A simulation method combining underground refinement and aboveground coarsening for a heating system

Abstract

This invention discloses a simulation method combining detailed underground simulation and coarse above-ground simulation for heating systems. For the underground soil heat extraction and storage module, the component-level Fluent software is used for detailed simulation, accurately describing the actual heat exchange process between the buried pipes and the soil at the component level. For the above-ground solar collector subsystem, ground source heat pump heating subsystem, and building heating terminals, the system-level TRNSYS software is used for coarse simulation, describing the operation of each above-ground system at the system level. A dedicated software interface program enables bidirectional data transmission between Fluent and TRNSYS, achieving a combined detailed underground simulation and coarse above-ground simulation for ground source heat pump heating systems. This method achieves high-precision component-level simulation of the underground soil heat extraction and storage module while simultaneously providing system-level simulation of the above-ground subsystems.

Description

Technical Field

[0001] This invention relates to the field of building energy conservation technology, and in particular to a simulation method that combines underground refinement and above-ground coarsening for heating systems. Background Technology

[0002] Focusing on the environmental pollution caused by traditional building heating, ground source heat pump heating technology has become the mainstream energy-saving technology to address this issue. However, long-term use of pure ground source heat pump heating can cause soil thermal imbalance. Introducing solar interseasonal heat storage technology can solve this problem. Performance studies on solar interseasonal heat storage-ground source heat pump coupled heating systems are generally divided into experimental studies and simulation studies. Experimental studies often have high requirements in terms of site and cost, and face long development cycles in practice. Therefore, conducting simulation studies is particularly important to overcome the limitations of experimental conditions.

[0003] Currently, most simulation studies of solar-driven seasonal heat storage-ground source heat pump coupled heating systems are based on the instantaneous system simulation program (TRNSYS). While it can perform system-level simulations of the entire system, the simplified model of the soil heat extraction-storage components in this software prevents detailed simulations of underground heat exchange components. It also fails to study the impact of well layout and groundwater seepage on the actual heat exchange process between the underground soil and buried pipes. Fluent, a commercial computational fluid dynamics (CFD) software package, can perform high-precision component-level simulations of the actual heat exchange process between the underground soil and buried pipes, but it cannot simulate the above-ground solar collector subsystem, ground source heat pump heating subsystem, or building heating terminals at the system level. Therefore, since a single simulation tool cannot simultaneously meet the simulation requirements at the system level and the simulation accuracy at the component level, it is necessary to combine the advantages of both software programs to achieve simulation of the entire system, thereby ensuring high simulation accuracy of the underground soil heat extraction-storage components while performing above-ground system-level simulations. The key to achieving this goal is to develop a stable and efficient coupling simulation strategy between Fluent and TRNSYS. However, there is currently a lack of research in this area. Therefore, there is an urgent need to develop a coupling simulation method that combines coarsening studies of the above-ground system layer with refinement studies of the underground component layer.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a simulation method that combines detailed underground simulation and coarsening above-ground simulation for heating systems, thereby addressing the aforementioned technical problems in existing technologies. The method utilizes Fluent to perform detailed three-dimensional transient simulation of the actual heat exchange process of underground soil heat extraction and storage components, while simultaneously using TRNSYS to perform coarsening simulation of the above-ground solar collector subsystem, ground source heat pump heating subsystem, and building heating terminals. Key data (temperature, flow rate) can be exchanged in real time between the two software programs, thus achieving high-precision component-level simulation of the underground soil heat extraction and storage module while also considering system-level simulation of various above-ground subsystems.

[0006] The objective of this invention is achieved through the following technical solution: A simulation method combining underground detailing and above-ground coarsening for heating systems, the method comprising: Step 1: For the underground soil heat extraction and storage module, use the component-level commercial computational fluid dynamics software package Fluent to perform a detailed simulation of the underground soil heat extraction and storage module, accurately describing the actual heat exchange process between the buried pipe and the soil at the component level. Step 2: For the ground-based solar thermal collector subsystem, ground source heat pump heating subsystem, and building heating terminals, use the system-level instantaneous system simulation program TRNSYS to perform coarse simulation to describe the operation process of each ground-based system at the system level. Step 3: Through a dedicated software interface program, bidirectional data transmission is performed between Fluent and TRNSYS to achieve a combined simulation of underground refinement and above-ground coarsening for ground source heat pump heating systems.

[0007] Compared with existing technologies, the method provided by this invention utilizes Fluent to perform a detailed three-dimensional transient simulation of the actual heat exchange process of underground soil heat extraction and storage components, while using TRNSYS to perform coarse simulation of the above-ground solar thermal collector subsystem, ground source heat pump heating subsystem, and building heating terminals. Key data (temperature, flow rate) between the two software programs can be exchanged in real time, thereby achieving high-precision component-level simulation of the underground soil heat extraction and storage module while also taking into account system-level simulation of each above-ground subsystem. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1This is a schematic diagram of the simulation method for combining underground refinement and above-ground coarsening for heating systems provided in an embodiment of the present invention. Figure 2 This is a schematic diagram showing the grid division results of the buried pipe and thermal storage soil described in an embodiment of the present invention; Figure 3 This is a schematic diagram of the overall structure of the simulation combining underground refinement and above-ground coarsening as described in an embodiment of the present invention; Figure 4 This is a flowchart illustrating the simulation of the combination of underground refinement and above-ground coarsening as described in an embodiment of the present invention. Figure 5 This is a schematic diagram comparing the cumulative soil heat extraction during the entire heating season and the heat storage season as described in the embodiments of the present invention. Figure 6 This is a schematic diagram comparing the cumulative heat storage in the soil during the entire heating season and the heat storage season as described in the embodiments of the present invention. Detailed Implementation

[0010] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them, and do not constitute a limitation on the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0011] First, the following explanations are provided for the terms that may be used in this article: The term "and / or" means that either or both can be achieved simultaneously. For example, X and / or Y means that it includes both "X" or "Y" as well as the three cases of "X and Y".

[0012] The terms "comprising," "including," "containing," "having," or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example, including a technical feature element (such as raw material, component, ingredient, carrier, dosage form, material, size, part, component, mechanism, device, step, process, method, reaction conditions, processing conditions, parameter, algorithm, signal, data, product or article of manufacture, etc.) should be interpreted as including not only the expressly listed technical feature element, but also other technical feature elements that are not expressly listed and are well-known in the art.

[0013] The term "composed of" excludes any technical features not expressly listed. When used in a claim, it closes the claim to exclude all technical features other than those expressly listed, except for associated conventional impurities. If the term appears only in a clause of a claim, it limits the claim to the elements expressly listed in that clause; elements recited in other clauses are not excluded from the overall claim.

[0014] The technical solution provided by this invention will be described in detail below. Contents not described in detail in the embodiments of this invention are prior art known to those skilled in the art. Where specific conditions are not specified in the embodiments of this invention, they shall be performed according to conventional conditions in the art or conditions recommended by the manufacturer. Reagents or instruments used in the embodiments of this invention whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0015] like Figure 1 The diagram shown is a schematic flowchart of a simulation method combining underground refinement and above-ground coarsening for heating systems, provided by an embodiment of the present invention. The method includes: Step 1: For the underground soil heat extraction and storage module, use the component-level commercial computational fluid dynamics software package Fluent to perform a detailed simulation of the underground soil heat extraction and storage module, accurately describing the actual heat exchange process between the buried pipe and the soil at the component level. In this step, the three-dimensional solid direct modeling software Spaceclaim is first used to establish a refined three-dimensional geometric model for simulating the unsteady heat exchange process of the underground soil heat extraction-storage module, and to refine the three core areas of the double U-shaped buried pipe, backfill material and heat storage soil. The three-dimensional geometric model was meshed using the meshing software Ansys Mesh. The mesh data was then imported into the Fluent solver. Material properties and boundary conditions were set according to the actual working conditions, and the initialization was performed. The time step and number of time steps were also set.

[0016] like Figure 2 The diagram shown is a schematic diagram of the mesh generation result of the buried pipe and the heat storage soil according to the embodiment of the present invention. In the specific implementation, when using Ansys Mesh to mesh the three-dimensional geometric model, only the pipe wall of the double U-shaped buried pipe and the heat storage soil are meshed. Since a simplified and fast calculation method is used for the heat transfer solution of the fluid inside the pipe, this method does not require mesh generation of the fluid domain inside the pipe. Import the grid data into the Fluent solver and set the physical property parameters of the thermal storage soil, backfill material, and double U-shaped buried pipe according to the actual working conditions; A simplified and rapid calculation method is used to solve the flow and heat transfer between the fluid inside the pipe and the wall of the buried pipe. Specifically: By writing a user-defined function (UDF), the average Nusselt number (Nu) of the fluid inside the pipe is calculated using empirical correlations. Then, the convective heat transfer coefficient (h) of the inner wall of the buried pipe is calculated using heat transfer formulas. Specifically, there are two empirical correlations for the average Nusselt number (Nu): the Dittus-Boelter correlation and the Gnielinski correlation. Compared to the Dittus-Boelter correlation, the Gnielinski correlation can calculate Nu over a wider range of Reynolds numbers (Re) and Prandtl numbers (Pr). Since the fluid flow regime is usually transitional to vigorous turbulence, the Gnielinski correlation is chosen as the formula for calculating the average Nu inside the pipe, thus obtaining the convective heat transfer coefficient (h) of the inner wall of the buried pipe. Then, the friction temperature of the fluid inside the pipe is obtained using the heat balance method, and a third type of boundary condition is constructed on the inner wall of the pipe. This simplifies and accelerates the calculation, replacing the traditional turbulence model for solving the heat transfer process inside the pipe, thereby improving computational accuracy and efficiency.

[0017] Among them, the boundary type of the inner wall surface of the buried pipe heat exchanger is the third type of boundary condition, which is represented as: (1) In the above formula, λ is the temperature gradient of the pipe's inner wall, K / m; λ1 is the thermal conductivity of the pipe wall, W / (m·K); h f The convective heat transfer coefficient of the inner wall of the buried pipe is W / (m²). 2 ·K);t w It is the temperature of the inner wall surface of the pipe, K; t f Let K be the friction temperature of the fluid inside the pipe. The core of simplifying and accelerating calculations lies in how to calculate the convective heat transfer coefficient h in equation (1). f and the friction temperature t of the fluid inside the pipe f The solution method is as follows: The average Nusselt number (Nu) of the fluid inside the pipe is calculated using the Gnielinski correlation and is expressed as: (2) Then, the convective heat transfer coefficient h of the inner wall of the buried pipe can be obtained from the following formula (3): (3) Where Nu represents the Nusselt number, characterizing the intensity of convective heat transfer; f is the Darcy friction factor, reflecting flow resistance; Re is the Reynolds number, used to determine the flow state inside the pipe; Pr is the Prandtl number, a physical property parameter of the fluid; and d is the pipe inner diameter, in meters. The formulas for calculating f, Re, and Pr are as follows: (4) (5) (6) Where ρ1 is the fluid density inside the pipe, kg / m³ 3 u is the fluid velocity inside the pipe, m / s; μ is the fluid dynamic viscosity, Pa·s; c p1 It is the isobaric specific heat capacity of the fluid inside the pipe, J / (kg·K); The above formulas are only applicable to forced convection within the pipe. If the soil heat extraction-storage process is paused and the flow velocity inside the buried pipe is 0, then the pipe is in a pure heat conduction state. In this case, the pipe temperature t along the pipe is still calculated using the third type of boundary conditions on the inner wall of the pipe and the structural heat balance method. f The natural convection coefficient h inside the pipe is calculated using the following formula: (7) Where λ2 is the thermal conductivity of the fluid inside the pipe, W / (m·K); D represents the characteristic length, which is the inner diameter of the buried pipe in meters. Calculate the friction temperature t of the fluid inside the pipe. f Using the heat balance method, the internal area of ​​the buried pipe is first divided into several fluid units along the flow direction. Then, the heat balance method is applied to each fluid unit to solve for the fluid temperature. The heat balance of each unit is shown in the following equation (8): (8) Where ΔQ represents the heat change of the fluid unit; Q up The heat flowing in from the upstream boundary; Q down The heat flowing out from the downstream boundary; Q wall This refers to the heat conducted through the wall. As the calculation progresses from time layer n to time layer n+1, formula (8) is further expressed as: (9) Substituting the parameters of the fluid element into equation (9) above, we get: ; (10) in, Let J be the thermal energy of the fluid element i at time n+1. Let J be the thermal energy of fluid element i at time n. For fluid element i at time step Energy flowing in from the upstream boundary, J; For fluid element i at time step The heat energy flowing out from the downstream boundary, J; For fluid element i at time step Heat conducted through the wall, J; V is the volume of the fluid unit, m³. 3 ; Let K be the temperature of the layer at the (n+1)th time in unit i. Let S be the temperature of the nth layer in unit i, in K; and let S be the cross-sectional area of ​​the pipe, in m. 2 ; Let be the fluid-side time step, in seconds; Let K be the temperature of the layer at time n in unit i-1. Let be the temperature of the layer at time n in unit i+1, in K; λ3 is the thermal conductivity of the pipe, in W / (m·K); A i Let m be the area of ​​a mesh on a certain face of the pipe wall corresponding to fluid element i. 2 ; Let K be the node temperature of the mesh. Δd represents the node temperature of the adjacent internal mesh of this surface mesh, in K; Δd represents the distance between two adjacent nodes, in m; For the calculation on the soil side outside the pipe, neglecting the influence of underground seepage, this process is simplified to a pure heat conduction process, and only the energy equation is solved, which is expressed as: (11) In the above formula, λ4 is the thermal conductivity of the soil, W / (m·K); ρ2 is the soil density, kg / m³. 3 ;c p2 The specific heat capacity of soil is J / (kg·K); The soil surface boundary conditions are set to Type III boundary conditions, as follows: (12) In the above formula, λ4 is the thermal conductivity of the soil, W / (m·K); Normal temperature gradient, K / m; h top It is the convective heat transfer coefficient between air and soil, W / (m·K); t air The atmospheric average temperature is K; t top The average temperature of the soil surface, K; The soil is surrounded by an adiabatic boundary, which is a type of boundary condition. (13) The soil bottom boundary is set as a first-type temperature boundary condition, expressed as: (14) C is a constant; Then, horizontal and vertical monitoring sections of the soil area are created to observe temperature cloud maps of the soil layer and the vicinity of the buried pipe, and to study the actual heat exchange process between the soil and the buried pipe at the component level.

[0018] Step 2: For the ground-based solar thermal collector subsystem, ground source heat pump heating subsystem, and building heating terminals, use the system-level instantaneous system simulation program TRNSYS to perform coarse simulation to describe the operation process of each ground-based system at the system level. In this step, such as Figure 3 The diagram shown is a schematic representation of the overall structure of the simulation combining underground refinement and aboveground coarsening according to an embodiment of the present invention. The underground refinement simulation refers to the integration of underground soil heat extraction and storage modules (…). Figure 3 Part ⑤ of the study uses component-level Fluent software for detailed analysis; ground-based coarsening simulation refers to the simulation of ground-based solar thermal collector subsystems, ground source heat pump heating subsystems, building heating terminals, etc. Figure 3 Parts ②, ③, and ① of the study employ system-level TRNSYS software for coarsening analysis; based on this, an interface program for real-time data communication between Fluent and TRNSYS is developed. Figure 3 (Part ④ of the simulation). This achieves a combination of detailed underground simulation and coarse above-ground simulation for ground source heat pump heating systems.

[0019] Specifically, simulation models of each subsystem are built in TRNSYS, and heat load models are designed based on actual operating conditions; Select appropriate operating parameters for solar collectors, hot water storage tanks, water pumps, and heat pump units; Configure the calculation method for each energy integral to be used for subsequent statistical energy data and calculation of system performance indicators, and set the same time step in TRNSYS as the Fluent side.

[0020] like Figure 4 The diagram shown is an interface flowchart for the simulation combining underground refinement and aboveground coarsening according to an embodiment of the present invention. Specifically, a solar thermal collector subsystem is built in TRNSYS, including a weather module, a solar collector, a solar thermal pump, and a hot water storage tank, wherein: The heat collection efficiency parameter in a solar collector is calculated using formula (15): (15) In the above formula, a0 is the interception efficiency; a1 is the first correction coefficient; a2 is the second correction coefficient; T i The inlet temperature of the working fluid in the solar collector is ℃; T a G represents ambient temperature (°C); G represents solar radiation intensity (W / m²). 2 ; A heat pump heating subsystem was built in TRNSYS, including a heat pump assembly, a load-side water pump assembly, a ground-source water pump assembly, and a Type 155 component used to transmit buried pipe inlet data to Fluent and receive underground heat exchange result data from Fluent. In the system studied, the ground-source heat pump is only used for heating and its cooling function is not used. The heating capacity Q of the heat pump assembly is... hp and power P hp The formula for calculation is: (16) (17) In the above formula, CAP0 is the heating / cooling capacity of the unit under rated operating conditions, in kW; P0 is the heating capacity correction factor for the unit under actual operating conditions; P0 is the input power of the unit under rated operating conditions, in kW. This is the input power correction factor under full-load operating conditions of the unit; This is the input power correction factor under partial load operating conditions of the unit; The energy efficiency of the heat pump assembly is obtained according to equations (16) and (17). The expression is: (18) The heat Q absorbed by the heat pump component from the soil ab The formula for calculation is: (19) The actual operation strategy is embedded into the built system, and then the system process is correctly connected. The control process uses the 0 / 1 signals of the components to control the start and stop of each water pump. 1 indicates that the pump is on, and 0 indicates that the pump is off, thus controlling the on / off state of each subsystem. The mathematical model of the component carrying the operation strategy is as follows: (20) In the above formula, T h Indicates the upper limit temperature input, in °C; T l Indicates the lower limit temperature input, in °C; ΔT on Indicates the activation threshold; ΔT off Indicates the threshold for closing; U t-1 Indicates the control state at the previous moment; U t This indicates the current control status.

[0021] Step 3: Through a dedicated software interface program, bidirectional data transmission is performed between Fluent and TRNSYS to achieve a combined simulation of underground refinement and above-ground coarsening for ground source heat pump heating systems.

[0022] In this step, the UDF is compiled and loaded on the Fluent side, and the simulation time of the current time layer and the average temperature of the U-shaped buried pipe outlet are written into the Fluent result file. At the same time, the relevant functions in the UDF are used to pre-read the simulation time of the next time layer and the average temperature data of the U-shaped buried pipe inlet from the TRNSYS result file. The average temperature of the U-shaped buried pipe inlet of the corresponding time layer is applied to the buried pipe inlet boundary in Fluent, and the simulation calculation for the next time layer continues. On the TRNSYS side, a script was written using MATLAB to output and read simulation time and temperature data for TRNSYS. TRNSYS correctly called MATLAB to run the script through component Type155. The input parameters of component Type155 are the average temperature and flow rate at the inlet of the U-shaped buried pipe, and the output parameters are the average temperature and flow rate at the outlet of the U-shaped buried pipe. The MATLAB script file controls TRNSYS to output the inlet parameters of component Type155 to the TRNSYS result file for Fluent to read, provides Fluent with new pipe inlet boundary conditions, and waits for Fluent to calculate the average temperature data of the buried pipe outlet in this time layer. After Fluent completes the calculation, it outputs the relevant data to the Fluent result file. TRNSYS calls MATLAB to access the Fluent results file to read the pipe outlet temperature average data corresponding to the simulation time, and maps it to the outlet of component Type155, realizing real-time bidirectional transmission of Fluent and TRNSYS simulation data.

[0023] In the specific implementation, two data files are first created based on the calculation results of Fluent and TRNSYS, namely the Fluent result file and the TRNSYS result file. In the following description, file a refers to the Fluent result file, which contains the simulation time and the outlet temperature data of the buried pipe; file b refers to the TRNSYS result file, which contains the simulation time, the average inlet temperature of the buried pipe, and the flow rate of the medium in the pipe. On the Fluent side, data is first read from file b and assigned to the boundary of the U-shaped buried pipe inlet for iterative calculation. Then, the U-shaped buried pipe outlet data is obtained and output to file a. Specifically, a `Read-input-file(time, temperature, flow rate)` function is constructed in the UDF to read the time, temperature, and flow rate data of the U-shaped buried pipe in file `b`. A `while` loop is embedded within this `Read-input-file` function: at specific simulation times, it searches file `b` for the time value that matches the current simulation time. If the value exists in file `b`, it reads the buried pipe inlet temperature data from the line containing that time value, and then reads the flow rate data from that line, calculating it as velocity data. At this point, the code exits the loop. The `DEFINE_ADJUST` macro then applies the read temperature and flow rate data to the buried pipe inlet boundary, and Fluent performs iterative calculations based on the new inlet boundary. After completing the specific calculations... After the time-step calculation, the DEFINE_EXECUTE_AT_END macro is used to output the current simulation time and the buried pipe outlet temperature data to file a; then the Read-input-file function continues to retrieve the buried pipe inlet data from the next time layer from TRNSYS in file b; when a new boundary value from TRNSYS is retrieved, the Read-input-file function reads it in, and then the DEFINE_ADJUST macro is used to update the boundary conditions, and Fluent continues the iterative calculation; in this way, the results data of TRNSYS and Fluent are coupled and interact within the same time layer, realizing the co-simulation between the software.

[0024] On the TRNSYS side, a MATLAB script file was written to output and read key data of the U-shaped buried pipe inlet and outlet. TRNSYS calls MATLAB through component Type155 to run this script. The overall operating logic of TRNSYS is as follows: First, output the inlet data of the U-shaped buried pipe for Fluent to read, so that it can perform iterative calculations based on the new boundary. After Fluent completes the calculation, TRNSYS reads the outlet temperature data of the U-shaped buried pipe in file a, maps it to the outlet of component Type155, and thus connects the system process. Specifically, the input parameters for component Type155 are the average temperature and flow rate of the U-shaped buried pipe inlet. In the constructed MATLAB script, the if statement (if mod(time, 900)) is used, which means that after each specific time (900s) calculation, the current simulation time, the temperature and flow rate of the U-shaped buried pipe inlet are output to file b, thus outputting the current simulation time and the two input parameters of component Type155. After that, in order to read the outlet temperature data of the U-shaped buried pipe at the same time layer from the Fluent calculation, a composite loop control conditional expression is constructed: while isempty(idx)&&retry-count<max-retries, and its loop logic is: as long as the matching data is not found and the maximum number of retries is not exceeded, the loop body will continue to be executed; use this composite loop control conditional expression to retrieve the Fluent result data at the same time layer in file a, and the retrieval method is: Retrieve the time value in file a that is the same as the current simulation time. If the time value is retrieved, then read the outlet temperature data of the U-shaped buried pipe in the row where the time value is located in file a, and map it to the outlet of component Type155 as the outlet temperature data of the buried pipe in the soil heat extraction-thermal storage module on the TRNSYS side; if the time value that is the same as the current simulation time is not retrieved, repeat the retrieval until the corresponding data is retrieved. Due to the characteristics of the composite loop control conditional expression, when the corresponding result data from Fluent in file a is not retrieved, the code cannot jump out of the loop of this conditional statement, causing the TRNSYS calculation to pause, achieving the effect that TRNSYS waits for Fluent to complete the calculation, thereby ensuring the coupling and interaction of the result data of the two at the same time layer and realizing the co-simulation between software.

[0025] It should be noted that the content not described in detail in the embodiments of the present invention belongs to the prior art well-known to those skilled in the art.

[0026] In the embodiments based on this method, as Figure 5 shown is the schematic diagram of the comparison of the cumulative soil heat extraction during the entire heating season and the thermal storage season of the method described in the embodiments of the present invention. As Figure 6 shown is the schematic diagram of the comparison of the cumulative thermal storage. Comparing the final integral result with the pure TRNSYS simulation result, the difference is only 1.1% and 2.33%, indicating that using the simulation method proposed by the present invention for simulation can accurately reflect the actual heat exchange of underground components, verifying the accuracy of this method.

[0027] In summary, the method described in the embodiments of the present invention can, on the one hand, perform above-ground system-level simulation on the solar seasonal thermal storage-ground source heat pump coupling heating system and at the same time take into account the refined simulation of underground soil heat extraction-thermal storage components; on the other hand, it can also be applied to any multi-scale simulation scenario involving the combination of system simulation and refined simulation of local components, and has good versatility and adaptability.

[0028] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims. The information disclosed in the background section is intended only to enhance the understanding of the overall background technology of the present invention and should not be construed as an admission or implication in any way that such information constitutes prior art known to those skilled in the art.

Claims

1. A simulation method combining underground refinement and above-ground coarsening for heating systems, characterized in that, The method includes: Step 1: For the underground soil heat extraction and storage module, use the component-level commercial computational fluid dynamics software package Fluent to perform a detailed simulation of the underground soil heat extraction and storage module, accurately describing the actual heat exchange process between the buried pipe and the soil at the component level. Step 2: For the ground-based solar thermal collector subsystem, ground source heat pump heating subsystem, and building heating terminals, use the system-level instantaneous system simulation program TRNSYS to perform coarse simulation to describe the operation process of each ground-based system at the system level. Step 3: Through a dedicated software interface program, bidirectional data transmission is performed between Fluent and TRNSYS to achieve a combined simulation of underground refinement and above-ground coarsening for ground source heat pump heating systems.

2. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 1, characterized in that, In step 1, First, a refined three-dimensional geometric model was established using the three-dimensional solid direct modeling software Spaceclaim to simulate the unsteady heat exchange process of the underground soil heat extraction-storage module, and the three core areas of double U-shaped buried pipe, backfill material and heat storage soil were characterized in detail. The three-dimensional geometric model was meshed using the meshing software Ansys Mesh. The mesh data was then imported into the Fluent solver. Material properties and boundary conditions were set according to the actual working conditions, and the initialization was performed. The time step and number of time steps were also set.

3. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 2, characterized in that, In step 1, When using Ansys Mesh to mesh a 3D geometric model, only the pipe wall of the double U-shaped buried pipe and the heat storage soil are meshed, and there is no need to mesh the fluid domain inside the pipe. Import the grid data into the Fluent solver and set the physical property parameters of the thermal storage soil, backfill material, and double U-shaped buried pipe according to the actual working conditions; A simplified and rapid calculation method is used to solve the flow and heat transfer between the fluid inside the pipe and the wall of the buried pipe. Specifically: By writing a user-defined function (UDF), the average Nusselt number Nu of the fluid inside the pipe is calculated using empirical correlations. Then, the convective heat transfer coefficient h of the inner wall of the buried pipe is calculated using heat transfer formulas. Finally, the friction temperature of the fluid inside the pipe is obtained using the heat balance method, and the third type of boundary conditions of the inner wall of the pipe are constructed to achieve simplified and rapid calculation. Among them, the boundary type of the inner wall surface of the buried pipe heat exchanger is the third type of boundary condition, which is represented as: (1) In the above formula, λ is the temperature gradient of the pipe's inner wall, K / m; λ1 is the thermal conductivity of the pipe wall, W / (m·K); h f The convective heat transfer coefficient of the inner wall of the buried pipe is W / (m²). 2 ·K);t w It is the temperature of the inner wall surface of the pipe, K; t f Let K be the friction temperature of the fluid inside the pipe. The core of simplifying and accelerating calculations lies in how to calculate the convective heat transfer coefficient h in equation (1). f and the friction temperature t of the fluid inside the pipe f The solution method is as follows: The average Nusselt number (Nu) of the fluid inside the pipe is calculated using the Gnielinski correlation and is expressed as: (2) Then, the convective heat transfer coefficient h of the inner wall of the buried pipe can be obtained from the following formula (3): (3) Where Nu represents the Nusselt number, characterizing the intensity of convective heat transfer; f is the Darcy friction factor, reflecting flow resistance; Re is the Reynolds number, used to determine the flow state inside the pipe; Pr is the Prandtl number, a physical property parameter of the fluid; and d is the pipe inner diameter, in meters. The formulas for calculating f, Re, and Pr are as follows: (4) (5) (6) Where ρ1 is the fluid density inside the pipe, kg / m³ 3 u is the fluid velocity inside the pipe, m / s; μ is the fluid dynamic viscosity, Pa·s; c p1 It is the isobaric specific heat capacity of the fluid inside the pipe, J / (kg·K); If the soil heat extraction-storage process is suspended and the flow velocity inside the buried pipe is 0, then the pipe is in a pure heat conduction state. The friction temperature t of the fluid inside the pipe can still be solved using the third type of boundary conditions on the inner wall of the pipe and the structural heat balance method. f The natural convection coefficient h inside the pipe is calculated using the following formula: (7) Where λ2 is the thermal conductivity of the fluid inside the pipe, W / (m·K); D represents the characteristic length, which is the inner diameter of the buried pipe in meters. Calculate the friction temperature t of the fluid inside the pipe. f Using the heat balance method, the internal area of ​​the buried pipe is first divided into several fluid units along the flow direction. Then, the heat balance method is applied to each fluid unit to solve for the fluid temperature. The heat balance of each unit is shown in the following equation (8): (8) Where ΔQ represents the heat change of the fluid unit; Q up The heat flowing in from the upstream boundary; Q down The heat flowing out from the downstream boundary; Q wall This refers to the heat conducted through the wall. As the calculation progresses from time layer n to time layer n+1, formula (8) is further expressed as: (9) Substituting the parameters of the fluid element into equation (9) above, we get: ； (10) in, Let J be the thermal energy of the fluid element i at time n+1. Let J be the thermal energy of fluid element i at time n. For fluid element i at time step Energy flowing in from the upstream boundary, J; For fluid element i at time step The heat energy flowing out from the downstream boundary, J; For fluid element i at time step Heat conducted through the wall, J; V is the volume of the fluid unit, m³. 3 ; Let K be the temperature of the layer at the (n+1)th time of unit i. Let S be the temperature of the nth layer in unit i, in K; and let S be the cross-sectional area of ​​the pipe, in m. 2 ; Let be the fluid-side time step, in seconds; Let K be the temperature of the layer at time n in unit i-1. Let be the temperature of the layer at time n in unit i+1, in K; λ3 is the thermal conductivity of the pipe, in W / (m·K); A i Let m be the area of ​​a mesh on a certain face of the pipe wall corresponding to fluid element i. 2 ; Let K be the node temperature of the mesh. Δd represents the node temperature of the adjacent internal mesh of this surface mesh, in K; Δd represents the distance between two adjacent nodes, in m; For the calculation on the soil side outside the pipe, neglecting the influence of underground seepage, this process is simplified to a pure heat conduction process, and only the energy equation is solved, which is expressed as: (11) In the above formula, λ4 is the thermal conductivity of the soil, W / (m·K); ρ2 is the soil density, kg / m³. 3 c p2 The specific heat capacity of soil is J / (kg·K); The soil surface boundary conditions are set to Type III boundary conditions, as follows: (12) In the above formula, λ4 is the thermal conductivity of the soil, W / (m·K); For the normal temperature gradient, K / m; h top It is the convective heat transfer coefficient between air and soil, W / (m·K); t air The atmospheric average temperature is K; t top The average temperature of the soil surface, K; The soil is surrounded by an adiabatic boundary, which is a type of boundary condition. (13) The soil bottom boundary is set as a first-type temperature boundary condition, expressed as: (14) C is a constant; Then, horizontal and vertical monitoring sections of the soil area are created to observe temperature cloud maps of the soil layer and the vicinity of the buried pipe, and to study the actual heat exchange process between the soil and the buried pipe at the component level.

4. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 1, characterized in that, In step 2, simulation models of each subsystem are built in TRNSYS, and thermal load models are designed based on actual operating conditions. Select appropriate operating parameters for solar collectors, hot water storage tanks, water pumps, and heat pump units; Configure the calculation method for each energy integral to be used for subsequent statistical energy data and calculation of system performance indicators, and set the same time step in TRNSYS as the Fluent side.

5. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 4, characterized in that, In step 2, a solar thermal collector subsystem is specifically built in TRNSYS, including a weather module, a solar collector, a solar thermal pump, and a hot water storage tank, wherein: The heat collection efficiency parameter in a solar collector is calculated using formula (15): (15) In the above formula, a0 is the interception efficiency; a1 is the first correction coefficient; a2 is the second correction coefficient; T i The inlet temperature of the working fluid in the solar collector is ℃; T a G represents ambient temperature (°C); G represents solar radiation intensity (W / m²). 2 ; A heat pump heating subsystem is built in TRNSYS, including a heat pump assembly, a load-side water pump assembly, a ground-source water pump assembly, and a Type 155 component used to transmit buried pipe inlet data to Fluent and receive underground heat exchange result data from Fluent; the heating capacity Q of the heat pump assembly is... hp and power P hp The formula for calculation is: (16) (17) In the above formula, CAP0 is the heating / cooling capacity of the unit under rated operating conditions, in kW; P0 is the heating capacity correction factor for the unit under actual operating conditions; P0 is the input power of the unit under rated operating conditions, in kW. This is the input power correction factor under full-load operating conditions of the unit; This is the input power correction factor under partial load operating conditions of the unit; The energy efficiency of the heat pump assembly is obtained according to equations (16) and (17). The expression is: (18) The heat Q absorbed by the heat pump component from the soil ab The formula for calculation is: (19) The actual operation strategy is embedded into the built system, and then the system process is correctly connected. The control process uses the 0 / 1 signals of the components to control the start and stop of each water pump. 1 indicates that the pump is on, and 0 indicates that the pump is off, thus controlling the on / off state of each subsystem. The mathematical model of the component carrying the operation strategy is as follows: (20) In the above formula, T h Indicates the upper limit temperature input, in °C; T l Indicates the lower limit temperature input, in °C; ΔT on Indicates the activation threshold; ΔT off Indicates the threshold for closing; U t-1 Indicates the control state at the previous moment; U t This indicates the current control status.

6. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 1, characterized in that, In step 3, the UDF is compiled and loaded on the Fluent side. The simulation time of the current time layer and the average temperature of the U-shaped buried pipe outlet are written into the Fluent result file. At the same time, the relevant functions in the UDF are used to pre-read the simulation time of the next time layer and the average temperature data of the U-shaped buried pipe inlet from the TRNSYS result file. The average temperature of the U-shaped buried pipe inlet of the corresponding time layer is applied to the buried pipe inlet boundary in Fluent, and the simulation calculation for the next time layer continues. On the TRNSYS side, a script was written using MATLAB to output and read simulation time and temperature data for TRNSYS. TRNSYS correctly called MATLAB to run the script through component Type155. The input parameters of component Type155 are the average temperature and flow rate at the inlet of the U-shaped buried pipe, and the output parameters are the average temperature and flow rate at the outlet of the U-shaped buried pipe. The MATLAB script file controls TRNSYS to output the inlet parameters of component Type155 to the TRNSYS result file for Fluent to read, provides Fluent with new pipe inlet boundary conditions, and waits for Fluent to calculate the average temperature data of the buried pipe outlet in this time layer. After Fluent completes the calculation, it outputs the relevant data to the Fluent result file. TRNSYS calls MATLAB to access the Fluent results file to read the pipe outlet temperature average data corresponding to the simulation time, and maps it to the outlet of component Type155, realizing real-time bidirectional transmission of Fluent and TRNSYS simulation data.

7. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 6, characterized in that, In step 3, two data files are first created based on the calculation results of Fluent and TRNSYS, namely the Fluent result file and the TRNSYS result file. In the following description, file a refers to the Fluent result file, which contains the simulation time and the outlet temperature data of the buried pipe; file b refers to the TRNSYS result file, which contains the simulation time, the average inlet temperature of the buried pipe, and the flow rate of the medium in the pipe. On the Fluent side, data is first read from file b and assigned to the boundary of the U-shaped buried pipe inlet for iterative calculation. Then, the U-shaped buried pipe outlet data is obtained and output to file a. Specifically, a Read-input-file function is constructed in the UDF to read the time, U-shaped buried pipe inlet temperature, and flow rate data from file b. A while conditional loop is embedded in this Read-input-file function: at each specific simulation time, the time value that is the same as the current simulation time is searched in file b. If the value exists in file b, the buried pipe inlet temperature data in the line containing the time value is read, and the flow rate data in the same line is read and calculated as flow velocity data. At this time, the code exits the conditional loop. The DEFINE_ADJUST macro then applies the read temperature and flow data to the inlet boundary of the buried pipe, and Fluent performs iterative calculations based on the new inlet boundary. After completing the calculation at a specific time step, the DEFINE_EXECUTE_AT_END macro is used to output the current simulation time and the buried pipe outlet temperature data to file a; then the Read-input-file function continues to retrieve the buried pipe inlet data from the next time layer from TRNSYS in file b; when a new boundary value from TRNSYS is retrieved, the Read-input-file function reads it in, and then the DEFINE_ADJUST macro is used to update the boundary conditions, and Fluent continues the iterative calculation; This ensures that the results data from TRNSYS and Fluent are coupled and interact within the same time layer, enabling collaborative simulation between the software.

8. The simulation method combining underground refinement and above-ground coarsening for heating systems according to claim 7, characterized in that, In step 3, on the TRNSYS side, a MATLAB script file is written to output and read key data of the U-shaped buried pipe inlet and outlet. TRNSYS calls MATLAB through component Type155 to run this script. The overall operating logic of TRNSYS is as follows: First, output the inlet data of the U-shaped buried pipe for Fluent to read, so that it can perform iterative calculations based on the new boundary. After Fluent completes the calculation, TRNSYS reads the outlet temperature data of the U-shaped buried pipe in file a, maps it to the outlet of component Type155, and thus connects the system process. Specifically, the input parameters of component Type155 are the average temperature and flow rate of the U-shaped buried pipe inlet. In the constructed MATLAB script, the if statement is used, that is, after each specific time is calculated, the current simulation time, the temperature and flow rate of the U-shaped buried pipe inlet are output to file b, and the current simulation time and the two input parameters of component Type155 are output. Then, in order to read the outlet temperature data of the U-shaped buried pipe from the same time layer calculated by Fluent, a compound loop control condition expression is constructed. Its loop logic is: as long as no matching data is found and the maximum number of retries has not been exceeded, the loop body continues to execute. This compound loop control condition expression is then used to retrieve the Fluent result data from the same time layer in file a. The retrieval method is as follows: Search file a for a time value that matches the current simulation time. If the time value is found, read the U-shaped buried pipe outlet temperature data in the line containing the time value in file a and map it to the outlet of component Type155 as the buried pipe outlet temperature data in the TRNSYS side soil heat extraction-storage module. If no time value matches the current simulation time, repeat the search until the corresponding data is found. Due to the characteristics of the compound loop control condition expression, the code cannot exit the condition statement loop when the corresponding result data from Fluent in file a is not retrieved, causing TRNSYS calculation to pause. This achieves the effect of TRNSYS waiting for Fluent to complete the calculation, thereby ensuring that the result data of the two are coupled and interact within the same time layer, realizing collaborative simulation between the software.

Images