Effective heat capacity of interior planar thermal mass (iPTM) subject to periodic heating and cooling

Thermal mass can be effectively used for controlling temperature in buildings. In this paper, the dynamic heat transfer performance of interior Planar Thermal Mass (iPTM) subject to sinusoidal heating and cooling is investigated. Analytical solutions of temperature distribution and heat flux in iPTM are deduced. It is shown that the effective heat storage capacity of iPTM reaches maxima at an optimal thermal mass thickness. Therefore, from the consideration of building material as thermal mass rather than as structural material, there is no rationale of using thickness greater than optimal thickness.The convective effect at iPTM surface is analyzed. A virtual average heat flux and an effective thermal resistance are defined. It is concluded that, for most common indoor building materials, the convective effect cannot be neglected. Because of the convective effect and the nonlinearity of the heat storage of iPTM, it is shown that the lumped method, which is used to do interior thermal mass calculation in most papers and softwares, is incorrect under most circumstances.