The BAYREB project proposes investigating the theoretical potential of Bayesian inference applied to the diagnostics of existing buildings before their refurbishment. The largest potential for energy savings in the building sector lies in the renovation of the existing building stock. As a result, an increasing amount of research is being dedicated to encourage decision makers. Guaranteeing the performance of a building after renovation would be an efficient incitation, but is still difficult to perform in practice. A necessary condition for a cost-effective refurbishment, adapted to each specific building, is to perform detailed diagnostics of its performance prior to picking solutions: for instance, to estimate which proportion of the energy consumption is caused by air leakage, by transfer through the envelope, or by a dysfunction of the heating systems. The solution for establishing such diagnostics is to implement inverse techniques, which are able to automatically learn from in-situ measurement data in order to construct a realistic representation of the characteristics of a building. The importance of the energy audit of existing buildings has already motivated several projects which underlined the difficulty of applying inverse methods for the identification of building properties. The overall observation of these projects is that a reliable energy audit requires a rigorous theoretical basis in order to explore its full capabilities. Moreover, previous works on the topic of building energy performance characterisation meet two main problems: - The most common inverse methods in engineering are deterministic and do not ensure finding the global optimum in the search space. Moreover, they often only offer point estimates of the sought properties: confidence intervals on identified parameters can only be obtained by a separate forward sensitivity analysis. - When applied to building physics, inverse methods always rely on a simplified modelling of the buildings (RC models) and may exceedingly overlook important influences on the energy performance: occupant behaviour, HVAC control strategies and coupled influences of heat, air and moisture. While always keeping in mind the realities of the energy performance monitoring of buildings, the BAYREB project will attempt to go closer to the fundamentals of inverse techniques, in order to apply them for this purpose. The novelty of the BAYREB proposal compared to previous projects is the specific choice of the Bayesian statistical framework, and fundamental research on the capabilities and limitations of inverse methods applied to building physics. The principle of Bayesian inference is to draw conclusions from incomplete observations of a system, and update knowledge as more data is available. Given a set of records (sensor data and inaccuracy), and some prior assumption on the model structure (expert knowledge), one can compute the probability of their causes (energy audit, envelope properties…) by means of conditional probability and the Bayes theorem. The particularity of Bayesian inference, as opposed to other inverse methods, is that it inherently performs an inverse propagation of uncertainty: missing data, sensor inaccuracy, or simplifying model assumptions, will have a direct effect on the assessment of building characteristics and their confidence intervals. A second advantage is the fact that it can be applied to any class of mathematical function, from white-box to black-box models, as it does not require the computation of sensitivity gradients. The ambition of the BAYREB project, compared to related work on building parameter identification, is therefore twofold: to address the problem in a fully stochastic manner which will account for all model and measurement uncertainty; and to not force end users to a given building simulation software.

Because the energy and raw material consumptions need nowadays to be reduced, researches more and more deal with sustainable construction design, with a reliable stability. This project, VBATCH, addresses a critical issue which is vulnerability, with respect to hydric conditions, of a low environmental impact building material, namely raw earth. This research will be developed at the interface between energy approach and mechanical approach often adopted for this material, aiming to analyze hydric effects on the mechanical behavior and stability of earth building. The project will be led in three stages: the experimental analysis at the material scale for a uniform hydro-mechanical problem, experimental analysis at the structural scale for a heterogeneous hydro-mechanical problem and numerical modelling, adjusted from the material scale experiments and validated from structural scale ones. Furthermore, a solution for geophysical monitoring of hydric properties, namely water content, will be investigated not only for the needs of the project, but also to be applied by professionals for inspection and diagnosis of existing buildings. The project presents 4 strong originalities: the adaptation of non-saturated soil mechanics concepts for experiments and modelling, the experimental campaign non only at the material scale but also at the structural scale, the investigation of hydric history influence in addition to hydric state influence and the adaptation of geophysical methods for continuous and non-destructive water content investigation. The project will benefits from multidisciplinary skills, put in common for the same specific aim. This multidisciplinary work will be possible by the project leader (Noémie Prime) experience on the mechanical and hydric soil behaviour and by the complementary experience of the other permanent members of the team (Olivier Plé, André Revil, Anne Cécile Grillet, David Cloet).

Environmental issues in building sector are huge, particularly in the context of reducing greenhouse gas emissions. This concerns not only the construction phase, but also operation phase and end of life of buildings. Within this framework and following new RE2020 regulations, this project aims to investigate the multi-physical behaviour of raw earth building insulated with bio-based materials. PACS+ project will focus on different scientific issues: the in situ measurement (large scale) of thermal and hygric fields with non-destructive methods; a detailed understanding of hygric effects within porous materials with the help of modelling; the description of the coupled hygro-thermo-mechanical behaviour specifically at the interface between raw earth and bio-based materials; the evaluation of insulation effect on global performance from both energy and structural point of view. The originality of the current proposition is considering together the association of 2 materials –earth and bio-based insulating- and the relative effects between both. It is chosen to deal with the whole multi-physical effects that take place in such building panels. Another original point is to focus on real scale; the development of original non-destructive tools, at this scale, seems to be promising in the perspective of in situ diagnostic. That’s why, tools will be used on materials and panels at both scales for characterization, with a particular attention to the scale effects. On one hand, on a composite sample, the coupled hygro-thermo-mechanical behaviour will be characterized, interpreted and reproduced by suited models. On the other hand, on large scale panels, the influence of insulation on energy and structural performances will be evaluated both in transient phase and in steady state.

The use of local materials is characteristic of most of millions of housing built before 1948 in France. These materials are not industrially processed and therefore lead to a significant decrease of grey energy consumption. However, due to lack of scientific knowledge, there is currently no clear recognized guidance for their set-up, or means of measurement to guarantee their performance. This lack commonly leads to apply renovation and construction methods which are unsuitable, and / or to prefer other building materials, environmentally less efficient, but benefiting from standardized testing procedure. In the best case, companies rely on their empirical knowledge of these buildings. Thus, the challenge of this proposal is to explore ways to measure and guarantee hygrothermal, mechanical and seismic performances of local materials and ensure their dissemination and development through an analysis of institutional conditions. To achieve this objective, we propose to identify and measure, through physico-mechanical modeling and experiments at different scales (laboratory, on site), the key parameters needed to describe the hydro-thermal behavior of buildings and seismic. In this context, we will study the impact of natural vegetable fibers additions on the behavior of the studied clay soils. The approach will be validated on the rammed earth and rough masonry constructions, which are the most representative of old buildings (before 1948). Ultimately, PRIMATERRE project will allow the development of design guidance and training modules.

Lithium-bromide systems can play a strategical role in the recovery of unused low exergy level energy source, in particular in the current context where the priority relationship between initial investment and running constraints (cost and electricity consumption reduction/deletion) have shifted. Despite this strategical interest and, among the low Coefficient of Performance, the systems are bulky and the investment cost is high compared to conventional system. To improve the performance of these system, the project proposes to study a new concept of generation of liquid films in the wall allowing to reduce considerably their thickness and to improve the performances of boiler by taking advantage of the boiling phenomenon which can occur there. The application targeted is a lithium-bromide absorption heat-pump of type II driven by a low exergetic level source (˜ 40°C). By the design of modular experimental channels, the development of a new laser-induced fluorescence methodology to access the volumetric mean temperature and LiBr concentration, complex phenomena occurring inside the experimental set-up will be analysed, characterised and modelized. In particular, the impact of the confinement of the fluid inside the channel, the working pressure and the wall superheat on the exchanger performances will be analysed and quantifyed. Novel asymptotic models to capture the drying dynamic of water and water-bromide solution, as well as the interplay between heat and mass transfer will be developed. Tools and performances maps developed in the context of this project will then be exploited to design a compact low-pressure water-based heat- exchangers and a rational design of a LiBr boiler will be proposed.