Progettazione di un modulo di rinnovo dell'aria ambiente con recupero termico. Applicazione ad un caso reale

L’elaborato riguarda la progettazione di un modulo di rinnovo dell’aria ambiente con recupero termico, che integri anche la funzione di climatizzazione invernale ed estiva. L’applicazione è partita dall’analisi di un caso reale, ossia la palazzina uffici dell’azienda Galletti S.p.A. Per tutti gli uffici interessati si è proceduto alla verifica del carico termico invernale, nonché dei fabbisogni di aria di rinnovo sulla base dei tassi di occupazione previsti dalle norme e parallelamente dei tassi di occupazione reali. In tale elaborato vengono illustrate le due normative relative alla ventilazione applicabili in Italia, quella italiana (UNI 10339) e quella europea (UNI EN 16798-1), le quali permetteranno di ottenere i valori di ricambi d’aria necessari per i singoli ambienti. Per effettuare i ricambi di aria si è scelto di dimensionare un sistema di VMC puntuale. Successivamente si sono analizzati i principali inquinanti indoor e tra questi è stata scelta come indice di qualità dell’aria interna la concentrazione di CO2, in quanto il controllo della sua concentrazione permette di avere un indice di un corretto ricambio dell’aria ambiente. Per effettuare il dimensionamento della macchina si sono presi come locali tipo undici uffici dello stabilimento Galletti. Nel lavoro di selezione sono stati individuati i recuperatori a piastre in alluminio e i ventilatori necessari. Si è poi applicato un modello dinamico di accumulo di CO2 in ambienti chiusi creato in Galletti per monitorare l’andamento della concentrazione di CO2 nel tempo con diversi valori di portata di rinnovo, considerando tre livelli di isolamento dell’involucro. Il modello fornisce indicazioni sul tipo di regolazione che si prevede per la macchina. Per ciascun ambiente è stata formulata una proposta di sostituzione dell’unità di climatizzazione presente (fan coil) con una nuova unità in grado di fare fronte al tasso di rinnovo richiesto ed alla climatizzazione invernale in condizioni di progetto.

Correlation between urban form and PM2.5 concentration — Evidence from the New York metropolitan Area and Shanghai city

With the development of the economy and society, air pollution has posed a huge threat to public health around the world, especially to people who live in urban areas. Typically, urban development patterns can be roughly divided into compact cities and urban sprawl. In recent years, the relationship between urban form and air quality (especially PM2.5) is gaining more and more attention from urban planners, environmentalists, and governments. This study is focusing on The New York metropolitan area and Shanghai city, which are both megacities but with different urban spatial forms. For both study areas,there are five main variables to measure the urban form metrics, naming Population Density, Artificial Land Area Per Ten Thousand People, Road Density, Green Land Area Ratio and Artificial Land Area Ratio. In addition, considering the impact of economic activities and public transportation, GDP per capita, Number of bus stop and Number of subway station are used as control variables. Based on the results of regression, a megacity like the New York metropolitan area with urban sprawl shows a low spatial correlation on PM2.5 concentration. Meanwhile, almost all the spatial form indicators effect on PM2.5 concentration is not significant. However, a compact megacity like Shanghai shows a diametrically opposite result. Urban form, especially population density, has a strong relationship with PM2.5 concentration. It can be predicted that a reduction in population density would lead to significant improvements on decrease the PM2.5 concentration in Shanghai. Meanwhile, increasing the ratio of green land and construction area per capita will get a positive influence on reducing PM2.5 concentration as well. Road density is not a significant factor for a megacity in both two urban forms. The way and type of energy used by vehicles on megacities maybe more critical.

Impact of convective motions on pollutant dispersion in urban canyons: an analysis through RANS simulations

Since the majority of the population of the world lives in cities and that this number is expected to increase in the next years, one of the biggest challenges of the research is the determination of the risk deriving from high temperatures experienced in urban areas, together with improving responses to climate-related disasters, for example by introducing in the urban context vegetation or built infrastructures that can improve the air quality. In this work, we will investigate how different setups of the boundary and initial conditions set on an urban canyon generate different patterns of the dispersion of a pollutant. To do so we will exploit the low computational cost of Reynolds-Averaged Navier-Stokes (RANS) simulations to reproduce the dynamics of an infinite array of two-dimensional square urban canyons. A pollutant is released at the street level to mimic the presence of traffic. RANS simulations are run using the k-ɛ closure model and vertical profiles of significant variables of the urban canyon, namely the velocity, the turbulent kinetic energy, and the concentration, are represented. This is done using the open-source software OpenFOAM and modifying the standard solver simpleFoam to include the concentration equation and the temperature by introducing a buoyancy term in the governing equations. The results of the simulation are validated with experimental results and products of Large-Eddy Simulations (LES) from previous works showing that the simulation is able to reproduce all the quantities under examination with satisfactory accuracy. Moreover, this comparison shows that despite LES are known to be more accurate albeit more expensive, RANS simulations represent a reliable tool if a smaller computational cost is needed. Overall, this work exploits the low computational cost of RANS simulations to produce multiple scenarios useful to evaluate how the dispersion of a pollutant changes by a modification of key variables, such as the temperature.