Thermal performance investigation of a phase change materials based thermal energy storage system with multiple sets of U-tubes in severe cold region: An experimental study

With the growing demand for improved comfort and energy efficiency in buildings, latent heat thermal energy storage (LHTES) systems have been rapidly developed to address the mismatch between energy supply and demand in buildings. However, the advancement of LHTES systems is constrained by the low thermal conductivity of phase change materials (PCMs). This study presents the design experimental evaluation of an LHTES system, which was integrated into a multi-energy complementary near-zero energy building located in a severe cold region. The system incorporated a PCM tank with internal U-tubes and spiral fins to enhance heat transfer efficiency. The system's thermal performance was systematically investigated during thermal energy storage (TES) and release (TER) processes. The results revealed that the formation and deformation of the mushy zone, along with the buoyancy-driven phase separation, significantly influenced the temperature distributions within the PCM tank. In contrast, the thermal convection dominated the temperature distributions in the water tank. The PCM-based system demonstrated superior performance, achieving a 64 % higher thermal storage capacity and a 110 % greater thermal release capacity than the conventional water-based system. Furthermore, increasing the inlet temperature and flow rate significantly enhanced thermal storage capacity and reduced storage time by improving heat exchange efficiency for both systems. These findings provide critical insights into the design and optimization of LHTES systems, offering practical implications for advancing building energy management in severe cold climates.