A numerical analysis of the heat transfer characteristics of a vertical borehole heat exchanger as used in ground-coupled heat pump (GCHP) systems is performed to investigate the effects of adding micro-encapsulated, paraffin-based phase-change material (PCM) into the borehole grout. As with any thermal energy storage scheme, its purpose is to reduce the size of equipment and devices required to meet peak loads, and thus the purpose of PCM in this study is to dampen peak temperature response of the borehole, and potentially allow for reduction in design borehole length, and therefore cost, of the borehole array. A parametric study of the PCM thermal properties was conducted to establish design recommendations for the vertical heat exchange borehole grout. Results of this study show that adding PCM into the borehole does not always improve the overall performance of the GCHP system; rather, it could deteriorate the system performance if the PCM thermal properties and melt temperature are not correctly chosen. An optimum mass of PCM exists for borehole grout due to the competing factors of PCM thermal conductivity and its latent heat capacity, but to be effective, the PCM thermal conductivity should be approximately equivalent to that of the grout material. Further, the optimal melt temperature of the PCM was found to be that which results in almost all of the PCM mass to change phase at the time of peak load, and that temperature was found to be about midway between the undisturbed ground temperature and the peak design heat pump entering fluid temperature. The potential reduction in the required BHE-length due to optimal addition of paraffin-based, micro-encapsulated PCM in borehole grout was found to be up to 7% in this study, but this length reduction does not guarantee a reduction in the overall cost of the system owing to the current relatively high cost of the PCM. Thus, from an economic standpoint, the results of this work suggest that enhancing the grout thermal conductivity is currently more cost-effective than adding PCM to the grout.

对地耦合热泵 (GCHP) 系统中使用的立式埋管换热器的传热特性进行了数值分析，以研究将微封装的石蜡基相变材料 (PCM) 添加到管道中的效果。钻孔灌浆。与任何热能存储方案一样，其目的是减小满足峰值负荷所需的设备和装置的尺寸，因此本研究中 PCM 的目的是抑制钻孔的峰值温度响应，并有可能减少钻孔阵列的设计钻孔长度和成本。进行了 PCM 热性能的参数研究，以建立垂直热交换钻孔灌浆的设计建议。这项研究的结果表明，在钻孔中加入 PCM 并不总是能提高 GCHP 系统的整体性能；相反，如果未正确选择 PCM 热性能和熔体温度，则可能会降低系统性能。由于 PCM 热导率及其潜热容量的竞争因素，PCM 的最佳质量存在于钻孔灌浆中，但为了有效，PCM 热导率应近似等于灌浆材料的热导率。此外，发现 PCM 的最佳熔化温度是导致几乎所有 PCM 质量在峰值负载时改变相的温度，并且发现该温度大约在未受干扰的地面温度和峰值之间的中间。设计热泵进入流体温度。在本研究中发现，由于在钻孔灌浆中最佳添加石蜡基微封装 PCM，所需 BHE 长度的潜在减少高达 7%，但这种长度减少并不能保证总成本的降低由于当前 PCM 的成本相对较高，因此系统的性能不佳。因此，从经济的角度来看，这项工作的结果表明，目前提高水泥浆的导热性比在水泥浆中添加 PCM 更具成本效益。