OPTIMAL OPERATION OF SMALL GEOTHERMAL SYSTEMS THROUGH ENTROPY GENERATION ANALYSIS

Geothermal systems often experience non homogeneous behavior between the various boreholes, due to possible issues in the installation or to differences in the stratigraphy. In the case of small systems, this may create important inefficiencies or operational problems. In this paper, the use of entropy generation analysis is proposed in order to optimize the global performances, taking fluid dynamic and thermal phenomena into account. The possible anomalous scenarios that are considered include borehole ovalization and differences in the heat transfer between borehole and ground due to fouling, groundwater level, etc. The analysis is conducted considering a transient model of the entire system, composed by the ground, boreholes and heat pump. Various operating scenarios are also considered. Results show that non negligible improvements in the efficiency can be obtained by proper selection of the operating conditions.