Microencapsulated Phase Change Materials for Thermal Energy Storage in Buildings: Design, Characterization and Modelling

Abstract

Thermal energy storage (TES) has a significant role in saving thermal energy and improving indoor climate. Latent heat thermal energy storage (LHTES) using Phase Change Materials (PCM) in heating, ventilation, and air-conditioning (HVAC) building applications allows storage of a substantial amount of energy in a relatively small volume and absorbs/releases it in a narrow temperature range. The main objective of the current study was to develop and thermally characterize microencapsulated PCM for LHTES in building applications. The microencapsulated PCM stores substantial energy, and leakage or phase separation is avoided compared to PCM in bulk and PCM emulsions. In the current thesis, seven PCM belonging to the categories of organic paraffins, organic non-paraffins, and inorganic salts were thermally characterized. Additionally, this study presents the development of PCM emulsions, PCM polymers, and PCM electrospun fiber matrices. All variations of PCM emulsions, polymer, and electrospun fibers were characterized thermally and morphologically. Commercial organic paraffin RT18™ with a melting temperature of 18°C in bulk, emulsion, and electrospun fiber forms was found suitable for application in LHTES systems in HVAC building applications. Bulk RT18™ showed latent heats of melting/solidification of 137-139 kJ/kg, while RT18™ water emulsion possessed latent heats of about 180 kJ/kg. PCM core-PCL shell electrospun fibers of organic paraffin RT18™ showed latent heats of melting solidification of 102.1/82.21 kJ/kg. Additionally, after conducting experimental studies on PCM, a numerical analysis of LHTES systems of different geometries was carried out using Comsol Multiphysics 6.0 FEM software. The effect of internal and external fins in a double tube encapsulating bulk PCM in the annular space was studied. Additionally, a singletube LHTES using PCM electrospun fiber matrix in direct contact with water was analyzed. The phase change processes were accelerated with an increase in the length of fins.