Air conditioner

Abstract

An air conditioner (1) comprises a first heat exchanger (100) and a second heat exchanger (200). The first heat exchanger (100) causes heat exchange between a carbon dioxide refrigerant flowing through a first heat transfer tube (110) having an outer diameter (O1) of 5.5 mm or less and outdoor air flowing outside the first heat transfer tube (110). The second heat exchanger (200) causes heat exchange between a carbon dioxide refrigerant flowing through a second heat transfer tube (210) having an outer diameter (O2) of 5.5 mm or less and indoor air flowing outside the second heat transfer tube (210). The distance (L1) from the airflow upstream end (127) of a first fin (120) to the airflow upstream end (117) of the first heat transfer tube (110) is longer than the distance (L2) from the airflow upstream end (227) of a second fin (220) to the airflow upstream end (217) of the second heat transfer tube (210).

Description

Air conditioner

[0001] The present invention relates to an air conditioner.

[0002] Conventionally, as disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2010-48551), a cross-fin type heat exchanger is known as a heat exchanger used in air conditioners. The heat exchanger of Patent Document 1 has a plurality of fins stacked at intervals from one another, and a plurality of heat transfer tubes penetrating the fins in the stacking direction, and heat exchange is performed between the fluid inside the heat transfer tubes and the fluid outside the heat transfer tubes via the heat transfer tubes and the fins. In the heat exchanger of Patent Document 1, a metal pipe or the like with an outer diameter of 7 mm or 9.52 mm is used for the heat transfer tubes (Paragraph 0018).

[0003] However, in the above Patent Document 1, when carbon dioxide refrigerant is used as the fluid in the heat transfer tubes, it is necessary to increase the thickness of the heat transfer tubes.

[0004] An air conditioner according to a first aspect includes a first heat exchanger and a second heat exchanger. The first heat exchanger is a cross-fin type heat exchanger disposed outdoors. The second heat exchanger is a cross-fin type heat exchanger disposed indoors. The first heat exchanger has first heat transfer tubes and first fins. The first heat transfer tubes have an outer diameter of 5.5 mm or less. The first fins are joined to the first heat transfer tubes. The first heat exchanger performs heat exchange between carbon dioxide refrigerant flowing inside the first heat transfer tubes and outdoor air flowing outside the first heat transfer tubes. The second heat exchanger has second heat transfer tubes and second fins. The second heat transfer tubes have an outer diameter of 5.5 mm or less. The second fins are joined to the second heat transfer tubes. The second heat exchanger performs heat exchange between carbon dioxide refrigerant flowing inside the second heat transfer tubes and indoor air flowing outside the second heat transfer tubes. The distance from the upstream end of the air flow of the first fin to the upstream end of the air flow of the first heat transfer tube is larger than the distance from the upstream end of the air flow of the second fin to the upstream end of the air flow of the second heat transfer tube.

[0005] The pressure resistance of heat transfer tubes filled with carbon dioxide refrigerant is higher than that of heat transfer tubes filled with refrigerants such as R32. Therefore, when filling heat transfer tubes with an outer diameter of 7 mm or 9.52 mm as disclosed in Patent Document 1, the thickness of the heat transfer tubes needs to be increased. In contrast, in the air conditioner of the first aspect, the outer diameter of the first and second heat transfer tubes is 5.5 mm or less, so even when carbon dioxide refrigerant is filled into the first and second heat transfer tubes, it is possible to suppress an increase in the thickness of the first and second heat transfer tubes. Therefore, it is possible to suppress an increase in cost.

[0006] On the other hand, in heat exchangers located outdoors, if the fins are reduced in size while maintaining a similar shape so that the outer diameter of the heat transfer tubes (7 mm or 9.52 mm) is reduced to 5.5 mm or less, the distance from the upstream end of the airflow on the fins to the upstream end of the airflow on the heat transfer tubes becomes smaller, reducing the frost resistance. Furthermore, heat exchangers located indoors must be placed in the limited space of the indoor unit. Thus, the required functions of heat exchangers located outdoors and those located indoors are different.

[0007] Therefore, in the first-viewpoint air conditioner, the distance from the upstream end of the airflow of the first fin to the upstream end of the airflow of the first heat transfer tube is made greater than the distance from the upstream end of the airflow of the second fin to the upstream end of the airflow of the second heat transfer tube. As a result, in the first heat exchanger located outdoors, the distance between the upstream end of the airflow of the first fin, which is prone to frost formation, and the first heat transfer tube through which the carbon dioxide refrigerant flows is increased. Therefore, the cold energy of the carbon dioxide refrigerant flowing through the first heat transfer tube is less likely to be transferred to the upstream end of the airflow of the first fin, thus suppressing a decrease in frost resistance. Furthermore, in the second heat exchanger located indoors, the distance from the upstream end of the airflow of the second fin to the second heat transfer tube is reduced. As a result, the second heat exchanger can be made smaller.

[0008] The air conditioner in the second perspective is the same as the air conditioner in the first perspective, and the outer diameter of the second heat transfer tube is the same as the outer diameter of the first heat transfer tube.

[0009] In the air conditioner from the second perspective, assuming that the outer diameters of the first heat transfer tube and the second heat transfer tube are the same, the distance from the upstream end of the airflow of the first fin to the upstream end of the airflow of the first heat transfer tube is greater than the distance from the upstream end of the airflow of the second fin to the upstream end of the airflow of the second heat transfer tube. Therefore, the reduction in the frost resistance of the first heat exchanger can be suppressed, and the second heat exchanger can be made smaller.

[0010] The air conditioner of the third perspective is an air conditioner of the first or second perspective, wherein the first fins are arranged in multiples in the direction in which the first heat transfer tube extends. The second fins are arranged in multiples in the direction in which the second heat transfer tube extends. The pitch of the first fins is greater than the pitch of the second fins.

[0011] In the third-party air conditioner, the pitch of the first fin is larger than that of the second fin, which helps to prevent frost buildup on the first fin from obstructing the passage of outside air.

[0012] The air conditioner in the fourth view is an air conditioner according to any of the first or third views, wherein the first fin has a waffle shape.

[0013] In the heat exchanger of the fourth perspective, since the first fin has a waffle shape, it is possible to improve the heat exchange efficiency between carbon dioxide refrigerant and outdoor air in the first heat exchanger while suppressing a decrease in frost resistance.

[0014] The fifth aspect of the air conditioner is an air conditioner according to any of the first or fourth aspects, wherein the second fin has at least one of a slit and a louver formed thereon.

[0015] In the heat exchanger of the fifth perspective, at least one of slits and louvers is formed on the second fin, so that the heat exchange efficiency between carbon dioxide refrigerant and indoor air can be further improved in the second heat exchanger.

[0016] The sixth air conditioner is an air conditioner according to either the first or fifth perspective, wherein multiple first heat transfer tubes are arranged in the first direction, which is the longitudinal direction of the first fin. Multiple second heat transfer tubes are arranged in the second direction, which is the longitudinal direction of the second fin. The pitch of the first heat transfer tubes in the third direction, which is along the fin surface and intersects the first direction, is greater than the pitch of the first heat transfer tubes in the first direction. The pitch of the second heat transfer tubes in the fourth direction, which is along the fin surface and intersects the second direction, is smaller than the pitch of the second heat transfer tubes in the second direction.

[0017] In the sixth aspect of the air conditioner, the pitch of the first heat transfer tubes in the first heat exchanger is made larger in the third direction, which is the direction of airflow, than in the first direction. This further suppresses the decrease in the frost resistance of the first heat exchanger. On the other hand, for the second heat transfer tubes in the second heat exchanger, which does not require consideration of frost formation, the pitch in the fourth direction, which is the direction of airflow, is made smaller than in the second direction. This allows for miniaturization of the second heat exchanger.

[0018] This is a schematic diagram of an air conditioner according to one embodiment of the present disclosure. This is an external view of an air conditioner according to one embodiment of the present disclosure. This is a perspective view of the first heat exchanger. This is a cross-sectional view of the first heat transfer tube. This is a cross-sectional view of region V in Figure 3. This is a cross-sectional view of the first fin along the line VI-VI in Figure 5. This is a cross-sectional view along the line VII-VII in Figure 5. This is a schematic diagram of the second heat exchanger. This is a cross-sectional view of region IX in Figure 8. This is a schematic diagram of the second heat transfer tube. This is a cross-sectional view along the line XI-XI in Figure 9. This is an enlarged perspective view of the first heat exchanger. This is an enlarged perspective view of the second heat exchanger. This is a graph showing the relationship between the fin width and the end face temperature in the embodiment.

[0019] (1) Overall Configuration An air conditioner according to one embodiment of the present disclosure will be described with reference to the drawings. As shown in Figure 1, the air conditioner 1 is a device used for heating and cooling the interior of a building, etc., by operating a vapor compression type refrigeration cycle.

[0020] As shown in Figures 1 and 2, the air conditioner 1 mainly consists of an outdoor unit 2, an indoor unit 3, and a connecting pipe 4 that connects the outdoor unit 2 and the indoor unit 3. The vapor compression type refrigerant circuit 5 of the air conditioner 1 is configured by connecting the outdoor unit 2 and the indoor unit 3 via the connecting pipe 4.

[0021] Carbon dioxide refrigerant flows through refrigerant circuit 5. The carbon dioxide refrigerant is a refrigerant that contains carbon dioxide, and may be a single carbon dioxide refrigerant or a mixture of carbon dioxide refrigerant and other refrigerants. Hereinafter, carbon dioxide refrigerant will also be simply referred to as refrigerant.

[0022] (1-1) Outdoor unit The outdoor unit 2 is located outdoors. As shown in Figure 1, the outdoor unit 2 mainly consists of a compressor 11, a switching mechanism 12, a first heat exchanger 100, and an expansion mechanism 14.

[0023] The compressor 11 is a mechanism that compresses the low-pressure refrigerant in the refrigeration cycle until it reaches a high pressure.

[0024] The switching mechanism 12 is a mechanism that switches the direction of refrigerant flow when switching between cooling operation and heating operation. During cooling operation, the switching mechanism 12 connects the discharge side of the compressor 11 to the gas side of the first heat exchanger 100, and also connects the gas side of the second heat exchanger 200 (described later) to the suction side of the compressor 11 via the gas side connecting pipe 4 (see the solid line of the switching mechanism 12 in Figure 1). During heating operation, the switching mechanism 12 connects the discharge side of the compressor 11 to the gas side of the second heat exchanger 200 via the gas side connecting pipe 4, and also connects the gas side of the first heat exchanger 100 to the suction side of the compressor 11 (see the dashed line of the switching mechanism 12 in Figure 1).

[0025] The first heat exchanger 100 functions as a refrigerant radiator during cooling operation and as a refrigerant evaporator during heating operation. The liquid side of the first heat exchanger 100 is connected to the expansion mechanism 14, and the gas side is connected to the switching mechanism 12.

[0026] The expansion mechanism 14 is a mechanism that, during cooling operation, reduces the pressure of the high-pressure liquid refrigerant that has released heat in the first heat exchanger 100 before sending it to the second heat exchanger 200, and during heating operation, reduces the pressure of the high-pressure liquid refrigerant that has released heat in the second heat exchanger 200 before sending it to the first heat exchanger 100.

[0027] Furthermore, the outdoor unit 2 is equipped with a first fan 15 for drawing in outdoor air into the outdoor unit 2, supplying the outdoor air to the first heat exchanger 100, and then discharging it outside the outdoor unit 2.

[0028] (1-2) Indoor unit The indoor unit 3 is located inside the room. The indoor unit 3 mainly consists of a second heat exchanger 200 and a second fan 16.

[0029] The second heat exchanger 200 functions as a refrigerant evaporator during cooling operation and as a refrigerant radiator during heating operation. The liquid side of the second heat exchanger 200 is connected to the liquid side connecting pipe 4, and the gas side is connected to the gas side connecting pipe 4.

[0030] Furthermore, the indoor unit 3 is equipped with a second fan 16 for drawing in indoor air into the indoor unit 3, supplying the indoor air to the second heat exchanger 200, and then discharging it outside the indoor unit 3.

[0031] (1-3) Operation (1-3-1) Cooling Operation When the air conditioner 1 performs cooling operation, the low-pressure refrigerant in the refrigeration cycle is drawn into the compressor 11, compressed to the high pressure in the refrigeration cycle, and then discharged. The high-pressure refrigerant discharged from the compressor 11 is sent to the first heat exchanger 100 through the switching mechanism 12. The high-pressure refrigerant sent to the first heat exchanger 100 dissipates heat by exchanging heat with the outdoor air supplied by the first fan 15 in the first heat exchanger 100. The high-pressure refrigerant that has dissipated heat in the first heat exchanger 100 is sent to the expansion mechanism 14, where it is reduced in pressure to the low pressure in the refrigeration cycle. The low-pressure refrigerant reduced in pressure in the expansion mechanism 14 is sent to the second heat exchanger 200 through the liquid-side connecting pipe 4. The low-pressure refrigerant sent to the second heat exchanger 200 evaporates by exchanging heat with the indoor air supplied by the second fan 16 in the second heat exchanger 200. As a result, the indoor air is cooled and blown into the room. The low-pressure refrigerant evaporated in the second heat exchanger 200 is drawn back into the compressor 11 through the gas-side connecting pipe 4 and the switching mechanism 12.

[0032] (1-3-2) Heating Operation When the air conditioner 1 performs heating operation, the low-pressure refrigerant in the refrigeration cycle is drawn into the compressor 11, compressed to the high pressure in the refrigeration cycle, and then discharged. The high-pressure refrigerant discharged from the compressor 11 is sent to the second heat exchanger 200 through the switching mechanism 12 and the gas-side connecting pipe 4. The high-pressure refrigerant sent to the second heat exchanger 200 exchanges heat with the indoor air supplied by the second fan 16 and dissipates heat. As a result, the indoor air is heated and blown into the room. The high-pressure refrigerant that has dissipated heat in the second heat exchanger 200 is sent to the expansion mechanism 14 through the liquid-side connecting pipe 4 and is reduced in pressure to the low pressure in the refrigeration cycle. The low-pressure refrigerant reduced in pressure in the expansion mechanism 14 is sent to the first heat exchanger 100. The low-pressure refrigerant sent to the first heat exchanger 100 exchanges heat with the outdoor air supplied by the first fan 15 and evaporates. The low-pressure refrigerant evaporated in the first heat exchanger 100 is drawn back into the compressor 11 through the switching mechanism 12.

[0033] (2) Detailed Configuration The details of the first and second heat exchangers will be described below. In the following description, expressions indicating directions such as "up," "down," "left," "right," "front," and "back" will be used as appropriate, but these represent the directions in the normal operating state and are not limited to those directions.

[0034] (2-1) First heat exchanger The first heat exchanger 100 is an outdoor heat exchanger located outside the room. The first heat exchanger 100 is a cross-fin type heat exchanger. The first heat exchanger performs heat exchange between the outdoor air and the carbon dioxide refrigerant without mixing them.

[0035] As shown in Figure 3, the first heat exchanger 100 exchanges heat between the outdoor air blown from the back to the front of the outdoor unit 2 casing by the first fan 15 and the carbon dioxide refrigerant flowing inside the first heat transfer tube 110. In Figure 3, the first heat exchanger 100 is L-shaped.

[0036] As shown in Figure 3, the first heat exchanger 100 has a plurality of first heat transfer tubes 110 and a plurality of first fins 120.

[0037] The first heat transfer tube 110 has carbon dioxide refrigerant flowing through it. The first heat transfer tube 110 has a cylindrical shape. Here, the first heat transfer tube 110 is a round tube. The first heat transfer tube 110 has through holes through which the carbon dioxide refrigerant, which is exchanged with the outside air in the first heat exchanger 100, passes.

[0038] As shown in Figure 4, the outer diameter O1 of the first heat transfer tube 110 is 5.5 mm or less. The outer diameter O1 is the equivalent diameter of a circle having an area equal to the cross-sectional area of ​​the first heat transfer tube 110. The lower limit of the outer diameter O1 of the first heat transfer tube 110 is, for example, 4.0 mm, and preferably 5.0 mm.

[0039] The thickness T1 of the first heat transfer tube 110 is, for example, 0.43 mm or less. Therefore, the inner diameter I1 of the first heat transfer tube is, for example, 5.1 mm or less, preferably 4.6 mm or less, and more preferably 4.5 mm or less.

[0040] Such first heat transfer tubes 110 can be realized, for example, by expanding a tube with an outer diameter of 5.0 mm or less. Specifically, through-holes larger than the outer diameter of the tube are formed in the first fins 120, and the tube is passed through the through-holes. Then, a ball with a diameter larger than the inner diameter of the tube is passed through the interior of the tube, mechanical pressure is applied to the tube to expand it, and the outer diameter of the tube is increased, thereby forming the first heat transfer tube 110. In addition, the first fins 120 are joined to the first heat transfer tube 110 by tube expansion.

[0041] A plurality of the first heat transfer tubes 110 are arranged in the first direction, as indicated by hatching in the cross-sectional view shown in FIG. 5. The first direction is the longitudinal direction of the first fins 120. The first direction here is the vertical direction. The centers of the first heat transfer tubes 110 adjacent to each other in the first direction are located on a single virtual line extending in the first direction.

[0042] The first heat transfer tube 110 extends in the fifth direction. In FIG. 3, the first heat transfer tube 110 has an L-shape when viewed in the first direction. Here, the first heat transfer tube 110 is composed of an L-shaped long side portion and an L-shaped short side portion. Specifically, the first heat transfer tube 110 has a portion extending in the left-right direction as the long side portion, and a portion extending in the front-rear direction as the short side portion.

[0043] In the present embodiment, as shown in FIG. 5, a plurality of the first heat transfer tubes 110 are arranged in the third direction. Although two rows are illustrated as the plurality in FIG. 5, three or more rows may be provided. The third direction is along the fin surfaces of the first fins 120 and intersects the first direction. Here, the third direction is along the fin surfaces and perpendicular to the first direction. Note that the third direction intersects the first direction and the fifth direction, and is orthogonal to the first direction and the fifth direction here.

[0044] As shown in FIG. 3, at the long side portion of the first heat transfer tube 110, the third direction is the front-rear direction, and the fifth direction is the left-right direction. At the short side portion of the first heat transfer tube 110, the third direction is the left-right direction, and the fifth direction is the front-rear direction. As such, in the present embodiment, the third direction and the fifth direction do not necessarily match the front-rear and left-right directions.

[0045] The centers of the first heat transfer tubes 110 adjacent in the third direction are not positioned on a single virtual line extending in the third direction, and are offset from each other.

[0046] The third pitch P3 of the first heat transfer tubes 110 in the third direction is larger than the first pitch P1 of the first heat transfer tubes 110 in the first direction, and is preferably 1.1 times or more.

[0047] Note that the first pitch P1 is the distance connecting the centers of the first heat transfer tubes 110 adjacent in the first direction. The third pitch P3 is the distance obtained by moving the centers of the two first heat transfer tubes 110 adjacent in the third direction onto a single virtual line extending in the third direction.

[0048] The first fin 120 is joined to the first heat transfer tube 110. Here, the first fin 120 is in contact with the first heat transfer tube 110. The first fin 120 increases the heat transfer area between the first heat transfer tube 110 and the outdoor air, and promotes heat exchange between the carbon dioxide refrigerant and the outdoor air.

[0049] As shown in FIG. 3, a plurality of the first fins 120 are arranged side by side in the extending direction of the first heat transfer tubes 110. Here, the plurality of first fins are arranged in the third direction and the fifth direction. The first fins 120 are disposed so as to intersect (here, be orthogonal to) the extending direction of the first heat transfer tubes 110. In the present embodiment, the plurality of first fins 120 are arranged in parallel and at equal intervals. The first fin 120 has a fin surface on one side and a fin surface on the other side.

[0050] As shown in FIGS. 5 to 7, the first fin 120 includes a main body portion 121 and a collar portion 122. The main body portion 121 has a plate shape extending in the first direction. The main body portion 121 constitutes the fin surface of the first fin 120. As shown in FIGS. 5 and 6, the main body portion 121 has a waffle shape for improving the heat transfer performance of the first fin 120. The waffle shape is a shape that protrudes toward one side in the thickness direction (the fifth direction) of the main body portion 121, as shown in FIG. 6.

[0051] As shown in FIGS. 5 and 7, the collar portion 122 allows the first heat transfer tube 110 to pass therethrough. Specifically, the collar portion 122 has a through hole for allowing the first heat transfer tube 110 to pass therethrough.

[0052] The colored portion 122 has a first portion 123, a second portion 124, a third portion 125, and a fourth portion 126. The first portion 123, the second portion 124, the third portion 125, and the fourth portion 126 are made from a single component. Here, the first portion 123, the second portion 124, the third portion 125, and the fourth portion 126 are nested.

[0053] The first part 123 extends from the main body 121 in the directions of the composite components in the third and fifth directions, as well as in the first direction. The second part 124 extends from the first part 123 toward the first heat transfer tube 110. In other words, the second part 124 extends in the third direction. The third part 125 extends from the second part 124 along the first heat transfer tube 110 in the fifth direction, as well as in the first direction. The third part 125 is in contact with the first heat transfer tube 110. The fourth part 126 extends from the third part 125 toward the outer circumference. In other words, the fourth part 126 extends in the third direction, as well as in the first direction.

[0054] Furthermore, each first fin 120 may be separated or integrated for each portion corresponding to a row of first heat transfer tubes 110 arranged in a first direction. In Figure 5, the edges 128 of the first fin 120 corresponding to a row of first heat transfer tubes 110 may be separated or integrated.

[0055] (2-2) Second Heat Exchanger The second heat exchanger 200 is an indoor heat exchanger located inside the room. The second heat exchanger 200 is a cross-fin type heat exchanger. The second heat exchanger 200 performs heat exchange between indoor air and carbon dioxide refrigerant without mixing them.

[0056] As shown in Figure 8, the second heat exchanger 200 performs heat exchange between indoor air, which is blown by the second fan 16 toward the front side of the casing of the indoor unit 3, and carbon dioxide refrigerant flowing inside the second heat transfer tube 210.

[0057] As shown in Figure 9, the second heat exchanger 200 has a plurality of second heat transfer tubes 210 and a plurality of second fins 220.

[0058] The second heat transfer tube 210 has carbon dioxide refrigerant flowing through it. The second heat transfer tube 210 has a cylindrical shape. Here, the second heat transfer tube 210 is a round tube. The second heat transfer tube 210 has through holes through which the carbon dioxide refrigerant, which is exchanged with the room air in the second heat exchanger 200, passes.

[0059] As shown in Figure 10, the outer diameter O2 of the second heat transfer tube 210 is 5.5 mm or less. The outer diameter O2 is the equivalent diameter of a circle having an area equal to the cross-sectional area of ​​the second heat transfer tube 210. The lower limit of the outer diameter O2 of the second heat transfer tube 210 is, for example, 4.0 mm, and preferably 5.0 mm.

[0060] The thickness T1 of the second heat transfer tube 210 is, for example, 0.43 mm or less. Therefore, the inner diameter I2 of the second heat transfer tube is, for example, 5.1 mm or less, 4.6 mm or less, and more preferably 4.5 mm or less.

[0061] Such a second heat transfer tube 210 can be realized, like the first heat transfer tube 110, for example, by expanding a tube with an outer diameter of 5.0 mm or less.

[0062] Multiple second heat transfer tubes 210 are arranged in the second direction, as indicated by the hatching in the cross-sectional view shown in Figure 9. The second direction is the longitudinal direction of the second fin 220. The centers of adjacent second heat transfer tubes 210 in the second direction are located on a single imaginary line extending in the second direction.

[0063] In the cross-sectional view shown in Figure 9, the second heat transfer tubes 210 are arranged in a fourth direction. The fourth direction intersects the second direction and, in this embodiment, is perpendicular to the second direction. More specifically, in the cross-sectional view of the second heat transfer tubes 210, the fourth direction runs along the fin surface of the second fin 220 and intersects the second direction. In this embodiment, the fourth direction runs along the fin surface and is perpendicular to the second direction. The centers of adjacent second heat transfer tubes 210 in the fourth direction are offset and not located on a single imaginary line extending in the fourth direction.

[0064] The fourth pitch P4 of the second heat transfer tube 210 in the fourth direction is smaller than the second pitch P2 of the second heat transfer tube 210 in the second direction, preferably 0.9 times or less.

[0065] The second pitch P2 is the distance between the centers of adjacent second heat transfer tubes 210 in the second direction. The fourth pitch P4 is the distance between the centers of two adjacent second heat transfer tubes 210 in the fourth direction, shifted onto a single imaginary line extending in the fourth direction.

[0066] The second fin 220 is joined to the second heat transfer tube 210. Here, the second fin 220 is in contact with the second heat transfer tube 210. The second fin 220 increases the heat transfer surface area between the second heat transfer tube 210 and the indoor air, thereby promoting heat exchange between the carbon dioxide refrigerant and the outdoor air.

[0067] Multiple second fins 220 are arranged in the direction in which the second heat transfer tube 210 extends. The second fins 220 are positioned so as to intersect (in this case, perpendicular to) the direction in which the second heat transfer tube 210 extends. In this embodiment, the multiple second fins 220 are arranged parallel to each other and at equal intervals. Each second fin 220 has a fin surface on one side and a fin surface on the other side.

[0068] As shown in Figures 9 and 11, the second fin 220 includes a main body portion 221 and a collar portion 222. In Figure 11, the direction in which the second heat transfer tube 210 extends is defined as the sixth direction. The main body portion 221 is plate-shaped and extends in the first direction. The main body portion 221 has slits 229 formed therein to improve the heat transfer performance of the second fin 220. The slits 229 are openings cut and raised on one side in the thickness direction of the main body portion 221. Multiple slits 229 are arranged in the second and fourth directions.

[0069] The collar portion 222 allows the second heat transfer tube 210 to pass through. More specifically, the collar portion 222 has a through hole for the second heat transfer tube 210 to pass through.

[0070] As shown in Figure 11, the color portion 222 has a first portion 223, a second portion 224, a third portion 225, and a fourth portion 226. The first portion 223, the second portion 224, the third portion 225, and the fourth portion 226 are made from a single component. Here, the first portion 223, the second portion 224, the third portion 225, and the fourth portion 226 are nested.

[0071] The first part 223 extends from the main body 221 along the direction in which the second heat transfer tube 210 extends. The second part 224 extends from the first part 223 toward the second heat transfer tube 210. In other words, the second part 224 extends in the fourth direction. The third part 225 extends from the second part 224 along the second heat transfer tube 210. The third part 225 is in contact with the second heat transfer tube 210. The fourth part 226 extends from the third part 225 toward the outer circumference. In other words, the fourth part 226 extends in the fourth direction.

[0072] Furthermore, each second fin 220 may be separated or integrated for each portion corresponding to a row of second heat transfer tubes 210 arranged in the second direction. In Figure 9, the edges 228 of the second fin 220 corresponding to a row of second heat transfer tubes 210 may be separated or integrated.

[0073] (2-3) Relationship between the first heat exchanger and the second heat exchanger The distance L1 from the upstream end 127 of the airflow of the first fin 120 shown in Figure 5 to the upstream end 117 of the airflow of the first heat transfer tube 110 is greater than the distance L2 from the upstream end 227 of the airflow of the second fin 220 shown in Figure 9 to the upstream end 217 of the airflow of the second heat transfer tube 210, and is preferably 1.1 times or more.

[0074] In Figures 5 and 9, the airflow is indicated by arrows, with the right side representing the upstream direction and the left side representing the downstream direction. Here, the upstream end 127 of the first fin 120 extends in the first direction. The upstream end 227 of the second fin 220 extends in the second direction.

[0075] On the other hand, the outer diameter O2 of the second heat transfer tube 210 shown in Figure 10 is the same as the outer diameter O1 of the first heat transfer tube 110 shown in Figure 4. Here, "same" includes cases where the values ​​are exactly the same and cases where the values ​​are considered to be substantially the same. Cases where the values ​​are considered to be substantially the same include, for example, when the outer diameter O2 of the second heat transfer tube 210 is within the range of 90% to 110% of the outer diameter O1 of the first heat transfer tube 110.

[0076] Furthermore, the pitch P120 of the first fin 120 shown in Figure 12 is larger than the pitch P220 of the second fin 220 shown in Figure 13, preferably 1.1 times or more. The pitch P120 is the distance between adjacent first fins 120. More specifically, the fin pitch P120 is the distance between the opposing faces of adjacent first fins 120. Similarly, the fin pitch P220 is the distance between adjacent second fins 220. More specifically, the pitch P220 is the distance between the opposing faces of adjacent second fins 220.

[0077] The width of the first fin 120 and the width of the second fin 220 may be the same or different. Here, the width L120 (see Figure 5) of the first fin 120 corresponding to one row of first heat transfer tubes 110 is larger than the width L220 (see Figure 9) of the second fin 220 corresponding to one row of second heat transfer tubes 210. The width L120 is the length in the third direction of the first fin 120 that is joined to one row of first heat transfer tubes 110 arranged in the first direction. The width L220 is the length in the fourth direction of the second fin 220 that is joined to one row of second heat transfer tubes 210 arranged in the second direction.

[0078] (3) Features (3-1) The air conditioner 1 of this embodiment comprises a first heat exchanger 100 and a second heat exchanger 200. The first heat exchanger 100 is a cross-fin type heat exchanger located outdoors. The second heat exchanger 200 is a cross-fin type heat exchanger located indoors. The first heat exchanger 100 has a first heat transfer tube 110 and a first fin 120. The first heat transfer tube 110 has an outer diameter O1 of 5.5 mm or less. The first fin 120 is joined to the first heat transfer tube 110. The first heat exchanger 100 performs heat exchange between carbon dioxide refrigerant flowing inside the first heat transfer tube 110 and outdoor air flowing outside the first heat transfer tube 110. The second heat exchanger 200 has a second heat transfer tube 210 and a second fin 220. The second heat transfer tube 210 has an outer diameter O2 of 5.5 mm or less. The second fin 220 is joined to the second heat transfer tube 210. The second heat exchanger 200 performs heat exchange between carbon dioxide refrigerant flowing inside the second heat transfer tube 210 and room air flowing outside the second heat transfer tube 210. The distance L1 from the airflow upstream end 127 of the first fin 120 to the airflow upstream end 117 of the first heat transfer tube 110 is greater than the distance L2 from the airflow upstream end 227 of the second fin 220 to the airflow upstream end 217 of the second heat transfer tube 210.

[0079] The pressure resistance of heat transfer tubes filled with carbon dioxide refrigerant is higher than that of heat transfer tubes filled with refrigerants such as R32. For this reason, when filling heat transfer tubes with an outer diameter of 7 mm or more with carbon dioxide refrigerant, as in the above-mentioned Patent Document 1, it is necessary to increase the thickness of the heat transfer tubes.

[0080] In contrast, in the air conditioner 1 of this embodiment, the outer diameter O1 of the first heat transfer tube 110 and the outer diameter O2 of the second heat transfer tube 210 are set to 5.5 mm or less. Therefore, even when carbon dioxide refrigerant is sealed in the first and second heat transfer tubes, it is possible to suppress an increase in the thickness of the first and second heat transfer tubes 110 and 210. In detail, the pressure resistance P of the heat transfer tube is expressed by the formula P = 2σt / D. In this formula, σ is the tensile strength, t is the thickness of the heat transfer tube, and D is the inner diameter of the heat transfer tube. If the material of the heat transfer tube is the same, the tensile strength is the same, so in order for the heat transfer tube to have a predetermined pressure resistance P, the thickness can be reduced by reducing the inner diameter of the heat transfer tube. Therefore, in this embodiment, it is possible to suppress an increase in cost that would occur as the thickness of the first and second heat transfer tubes 110 and 210 increases.

[0081] On the other hand, in heat exchangers located outdoors, if the fins are reduced in size while maintaining a similar shape so that the outer diameter of the heat transfer tubes is 7 mm or more to 5.5 mm or less, the distance from the upstream end of the airflow on the fins to the upstream end of the airflow on the heat transfer tubes becomes smaller, reducing the frost resistance. Furthermore, the second heat exchanger located indoors must be placed in the limited space of the indoor unit. Thus, the required functions of heat exchangers located outdoors and heat exchangers located indoors are different.

[0082] Therefore, in the air conditioner 1 of this embodiment, the distance L1 from the upstream end 127 of the airflow of the first fin 120 to the upstream end 117 of the airflow of the first heat transfer tube 110 is made larger than the distance L2 from the upstream end 227 of the airflow of the second fin 220 to the upstream end of the airflow of the second heat transfer tube 210. As a result, in the first heat exchanger 100 located outdoors, the distance L1 between the upstream end 127 of the airflow of the first fin 120, which is prone to frost formation, and the first heat transfer tube 110 through which the carbon dioxide refrigerant flows is increased. Consequently, during heating operation, the cold energy of the carbon dioxide refrigerant flowing through the first heat transfer tube 110 is less likely to be transmitted towards the upstream end 127 of the airflow of the first fin 120, so that even if the outer diameter O1 is 5.5 mm or less, the frost resistance can be improved to the same level as that of a heat transfer tube with an outer diameter of about 7 mm. Therefore, a decrease in frost resistance can be suppressed.

[0083] Furthermore, in the second heat exchanger 200 located inside the room, the distance L2 from the upstream end 227 of the airflow of the second fin 220 to the second heat transfer tube 210 becomes smaller. Therefore, the second heat exchanger 200 can be made smaller.

[0084] Thus, the air conditioner 1 of this embodiment suppresses the cost of air conditioners using carbon dioxide refrigerant, while also achieving both the frost resistance required for heat exchangers located outdoors and the compactness required for heat exchangers located indoors.

[0085] Therefore, the air conditioner 1 of this embodiment makes it possible to delay frost formation, shorten the time required for defrosting when frost forms, and improve heat transfer performance by increasing the heat transfer area of ​​the first fin 120.

[0086] (3-2) In the air conditioner of this embodiment, the outer diameter O2 of the second heat transfer tube 210 is the same as the outer diameter O1 of the first heat transfer tube 110.

[0087] Here, assuming that the outer diameter O1 of the first heat transfer tube 110 and the outer diameter O2 of the second heat transfer tube 210 are the same, the distance L1 from the upstream end 127 of the airflow of the first fin 120 to the upstream end 117 of the airflow of the first heat transfer tube 110 is greater than the distance L2 from the upstream end 227 of the airflow of the second fin 220 to the upstream end 217 of the airflow of the second heat transfer tube 210. As a result, the reduction in the frost resistance of the first heat exchanger 100 can be suppressed, and the second heat exchanger 200 can be made smaller.

[0088] (3-3) In the air conditioner 1 of this embodiment, the first fins 120 are arranged in a plurality in the direction in which the first heat transfer tube 110 extends. The second fins 220 are arranged in a plurality in the direction in which the second heat transfer tube 210 extends. The pitch P120 of the first fins 120 is greater than the pitch P220 of the second fins 220.

[0089] Here, the pitch P120 of the first fin 120 is made larger than the pitch P220 of the second fin 220, so that when frost forms, it is possible to suppress the obstruction of outside air passage due to frost adhering to the first fin 120. In other words, it is possible to suppress the blockage of the space between adjacent first fins 120 by frost. Therefore, it is possible to suppress the deterioration of the performance of the first heat exchanger 100.

[0090] Furthermore, because the pitch P220 of the second fin 220 is small, the second heat exchanger 200 can be made smaller.

[0091] (3-4) In the air conditioner 1 of this embodiment, the first fin 120 has a waffle shape.

[0092] Here, since the first fin 120 has a waffle shape, the heat exchange efficiency between the carbon dioxide refrigerant and the outdoor air in the first heat exchanger 100 can be improved. In addition, since the waffle shape does not have openings for air to pass through, a decrease in frost resistance can be suppressed.

[0093] (3-5) In the air conditioner 1 of this embodiment, a slit 229 is formed in the second fin 220.

[0094] In this case, since frost formation does not need to be considered for the second fin 220, the heat exchange efficiency between carbon dioxide refrigerant and indoor air in the second heat exchanger 200 can be further improved by forming the slit 229.

[0095] (3-6) In the air conditioner 1 of this embodiment, multiple first heat transfer tubes 110 are arranged in a first direction which is the longitudinal direction of the first fin 120. Multiple second heat transfer tubes 210 are arranged in a second direction which is the longitudinal direction of the second fin 220. The pitch P3 of the first heat transfer tubes 110 in a third direction which is along the fin surface of the first fin 120 and intersects the first direction is greater than the pitch P1 of the first heat transfer tubes 110 in the first direction. The pitch P4 of the second heat transfer tubes 210 in a fourth direction which is along the fin surface of the second fin 220 and intersects the second direction is smaller than the pitch P2 of the second heat transfer tubes 210 in the second direction.

[0096] Here, for the first heat transfer tube 110 of the first heat exchanger 100, the pitch P3 in the third direction, which is the airflow direction, is made larger than the pitch P1 in the first direction. This further suppresses the decrease in the frost resistance of the first heat exchanger 100. On the other hand, for the second heat transfer tube 210 of the second heat exchanger 200, which does not require consideration of frost formation, the pitch P4 in the fourth direction, which is the airflow direction, is made smaller than the pitch P2 in the second direction. This makes it possible to miniaturize the second heat exchanger 200.

[0097] (4) Modified Examples (4-1) Modified Example 1 In the above embodiment, a first heat exchanger 100 in which multiple first heat transfer tubes 110 are arranged in the first and third directions of the first fin 120, and a second heat exchanger 200 in which multiple second heat transfer tubes 210 are arranged in the second and fourth directions of the second fin 220 were described as examples, but the invention is not limited thereto. In this modified example, in the first heat exchanger 100, multiple first heat transfer tubes 110 are arranged in the first direction of the first fin 120, but there is only one first heat transfer tube 110 arranged in the third direction of the first fin 120. Also, in the second heat exchanger 200, multiple second heat transfer tubes 210 are arranged in the second direction of the second fin 220, but there is only one second heat transfer tube 210 arranged in the fourth direction of the second fin 220.

[0098] In this case, the pitch P3 of the first heat transfer tube 110 in the third direction is the width of the first fin 120. Also, the pitch P4 of the second heat transfer tube 210 in the fourth direction is the width of the second fin 220.

[0099] (4-2) Modification 2 In the above embodiment, a slit 229 is formed on the second fin 220, but it is not limited thereto. A louver may be formed on the second fin 220 instead of the slit 229, or in combination with the slit 229. The louver is formed by cutting and raising a portion of the upwind side so that the downwind side is open, in order to improve the heat transfer performance of the second fin 220.

[0100] Thus, in the air conditioner 1, it is preferable that at least one of the slits 229 and louvers is formed on the second fin 220. This makes it possible to further improve the heat exchange efficiency between the carbon dioxide refrigerant and the outdoor air in the second heat exchanger 200.

[0101] (4-3) Modification 3 In the embodiments and modification 2 described above, the shape, number, arrangement, etc., of at least one of the waffle portion for heat transfer promotion formed on the first fin 120 and the slit 229 and louvers formed on the second fin 220 are not limited. The waffle portion, slit and louvers may extend in other directions and may protrude to the other side of the fin.

[0102] (5) Example In this example, the effect of increasing the distance from the upstream end of the airflow on the fins to the upstream end of the airflow on the heat transfer tubes in a heat exchanger located outdoors was investigated.

[0103] Specifically, for a first heat exchanger equipped with a first heat transfer tube with an outer diameter of 5.3 mm, the temperature of the first fin 120 during heating operation was simulated when the width L120 in Figure 5 was varied in various ways. The refrigerant flowing through the first heat transfer tube was carbon dioxide as the sole refrigerant. The wind speed of the outdoor air was set to 1.0 [m / s]. As a result, the temperature of the first fin 120 was lowest at the upstream end 127 of the airflow.

[0104] As a result of the simulation, Figure 14 shows the temperature of the upstream end 127 of the airflow of the first fin 120 for each width L120. In Figure 14, the horizontal axis represents the width of the first fin when the first heat transfer tubes are in a single row, and the vertical axis represents the temperature (end face temperature) of the upstream end of the airflow of the first fin.

[0105] Furthermore, as a comparative example, a simulation was performed under similar conditions on an outdoor heat exchanger of the comparative example, which had an outer diameter of 7.4 mm and a width of 13.6 mm for the heat transfer tubes. The result showed that the temperature at the upstream end 127 of the airflow of the first fin was -8.3°C. Figure 14 shows the temperature of the comparative example as a dotted line.

[0106] As shown in Figure 14, it was found that for a first heat exchanger using a first heat transfer tube with an outer diameter of 5.5 mm or less, increasing the width of the first fin can raise the temperature at the upstream end of the airflow of the first fin. As a result, the cold energy of the carbon dioxide refrigerant flowing through the first heat transfer tube is less likely to be transferred to the upstream end of the airflow of the first heat transfer tube, thereby suppressing a decrease in frost resistance.

[0107] Furthermore, as shown in Figure 14, even when the outer diameter O1 of the first heat transfer tube is 5.5 mm, it was found that by setting the width L120 of the first fin to 14 mm, the temperature at the upstream end of the airflow of the first fin becomes approximately the same as when the outer diameter of the heat transfer tube is 7 mm.

[0108] In particular, it was found that when the outer diameter O1 of the first heat transfer tube is 5.5 mm, the reduction in frost resistance can be effectively suppressed by making the width L120 of the first fin 18 mm or more. In this case, the distance L1 from the upstream end of the airflow of the first fin 120 to the upstream end of the airflow of the first heat transfer tube 110 is 7.5 mm. For this reason, it was found that it is preferable for the distance L1 from the upstream end of the airflow of the first fin 120 to the upstream end of the airflow of the first heat transfer tube 110 to be 7.5 mm or more.

[0109] While embodiments of this disclosure have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of this disclosure as described in the claims.

[0110] 1: Air conditioner 100: First heat exchanger 110: First heat transfer tube 117: Upstream end 120: First fin 127: Upstream end 200: Second heat exchanger 210: Second heat transfer tube 217: Upstream end 220: Second fin 227: Upstream end 229: Slit L1, L2: Distance O1, O2: Outer diameter P1, P2, P3, P4, P120, P220: Pitch

[0111] Japanese Patent Publication No. 2010-48551

Claims

1. A cross-fin type first heat exchanger (100) located outdoors, and a cross-fin type second heat exchanger (200) located indoors, wherein the first heat exchanger has a first heat transfer tube (110) with an outer diameter (O1) of 5.5 mm or less, and a first fin (120) joined to the first heat transfer tube, and performs heat exchange between carbon dioxide refrigerant flowing inside the first heat transfer tube and outdoor air flowing outside the first heat transfer tube, and the second heat exchanger has a second heat transfer tube (210) with an outer diameter (O2) of 5.5 mm or less, and a second fin (220) joined to the second heat transfer tube, and performs heat exchange between carbon dioxide refrigerant flowing inside the second heat transfer tube and indoor air flowing outside the second heat transfer tube, An air conditioner (1) in which the distance (L1) from the upstream end (127) of the airflow of the first fin to the upstream end (117) of the airflow of the first heat transfer tube is greater than the distance (L2) from the upstream end (227) of the airflow of the second fin to the upstream end (217) of the airflow of the second heat transfer tube.

2. The air conditioner according to claim 1, wherein the outer diameter of the second heat transfer tube is the same as the outer diameter of the first heat transfer tube.

3. The air conditioner according to claim 1 or 2, wherein the first fins are arranged in a plurality in the direction in which the first heat transfer tube extends, the second fins are arranged in a plurality in the direction in which the second heat transfer tube extends, and the pitch of the first fins (P120) is greater than the pitch of the second fins (P220).

4. The air conditioner according to any one of claims 1 to 3, wherein the first fin has a waffle shape.

5. The air conditioner according to any one of claims 1 to 4, wherein at least one of a slit (229) and a louver is formed on the second fin.

6. The air conditioner according to any one of claims 1 to 5, wherein the first heat transfer tubes are arranged in a plurality in a first direction which is the longitudinal direction of the first fin, and the second heat transfer tubes are arranged in a plurality in a second direction which is the longitudinal direction of the second fin, and the pitch (P3) of the first heat transfer tubes in a third direction which is along the fin surface and intersects the first direction is greater than the pitch (P1) of the first heat transfer tubes in the first direction, and the pitch (P4) of the second heat transfer tubes in a fourth direction which is along the fin surface and intersects the second direction is smaller than the pitch (P2) of the second heat transfer tubes in the second direction.

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