Thermal Comfort Maps to estimate the impact of urban greening on the outdoor human comfort

Outdoor human comfort is an important factor in the evaluation of the liveability of a city as well as for promoting people’s health and well-being. In hot arid climates in particular, urban planning and design can considerably impact the day-to-day thermal comfort of the pedestrians, for better or for worse. Strategies to reduce thermal discomfort include shading structures, water bodies, and the promotion of natural ventilation – and most significantly, green areas. Trees have a major impact on the pedestrians in the built environment as they not only provide shading but also improve the microclimate in urban areas, thereby reducing the time during which discomfort is felt. The objective of this paper is to present a new methodology for dynamically quantifying the impact of different plants in urban areas on outdoor human comfort, through 3D urban energy modelling. The proposed methodology makes use of an urban energy modelling tool, providing a comprehensive view of the city energy fluxes, with a focus on the impact of trees on the human thermal comfort. Outdoor human comfort is assessed using the Index of Thermal Stress for the campus of the Swiss International Scientific School of Dubai (UAE), where “Thermal Comfort Maps” are designed to quantify the pedestrian thermal sensation and its variation in time and space. Additionally, the energy fluxes impinging on the urban pedestrians are quantified, dynamically, in hourly time step, providing an important instrument to understand their thermal stress, and the environmental factors affecting it. Based on the simulations, thanks to native greening, a significant improvement in outdoor comfort conditions was achieved in the campus, reducing the “warm/hot” and “very hot” thermal sensations from 1,291 h (on average over the entire campus) to less than 300 h by planting Ghaf and Acacia trees.

Biocides in paints in urban areas: Modelling an underestimated source of environmental contamination

David Andrew Barry, Sylvain Coutu, Luca Rossi, Chiara Rota

Biocide contamination of receiving waters is generally linked with agriculture. However, recent studies have shown that urban contributions should be also considered. One of the suspected biocide sources in the urban environment is building paint. Biocides like diuron, irgarol, terbutryn, carbendazim, etc., are conventionally used in paint to control fungi, algae, bacteria and other microorganisms that can colonize building façades. The problem of biocides in urban areas is closely linked to meteorological conditions and in particular to rain events. As a consequence, it is important to understand how rainwater collects and transports biocides from façades and how these biocides are transported in sewer systems to receiving waters. In this study, we present a conceptual model describing façade leaching and couple it with a Wind Driven Rain model and a classical hydrological model to compute the contribution of a city to the biocide load from building paint. For the entire city of Lausanne (Switzerland, 200’000 inhabitants), a global production of 2200 kg/year of terbutryn leached by rain was estimated considering local building characteristics and meteorological information. The leaching model fitted well the peak in concentration measured at the bottom of the wall at the initial stage of the rain event. However, concentrations measured in an urban river in the watershed leads to the conclusion that most of this leachate does not reach directly receiving waters, but is infiltrated into soil or reaches the sewers after some delays in drainage pipes. Release of biocides from façade leaching in the environment is systematic during rain event. It is of greater importance to estimate the dynamic of biocides during rain events and to compare these values with dedicated time varying environmental quality criteria.

2011

Bioclimatic Design of Sustainable Campuses using Advanced Optimisation Methods

Silvia Coccolo

Cities occupy 0.5% of the earth surface, but they consume 75% of worldwide energy, and they are responsible of 50% to 80% of CO2 emissions. Cities are directly responsible for the climate change. However, they are the key for providing solutions to this problem. More specifically, a city comprises a very large number of microclimates, according to their urban and environmental design. A sustainable and liveable urban planning could well improve the urban environmental conditions by mitigating the energy fluxes of the city. The objective of this thesis is to address the energy fluxes within the urban environment, in time and space. The study focuses on the improvement of the energy demand of buildings as well as the outdoor human comfort. To do so, we try to establish a new bridge between the biometeorology and the architecture and to find a simplified approach to bring this research into practice. More specifically, the human comfort is well addressed in the research domain but, due to its complexity, it is quite difficult to use it in the real practice. In order to overcome this problem, we introduce three new modules in the software CitySim Pro. CitySim is an urban energy modelling tool which is able to quantify, dynamically, the energy demand from a building scale to the city scale. A first module, developed in this doctoral thesis, focuses on the quantification of the outdoor human comfort by the Index of Thermal Stress (ITS) and the COMFA* budget. The second module aims to understand the radiative environment by the calculation of the Mean Radiant Temperature (MRT). The third module focuses on the cooling potential of the vegetation and evaluates the shadings and the evapotranspiration provided by greenings. Based on the modules, Comfort Maps are designed, representing an important instrument to bring the research into practice: these maps are proposed as an effective way to share information between architects and municipalities, providing indications on the urban microclimatic conditions. Finally, the developed modules are used to optimize, using the hybrid CMA-ES/HDE evolutionary algorithm, the energy demand and the outdoor human comfort of two campuses: EPFL campus in Lausanne (Switzerland), and the Swiss International School (SISD) campus in Dubai (United Arab Emirates). On site monitoring, realized in the SISD campus, underlined the impact of the built environment, as well as the shadowing strategies, by punctual monitoring in five locations of the campus. The results show that i) we should not limit an architectural design to a single building, but it is important to think and design at the district/ city scale. There is ii) a strong relationship between the energy demand of buildings and the outdoor human comfort, consequently both of them should be jointly addressed by architects and urban planners, focusing on the building and the "space between buildings" design. Finally, iii) a sound urban design should derive from the bioclimatology, transforming the climatic adversities into design opportunities. Finally, a list of practical recommendations is defined, providing a support for a sound architectural design in time, and space.

EPFL2017

Métropolisation, habitat précaire et relogement forcé: entre phénomènes d'exclusion et tactiques populaires d'intégration

Sébastien Wust

This work was carried out within the interdisciplinary scientific program named "Sustainable Development, Metropolisation and Pollution of Natural Resources in Ho Chi Minh-City, Vietnam". This program, launched in 1994, is financed by the Swiss National Science Foundation (Priority Program Environment, Module 7 "Environment and development"). The main goal of this thesis is to grasp the social, economic and spatial dimensions at stake of involuntary resettlement of precarious settlements. in the context of developing countries' metropolisation. One of the approach selected fits within a thorough study of southern metropolis evolution dynamics, more precisely that of disadvantaged neighbourhoods. Moreover, we decided to develop a specific approach of involuntary resettlement, which is constructed using mainly two dialectical and interdependent concepts: exclusion and integration. In this way, this work differs from the most frequently used theoretical models, which are based on impoverishment or stress dimensions. In third world metropolis, government forces have an increasing tendency to turn to involuntary resettlement in order to implement or promote urban planning. Every year, approximately 6 million people are forced to move into an urban environment. This concerns mainly the most underprivileged sections of the population corning from precarious settlements. In recent times, this phenomenon has grown to such a point that some international institutions have even talked about the century of involuntary resettlement. The theoretical framework of this thesis refers to three different fields of knowledge, which nevertheless are linked to one another. The first field concerns developing countries metropolisation. Closely associated with the globalisation and polarisation of international trade, this process leads not only to the rise of exclusion but also to the dualisation of economic, social and political spheres and the fragmentation of urban spaces. The second theoretical field of study is based on questions raised by precarious settlements in southern metropolis. We analyse the way vulnerable populations living in disadvantaged neighbourhoods develop urban integration tactics in order to counter metropolitan exclusion forces and to alleviate precariousness. Finally, the third field is part of involuntary resettlement problematic. While it shares a close link to public policy evaluation, this problematic analyses the institutional values, norms, and practices underlying relocation policies of the people living in disadvantaged neighbourhoods. Our goal is also to develop a better understanding of the consequences associated to this kind of urban program and the way they might contribute to strengthening living conditions as well as residential situation precariousness for those who have been forced to move, leading them to develop defence mechanisms in order to guaranty their integration in the metropolis. In this analysis, we will focus on Ho Chi Minh-City and on the relocation program concerning the populations living in Nhieu Loc-Thi Nghe canal's precarious settlements. In the empirical part of this work, we will analyse and measure the consequences of this policy on their living conditions as well as on their behaviour. We will try to analyse to what extent those consequences tend to increase exclusion of underprivileged populations, limit their integration capacity, and enhances their residential mobility towards new precarious settlements that fit more to the aspirations, and above all, to the means of the underprivileged. Given the complexity of the topic covered in this work, we opted for an interdisciplinary approach. It appeals to different fields of social sciences: sociology, economics, geography, political sciences, but also architecture and urban planning. Moreover, we chose a quantitative as well as a qualitative method. Based on a multidimensional analysis of Nhieu Loc-Thi Nghe canal's population living in precarious settlements, we will be able to grasp the discriminating dimension of involuntary resettlement policy set up by metropolitan authorities as well as its severe impact on the population at a residential, social and economical level. Restrictive economic criteria or in some cases insufficient compensations offered by public authorities are such that a number of persons are excluded from the program. But on top of that, part of the families relocated in modern and salubrious apartments suffer from exclusion. As regards housing, the new apartments are characterised by their limited residential functions. This is mainly due to constraints linked to high rise housing, which acts as an economic and social barrier. In terms of social organisation, involuntary resettlement leads to a family nuclearisation process, and traditional sociability tends to turn to a more individualistic way of life, a phenomenon which results in a partial deconstruction of solidarity and protection networks. Finally, at the domestic economy level, resettled populations have to deal with an increase in service charges as well as working conditions deterioration which involve decreasing incomes. Although this modern way of life appeals to resettled families, most of them are brought to develop new integration tactics in order to limit involuntary resettlement exclusion effects. These tactics are to a large extent conservative inasmuch as they tend to reproduce ways of life and space habits characteristic of the former residential areas. To a large extent, they are characterised by palliative measures of space utilisation, professional insertion, income improvement and domestic means reallocation. Despite their willingness, families have a hard time fighting against resettlement exclusion forces. Residential mobility as well as subsidised apartments resale then become the way for some families to minimise precarious living conditions. Nevertheless, the benefits they gain from these illegal practices are often insufficient for them to buy or build an accommodation close to the center of the metropolis. The only possibility left to the reseller is then to rent a dwelling unit in a disadvantaged neighbourhoods or to move on the outskirts. While residential mobility leads to the creation of new precarious settlements in Ho Chi Minh-City, some families living conditions as well as residential situation keep on deteriorating, a decline which might bring some of them to experience a kind of urban nomadism. While the results of our study confirm the hypothesis stated at the beginning of this work, they also point out how hard it is to fulfill the housing aspirations of the most underprivileged considering the precariousness of their living conditions. The inadequacy of precarious settlements relocation policy is even worse when based on a modernist and standardised approach of the housing problem which favours typological and technical dimensions of residential space to the detriment of social, economic and ecological dimensions. What is at stake in involuntary resettlement concerns mainly the multidimensional mechanisms of exclusion and integration of which depends the subsistence of the most underprivileged in Ho Chi Minh-City. Urban authorities need to make political adjustments if they want resettlement impacts to fit the goals of sustainable development. In order to achieve this objective, popular participation and exchange between involved actors is the first condition they need to fulfill for the implementation of any policy in order to fight against exclusion and promote the integration of the most underprivileged as well as for any policy which aims to take into account the capacity of urban ecosystems.

EPFL2001