Energy saving and CO2 reduction potential of external building walls containing two layers of phase change material

Using two layers of phase change material (PCM) instead of one to improve the thermal energy storage of PCM is a promising way to minimize thermal loads in buildings. This study aimed to maximize the latent heat utilization by splitting the PCM into two layers and adjusting their location and melting temperature. Seven scenarios were created using one or two PCM layers on the inner side, outer side or both sides of an external wall. Energy savings analysis was carried out using a verified numerical model. The results indicated that the monthly optimum PCM melting temperature ranged from 5 °C to 30 °C. Two PCM layers, one on the outside side of the wall with a melting temperature of 17 °C and the other on the interior side with a melting temperature of 25 °C, resulted in higher annual energy savings (17.2%), compared to a single PCM layer (16.8%). With two PCM layers, the energy saving due to latent heat activation increased from 2.5% to 3.2%. Furthermore, this design reduced CO2 emissions by up to 18.4% and caused the surface temperature to approach the comfortable room temperature thereby decreasing thermal loads and improving thermal comfort.