Salt hydrate/expanded vermiculite composite as a form-stable phase change material for building energy storage

An investigation on a new type of shape-stabilized phase change material (PCM) prepared by impregnating eutectic salt hydrate (Na 2 SO 4 ·10H 2 O-Na 2 CO 3 ·10H 2 O with 1:1 in mass ratio) into expanded vermiculite (EV) is carried out in this study. The maximum mass percentage of Na 2 SO 4 ·10H 2 O-Na 2 CO 3 ·10H 2 O eutectic within the composite is determined as 60%. The chemical composition of EV is measured by X-Ray Fluorescence Spectrometer (XRF). The specific surface area of EV and raw vermiculite (RV) is characterized by Brunauer-Aemmett-Teller (BET) method. The results from Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) tests reveal that eutectic salt hydrate fully filled in the multilayer structure of EV and had good compatibility among the components of the composites. The phase change temperature and the melting enthalpy of the composites are 23.98 °C and 110.3 J/g respectively, which are measured by differential scanning calorimetry (DSC). Good thermal and structural reliability are also demonstrated by thermal gravimetric analysis (TG) techniques and thermal cycling tests. Moreover, the low thermal conductivity with 0.192 W/ (m K) tested by the Hot Disk via transient plane source method certifies that the composite is very applicable for insulation. The composite PCM is then tested in a reduced-scale test chamber outfitted with four thin PCM panels as insulated wallboards. The indoor temperature variations of the PCM room is compared with another identical chamber without PCM layer for evaluating the thermal regulating performance. The results show that the composite has the function of maintaining the indoor temperature at a comfortable range for a longer period and distinctly influenced the time delay. All analysis results indicate that the low-cost salt hydrate/EV composite can exert a great deal of influence on insulation in building energy conservation .