Improving thermal and energy performance of buildings in summer with internal phase change materials

In warm climates, internally applied phase change materials may substitute insufficient thermal mass in lightweight constructions. A simplified model was developed for devising initial-design data for phase change material products applied on the inner surface of walls. The model enabled estimating the thickness of the phase change material layer that can be fully discharged via night ventilation and, for a given product thickness, the total area required for storing the internal heat gains occurring during the day. Thermal and energy performance of three building types in the Mediterranean climate was further analysed using the dynamic program EnergyPlus. Results showed that intensive night ventilation is essential for discharging daily stored energy. During the hottest period, only a thin layer of several millimetres can be fully discharged overnight. Minimal thicknesses were very effective in reducing cooling energy demand in lightweight offices but much less effective in semi-lightweight classrooms. Increased phase change material thickness increased energy savings, and by reducing surface temperatures during occupancy periods, improved thermal comfort. In heavyweight construction, phase change material improved thermal comfort but not energy performance.