A method for modeling and dynamic simulation of multiple components coupling of water chiller based on Simscape

Abstract

The application discloses a kind of based on Simscape's chiller multi-component coupling modeling and dynamic simulation method, belong to the technical field of heating ventilation air conditioning, the multi-physics field simulation model of compressor, condenser, evaporator and thermal expansion valve is respectively constructed by modularization mode, and four main stages are realized in system level, the state evolution and thermodynamic conversion of compression, condensation, throttling and evaporation;Modeling process combines thermodynamics, fluid mechanics and heat transfer theory, adjustable modeling is carried out to the internal thermophysical equation, structure parameter and flow boundary of each component using Matlab / Simscape language, to form complete closed loop dynamic simulation system.The application adopts the above-mentioned one based on Simscape's chiller multi-component coupling modeling and dynamic simulation method, can realize component level modeling, system level coupling, adjustable parameter setting and simulation checking integration, improve the accuracy, universality and engineering adaptability of model.

Description

Technical Field

[0001] This invention relates to the field of refrigeration equipment modeling and simulation technology in HVAC systems, and in particular to a multi-component coupled modeling and dynamic simulation method for chillers based on Simscape. Background Technology

[0002] Chillers, as core equipment in central air conditioning systems, are widely used in large buildings, data centers, and industrial cooling applications. Their operational performance is closely related to system energy efficiency. With the advancement of dual-carbon technologies, improving the modeling accuracy and operational efficiency of chillers has become a research hotspot.

[0003] Currently, modeling methods for chiller units mainly include simplified models based on empirical formulas and black-box modeling methods based on operational data. The former suffers from insufficient accuracy when describing complex operating mechanisms, while the latter relies on a large amount of high-quality operating data, has weak generalization ability, and lacks physical interpretability. These methods have significant shortcomings in multi-condition simulation, fault simulation, and system design verification, making it difficult to meet the requirements of scalability and accuracy in practical engineering.

[0004] With the development of multiphysics modeling platforms, tools such as Simscape have provided a technological foundation for constructing component-level models with physical interpretability and reusability. However, there are still few complete modeling solutions for chiller units, and a systematic approach that can support modular development, system-level integration, and simulation verification is lacking. In particular, how to reasonably combine thermodynamics, fluid mechanics, and control logic, as well as achieve coupling and performance verification between components, remains a challenge in current research and engineering practice.

[0005] Therefore, there is an urgent need to propose a simulation method for chiller units based on Simscape, which can realize modular modeling, coupled simulation and state point verification of key components such as compressors, condensers, evaporators and throttling devices, and provide effective support for digital modeling and performance evaluation of chiller refrigeration systems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape, which can realize the integration of component-level modeling, system-level coupling, adjustable parameter setting and simulation verification, improve the accuracy, versatility and engineering adaptability of the model, and provide effective technical support for the modeling, simulation and optimization of chiller refrigeration systems.

[0007] To achieve the above objectives, this invention provides a method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape, comprising the following steps: S1. Obtain operating parameters: By summarizing the typical operating requirements of chiller units in building HVAC, extract the cooling capacity, condensing temperature, evaporating temperature, refrigerant type and cooling water flow rate, and determine the four typical state points corresponding to the pH diagram. S2. Module Decomposition: The chiller refrigeration cycle process is decomposed into compression module, condensation module, throttling module and evaporation module according to the modular principle, and multiphysics field models of four key components, namely compressor, condenser, thermostatic expansion valve and evaporator, are constructed to support thermodynamic coupling, momentum transfer and heat exchange simulation. S3. Introduce sub-models into each component model; S4. Build a full-process closed-loop simulation system in Simscape: Use a combination of system-level and physical-level modules to build a full-process simulation model, including setting initial parameters, connection logic of each component, sensor output, signal controller and liquid receiver dynamic modeling module, to form a physical simulation system of chiller unit that can operate in a closed loop. S5. Perform simulation, verify the pH chart, and iteratively optimize the model parameters.

[0008] Preferably, the compression module in S2 adopts a steady-state thermodynamic modeling method, ignoring the dynamic behavior of the time derivative term, and establishes a calculation model for refrigerant flow rate and output power through the following steps: The refrigerant mass flow rate is calculated using an empirical polynomial equation, expressed as: ; in, This refers to the compressor speed, measured in Hz. This refers to the compressor displacement, measured in internal volume per revolution (m). 3 / r; This refers to the density of the refrigerant at the compressor suction port, expressed in kg / m³. 3 ; , These are the evaporation and condensation temperatures, in Kelvin (K); coefficients. ~ Data derived from compressor prototype experiments; The compressor discharge enthalpy is determined by isentropic efficiency. After correcting for the ideal enthalpy difference, the following calculation formula is used: ; in, The specific enthalpy of refrigerant absorption. The ideal exhaust enthalpy is obtained based on the isentropic process. This refers to the compressor's discharge enthalpy; the actual input power is obtained through one of the following two methods: Based on compressor electrical efficiency Calculate the compression work using enthalpy difference: ; Alternatively, it can be calculated based on the empirical algebraic polynomial relationship between temperature parameters and input power, in the form of: ; in, ~ To provide adjustable parameters for fitting based on compressor type and operating conditions, adjustable simulations can be implemented in Simscape via Lookup Table or Expression Module.

[0009] Preferably, the condensation module and evaporation module in S2 adopt a three-segment heat transfer modeling method. Combining the thermodynamic coupling relationship, the refrigerant flow process is divided into a subcooled zone, a gas-liquid mixing zone, and a superheated zone. A heat transfer and pressure drop model is established in each segment, and the heat transfer process in each segment is based on the efficiency-number of heat transfer units method. -NTU setup, heat transfer efficiency This is determined by the following relationship: ; Among them, the number of heat transfer units , The overall heat transfer coefficient, For effective heat exchange area, The ratio of heat capacity factor, It is a relatively small thermal capacity flow rate in both hot and cold fluids; The heat exchange capacity of each section is calculated using the following formula: ; in, It is the heat capacity factor of the small fluid in this region, that is, the mass flow rate multiplied by the specific heat; It is the inlet temperature of the two-phase fluid in this area; It is the inlet temperature of the hot fluid in this area; Section heat transfer coefficient h Obtained through correlations of different flow regimes: In the single-phase flow section, the Nusselt number is calculated using the Gnielinski formula. : ; ; in, d For pipe diameter, λ Thermal conductivity, h i The local convective heat transfer coefficient is... The Reynolds number is the fluid's Reynolds number. The Prandtl number is the fluid's characteristic value. , Friction factor; The gas-liquid mixing section uses the Cavallini-Zecchin two-phase heat transfer coefficient model: ; in, Nu tp The Nusselt number is a two-phase number that depends on the liquid-to-gas density ratio, Reynolds number, and Prandtl number. The total thermal resistance R of each section takes into account internal and external convection, wall conduction, fouling thermal resistance, and fin correction factor: ; in, The overall heat transfer coefficient in the two-phase region is... For the effective heat transfer area of ​​the fins in the two-phase region, This is the thermal resistance correction factor for the two-phase region fins. For the thermal resistance of the heat exchanger tube wall, This is a correction factor for the thermal resistance of fins in the single-phase region. For the effective heat transfer area of ​​the fins in the single-phase region, The heat transfer coefficient is the single-phase heat transfer coefficient. Pressure loss along each section Calculated using the Darcy-Weisbach formula: ; in, For fluid density, It is the acceleration due to gravity. The average flow velocity of the fluid. The length of the flow path. The cross-sectional area of ​​the pipe. For fluid mass flow rate, Friction factor; Overall heat transfer of the module The total heat exchange in the three zones: ; in, For total heat transfer, For heat transfer in the liquid phase region, For heat transfer in the two-phase region, For heat transfer in the gas phase region; Simultaneously, a set of mass conservation and energy conservation equations is established to ensure the physical consistency of each working fluid branch in the simulation: ; ; in, The mass flow rate of the fluid inflow. The outflow mass flow rate of the fluid. This represents the change in specific enthalpy per unit mass of fluid during the heat exchange process.

[0010] Preferably, in step S3, the submodule includes a thermostatic expansion valve module. This module simulates the force state of the expansion valve core, the response delay of the temperature sensing bulb, and the refrigerant mass flow rate regulation behavior. A small-orifice flow model is used to establish the refrigerant mass flow rate calculation equation. ; in, It is the flow coefficient; It is the instantaneous open area of ​​the orifice; It is the cross-sectional area of ​​ports A and B; It is the average density of the fluid. It is the control pressure measured by the temperature sensing bulb. It is the pressure loss correction factor. , It is the refrigerant pressure at both ends of the valve; Establish the force balance relationship of the valve core: ; in, This refers to the area of ​​the expansion valve diaphragm. For the pressure of the temperature sensing bulb; The outlet pressure of the expansion valve connected to the evaporator. For the diaphragm spring stiffness, This is the original position of the spring. This represents the current spring compression or valve core displacement. The valve opening control equation is calculated using a superposition method of static superheat and dynamic response: ; in, This represents the current spring displacement. This represents the initial spring displacement. The effective area of ​​the diaphragm; The dynamic temperature response of the temperature sensing bulb is modeled using a first-order inertial system. ; in, It measures the temperature at the evaporator outlet; It is the temperature of the temperature sensor. The thermal inertia time constant of the temperature sensing bulb It is a time variable.

[0011] Preferably, in step S3, the submodule includes a liquid receiver modeling module. This module is used to simulate the dynamic mass and energy changes of the liquid receiver in the refrigeration system, employing the following physical modeling method: Treating the reservoir as a fixed-volume control volume, based on the principle of mass conservation, the change in the mass of the working fluid within its cavity satisfies the following formula: ; in, , , , These are the mass flow rates at ports A, B, C, and D, respectively. For the quality of the working fluid; The density change is determined by the derivatives of pressure and temperature. Combining the bulk modulus and coefficient of thermal expansion of the fluid, the expression for the density change is: ; in, For system pressure, For system temperature, The coefficient of volume expansion. The isothermal compressibility coefficient, The density of the system fluid, To control volume; The change in internal energy of the liquid reservoir over time is modeled using the energy conservation equation, and its energy balance is determined by: ; in, For the mass inside the cavity, Enthalpy per unit fluid mass , , , These represent the energy flow rates at ports A, B, C, and D, respectively. It is the heat flow from port H; Considering the momentum change of the working fluid inside the reservoir, the following governing equations are established based on momentum conservation: ; in, To ensure uniform control pressure within the expansion vessel, The pressure at which the working fluid enters the container from end A of path A. The pressure at which the working fluid enters the container from end B of path B. The pressure at which the working fluid enters the container from end C of the path. The pressure at which the working fluid enters the container from end D of the path.

[0012] Preferably, the liquid reservoir module considers the inertial characteristics of the working fluid during the flow process and establishes a descriptive model of the flow state inside and outside the liquid reservoir based on the principle of momentum conservation: when the system is running in an unsteady state, the flow velocity and pressure of the working fluid inside the liquid reservoir fluctuate, and the dynamic response characteristics of the system are characterized by describing the momentum changes of the working fluid during inflow, outflow and under the influence of external pipeline forces.

[0013] Preferably, step S4 introduces a thermodynamic state point verification mechanism based on a pH diagram, i.e., a pressure-enthalpy diagram, to verify the thermodynamic parameters of key nodes in each stage of compression, condensation, throttling, and evaporation, ensuring that the pressure and enthalpy values ​​at each state point of the established model meet the rated design conditions. The state point verification method includes the following steps: S4.1 Based on the thermodynamic properties of refrigerant R134a, and considering the rated evaporation and condensation temperatures, obtain the corresponding four typical state points on the pH diagram. P 1, h 1) ( P 2, h 2), ( P 3, h 3), ( P 4, h 4); S4.2 Compare the measured transient state of the refrigerant in the simulation results with the target value, and calculate the error Δ. P i ; S4.3 If the error at any state point exceeds the allowable threshold, the system parameters are iteratively optimized by adjusting the component parameters. S4.4, until satisfied: , , For the first The difference between the specific enthalpy calculated by simulation at each state point and the theoretically set specific enthalpy is used to ensure the closure and thermodynamic consistency of the simulation operating condition path on the pH diagram.

[0014] Therefore, the present invention employs the above-mentioned Simscape-based multi-component coupled modeling and dynamic simulation method for chiller units, which has the following beneficial effects: (1) Establish a unified modeling framework: Based on the MATLAB / Simscape platform, modular modeling is integrated with the principles of multiple disciplines to realize the complete closed-loop dynamic simulation of the chiller unit. The physical credibility and stability are better than the traditional empirical model.

[0015] (2) Improved accuracy through component-level fine modeling: The key components adopt the lumped parameter method, especially the three-section (subcooled zone, mixing zone, and superheated zone) thermodynamic analysis method introduced in the modeling of condenser and evaporator, so that the simulation results are closer to reality under all working conditions.

[0016] (3) Introduce a pH diagram state point verification mechanism: Based on the R134a pressure-enthalpy diagram, set 4 state points, compare them with the simulation results to construct a verification closed loop, and optimize the model accuracy.

[0017] (4) Energy and mass modeling of the reservoir: The proposed reservoir model is constructed based on the equations of mass conservation, energy conservation and momentum conservation, taking into account the flow of working fluid and changes in the cavity, and realistically simulating the unsteady dynamic behavior of the system.

[0018] (5) Advantages of engineering deployment: The module supports parameterized adjustment and is compatible with various chiller units. Compared with pure flow field simulation methods such as CFD, it has higher modeling efficiency and lower computational load, making it easier for engineering design evaluation and verification.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is an overall flowchart of an embodiment of the method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to the present invention; Figure 2 This is a flowchart illustrating the thermodynamic parameter verification process for key nodes of the chiller condenser at each stage, according to an embodiment of the Simscape-based multi-component coupled modeling and dynamic simulation method for chillers. Figure 3 This is a schematic diagram of four thermodynamic state points of a chiller unit as determined in the R134a pressure-enthalpy diagram, according to an embodiment of the present invention's method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape. Figure 4 This is a simulation curve of the response characteristics of the thermostatic expansion valve opening of a chiller unit as a function of time, according to an embodiment of the Simscape-based multi-component coupled modeling and dynamic simulation method for chiller units. Figure 5 This is a simulation result diagram of the liquid level change of the chiller unit over time, based on an embodiment of the Simscape-based multi-component coupled modeling and dynamic simulation method for chiller units according to the present invention. Figure 6 This is a structural diagram of the overall simulation model of a closed-loop refrigeration system built on the Simscape platform, which is an embodiment of the Simscape-based multi-component coupled modeling and dynamic simulation method for chillers according to the present invention. Figure 7 This is a comparison chart of simulated and measured values ​​of the output heat of the chiller evaporator in the chiller circuit in an embodiment of the Simscape-based multi-component coupled modeling and dynamic simulation method for chiller units according to the present invention. Figure 8 This is a comparison chart of simulated and measured values ​​of heat transfer load on the condenser side of a chiller unit in a hot water circuit, according to an embodiment of the Simscape-based multi-component coupling modeling and dynamic simulation method for chiller units. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0023] Example 1 like Figures 1 to 2 As shown, this invention provides a method for multi-component coupled modeling and dynamic simulation of chillers based on Simscape, including the following steps: S1. Obtain operating parameters: By summarizing the typical operating requirements of chiller units in building HVAC, extract key rated operating parameters such as chiller cooling capacity, condensing temperature, evaporating temperature, refrigerant type (R134a), and chilled / cooling water flow rate, and determine the four typical state points corresponding to the pH diagram.

[0024] S2. Module Decomposition: The chiller refrigeration cycle process is decomposed into compression module, condensation module, throttling module and evaporation module according to the modular principle, and multiphysics field models of four key components, namely compressor, condenser, thermostatic expansion valve and evaporator, are constructed to support thermodynamic coupling, momentum transfer and heat exchange simulation.

[0025] The compression module adopts a steady-state thermodynamic modeling approach, ignoring the dynamic behavior of the time derivative term. The refrigerant flow rate and output power calculation model are established through the following steps: The refrigerant mass flow rate is calculated using an empirical polynomial equation, expressed as: ; in, This refers to the compressor speed, measured in Hz. This refers to the compressor displacement, measured in internal volume per revolution (m). 3 / r; This refers to the density of the refrigerant at the compressor suction port, expressed in kg / m³. 3 ; , These are the evaporation and condensation temperatures, in Kelvin (K); coefficients. ~ Data derived from compressor prototype experiments; The compressor discharge enthalpy is determined by isentropic efficiency. After correcting for the ideal enthalpy difference, the following calculation formula is used: ; in, The specific enthalpy of refrigerant absorption. The ideal exhaust enthalpy is obtained based on the isentropic process. This refers to the compressor's discharge enthalpy; the actual input power is obtained through one of the following two methods: a) Based on the compressor's electrical efficiency Calculate the compression work using enthalpy difference: ; b) Calculated based on the empirical algebraic polynomial relationship between temperature parameters and input power, in the form of: ; in, ~ To provide adjustable parameters for fitting based on compressor type and operating conditions, adjustable simulations can be implemented in Simscape via Lookup Table or Expression Module.

[0026] The condensing and evaporating modules employ a three-segment heat transfer modeling method. Combining thermodynamic coupling, the refrigerant flow process is divided into a subcooled zone, a gas-liquid mixing zone, and a superheated zone. Heat transfer and pressure drop models are established for each segment, and the heat transfer process in each segment is based on the efficiency-number of heat transfer units method. -NTU setup, heat transfer efficiency This is determined by the following relationship: ; Among them, the number of heat transfer units , The overall heat transfer coefficient, For effective heat exchange area, The ratio of heat capacity factor, It is a relatively small thermal capacity flow rate in both hot and cold fluids; The heat exchange capacity of each section is calculated using the following formula: ; in, It is the heat capacity factor of the small fluid in this region, that is, the mass flow rate multiplied by the specific heat; It is the inlet temperature of the two-phase fluid in this area; It is the inlet temperature of the hot fluid in this area; Section heat transfer coefficient h Obtained through correlations of different flow regimes: a) The Nusselt number for the single-phase flow section is calculated using the Gnielinski formula. : ; ; in, d For pipe diameter, λ Thermal conductivity, h i The local convective heat transfer coefficient is... The Reynolds number is the fluid's Reynolds number. The Prandtl number is the fluid's characteristic value. , It is the friction factor.

[0027] b) The Cavallini-Zecchin two-phase heat transfer coefficient model is used in the gas-liquid mixing section: ; in, Nu tp The Nusselt number is a two-phase number that depends on the liquid-to-gas density ratio, Reynolds number, and Prandtl number.

[0028] The total thermal resistance R of each section takes into account internal and external convection, wall conduction, fouling thermal resistance, and fin correction factor: ; in, The overall heat transfer coefficient in the two-phase region is... For the effective heat transfer area of ​​the fins in the two-phase region, This is the thermal resistance correction factor for the two-phase region fins. For the thermal resistance of the heat exchanger tube wall, This is a correction factor for the thermal resistance of fins in the single-phase region. For the effective heat transfer area of ​​the fins in the single-phase region, The heat transfer coefficient is the single-phase heat transfer coefficient. Pressure loss along each section Calculated using the Darcy-Weisbach formula: ; in, For fluid density, It is the acceleration due to gravity. The average flow velocity of the fluid. The length of the flow path. The cross-sectional area of ​​the pipe. For fluid mass flow rate, Friction factor; Overall heat transfer of the module The total heat exchange in the three zones: ; in, For total heat transfer, For heat transfer in the liquid phase region, For heat transfer in the two-phase region, For heat transfer in the gas phase region; Simultaneously, a set of mass conservation and energy conservation equations is established to ensure the physical consistency of each working fluid branch in the simulation: ; ; in, The mass flow rate of the fluid inflow. The outflow mass flow rate of the fluid. This represents the change in specific enthalpy per unit mass of fluid during the heat exchange process.

[0029] The above modeling method is expressed in the form of lumped parameters in the Simscape platform and supports the parameterized definition of heat exchanger type (co-current, counter-current, cross-flow) and structural parameters (tube length, fin coefficient, etc.).

[0030] S3. Introduce sub-models into each component model: for example, establish a dynamic response control module for the temperature sensing bulb, a diaphragm force model, and a mass flow rate regulation module in the thermostatic expansion valve model; introduce a three-stage heat exchange zone model into the heat exchanger model and... -NTU method for calculating heat transfer efficiency.

[0031] The submodule includes a thermostatic expansion valve module, which simulates the force state of the expansion valve core, the response delay of the temperature sensing bulb, and the refrigerant mass flow rate regulation behavior. Specifically, it includes: (1) The refrigerant mass flow rate calculation equation is established using the orifice flow model: ; in, It is the flow coefficient; It is the instantaneous open area of ​​the orifice; It is the cross-sectional area of ​​ports A and B; It is the average density of the fluid. It is the control pressure measured by the temperature sensing bulb. It is the pressure loss correction factor. , It is the refrigerant pressure at both ends of the valve; (2) Establish the force balance relationship of the valve core: ; in, This refers to the area of ​​the expansion valve diaphragm. For the pressure of the temperature sensing bulb; The outlet pressure of the expansion valve connected to the evaporator. For the diaphragm spring stiffness, This is the original position of the spring. This represents the current spring compression or valve core displacement. (3) The valve opening control equation is calculated by superimposing static superheat and dynamic response: ; in, This represents the current spring displacement. This represents the initial spring displacement. The effective area of ​​the diaphragm; (4) The dynamic temperature response of the temperature sensing bulb is modeled using a first-order inertial system: ; in, It measures the temperature at the evaporator outlet; It is the temperature of the temperature sensor. The thermal inertia time constant of the temperature sensing bulb It is a time variable.

[0032] The submodule also includes a liquid receiver modeling module, which is used to simulate the dynamic mass and energy changes of the liquid receiver in the refrigeration system, using the following physical modeling method: (1) Considering the reservoir as a fixed volume control volume, based on the principle of mass conservation, the change in the mass of the working fluid inside its cavity satisfies the following formula: ; in, , , , These are the mass flow rates at ports A, B, C, and D, respectively. For the quality of the working fluid; (2) The density change is determined by the differentials of pressure and temperature. Combining the bulk modulus and thermal expansion coefficient of the fluid, the expression for the density change is: ; in, For system pressure, For system temperature, The coefficient of volume expansion. The isothermal compressibility coefficient, The density of the system fluid, To control volume; (3) The change in internal energy of the reservoir over time is modeled using the energy conservation equation, and its energy balance is determined by: ; in, For the mass inside the cavity, Enthalpy per unit fluid mass , , , These represent the energy flow rates at ports A, B, C, and D, respectively. It is the heat flow from port H; (4) Considering the momentum change of the working fluid in the reservoir, the following governing equations are established based on the conservation of momentum: ; in, To ensure uniform control pressure within the expansion vessel, The pressure at which the working fluid enters the container from end A of path A. The pressure at which the working fluid enters the container from end B of path B. The pressure at which the working fluid enters the container from end C of the path. The pressure at which the working fluid enters the container from end D of the path.

[0033] The reservoir module considers the inertial characteristics of the working fluid flow process and establishes a descriptive model of the flow state inside and outside the reservoir based on the principle of momentum conservation. During unsteady-state operation, the working fluid velocity and pressure inside the reservoir may fluctuate. This model characterizes the dynamic response characteristics of the system by describing the momentum changes of the working fluid during inflow, outflow, and under the influence of external pipeline forces. Specifically, the flow inertia at the reservoir inlet and outlet can be calculated through the relationship between the inlet / outlet momentum difference, additional force, and rate of change of mass; that is, the "net thrust" on the system is equal to the rate of change of the working fluid's momentum. In Simscape, this can be achieved by linking an inertial module (such as the Translational Mechanical Converter) with the fluid pipeline model to simulate the system response under rapid pressure changes or sudden changes in operating conditions.

[0034] In addition, to improve the completeness and adaptability of system modeling, the chiller system can further include the following auxiliary modeling modules: (1) Pipeline and connector model A model is established to represent the pipe resistance in the system, considering the effects of friction along the pipe and structural elements such as local bends on pressure. The pressure drop varies with pipe length, flow velocity, and fluid characteristics. This part can be achieved using a lumped parameter model, providing a relatively accurate flow resistance estimate without the need for three-dimensional CFD calculations.

[0035] (2) Sensing and Control Interface Model Temperature, pressure, and flow sensing modules are placed at key locations in the system (such as the compressor suction end, evaporator return end, and expansion valve outlet). By linking with the Simulink control subsystem, a real-time closed-loop control loop is constructed to automatically adjust the expansion valve opening or compressor speed.

[0036] (3) Initial operating condition configuration module To ensure rapid and stable operation of the system simulation in its initial stage, the model supports presetting the initial pressure, temperature, and mass flow rate parameters of each subsystem within the Simscape environment. By setting parameters such as "Initial Target" and "Priority," the simulation can actively converge to the specified rated operating conditions at the start, avoiding numerical oscillations or simulation failures.

[0037] By integrating the above modules, the constructed chiller unit simulation system can not only accurately describe the heat transfer and flow processes of each stage of the refrigeration cycle under steady-state conditions, but also simulate dynamic behaviors such as startup and load changes during actual operation, supporting the optimization design and verification of various control strategies and structural parameters.

[0038] S4. Build a full-process closed-loop simulation system in Simscape: Use a combination of system-level and physical-level modules to build a full-process simulation model, including setting initial parameters, connection logic of each component, sensor output, signal controller and liquid receiver dynamic modeling module, to form a physical simulation system of chiller unit that can operate in a closed loop. like Figures 4 to 8 As shown, a thermodynamic state point verification mechanism based on a pressure-enthalpy diagram (PH diagram) is introduced to check the thermodynamic parameters of key nodes in each stage of compression, condensation, throttling, and evaporation, to ensure that the pressure and enthalpy values ​​at each state point of the established model meet the rated design conditions. The state point verification method includes the following steps: S4.1 Based on the thermodynamic properties of refrigerant R134a, and considering the rated evaporation and condensation temperatures, obtain the corresponding four typical state points on the pH diagram. P 1, h 1) ( P 2, h 2), ( P 3, h 3), ( P 4, h 4), such as Figure 3 As shown; S4.2 Compare the measured transient state of the refrigerant in the simulation results with the target value, and calculate the error Δ. P i ; S4.3 If the error at any state point exceeds the allowable threshold, the system parameters are iteratively optimized by adjusting the component parameters. S4.4, until satisfied: , , For the first The difference between the specific enthalpy calculated by simulation at each state point and the theoretically set specific enthalpy is used to ensure the closure and thermodynamic consistency of the simulation operating condition path on the pH diagram.

[0039] S5. Perform simulation, verify the pH chart, and iteratively optimize the model parameters: Run the simulation by setting the state point temperature, pressure, and enthalpy under rated operating conditions, and compare the output results with the pH chart data to verify the accuracy of the simulation model; further adjust the model parameters of each component based on the data collected from the test platform to optimize the model accuracy and ensure that the simulation output is highly consistent with the actual operating condition response.

[0040] Therefore, the present invention adopts the above-mentioned Simscape-based multi-component coupling modeling and dynamic simulation method for chiller units, which can realize the integration of component-level modeling, system-level coupling, adjustable parameter setting and simulation verification, improve the accuracy, versatility and engineering adaptability of the model, and provide effective technical support for the modeling, simulation and optimization of chiller refrigeration systems.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for coupled multi-component modeling and dynamic simulation of chiller units based on Simscape, characterized in that: Includes the following steps: S1. Obtain operating parameters: By summarizing the typical operating requirements of chiller units in building HVAC, extract the cooling capacity, condensing temperature, evaporating temperature, refrigerant type and cooling water flow rate, and determine the four typical state points corresponding to the pH diagram. S2. Module Decomposition: The chiller refrigeration cycle process is decomposed into compression module, condensation module, throttling module and evaporation module according to the modular principle, and multiphysics field models of four key components, namely compressor, condenser, thermostatic expansion valve and evaporator, are constructed to support thermodynamic coupling, momentum transfer and heat exchange simulation. S3. Introduce sub-models into each component model; S4. Build a full-process closed-loop simulation system in Simscape: Use a combination of system-level and physical-level modules to build a full-process simulation model, including setting initial parameters, connection logic of each component, sensor output, signal controller and liquid receiver dynamic modeling module, to form a physical simulation system of chiller unit that can operate in a closed loop. S5. Perform simulation, verify the pH chart, and iteratively optimize the model parameters.

2. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 1, characterized in that: The compression module in S2 adopts a steady-state thermodynamic modeling approach, ignoring the dynamic behavior of the time derivative term. The refrigerant flow rate and output power calculation model are established through the following steps: The refrigerant mass flow rate is calculated using an empirical polynomial equation, expressed as: ； in, This refers to the compressor speed, measured in Hz. This refers to the compressor displacement, measured in internal volume per revolution (m). 3 / r; This refers to the density of the refrigerant at the compressor suction port, expressed in kg / m³. 3 ; , These are the evaporation and condensation temperatures, in Kelvin (K); coefficients. ~ Data derived from compressor prototype experiments; The compressor discharge enthalpy is determined by isentropic efficiency. After correcting for the ideal enthalpy difference, the following calculation formula is used: ； in, The specific enthalpy of refrigerant absorption. The ideal exhaust enthalpy is obtained based on the isentropic process. This refers to the compressor's discharge enthalpy; the actual input power is obtained through one of the following two methods: Based on compressor electrical efficiency Calculate the compression work using enthalpy difference: ； Alternatively, it can be calculated based on the empirical algebraic polynomial relationship between temperature parameters and input power, in the form of: ； in, ~ To provide adjustable parameters for fitting based on compressor type and operating conditions, adjustable simulations can be implemented in Simscape via LookupTable or expression modules.

3. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 1, characterized in that: The condensation and evaporation modules in S2 employ a three-segment heat transfer modeling method. Combining thermodynamic coupling, the refrigerant flow process is divided into a subcooled zone, a gas-liquid mixing zone, and a superheated zone. Heat transfer and pressure drop models are established for each segment, and the heat transfer process in each segment is based on the efficiency-number of heat transfer units method. -NTU setup, heat transfer efficiency It is determined by the following relationship: ； Among them, the number of heat transfer units , The overall heat transfer coefficient, For effective heat exchange area, The ratio of heat capacity factor, It is a relatively small thermal capacity flow rate in both hot and cold fluids; The heat exchange capacity of each section is calculated using the following formula: ； in, It is the heat capacity factor of the small fluid in this region, that is, the mass flow rate multiplied by the specific heat; It is the inlet temperature of the two-phase fluid in this area; It is the inlet temperature of the hot fluid in this area; Section heat transfer coefficient h Obtained through correlations of different flow regimes: In the single-phase flow section, the Nusselt number is calculated using the Gnielinski formula. : ； ； in, d For pipe diameter, λ Thermal conductivity, h i The local convective heat transfer coefficient is... The Reynolds number is the fluid's Reynolds number. The Prandtl number is the fluid's characteristic value. , Friction factor; The gas-liquid mixing section uses the Cavallini-Zecchin two-phase heat transfer coefficient model: ； in, Nu tp The Nusselt number is a two-phase number that depends on the liquid-to-gas density ratio, Reynolds number, and Prandtl number. The total thermal resistance R of each section takes into account internal and external convection, wall conduction, fouling thermal resistance, and fin correction factor: ； in, The overall heat transfer coefficient in the two-phase region is... For the effective heat transfer area of ​​the fins in the two-phase region, This is the thermal resistance correction factor for the two-phase region fins. For the thermal resistance of the heat exchanger tube wall, This is a correction factor for the thermal resistance of fins in the single-phase region. For the effective heat transfer area of ​​the fins in the single-phase region, The heat transfer coefficient is the single-phase heat transfer coefficient. Pressure loss along each section Calculated using the Darcy-Weisbach formula: ； in, For fluid density, It is the acceleration due to gravity. The average flow velocity of the fluid. The length of the flow path. The cross-sectional area of ​​the pipe. For fluid mass flow rate, Friction factor; Overall heat transfer of the module The total heat exchange in the three zones: ； in, For total heat transfer, For heat transfer in the liquid phase region, For heat transfer in the two-phase region, For heat transfer in the gas phase region; Simultaneously, a set of mass conservation and energy conservation equations is established to ensure the physical consistency of each working fluid branch in the simulation: ； ； in, The mass flow rate of the fluid inflow. The outflow mass flow rate of the fluid. This represents the change in specific enthalpy per unit mass of fluid during the heat exchange process.

4. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 1, characterized in that: In S3, the submodule includes a thermostatic expansion valve module. The thermostatic expansion valve module simulates the force state of the expansion valve core, the response delay of the temperature sensing bulb, and the refrigerant mass flow rate regulation behavior. A small-orifice flow model is used to establish the refrigerant mass flow rate calculation equation. ； in, It is the flow coefficient; It is the instantaneous open area of ​​the orifice; It is the cross-sectional area of ​​ports A and B; It is the average density of the fluid. It is the control pressure measured by the temperature sensing bulb. It is the pressure loss correction factor. , It is the refrigerant pressure at both ends of the valve; Establish the force balance relationship of the valve core: ； in, This refers to the area of ​​the expansion valve diaphragm. For the pressure of the temperature sensing bulb; The outlet pressure of the expansion valve connected to the evaporator. For the diaphragm spring stiffness, This is the original position of the spring. This represents the current spring compression or valve core displacement. The valve opening control equation is calculated using a superposition method of static superheat and dynamic response: ； in, This represents the current spring displacement. This represents the initial spring displacement. The effective area of ​​the diaphragm; The dynamic temperature response of the temperature sensing bulb is modeled using a first-order inertial system. ； in, It measures the temperature at the evaporator outlet; It is the temperature of the temperature sensor. The thermal inertia time constant of the temperature sensing bulb It is a time variable.

5. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 1, characterized in that: In S3, the submodule includes a liquid receiver modeling module, which is used to simulate the dynamic mass and energy changes of the liquid receiver in the refrigeration system, and adopts the following physical modeling method: Treating the reservoir as a fixed-volume control volume, based on the principle of mass conservation, the change in the mass of the working fluid within its cavity satisfies the following formula: ； in, , , , These are the mass flow rates at ports A, B, C, and D, respectively. For the quality of the working fluid; The density change is determined by the derivatives of pressure and temperature. Combining the bulk modulus and coefficient of thermal expansion of the fluid, the expression for the density change is: ； in, For system pressure, For system temperature, The coefficient of volume expansion. The isothermal compressibility coefficient, The density of the system fluid, To control volume; The change in internal energy of the liquid reservoir over time is modeled using the energy conservation equation, and its energy balance is determined by: ； in, For the mass inside the cavity, Enthalpy per unit fluid mass , , , These represent the energy flow rates at ports A, B, C, and D, respectively. It is the heat flow from port H; Considering the momentum change of the working fluid inside the reservoir, the following governing equations are established based on momentum conservation: ； in, To ensure uniform control pressure within the expansion vessel, The pressure at which the working fluid enters the container from end A of path A. The pressure at which the working fluid enters the container from end B of path B. The pressure at which the working fluid enters the container from end C of the path. The pressure at which the working fluid enters the container from end D of the path.

6. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 5, characterized in that: The liquid storage module considers the inertial characteristics of the working fluid during the flow process and establishes a descriptive model of the flow state inside and outside the liquid storage through the principle of momentum conservation: when the system is running in an unsteady state, the flow velocity and pressure of the working fluid inside the liquid storage fluctuate. The dynamic response characteristics of the system are characterized by describing the momentum changes of the working fluid during inflow, outflow and under the influence of external pipeline forces.

7. The method for multi-component coupled modeling and dynamic simulation of chiller units based on Simscape according to claim 1, characterized in that: The S4 introduces a thermodynamic state point verification mechanism based on the PH diagram, i.e., the pressure-enthalpy diagram, to verify the thermodynamic parameters of key nodes in each stage of compression, condensation, throttling and evaporation, so as to ensure that the pressure and enthalpy values ​​of each state point of the established model meet the rated design conditions. The state point verification method includes the following steps: S4.1 Based on the thermodynamic properties of refrigerant R134a, and considering the rated evaporation and condensation temperatures, obtain the corresponding four typical state points on the pH diagram. P 1, h 1) ( P 2, h 2), ( P 3, h 3), ( P 4, h 4); S4.2 Compare the measured transient state of the refrigerant in the simulation results with the target value, and calculate the error Δ. P i ; S4.3 If the error at any state point exceeds the allowable threshold, the system parameters are iteratively optimized by adjusting the component parameters. S4.4, until the following condition is met: max(Δ) h i )≤ , i ∈{1,2,3,4},Δ h i The difference between the specific enthalpy calculated by simulation at the i-th state point and the theoretically set specific enthalpy is used to ensure the closure and thermodynamic consistency of the simulation operating condition path on the pH diagram.

Images