Refrigerator

Abstract

To solve a problem with deterioration in capacity of a refrigerator having a two-stage compression mechanism comprising a low-stage side compressor and a high-stage side compressor, the deterioration caused by a small compression ratio of the low-stage side compressor during a pull-down operation that requires high refrigerating capacity due to a small difference between a temperature of a target space and an outside air temperature.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, an expansion mechanism and a utilization side heat exchanger 31 are sequentially connected. The refrigerant circuit 10 includes a gas-liquid separator 26, sixth piping 56, second piping 52 and bypass piping 59. The sixth piping 56 guides a gas refrigerant in the gas-liquid separator 26 to a suction side of the second compressor 22. The second piping 52 guides a refrigerant discharged from the first compressor 21 to the suction side of the second compressor 22. While the refrigerant discharged from the first compressor 21 is not flowing in the second piping 52, the bypass piping 59 guides the refrigerant discharged from the first compressor 21 to the discharge side of the second compressor 22.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] It relates to a refrigeration device.

Background Art

[0002] As described in Patent Document 1 (Japanese Patent Application Laid-Open No. 2016-128734), a refrigeration device is known that uses carbon dioxide as a refrigerant and has a two-stage compression mechanism including a low-stage compressor and a high-stage compressor. This refrigeration device is used to cool the air in the target space by the heat absorption action of the evaporator of the refrigerant installed in the target space.

Summary of the Invention

Problems to be Solved by the Invention

[0003] When the above refrigeration device is used in an environment where the difference between the set temperature of the target space and the outside air temperature is large, during the pull-down operation where the difference between the temperature of the target space and the outside air temperature is small and a high refrigeration capacity is required, it is necessary to maintain a high pressure of the refrigerant on the high-pressure side. However, since the pressure of the refrigerant in the gas-liquid separator needs to be lower than the critical pressure of the refrigerant, during the pull-down operation where the evaporation temperature of the refrigerant is high, the compression ratio of the low-stage compressor becomes small, and there is a risk that the refrigeration capacity will decrease.

Means for Solving the Problems

[0004] The refrigeration device of the first aspect includes a refrigerant circuit in which a first compressor, a second compressor, a first heat exchanger, an expansion mechanism, and a second heat exchanger are sequentially connected. The first heat exchanger functions as a radiator for the refrigerant compressed by the first compressor or the second compressor. The second heat exchanger functions as a heat absorber for the refrigerant decompressed by the expansion mechanism. The refrigerant circuit includes a gas-liquid separator or a third heat exchanger, a first flow path, a second flow path, and a third flow path. The gas-liquid separator separates the refrigerant in a gas-liquid two-phase state decompressed by the expansion mechanism into liquid refrigerant and gas refrigerant. The third heat exchanger performs heat exchange between the refrigerant decompressed by the decompression mechanism after radiating heat in the first heat exchanger and the refrigerant after radiating heat in the first heat exchanger and before being decompressed by the expansion mechanism. The first flow path connects the gas-liquid separator or the third heat exchanger to the suction side of the second compressor. The second flow path connects the discharge side of the first compressor to the suction side of the second compressor. The third flow path connects the discharge side of the first compressor to the discharge side of the second compressor. The first flow path guides the gas refrigerant in the gas-liquid separator or the refrigerant decompressed by the decompression mechanism and heat-exchanged in the third heat exchanger to the suction side of the second compressor. The second flow path guides the refrigerant discharged from the first compressor to the suction side of the second compressor. The third flow path guides the refrigerant discharged from the first compressor to the discharge side of the second compressor in a state where the refrigerant discharged from the first compressor does not flow through the second flow path.

[0005] The refrigeration device of the first aspect can perform two-stage compression operation using a low-stage compressor and a high-stage compressor, and single-stage compression operation using only the low-stage compressor. This refrigeration device can ensure the compression ratio of the low-stage compressor and maintain the pressure of the refrigerant on the high-pressure side high by performing single-stage compression operation during pull-down operation when the difference between the temperature of the target space and the outside air temperature is small. Therefore, the refrigeration device of the first aspect can suppress the reduction in capacity during pull-down operation.

[0006] The refrigeration device from the second perspective is the refrigeration device from the first perspective, and further includes a control unit that switches the refrigerant circuit between a first state and a second state. In the first state, the refrigerant discharged from the first compressor flows through the second flow path, merges with the gaseous refrigerant flowing through the first flow path, and is inhaled into the second compressor. In the second state, the refrigerant discharged from the first compressor flows through the third flow path without flowing through the second flow path, and merges with the refrigerant discharged from the second compressor. The refrigerant circuit further includes a first valve provided in the second flow path and a second valve which is a check valve provided in the third flow path. The control unit opens the first valve when in the first state and closes the first valve when in the second state.

[0007] The refrigeration device from the second perspective can switch between a state of performing two-stage compression operation and a state of performing single-stage compression operation by controlling the opening and closing of a valve provided in the refrigerant circuit.

[0008] The refrigeration device from the third perspective is the refrigeration device from the second perspective, and the control unit switches the refrigerant circuit from the second state to the first state when the temperature of the refrigerant inhaled into the first compressor drops to a first value and the temperature of the refrigerant discharged from the first compressor rises to a second value when the refrigerant circuit is in the second state.

[0009] The refrigeration device from the third perspective shifts to a state of performing two-stage compression operation when the load of the low-stage compressor increases in a state of performing single-stage compression operation. Therefore, the refrigeration device from the third perspective can reduce the load of the low-stage compressor and suppress a decrease in the reliability of the low-stage compressor.

[0010] The refrigeration device from the fourth perspective is the refrigeration device from the second or third perspective, and the control unit switches the refrigerant circuit from the first state to the second state when the temperature of the refrigerant inhaled into the first compressor rises to a third value or when the rotational speed of the first compressor is lower than the rotational speed of the second compressor when the refrigerant circuit is in the first state.

[0011] In the state where the refrigeration device of the fourth aspect performs two-stage compression operation, when the load of the high-stage compressor increases, it shifts to the state of performing single-stage compression operation. Therefore, the refrigeration device of the fourth aspect can reduce the load of the high-stage compressor and suppress the decrease in the reliability of the high-stage compressor.

[0012] The refrigeration device of the fifth aspect is any one of the refrigeration devices of the second to fourth aspects, and the control unit switches the refrigerant circuit among a first state, a second state, and a third state. In the third state, refrigerant is not sucked into the second compressor, and the refrigerant discharged from the first compressor flows through the third flow path without flowing through the second flow path. The refrigerant circuit further has a third valve provided in the first flow path. The control unit opens the third valve in the first state or the second state, and closes the third valve in the third state.

[0013] In the state where the refrigeration device of the fifth aspect performs single-stage compression operation, the switching between the state of performing the gas extraction operation of compressing the gas refrigerant in the gas-liquid separator with the high-stage compressor and the state of not performing it can be performed by the opening and closing control of the valve provided in the refrigerant circuit.

[0014] The refrigeration device of the sixth aspect is the refrigeration device of the fifth aspect, and the control unit switches the refrigerant circuit in the order of the third state, the second state, and the first state when starting the first compressor and the second compressor.

[0015] The refrigeration device of the sixth aspect performs control to not perform the gas extraction operation when the amount of refrigerant on the high-pressure side is small at startup, and to start the gas extraction operation when the amount of refrigerant on the high-pressure side increases. Therefore, the refrigeration device of the sixth aspect can reduce the load of the high-stage compressor and suppress the reduction in capacity.

[0016] The refrigeration device of the seventh aspect is any one of the refrigeration devices of the first to sixth aspects, and the refrigerant circuit has a gas-liquid separator and further has a fourth flow path. The fourth flow path connects the gas-liquid separator and the first flow path. The fourth flow path guides the refrigeration machine oil in the gas-liquid separator, together with the liquid refrigerant in the gas-liquid separator, to the suction side of the second compressor via the first flow path.

[0017] The refrigeration device according to the seventh aspect can suppress a shortage of refrigerating machine oil in the high-pressure side compressor.

[0018] The refrigeration device according to the eighth aspect is any one of the refrigeration devices according to the first to seventh aspects, and the refrigerant circuit further has a fifth flow path. The fifth flow path connects the discharge side of the second compressor and the suction side of the second compressor. The fifth flow path guides the refrigerating machine oil discharged from the second compressor to the suction side of the second compressor. An oil separator for separating the refrigerating machine oil from the mixture of the refrigerant and the refrigerating machine oil is provided in the fifth flow path.

[0019] The refrigeration device according to the eighth aspect can suppress a shortage of refrigerating machine oil in the high-pressure side compressor.

[0020] The refrigeration device according to the ninth aspect is any one of the refrigeration devices according to the first to eighth aspects, and the refrigerant circuit has a gas-liquid separator and further has a fourth heat exchanger. The fourth heat exchanger exchanges heat with and heats the gas refrigerant in the gas-liquid separator and the refrigerant after being radiated by the first heat exchanger and before being depressurized by the expansion mechanism.

[0021] The refrigeration device according to the ninth aspect can keep the performance of the radiator high by increasing the superheat degree of the refrigerant sucked into the high-stage side compressor and increasing the difference between the temperature of the radiator and the outside air temperature. Further, the refrigeration device according to the ninth aspect can suppress a decrease in the reliability of the compressor by reducing the dryness of the refrigerant depressurized by the expansion mechanism and suppressing a shortage of the refrigerant sucked into the low-stage side compressor.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

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Figure 8

Figure 9

Modes for Carrying Out the Invention

[0023] -First Embodiment- (1) Configuration of the refrigeration apparatus 100 As shown in FIG. 1, the refrigeration apparatus 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 controller 8, and a control unit 70. In the refrigeration apparatus 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, thereby forming a refrigerant circuit 10 through which the refrigerant circulates.

[0024] In the refrigeration apparatus 100, a vapor compression refrigeration cycle is performed in which the refrigerant enclosed in the refrigerant circuit 10 is compressed, condensed, depressurized, evaporated, and then compressed again. The refrigeration apparatus 100 cools the air in the target space by the evaporation of the refrigerant circulating in the refrigeration cycle. The refrigeration apparatus 100 is attached to, for example, a marine container and cools the air in the target space inside the container.

[0025] The refrigeration apparatus 100 may include a plurality of utilization units 3. In this case, a plurality of utilization units 3 are connected in parallel to one heat source unit 2, thereby forming the refrigerant circuit 10.

[0026] The refrigerant enclosed in the refrigerant circuit 10 is carbon dioxide (R744). Carbon dioxide is a non-flammable natural refrigerant with a small global warming potential (GWP) compared to fluorine-containing refrigerants. In the refrigerant circuit 10, the high-pressure refrigerant in the refrigeration cycle is in a supercritical state where its pressure is greater than the critical pressure.

[0027] (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 outdoors, for example. As shown in FIG. 1, the heat source unit 2 includes 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 shut-off valve 28, a gas side shut-off valve 29, a gas vent valve 41, a first shut-off valve 43, and a second shut-off valve 44.

[0028] The heat source unit 2 has first to sixth pipes 51 to 56 and a bypass pipe 59, which are pipes through which the refrigerant circulating in the refrigerant circuit 10 flows. The first pipe 51 connects the gas side shut-off 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 shut-off valve 28. The sixth pipe 56 connects the gas outlet side of the gas-liquid separator 26 and the second pipe 52. The bypass pipe 59 connects the second pipe 52 and the third pipe 53.

[0029] The first compressor 21 and the second compressor 22 constitute the compression mechanism of the refrigeration device 100, and compress the low-pressure refrigerant in the refrigeration cycle until it becomes a high-pressure refrigerant. When the refrigeration device 100 performs the two-stage compression operation described later, the low-pressure refrigerant in the refrigeration cycle is compressed by the first compressor 21 to become a medium-pressure refrigerant. The medium-pressure refrigerant is compressed by the second compressor 22 to become a high-pressure refrigerant. The intermediate pressure in the refrigeration cycle is the pressure between the low pressure and the high pressure. The intermediate-pressure refrigerant in the refrigeration cycle is in a state where its pressure is lower than the critical pressure. The first compressor 21 and the second compressor 22 have a sealed structure in which volume-variable compression elements such as rotary type or scroll type are rotationally driven 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 be controlled in terms of the operating frequency (the rotational speed of the first compressor 21 and the second compressor 22) by an inverter.

[0030] 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.

[0031] The heat source side heat exchanger 23 is a gas cooler that functions as a radiator (condenser) for the high-pressure refrigerant in the refrigeration cycle.

[0032] The heat source side fan 24 supplies air (outside air, etc.) outside the target space to the heat source side heat exchanger 23, and after heat exchange with the refrigerant in the heat source side heat exchanger 23, generates an air flow for discharging to the outside of the heat source unit 2. The heat source side fan 24 is rotationally driven by the heat source side fan motor 24a.

[0033] The first heat source side expansion valve 25a is provided in the fourth pipe 54. The second heat source side expansion valve 25b is provided in the fifth pipe 55. The first heat source side expansion valve 25a and the second heat source side expansion valve 25b constitute the expansion mechanism of the refrigeration device 100, and decompress the high-pressure refrigerant in the refrigeration cycle until it becomes a low-pressure refrigerant. The high-pressure refrigerant in the refrigeration cycle is decompressed by the first heat source side expansion valve 25a to become a medium-pressure refrigerant. The medium-pressure refrigerant is decompressed by the second heat source side expansion valve 25b to become 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 degrees can be adjusted by the control of the control unit 70.

[0034] The gas-liquid separator 26 is a container for separating the refrigerant that has been decompressed by the first heat source side expansion valve 25a and has become a gas-liquid two-phase state into a liquid refrigerant and a gas refrigerant. The gas-liquid two-phase 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 by the gas-liquid separator 26 flows out from the gas outlet side of the gas-liquid separator 26. The liquid refrigerant separated by the gas-liquid separator 26 flows out from the liquid outlet side of the gas-liquid separator 26.

[0035] The intermediate heat exchanger 27 performs heat exchange between the refrigerant after being cooled by the heat source side heat exchanger 23 and before being decompressed 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 decompressed 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.

[0036] The liquid side shut-off valve 28 is a manual valve arranged at the connection part with the liquid side refrigerant connecting pipe 6.

[0037] The gas side shut-off valve 29 is a manual valve arranged at the connection part with the gas side refrigerant connecting pipe 7.

[0038] The gas vent valve 41 is provided in the sixth pipe 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 pipe 56. The gas vent valve 41 is an electric expansion valve whose opening degree can be adjusted by the control of the control unit 70.

[0039] The first shut-off valve 43 is provided in the second pipe 52. As shown in FIG. 1, in the second pipe 52, a connection portion with the bypass pipe 59, the first shut-off valve 43, and a connection portion with the sixth pipe 56 are provided in order from the discharge side of the first compressor 21 toward the suction side of the second compressor 22. The first shut-off valve 43 is an electric expansion valve whose opening degree can be adjusted by the control of the control unit 70. While the first shut-off valve 43 is closed, it shuts off the flow of refrigerant from the discharge side of the first compressor 21 toward the suction side of the second compressor 22.

[0040] The second shut-off valve 44 is provided in the bypass pipe 59. The second shut-off valve 44 is a check valve. The second shut-off valve 44 allows the flow of refrigerant from the second pipe 52 toward the third pipe 53. The second shut-off valve 44 shuts off the flow of refrigerant from the third pipe 53 toward the second pipe 52. The second shut-off valve 44 may be an electric expansion valve whose opening degree can be adjusted by the control of the control unit 70.

[0041] The heat source unit 2 has a heat source unit control unit 20 that controls the operations of the components constituting the heat source unit 2. The heat source unit control unit 20 constitutes the control unit 70. The heat source unit control unit 20 is, for example, a microcomputer including a CPU and a memory. 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 performs transmission and reception of control signals and the like.

[0042] Further, the heat source unit 2 further has first temperature sensors 61 to fifth temperature sensors 65.

[0043] 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 the 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 undergoes heat exchange in the heat source side heat exchanger 23.

[0044] The second temperature sensor 62 is installed outdoors. The second temperature sensor 62 is attached, for example, to the outer surface of the casing of the heat source unit 2. The second temperature sensor 62 measures the second temperature, which is the temperature of the air that undergoes heat exchange with the refrigerant in the heat source side heat exchanger 23. The second temperature is substantially equal to the outside air temperature.

[0045] The third temperature sensor 63 is installed in the target space. The third temperature sensor 63 is attached, for example, to the outer surface of the casing of the utilization unit 3. The third temperature sensor 63 measures the third temperature, which is the temperature of the target space where the utilization unit 3 is installed.

[0046] The fourth temperature sensor 64 is attached to the first pipe 51. The fourth temperature sensor 64 is attached, for example, near the suction side of the first compressor 21. The fourth temperature sensor 64 measures the fourth temperature, which is the temperature of the refrigerant sucked into the first compressor 21. The fourth temperature is substantially equal to the evaporation temperature of the refrigerant.

[0047] The fifth temperature sensor 65 is attached to the second pipe 52. The fifth temperature sensor 65 is attached, for example, near the discharge side of the first compressor 21. The fifth temperature sensor 65 measures the fifth temperature, which is the temperature of the refrigerant discharged from the first compressor 21.

[0048] (1-2) Utilization unit 3 The utilization unit 3 is installed in the target space. As shown in FIG. 1, the utilization unit 3 includes a utilization side heat exchanger 31 and a utilization side fan 32.

[0049] The utilization-side heat exchanger 31 functions as a heat absorber (evaporator) for the low-pressure refrigerant in the refrigeration cycle. The pipe extending from the inlet side of the utilization-side heat exchanger 31 is connected to the liquid-side refrigerant connection pipe 6. The pipe extending from the outlet side of the utilization-side heat exchanger 31 is connected to the gas-side refrigerant connection pipe 7. Thereby, 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 sequentially connected to form a refrigerant circulation flow path.

[0050] The utilization-side fan 32 supplies the air in the target space to the utilization-side heat exchanger 31, and after heat exchange with the refrigerant in the utilization-side heat exchanger 31, generates an air flow for discharging to the target space. The utilization-side fan 32 is rotationally driven by the utilization-side fan motor 32a.

[0051] The utilization unit 3 has a utilization unit control unit 30 that controls the operations of the components constituting the utilization unit 3. The utilization unit control unit 30 constitutes the control unit 70. The utilization unit control unit 30 is, for example, a microcomputer including a CPU and a memory. 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 performs transmission and reception of control signals and the like.

[0052] (1-3) Remote controller 8 The remote controller 8 functions as an input device for a user of the refrigeration apparatus 100 to input various instructions to the refrigeration apparatus 100. The user, for example, operates the remote controller 8 to adjust the set temperature and set humidity of the target space. The remote controller 8 also functions as a display device for displaying the operating state of the refrigeration apparatus 100 and predetermined notification information. The remote controller 8 is connected to the heat source unit control unit 20 and the utilization unit control unit 30 via a communication line and performs signal transmission and reception with each other.

[0053] (1-4) Control unit 70 In the refrigeration device 100, a control unit 70, which is hardware for controlling the operation of the refrigeration device 100, is configured by connecting a heat source unit control unit 20 and a utilization unit control unit 30 via a communication line. 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 integrally.

[0054] As shown in FIG. 2, the control unit 70 is electrically connected to the actuators included in the heat source unit 2. The actuators included in the heat source unit 2 are specifically a first compressor motor 21a, a second compressor motor 22a, a heat source side fan motor 24a, a first heat source side expansion valve 25a, a second heat source side expansion valve 25b, a gas vent valve 41, and a first shut-off valve 43. The control unit 70 is also electrically connected to the first temperature sensor 61 to the fifth temperature sensor 65, a remote control 8, and the actuators included in the utilization unit 3. The actuator included in the utilization unit 3 is specifically a utilization side fan motor 32a.

[0055] As shown in FIG. 2, the control unit 70 includes a storage unit 71, a communication unit 72, an actuator control unit 74, and a display control unit 75. These elements realize specific functions of the control unit 70. The control unit 70 executes these functions by executing a control program stored in a ROM, a RAM, a flash memory, etc.

[0056] The storage unit 71 stores predetermined information in a predetermined storage area in response to requests from other elements of the control unit 70. The predetermined information is, for example, the result of calculations executed by the control unit 70 and commands input to the remote control 8.

[0057] 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. The communication unit 72 receives a request from the actuator control unit 74 and transmits a predetermined signal to the designated actuator. The communication unit 72 receives the signal output from the remote control 8 or the like and requests the storage unit 71 to store it in a predetermined storage area. Further, the communication unit 72 receives the temperatures measured by the first temperature sensor 61 to the fifth temperature sensor 65 from the first temperature sensor 61 to the fifth temperature sensor 65.

[0058] The actuator control unit 74 controls the operations of the actuators included in the refrigeration apparatus 100 based on a control program. Specifically, the actuator control unit 74 has a 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 first shut-off valve 43.

[0059] 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 outputs predetermined information to the remote control 8 in order to notify the user of information regarding the operation state and situation of the refrigeration apparatus 100. For example, the display control unit 75 causes the remote control 8 to display the set temperature or the like on the display.

[0060] (2) Operation of the refrigeration apparatus 100 Next, with reference to the Mollier diagrams shown in FIGS. 3 and 4, the change in the state of the refrigerant circulating in the refrigerant circuit 10 of the refrigeration apparatus 100 will be described. In FIGS. 3 and 4, a saturated liquid line L1, a dry saturated vapor line L2, and a critical point CP of the refrigerant are drawn. The critical point CP is the end point on the high-pressure side 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.

[0061] During the operation of the refrigeration device 100, the refrigerant circuit 10 assumes either the first state or the second state. In the first state, the gas bleeding valve 41 is closed and the first shut-off valve 43 is open. In the second state, the gas bleeding valve 41 is open and the first shut-off valve 43 is closed.

[0062] FIG. 3 is a Mollier diagram when the refrigerant circuit 10 is in the first state. The first state is a state in which the refrigeration device 100 performs two-stage compression operation. The two-stage compression operation is an operation of compressing the gas refrigerant heat-exchanged in the utilization-side heat exchanger 31 by the first compressor 21 and the second compressor 22.

[0063] During the two-stage compression operation, the low-pressure refrigerant in the refrigeration cycle is sequentially compressed by the low-stage first compressor 21 and the high-stage second compressor 22 to become the high-pressure refrigerant in the refrigeration cycle. Specifically, during the two-stage compression operation, the first compressor 21 sucks and compresses the low-pressure refrigerant flowing through the first pipe 51 and discharges the intermediate-pressure refrigerant into the second pipe 52. The intermediate-pressure refrigerant discharged into the second pipe 52 passes through the first shut-off valve 43. The second compressor 22 sucks and compresses the intermediate-pressure refrigerant flowing through the second pipe 52 and discharges the high-pressure refrigerant into the third pipe 53.

[0064] FIG. 4 is a Mollier diagram when the refrigerant circuit 10 is in the second state. The second state is a state in which the refrigeration device 100 performs single-stage compression / gas bleeding operation. During the single-stage compression / gas bleeding operation, single-stage compression operation and gas bleeding operation are performed. The single-stage compression operation is an operation of compressing the gas refrigerant heat-exchanged in the utilization-side heat exchanger 31 by the first compressor 21. The gas bleeding operation is an operation of compressing the gas refrigerant separated by the gas-liquid separator 26 by the second compressor 22.

[0065] During single-stage compression operation, the low-pressure refrigerant in the refrigeration cycle is compressed by the first compressor 21 to become the high-pressure refrigerant in the refrigeration cycle. Specifically, the first compressor 21 sucks in and compresses the low-pressure refrigerant flowing through the first pipe 51, and discharges the high-pressure refrigerant into the second pipe 52. The high-pressure refrigerant discharged into the second pipe 52 cannot pass through the first shut-off valve 43 and flows into the bypass pipe 59. The high-pressure refrigerant flowing into the bypass pipe 59 passes through the second shut-off valve 44 and flows into the third pipe 53.

[0066] During gas extraction operation, the intermediate-pressure refrigerant in the refrigeration cycle is compressed by the second compressor 22 to become the high-pressure refrigerant in the refrigeration cycle. Specifically, the second compressor 22 sucks in and compresses the intermediate-pressure gas refrigerant flowing from the gas-liquid separator 26 into the second pipe 52 through the sixth pipe 56, and discharges the high-pressure refrigerant into the third pipe 53.

[0067] During single-stage compression / gas extraction operation, the high-pressure refrigerant discharged from the first compressor 21 by single-stage compression operation and the high-pressure refrigerant discharged from the second compressor 22 by gas extraction operation merge in the third pipe 53. The refrigerant merged in the third pipe 53 flows into the heat source side heat exchanger 23.

[0068] (2-1) Change in the state of the refrigerant in the first state As shown in FIG. 3, 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 slightly dissipates heat when passing through the second pipe 52 (P2→P3). Thereafter, the intermediate-pressure refrigerant is 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 flowing into the heat source side heat exchanger 23 exchanges heat with the outside air and dissipates heat (P4→P5).

[0069] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 is depressurized by the first heat source side expansion valve 25a to become a refrigerant at an intermediate pressure (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 by 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 shut-off valve 28 and the liquid side refrigerant connection pipe 6 and flows into the utilization unit 3, and then flows into the utilization side heat exchanger 31. The low-pressure liquid refrigerant flowing into the utilization side heat exchanger 31 exchanges heat with the air in the target space where 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 connection pipe 7 and flows into the heat source unit 2 from the gas side shut-off valve 29. The low-pressure refrigerant flowing into the heat source unit 2 is sucked into the first compressor 21.

[0070] (2-2) Change in the state of the refrigerant in the second state As shown in FIG. 4, 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 a high-pressure refrigerant (P1 → P2). The gas refrigerant separated by the gas-liquid separator 26 and heated to an intermediate pressure in the intermediate heat exchanger 27 is compressed in the second compressor 22 to become a high-pressure refrigerant (P3 → P4). The high-pressure refrigerant discharged from the first compressor 21 and the second compressor 22 merges and flows into the heat source side heat exchanger 23. The high-pressure refrigerant flowing into the heat source side heat exchanger 23 exchanges heat with the outside air and dissipates heat (P2, P4 → P5).

[0071] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 exchanges heat with the gaseous refrigerant separated by the gas-liquid separator 26 in the intermediate heat exchanger 27 and further dissipates heat (P5→P6). 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 a refrigerant at an intermediate pressure (P6→P7). The refrigerant that has been depressurized by the first heat source side expansion valve 25a and has become a gas-liquid two-phase state flows into the gas-liquid separator 26 and is separated into a liquid refrigerant and a gaseous refrigerant (P7→P8, P9). The liquid refrigerant separated by the gas-liquid separator 26 is further depressurized by the second heat source side expansion valve 25b to become a low-pressure refrigerant (P8→P10). The liquid refrigerant depressurized by the second heat source side expansion valve 25b passes through the liquid side shut-off valve 28 and the liquid side refrigerant connection pipe 6 and flows 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 where the utilization unit 3 is installed, absorbs heat, and becomes a gaseous refrigerant (P10→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 has flowed into the heat source unit 2 is sucked into the first compressor 21.

[0072] The gaseous refrigerant separated by the gas-liquid separator 26 flows through the sixth pipe 56 and is slightly depressurized when passing through the gas vent valve 41 (P9→P11). The depressurized gaseous refrigerant exchanges heat with the refrigerant before being depressurized by the first heat source side expansion valve 25a in the intermediate heat exchanger 27, is heated, and is sucked into the second compressor 22 (P11→P3).

[0073] (3) Control of the refrigeration device 100 During the operation of the refrigeration device 100, the control unit 70 controls the state of the refrigerant circuit 10 in real time based on at least one of the first temperature to the fifth temperature acquired from the first temperature sensor 61 to the fifth temperature sensor 65.

[0074] Immediately after the refrigeration device 100 is started, the refrigerant circuit 10 is in the second state, and the refrigeration device 100 performs a single-stage compression / gas extraction operation. When the refrigeration device 100 is started, a pull-down operation is performed. The pull-down operation is an operation in which the difference between the temperature of the target space of the refrigeration device 100 and the outside air temperature is small, and a high refrigeration capacity is required to lower the temperature of the target space to the set temperature of the target space. At the start of the pull-down operation, for example, the difference between the temperature of the target space and the outside air temperature is zero.

[0075] When the refrigeration device 100 is performing a single-stage compression / gas extraction operation, the control unit 70 switches the refrigerant circuit 10 from the second state to the first state when a predetermined first condition is satisfied. Thereby, the refrigeration device 100 stops the single-stage compression / gas extraction operation and starts a two-stage compression operation. The control unit 70 switches the refrigerant circuit 10 from the second state to the first state by closing the gas extraction valve 41 and opening the first shut-off valve 43. The first condition is satisfied when the temperature of the refrigerant sucked into the first compressor 21 drops to a first value and the temperature of the refrigerant discharged from the first compressor 21 rises to a second value. The control unit 70 uses the fourth temperature measured by the fourth temperature sensor 64 as the temperature of the refrigerant sucked into the first compressor 21. The control unit 70 uses the fifth temperature measured by the fifth temperature sensor 65 as the temperature of the refrigerant discharged from the first compressor 21.

[0076] When the refrigeration device 100 is performing two-stage compression operation, the control unit 70 switches the refrigerant circuit 10 from the first state to the second state when a predetermined second condition is satisfied. Thereby, the refrigeration device 100 stops the two-stage compression operation and starts the single-stage compression / gas extraction operation. The control unit 70 switches the refrigerant circuit 10 from the first state to the second state by opening the gas extraction valve 41 and closing the first shut-off valve 43. The second condition is satisfied when the temperature of the refrigerant sucked into the first compressor 21 rises to a third value or when the rotational speed of the first compressor 21 falls below the rotational speed of the second compressor 22. The control unit 70 uses the fourth temperature measured by the fourth temperature sensor 64 as the temperature of the refrigerant sucked into the first compressor 21. The control unit 70 acquires the rotational speeds of the first compressor 21 and the second compressor 22 from the actuator control unit 74.

[0077] (4) Effects of the refrigeration device 100 (4-1) Conventionally, a refrigeration device having a refrigeration cycle in which carbon dioxide circulates as a refrigerant has been used. When this refrigeration device is used in an environment where the outside air temperature is high, a two-stage compression mechanism is employed to increase the temperature and pressure of the refrigerant flowing into the radiator of the refrigeration cycle. Further, when this refrigeration device is used in an environment where the difference between the outside air temperature and the set temperature of the target space is large, it is preferable to provide a gas-liquid separator. In this case, the pressure of the refrigerant in the gas-liquid separator needs to be lower than the pressure at the critical point (31.1 °C, 7.38 MPa) of the refrigerant. Therefore, a refrigeration device having a two-stage compression mechanism and a gas-liquid separator and using carbon dioxide as a refrigerant may have a small desired compression ratio of the low-stage compressor during pull-down operation with a high evaporation temperature of the refrigerant, resulting in insufficient refrigeration capacity.

[0078] The refrigeration device 100 of the present embodiment can perform two-stage compression operation and single-stage compression / gas extraction operation. The control unit 70 of the refrigeration device 100 can mutually switch between a first state in which two-stage compression operation is performed and a second state in which single-stage compression / gas extraction operation is performed by controlling the gas extraction valve 41 and the first shut-off valve 43.

[0079] During the pull-down operation of the refrigeration device 100, since high refrigeration capacity is required, it is necessary to maintain a high pressure of the refrigerant on the high-pressure side of the refrigeration cycle. The refrigeration device 100 can sufficiently ensure the compression ratio of the first compressor 21 as shown in FIG. 4 by performing a single-stage compression / gas extraction operation during the pull-down operation. Therefore, the refrigeration device 100 can maintain a high pressure of the refrigerant on the high-pressure side of the refrigeration cycle during the pull-down operation.

[0080] Therefore, the refrigeration device 100 can suppress a decrease in refrigeration capacity due to insufficiently ensuring the compression ratio of the first compressor 21 on the low-stage side during the pull-down operation.

[0081] (4-2) When the load of the first compressor 21 increases while the refrigerant circuit 10 is in the second state, the control unit 70 switches the refrigeration device 100 from the second state in which the single-stage compression / gas extraction operation is performed to the first state in which the two-stage compression operation is performed. When the control unit 70 determines that the above-described first condition is satisfied, the control unit 70 performs the switching from the second state to the first state. The first condition is satisfied when the temperature of the refrigerant sucked into the first compressor 21 (the evaporation temperature of the refrigerant) drops to a predetermined value and the temperature of the refrigerant discharged from the first compressor 21 rises to a predetermined value.

[0082] The control unit 70 may use the fourth temperature measured by the fourth temperature sensor 64 as the temperature of the refrigerant sucked into the first compressor 21. The control unit 70 may use the fifth temperature measured by the fifth temperature sensor 65 as the temperature of the refrigerant discharged from the first compressor 21. In this case, when the control unit 70 detects that the first condition is satisfied during the single-stage compression / gas extraction operation, the control unit 70 controls the gas extraction valve 41 and the first shut-off valve 43 to perform the switching from the second state to the first state. Thereby, the refrigeration device 100 stops the single-stage compression / gas extraction operation and starts the two-stage compression operation.

[0083] When the refrigeration device 100 performs a single-stage compression / gas extraction operation during pull-down operation, the evaporation temperature of the refrigerant decreases, the compression ratio of the first compressor 21 increases, and the temperature of the refrigerant on the high-pressure side of the refrigeration cycle (the temperature of the refrigerant discharged from the first compressor 21) increases. As a result, the load on the first compressor 21 increases, and there is a risk that the reliability of the first compressor 21 will decrease. When the refrigeration device 100 determines that the compression ratio of the first compressor 21 has become sufficiently large and the temperature of the refrigerant discharged from the first compressor 21 has become sufficiently high during the execution of the single-stage compression / gas extraction operation, the refrigeration device 100 stops the single-stage compression / gas extraction operation and starts a two-stage compression operation.

[0084] Therefore, the refrigeration device 100 can reduce the load on the low-stage first compressor 21 during the execution of the single-stage compression / gas extraction operation, and suppress a decrease in the reliability of the first compressor 21. Thereby, since the refrigeration device 100 can effectively utilize the first compressor 21, it is possible to adopt the first compressor 21 having a small capacity, and it is possible to reduce costs and power consumption.

[0085] (4-3) When the load on the second compressor 22 increases while the refrigerant circuit 10 is in the first state, the control unit 70 switches the refrigeration device 100 from the first state in which the refrigeration device 100 performs a two-stage compression operation to the second state in which the refrigeration device 100 performs a single-stage compression / gas extraction operation. When the control unit 70 determines that the above-described second condition is satisfied, the control unit 70 performs the switching from the first state to the second state. The second condition is satisfied when the temperature of the refrigerant sucked into the first compressor 21 (the evaporation temperature of the refrigerant) rises to a predetermined value, or when the rotational speed of the first compressor 21 falls below the rotational speed of the second compressor 22.

[0086] The control unit 70 may use the fourth temperature measured by the fourth temperature sensor 64 as the temperature of the refrigerant sucked into the first compressor 21. In this case, when the control unit 70 detects that the second condition has been satisfied during the two-stage compression operation, the control unit 70 controls the gas extraction valve 41 and the first shut-off valve 43 to perform the switching from the first state to the second state. Thereby, the refrigeration device 100 stops the two-stage compression operation and starts the single-stage compression / gas extraction operation.

[0087] While the refrigeration device 100 is performing two-stage compression operation, the temperature of the refrigerant sucked into the first compressor 21 (the evaporation temperature of the refrigerant) may gradually increase. Since the pressure of the refrigerant in the gas-liquid separator 26 (the pressure of the refrigerant at the intermediate pressure) needs to be lower than the critical pressure of the refrigerant (7.38 MPa), it needs to be suppressed to about 7 MPa at most. Therefore, when the evaporation temperature of the refrigerant increases during two-stage compression operation, the compression ratio of the first compressor 21 may decrease. When the refrigeration device 100 determines that the temperature of the refrigerant sucked into the first compressor 21 has become sufficiently high during the execution of two-stage compression operation, it stops the two-stage compression operation and starts a single-stage compression / gas extraction operation.

[0088] Therefore, the refrigeration device 100 can sufficiently ensure the compression ratio of the first compressor 21 on the low-stage side and suppress a decrease in refrigeration capacity.

[0089] Also, while the refrigeration device 100 is performing two-stage compression operation, the rotational speed of the first compressor 21 may be lower than the rotational speed of the second compressor 22, and the load on the second compressor 22 may become excessive. In this case, by performing a gas extraction operation on the second compressor 22, the load on the second compressor 22 can be reduced. When the refrigeration device 100 determines that the rotational speed of the first compressor 21 is lower than the rotational speed of the second compressor 22 during the execution of two-stage compression operation, it stops the two-stage compression operation and starts a single-stage compression / gas extraction operation.

[0090] Therefore, the refrigeration device 100 can reduce the load on the second compressor 22 on the high-stage side during the execution of two-stage compression operation and suppress a decrease in the reliability of the second compressor 22. As a result, since the refrigeration device 100 can effectively utilize the second compressor 22, it can adopt a second compressor 22 with a small capacity, and can reduce costs and power consumption.

[0091] (4-4) When the refrigeration device 100 executes a single-stage compression / gas extraction operation, the refrigerant at the outlet of the heat source side heat exchanger 23 is cooled by heat exchange with the gas refrigerant separated by the gas-liquid separator 26 using the intermediate heat exchanger 27. As a result, the dryness of the refrigerant decompressed by passing through the first heat source side expansion valve 25a decreases.

[0092] Therefore, the refrigeration device 100 can suppress a shortage of the refrigerant sucked into the first compressor 21 on the low-stage side.

[0093] (4-5) The refrigeration device 100 can determine whether to perform a single-stage compression / gas extraction operation or a two-stage compression operation according to the outside air temperature and the temperature of the target space. The control unit 70 may use the second temperature measured by the second temperature sensor 62 as the outside air temperature. The control unit 70 may use the third temperature measured by the third temperature sensor 63 as the temperature of the target space. In this case, when the second temperature is equal to or higher than a predetermined value and the difference between the second temperature and the third temperature is equal to or less than a predetermined value at the time of starting the refrigeration device 100, the control unit 70 starts a single-stage compression / gas extraction operation as a pull-down operation. Further, when the second temperature is less than a predetermined value or the difference between the second temperature and the third temperature is greater than a predetermined value at the time of starting the refrigeration device 100, the control unit 70 starts a two-stage compression operation for the pull-down operation.

[0094] Therefore, the refrigeration device 100 can suppress a decrease in refrigerating capacity by performing a pull-down operation in consideration of the balance between the load of the first compressor 21 on the low-stage side and the load of the second compressor 22 on the high-stage side.

[0095] - Second Embodiment - The basic configuration and operation of the refrigeration device 100 of the present embodiment are the same as those of the refrigeration device 100 of the first embodiment. Hereinafter, the description will focus on the differences between the refrigeration device 100 of the present embodiment and the refrigeration device 100 of the first embodiment.

[0096] (1) Configuration of the refrigeration device 100 The refrigeration device 100 of the present embodiment has the configuration shown in FIG. 1, similar to the first embodiment. The control unit 70 of the refrigeration device 100 of the present embodiment has the configuration shown in FIG. 2, similar to the first embodiment.

[0097] (2) Operation of the refrigeration device 100 During the operation of the refrigeration device 100, the refrigerant circuit 10 takes one of the first state, the second state, and the third state. The first state is a state in which the refrigeration device 100 performs two-stage compression operation shown in FIG. 3, similar to the first embodiment. The second state is a state in which the refrigeration device 100 performs single-stage compression / gas extraction operation shown in FIG. 4, similar to the first embodiment.

[0098] FIG. 5 is a Mollier diagram when the refrigerant circuit 10 takes the third state. In FIG. 5, a saturated liquid line L1, a dry saturated vapor line L2, and a critical point CP of the refrigerant are drawn. 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 third state is a state in which the refrigeration device 100 performs single-stage compression operation. In the third state, gas extraction operation is not performed. In the third state, the gas extraction valve 41 and the first shut-off valve 43 are closed.

[0099] Next, the change in the state of the refrigerant in the third state will be described.

[0100] 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 a high-pressure refrigerant (P1→P2). The high-pressure refrigerant discharged from the first compressor 21 flows into the heat source side heat exchanger 23. The high-pressure refrigerant flowing into the heat source side heat exchanger 23 exchanges heat with the outside air and dissipates heat (P2→P3).

[0101] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 is depressurized by the first heat source side expansion valve 25a to become a refrigerant at an intermediate pressure (P3→P4). 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 (P4→P5, P6). The liquid refrigerant separated by the gas-liquid separator 26 is further depressurized by the second heat source side expansion valve 25b to become a low-pressure refrigerant (P5→P7). The liquid refrigerant depressurized by the second heat source side expansion valve 25b passes through the liquid side shut-off valve 28 and the liquid side refrigerant connection pipe 6 and flows into the utilization unit 3, and then 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 where the utilization unit 3 is installed, absorbs heat, and becomes a gas refrigerant (P7→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 has flowed into the heat source unit 2 is sucked into the first compressor 21.

[0102] (3) Control of the refrigeration device 100 When starting the first compressor 21 and the second compressor 22, the control unit 70 switches the state of the refrigerant circuit 10 in the order of the third state, the second state, and the first state. Specifically, when the refrigeration device 100 starts up, the control unit 70 controls the gas vent valve 41 and the first shut-off valve 43 so that the refrigeration device 100 performs single-stage compression operation, single-stage compression / gas venting operation, and two-stage compression operation in this order. When the refrigeration device 100 is in the state of performing single-stage compression operation, the control unit 70 performs control to open the gas vent valve 41 to stop the single-stage compression operation and start the single-stage compression / gas venting operation.

[0103] (4) Effect of the refrigeration device 100 Immediately after the refrigeration device 100 starts up, since the amount of refrigerant on the high-pressure side of the refrigeration cycle is small, the amount of gas refrigerant in the gas-liquid separator 26 is small. Therefore, when the amount of refrigerant on the high-pressure side of the refrigeration cycle is small at startup, the refrigeration device 100 does not perform gas venting operation, and starts gas venting operation after a predetermined time has elapsed after startup and the amount of refrigerant on the high-pressure side of the refrigeration cycle has increased to a predetermined amount. Thereby, the refrigeration device 100 can reduce the load on the second compressor 22 due to the gas venting operation and suppress the decrease in refrigeration capacity.

[0104] - Third Embodiment - The basic configuration and operation of the refrigeration device 200 in this embodiment are the same as those of the refrigeration device 100 in the first embodiment. Hereinafter, the description will focus on the differences between the refrigeration device 200 in this embodiment and the refrigeration device 100 in the first embodiment.

[0105] (1) Configuration of Refrigeration Device 200 The main differences between the refrigeration device 200 and the refrigeration device 100 in the first embodiment are the heat source unit 2 and the control unit 70.

[0106] As shown in FIG. 6, the heat source unit 2 of the refrigeration device 200 is the heat source unit 2 of the refrigeration device 100 in the first embodiment, and has a configuration in which a seventh pipe 57, a liquid injection valve 42, an oil return pipe 58, and an oil separator 60 are further added.

[0107] 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 connection part with the second pipe 52 and the intermediate heat exchanger 27.

[0108] 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 the control of the control unit 70.

[0109] The oil return pipe 58 is a pipe through which the refrigerant circulating in the refrigerant circuit 10 flows. The oil return pipe 58 connects the second pipe 52 and the third pipe 53. One end of the oil return pipe 58 is connected to the second pipe 52 between the connection part with the sixth pipe 56 and the second compressor 22. The other end of the oil return pipe 58 is connected to the third pipe 53 between the connection part with the bypass pipe 59 and the heat source side heat exchanger 23.

[0110] The oil separator 60 is provided in the oil return pipe 58. The oil separator 60 separates the refrigerating machine oil from the mixture of the refrigerant and the refrigerating machine oil.

[0111] As shown in FIG. 7, the actuator control unit 74 of the control unit 70 has a function of controlling in real time the rotational speed of the first compressor 21, the rotational speed of the second compressor 22, the rotational 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 rotational speed of the utilization side fan 32, the opening degree of the gas vent valve 41, the opening degree of the liquid injection valve 42, and the opening degree of the first shut-off valve 43.

[0112] (2) Operation of the refrigeration device 200 In the refrigeration device 200, a part of the liquid refrigerant separated by the gas-liquid separator 26 flows into the seventh pipe 57 together with the refrigerating machine oil in the refrigerant circuit 10. The refrigerant and the refrigerating machine oil that have passed through the liquid injection valve 42 in the seventh pipe 57 merge with the refrigerant that has flowed through the sixth pipe 56 and has been heat-exchanged by the intermediate heat exchanger 27. As a result, the mixture of the refrigerant and the refrigerating machine oil flows into the second pipe 52 via the seventh pipe 57 and the sixth pipe 56.

[0113] Also, a part of the gas refrigerant discharged from the first compressor 21 and the second compressor 22 flows through the third pipe 53 and flows into the oil return pipe 58 together with the refrigerating machine oil in the refrigerant circuit 10. As a result, the mixture of the refrigerant and the refrigerating machine oil flows through the oil return pipe 58. The mixture of the refrigerant and the refrigerating machine oil flows into the oil separator 60 provided in the oil return pipe 58. In the oil separator 60, the refrigerating machine oil is separated from the mixture of the refrigerant and the refrigerating machine oil. The refrigerating machine oil separated by the oil separator 60 flows through the oil return pipe 58 and flows into the second pipe 52.

[0114] In this way, in the refrigeration device 200, in the heat source unit 2, the refrigerating machine oil mixed with the refrigerant discharged from the first compressor 21 and the second compressor 22 is returned to the suction side of the second compressor 22.

[0115] (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. Further, during the operation of the refrigeration device 200, the control unit 70 controls the opening degree of the liquid injection valve 42 to adjust the amount of the mixture of the refrigerant and the refrigeration oil flowing through the seventh pipe 57.

[0116] (4) Effects of the refrigeration device 200 The refrigeration device 200 can return the refrigeration oil flowing through the refrigerant circuit 10 to the suction side of the second compressor 22. Therefore, the refrigeration device 200 can suppress the shortage of the refrigeration oil in the second compressor 22.

[0117] - Modification example - (1) Modification example A The refrigeration devices 100 and 200 of the first to third embodiments may further perform a degassing operation when the refrigerant circuit 10 is in the first state. In other words, the refrigeration devices 100 and 200 may perform both the two-stage compression operation and the degassing operation simultaneously. In this case, the control unit 70 can perform both the two-stage compression operation and the degassing operation simultaneously by opening both the degassing valve 41 and the first shut-off valve 43.

[0118] In this modification example, while the refrigeration devices 100 and 200 are performing both the two-stage compression operation and the degassing operation simultaneously, in the intermediate heat exchanger 27, the gas refrigerant separated by the gas-liquid separator 26 is heated 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 flows into the second pipe 52 and is mixed with the refrigerant before being sucked into the second compressor 22. As a result, the superheat degree of the refrigerant sucked into the second compressor 22 increases, so the temperature of the refrigerant discharged from the second compressor 22 increases. Therefore, the refrigeration devices 100 and 200 can increase the difference between the first temperature and the second temperature and keep the performance of the heat source side heat exchanger 23 high.

[0119] (2) Modification example B (2-1) Configuration of the refrigeration device 300 The refrigeration apparatuses 100 and 200 according to the first to third embodiments may not include the gas-liquid separator 26. The refrigeration apparatus 300 of this modification example is the refrigeration apparatus 100 of the first embodiment and does not include the gas-liquid separator 26. 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.

[0120] As shown in FIG. 8, the heat source unit 2 includes 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, a cooler 127, a liquid side shut-off valve 28, a gas side shut-off valve 29, a pressure reducing valve 141, a first shut-off valve 43, and a second shut-off valve 44.

[0121] The heat source unit 2 has first to sixth pipes 51 to 56 which are pipes through which the refrigerant circulating in the refrigerant circuit 10 flows. The first to third pipes 51 to 53 are the same as the first to third pipes 51 to 53 of the first embodiment. 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 shut-off valve 28. The sixth pipe 56 connects the fourth pipe 54 and the second pipe 52.

[0122] 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 apparatus 300 and decompresses the high-pressure refrigerant in the refrigeration cycle until it becomes a low-pressure refrigerant.

[0123] The pressure reducing valve 141 is provided in the sixth pipe 56. The pressure reducing valve 141 decompresses the high-pressure refrigerant in the refrigeration cycle until it becomes an intermediate-pressure refrigerant. The pressure reducing valve 141 adjusts the amount of liquid refrigerant flowing through the sixth pipe 56. The pressure reducing valve 141 is an electric expansion valve whose opening degree can be adjusted by control by the control unit 70.

[0124] The cooler 127 performs heat exchange between the refrigerant after being radiated by the heat source side heat exchanger 23 and then depressurized by the pressure reducing valve 141, and the refrigerant after being radiated by the heat source side heat exchanger 23 and before being depressurized by the second heat source side expansion valve 25b.

[0125] The actuator control unit 74 of the control unit 70 has a function of controlling in real time the rotational speed of the first compressor 21, the rotational speed of the second compressor 22, the rotational speed of the heat source side fan 24, the opening degree of the second heat source side expansion valve 25b, the rotational speed of the utilization side fan 32, the opening degree of the pressure reducing valve 141, and the opening degree of the first shut-off valve 43.

[0126] In the gas venting operation performed by the refrigeration device 300, the intermediate pressure refrigerant depressurized by the pressure reducing valve 141 and heated by heat exchange in the cooler 127 flows through the sixth pipe 56 and the second pipe 52 and is sucked into the second compressor 22. The gas venting operation performed by the refrigeration device 300 has the same effect as the gas venting operation performed by the refrigeration devices 100 and 200 of the first to third embodiments.

[0127] (2-2) Operation of the refrigeration device 300 During the operation of the refrigeration device 300, the refrigerant circuit 10 takes either one of the first state and the second state. The first state is a state in which the refrigeration device 300 performs two-stage compression operation. The second state is a state in which the refrigeration device 300 performs single-stage compression / gas venting operation. In the first state, the pressure reducing valve 141 is closed and the first shut-off valve 43 is opened. In the second state, the pressure reducing valve 141 is opened and the first shut-off valve 43 is closed.

[0128] FIG. 9 is a Mollier diagram when the refrigerant circuit 10 takes the second state. In FIG. 9, a saturated liquid line L1, a dry saturated vapor line L2, and a critical point CP of the refrigerant are drawn. The critical point CP is the end point on the high pressure side of the saturated liquid line L1 and the dry saturated vapor line L2.

[0129] Next, the change in the state of the refrigerant in the second state will be described.

[0130] 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 a high-pressure refrigerant (P1→P2). The high-pressure refrigerant discharged from the first compressor 21 merges with the high-pressure refrigerant discharged from the second compressor 22 and flows into the heat source side heat exchanger 23. The high-pressure refrigerant flowing into the heat source side heat exchanger 23 exchanges heat with the outside air and dissipates heat (P2→P3).

[0131] The refrigerant that has dissipated heat in the heat source side heat exchanger 23 flows through the fourth pipe 54 and then branches into the fifth pipe 55 and the sixth pipe 56. The refrigerant flowing through the fifth pipe 55 is decompressed by the decompression valve 141 and flows into the cooler 127 (P3→P4). The refrigerant flowing through the sixth pipe 56 flows into the cooler 127 before being decompressed by the second heat source side expansion valve 25b. In the cooler 127, heat exchange is performed between the refrigerant decompressed by the decompression valve 141 and flowing through the fifth pipe 55 and the refrigerant flowing through the sixth pipe 56. The refrigerant flowing through the fifth pipe 55 is heated by the heat exchange (P4→P5). The refrigerant flowing through the sixth pipe 56 is cooled by the heat exchange (P3→P6).

[0132] The refrigerant flowing through the sixth pipe 56 is cooled in the cooler 127 and then decompressed by the second heat source side expansion valve 25b to become a low-pressure refrigerant (P6→P7). The liquid refrigerant decompressed by the second heat source side expansion valve 25b passes through the liquid side shut-off valve 28 and the liquid side refrigerant connection pipe 6 and flows into the utilization unit 3, and then flows into the utilization side heat exchanger 31. The low-pressure liquid refrigerant flowing into the utilization side heat exchanger 31 exchanges heat with the air in the target space where the utilization unit 3 is installed, absorbs heat, and becomes a gas refrigerant (P7→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 flowing into the heat source unit 2 is sucked into the first compressor 21.

[0133] The refrigerant flowing through the fifth pipe 55 is heated in the cooler 127, then flows through the second pipe 52, and is compressed in the second compressor 22 to become a high-pressure refrigerant (P5→P8). The refrigerant compressed by the second compressor 22 merges with the refrigerant compressed by the first compressor 21 before flowing into the heat source side heat exchanger 23 (P8→P2).

[0134] The second embodiment and Modification Example A are applicable to this modification example. The oil return pipe 58 and the oil separator 60 of the third embodiment are applicable to this modification example.

[0135] (3) Modification Example C The refrigeration devices 200 of the third embodiment, Modification Example A, and Modification Example B include a seventh pipe 57 and an oil return pipe 58 for returning the refrigeration machine oil from the discharge side to the suction side of the second compressor 22. However, the refrigeration device 200 may include only one of the seventh pipe 57 and the oil return pipe 58.

[0136] (4) Modification Example D The refrigeration devices 100 and 200 of the first to third embodiments, Modification Example A, and Modification Example C may not include the intermediate heat exchanger 27.

[0137] (5) Modification Example E In the first to third embodiments and Modification Examples A to D, the first shut-off valve 43 and the second shut-off valve 44 may be any members that can switch the state (the first to third states) of the refrigerant circuit 10. For example, a three-way switching valve or a four-way switching valve may be used as the first shut-off valve 43 and the second shut-off valve 44.

[0138] As described above, the embodiments of the present disclosure have been described. It will be understood that various changes in form and details are possible without departing from the spirit and scope of the present disclosure described in the claims.

Explanation of Reference Numerals

[0139] 10: Refrigerant circuit 21: First compressor 22: Second compressor 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 (fourth heat exchanger) 31: Utilization side heat exchanger (second heat exchanger) 41: Gas vent valve (third valve) 43: First shut-off valve (first valve) 44: Second shut-off valve (second valve) 52: Second pipe (second flow path) 56: Sixth pipe (first flow path) 57: Seventh pipe (fourth flow path) 58: Oil return pipe (fifth flow path) 59: Bypass pipe (third flow path) 60: Oil separator 70: Control unit 100: Refrigeration device 127: Cooler (third heat exchanger) 141: Pressure reducing mechanism (pressure reducing valve) 200: Refrigeration device 300: Refrigeration device

Prior art documents

Patent documents

[0140]

Patent Document 1

Claims

1. A refrigerant circuit (10) is formed in which a first compressor (21), a second compressor (22), a first heat exchanger (23), expansion mechanisms (25a, 25b), and a second heat exchanger (31) are connected in sequence. A control unit (70) that switches the refrigerant circuit between a first state and a second state, Equipped with, The first heat exchanger functions as a heat exchanger for the refrigerant compressed by the first compressor or the second compressor. The second heat exchanger functions as a heat absorber for the refrigerant that has been depressurized by the expansion mechanism. The aforementioned refrigerant circuit is A gas-liquid separator (26) or a third heat exchanger (127), A first valve (43) is positioned, and a main passage (52) connects the discharge side of the first compressor and the suction side of the second compressor, A branch channel (56) connecting the gas-liquid separator or the third heat exchanger and the main channel, A bypass passage (59) connects the main passage (52) and the discharge side of the second compressor, bypassing the first valve, It has, The gas-liquid separator separates the gas-liquid two-phase refrigerant, which has been depressurized by the expansion mechanism, into liquid refrigerant and gaseous refrigerant. The third heat exchanger performs heat exchange between the refrigerant that has been depressurized by the depressurization mechanism (141) after heat has been released in the first heat exchanger, and the refrigerant that has been released in the first heat exchanger but has not yet been depressurized by the expansion mechanism. The control unit opens the first valve when in the first state and closes the first valve when in the second state. The control unit switches the refrigerant circuit from the second state to the first state when the temperature of the refrigerant drawn into the first compressor drops to a first value and the temperature of the refrigerant discharged from the first compressor rises to a second value, while the refrigerant circuit is in the second state. Refrigeration device (100).

2. The branching channel is provided with a second valve (41, 141), The control unit, When switching the refrigerant circuit from the second state to the first state, the second valve is closed and the first valve is opened. When switching the refrigerant circuit from the first state to the second state, the second valve is opened and the first valve is closed. The refrigeration apparatus according to claim 1.

3. The control unit switches the refrigerant circuit from the first state to the second state when the temperature of the refrigerant drawn into the first compressor rises to a third value, or when the rotational speed of the first compressor falls below the rotational speed of the second compressor, while the refrigerant circuit is in the first state. The refrigeration apparatus according to claim 1 or 2.

4. The control unit switches the refrigerant circuit between the first state, the second state, and the third state. The control unit closes the first valve and the second valve when the third state is reached. The refrigeration apparatus according to claim 2.

5. The control unit switches the refrigerant circuit in the order of the third state, the second state, and the first state when the first and second compressors are started. The refrigeration apparatus according to claim 4.

6. The main flow path is composed of a first main flow path from the discharge side of the first compressor to the first valve, and a second main flow path from the first valve to the suction side of the second compressor, In the first state, the refrigerant discharged from the first compressor flows through the main passage and is drawn into the second compressor. In the second state, the refrigerant discharged from the first compressor flows through the first main flow path and the bypass flow path, and merges with the refrigerant discharged from the second compressor. A refrigeration apparatus according to any one of claims 1 to 5.

7. The bypass passage is configured such that a third valve (44) is located A refrigeration apparatus according to any one of claims 1 to 6.

8. An intake-side temperature sensor (64) is disposed on the intake side of the first compressor, A discharge-side temperature sensor (65) is located on the discharge side of the first compressor, Furthermore, The control unit switches the refrigerant circuit between the first state and the second state using the temperatures measured by the intake side temperature sensor and the discharge side temperature sensor. A refrigeration apparatus according to any one of claims 1 to 7.

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