Abstract:

Ground temperature distribution around vertical borehole heat exchangers (BHEs) has significant impacts on the performance of ground source heat pumps (GSHPs).It is essential to predict the long-term ground temperature distribution in the design and application of GSHPs.This study develops a three-dimensional numerical model for predicting the ground temperature distribution and GSHP operating performance.Air boundary, groundwater seepage and soil stratification have been taken into account.In order to minimize the computational load, the whole BHE is regarded as a linear heat source.The top boundary condition is set to the Cauchy boundary condition.The unsteady energy equation is calculated to improve the computational stability using the Alternating Direction Implicit method.Finally, this model is validated against data in literatures.Results have shown that absolute errors are all less than ±1.00℃.Predicted temperatures inside the soil are highly accurate (errors less than ±0.20℃) while the biggest error occurs at the outer wall of BHE.Therefore, this model can accurately and quickly predict the long-term ground temperature distribution and GSHP operating performance, especially in areas where complex seepages and apparent soil stratifications exist.

Key words: ground source heat pump, borehole heat exchanger, ground temperature distribution, groundwater seepage, heat transfer, numerical simulation, prediction

摘要：

垂直地埋管换热器周围地温场的变化对地源热泵的性能会产生重大影响。为长期准确高效地预测地温场，提出了一种耦合地源热泵系统COP的地温场三维模型，考虑空气边界、地下水渗流和土壤分层带来的影响。为降低计算负荷，将整个地埋管换热器简化为一维线热源。计算区域顶部设置第三类边界条件，以模拟土壤与空气的对流传热。采用交替方向隐式差分法离散非稳态能量方程，以提高计算稳定性。利用文献中的数据对模型进行验证，结果表明，所有温度预测值的绝对误差均小于±1.00℃，土壤内部测点温度尤其准确（均小于±0.20℃），最大误差出现在钻孔外壁。因此，模型能够准确快速地预测地温场的分布和地源热泵系统的性能。该模型尤其适用于地下水渗流复杂、存在明显土壤物性分层的地区。

关键词: 地源热泵, 地埋管换热器, 地温场, 地下水渗流, 传热, 数值模拟, 预测