Internal thermal mass for passive cooling and ventilation: Adaptive comfort limits, ideal quantities, embodied carbon

How effective is naturally ventilated internal thermal mass for obviating air-conditioning, mitigating heatwaves and storing carbon in buildings? This study combines detailed climate model outputs with scaling rules for optimizing internal thermal mass coupled with buoyancy ventilation. It identifies regions where this passive design strategy is most effective during future heatwaves and determines how much internal thermal mass each person needs to stay comfortable in these regions, with a special focus on Canada. Results suggest that naturally ventilated internal thermal mass is likely to become less effective due to future global heating. Regions where internal thermal mass will no longer be sufficient to obviate air-conditioning and where it can still play a significant role in hybrid cooling are identified. By comparing the ideal per capita thermal mass quantities in different regions, it is found that biomass-based materials require approximately 3.5 times the volume of cementitious materials to perform equivalently, if thermal proportions for surface area and thickness are respected. Finally, an analysis of the per capita embodied carbon of these ideal internal thermal mass quantities is undertaken, suggesting a fair functional unit to compare thermal mass materials. PRACTICE RELEVANCE High-resolution Canadian maps and lower-resolution global maps are developed in this study to allow practitioners to distinguish between areas where internal thermal mass should be sufficient to obviate air-conditioning and where supplementary cooling is needed. Ideal per capita quantities of different thermal mass materials are given for each region, with guidelines for how to distribute this thermal mass internally in walls, floors and ceilings, and how the surface area and thickness of the thermal mass scales with the thermal properties of the material and the per capita heat loads and ventilation and temperature damping requirements. As such, this study suggests how thermal mass materials can be compared fairly in terms of performance and embodied carbon at the preliminary stages of design.