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

Abstract

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.

The relevance of cut-stone to strategies for low-carbon buildings

“…• Increased comfort and reduced operational carbon impact during the summer, owing to the ability of high thermal masses to passively cool interior spaces and trigger stackdriven ventilation flows that both decrease reliance on energy-intensive air-conditioning systems (de Toldi et al 2022), as compared with light-inertia buildings, which are subject to overheating and require mechanical cooling.…”