A novel truncated cone helix energy pile: Modelling and investigations of thermal performance

Abstract Cylinder helix energy pile (CyHEP) is a new popular ground heat exchanger which have the advantages of large heat exchange rate and low initial cost. However, severe thermal interferences exist in the radial and generatrix directions duo to the limited thermal heat capacity of pile and small ratio between coils pitch and radius of pile. Therefore, a novel truncated cone helix energy pile (CoHEP) is presented to weaken the thermal interferences and improve the heat transfer efficiency. Further, an analytical solution model for CoHEP is proposed based on Green’s function to discuss the dynamic characteristics of thermal interferences and heat transfer performance. A laboratory experiment is carried out to validate the presented model. The results indicate that the generatrix thermal interference in the bottom of the novel energy pile is significantly weakened and the radius thermal interference in the top of the novel energy pile is also weakened. Therefore, the heat transfer of the novel energy pile is enhanced compared with CyHEP and better performance of novel energy pile can be obtained by setting bigger cone angle. Besides, the thermal response characteristics of helix energy piles are discussed under the influences of dynamic load and the results show that the average temperature rise on the pipe wall of CoHEP is lower than that of CyHEP in the period of heat rejections while the average temperature of CoHEP is higher than CyHEP in the period of heat extraction. It is indicated that the energy efficiency of ground source heat pump coupled with CoHEP is higher than that coupled with the popular CyHEP.