Digitalizing the urban landscape. Microclimate, energy systems and comfort

Urban Green Infrastructures (UGI) play a major role in mitigating the urban climatic conditions, as well as improving people’s health and wellbeing. Indeed, nature has a positive impact both on the pedestrian thermal and psychological perception, increasing productivity and creativity due to their restorative properties. Additionally, UGI mitigate the urban climatic conditions, reducing the energy demand of buildings and affecting the energy systems. The objective of this work is to develop a digital platform to arrive at urban planning decisions considering the impact of greenings on the urban microclimates, thermal perception of the pedestrians and energy infrastructure. The greening module developed within the tool CitySim [1] is coupled with the Canopy Interface Model [2], in order to compute the impact of greening (trees and grass) on the air temperature and wind speed. The study is performed for several urban configurations, focusing on the Lausanne climatic conditions. Greenings are designed as grass (varying their f-factor as function of the water supply), and trees (varying their leaf area index and height). The microclimatic conditions are used to quantify the hourly human thermal comfort, by the bio-meteorological index COMFA* budget. The proposed methodology also integrates energy systems optimizations [3], focusing on the impact of greenings on the renewable energy systems and its influence in smoothing the peak demand. The simulations performed provide the dynamic hourly variation of the wind speed and air temperature within the urban canyon, as function of the greening design (evapotranspiration capacity, geometrical properties of trees). The human thermal comfort is computed, in time and space, showing the positive impact of greening in reducing the “warm” and “hot” thermal sensations during the warmer months. The hourly energy demand of buildings is also computed, and the results are analysed focusing on the renewable energy systems. Results indicate the positive impact of greening in mitigating the urban climatic conditions, as function of the canyon design and the evapotranspiration capacity of the landscape. The important impact on the energy demand of buildings and the energy systems is also presented, providing recommendations for a smart urban systems design. The proposed digital platform provides an interactive display, a common ground of discussion for urban planners, architects, engineers and biometeorologists. Thanks to the work developed, an interdisciplinary knowledge is defined, which will be used as a teaching instrument within the ENAC faculty.

A review of assessment methods for the urban environment and its energy sustainability to guarantee climate adaptation of future cities

Silvia Coccolo, Dasaraden Mauree, Vahid Moussavi Nik, Emanuele Naboni, Amarasinghage Tharindu Dasun Perera, Jean-Louis Scartezzini

The current climate change is calling for a drastic reduction of energy demand as well as of greenhouse gases. Besides this, cities also need to adapt to face the challenges related to climate change. Cities, with their complex urban texture and fabric, can be represented as a diverse ecosystem that does not have a clear and defined boundary. Multiple software tools that have been developed, in recent years, for assessment of urban climate, building energy demand, the outdoor thermal comfort and the energy systems. In this review, we, however, noted that these tools often address only one or two of these urban planning aspects. There is nonetheless an intricate link between them. For instance, the outdoor comfort assessment has shown that there is a strong link between biometeorology and architecture and urban climate. Additionally, to address the challenges of the energy transition, there will be a convergence of the energy needs in the future with an energy nexus regrouping the energy demand of urban areas. It is also highlighted that the uncertainty related to future climatic data makes urban adaptation and mitigation strategies complex to implement and to design given the lack of a comprehensive framework. We thus conclude by suggesting the need for a holistic interface to take into account this multi-dimensional problem. With the help of such a platform, a positive loop in urban design can be initiated leading to the development of low carbon cities and/or with the use of blue and green infrastructure to have a positive impact on the mitigation and adaptation strategies.

PERGAMON-ELSEVIER SCIENCE LTD2019

The impact of urban texture on energy system design process

Silvia Coccolo, Dasaraden Mauree, Sameh Monna, Amarasinghage Tharindu Dasun Perera, Jean-Louis Scartezzini

This study evaluates the impact of urban planning decisions regarding building stock on energy system design and operation. Three urban planning scenarios are considered for an archetype neighbourhood in Nablus in Palestine. The distinguishing difference is that they have different albedo values for the building stock. A computational platform that combines building simulation, urban climate and energy system optimization (considering Net Present Value (NPV) and Grid Integration Level) is used to assess the scenarios. The study reveals that the annual or peak energy demand is not sufficient to compare two scenarios; it is important to consider energy demand pattern and the renewable energy potential, where an energy system design tool is important. Therefore, it can be concluded that the energy system design tools will play a major role in sustainable urban planning processes.

IOP2019

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

What will the cities of tomorrow look like? This is a crucial question because in the four and a half billion years of its existence, the Earth has never been so threatened, as it is today. Since 2008 half of the world's population has lived in towns – more than 70% in rich nations. Three quarters of CO2 emissions are produced in towns, 75% of the world's energy is consumed in towns. The battle for our climate, for the continuation of our species and all other life, will be largely waged in cities. Will it be possible to create the ideal ecological town? The objective of this study is to compare actual and theoretical urban forms in order to explore the diverse effects of daylighting and solar potential on densely built-up sites. Indeed, the search for ideal solar orientations has been a persistent problem from the 19th century until the beginning of the 20th. Even today, for all our scientific knowledge and empirical experience of solar energy, making the correct choice has still not crossed the boundary from an enigmatic, tricky art into the field of an exact science. As a first step, six existing urban sites in Switzerland and Brazil, as well as two projects in the United Kingdom, a few generic models and a utopian city, were modelled and analyzed. The goal was not merely the construction of new, exemplary districts but also the transformation of existing towns. The findings have been used to assess the potential of façades and roofs located in urban areas for active and passive solar heating, photovoltaic electricity generation and daylighting. The results obtained from these different case studies revealed large variations of the potential for solar energy collection on the buildings' façades and roofs. Ideally, these investigations are expected to help architects and town planners understand how to optimise solar collection on buildings design. In addition, a study was made of the Contemporary City of Three Million Inhabitants created by Le Corbusier. According to the latter, the Contemporary City could increase the urban capacity and at the same time improve the urban environment and the efficiency of the city. Therefore the present study extracted the solar potential of this utopian city in order to assess Le Corbusier's propositions. Since 1922, Le Corbusier's studies have influenced architects and town-planners in their choice of orientations and urban forms: it was therefore crucial to discover if this reliance on Le Corbusier was justified. Solar irradiation and illuminance values obtained through numerical simulations form the core part of the method. The method adopted for the entire set of computer simulations consisted in modelling — via a computer-aided drawing piece of software, namely AutoCAD — the digital model of each building or group of buildings prior to exporting them to an urban performance analysis software (PPF/RADIANCE software package). Spatial distributions of solar irradiation and daylight fluxes over the overall building façades and roofs were calculated using ray-tracing simulation techniques to determine the appropriate placement of different solar technologies (passive and active solar, photovoltaic and daylighting). Performance indicators were used to assess the solar utilisation potential of the urban sites (e.g. statistics of sky view factors and daylight factors) in order to determine the optimal solar strategies for a given urban context. In addition, various works and sun-related recommendations that have appeared mainly since the end of the nineteenth century, together with the various scientific models and software tools pertaining to this topic, are presented in this study.

EPFL2010

Optimisation of Urban Form by the Evaluation of the Solar Potential

Marylène Montavon

EPFL2010