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The building stock is responsible for 24% of carbon emissions in Switzerland and 44% of the final energy use. Considering that most of the existing stock will still be in place in 2050, it becomes essential to better understand this source of emissions. Although the Swiss Cantonal Energy Certificate for Buildings (CECB) database has been used in previous research, no comprehensive characterization of the buildings can be found. This data paper presents an analysis and classification of the Swiss building stock based on the data found in the database. The objective is to create a knowledge foundation that can be used in future research on the performance of existing buildings. Using a sample of almost 50,000 buildings and a Python script, datasheets were created for single-family houses and multi-family houses for nine construction periods. These archetypes are described through selected available energy-related parameters, such as energy reference area, U-values, and energy source with indicators such as median, 25th percentile, and 75th percentile or distributions. The resulting data can be used for different purposes: (1) to calibrate energy models; (2) for analysis that requires scaling-up strategies to the whole stock; and (3) to identify weak and/or relevant classes of buildings throughout the stock., Buildings, 13 (1), ISSN:2075-5309

Generally, the environmental impacts of buildings are benchmarked per square meter as a functional unit. However, this practice prevents developing a user-centered approach in which performance is linked to real usage and not building size. Currently, the less a building is used, the lower the energy consumed during its use and, consequently, the impact per square meter, which does not make sense regarding both usability and environmental performance. Following user-centered design principles, the goal of the present research is to assess the environmental impact of buildings based on novel user-based functional units and to understand the environmental impact consequences of office occupation density. An experiment within the area of an academic office offered the opportunity to test the densification of working spaces and evaluate the resulting environmental and comfort impacts. In the end, the new user-based functional units highlight a reduction of all environmental indicators by almost 50 %. Also, the functional unit "eq-nominal people per effective presence" is introduced as most suitable to evaluate environmental performance according to real building usage, as a complement to square meter function units.

Huge amount of energy resources greenhouse gas (GHG) emissions is devoted to the built environment. Therefore, an accurate assessment method of these indicators is compulsory. To take advantage of the temporal variation in the primary energy use and associated GHG emissions of the energy supply, we propose two ways of integrating hourly life-cycle conversion factors in building energy systems. First, to appraise the energy system design, we developed a versatile modelling and performance assessment framework using a multi-criteria approach. The simulated performances of possible energy systems are compared, and help designers systematically choose appropriate energy production and storage systems. Second, for the operation of the building, we propose an energy management procedure (EMP) that always feeds in the energy source with the least global warming potential (GWP). These two developments are tested on a case study consisting in an architectural project that should respect the 2000 W society targets. The running conditions of several energy systems are simulated and compared. The most promising scenario is identified. Compared to traditional methods, the assessment framework has a promising future but the GWP-based energy management procedure offers, in the context of the case study, limited GHG emissions mitigation at very high primary energy cost.

It is a frequent practice nowadays to use mean annual conversion factors (CFs) when performing life-cycle assessment (LCA) of processes and products that use electricity supplied by the grid. In this paper, we conduct an hourly assessment of the greenhouse gas (GHG) emission factor, along with the conversion factors for the cumulative energy demand (CED) and its non-renewable part (CEDnr), of electricity supplied by the Swiss grid and its direct neighboring countries (France, Germany, and Austria; Italy being neglected). Based on an hourly inventory of energy flows during a one-year period (2015–2016), this attributional approach allows performance of various certification procedures of process or product manufacturing, and comparison of energy and carbon intensities of different national mixes. Hourly calculation allows evaluation of the order of magnitude of errors made when considering an annual mix. Visualization techniques are used to better understand the obtained data and to detect when strategies involving timing optimization of electricity use may be efficient. A case study is chosen to illustrate the relevance of hourly CFs when performing LCA associated to the exploitation of a given building. Moreover, mean annual CFs of interest are discriminated by electricity end-use sectors. This could be of great help for system designers willing to improve the assessment accuracy when hourly CFs are not readily available.

Building envelope design has gained importance as a means to reduce heating and cooling demand related to a building’s operational phase. However, in high internal load buildings, such as offices, internal gains can easily lead to overheating. Thermal inertia (TI) and night ventilation have a great potential for reducing heat loads and temperature. However, their influence is difficult to predict due to the complex nature of the TI phenomenon, which is related to the interactions of multiple factors such as architecture, building physics and external conditions. Moreover, TI efficacy has often been studied in relation to energy savings or temperature analysis, overlooking other aspects implicated in buildings’ efficiency, such as the embodied energy involved. This paper presents a multidimensional approach to evaluate ventilative cooling and thermal inertia as a sustainable strategy to improve building performances. To that end, several scenarios of night ventilation strategies have been applied to the case study of an experimental double-office room placed in Fribourg (Switzerland). Based on this monitoring, a dynamic software simulation tool has been calibrated and used to analyze the energy savings potential and the life-cycle performance of TI. A new ratio index has been introduced to easily evaluate the life cycle efficiency. The results show the importance of balancing operational and embodied impacts when evaluating a design choice. Although high TI levels have great benefits on reducing the cooling loads, the results are completely different when a life cycle assessment is applied. Natural ventilation coupled with middle levels of TI have been identified as the best strategy to optimize the building’s energy and environmental performances, without compromising indoor temperatures.

Buildings are increasingly required to be efficient not just in their operation, but from construction to demolition. Thus, interest in natural construction materials with low embodied environmental impacts has increased, (re)inventing materials and components from vernacular architecture. Compressed Earth Bricks (CEBs) are an example of this kind of component. They are flexible in a wide range of applications and their natural features favour their usage as thermally massive elements to increase a building’s thermal inertia (TI). The ability to store heat during the day and release it later helps buildings in dampening thermal swings, making TI a good strategy for preventing overheating in offices usually characterized by critical internal loads. Previous studies highlighted the difference between the thermal behaviour results obtained with tests on the materials, like experiments in controlled climatic chambers and real-world applications. In this study, an application of CEBs is taken as a case-study to analyse the thermal behaviour of an earthen wall and the potential of coupling night ventilation to stabilize temperatures and increase indoor comfort. Comparing the results obtained in two different rooms, representative of lightweight and heavyweight earthen construction, it was possible to quantify the contribution of CEBs walls to the passive cooling strategy in office buildings, according to different ventilation profiles/scenarios.

To investigate the relationship between occupants’ perception of control over building elements and their comfort, we conducted a study where two prototype office rooms were compared: while the first room allowed occupants to open or close the window and configure the shading, the second one was fully automated. The quantitative analysis of collected data a) supports the existing results in the literature reporting higher satisfaction where manual control is maintained, and b) uncovers a new impact of highly automated systems: lower control over building elements can increase the occupant’s consciousness of the environmental factors and the saliency of comfort parameters.

Environmental performance assessment of the built environment tends to focus mostly on operational final energy consumption of buildings located within a specific context. Such a limited scope prevents broader usability of findings in practice. In Switzerland, the ‘2000-W society’ vision provides a theoretical framework towards energy transition. Intermediate targets for 2050 relate to an extensive assessment incorporating environmental impacts of construction materials and use of a building, and of induced mobility of its occupants. Accordingly, it becomes crucial to gather information about the current building stock performance and its transition potential. The paper aims at contributing to the sustainability transition debate by providing a comparative assessment of retrofitted and new residential buildings representative of the Swiss building stock. A direct output could constitute in establishing a reliable reference dataset to support practitioners’ or lawmakers’ future decisions. The novelty of the study relies on two aspects: (1) on adopting an interdisciplinary approach to propose an overview of the current status and transition potential of the built environment, and (2) on building a methodology able to extrapolate results for large-scale studies of neighbourhoods or larger built areas. Based on the definition of four building archetypes, this study assesses four scenarios decomposed into four to six variants. The scenarios consist in varying the building energy-performance, while the variants implement different locations—among urban, peripheral and rural areas—and different passive or active strategies. Results are expressed in terms of non-renewable primary energy consumption and global warming potential. They highlight in particular the performances of renovation projects that can decrease the impacts of current building stock by 75 to 85%, the effect of high-energy performance on embodied impacts, the high-level of performance of multi-family houses with 37% lower impacts compared to those of single-family houses and the significant impact of mobility (around 50%).

The data presented in this article are related to the research article entitled “Temporal variations in the primary energy use and greenhouse gas emissions of the electricity provided to the Swiss grid” Vuarnoz and Jusselme (2018). The provided data are the hourly CO2-eq emission factors, and the hourly conversion factors for the cumulative energy demand and its non-renewable part for the Swiss electricity mix over one year. These data have been assessed on the basis of an inventory of the technology used for electricity generation and an attributional life-cycle approach. The presented data are necessary for life-cycle assessment of all processes and products using electricity in Switzerland. They serve also as a sustainable benchmark when implementing renewable energy systems and energy storage.

Environmental performance objectives in terms of energy consumption and carbon emission targets can be found in various building norms and certifications schemes. These targets are often dependent upon the building program (e.g. office), but independent from its context; the same value is imposed for two buildings of the same program regardless of other possibly influential characteristics (e.g. solar exposure). Such targets serve as references against which a project's performance is measured following its description and assessment using an evaluation tool. In this paper, we question the suitability of this procedure within the context of urban planning by asking: should a district-level performance objective be allocated in a ‘uniform’ manner or through a ‘contextual’ approach, capable of capturing specificities throughout the site and allowing compensation between areas? To address this question, a novel method is proposed to distribute a site-level target differently between lots presenting distinct conditions over the site, through a combined top-down and bottom-up approach. The method relies on the exploration of databases of lot-specific scenarios, generated by varying design parameters that have not yet been fixed at the planning stage, such as building shape and construction materials. Applied on a case-study district in Switzerland, the contextual method results in differentiated lot-specific targets that are up to 11% away from the uniform targets. Although apparently small, these shifts can increase the feasibility of reaching the site-level target by up to 30%. Such information can guide the design team towards defining a coherent environmental strategy and making informed decisions.

While ambitious environmental objectives are being set for new constructions in Switzerland, the assessment of urban-scale projects and comparison of their performance to national targets are made possible by a growing number of life-cycle assessment (LCA) tools. However, previous research emphasizes the lack of existing tools to support the decision-making process at the early design stage, characterized by a low level of project details. This paper presents a comparison between three LCA tools. The first, stemming from a research and development project (SETUP), is an exploration tool relying on a database of urban-level scenarios and their environmental performance, able to convert district targets (e.g. 2000-Watt society objectives) into specific sub-targets at the building or component levels. The other two are online LCA tools currently available to practitioners (Sméo and Calculation tool for 2000-Watt-society-sites RH II ), that allow assessing the project and verifying its compliance with a given target. Each tool was applied to a low-carbon case study, the blueFactory district in Fribourg (Switzerland), in two hypothetical contexts corresponding to the schematic and detailed project development phases, characterized by different levels of details. When used for the assessment of a project at a more advanced development stage with a high resolution of detail, findings indicate that Smeo and RH II provide similar environmental performance results. However, in early planning stages, SETUP shows better abilities to support decision-making by providing ranges of results and highlighting uncertainties and the influence of design parameters that have not yet been fixed.

To face climate change, greenhouse gas (GHG) emission targets are specified into national policies. In France, the objective is to divide by 4 (Factor 4) the GHG emissions by 2050 comparing to 1990. The built environment, as a main contributor, is targeted by these policies: the future 2020 French regulation will set up GHG emissions targets for the building life cycle. However, the implementation of this regulation and its labels into real-estate development is challenging because it is uncorrelated to factor 4, architectural and technical constraints due to these labels are yet unknown and targets are defined at building scale and not at the district scale. This paper offers some answers to this challenges based on a case study from a real estate developer who wanted to implement a 2025 objective to a new district in Lyon, France. It was done thanks to a review on Factor 4 and labels' history, on calculation of GHG emissions from 1990s building and objectives for 2050 and illustration of labels' constraints. Finally, objectives were allocated at building scale to meet the overall district ambition.

Solar control strategies are essential for the glare control and decreasing cooling needs or overheating risks (in the absence of active cooling system), however, they come with their own embodied energy. With the carbon neutrality objective looking at the 2050 horizon, life-cycle assessment (LCA) approach is needed to evaluate the impact of decisions made on the different building components, including solar shading systems. To that end, this paper applies a relatively new concept defined as the Life-Cycle Efficiency Ratio (LCER) to quantify the trade-off between operational and embodied energy. Results based on a low-carbon case study suggests that adding solar shadings does not reduce the life cycle carbon emissions of this project. Also, analyses show that the ratio between operational benefits and embodied impacts of external fabric blind is the highest, while this ratio is the lowest for the internal fabric blinds in this case study.

The impact of daylighting strategies on a building’s carbon emissions have so far been assessed mostly based on the building’s use phase and their resulting operational benefits, overlooking embodied carbon emissions of material production, construction, maintenance and end of life. This paper proposes a new methodological framework that combines different techniques including sensitivity analysis, target cascading and a method called Design Space Exploration. The framework was tested on a case study, namely the winning entry of Solar decathlon 2012, to evaluate daylighting strategies based on both daylight availability and embodied carbon emissions. . This study allowed to show through a formal process that while choices made on window head height, glazing type, interior surface reflectance and window-to-wall ratio (WWR) basically define daylight access potential, they only have a minor impact on embodied carbon emissions.

The built environment is facing environmental regulations more ambitious than ever before. In Europe, a law will lead all new buildings to the Nearly Zero-Energy performance level. However, even if a building does not have any energy consumption for its operation phase, it still has embodied impacts. To that end, Life-Cycle Assessment (LCA) methods have been developed and improved since the 1960s. However, LCAs are still not used as a standard practice among the architecture, engineering and construction industry. This study aims to discover the reasons for the low use of life-cycle performance approaches thanks to a web survey targeting practitioners, and to formulate key recommendations to improve their usability. This research reveals the low penetration rate of LCA software among building designers due to their limited efficiency within the design context. The main reasons for this situation are the cost of use, too heavy for the early design stage constraints, and the functionality, which is limited to the environmental assessment. Indeed, practitioners expect much more design support functionalities (multi-criteria approach, exploration mode, etc.). The survey findings aim to support the usability improvement of new LCA-based methods and the research and development of new tools at early design stages.

Exploration methods combine parametric energy assessments and data visualization to support building designers at early design stages. When exploration methods come to Life-Cycle Assessment (LCA) and the Global Warming Potential (GWP) assessment, a larger number of input parameters induces a very high computation load. Previous researches suggested using Sensitivity Analysis (SA) to decrease the space exploration thanks to their sampling techniques, and input sensitivities. However, this theoretical framework has almost never been applied to building LCA so far and underline two major issues. Upon SA techniques, which one is most suitable for LCA input specificities? How is it possible to extend the exploration process outside the limits of SA samples? This article addressed these questions thanks to an extensive state-of-the-art, the description of a new method combining Sobol SA and Artificial Neural Network (ANN), and a case study. The Sobol method delivered satisfying results with the computation of quantitative indices. Then, an Artificial Neural Network trained on the data generated by the SA was used to predict the GWP of new design alternatives in a small amount of time, and with a coefficient of determination higher than 0.9. Finally, the proposed method adapted exploration methods to the LCA complexity.

There is now clear evidence regarding the extensive use of furniture and appliances in daily human life, but there is less evidence of their impact on the environment. Responding to this gap in knowledge, this study focuses on an assessment of the environmental impacts of furniture and appliances as used in highly energy efficient buildings. Their primary energy, non-renewable energy and global warming potential indicators have been assessed by extending the boundaries of the Life Cycle Assessment (LCA) study beyond the building itself. In conclusion, we found that furniture and appliances were responsible for around 30% of greenhouse gas emissions and non-renewable energy consumption and 15% of primary energy consumption comparing to the overall impacts of the building. Since embodied impacts represent the largest values, the process for labelling the appliances' energy efficiency should encompass a life-cycle point of view, not just a usage point of view as the case currently. Among office appliances, computer equipment was ranked as the highest impacting element, especially laptops and monitors. As for domestic appliances, refrigerators and electric ovens had the biggest impacts. Concerning furniture, the greatest impacts were from office and kitchen cabinets.

Recognized as a powerful methodology for the evaluation of environmental burdens, life cycle assessment (LCA) must be performed with close-to-reality inputs to be robust and accurate. However, the necessary real-world data is hardly available at the design stage, resulting in current LCA practice being mainly based on standards and norms as hypothesis of building contexts, therefore inducing uncertainties in results. The current paper presents a methodology to collect a subset of such input data in a function of the context more accurately than the standards. It then studies the impact of such uncertainties in the LCA results. Through an academic building case study that measured data concerning the building occupancy (A), i.e. the hourly occupancy rate and density, the hourly appliance consumption rate (B), and the hourly conversion factors of environmental impact of the electricity mix (C), the LCA results for the GHG emissions and primary energy consumption are compared between normative- and measurements-based input parameters. The measured occupancy rate (A) is shown to impact the LCA results the most, especially the embedded impacts, by implying a new occupancy density: the building population increase of +32% leads to a significant increase of the embedded impacts related to furniture. The variability in appliance usage (B) is marginal between measures and standards and therefore does not lead to a significant change in LCA results. The use of hourly conversion factors (C) indicates an underestimation of the GHG emissions and, at the same time, an overestimation of the primary energy when assessed with mean annual values. The combined effect of simultaneously using the three reality-based input parameters (A, B, C) mostly affects the non-renewable part of the cumulative energy demand indicator (-9% reduction of the operational part), followed by the cumulative energy demand (-7%) and GHG emissions indicators (-3%). The research findings affect not only LCA research but also practitioners such as architects or building contractors who need to respect ambitious environmental targets.

The built environment is one of the major contributors of greenhouse gas (GHG) emissions. To tackle climate change, global targets have been set for this sector. Although life-cycle assessment (LCA) methods are typically used to evaluate a building project's embodied energy in its final stages of development, this evaluation would be especially valuable at early design stages, when the opportunity to modify the design is greatest. In this paper, an extensive review of methods to improve the usability of LCA at the early design stage is presented. Three major issues regarding the application of LCA arose from this analysis at this stage: its time consumption, the lack of design details, and the non-reproducibility of results. Moreover, LCA makes it possible to assess environmental performance, but does not provide design alternatives, which are crucial to introduce environmental targets into an iterative design process. To that end, existing techniques that can address the major LCA issues were identified, together with their respective limits. These include some promising tools that provide and explore design alternatives and their respective environmental performances. Among these tools are exploration methods, which have not been applied to LCA insofar as it is not possible to do so in a reasonable computational time. To bridge this gap, the paper outlines the structure of an LCA-based data-driven design method, which uses a combination of LCA, parametric analysis, data visualization, sensitivity analysis, and target cascading techniques.

Coupling photovoltaic (PV) systems with energy storage (ES) in buildings, enables to increase the building’s energy autonomy and the self-consumption of onsite renewables. ES increases nonetheless the life cycle environmental impact of the stored energy. As such, there exists a threshold where the GHG emission benefits of using ES start to compensate its own embedded and operational impact. In this study, a methodology to assess this neutral global warming potential target of ES is proposed, and is extended to the primary energy and its non-renewable part. The methodology is tested on a case study consisting of a feasibility project of a building located in Switzerland. When the surplus of renewable energy that cannot be used or stored directly is exportable to the grid, the operational benefits of the ES cannot balance anymore its embedded impact. In regards to market products, these neutral targets are tighter for GHG emissions than energy. Neutral targets are greatly affected by the characteristics of the grid mix supplying the building so the use of energy storage for the mitigation of GHG emissions in buildings may be efficient in Germany, but might be technologically more challenging with low-carbon French electricity.

The international greenhouse gas agreements call for mitigations in the building industry. Thus, the number of scientific publications about life-cycle performance assessment (LCPA) follows an exponential trend since the 2000s. However, previous surveys highlighted that the use of these methods is still not a common practice. Hence, it is of primary importance to understand the gap between the research intensity, and its low-benefits on the practice. To that end, a set of questions has been compiled and spread as an online survey targeting architects and engineers at the European scale. Thanks to 500 answers, three major obstacles have been highlighted. First, there is a clear lack of demand from real estate developers in a context where there is no lifecycle performance regulation yet. Second, the high cost of the use of LCPA methods disqualifies their use at early design, where the financial risk is at its highest level. Last, there are collaboration issues between architects and engineers, decreasing the LCPA benefits. In addition to previous surveys focusing on the scientific issues of the LCA methodology only, these results provide a unique user-centred knowledge for LCPA software and method developers.

As of 2020, every new building in the European Union will have to reach the nearly Zero Energy Building (nZEB) performance. However, building nZEB will not be sufficient to reach carbon neutrality in 2050 as required by the last IPCC report: indeed, even nZEB consume energy due to their embodied impacts. Thus, life-cycle assessment will become a mandatory approach to mitigate environmental impact of buildings beyond the nZEB performance. However, the complexity of Life-Cycle Assessments (LCA) continues to make it difficult for it to be effectively used at the early design stage. A promising theoretical framework called LCA-based data-driven method had been proposed in prior work by the authors to tackle these issues (Jusselme et al. 2018a). This paper presents the prototype that has been built for the developed method to be tested in a first application. The case study chosen for this application is the future building of the smart living lab in Fribourg, which aims to reach the SIA2040 performance threshold. A specific knowledge database of 20’000 design alternatives – with a LCA performed for each of them – was thus generated with a parametric approach. First, the method provides sensitivity indices so as to better understand the influence of different design parameters. Second, performance target values are provided at the building component level in order to choose building techniques and materials in accordance to the SIA2040 objectives. Ultimately, the method offers site-specific guidance with an exploratory perspective. By literally exploring a database of design alternatives generated specifically for that site and urban context, the user (designer) gets valuable insights about the choices still available when other decisions are made if the SIA2040 performance ambitions are to be kept. In comparison to current practices, this case study demonstrates the ability of the method to provide a highest amount of design insights beyond the simple assessment process, in a shorter time. Further research needs to be carry out to verify the benefits of the method in the frame of a real design process, thanks to practitioner’s evaluations and feedbacks.