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Abstract In this paper, a detailed numerical analysis of a Combined Cooling, Heating and Power system is presented, aiming at determining its optimal operating strategy in a real industrial application. The system layout includes a reciprocating engine, fuelled by natural gas, heat exchangers for waste-heat recovery, pumps, storage tanks, a single-effect water lithium bromide absorption chiller, a cooling tower, a back-up vapour-compression electric chiller, mixers and valves. A dynamic simulation model of the whole system was developed in TRNSYS. A case study was analysed, referred to a real industrial application, where the system under evaluation should be installed in the near future, providing electricity, mainly used for the production process, and space cooling. Real measured data were used to estimate the electric energy demand of the factory. A detailed building simulation model was used to calculate heating and cooling demands. A detailed economic analysis was carried out, aiming at evaluating: (i) the optimal size of the Combined Cooling, Heating and Power system; (ii) the optimum control strategy, from a thermo-economic point of view, comparing three different cases: Base-Load operation, electric load tracking and a new hybrid strategy based on the simultaneous tracking of electric and thermal-loads. The results showed that the optimal capacity of the system was lower than that selected by the designers of the real unit to be installed. The hybrid control strategy obtained the best profitability, achieving a simple pay-back period equal to 3.8 years, compared to 4.1 years achieved in case of electric-load tracking.

Abstract The paper presents a thermoeconomic comparison between two different solar thermal technologies, namely Linear Fresnel Reflector (LFR) and evacuated tube solar collectors (ETC), integrated into a polygeneration plant. The system produces space heating and cooling, domestic hot water and drinkable desalinated water, by means of a multi-effect distillation (MED) system. In the ETC layout, a single-effect LiBr H2O absorption chiller (ACH) is included; in the second layout, based on LFR collectors, a double-effect ACH is considered. An auxiliary biomass-fired heater is used to supply the additional heat required by the MED unit, in case of low availability of solar radiation. Both plants are simulated by means of a zero-dimensional dynamic simulation energy model, developed in TRNSYS environment. The model also includes detailed thermo-economic calculations. The results show that in some winter weeks, the solar fraction for freshwater production ranges between 15% and 20% for the ETC-based system, whereas is zero in case of LFR, when the MED unit is supplied only by the biomass auxiliary heater. Therefore, for the analysed case study, ETCs resulted more profitable than LFRs, achieving simple pay-back periods of about 4–5 years.

Abstract This paper presents a novel methodology for the management of the solar energy and seawater desalination, using water storage systems. The investigated plant includes photovoltaic panels, supplying a reverse osmosis unit for freshwater production. This novel methodology, based on the use of a water storage basin, allows one to avoid electric storage systems, determining a stable water production and maximizing the water self-consumption. The water storage basin allows one to obtain a significantly different trend of the freshwater availability with respect to the photovoltaic production, mainly occurring during the central hours of the day. The plant is dynamically simulated in TRNSYS environment. The proposed plant is assumed to operate in small Mediterranean islands, rich in solar energy and seawater availability, featured by a scarce freshwater availability and dramatically high freshwater costs. As main case study, Pantelleria Island (South Italy) is selected. The system energy performance is calculated in detail implementing accurate models for all the system components. Special control strategies are implemented in order to maximize the system profitability, evaluated by considering both capital and operating costs. The developed system is extremely profitable: the achieved payback period is about 1.3 years, mainly due to high capital cost of freshwater in the reference scenario. A remarkable water saving equal to 80% is obtained, also reducing the dependency of the Island from the water transported by the tank ships. For the selected case study, the sensitivity analyses suggest adopting a solar field area equal to 6436 m2, avoiding an increase of the water storage basin and of the maximum and minimum operating pressures of the reverse osmosis unit single train.