An Analytical Model For Energy Piles In Ground Source Heat Pump System And It’s Application

Ground-source heat pump systems have been vigorously promoted due to their energy saving and environmental protection advantages.For traditional borehole heat exchangers,technical codes and researches on heat transfer characteristics are very specific and in-depth.However,for the energy pile,related research needs to be deepened and lacks specific implementation specifications.There is no clear stipulation on the thermal response test and system design process of energy piles.One of the application bottlenecks of pile-buried pipe heat exchangers is that the energy pile has a large diameter and the long-term influence of transient heat transfer in the hole.At present,there is no effective calculation model for the heat transfer process in composite medium.In this paper,a two-dimensional analytical model suitable for large-diameter pile-buried tube heat exchangers: a composite line heat source model is proposed through in-depth analysis of heat transfer characteristics of energy pile.The model consists of three existing one-dimensional analytical models,which make up for the shortcomings of the existing homogeneous models and surface heat source models.At the same time,a hybrid algorithm of numerical and analytical is proposed to further improve the model calculation speed.By comparison with the two-dimensional numerical model,the reliability of the new model in simulating energy pile cases with various input parameters is verified.Based on the experimental data provided in the literature,the new model is further compared with models proposed by other researchers to verify the accuracy of the new model in short-term simulations.Finally,based on energy cases,the new model is compared with a typical composite model to prove the superiority of the new model in modelling energy pile.According to the characteristics of the new model,this paper proposes a four-parameter estimation method,a stepwise four-parameter estimation method,and a two-parameter estimation method for energy pile thermal response test(TRT).Based on virtual TRTs,the reliability of the three parameter estimation methods was proved,and the minimum test duration for the two-parameter estimation method was further studied.In terms of model application,this paper uses the new model to analyze the in-situ measurements of energy pile TRT,and compares it with the models proposed by other researchers to prove the accuracy of the model for parameter estimation.In addition,the new model was used to calculate the unit heat transfer rate of the energy pile under design conditions,and compares the results of commonly used models,proving the feasibility of the new model in design purpose.This paper proposes a new composite-medium line-source model,which makes up for the shortcomings of the current heat transfer for energy piles,discusses the application of the new model in the energy piles,and provides the design of ground-source heat pump systems with a feasible practical calculation model,which is superior to existing methods.