Control device, control method, and control program

Abstract

The present invention quickly detects liquid backflow.　A first temperature sensor (510) and a second temperature sensor (520) are disposed on the outlet side of an evaporator (200) of a refrigeration system. The second temperature sensor (520) is disposed at a predetermined distance from the first temperature sensor (510). Liquid backflow from the evaporator (200) is detected on the basis of measurement values of the first temperature sensor (510) and the second temperature sensor (520).

Description

Control Device, Control Method, and Control Program

[0001] The present invention relates to a control device, a control method, and a control program.

[0002] In a vapor compression refrigeration cycle, in order to prevent liquid backflow from the evaporator to the compressor (that is, unvaporized refrigerant (mist-like refrigerant) flows out from the evaporator toward the compressor), the expansion valve is controlled so that the superheat degree, which is the difference between the temperature of the refrigerant flowing out from the evaporator and the evaporation temperature of the refrigerant, reaches a certain value (for example, 5 to 10°C). As the expansion valve, for example, an electronic expansion valve is used (Patent Documents 1 and 2).

[0003] The superheat degree is calculated using the measured values of a temperature sensor and a pressure sensor. Due to the accuracy of the temperature sensor and the pressure sensor, the installation state of the temperature sensor and the pressure sensor, insufficient heat insulation of the temperature sensor, etc., the actual temperature-pressure characteristics may change. Currently, azeotropic refrigerant mixtures are used as refrigerants. In azeotropic refrigerant mixtures, the temperature-pressure characteristics may change due to component changes. Thus, when the temperature-pressure characteristics change, the superheat degree calculated using the measured values of the temperature sensor and the pressure sensor may have an error from the actual superheat degree. As a result, in control that maintains the target value of the superheat degree at a constant value, liquid backflow may occur. Therefore, for example, in the method disclosed in Patent Document 3, liquid backflow is detected based on the change rate of the superheat degree, and if liquid backflow is detected, the target value of the superheat degree is increased to prevent liquid backflow.

[0004] Japanese Patent Application Laid-Open No. 2003-329157, Japanese Patent Application Laid-Open No. 62-87775, Japanese Patent Publication No. 8-33244

[0005] However, in the method disclosed in Patent Document 3, the calculation of the change rate of the superheat degree is performed every time the data storage period ends, and it takes 16 minutes or more from the start to the end of this data storage period. Therefore, in the method disclosed in Patent Document 3, it took 16 minutes or more to detect liquid backflow.

[0006] An object of the present invention is to perform liquid backflow detection in a short time.

[0007] To solve the above problems, a control device according to one embodiment of the present invention is a control device for a refrigeration system, the refrigeration system comprising an electronic expansion valve, an evaporator, a compressor, and a condenser, the electronic expansion valve, the evaporator, the compressor, and the condenser being connected in a ring by piping, the refrigerant circulating in the order of the electronic expansion valve, the evaporator, the compressor, and the condenser, the control device comprising a first temperature sensor, a second temperature sensor, and a control unit, the first temperature sensor and the second temperature sensor being positioned on the outlet side of the evaporator, the second temperature sensor being positioned at a predetermined distance from the first temperature sensor, and the control unit detecting liquid back from the evaporator based on the measured values ​​of the first temperature sensor and the second temperature sensor.

[0008] The control unit may also detect liquid backflow from the evaporator based on the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor.

[0009] The control unit may also detect liquid backflow from the evaporator based on the time change in the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor.

[0010] The second temperature sensor may be located on the compressor side, and the control unit may determine that liquid backflow has begun at the location where the first temperature sensor is located when the amount of change over time of the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor exceeds a first threshold.

[0011] The second temperature sensor may be located on the compressor side, and the control unit may determine that liquid backflow has begun at the location where the second temperature sensor is located when the amount of change over time of the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor falls below a second threshold.

[0012] The control unit may also control the flow rate of the refrigerant in the refrigeration system if liquid backflow from the evaporator is detected.

[0013] The control unit may change the control of the refrigerant flow rate in the refrigeration system based on the position where the liquid back is detected.

[0014] The control unit may also control the flow rate of the refrigerant in the refrigeration system by controlling the expansion valve of the refrigeration system.

[0015] The control device further includes a third temperature sensor located on the inlet side of the evaporator, and the control unit calculates the degree of superheating of the refrigeration system based on the measurement values ​​of the first temperature sensor and the third temperature sensor, controls the expansion valve of the refrigeration system based on the calculated degree of superheating, calculates a correction amount for the calculated degree of superheating if liquid back is detected, corrects the calculated degree of superheating using the correction amount after the liquid back is resolved, and controls the expansion valve of the refrigeration system based on the corrected degree of superheating.

[0016] A control method according to one embodiment of the present invention is a control method performed by a control device of a refrigeration system, wherein the refrigeration system comprises an electronic expansion valve, an evaporator, a compressor, and a condenser, the electronic expansion valve, the evaporator, the compressor, and the condenser are connected in a ring by piping, the refrigerant circulates in the order of the electronic expansion valve, the evaporator, the compressor, and the condenser, a first temperature sensor and a second temperature sensor are located on the outlet side of the evaporator, the second temperature sensor is located at a predetermined distance from the first temperature sensor, and the control method includes a detection step of detecting liquid back from the evaporator based on the measured values ​​of the first temperature sensor and the second temperature sensor.

[0017] A control program according to one embodiment of the present invention causes a computer to execute the above control method.

[0018] This invention makes it possible to perform liquid back detection in a short amount of time.

[0019] This figure shows a refrigeration system according to one embodiment of the present invention. This figure shows an example of a control device 500. This figure shows an example of a control unit 530. This figure illustrates the situation in which liquid backflow begins to occur at the position where the first temperature sensor 510 is located. This figure shows the time change of the measured value T1 of the first temperature sensor 510, the measured value T2 of the second temperature sensor 520, the difference T21 (= T2 - T1) between the measured values ​​T1 and T2, and the derivative value dT21 / dt of the difference T21. This figure illustrates the situation in which liquid backflow begins to occur at the position where the second temperature sensor 520 is located. This figure shows the time change of the measured value T1 of the first temperature sensor 510, the measured value T2 of the second temperature sensor 520, the difference T21 (= T2 - T1) between the measured values ​​T1 and T2, and the derivative value dT21 / dt of the difference T21. This figure shows an example of processing operation in the control unit 530. This figure shows another example of the refrigeration system according to this embodiment. This figure shows another example of the refrigeration system according to this embodiment. This figure shows another example of a control device 500. This figure shows another example of a control unit 530. This figure shows an example of processing operations performed in another example of the control unit 530 before liquid backing is detected. This figure shows an example of processing operations performed in another example of the control unit 530 after liquid backing has been resolved. This figure shows another example of the refrigeration system according to this embodiment. This figure shows another example of the refrigeration system according to this embodiment. This figure shows another example of the refrigeration system according to this embodiment.

[0020] <Refrigeration System> Figure 1 is a diagram showing a refrigeration system according to one embodiment of the present invention. The refrigeration system according to this embodiment is a refrigeration system using a vapor compression refrigeration cycle and includes an electronic expansion valve 100, an evaporator 200, a compressor 300, a condenser 400, and a control device 500.

[0021] The electronic expansion valve 100, evaporator 200, compressor 300, and condenser 400 are connected in a ring by piping 600, and the refrigerant circulates in the order of electronic expansion valve 100, evaporator 200, compressor 300, and condenser 400. This circulation of the refrigerant forms a well-known refrigeration cycle consisting of depressurization (expansion), evaporation, compression, and condensation. The refrigerant may be, for example, a fluorocarbon (e.g., chlorofluorocarbon (CFC) or hydrochlorofluorocarbon (HCFC)), a fluorocarbon alternative (e.g., hydrofluorocarbon (HFC)), or a non-fluorocarbon refrigerant (e.g., hydrofluorocarbon (HFC) or carbon dioxide).

[0022] The electronic expansion valve 100 is positioned between the condenser 400 and the evaporator 200, and the refrigerant condensed and liquefied in the condenser 400 flows into the electronic expansion valve 100 from the piping 600. The electronic expansion valve 100 depressurizes and expands this liquefied refrigerant. The refrigerant expanded by the electronic expansion valve 100 flows out of the electronic expansion valve 100 into the piping 600 toward the evaporator 200. The electronic expansion valve 100 is a valve whose opening degree can be controlled, for example, by the flow rate control processing unit 532 of the control device 500 described later. By adjusting the opening degree of the electronic expansion valve 100, the degree of depressurization and expansion of the refrigerant can be adjusted. The electronic expansion valve 100 is, for example, a stepping motor type electronic expansion valve (for example, the electronic expansion valve described in Patent Document 1). Alternatively, the electronic expansion valve 100 may be a solenoid valve of the type described in Patent Document 2, and the type of the electronic expansion valve 100 is not specified.

[0023] The evaporator 200 is positioned between the electronic expansion valve 100 and the compressor 300, and the refrigerant expanded by the electronic expansion valve 100 flows into the evaporator 200 from the piping 600. In the evaporator 200, this expanded refrigerant absorbs heat from the surroundings, cools the area around the evaporator 200, and vaporizes. The vaporized refrigerant in the evaporator 200 flows out of the evaporator 200 into the piping 600 toward the compressor 300.

[0024] The compressor 300 is positioned between the evaporator 200 and the condenser 400, and the refrigerant vaporized in the evaporator 200 flows into the compressor 300 from the piping 600. The compressor 300 compresses this vaporized refrigerant. The refrigerant compressed by the compressor 300 flows out of the compressor 300 into the piping 600 toward the condenser 400. The compressor 300 may also have its refrigerant discharge amount (i.e., refrigerant circulation amount) controlled by the flow rate control section 532 of the control device 500 described later.

[0025] The condenser 400 is positioned between the compressor 300 and the electronic expansion valve 100, and the refrigerant compressed by the compressor 300 flows into the condenser 400 from the piping 600. In the condenser 400, this compressed refrigerant is cooled and liquefied as heat is absorbed by the surroundings of the condenser 400. The liquefied refrigerant in the condenser 400 flows out of the condenser 400 into the piping 600 toward the electronic expansion valve 100.

[0026] The control device 500 detects liquid back from the evaporator 200, and if liquid back is detected, controls the flow rate of the refrigerant in the refrigeration system. As shown in Figure 1, the control device 500 has a first temperature sensor 510 and a second temperature sensor 520 on the outlet side of the evaporator 200 (i.e., between the evaporator 200 and the compressor 300). The first temperature sensor 510 is installed, for example, immediately after the outlet of the evaporator 200. The second temperature sensor 520 is positioned on the compressor 300 side (downstream of the first temperature sensor 510) at a predetermined distance from the first temperature sensor 510.

[0027] The control device 500 detects liquid back from the evaporator 200 based on the measurement values ​​from the first temperature sensor 510 and the second temperature sensor 520. The first temperature sensor 510 and the second temperature sensor 520 are positioned, for example, outside the piping 600 connecting the evaporator 200 and the compressor 300, in contact with the piping 600, and measure the temperature of the piping 600 in contact with it (i.e., the temperature of the refrigerant flowing through the piping 600).

[0028] <Control device 500> Figure 2 shows an example of the control device 500. The control device 500 has a first temperature sensor 510, a second temperature sensor 520, and a control unit 530. The control unit 530 is, for example, an information processing device such as a computer.

[0029] Figure 3 shows an example of the control unit 530. The control unit 530 includes a detection processing unit 531 and a flow rate control processing unit 532.

[0030] The detection processing unit 531 acquires the measurement value from the first temperature sensor 510 and the measurement value from the second temperature sensor 520, and detects liquid backflow from the evaporator 200 based on the acquired measurement values ​​from the first temperature sensor 510 and the second temperature sensor 520.

[0031] The flow rate control unit 532 controls the flow rate of the refrigerant in the refrigeration system. If the detection unit 531 detects liquid back from the evaporator 200, the flow rate control unit 532 controls the flow rate of the refrigerant so that it decreases. At this time, the flow rate control unit 532 may control the flow rate of the refrigerant by controlling the electronic expansion valve 100, or by controlling the compressor 300.

[0032] As shown in Figure 4, when liquid backflow begins at the location where the first temperature sensor 510 is positioned (for example, immediately after the outlet of the evaporator 200), the temperature of the first temperature sensor 510 decreases as heat is absorbed by the vaporizing refrigerant through the piping 600 (i.e., by latent heat), and the measured value T1 of the first temperature sensor 510 drops sharply, as shown in Figure 5. On the other hand, since liquid backflow does not occur at the location of the second temperature sensor 520, there is no sharp change in the measured value T2 of the second temperature sensor 520. This is because, at the location of the second temperature sensor 520, the refrigerant is a complete gas and is superheated by the surrounding heat (i.e., undergoing a sensible heat change). Therefore, as shown in Figure 5, the difference T21 (= T2 - T1) between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520 rises sharply. During normal operation of the refrigeration system, the refrigerant completely evaporates in the evaporator 200 and becomes a complete gas at the location of the first temperature sensor 510, which is positioned on the outlet side of the evaporator 200. It is then superheated between the evaporator 200 and the compressor 300. If liquid back occurs in the piping 600 on the outlet side of the evaporator 200, the evaporating refrigerant (refrigerant undergoing latent heat change) absorbs a far greater amount of heat from the surroundings than the superheated refrigerant (refrigerant undergoing sensible heat change). Therefore, the temperature sensor reading changes rapidly at the boundary between the liquid state (evaporating refrigerant) and the gaseous state (superheated refrigerant), that is, at the point where liquid back begins to occur.

[0033] Therefore, the detection processing unit 531 is configured to detect liquid backflow from the evaporator 200 based on the difference T21 (= T2 - T1) between the measurement value T1 of the first temperature sensor 510 and the measurement value T2 of the second temperature sensor 520. The detection processing unit 531 is configured to determine, for example, that liquid backflow has begun at the location where the first temperature sensor 510 is positioned when the difference T21 changes rapidly.

[0034] Furthermore, when liquid backflow begins to occur at the position where the first temperature sensor 510 is located, the difference T21 (= T2 - T1) between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520 increases rapidly, and as shown in Figure 5, the time derivative of the difference T21 (for example, the temperature change per unit time) dT21 / dt increases.

[0035] Therefore, the detection processing unit 531 may detect liquid backflow from the evaporator 200 based on the time change of the difference T21 between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520 (for example, the time derivative value dT21 / dt of the difference T21). For example, the detection processing unit 531 may determine that liquid backflow has started to occur at the position where the first temperature sensor 510 is located when the amount of time change of the difference T21 between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520 exceeds a first threshold TH1. Here, the first threshold TH1 is a positive value (TH1 > 0), for example, as shown in Figure 5. The time derivative value dT21 / dt of the difference T21 may be calculated, for example, by dividing the amount of change ΔT21 of the difference T21 over a predetermined time Δt by this predetermined time Δt (dT21 / dt = ΔT21 / Δt). The predetermined time Δt is set appropriately so as to detect a rapid change in the difference T21 between the measurement value T1 of the first temperature sensor 510 and the measurement value T2 of the second temperature sensor 520. The predetermined time Δt is, for example, the sampling period τ (for example, 1 second).

[0036] As described above, the second temperature sensor 520 is located downstream of the first temperature sensor. As shown in Figure 6, when liquid backflow begins at the location where the second temperature sensor 520 is located, the temperature of the second temperature sensor 520 decreases as heat is absorbed by the vaporizing refrigerant through the piping 600 (i.e., by latent heat), and the measured value T2 of the second temperature sensor 520 drops sharply, as shown in Figure 7. In the example shown in Figure 7, the sharp decrease in the measured value T2 of the second temperature sensor 520 begins at time t2. On the other hand, at the location of the first temperature sensor 510, the refrigerant does not vaporize, so there is no sharp change in the measured value T1 of the first temperature sensor 510. This is because, at the location of the first temperature sensor 510, the refrigerant is liquid but does not evaporate and is superheated by the surrounding heat (undergoing a sensible heat change). Therefore, as shown in Figure 7, the difference T21 (= T2 - T1) between the measurement value T1 of the first temperature sensor 510 and the measurement value T2 of the second temperature sensor 520 decreases rapidly. As a result, when liquid backflow begins to occur at the position where the second temperature sensor 520 is located, as shown in Figure 7, the detection processing unit 531 determines that the time derivative value dT21 / dt (for example, the temperature change per unit time) of the difference T21 between the measurement value T1 of the first temperature sensor 510 and the measurement value T2 of the second temperature sensor 520 decreases rapidly.

[0037] Therefore, the detection processing unit 531 is configured to determine that liquid backflow has begun at the location where the second temperature sensor 520 is located when the amount of change over time of the difference T21 between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520 (for example, the time derivative value dT21 / dt of the difference T21) falls below the second threshold TH2. Here, the second threshold TH2 is a negative value (TH2 < 0), as shown in Figure 7, for example.

[0038] Thus, in this embodiment, it is possible to detect the timing at which liquid backflow begins, and as a result, liquid backflow can be detected in a short time. Furthermore, in this embodiment, liquid backflow is detected by the change in the difference in the measured values ​​of multiple temperature sensors that are placed in isolation, so liquid backflow can be detected with high accuracy, and as a result, liquid backflow into the compressor can be prevented, thus avoiding liquid compression of the compressor and improving the robustness of the refrigeration system. In addition, in this embodiment, since the relative change in measured values ​​rather than the absolute values ​​of the measured values ​​of individual temperature sensors is used to detect liquid backflow, liquid backflow can be detected regardless of the measurement accuracy of individual temperature sensors, and as a result, high-precision temperature sensors are not required. Furthermore, in this embodiment, high-precision mounting of temperature sensors is not required. As a result, in this embodiment, the installation cost and maintenance cost of the refrigeration system can be reduced.

[0039] If the distance D between the first temperature sensor 510 and the second temperature sensor 520 is too short, or if the sampling period τ of the measurements from the first temperature sensor 510 and the second temperature sensor 520 is too long, changes in the measurement value of the first temperature sensor 510 and changes in the measurement value of the second temperature sensor 520 may occur simultaneously. As described above, it is necessary to capture the change per unit time of the difference T21 between the measurement value T1 of the first temperature sensor 510 and the measurement value T2 of the second temperature sensor 520. Therefore, the first temperature sensor 510 and the second temperature sensor 520 need to be isolated to some extent. Accordingly, the distance D between the first temperature sensor 510 and the second temperature sensor 520 should be determined, for example, based on the rate of liquid backflow V due to the refrigerant in the piping 600 and the sampling period τ. The distance D between the first temperature sensor 510 and the second temperature sensor 520 should be, for example, a value greater than or equal to the product of the rate of liquid backflow V and the sampling period τ (D ≥ V・τ).

[0040] The flow rate control processing unit 532 may change the control of the refrigerant flow rate based on the location where liquid back is detected. For example, if the detection processing unit 531 determines that liquid back has started to occur at the location where the second temperature sensor 520 is located, the flow rate control processing unit 532 may control the refrigerant flow rate to be reduced more than when liquid back has started to occur at the location where the first temperature sensor 510 is located.

[0041] Figure 8 shows an example of processing operation in the control unit 530. The processing shown in Figure 8 is executed, for example, at predetermined time intervals. The predetermined time interval is, for example, the sampling period τ (for example, 1 second). The detection processing unit 531 calculates the time derivative value dT21 / dt of the difference T21 between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520, and checks whether the calculated time derivative value dT21 / dt exceeds the first threshold TH1 (step S801). If the time derivative value dT21 / dt exceeds the first threshold TH1 (step S801, YES), the detection processing unit 531 determines that liquid back has started to occur at the position where the first temperature sensor 510 is located (step S802), and the flow rate control processing unit 532 controls the flow rate of the refrigerant so that the flow rate of the refrigerant decreases (step S803). If the time derivative dT21 / dt does not exceed the first threshold TH1 (step S801, NO), the process is terminated.

[0042] The refrigeration system according to this embodiment may further include an accumulator 700 positioned between the evaporator 200 and the compressor 300, as shown in Figure 9. This makes it possible to more reliably prevent liquefied refrigerant (refrigerant mist) from flowing into the compressor 300. When the refrigeration system has an accumulator 700, the first temperature sensor 510 and the second temperature sensor 520 of the control device 500 are positioned between the evaporator 200 and the accumulator 700, as shown in Figure 9.

[0043] <Overheat Controller> The control device 500 may be an overheat controller. At this time, as shown in FIGS. 10 and 11, the control device 500 further has a third temperature sensor 540, and as shown in FIG. 12, the control unit 530 of the control device 500 further has an overheat control processing unit 533.

[0044] The third temperature sensor 540 is disposed on the inlet side of the evaporator 200 (that is, between the electronic expansion valve 100 and the evaporator 200). The third temperature sensor 540 is disposed, for example, immediately before the inlet of the evaporator 200. The third temperature sensor 540 is disposed, for example, outside the pipe 600 connecting the electronic expansion valve 100 and the evaporator 200 so as to contact the pipe 600.

[0045] The overheat control processing unit 533 calculates the overheat degree SH of the refrigeration system and controls the electronic expansion valve 100 based on the calculated overheat degree SH. The overheat degree SH is the difference between the temperature of the refrigerant flowing out of the evaporator 200 and the evaporation temperature of the refrigerant. The overheat control processing unit 533 calculates the overheat degree SH of the refrigeration system, for example, based on the measured value T3 of the third temperature sensor 540 which is the evaporation temperature and the measured value T1 of the first temperature sensor 510 which is the refrigerant temperature. When the third temperature sensor 540 is disposed immediately before the inlet of the evaporator 200 and the first temperature sensor 510 is disposed immediately after the outlet of the evaporator 200, the measured value T3 of the third temperature sensor 540 is the evaporation temperature of the refrigerant, the measured value T1 of the first temperature sensor 510 is the temperature of the refrigerant flowing out of the evaporator 200, and the difference T13 (= T1 - T3) between the measured value T3 of the third temperature sensor 540 and the measured value T1 of the first temperature sensor 510 is the overheat degree SH (SH = T1 - T3).

[0046] The fact that liquid back starts to occur at the position where the first temperature sensor 510 is disposed indicates that the control by the overheat degree SH calculated by the overheat control processing unit 533 is not working well because the overheat degree SH calculated by the overheat control processing unit 533 deviates from the actual overheat degree. The deviation of the calculated overheat degree SH from the actual overheat degree is caused by factors such as the accuracy of the temperature sensor, the installation state of the temperature sensor, insufficient heat insulation of the temperature sensor, and component changes of the zeotropic mixture refrigerant.

[0047] When liquid backflow occurs at the outlet of the evaporator 200 (i.e., the position where the first temperature sensor 510 is located), the refrigerant has not completely vaporized in the evaporator 200, and the refrigerant is not superheated in the evaporator 200. Therefore, when liquid backflow occurs at the position where the first temperature sensor 510 is located, the actual degree of superheating is 0°C. Accordingly, if the detection processing unit 531 determines that liquid backflow has begun at the position where the first temperature sensor 510 is located (for example, the outlet of the evaporator 200), the superheating control processing unit 533 calculates the error between the superheating degree SH calculated at the time of this determination and the actual degree of superheating (0°C) as a correction amount ΔSH. In other words, since the actual degree of superheating is 0°C, the superheating degree SH calculated when the detection processing unit 531 determined that liquid backflow had begun at the position where the first temperature sensor 510 is located (for example, the outlet of the evaporator 200) becomes the correction amount ΔSH (ΔSH = SH - 0 = SH). Then, after the liquid backing is resolved (for example, after the detection processing unit 531 determines that liquid backing has begun and the liquid backing is resolved by the refrigerant flow rate control by the flow rate control processing unit 522 as described above), the superheat control processing unit 533 calculates a corrected superheat SH' (SH' = SH - ΔSH) by offsetting the superheat SH calculated by the superheat control processing unit 533 by a correction amount ΔSH, and uses this corrected superheat SH' to control the electronic expansion valve 100. In other words, in this embodiment, the superheat when liquid backing is detected is considered to be 0°C, the difference between this and the superheat calculated from the measured values ​​T1 and T3 is calculated as an error, and in the superheat control after the liquid backing is resolved, the superheat is corrected by offsetting the superheat calculated from the measured values ​​T1 and T3 by the error, and superheat control is performed using this corrected superheat.

[0048] By doing so, it becomes possible to calculate the superheat degree without being affected by the measurement error of the temperature sensor. As a result, it becomes possible to control the electronic expansion valve 100 based on the superheat degree without being affected by the measurement error of the temperature sensor. Usually, in order to enhance the stability of the refrigeration system, the electronic expansion valve is controlled such that the superheat degree becomes 5 to 10 °C. The superheat degree is the degree to which the refrigerant is superheated between the time when the refrigerant is completely evaporated in the evaporator and the outlet of the evaporator. Therefore, if the superheat degree becomes too large, the portion that does not contribute to heat exchange in the evaporator increases. Thus, when the portion that does not contribute to heat exchange in the evaporator increases, the capacity of the evaporator cannot be fully utilized, resulting in waste. Extra power of the compressor is required for this waste portion, consuming extra energy. As described above, by using the superheat degree at the time when liquid back occurs as a correction amount and controlling the electronic expansion valve based on the corrected superheat degree, it becomes possible to control at an optimal superheat degree according to the capacity of the evaporator and prevent the consumption of extra energy.

[0049] Figure 13 shows an example of processing operations performed in the control unit 530 before liquid back is detected. The processing shown in Figure 13 is performed, for example, at predetermined time intervals. The overheating control processing unit 533 calculates the overheating degree SH based on the measured value T1 of the first temperature sensor 510 and the measured value T3 of the third temperature sensor 540 (step S1301). The detection processing unit 531 calculates the time derivative value dT21 / dt of the difference T21 between the measured value T1 of the first temperature sensor 510 and the measured value T2 of the second temperature sensor 520, and checks whether the calculated time derivative value dT21 / dt exceeds the first threshold TH1 (step S1302). If the time derivative value dT21 / dt exceeds the first threshold TH1 (step S1302, YES), the detection processing unit 531 determines that liquid back has begun to occur at the position where the first temperature sensor 510 is located (step S1303), the flow rate control processing unit 532 controls the flow rate of the refrigerant so that the flow rate of the refrigerant decreases, and the superheat control processing unit 533 calculates the error between the calculated superheat SH and the actual superheat (0°C) as a correction amount ΔSH (step S1304). If the time derivative value dT21 / dt does not exceed the first threshold TH1 (step S1302, NO), the superheat control processing unit 533 controls the electronic expansion valve 100 based on the calculated superheat SH without correcting the calculated superheat SH (step S1305).

[0050] Figure 14 shows an example of a processing operation performed by the control unit 530 after liquid backflow has been resolved. The processing operation shown in Figure 14 is performed at predetermined intervals, for example, when the detection processing unit 531 determines that liquid backflow has begun in step S1303 of the processing operation in Figure 13, and after the liquid backflow has been resolved by the flow rate control processing unit 532 controlling the refrigerant flow rate. The superheat control processing unit 533 calculates the superheat based on the measured value T1 of the first temperature sensor 510 and the measured value T3 of the third temperature sensor 540 (step S1401). The superheat control processing unit 533 calculates a corrected superheat SH' by offsetting the calculated superheat SH by an error ΔSH (step S1402). Then, the superheat control processing unit 533 controls the electronic expansion valve 100 using this corrected superheat SH' (step S1403).

[0051] In this embodiment, temperature measurement using a third temperature sensor 540 attached to the inlet of the evaporator 200 was used to calculate the degree of superheating (temperature-temperature formula). However, instead of the third temperature sensor 540 at the inlet of the evaporator 200, a pressure sensor may be attached to the inlet or outlet of the evaporator 200, the refrigerant pressure inside the evaporator 200 may be measured using the pressure sensor, the temperature equivalent to the evaporation pressure may be calculated from this refrigerant pressure, and the degree of superheating may be calculated from this temperature equivalent to the evaporation pressure and the measurement value of the first temperature sensor 510 at the outlet of the evaporator (pressure-temperature formula). By doing so, the degree of superheating is less affected by the accuracy and error of the temperature sensor (or pressure sensor).

[0052] <Multiple First Temperature Sensors 510, Multiple Second Temperature Sensors 520> As shown in Figures 15 and 16, when the refrigeration system has multiple evaporators 200-1 to 200-N, the control device 500 should have the same number of first temperature sensors 510-1 to 510-N as there are evaporators 200-1 to 200-N, and one first temperature sensor 510 should be positioned corresponding to the outlet side of each of the multiple evaporators 200-1 to 200-N. In this way, it becomes possible to detect the occurrence of liquid back in each of the evaporators 200-1 to 200-N. In the example shown in Figure 15, the refrigeration system has one electronic expansion valve 100, and the refrigerant discharged from the electronic expansion valve 100 is distributed to multiple evaporators 200-1 to 200-N by a distributor 800. In the example shown in Figure 16, the refrigeration system has the same number of electronic expansion valves 100-1 to 100-N as there are evaporators 200-1 to 200-N, and one electronic expansion valve 100 is located on the inlet side of each of the multiple evaporators 200-1 to 200-N.

[0053] As shown in Figure 17, the control device 500 may have a plurality of second temperature sensors 520-1 to 520-M. In this case, the detection processing unit 531 determines that liquid back has started to occur at the position where the second temperature sensor 520-m is located when the amount of change over time of the difference T21m (= T2m - T1) between the measured value T1 of the first temperature sensor 510 and the measured value T2m of the second temperature sensor 520-m (m = 1, ..., M) falls below a predetermined value TH2m (for example, the time derivative value dT21m / dt of the difference T21m).

[0054] The flow rate control unit 532 then changes the control of the refrigerant flow rate based on the location where liquid back is detected. For example, if the detection unit 531 determines that liquid back has started to occur at the location where the second temperature sensor 520-m1 (m1 = 1, ..., M) is located, the flow rate control unit 532 controls the refrigerant flow rate to be lower than when liquid back has started to occur at the location where the second temperature sensor 520-m2 (m2 = 1, ..., M-1, m2 < m1) is located on the evaporator 200 side of the second temperature sensor 520-m1.

[0055] The present invention has been described above with reference to preferred embodiments. While the present invention has been described with reference to specific examples, various modifications and changes can be made to these examples without departing from the spirit and scope of the invention as described in the claims.

[0056] 100 Electronic expansion valve 200 Evaporator 300 Compressor 400 Condenser 500 Control device 510 First temperature sensor 520 Second temperature sensor 530 Control unit 531 Detection unit 532 Flow rate control unit 533 Superheating degree control unit 540 Third temperature sensor 600 Piping 700 Accumulator 800 Distributor

Claims

1. A control device for a refrigeration system, wherein the refrigeration system comprises an electronic expansion valve, an evaporator, a compressor, and a condenser, the electronic expansion valve, the evaporator, the compressor, and the condenser are connected in a ring by piping, the refrigerant circulates in the order of the electronic expansion valve, the evaporator, the compressor, and the condenser, the control device comprises a first temperature sensor, a second temperature sensor, and a control unit, the first temperature sensor and the second temperature sensor are located on the outlet side of the evaporator, the second temperature sensor is located at a predetermined distance from the first temperature sensor, and the control unit detects liquid back from the evaporator based on the measured values ​​of the first temperature sensor and the second temperature sensor.

2. The control device according to claim 1, wherein the control unit detects liquid back from the evaporator based on the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor.

3. The control device according to claim 2, wherein the control unit detects liquid backflow from the evaporator based on the time change of the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor.

4. The control device according to claim 3, wherein the second temperature sensor is located on the compressor side, and the control unit determines that liquid back has begun to occur at the location where the first temperature sensor is located when the amount of change over time of the difference between the measured value of the first temperature sensor and the measured value of the second temperature sensor exceeds a first threshold.

5. The control device according to claim 3, wherein the second temperature sensor is located on the compressor side, and the control unit determines that liquid back has begun to occur at the location where the second temperature sensor is located when the amount of change over time of the difference between the measurement value of the first temperature sensor and the measurement value of the second temperature sensor falls below a second threshold.

6. The control device according to any one of claims 1 to 5, wherein the control unit controls the flow rate of the refrigerant in the refrigeration system if liquid backflow from the evaporator is detected.

7. The control device according to claim 6, wherein the control unit changes the control of the refrigerant flow rate in the refrigeration system based on the position where the liquid back is detected.

8. The control device according to claim 6, wherein the control unit controls the flow rate of refrigerant in the refrigeration system by controlling the expansion valve of the refrigeration system.

9. The control device according to any one of claims 1 to 5, wherein the control device further comprises a third temperature sensor located on the inlet side of the evaporator, the control unit calculates the degree of superheating of the refrigeration system based on the measurement value of the first temperature sensor and the measurement value of the third temperature sensor, controls the expansion valve of the refrigeration system based on the calculated degree of superheating, calculates a correction amount for the calculated degree of superheating if liquid back is detected, corrects the calculated degree of superheating using the correction amount after the liquid back has been resolved, and controls the expansion valve of the refrigeration system based on the corrected degree of superheating.

10. A control method performed by a control device for a refrigeration system, wherein the refrigeration system comprises an electronic expansion valve, an evaporator, a compressor, and a condenser, the electronic expansion valve, the evaporator, the compressor, and the condenser are connected in a ring by piping, the refrigerant circulates in the order of the electronic expansion valve, the evaporator, the compressor, and the condenser, a first temperature sensor and a second temperature sensor are located on the outlet side of the evaporator, the second temperature sensor is located at a predetermined distance from the first temperature sensor, and the control method comprises a detection step of detecting liquid back from the evaporator based on measurements from the first temperature sensor and the second temperature sensor.

11. A control program that causes a computer to execute the control method described in claim 10.

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