Energy and economic analysis of geothermal-solar trigeneration systems: a case study for a hotel building in Ischia

This paper presents the design, simulation and optimisation of a small trigeneration plant supplied by geothermal and solar energies. Different technologies are implemented in a dynamic simulation model purposely developed for research scope: a 6 kWe micro Organic Rankine Cycle (ORC); a 30 kWf single stage H2O/LiBr absorption chiller; a geothermal well; a solar field obtained by new prototypal flat-plate evacuated solar collectors. The simulation model is implemented in TRNSYS environment. A case study is developed in order to test the energy and economic performance of this innovative micro-trigeneration plant. In particular, the above mentioned model is applied to the Regina Isabella hotel in Ischia (Naples, South Italy), famous for its geothermal sources. Currently, such hotel is already equipped by a geothermal system (by several hot water wells) for thermal cares, domestic hot water production and space heating. By TRNSYS the optimisation of the system design parameters and the calculation of the thermo-economic conditions were performed. The system showed excellent energy performance indexes. In fact, the average yearly efficiency of the solar thermal collectors is close to 60%, whereas the average yearly ORC electric efficiency is about 6%, which is a good achievement considering the system driving temperature.