PhD Position – Numerical and experimental modeling of heat and humidity transfers within bio-sourced materials: Application to evaluating the energy and environmental performance of buildings with green roofs

Important Information

Description of the subject

The research theme of heat and humidity transfers respond to major societal concerns related to improving building occupants’ living environment through energy-efficient solutions with a low environmental footprint. Indeed, the current thermal regulations recommend designing buildings that are more and more thermally insulated with a very low envelope permeability. Admittedly, this makes it possible to reduce the energy and environmental impacts but brings up new challenges because it risks altering summer comfort and the quality of indoor air. Another consequence is seeing these “hermetic” buildings deteriorate due to humidity in habitable environments. Thus, water (in vapor and liquid phases) is responsible for fungal growth and degradation of plant-based insulations. In addition, it constitutes the transport vector for aggressive agents such as chlorides and sulfates and the seat of chemical reactions such as carbonation.

Moreover, second-order phenomena hitherto neglected have become increasingly important to the point where they strongly contribute to the overall heat balance of buildings and, therefore, cannot be ignored. Mass transfers (particularly humidity) are the main ones. In addition, the use of materials with low environmental impacts, such as eco-materials, bio-sourced materials, and recycled materials, remains limited. This is due to the lack of databases defining their intrinsic properties and the lack of guaranteeing their properties’ evaluation with time.

This doctoral research will study mass transfers, mainly humidity, air, and heat, at different scales: microstructural, porous materials, and envelopes constituting buildings’ vegetated walls (facades and roofs). They will be based on the work developed at LaSIE by [Belarbi et al., 2006], [Qin, 2007], [Belarbi et al., 2008], [Trabelsi, 2010], [Abahri, 2012], [Issaadi, 2015 ], [Ferroukhi, 2015], [Bachawati, 2016], [Bennai, 2017], [Yousri, 2018], [Koura, 2018], [Maaroufi, 2019], [Benmahiddine, 2020], [Boukhelf, 2020]. This thesis work aims to better control the behavior of innovative materials according to their ages through a multi-scale approach (from the microstructural scale to the scale of the building envelope). It will promote the use of innovative materials (eco-materials, bio-sourced materials, and recycled materials) in the construction and rehabilitation of buildings.

This doctoral thesis work will be structured around five complementary parts:
Part 1:
The first part will consist of state-of-the-art, making it possible to synthesize the work of the literature dedicated to this research theme. It will be a question of establishing a phenomenological study on hygrothermal transfers within porous media to understand the different modes of water fixation at the microscopic scale and better understand the mechanisms involved during these transfers. This is followed by a phase dedicated to the various experimental methods and protocols, allowing the materials’ main microstructural, mechanical, thermal, hydric, fixation, and moisture storage properties to be characterized.
Part 2:
The second will be devoted to a detailed characterization of the materials’ main intrinsic properties studied over time to assess the effect of aging on these properties. These properties will be evaluated experimentally and numerically through parameter identification methods according to their thermal and hydric states. It will be necessary to propose phenomenological models of the aging of the properties of materials. They will constitute the input parameters of the hygrothermal transfer models.
Part 3:
At the scale of the porous material, particular attention will be paid to the physical phenomena generated during the coupled transfers. A model of coupled transfers of heat, air, and humidity will be developed on the numerical side. It is distinguished by taking into account not only the transfers of the species present (water: vapor + liquid and dry air) but also the phenomena of thermo diffusion or even advection, thus making it possible to overcome the constant total pressure hypothesis. These last two phenomena have been demonstrated experimentally, and their sensitivity to transfers has been established. Also, the prediction model will take the hysteresis phenomenon into account. It will improve the quality of the prediction of hygrothermal transfers within envelope materials following the confrontation of numerical results and those resulting from experimentation.
Part 4:
Also, the experimental bench representing an urban scene will be developed on the site of the University of Balamand. It will consist of 4 rows of building models (reference roof, extensive green roof, reference roof + photovoltaic solar panel, green roof + photovoltaic solar panel) and four canyon streets subject to variable and realistic climatic conditions. This platform will study the response of walls and buildings to varying climatic stresses and simulates these responses concerning scenarios of extreme climatic stresses. It will make it possible to compare the numerical modeling results with those obtained experimentally to make the numerical simulation tool more reliable.
Part 5:
Finally, a life cycle analysis will be undertaken on the various solutions retained to assess each configuration’s environmental footprint.

Keywords: Green Roofs; Sustainability; Bio-sourced materials; Recycled materials; Ecofriendly; Circular economy.

List of References

• Réda Allam «The heat and moisture effect on the structure» soutenue à l’Université de Mansoura le 18 décembre 2018. Financement l’Ambassade d’Egypte en France.
• Kamilia Abahri, Modélisation des transferts couplés de chaleur, d’air et d’humidité dans les matériaux poreux de construction, Thèse de doctorat, Université de La Rochelle, France (2012).
• R. Belarbi, A. Aït-Mokhtar, M. Qin, O. Omikrine, Development of simplified approach to model the moisture transfer in building materials, European Journal of Environmental and Civil Engineering, (10)9: 1033-1048, 2006.
• R. Belarbi, M. Qin, A. Aït-Mokhtar, L.O. Nilsson, Experimental and Theoretical Investigation of Nonisothermal Transfer in Hygroscopic Building Materials, Building and Environment, (43) N°12, 2154- 2162, 2008.
• El Bachawati, M., Manneh, R., Belarbi, R., Dandres, T., Nassab, C., & El Zakhem, H. (2016). Cradle-to-gate life cycle assessment of traditional gravel ballasted, white reflective, and vegetative roofs: A Lebanese case study, Journal of Cleaner Production.
• Ferhat Benmahiddine « Etudes des transferts couplés de chaleur, d’air et d’humidité par des techniques de changement d’échelle (microscopique-macroscopique). Application là l’évaluation de la performance énergétique des bâtiments et à la durabilité des matériaux de construction ». Thèse soutenue le 08 décembre 2020 à La Rochelle Université en cotutelle avec l’Université de Béjaïa. Financement : Programme PROFAS B+ (Franco-Algérien) et le projet CPER-FEDER MADUR (La Rochelle Université).
• Fares Bennai « Étude des mécanismes de transferts couplés de chaleur et d’humidité dans les matériaux poreux de construction en régime insaturé » : Programme PROFAS B+ (Franco-Algérien).
• Thèse en cotutelle Université de La Rochelle -Université de Béjaïa, 28 juin 2017.
• Fouad Boukhelf « Proposition d’une nouvelle formulation mathématique pour l’analyse du comportement thermo - hydro - mécanique des structures fonctionnellement graduée ». Thèse soutenue le 09 décembre 2020 à La Rochelle Université en cotutelle avec l’Université de Sidi Bel Abbès, Financement : Programme PROFAS B+ (Franco-Algérien) et Projet CPER-FEDER MADUR (La Rochelle Université).
• Mohammed Yacine Ferroukhi, Modélisation des transferts thermo-hydro-aérauliques dans les enveloppes de bâtiments : évaluation des désordres causés par l’humidité, Thèse de doctorat, Université de La Rochelle, 01 décembre, France (2015).
• M.Y. Ferroukhi, R. Djedjig, K. Limam, R. Belarbi, Hygrothermal behavior modeling of the hygroscopic envelopes of buildings: A dynamic co-simulation approach, Building Simulation, October 2016, Volume 9, Issue 5, pp 501-512.
• El Bachawati, M., Manneh, R., Belarbi, R., & El Zakhem, H. (2016). Real-time temperature monitoring for traditional gravel ballasted and extensive green roofs: A Lebanese case study, Energy and Buildings.
• M.Y. Ferroukhi, R. Belarbi, K. Limam, W. Bosschaerts, Impact of coupled heat and moisture transfer effects on buildings energy consumption, Journal Thermal Science, Volume 21, Issue 3, 2017, Pages 1359-1368.
• Maroua Maaroufi, « Modélisation des transferts thermo-hygro-aérauliques dans les enveloppes des bâtiments. Incidences de l’hystérésis sur la prédiction de la qualité des ambiances habitables », soutenue le 12 décembre2019 à l’Université de La Rochelle, Financement : Ministère (MESR).
• Nabil Issaadi « Effets de la variabilité des propriétés de matériaux cimentaires sur les transferts hygrothermiques : développement d’une approche probabiliste ». Thèse de doctorat, Université de La Rochelle, 02 Décembre, France (2015).
• Abdelkrim Trabelsi, Études numérique et expérimentale des transferts hygrothermiques dans les matériaux poreux de construction, Thèse de doctorat, Université de La Rochelle, France (2010).
• Menghao Qin, Etude des phénomènes de transfert hygrothermiques dans les parois des bâtiments. Thèse de doctorat, La Rochelle Université (2007).

Profile of the candidate

• The candidate must be registered or graduated from one of the partner institutions.
• The candidate must have a Masters's Degree or equivalent in Chemical Engineering, Environmental engineering, or a related field.
• The candidate must speak fluent English and/or French.
• The candidate must have a strong affinity for field activities.
• The candidate must have a good capacity for using digital tools (modeling, statistical analysis, etc..)

Modality of the application

1. Create a student account. Click here.
2. Download the guide for applicants, application Form#1, and application Form N#2.
3. Prepare, sign, and submit your full application online no later than October 16, 2022.

Candidates are invited to download the SWaTH Mobile App and Log In to check the updated status of their application.

Candidates who pass Stage 2 will be invited for an online presentation between 19 and 21 October 2022.

The Ph.D. thesis will start on November 01, 2022, and 3-month mobilities will take place twice a year for a period of 3 years.