Energy pile group is an important component of ground source heat pumps with foundation piles as ground heat exchangers. Among different energy piles, those with spiral pipes have a large heat exchange area between the pipe and the concrete, achieving good heat exchanging performance and wide applications. To analyze the influence of geometrical parameters (pile layout, pile spacing and pile depth) and external parameter (groundwater velocity) on the heat transfer of spiral-coil energy pile groups, a three-dimensional analytical model of spiral-coil energy pile groups with seepage is used, considering the thermal interaction among different piles, the geometry of spiral pipe and the velocity of groundwater. The soil temperature distribution in the energy pile group is studied under conditions with different factors (pile layouts: 3 × 2, L shape and line shape; pile spacing distances: 3, 5 and 7 m; pile depths: 10, 30 and 50 m; and groundwater velocities: 0, 1.2 × 10⁻⁶ and 2.0 × 10⁻⁶ m/s). The 3-year outlet fluid temperature of energy pile group affected by the above different factors under different inlet fluid temperatures and velocities or soil thermal exchange ratios is investigated. Results show that for the low fluid velocity inside the piles, the influence of above factors on the thermal performance of energy piles is more obvious. Large groundwater velocity, line shape pile layout, large pile spacing distance and short pile depth can alleviate the long-term temperature variation caused by unbalanced soil heat exchange. This work will facilitate the research, design and application of the energy pile group in ground source heat pumps.

中文翻译：

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不同因素对带渗流的螺旋线圈能量桩群三维传热的影响

能量桩组是地源热泵的重要组成部分，地基热泵以地基桩为地面热交换器。在不同的能量桩中，具有螺旋管的能量桩在管与混凝土之间具有较大的热交换面积，从而实现了良好的热交换性能和广泛的应用。为了分析几何参数（桩布局，桩间距和桩深）和外部参数（地下水流速）对螺旋线圈能量桩组传热的影响，建立了螺旋线圈能量桩组的三维解析模型考虑到不同桩之间的热相互作用，螺旋管的几何形状和地下水流速，使用了渗流。在不同因素条件下研究了能量桩组中的土壤温度分布（桩布局：3×2，L形和线形；桩距：3、5和7 m；桩深：10、30和50 m; 和地下水速度：0，1.2×10^-6和2.0×10 ^-6  m / s）。研究了在不同进水温度，速度或土壤热交换率的作用下，上述因素对能量桩组3年出水温度的影响。结果表明，对于桩内低流速，上述因素对能量桩热性能的影响更为明显。较大的地下水流速，线形的桩布置，较大的桩间距和较短的桩深度可以缓解土壤热交换不平衡引起的长期温度变化。这项工作将有助于地源热泵中能量桩组的研究，设计和应用。