Yolaine Adihou has successfully presented the defense of her PhD thesis on « Exergy modelling and optimisation of low-temperature thermal networks ». This thesis is a codirection between the Thermal & Energy Laboratory (LTE) of the School of Engineering and Architecture of Fribourg (HEIA-FR) and the Building Energy Processes Laboratory (LOCIE) of the University of Savoie Mont Blanc (USMB). A PhD thesis presentation will take place on Thursday, 15 December 2022 at 11:00 at the blue Hall of bluefactory in Fribourg (room HBL0 21A), followed by a shared lunch (please sign up for lunch).

The evolution of thermal networks towards low temperatures is motivated by the reduction of heat losses, the promotion of low-temperature Renewable and Recoverable Energy sources and the improvement of centralised generation units' efficiency. However, the temperature of the network must be adapted to the thermal needs of the district. Designing the different technologies requires a systemic modelling approach to support industrials in integrating more renewable energies and to improve the performance of their networks.

Exergy (thermodynamically, the maximum work that can be extracted from a quantity of energy in relation to a reference environment) is used to define the quality of energy and to analyse the performances of energy systems on a common basis. Therefore, the canton of Geneva has defined exergy efficiency as a criterion for the rational use of energy in its law. However, besides the abstraction of the concept, its interest is sometimes difficult to perceive for industries because exergy analysis enables to locate the losses without explicitly explaining their origin. It limits the decision-making process for acting on inefficient components. Furthermore, exergy is rarely used as the unique criterion for designing network components.

The thesis aims to develop an exergy-based methodology, adapted to the industry, for modelling and optimising low-temperature thermal networks. Generic and explicit formulations are developed to simplify the calculation of exergy losses generated by the network components. These formulations are expressed as a function of the design and operating parameters on which the engineer can act. They are integrated into the ADVENS software which simulates the thermal-hydraulic behaviour of thermal networks. Finally, an exergy-based optimisation process is implemented to determine the network optimal temperature level and configurations (energy-mix, generation units, substations).
To assess and validate the methodology, two industrial partners are involved: Groupe E SA in
Switzerland and SCDC ENGIE Solutions in France.