Luigi Mongibello

Parametric Analysis of a High Temperature Sensible Heat Storage System by Numerical Simulations

This work has been realized in the framework of the Elioslab project, financed by the Italian Ministry of Education, University and Research (MIUR), which aims to create a research platform in order to develop components and systems for the production and utilization of medium and high temperature heat using concentrated solar energy. As regards high temperature heat production, a 30 kW solar furnace that consists of a heliostat with flat mirrors and a parabolic concentrator with off-axis alignment is being realized in order to achieve a solar radiation concentration peak of about 2000 suns. The energy flux relative to the concentrated radiation will be converted to high temperature heat by a cavity receiver cooled with CO2, and finally transferred to a device operating at high temperature consisting in a thermochemical reactor for hydrogen production. Due to the intermittency of solar radiation, a high temperature (>800 °C) packed bed sensible heat storage system, with alumina balls as heat storage material, has been developed in order to provide continuity to the user operation. This paper focuses on the parametric analysis that has been carried out by means of numerical simulations to evaluate the set of variable parameters that maximize the efficiency of the heat storage system of the solar furnace. The charging and discharging phases of the heat storage tank have been numerically simulated by means of an analytical model that takes into account the conductive, convective, and radiative heat transfer as well as turbulent diffusion due to the solid–fluid interaction. The results of the numerical parametric analysis are presented together with the experimental validation of the adopted analytical model accomplished by using a reduced-scale high temperature storage system.

Optimal Operation of Micro-CHP Systems for a Single-Family House in Italy

In this work the scheduling optimization of micro-CHP systems producing electricity and heat for a single-family house situated in Italy is addressed. Three different commercial prime movers have been analyzed separately, and for each of them the operation scheduling that maximizes the revenues for the energy cogeneration with respect to the separate generation has been evaluated by means of an optimization algorithm.

Numerical Simulation of a Solar Domestic Hot Water System

An innovative transient numerical model is presented for the simulation of a solar Domestic Hot Water (DHW) system. The solar collectors have been simulated by using a zerodimensional analytical model. The temperature distributions in the heat transfer fluid and in the water inside the tank have been evaluated by one-dimensional models. The reversion elimination algorithm has been used to include the effects of natural convection among the water layers at different heights in the tank on the thermal stratification. A finite difference implicit scheme has been implemented to solve the energy conservation equation in the coil heat exchanger, and the energy conservation equation in the tank has been solved by using the finite difference Euler implicit scheme. Energy conservation equations for the solar DHW components models have been coupled by means of a home-made implicit algorithm. Results of the simulation performed using as input data the experimental values of the ambient temperature and the solar irradiance in a summer day are presented and discussed.

Exergy-efficient management of energy districts

Sustainable development requires not only the use of sustainable energy resources, but also the efficient use of all energy resources. The latter should be reached by considering the concept of energy as well as exergy - the true magnitude of thermodynamic losses. Exergy describes the quality of an energy flow as the percentage that can be completely transformed into any other form of energy. Reduction of exergy losses represents a more efficient use of energy resources, which is essential in the long run, but it is not captured by standard energy costs, which are crucial in the short run. In this paper, exergy analysis is used in the context of a multi-carrier energy district to match the supply and demand not only in quantity but also in quality. The innovative contribution of this paper is the offering of a trade-off between reducing exergy losses and energy costs, thereby attaining sustainability of the energy district. A mixed-integer programming problem considering several energy devices is formulated to minimize a weighted sum of exergy losses and energy costs while satisfying time-varying user demands. The problem is solved by branch-and-cut. Numerical results demonstrate that the optimized operation of the energy devices makes the energy district sustainable in terms of exergy efficiency and costs.

Assessment of pollutants emission of two residential micro-CHP systems

In this work the characterization of pollutants emission of two different commercial prime movers producing electricity and heat during the cold season for a multi-apartment housing situated in Italy is addressed. In particular, an internal combustion engine and a microturbine, both fed by natural gas, have been analyzed separately. For each prime mover, the emission of CO2, CO and NOx resulting from two different optimized operation modes are reported and discussed. The results show that the micro-CHP system with the internal combustion engine as prime mover involves a marked augmentation of dangerous CO and NOX emissions on a local scale.

ELIOSLAB project: Design and realization of a 30 kW optical power peak solar furnace

This paper presents the design of the main components of the solar furnace that is being installed at ENEA Portici Research Centre in the framework of the ELIOSLAB project financed by the Italian Ministry of Education, University and Research (MIUR), which aims to create a research platform in order to develop components and systems for the production and utilization of medium and high temperature heat using concentrated solar energy. In the present work the details about the design and the on-site installation of the heliostat and the off-axis primary collector are provided, and the design of the main components of the furnace thermal circuit, namely the solar cavity receiver and the high temperature packed bed sensible heat storage system, will be discussed as well.

Experimental test of a hot water storage system including a macro-encapsulated phase change material (PCM)

Thermal energy storage systems (TESs) are of fundamental importance for many energetic systems, essentially because they permit a certain degree of decoupling between the heat or cold production and the use of the heat or cold produced. In the last years, many works have analysed the addition of a PCM inside a hot water storage tank, as it can allow a reduction of the size of the storage tank due to the possibility of storing thermal energy as latent heat, and as a consequence its cost and encumbrance. The present work focuses on experimental tests realized by means of an indoor facility in order to analyse the dynamic behaviour of a hot water storage tank including PCM modules during a charging phase. A commercial bio-based PCM has been used for the purpose, with a melting temperature of 58°C. The experimental results relative to the hot water tank including the PCM modules are presented in terms of temporal evolution of the axial temperature profile, heat transfer and stored energy, and are compared with the ones obtained by using only water as energy storage material. Interesting insights, relative to the estimation of the percentage of melted PCM at the end of the experimental test, are presented and discussed.

Influence of energy quality management on CO 2 emissions in operation optimization of a distributed energy system

Efficiency of energy resource use is a key factor for a sustainable energy future. By matching the exergy levels of supply and demand, Energy Quality Management (EQM) of building energy supply systems may achieve more efficient use of energy resources. Beyond this, environmental impact of energy supply systems is another essential issue. This work addresses the influence of EQM on CO2 emissions in the operation optimization of a Distributed Energy System (DES). A multi-objective linear programming problem is formulated to reduce energy costs and increase the overall exergy efficiency. Total CO2 emissions are evaluated for the optimized operation strategies of the DES. The operators of the DES can choose the operation strategy from the Pareto front, based on their priorities and also aware of effects on CO2 emissions. Results demonstrate more efficient use of energy resources and reduction in CO2 emissions through EQM, as compared with conventional energy supply systems.

Optimal operation of residential micro-CHP systems with thermal storage losses modelling

In this study the optimal operation of micro-CHP systems producing electricity and heat for a single-family house situated in Italy is addressed considering the effects of heat dissipation relative to thermal storage systems. Three different prime movers have been analyzed separately, and for each of them the operation scheduling that maximizes the revenues for the energy cogeneration with respect to the separate generation has been evaluated by means of an optimization algorithm.