Outdoor unit and refrigeration cycle device

Abstract

This outdoor unit is provided with a compressor, an outdoor heat exchanger having a plurality of heat transfer tubes that extend in the vertical direction, and an auxiliary heat exchanger that supercools a refrigerant flowing out from the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser. The dryness of refrigerant at a refrigerant outlet of the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser is 0.

Description

Outdoor unit and refrigeration cycle system

[0001] This disclosure relates to an outdoor unit and a refrigeration cycle system equipped with a heat exchanger.

[0002] Conventionally, a vertical heat transfer tube heat exchanger is known, comprising a plurality of flattened tubes arranged horizontally with spacing between them, with the vertical direction being the direction of tube extension; a plurality of fins connected between adjacent flattened tubes to transfer heat to the flattened tubes; and headers provided at the upper and lower ends of the plurality of flattened tubes, respectively (see, for example, Patent Document 1).

[0003] Japanese Patent Publication No. 2014-194339

[0004] In vertical heat transfer tube heat exchangers, liquid stagnation can occur due to the effect of liquid head as the gaseous refrigerant flowing into the heat exchanger rises. To reduce liquid head, it is desirable for the refrigerant flowing through the heat exchanger to be in a two-phase state. However, if the refrigerant flowing out of the heat exchanger is not sufficiently subcooled, the two-phase refrigerant will flow into the expansion valve, causing problems such as abnormal noise in the expansion valve.

[0005] This disclosure aims to solve the above-mentioned problems and to provide an outdoor unit and refrigeration cycle system that can suppress both liquid stagnation in the heat exchanger and the generation of abnormal noise in the expansion valve.

[0006] The outdoor unit according to this disclosure comprises a compressor, an outdoor heat exchanger having a plurality of heat transfer tubes extending in the vertical direction, and an auxiliary heat exchanger that subcools the refrigerant flowing out of the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser, wherein the dryness of the refrigerant at the refrigerant outlet of the outdoor heat exchanger is 0 when the outdoor heat exchanger functions as a condenser.

[0007] The refrigeration cycle system relating to this disclosure comprises the above-mentioned outdoor unit and an indoor unit equipped with an indoor heat exchanger and connected to the outdoor unit by piping.

[0008] According to the outdoor unit and refrigeration cycle system of this disclosure, both liquid stagnation in the outdoor heat exchanger and the generation of abnormal noise in the expansion valve can be suppressed.

[0009] This is a schematic diagram of the refrigeration cycle device according to Embodiment 1. This is a flowchart showing the flow of bypass valve opening control by the control device according to Embodiment 1. This is a perspective view of the outdoor heat exchanger according to Embodiment 1. This is a front view of the outdoor heat exchanger according to Embodiment 1. This is a diagram illustrating liquid stagnation in the heat exchanger. This is a p-h diagram of the refrigeration cycle device according to Embodiment 1 during cooling operation. This is a flowchart showing the control flow of the compressor and outdoor fan by the control device according to Embodiment 2. This is a perspective view of the outdoor heat exchanger according to Modification 1. This is a perspective view of the outdoor heat exchanger according to Modification 2. This is a diagram illustrating the shower pipe according to Modification 3. This shows the total flow path cross-sectional area and ΔP of the heat exchanger core of the heat exchanger. ＨＥＸ / ΔP ＨＥＡＤ This is a diagram showing the relationship between the two.

[0010] The embodiments of the outdoor unit and refrigeration cycle device relating to this disclosure will be described below with reference to the drawings. In each drawing, components denoted by the same reference numerals are the same or equivalent components, and this is common throughout the entire specification. However, the relative dimensions or shapes of the components in each drawing may differ from those of the actual components. Furthermore, the high and low values ​​of pressure and temperature are not determined in relation to absolute values, but rather are determined relatively in relation to the state and operation of the device, etc.

[0011] Embodiment 1. Figure 1 is a schematic diagram of the refrigeration cycle device 100 according to Embodiment 1. The refrigeration cycle device 100 in this embodiment is a direct-expansion type air conditioning device for air conditioning a room. However, the refrigeration cycle device 100 is not limited to a direct-expansion type air conditioning device, and may also be a heat pump chiller that uses chilled or hot water for air conditioning, a cooling-only device without a cooling / heating switch, or a chiller for cooling a refrigerated warehouse.

[0012] As shown in Figure 1, the refrigeration cycle system 100 comprises an outdoor unit 1 installed outdoors, an indoor unit 2 installed in a room that is the space to be air-conditioned, and a control device 3. The outdoor unit 1 and the indoor unit 2 are connected by refrigerant piping 4 and wiring such as power lines or signal lines. Furthermore, the outdoor unit 1 and the indoor unit 2 and the control device 3 are connected via wired or wireless communication.

[0013] The outdoor unit 1 includes a compressor 11, a flow path switching valve 12, an outdoor heat exchanger 13, an auxiliary heat exchanger 14, a bypass valve 15, an accumulator 16, and an outdoor fan 17. The indoor unit 2 includes an expansion valve 21, an indoor heat exchanger 22, and an indoor fan 23.

[0014] The compressor 11, flow path switching valve 12, outdoor heat exchanger 13, auxiliary heat exchanger 14, expansion valve 21, indoor heat exchanger 22, and accumulator 16 are connected by piping in this order to form a refrigerant circuit. The refrigerant circulating in the refrigerant circuit of the refrigeration cycle device 100 is, for example, a natural refrigerant such as carbon dioxide, hydrocarbons, or helium, a chlorine-free refrigerant such as HFC410A or HFC407C, or a fluorocarbon refrigerant such as R22 or R134a.

[0015] The compressor 11 draws in low-pressure gaseous refrigerant, compresses it, and discharges it as high-pressure gaseous refrigerant. Examples of compressors used for the compressor 11 include reciprocating, rotary, scroll, and screw compressors. The operating frequency of the compressor 11 is controlled by the control device 3.

[0016] The flow path switching valve 12 switches between cooling operation, in which the outdoor heat exchanger 13 functions as a condenser, and heating operation, in which the outdoor heat exchanger 13 functions as an evaporator. The flow path switching valve 12 is, for example, a four-way valve, and its switching is controlled by the control device 3. During cooling operation, the flow path switching valve 12 is switched so that the refrigerant discharged from the compressor 11 flows into the outdoor heat exchanger 13, as shown by the solid line in Figure 2. During heating operation, the flow path switching valve 12 is switched so that the refrigerant discharged from the compressor 11 flows into the indoor heat exchanger 22, as shown by the dashed line in Figure 1.

[0017] The outdoor heat exchanger 13 is, for example, a fin-tube type heat exchanger, and performs heat exchange between the refrigerant circulating inside the heat transfer tubes 131 (Figure 3) and the air supplied by the outdoor fan 17. The outdoor heat exchanger 13 is positioned between the flow path switching valve 12 and the auxiliary heat exchanger 14. The outdoor heat exchanger 13 functions as a condenser during cooling operation and as an evaporator during heating operation.

[0018] The auxiliary heat exchanger 14 is, for example, a double-pipe or plate-type heat exchanger. The auxiliary heat exchanger 14 has a first flow path 14a and a second flow path 14b, and is a refrigerant-to-refrigerant heat exchanger that performs heat exchange between the refrigerant flowing through the first flow path 14a and the refrigerant flowing through the second flow path 14b. When the refrigeration cycle device 100 is in cooling operation, the refrigerant that has flowed out from the outdoor heat exchanger 13 flows through the first flow path 14a of the auxiliary heat exchanger 14, and the refrigerant that has passed through the first flow path 14a and the bypass piping 41 of the auxiliary heat exchanger 14 flows through the second flow path 14b. By exchanging heat between these refrigerants in the auxiliary heat exchanger 14, the refrigerant that has flowed out from the outdoor heat exchanger 13 is supercooled.

[0019] The bypass piping 41 is a pipe that connects the refrigerant outlet of the first flow path 14a of the auxiliary heat exchanger 14 during cooling operation to the refrigerant inlet of the second flow path 14b of the auxiliary heat exchanger 14. The bypass piping 41 is provided with a bypass valve 15. The bypass valve 15 is, for example, an electronic expansion valve, and adjusts the amount of refrigerant flowing through the bypass piping 41. The opening degree of the bypass valve 15 is controlled by the control device 3.

[0020] The refrigerant outlet of the second flow path 14b of the auxiliary heat exchanger 14 is connected to the refrigerant inlet side of the accumulator 16 via piping 42. The refrigerant that has exchanged heat with the refrigerant flowing through the first flow path 14a via the second flow path 14b of the auxiliary heat exchanger 14 flows into the accumulator 16 via piping 42.

[0021] The accumulator 16 stores excess refrigerant. The accumulator 16 is connected to the intake port of the compressor 11 and separates the refrigerant flowing in from the outdoor heat exchanger 13 or indoor heat exchanger 22 into gaseous refrigerant and liquid refrigerant, stores the liquid refrigerant, and discharges the gaseous refrigerant to the compressor 11. Note that the accumulator 16 is not an essential component and may be omitted.

[0022] The outdoor fan 17 sucks in outdoor air, passes it through the outdoor heat exchanger 13, and blows it outdoors. The outdoor fan 17 is, for example, a propeller fan, a turbo fan, a sirocco fan, or a cross-flow fan driven by a motor. The air volume (rotation speed) of the outdoor fan 17 is controlled by the control device 3.

[0023] The expansion valve 21 is, for example, an electronic expansion valve with a variable opening degree, which reduces the pressure of the refrigerant and expands it. The opening degree of the expansion valve 21 is controlled by the control device 3. The expansion valve 21 is disposed between the auxiliary heat exchanger 14 and the indoor heat exchanger 22. In FIG. 1, the expansion valve 21 is disposed in the indoor unit 2, but it may also be disposed in the outdoor unit 1.

[0024] The indoor heat exchanger 22 is, for example, a fin-tube type heat exchanger, which performs heat exchange between the refrigerant flowing inside the heat transfer tube and the air blown by the indoor fan 23. The indoor heat exchanger 22 is disposed between the expansion valve 21 and the flow path switching valve 12. The indoor heat exchanger 22 functions as an evaporator during the cooling operation and as a condenser during the heating operation.

[0025] The indoor fan 23 sucks in indoor air, passes it through the indoor heat exchanger 22, and blows it indoors. The indoor fan 23 is, for example, a propeller fan, a turbo fan, a sirocco fan, or a cross-flow fan driven by a motor. The air volume (rotation speed) of the indoor fan 23 is controlled by the control device 3.

[0026] Furthermore, the refrigeration cycle device 100 is equipped with various sensors for detecting the state of the refrigerant circuit. Specifically, the outdoor heat exchanger 13 is equipped with a refrigerant pressure sensor 51 for measuring the pressure of the refrigerant flowing through the outdoor heat exchanger 13. In addition, the refrigerant outlet of the first flow path 14a of the auxiliary heat exchanger 14 during cooling operation is equipped with a refrigerant temperature sensor 52 for measuring the temperature of the refrigerant that has flowed out from the first flow path 14a. Furthermore, the refrigeration cycle device 100 may also be equipped with a discharge pressure sensor for measuring the pressure of the refrigerant discharged by the compressor 11, and an suction pressure sensor for measuring the pressure of the refrigerant drawn in by the compressor 11. The refrigeration cycle device 100 may also be equipped with sensors for measuring environmental information, such as an outside air temperature sensor for measuring the temperature of the outside where the outdoor unit 1 is installed, and an indoor temperature sensor for measuring the temperature of the room where the indoor unit 2 is installed. The measurement results of each sensor are transmitted to the control device 3.

[0027] The control device 3 is composed of a computer, a dedicated processing circuit such as an ASIC or FPGA, or both, which includes a memory for storing data and programs necessary for control and a processor such as a CPU for executing programs. The control device 3 controls the operation of the refrigeration cycle device 100 based on instructions from the user input via a remote controller and the measurement results of each sensor. In Figure 1, the control device 3 is installed on the outdoor unit 1, but the control device 3 may be installed on the indoor unit 2, or separate control devices 3 may be installed on the outdoor unit 1 and the indoor unit 2, and they may communicate with each other. Alternatively, the control device 3 may be installed in a location away from the outdoor unit 1 and the indoor unit 2.

[0028] Next, the operation of the refrigeration cycle device 100 during operation will be explained based on Figure 1. First, the operation of each component in the refrigerant circuit during heating operation will be explained based on the flow of the refrigerant. In heating operation, the control device 3 completely closes the bypass valve 15. The dashed arrows in Figure 1 indicate the flow of the refrigerant during heating operation. The high-temperature, high-pressure gaseous refrigerant compressed and discharged by the compressor 11 flows into the indoor heat exchanger 22 through the flow path switching valve 12. The gaseous refrigerant that flows into the indoor heat exchanger 22 condenses and liquefies by exchanging heat with the indoor air as it passes through the indoor heat exchanger 22. The indoor air heated by the refrigerant is blown into the room by the indoor fan 23, and the room is heated.

[0029] In the indoor heat exchanger 22, the refrigerant condenses and liquefies, then the pressure is reduced by the expansion valve 21, resulting in a gas-liquid two-phase state. The refrigerant, now in a gas-liquid two-phase state after being reduced by the expansion valve 21, flows into the outdoor heat exchanger 13 through the first flow path 14a of the auxiliary heat exchanger 14. Here, since the bypass valve 15 is closed, no heat exchange occurs between the refrigerants in the auxiliary heat exchanger 14. The refrigerant that has passed through the auxiliary heat exchanger 14 flows into the outdoor heat exchanger 13, where it evaporates and turns into a gas by exchanging heat with the outdoor air. The gaseous refrigerant then passes through the flow path switching valve 12 and the accumulator 16 and is drawn back into the compressor 11.

[0030] Next, the operation of each component in the refrigerant circuit during cooling operation will be explained based on the flow of the refrigerant. During cooling operation, the control device 3 opens the bypass valve 15, allowing the refrigerant to pass through the bypass piping 41. The solid arrows in Figure 1 indicate the flow of the refrigerant during cooling operation. The high-temperature, high-pressure gaseous refrigerant compressed and discharged by the compressor 11 flows into the outdoor heat exchanger 13 through the flow path switching valve 12. The refrigerant that flows into the outdoor heat exchanger 13 condenses and liquefies by exchanging heat with the outdoor air supplied by the outdoor fan 17.

[0031] The refrigerant flowing out of the outdoor heat exchanger 13 flows into the first channel 14a of the auxiliary heat exchanger 14 and exchanges heat with the refrigerant flowing in the second channel 14b. A portion of the refrigerant flowing out of the first channel 14a of the auxiliary heat exchanger 14 passes through the bypass piping 41, is depressurized at the bypass valve 15, and flows into the second channel 14b of the auxiliary heat exchanger 14. Through heat exchange between the refrigerant flowing in the first channel 14a and the refrigerant flowing in the second channel 14b, the refrigerant flowing in the first channel 14a of the auxiliary heat exchanger 14 is supercooled.

[0032] The control device 3 controls the opening degree of the bypass valve 15 so that the degree of subcooling of the liquid refrigerant flowing out from the first flow path 14a of the auxiliary heat exchanger 14 during cooling operation is within a target range. The target range of subcooling is set in advance and stored in the control device 3. Figure 2 is a flowchart showing the flow of control of the opening degree of the bypass valve 15 by the control device 3 according to Embodiment 1.

[0033] The control device 3 acquires the refrigerant pressure flowing through the outdoor heat exchanger 13, as measured by the refrigerant pressure sensor 51 (S1). When the refrigeration cycle device 100 is operating in cooling mode, the refrigerant pressure flowing through the outdoor heat exchanger 13, as measured by the refrigerant pressure sensor 51, corresponds to the condensation pressure. The control device 3 calculates the condensation temperature CT from the condensation pressure measured by the refrigerant pressure sensor 51 (S2).

[0034] The control device 3 obtains the subcooled refrigerant temperature TO, which is the temperature of the refrigerant flowing out of the first flow path 14a of the auxiliary heat exchanger 14, as measured by the refrigerant temperature sensor 52 (S3). The control device 3 then calculates the degree of subcooling SC (= condensation temperature CT - subcooled refrigerant temperature TO), which is the difference between the condensation temperature CT and the subcooled refrigerant temperature TO (S4).

[0035] The control device 3 checks if the calculated supercooling degree SC is the lower limit of the predetermined target range of supercooling degree SC. Ｌ Determine whether it is smaller than (S5). The calculated supercooling degree SC is the lower limit of the target range SC. Ｌ If it is smaller than (S5: YES), the control device 3 reduces the opening of the bypass valve 15, i.e., it reduces the opening (S6).

[0036] The calculated supercooling degree SC is the lower limit of the target range SC ＬIn the above case (S5: NO), the control device 3 sets the calculated supercooling degree SC to the upper limit of the predetermined target range of supercooling degree SC. Ｕ It is determined whether the calculated supercooling degree SC is greater than or equal to the upper limit of the target range SC. Ｕ If it is greater than (S7: YES), the control device 3 increases the opening of the bypass valve 15, i.e., increases the opening (S8). The calculated supercooling degree SC is the upper limit of the target range SC. Ｕ In the following case (S7: NO), the control device 3 maintains the opening of the bypass valve 15 at the current opening (S9). The control device 3 repeats the processes of steps S1 to S9 at predetermined time intervals while the cooling operation is being performed.

[0037] Returning to Figure 1, a portion of the refrigerant that flows out from the first flow path 14a of the auxiliary heat exchanger 14 flows into the expansion valve 21 of the indoor unit 2, where it is depressurized by the expansion valve 21 and becomes a gas-liquid two-phase state. The refrigerant in the gas-liquid two-phase state flows into the indoor heat exchanger 22, where it evaporates and turns into a gas by exchanging heat with the air in the space to be air-conditioned. The indoor air cooled by the refrigerant is blown into the room by the indoor fan 23, and the room is cooled. The refrigerant in the gaseous state passes through the flow path switching valve 12 and the accumulator 16 and is drawn back into the compressor 11.

[0038] Next, the configuration of the outdoor heat exchanger 13 of this embodiment will be described. Figure 3 is a perspective view of the outdoor heat exchanger 13 according to Embodiment 1. Figure 4 is a front view of the outdoor heat exchanger 13 according to Embodiment 1. The dashed arrows in Figure 3 and the white arrows in Figure 4 indicate the flow of refrigerant during cooling operation. Figure 4 also shows the height H and width L of the heat exchanger core 130, which will be described later.

[0039] As shown in Figure 3, the outdoor heat exchanger 13 includes a heat exchanger core 130 having a plurality of heat transfer tubes 131 and a plurality of fins 132. The heat transfer tubes 131 are, for example, flat tubes with a flattened cross-section. Multiple flow paths are formed in the heat transfer tubes 131. The heat transfer tubes 131 are arranged in parallel horizontally (left-right direction in Figure 3) with gaps between them so that air generated by the outdoor fan 17 can flow through them, and the refrigerant flows vertically through the tubes that extend vertically (up-down direction in Figure 3). The fins 132 are connected between adjacent heat transfer tubes 131 and transfer heat to the heat transfer tubes 131. The fins 132 improve the heat exchange efficiency between air and refrigerant, and for example, corrugated fins are used. The configuration of the heat transfer tubes 131 and fins 132 is not limited to the above. For example, since heat exchange between air and refrigerant takes place on the surface of the heat transfer tubes 131, the fins 132 may be omitted.

[0040] A first header 133 is provided at the lower end of the heat exchanger core 130. The lower ends of the heat transfer tubes 131 of the heat exchanger core 130 are directly inserted into the first header 133. A second header 134 is provided at the upper end of the heat exchanger core 130. The upper ends of the heat transfer tubes 131 of the heat exchanger core 130 are directly inserted into the second header 134.

[0041] A gas refrigerant inlet 135 is formed at one end of the first header 133. The gas refrigerant inlet 135 is connected to the gas piping 43 (Figure 1) of the refrigeration cycle device 100. The first header 133 allows high-temperature, high-pressure gas refrigerant from the compressor 11 to flow into the outdoor heat exchanger 13 during cooling operation, and allows the low-temperature, low-pressure gas refrigerant, after heat exchange in the outdoor heat exchanger 13, to flow out to the flow path switching valve 12 during heating operation. Here, the gas refrigerant is not limited to a single-phase gas refrigerant, but may also be a two-phase gas-liquid refrigerant containing a gas phase above 0°C.

[0042] A refrigerant outlet 136 is formed at one end of the second header 134. The refrigerant outlet 136 is connected to the liquid piping 44 (Figure 1) of the refrigeration cycle device 100. The second header 134 allows low-temperature, low-pressure two-phase refrigerant to flow into the outdoor heat exchanger 13 during heating operation, and allows the low-temperature, high-pressure liquid refrigerant, which has undergone heat exchange in the outdoor heat exchanger 13, to flow out to the auxiliary heat exchanger 14 during cooling operation.

[0043] The multiple heat transfer tubes 131, the multiple fins 132, the first header 133, and the second header 134 are all made of aluminum and are joined together by brazing.

[0044] As shown in Figures 3 and 4, when cooling is performed, the gaseous refrigerant discharged from the compressor 11 flows from the gas piping 43 through the gaseous refrigerant inlet 135 of the outdoor heat exchanger 13 into the first header 133, where it is distributed to each heat transfer tube 131. The refrigerant that flows into each heat transfer tube 131 flows into the second header 134 as an upward flow, which is a vertical upward flow, and flows out into the liquid piping 44 from the refrigerant outlet 136.

[0045] Figure 5 illustrates liquid stagnation in a heat exchanger. In the outdoor heat exchanger 13 of this embodiment, when the heat transfer tubes extend vertically and the gaseous refrigerant flowing into the heat exchanger rises from bottom to top, the gaseous refrigerant is cooled as it flows through the heat transfer tubes, and the liquid phase increases as it moves downstream in the direction of refrigerant flow. As the high-temperature, high-pressure gaseous refrigerant flows through the heat transfer tubes as an upward flow, the liquefied refrigerant cannot rise due to the influence of gravity, causing liquid stagnation to occur downstream in the direction of refrigerant flow in the heat exchanger (inlet header). Liquid stagnation in the heat exchanger reduces the heat exchange efficiency of the heat exchanger.

[0046] Therefore, the outdoor heat exchanger 13 of this embodiment is configured such that the refrigerant flowing through the heat transfer tubes 131 is in a two-phase state, and the dryness of the refrigerant at the refrigerant outlet 136 becomes 0. Specifically, the outdoor heat exchanger 13 has a size such that the dryness of the refrigerant at the refrigerant outlet 136 becomes 0.

[0047] Figure 6 is a p-h diagram of the refrigeration cycle device 100 according to Embodiment 1 during cooling operation. In this embodiment, when the outdoor heat exchanger 13 is performing cooling operation, that is, when it functions as a condenser, the size of the heat exchanger core 130 is set so that the dryness of the refrigerant at the refrigerant outlet 136 of the outdoor heat exchanger 13 becomes 0. In other words, as shown in Figure 6, the size of the heat exchanger core 130 is set so that the refrigerant temperature at the refrigerant outlet 136 of the outdoor heat exchanger 13 is the saturated liquid temperature. The size of the heat exchanger core 130 is set by the height H and width L of the heat exchanger core 130, or by the vertical length and the number of horizontally arranged heat transfer tubes 131 provided in the heat exchanger core 130.

[0048] In this disclosure, "the dryness of the refrigerant is 0" includes not only cases where the dryness is exactly 0, but also cases where it is close to 0 within the range where the effects of this disclosure can be obtained. Here, if two-phase refrigerant flows out from the refrigerant outlet 136 of the outdoor heat exchanger 13, the refrigerant can be supercooled by the auxiliary heat exchanger 14. However, if the dryness is so high that it cannot be sufficiently supercooled even with the auxiliary heat exchanger 14, two-phase refrigerant will flow into the expansion valve 21, causing problems such as the generation of abnormal noise. On the other hand, if liquid refrigerant flows out from the refrigerant outlet 136 of the outdoor heat exchanger 13, the refrigerant can be sufficiently supercooled by adjusting the amount of heat exchange in the auxiliary heat exchanger 14. Therefore, even if the dryness of the refrigerant flowing out from the refrigerant outlet 136 of the outdoor heat exchanger 13 is not exactly 0 depending on the installation environment or usage conditions of the outdoor unit 1, it is preferable to set the size of the outdoor heat exchanger 13 so that the refrigerant flowing out from the refrigerant outlet 136 is liquid refrigerant.

[0049] The size of the heat exchanger core 130 is determined experimentally. Specifically, experiments are conducted using an actual refrigerant circuit to determine at what temperature range the dryness of the refrigerant outlet 136 becomes zero for each size of the heat exchanger core 130. For example, the size that results in zero dryness under conditions where the cooling load is highest, such as during the hottest part of summer, is determined. In other words, the size is determined so that the dryness of the refrigerant at the outlet of the outdoor heat exchanger 13 becomes zero when the space where the outdoor unit 1 is installed is in the summer temperature range, the operating frequency of the compressor 11 is high, and the airflow of the outdoor fan 17 is at its maximum when the refrigeration cycle device 100 is in cooling operation. As a result, the two-phase refrigerant flows throughout the entire heat exchanger core 130 of the outdoor heat exchanger 13, reducing the liquid head and suppressing liquid stagnation in the outdoor heat exchanger 13.

[0050] Furthermore, the refrigeration cycle device 100 of this embodiment is equipped with an auxiliary heat exchanger 14 downstream of the outdoor heat exchanger 13 during cooling operation, and the auxiliary heat exchanger 14 supercools the refrigerant that has flowed out of the outdoor heat exchanger 13. This allows sufficient supercooling to be applied to the refrigerant flowing out of the outdoor unit 1, thereby suppressing an increase in pressure loss in the refrigerant piping 4 connecting the outdoor unit 1 and the indoor unit 2, and preventing the generation of abnormal noise in the expansion valve 21.

[0051] As described above, in the refrigeration cycle device 100 of this embodiment, the size of the outdoor heat exchanger 13 is set to a size that results in a dryness of 0 at the refrigerant outlet 136, and an auxiliary heat exchanger 14 is provided downstream of the outdoor heat exchanger 13, thereby enabling sufficient supercooling of the refrigerant. This makes it possible to suppress both liquid stagnation in the outdoor heat exchanger 13 and the generation of abnormal noise in the expansion valve 21.

[0052] Also, conventionally, the configuration was such that the refrigerant was supercooled in the outdoor heat exchanger 13 and then allowed to flow out during the cooling operation. However, in the present embodiment, by not supercooling the refrigerant in the outdoor heat exchanger 13, the outdoor heat exchanger 13 can be made smaller than in the prior art. As a result, it is also possible to miniaturize the outdoor unit 1. Furthermore, by not supercooling the refrigerant in the outdoor heat exchanger 13, the heat exchange capacity of the outdoor heat exchanger 13 itself can be made lower than that of a heat exchanger that supercools the conventional refrigerant. Therefore, members such as a shower pipe for improving the heat exchange capacity can be omitted, and the number of parts and cost of the outdoor unit 1 can be reduced.

[0053] Embodiment 2. Embodiment 2 will be described. In Embodiment 2, it is different from Embodiment 1 in that by controlling at least one of the operating frequency of the compressor 11 and the air volume of the outdoor fan 17 during the cooling operation, the dryness of the refrigerant at the refrigerant outlet 136 of the outdoor heat exchanger 13 is made zero. The configuration of the refrigeration cycle device 100 of the present embodiment is the same as that of Embodiment 1. However, the outdoor heat exchanger 13 of the present embodiment does not have to be sized such that the dryness of the refrigerant at the refrigerant outlet 136 becomes zero.

[0054] FIG. 7 is a flowchart showing the control flow of the compressor 11 and the outdoor fan 17 by the control device 3 according to Embodiment 2. First, the control device 3 acquires the refrigerant pressure flowing through the outdoor heat exchanger 13 measured by the refrigerant pressure sensor 51 (S21). When the refrigeration cycle device 100 performs the cooling operation, the refrigerant pressure flowing through the outdoor heat exchanger 13 measured by the refrigerant pressure sensor 51 corresponds to the condensation pressure. The control device 3 calculates the condensation temperature CT from the condensation pressure measured by the refrigerant pressure sensor 51 (S22).

[0055] The control device 3 determines whether the condensation temperature CT is smaller than the lower limit value CT of the target range of the preset condensation temperature. Ｌ The target range of the condensation temperature is the temperature range when the dryness of the refrigerant at the refrigerant outlet 136 of the outdoor heat exchanger 13 is 0, and is preset and stored in the control device 3. The calculated condensation temperature CT is the lower limit value CT of the target range. ＬIf it is smaller than (S23: YES), the control device 3 increases the operating frequency of the compressor 11 and the airflow of the outdoor fan 17 (S24).

[0056] The calculated condensation temperature CT is the lower limit CT of the target range. Ｌ In the above case (S23: NO), the control device 3 determines that the calculated condensation temperature CT is the upper limit CT of the preset target range of condensation temperature. Ｕ Determine whether it is greater than or equal to (S25). The calculated condensation temperature CT is the upper limit value CT of the target range. Ｕ If it is greater than (S25: YES), the control device 3 reduces the operating frequency of the compressor 11 and the airflow of the outdoor fan 17 (S26). The calculated condensation temperature CT is the upper limit value CT of the target range. Ｕ In the following case (S25: NO), the control device 3 maintains the operating frequency of the compressor 11 and the airflow rate of the outdoor fan 17 at their current values ​​(S27). The control device 3 repeats the process of steps S21 to S27 at predetermined time intervals while the cooling operation is being performed. Although the above description explains the case where both the operating frequency of the compressor 11 and the airflow rate of the outdoor fan 17 are controlled, it is sufficient to control at least one of the operating frequency of the compressor 11 and the airflow rate of the outdoor fan 17.

[0057] As described above, in the refrigeration cycle device 100 of this embodiment, an auxiliary heat exchanger 14 is provided downstream of the outdoor heat exchanger 13, and at least one of the compressor 11 and the outdoor fan 17 is controlled so that the dryness of the refrigerant outlet 136 of the outdoor heat exchanger 13 becomes 0. This makes the refrigerant flowing through the outdoor heat exchanger 13 into a two-phase state and allows the refrigerant flowing into the expansion valve 21 to be sufficiently subcooled. This makes it possible to suppress both liquid stagnation in the outdoor heat exchanger 13 and the generation of abnormal noise in the expansion valve 21. Furthermore, by controlling the compressor 11 and the outdoor fan 17, the dryness of the refrigerant outlet 136 of the outdoor heat exchanger 13 can be set to 0 over a wider temperature range compared to Embodiment 1.

[0058] The above describes the embodiments, but this disclosure is not limited to the above embodiments and can be modified in various ways without departing from the spirit of this disclosure. Furthermore, this disclosure includes all possible combinations of the configurations shown in the above embodiments. For example, Embodiment 1 and Embodiment 2 may be combined, and the outdoor heat exchanger 13 may be sized such that the dryness of the refrigerant outlet 136 becomes 0, and at least one of the operating frequency of the compressor 11 and the airflow rate of the outdoor fan 17 may be controlled based on the condensation temperature.

[0059] Furthermore, the configuration of the auxiliary heat exchanger 14 is not limited to the configuration of the above embodiment. For example, the bypass valve 15 provided in the bypass piping 41 may be omitted. Alternatively, the refrigerant that has flowed out of the indoor heat exchanger 22 during cooling operation may be flowed into the second flow path 14b of the auxiliary heat exchanger 14 and exchanged heat with the refrigerant flowing in the first flow path 14a. Moreover, the auxiliary heat exchanger 14 is not limited to self-cooling by exchanging heat between refrigerants flowing in the refrigerant circuit, but may also exchange heat with a heat transfer medium other than the refrigerant flowing in the refrigerant circuit, such as water or antifreeze.

[0060] Furthermore, the configuration of the outdoor heat exchanger 13 of the refrigeration cycle device 100 is not limited to the example of the above embodiment. Modifications of the outdoor heat exchanger 13 are described below. Note that each of the following modifications can be arbitrarily combined with Embodiment 1, Embodiment 2, and other modifications.

[0061] (Modification 1) Figure 8 is a perspective view of the outdoor heat exchanger 13A according to Modification 1. The dashed arrows and white arrows in Figure 8 indicate the flow of refrigerant during cooling operation. The outdoor heat exchanger 13A of this modification comprises two heat exchanger cores 130 connected in series. Specifically, the outdoor heat exchanger 13A comprises a first heat exchanger core 130a having a plurality of heat transfer tubes 131 and a plurality of fins 132, and a second heat exchanger core 130b having a plurality of heat transfer tubes 131 and a plurality of fins 132. The first heat exchanger core 130a and the second heat exchanger core 130b are arranged side by side facing each other in the direction in which the air supplied by the outdoor fan 17 flows. Furthermore, during cooling operation of the refrigeration cycle device 100, the second heat exchanger core 130b is located downstream of the first heat exchanger core 130a in the direction of refrigerant flow, as they are connected in series. The configuration of the heat transfer tubes 131 and fins 132 is the same as in Embodiment 1.

[0062] A first header 133 is provided at the lower end of the first heat exchanger core 130a. The lower ends of the heat transfer tubes 131 of the first heat exchanger core 130a are directly inserted into the first header 133. A second header 134 is provided at the lower end of the second heat exchanger core 130b. The lower ends of the heat transfer tubes 131 of the second heat exchanger core 130b are directly inserted into the second header 134. Similar to Embodiment 1, a gas refrigerant inlet 135 is formed at one end of the first header 133, and a refrigerant outlet 136 is formed at one end of the second header 134.

[0063] A third header 137 is provided at the upper ends of the first heat exchanger core 130a and the second heat exchanger core 130b. The upper ends of the heat transfer tubes 131 of the first heat exchanger core 130a and the upper ends of the heat transfer tubes 131 of the second heat exchanger core 130b are directly inserted into the third header 137.

[0064] During cooling operation of the refrigeration cycle device 100, the gaseous refrigerant flowing in from the gaseous refrigerant inlet 135 flows from the first header 133 into each heat transfer tube 131 of the first heat exchanger core 130a, and flows into the third header 137 as an upward flow, which is a vertical upward flow. The refrigerant flowing into the third header 137 has its flow direction changed to downward and flows into each heat transfer tube 131 of the second heat exchanger core 130b. The refrigerant flowing into each heat transfer tube 131 of the second heat exchanger core 130b flows vertically downward into the second header 134 and flows out into the liquid piping 44 from the refrigerant outlet 136.

[0065] The outdoor heat exchanger 13A in this modified example also has a size such that the degree of dryness of the refrigerant at the refrigerant outlet 136 is 0. In this modified example, because it is equipped with two heat exchanger cores, the heat exchange performance is lower than that of the outdoor heat exchanger 13 in Embodiment 1, and therefore the degree of dryness of the refrigerant at the refrigerant outlet 136 is closer to 0 than that of the outdoor heat exchanger 13 in Embodiment 1. Alternatively, instead of the third header 137, a hairpin section may be provided that connects the upper end of the first heat exchanger core 130a and the upper end of the second heat exchanger core 130b, changing the direction of the refrigerant flow from upward to downward.

[0066] (Modification 2) Figure 9 is a perspective view of the outdoor heat exchanger 13B according to Modification 2. The dashed arrows and white arrows in Figure 9 indicate the flow of refrigerant during cooling operation. As shown in Figure 9, the outdoor heat exchanger 13B is formed by connecting the outdoor heat exchanger 13A of Modification 2 in series. In this case, a gas refrigerant inlet 135 is formed at one end of the first header 133 of the outdoor heat exchanger 13A on the upstream side (left side in Figure 9) of the refrigerant flow direction during cooling operation, and a refrigerant outlet 136 is formed at one end of the second header 134 of the outdoor heat exchanger 13A on the downstream side (right side in Figure 9).

[0067] The outdoor heat exchanger 13B in this modified example also has a size such that the degree of dryness of the refrigerant at the refrigerant outlet 136 is 0. That is, the sizes of the first heat exchanger core 130a and the second heat exchanger core 130b of the two outdoor heat exchangers 13A are set so that the degree of dryness of the refrigerant at the refrigerant outlet 136 is 0.

[0068] In this modified example, the outdoor heat exchanger 13B is configured with two outdoor heat exchangers 13A connected in series, but three or more outdoor heat exchangers 13A may be connected in series. Alternatively, the outdoor heat exchanger 13B may be a configuration in which multiple outdoor heat exchangers 13 from Embodiment 1 are connected in series.

[0069] Furthermore, in the refrigeration cycle device 100 equipped with the outdoor heat exchanger 13B of this modified configuration, a plurality of outdoor fans 17 may be provided for each outdoor heat exchanger 13A. The control device 3 may also increase the airflow rate of the outdoor fan 17 that sends air to the outdoor heat exchanger 13A furthest downstream in the refrigerant flow direction during cooling operation compared to the airflow rates of the other outdoor fans 17. This promotes heat exchange downstream where liquid stagnation is likely to occur and suppresses the occurrence of liquid stagnation.

[0070] (Modification 3) In the above embodiment 1, it was explained that the shower pipe can be omitted, but as modification 3, a shower pipe 138 may be provided inside the first header 133 or the second header 134 of the outdoor heat exchangers 13, 13A, and 13B. Figure 10 is a diagram illustrating the shower pipe 138 according to modification 3. In the example of Figure 10, the shower pipe 138 is provided inside the first header 133. The shower pipe 138 is a pipe that extends in the extension direction of the first header 133. Multiple orifices 138a formed by through holes are provided on the peripheral wall of the shower pipe 138 at intervals in the extension direction.

[0071] The gas-liquid two-phase refrigerant flowing into the shower pipe 138 passes through each orifice 138a and flows into the first header 133. This equalizes the gas-liquid ratio of the gas-liquid two-phase refrigerant within the first header 133, allowing the gas-liquid two-phase refrigerant with the same gas-liquid ratio to be branched and flowed into the heat transfer tubes 131. For this reason, the shower pipe 138 is preferably installed in a header located downstream in the direction of refrigerant flow during cooling operation. For example, in the case of the outdoor heat exchanger 13B of Modification 2, it is preferably installed in the first header 133 of the outdoor heat exchanger 13A on the downstream side (right side in Figure 9). This further suppresses liquid stagnation within the outdoor heat exchanger 13.

[0072] (Modification 4) Alternatively, the total flow path cross-sectional area of ​​the heat exchanger core 130 of the outdoor heat exchanger 13 may be determined from the differential pressure and liquid head of the refrigerant flow path in the outdoor heat exchanger 13. If the total flow path cross-sectional area of ​​the heat exchanger core 130 of the outdoor heat exchanger 13 is defined as A, the total flow path cross-sectional area A can be calculated using the following formula (1).

[0073] A = a × N [m] ２ ]...(1) a: Flow path cross-sectional area of ​​one heat transfer tube 131 [m ２ ] N: Number of heat transfer tubes 131 [pieces]

[0074] Furthermore, the differential pressure in the refrigerant flow path (hereinafter referred to as the flow path differential pressure) is ΔP ＨＥＸ , the liquid head ΔP ＨＥＡＤ If defined as, ΔP ＨＥＸ / ΔP ＨＥＡＤ This can be calculated using the following equation (2). Note that the flow differential pressure ΔP ＨＥＸ This is the differential pressure in the flow path through which the gaseous refrigerant flows as an upward flow during cooling operation, and is the differential pressure at the upper and lower ends of the heat transfer tubes 131 in the heat exchanger core 130.

[0075] ΔP ＨＥＸ / ΔP ＨＥＡＤ = (5.94635 × 10 －４ ×A －１．７５０３０ ) / (Y × (8.4303H + 0.8779)) ... (2) A: Total flow path cross-sectional area of ​​heat exchanger core 130 [m ２ ] H: Height of the heat exchanger core 130 [m] Here, the height H of the heat exchanger core 130 is the length between the upper end of the first header 133 and the lower end of the second header 134, and is the length of the exposed portion of the heat transfer tube 131 (Figure 4). Y is a coefficient that represents the effect of suppressing the liquid retention area (Figure 5) of the outdoor heat exchanger 13 by supercooling the refrigerant with the auxiliary heat exchanger 14, and is a value of 0.7 or more and less than 1, which is proportional to the degree of supercooling. The above equation (2) and coefficient Y are empirical formulas obtained from numerical analysis and experimental results.

[0076] Figure 11 shows the total flow path cross-sectional area and ΔP of the heat exchanger core. ＨＥＸ / ΔP ＨＥＡＤThis figure shows the relationship. In Figure 11, ΔP is obtained when the height H of the heat exchanger core 130 is fixed and the total flow path cross-sectional area A of the heat exchanger core 130 is changed. ＨＥＸ / ΔP ＨＥＡＤ This shows the change. The solid line in Figure 11 is a graph of the case where the refrigerant is supercooled by the auxiliary heat exchanger 14 as in Embodiment 1, and the dashed solid line in Figure 11 is a graph of the case where the refrigerant is supercooled by the outdoor heat exchanger as in the conventional technology. As shown in Figure 11, the total flow path cross-sectional area A [m²] of the heat exchanger core 130 ２ As ] increases, ΔP ＨＥＸ / ΔP ＨＥＡＤ The trend is decreasing. Also, when the refrigerant is supercooled by the auxiliary heat exchanger 14, ΔP is lower compared to when the refrigerant is supercooled by the outdoor heat exchanger. ＨＥＸ / ΔP ＨＥＡＤ It decreases. And ΔP ＨＥＸ / ΔP ＨＥＡＤ When ≤ 1, when the gaseous refrigerant flowing into the first header 133 flows as an upward flow through the heat transfer tubes 131 of the heat exchanger core 130, liquid stagnation occurs in a part of the gas flow area where the liquefied refrigerant cannot rise due to the effect of gravity and remains stagnant. Note that ΔP ＨＥＸ / ΔP ＨＥＡＤ Under the condition that is 1 or less, ΔP ＨＥＸ / ΔP ＨＥＡＤ The smaller the value, the larger the liquid retention area.

[0077] And, based on the experimental results, ΔP ＨＥＸ / ΔP ＨＥＡＤ >1 It is known that the occurrence of liquid stagnation can be suppressed. Therefore, in addition to making the outdoor heat exchanger 13 sized so that the dryness of the refrigerant outlet 136 becomes 0, ΔP ＨＥＸ / ΔP ＨＥＡＤ The outdoor heat exchanger 13 may be configured to satisfy condition 1. This further suppresses liquid stagnation in the outdoor heat exchanger 13.

[0078] 1 Outdoor unit, 2 Indoor unit, 3 Control device, 4 Refrigerant piping, 11 Compressor, 12 Flow path switching valve, 13, 13A, 13B Outdoor heat exchanger, 14 Auxiliary heat exchanger, 14a First flow path, 14b Second flow path, 15 Bypass valve, 16 Accumulator, 17 Outdoor fan, 21 Expansion valve, 22 Indoor heat exchanger, 23 Indoor fan, 41 Bypass piping, 42 Piping, 43 Gas piping, 44 Liquid piping, 51 Refrigerant pressure sensor, 52 Refrigerant temperature sensor, 100 Refrigeration cycle device, 130 Heat exchanger core, 130a First heat exchanger core, 130b Second heat exchanger core, 131 Heat transfer tube, 132 Fins, 133 First header, 134 Second header, 135 Gas refrigerant inlet, 136 Refrigerant outlet, 137 Third header, 138 Shower pipe, 138a orifice.

Claims

1. An outdoor unit comprising: a compressor; an outdoor heat exchanger having a plurality of heat transfer tubes extending in the vertical direction; and an auxiliary heat exchanger that subcools the refrigerant flowing out of the outdoor heat exchanger when the outdoor heat exchanger functions as a condenser, wherein the dryness of the refrigerant at the refrigerant outlet of the outdoor heat exchanger is 0 when the outdoor heat exchanger functions as a condenser.

2. The outdoor unit according to claim 1, wherein the outdoor heat exchanger is sized such that the degree of dryness of the refrigerant at the refrigerant outlet is 0 when the outdoor heat exchanger functions as a condenser.

3. The outdoor unit according to claim 1 or 2, further comprising: an outdoor fan that supplies air to the outdoor heat exchanger; and a control device that controls at least one of the operating frequency of the compressor and the airflow rate of the outdoor fan so that the degree of dryness of the refrigerant at the refrigerant outlet becomes zero when the outdoor heat exchanger functions as a condenser.

4. The outdoor unit according to any one of claims 1 to 3, wherein the outdoor heat exchanger comprises: a first heat exchanger core having a plurality of heat transfer tubes and a plurality of fins; a second heat exchanger core having a plurality of heat transfer tubes and a plurality of fins; a first header connected to the lower end of the first heat exchanger core; a second header connected to the lower end of the second heat exchanger core; and a third header or hairpin portion connected to the upper ends of the first heat exchanger core and the second heat exchanger core.

5. The outdoor unit according to any one of claims 1 to 4, wherein a plurality of outdoor heat exchangers are connected in series.

6. The outdoor unit according to claim 5, further comprising: a plurality of outdoor fans that supply air to a plurality of outdoor heat exchangers, each of which is a plurality of outdoor fans; and a control device that increases the airflow rate of the outdoor fan that supplies air to the outdoor heat exchanger located at the bottom in the refrigerant flow direction when the outdoor heat exchanger functions as a condenser, compared to the airflow rates of the other outdoor fans.

7. The outdoor unit according to any one of claims 1 to 6, wherein the outdoor heat exchanger is equipped with a shower pipe.

8. The outdoor heat exchanger includes a heat exchanger core having a plurality of the heat transfer tubes and a plurality of fins. When the flow path cross-sectional area of each heat transfer tube is a [m ２ , and the total flow path cross-sectional area of the heat exchanger core when the number of the heat transfer tubes is N [pieces] is A [m ２ = a × N [m ２ , the height of the heat exchanger core is H [m], the differential pressure of the refrigerant flow path is ΔP ＨＥＸ , and the liquid head is ΔP ＨＥＡＤ , when defined, ΔP ＨＥＸ / ΔP ＨＥＡＤ = (5.94635 × 10 －４ × A －１．７５０３０ ) / (Y × (8.4303H + 0.8779)) > 1 is satisfied, and Y is 0.7 or more and less than 1. The outdoor unit according to any one of claims 1 to 7.

9. A refrigeration cycle device comprising an outdoor unit according to any one of claims 1 to 8, and an indoor unit equipped with an indoor heat exchanger and connected to the outdoor unit by piping.

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