Indirect air-cooled tower circulating water temperature control method
By employing a multi-factor parameter control method in the indirect air-cooled tower, combining the proportional and integral terms related to the heat dissipation performance and opening degree of the louvers, the problems of high energy consumption and unstable regulation in traditional PID control are solved, achieving rapid and stable regulation of circulating water temperature and improving the system's economy.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHUANGLIANG ECO ENERGY SYST CO LTD
- Filing Date
- 2023-01-16
- Publication Date
- 2026-05-26
AI Technical Summary
Traditional PID control methods cannot achieve effective and economical circulating water temperature regulation in indirect air-cooled towers. Especially in summer, they can easily lead to high energy consumption, increased back pressure, and actuator damage. Furthermore, they are difficult to adapt to changes in ambient temperature and the heat dissipation performance of louvers.
A multi-factor parameter control method, including proportional and integral terms, is adopted. Based on the proportional gain Kp and integral gain Ki related to the heat dissipation performance coefficient and opening degree of the louver, and combined with the nonlinear adjustment correction coefficient CT, the calculation of the louver opening and closing rate is optimized, and the louver opening degree is adjusted in real time to achieve intelligent control.
It achieves rapid and stable adjustment of circulating water temperature, reduces energy consumption, decreases the frequency and amplitude of louver changes, and improves the system's economy and safety.
Smart Images
Figure CN116147375B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of indirect air-cooled tower technology, specifically relating to a method for regulating the temperature of circulating water in an indirect air-cooled tower. Background Technology
[0002] Indirect air-cooled towers typically regulate circulating water temperature by adjusting the opening of louvers. Early louver adjustments were manual or semi-automatic, timed, stepped adjustments. Under normal summer conditions (defined in this invention as ambient temperatures greater than or equal to 2°C), the louvers were generally kept fully open without real-time adjustment. In spring and autumn, minor adjustments were made in the mornings, evenings, and at night. In winter conditions, adjustments were generally based on temperature or time settings. However, because ambient temperatures can sometimes be very low, the circulating water temperature can easily become too low, causing localized radiator malfunctions. Therefore, there is an urgent need for real-time automatic regulation of the circulating water temperature in indirect air-cooled towers.
[0003] The most mature automatic control technology currently used is PID (proportional, integral, derivative) technology, which can achieve uniform intelligent control throughout the year. However, in the temperature regulation process, the cumulative error and the louver opening adjustment are generally calculated based on the temperature difference between the cold / hot water main pipes within a fixed period before and after the temperature regulation, and the PID coefficients, proportional gain Kp, integral gain Ki, and derivative gain Kd, are usually fixed.
[0004] The relationship between input and output in traditional PID control is as follows:
[0005]
[0006] After discretization, we get
[0007]
[0008] Where e(t) is the water temperature deviation at time t, u(t) is the louver opening and closing rate at time t (i.e., the change in opening and closing amplitude per unit time; in this project, 30s is used as one unit time for the control variable), e(k) and u(k) are the corresponding values at sampling time k, and Δt is the sampling interval.
[0009] Because the external environment, especially ambient temperature and the actual heat dissipation performance curve of the controlled object's louvered heat sink, varies in actual operation of indirect air-cooled towers, traditional PID control is not ideal. Temperature is difficult to adjust accurately, and even when it is, the adjustment time is long, energy loss is significant, and oscillations are common. Particularly in summer, louvered heat sink adjustment must ensure the lowest possible back pressure (back pressure refers to the resistance encountered by water flowing through the tube bundle) to maximize heat dissipation efficiency. However, excessive and frequent adjustments by traditional PID control can increase back pressure, leading to increased energy consumption (measured in standard coal consumption per unit time) and actuator damage. Furthermore, considering the significantly higher ambient temperature in summer, the heat dissipation performance of the louvered heat sink differs significantly from that in winter. Using the same adjustment coefficient and PID control method as in winter makes it difficult to achieve effective and economical temperature regulation of the circulating water in indirect air-cooled towers. Summary of the Invention
[0010] To address the above problems, this invention designs an indirect air-cooled tower circulating water temperature control method. For ambient temperatures greater than or equal to 2℃, it can achieve real-time, multi-factor intelligent control of the air-cooling system, thereby achieving goals such as reducing energy consumption and effective regulation.
[0011] The present invention discloses an indirect air-cooled tower circulating water temperature control method. The method is characterized in that, for the case where the ambient temperature is greater than or equal to 2℃, the adjustment term includes a proportional term and an integral term. The determination of the proportional gain Kp and the integral gain Ki is related to the heat dissipation performance coefficient of the louvers and the opening degree of the louvers. The heat dissipation performance coefficient of the louvers includes the proportional performance coefficient Cp and the integral performance coefficient Ci.
[0012]
[0013]
[0014]
[0015] in,
[0016] Let t be the opening degree of the venetian blinds at the current time. The point where the opening size changes from large to small, also known as the inflection point, is expressed as a percentage.
[0017] dt is the integration time, also known as the sampling time;
[0018] e(t) is the water temperature deviation at time t, that is, the temperature difference between the current water temperature and the set target water temperature;
[0019] C T This is the correction coefficient for nonlinear adjustment of water temperature deviation;
[0020] u(t) represents the opening and closing amplitude of the louvers during the integral time at time t, which is the opening and closing rate of the louvers, or the change in opening and closing amplitude per unit time. Regarding the adjustment direction, in actual engineering, the direction of louver opening adjustment is determined according to the sign of the water temperature deviation. When the water temperature deviation is positive, i.e., the water temperature is too high, the louver opening should be adjusted to increase. When the water temperature deviation is negative, i.e., the water temperature is too low, the louver opening should be adjusted to decrease.
[0021] It should be noted that the unit time mentioned here in this invention is a custom integral time. After u(t) is calculated in real time, it is sent to the louver control system. Combined with other control rules, it can realize intelligent control of the louvers based on environmental perception, thereby achieving the purpose of effective control of the circulating water temperature of the indirect air-cooled tower.
[0022] The design principles of Formulas 1 and 2 are as follows: Based on the influence characteristics of louver opening on heat exchange performance (i.e., the sensitivity of louver opening and closing rate to heat exchange performance), the opening and closing rate has a smaller impact on performance when the opening is large; the opening and closing rate has a larger impact on performance when the opening is small. Considering the exponential function characteristics of the measured curve, it is reasonable to use 40% opening as the transition point for the change in size, and the measured results are basically consistent with the expectations.
[0023] Regarding the design principle of Formula 3: Generally, the derivative term is helpful in reducing short-term changes in the controller. In conventional PID controllers, the rate is controlled at the second level, and the water temperature cannot be fed back in time. The first derivative of the derivative term is needed for error calculation, but this method is prone to overspeed control and louver oscillation. Considering that the system implemented in this invention uses a 30-second data cycle in combination with the water temperature change frequency, the system has enough time to receive feedback after control, so the derivative term is not needed. In fact, when the project team conducted tests with the derivative term retained, a good control effect could only be obtained when the derivative gain Kd was very small. Therefore, Formula 3 only retains the proportional and integral terms. On the other hand, considering the nonlinear characteristics of the deviation temperature value on the control quantity, based on experience, an adjustment factor related to the absolute value of the deviation temperature was added to the traditional PID control based on the linear characteristics of the deviation temperature, i.e., |e(t)|+C. T It can have a good regulatory effect.
[0024] The proportional performance coefficient Cp, integral performance coefficient Ci, and large / small opening conversion point Water temperature deviation nonlinear adjustment correction coefficient C T The values are determined based on experience, experimental measurement, or simulation measurement. The simulation measurement involves establishing a heat transfer model of the environment and the indirect air-cooled tower, determining the optimal parameter combination through finite numerical optimization, and verifying it through physical experiments when necessary to correct the original model.
[0025] Furthermore, the proportional performance coefficient Cp ranges from 2.0 to 5.5, and the integral performance coefficient Ci ranges from 0.05 to 0.4. Generally, the proportional performance coefficient Cp and the integral performance coefficient Ci are obtained through experimental testing and are considered empirical coefficients.
[0026] Furthermore, the proportional performance coefficient Cp is set to 4.2 and the integral performance coefficient Ci is set to 0.18.
[0027] Furthermore, the proportional performance coefficient Cp is set to 5.0 and the integral performance coefficient Ci is set to 0.2.
[0028] Furthermore, the proportional performance coefficient Cp is set to 3.2 and the integral performance coefficient Ci is set to 0.2.
[0029] Furthermore, the size opening conversion point The value range is 0.3 to 0.6.
[0030] Furthermore, the size opening conversion point The value is 0.4.
[0031] Furthermore, the nonlinear adjustment correction coefficient C for the water temperature deviation T The value should be taken as a reference for the allowable water temperature deviation.
[0032] Furthermore, the nonlinear adjustment correction coefficient C for the water temperature deviation T The value range is 0.2 to 0.5.
[0033] Furthermore, the nonlinear adjustment correction coefficient C for the water temperature deviation T The value is 0.3.
[0034] The advantages and beneficial effects of this invention are as follows: Compared with the prior art, the circulating water temperature control method of the indirect air-cooled tower designed in this invention, based on modern control theory, adopts multi-factor parameter control that matches the actual operation of the indirect air-cooled tower, replacing the original parameter setting that only considers the single curve of water temperature deviation. Empirical parameters are derived through historical data mining and analysis of the air-cooled tower temperature field. This reduces the debugging and configuration work during the implementation of cooling tower control. Combined with the heat dissipation performance of thermodynamic louvers, it overcomes the overly sensitive differential control characteristic of traditional PID control in air-cooled towers. This system can be widely used in the upgrading of indirect air-cooled tower systems, with short time, low frequency and small amplitude of louver changes, high overall efficiency, and improved economy and safety of indirect air-cooled tower systems. Attached Figure Description
[0035] Figure 1 It is a graph showing the relationship between the opening and closing rate of the louvers at different opening degrees and the deviation of different water temperatures. Detailed Implementation
[0036] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.
[0037] The present invention provides a method for controlling the circulating water temperature of an indirect air-cooled tower. For cases where the ambient temperature is greater than or equal to 2°C, the adjustment terms include a proportional term and an integral term. The determination of the proportional gain Kp and the integral gain Ki is related to the heat dissipation performance coefficient of the louvers and the opening degree of the louvers. The heat dissipation performance coefficient of the louvers includes a proportional performance coefficient Cp and an integral performance coefficient Ci.
[0038]
[0039]
[0040]
[0041] in,
[0042] Let t be the opening degree of the venetian blinds at the current time. The points representing the transition between large and small openings are all expressed as percentages.
[0043] dt is the integration time, which is generally taken as 5s-60s. In this embodiment, 5s, 30s and 60s were tested respectively, and all of them are usable. The result is better when the value is 30s.
[0044] e(t) represents the water temperature deviation at time t, which is the actual sampled value;
[0045] C T This is the correction coefficient for nonlinear adjustment of water temperature deviation;
[0046] u(t) represents the opening and closing amplitude of the blinds during the integration time at time t.
[0047] It should be noted that this project focuses on the calculation method of theoretical adjustment amount for louvers affected by factors such as ambient temperature, louver heat dissipation performance, and water temperature deviation, and does not focus on complete adjustment rules. These rules can be implemented with reference to existing louver adjustment technologies. For example, if the current opening is already at its maximum, the calculation result of further increases in adjustment amount will not be executed; when the adjustment amount required per unit time is greater than the maximum movement speed of the mechanical structure, the actual maximum movement speed will be used as the limit; when the water temperature deviation is less than a certain threshold, such as 0.2℃, no temperature adjustment will be performed, etc.
[0048] The proportional performance coefficient Cp, integral performance coefficient Ci, and large / small opening conversion point Water temperature deviation nonlinear adjustment correction coefficient C TThe values are determined based on experience, experimental measurement, or simulation measurement. The simulation measurement involves establishing a heat transfer model of the environment and the indirect air-cooled tower, determining the optimal parameter combination through finite numerical optimization, and verifying it through physical experiments when necessary to correct the original model.
[0049] According to the appendix Figure 1 The curves showing the relationship between the switching rate and different water temperature deviations under different louver opening degrees are illustrated in the attached figure for clarity. Following engineering practice, the percentage signs for both louver opening degree and switching rate values have been omitted. Traditional PID control methods, which use water temperature deviation as the sole control parameter and rely primarily on linear relationships, differ significantly from the actual curves. The curves in the figure show that when the water temperature deviation is small, there is a certain linearity between the adjustment amount and the deviation value; however, when the water temperature deviation is large, the relationship exhibits significant nonlinearity. Formula 3 of this invention can better fit these curve characteristics.
[0050] Preferably, the proportional performance coefficient Cp ranges from 2.0 to 5.5, and the integral performance coefficient Ci ranges from 0.05 to 0.4.
[0051] Preferably, the size opening conversion point The value range is 0.3 to 0.6.
[0052] Preferably, further, the water temperature deviation nonlinear adjustment correction coefficient C T The value should be taken as a reference for the allowable water temperature deviation.
[0053] Preferably, the water temperature deviation nonlinear adjustment correction coefficient C T The value range is 0.2 to 0.5.
[0054] In this embodiment, the louvers of the all-steel indirect air-cooled tower are generally made of aluminum alloy, with a rough, slightly arc-shaped surface. The proportional performance coefficient Cp, integral performance coefficient Ci, and large / small opening transition point are used. Water temperature deviation nonlinear adjustment correction coefficient C T The values are 4.2, 0.18, 0.4, and 0.3, respectively. When the heat dissipation performance of the louver material and surface changes significantly, it is generally necessary to conduct experiments again to determine new coefficients. However, in reality, the value of these coefficients does not change much, and the empirical coefficients used in this embodiment can still achieve good adjustment results.
[0055] Based on the above empirical parameters, the test results are as follows: With a target water temperature of 41℃, an actual water temperature of 44.35℃, an initial louver opening of 41%, and an ambient temperature of 29.9℃, the circulating water temperature stabilizes in approximately 10 minutes using the method of this invention, with a maximum louver change of 39%; while traditional PID control requires approximately 20 minutes for the circulating water temperature to stabilize, with a maximum louver change of 77%. Figure 1 The figure shows the relationship curves between the opening and closing rate and different water temperature deviations under different louver opening degrees in this test case.
[0056] Another embodiment, 2, differs from embodiment 1 in the proportional performance coefficient Cp, integral performance coefficient Ci, and the large / small opening transition point. Water temperature deviation nonlinear adjustment correction coefficient C T The values were 3.2, 0.2, 0.4, and 0.3, respectively. Experimental results: The circulating water temperature stabilized in approximately 14 minutes, and the maximum change in the louvered temperature was 47%.
[0057] Another embodiment, 3, differs from embodiment 1 in the proportional performance coefficient Cp, integral performance coefficient Ci, and the large / small opening transition point. Water temperature deviation nonlinear adjustment correction coefficient C T The values were 5.0, 0.2, 0.4, and 0.3, respectively. Experimental results: Within 16 minutes of the circulating water temperature stabilizing, the maximum change in the louvered temperature was 44%.
[0058] The above embodiments primarily focus on summer operating conditions. Methods for controlling the temperature of the circulating water in winter, when the ambient temperature is below 2℃, will be studied and presented separately. All embodiments were implemented using Python code related to the indirect air-cooled tower circulating water temperature control method. Partial code is shown below:
[0059]
[0060]
[0061] The parameters have the following meanings:
[0062]
[0063]
[0064]
[0065] The basic principle of this invention is as follows: Based on the heat exchange principle of indirect air-cooled towers and the analysis of measured curves showing the relationship between switching rate and water temperature deviation under different ambient temperature conditions and louver opening degrees, combined with the problems existing in traditional PID control methods, a method for calculating the proportional coefficient adjustable according to different louver opening degrees is established through comparison of multiple sets of data. Considering that the differential term has almost no regulatory effect when the ambient temperature is high, and is more likely to cause oscillation, the differential term in the traditional PID control method is omitted. In the calculation of the louver control quantity, both the linear and nonlinear relationships between the control quantity and the water temperature deviation are taken into account, and a denominator adjustment factor is added, while retaining the linear term characteristics in the traditional PID control method. Through experimental testing, empirical parameters can be obtained and verified, realizing the simulation fitting of complex heat exchange processes in indirect air-cooled towers that are nonlinear, time-varying, coupled, and have uncertain parameters and structures. This makes up for the shortcomings of traditional PID controllers in effectively controlling complex heat exchange processes in indirect air-cooled towers. The new control method is simpler, more efficient, and more practical.
[0066] The above description is only a limited embodiment of the indirect air-cooled tower circulating water temperature control method of the present invention, ignoring the proportional performance coefficient Cp, integral performance coefficient Ci, and the large / small opening degree conversion point. Water temperature deviation nonlinear adjustment correction coefficient C T The methods employed include directly substituting empirical values, different combinations of measured and empirical values, or adding a differential term with a differential gain coefficient Kd that is zero or close to zero. However, the adjustment effect is minimal, and the essence remains within the scope of the method of this invention. These combinations should also be considered within the scope of protection of this invention, and will not be listed individually here.
Claims
1. A method for regulating the temperature of circulating water in an indirect air-cooled tower, characterized in that, For ambient temperatures greater than or equal to 2℃, the adjustment terms include proportional terms and integral terms. The determination of proportional gain Kp and integral gain Ki is related to the heat dissipation performance coefficient of the louvers and the opening degree of the louvers. The heat dissipation performance coefficient of the louvers includes proportional performance coefficient Cp and integral performance coefficient Ci. in, Let t be the opening degree of the venetian blinds at the current time. The points representing the transition between large and small openings are all expressed as percentages. dt is the integration time; e(t) represents the water temperature deviation at time t; C T This is the correction coefficient for nonlinear adjustment of water temperature deviation; u(t) represents the opening and closing amplitude of the blinds during the integration time at time t; The proportional performance coefficient Cp, integral performance coefficient Ci, and large / small opening conversion point Water temperature deviation nonlinear adjustment correction coefficient C T The value is determined by experimental or simulation measurements.
2. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The proportional performance coefficient Cp ranges from 2.0 to 5.5, and the integral performance coefficient Ci ranges from 0.05 to 0.
4.
3. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The proportional performance coefficient Cp is set to 4.2 and the integral performance coefficient Ci is set to 0.
18.
4. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The proportional performance coefficient Cp is set to 5.0 and the integral performance coefficient Ci is set to 0.
2.
5. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The proportional performance coefficient Cp is set to 3.2 and the integral performance coefficient Ci is set to 0.
2.
6. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The size opening conversion point The value range is 0.3 to 0.
6.
7. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The size opening conversion point The value is 0.
4.
8. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The water temperature deviation nonlinear adjustment correction coefficient C T The value range is 0.2 to 0.
5.
9. The method for regulating the circulating water temperature of an indirect air-cooled tower according to claim 1, characterized in that, The water temperature deviation nonlinear adjustment correction coefficient C T The value is 0.3.