Stefano Grignaffini

Optimum design of vertical rectangular fin arrays

Abstract The goal of this analysis has been the search for the optimal configuration for a finned plate (with rectangular and vertical fins) to be cooled in natural convection. Utilizing a simplified relation of the fins heat exchange some simple expressions for the determination of the optimum value of the fins spacing have been developed as a function of the parameters which feature in the configuration: dimensions, thermal conductivity, fins absorption coefficient and fluid thermo-physical properties.

Effects of different building automation systems on the energy consumption for three thermal insulation values of the building envelope

The goal of this paper was to evaluate the energy savings achieved through the use of different building thermal automation systems by means of software TRNSYS. The reference building is sited in Milan in a street canyon and its thermophisical caratheristics of the envelope are as current law require. The idea comes from the study of the European Standard CEN EN15232 “Energy performance of buildings - Impact of Automation, Controls and Building Management” which highlights how the inclusion in buildings (residential and tertiary) of Control Systems and Automation lead to a reduction of energy consumption. They then evaluate these reductions in function of the type of automation implemented. This evaluations are made only for heating system and for a residential building.

Energy retrofit of a non-residential and historic building in Rome

The purpose of this manuscript is to analyze the interventions of energy retrofit of a non-residential and historic building, through a dynamic simulation by the use of the TRNsys code. The study is made up of some steps: · the analysis of the building and utility data, including study of the installed equipment and analysis of energy bills; · the survey of the real operating conditions; · the selection and the evaluation of energy saving measures; · the identification of interventions of energy retrofit; · TRNsys simulation of the effects of these interventions on energy behavior of the building. The paper aims to show the results of the study, to discuss the expected energy behaviour of the building and to comment on the options for introducing energy saving techniques.

Optimal Inclination for Maximum Convection Heat Transfer in Differentially-Heated Enclosures Filled with Water Near 4°C

ABSTRACT Natural convection in water-filled square cavities inclined with respect to gravity, having one wall cooled at 0°C and the opposite wall heated at a temperature ranging between 4°C and 30°C, is studied numerically for cavity widths spanning from 0.02 m to 0.1 m in the hypothesis of temperature-dependent physical properties, with the main aim to determine the optimal tilting angle for maximum heat transfer. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. Once the vertical configuration, in which the cavity is differentially heated at sides, is identified by the zero tilting angle, and positive angles denote configurations with the heated wall facing upwards, it is found that the optimal tilting angle is positive if the heating temperature is equal or higher than 8°C, whereas it is negative whenever the heating temperature is lower than 8°C. Moreover, the optimal tilting angle is found to increase as the cavity width is decreased and the temperature of the heated wall is either decreased or increased, according as it is higher or lower than 8°C. Sets of dimensionless correlating equations are developed for the prediction of both the optimal tilting angle and the heat transfer rate across the enclosure.

Buoyancy-Induced Convection of Alumina-Water Nanofluids in Laterally Heated Vertical Slender Cavities

ABSTRACT A two-phase model based on the double-diffusive approach is used to perform a numerical study of natural convection of alumina-water nanofluids in differentially heated vertical slender cavities. In the mathematical formulation, Brownian diffusion and thermophoresis are assumed to be the only slip mechanisms by which the solid phase can develop a significant relative velocity with respect to the liquid phase. The system of the governing equations of continuity, momentum and energy for the nanofluid, and continuity for the nanoparticles is solved through a computational code relying on the SIMPLE-C algorithm for the pressure-velocity coupling. The effective thermal conductivity and dynamic viscosity of the nanofluid, and the coefficient of thermophoretic diffusion of the suspended solid phase, are evaluated using three empirical correlations based on a high number of experimental data available from diverse sources, and validated by way of literature data different from those used in generating them. Numerical simulations are executed for different height-to-width aspect ratios of the enclosure, as well as different average temperatures of the nanofluid. The heat transfer performance of the nanoparticle suspension relative to that of the base fluid is found to increase as the nanofluid average temperature is increased and, at low to moderate temperatures, the aspect ratio of the enclosure is decreased. Moreover, at temperatures higher than room temperature, a peak at an optimal particle loading is found to exist for any investigated configuration.

Study of energy performance and analysis of possible retrofit strategies in a public school building in Rome

Schools represent a large slice of the non-residential building stock if you think that their usual users spend a lot of time time in their spaces. This paper presents a study of the energy performance in a school building in Rome. The main purpose is the determination of the energy demands according to UNI TS 11300 and the comparison of these results with those obtained by means of dynamic analyses and with the actual energy consumptions. This issue is very important not only because of the criticality of current energy situation but also because the reasons of the energy wastes are strongly related to the inefficiencies in the management of structures and technologic plants which may be widely avoided with smart and low cost interventions.

A New Tri-Generation System: Thermodynamical Analysis of a Micro Compressed Air Energy Storage

There is a growing interest in the electrical energy storage system, especially for matching intermittent sources of renewable energy with customers’ demand. Furthermore, it is possible, with these system, to level the absorption peak of the electric network (peak shaving) and the advantage of separating the production phase from the exertion phase (time shift). CAES (compressed air energy storage systems) are one of the most promising technologies of this field, because they are characterized by a high reliability, low environmental impact and a remarkable energy density. The main disadvantage of big systems is that they depend on geological formations which are necessary to the storage. The micro-CAES system, with a rigid storage vessel, guarantees a high portability of the system and a higher adaptability even with distributed or stand-alone energy productions. This article carries out a thermodynamical and energy analysis of the micro-CAES system, as a result of the mathematical model created in a Matlab/Simulink environment. New ideas will be discussed, as the one concerning the quasi-isothermal compression/expansion, through the exertion of a biphasic mixture, that will increase the total system efficiency and enable a combined production of electric, thermal and refrigeration energies. The exergy analysis of the results provided by the simulation of the model reports that more than one third of the exergy input to the system is lost. This is something promising for the development of an experimental device.