| Trans-seasonal soil heat storage system is a valid methodology to adjust the inhomogeneous distribution of solar energy.By injecting the solar thermal energy to underground in spring,summer,autumn and re-using it in winter,the clean heating without coal is achieved.With the development of computer technology,numerical simulation method has been widely used in the investigation of trans-seasonal soil heat storage system.To overcome the shortcomings,including complex governing equations,high mesh quantity requirement and long computational time due to the small time step,of traditional simulation method,an efficient simplified simulation method for solar energy trans-seasonal soil heat storage system is proposed in this work.Based on this method,the“Unit-System”intergrated simulation method is built to uncover the influencing factors on system capability.In addition,a multi-objective optimization design method for solar energy trans-seasonal soil heat storage system is put forward by integrating this numerical simulation method with intelligent algorithm.The optimum design parameters is obtained at last.Firstly,a simulation model on the borehole heat exchangers(BHEs)of solar energy trans-seasonal soil heat storage system is established.Based on Fluent software plantform,the third boundary condition inside BHEs is defined by obtaining the convective heat transfer coefficient via Gnielinski correlation and fluid temperature distribution along the tube via heat balance method.Based on above,an efficient simplified simulation method for solar energy trans-seasonal soil heat storage system is proposed and the simulation of flow and heat transfer inside BHE by traditional simulation method is replaced.The efficient simplified simulation method not only could obtain the accurate results with less mesh and higher accuracy and computational efficiency,but also is suitable for complex conditions and large time step size.Secondly,the“Unit-System”intergrated simulation method for solar energy trans-seasonal soil heat storage system is built based on the simplified simulation method for key equipment and energy balance between subsystems.The accuracy of this method is verified by comparing with experimental results.The influencing factors on soil temperature rise and system coefficient of performance(COP)are analyzed with the“Unit-System”intergrated simulation method.Results show that the solar collector area has a dominating influence on soil temperature rise and system COP and provides the guidance for the following multi-objective system optimization design.Finally,the prediction model on system COP and soil temperature rise based on support vector machine(SVM)method is established by integrating above numerical simulation method and intelligent algorithm.The multi-objective optimization design for solar energy trans-seasonal soil heat storage heating system is carried out with the combination of prediction model and the annual cost formula as the objective function of NSGAⅡalgorithm.The optimum design parameters for the system are:solar collector area 119m~2,heat storage water tank volume 3m~3,heat storage temperature 321K.With these parameters,the final COP is 3.85,the annual cost is 14000 yuan and the soil temperature rise is 3.23K.This work provides an effective approach for the further study on solar energy trans-seasonal soil heat storage heating system and is of great meaning to engineer practice. |
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