Augmenting Thermal Mass Performance without Added Carbon Footprint: Surface Area Modulation of Structural Slabs in Naturally Ventilated Buildings

Zherui Wang, Xiang Zhang, Xiaoxiao Peng, Saeran Vasanthakumar, Dorit Aviv

Internal thermal mass (ITM) is a well-known passive technique that provides lag and damping for extreme diurnal temperature fluctuations when combined with natural ventilation and night flushing. Thermally massive concrete slab elements, vital for ITM, often feature a compact solid design, limiting their thermal storage potential due to restricted contact with indoor airflow. With the advent of architectural geometry and digital fabrication, floor elements can be designed and fabricated with greater exposed surface area under the constraint of the same material volume, thus maintaining the same embodied carbon footprint but increasing thermal performance potential. This study examines the impact of increasing the exposed surface area of ITM through geometric modulation while keeping the material volume constant to reduce the building’s embodied carbon. The objective is to investigate how varying ITM surface area, within a fixed material volume constraint, influences indoor thermal comfort in a free-running building. We examine a case study of a midsize office building in two climatic zones (Tucson, AZ, and San Diego, CA) with an increased ITM ceiling surface area of the structural slab. We then apply natural ventilation optimization and night flushing to further enhance ITM performance. The results show that in the hot-dry and marine climates, expanding ITM surface area by 1.7 times yields an improvement of 6% and 7% annual thermal comfort hours when coupled with natural ventilation. These findings suggest a substantial energy-saving potential for enlarging the surface area of ITM in buildings within the studied climates.

Read the full article in the SimBuild 2024 conference proceeding.