Temperature distribution in the vicinity of a borehole heat exchanger for intermittent heat extraction: An analytical solution

摘要

Existing analytical solutions for thermal analysis of closed-loop ground heat exchangers systemsrnevaluate temperature change in the heat carrier-fluid and the surrounding ground in the production period ofrnBorehole Heat Exchangers (BHE) only if a continuous heat load is assigned. In the present study, we solvernanalytically the heat conduction/advection/dispersion equation in porous media, for intermittent heat extraction.rnWe convolute rectangular function or pulses in time domain both for single and multi-BHEs field. Thernsolution includes non-symmetric configurations around the BHEs by considering anisotropic features inducedrnby groundwater convection or intrinsic anisotropy of thermal conductivity. Thermal dispersivity linked to thernground water flow is also considered.rnThe validity of the analytical model is checked through the comparison with results obtained from numericalrnfinite element code. The comparison results agree well with numerical results both for conduction and advectionrndominated heat transfer systems, and analytical solutions provide significantly shorter runtime compared tornnumerical simulations. The developed tool allows also to investigate the recovery aspects and the sustainabilityrnof closed-loop ground heat exchangers systems in terms of temperature and the energy deficit of the ground.