Research On Thermal Response Model And Heat Transfer Analysis Of Vertical Ground Heat Exchangers

Ground source heat pump(GSHP)is a kind of energy-saving and efficient air-condition system,which is able to utilize shallow geothermal resources,then can be used for heating and cooling the building.The long-term heat transfer analysis of the geothermal heat exchangers(GHEs)is the foundation of the research of the ground source heat pump system.However the existing heat transfer analysis model is more complex and the computation speed is quite slower in long-term hourly simulation.In this paper,we introduce more efficient and accurate thermal response models for the long-term heat transfer simulation of the geothermal heat exchangers.Then the validity of the introduced models have been verified by experimental data.The analysis of the geothermal heat exchangers is usually divided into two regions with the wall of borehole,including the inner region of the borehole and the outside of the borehole.For the heat transfer model in borehole,the quasi three-dimensional heat transfer model and the optimal p-linear nondimensional average temperature can describe the borehole resistance more accurately.For the heat transfer model outside the borehole wall,the long-term heat transfer performance of the GHEs can be simulated accurately by finite line-source model.By improving the existing line heat source model,the new thermal response model not only guarantee simulation precision but also improve the simulation speed.Combining with the virtual heat source method and Green's function,this paper analyzes the finite line-source model which considers the borehole depth and the H-function of the thermal response factor to slove the borehole wall temperature.Then the improved h-function is obtained by implement segmentation simulation of borehole and the accuracy of the h-function and the improved h-function model is verified by programming simulation.On the basis of single bore hole,three boundary conditions are introduced to solve the multiple borehole wall temperature response multiple borehole under varying loads.The difference of temperature response of the simulated multi-drilled borehole wall with the improved h-function under three boundary conditions is discussed respectively.In practical project,the effect of heat flux on geothermal heat exchangers varies over time.In this paper,we proposed a new thermal response factors(referred to as ?-function)to calculate the ground temperature response of bore field to a unit rectangular heat pulse.In order to improve the computational efficiency of the model,the Fast Fourier transform(FFT algorithm)is introduced to reconstruct the convolution in ?-function,which greatly improves the computational speed.The computational accuracy and time of the thermal response models(h-function,8-function)are compared systematically.The new models proposed in this paper were verified by experimental data.The results of comparison show that,the simulation results are in good agreement with experimental data.