Abstract Ground-Coupled Heat Pumps (GCHPs) are known as a promising technology for building climatization and domestic hot water production. The main concern to employ these systems in urban areas is their high drilling and initial cost. This cost could be rebated by lowering the borehole thermal resistance and by shortening the borehole depth. In the present paper, a novel and simple design of the Ground Heat Exchanger (GHE), namely the vertical GHE with an elliptical U-tube, is proposed to improve thermal performance of GCHP systems. To prove that; a series of 3D finite element simulations are performed to study the thermal comportment of elliptical U-tubes and to compare their performance with typical single U-tubes. A dimensionless shape factor γ is introduced to evaluate effect of the elliptical U-tube geometry on thermal performance of the GHE. Furthermore, influential parameters on thermal performance of elliptical U-tubes are investigated and the decrement percentage of the borehole thermal resistance, with reference to the typical U-tube, are compared for each parameter. The results show that elliptical U-tubes could enhance heat transfer to significant extent and could decrease the borehole thermal resistance by more than 17 %, compared with typical single U-tubes. It is shown that the higher value of the shape factor γ leads to the better heat transfer enhancement. It is concluded that elliptical U-tubes are able to decrease the borehole thermal resistance and to boost the coefficient of performance (COP) of GCHP systems.

中文翻译：

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新型椭圆形单U型管立式地埋式换热器的热性能

摘要 地面耦合热泵（GCHPs）被认为是一种用于建筑气候和生活热水生产的有前途的技术。在城市地区使用这些系统的主要问题是它们的高钻探和初始成本。可以通过降低钻孔热阻和缩短钻孔深度来降低成本。在本论文中，提出了一种新颖且简单的地面换热器 (GHE) 设计，即带有椭圆 U 形管的垂直 GHE，以提高 GCHP 系统的热性能。证明这一点；执行一系列 3D 有限元模拟以研究椭圆形 U 形管的热性能，并将其性能与典型的单个 U 形管进行比较。引入无量纲形状因子 γ 来评估椭圆 U 形管几何形状对 GHE 热性能的影响。此外，研究了影响椭圆 U 形管热性能的参数，并比较了每个参数相对于典型 U 形管的钻孔热阻下降百分比。结果表明，与典型的单U形管相比，椭圆形U形管可以显着提高传热效果，并使钻孔热阻降低17%以上。结果表明，形状因子 γ 的值越高，传热增强效果越好。结论是椭圆U形管能够降低钻孔热阻并提高GCHP系统的性能系数（COP）。研究了影响椭圆 U 形管热性能的参数，并比较了每个参数相对于典型 U 形管的钻孔热阻下降百分比。结果表明，与典型的单U形管相比，椭圆形U形管可以显着提高传热效果，并使钻孔热阻降低17%以上。结果表明，形状因子 γ 的值越高，传热增强效果越好。结论是椭圆U形管能够降低钻孔热阻并提高GCHP系统的性能系数（COP）。研究了影响椭圆 U 形管热性能的参数，并比较了每个参数相对于典型 U 形管的钻孔热阻下降百分比。结果表明，与典型的单U形管相比，椭圆形U形管可以显着提高传热效果，并使钻孔热阻降低17%以上。结果表明，形状因子 γ 的值越高，传热增强效果越好。结论是椭圆U形管能够降低钻孔热阻并提高GCHP系统的性能系数（COP）。对每个参数进行比较。结果表明，与典型的单U形管相比，椭圆形U形管可以显着提高传热效果，并使钻孔热阻降低17%以上。结果表明，形状因子 γ 的值越高，传热增强效果越好。结论是椭圆U形管能够降低钻孔热阻并提高GCHP系统的性能系数（COP）。对每个参数进行比较。结果表明，与典型的单U形管相比，椭圆形U形管可以显着提高传热效果，并使钻孔热阻降低17%以上。结果表明，形状因子 γ 的值越高，传热增强效果越好。结论是椭圆U形管能够降低钻孔热阻并提高GCHP系统的性能系数（COP）。