Preparation and characterizations of a novel temperature-tuned phase change material based on sodium acetate trihydrate for improved performance of heat pump systems

Application of latent heat thermal energy storage unit is regarded as an effective method to improve the coefficient of performance of hot water heat pump systems (HWHPS). With consideration of energy efficiency and domestic hot water usage, phase change materials with a melting temperature range of 45–48 °C are suitable for practical applications. The most commonly used PCMs, paraffin-based materials, are costly and have low latent heat density, which restrains their applications. This study therefore aims to prepare a novel sodium acetate trihydrate based composite PCM with suitable phase change temperature and cost-effectiveness for HWHPs. A series of SAT-based composites with varying mass fraction of potassium chloride (KCl), urea, disodium phosphate dodecahydrate (DSP) and carboxyl methyl cellulose (CMC) were prepared. Their thermophysical properties and stability were investigated by freezing-melting cycling tests, differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). The experimental results indicated that the optimized SAT-based CPCM with 8 wt% KCl, 3 wt% urea, 6 wt% CMC and 1.5 wt% DSP displayed a favorable phase change temperature of 47.8 °C and a higher latent heat of 242.0 kJ/kg. Meanwhile, the results demonstrated that it has extraordinary thermal cycling performance, negligible vibration in phase change temperature and latent heat, and good stability in chemical properties.