The improved model CaRM for the simulation of vertical ground-coupled heat exchangers

A model is presented to simulate the thermal processes in ground heat exchangers connected to ground-source heat pumps. The considered approach is based on the electrical analogy, for this reason named CaRM (CApacity Resistance Model). The model here presented allows to consider the fluid flow pattern along the classical vertical ground heat exchangers shaped as a single U-tube, a double U-tube, helix or coaxial pipes. Besides, ground temperature at different distances from borehole are calculated, taking into account also the thermal interference between more boreholes. Starting from the supply temperature to the heat exchanger, the outlet fluid temperature and the ground temperature are calculated in each node, step by step. The model has been validated and its exemplary use has been shown extensively with reference to a real plant.