Heat exchange phenomena and COP evaluation in heat pump systems coupled to single borehole heat exchangers

In recent years a growing interest in Borehole Heat Exchangers (BHEs) has been shown in Europe thanks to the increase of installations in systems connected to Ground Source Heat Pumps (GSHPs) used for heating and cooling needs. Different geometries and technical solutions have been de- veloped in order to improve heat exchange with the ground, accompanied by several descriptive models. Recently, innovative technologies as optical fiber for a new Distributed Thermal Response Test (DTRT) have been proposed. This method allows the quantification of the BHE local perfor- mances, so that a more accurate punctual analysis of thermal phenomena is allowed. The aim of this thesis is to locate an analytical model thanks to the most recent data, to achieve the definition of overall efficiency of a single BHE in terms of thermal resistance and of a BHE-GSHP system in terms of evaluation of the Coefficient of Performance. This model accuracy will be verified with new measures in a real installation. A particular attention will be given to the thermal-fluid-dynamics aspects, defining semi-empirical correlation for free and forced convection within the BHE groundwater filling.