A review of the importance of regional groundwater advection for ground heat exchange

The science of hydrogeology has its origins in heat conduction theory (e.g. Darcy's Law is analogous to Fourier's earlier law; Theis's equation is derived from Carslaw's line source heat equation; the Ogata-Banks dispersion equation). The science of thermogeology, which describes the behaviour and exploitation of low enthalpy heat in the ground, is now well established, but requires an understanding of its coupling with hydrogeology to account for the enhanced heat transfer (in addition to pure conduction) provided by groundwater advection. This paper reviews existing analytical approaches to groundwater interaction with closed-loop borehole heat exchangers and, briefly, open-loop well doublet systems. Heat transfer in the vertical dimension (with the atmosphere and underlying or overlying rocks) is found to be important for detailed modelling of their performance.