JP2008032251A - Method and device for controlling refrigerating air-conditioning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of controlling a refrigerating air-conditioning system capable of higher accuracy, and to provide its device. <P>SOLUTION: In the method of controlling the refrigerating air-conditioning system, a refrigerating cycle is constructed with a compressor, a condenser, an expansion valve and an evaporator connected together via pipes for refrigerant to be circulated in the pipes. The method includes an evaporation completing point position calculating step of calculating the position of an evaporation completing point as a boundary between a vapor-liquid two-phase region and a superheated vapor region of the refrigerant in the evaporation pipe in accordance with temperature distribution in the evaporation pipe of the evaporator, and an opening control step of controlling the opening of the expansion valve so that a deviation between the calculated position of the evaporation completing point and a target position of the evaporation completing point falls in a predetermined permissible range. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a control method and a control device for a refrigeration air conditioner, and more specifically, a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a pipe and a refrigerant is circulated through the pipe. The present invention relates to a control method and a control device for an air conditioner.

  Conventionally, a refrigerating and air-conditioning apparatus having a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a pipe and a refrigerant is circulated through the pipe has been disclosed (see Patent Documents 1 and 2).

  In this type of refrigerating and air-conditioning apparatus, first, the refrigerant that has exited the evaporator and turned into a low-temperature and low-pressure gas is compressed by the compressor into a high-temperature and high-pressure gas. Next, the refrigerant that has become the high-temperature and high-pressure gas is deprived of heat by passing through the condenser and condensed to become a high-temperature and high-pressure liquid. Next, the refrigerant that has become a high-temperature and high-pressure liquid passes through an electronic expansion valve and expands and becomes a low-temperature and low-pressure liquid. When entering the evaporator, the refrigerant that has become a low-temperature and low-pressure liquid enters a gas-liquid two-phase state in which saturated liquid and saturated vapor are mixed, and the ratio of saturated vapor gradually increases as heat is absorbed from the surroundings as latent heat of vaporization. At a certain position, the ratio of saturated liquid becomes zero and all becomes saturated steam. This position is called the evaporation completion point, and the area before the evaporation completion point is called a gas-liquid two-phase area. The refrigerant basically does not change in temperature due to the latent heat of vaporization in the gas-liquid two-phase region up to the point of completion of evaporation, but the heat absorbed in the subsequent positions contributes to the temperature rise of the saturated vapor, and the refrigerant is superheated vapor. Become. The area after the evaporation completion point is called the superheated steam area, and the temperature rise of the refrigerant in the superheated steam area is called the superheat degree. Thereafter, the refrigerant that has become low-temperature and low-pressure superheated steam exits the evaporator, enters the compressor again, and repeats the above cycle. This cycle is called a refrigeration cycle.

  In the above refrigerating and air-conditioning apparatus, the role of the electronic expansion valve is to maintain the evaporation completion point near the outlet of the evaporator, so that the refrigerant enters the compressor while containing the saturated liquid and breaks the compressor. This is to prevent the phenomenon called liquid back and to effectively use the entire evaporator. The position of the evaporation completion point is related to the length of the superheated steam region, and the degree of superheat increases as the evaporation completion point moves away from the outlet of the evaporator. That is, the evaporator is maintained at an appropriate degree of superheat by adjusting the flow rate of the refrigerant by controlling the opening of the electronic expansion valve.

  The conventional control of the electronic expansion valve detects the temperature of the outlet portion of the evaporator and the temperature of the inlet portion or the central portion, and uses the difference between the detected temperature of the outlet portion and the temperature of the inlet portion or the central portion as the superheat degree. By a control device that controls by PID control or fuzzy control using a deviation between the instructed superheat degree and the calculated superheat degree so that the calculated superheat degree matches the target superheat degree instructed from outside Is going. The electronic expansion valve can freely adjust the opening according to the opening command of the valve output from the control device, and the opening command can be controlled by the control device with an arbitrary algorithm. Control with freely setting the control range of the flow rate is possible. Patent Document 2 discloses a method for adjusting the opening degree of an electronic expansion valve for controlling the degree of superheat to be close to zero in order to maximize the operation efficiency of the evaporator.

Japanese Examined Patent Publication No. 58-47628 Japanese Patent Laid-Open No. 9-303885

  However, since the control device of the conventional refrigeration air conditioner controls the electronic expansion valve using the degree of superheat, there is a problem that it may be difficult to perform high-precision control.

  This invention is made | formed in view of the above, Comprising: It aims at providing the control method and control apparatus of the refrigerating air-conditioner which can perform more highly accurate control.

  In order to solve the above-described problems and achieve the object, a control method for a refrigerating and air-conditioning apparatus according to the present invention connects a compressor, a condenser, an expansion valve, and an evaporator with a pipe and circulates the refrigerant through the pipe. A method for controlling a refrigeration air conditioner that constitutes a refrigeration cycle, wherein an evaporation completion point that is a boundary between a gas-liquid two-phase region and a superheated steam region of a refrigerant in the evaporator pipe based on a temperature distribution in the evaporator pipe of the evaporator The evaporation completion point position calculating step for calculating the position of the expansion valve, and the opening of the expansion valve so that the deviation between the calculated evaporation completion point position and the target evaporation completion point position is within a predetermined allowable range. And an opening degree control step to be controlled.

  In addition, the control device for a refrigeration air conditioner according to the present invention is a control device for a refrigeration air conditioner that configures a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected by a pipe and a refrigerant is circulated through the pipe. An evaporation completion point position calculating means for calculating a position of an evaporation completion point which is a boundary between a gas-liquid two-phase region and a superheated steam region of the refrigerant in the evaporation tube based on a temperature distribution in the evaporation tube of the evaporator; Opening degree control means for controlling the opening degree of the expansion valve so that the deviation between the calculated evaporation completion point position and the target evaporation completion point position is within a predetermined allowable range. Features.

  Further, in the control device for a refrigerating and air-conditioning apparatus according to the present invention, in the above invention, the evaporation completion point position calculating means detects a temperature at the separated position provided at a separated position on the evaporation pipe. Means, temperature distribution calculating means for calculating the temperature distribution in the evaporation pipe using the detected temperature, and position calculating means for calculating the position of the evaporation completion point using the calculated temperature distribution. It is characterized by.

  Moreover, the control apparatus of the refrigerating and air-conditioning apparatus according to the present invention is characterized in that, in the above invention, the temperature distribution calculating means calculates the temperature distribution using a polygonal line or a first-order lag characteristic curve as an approximate curve.

  Further, in the control device for a refrigerating and air-conditioning apparatus according to the present invention, in the above invention, the evaporation completion point position calculating means includes a resistor continuously provided over a predetermined section in the length direction on the evaporation pipe, A resistance value measuring means connected to a resistor and measuring a resistance value between both ends of the resistor, and a predetermined temperature distribution curve showing a temperature distribution in the evaporation tube, and using the predetermined temperature distribution curve, the evaporation completion point And a position calculating means for calculating the position.

  The control device for a refrigerating and air-conditioning apparatus according to the present invention is the above-described invention, wherein the evaporation completion point position calculating means detects the temperature of the inlet portion provided at the inlet portion of the evaporator. The position calculation means calculates the position of the evaporation completion point using the temperature of the inlet.

  Moreover, the control device for a refrigerating and air-conditioning apparatus according to the present invention is the above-described invention, wherein the evaporation completion point position calculating means detects the temperature of the outlet provided at the outlet of the evaporator. The position calculation means calculates the position of the evaporation completion point using the temperature of the outlet portion.

  In the control device for a refrigerating and air-conditioning apparatus according to the present invention, in the above invention, the position calculating means calculates the position of the evaporation completion point using a temperature distribution curve approximated using a polygonal line or a first-order lag characteristic curve. It is characterized by doing.

  Moreover, the control apparatus of the refrigerating and air-conditioning apparatus according to the present invention is characterized in that, in the above invention, the resistor is spirally wound around the evaporation pipe.

  According to the present invention, the position of the evaporation completion point is directly calculated based on the temperature distribution in the evaporation pipe of the evaporator, and the deviation between the calculated evaporation completion point position and the target evaporation completion point position is predetermined. Since the opening degree of the expansion valve is controlled so as to be within the range, the refrigeration and air-conditioning apparatus with higher accuracy than when using the degree of superheat, which is an amount that indirectly represents the position of the evaporation completion point, as a control amount as in the past There is an effect that can be controlled.

  Embodiments of a control method and a control device for a refrigeration air-conditioning apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a refrigerating and air-conditioning apparatus including a control device according to Embodiment 1 of the present invention. FIG. 2 is a control block diagram of the control device shown in FIG. As shown in FIGS. 1 and 2, the control device 10 a connects the compressor 2, the condenser 3, the electromagnetic valve 4, the electronic expansion valve 5, and the evaporator 6 through a pipe 13 and circulates a refrigerant through the pipe 13. This is provided in the refrigeration air conditioner 1a constituting the same refrigeration cycle as in the prior art. The control device 10a includes n temperature sensors 8-1 to 8-n which are n (n is an integer of 3 or more) temperature detection means provided at spaced positions on the evaporation pipe 61 of the evaporator 6, and And a controller 7a. Further, the controller 7 a includes a temperature distribution calculation unit 71, a position calculation unit 72, and an opening degree control unit 73.

The temperature sensors 8-1 to 8-n, the temperature distribution calculating unit 71, and the position calculating unit 72 constitute evaporation completion point position detecting means. The temperature distribution calculation unit 71 calculates the temperature distribution in the evaporation pipe 61 using θ1 to θn that are temperatures detected by the temperature sensors 8-1 to 8-n. Position calculating unit 72 calculates the the position of the evaporation completion point x _p using the temperature distribution temperature distribution calculator 71 has calculated.

The opening degree control unit 73 controls the opening degree of the electronic expansion valve 5 so that the calculated evaporation completion point position _xp becomes the target evaporation completion point position. The opening degree control unit 73 includes a subtracter 731 and an opening degree calculation unit 732. The subtracter 731 calculates a difference between the target evaporation completion point position x _pr and the calculated evaporation completion point position x _p , that is, a position deviation, x _pe = x _pr −x _p . The target evaporation completion point position x _pr is instructed from the main controller of the refrigeration air conditioner according to, for example, the temperature of the refrigeration air conditioner set by the user.

On the other hand, the opening calculation unit 732 calculates a command value ν for the opening of the electronic expansion valve 5 using the position deviation x _pe and outputs the command value ν to the electronic expansion valve 5 so that the position deviation x _pe falls within a predetermined allowable range. The opening degree of the electronic expansion valve 5 is controlled so as to be accommodated. Since the opening degree of the expansion valve is controlled using the position deviation as a control amount as described above, the refrigeration air conditioner can be controlled with high accuracy.

Next, a control method for the refrigerating and air-conditioning apparatus will be described with reference to a control block diagram of the control apparatus shown in FIG. First, the temperature sensors 8-1 to 8-n detect the temperatures θ1 to θn at spaced positions on the evaporation pipe 61 and output them to the controller 7a. Next, in the controller 7a, the temperature distribution calculation unit 71 receives the temperatures θ1 to θn, calculates the temperature distribution in the evaporation pipe 61 using these temperatures, and sends the temperature distribution information to the position calculation unit 72. Output. Next, the position calculation unit 72 receives temperature distribution information, calculates the position of the evaporation completion point using this temperature distribution information, and outputs the calculated position x _p of the evaporation completion point to the opening degree control unit 73. In the opening degree control unit 73, the subtractor 731 receives the target evaporation completion point position x _pr instructed from the main control device of the refrigerating and air-conditioning apparatus 1a, and the position of the evaporation completion point calculated by the position calculation unit 72. x _p is received, x _pe which is a position deviation is calculated and output to the opening calculation unit 732.

Next, the opening degree calculation unit 732 calculates a command value ν for the opening degree of the electronic expansion valve 5 using the position deviation _xpe . Then, the opening calculation unit 732 outputs a command value ν for the opening to the electronic expansion valve 5 and controls the opening of the electronic expansion valve 5 so that the position deviation x _pe falls within a predetermined allowable range. Since the opening degree of the electronic expansion valve 5 is feedback controlled using the position deviation as a control amount, the refrigeration air conditioner can be controlled with high accuracy. Note that PID control, fuzzy control, or the like can be used for the feedback control. In addition, the above allowable range is, for example, the target evaporation completion point position x so that desired control accuracy, response speed, and stability can be realized according to the operating state of the refrigeration air conditioner 1a, the calculated position deviation _xpe, and the like. The range is about ± 1 to 5% of _pr .

  Next, a specific method for calculating the position of the evaporation completion point by the temperature distribution calculating unit 71 and the position calculating unit 72 in the first embodiment will be described with reference to FIG. The temperature distribution calculating unit 71 according to the first embodiment calculates a temperature distribution using a broken line as an approximate curve for the temperature distribution curve indicating the temperature distribution.

FIG. 3 is a diagram for explaining a specific method for calculating the position of the evaporation completion point in the first embodiment, and is a diagram showing each region in the evaporation pipe 61 and the temperature distribution. As shown in the upper side of FIG. 3, the inside of the evaporation pipe 61 in which the refrigerant flows from the left to the right of the drawing is composed of a gas-liquid two-phase region in which saturated liquid and saturated steam are mixed, and a superheated steam region consisting of only saturated steam. Thus, the boundary between the gas-liquid two-phase region and the superheated steam region is the evaporation completion point. It is assumed that the ambient temperature of the evaporation pipe 61 is Ta and the evaporation temperature of the refrigerant is Te. The lower side of FIG. 3 shows the relationship between the position x and the temperature T with the inlet in the evaporation pipe 61 as the origin, but the temperature distribution calculation unit 71 according to the first embodiment is T (x ) Is approximated by a straight line C ₁ in the gas-liquid two-phase region, and approximated by a straight line C ₂ in the superheated steam region. The position x _p1 of the evaporation completion point is the intersection of the straight line C ₁ and the straight line C ₂ . Note that the straight line C ₁ has a negative slope due to the pressure loss. Further, it is assumed that the straight line C ₂ has a constant positive slope a ₂ . Further, the area from the inlet portion of the evaporation pipe 61 to the evaporation completion point position x _p1 corresponds to the effective heat transfer area of the evaporation pipe 61.

Hereinafter, temperature sensors 8-k1 and 8-k3 provided at positions corresponding to the gas-liquid two-phase region on the evaporation pipe 61 and a temperature sensor 8-k2 provided at a position corresponding to the superheated steam region are used for temperature detection. Use. The three temperature sensors 8-k1 to 8-k3 can be appropriately selected from any one of the temperature sensors 8-1 to 8-n. If the combinations of the positions of these three temperature sensors 8-k1 to 8-k3 and the detected temperatures are (x ₁ , T ₁ ), (x ₂ , T ₂ ), (x ₃ , T ₃ ), respectively, the temperature T (x) indicating the distribution curve is expressed by Equations (1) and (2). T ₂ is a value equal to or lower than the ambient temperature Ta, and T ₁ and T ₃ are equal to or lower than the evaporation temperature Te calculated from the pressure in the section between the evaporator 6 and the electronic expansion valve 5 and are compressed with the evaporator 6. It is a value equal to or higher than the evaporation temperature Te calculated from the pressure in the section with the machine 2.

なお、数式（２）において、傾きａ₂は過熱蒸気領域の温度上昇特性を表現している。傾きａ₂の値は温度上昇特性の一次遅れ特性曲線を微分して折れ線近似することにより求めたり、温度上昇特性の実測値からも同様に求めることができる。傾きａ₂の値はたとえば２．１［℃／ｍ］である。

In Equation (2), the slope a ₂ represents the temperature rise characteristic in the superheated steam region. The value of the slope a ₂ can be obtained by differentiating the first-order lag characteristic curve of the temperature rise characteristic and approximating a polygonal line, or can be obtained in the same manner from the measured value of the temperature rise characteristic. The value of the slope a ₂ is 2.1 [° C./m], for example.

The temperature distribution calculation unit 71 outputs information on the straight lines C ₁ and C ₂ to the position calculation unit 72. Then, the position calculation unit 72 calculates the evaporation completion point position x _p1 that is the intersection of the straight line C ₁ and the straight line C ₂ using Equation (3). As described above, the position of the evaporation completion point is calculated based on the temperature distribution in the evaporation pipe 61.

  Next, as a modification of the first embodiment, a case where the temperature distribution calculation unit 71 calculates a temperature distribution using a first-order lag characteristic curve as an approximate curve will be described. FIG. 4 is a diagram for explaining a specific method for calculating the position of the evaporation completion point in this modification, and is a diagram showing each region in the evaporation pipe 61 and the temperature distribution as in FIG. 4, as in FIG. 3, the inside of the evaporation pipe 61 is composed of a gas-liquid two-phase region and a superheated steam region, and the boundary between the gas-liquid two-phase region and the superheated steam region is an evaporation completion point. Indicates.

The lower side of FIG. 4 shows the relationship between the position x and the temperature T with the inlet in the evaporation pipe 61 as the origin, but the temperature distribution calculation unit 71 according to this modification uses T (x) indicating the temperature distribution curve. The gas-liquid two-phase region is approximated by a straight line C ₃ , and the superheated steam region is approximated by a curve C ₄ . The position x _p1 of the evaporation completion point is the intersection of the straight line C ₃ and the curve C ₄ . In the approximation used in this modification, the inside of the evaporation pipe 61 is close to the evaporation temperature Te in the gas-liquid two-phase region, and the temperature rise from the evaporation temperature Te starts at the evaporation completion point. In this modification, the temperature distribution characteristic is approximated by a first-order lag characteristic in the superheated steam region.

Below, temperature sensor 8-k4 provided in the position corresponding to a gas-liquid two-phase area | region on the evaporation pipe | tube 61, and temperature sensor 8-k5 provided in the position corresponding to a superheated steam area | region are used for temperature detection. The two temperature sensors 8-k4 and 8-k5 can be appropriately selected from any one of the temperature sensors 8-1 to 8-n. If the combination of the position of these two temperature sensors 8-k4, 8-k5 and the detected temperature is (x ₄ , T ₄ ), (x ₅ , T ₅ ), T (x) indicating a temperature distribution curve Is expressed by equations (4) and (5).

Note that ΔT is the upper limit of the temperature rise in the superheated steam region, and ΔT≈Ta−Te. Τ is a predetermined parameter. Further, since the inside of the evaporation pipe 61 is close to the evaporation temperature Te in the gas-liquid two-phase region as described above, T ₄ = Te may be set. Te may be calculated from the pressure of the refrigerant detected by the pressure sensor installed in the low pressure part of the refrigeration cycle of the refrigeration air conditioner 1a. Here, the low pressure portion of the refrigeration cycle is a portion between the outlet of the electronic expansion valve 5 and the inlet of the compressor 2. ΔT may be obtained as ΔT = Ta−T ₄ from the ambient temperature Ta and T ₄ . Here, since the curve C ₄ passes through (x ₅ , T ₅ ), Expression (6) is established.

The temperature distribution calculation unit 71 outputs information on the straight line C ₃ and the curve C ₄ to the position calculation unit 72. Then, the position calculation unit 72 calculates the position x _p2 of the evaporation completion point that is the intersection of the straight line C ₃ and the curve C ₄ using Equation (7). As described above, the position of the evaporation completion point is calculated based on the temperature distribution in the evaporation pipe 61.

  As described above, the control device 10a of the refrigerating and air-conditioning apparatus according to the first embodiment and the modification thereof detects the temperature at the separated position on the evaporation pipe 61, and uses the detected temperature in the evaporation pipe 61. This temperature distribution is used to directly calculate the position of the evaporation completion point, and control the position deviation, which is the difference between the target evaporation completion point position and the calculated evaporation completion point position. Since the opening degree of the electronic expansion valve 5 is feedback controlled as an amount, the refrigeration air conditioner can be controlled with high accuracy. Especially when the evaporation completion point is close to the inlet side of the evaporator, the sensitivity of the change in superheat to the change in the position of the evaporation completion point is significantly reduced, so the conventional method using superheat has a high accuracy in the position of the evaporation completion point. However, the control device for the refrigerating and air-conditioning apparatus according to the first embodiment can control with high accuracy. Further, since the evaporation completion point position can be controlled with high accuracy, liquid back can be prevented more reliably, and the evaporation completion point position can be stably controlled near the evaporator outlet. The use efficiency of the refrigeration and air-conditioning apparatus 1a can be improved stably, and there is an effect that energy saving of the refrigeration air conditioner 1a can be achieved.

(Embodiment 2)
Next, a control device for a refrigerating and air-conditioning apparatus according to Embodiment 2 of the present invention will be described. The control device for the refrigeration air conditioner according to the second embodiment is the same as the control device for the refrigeration air conditioner according to the first embodiment in that the position of the evaporation completion point in the evaporation tube is calculated based on the temperature distribution in the evaporation tube. Similarly, the resistance value between both ends of a resistor continuously provided over a predetermined section in the length direction on the evaporation tube is measured, and the resistance value is determined using a predetermined temperature distribution curve indicating the temperature distribution in the evaporation tube. The difference is that the position of the evaporation completion point is calculated by calculating backward from.

  FIG. 5 is a block diagram illustrating a configuration of a refrigerating and air-conditioning apparatus including the control device according to the second embodiment. FIG. 6 is a control block diagram of the control device shown in FIG. As shown in FIGS. 5 and 6, the control device 10 b is provided in a refrigeration air conditioner 1 b having the same configuration as the refrigeration air conditioner 1 a according to the first embodiment. The control device 10b includes a resistor 9a provided on the evaporation pipe 61 and a controller 7b. The controller 7b includes a resistance value measuring unit 74, a position calculating unit 75, and an opening degree controlling unit 73.

  The resistor 9 a is a single strip-like or linear resistor continuously and linearly provided over a predetermined section in the length direction of the evaporation tube 61. The resistor 9a is sufficiently thin or thin so that the heat capacity can be ignored as compared with the evaporation tube 61. As a result, the resistor 9a has the same temperature distribution as the inside of the evaporator tube over the length direction, so that the resistivity distribution also reflects the temperature distribution in the evaporator tube.

The resistance value measuring unit 74 and the position calculating unit 75 constitute evaporation completion point position calculating means. The resistance value measuring unit 74 is connected to the resistor 9 a, measures the resistance value between both ends of the resistor 9 a, and outputs R that is the resistance value to the position calculating unit 75. The position calculation unit 75 calculates the position of the evaporation completion point by calculating backward from the resistance value R using a predetermined temperature distribution curve. That is, since the resistance value R can be expressed by using a resistivity distribution that reflects the temperature distribution including information on the position of the evaporation completion point, in the second embodiment, on the contrary, by using this relationship, The reverse calculation is performed to calculate x _p which is the position of the evaporation completion point.

Similarly to the case of the first embodiment, the opening degree control unit 73 controls the opening degree of the electronic expansion valve 5 so that the calculated evaporation completion point position _xp becomes the target evaporation completion point position. To do. As a result, the refrigeration air conditioner can be controlled with high accuracy.

Next, a control method for the refrigerating and air-conditioning apparatus will be described with reference to a control block diagram of the control apparatus shown in FIG. First, in the controller 7 b, the resistance value measuring unit 74 measures the resistance value between both ends of the resistor 9 a and outputs the resistance value R to the position calculating unit 75. Then, the position calculating unit 75 calculates and outputs the position x _p of the evaporation completion point by back calculation from the resistance value R, the position x _p of the calculated evaporation completion point in the opening control unit 73. In the opening degree control unit 73, as in the case of the first embodiment, the subtractor 731 calculates _xpe , which is a position deviation, and outputs it to the opening degree calculation unit 732, which then calculates the position deviation x. _{Using pe} , a command value ν for the opening degree of the electronic expansion valve 5 is calculated and output to the electronic expansion valve 5, and the opening degree of the electronic expansion valve 5 is controlled so that the position deviation x _pe falls within a predetermined allowable range. To do. As a result, the refrigeration air conditioner can be controlled with high accuracy.

  Next, with reference to FIGS. 7 and 8, a specific method by which the position calculation unit 75 calculates the position of the evaporation completion point in the second embodiment will be described. The evaporation completion point position calculation unit 75 according to the second embodiment uses a first-order lag characteristic curve as an approximate curve of the temperature distribution curve in the evaporation pipe 61.

  FIG. 7 is a diagram for explaining a specific method for calculating the evaporation completion point position in the second embodiment, and is a diagram showing each region in the evaporation pipe 61 and the temperature distribution. As shown in the upper side of FIG. 7, the inside of the evaporation pipe 61 is composed of a gas-liquid two-phase region and a superheated steam region, and a boundary between the gas-liquid two-phase region and the superheated steam region is an evaporation completion point. It is assumed that the ambient temperature of the evaporation pipe 61 is Ta and the evaporation temperature of the refrigerant is Te. A strip-shaped resistor 9 a is provided on the evaporation pipe 61.

The lower side of FIG. 7 shows the relationship between the position x and the temperature T with the position of the end of the resistor 9a close to the inlet of the evaporation pipe 61 as the origin, and the evaporation completion point position calculation unit 75 according to the second embodiment. Is approximated by a straight line C ₅ in the gas-liquid two-phase region and approximated by a curve C ₆ in the superheated steam region. The evaporation completion point position x _p3 is the intersection of the straight line C ₅ and the curve C ₆ . In the approximation used in the second embodiment, the inside of the evaporation pipe 61 is close to the evaporation temperature Te in the gas-liquid two-phase region, and the temperature rise from the evaporation temperature Te starts at the evaporation completion point. When the length of the resistor 9a is L and the length of the superheated steam region is l, the position of the evaporation completion point is Ll, and T (x) indicating the temperature distribution curve is expressed by Equations (8), ( 9).

Note that ΔT is the upper limit of the temperature rise in the superheated steam region, and ΔT≈Ta−Te. Τ is a predetermined parameter. Further, the temperature T ₀ of the gas-liquid two-phase region may be approximated by the evaporation temperature Te. In that case, Te may be used instead of T ₀ . Further, a temperature sensor may be provided at the inlet of the evaporator 6 to detect the temperature of the inlet, and the detected inlet temperature may be used instead of T ₀ . Te may be calculated from the pressure of the refrigerant detected by the pressure sensor installed in the low pressure part of the refrigeration cycle of the refrigeration air conditioner 1a. ΔT may be obtained as ΔT = Ta−T ₀ from the ambient temperature Ta and T ₀ . Further, a temperature sensor may be provided at the outlet of the evaporator 6 to detect the temperature of the outlet, and the detected outlet temperature may be used instead of Ta.

  Next, a method in which the position calculation unit 75 calculates the evaporation completion point from the resistance value R of the resistor 9a will be described. FIG. 8 shows the resistor 9a provided on the evaporation tube 61 and its temperature distribution and resistivity distribution. The resistor 9 a is made of a uniform material having a resistivity ρ, and the cross-sectional area thereof has a constant value S regardless of the length direction of the evaporation pipe 61. Further, it is assumed that the resistivity ρ has a temperature characteristic represented by Expression (10).

Note that ρ ₀ is the resistivity at the temperature T = 0, and α ₀ is the temperature coefficient at the temperature T = 0. At this time, ρ (x) indicating the resistivity distribution curve is approximated by a straight line C ₇ in the gas-liquid two-phase region, and is approximated by a curve C ₈ in the superheated steam region. The straight line C ₇ and the curve C ₈ are obtained by substituting Equations (8) and (9) into Equation (10), respectively. As a result, the resistance value R is expressed by Equation (11), and the resistance value per unit cross-sectional area is expressed by Equation (12).

  In addition, in Formula (12), it deform | transformed using Formula (13).

  Further, when Expression (12) is transformed, Expression (14) is obtained.

The left side of Equation (14) is a function f (l) of l, while the right side is a quantity that can be calculated from a measured value and a known value including the measured resistance value R, and this is defined as l ₀ . Therefore, the position x _p3 of the evaporation completion point is obtained as L−1 using the value l obtained from the equation (15) by calculating back the equation (14).

The position calculation unit 75 obtains the evaporation completion point position x _p3 by the above procedure. However, since f (l) = l ₀ is an implicit function expression related to l and cannot be expressed in the form of an explicit function f ⁻¹ (•), the position calculation unit 75 can handle (l, f (l)). A table may be stored in advance, and l satisfying Equation (13) may be obtained by using an interpolation operation together.

The above l ₀ can be considered as the length of the superheated steam region when the temperature distribution curve is approximated by a rectangle with τ → 0 in Equation (9). Therefore, L-l ₀ can be used as an approximate value of the position of the evaporation completion point. When considered in this way, the calculation error e of the superheated steam region and the evaporation completion point position is expressed by Expression (16).

  Since τ ≧ 0 normally, the calculation error e usually takes a negative value. That is, an error occurs so that the calculated value of the length of the superheated steam region is shorter than the actual value. Therefore, if the position of the evaporation completion point calculated in the above procedure is used for control, an error occurs in the direction of the evaporation completion point away from the outlet of the evaporator. An error will occur.

If the evaporation completion point position calculation unit 75 obtains an approximate value of l as follows, the above calculation error is further improved. In one method, first, an approximate value e ₀ of a calculation error is obtained by Equation (17) using l ₀ . Then, using this, a correction value l ₁ for l ₀ is obtained by equation (18). If L- ₁₁ is used as an approximate value of the position of the evaporation completion point, the position of the evaporation completion point with fewer errors can be calculated.

In another method, first, assuming that l >> τ, an approximate value e ₁ of a calculation error is obtained by Expression (19). Then, using this, a correction value l ₂ for l ₀ is obtained by equation (20). And the use of the L-l ₂ as an approximation of the evaporation completion point position can be calculated more error less evaporation completion point position.

  As described above, the control device 10b of the refrigeration air conditioner according to the second embodiment can control the refrigeration air conditioner with high accuracy, similarly to the control device 10a of the refrigeration air conditioner according to the first embodiment. The liquid back can be prevented more reliably, and there is an effect that energy saving of the refrigeration air conditioner 1b can be achieved. In addition, since a single resistor is used to calculate the position of the evaporation completion point, it is not necessary to provide a large number of temperature sensors, and the number of temperature sensors used can be reduced.

  As a modification of the second embodiment, the resistor provided on the evaporation tube may be a spiral wound around the evaporation tube. FIG. 9 is a view showing a cross section and a side surface of an evaporation tube provided with a resistor according to this modification. As shown in FIG. 9, the resistor 9 b according to this modification is wound around the evaporator tube 61 in a spiral shape. Reference numerals 91b and 92b denote resistance value measuring terminals provided at both ends of the resistor 9b.

  According to this modification, even when the temperature distribution occurs in the circumferential direction of the cross section of the evaporator tube due to the complicated distribution characteristics of the refrigerant and oil in the evaporator tube, the resistance wound in a spiral shape Since the resistance value at both ends of the body 9b is a value obtained by averaging the temperature distribution in the circumferential direction described above, the position of the evaporation completion point can be calculated stably and accurately. Further, when the length of the spirally wound resistor 9b is k times the length of the section around which the resistor 9b is wound on the evaporation tube 61, as in the resistor 9a according to the second embodiment. The temperature position resolution can be increased by a factor of k compared to a case where the temperature is linearly provided. In addition, by multiplying the resistivity distribution of the spirally wound resistor by 1 / k in the position direction, it can be easily converted into the resistivity distribution of the linearly provided resistor.

It is a block diagram which shows the structure of the refrigerating air conditioning apparatus provided with the control apparatus which concerns on Embodiment 1 of this invention. It is a control block diagram of the control apparatus shown in FIG. 6 is a diagram illustrating a specific method for calculating the position of the evaporation completion point in the first embodiment. FIG. FIG. 10 is a diagram for explaining a specific method for calculating the position of the evaporation completion point in the modification of the first embodiment. It is a block diagram which shows the structure of the refrigerating air conditioner provided with the control apparatus which concerns on Embodiment 2 of this invention. FIG. 6 is a control block diagram of the control device shown in FIG. 5. FIG. 10 is a diagram for describing a specific method for calculating the position of an evaporation completion point in the second embodiment. It is a figure which shows the resistor provided on the evaporation pipe in Embodiment 2, its temperature distribution, and resistivity distribution. It is the figure which showed the cross section and side surface of the evaporation pipe | tube which provided the resistor which concerns on the modification of Embodiment 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Refrigeration air conditioner 10a, 10b Control apparatus of refrigeration air conditioner 2 Compressor 3 Condenser 4 Electromagnetic valve 5 Electronic expansion valve 6 Evaporator 61 Evaporating pipe 7a, 7b Controller 71 Temperature distribution calculation part 72, 75 Position calculation part 73 Opening Control Unit 731 Subtractor 732 Opening Calculation Unit 74 Resistance Measurement Units 8-1 to 8-n, 8-k1 to 8-k5 Temperature Sensors 9a and 9b Resistors 91b and 92b Terminals 13 Piping

Claims (9)

A control method for a refrigeration air conditioner comprising a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected by piping and a refrigerant is circulated through the piping,
An evaporation completion point position calculating step for calculating a position of an evaporation completion point which is a boundary between a gas-liquid two-phase region and a superheated steam region of the refrigerant in the evaporation tube based on a temperature distribution in the evaporation tube of the evaporator;
An opening degree control step for controlling the opening degree of the expansion valve so that the deviation between the calculated evaporation completion point position and the target evaporation completion point position is within a predetermined allowable range;
The control method of the refrigerating air-conditioning apparatus characterized by including. A control device for a refrigerating and air-conditioning apparatus comprising a refrigeration cycle in which a compressor, a condenser, an expansion valve, and an evaporator are connected by piping and a refrigerant is circulated through the piping,
An evaporation completion point position calculating means for calculating a position of an evaporation completion point which is a boundary between a gas-liquid two-phase region and a superheated steam region of the refrigerant in the evaporation tube based on a temperature distribution in the evaporation tube of the evaporator;
An opening degree control means for controlling the opening degree of the expansion valve so that a deviation between the calculated evaporation completion point position and a target evaporation completion point position is within a predetermined allowable range;
A control device for a refrigerating and air-conditioning apparatus, comprising: The evaporation completion point position calculating means includes:
Temperature detecting means for detecting the temperature at the separated position provided at a separated position on the evaporation pipe;
A temperature distribution calculating means for calculating a temperature distribution in the evaporation tube using the detected temperature;
Position calculating means for calculating the position of the evaporation completion point using the calculated temperature distribution;
The control apparatus of the refrigerating and air-conditioning apparatus according to claim 2, comprising:   The said temperature distribution calculation means calculates the said temperature distribution using a broken line or a first-order lag characteristic curve as an approximated curve, The control apparatus of the refrigeration air conditioner of Claim 3 characterized by the above-mentioned. The evaporation completion point position calculating means includes:
A resistor provided continuously over a predetermined section in the length direction on the evaporation tube;
A resistance value measuring means connected to the resistor and measuring a resistance value between both ends of the resistor;
Position calculating means for calculating the position of the evaporation completion point by calculating backward from the resistance value using a predetermined temperature distribution curve indicating the temperature distribution in the evaporation pipe;
The control apparatus of the refrigerating and air-conditioning apparatus according to claim 2, comprising: The evaporation completion point position calculating means includes an inlet temperature detecting means for detecting the temperature of the inlet provided at the inlet of the evaporator,
The said position calculation means calculates the position of the said evaporation completion point using the temperature of the said inlet part, The control apparatus of the refrigerating air conditioner of Claim 5 characterized by the above-mentioned. The evaporation completion point position calculating means includes outlet temperature detecting means for detecting the temperature of the outlet provided at the outlet of the evaporator,
The control device for a refrigerating and air-conditioning apparatus according to claim 5 or 6, wherein the position calculating means calculates the position of the evaporation completion point using the temperature of the outlet.   The said position calculation means calculates the position of the said evaporation completion point using the temperature distribution curve approximated using the broken line or the first-order lag characteristic curve, The one of Claims 5-7 characterized by the above-mentioned. Control device for refrigeration air conditioner.   The control device for a refrigerating and air-conditioning apparatus according to any one of claims 5 to 8, wherein the resistor is spirally wound around the evaporation pipe.

Images