This study proposes a new three-dimensional implicit numerical model to simulate a borehole field heat exchanger that accounts for seasonal fluctuations of the soil temperature. The model uses an alternating-direction implicit finite difference approach to perform the simulation. The effect of seasonal changes in the soil temperature is considered using an internal heat source term in the governing equations. The model is validated against several published in-situ tests as well as a laboratory experimental study and the results obtained from a TRNSYS version of the duct storage (DST) model, demonstrating an average error of less than 3%.

The validated model is then applied to analyse the impact of accounting for seasonal soil temperature fluctuations at various borehole lengths and climate zones. This analysis compares the results obtained from a model that uses constant temperature boundary conditions against those from a model that contains the internal heat source term and uses adiabatic boundary conditions. A significant discrepancy between the outputs of the two models has been observed for shallow borehole heat exchangers (H < 60 m) and at locations with a high annual amplitude of the surface temperature variations ($\Delta T_a$ > 5°C). Thus, the assumption of constant temperature at the ground surface is only appropriate for deep boreholes (H > 60 m) or at locations with a relatively low annual amplitude of the surface temperature variations ($\Delta T_a$ < 5°C).

本研究提出了一种新的三维隐式数值模型来模拟考虑土壤温度季节性波动的钻孔现场换热器。该模型使用交替方向隐式有限差分方法来执行模拟。使用控制方程中的内部热源项来考虑土壤温度的季节性变化的影响。该模型根据多项已发表的现场测试以及实验室实验研究和从 TRNSYS 版本的风管存储 (DST) 模型获得的结果进行了验证，表明平均误差小于 3%。

然后应用经过验证的模型来分析考虑不同钻孔长度和气候带的季节性土壤温度波动的影响。此分析将使用恒温边界条件的模型与包含内部热源项并使用绝热边界条件的模型的结果进行比较。对于浅埋管换热器（H < 60 m）和地表温度年变化幅度较大的位置，已观察到两种模型的输出之间存在显着差异（$\Delta {吨}_{\mathrm{一种}}$> 5°C）。因此，地表恒温假设仅适用于深钻孔（H > 60 m）或地表温度年变化幅度相对较低的位置（$\Delta {吨}_{\mathrm{一种}}$ < 5°C）。