## 1 Introduction
Moreover, the electric power of current geothermal systems is usually larger than 200 kW\({}_{\text{el}}\) with values also higher than 50 MW\({}_{\text{el}}\)[14; 15; 33; 34]. On the other hand, few examples on small-scale ORCs are present, owing to higher specific costs and lower electric production [16; 35]. As a consequence, further investigations are required to improve their performance [12; 36]. Many scientific works concern geothermal ORC systems for electricity production. [PERSON] et al. recently provided a comprehensive review on this topic [7]. At the same time, the flexibility of geothermal-driven CHF systems based on ORCs has been receiving great attention from both the scientific community and industry [37; 38; 39; 40; 41]. In particular, a great amount of energy and techno-economic analysis and optimisation approaches are usually proposed for medium and large-scale geothermal power plants (electric power higher than 200 kW\({}_{\text{el}}\)) and for different system arrangements [37; 42; 43]. The objective functions combine energy parameters (i.e., first and second law analysis [44; 45; 46], electric power [41], heat exchanger areas [44; 47], etc.) and economic purposes (e.g., specific cost of investment and levelized cost of energy, energy production cost [48; 49; 50]). In this work, an innovative transcritical geothermal-driven ORC system for small-scale applications was investigated. To this purpose, the ORC unit is coupled with a traditional geothermal heat exchanger for the direct production of thermal energy. The sub-systems work in parallel to satisfy the electric and thermal demand of a small commercial centre. In a parallel arrangement, the heat is delivered to both the thermal user and the ORC at a high temperature and at a lower flow rate [43; 51]. In a series design,the same geothermal flow passes through the ORC and subsequently through the heat exchanger [43; 51]. As a consequence, the ORC unit significantly limits the thermal level of the heat generation in series arrangements [52; 53]. According to the literature [43], the parallel configuration is the most suitable solution for supply and return temperatures higher or close to 80 and 60 \({}^{\circ}\)C [43], respectively, typical of space heating applications [7]. On the other hand, the series configuration is recommended for applications with lower temperatures (supply and return temperature close to 50 \({}^{\circ}\)C and 30 \({}^{\circ}\)C [25; 30; 43]) suitable for soil warming, swimming pools, de-icing, etc. [7]. Furthermore, the parallel configuration guarantees better ORC electric performance, owing to the lower condensation temperatures compared to series arrangements and higher flexibility. An innovative high-energy geothermal CHP demonstrator in parallel configuration is developing within the Fongeosec project [54; 55]. Specifically, the geothermal source will be used to feed a 5.5 MW\({}_{\text{el}}\) subcritical ORC and a 15 MW\({}_{\text{th}}\) district heating network in Alsace (France) [56]. Parallel arrangements are also available in Bavaria (Germany) with Traunreut and Oberhaching geothermal plants. The global electric and thermal power is equal to 8.4 MW\({}_{\text{el}}\) and 52.0 MW\({}_{\text{th}}\), respectively, while the net electric process efficiency ranges between 8.9% and 13.1% [57]. A lot of research effort is currently focused on organic Rankine cycles for CHP applications operating in subcritical conditions and driven by relatively low-temperature sources. The novelty of this work consists in the adoption of a transcritical ORC configuration with superheated conditions at the expander inlet. Transcritical systems show, in fact, higher performance compared to subcritical configurations [33; 58] and provide a more efficient thermal exchange between the geofluid and organic fluid and lower irreversibility and exergy destruction [59]. Another benefit is the component downsizing due to the higher density of fluid.