A comparative study on PCM-impregnated shape-stable expanded vermiculite used in bricks for stabilizing indoor temperature and enhancing energy efficiency of buildings

Abstract

The building sector is considered a major driver of global energy consumption. Due to its ability to control heat flow between the exterior and interior environments and its direct impact on overall energy demand, it has become a prominent component for improving thermal comfort and minimizing energy demand. Walls are a primary element of heat transfer within building envelopes, and bricks, a common construction material used in walls, play a decisive role in improving the passive energy performance of building envelopes through both their structural integrity and thermal properties. While conventional bricks have received significant attention for their structural functionality, their impact on thermal performance remains limited. Bricks enhanced with phase change materials (PCM) are attracting attention as passive strategies that can be implemented for sustainable and efficient building approaches thanks to their contribution to thermal mass through their thermal energy storage (TES) capacity. In the current research, the effect of integrating a shape-stable PCM composite prepared using expanded vermiculite (EV) and methyl palmitate (MP) into brick cavities on thermal performance was investigated. The EV/MP composite has a melting enthalpy of 109.2 J/g at 26.81 degrees C and a solidification enthalpy of 107.1 J/g at 24.83 degrees C. The variation in internal temperature fluctuations and heating-cooling loads, depending on the PCM content, was analyzed for different locations and amounts of PCM. The results revealed that, compared to hollow bricks, PCM- developed bricks provided 5.2 degrees C lower indoor temperature during the daytime, and this effect persisted for more than 6 h. At night, PCM integration resulted in a 1.58 degrees C higher indoor temperature, providing a thermal comfort advantage for 6 h and 54 min. The effect of partly-PCM addition (PCM(S)) was clearly seen in reducing the cooling load during the daytime, while full-PCM addition (PCM-(F)) played an active role in reducing the heating load at night. Furthermore, a new dimensionless temperature expression proposed to evaluate heat retention ability showed that PCM-(F) and PCM-(S) configurations exhibited up to 108 % and 62 % higher heat storage capacity compared to hollow bricks, respectively. These findings highlight the importance of PCM-integrated bricks as a practical and scalable solution for increasing thermal stability, minimizing heat loads, and improving the energy efficiency of building envelopes.