This paper discusses the advantages of medium-deep geothermal energy and describes the structural principles of coaxial pipe and U-type deep borehole heat exchangers (BHEs). The heat transfer performances of the two types of deep BHEs are compared. The preconditions and heat transfer mechanism are explained to reveal the substance of heat transmission. Energy equations are established for circulating fluid, grout, steel pipe and underground media, and the implications of related parameters are discussed. The heat transfer performances of deep BHEs are analyzed, the heat extractions and the temperatures of circulating fluid and rock soils are investigated, and related elements influencing these parameters are explored. Therefore, the changes of heat absorption or temperatures with the correlative elements are shown, and comparisons are made to demonstrate the differences of the two types of deep BHEs. The heat transfer performance of a U-type deep BHE is better than that of a coaxial pipe deep BHE. The comparative analysis of coaxial pipe and U-type deep BHEs enables the selection of BHEs according to a project's actual situation. This is beneficial to the rational utilization of medium-deep geothermal energy, and it promotes the development of heating technology used in geothermal energy applications.

本文讨论了中深地热能的优势，并描述了同轴管和 U 型深埋管换热器 (BHE) 的结构原理。比较了两种深部 BHE 的传热性能。解释了先决条件和传热机制，以揭示传热的实质。建立了循环流体、灌浆、钢管和地下介质的能量方程，并讨论了相关参数的含义。分析了深部BHE的传热性能，研究了循环流体和岩土的热提取和温度，并探讨了影响这些参数的相关因素。因此，显示了吸热或温度随相关元素的变化，并进行比较以证明两种类型的深 BHE 的差异。U型深BHE的传热性能优于同轴管深BHE。同轴管与U型深埋管换热器对比分析，可根据工程实际情况选择埋管换热器。这有利于中深层地热能的合理利用，促进地热能应用采暖技术的发展。