Method for optimization and performance diagnosis of a cross flow cooling tower

Abstract

This invention discloses an optimization and performance diagnosis method for crossflow cooling towers, specifically comprising: 1. Simplifying the packing material on both sides of the crossflow cooling tower into an x-z ​​two-dimensional heat transfer model; 2. Dividing the two-dimensional heat transfer model into several equal grids, with each grid serving as a heat and moisture exchange micro-element; 3. Establishing a heat and moisture exchange model to calculate the water flow state and air state output by each heat and moisture exchange micro-element; 4. Calculating the outlet water temperature t of the cooling tower based on the water flow state output by the last heat and moisture exchange micro-element. wo 5. If t wo Compared with the measured value t wo If the absolute value of the difference between the two values ​​is greater than the first threshold, then update the heat and moisture exchange model; otherwise, optimize the airflow of the cooling tower. 6. Calculate the outlet water temperature t of the crossflow cooling tower under the current conditions using the initial heat and moisture exchange model. w2 If t wo 'and t w2 If the difference is greater than or equal to the second threshold, the tower performance is considered to have degraded; this invention realizes the accurate calculation of the optimal operating parameters of the cooling tower and the accurate diagnosis of performance faults.

Description

Technical Field

[0001] This invention belongs to the field of refrigeration system technology. Background Technology

[0002] As a crucial heat dissipation device on the cold source side of a central air conditioning system, the cooling tower plays a vital role in releasing condensation heat into the ambient air and producing low-temperature cooling return water. The cooling tower return water temperature is a critical control parameter, significantly impacting not only the cooling tower's own power consumption but also the power consumption of the chiller unit and cooling water pump. If the cooling return water temperature setpoint is too high, the cooling tower's cooling capacity will be underutilized, increasing the chiller unit's power consumption. Conversely, if the setpoint is too low, it will increase the power consumption of the cooling tower fan and cooling water pump.

[0003] From the perspective of optimizing cooling tower operating parameters, it is necessary to determine an appropriate cooling tower return water temperature setpoint to ensure that the overall power consumption of the cold source side, consisting of the chiller, cooling tower, and cooling water pump, is minimized.

[0004] From the perspective of cooling tower performance diagnosis, after a period of operation, open cooling towers may experience performance failures such as uneven liquid distribution, nozzle blockage, packing scaling, and local blockage. These will lead to a significant decrease in the heat and mass transfer capacity of the cooling tower and an increase in the outlet water temperature. However, since there are many factors affecting the heat and mass transfer capacity and outlet water temperature of the cooling tower, it is only by comparing the heat exchange capacity and outlet water temperature under the same outdoor temperature, humidity, air volume, water flow rate, and inlet water temperature that the performance of the cooling tower can be accurately determined to be degraded.

[0005] Current simulation models for crossflow cooling towers can be broadly categorized into mechanistic models and data-driven models. Mechanistic models fall into two categories: one type directly constructs a crossflow tower model based on physical laws, where each parameter has a clear physical meaning, but involves many structural parameters that are difficult to obtain; the other type modifies the counterflow tower model, involving complex iterative calculations, which can easily lead to model non-convergence and large errors. Data-driven models require a large number of data samples for learning, cannot reveal the distribution patterns of temperature and humidity fields inside the tower, and their generalization ability is difficult to guarantee. Summary of the Invention

[0006] Purpose of the invention: In order to solve the problems existing in the prior art, the present invention provides a method for optimizing and diagnosing the performance of crossflow cooling towers.

[0007] Technical solution: This invention provides a method for optimizing and diagnosing the performance of a crossflow cooling tower, specifically including the following steps:

[0008] Step 1: Based on the air flow direction and cooling water flow direction during the heat and moisture exchange process in the crossflow cooling tower, the packing on both sides of the crossflow cooling tower is simplified into two xz two-dimensional heat exchange models, where the x direction is the air flow direction and the z direction is the cooling water flow direction.

[0009] Step 2: Divide each xz 2D heat transfer model into an N*N grid, and treat each grid as a heat and moisture exchange micro-element;

[0010] Step 3: Establish a heat and humidity exchange model. Randomly select an N*N grid and use the heat and humidity exchange model to calculate the water flow state and air state output by each heat and humidity exchange micro-element in the selected N*N grid; the water flow state includes the cooling water temperature t. w and cooling water flow rate (m) w ;

[0011] Step 4: Calculate the outlet water temperature t of the crossflow cooling tower based on the water flow state output by the last row of heat and moisture exchange micro-elements in the N*N grid. wo The N*N grid in this step is the N*N grid selected in step 3;

[0012] Step 5: Optimize runtime parameters: Calculate t wo With t wo The absolute value of the difference, t wo 'The measured value of the outlet water temperature of the crossflow cooling tower. If the absolute value is greater than the preset first threshold, the heat and humidity exchange model is updated; otherwise, the optimal outlet water temperature of the crossflow cooling tower is calculated with the goal of minimizing the overall power consumption of the cooling tower, cooling water pump, and chiller unit, and the air volume of the crossflow cooling tower is optimized and adjusted based on the optimal outlet water temperature of the crossflow cooling tower.'

[0013] Step 6: Performance Diagnosis: Using the initial heat and moisture exchange model under fault-free conditions at the beginning of operation, calculate the outlet water temperature t of the crossflow cooling tower under the current conditions. w2 Calculate t wo 'and t w2 If the difference is greater than or equal to a preset second threshold, the performance of the crossflow cooling tower is considered to have degraded; the current situation includes the current outdoor air temperature and humidity, the air volume of the crossflow cooling tower, the water flow rate entering the crossflow cooling tower, and the inlet water temperature.

[0014] Furthermore, the heat and moisture exchange model in step 3 is as follows:

[0015] If the air humidity content X in a certain heat and moisture exchange micro-element is... a The saturated air moisture content X at the temperature of the heat and moisture exchange micro-element air is less than that of the micro-element air. sa Then, the following heat and moisture exchange model is used to calculate the water flow state and air state output by the heat and moisture exchange micro-element, wherein the air state includes: air mass flow rate m a air temperature t a and moisture content X a ;

[0016]

[0017] Where the subscript 'in' indicates input and 'out' indicates output, A, B, and C are model parameters characterizing the heat and mass transfer performance of the cooling tower. The values ​​of A, B, and C are obtained by linear fitting using the least squares method. M w M represents the total cooling water flow rate at the inlet of the crossflow cooling tower. a This refers to the inlet air mass flow rate of the crossflow cooling tower. c pw For the specific heat capacity of cooling water at constant pressure, c pv For the isobaric specific heat capacity of water vapor, c pa Let be the specific heat capacity of air at constant pressure, r0 be the latent heat of vaporization of cooling water at 0℃; dx be the infinitesimal length of the airflow direction, dz be the infinitesimal length of the cooling waterflow direction, and X be the infinitesimal length of the cooling waterflow direction. sw Moisture content of saturated air with water temperature as the defining temperature;

[0018] If X within a certain heat and moisture exchange microelement a Greater than or equal to X sa Then, the following heat and moisture exchange model is used to calculate the water flow state and air state output by the heat and moisture exchange micro-element:

[0019]

[0020] Furthermore, in an N*N grid, let j represent the j-th row and i represent the i-th column, j = 1, 2, ..., N, i = 1, 2, ..., N; when j = 2, ..., N, i = 2, ..., N, when using the heat and humidity exchange model to calculate the air and water flow states of the heat and humidity exchange microelement in the j-th row and i-th column, the air state input to the heat and humidity exchange model is the air state output by the heat and humidity exchange microelement in the j-th row and i-th column, and the water flow state input to the heat and humidity exchange model is the water flow state output by the heat and humidity exchange microelement in the j-th row and i-th column; when j = 1, when using the heat and humidity exchange model to calculate the air and water flow states of the heat and humidity exchange microelement in the 1st row and i-th column, the cooling water flow rate input to the heat and humidity exchange microelement in the 1st row and i-th column is M. w Compared to the total number of infinitesimal elements in the first row of the two N*N grids, 2N, the cooling water temperature input to the heat and moisture exchange infinitesimal element in the first row and i-th column is the same as the cooling water temperature input to the crossflow cooling tower; when i=1, when using the heat and moisture exchange model to calculate the air state and water flow state of the heat and moisture exchange infinitesimal element in the j-th row and 1-th column, the air mass flow rate input to the heat and moisture exchange infinitesimal element in the j-th row and 1-th column is M. a Compared to 2N, the air temperature and humidity input to the heat and humidity exchange micro-element in the j-th row and 1-th column are the same as the air temperature and humidity input to the crossflow cooling tower;

[0021] When using the heat and moisture exchange model for calculation, the calculation order is as follows: first calculate a row along the air direction, and then proceed to the next row along the cooling water flow direction.

[0022] Furthermore, in step 4, the outlet water temperature t of the crossflow cooling tower is calculated according to the following formula. wo :

[0023]

[0024] Where i represents the i-th column, m w(N,i) Let t be the cooling water flow rate output by the infinitesimal element in the Nth row and i-th column of an N*N grid. w(N,i) Let i be the temperature of the cooling water output by the infinitesimal element in the Nth row and ith column of an N*N grid, where i = 1, 2, ..., N.

[0025] Furthermore, in step 5, the calculation of the optimal cooling tower outlet water temperature with the aim of minimizing the overall power consumption of the cooling tower, cooling water pump, and chiller unit specifically involves:

[0026] The heat and humidity exchange model is used to calculate the outlet water temperature t of a crossflow cooling tower under different cooling tower air volumes based on the current outdoor air temperature and humidity and inlet water temperature. w1 Based on the crossflow cooling tower airflow and the corresponding outlet water temperature, the overall power consumption of the cooling tower, cooling water pump, and chiller unit is calculated. The outlet water temperature corresponding to the minimum overall power consumption is taken as the optimal crossflow cooling tower outlet water temperature, and the cooling tower airflow at this point is taken as the optimal crossflow cooling tower airflow. The overall power consumption P is... ref for:

[0027] P ref =P cwp +P ct +P chiller

[0028] P cwp =a0+a1M w +a2M w 2

[0029] P ct =b0+b1M a +b2M a 2

[0030] P chiller =c0+c1PLR+c2t w1 +c3t eo +c4PLR 2 +c5t w1 2 +c6t eo 2 +c7tw1 PLR+c8t eo PLR+c9t eo t w1

[0031] Among them, P cwp For the power consumption of the cooling water pump, P ct For the power consumption of the cooling tower fan, P chiller The power consumption of the chiller unit is denoted by ; a0, a1, a2, b0, b1, b2, c0~c9 are fitting coefficients; PLR is the chiller unit load rate, t eo This refers to the chilled water outlet temperature of the chiller unit.

[0032] Furthermore, the range of the second threshold in step 6 is [0.6 1].

[0033] Beneficial effects: This invention requires only a small amount of readily available measured data and structural parameters to establish a cooling tower simulation model. The simulation process does not involve iterative calculations, and the model will not diverge or fall into an infinite loop, ensuring the stability and reliability of the model operation process. It realizes the accurate calculation of cooling tower operating parameters and the accurate diagnosis of performance faults, saving energy consumption of central air conditioning systems. This invention can also detect cooling tower performance degradation early, avoiding parameter missetting and fault misjudgment caused by insufficient experience of operation and maintenance personnel. Attached Figure Description

[0034] Figure 1 This is a flowchart of the method of the present invention.

[0035] Figure 2 This is a schematic diagram of the mesh generation for the cooling tower model established in this invention.

[0036] Figure 3 A comparison chart of simulation results and actual values ​​of the model established for this invention.

[0037] Figure 4 The graph shows the temperature rise of the cooling tower outlet water under different operating conditions when the heat transfer and mass transfer coefficients are reduced by 10%, 20%, 30%, 40%, and 50%, respectively. Detailed Implementation

[0038] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0039] like Figure 1 As shown in the figure, this embodiment proposes an optimization and performance diagnosis method for crossflow cooling towers, including the following steps:

[0040] (1) Based on the air and water flow direction during the heat and moisture exchange process of the crossflow cooling tower, a two-dimensional heat exchange model of the packing on both sides of the crossflow tower is established.

[0041] (2) Solve for the model parameters based on the measured data and verify the accuracy of the model;

[0042] (3) Calculate the cooling tower outlet water temperature t based on the above two-dimensional heat transfer model. wo If compared with the measured value t wo If the absolute value of the deviation is less than the set value, the cooling tower outlet water temperature control value is optimized; otherwise, the heat exchange model is updated.

[0043] (4) The outlet water temperature t calculated by the initial heat and moisture exchange model under the fault-free condition at the beginning of operation is used under the current operating conditions. w2 Compared with the measured value t wo 'Compare, if t wo '-t w2 If the difference is greater than or equal to the preset second threshold, the performance of the crossflow cooling tower is considered to have degraded.

[0044] This embodiment describes in detail the modeling, operating parameter optimization, and performance diagnosis methods based on actual operating data of a crossflow cooling tower. The crossflow tower's structure and mesh generation are as follows: Figure 2 As shown, x = 1m, z = 2.5m, N = 100.

[0045] Step 1: Establish a general model for crossflow cooling towers.

[0046] Based on the air and water flow directions during heat and moisture exchange in a crossflow cooling tower, the packing material on both sides of the tower is simplified into a two-dimensional heat transfer model (x-z), where x represents the air flow direction and z represents the water flow direction. The x-z two-dimensional plane is divided into N equal parts to form an N*N grid (since there is packing material on both sides, there are two N*N grids; the calculation results of the two N*N grids are the same, so this embodiment randomly selects one N*N grid for calculation). Each grid represents a heat and moisture exchange micro-element. Within each heat and moisture exchange micro-element, a simplified mechanism model, i.e., the heat and moisture exchange model, is established as follows:

[0047] When the air inside the heat and moisture exchange micro-element is not saturated (X) a <X sa When X sa Moisture content of saturated air with air temperature as the qualitative temperature:

[0048]

[0049] When the air inside the heat and moisture exchange micro-element reaches saturation (X) a ≥X sa When this occurs, the heat and moisture exchange process within the infinitesimal element is considered to involve only sensible heat exchange:

[0050]

[0051] In the above model, the heat and moisture exchange process of the air-water system follows the Lewis relation, and the heat transfer coefficient is expressed by the mass transfer coefficient, i.e.: α = βc pa .

[0052] In the above formula, m a For air mass flow rate, t a h represents the air temperature. a X is the enthalpy of air. a X represents the humidity content of the air. sw The moisture content of saturated air is expressed as a function of water temperature, m w For cooling water mass flow rate, t w Let be the cooling water temperature, α be the heat transfer coefficient, β be the mass transfer coefficient, a be the specific surface area of ​​the packing, y be the packing length perpendicular to the air and water flow directions, dx be the infinitesimal length in the air flow direction, dz be the infinitesimal length in the water flow direction, and c be the temperature of the cooling water. pw c is the specific heat capacity of water at constant pressure. pv For the isobaric specific heat capacity of water vapor, c pa R0 is the specific heat capacity of air at constant pressure, and r0 is the latent heat of vaporization of water at 0°C.

[0053] In the simplified mechanism model, βay is a parameter that needs to be solved based on measured data. Since the heat and mass transfer coefficients vary with air and water flow rates, βay will also vary with operating conditions. Therefore, βay is expressed as an expression formed by fixed model parameters to characterize the structural characteristics of the cooling tower.

[0054]

[0055] In the above formula, M w M represents the total cooling water flow rate at the cooling tower inlet. a Let A be the total air volume at the inlet of the cooling tower, and let B, C be the undetermined model parameters. These model parameters reflect the structural characteristics of the cooling tower and are constant under fault-free conditions.

[0056] When solving for the model parameters using least squares fitting with multiple sets of measured data (the measured data includes input parameters: cooling tower inlet air temperature, humidity, total air volume, cooling tower inlet water temperature, and total cooling water flow rate; output parameter: cooling tower outlet cooling water temperature), the expression for βay needs to be linearized as shown in the above equation:

[0057] ln(βay)=ln(A)+B·ln(M w )+C·ln(M a )

[0058] Let A' = ln(A), then we have:

[0059] ln(βay)=A'+B·ln(M w)+C·ln(M a );

[0060] For several groups (M) w M a The overdetermined equations consisting of βay) can be linearly fitted using the least squares method to obtain the model parameters A, B, and C.

[0061] The simplified mechanism model is further expressed in the following form for easy programming implementation:

[0062] The air inside the heat and moisture exchange micro-element is not saturated (X) a <X sa )hour:

[0063]

[0064] The air inside the heat and moisture exchange micro-element reaches a saturated state (X) a ≥X sa )hour:

[0065]

[0066] The subscript 'in' indicates input, and the subscript 'out' indicates output. The calculation represents the cooling tower airflow (m) within each infinitesimal element. a The value remains unchanged.

[0067] like Figure 2 As shown, the simulation calculation process of this model involves calculating the airflow state of each row of heat and moisture exchange micro-elements along the airflow direction. The air state output of the previous micro-element is used as the air state input of the next micro-element. After completing the calculation of a certain row, the calculation of the next row of micro-elements is performed along the cooling water flow direction, and the cooling water state output of the previous row is used as the cooling water state input of the current row (that is, when using the heat and moisture exchange model to calculate the air and water flow states of the heat and moisture exchange micro-element in the j-th row and i-th column, the air state input to the heat and moisture exchange model is the air state output of the heat and moisture exchange micro-element in the j-th row and i-th column, and the water flow state input to the heat and moisture exchange model is the water flow state output of the heat and moisture exchange micro-element in the j-th row and i-th column). The specific calculation method for the heat and moisture exchange micro-element in the j-th row and i-th column is as follows:

[0068] The air inside the heat and moisture exchange micro-element is not saturated (X) a <X sa )hour:

[0069]

[0070]

[0071]

[0072]

[0073] The air inside the heat and moisture exchange micro-element reaches a saturated state (X) a ≥X sa )hour:

[0074] X a(j,i) =X a(j,i-1)

[0075] m w(j,i) =m w(j-1,i)

[0076]

[0077]

[0078] In the above formula, the subscript i indicates that the calculated infinitesimal element is in the i-th column of the air flow direction, and j indicates that the calculated infinitesimal element is in the j-th row of the water flow direction.

[0079] When j=1, when using the heat and moisture exchange model to calculate the air and water flow states of the heat and moisture exchange micro-element in the first row and i-th column, the cooling water temperature input to the heat and moisture exchange micro-element in the first row and i-th column is the same as the cooling water temperature input to the crossflow cooling tower, and the cooling water flow rate input to the heat and moisture exchange micro-element in the first row and i-th column is M. w The ratio of the total number of infinitesimal elements in the first row of two N*N grids to 2N, where the water flow rate input m for each infinitesimal element in the first row. w(0,i) for:

[0080] m w(0,i) =M w / 2 / N, where i = 1, 2, ..., N

[0081] When i=1, when using the heat and humidity exchange model to calculate the air and water flow states of the heat and humidity exchange micro-element in the j-th row and 1-th column, the air temperature and humidity input to the heat and humidity exchange micro-element in the j-th row and 1-th column are the same as the air temperature and humidity input to the crossflow cooling tower, and the air mass flow rate m input to the heat and humidity exchange micro-element in the j-th row and 1-th column is... a(j,0) For M a Compared to 2N,

[0082] m a(j,0) =M a / 2 / N, where j=1,2,…,N.

[0083] The simulation calculation process does not involve iterative operations, so the model will not diverge or fall into an infinite loop, ensuring the stability and reliability of the model operation in practical applications.

[0084] Step 2: Substitute the measured operating data and structural parameters of the cooling tower under variable water and air volume conditions at the beginning of commissioning into the model. Based on the mesh division, dx = x / N and dz = z / N, therefore dx = 0.01m and dz = 0.025m. Solving the model parameters from the measured data yields A = 0.744787, B = 0.279582, and C = 0.481102, which gives βay = 0.744787M. w 0.279582 M a 0.481102 It can be seen that both the cooling tower air volume and water flow rate are positively correlated with the heat and mass transfer coefficient, and the change in air volume has a greater impact on the heat and mass transfer coefficient. Substituting the obtained parameters into the model for calculation, the cooling water temperature and flow rate output by the heat and moisture exchange micro-element in the last row of the N*N grid are obtained. The average value of this water temperature after weighting by the flow rate is taken as the outlet water temperature t of the crossflow cooling tower. wo The specific expression is as follows:

[0085]

[0086] Where i represents the i-th column, m w(N,i) Let t be the cooling water flow rate output by the infinitesimal element in the Nth row and i-th column of an N*N grid. w(N,i) Let i be the temperature of the cooling water output by the infinitesimal element in the Nth row and ith column of an N*N grid, where i = 1, 2, ..., N.

[0087] Figure 3 The simulation results of the model established in this invention are compared with the actual values. Figure 3 It can be seen that the model established by this invention has high simulation accuracy.

[0088] Step 3: Model Optimization and Performance Improvement

[0089] After a period of operation, open cooling towers are prone to problems such as nozzle blockage, uneven liquid distribution, and packing scaling due to the accumulation of fallen leaves and dust. This leads to changes in the specific surface area of ​​the packing and the heat and mass transfer relationship. Therefore, before optimizing the operating parameters, it is necessary to verify the outlet water temperature t of the crossflow cooling tower calculated by the heat and moisture exchange model under the current operating conditions. wo The measured outlet water temperature t of the crossflow cooling tower wo The difference between the values ​​is such that when the absolute value of the difference is less than the preset first threshold, such as 0.3℃, parameter optimization can proceed; otherwise, the current measured operating data should be obtained and the model updated online (i.e., the parameters in the model should be updated).

[0090] When optimizing the operating parameters of a cooling tower, simulation calculations are performed to determine the outlet water temperature t of a crossflow cooling tower under different cooling tower air volumes based on the current outdoor air temperature and humidity, inlet water temperature, and cooling tower airflow. w1The cooling tower air volume and the corresponding outlet water temperature are output to the chiller power consumption, cooling water pump power consumption, and cooling tower fan power consumption calculation model. With the goal of minimizing overall power consumption, the cooling tower outlet water temperature control value is optimized.

[0091] Cooling water pump power consumption:

[0092] P cwp =a0+a1M w +a2M w 2

[0093] Cooling tower fan power consumption:

[0094] P ct =b0+b1M a +b2M a 2

[0095] Chiller power consumption:

[0096] P chiller =c0+c1PLR+c2t w1 +c3t eo +c4PLR 2 +c5t w1 2 +c6t eo 2 +c7t w1 PLR+c8t eo PLR+c9t eo t w1

[0097] Overall power consumption:

[0098] P ref =P cwp +P ct +P chiller

[0099] Where a0, a1, a2, b0, b1, b2, c0~c9 are all fitting coefficients; PLR is the chiller unit load rate, t eo This refers to the chilled water outlet temperature of the chiller unit.

[0100] Step 4: Performance Diagnosis.

[0101] The fault-free state model constructed using initial operational data in step two is used for real-time calculation of the cooling tower's operating status, with the cooling tower outlet water temperature serving as a key indicator for cooling tower performance diagnosis. Under the same outdoor air temperature and humidity, airflow, cooling tower water flow rate, and inlet water temperature, if the measured value t of the crossflow cooling tower outlet water temperature... wo The outlet water temperature t of the crossflow cooling tower calculated by the fault-free state model.w2 If the difference between the values ​​is greater than or equal to the preset second threshold, it can be determined that the cooling tower performance has deteriorated, and there may be faults such as uneven cooling tower liquid distribution, packing scaling, and local blockage, prompting maintenance personnel to carry out inspection and maintenance; in this embodiment, the value range of the second threshold is [0.6 1].

[0102] like Figure 4 As shown, when the mass transfer coefficient β decreases by 20%, the temperature rise of the cooling tower outlet water is less than 0.6℃ under all operating conditions; when the mass transfer coefficient β decreases by 30%, the temperature rise of the cooling tower outlet water is greater than 0.6℃ under most operating conditions. Therefore, in order to accurately identify the fault of cooling tower mass transfer coefficient decreasing by more than 30%, this embodiment preferably sets the second threshold to 0.6℃.

[0103] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A method for optimizing and diagnosing the performance of a crossflow cooling tower, characterized in that, Specifically, the steps include the following: Step 1: Based on the air flow direction and cooling water flow direction during the heat and moisture exchange process in the crossflow cooling tower, the packing on both sides of the crossflow cooling tower is simplified into two xz two-dimensional heat exchange models, where the x direction is the air flow direction and the z direction is the cooling water flow direction. Step 2: Divide each xz 2D heat transfer model into an N*N grid, and treat each grid as a heat and moisture exchange micro-element; Step 3: Establish a heat and humidity exchange model. Randomly select an N*N grid and use the heat and humidity exchange model to calculate the water flow state and air state output by each heat and humidity exchange micro-element in the selected N*N grid; the water flow state includes the cooling water temperature t. w and cooling water flow rate (m) w ; Step 4: Calculate the outlet water temperature t of the crossflow cooling tower based on the water flow state output by the last row of heat and moisture exchange micro-elements in the N*N grid. wo The N*N grid in step 4 is the N*N grid selected in step 3. Step 5: Optimize runtime parameters: Calculate t wo With t wo The absolute value of the difference, t wo 'The measured value of the outlet water temperature of the crossflow cooling tower. If the absolute value is greater than the preset first threshold, the heat and humidity exchange model is updated; otherwise, the optimal outlet water temperature of the crossflow cooling tower is calculated with the goal of minimizing the overall power consumption of the cooling tower, cooling water pump, and chiller unit, and the air volume of the crossflow cooling tower is optimized and adjusted based on the optimal outlet water temperature of the crossflow cooling tower.' Step 6: Performance Diagnosis: Using the initial heat and moisture exchange model under fault-free conditions at the beginning of operation, calculate the outlet water temperature t of the crossflow cooling tower under the current conditions. w2 Calculate t wo 'and t w2 If the difference is greater than or equal to a preset second threshold, the performance of the crossflow cooling tower is considered to have degraded; the current situation includes the current outdoor air temperature and humidity, the air volume of the crossflow cooling tower, the water flow rate entering the crossflow cooling tower, and the inlet water temperature.

2. The method for optimizing and diagnosing the performance of a crossflow cooling tower according to claim 1, characterized in that, The heat and moisture exchange model in step 3 is as follows: If the air humidity content X in a certain heat and moisture exchange micro-element is... a The saturated air moisture content X at the temperature of the heat and moisture exchange micro-element air is less than that of the micro-element air. sa Then, the following heat and moisture exchange model is used to calculate the water flow state and air state output by the heat and moisture exchange micro-element, wherein the air state includes: air mass flow rate m a air temperature t a and moisture content X a ; Where the subscript 'in' indicates input and 'out' indicates output, A, B, and C are model parameters characterizing the heat and mass transfer performance of the cooling tower. The values ​​of A, B, and C are obtained by linear fitting using the least squares method. M w M represents the total cooling water flow rate at the inlet of the crossflow cooling tower. a This represents the total air mass flow rate at the inlet of the crossflow cooling tower. c pw For the specific heat capacity of cooling water at constant pressure, c pv For the isobaric specific heat capacity of water vapor, c pa Let be the specific heat capacity of air at constant pressure, and r0 be the latent heat of vaporization of the cooling water at 0℃; dx is the infinitesimal length of the airflow direction, and dz is the infinitesimal length of the cooling waterflow direction; X sw Moisture content of saturated air with water temperature as the defining temperature; If X within a certain heat and moisture exchange microelement a Greater than or equal to X sa Then, the following heat and moisture exchange model is used to calculate the water flow state and air state output by the heat and moisture exchange micro-element:

3. The method for optimizing and diagnosing the performance of a crossflow cooling tower according to claim 2, characterized in that, In an N*N grid, j represents the j-th row and i represents the i-th column, j = 1, 2, ..., N, i = 1, 2, ..., N; when j = 2, ..., N and i = 2, ..., N, when the heat and humidity exchange model is used to calculate the air state and water flow state of the heat and humidity exchange micro-element in the j-th row and i-th column, the air state input to the heat and humidity exchange model is the air state output by the heat and humidity exchange micro-element in the j-th row and i-1-th column, and the water flow state input to the heat and humidity exchange model is the water flow state output by the heat and humidity exchange micro-element in the j-1-th row and i-th column. When j=1, when using the heat and humidity exchange model to calculate the air state and water flow state of the heat and humidity exchange micro-element in the first row and i-th column, the cooling water flow rate input to the heat and humidity exchange micro-element in the first row and i-th column is M. w The cooling water temperature input to the heat and moisture exchange micro-element in the first row of the two N*N grids is the same as the cooling water temperature input to the crossflow cooling tower, compared to the total number of micro-elements in the first row of the two N*N grids, which is 2N. When i=1, when using the heat and moisture exchange model to calculate the air and water flow states of the heat and moisture exchange microelement in the j-th row and 1-th column, the air mass flow rate input to the heat and moisture exchange microelement in the j-th row and 1-th column is M. a Compared to 2N, the air temperature and humidity input to the heat and humidity exchange micro-element in the j-th row and 1-th column are the same as the air temperature and humidity input to the crossflow cooling tower; When using the heat and moisture exchange model for calculation, the calculation order is as follows: first calculate a row along the air direction, and then proceed to the next row along the cooling water flow direction.

4. The method for optimizing and diagnosing the performance of a crossflow cooling tower according to claim 1, characterized in that, In step 4, the outlet water temperature t of the crossflow cooling tower is calculated according to the following formula. wo : Where i represents the i-th column, m w(N,i) Let t be the cooling water flow rate output by the infinitesimal element in the Nth row and i-th column of an N*N grid. w(N,i) Let i be the temperature of the cooling water output by the infinitesimal element in the Nth row and ith column of an N*N grid, where i = 1, 2, ..., N.

5. The method for optimizing and diagnosing the performance of a crossflow cooling tower according to claim 1, characterized in that, In step 5, the calculation of the optimal cooling tower outlet water temperature, with the aim of minimizing the overall power consumption of the cooling tower, cooling water pump, and chiller unit, specifically involves: The heat and humidity exchange model is used to calculate the outlet water temperature t of a crossflow cooling tower under different cooling tower air volumes based on the current outdoor air temperature and humidity and inlet water temperature. w1 Based on the crossflow cooling tower airflow and the corresponding outlet water temperature, the overall power consumption of the cooling tower, cooling water pump, and chiller unit is calculated. The outlet water temperature corresponding to the minimum overall power consumption is taken as the optimal crossflow cooling tower outlet water temperature, and the cooling tower airflow at this point is taken as the optimal crossflow cooling tower airflow. The overall power consumption P is... ref for: P ref =P cwp +P ct +P chiller P cwp =a0+a1M w +a2M w 2 P ct =b0+b1M a +b2M a 2 P chiller =c0+c1PLR+c2t w1 +c3t eo +c4PLR 2 +c5t w1 2 +c6t eo 2 +c7t w1 PLR+c8t eo PLR+c9t eo t w1 Among them, P cwp For the power consumption of the cooling water pump, P ct For the power consumption of the cooling tower fan, P chiller The power consumption of the chiller unit is denoted by ; a0, a1, a2, b0, b1, b2, c0~c9 are fitting coefficients; PLR is the chiller unit load rate, t eo M represents the chilled water outlet temperature of the chiller unit. w M represents the total cooling water flow rate at the inlet of the crossflow cooling tower. a This represents the total air mass flow rate at the inlet of the crossflow cooling tower.

6. The method for optimizing and diagnosing the performance of a crossflow cooling tower according to claim 1, characterized in that, The range of the second threshold in step 6 is [0.6, 1].

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