Andrea Vallati

Differents Methods to Estimate the Mean Radiant Temperature in an Urban Canyon

The mean radiant temperature is one of the meteorological key parameters governing human energy balance and the thermal comfort of human body. This variable can be considered as the sum of all direct and reflected radiation fluxes to which the human body is exposed. After the basics of the Tmrt calculation a comparison between two methods suitable for obtaining Tmrt in a street canyon will be presented. One of the discussed methods of obtaining Tmrt is based on the utilization of a globe thermometer. The other method is the radiation environment simulation through three PC software (RayMan, ENVI-met and SOLWEIG).

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.

Numerical Analysis and Measures for the Evaluation of Comfort Inside Buses Used for Public Transport

This paper on thermo-hygrometric conditions inside buses used for public transport is from the proceedings of 14th international Conference on Urban Transport and the Environment in the 21st Century, which was held in Malta in 2008. The authors used techniques from analysis of the thermo-hygrometric conditions inside trains to understand the conditions inside buses, to maximize the air conditioning system and the installation of the air distribution terminals. They stress that summer is the most important time of the year for thermo-hygrometric conditions inside buses because of the frequent opening of doors, which makes the internal temperature uneven, due to the strong air drafts. The simulation pattern, produced with Airpack 2.1 (Fluent) software, was then validated with a series of measures and used for the analysis of the main issues concerning discomfort. The authors conclude with a discussion of the use of air screened doors that result in a reduction in the heat exchange between the inside and the outside of the air-conditioned bus. This technology transforms the air barrier from a simple separation element to a full system component of thermo-hygrometric control of the internal room. The thermo fluid dynamic results guarantee a significant improvement in thermo-hygrometric comfort for the bus passengers.

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.

A Numerical Investigation of Flow and Heat Transfer of Laminar Multiple Slot Jets Impinging on Multiple Protruding Heat Sources

Abstract The flow and heat transfer behavior of laminar incompressible slot jets impingement cooling of an array of heated surfaces in a channel have been investigated numerically. The computations are done for a variety of values of slot jets Reynolds number, channel height and distance between two heated blocks. The influences of these geometrical and physical parameters are predicted. The results, streamline contour, velocity profile, isothermal contour, local Nusselt number, and average Nusselt number are compared and documented. The first and second recirculation cells size are gradually increased, and the highest heat transfer rate is attained when Reynolds number increased. However, the heat transfer rates are decreased when channel height increased. The peak local Nusselt number value is noticed at stagnation point of the first block by first jet, and the second peak local Nusselt number value is observed at fourth block by second jet. The distances between two blocks play a significant role in the downstream velocity which leads to create the strong recirculation cells in between the two heated blocks when the distance between the two blocks increased.

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.

Use of nanofluids as coolants in buoyancy-driven thermal management of embedded heating components of small-scale devices

A two-phase model based on the double-diffusive approach is used to perform a numerical study on natural convection of water-based nanofluids in square cavities partially heated at the bottom wall and cooled at both sides, assuming that Brownian diffusion and thermophoresis are the only slip mechanisms by which the solid phase can develop a significant relative velocity with respect to the liquid phase. Numerical simulations are basically executed for Al2O3 + H2O, using the diameter and the average volume fraction of the suspended nanoparticles, the cavity width, the heated fraction of the bottom wall, the average temperature and the temperature difference imposed across the cavity, as independent variables. Additional simulations are also performed using CuO or TiO2 nanoparticles. It is found that the cooperation between the solutal and thermal buoyancy forces results in a significant enhancement of the heat transfer performance of the nanofluid compared with the pure base liquid.

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.