Refrigeration device

Abstract

This refrigeration device (10) comprises: a first refrigerant circuit (21) that includes a first heat exchanger (26) that dissipates heat from a first refrigerant, which is carbon dioxide; a second refrigerant circuit (22) that includes a second heat exchanger (36) that dissipates heat from a second refrigerant having combustibility or toxicity, or a second refrigerant having a global warming potential of 4 or more, and a pressure reducer (38) that decompresses the second refrigerant; and a third heat exchanger (27) that exchanges heat between the first refrigerant after has been dissipated therefrom by the first heat exchanger (26) and the second refrigerant decompressed by the pressure reducer (38) after heat has been dissipated therefrom by the second heat exchanger (36). The second heat exchanger (36) has a plurality of flat multi-hole pipes (36b).

Description

Refrigeration equipment

[0001] The present disclosure relates to refrigeration devices.

[0002] Patent Document 1 discloses a cascade refrigeration system having a low-stage refrigeration cycle and a high-stage refrigeration cycle. The low-stage refrigeration cycle is used to adjust the temperature of an indoor load device, such as a showcase. Therefore, the low-stage refrigeration cycle uses a refrigerant such as carbon dioxide, which has a low global warming potential, because the refrigerant circuit may be opened due to, for example, rearrangement of the showcase, which may result in refrigerant leakage. In contrast, the high-stage refrigeration cycle is used to further cool the refrigerant cooled by the radiator of the low-stage refrigeration cycle. Unlike the refrigerant circuit of the low-stage refrigeration cycle, the refrigerant circuit of the high-stage refrigeration cycle is never opened, so a refrigerant such as R32, which has a higher global warming potential but higher heat exchange efficiency than the refrigerant of the low-stage refrigeration cycle, is used.

[0003] International Publication No. 2014 / 181399

[0004] Refrigerants such as R32 used in high-temperature refrigeration cycles can be flammable and toxic, so it is desirable to use as little of them as possible.

[0005] The present disclosure aims to reduce the amount of flammable or toxic refrigerant used in a refrigeration system having two refrigerant circuits using different refrigerants.

[0006] (1) The refrigeration device of the present disclosure comprises: a first refrigerant circuit including a first heat exchanger that dissipates heat from a first refrigerant that is carbon dioxide; a second refrigerant circuit including a second heat exchanger that dissipates heat from a second refrigerant that is flammable or toxic, or a second refrigerant that has a global warming potential (GWP) of 4 or more, and a pressure reducer that reduces the pressure of the second refrigerant; and a third heat exchanger that exchanges heat between the first refrigerant after dissipating heat in the first heat exchanger and the second refrigerant that has dissipated heat in the second heat exchanger and then been reduced in pressure by the pressure reducer, wherein the second heat exchanger has a plurality of flat multi-hole tubes.

[0007] This configuration allows the second heat exchanger with flat multi-hole tubes to perform heat exchange more efficiently than a heat exchanger with typical circular heat transfer tubes, thereby reducing the amount of refrigerant used and reducing the risk of leakage of a flammable or toxic second refrigerant or a second refrigerant with a GWP of 4 or more.

[0008] (2) In the refrigeration device of (1) above, preferably, the refrigeration device further comprises a control device that controls the operation of the first refrigerant circuit and the second refrigerant circuit, and a fan that generates an air flow to be supplied to the first heat exchanger and the second heat exchanger, wherein the first heat exchanger and the second heat exchanger are arranged side by side in the flow direction of the air flow generated by the fan, and the control device operates both the first refrigerant circuit and the second refrigerant circuit to execute a first mode in which the first heat exchanger dissipates heat from the first refrigerant and the second heat exchanger dissipates heat from the second refrigerant, and a second mode in which the first refrigerant circuit is operated alone to evaporate the first refrigerant by the first heat exchanger.

[0009] The flat multi-hole tubes of the second heat exchanger have an elongated cross-sectional shape in the direction of the air flow and are less likely to provide resistance to the air flow, so in the second mode in which the first refrigerant circuit is operated alone, a decrease in heat exchange efficiency in the first heat exchanger can be suppressed.

[0010] (3) In the refrigeration device of (1) or (2) above, the second heat exchanger preferably includes a plurality of the flat multi-hole tubes and serpentine fins arranged between adjacent flat multi-hole tubes.

[0011] The second heat exchanger having serpentine fins (so-called corrugated fins) has poor drainage of water that has entered the corrugated fins. In the refrigeration apparatus of the present disclosure, the second heat exchanger is used as a radiator that radiates heat from the refrigerant, so that the water that has entered the second heat exchanger can be prevented from freezing.

[0012] (4) In the refrigeration device described in any one of (1) to (3) above, preferably, the amount of the second refrigerant used in the second refrigerant circuit is 1000 g or less.

[0013] According to this configuration, by using a flat multi-hole pipe, it is possible to reduce the amount of second refrigerant used to 1000 g or less, thereby reducing the risk of leakage.

[0014] (5) In the refrigeration apparatus according to any one of (4) above, preferably, the amount of the second refrigerant used in the second refrigerant circuit is 150 g or less.

[0015] According to the above configuration, by using a flat multi-hole pipe, it is possible to reduce the amount of second refrigerant used to 150 g or less, thereby further reducing the risk of leakage.

[0016] Fig. 1 is a refrigerant circuit diagram of a refrigeration device according to an embodiment of the present disclosure. Fig. 2 is a plan view showing the interior of an outdoor unit in the refrigeration device. Fig. 3 is a side view showing the interior of the outdoor unit in the refrigeration device. Fig. 4 is an explanatory diagram schematically showing a first outdoor heat exchanger in the refrigeration device. Fig. 5 is an explanatory diagram schematically showing a second outdoor heat exchanger in the refrigeration device. Fig. 6 is an enlarged cross-sectional view of the second outdoor heat exchanger. Fig. 7 is a Mollier diagram for explaining the refrigeration cycle of a first refrigerant circuit during cooling operation.

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. (Overall Configuration of Refrigeration Device) Fig. 1 is a refrigerant circuit diagram of a refrigeration device according to one embodiment of the present disclosure. As shown in Fig. 1, the refrigeration device 10 of this embodiment is an air conditioner that adjusts the temperature of air in a room, which is a space to be air-conditioned, to a predetermined target temperature. The refrigeration device 10 of this embodiment performs cooling and heating of the room. However, the refrigeration device 10 may also be dedicated to cooling. The refrigeration device 10 may also be a refrigerator, freezer, or the like that cools the air inside the refrigerator.

[0018] The refrigeration device 10 has an outdoor unit 11 (heat source unit) and an indoor unit 12 (utilization unit). The refrigeration device 10 has, for example, one outdoor unit 11 and one indoor unit 12 connected to the outdoor unit 11. However, the refrigeration device 10 may have multiple indoor units 12 connected in parallel to the outdoor unit 11. The refrigeration device 10 may be equipped with multiple outdoor units 11.

[0019] The refrigeration system 10 has a first refrigerant circuit 21 and a second refrigerant circuit 22. The first refrigerant circuit 21 circulates a first refrigerant, and the second refrigerant circuit 22 circulates a second refrigerant. In this embodiment, carbon dioxide is used as the first refrigerant. In this embodiment, a flammable or toxic refrigerant or a refrigerant with a high global warming potential (GWP) is used as the second refrigerant. For example, R290 (propane) is used as the second refrigerant. The refrigeration system 10 further has an auxiliary heat exchanger 27, a control device 51, an outdoor fan 41, and an indoor fan 42.

[0020] (Configuration of First Refrigerant Circuit 21) The first refrigerant circuit 21 circulates a first refrigerant between the indoor unit 12 and the outdoor unit 11. The first refrigerant circuit 21 includes a first compressor 24, a four-way switching valve 25, a first outdoor heat exchanger (heat source heat exchanger; first heat exchanger) 26, a first expansion valve 28, a first shut-off valve 29, an indoor heat exchanger (utilization heat exchanger) 30, a second shut-off valve 31, a first accumulator 32, and refrigerant piping 40 connecting these components.

[0021] The outdoor unit 11 includes a first compressor 24, a four-way switching valve 25, a first outdoor heat exchanger 26, a first expansion valve 28, a first shut-off valve 29, a second shut-off valve 31, and a first accumulator 32, which constitute a first refrigerant circuit 21. The indoor unit 12 includes an indoor heat exchanger 30, which constitutes the first refrigerant circuit 21. The outdoor unit 11 is provided with an outdoor fan 41 that takes in outdoor air into the outdoor unit 11 and supplies it to the first outdoor heat exchanger 26. The indoor unit 12 is provided with an indoor fan 42 that takes in indoor air into the indoor unit 12 and supplies it to the indoor heat exchanger 30.

[0022] The first compressor 24 draws in a low-pressure gaseous first refrigerant and discharges a high-pressure gaseous first refrigerant. The first compressor 24 is equipped with a motor whose operating speed can be adjusted by inverter control. The first compressor 24 is a variable displacement type (variable capacity type) whose capacity (capacity) can be changed by inverter control of the motor. However, the first compressor 24 may also be a fixed displacement type. A plurality of first compressors 24 may be provided. In this case, variable displacement compressors and fixed displacement compressors may be mixed.

[0023] The four-way switching valve 25 reverses the flow of the first refrigerant in the refrigerant pipe 40, and switches the first refrigerant discharged from the first compressor 24 to be supplied to either the first outdoor heat exchanger 26 or the indoor heat exchanger 30. This allows the refrigeration system 10 to switch between cooling operation and heating operation.

[0024] The first outdoor heat exchanger 26 is a cross-fin tube type heat exchanger. The first outdoor heat exchanger 26 exchanges heat between the first refrigerant and outdoor air taken in by the outdoor fan 41, thereby dissipating heat or evaporating the first refrigerant. The first outdoor heat exchanger 26 may be a microchannel type heat exchanger similar to the second outdoor heat exchanger 36 described below.

[0025] The first expansion valve 28 is a pressure reducer that reduces the pressure of the first refrigerant to expand it. The first expansion valve 28 is configured as an electric valve that can adjust the refrigerant flow rate, etc. The first expansion valve 28 reduces the pressure of the high-pressure gaseous first refrigerant that has dissipated heat in the first outdoor heat exchanger 26 and an auxiliary heat exchanger 27 (described later) to expand it, thereby converting it into a low-pressure gas-liquid two-phase refrigerant. A capillary tube may be used as the pressure reducer instead of the first expansion valve 28.

[0026] The first shut-off valve 29 is a manually operated on-off valve that blocks the flow of the first refrigerant through the refrigerant pipe 40 when closed, and allows the flow of the first refrigerant through the refrigerant pipe 40 when open.

[0027] The indoor heat exchanger 30 is, for example, a cross-fin tube type or a microchannel type heat exchanger. The indoor heat exchanger 30 exchanges heat between the first refrigerant and the indoor air taken in by the indoor fan 42, thereby dissipating heat or evaporating the first refrigerant.

[0028] The second shutoff valve 31 is a manually operated on-off valve. When closed, the second shutoff valve 31 blocks the flow of the first refrigerant through the refrigerant pipe 40, and when open, the second shutoff valve 31 allows the flow of the first refrigerant through the refrigerant pipe 40.

[0029] The first accumulator 32 is provided in the suction pipe of the first compressor 24. The first accumulator 32 temporarily stores the low-pressure first refrigerant before it is drawn into the first compressor 24, and separates the first refrigerant into gas refrigerant and liquid refrigerant. The first refrigerant that is the gas refrigerant separated in the first accumulator 32 is drawn into the first compressor 24.

[0030] (Configuration of second refrigerant circuit 22) The second refrigerant circuit 22 circulates a refrigerant inside the outdoor unit 11. The second refrigerant circuit 22 uses R290 (propane) as a second refrigerant. The second refrigerant circuit 22 includes a second compressor 34, a second outdoor heat exchanger (second heat exchanger) 36, a second expansion valve 38, a second accumulator 39, and refrigerant piping 50 connecting these components.

[0031] The second compressor 34 draws in a low-pressure gaseous second refrigerant and discharges a high-pressure gaseous second refrigerant. The second compressor 34 is equipped with a motor whose operating rotation speed can be adjusted by inverter control. The second compressor 34 is a variable displacement type (variable capacity type) whose capacity (capacity) can be changed by inverter control of the motor. However, the second compressor 34 may also be a fixed displacement type. A plurality of second compressors 34 may be provided. In this case, variable displacement type second compressors and fixed displacement type second compressors may be mixed.

[0032] The second outdoor heat exchanger 36 is a microchannel heat exchanger that exchanges heat between the refrigerant and outdoor air supplied by the outdoor fan 41, causing the refrigerant to release heat (condense).

[0033] The second expansion valve 38 is a pressure reducer that reduces the pressure of the second refrigerant to expand it. In this embodiment, the second expansion valve 38 is configured as an electric valve that can adjust the refrigerant flow rate, etc. The second expansion valve 38 reduces the pressure of the high-pressure second refrigerant that has dissipated heat in the second outdoor heat exchanger 36 and expands it to produce a low-pressure gas-liquid two-phase refrigerant. A capillary tube may be used as the pressure reducer instead of the second expansion valve 38.

[0034] The second accumulator 39 is provided in the suction pipe of the second compressor 34. The second accumulator 39 temporarily stores the low-pressure second refrigerant before it is drawn into the second compressor 34, and separates the second refrigerant into gas refrigerant and liquid refrigerant. The second refrigerant that is the gas refrigerant separated in the second accumulator 39 is drawn into the second compressor 34.

[0035] (Configuration of Auxiliary Heat Exchanger 27) The auxiliary heat exchanger (third heat exchanger) 27 further dissipates heat from the first refrigerant that has dissipated heat in the first outdoor heat exchanger 26. The auxiliary heat exchanger 27 evaporates the second refrigerant that has dissipated heat in the second outdoor heat exchanger 36 and has been decompressed by the second expansion valve 38. The auxiliary heat exchanger 27 is, for example, a plate-type heat exchanger.

[0036] Specifically, the auxiliary heat exchanger 27 has a first heat transfer pipe (first heat transfer flow path) 27a and a second heat transfer pipe (second heat transfer flow path) 27b. One end of the first heat transfer pipe 27a is connected to a refrigerant pipe extending to the first outdoor heat exchanger 26. The other end of the first heat transfer pipe 27a is connected to a refrigerant pipe extending to the first expansion valve 28. One end of the second heat transfer pipe 27b is connected to a refrigerant pipe extending to the second expansion valve 38. The other end of the second heat transfer pipe 27b is connected to a refrigerant pipe extending to the second accumulator 39.

[0037] The auxiliary heat exchanger 27 exchanges heat between the first refrigerant flowing through the first heat transfer pipe 27a and the second refrigerant flowing through the second heat transfer pipe 27b. The first refrigerant (gaseous refrigerant) whose heat has been dissipated in the first outdoor heat exchanger 26 flows into the first heat transfer pipe 27a. The second refrigerant (gas-liquid two-phase refrigerant) that has been decompressed and expanded by the second expansion valve 38 flows into the second heat transfer pipe 27b.

[0038] Therefore, the auxiliary heat exchanger 27 exchanges heat between the first refrigerant that has passed through the first outdoor heat exchanger 26 and flows through the first heat transfer pipe 27a and the second refrigerant that has passed through the second expansion valve (pressure reducer) 38 and flows through the second heat transfer pipe 27b. The auxiliary heat exchanger 27 dissipates heat from the first refrigerant that has flowed through the first heat transfer pipe 27a, and evaporates the second refrigerant that has flowed through the second heat transfer pipe 27b.

[0039] As described above, the auxiliary heat exchanger 27 is included in the first refrigerant circuit 21 and the second refrigerant circuit 22. Therefore, the auxiliary heat exchanger 27 can also be said to be a component of the first refrigerant circuit 21 and the second refrigerant circuit 22.

[0040] (Configuration of the Control Device 51) The control device 51 controls the operation of the first compressor 24, the four-way switching valve 25, the first expansion valve 28, the outdoor fan 41, the indoor fan 42, the second compressor 34, the second expansion valve 38, and the like. The control device 51 includes a processor and a memory. The processor of the control device 51 is configured with a central processing unit (CPU), an application specific integrated circuit (ASIC), a gate array, a field programmable gate array (FPGA), or the like. The programmable logic device, such as the ASIC, gate array, or FPGA, is configured to be able to execute the same processing as the control program. The memory of the control device 51 includes volatile memory, such as static random access memory (SRAM) or dynamic random access memory (DRAM), and non-volatile memory, such as flash memory, a hard disk, or a read-only memory (ROM). The non-volatile memory stores the control program, which is a computer program, and control data.

[0041] The controller 51 performs various functions by executing a control program using a processor. Specifically, the controller 51 performs a first mode, which is a cooling operation, and a second mode, which is a heating operation.

[0042] (Cooling Operation) When the refrigeration system 10 performs cooling operation, the control device 51 drives both the first refrigerant circuit 21 and the second refrigerant circuit 22. The four-way selector valve 25 is maintained in the state indicated by the solid line in FIG. 1 . The first compressor 24 of the first refrigerant circuit 21 discharges a high-temperature, high-pressure gaseous first refrigerant. The first refrigerant flows into the first outdoor heat exchanger 26 via the four-way selector valve 25. In this embodiment, the first refrigerant is carbon dioxide, and is pressurized by the first compressor 24 to a pressure exceeding its critical point. The first refrigerant exchanges heat with outdoor air by operating the outdoor fan 41, thereby releasing heat. The first refrigerant then flows into the auxiliary heat exchanger 27.

[0043] Meanwhile, the second compressor 34 of the second refrigerant circuit 22 discharges a high-temperature, high-pressure gaseous second refrigerant. The second refrigerant flows into the second outdoor heat exchanger 36, where it exchanges heat with outdoor air and dissipates heat (condenses) due to the operation of the outdoor fan 41. The second refrigerant then flows into the second expansion valve 38, where it is reduced in pressure to a predetermined low level. The second refrigerant then flows into the auxiliary heat exchanger 27.

[0044] In the auxiliary heat exchanger 27, the first refrigerant in the first refrigerant circuit 21 exchanges heat with the second refrigerant in the second refrigerant circuit 22 and releases heat. The first refrigerant is then reduced in pressure and expanded in the first expansion valve 28 and flows into the indoor heat exchanger 30 of the indoor unit 12. In the indoor unit 12, the first refrigerant exchanges heat with indoor air in the indoor heat exchanger 30 and evaporates. The indoor air cooled by the evaporation of the first refrigerant is blown into the room by the indoor fan 42, cooling the room. The first refrigerant evaporated in the indoor heat exchanger 30 returns to the outdoor unit 11 through the refrigerant piping 40, passes through the four-way switching valve 25 and the first accumulator 32, and is drawn into the first compressor 24.

[0045] In the auxiliary heat exchanger 27, the second refrigerant in the second refrigerant circuit 22 exchanges heat with the first refrigerant in the first refrigerant circuit 21 and evaporates. The second refrigerant then passes through the second accumulator 39 and is sucked into the second compressor 34.

[0046] (Heating Operation) When the refrigeration apparatus 10 performs heating operation, the control device 51 drives the first refrigerant circuit 21 and stops the second refrigerant circuit 22. The four-way selector valve 25 is maintained in the state shown by the dashed lines in FIG. 1 . The high-temperature, high-pressure gaseous first refrigerant discharged from the first compressor 24 passes through the four-way selector valve 25 and flows into the indoor heat exchanger 30 of the indoor unit 12. In the indoor heat exchanger 30, the first refrigerant exchanges heat with indoor air and dissipates heat. The indoor air heated by the heat dissipation of the first refrigerant is blown into the room by the indoor fan 42, heating the room.

[0047] The first refrigerant then returns to the outdoor unit 11 through the refrigerant pipe 40, is decompressed to a predetermined low pressure by the first expansion valve 28, passes through the auxiliary heat exchanger 27, and flows into the first outdoor heat exchanger 26. Since the second refrigerant circuit 22 is not driven, heat exchange between the first refrigerant and the second refrigerant does not actually occur in the auxiliary heat exchanger 27. The first refrigerant that flows into the first outdoor heat exchanger 26 exchanges heat with the outdoor air and evaporates. The first refrigerant that has evaporated in the first outdoor heat exchanger 26 is drawn into the first compressor 24 via the four-way selector valve 25.

[0048] (Defrosting Operation) The refrigeration system 10 is capable of performing a defrosting operation to remove frost that has formed on the first outdoor heat exchanger 26 during heating operation. The defrosting operation can be performed, for example, in the same manner as in the cooling operation described above, by causing a high-temperature, high-pressure first refrigerant to flow into the first outdoor heat exchanger 26.

[0049] (Refrigeration Cycle of the First Refrigerant Circuit During Cooling Operation) FIG. 7 is a Mollier diagram illustrating the refrigeration cycle of the first refrigerant circuit during cooling operation. In FIG. 7, the symbol L indicates an isotherm at, for example, an outdoor temperature in summer. The first refrigerant used in the first refrigerant circuit 21 is carbon dioxide, which is pressurized by the first compressor 24 to a pressure exceeding its critical point P. Therefore, during cooling operation, the first outdoor heat exchanger 26 only releases heat to the outdoor temperature, thereby achieving only the enthalpy difference Δh1 shown in FIG. 7 . In this embodiment, by exchanging heat between the first refrigerant and a second refrigerant that is lower in temperature than the outdoor temperature in the auxiliary heat exchanger 27, the first refrigerant can further release heat and achieve a further enthalpy difference Δh2. This increases the refrigeration capacity H of the refrigeration system 10 using carbon dioxide refrigerant.

[0050] The refrigerant pipe 40 of the first refrigerant circuit 21 may be removed, for example, when the indoor unit 12 is replaced. At this time, the first refrigerant circuit 21 is opened, which may result in a refrigerant leak. Because the first refrigerant circuit 21 uses carbon dioxide as the first refrigerant, the adverse effects of a leak are small. In contrast, the second refrigerant circuit 22 circulates the second refrigerant only within the outdoor unit 11, and is therefore rarely opened. In this embodiment, R290 (propane), which is flammable, is used as the second refrigerant, but because the second refrigerant circuit 22 is rarely opened, the possibility of a leak is low.

[0051] Fig. 2 is a plan view showing the interior of the outdoor unit of the refrigeration system. Fig. 3 is a side view showing the interior of the outdoor unit of the refrigeration system. The outdoor unit 11 includes a casing 55. The casing 55 is formed in a rectangular parallelepiped shape. As shown in Fig. 2, the interior of the casing 55 is divided into a machine chamber S1 and a heat exchange chamber S2 by a partition wall 56. Air intakes 55a1 and 55b1 are formed in two adjacent side walls 55a and 55b of the casing 55 arranged on the heat exchange chamber S2 side. An air outlet 55c1 is formed in the other side wall 55c adjacent to the one side wall 55b in which the air intake 55b1 is formed.

[0052] The machine chamber S1 of the casing 55 houses the first compressor 24, the second compressor 34, the first accumulator 32, the second accumulator 39, the auxiliary heat exchanger 27, etc. The heat exchange chamber S2 of the casing 55 houses the first outdoor heat exchanger 26, the second outdoor heat exchanger 36, the outdoor fan 41, etc. The outdoor fan 41 rotates around a rotation axis c. The outdoor fan 41 takes air into the casing 55 through air intakes 55a1 and 55b1 and discharges the air to the outside of the casing 55 through an air outlet 55c1. Arrows a in FIGS. 2 and 3 indicate the direction of air flow that is taken into the casing 55 through the air intakes 55a1 and 55b1 and passes through the first and second outdoor heat exchangers 26 and 36, and arrow b indicates the direction of air flow that is discharged to the outside of the casing 55 through the air outlet 55c1.

[0053] 2, the first outdoor heat exchanger 26 is formed in a generally L-shape when viewed from above. The first outdoor heat exchanger 26 is bent near a corner d between the two side walls 55a, 55b where the air intakes 55a1, 55b1 are formed, and is disposed along the two side walls 55a, 55b.

[0054] 2, the second outdoor heat exchanger 36 is formed in a linear shape when viewed from above. The second outdoor heat exchanger 36 is disposed substantially along the side wall 55a of the casing 55. When viewed from above, the length of the second outdoor heat exchanger 36 is shorter than the length of the first outdoor heat exchanger 26.

[0055] 3 , the vertical length of the second outdoor heat exchanger 36 is smaller than the vertical length of the first outdoor heat exchanger 26. The lower ends of the second outdoor heat exchanger 36 and the first outdoor heat exchanger 26 are installed on the bottom plate of the casing 55 and are disposed at approximately the same height. Therefore, the first outdoor heat exchanger 26 protrudes higher than the second outdoor heat exchanger 36. As a result, the air passage area of ​​the first outdoor heat exchanger 26 is larger than the air passage area of ​​the second outdoor heat exchanger 36.

[0056] The first outdoor heat exchanger 26 and the second outdoor heat exchanger 36 are supplied with air by a common outdoor fan 41. The second outdoor heat exchanger 36 is disposed downstream of the first outdoor heat exchanger 26 in the air flow direction a caused by the outdoor fan 41. Therefore, the second outdoor heat exchanger 36 is supplied with air that has passed through the first outdoor heat exchanger 26.

[0057] 4 is a schematic diagram illustrating a first outdoor heat exchanger 26 in a refrigeration system. The first outdoor heat exchanger 26 has a number of fins 26a and heat transfer tubes 26b. The fins 26a are formed in a rectangular plate shape in side view and are arranged parallel to one another. The fins 26a are arranged with their plate surfaces aligned vertically.

[0058] The heat transfer tubes 26b are cylindrical tubes with a circular cross section. The heat transfer tubes 26b are made of a material primarily composed of copper. The heat transfer tubes 26b are made of copper or a copper alloy. The heat transfer tubes 26b include multiple straight pipe sections 26b1 formed linearly and curved pipe sections 26b2 formed in a U-shape. The straight pipe sections 26b1 extend in the direction in which the multiple fins 26a are arranged and penetrate the fins 26a. The curved pipe sections 26b2 are disposed at both ends of the first outdoor heat exchanger 26 in a top view and connect two adjacent straight pipe sections 26b1 to each other. The multiple straight pipe sections 26b1 are arranged in a staggered pattern in the vertical direction and the airflow direction a, as shown in FIG. 3 . Tube sheets 26c are provided at both ends of the first outdoor heat exchanger 26 in a top view. The tube sheets 26c maintain the shape of the first outdoor heat exchanger 26.

[0059] Fig. 5 is an explanatory diagram schematically illustrating a second outdoor heat exchanger in a refrigeration system. Fig. 6 is an enlarged cross-sectional view of the second outdoor heat exchanger. The second outdoor heat exchanger 36 has a large number of fins 36a, a plurality of heat transfer tubes 36b, and headers 36c and 36d. The heat transfer tubes 36b are formed of a material containing aluminum as a main component. The heat transfer tubes 36b are made of aluminum or an aluminum alloy. The plurality of heat transfer tubes 36b are arranged vertically and parallel to one another. Each heat transfer tube 36b is arranged substantially horizontally.

[0060] The headers 36c, 36d are connected to one longitudinal end and the other longitudinal end of each heat transfer tube 36b, respectively. The headers 36c, 36d include a liquid header 36c through which liquid refrigerant flows and a gas header 36d through which gas refrigerant flows. The headers 36c, 36d distribute the second refrigerant that flows in from outside the second outdoor heat exchanger 36 to each heat transfer tube 36b, and merge the second refrigerant that flows in from each heat transfer tube 36b and cause it to flow out of the second outdoor heat exchanger 36.

[0061] As shown in FIG. 6 , the heat transfer tube 36b of this embodiment is a multi-hole tube having a plurality of refrigerant flow paths 36b1 arranged in a row along the airflow direction a. The cross-section of the heat transfer tube 36b cut perpendicular to the longitudinal direction is longitudinally aligned in the airflow direction a, along which the plurality of refrigerant flow paths 36b1 are aligned. In other words, the heat transfer tube 36b is a flat tube whose length L2 in the airflow direction a (horizontal direction) is greater than its length L1 (thickness) in the vertical direction. Hereinafter, the heat transfer tube 36b of the second outdoor heat exchanger 36 will also be referred to as a "flat multi-hole tube." The upper and lower surfaces of the flat multi-hole tube 36b are arranged substantially horizontally.

[0062] The vertical length L1 of the flat multi-hole tube 36b is set to, for example, 1 mm to 3 mm. The length L2 of the flat multi-hole tube 36b in the air flow direction a is set to, for example, 10 mm to 30 mm. In contrast, the outer diameter of the heat transfer tube 26b in the first outdoor heat exchanger 26 is set to, for example, 5 to 10 mm. Therefore, when viewed from the air flow direction a, the flat multi-hole tube 36b has a shorter vertical length than the heat transfer tube 26b, thereby reducing resistance to the air flow. Because the length L1 of the flat multi-hole tube 36b in the air flow direction a (horizontal direction) in the cross section is greater than the vertical length L2, the flat multi-hole tube 36b has a structure that makes it easy for water to collect (remain) on its upper surface.

[0063] On the other hand, the heat transfer tubes 26b in the first outdoor heat exchanger 26 have a greater vertical length and therefore greater strength than the flat multi-hole tubes 36b in the second outdoor heat exchanger 36. In this embodiment, the first outdoor heat exchanger 26 is disposed closer to the exterior of the outdoor unit 11 than the second outdoor heat exchanger 36 (closer to the side walls 55a, 55b), but because the stronger first outdoor heat exchanger 26 is disposed closer to the exterior, damage to the first and second outdoor heat exchangers 26, 36 caused by external impacts to the outdoor unit 11, etc., can be suppressed.

[0064] The area of ​​each refrigerant flow path 36b1 of the flat multi-hole tubes 36b in the second outdoor heat exchanger 36 is smaller than the area of ​​the refrigerant flow path of the heat transfer tubes (cylindrical tubes) 26b in the first outdoor heat exchanger 26. Therefore, the second refrigerant in the second outdoor heat exchanger 36 has more opportunities to come into contact with the flat multi-hole tubes 36b, enabling more efficient heat exchange than in the first outdoor heat exchanger 26. This allows for as little second refrigerant as possible to be used. Because the second refrigerant in this embodiment is flammable R290 (propane), reducing the amount of second refrigerant used is extremely effective in reducing the risk of leakage. For example, the amount of second refrigerant used can be 1000 g or less. Preferably, the amount of second refrigerant used can be 150 g or less.

[0065] The fins 36a of the second outdoor heat exchanger 36 are so-called corrugated fins. The fins 36a are arranged between adjacent flat multi-hole tubes 36b in the vertical direction. The fins 36a are formed by bending a plate material into a wave shape. Therefore, the fins 36a extend in the longitudinal direction of the flat multi-hole tubes 36b, meandering up and down between the upper and lower flat multi-hole tubes 36b. The upper and lower ends of each fin 36a are joined to the flat multi-hole tubes 36b by brazing. Because the corrugated fins 36a meander between the upper and lower flat multi-hole tubes 36b, they are designed to prevent water from entering and being easily expelled.

[0066] In the refrigeration system 10 of this embodiment, when performing heating operation, only the first refrigerant circuit 21 is operated, and the second refrigerant circuit 22 is stopped. Therefore, the airflow generated by the outdoor fan 41 exchanges heat with the first refrigerant flowing through the first outdoor heat exchanger 26, and simply passes through the second outdoor heat exchanger 36. The flat multi-hole tubes 36b of the second outdoor heat exchanger 36 have a slender cross-sectional shape elongated in the airflow direction a, and offer little resistance to the airflow, thereby suppressing a decrease in heat exchange efficiency in the first outdoor heat exchanger 26.

[0067] Furthermore, because the second outdoor heat exchanger 36 is not used during heating operation, frost rarely forms on the second outdoor heat exchanger 36, and water rarely melts and accumulates on the flat multi-hole tubes 36b or in the corrugated fins 36a, or freezes. This prevents damage to the adhesive joints (brazed joints) between the flat multi-hole tubes 36b and the corrugated fins 36a due to freezing of water that has entered the corrugated fins 36a. Although frost may form on the first outdoor heat exchanger 26 during heating operation, even if frost melts and water drips during defrosting operation or the like, it is unlikely for the water to accumulate on the heat transfer tubes 26b, preventing the water from refreezing.

[0068] [Other Embodiments] In the above embodiment, R290 (propane) is exemplified as the second refrigerant used in the second refrigerant circuit 22, but the present invention is not limited to this. Other flammable and toxic refrigerants can be used as the second refrigerant. Furthermore, it is possible to use refrigerants with a relatively high GWP (global warming potential) (for example, a refrigerant with a GWP of 4 to 675, which is higher than that of natural refrigerants). In addition to the above-mentioned R290 (propane), R32, R1234yf, R474a, R600a (isobutane), and the like can be used as flammable refrigerants. Toxic refrigerants include NH ３ Ammonia, etc. can be used. Refrigerants with high GWP include R32, R454B, R454C, etc. Among these, R32 has the highest GWP of 675.

[0069] The second outdoor heat exchanger 36 may have flat multi-hole tubes 36b arranged vertically, for example, the second outdoor heat exchanger 36 shown in Fig. 5 rotated by 90°. Even in such a case, water that has entered the inside of the corrugated fins 36a is difficult to drain, but because the second outdoor heat exchanger 36 is used as a radiator that radiates heat from the second refrigerant and not as an evaporator, the formation of frost and the accumulation or freezing of water due to melting frost are suppressed.

[0070] The second outdoor heat exchanger 36 may have rectangular flat fins similar to the fins 26a of the first outdoor heat exchanger 26, instead of the corrugated fins 36a. In this case, a large number of fins may be arranged vertically, and the flat multi-hole tubes 36b may penetrate the fins. In this case, the fins may be notched so that one end of the flat multi-hole tubes 36b in the air flow direction a is exposed.

[0071] [Operation and Effects of the Embodiment] (1) The refrigeration system 10 of the above embodiment includes a first refrigerant circuit 21 including a first heat exchanger (first outdoor heat exchanger) 26 that dissipates heat from a first refrigerant that is carbon dioxide, a second heat exchanger (second outdoor heat exchanger) 36 that dissipates heat from a second refrigerant that is flammable or toxic or has a GWP (global warming potential) of 4 or more, and a second refrigerant circuit 22 including a pressure reducer (second expansion valve) 38 that reduces the pressure of the second refrigerant, and a third heat exchanger (auxiliary heat exchanger) 27 that exchanges heat between the first refrigerant that has dissipated heat in the first heat exchanger 26 and the second refrigerant that has dissipated heat in the second heat exchanger 36 and then been reduced in pressure by the pressure reducer 38. The second heat exchanger 36 has a plurality of flat multi-hole tubes 36b.

[0072] In general, a heat exchanger having flat multi-hole tubes can perform heat exchange more efficiently than a heat exchanger having a typical circular heat transfer tube, and therefore can reduce the amount of refrigerant used. In the above embodiment, since the second heat exchanger 36 has the flat multi-hole tubes 36b, the amount of the second refrigerant that is flammable or toxic, or has a GWP of 4 or more, that is used can be reduced, and the risk of leakage of the second refrigerant can be reduced.

[0073] (2) The refrigeration device 10 of the above embodiment further includes a control device 51 that controls operation of the first refrigerant circuit 21 and the second refrigerant circuit 22, and a fan (outdoor fan) 41 that generates an airflow to be supplied to the first heat exchanger 26 and the second heat exchanger 36. The first heat exchanger 26 and the second heat exchanger 36 are arranged side by side in the flow direction a of the airflow generated by the fan 41. The control device 51 executes a first mode (operation mode for cooling operation) in which both the first refrigerant circuit 21 and the second refrigerant circuit 22 are operated to cause the first heat exchanger 26 to radiate heat from the first refrigerant and the second heat exchanger 36 to radiate heat from the second refrigerant, and a second mode (operation mode for heating operation) in which the first refrigerant circuit 21 is operated alone to evaporate the first refrigerant by the first heat exchanger 26.

[0074] In the second mode in which the first refrigerant circuit 21 operates alone, the airflow generated by the fan 41 exchanges heat with the first refrigerant flowing through the first heat exchanger 26 and simply passes through the second heat exchanger 36. The flat multi-hole tubes 36b of the second heat exchanger 36 have a slender cross-sectional shape elongated in the airflow direction a and are unlikely to provide resistance to the airflow, thereby preventing a decrease in heat exchange efficiency in the first heat exchanger 26.

[0075] (3) In the refrigeration device 10 of the above embodiment, the second heat exchanger 36 includes a plurality of flat multi-hole tubes 36b and serpentine fins (corrugated fins) 36a arranged between adjacent flat multi-hole tubes 36b.

[0076] In the second heat exchanger 36 having fins 36a that snake between adjacent flat multi-hole tubes 36b, water that gets into the fins 36a is difficult to drain, and the accumulated water may freeze and damage the bonded joints (brazed joints) between the corrugated fins 36a and the flat multi-hole tubes 36b. In the refrigeration system 10 of this embodiment, the second heat exchanger 36 is used as a radiator, which prevents frost from forming and the accumulation of water due to melting frost. Furthermore, the corrugated fins have high heat exchange efficiency, making it possible to reduce the amount of refrigerant used.

[0077] (4) In the refrigeration system 10 of the above embodiment, the amount of the second refrigerant used in the second refrigerant circuit 22 is 1000 g or less. The second heat exchanger 36 having the flat multi-hole tubes 36 b described above can perform heat exchange more efficiently than the first heat exchanger 26 having the circular heat transfer tubes 26 b, so the amount of refrigerant used can be reduced to 1000 g or less. This reduces the risk of leakage of the second refrigerant.

[0078] (5) In the refrigeration system 10 of the above embodiment, the amount of the second refrigerant used in the second refrigerant circuit 22 is 150 g or less. The second heat exchanger 36 having the flat multi-hole tubes 36 b described above can perform heat exchange more efficiently than the first heat exchanger 26 having the circular heat transfer tubes 26 b, so the amount of refrigerant used can be reduced to 150 g or less. This further reduces the risk of leakage of the second refrigerant.

[0079] Although the embodiments 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 claims.

[0080] 10: Refrigeration device 21: First refrigerant circuit 22: Second refrigerant circuit 26: First outdoor heat exchanger (first heat exchanger) 27: Auxiliary heat exchanger (third heat exchanger) 36: Second outdoor heat exchanger (second heat exchanger) 36a: Corrugated fin 36b: Flat multi-hole tube 38: Second expansion valve (pressure reducer) 41: Outdoor fan 51: Control device a: Air flow direction

Claims

1. A refrigeration device comprising: a first refrigerant circuit (21) including a first heat exchanger (26) that dissipates heat from a first refrigerant which is carbon dioxide; a second refrigerant circuit (22) including a second heat exchanger (36) that dissipates heat from a second refrigerant which is flammable or toxic, or a second refrigerant which has a global warming potential of 4 or more, and a pressure reducer (38) that reduces the pressure of the second refrigerant; and a third heat exchanger (27) that exchanges heat between the first refrigerant after heat dissipation in the first heat exchanger (26) and the second refrigerant which has been dissipated heat in the second heat exchanger (36) and then reduced in pressure in the pressure reducer (38), wherein the second heat exchanger (36) has a plurality of flat multi-hole tubes (36b).

2. The refrigeration system according to claim 1, further comprising: a control device (51) for controlling operation of the first refrigerant circuit (21) and the second refrigerant circuit (22); and a fan (41) for generating an air flow to be supplied to the first heat exchanger (26) and the second heat exchanger (36), wherein the first heat exchanger (26) and the second heat exchanger (36) are arranged side by side in a flow direction (a) of the air flow generated by the fan (41), and the control device (51) operates both the first refrigerant circuit (21) and the second refrigerant circuit (22) to execute a first mode in which the first refrigerant is dissipated by the first heat exchanger (26) and the second refrigerant is dissipated by the second heat exchanger (36), and a second mode in which the first refrigerant circuit (21) is operated alone to evaporate the first refrigerant by the first heat exchanger (26).

3. A refrigeration apparatus as described in claim 1 or 2, wherein the second heat exchanger (36) comprises a plurality of the flat multi-hole tubes (36b) and serpentine fins (36a) arranged between adjacent flat multi-hole tubes (36b).

4. The refrigeration system according to any one of claims 1 to 3, wherein the amount of the second refrigerant used in the second refrigerant circuit (22) is 1000 g or less.

5. The refrigeration system according to claim 4, wherein the amount of the second refrigerant used in the second refrigerant circuit (22) is 150 g or less.

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