PhD Student in the Field of Energy and Thermal Sciences

Job description

Thesis title

Experimental and numerical evaluation of the overall performance of humidity-sensitive ventilation systems with improved consideration of the hygroscopic buffer of buildings.

Description of the thesis project

Context

The quality of indoor environments is an important issue for the comfort and health of occupants, who spend over 90% of their time in buildings. One of the most important parameters of the indoor environment is the relative humidity of the ambient air. This affects both the comfort and health of occupants, and the deterioration of buildings. Building ventilation plays a key role in maintaining indoor air quality by supplying fresh air and removing pollutants. In particular, it helps control humidity in the indoor environment by evacuating excess moisture. Ventilation thus contributes to creating conditions of comfort and health in buildings, but at the same time impacts their energy performance through heat losses linked to air renewal in winter (and conversely, heat gains in summer), added to which are the possible electrical consumption of fans. In today's context of environmental transition, ventilation is subject to a dual injunction: to maintain healthy, comfortable indoor environments, while reducing the energy consumption of buildings.

The installation of a ventilation system meets prescriptive regulatory requirements that have encouraged the development of Controlled Mechanical Ventilation (VMC) systems in housing since 1982. VMC allows air to be renewed, eliminates humidity and unpleasant odors, ensures user hygiene and comfort, preserves the home by preventing the growth of mold and mildew, and controls air flow to save energy. There are single exhaust or balanced ventilation, self-regulating or humidity-sensitive VMC solutions. In particular, humidity-sensitive single exhaust VMC, widely installed in homes built after 1983, enables air renewal rates to be modulated according to occupancy needs, thus reducing heat loss/contribution. Humidity-controlled ventilation is an intelligent ventilation system, providing minimal ventilation when the room is unoccupied and increased ventilation when demand is high. This system has proved highly effective in controlling humidity in buildings, although its effectiveness in reducing other pollutants is still under investigation. Moreover, when it comes to optimizing energy performance, the scope for innovation is limited by prescriptive regulations. As an alternative, a performance-based approach has been developed for the regulation of ventilation systems to assess the ability of a ventilation system to provide good indoor air quality and avoid risks to occupant health. The use of a performance-based approach raises a number of questions concerning, on the one hand, the reliability of the numerical models used to calculate the transfer of air and pollutants in buildings, as well as the choice of pollutants and/or relevant parameters to be used in the calculation of performance indicators, and the definition of relevant input data.

The study of the performance of VMC systems must be carried out in a comprehensive way, taking into account the various aspects linked in particular to indoor air quality, thermal comfort and energy consumption under different conditions of heating in winter and cooling in summer. To achieve this, it is necessary to take into account the actual behavior of humidity-controlled VM systems in terms of the production of humidity by the presence of occupants and their activities, and its absorption by the walls and furniture in the building. Various phenomena that can impact humidity distribution need to be taken into account when designing each VM system, in particular the production, temporal phase shift and sorption/desorption effects of humidity by building walls and furnishings, especially in the presence of hygroscopic materials such as bio-based materials, the use of which is reinforced with the new RE2020 environmental regulations.

Objective and methodology

The aim of this thesis is to characterize the overall performance of humidity-sensitive ventilation systems in terms of energy performance, IAQ and thermal comfort in winter and summer in current and future climates. This requires a thorough understanding of the actual operation of humidity-sensitive ventilation in new and renovated homes, taking into account interactions with the hygrothermal behavior of the building (walls and furnishings), as well as with occupants (generation of humidity linked to their presence and activities, occupants' actions on the envelope and systems).

The thesis work will include both experimental and modeling aspects:

1. The first part will involve laboratory experiments to test and study the behavior of humidity-controlled ventilation systems. In particular, the aim is to develop a humidity generation device capable of simulating the metabolic production of humidity by occupants in a multi-zone house. This will make it possible to test the real operation of humidity-controlled ventilation systems in experimental houses on a scale under controlled conditions, taking into account humidity production and the building's hygroscopic buffer (walls and furnishings).

2. The second part of the modelling is aimed at adapting the building thermo-aerodynamic models, with improved consideration of the building's hygroscopic buffer (calibration and validation in relation to experimentation). The improved model will make it possible to assess the overall performance (energy, thermal comfort and IAQ) of humidity-sensitive ventilation in winter (interaction with heating) and summer (interaction with passive or active cooling) in current and future climates (with hotter or even scorching summers).

Required skills

This position is open to a holder of an M2 in building thermics/energy.

• Skills:

o Scientific mastery of physics: heat transfer and aeraulics, building physics.

o Proficiency in computer tools and calculation codes (Matlab, R, Python, etc.).

o Knowledge of physical measurements and instrumentation, and an appetite for experimental work.

o Ideally, knowledge of the building and ventilation trades.

o Fluency in French and English required for reading, writing and discussion.

• Personal skills :

o Curiosity, adaptability and creativity, analysis and synthesis, sense of commitment, rigor, autonomy, sense of communication and collective organization.

Thesis supervision

GROUPE ATLANTIC

• Mahdi MAJIDNIYA (co-supervisor), Groupe Atlantic, 17 Rue de la Croix Fauchet, 45140 Saint-Jean-de-la-Ruelle, mmajidniya[at]groupe-atlantic.com, Tél . 02 38 71 51 89

Research team BPE, CEREMA

• Sihem GUERNOUTI (Thesis director), researcher-HDR, Cerema Ouest, 9 rue René VIVIANI, 44262 Nantes, sihem.guernouti[at]cerema.fr, Tél : 07 63 61 83 55

• Bassam MOUJALLED (co-supervisor), researcher, Cerema Centre-Est, 46 rue Saint-Théobald, 38080 L’Isle d’Abeau, bassam.moujalled[at]cerema.fr, Tél . 07 60 82 35 55

Conditions for hosting the thesis project

The doctoral student will be employed by GROUPE ATLANTIC on a fixed-term doctoral contract starting in January/February 2025, for a period of 3 years (exact dates to be agreed with the doctoral student).

The thesis will be co-supervised by Cerema's BPE research team (at the Nantes and Isle d'Abeau sites) and by GROUPE ATLANTIC (at the Orléans site). The first 12 to 18 months will be spent at Atlantic in Orléans (depending on the progress of the experimental part), followed by the second part at Cerema in Nantes and L’Isle d'Abeau..

• Groupe Atlantic, 17 Rue de la Croix Fauchet, 45140 Saint-Jean-de-la-Ruelle

• Cerema Ouest- MAN, 9 rue René VIVIANI, 44262 Nantes

• Cerema Centre-Est, 46 rue Saint-Théobald, 38080 L’Isle d’Abeau

The arrangements will enable the doctoral student to benefit from the training provided by the doctoral school of registration.

Content of the application file

Please send your complete application (documents below) by email to all supervisors (mmajidniya[at]groupe-atlantic.com, sihem.guernouti[at]cerema.fr, bassam.moujalled[at]cerema.fr) before 30/09/2024 (due to size limitations of documents on our recruitment site, we kindly ask you to submit your application by email only):

• CV

• Copy of identity card or passport

• Master's grades (at least Master's 1 if Master's 2 grades are not available)

• Copy of most recent diploma (master's degree, engineering degree, research master's degree if already defended).

• Cover letter explaining your interest in the subject (maximum 1 double-sided page).

• Letter of recommendation