a new approach for the dimensioning of an air conditioning system with cold thermal energy storage

Abstract In this work, a new approach for the design of air conditioning systems with cold thermal energy storage is described and tested, considering the case study represented by a vapor-compression chiller, coupled with a chilled water storage system, producing cooling for a small multi-apartment building situated in Italy. In the present approach, at the aim of limiting shut-downs and start-ups of the chiller, which involve inefficiencies during transients, and can lead to a drastic reduction of the equipment lifetime, the nominal power of the chiller, and the amount of cooling to be stored are first estimated in a pre-design phase. Successively, the outputs of the pre-design are used to fix the size of the cold storage tank, and to set up the numerical simulation of the cold thermal energy storage system. Finally, the results of the numerical simulation of the cold storage system are used to evaluate the effective size of the chiller. Both the pre-design and the numerical simulations of the cold storage systems have been done by means of home-made numerical tool realized with Simulink. In the paper, the specifications relative to the operational strategy are explored, and the analytical models used for the numerical simulation of the cold storage system relative to the Italian case study are reported in detail. Finally, the results of the pre-design, and of the cold storage system simulations relative to the case study are presented and discussed. The results relative to the Italian case study demonstrates the effectiveness of the present approach in limiting the number of shut-downs and start-ups of the chiller. The present approach can represent a useful tool for the economic optimization of the design of air conditioning systems

analysis of a biomass fired cchp system considering different design configurations

Abstract This work aims to present the results of an energetic and economic analysis of a biomass fueled CCHP system operating according to different design configurations. The investigated system consists of a biomass-fueled cogeneration unit, an absorption chiller, a thermal energy storage system and a cold one, providing electricity, heat and cooling to an Italian cluster of buildings. For each simulated configuration, the feasible investment cost of the CHP unit is evaluated considering the economic savings obtained with respect to separate generation of electricity, heat and cooling. The best configuration from the economic point of view is indicated, and the incidence of the variation of the absorption chiller and storage systems sizes on the feasible investment cost of the CHP unit is evaluated and discussed as well. Results indicate that the most influencing parameter is represented by the absorption chiller power

Methodology for the characterization of the humidity behavior inside CPV modules

In this study the characterization of the humidity behavior inside concentrating photovoltaic (CPV) modules is addressed. To this purpose, several experimental tests have been carried out by using two different CPV modules and three different breathers, collecting in each analyzed case the evolution of temperature, relative and specific humidity of the air volume contained inside the module for many days. Results indicates that, for each of the CPV modules analyzed, it is possible to construct a characteristic curve in the temperature-specific humidity psychrometric chart, that can be used for estimating the specific humidity of the air inside the CPV module as a function of the internal air temperature. The characteristic curve can be also used to estimate the saturation temperature of the air inside the CPV module, and consequently to detect the eventuality of moisture condensation during cloudy days or night-time, namely when the temperature of the air inside the module is low and reaches the external ambient one. This methodology can be used in CPV modules design for the choice of the breather and of the construction materials, in order to obtain a saturation temperature as low as possible

experimental validation of a tool for the numerical simulation of a commercial hot water storage tank

Abstract This work focuses on the experimental validation of a numerical tool realized to simulate a commercial hot water storage tank. The tool implements unsteady 1D models to simulate the temporal evolution of the temperature field inside the hot water storage tank, and the one relative to the heat transfer fluid flowing through the immersed coil heat exchanger. It has been implemented by means of the Simulink tool of Matlab. The first part of the paper is dedicated to the description of the indoor experimental facility used to realize the experimental test. Successively, the analytical models, and the numerical schemes and algorithms used to perform the numerical simulations are described. Finally, the results of the experimental validation of the tool, accomplished by comparing the experimental temperature profiles inside the tank, and the measured temperatures at the coil heat exchanger exit section over the entire experimental test duration, with the numerical results obtained from simulations performed using different correlations for the evaluation of the heat transfer rate between the tank water and the heat transfer fluid through the coil, are reported and discussed

Transient Analysis of a Solar Domestic Hot Water System Using Two Different Solvers

Abstract In the present work the unsteady numerical simulation of a solar domestic hot water (DHW) system composed of two flat plate collectors, a water tank for heat storage, and a coil heat exchanger is addressed. The simulations have been performed using two different solvers, namely a home-made code written in Matlab, and TRNSYS 17. In the first part of the paper, the analytical models used in the Matlab code, and the TRNSYS case are reported in detail. Successively, the results of the simulations realized by means of the two solvers are presented and compared

design optimization of a distributed energy system through cost and exergy assessments

Abstract In recent years, Distributed Energy Systems (DESs) have been recognized as a good option for sustainable development of future energy systems. With growing environmental concerns, design optimization of DESs through economic assessments only is not sufficient. To achieve long-run sustainability of energy supply, the key idea of this paper is to investigate exergy assessments in DES design optimization to attain rational use of energy resources while considering energy qualities of supply and demand. By using low-temperature sources for low-quality thermal demand, the waste of high-quality energy can be reduced, and the overall exergy efficiency can be increased. Based on a pre-established superstructure, the aim is to determine numbers and sizes of energy devices in the DES and the corresponding operation strategies. A multi-objective linear problem is formulated to reduce the total annual cost and increase the overall exergy efficiency. The Pareto frontier is found to provide different design options for planners based on economic and sustainability priorities, through minimizing a weighted-sum of the total annual cost and primary exergy input, by using branch-and-cut. Numerical results demonstrate that different optimized DES configurations can be found according to the two objectives. Moreover, results also show that the total annual cost and primary exergy input are reduced by 20% - 30% as compared with conventional energy supply systems

Thermal analysis of a BIPV system by various modelling approaches

This work presents various models developed and implemented within the SOPHIA European project in order to thermally characterize PV modules in a rooftop BIPV configuration. Different approaches have been considered, including a linear model, lumped elements models and models that make use of commercial software solvers. The validation of the models performed by comparing the results of simulations with experimental data recorded on a test bench over an entire year is presented and discussed on a seasonal basis. The results have shown that all the models implemented allow achieving a good prediction of the PV modules back surface temperature, with the minimum value of the coefficient of determination R2 around 95% on a yearly basis. Moreover, the influence of season weather conditions and of the incident solar irradiance magnitude on the accuracy of the considered thermal models is highlighted. The major result of the present study is represented by the fact that it has been possible to perform a better thermal characterization of the BIPV module by tuning some of the heat transfer coefficients, such as those relative to the effects of the wind velocity, and to the evaluation of sky temperature.The experimental data used for the thermal simulation of BIPV system behavior were obtained in the framework of the project Performance BIPV supported by the French research agency (ANR), within the research program ANR HABISOL. Authors would like to thank the European Community that supported the SOPHIA project with the funding of FP7-SOPHIA grant agreement no. 262533

Numerical Simulation of an Aluminum Container including a Phase Change Material for Cooling Energy Storage

Thermal energy storage systems can be determinant for an effective use of solar energy, as they allow to decouple the thermal energy production by the solar source from thermal loads, and thus allowing solar energy to be exploited also during nighttime and cloudy periods. The current study deals with the modelling and simulation of a cooling thermal energy storage unit consisting of an aluminum container partially filled with a phase change material (PCM). Two unsteady models are implemented and discussed, namely a conduction-based model and a conduction-convection-based one. The equations systems relative to both the models are solved by means of the Comsol Multiphysics finite element solver, and results are presented in terms of temporal variation of temperature in different points inside the PCM, of the volume average liquid fraction, and of the cooling energy stored and released through the aluminum container external surface during the charge and discharge, respectively. Moreover, the numerical results obtained by the implementation of the above different models are compared with experimental ones obtained with a climatic chamber. The comparison between numerical and experimental results indicate that, for the considered cooling energy storage unit, free convection plays a crucial role in the heat transfer inside the liquid PCM and cannot be neglected

Analisi del campo di moto generato da attuatori di flow control a getto sintetico mediante simulazione numerica.

L'obiettivo principale della Tesi di Dottorato è stato quello di analizzare il campo di moto relativo ad attuatori di flow control a getto sintetico a mezzo di simulazioni numeriche. Le metodologie sviluppate sono state di tipo numerico. È stato, infatti, sviluppato un codice di calcolo fatto ad hoc per la simulazione numerica di campi di moto relativi sia a getti sintetici isolati sia all’interazione di un getto sintetico con un crossflow. Si tratta di un codice ai volumi finiti con griglia cartesiana e arrangiamento delle variabili su griglia di tipo co-locato, denominato SyntJet, che risolve il sistema di equazioni U-RANS 2D per flusso incompressibile nella formulazione integrale. Il modello di turbolenza utilizzato è il k-ε Jones & Launder. La tesi è divisa essenzialmente in due parti. Nella prima parte vengono descritte in dettaglio le caratteristiche del codice. Nella seconda vengono analizzati i risultati ottenuti e viene effettuato un confronto con i risultati relativi ad alcuni tra i più importanti lavori sul getto sintetico presenti in letteratura. I principali risultati ottenuti hanno riguardato la dinamica di un getto sintetico generato da un attuatore a membrana piezoelettrica montato su una lastra piana ed, inoltre, hanno riguardato l’interazione tra un getto sintetico ed un crossflow sempre su lastra piana. Tali risultati sono originali in quanto costituiscono una sorta di validazione numerica del modello di turbolenza utilizzato per la simulazione numerica del getto sintetico. Inoltre hanno permesso di mettere in evidenza il comportamento self-similar del getto sintetico isolato, analogo a quello del getto continuo piano turbolento, e l’effetto, relativo all’interazione del getto sintetico ed un crossflow, detto “virtual shaping”. Le ricadute in campo applicativo sono molteplici. Si è visto sperimentalmente che i getti sintetici permettono di ritardare il distacco dello strato limite su profili alari NACA 0015, con notevoli benefici in termini di portanza e resistenza aerodinamica. È stato dimostrato che i getti sintetici velocizzano il processo di mixing all’interno di getti convenzionali ed, inoltre, che essi possono essere utilizzati per ottenere il jet-vectoring di getti convenzionali

Cold Storage for a Single-Family House in Italy

This work deals with the operation, modeling, simulation, and cost evaluation of two different cold storage systems for a single-family house in Italy, that differ from one another on the cold storage material. The two materials used to perform the numerical simulations of the cold storage systems are represented by cold water and a phase change material (PCM), and the numerical simulations have been realized by means of numerical codes written in Matlab environment. The main finding of the present work is represented by the fact that, for the considered user characteristics, and under the Italian electricity tariff policy, the use of a proper designed cold storage system characterized by an effective operation strategy could represent a viable solution from an economical point of view