Effect of masonry material and surface absorptivity on critical thermal mass in insulated building walls

Effects of type of masonry material and surface absorptivity to solar radiation on critical thermal mass thickness in insulated building walls are investigated for a fixed wall nominal thermal resistance (Rn-value). The concepts of “thermal-mass energy-savings potential” (Δ) and “critical thermal mass thickness” (Lmas,cr), developed in a previous study, are utilized to determine the thermal mass thickness required for a desired percentage energy savings. Transmission loads are calculated under the climatic data of Riyadh, assuming steady periodic conditions, by using a previously validated computer model. Effects of masonry materials are investigated by using solid and hollow concrete blocks, while surface absorptivity (λ) influence is studied for λ=0.4 and 0.2. Walls are considered where thermal mass is located on the inside or on the outside relative to insulation layer. Thermal mass thickness is varied between 0 and 50cm while keeping Rn-value constant. The results show that for a given critical thermal mass thickness, higher energy savings potential is obtained with: (i) walls with solid concrete blocks, (ii) walls with lower surface absorptivity, and (iii) walls with inside thermal mass. Charts are developed for Lmas,cr versus Δ under the different conditions for the benefit of building envelope designers.