Improvement in modeling of heat transfer in vertical ground heat exchangers

The heat transfer model of vertical ground heat exchangers for ground-source heat pump sys-tems is discussed. An explicit solution of a finite line-source model has been derived to better describe temperature response of boreholes for long time steps, which can be easily incorpo-rated into computer programs for thermal analysis of ground heat exchangers. A quasi-three-dimensional model is also presented for heat transfer inside the borehole, account-ing for thermal interference between the U-tube legs. On this basis a concise expression is obtained for the thermal resistance inside the borehole. These models have a more solid theoret-ical basis, would help to improve design procedures recommended by available literature, and are yet suitable for engineering applications