Novel wall panels containing CaCl2·6H2O-Mg(NO3)2·6H2O/expanded graphite composites with different phase change temperatures for building energy savings

To explore phase change materials (PCMs) with different melting points for building energy saving in different seasons, Mg(NO3)2·6H2O was mixed with CaCl2·6H2O at different mass fractions to prepare eutectics. And the obtained two eutectics were selected as the two appropriate PCMs to combine with expanded graphite (EG), one of which is CaCl2·6H2O-8wt%Mg(NO3)2·6H2O/EG (PCM1), exhibiting a onset point and melting peak temperature of 21.17 and 27.87 °C and latent heat of 105.4 J/g, and the other one is CaCl2·6H2O-15wt%Mg(NO3)2·6H2O/EG (PCM2), having a onset point and melting peak temperatures of 14.23 and 23.17 °C and latent heat of 80.19 J/g. Then, two EG-based composites were formed into PCM panels by vacuum compression, respectively, and a kind of double-layer panel was fabricated by integrating the single-layer one together. The experimental investigation on the thermal performance of the chamber equipped with PCM panels was carried out, and the obtained results were used to validate a numerical simulation method. Finally, by employing the validated numerical model, the thermal performance of the concrete room containing PCM1, PCM2 and double-layer panels were investigated, respectively. It is shown that the better energy saving potential of the room can be achieved by placing PCM1 and PCM2 on the roof and southern wall, respectively. The wall panels fabricated from the CaCl2·6H2O-Mg(NO3)2·6H2O/EG composites with suitable phase change temperatures show potentials in practical applications.