Air conditioner

Abstract

The present application aims at controlling the injection amount without acquiring a large amount of data. An air conditioner includes a main refrigerant circuit having a compressor, a heat source side heat exchanger, a first expansion valve, and a utilization side heat exchanger; a bypass passage that combines a portion of refrigerant flowing from the utilization side heat exchanger to the heat source side heat exchanger with refrigerant compressed to an intermediate pressure of the compressor; a second expansion valve that depressurizes refrigerant flowing in the bypass passage; an internal heat exchanger that gives heat of refrigerant of the main refrigerant circuit flowing from the utilization side heat exchanger to the heat source side heat exchanger to refrigerant depressurized in the bypass passage; an opening adjustment unit that adjusts an opening of the second expansion valve based on a temperature difference of refrigerant temperatures of an outlet and an inlet of the internal heat exchanger in the bypass passage and a target temperature difference in heating operation; and a setting unit that sets the target temperature difference based on a degree of subcooling of the utilization side heat exchanger.

Description

Technical Field

[0001] This invention relates to an air conditioner. Background Technology

[0002] In a refrigeration cycle, as the outside gas temperature decreases, the compressor suction density decreases, thus reducing heating capacity even at the same compressor speed. In contrast, Patent Document 1 discloses an air conditioner that injects a portion of high-pressure liquid refrigerant to improve heating capacity. Furthermore, Patent Document 2 discloses a technique that controls the opening of the expansion valve in the injection circuit to adjust the flow rate of the refrigerant flowing in the injection circuit so that the compressor discharge temperature matches a target value, thereby improving heating capacity when the outside air is cold. Moreover, Patent Document 2 discloses a method that allows setting the target value of the compressor discharge temperature to the value with maximum heating capacity and maximum operating efficiency.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-274859

[0006] Patent Document 2: Japanese Patent No. 4767340 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, compressor characteristics (operating efficiency) vary depending on the compressor type, speed, compression ratio, and other operating conditions. Sometimes the suction and discharge pressures are the same, and even if the suction temperature is the same, the discharge temperature will differ. Therefore, the target value for the compressor's discharge temperature during injection needs to vary depending on the compressor type and operating conditions. Moreover, determining the target value requires a large amount of data to ensure that the heating capacity and operating efficiency are maximized, resulting in time-consuming setup.

[0009] This invention was made in view of the following problem, and its purpose is to control the amount of injection without requiring a large amount of data.

[0010] Solution for solving the problem

[0011] Therefore, the present invention is an air conditioner comprising: a main refrigerant circuit having a compressor, a heat source-side heat exchanger, a first expansion valve, and a utilization-side heat exchanger; a bypass path that allows a portion of the refrigerant flowing from the utilization-side heat exchanger to the heat source-side heat exchanger to merge with refrigerant compressed to the intermediate pressure of the compressor; a second expansion valve that depressurizes the refrigerant flowing in the bypass path; an internal heat exchanger that imparts heat from the refrigerant flowing from the utilization-side heat exchanger to the depressurized refrigerant in the bypass path; an opening adjustment unit that, during heating operation, adjusts the opening of the second expansion valve based on the temperature difference between the refrigerant temperatures at the outlet and inlet of the internal heat exchanger in the bypass path and a target temperature difference; and a setting unit that sets the target temperature difference based on the subcooling degree of the utilization-side heat exchanger.

[0012] Invention Effects

[0013] According to the present invention, the amount of injection can be controlled without obtaining a large amount of data. Attached Figure Description

[0014] Figure 1 This is a structural diagram of an air conditioner.

[0015] Figure 2 It's a pH graph.

[0016] Figure 3 It is a flowchart representing control. Detailed Implementation

[0017] Figure 1 This is a diagram illustrating an air conditioner implementation. The air conditioner 1 regulates air temperature by circulating refrigerant in a refrigeration cycle. The air conditioner 1 includes an indoor unit 10 installed indoors (in the air temperature regulation space) and an outdoor unit 20 installed outdoors. The indoor unit 10 and the outdoor unit 20 are connected via a main refrigerant circuit Q1 formed by refrigerant piping. Furthermore, Figure 1 The solid arrows shown indicate the flow of refrigerant during heating operation. Additionally, Figure 1 The dashed arrows shown indicate the flow of refrigerant during refrigeration operation.

[0018] The indoor unit 10 includes a utilization-side heat exchanger 11 and a utilization-side fan 12. In the utilization-side heat exchanger 11, heat exchange occurs between the refrigerant flowing through its heat transfer pipes (not shown) and indoor air supplied from the utilization-side fan 12. The utilization-side heat exchanger 11 operates as either a condenser or an evaporator by switching a four-way valve 22. The utilization-side fan 12 is located near the utilization-side heat exchanger 11. The utilization-side fan 12, driven by a utilization-side fan motor 12a, supplies indoor air into the utilization-side heat exchanger 11.

[0019] The outdoor unit 20 includes a compressor 21, a four-way valve 22, a heat source-side heat exchanger 23, a heat source-side fan 24, a first expansion valve 25, a second expansion valve 26, an internal heat exchanger 27, and a control unit 28. The compressor 21 compresses a low-temperature, low-pressure gaseous refrigerant and discharges it as a high-temperature, high-pressure gaseous refrigerant. In the heat source-side heat exchanger 23, heat exchange occurs between the refrigerant flowing through the heat transfer tubes and the external air supplied from the heat source-side fan 24. The heat source-side heat exchanger 23 operates as either a condenser or an evaporator by switching the four-way valve 22.

[0020] A heat source-side fan 24 is located near the heat source-side heat exchanger 23. Driven by a heat source-side fan motor 24a, the heat source-side fan 24 supplies outside air to the heat source-side heat exchanger 23. A first expansion valve 25 functions to depressurize the refrigerant after it has condensed in the "condenser" (one of the heat source-side heat exchanger 23 and the utilization-side heat exchanger 11). Furthermore, the refrigerant depressurized in the first expansion valve 25 is guided to the "evaporator" (the other of the heat source-side heat exchanger 23 and the utilization-side heat exchanger 11).

[0021] The four-way valve 22 is a valve that switches the refrigerant flow path according to the operating mode of the air conditioner 1. By switching the four-way valve 22, during cooling operation, as shown by the dashed arrow, the refrigerant circulates in the order of compressor 21, heat source-side heat exchanger 23 (condenser), first expansion valve 25, and utilization-side heat exchanger 11 (evaporator). Conversely, by switching the four-way valve 22, during heating operation, as shown by the solid arrow, the refrigerant circulates in the order of compressor 21, utilization-side heat exchanger 11 (condenser), first expansion valve 25, and heat source-side heat exchanger 23 (evaporator). That is, in the main refrigerant circuit Q1, where the refrigerant circulates sequentially through compressor 21, "condenser," first expansion valve 25, and "evaporator" in the cooling cycle, one of the aforementioned "condenser" and "evaporator" is the heat source-side heat exchanger 23, and the other is the utilization-side heat exchanger 11.

[0022] Thus, in the air conditioner 1, a main refrigerant circuit Q1 is formed by the utilization-side heat exchanger 11, compressor 21, four-way valve 22, heat source-side heat exchanger 23, and first expansion valve 25. Furthermore, the air conditioner 1 includes a bypass circuit Q2 in the main refrigerant circuit Q1, branching off from the utilization-side heat exchanger 11 and heat source-side heat exchanger 23 and merging with the middle section of compressor 21. Through the bypass circuit Q2, a portion of the refrigerant flowing from the utilization-side heat exchanger 11 to the heat source-side heat exchanger 23 in the main refrigerant circuit Q1 merges with the refrigerant compressed to intermediate pressure in compressor 21. A second expansion valve 26 and an internal heat exchanger 27 are provided in the bypass circuit Q2. The second expansion valve 26 reduces the pressure of the refrigerant flowing from the main refrigerant circuit Q1. The internal heat exchanger 27 performs heat exchange between the refrigerant in the main refrigerant circuit Q1 and the refrigerant in the bypass circuit Q2. That is, the internal heat exchanger 27 provides heat from the refrigerant in the main refrigerant circuit Q1, which flows from the utilization side heat exchanger 11 to the heat source side heat exchanger 23, to the refrigerant after pressure reduction by the second expansion valve 26 of the bypass circuit Q2.

[0023] In addition, a first temperature sensor 31 is provided on the discharge side of the compressor 21. A second temperature sensor 32 is provided at the inlet and outlet of the four-way valve 22 in the heat source side heat exchanger 23. A third temperature sensor 33 is provided at the inlet and outlet of the internal heat exchanger 27 in the utilization side heat exchanger 11. In the bypass circuit Q2, a fourth temperature sensor 34 and a fifth temperature sensor 35 are provided on the suction and discharge sides of the internal heat exchanger 27, respectively. Furthermore, a first pressure sensor 41 is provided on the discharge side of the compressor 21, and a second pressure sensor 42 is provided between the compressor 21 and the four-way valve 22.

[0024] Figure 2 This is a pH graph during heating operation. During heating, in the bypass circuit Q2, a portion of the refrigerant condensed in the utilization-side heat exchanger 11 is depressurized by the second expansion valve 26 (AB). Furthermore, in the internal heat exchanger 27, the refrigerant in the main refrigerant circuit Q1 exchanges heat with the refrigerant in the bypass circuit Q2, thereby subcooling the refrigerant in the main refrigerant circuit Q1 (AD) and vaporizing the refrigerant in the bypass circuit Q2 (BC), which is then injected into the compressor 21. Thus, a gas injection cycle is formed through the bypass circuit Q2.

[0025] By injecting refrigerant, the amount of refrigerant discharged from compressor 21 becomes the sum of the intake refrigerant amount Gr and the injected refrigerant gr (Gr+gr), which is higher than the intake refrigerant amount. Therefore, the amount of refrigerant flowing to the utilization-side heat exchanger 11, which operates as a condenser, increases, and the heating capacity increases. On the other hand, gaseous refrigerant is injected into compressor 21 at intermediate pressure, thus reducing the compression work from low pressure to intermediate pressure. As a result, the heating capacity of compressor 21 is improved when the outside air is cold, and the operating efficiency is improved.

[0026] On the other hand, the operating efficiency of the air conditioner 1 is also affected by the pressure state. If the subcooling at the outlet of the utilization-side heat exchanger 11 of the indoor unit 10 increases, the enthalpy difference increases, and the condensing capacity increases. However, along with the increase in subcooling, the heat transfer rate of the refrigerant side in the condenser decreases. Therefore, the overall performance of the utilization-side heat exchanger 11 decreases, and the high pressure increases. As a result, the compression work increases, and thus there exists a subcooling level at which the operating efficiency is maximized. Therefore, in the air conditioner 1, it is preferable to appropriately adjust the subcooling of the utilization-side heat exchanger 11.

[0027] The control unit 28 of the outdoor unit 20, as a structure for performing such control, includes an opening adjustment unit 281 and a setting unit 282. The opening adjustment unit 281 adjusts the opening degree of the first expansion valve 25 and the second expansion valve 26. The setting unit 282 sets a target temperature difference in the bypass circuit Q2 as a target value for the difference between the refrigerant temperature at the outlet and inlet of the internal heat exchanger 27. The control unit 28 includes a processor, a main storage device, and an auxiliary storage device. The opening adjustment unit 281 and the setting unit 282 are implemented by the processor executing the program stored in the auxiliary storage device. Alternatively, as another example, the opening adjustment unit 281 and the setting unit 282 may also be implemented in hardware.

[0028] Figure 3 This is a flowchart illustrating the control of the control unit 28 during heating operation. This control is executed at constant intervals. In this control, firstly, in S100, the control unit 28 determines the degree of subcooling. Specifically, the control unit 28 determines the degree of subcooling as the difference between the refrigerant temperature calculated based on the saturation temperature at the discharge pressure detected by the first pressure sensor 41 and the refrigerant temperature detected by the third temperature sensor 33 at the outlet side of the utilization-side heat exchanger 11 in operation. Furthermore, the method for determining the degree of subcooling is not limited to this embodiment. As another example, a temperature sensor may be arranged at the middle position of the utilization-side heat exchanger 11, and the control unit 28 may determine the degree of subcooling as the difference between the temperature of the gas-liquid two-phase state detected by this temperature sensor and the refrigerant temperature detected by the third temperature sensor 33 at the outlet side of the utilization-side heat exchanger 11.

[0029] Next, in S102, the control unit 28 determines the temperature difference between the inlet and outlet of the internal heat exchanger 27. Specifically, the control unit 28 acquires the outlet-side refrigerant temperature detected by the fifth temperature sensor 35 on the outlet side of the internal heat exchanger 27 and the inlet-side refrigerant temperature detected by the fourth temperature sensor 34 on the inlet side of the internal heat exchanger 27. Furthermore, the control unit 28 determines the difference between the outlet-side refrigerant temperature and the inlet-side refrigerant temperature as the temperature difference.

[0030] Next, in S104, the setting unit 282 determines the target temperature difference. Here, the target temperature difference is the target value of the temperature difference between the inlet and outlet of the internal heat exchanger 27. The target temperature difference is a value determined based on the degree of supercooling, and it is a value that decreases as the degree of supercooling increases. For example, the target temperature difference when the degree of supercooling is a first value is larger than the target temperature difference when the degree of supercooling is a second value that is larger than the first value. The setting unit 282 determines the target temperature difference based on the degree of supercooling. Furthermore, the setting unit 282 determines the target temperature difference based on the degree of supercooling by using a pre-set function that represents the correspondence between the degree of supercooling and the target temperature difference. As another example, a correspondence table representing the correspondence between the target temperature difference and the degree of supercooling may be pre-set in the control unit 28, and the setting unit 282 determines the target temperature difference based on the degree of supercooling according to the correspondence table.

[0031] As mentioned above, there exists a supercooling degree that maximizes operating efficiency. This supercooling degree, where operating efficiency is maximized, is set as the target supercooling degree, and the target temperature difference is determined in such a way that the supercooling degree becomes the target supercooling degree. That is, the target temperature difference is set based on the supercooling degree and the target supercooling degree.

[0032] Next, in S106, the opening adjustment unit 281 of the control unit 28 adjusts the opening of the second expansion valve to make the actual temperature difference the target temperature difference. For example, if the subcooling degree is greater than the target subcooling degree, a value smaller than the actual temperature difference is set as the target temperature difference. In this case, the opening adjustment unit 281 increases the opening of the second expansion valve 26 to reduce the temperature difference and approach the target temperature difference. As a result, the amount of refrigerant flowing in the bypass circuit Q2 increases, the amount of heat exchange in the internal heat exchanger 27 also increases, and the subcooling degree at the inlet side of the heat source side heat exchanger 23 of the main refrigerant circuit Q1 increases. Since the density of liquid refrigerant is relatively high, the amount of refrigerant in the heat source side heat exchanger 23 increases, while the amount of refrigerant in the utilization side heat exchanger 11 decreases. As a result, the subcooling degree at the outlet side of the utilization side heat exchanger 11 decreases. Thus, in the case of a large subcooling degree, by increasing the opening of the second expansion valve in a manner that becomes the target temperature difference, the subcooling degree can be further reduced.

[0033] On the other hand, when the subcooling degree is smaller than the target subcooling degree, a value larger than the actual temperature difference is set as the target temperature difference. In this case, the opening adjustment unit 281 reduces the opening of the second expansion valve 26 to increase the temperature difference and approach the target temperature difference. As a result, the amount of refrigerant flowing in the bypass circuit Q2 decreases, and the subcooling degree at the outlet side of the utilization heat exchanger 11 increases. Thus, when the subcooling degree is small, by reducing the opening of the second expansion valve 26 to achieve the target temperature difference, the subcooling degree can be further increased. In this way, by setting the target temperature difference based on the subcooling degree and adjusting the opening of the second expansion valve 26 based on the target temperature difference, the injection quantity can be adjusted, thereby improving operating efficiency.

[0034] It should be noted that in S106, the control unit 28 makes the temperature difference close to the target temperature difference by repeatedly increasing or decreasing the opening of the second expansion valve 26 by a constant amount and then reconfirming the temperature difference between the inlet and outlet of the internal heat exchanger 27 after a constant time.

[0035] Next, in S108, the control unit 28 obtains the discharge refrigerant temperature of the compressor 21 detected by the first temperature sensor 31. Then, in S110, the control unit 28 determines the suction superheat of the compressor 21. Specifically, the control unit 28 determines the suction superheat as the difference between the refrigerant temperature calculated based on the evaporation temperature under pressure detected by the second pressure sensor 42 and the refrigerant temperature detected by the second temperature sensor 32 at the outlet side of the heat source-side heat exchanger 23. Furthermore, the method for determining the superheat is not limited to this embodiment. As another example, a temperature sensor may be placed at the middle position of the heat source-side heat exchanger 23, and the control unit 28 may determine the superheat as the difference between the temperature of the gas-liquid two-phase state detected by this temperature sensor and the refrigerant temperature detected by the second temperature sensor 32 at the outlet side of the heat source-side heat exchanger 23.

[0036] Next, in S112, the opening adjustment unit 281 adjusts the opening of the first expansion valve 25 based on the discharge refrigerant temperature and the suction superheat of the compressor 21. Specifically, when the discharge refrigerant temperature exceeds a preset target temperature, the opening adjustment unit 281 increases the opening of the first expansion valve 25. On the other hand, when the suction superheat is less than the superheat target value, the opening adjustment unit 281 decreases the opening of the first expansion valve 25. When the suction superheat exceeds the superheat target value, the opening adjustment unit 281 increases the opening of the first expansion valve 25. Here, the superheat target value is a predetermined value. It should be noted that sometimes it is necessary to increase the opening based on the discharge refrigerant temperature and decrease the opening based on the suction superheat. In this case, the opening adjustment unit 281 calculates the average opening of the increase and decrease amounts and adjusts it to this opening.

[0037] During heating operation, the opening of the first expansion valve 25 is typically controlled based on the superheat at the outlet of the heat exchanger 23 on the heat source side or the suction superheat of the compressor 21. When the outside air is cold, operation becomes high-compression-ratio, and the discharge temperature of the compressor 21 tends to rise. As described above, by injecting refrigerant into the bypass circuit Q2, the discharge temperature can be reduced. However, the second expansion valve 26 uses a relatively small capacity, and since it injects refrigerant into the compressor 21 at intermediate pressure, the injection quantity is limited. Therefore, as described above, in the air conditioner 1 of this embodiment, in addition to adjusting the injection quantity, the opening of the first expansion valve 25 in the main refrigerant circuit Q1 is also adjusted. This suppresses a sharp rise in the discharge temperature of the compressor 21.

[0038] As described above, in this embodiment, the air conditioner 1 determines the target temperature difference between the inlet and outlet of the internal heat exchanger 27 based on the subcooling degree of the utilization side heat exchanger 11, and adjusts the opening of the second expansion valve 26 in such a way that the temperature difference between the inlet and outlet becomes the target temperature difference. Thus, the air conditioner 1 adjusts the opening of the second expansion valve 26 based on a target value (target temperature difference) independent of the type and operating condition of the compressor 21, rather than the discharge temperature of the compressor 21. Therefore, it is possible to control the injection volume without acquiring a large amount of data corresponding to the type and operating condition of the compressor 21.

[0039] Furthermore, if the subcooling at the outlet side of the heat exchanger 11 is too large, the enthalpy difference of the condenser increases, but the performance of the heat exchanger decreases, and the high pressure rises. Therefore, there exists a subcooling degree that maximizes operating efficiency. The air conditioner 1 of this embodiment uses this subcooling degree that maximizes operating efficiency as the target subcooling degree, determines the target temperature difference based on the target subcooling degree, and adjusts the opening of the second expansion valve 26 based on the target temperature difference. As a result, the operating efficiency of the air conditioner 1 can be improved. In addition, when the outside air is cold, the suction pressure of the compressor 21 decreases, and the suction density decreases. Therefore, the refrigerant content in the heat source side heat exchanger 23 decreases relatively, and the subcooling degree of the heat exchanger 11 increases. Under such circumstances, the air conditioner 1 of this embodiment can increase the injection volume and improve the heating capacity by reducing the target temperature difference.

[0040] Furthermore, the present invention is not limited to this specific embodiment. For example, variations of a certain embodiment can be applied to other embodiments or other variations. Within the scope of the spirit of the present invention as described in the claims, various modifications and alterations are possible.

[0041] As a first variation, the air conditioner 1 may also have multiple indoor units. In this case, a utilization-side heat exchanger is provided in each indoor unit. The control unit calculates the average value of the subcooling degree of the multiple utilization-side heat exchangers and determines the target temperature difference based on the subcooling degree.

[0042] As a second variation, the target temperature difference is a value determined based on the degree of supercooling. It can be a value that decreases as the degree of supercooling increases, or it can be a value that does not require the operating efficiency to be maximized.

[0043] The third variation will be described. In this embodiment, the opening adjustment unit 281 adjusts the opening of the first expansion valve 25 based on both the discharge refrigerant temperature and the suction superheat of the compressor 21. However, the opening adjustment unit 281 may also adjust the opening of the first expansion valve based solely on the discharge refrigerant temperature. For example, if the discharge temperature exceeds a predetermined target temperature, the opening of the first expansion valve 25 may be increased. In this case, the discharge temperature can also be reduced.

[0044] Symbol Explanation

[0045] 1—Air conditioner; 10—Indoor unit; 11—Utilizing side heat exchanger; 12—Utilizing side fan; 20—Outdoor unit; 21—Compressor; 22—Four-way valve; 23—Heat source side heat exchanger; 24—Heat source side fan; 25—First expansion valve; 26—Second expansion valve; 27—Internal heat exchanger; 31-35—First-fifth temperature sensors; 41, 42—Pressure sensors; Q1—Main refrigerant circuit; Q2—Bypass circuit.

Claims

1. An air conditioner, characterized in that, have: The main refrigerant circuit includes a compressor, a heat source-side heat exchanger, a first expansion valve, and a utilization-side heat exchanger. A bypass path that allows a portion of the refrigerant flowing from the utilization-side heat exchanger to the heat source-side heat exchanger to merge with refrigerant compressed to the intermediate pressure of the compressor; The second expansion valve reduces the pressure of the refrigerant flowing in the bypass path; An internal heat exchanger imparts heat from the refrigerant in the main refrigerant circuit flowing from the utilization-side heat exchanger to the heat source-side heat exchanger to the refrigerant whose pressure is reduced in the bypass path. The opening adjustment unit adjusts the opening of the second expansion valve during heating operation based on the temperature difference between the refrigerant temperature at the outlet and inlet of the internal heat exchanger in the bypass path and the target temperature difference. as well as The setting unit sets the target temperature difference based on the subcooling degree of the utilization-side heat exchanger.

2. The air conditioner according to claim 1, characterized in that, The target temperature difference when the supercooling degree is a first value is greater than the target temperature difference when the supercooling degree is a second value greater than the first value.

3. The air conditioner according to claim 1, characterized in that, The setting unit sets the target temperature difference based on the subcooling of the utilization side heat exchanger and a pre-set target subcooling.

4. The air conditioner according to claim 1, characterized in that, It also includes a temperature sensor that detects the refrigerant temperature on the discharge side of the compressor. The opening adjustment unit adjusts the opening of the first expansion valve based on the refrigerant temperature detected by the temperature sensor and the target temperature.

5. The air conditioner according to claim 4, characterized in that, The opening adjustment unit also adjusts the opening of the first expansion valve based on the suction superheat of the compressor.

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