Short-Term Behavior and Steady-State Value of BHE Thermal ResistanceS. Lazzari, A. Priarone,
DIN, University of Bologna, Bologna, Italy
DIME-TEC, University of Genova, Genova, Italy
The transient behavior of the thermal resistance of single and double U-tube borehole heat exchangers (BHEs) is investigated numerically by means of COMSOL Multiphysics® software with reference to the 2D cross section of usually employed BHEs. The study is performed in a dimensionless parametrical form, the parameters being the ratio between the thermal conductivities of grout and ground, the ratio between the heat capacities per unit volume of grout and ground and the distance between the tubes. The results show that the pipe spacing and the heat capacity ratio play an important role in the transient behavior of the BHE internal resistance, whereas the pipe spacing and the conductivity ratio play an important role in the steady value of the BHE thermal resistance.