The effect of thermal cycling on the thermal and chemical stability of paraffin phase change materials (PCMs) composites

This paper is the first study to present the long-term performance of a gypsum and cement plasters which can be used to retrofit existing buildings and reduce their energy consumption. It is comprised of high energy storage loaded granules, known as composite PCMs or form-stable PCMs (FSPCMs), containing three types of organic phase change materials (PCM), with phase change transitions between 18 °C and 25 °C. PCMs are effective thermal energy storage systems as they improve thermal comfort of occupants in buildings by reducing temperature fluctuations. As PCMs will undergo many phase transitions throughout their normal life cycle, the effects of thermal cycling on their long-term stability and performance are important considerations in their selection. The limited understanding on the long-term stability and potential for degradation of PCMs has restricted wider use of these materials in the construction sector. In this research, cement mortar and gypsum plaster specimens were subjected to 700 thermal cycles using an environmental chamber. After cycling, experimental results revealed a reduction of latent heat in the solidification process by up to 23% for the pure PCMs and up to 57% for the PCM loaded granules. However, once the PCMs had been incorporated into either the gypsum plaster or cement mortars, there was no significant reduction in the thermal conductivity or the specific heat capacity of these materials. Thermal cycling did not decrease the effectiveness of PCM composites, and so increasing their potential for wider acceptance of these products and use by the construction industry. This will aid the retrofitting of existing low energy efficient buildings to achieve Net-Zero targets.