A complete numerical model for low temperature composite form-stable phase change material slab based on dynamically simplified temperature transforming method

Phase change material (PCM) that is used in the roof top slab can minimize the heat infiltration into the living space from the building envelope and increase the indoor thermal comfort level. The major disadvantage of PCM is leakage at liquid state. Expanded graphite (EG) is used here as supporting material for PCM to prevent the leakage and maintains the form stability. The composite PCMs are prepared by adding the EG with various mass ratios, i.e. 3%, 6%, and 9%. The thermal properties of all composite PCMs are determined by DSC and thermal conductivity analyzer. The optimum PCM composition was found at 9% of EG. In this study, the shape-stabilized PCM-integrated roof top was analyzed by simplified temperature transforming (TT) numerical model. The main advantage of this model is that it is used to combine the equivalent enthalpy and heat capacity. The numerical results are validated with experimental values and show the lower mean absolute percentage error (MAPE), i.e. 6.91%. This indicates that present model is well suitable to predict the thermal performance of composite PCM incorporated roof top. The effect of various parameters like thickness of the PCM slab, wind velocity, percentage of EG mass ratio, and location of PCM are investigated by simplified TT model. The results showed that the maximum inner surface temperature reach up to 53°C for BG model (concrete and gypsum) by distributing constant heat flux, i.e. 1,000 W/m² for 180 min. At this same condition, the inner surface temperature of other PCM models PBG (PCM, concrete, gypsum) and BPG (concreate, PCM, Gypsum) reaches to 50°C and 41°C, respectively. PBG model exhibits excellent thermal performance compared to BPG model. The thermal performance of PCM slab is also investigated by varying the thickness of the PCM layer and found that time lag is raised with the thickness of the PCM slab.