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 6kWe micro Organic Rankine Cycle (ORC); a 30kWf single stage H2O/LiBr absorption chiller; a geothermal well; a solar field obtained by new prototypal flat-plate evacuated solar collectors. The ORC is supplied by heat obtained by a geothermal well in which geothermal brine is about at 95°C. In order to improve system performance, additional heat is provided by solar energy obtained through a 25m2 solar field. Diathermic oil (up to 130°C) is adopted as working fluid in order to supply heat to the ORC evaporator. A suitable oil storage tank is modelled in order to mitigate the temperature fluctuations due to the variability of solar energy availability. The output power of the ORC depends on the availability of solar energy. The absorption chiller is switched-on in summer time and it is fed by geothermal energy only. This simulation model is implemented in TRNSYS environment. The ORC is modelled by zero-dimensional energy and mass balances implemented in Engineering Equation Solver (EES).