Deep borehole heat exchanger (DBHE) based ground source heat pump (GSHP) is a promising system for geothermal energy application in medium-deep layer. In this study, DBHE with non-uniform pipe insulation is proposed and numerically investigated. An effective analytical model is built based on segmented finite line-source method and a newly derived water heat transfer model. The year-round field test data are used for model verification. In-depth analyses are given to a comparison between the uniform and non-uniform insulation cases in both heating and cooling modes, and sensitivity analysis on non-uniformity of insulation. A orthogonal test is conducted for energy performance evaluation and optimization. It is found that DBHE with non-uniform insulation can outperform the one with full insulation in cooling mode, which offers new insights. In addition, an optimum insulation length can be identified through the non-uniformity analysis on insulation. It shows that the order of influence factor is heating season duration ratio, flow rate of working fluid, material thermal resistance non-uniformity of the center pipe, pipe sizing ratio, borehole depth, and insulation length non-uniformity of the center pipe. By choosing the proper system design parameters, the system energy saving could be up to 21.8%.

基于深孔换热器（DBHE）的地源热泵（GSHP）是用于中深层地热能的有前途的系统。在这项研究中，提出了不均匀管道保温的DBHE并进行了数值研究。基于分段有限线源法和新推导的水热传递模型，建立了有效的分析模型。全年的现场测试数据用于模型验证。深入分析了在加热和冷却模式下均匀和不均匀绝缘情况之间的比较，以及对绝缘不均匀性的敏感性分析。进行正交测试以评估和优化能源性能。发现在冷却模式下，具有不均匀绝缘的DBHE可以胜过具有完全绝缘的DBHE，这提供了新的见解。另外，可以通过绝缘的不均匀性分析来确定最佳绝缘长度。结果表明，影响因素的顺序为加热季节持续时间比率，工作流体的流量，中心管的材料热阻不均匀性，管道尺寸比，钻孔深度和中心管的保温长度不均匀性。通过选择适当的系统设计参数，系统节能可达21.8％。