Compact cities in a sustainable manner

Densification is generally assumed to exert negative impacts on urban daylight and solar potential, however, this paper demonstrates the possibilities to increase usable floor area and plot ratio without undermining the opportunities of daylight and solar applications. The paper investigates the diverse influences of built density on daylight access and the potential of two solar systems. The findings suggest that plot ratio is influential to quantities such as daylight factor, sky view factor and the potential of solar thermal and photovoltaic applications on roof, whilst the potential of solar thermal and photovoltaic applications on building facades are more dependent on site coverage and the extent of horizontal obstruction.

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

Building envelope and solar energy optimization: a new “wizard” for architects

Marja Edelman, Maria Cristina Munari Probst, Christian Roecker

When designing a project, architects are facing more and more constraints on the building’s energy efficiency. Tougher values on insulation and energy consumption are now often combined with compulsory implementation of active solar systems - photovoltaics or solar thermal. With natural lighting, passive and active solar all competing for envelope areas, comparing results of architectural variants becomes more important and at the same time more complex. To help overcome this situation, a renowned “energy balance calculation/certification” software tool has been improved and adapted, proposing a wizard developed to meet a growing demand: obtain a quick feedback on building envelope, energy efficiency and solar strategies, especially in the early design stage, when strategies are defined. The wizard helps fulfilling various norms of different European countries, allowing architects to compare variants during this crucial phase. By simplifying data entry using smart default values derived from appropriate general choices, and by presenting a clear and intuitive user’s interface, this new tool offers practicing architects an easy access to building envelope and solar energy use optimization.

Université Catholique de Louvain-la-Neuve2011

Criteria and policies to master the visual impact of solar systems in urban environments: The LESO-QSV method

Maria Cristina Munari Probst, Christian Roecker

Increased use of solar collectors in buildings is necessary but poses major challenges in existing built environ ments, especially where architectural quality is an issue. The large size of solar systems at the building scale requires careful planning, as they may easily end up compromising the aesthetics of buildings, threatening the identity of entire contexts. A new method named LESO-QSV(for Laboratoire d'Energie SOlaire - Qualite Sensibilite-Visibilite) has been developed to help authorities promote solar energy use while preserving the quality of pre-existing urban areas. The vision underlining the approach is that solar integration is possible also in delicate contexts, if appropriate design efforts and adequate cost investments are made. The issue is then no longer to be in favour or against the use of solar systems in cities, but rather to define appropriate local levels of integration quality, and to identify the factors needed to initiate smart solar energy policies able to preserve the quality of pre-existing urban contexts while promoting solar energy use. The LESO-QSV method helps tackle these issues with clear and objective proposals: First it clarifies the notion of architectural integration quality and proposes a simple evaluation method, based on a set of criteria derived from pre-existing literature. Then it helps authorities set and implement local acceptability requirements, introducing the notion of architectural "criticity" of city surfaces (LESO-QSV acceptability). The concept of "criticity", at the basis of the whole approach, is defined by the Sensitivity of the urban context where the solar system is planned, combined with its Visibility (close and remote) from the public domain. The more sensitive the urban area and the more visible the system (high "criticity"), the higher the need for integration quality. In practice, authorities will be in charge to set the desired integration quality levels for each of the defined "criticity" situations, considering local specificities (energy context, available energy sources, political and social considerations, city identity and topography, among others). To help authorities set these quality expectations, the software LESO-QSV Grid has been developed. It illustrates the acceptance impact of pre-defined sets of quality requirements, using a large number of integration examples (150 emblematic cases). These detailed examples are provided to show authorities how to objectively evaluate integration quality, but they also constitute a large set of learning examples, good and bad, for architects, installers and building owners. Finally the method proposes a way to tailor solar energy policies to local urban specificities by mapping the architectural "criticity" of city buildings surfaces, and crossing this information with a city solar irradiation map (LESO-QSV crossmapping), hence completing the characterization of the building surfaces with the potentially required effort of integration.