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Simulation and analysis of a solar-assisted trigeneration system

This thesis aims to develop a detailed numerical model of a trigeneration system generating space heating, cooling and electricity for a public hospital building, through the usage of concentrating solar technology.
In particular, the work is centred on the optimization and the control strategy development of the high temperature solar loop, which delivers the input energy to the cogeneration unit, represented by an Organic Rankine Cycle (ORC) machine.
The high temperature circuit uses thermal oil as heat transfer fluid and includes a number of parabolic through collectors and an auxiliary gas boiler.
Heating and cooling production are based on wasted thermal energy from the power cycle, with the latter provided by an adsorption chiller.
Such set of technologies represents an innovative solution for building size energy systems and few examples can be found in literature. Main critical issues of a solar-assisted trigeneration system are the variability of the renewable energy source, the limited ORC efficiency at low heat source temperatures and the technical and control requirements for coupling low-grade rejected heat with an efficient cooling cycle.
Even well-known benefits of combining heat and power generation from the same energy resource might be affected by the mentioned technical difficulties and, for this reason, the development of an effective system control is a core part of the work.
Energetic advantages of trigeneration systems are expected to be remarkable even in small-scale applications, but their economic feasibility is still to be probed. Therefore, making use of numerical simulation results, a performance and economic analysis of the system is also carried out. The final conclusion of this analysis is the definition of an optimal design for further development of the given system.
Chance of investigating such an innovative energy system is given by the European project named BRICKER, which involves the design and construction of a demonstrator trigeneration system.

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UNIVERSITY OF TRIESTE _________________________________________________________________________ Simone De Luca – Master thesis - 19 - Abstract This work aims to assess energetic and economic performance of a solar-assisted trigeneration system that provides heating, cooling and electricity to a public hospital building. This analysis is based on a transient numerical model. The core objective is the development of a cost-effective control strategy for the solar field, which collects the thermal energy supplied by concentrating collectors and delivers this amount of heat to a cogeneration unit, represented by an Organic Rankine Cycle machine. Heating and cooling production are based on wasted thermal energy from the power unit, with the latter provided by an adsorption chiller. Such set of technologies represents an innovative solution for building size energy systems with few installed plants worldwide. Main critical issues are the variability of the solar energy source, the limited power cycle efficiency at low evaporation temperatures and the technical and control requirements for coupling low-grade rejected heat with an efficient cooling cycle. Energetic advantages of combined cooling, heat and power are expected to be remarkable even in small-scale applications, but the economic feasibility is still questionable. Therefore, a performance and economic analysis of the system is carried out using numerical simulation results. The final goal of this analysis is the definition of an optimal design for further development of the studied system. In order to achieve the proposed objectives, some tasks have been completed. Firstly, technical features of solar trigeneration systems are examined in order to define the state of the art of such systems. That investigation aims to rate the actual performance of such systems and understand which kind of improvements can be applied through an optimization process. After the theoretical study of each main component, a transient numerical model of the whole system is implemented using the TRNSYS simulation software. The thermal oil loop is completely modelled within this work, while heating and cooling circuits are simulated using an existing numerical model adapted to the studied system specifications. An overall control strategy is also elaborated, with particular attention to the minimization of the backup heater fuel consumption and the maximization of average solar output throughout the year. The control logic is implemented in the same transient model. Simulation results are used to evaluate performance of the obtained system. Electrical and thermal outputs are evaluated in terms of annual and seasonal amounts of energy, while consumption is considered through Final Energy and Primary Energy indicators. A comparison with two reference systems, for heating and cooling production, respectively, is the base for the evaluation of energy and economic savings related to the studied system. Last analysis aims to assess the economic feasibility of the project, by means of calculating an approximate return of investment, using actual costs of the components. Since the involved technology is costly, a further optimization of the system is considered to achieve higher economic performance by changing some model parameters. Chance of investigating this innovative trigeneration system is given by the European research project BRICKER.

Tesi di Laurea Magistrale

Facoltà: Ingegneria

Autore: Simone De Luca Contatta »

Composta da 176 pagine.

 

Questa tesi ha raggiunto 68 click dal 31/07/2017.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.