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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.

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.

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%).

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.

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.

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.