Towards Solar Decathlon: Concepts for a Sustainable Urban Water Management in a new eco-district

Water is rarely considered to be a crucial aspect in sustainable housing. In fact, water sustainability in eco-districts and in ecological architecture is frequently limited to recycling and reuse solutions. Why less water? What could explain the choice of an installation, of a specific strategy or of a criterion trying to decrease water needs? Terms as ecological footprint or sustainability are becoming more and more used, however, how can sustainability be measured? What does sustainable water mean? What are the parameters that quantify the ecological footprint of a water management system? Within this project, some possible concepts of optimization and valorization of sustainable urban water system have been defined and explored. Numerous studies about water management, water distribution, sanitary technologies, recycling, etc. have already been done. Nevertheless, it is less common to identify the reasons that are able to justify a reduced consumption of water. Eco-district labels propose several solutions for sustainable water, however they are limited by scale or simply focused on one stage of the water cycle. The aim of this project is then to consider water from a larger point of view: through a Life Cycle Analysis approach, needs and properties of different urban water management systems are compared and evaluated. The scale considered for such reflections is effectively a central parameter; in this case, hypothesis will be applied to collective habitations inserted in a district and part of a specific urban context: the city of Fribourg. The urban environment has particular features in relation to surrounding rural areas: energy exchanges, hydrology characteristics and limited ecosystems. The relationship between the use of natural resources and urban development is becoming more and more important; the purpose of this thesis is then to define a methodology able to suggest a sustainable use of water through environmental, political and economic issues. A real urban case study with its current water management system defines what has to be analyzed and allows evaluating the limits and the possible enhancements of such system. Thus, in order to have an idea about the potential of sustainable water management solutions, an ambitious analysis of energy related to water uses and disposals is created and is used to show the reasons for change in a real model as the city of Fribourg. A comparison between two extreme scenarios of Fribourg’s selected zones is finally developed, discussed and implied in the conclusions through specific actions and facts. The results show that a high potential of improvements exist. Using them to elaborate new strategies in collaboration with the several stakeholders contacted may contribute to achieve many of today’s objectives for a sustainable urban water management. The best scenario, chosen with a new concept of eco-label, summarizes and concludes the analysis.

Méthodologie multicritère d'aide à la décision pour le renouvellement urbain à l'échelle du quartier

Maria Gracia Riera Perez

The present work develops a new methodology for assessing urban renewal scenarios at the neighborhood scale. Entitled URBIUS, this methodology seeks to meet the needs of municipalities in terms of planning for the development of their urban built fabric. It is now widely recognized that the urban population growth, along with the increase in the use of private vehicles, has led to a generalized urban sprawl. This land use is not sustainable in environmental, social and economic terms. Because most European cities are in this situation, it appears necessary to bring new developments within the urban built fabric, in order to raise their density. However, to rely on densification alone is not sufficient in order to move towards a more sustainable urban environment and to attract new residents looking for quality living spaces. Therefore, the transformation of the city requires a holistic vision, integrating different objectives. In this perspective, the neighborhood scale has been identified as an operational scale which integrates both the specific objectives of stakeholders taking part in the making of the city and the broader objectives of the city itself. In this context, this work seeks to contribute to the inward development of the cities in a qualitative way, by providing URBIUS, a new methodology for assessing the sustainability of urban renewal strategies at the neighborhood level. Prior to the creation of this methodology, an operational definition of sustainable neighborhoods has been developed. This one includes six goals: to ensure the feasibility of the urban renewal strategy, to provide housing to all residents, to balance the supply of jobs and housing, to save energy resources, to upgrade the local natural resources and to promote the balance between density and urban quality. Hence, the methodology is structured following these six goals and declines them in criteria and indicators for the purpose of the assessment. For each indicator, both quantitative and qualitative, assessment thresholds are set: a limit value and a target value. These thresholds are used to assess the strategies positively if the value is better than the target value, negatively if it is worse than the limit value, and uncertain for values lying between the limit value and the target value. However, in order to adjust the assessment to the specific potential of a neighborhood, an adaptation technique has been developed based on a dynamic approach. The assessment thresholds are adapted depending on the evaluation of the existing state of the neighborhood and on its underlying trend, that is to say the assessment of the neighborhood at a given time whereas no special action is planned. Finally, the new methodology is tested on four neighborhoods taken as case studies. The chosen neighborhoods have all a good quality public transportation system, with potential for densification and capacity to provide quality living space. They are located in the canton of Vaud, Switzerland: Lausanne, Prilly, Echallens and Yverdon-les-Bains. This work highlights the potential of urban renewal strategies at the neighborhood scale in the process of the transformation of the city towards greater sustainability and the contribution of sustainability assessment methodologies. In this sense, URBIUS is a relevant methodology to assist and foster sustainable urban renewal. Now it is up to the key stakeholders to undertake such efforts in urban renewal in a concerted and sustained effort.

EPFL2016

Development and application of a numerical simulation system to evaluate the impact of anthropogenic heat fluxes on urban boundary layer climate

Andrea Krpo

Increasing economic development, and growing population, generated during the last decades a very important growth of cities. Urban regions include nowadays more than half of the global population and, by 2030, this proportion is forecasted to increase to three quarters. A consequent more and more extensive use of natural resources, together with increasing anthropogenic activities such as emissions from traffic and factories, or heating from air-conditioning facilities, modify local climate in many different ways, leading to a progressive degradation of life quality in urban areas. Taking these facts into account, there is nowadays a real need for efficient urban planning guidelines and sustainability policies in order to improve life quality in urban areas. Different points should be considered including urban warming, air pollution, human health, economic, and cooling energy needs. The present work goes in this direction, aiming at developing a simulation system for the study of the complex interactions between buildings and the atmosphere. The system of equations describing atmospheric flows is highly non linear and it is common to employ numerical techniques in order to solve them. Moreover, the representation of urban canopy climate, and related air pollution problems, requiree taking the interaction between urban scale (tens of kilometers), and mesoscale (hundreds of kilometers) processes into account. At first, starting from previous studies, a mesoscale meteorological model has been developed as part of this work. Urban induced processes have been considered by implementing inside the model a detailed urban parameterization scheme developed in a previous work. The scheme is able to capture different urban processes, and reproduces the effects of cities in a more accurate way than traditional methods usually used in mesoscale models. However, the heat generated in buildings, and the way this heat is exchanged with the exterior, was not explicitly resolved. In particular, recent studies indicated that anthropogenic heat from air-conditioning facilities can play an important role and should be taken into account for more complete urban climate studies. To this purpose, a Building Energy Model (BEM) has been developed, and coupled to the Urban Canopy Parameterisation (UCP). This building model takes into account the diffusion of heat through walls, roofs, and floors, the natural ventilation, the generation of heat from occupants and equipments, and the consumption of energy through air conditioning systems. Comparisons with other programs indicate that BEM is able to accurately simulate the basic heat transfer phenomena, and to reproduce the heat fluxes exchanged between buildings and the atmosphere. In a second part of the work, the simulation system composed by the Mesoscale Model (MM), UCP, and BEM is tested with respect to one, and two-dimensional configurations. In particular, the impact of BEM on the meteorological variables is analyzed, as well as the efficiency of different urban warming countermeasures, and cooling energy demands control strategies. Two-dimensional results are then utilized as guidance for the application of MM-UCP-BEM over the realistic configuration including the city of Basel and the surrounding areas. At first, comparisons of urban and rural simulated temperatures with measures provided by the BUBBLE project (Basel Urban Boundary Layer Experiment), have shown that the model could reasonably well reproduce the variations in outdoor air temperature. In a second time, the simulations considered for the two-dimensional configuration are applied to the case of Basel. Numerical results confirm that anthropogenic fluxes from air-conditioning facilities can have a non negligent impact on the urban meteorology. Typically, they modify the outdoor temperature and increase the Urban Heat Island (UHI) phenomenon. In the last part of the study, the applicability of the model in performing urban warming countermeasures, and cooling energy demands control strategies, is evaluated. In this purpose in mind, a sensitivity analysis is carried out indicating that appropriate physical properties of built materials, efficient air-conditioning systems, and the application of simple energy saving policies, can lead to very important cooling energy savings. In general, the application of BEM inside the UCP allows computing the heat released into the atmosphere by air-conditioning facilities, as well as the corresponding feedbacks produced on the different meteorological variables. It also increases the capability of the urban parameterisation to provide more detailed studies of urban warming countermeasures, and cooling energy demands in real cities.

EPFL2009

The energy transition – an integrative analysis

Claudia Rebeca Binder Signer

The ongoing energy transition is seen as a key component for the transition towards a more sustainable society. An important component in the move towards a sustainable energy system is the transition from a mainly centralized, fossil-fuel system to a more localized, renewable one. This transition, however, requires not only the development of new energy technologies but also radical, systemic shifts in deeply held values and beliefs, in patterns of social behavior, and in governance regimes. Thereby the ecological, technical and social systems have to be conceptualized as Social-Ecological-Technical Systems (SETS) and new integrative, interdisciplinary research approaches are needed which consider the interaction between these subsystems. We present results of an integrative analysis of transitions which occurred in two Austrian energy regions during the last 20 years. We show (i) how institutional development and infrastructure development are related to each other within time; (ii) whether and how demand and supply of renewable energy carries can be met at the regional level; and (iii) which factors in household behavior affect decision making- and consequently energy demand in the housing sector. Finally, we present some thoughts on the resilience of such transition processes and discuss the need for further research. Socio-ecological transitions are defined as transitions between different societal regimes and co-dependent ecological changes. In the past, two major transitions have occurred as are the transition from the hunter and gatherers society to the agricultural society and from the latter to the industrial society. These transitions have both been characterized by an increased material and energy consumption per capita and an increase in urban population. Scholars have stated that we are in the middle of a new transition maybe towards a sustainable society. This transition is likely to encompass a further increase in the share of the population living in urban areas, however linked to significant efforts to change the metabolism of cities by e.g., transforming the energy system away from a fossil fuel based towards a renewable energy system. The experiences of various scholars have led to the insight that this transition cannot be analyzed with disciplinary approaches alone. They have to be dealt with in an integrative, interdisciplinary way that considers the dynamics and interactions between social and ecological systems. This presentation will show how inter- and transdisciplinary research could be framed to better understand, simulate, and provide policy recommendations for the ongoing transition. These approaches significantly feed into the new research foci in urban ecology, as they specifically study the dynamics within and the interaction between the social and ecological systems. Empirical results for the transition of energy regions will be presented.

2016