Le mur à haute performance thermique

The scope of this research includes the development of composite concrete façade elements that are thin, loadbearing and of high thermal performance. The research applies to manufactured precast concrete elements and focuses on improving their structure in terms of their construction but also their cost and environmental impact. During the last four decades, society’s energy efficiency awareness has been steadily growing in everyday life and in scientific circles. The Swiss Federal Institutes of Technology are promoting a plan known as the 2000 Watt Society (Société à 2000 Watts) which would reduce the energy consumption of the country’s inhabitants. In the context of Swiss construction, Minergie type labels are a requirement ensuring improved living conditions at lower energy consumption levels. These new ambitions increase the thermal requirements which in turn lead to the inevitable thickening of the building envelope. In a Swiss urban context, such as the Geneva region in particular, land is increasingly rare and the price of leasable surface continues to rise. As a result, the materials commonly used for insulation are economical but bulky ; they increase the thickness of the façades and significantly reduce the usable surface available for buildings. In an urban context such as this, what is the suitable dimension and fair price of a wall ? The method used was to analyze the strategies that would result in the correct dimensions of high thermal performance walls. Diminishing their width increases the area of livable surface while maintaining the wall’s thermal, static and sustainable standards. The objective was to establish a process for determining the composition of products that carry the Minergie-P and Minergie-Eco label. To this end, several tests and a pilot project for an individual house were carried out using optimum high thermal performance precast concrete walls as a model. The test demonstrated the feasibility of this type of wall. The innovation was to place between the two layers of concrete, a high thermal performance Vacuum Insulated Panel (VIP) type material and a traditional one. This combination allowed optimizing the thickness of the wall while responding to construction constraints. The proportion of the combination of insulation materials was selected according to their thermal performance, environmental impact and price. The goal was to maintain a constant thickness from the stages of project design to its completion. The argument of this dissertation is based on the conviction and the importance to commit to the use of high thermal performance construction materials overall in the future. At present, in the midst of a fossil fuel crisis, this is no longer just an individual concern. Indeed, the scarcity of fossil fuels and global warming are vital and critical problems that can be solved by using appropriate architecture solutions such as heat traps.

Active façades : life cycle environmental impacts and savings of photovoltaic power plants integrated into the building envelope

Gianluca Cattaneo, Angela Clua Longas

Aim and approach used Increased energy supply from photovoltaics is a main priority in the “Energy Strategy 2050”. Within the joint research project "Next generation photovoltaics" funded by the Swiss National Science Foundation, we analysed different options for the enhanced integration of photovoltaic technologies into the envelope of Swiss buildings (BIPV). The PV modules for building integration are using novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC) with adaptions to improve the visual acceptance. In a joint effort of product developers, architects and scientists, this project aimed at providing pathways for the wide-scale use of BIPV façade solutions, and developing integrated designs based on emerging high-efficiency module technologies to improve the visual aspect and acceptance of PV systems installed in Switzerland. These so-called active façades incorporating BIPV modules to generate electricity can provide a significant contribution to the energy transition away from fossil and nuclear fuels. We compared the environmental impacts of different façade construction systems with and without SHJ-PSC BIPV modules with improved visual design, using a prospective life cycle assessment with a time horizon of 2025. The comparison includes a conventional brick and roughcast façade, a timber frame façade, and the Advanced Active Façade (AAF), which integrates SHJ-PSC BIPV modules in a low embodied impact façade substructure. In addition, we compared the environmental impacts caused by the construction of the above described façades with the environmental impacts saved due to the electricity produced by BIPV modules incorporated into the AAF. 2. Scientific innovation and relevance Our research focuses on the combined expertise of life cycle thinking, PV module development and façade design. The major scientific innovations are: 1) the prospective life cycle assessment of novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC); 2) the comparison of different façade construction systems and their environmental impacts; 3) the quantification of the saved environmental impacts arising from the electricity generated by the active façade; and 4) the visual adjustments of PV modules to improve their acceptance. The main advantage of integrating PV into building façades is the large available area, which can be limited on rooftops. In order to reach the market penetration for PV required for the energy transition, PV modules must be integrated into façades as well as into rooftops. 3. Results and conclusions An equilibrium must be achieved among different technical and aesthetic issues when integrating energy generation systems into the building envelope, especially into the façade for its public condition and exposure. Based on these prerequisites, the research team has developed the AAF which combines passive and active energy design strategies while meeting contemporary architectural requirements. This façade design is based on low-embodied-energy construction principles, it is defined by a non-loadbearing wood-panel substructure and it integrates a double layer of natural insulation: cellulose and wood-fibre. In addition, its design incorporates an opaque SHJ-PSC BIPV façade-cladding following contemporary façade design trends. (Figure 1). The use of photovoltaic modules integrated into the façade cladding or roof will increase the environmental impact of the building envelope, compared to using conventional construction materials. The environmental impacts of the AAF using PV modules are two to four times higher compared to a conventional façade. The PV modules cause the highest share of greenhouse gas emissions of the AAF with about 375 kg CO2-eq per square meter (see Figure 2). The additional materials required to build the AAF including exterior panels, insulation and other materials cause about 75 kg CO2-eq per square meter of façade. The brick and timber frame façades cause greenhouse gas emissions around 200 and 100 kg CO2-eq, respectively. If the greenhouse gas emissions caused by the PV module is excluded this will result in a reduction between 25 and 125 kg CO2-eq per square meter of façade. However, the environmental impacts of the AAF are significantly reduced if the whole life cycle is considered due to the PV electricity produced by the building. Therefore, we calculated the saved greenhouse gas emissions due to the electricity produced by the advanced active façade and fed to the European electricity grid using the greenhouse gas emissions caused by the current European electricity mix as reference. These calculated savings due to the electricity produced by the BIPV are about 4 times higher than the impacts of the advanced active façade. Incorporating BIPV panels into building’s façades will cause net savings of about 1700 kg CO2-eq per square meter over the whole life cycle of BIPV façades, while simultaneously saving up to 125 kg CO2-eq per square meter of façade for the reduced material demand to build the façade (see Figure 3). We performed this analysis for 16 different environmental impacts according to the recommended midpoints by the Joint Research Council of the European Commission. The results were comparable to greenhouse gas emissions with the net saved environmental impacts being many times higher for all the environmental impacts analysed except mineral resource use caused by the indium used in the novel SHJ-PSC tandem module (see Figure 4). To conclude, the use of PV modules in AAF can reduce the greenhouse gas emissions per square meter of façade between 25 and 60 % if the production of the PV module and its produced electricity are excluded. If the production and life cycle of the PV modules are included into the analysis the AAF will cause net greenhouse gas savings up to four times higher than the production of the AAF itself. The results for environmental impacts other than greenhouse gases were similar except for mineral resource depletion. Overall, the building integration of photovoltaic modules as AAF will reduce the environmental impacts of the building while simultaneously providing a visually appealing building envelope.

2019

Designing Energy-Efficient Façades to Meet Energy Transition Targets

Angela Clua Longas

The contemporary energy context can be considered as a period of energy transition, where the latest protocols focus on limiting greenhouse gas (GHG) emissions and improving energy efficiency across the different energy consumption sectors. As the largest single energy consumer in Europe, the building sector faces the particular challenge of meeting the latest energy efficiency requirements in the prospect of a growing population, whose growing demand results in increased construction activity and energy consumption. In line with the objectives of the energy transition, the European Union (EU) is committed to drastically reduce its GHG emissions by 2050. This objective is applied to the construction sector through new building energy efficiency requirements specified in the latest building directives. The latter highlight the potential of the building envelope to yield energy efficiency by passively reducing energy demand and through the incorporation of active energy generation systems, including solar systems. Among the latter, Building-integrated photovoltaic (BIPV) systems have a demonstrated potential to increase energy efficiency, especially when they are an integral part of the buildingâs design and construction. However, despite their energy-efficiency improvement potential, BIPV systems are not widely used among architectural practices. This results simultaneously from the particular attention required by BIPV in terms of design and construction, the still low number of examples of successful architectural integration, the generalised lack of awareness among professionals and the perception of the high cost of this technology. These barriers, among others, reveal a tangible gap between the potential of energy-efficient technologies and their application to current architectural practices, specifically with regards to faÃ§ade design due to its public character as an urban landscape generator. To contribute bridging this gap in the context of energy transition, this thesis proposes a research-by-design methodology structured in different interdisciplinary research phases. These phases aim to design and assess an energy-efficient faÃ§ade solution with the potential of contributing to the building sector's energy transition. The research adopts an architectural approach to explore the collective residential faÃ§ade design potential and improve its construction energy efficiency. The research process entails an analysis of the contemporary residential faÃ§ade design currents and the advanced practices on energy-efficient construction. The research methodology is structured in three iterative phases: the design of an energy-efficient faÃ§ade, its quantitative assessment and the evaluation of its transfer potential towards professional practices. The concrete contribution of this research is to provide architecture professionals with energy-efficient architectural visions that can guide them to explore such energy-efficient strategies, integrate these issues in their own design processes and thus contribute to the energy transition at that scale. Similarly, the design methodology and the assessment processes can support construction stakeholdersâ decisions concerning the integration of energy-efficient design strategies into building development, improving contemporary faÃ§ade construction practices.

EPFL2019

The development of material-adapted structural form

Sean Dooley

New structural materials can potentially change the technics and economics of the building and construction industry in a profound way. It is important to identify applications and develop forms that exploit a material's unique properties. The developer of a material can use the knowledge of how materials such as steel and reinforced concrete were first introduced to advance the development and application of new materials today. This project examines why structural forms have evolved as they have and what influences the process of creating form, or form-finding. The purpose of this analysis is to aid the development of structural forms that make the most efficient use of material and take advantage of a material's processing and constructive attributes. Such forms are called material-adapted. This thesis is based on the general history of structural materials used in construction. This research is summarized in six appended case studies that comprise the data of the thesis. The research has extended well beyond these case studies; some of this data is included in the main text. The research showed that the influences on form-finding are: Function; Material Properties; Processing Technologies; Connection Technology; Construction Process; Economics; Socio- Political Factors; Knowledge; and Technological Thought. A Form-Finding Influence Interaction Model summarizes the inter-relationships of these influences. It was first assumed that material-adapted form is determined by material properties alone. Further research showed this untrue. The hypothesis of this thesis is that material properties do not unilaterally determine material-adapted structural form. This statement is true because the nature of a material is a function of its properties and its processing and constructive attributes. A material's processing and constructive attributes are dependent on technology and organizational systems that are not specific to the material. It was further hypothesized that new materials are first used substitutionally in forms and applications of known materials. This concept was found to be misleading and untrue for a number of materials. The knowledge of this thesis was used to examine the current development of fiber reinforced polymer composite materials. It is shown that a material's development can be analyzed not only by the aforementioned influences, but also by characteristics of other material developments. This information is used to suggest how these materials might develop in the future.

EPFL2004