Computer simulations of heat transfer in a building integrated heat storage unit made of PCM composite

The paper presents the results of parametric study of thermal performance characteristics of thermal energy storage unit integrated in building structure being also a part of building's ventilation system. A storage unit is in the form of a ceiling panel with internal channels through which air taken from the environment flows before it is delivered into the rooms. Thermal storage potential of the panel is thanks to phase change material (PCM) which is mixed with gypsum mortar, creating in this way a composite of high thermal capacity in the temperature range corresponding to the temperature required for thermal comfort. In order to perform the analysis of the storage unit a computer program was developed which was based on the mathematical model of complex heat transfer occurring inside the panel, inside a composite material, as well as on the boundary between the panel and air flowing through internal channels. A procedure describing variations of convective heat transfer intensity along the channel can be regarded as a unique achievement in this research. This function was validated based on measurements conducted on the experimental set-up specially prepared for this study. Using the program many computer simulations were performed. Based on the results of this analysis a detailed information on the performance of the panel for different operational parameters, e.g. air mass flow rates, were obtained. Contrary to the study reported in an earlier publication, these simulations were conducted for real environmental conditions, i.e. real ambient temperatures during summer in Central Poland. Also, important conclusions regarding selection of PCM, mainly its melting temperature range, were formulated.