PhD Defense by Maria Aurely YEDMEL the 03rd of December 2025

Jury : 

Laurent ROYON, Professor, Université Paris Cité, Reviewer

Marie DUQUESNE, Professor, La Rochelle Université, Reviewer

Jean Pierre BEDECARRATS, Professor, Université de Pau et des Pays de l'Adour, Member

Fatou-Toutie NDOYE, PhD, Université Paris Saclay, INRAE, Member

Direction and supervision : 

PhD Director : Anthony DELAHAYE (INRAE Frise)
Supervisor : Denis LEDUCQ, INRAE Frise

Abstract : Food systems contribute to approximately 37 % of global greenhouse gas emissions, with refrigeration representing a significant share. This research was conducted within the European project ENOUGH, which aims to reduce food chain emissions by at least 50 % by 2050. The specific contribution focuses on the use of Thermal Energy Storage (TES) in refrigeration systems for Demand-Side Management (DSM), which refers to strategies that adjust when and how electricity is consumed to better match grid availability. In this context, TES is used to store energy during periods of low demand and release it during peak periods, helping to regulate consumption and indirectly reduce greenhouse gas emissions.

To this end, an innovative cold storage device, the Thermosiphon Thermal Accumulator (TTA), is proposed. It combines phase change material (PCM) with the principle of a two-phase closed-loop thermosiphon, in order to maximise the benefits of TES. The TTA is directly integrated into the vapour compression cycle (VCC) of a closed-door refrigerated display cabinet (RDC). Direct heat transfer between the refrigerant and the PCM enhances the overall efficiency of the system. The accumulator can be connected to any VCC without requiring secondary fluids, additional cooling units or cabinet modifications, thereby improving thermodynamic efficiency while avoiding the cost of a secondary loop. During charging, the refrigerant transfers part of its cooling capacity to the PCM before passing through the evaporator to exchange with the cabinet air. During discharging (DSM), the thermosiphon effect enables the stored cold energy to be released to the evaporator without pumping energy.    The aim of this research is to characterise the TTA as a DSM solution integrated into an RDC. To achieve this, DSM events were conducted under various operating conditions (thermostat settings, ambient temperature, door-opening regimes, PCM type, etc.). The technical concept was first validated by assessing temperature stability, followed by evaluation of energy consumption and the charge-discharge kinetics. Results showed that the TTA can maintain regulatory cabinet temperatures without additional energy consumption.
To enhance system performance, design optimisations of the accumulator were investigated through COMSOL simulations, identifying the most effective configurations for rapid kinetics and high storage density. Complementary, characterisation of the TPCLT was conducted to examine the influence of key parameters (e.g., evaporator power exchanged, refrigerant charge in the loop) and to deepen the understanding of the flow mechanisms, which are essential for ensuring efficient cold transfer from the cold storage device to the evaporator. An economic and environmental assessment was also performed to benchmark the TTA against conventional storage technologies.
The results demonstrate that the TTA holds strong potential for supporting the energy transition in the food sector, offering real flexibility to the electricity grid while ensuring the preservation of food products.