Phase Change Materials (PCM) have been incorporated into a range of building envelope materials with varied success. This study investigates two different methods of combining concrete and phase change materials to form PCM/concrete composite panels. The first method involves adding microencapsulated paraffin to fresh concrete during the mixing process. The second method involves vacuum impregnating butyl stearate into lightweight aggregate which is then included in the concrete mix design. The primary aim of the study is to determine which method is the most effective way to improve the thermal mass characteristics of a concrete panel in the context of a thermal energy storage system for space heating in a building. The study observes the rate at which the panels absorb and emit heat, ie, the heat flux, and also how the heat flux changes throughout the depth of the panel. The panels are heated in a controlled environment provided by a specifically designed light box. Radiation is used as the heat transfer mechanism. Surface and internal temperatures of the panels are recorded during heating and cooling periods. The data recorded, together with the determined densities and thermal conductivities, are used to compare the thermal mass behaviour of each type of panel and to determine the influence that the method of incorporating a phase change material into a concrete panel has on the effectiveness of the PCM to improve the thermal mass characteristics of the concrete panel. The study highlighted the complexity of thermal behaviour of PCM/concrete composites. The panels containing PCM displayed significantly greater thermal storage capacity despite having reduced thermal conductivity and density. The study concluded that the panel containing lightweight aggregate/PCM composite is more effective at providing additional thermal storage particularly within the first 100mm of depth of an element of structure
