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.