JP2025007831A - Refrigeration equipment - Google Patents

Abstract

To provide a refrigerating device that comprises two refrigerant circuits using different refrigerants, and solves a problem of draining performance in heat exchangers.SOLUTION: A refrigerating device 10 comprises: a first refrigerant circuit 21 including a first heat exchanger 26 for dissipating heat of a first refrigerant that is carbon dioxide; a second refrigerant circuit 22 including a second heat exchanger 36 for dissipating heat of a second refrigerant having combustibility or toxicity, or a second refrigerant having a global warming coefficient of 4 or more, and a pressure reducer 38 for reducing the pressure of the second refrigerant; and a third heat exchanger 27 for exchanging heat between the first refrigerant whose heat has been dissipated by the first heat exchanger 26, and the second refrigerant whose heat has been dissipated by the second heat exchanger 36, and whose pressure has been reduced by the pressure reducer 38 after that. The second heat exchanger 36 comprises a plurality of flat perforated pipes 36b.SELECTED DRAWING: Figure 3

Description

This disclosure relates to a refrigeration device.

Patent Document 1 discloses a dual-stage 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. For this reason, the low-stage refrigeration cycle uses a refrigerant such as carbon dioxide, which has a low global warming potential, since the refrigerant circuit may be opened due to rearrangement of the showcase, etc., which may cause 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.

International Publication No. 2014/181399

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.

The purpose of this disclosure is to reduce the amount of flammable or toxic refrigerant used in a refrigeration system equipped with two refrigerant circuits using different refrigerants.

(1) A refrigeration device according to the present disclosure includes a first refrigerant circuit including a first heat exchanger that dissipates heat from a first refrigerant, which 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;
a third heat exchanger that exchanges heat between the first refrigerant after heat dissipation in the first heat exchanger and the second refrigerant after heat dissipation in the second heat exchanger and reduced in pressure by the pressure reducer;
The second heat exchanger includes a plurality of flat multi-hole tubes.

According to this configuration, the second heat exchanger having flat multi-hole tubes can perform heat exchange more efficiently than a heat exchanger having a typical circular heat transfer tube, so the amount of refrigerant used can be reduced. This reduces the risk of leakage of a second refrigerant that is flammable or toxic, or has a GWP of 4 or more.

(2) In the refrigeration device of (1) above, preferably, the refrigeration device further includes a control device that controls 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,
the first heat exchanger and the second heat exchanger are arranged side by side in a flow direction of the airflow generated by the fan,
The control device executes a first mode in which both the first refrigerant circuit and the second refrigerant circuit are operated to cause the first refrigerant to dissipate heat through the first heat exchanger and the second refrigerant to dissipate heat through the second heat exchanger, and a second mode in which the first refrigerant circuit is operated alone to evaporate the first refrigerant through the first heat exchanger.

The flat multi-hole tubes of the second heat exchanger have a long and narrow cross-sectional shape in the direction of the air flow and are unlikely to provide resistance to the air flow, so that in the second mode in which the first refrigerant circuit is operated alone, a decrease in the heat exchange efficiency in the first heat exchanger can be suppressed.

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

The second heat exchanger, which has serpentine fins (so-called corrugated fins), has poor drainage of water that gets into the corrugated fins. In the refrigeration device disclosed herein, the second heat exchanger is used as a radiator that dissipates heat from the refrigerant, so that the water that gets in can be prevented from freezing.

(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.

With this configuration, by using a flat multi-hole tube, it is possible to reduce the amount of second refrigerant used to 1,000 g or less, thereby reducing the risk of leakage.

(5) In the refrigeration device described in any of (4) above, the amount of the second refrigerant used in the second refrigerant circuit is preferably 150 g or less.

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, further reducing the risk of leakage.

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 inside of the outdoor unit of the refrigeration apparatus. FIG. 2 is a side view showing the inside of an outdoor unit in the refrigeration apparatus. FIG. 2 is an explanatory diagram illustrating a schematic configuration of a first outdoor heat exchanger in the refrigeration device. FIG. 4 is an explanatory diagram illustrating a second outdoor heat exchanger in the refrigeration device. FIG. 4 is an enlarged cross-sectional view of the second outdoor heat exchanger. FIG. 4 is a Mollier diagram for explaining the refrigeration cycle of the first refrigerant circuit during cooling operation.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
(Overall configuration of the 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 cools and heats the room. However, the refrigeration device 10 may be dedicated to cooling. The refrigeration device 10 may also be a refrigerator, a freezer, or the like that cools the air inside the storage unit.

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.

The refrigeration device 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 refrigerant that is flammable or toxic, or has a high global warming potential (GWP), is used as the second refrigerant. For example, R290 (propane) is used as the second refrigerant. The refrigeration device 10 further has an auxiliary heat exchanger 27, a control device 51, an outdoor fan 41, and an indoor fan 42.

(Configuration of the 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.

The outdoor unit 11 is equipped with 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 that constitute a first refrigerant circuit 21. The indoor unit 12 is equipped with an indoor heat exchanger 30 that 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.

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 capacity type (variable capacity type) whose capacity (capacity) can be changed by inverter control of the motor. However, the first compressor 24 may be a fixed capacity type. Multiple first compressors 24 may be provided. In this case, variable capacity compressors and fixed capacity compressors may be mixed.

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

The first outdoor heat exchanger 26 is a cross-fin tube type heat exchanger. The first outdoor heat exchanger 26 exchanges heat between the outdoor air taken in by the outdoor fan 41 and the first refrigerant, and dissipates heat or evaporates 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 later.

The first expansion valve 28 is a pressure reducer that reduces the pressure of the first refrigerant and expands 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 had heat dissipated in the first exterior heat exchanger 26 and the auxiliary heat exchanger 27 described below, and expands it to create 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.

The first shut-off valve 29 is a manually operated on-off valve. When closed, the first shut-off valve 29 blocks the flow of the first refrigerant in the refrigerant piping 40, and when open, allows the flow of the first refrigerant in the refrigerant piping 40.

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 indoor air taken in by the indoor fan 42 and the first refrigerant, and dissipates heat or evaporates the first refrigerant.

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 in the refrigerant piping 40, and when open, allows the flow of the first refrigerant in the refrigerant piping 40.

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 sucked into the first compressor 24, and separates the first refrigerant into gas refrigerant and liquid refrigerant. The first refrigerant, which is the gas refrigerant separated in the first accumulator 32, is sucked into the first compressor 24.

(Configuration of the second refrigerant circuit 22)
The second refrigerant circuit 22 circulates the 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 a refrigerant pipe 50 connecting these components.

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 speed can be adjusted by inverter control. The second compressor 34 is a variable capacity type (variable capacity type) whose capacity (capacity) can be changed by inverter control of the motor. However, the second compressor 34 may be a fixed capacity type. Multiple second compressors 34 may be provided. In this case, a variable capacity type second compressor and a fixed capacity type second compressor may be mixed.

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

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 had its heat dissipated in the second exterior heat exchanger 36 and expands it to produce a low-pressure gas-liquid two-phase refrigerant. A capillary tube may be used as a pressure reducer instead of the second expansion valve 38.

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 sucked into the second compressor 34, and separates the second refrigerant into gas refrigerant and liquid refrigerant. The second refrigerant, which is a gas refrigerant separated in the second accumulator 39, is sucked into the second compressor 34.

(Configuration of the auxiliary heat exchanger 27)
The auxiliary heat exchanger (third heat exchanger) 27 further dissipates heat from the first refrigerant that has had heat dissipated in the first exterior heat exchanger 26. The auxiliary heat exchanger 27 evaporates the second refrigerant that has had heat dissipated in the second exterior heat exchanger 36 and has been depressurized by the second expansion valve 38. The auxiliary heat exchanger 27 is, for example, a plate-type heat exchanger.

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

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

Therefore, the auxiliary heat exchanger 27 exchanges heat between the first refrigerant that passes through the first outdoor heat exchanger 26 and flows through the first heat transfer tube 27a, and the second refrigerant that passes through the second expansion valve (pressure reducer) 38 and flows through the second heat transfer tube 27b. The auxiliary heat exchanger 27 dissipates heat from the first refrigerant that flows through the first heat transfer tube 27a, and evaporates the second refrigerant that flows through the second heat transfer tube 27b.

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.

(Configuration of 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 CPU (Central Processing Unit), an ASIC (Application Specific Integrated Circuit), a gate array, or an FPGA (Field Programmable Gate Array), and the like. The ASIC, or a programmable logic device such as a gate array or an FPGA, is configured to be able to execute the same process as the control program. The memory of the control device 51 includes a volatile memory such as an SRAM (Static Random Access Memory) or a DRAM (Dynamic Random Access Memory), and a non-volatile memory such as a flash memory, a hard disk, or a ROM (Read Only Memory). The non-volatile memory stores a control program, which is a computer program, and control data.

The control device 51 performs various functions by the processor executing a control program. Specifically, the control device 51 executes a first mode, which is a cooling operation, and a second mode, which is a heating operation.

(Cooling operation)
When the refrigeration device 10 performs cooling operation, the control device 51 drives both the first refrigerant circuit 21 and the second refrigerant circuit 22. The four-way switching valve 25 is held in the state shown 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 switching valve 25. In this embodiment, the first refrigerant is carbon dioxide, and is pressurized by the first compressor 24 to a pressure exceeding the critical point. The first refrigerant exchanges heat with the outdoor air by operating the outdoor fan 41, and dissipates heat. Furthermore, the first refrigerant flows into the auxiliary heat exchanger 27.

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 the outdoor air and dissipates heat (condenses) when the outdoor fan 41 is activated. The second refrigerant then flows into the second expansion valve 38, where it is reduced in pressure to a predetermined low pressure. The second refrigerant then flows into the auxiliary heat exchanger 27.

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 decompressed 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 the 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 sucked into the first compressor 24.

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.

(Heating operation)
When the refrigeration system 10 performs heating operation, the control device 51 drives the first refrigerant circuit 21 and stops the second refrigerant circuit 22. The four-way switching valve 25 is held in the state shown by the dashed line in Fig. 1. The high-temperature, high-pressure gaseous first refrigerant discharged from the first compressor 24 passes through the four-way switching 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.

The first refrigerant then returns to the outdoor unit 11 through the refrigerant piping 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, the auxiliary heat exchanger 27 does not actually exchange heat between the first refrigerant and the second refrigerant. 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 sucked into the first compressor 24 through the four-way switching valve 25.

(Defrost operation)
The refrigeration system 10 is capable of a defrost operation for removing frost that has adhered to the first outdoor heat exchanger 26 during heating operation. The defrost operation can be performed, for example, by causing a high-temperature, high-pressure first refrigerant to flow into the first outdoor heat exchanger 26, similar to the above-described cooling operation.

(Refrigeration cycle of the first refrigerant circuit during cooling operation)
7 is a Mollier diagram for explaining the refrigeration cycle of the first refrigerant circuit during cooling operation, in which the reference character L indicates an isothermal line at an outside air temperature in summer, for example.
The first refrigerant used in the first refrigerant circuit 21 is carbon dioxide, and is pressurized by the first compressor 24 to a pressure exceeding the critical point P. Therefore, during cooling operation, the first outdoor heat exchanger 26 only releases heat from the first refrigerant to approximately the outside air temperature, and only the enthalpy difference Δh1 shown in FIG. 7 can be ensured. In this embodiment, by exchanging heat between the first refrigerant and a second refrigerant that is lower in temperature than the outside air temperature in the auxiliary heat exchanger 27, the first refrigerant can further release heat, and a further enthalpy difference Δh2 can be ensured. Therefore, the refrigeration capacity H of the refrigeration device 10 using the carbon dioxide refrigerant can be increased.

The refrigerant pipes 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, and there is a possibility of refrigerant leakage. Since the first refrigerant circuit 21 uses carbon dioxide as the first refrigerant, the adverse effects of leakage are small. In contrast, the second refrigerant circuit 22 circulates the second refrigerant only inside the outdoor unit 11, and is therefore rarely opened. In this embodiment, R290 (propane), which is flammable, is used as the second refrigerant, but since the second refrigerant circuit 22 is rarely opened, the possibility of leakage is low.

Fig. 2 is a plan view showing the inside of an outdoor unit of the refrigeration apparatus, and Fig. 3 is a side view showing the inside of the outdoor unit of the refrigeration apparatus.
The outdoor unit 11 includes a casing 55. The casing 55 is formed in a rectangular parallelepiped shape. As shown in Fig. 2, the inside 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.

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 the rotation axis c. The outdoor fan 41 takes in air into the casing 55 from the air intakes 55a1 and 55b1, and discharges air to the outside of the casing 55 from the air outlet 55c1. The arrow a shown in Figures 2 and 3 indicates the direction of the air flow that is taken into the casing 55 from the air intakes 55a1 and 55b1 and passes through the first and second outdoor heat exchangers 26 and 36, and the arrow b indicates the direction of the air flow that is discharged to the outside of the casing 55 from the air outlet 55c1.

As shown in FIG. 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 the 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.

As shown in FIG. 2, the second outdoor heat exchanger 36 is formed in a straight line 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 smaller than the length of the first outdoor heat exchanger 26.

As shown in FIG. 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 upward more than the second outdoor heat exchanger 36. As a result, the air passing area in the first outdoor heat exchanger 26 is larger than the air passing area in the second outdoor heat exchanger 36.

Air is supplied to the first outdoor heat exchanger 26 and the second outdoor heat exchanger 36 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.

FIG. 4 is an explanatory diagram that illustrates a schematic diagram of a first outdoor heat exchanger in the refrigeration system.
The first outdoor heat exchanger 26 has a number of fins 26a and a heat transfer tube 26b. The number of fins 26a are formed in a rectangular plate shape in a side view and are arranged parallel to each other. The number of fins 26a is arranged so that the plate surfaces are aligned in the vertical direction.

The heat transfer tube 26b is a cylindrical tube with a circular cross section. The heat transfer tube 26b is made of a material mainly composed of copper. The heat transfer tube 26b is made of copper or a copper alloy. The heat transfer tube 26b has a plurality of straight tube sections 26b1 formed in a straight line and a curved tube section 26b2 formed in a U-shape. The straight tube section 26b1 extends in the direction in which the many fins 26a are arranged and penetrates the fins 26a. The curved tube section 26b2 is arranged at both ends of the first outdoor heat exchanger 26 in a top view and connects two adjacent straight tube sections 26b1 to each other. The multiple straight tube sections 26b1 are arranged in a staggered manner in the vertical direction and the air flow direction a as shown in FIG. 3. Tube plates 26c are provided at both ends of the first outdoor heat exchanger 26 in a top view. The shape of the first outdoor heat exchanger 26 is maintained by the tube plates 26c.

Fig. 5 is an explanatory diagram that shows a schematic of a second outdoor heat exchanger in the refrigeration device, and 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, 36d. The heat transfer tubes 36b are formed of a material mainly composed of aluminum. The heat transfer tubes 36b are made of aluminum or an aluminum alloy. The plurality of heat transfer tubes 36b are arranged in parallel to each other in the vertical direction. Each heat transfer tube 36b is arranged substantially horizontally.

The headers 36c and 36d are connected to one end and the other end of each heat transfer tube 36b in the longitudinal direction. The headers 36c and 36d include a liquid header 36c through which liquid refrigerant flows and a gas header 36d through which gas refrigerant flows. The headers 36c and 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 allow it to flow out to the outside of the second outdoor heat exchanger 36.

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 inside. The plurality of refrigerant flow paths 36b1 are formed in a line along the air flow direction a. The cross-sectional shape of the heat transfer tube 36b cut in a direction perpendicular to the longitudinal direction is formed longitudinally in the air flow direction a, which is the direction in which the plurality of refrigerant flow paths 36b1 are arranged. In other words, the heat transfer tube 36b is a flat tube in which the length L2 in the air flow direction a (horizontal direction) is greater than the length (thickness) L1 in the vertical direction in the cross-section. Hereinafter, the heat transfer tube 36b of the second outdoor heat exchanger 36 is also referred to as a "flat multi-hole tube". The upper and lower surfaces of the flat multi-hole tube 36b are arranged approximately horizontally.

The length L1 in the vertical direction of the flat multi-hole tube 36b is set to, for example, 1 mm to 3 mm. The length L2 in the air flow direction a of the flat multi-hole tube 36b 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 smaller vertical length than the heat transfer tube 26b, and has a smaller resistance to the air flow. The flat multi-hole tube 36b has a structure in which water tends to collect (remain) on its upper surface because the length L1 in the air flow direction a (horizontal direction) in the cross section is greater than the length L2 in the vertical direction.

On the other hand, the heat transfer tube 26b in the first outdoor heat exchanger 26 has a greater vertical length than the flat multi-hole tube 36b in the second outdoor heat exchanger 36, and therefore has greater strength. In this embodiment, the first outdoor heat exchanger 26 is disposed closer to the exterior of the outdoor unit 11 (closer to the side walls 55a, 55b) than the second outdoor heat exchanger 36, 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 can be suppressed.

The area of each refrigerant flow path 36b1 of the flat multi-hole tube 36b in the second outdoor heat exchanger 36 is smaller than the area of the refrigerant flow path of the heat transfer tube (cylindrical tube) 26b in the first outdoor heat exchanger 26. Therefore, in the second outdoor heat exchanger 36, the second refrigerant has more opportunities to come into contact with the flat multi-hole tube 36b, and can perform heat exchange more efficiently than the first outdoor heat exchanger 26. This makes it possible to reduce the amount of the second refrigerant used as much as possible. Since the second refrigerant in this embodiment is R290 (propane), which has flammability, it is extremely effective to reduce the amount of the second refrigerant in order to reduce the risk of leakage. For example, the amount of the second refrigerant used can be 1000g or less. Preferably, the amount of the second refrigerant used can be 150g or less.

The fins 36a of the second outdoor heat exchanger 36 are so-called corrugated fins. The fins 36a are arranged between the flat multi-hole tubes 36b adjacent 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 while meandering up and down between the upper and lower flat multi-hole tubes 36b. The upper and lower ends of each fin 36a are respectively joined to the flat multi-hole tubes 36b by brazing. Since the corrugated fins 36a meander between the upper and lower flat multi-hole tubes 36b, they have a structure that makes it difficult for water to be discharged if it gets inside.

In the present embodiment, the refrigeration device 10 operates only the first refrigerant circuit 21 during heating operation, and stops the second refrigerant circuit 22. 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 tube 36b of the second outdoor heat exchanger 36 has an elongated cross-sectional shape in the airflow direction a, and has little resistance to the airflow, so that a decrease in the heat exchange efficiency in the first outdoor heat exchanger 26 can be suppressed.

In addition, since the second outdoor heat exchanger 36 is not used during heating operation, frost rarely occurs on the second outdoor heat exchanger 36, and water rarely melts and accumulates on the flat multi-hole tube 36b or in the corrugated fin 36a, or freezes. This prevents damage to the adhesive (brazed) portion between the flat multi-hole tube 36b and the corrugated fin 36a due to freezing of water that has entered the corrugated fin 36a. During heating operation, frost may occur on the first outdoor heat exchanger 26, but even if frost melts during defrost operation or the like and water drips, it is difficult for the water to accumulate on the heat transfer tube 26b, so the water is prevented from freezing again.

[Other embodiments]
In the above embodiment, R290 (propane) is exemplified as the second refrigerant used in the second refrigerant circuit 22, but is not limited thereto. As the second refrigerant, other refrigerants having combustibility and toxicity can be used. In addition, it is possible to use a refrigerant having a relatively high GWP (global warming potential) (for example, a refrigerant having a GWP of 4 or more and 675 or less, which is higher than that of natural refrigerants). As the refrigerant having combustibility, in addition to the above-mentioned R290 (propane), R32, R1234yf, R474a, R600a (isobutane), etc. can be used. As the refrigerant having toxicity, NH ₃ (ammonia), etc. can be used. As the refrigerant having a high GWP, R32, R454B, R454C, etc. can be used. Of these, the GWP of R32 is the maximum of 675.

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 90°. Even in such a case, water that has entered inside the corrugated fins 36a is difficult to drain, but since the second outdoor heat exchanger 36 is used as a radiator that radiates heat from the second refrigerant and not as an evaporator, the generation of frost and the accumulation or freezing of water due to melting of the frost are suppressed.

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 in a line along the vertical direction, and the flat multi-hole tube 36b may pass through the multiple fins. In this case, the fins may be notched so as to expose one end of the flat multi-hole tube 36b in the air flow direction a.

[Effects of the embodiment]
(1) The refrigeration device 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 a second refrigerant with 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 reduced in pressure by the pressure reducer 38. The second heat exchanger 36 has a plurality of flat multi-hole tubes 36b.

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

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

In the second mode in which the first refrigerant circuit 21 is operated 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 an elongated cross-sectional shape in the airflow direction a, and are unlikely to provide resistance to the airflow, so that a decrease in the heat exchange efficiency in the first heat exchanger 26 can be suppressed.

(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.

In the second heat exchanger 36, which has fins 36a that snake between adjacent flat multi-hole tubes 36b, if water gets into the fins 36a, it is difficult to drain, and there is a risk that the accumulated water will freeze and damage the adhesive (brazed) parts between the corrugated fins 36a and the flat multi-hole tubes 36b. In the refrigeration device 10 of this embodiment, the second heat exchanger 36 is used as a radiator, so the generation of frost and the accumulation of water due to melting frost are suppressed. In addition, the corrugated fins have high heat exchange efficiency, making it possible to reduce the amount of refrigerant used.

(4) In the refrigeration device 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 tube 36b as described above can perform heat exchange more efficiently than the first heat exchanger 26 having the circular heat transfer tube 26b, so the amount of refrigerant used can be reduced to 1000 g or less. This reduces the risk of leakage of the second refrigerant.

(5) In the refrigeration device 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 tube 36b as described above can perform heat exchange more efficiently than the first heat exchanger 26 having the circular heat transfer tube 26b, 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.

Although the embodiments have been described above, it will be understood that various changes in form and details are possible without departing from the spirit and scope of the claims.

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 (5)

A first refrigerant circuit (21) including a first heat exchanger (26) for dissipating heat from a first refrigerant, which is carbon dioxide;
a second refrigerant circuit (22) including a second heat exchanger (36) for dissipating heat of a second refrigerant that is flammable or toxic, or a second refrigerant that has a global warming potential of 4 or more, and a pressure reducer (38) for reducing the pressure of the second refrigerant;
a third heat exchanger (27) for exchanging heat between the first refrigerant after heat dissipation in the first heat exchanger (26) and the second refrigerant after heat dissipation in the second heat exchanger (36) and reduced in pressure in the pressure reducer (38),
The second heat exchanger (36) has a plurality of flat multi-hole tubes (36b). a control device (51) that controls operation of the first refrigerant circuit (21) and the second refrigerant circuit (22), and a fan (41) that generates an air flow 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 a flow direction (a) of the air flow generated by the fan (41),
2. The refrigeration device according to claim 1, wherein the control device (51) executes a first mode in which both the first refrigerant circuit (21) and the second refrigerant circuit (22) are operated to cause the first refrigerant to dissipate heat through the first heat exchanger (26) and the second refrigerant to dissipate heat through the second heat exchanger (36), and a second mode in which the first refrigerant circuit (21) is operated alone to evaporate the first refrigerant through the first heat exchanger (26). The refrigeration device according to 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). The refrigeration system according to claim 1 or 2, wherein the amount of the second refrigerant used in the second refrigerant circuit (22) is 1000 g or less. The refrigeration device 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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