Generic ground response functions for ground exchangers in the presence of groundwater flow

This paper describes a procedure for computing time-dependent ground response functions (G) of vertical ground exchangers in the presence of groundwater flow. The comprehensive methodology can account for multi-borehole fields and allows predicting accurately heat transfer over a large range of design parameters, ground properties and time scales. It combines two analytical models: infinite cylinder source (ICS) and moving finite line source (MFLS). A new mathematical development is introduced to enhance the computational efficiency of the G-functions with the MFLS model. The precision of the models as a function of time is verified with finite-element modeling. An application-oriented procedure allows expressing the G-functions as a function of all the variables by combining graphical tools and correlation fittings. This procedure is developed specifically to be easily implemented in borehole design methods. The G-functions obtained by this method are in good agreement (R2 = 0.9934) with the analytical solution developed, over the prescribed range of variables.