Air conditioning device

Abstract

An air conditioning device (100), in which a non-azeotropic refrigerant mixture is used, comprises: a refrigerant circuit (50) including a compressor (1), a condenser (3), an evaporator (6), and an expansion valve (4); a control device (80); a first sensor (21); a second sensor (22); a third sensor (23); and a fourth sensor (24). If a measurement value of the first sensor (21) is greater than a measurement value of the third sensor (23), the control device (80) adjusts the opening degree of the expansion valve (4) so that the value obtained by subtracting the measurement value of the second sensor (22) from the measurement value of the fourth sensor (24) is greater than a threshold value.

Description

air conditioning equipment

[0001] The present disclosure relates to an air conditioning apparatus.

[0002] In recent years, various next-generation refrigerants have been considered to comply with the European F-gas regulations and the Kigali Amendment to the Montreal Protocol. The European F-gas regulations, etc., require a reduction in the total Global Warming Potential (GWP) (= GWP × refrigerant charge amount). To comply with the regulations, it is necessary to reduce either the GWP or the refrigerant charge amount.

[0003] Low GWP refrigerants generally include HC refrigerants, such as R290, and HFO refrigerants, such as R1123 and R1132(E). Because HC refrigerants are highly flammable, strict regulations are imposed on the allowable refrigerant charge. Therefore, HC refrigerants are not suitable for direct expansion systems, especially systems with long piping lengths. While HFO refrigerants are non-flammable or slightly flammable, they can be toxic. Furthermore, many HFO refrigerants have poor performance as single refrigerants.

[0004] Therefore, refrigerants (mixed refrigerants) that are mixtures of HFO refrigerants and widely used HFC refrigerants are attracting attention from various companies as potential next-generation refrigerants. Examples of mixed refrigerants include R454 refrigerants, which are a mixture of R32 and R1234yf, and R474A, which is a mixture of R32, R1234yf, and R1132(E). These mixed refrigerants are called non-azeotropic mixed refrigerants and are characterized by a temperature gradient (difference between the dew point and boiling point).

[0005] Japanese Patent Laid-Open Publication No. 8-14674 (Patent Document 1) describes an air conditioner that uses a non-azeotropic refrigerant mixture. The air conditioner described in Patent Document 1 calculates the degree of superheat and operates an expansion valve according to the calculated degree of superheat.

[0006] Japanese Unexamined Patent Publication No. 8-14674

[0007] Generally, when a single refrigerant is used, pressure loss occurs as the refrigerant flows, causing a drop in the refrigerant temperature (saturation temperature). On the other hand, when a non-azeotropic refrigerant mixture is used, the refrigerant temperature either drops or rises as the refrigerant flows from the inlet to the outlet of the evaporator, depending on the magnitude of the pressure loss (the amount of refrigerant circulating).

[0008] Therefore, in an air conditioner using a non-azeotropic refrigerant mixture, it is necessary to take into consideration the characteristics of the non-azeotropic refrigerant mixture and adjust the opening of the expansion valve to appropriately control the degree of suction superheat.

[0009] The present disclosure has been made to solve such problems, and has an object to make it possible to appropriately control the degree of suction superheat in an air conditioner that uses a non-azeotropic refrigerant mixture.

[0010] The present disclosure relates to an air conditioning device that uses a non-azeotropic refrigerant mixture as a refrigerant, and that includes a refrigerant circuit including a compressor, a condenser, an evaporator, and an expansion valve, a control device, a first sensor that measures the temperature of the refrigerant flowing between the expansion valve and the evaporator, a second sensor that measures the temperature of the refrigerant flowing between the evaporator and the compressor, a third sensor that measures the temperature of the refrigerant flowing near the middle of the refrigerant piping included in the evaporator, and a fourth sensor that measures the temperature of the air that exchanges heat with the evaporator, and when the measurement value of the first sensor is greater than the measurement value of the third sensor, the control device adjusts the opening degree of the expansion valve so that the value obtained by subtracting the measurement value of the second sensor from the measurement value of the fourth sensor is greater than a threshold value.

[0011] According to the present disclosure, in an air conditioner that uses a non-azeotropic refrigerant mixture, the degree of suction superheat can be appropriately controlled.

[0012] 1 is a diagram schematically illustrating an example of an air conditioning apparatus according to Embodiment 1. FIG. 1 is a Ph diagram illustrating state changes of a single refrigerant circulating through a refrigerant circuit in a cooling operation mode. FIG. 2 is a Ph diagram illustrating state changes of a non-azeotropic refrigerant mixture circulating through a refrigerant circuit in a cooling operation mode. FIG. 3 is a diagram illustrating the relationship between suction superheat and theoretical COP for each type of refrigerant. FIG. 4 is a diagram illustrating the composition ratio of a typical non-azeotropic refrigerant mixture. FIG. 5 is a diagram for explaining counterflow. FIG. 6 is a diagram for explaining parallel flow. FIG. 7 is a graph illustrating the relationship between refrigerant temperature and air temperature in an evaporator with counterflow specifications. FIG. 8 is a graph illustrating the relationship between refrigerant temperature and air temperature in an evaporator with parallel flow specifications. FIG. 9 is a diagram illustrating a specific example of the relationship between refrigerant temperature and air temperature in an evaporator with counterflow specifications. FIG. 10 is a diagram illustrating a specific example of the relationship between refrigerant temperature and air temperature in an evaporator with parallel flow specifications.

[0013] The following describes embodiments in detail with reference to the drawings. While several embodiments will be described below, it was originally intended that the configurations described in each embodiment be combined as appropriate. Note that identical or corresponding parts in the drawings are designated by the same reference numerals, and their description will not be repeated.

[0014] Embodiment 1. Fig. 1 is a diagram schematically illustrating an example of an air conditioning apparatus 100 according to embodiment 1. Note that Fig. 1 functionally illustrates the connection relationships and arrangement of the devices in the air conditioning apparatus 100, and does not necessarily illustrate the physical spatial arrangement.

[0015] 1 , the air conditioning apparatus 100 includes an outdoor unit 10, an indoor unit 20, and a control device 80. The outdoor unit 10 and the indoor unit 20 include a refrigerant circuit 50. The refrigerant circuit 50 includes a compressor 1, a four-way valve 2, an outdoor heat exchanger 3, an expansion valve 4, a fan 5 corresponding to the outdoor heat exchanger 3, an indoor heat exchanger 6, a fan 7 corresponding to the indoor heat exchanger 6, and extension pipes 11 and 12.

[0016] In this disclosure, it is assumed that a non-azeotropic refrigerant mixture flows through the refrigerant circuit 50. A non-azeotropic refrigerant mixture is formed by mixing two or more refrigerants with different boiling points. Therefore, a non-azeotropic refrigerant mixture is characterized by a discrepancy between the saturated gas temperature and the saturated liquid temperature under a constant pressure. Generally, the saturated gas temperature is higher than the saturated liquid temperature. This temperature difference is called a temperature gradient. The existence of a temperature gradient can cause temperature imbalances within the heat exchanger.

[0017] Liquid refrigerant flows through the extension pipe 11. Gas refrigerant flows through the extension pipe 12. The indoor heat exchanger 6 is disposed in a room that is a space to be air-conditioned. The outdoor heat exchanger 3 is disposed outside the space to be air-conditioned.

[0018] The control device 80 is disposed in, for example, the outdoor unit 10. The control device 80 may be disposed in the indoor unit 20. The control device 80 may be disposed in a location separate from the outdoor unit 10 and the indoor unit 20. The control device 80 controls the compressor 1, the four-way valve 2, the expansion valve 4, and the fans 5 and 7.

[0019] The control device 80 includes a processor 81 and a memory 82. The processor 81 is a computing entity that executes various programs. The processor may be configured, for example, as a microcontroller, a central processing unit (CPU), or a micro-processing unit (MPU). The processor 81 has the function of executing various processes by executing programs, but some or all of these functions may be implemented using dedicated hardware circuits such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA).

[0020] The processor 81 is not limited to a processor in the narrow sense that executes processing using a stored program, such as a CPU or MPU, but may also include hardwired circuits such as an ASIC or FPGA. Therefore, the processor 81 can also be interpreted as a processing circuit whose processing is predefined by computer-readable code and / or hardwired circuits. The processor 81 may be configured on a single chip or multiple chips. Furthermore, the processor 81 and related processing circuits may be configured on multiple computers interconnected by wire or wirelessly via a local area network or a wireless network. The processor 81 and related processing circuits may also be configured as a cloud computer that performs remote calculations based on input data and outputs the calculation results to another device located at a distant location.

[0021] The memory 82 provides a storage area for storing program code, various variables, and the like when the processor 81 executes various programs. The memory 82 may be one or more non-transitory computer-readable media. Examples of the memory 82 include volatile memory such as dynamic random access memory (DRAM) and static random access memory (SRAM), and non-volatile memory such as read-only memory (ROM) and flash memory. The memory 82 may also be one or more computer-readable storage media. Examples of the memory 82 include storage devices such as hard disk drives (HDDs) and solid-state drives (SSDs). The processor 81 controls various devices included in the air conditioning apparatus 100 by executing the programs stored in the memory 82.

[0022] The compressor 1 changes the operation frequency under the control of the control device 80. The amount of refrigerant discharged from the compressor 1 changes in accordance with the change in the operation frequency.

[0023] The expansion valve 4 is configured by, for example, an electronic expansion valve, etc. The control device 80 adjusts the opening degree of the expansion valve 4 to adjust the amount of pressure reduction of the refrigerant.

[0024] The four-way valve 2 switches the circulation order of the refrigerant in the refrigerant circuit 50 between a first order and a second order under the control of the control device 80. In the first order, the refrigerant circulates through the compressor 1, the outdoor heat exchanger 3, the expansion valve 4, the indoor heat exchanger 6, and the compressor 1 in that order. In the second order, the refrigerant circulates through the compressor 1, the indoor heat exchanger 6, the expansion valve 4, the outdoor heat exchanger 3, and the compressor 1 in that order.

[0025] The control device 80 changes the operation mode from the cooling operation mode to the heating operation mode by switching the circulation order of the refrigerant in the refrigerant circuit 50 from the first order to the second order. The control device 80 changes the operation mode from the heating operation mode to the cooling operation mode by switching the circulation order of the refrigerant in the refrigerant circuit 50 from the second order to the first order. In the heating operation mode, the outdoor heat exchanger 3 functions as an evaporator, and the indoor heat exchanger 6 functions as a condenser. In the cooling operation mode, the outdoor heat exchanger 3 functions as a condenser, and the indoor heat exchanger 6 functions as an evaporator. The direction of the arrows shown in FIG. 1 indicates the direction in which the refrigerant flows through the refrigerant circuit 50 in the cooling operation mode.

[0026] The indoor heat exchanger 6 has a serpentine refrigerant pipe 13 arranged therein. The indoor heat exchanger 6 is provided with temperature sensors 21 to 23 for measuring the temperature of the refrigerant, and a temperature sensor 24 for measuring the temperature of the air drawn into the indoor heat exchanger 6. The temperature sensors 21 to 24 are, for example, thermistors. However, the temperature sensor may be configured as something other than a thermistor.

[0027] The following describes this embodiment based on the flow of refrigerant in the cooling operation mode. In this case, the outdoor heat exchanger 3 functions as a condenser, and the indoor heat exchanger 6 functions as an evaporator. A refrigerant inlet 601 and a refrigerant outlet 602 are formed by both ends of the refrigerant pipe 13 included in the indoor heat exchanger 6. When the indoor heat exchanger 6 functions as an evaporator, the refrigerant flows into the refrigerant inlet 601 and flows out from the refrigerant outlet 602. Hereinafter, the indoor heat exchanger 6 may be simply referred to as an evaporator.

[0028] Temperature sensor 21 is provided at the refrigerant inlet 601. Temperature sensor 22 is provided at the refrigerant outlet 602. Temperature sensor 23 is provided near the middle of refrigerant piping 13. More specifically, temperature sensor 23 is provided at a portion of refrigerant piping 13 where the distance from refrigerant inlet 601 is the same as the distance from refrigerant outlet 602. Temperature sensor 24 is provided near an intake port through which indoor unit 20 draws air from the space to be air-conditioned.

[0029] It should be noted that temperature sensor 23 does not have to be provided at a portion of refrigerant pipe 13 where the distance from refrigerant inlet 601 is exactly the same as the distance from refrigerant outlet 602. Temperature sensor 23 may be provided at a portion of refrigerant pipe 13 where the distance from refrigerant inlet 601 is approximately the same as the distance from refrigerant outlet 602. This is because even if the position of temperature sensor 23 is slightly shifted, the shift is absorbed by the error in the measurement value of temperature sensor 23.

[0030] The temperature sensor 21 measures the temperature Tei of the refrigerant flowing into the refrigerant inlet 601 of the evaporator (the condensation temperature of the refrigerant). The temperature sensor 22 measures the temperature Teo of the refrigerant flowing out from the refrigerant outlet 602 of the evaporator (the evaporation temperature of the refrigerant). The temperature sensor 23 measures the temperature Tem of the refrigerant flowing near the middle of the refrigerant pipe 13. The temperature sensor 24 measures the temperature Tairin of the air drawn into the indoor unit 20 from the space to be air-conditioned.

[0031] Fig. 2 is a Ph diagram showing the state change of a single refrigerant circulating through the refrigerant circuit 50 in the cooling operation mode. Fig. 3 is a Ph diagram showing the state change of a non-azeotropic refrigerant mixture circulating through the refrigerant circuit 50 in the cooling operation mode. Fig. 4 is a diagram showing the relationship between the suction superheat (suction SH) and the theoretical COP for each type of refrigerant. The characteristics of non-azeotropic refrigerant mixtures and the features of LEV (Linear Expansion Valve) control in this disclosure will be described using Figs. 2 to 4.

[0032] The slope of the isotherms in the two-phase region is significantly different between the graphs shown in Figure 2 and Figure 3. As shown in Figure 2, for a single refrigerant such as R32, the isotherms in the two-phase region are horizontal. That is, for a single refrigerant, the temperature does not change in the two-phase region if the pressure is constant. On the other hand, for non-azeotropic refrigerant mixtures such as R454C and R474A, the isotherms in the two-phase region are inclined, as shown in Figure 3. That is, non-azeotropic refrigerant mixtures have the characteristic that the temperature changes even if the pressure is constant.

[0033] In other words, with a single refrigerant, pressure loss occurs as the refrigerant flows, resulting in a drop in refrigerant temperature (saturation temperature). On the other hand, with a non-azeotropic refrigerant mixture, the magnitude of pressure loss (the amount of refrigerant circulation) determines whether the refrigerant temperature drops or rises as the refrigerant flows from the evaporator inlet to the evaporator outlet. Therefore, with a single refrigerant, it is easy to determine whether the refrigerant is overheated based on the difference between the evaporator inlet temperature and the evaporator outlet temperature. With a non-azeotropic refrigerant mixture, however, the amount of refrigerant circulation determines whether the refrigerant temperature drops, so the degree of refrigerant overheating cannot be determined uniquely from the difference between the evaporator inlet temperature and the evaporator outlet temperature, as with a single refrigerant.

[0034] In the present disclosure, it is assumed that a non-azeotropic refrigerant mixture is flowing through the refrigerant circuit 50. A non-azeotropic refrigerant mixture, particularly a non-azeotropic refrigerant mixture containing a large amount of R1234yf (such as R454C and R474A), has a better theoretical COP than a single refrigerant (such as R32) when the degree of superheat on the suction side of the compressor 1 (hereinafter referred to as suction superheat) is increased.

[0035] Figure 4 shows the relationship between suction superheat and theoretical COP for R32, a typical example of a single refrigerant, and R290, R454C, R454B, and R474A, which are typical examples of non-azeotropic refrigerant mixtures. As shown in Figure 4, with the exception of R454B, for non-azeotropic refrigerant mixtures, increasing suction superheat increases the theoretical COP. Therefore, the operating points at which efficient operation is achieved differ between non-azeotropic refrigerant mixtures such as a mixture of HFO and HFC refrigerants and current single refrigerants (such as R32 and R410A).

[0036] Specifically, since R32 has a characteristic that its discharge temperature easily rises, in order to operate efficiently, LEV control should be performed so that the dryness fraction on the suction side of the compressor 1 becomes 1.0. In this case, the control device 80 calculates the target discharge temperature from the condensation temperature (high pressure), evaporation temperature (low pressure), and operating frequency of the compressor 1, and adjusts the opening of the expansion valve 4 so that the difference between the actual discharge temperature and the target discharge temperature becomes a threshold value.

[0037] However, when a non-azeotropic refrigerant mixture is used, efficient operation cannot be achieved using conventional LEV control. Therefore, this disclosure proposes a method for adjusting the opening of the expansion valve 4 so as to obtain the required suction superheat, taking into account the characteristics of the non-azeotropic refrigerant mixture.

[0038] However, when a non-azeotropic refrigerant mixture flows through the refrigerant circuit 50, it is difficult to calculate the suction superheat degree from the difference between the two-phase temperature and the suction temperature.

[0039] Furthermore, when a non-azeotropic refrigerant mixture is used, as described above, the pressure loss (the amount of refrigerant circulating) determines whether the refrigerant temperature decreases or increases as the refrigerant flows from the inlet of the evaporator to the outlet of the evaporator.

[0040] Therefore, in the present disclosure, the control device 80 determines the magnitude of the refrigerant circulation rate and, based on the determination result, performs LEV control so as to obtain the required suction superheat. More specifically, the control device 80 determines the magnitude of the refrigerant circulation rate based on the difference between the temperature Tei of the refrigerant flowing into the refrigerant inlet 601 of the evaporator and the temperature Tem of the refrigerant flowing near the middle of the refrigerant pipe 13. Furthermore, the control device 80 adjusts the opening degree of the expansion valve 4 based on the difference between the temperature Tairin of the air drawn into the indoor unit 20 and the temperature Teo of the refrigerant flowing out of the refrigerant outlet 602 of the evaporator. This makes it possible to appropriately control the suction superheat of the compressor 1 even when a non-azeotropic refrigerant mixture (e.g., R474A) is used as the refrigerant.

[0041] FIG. 5 is a diagram showing the composition ratios of representative non-azeotropic refrigerant mixtures. All ratios shown in FIG. 5 are in wt %. R474A is a refrigerant mixture of R1132(E) and R1234yf, with a composition ratio of R1132(E):R1234yf=23.0:77.0. R454C is a refrigerant mixture of R32 and R1234yf, with a composition ratio of R32:R1234yf=21.5:78.5. R474A and R454C are examples of non-azeotropic refrigerant mixtures containing 77% or more R1234yf.

[0042] R479A is a refrigerant mixture of R1132(E), R32, and R1234yf, with a composition ratio of R1132(E):R32:R1234yf=28.0:21.5:50.5. R454B is a refrigerant mixture of R32 and R1234yf, with a composition ratio of R32:R1234yf=68.9:31.1.

[0043] 5, non-azeotropic refrigerant mixtures that are considered to be next-generation candidate refrigerants include R1234yf. The non-azeotropic refrigerant mixture that flows through the refrigerant circuit 50 may be, for example, R474A.

[0044] Next, the counterflow configuration and the parallel flow configuration will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a diagram for explaining the counterflow configuration, and Fig. 7 is a diagram for explaining the parallel flow configuration.

[0045] Here, in a heat exchanger, the flow of a refrigerant and a heat medium (air) that exchanges heat with the refrigerant in opposing directions is called a "counterflow." Therefore, in a "counterflow," the flow direction of the refrigerant and the flow direction of the heat medium (air) that exchanges heat with the refrigerant are opposite. In contrast, in a heat exchanger, the flow of a refrigerant and a heat medium (air) that exchanges heat with the refrigerant in parallel directions is called a "parallel flow." Therefore, in a "parallel flow," the flow direction of the refrigerant and the flow direction of the heat medium (air) that exchanges heat with the refrigerant are the same.

[0046] The indoor heat exchanger 6 is preferably configured to achieve counterflow when functioning as an evaporator. This is because, when a non-azeotropic refrigerant mixture flows, an evaporator operating in counterflow mode has a higher heat exchange rate than an evaporator operating in parallel flow mode. To clarify the difference between counterflow and parallel flow, an indoor heat exchanger 6 with parallel flow specifications will be described here in addition to an indoor heat exchanger 6 with counterflow specifications. For this reason, FIG. 6 shows an indoor heat exchanger 6 with counterflow specifications, and FIG. 7 shows an indoor heat exchanger 6 with parallel flow specifications. Note that both FIGS. 6 and 7 show the indoor heat exchanger 6 functioning as an evaporator.

[0047] 6 and 7 show a schematic cross-sectional structure of the indoor unit 20 as viewed from the side. As shown in FIGS. 6 and 7, the indoor heat exchanger 6 is housed in the indoor unit 20. The indoor unit 20 is provided with a fan 7. The fan 7 rotates during air-conditioning operation. This causes indoor air to be drawn into the indoor unit 20. The drawn air exchanges heat with the refrigerant flowing through the indoor heat exchanger 6, and is then blown out from the air outlet 9 into the room.

[0048] The refrigerant pipes 13 are arranged in a serpentine manner in the indoor heat exchanger 6. When the indoor heat exchanger 6 is viewed from the side, the refrigerant pipes 13 are serpentine in multiple rows. As shown in Figures 6 and 7 , the refrigerant pipes 13 serpentine in multiple rows include a first row of piping sections 61 and a second row of piping sections 62. Note that, although two rows of piping sections are illustrated here, the indoor heat exchanger 6 may be provided with refrigerant pipes 13 that form three or more rows of piping sections.

[0049] The refrigerant pipe 13 in the indoor heat exchanger 6 is formed with a refrigerant inlet 601 and a refrigerant outlet 602. When the indoor heat exchanger 6 functions as an evaporator, the refrigerant flows into the refrigerant inlet 601 and flows out from the refrigerant outlet 602.

[0050] As shown in Fig. 6, in the counterflow indoor heat exchanger 6, the refrigerant inlet 601 is formed in the first row of piping 61, and the refrigerant outlet 602 is formed in the second row of piping 62. As shown in Fig. 7, in the parallel flow indoor heat exchanger 6, the refrigerant inlet 601 is formed in the second row of piping 62, and the refrigerant outlet 602 is formed in the first row of piping 61.

[0051] 6, in the counterflow indoor heat exchanger 6, the flow direction of the refrigerant from the refrigerant inlet 601 to the refrigerant outlet 602 is opposite to the flow direction of the air from the room toward the fan 7 via the indoor heat exchanger 6. For this reason, when the indoor heat exchanger 6 functions as an evaporator, that is, in the cooling operation mode, the high-temperature air drawn into the indoor unit 20 exchanges heat first with the refrigerant flowing through the first row of piping 61 and the refrigerant flowing through the second row of piping 62.

[0052] 7, in the indoor heat exchanger 6 of parallel flow specification, the flow direction of the refrigerant from the refrigerant inlet 601 to the refrigerant outlet 602 is the same as the flow direction of the air from the room toward the fan 7 via the indoor heat exchanger 6. For this reason, when the indoor heat exchanger 6 functions as an evaporator, that is, in the cooling operation mode, the high-temperature air drawn into the indoor unit 20 first exchanges heat with the refrigerant flowing through the first row of piping 61 or the refrigerant flowing through the second row of piping 62.

[0053] Next, the effects of counterflow and parallel flow on the temperature of the refrigerant outlet 602 will be described using Figures 8 to 11. Figure 8 is a graph showing the relationship between refrigerant temperature and air temperature in an evaporator with counterflow specifications. Figure 9 is a graph showing the relationship between refrigerant temperature and air temperature in an evaporator with parallel flow specifications. Figure 10 is a diagram showing a specific example of the relationship between refrigerant temperature and air temperature in an evaporator with counterflow specifications. Figure 11 is a diagram showing a specific example of the relationship between refrigerant temperature and air temperature in an evaporator with parallel flow specifications.

[0054] 8 and 9 show graphs (a) to (d). In graphs (a) to (d), "Tairin" indicates the temperature of air drawn into the indoor unit 20 from inside the room, and "Tairout" indicates the temperature of air blown out from the air outlet 9 of the indoor unit 20. In graphs (a) to (d), "Tei" indicates the refrigerant temperature at the refrigerant inlet 601 of the evaporator (indoor heat exchanger 6), "Tem" indicates the refrigerant temperature near the middle of the refrigerant piping 13 included in the evaporator, and "Teo" indicates the refrigerant temperature at the refrigerant outlet 602 of the evaporator.

[0055] Graph (a) shows a case where the refrigerant circulation rate is large in a counterflow evaporator, while graph (b) shows a case where the refrigerant circulation rate is smaller than that in graph (a) in a counterflow evaporator. Graph (c) shows a case where the refrigerant circulation rate is large in a parallel flow evaporator, while graph (d) shows a case where the refrigerant circulation rate is smaller than that in graph (c) in a parallel flow evaporator. The heat exchange rate in the evaporator is the same in each of graphs (a) to (d).

[0056] Generally, the smaller the difference between the air temperature and the refrigerant temperature in the evaporator, the better the heat exchange performance of the evaporator. Therefore, in graphs (a) to (d), the smaller the area enclosed by the line segment representing the air temperature change and the broken line representing the refrigerant temperature change, the better the heat exchange efficiency. From this perspective, among graphs (a) to (d), the characteristics of graph (a) indicate the state with the highest heat exchange efficiency, while the characteristics of graph (d) indicate the state with the lowest heat exchange performance. Furthermore, by comparing graphs (a) and (b) for counterflow with graphs (c) and (d) for parallel flow, it can be seen that the counterflow evaporator has better heat exchange performance than the parallel flow evaporator.

[0057] Considering the characteristics of non-azeotropic refrigerant mixtures, it is necessary to control the air conditioning apparatus 100 so as to obtain the suction superheat. To achieve this, the temperature difference between the refrigerant temperature Teo at the refrigerant outlet 602 and the air blowout temperature Tairout is important. More specifically, it is necessary to control the refrigerant temperature Teo so that it does not become too low.

[0058] To achieve this, it is desirable to configure the evaporator (indoor heat exchanger 6) so that the high-temperature air drawn from the room comes into contact with the refrigerant pipe 13 in the evaporator (indoor heat exchanger 6) on the side closer to the refrigerant outlet 602, i.e., to configure the evaporator in a counterflow configuration. Here, a specific example of the relationship between the refrigerant temperature and the air temperature in an evaporator in a counterflow configuration will be described with reference to Figure 10.

[0059] 10 shows a schematic diagram of the indoor heat exchanger 6 functioning as an evaporator and a graph showing the relationship between the refrigerant temperature and the air temperature. The indoor heat exchanger 6 shown in FIG. 10 has multiple rows of piping sections, including a first row of piping section 61, a second row of piping section 62, and a third row of piping section 63. Here, it is assumed that the temperature of air drawn from the room toward the indoor heat exchanger 6 is 27°C and the refrigerant temperature at the refrigerant inlet 601 is 11°C.

[0060] The air drawn into the indoor heat exchanger 6 is cooled by exchanging heat with the refrigerant flowing through the indoor heat exchanger 6. After being cooled by the indoor heat exchanger 6, the temperature of the air blown into the room is, for example, 13°C. The high-temperature air drawn from the room toward the indoor heat exchanger 6 first passes through the third row of piping 63, which is located closer to the refrigerant outlet 602 among the multiple rows of piping. Therefore, as shown in the graph of FIG. 10 , the refrigerant temperature (for example, 15°C) at the refrigerant outlet 602 is not limited by the air temperature, and the evaporation temperature rises. As a result, the refrigerant temperature that has dropped inside the indoor heat exchanger 6 can be raised to a temperature at the refrigerant outlet 602 at which a sufficient degree of superheat is achieved.

[0061] Next, a specific example of the relationship between the refrigerant temperature and the air temperature in an evaporator of parallel flow specification will be described with reference to FIG.

[0062] Fig. 11 shows a schematic diagram of the indoor heat exchanger 6 functioning as an evaporator and a graph showing the relationship between refrigerant temperature and air temperature. Similar to the indoor heat exchanger 6 shown in Fig. 10, the indoor heat exchanger 6 shown in Fig. 11 has a first row of piping 61, a second row of piping 62, and a third row of piping 63. Here, it is assumed that the temperature of air drawn from the room toward the indoor heat exchanger 6 is 27°C and the refrigerant temperature at the refrigerant inlet 601 is 8°C.

[0063] The air drawn into the indoor heat exchanger 6 is cooled by exchanging heat with the refrigerant flowing through the indoor heat exchanger 6. After being cooled by the indoor heat exchanger 6, the temperature of the air blown into the room is, for example, 13°C. The high-temperature air drawn from the room toward the indoor heat exchanger 6 first passes through the third row of piping 63, which is located closer to the refrigerant inlet 601 among the multiple rows of piping. Therefore, as shown in the graph in FIG. 11 , the refrigerant temperature (for example, 12°C) at the refrigerant outlet 602 is limited by the air temperature, and the evaporation temperature is lowered. As a result, the refrigerant temperature that has dropped inside the indoor heat exchanger 6 cannot be raised to a temperature at the refrigerant outlet 602 that provides sufficient superheat.

[0064] As described above, when the indoor heat exchanger 6 functions as an evaporator, configuring the indoor heat exchanger 6 to achieve counterflow makes it easier to increase the refrigerant temperature at the refrigerant outlet 602 than configuring the indoor heat exchanger 6 to achieve parallel flow. In other words, configuring the indoor heat exchanger 6 to achieve counterflow makes it easier to control the suction superheat to a desired value.

[0065] Therefore, when a non-azeotropic refrigerant mixture is flowed through the refrigerant circuit 50, it is desirable to configure the indoor heat exchanger 6 so that counterflow occurs in the indoor heat exchanger 6 in the cooling operation mode.

[0066] 12 is a flowchart showing the processing steps of the control device 80 provided in the air conditioning apparatus 100 according to Embodiment 1. First, the control device 80 determines whether or not operation in the cooling operation mode has been detected (step S10). If operation in the cooling operation mode has not been detected, the control device 80 ends the processing based on this flowchart.

[0067] When the control device 80 detects operation in the cooling operation mode, it determines whether or not "refrigerant temperature Tei - refrigerant temperature Tem > 0" is true (step S11), where Tei is the temperature of the refrigerant flowing into the refrigerant inlet 601 of the evaporator (the condensation temperature of the refrigerant), and Tem is the temperature of the refrigerant flowing near the middle of the refrigerant pipe 13 that constitutes the evaporator.

[0068] In this embodiment, a non-azeotropic refrigerant mixture (for example, R474A) is used. Therefore, when the cooling capacity required for the air conditioning apparatus 100 is large, that is, when the refrigerant circulation rate is high, a temperature difference occurs between the refrigerant temperature Tei at the refrigerant inlet 601 of the evaporator and the refrigerant temperature Tem at the middle of the evaporator.

[0069] If the relationship "refrigerant temperature Tei - refrigerant temperature Tem > 0" holds, the control device 80 determines that the cooling operation is being performed with a large refrigerant circulation rate. In this case, the cooling operation is being performed with a pressure loss greater than the slope of the isotherm of the non-azeotropic refrigerant mixture shown in Figure 3.

[0070] Therefore, when "refrigerant temperature Tei - refrigerant temperature Tem > 0" is true, the control device 80 determines whether "air temperature Tairin - refrigerant temperature Teo > threshold value A" is true (step S12). Here, air temperature Tairin is the temperature of air drawn into the indoor unit 20 from the air-conditioned space, and Teo is the temperature of the refrigerant flowing out from the refrigerant outlet of the evaporator (evaporation temperature of the refrigerant). Threshold value A is set appropriately depending on the configuration of the air conditioning apparatus.

[0071] If the condition "air temperature Tairin - refrigerant temperature Teo > threshold A" is not met, the required suction superheat degree cannot be obtained. In this case, the compressor 1 draws in wet refrigerant. Therefore, if the condition "air temperature Tairin - refrigerant temperature Teo > threshold A" is not met, the control device 80 adjusts the opening of the expansion valve (LEV) 4 so that the opening of the expansion valve 4 is reduced (step S13).

[0072] The control device 80 repeats the process of reducing the opening of the expansion valve 4 until the condition "air temperature Tairin - refrigerant temperature Teo > threshold value A" is met. This increases the temperature of the refrigerant flowing out from the refrigerant outlet 602 of the evaporator. As a result, the degree of suction superheat increases. When the condition "air temperature Tairin - refrigerant temperature Teo > threshold value A" is met, the control device 80 ends the process based on this flowchart.

[0073] If the determination in step S11 is NO, i.e., if the control device 80 determines that the refrigerant circulation amount is low, the control device 80 does not execute the processes in steps S12 and S13 because if the processes in steps S12 and S13 are executed when the refrigerant circulation amount is low, the performance of the evaporator may be degraded.

[0074] That is, when the refrigerant circulation rate is low, the refrigerant temperature rises along the direction of refrigerant flow in the evaporator (see (b) of FIG. 8 and (d) of FIG. 9). Under such operating conditions (operating conditions with a small temperature difference between the indoors and outdoors and a low thermal load), in order to provide suction superheat, it is necessary to reduce the opening of the expansion valve 4 when the temperature difference between the air and refrigerant is small. In this case, the refrigerant temperature at the refrigerant inlet 601 of the evaporator further drops, which may result in a deterioration in the performance of the evaporator.

[0075] Therefore, when the determination in step S11 is NO, the control device 80 executes normal LEV control. That is, the control device 80 controls the opening degree of the expansion valve 4 to an appropriate value depending on the operating conditions (step S14).

[0076] Next, the control device 80 determines whether or not "refrigerant temperature Tei > 0°C" is true (step S15). If "refrigerant temperature Tei > 0°C" is not true, there is a risk of the refrigerant freezing. Therefore, if "refrigerant temperature Tei > 0°C" is not true, the control device 80 increases the opening of the expansion valve 4 (step S16) and ends the processing based on this flowchart. If the control device 80 determines YES in step S15, it ends the processing based on this flowchart without executing step S16.

[0077] As described above, according to this embodiment, in the air conditioner 100 that uses a non-azeotropic refrigerant mixture, the degree of suction superheat can be appropriately controlled. As a result, the operating frequency of the compressor 1 can be reduced while maintaining the enthalpy difference of the evaporator. This reduces the input power of the compressor 1, thereby improving the performance of the compressor 1. Furthermore, because the degree of suction superheat can be appropriately controlled, the power consumption of the air conditioner 100 can be reduced.

[0078] Embodiment 2 Next, embodiment 2 will be described with reference to Fig. 13 and Fig. 14. Fig. 13 is a diagram schematically showing an example of an air conditioning apparatus 101 according to embodiment 2. Fig. 14 is a flowchart showing the processing procedure of a control device 80 provided in the air conditioning apparatus 101 according to embodiment 2.

[0079] An air conditioning apparatus 101 according to the second embodiment differs from the air conditioning apparatus 100 according to the first embodiment in that a temperature sensor 25 is employed instead of the temperature sensor 22. As shown in Fig. 13 , the temperature sensor 25 is provided at the intake port 603 of the compressor 1. The temperature sensor 25 measures the temperature Ts of the refrigerant drawn into the compressor 1. The air conditioning apparatus 101 according to the second embodiment has the same configuration as the air conditioning apparatus 100 according to the first embodiment, except for the fact that the temperature sensor 25 is employed instead of the temperature sensor 22.

[0080] In the second embodiment, the control device 80 executes processing based on the flowchart shown in Fig. 14 instead of processing based on the flowchart shown in Fig. 12. The flowchart shown in Fig. 14 differs from the flowchart shown in Fig. 12 in that step S121 is employed instead of step S12.

[0081] In step S121, the control device 80 according to the second embodiment determines whether or not "air temperature Tairin - refrigerant temperature Ts > threshold value A" is true. That is, in the second embodiment, the control device 80 determines whether or not the required suction superheat can be obtained based on the temperature difference between the temperature Tairin of the air drawn into the indoor unit 20 and the temperature Ts of the refrigerant drawn into the compressor 1. In this way, the control device 80 may determine whether or not the required suction superheat can be obtained using the temperature Ts of the refrigerant drawn into the compressor 1, instead of the temperature Teo of the refrigerant flowing out from the refrigerant outlet 602 of the evaporator.

[0082] The process of the flowchart shown in Fig. 14 is the same as the process of the flowchart shown in Fig. 12 except for step S121, so description of that process will not be repeated here.

[0083] (Summary) The present embodiment will be summarized below.

[0084] (1) The present disclosure relates to an air conditioning device (100, 101) that uses a non-azeotropic refrigerant mixture as a refrigerant, and that includes a refrigerant circuit (50) including a compressor (1), a condenser (3), an evaporator (6), and an expansion valve (4), a control device (80), a first sensor (21) that measures the temperature of the refrigerant flowing between the expansion valve and the evaporator, a second sensor (22) that measures the temperature of the refrigerant flowing between the evaporator and the compressor, a third sensor (23) that measures the temperature of the refrigerant flowing near the middle of a refrigerant pipe (13) included in the evaporator, and a fourth sensor (24) that measures the temperature of air that exchanges heat with the evaporator, and when the measurement value of the first sensor is greater than the measurement value of the third sensor, the control device adjusts the opening of the expansion valve so that the value obtained by subtracting the measurement value of the second sensor from the measurement value of the fourth sensor is greater than a threshold value (steps S12, S13, and S121).

[0085] (2) In the air conditioner described in paragraph (1), the non-azeotropic refrigerant mixture contains 77 percent or more of R1234yf.

[0086] (3) In the air conditioner described in paragraph 1 or 2, the non-azeotropic refrigerant mixture is R474A.

[0087] (4) In the air conditioning apparatus described in any one of paragraphs 1 to 3, the first sensor is disposed at the refrigerant inlet (601) of the evaporator, and the second sensor is disposed at the refrigerant outlet (602) of the evaporator.

[0088] (5) In the air conditioning apparatus described in any one of paragraphs 1 to 3, the first sensor is disposed at the refrigerant inlet (601) of the evaporator, and the second sensor is disposed at the refrigerant suction port (603) of the compressor.

[0089] (6) In the air conditioning apparatus described in any one of paragraphs 1 to 5, the refrigerant piping forms multiple rows of piping sections (61 to 63) by meandering inside the evaporator, and the evaporator is configured so that the flow direction of the refrigerant flowing through the multiple rows of piping sections and the flow direction of the air flowing through the evaporator are countercurrent to each other.

[0090] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and is intended to include all modifications within the meaning and scope of the claims.

[0091] 1 Compressor, 2 Four-way valve, 3 Outdoor heat exchanger, 4 Expansion valve, 5 Fan, 6 Indoor heat exchanger, 7 Fan, 9 Air outlet, 10 Outdoor unit, 11, 12 Extension piping, 13 Refrigerant piping, 21-25 Temperature sensors, 61-63 Piping section, 80 Control device, 81 Processor, 82 Memory, 100, 101 Air conditioning device, 601 Refrigerant inlet, 602 Refrigerant outlet, 603 Refrigerant suction port.

Claims

1. An air conditioning system that uses a non-azeotropic refrigerant as the refrigerant, comprising: a refrigerant circuit including a compressor, a condenser, an evaporator, and an expansion valve; a control device; a first sensor that measures the temperature of the refrigerant flowing between the expansion valve and the evaporator; a second sensor that measures the temperature of the refrigerant flowing between the evaporator and the compressor; a third sensor that measures the temperature of the refrigerant flowing near the middle of the refrigerant piping included in the evaporator; and a fourth sensor that measures the temperature of the air exchanging heat with the evaporator, wherein when the measurement value of the first sensor is greater than the measurement value of the third sensor, the control device adjusts the opening of the expansion valve so that the value obtained by subtracting the measurement value of the second sensor from the measurement value of the fourth sensor is greater than a threshold value.

2. The air conditioning apparatus according to claim 1, wherein the non-azeotropic refrigerant mixture contains 77 percent or more of R1234yf.

3. An air-conditioning apparatus as described in claim 1 or 2, wherein the non-azeotropic refrigerant mixture is R474A.

4. An air conditioning apparatus as described in any one of claims 1 to 3, wherein the first sensor is arranged at a refrigerant inlet of the evaporator, and the second sensor is arranged at a refrigerant outlet of the evaporator.

5. An air conditioning apparatus as described in any one of claims 1 to 3, wherein the first sensor is arranged at a refrigerant inlet of the evaporator, and the second sensor is arranged at a refrigerant suction port of the compressor.

6. An air-conditioning apparatus as described in any one of claims 1 to 5, wherein the refrigerant piping forms multiple rows of piping sections by serpentine inside the evaporator, and the evaporator is configured so that the flow direction of the refrigerant flowing through the multiple rows of piping sections and the flow direction of the air flowing through the evaporator are counter-current.

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