Jan Zemanek, Alfons Vaclavik, Radim Hercík, Radek Byrtus, Zdeněk Macháček, Florian Schwär, Moritz Walter, Radek Martínek, Ibrahim A. Hameed, Jiří Koziorek
Latent heat thermal energy storage (LHTES) offers a compact and energy-dense solution for residential heat storage; however, its practical deployment remains limited by challenges such as low thermal conductivity, uncertainty in heat release from supercooled states, and a lack of experimentally validated system-level performance at the household scale. This study presents the innovative solution in the developed control system and the precise experimental evaluation of a modular phase change material (PCM)-based thermal storage system designed for domestic applications with controllable on-demand heat release. The developed heat thermal energy storage system is based on sodium acetate trihydrate (SAT) and is evaluated under realistic charging and discharging conditions using a controlled hydronic loop. A key methodological contribution is the integration of loop calorimetry with a dense three-dimensional network of 105 in-situ temperature sensors that enabled detailed system-level analysis. In addition, a transparent tank design provides direct optical process behavior and state access, allowing for improved interpretation of thermal processes and front propagation. The novelty of the work lies in combining controllable supercooling with a modular household-scale demonstrator and a multi-modal experimental approach for system-level validation. The experimental results show stable repeated charging and discharging without phase separation. Thermal mapping reveals that the heat-transfer front originates at the finned aluminum heat exchanger and propagates toward the peripheral regions of the PCM. The focus of the study is on a long-duration experiment, including an intentional idle period, system measurement data, and energy efficiency computation. These results demonstrate the feasibility of controllable, on-demand heat release in PCM-based storage and provide quantitative insights for system optimization in real residential applications.