As a safe and efficient source of clean energy, medium-deep geothermal energy has been widely used in building heating. The medium and deep borehole heat exchanger (MDBHE) is an essential apparatus for extracting medium-depth geothermal energy, which can be classified into the medium-deep coaxial borehole heat exchanger (MDCBHE) and the medium-deep U-type borehole heat exchanger (MDUBHE). During the heating period, multiple factors can affect the thermal performance of MDBHE. Therefore, to enhance the performance of MDBHE, it is crucial to conduct research on multiple factors. Nevertheless, most extant studies are predicated on a limited number of influencing factors, and more comprehensive and systematic research needs to be done on the factors of MDBHE. Based on this, the paper comprehensively reviews the current research on the effects of multiple factors on the heat extraction of MDBHE from three perspectives: operational conditions, wellbore structural properties, and geothermal properties, and clarifies the mechanisms of their influences. In addition, the effects of each factor in different studies are compared to obtain the optimal operating or design values. The heating characteristics of different MDBHE types are discussed, and the feasibility of using super-long gravity heat pipes for heating is also analyzed. Furthermore, an outlook for future research is presented in terms of the analysis of coupled system performance and economics, the influence of meteorological parameters on the system, the types of working fluids in operation, and multi-energy complementarity. This paper can guide the design and practice of MDBHE.

中文翻译：

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多因素对深埋管换热器热性能影响的系统综述


中深层地热能作为安全、高效的清洁能源，已广泛应用于建筑采暖。中深埋管换热器（MDBHE）是提取中埋地热能的重要设备，可分为中深同轴埋管换热器（MDCBHE）和中深U型埋管换热器（MDCBHE）。穆杜布赫）。在供暖期间，多种因素会影响MDBHE的热性能。因此，为了提高MDBHE的性能，对多种因素进行研究至关重要。然而，现有研究大多基于有限的影响因素，对于MDBHE的影响因素还需要进行更全面、系统的研究。在此基础上，从作业条件、井筒结构特性、地热特性三个角度，综合评述了多因素对MDBHE排热影响的研究现状，并阐明了其影响机制。此外，还比较不同研究中每个因素的影响，以获得最佳操作或设计值。讨论了不同MDBHE类型的加热特性，并分析了采用超长重力热管加热的可行性。此外，还从耦合系统性能与经济性分析、气象参数对系统的影响、运行工质类型、多能互补等方面对未来的研究进行了展望。本文可以指导MDBHE的设计和实践。