Comparative performance analysis of eutectic salt-water solutions in latent thermal energy storage for residential applications: Insights from the ECHO project

• 4 PCMs for cooling thermal energy storage in residential applications are identified. • Na 2 CO 3 /H 2 O properties align with the requirements of sub-zero CTES systems. • Adding graphite to Na 2 CO 3 /H 2 O significantly improves thermal conductivity. • A comprehensive approach is used to analyze the thermophysical properties of PCMs. • All selected PCMs exhibited subcooling below 2 K. This study investigates the potential of eutectic salt-water solutions as phase change materials (PCMs) for Cooling Thermal Energy Storage (CTES) systems, with a focus on residential applications under the Horizon Europe ECHO project. The research addresses the pressing need for sustainable, compact, and efficient thermal energy storage systems to reduce greenhouse gas emissions and improve energy efficiency in alignment with EU climate objectives. Among the evaluated PCMs, a Na 2 CO 3 /H 2 O eutectic solution, enhanced with graphite, demonstrated considerable performance, achieving a 78 % increase in thermal conductivity in the liquid phase and a 55 % improvement in the solid phase compared to the base solution, while maintaining a strong latent heat of melting (284 kJ/kg) and low subcooling (1.97 K). Comprehensive experimental methods, including Differential Scanning Calorimetry (DSC) and Transient Plane Source (TPS) analysis, were employed to characterize the thermophysical properties of the PCMs. These techniques ensured precise measurements of latent heat, specific heat capacity, and thermal conductivity, with uncertainties of ± 2 % and ± 5 % for DSC and TPS measurements, respectively. Comparative analysis of the custom-made Na 2 CO 3 /H 2 O solution with graphite and two commercial PCMs highlighted the advantages of the custom formulation, particularly in terms of reactivity and thermal conductivity, making it a strong candidate for CTES integration. This work provides significant contributions to the understanding of eutectics thermophysical properties, a critical yet underexplored area, and sets the stage for the practical implementation of advanced LTES systems. The findings emphasize the importance of precise experimental characterization for accurate modeling and system optimization, laying the foundation for future efforts in scaling and deploying full-scale CTES units for energy-efficient residential applications.