The high-pressure refrigerant discharged from the second compressor 22 flows into the heat source side heat exchanger 23. The high-pressure refrigerant that flows into the heat source side heat exchanger 23 exchanges heat with the outside air and releases heat (P11a→P5).

[0080] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 exchanges heat with the gas refrigerant separated in the gas-liquid separator 26 in the intermediate heat exchanger 27 and further dissipates heat (P5 → P12). After that, the refrigerant that has dissipated heat in the intermediate heat exchanger 27 is depressurized by the first heat source side expansion valve 25a to become an intermediate pressure refrigerant (P12 → P13). The refrigerant that has been depressurized in the first heat source side expansion valve 25a to become a gas-liquid two-phase state flows into the gas-liquid separator 26 and is separated into a liquid refrigerant and a gas refrigerant (P13 → P7, P8). The liquid refrigerant separated in the gas-liquid separator 26 is further depressurized by the second heat source side expansion valve 25b to become a low pressure refrigerant (P7 → P9). The liquid refrigerant that has been depressurized by the second heat source side expansion valve 25b flows into the utilization unit 3 through the liquid side stop valve 28 and the liquid side refrigerant connection pipe 6, and then flows into the utilization side heat exchanger 31. The low-pressure liquid refrigerant that flows into the utilization side heat exchanger 31 exchanges heat with the air in the target space in which the utilization unit 3 is installed, absorbing heat and becoming a gas refrigerant (P9 → P1). The refrigerant that has absorbed heat in the utilization side heat exchanger 31 passes through the gas side refrigerant connection pipe 7 and flows into the heat source unit 2 from the gas side shut-off valve 29. The low-pressure refrigerant that flows into the heat source unit 2 is sucked into the first compressor 21.

[0081] The gas refrigerant separated in the gas-liquid separator 26 flows through the sixth piping 56 and is slightly depressurized when passing through the gas vent valve 41 (P8 → P14). The depressurized gas refrigerant is heated in the intermediate heat exchanger 27 by heat exchange with the refrigerant before being depressurized by the first heat source side expansion valve 25a, and merges with the intermediate pressure refrigerant discharged from the first compressor 21 (P14 → P10a). A part of the liquid refrigerant separated in the gas-liquid separator 26 flows through the seventh piping 57 and merges with the refrigerant flowing through the sixth piping 56 and having been heat exchanged in the intermediate heat exchanger 27.

[0082] (3) Control of the refrigeration device 200 The control unit 70 of the refrigeration device 200 performs the same control as the control unit 70 of the first embodiment.

[0083] The control unit 70 controls the aperture of the gas vent valve 41 so that the first temperature is equal to or lower than the second value during operation of the refrigeration device 200. Specifically, when the first temperature is greater than the second value, the control unit 70 further performs control to increase the aperture of the liquid injection valve 42. In this case, a portion of the liquid refrigerant separated in the gas-liquid separator 26 merges with the refrigerant sucked into the second compressor 22, thereby decreasing the first temperature.

[0084] 6 shows a line segment P10-P11 representing the compression of the refrigerant in the second compressor 22 in the second state, and a line segment P10a-P11a representing the compression of the refrigerant in the second compressor 22 in the third state. The control unit 70 controls the liquid injection valve 42 to increase the opening degree, so that the refrigerant sucked into the second compressor 22 is cooled, and the line segment P10-P11 moves in the direction of lower specific enthalpy and becomes a line segment P10a-P11a.

[0085] (4) Effects of the refrigeration device 200 (4-1) The refrigeration system 200 uses a portion of the liquid refrigerant separated in the gas-liquid separator 26 to cool the refrigerant before it is drawn into the second compressor 22. In this way, the refrigeration system 200 can suppress overheating of the inlet refrigerant of the heat source side heat exchanger 23, and suppress deterioration in the reliability of the first compressor 21 and the second compressor 22.

[0086] (4-2) In the intermediate heat exchanger 27, the refrigeration apparatus 200 cools the refrigerant at the outlet of the heat source side heat exchanger 23 by heat exchange with the gas refrigerant separated in the gas-liquid separator 26. This reduces the dryness of the refrigerant that has been decompressed after passing through the first heat source side expansion valve 25a, and increases the amount of liquid refrigerant stored in the gas-liquid separator 26. Therefore, even if the refrigeration apparatus 200 uses a portion of the liquid refrigerant separated in the gas-liquid separator 26 to cool the refrigerant before it is sucked into the second compressor 22, it is possible to suppress a shortage of the refrigerant sucked into the first compressor 21.

[0087] (4-3) In the third state, the refrigeration device 200 uses the gas refrigerant in the gas-liquid separator 26 to heat the refrigerant before being drawn into the second compressor 22, and uses a part of the liquid refrigerant in the gas-liquid separator 26 to cool the refrigerant before being drawn into the second compressor 22. Thus, the control unit 70 can adjust the amount of gas refrigerant and liquid refrigerant mixed with the refrigerant before being drawn into the second compressor 22 by adjusting the opening degree of the gas vent valve 41 and the liquid injection valve 42 according to the state of the refrigeration device 200. Specifically, the control unit 70 may control the refrigerant circuit 10 by adjusting the opening degree of the gas vent valve 41 and the liquid injection valve 42 based on the first temperature and the second temperature so that the difference between the first temperature and the second temperature is equal to or greater than a first value, or the first temperature is equal to or less than a second value. Thus, the refrigeration device 200 can suppress a decrease in the reliability of the first compressor 21 and the second compressor 22 while maintaining high performance of the heat source side heat exchanger 23.

[0088] -Third embodiment- The basic configuration and operation of the refrigeration device 300 of this embodiment are the same as those of the refrigeration device 100 of the first embodiment. The following description will focus on the differences between the refrigeration device 300 of this embodiment and the refrigeration device 100 of the first embodiment.

[0089] (1) Configuration of Refrigeration Device 300 The main differences between the refrigeration apparatus 300 and the refrigeration apparatus 100 of the first embodiment are the heat source unit 2 and the control unit 70.

[0090] As shown in FIG. 7, the heat source unit 2 has a first compressor 21, a first accumulator 21b, a second compressor 22, a second accumulator 22b, a heat source side heat exchanger 23, a heat source side fan 24, a second heat source side expansion valve 25b, an intermediate heat exchanger 27, a liquid side shut-off valve 28, a gas side shut-off valve 29, and a gas vent valve 41.

[0091] The heat source unit 2 has a first pipe 51 to a sixth pipe 56, which are pipes through which the refrigerant circulating in the refrigerant circuit 10 flows. The first pipe 51 connects the gas side shutoff valve 29 and the suction side of the first compressor 21. The second pipe 52 connects the discharge side of the first compressor 21 and the suction side of the second compressor 22. The third pipe 53 connects the discharge side of the second compressor 22 and the inlet side of the heat source side heat exchanger 23. One end of the fourth pipe 54 is connected to the outlet side of the heat source side heat exchanger 23. The other end of the fourth pipe 54 is connected to one end of the fifth pipe 55 and one end of the sixth pipe 56. The fifth pipe 55 connects the fourth pipe 54 and the liquid side shutoff valve 28. The sixth pipe 56 connects the fourth pipe 54 and the second pipe 52.

[0092] The second heat source side expansion valve 25b is provided in the fifth pipe 55. The second heat source side expansion valve 25b constitutes an expansion mechanism of the refrigeration device 300, and reduces the pressure of the high-pressure refrigerant in the refrigeration cycle until it becomes a low-pressure refrigerant.

[0093] The gas vent valve 41 is provided in the sixth pipe 56. The gas vent valve 41 reduces the pressure of the high-pressure refrigerant in the refrigeration cycle to an intermediate-pressure refrigerant. The gas vent valve 41 adjusts the amount of liquid refrigerant flowing through the sixth pipe 56. The gas vent valve 41 is an electric expansion valve whose opening can be adjusted by control of the control unit 70.

[0094] The intermediate heat exchanger 27 exchanges heat between the refrigerant after heat has been dissipated in the heat source side heat exchanger 23 and after the refrigerant has been reduced in pressure by the gas vent valve 41, and the refrigerant after heat has been dissipated in the heat source side heat exchanger 23 and before the refrigerant has been reduced in pressure by the second heat source side expansion valve 25b.

[0095] As shown in FIG. 8, the actuator control unit 74 of the control unit 70 has the function of controlling the rotation speed of the first compressor 21, the rotation speed of the second compressor 22, the rotation speed of the heat source side fan 24, the opening degree of the second heat source side expansion valve 25b, the rotation speed of the utilization side fan 32, and the opening degree of the gas vent valve 41 in real time.

[0096] (2) Operation of the Refrigeration Device 300 Next, a change in state of the refrigerant circulating through the refrigerant circuit 10 of the refrigeration device 300 will be described using the Mollier diagram shown in Fig. 9. A saturated liquid line L1, a dry saturated vapor line L2, and a critical point CP of the refrigerant are depicted in Fig. 9. The critical point CP is the high-pressure side end point of the saturated liquid line L1 and the dry saturated vapor line L2. The refrigerant at a pressure higher than the critical point CP is in a supercritical state.

[0097] In the heat source unit 2, the low-pressure refrigerant flowing through the refrigerant circuit 10 is compressed in the first compressor 21 to become an intermediate-pressure refrigerant (P1 → P2). The intermediate-pressure refrigerant discharged from the first compressor 21 merges with the heated gas refrigerant in the intermediate heat exchanger 27 (P2 → P3). The intermediate-pressure refrigerant is then compressed in the second compressor 22 to become a high-pressure refrigerant (P3 → P4). The high-pressure refrigerant discharged from the second compressor 22 flows into the heat source side heat exchanger 23. The high-pressure refrigerant that has flowed into the heat source side heat exchanger 23 exchanges heat with the outside air and dissipates heat (P4 → P5).

[0098] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 is divided from the fourth pipe 54 to the fifth pipe 55 and the sixth pipe 56. The refrigerant flowing through the sixth pipe 56 is depressurized by the gas vent valve 41 to become an intermediate pressure refrigerant (P5 → P6). The refrigerant flowing through the fifth pipe 55 exchanges heat with the intermediate pressure refrigerant flowing through the sixth pipe 56 in the intermediate heat exchanger 27. In the intermediate heat exchanger 27, the refrigerant flowing through the fifth pipe 55 dissipates heat (P5 → P7). In the intermediate heat exchanger 27, the refrigerant flowing through the sixth pipe 56 is heated and merges with the intermediate pressure refrigerant discharged from the first compressor 21 (P6 → P3).

[0099] The refrigerant that flows through the fifth pipe 55 and exchanges heat in the intermediate heat exchanger 27 is depressurized by the second heat source side expansion valve 25b to become a low-pressure refrigerant (P7→P8). The liquid refrigerant depressurized by the second heat source side expansion valve 25b passes through the liquid side shutoff valve 28 and the liquid side refrigerant connection pipe 6 to flow into the utilization unit 3, and then flows into the utilization side heat exchanger 31. The low-pressure liquid refrigerant that flows into the utilization side heat exchanger 31 exchanges heat with the air in the target space in which the utilization unit 3 is installed, absorbs heat, and becomes a gas refrigerant (P8→P1). The refrigerant that absorbs heat in the utilization side heat exchanger 31 passes through the gas side refrigerant connection pipe 7 to flow into the heat source unit 2 from the gas side shutoff valve 29. The low-pressure refrigerant that flows into the heat source unit 2 is sucked into the first compressor 21.

[0100] (3) Control of the refrigeration device 300 The control unit 70 controls the aperture of the gas vent valve 41 so that the difference between the first temperature and the second temperature is equal to or greater than a first value during operation of the refrigeration device 300. Specifically, when the difference between the first temperature and the second temperature is less than the first value, the control unit 70 increases the aperture of the gas vent valve 41. This increases the amount of gas refrigerant that flows through the sixth pipe 56 and is heated in the intermediate heat exchanger 27, and the degree of superheat of the refrigerant sucked into the second compressor 22 increases. As a result, the temperature of the refrigerant discharged from the second compressor 22 increases, and the difference between the first temperature and the second temperature increases.

[0101] Moreover, during operation of the refrigeration device 300, the control unit 70 controls the opening degree of the gas vent valve 41 so that the first temperature is equal to or less than the second value. Specifically, when the first temperature is greater than the second value, the control unit 70 sets the opening degree of the gas vent valve 41 to a predetermined value or greater or to the maximum. This increases the amount of refrigerant flowing through the sixth pipe 56. Therefore, the refrigerant flowing through the sixth pipe 56 is not sufficiently heat exchanged in the intermediate heat exchanger 27 and merges with the refrigerant sucked into the second compressor 22, so that the first temperature decreases. Furthermore, when the first temperature is greater than the second value, the control unit 70 may increase the opening degree of the second heat source side expansion valve 25b. In this case, the pressure of the refrigerant in the heat source side heat exchanger 23 decreases, the compression ratio of the second compressor 22 decreases, and the first temperature decreases.

[0102] (4) Effects of the refrigeration device 300 The control unit 70 of the refrigeration device 300 controls the refrigerant circuit 10 so that the difference between the first temperature and the second temperature becomes equal to or greater than a first value, thereby suppressing a decrease in the degree of superheat of the refrigerant sucked into the second compressor 22. This suppresses a decrease in the first temperature and a decrease in the performance of the heat source side heat exchanger 23.

[0103] Furthermore, the control unit 70 controls the refrigerant circuit 10 so that the first temperature becomes equal to or lower than the second value, thereby suppressing deterioration of the refrigerating machine oil due to overheating of the heat source side heat exchanger 23.

[0104] Therefore, the refrigeration apparatus 300 can suppress a decrease in the reliability of the first compressor 21 and the second compressor 22 while maintaining high performance of the heat source side heat exchanger 23 which is a radiator.

[0105] --Variations-- (1) Variation A The refrigeration devices 100, 200, and 300 of the first to third embodiments include a two-stage compression mechanism including a first compressor 21 and a second compressor 22. The two-stage compression mechanism preferably has a mechanism for suppressing a decrease in the temperature of the refrigerant after it is discharged from the first compressor 21 and before it is sucked into the second compressor 22. For example, the two-stage compression mechanism preferably has a heat insulating member covering the second pipe 52. The heat insulating member suppresses heat exchange between the refrigerant flowing through the second pipe 52 and the gas outside the second pipe 52. This suppresses the refrigerant discharged from the first compressor 21 from releasing heat while flowing through the second pipe 52, and the temperature of the refrigerant discharged from the second compressor 22 increases.

[0106] Therefore, the refrigeration devices 100, 200, 300 of the present modified example can increase the temperature of the refrigerant undergoing heat exchange in the heat source side heat exchanger 23 which is a radiator, and can maintain high performance of the heat source side heat exchanger 23.

[0107] (2) Variation B The control unit 70 of the refrigeration devices 100, 200, 300 of the first to third embodiments preferably controls the first temperature to be 90°C or higher and 120°C or lower.

[0108] The refrigeration devices 100, 200, and 300 can maintain high performance of the heat source side heat exchanger 23 even when the outside air temperature is high by setting the temperature of the refrigerant undergoing heat exchange in the heat source side heat exchanger 23, which is a radiator, to a predetermined value or higher (e.g., 90°C or higher). Also, the refrigeration devices 100, 200, and 300 can suppress deterioration of the refrigeration oil and suppress deterioration in the reliability of the first compressor 21 and the second compressor 22 by setting the temperature of the refrigerant undergoing heat exchange in the heat source side heat exchanger 23 to a predetermined value or lower (e.g., 120°C or lower).

[0109] (3) Variation C The refrigeration devices 100, 200, 300 of the first to third embodiments are provided with a two-stage compression mechanism consisting of a first compressor 21 and a second compressor 22. However, a single compressor in which two compression mechanisms are housed in a casing may be used as the two-stage compression mechanism. In this case, the intermediate-pressure refrigerant flowing through the sixth pipe 56 of the refrigeration devices 100, 200, 300 is supplied to a refrigerant flow path between the discharge side of the compression mechanism on the low-pressure side and the suction side of the compression mechanism on the high-pressure side.

[0110] Also, a single-stage compression mechanism may be used instead of the two-stage compression mechanism. The single-stage compression mechanism is, for example, a scroll compressor. In this case, the intermediate-pressure refrigerant flowing through the sixth pipe 56 of the refrigeration device 100, 200, 300 is supplied to a compression chamber, which is a space within the scroll compressor and where the pressure of the compressed refrigerant becomes intermediate pressure.

[0111] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the present disclosure described in the claims. [Explanation of symbols]

[0112] 10: Refrigerant circuit 21: First compressor (compression mechanism) 22: Second compressor (compression mechanism) 23: Heat source side heat exchanger (first heat exchanger) 25a: First heat source side expansion valve (expansion mechanism) 25b: Second heat source side expansion valve (expansion mechanism) 26: Gas-liquid separator 27: Intermediate heat exchanger (third heat exchanger) 31: User side heat exchanger (second heat exchanger) 41: Gas release valve (adjustment mechanism) 42: Liquid injection valve (adjustment mechanism) 56: 6th pipe (1st flow path) 57: 7th pipe (2nd flow path) 100: Refrigeration equipment 200: Refrigeration equipment 300: Refrigeration equipment [Prior art documents] [Patent documents]

[0113] [Patent Document 1] JP 2016-128734 A

Claims

1. A compression mechanism (21, 22) having a first compressor (21) and a second compressor (22) for compressing the refrigerant discharged from the first compressor, A first heat exchanger (23) which functions as a heat exchanger for the refrigerant compressed by the compression mechanism, Expansion mechanism (25a, 25b), A second heat exchanger (31) functions as a heat absorber for the refrigerant whose pressure has been reduced by the expansion mechanism, A gas-liquid separator (26) separates the gas-liquid two-phase refrigerant, which has been depressurized by the expansion mechanism, into a liquid refrigerant and a gaseous refrigerant. A third heat exchanger (27) exchanges heat between the gaseous refrigerant in the gas-liquid separator and the refrigerant after it has been heated in the first heat exchanger and before it has been depressurized by the expansion mechanism, A first flow path (56) mixes the gaseous refrigerant that has undergone heat exchange in the third heat exchanger with the refrigerant before it is drawn into the second compressor, An adjustment mechanism (41) for adjusting the amount of the gaseous refrigerant flowing through the first flow path, A control unit (70) controls the adjustment mechanism, Equipped with, The control unit controls the difference between a first temperature, which is the temperature of the refrigerant at the inlet of the first heat exchanger, and a second temperature, which is the temperature of the air that is heat-exchanged with the refrigerant in the first heat exchanger, to be greater than or equal to a first value. The aforementioned refrigerant is carbon dioxide. Refrigeration device (100).

2. The control unit increases the opening of the adjustment mechanism (41) when the difference between the first temperature and the second temperature is less than the first value. The refrigeration apparatus according to claim 1.

3. The control unit sets the opening of the adjustment mechanism (41) to a predetermined value or the maximum value so that the first temperature is less than or equal to the second value. The refrigeration apparatus according to claim 1.

4. The invention further comprises a second flow path (57) for mixing the liquid refrigerant in the gas-liquid separator with the refrigerant before it is drawn into the second compressor, in order to cool the refrigerant before it is drawn into the second compressor. A refrigeration apparatus according to any one of claims 1 to 3.

5. The invention further comprises a second adjustment mechanism (42) for adjusting the amount of liquid refrigerant flowing through the second flow path. The refrigeration apparatus according to claim 4.

6. The control unit controls the first temperature to be between 90°C and 120°C. A refrigeration apparatus according to any one of claims 1 to 3.

Images