An analysis of heat flow through a borehole heat exchanger validated model

Earth heat exchangers are essential parts of the ground-source heat pumps and the accurate prediction of their performance is of fundamental importance. This paper presents the development and validation of a numerical model for the simulation of energy flows and temperature changes in and around a borehole heat exchanger when a fluid circulates through a U-tube. Based on the time-dependent convection–diffusion equation, the FlexPDE software package is employed to solve the resulting boundary value problem that model a heat exchanger. First, the mathematical model is validated through a comparison with data obtained from experiments with real borehole set-ups in Cyprus. Then the validated model is used to study the heat flow and the temperature variation in the heat-exchanger. Finally conclusions are extracted on how various parameters like the U-tube diameter, the variation of the ground thermal conductivity and specific heat and the borehole filling material affect the temperature of the inlet and outlet fluid.

► Numerical model for the energy flows in a U-tube borehole heat exchanger. ► Validation of the mathematical U-tube model with real borehole set-ups in Cyprus. ► Analysis of energy flows and temperature changes in and around the U-tube HE. ► Effect of various parameters on the temperature of the inlet and outlet fluid.