Model of an Organic Rankine Cycle thermal engine for geothermal application

The climate crisis stands as one of the most pressing challenges of our time, with recent years marking the hottest on record. By 2019, the global average temperature had increased by 1.1 K compared to pre- industrial levels, with extreme weather events such as droughts and heavy rainfall becoming increasingly frequent. In response, the European Union (EU) has set ambitious targets to combat climate change, including a 55% reduction in greenhouse gas emissions by 2030 and achieving climate neutrality by 2050. Key strategies outlined by the EU involve expanding renewable energy sources, promoting energy efficiency, electrification, and integrating advanced energy systems such as renewable hydrogen for high-carbon industrial processes. This work focuses on optimizing thermomechanical technologies, specifically Organic Rankine Cycle (ORC) machines, to support these objectives. It investigates the impact of the initial charge of working fluid, R1234ze(E), on the performance of a real geothermal ORC machine, working with hot water at 346,15 K (73 °C), aiming to maximize electricity generation. The study examines the various components of the ORC machine, modeling the system's thermodynamic performance using Engineering Equation Solver (EES) Academic Professional V10.998-3D software by F-Chart Software. The research evaluates the effect of working fluid mass charge on the machine's efficiency and energy output, with a focus on the specific case of a geothermal ORC machine located in the Colli Euganei region, in North-East Italy, realized by Kaymacor, an Italian company specialized in the production of small-scale ORCs. The results predicted by the model are in close agreement with the data measured in the real world and they highlight the importance of optimizing fluid charge to improve energy production and system efficiency, contributing to the broader goals of reducing emissions and advancing sustainable energy technologies. The work concludes with an analysis of the findings and suggests future developments for further optimization and application of ORCs machines in the exploitation of intermediate temperature geothermal sources.