Phase change materials in wallboards for heat management in building applications

The applications of thermal energy storage with phase change materials (PCMs) in buildings are studied in this thesis, especially focusing on the PCM wallboard. Some current applications of thermal energy storage with PCMs in buildings are reviewed. The optimal melting temperatures and diurnal heat storage of interior PCM wallboard and exterior PCM wallboard are theoretically studied. The optimal melting temperature of an interior PCM wallboard is related to the average room air temperature and the total radiation absorbed by PCM wallboard. The optimal melting temperature of an exterior PCM wallboard is related to the average room air temperature, the average outside temperature and the radiations absorbed from the inside and outside environment. The thermal performance of interior and exterior PCM wallboard is numerically studied by using COMSOL. Some design factors, such as melting temperature, melting range, latent heat, thermal conductivity and convective heat transfer coefficients of inner surface and outer surface are qualitatively discussed. The simulation results are agreed well with the theoretical work. The PCM wallboard can have a better performance if the thermal conductivity can be enhanced to around 0.4 W/mK. When designing a PCM wallboard, the convective heat transfer coefficients should be calculated carefully. To briefly evaluate the energy consumption and energy saving of PCM wallboard, a double-room building with normal constructions and PCM wallboards is modelled using EnergyPlus@. As most PCMs suffer a common problem of low thermal conductivity, heat transfer characteristics of PCMs embedded with porous materials are studied. Paraffin wax RT 27 and calcium chloride hexahydrate are employed as the heat storage media. The results indicate that the addition of porous materials can enhance the heat transfer rate of PCMs, especially for metal foams which can double the overall heat transfer rate during the melting processes. The effect of mass ratio of expanded graphite on heat transfer is also examined.