Abstract
In 2015 buildings accounted for about 40% of the total energy consumption in the European Union. The sector continues to expand, and energy consumption is projected to increase in the next years. Therefore, the recent European policies encourage the reduction of energy consumption and the use of energy from renewable sources in the buildings sector. These represent important measures needed to reduce the Union's energy dependence and greenhouse gas emissions. This fact, combined with the increase in both number and extension of urbanized areas, poses buildings as the most important factors controlling energy, mass and momentum exchanges between the earth surface and the atmosphere. In this framework, numerical models represent a reliable tool to study the interactions between cities and the atmosphere. In particular, meso-scale models can be coupled with parameterizations of averaged urban morphology features, in order to estimate the mean thermal and dynamical effects of the cities on the atmosphere. In addition, through a connection with simple building energy models, an improvement in the estimation of exchanges energy between the interior of buildings and the outdoor atmosphere has been achieved, being an important component of the urban energy budget. In this thesis the Weather Research and Forecasting (WRF) mesoscale model is used, coupled with the Building Effect Parametrization (BEP) and the Building Energy Model (BEM) multilayer urban schemes, focusing in particular on the impact of urbanization effects on the urban environment and on the building energy consumption. In addition, the assessment of the impact of different mitigation strategies, involving the use of vegetation, is carried out. Fine-scale parameters quantifying urban morphology (e.g. building plan and area fraction, average and distribution of building height) and the spatial distribution of vegetation are evaluated, in order to provide high-resolution input datasets for the urban parameterization scheme. The outputs of the meteorological model are validated through a comparison with data from a network of permanent conventional weather stations and observed total annual energy consumption in the urban area. The city taken as a case study is Bolzano, located in the northeastern Italian Alps, in a basin where three valleys join. Climatic conditions in the city are tightly connected with the complex topography of the surrounding area, influencing in particular the flow field, mainly characterized by daily-periodic up- and down-valley winds from tributary valleys, especially in the warm season, while ground-based persistent thermal inversions (especially in calm wind conditions) occur during wintertime. The present work is organized as follows. Chapter 1 provides an introduction about the state-of-the-art of numerical models and urban parameterization schemes. Chapter 2 presents the methodology for the calculation of Urban Canopy Parameters (UCPs), which describe in detail both the morphology of the city and the vegetation distribution (i.e ground vegetation and green roofs) in Bolzano. These parameters are then used as input in the Building Effect Parameterization (BEP) urban scheme. Chapter 3 presents simulations performed with the Weather Research and Forecasting (WRF) model, coupled with the Building Effect Parameterization (BEP) urban scheme (WRF/Urban), in order to provide an accurate description of the meteorological field at the urban scale, which is used as input data for the building energy model implemented with TRNSYS 17. Simulations are performed in order to assess the impact of WRF/Urban output on the dynamic energy consumption of a sample building. Chapter 4 aims at investigating the impacts of different parameters describing the urban environment on both urban climatic conditions and building energy consumption in several Local Climate Zones (LCZ), through a series of idealized two dimensional simulations. Chapter 5 assesses the urban heating energy consumption in the urban area of Bolzano, simulating heat consumption during a typical winter day, using the BEP+BEM model. Chapter 6 focuses on the impacts of green infrastructures (i.e. ground vegetation and green roofs) on both the urban environment and the building energy consumption, by means of the WRF model. A comparison of different realistic greening scenarios is carried out through a sensitivity analysis. Finally, Chapter 7 draws the conclusions of this research and suggests some topics which could be investigated in future works.