On Monday, December 3, 2018, Gaëlle VOISIN, a PhD student in energy and process engineering at the Laboratoire d'Optimisation de la Conception et Ingénierie de l'Environnement (LCOIE), will submit her thesis "Towards better consideration of indoor air quality and health in low-energy single-family housing: Development of a performance-based approach to ventilation".
The defense will take place at 1:30 pm, in the amphitheater of building B2, at Polytech Annecy-Chambéry, on the Bourget-du-Lac campus.
Summary of the thesis
Future regulations up to 2020 will incorporate the notion of overall building performance, including indoor air quality (IAQ). In the field of energy, performance-based approaches have been developed to ensure that buildings meet maximum energy consumption levels at the design stage. However, in the field of ventilation, regulations are generally based on prescriptive approaches, setting ventilation rates. The aim of this thesis is therefore to develop a performance-based approach to ensure, right from the design stage, that ventilation avoids any risk to occupants' health. Furthermore, with the widespread adoption of near-zero energy buildings, air permeability is now increasingly integrated into thermal regulations in Europe. As performance assessment often focuses on energy efficiency, and rarely on IAO, the impact of the presence of several zones, interconnected by air permeability defects on interior partitions (interior permeability), combined with non-uniformity of envelope permeability, is a problem rarely studied and addressed in this thesis. To address this issue, a ground-breaking campaign to measure air permeability distributions in 23 houses has led to the development of a database. Its analysis revealed that interior permeability is not negligible in the face of door unhinging, and that the type of structure (light/heavy) has a considerable impact. At the end of this work, we proposed input data for multi-zone models on these air permeability distributions. We then quantified the impact of these detailed distributions on IAQ using a case study modeling C02, humidity and formaldehyde in a low-energy house. The house is equipped with either single-flow ventilation (SF) or double-flow ventilation (OF). Significant impacts were identified. To assess OAI, it is therefore necessary to model envelope and interior air permeability in detail. Following intensive bibliographical work, combined with the complementary analyses presented above, we have been able to propose a performance-based approach to ventilation for use in a regulatory study at the design stage. We proposed 5 IAQ indicators to be taken into account, including doses of C02, formaldehyde and PM2.5, and two humidity indicators to assess the risk of condensation and occupant health. We also proposed occupancy and pollutant emission scenarios to be taken into account. Finally, we described the type of multi-zone model to be implemented, the physical models and associated assumptions, and the boundary conditions to be used. We wished to test this approach by applying it to a low-energy house used as a case study. We therefore assumed that the house was at the design stage, and would have to comply with a hypothetical regulation setting IAQ performance targets. We then demonstrated how such an approach would enable key choices to be made at the design stage, such as the type of structure (in view of its impact on permeability distributions), the type of ventilation system, the level of indoor pollution (in connection with the choice of labels or labelling, for example), with regard to their impact on IAQ. Indeed, in our case study, only OF ventilation combined with low or medium formaldehyde emissions enables IAQ objectives to be met. We have also shown that such an approach would be useful at the design stage to better size the distribution of air inlets or extract units, or even ventilation flow rates, in order to achieve IAO objectives.