A novel 2-D equivalent numerical model of helix energy pile based on heat transfer characteristics of internal heat convection

Numerical modeling has been widely used to simulate the heat transfer of ground heat exchanger (GHE), However, there is a lack of analysis and comparison of different models and methods, for helix energy pile, there is a lack of an efficient and accurate numerical model to study the complex heat transfer problems. In this paper, taking a novel truncated cone helix energy pile (CoHEP) as the object, a two-dimensional(2-D) equivalent heat conduction model considering the heat transfer characteristics of the heat convection in the buried pipe was established, at the same time, a three-dimensional(3-D) full scale model and a 2-D ring coils model were established. By comparing the simulation results of three numerical models with the experimental results under the same conditions, the effects and suggestions of meshing on different models, the model characteristics and main error sources of different models were analyzed. The long-term and short-term simulation results and temperature distribution characteristics of different models were further analyzed. The study shows that the 3-D model has the highest accuracy in the simulation process, but the simulation efficiency is low, and it is easy to be affected by meshing. The 2-D ring coils model has high simulation efficiency, but the long-term simulation error is large, and the thermal influence radius of the pipe is smaller than the actual situation. For the 2-D equivalent model, the simulation error is small, and the thermal influence radius is close to those of the 3-D full scale model, and the effect of long-term simulation is obviously better than that of the 2-D ring coils model. The results indicate that the 2-D equivalent model effectively improves the simulation accuracy of the 2-D heat conduction numerical model, it can obtain the temperature distribution inside and outside the buried pipe which is closer to the actual situation with less calculation and higher simulation accuracy.