Arranging the inherent thermal mass of urban buildings enhances passive energy harvesting in winter

High-density urban buildings contain substantial inherent thermal mass that stores considerable energy. However, this potential remains underutilized due to limited attention and the complexities of environmental and structural variations, which cause diverse component thermal behaviors that previous experiments struggled to capture. This study aims to harness this stored energy through strategic thermal mass arrangements at the design stage for energy efficiency. Measurements from 68 rooms reveal diverse component thermal behaviors, with impact factors identified via kernel density estimation and stepwise regression. The strategies are then developed and validated through measurements and simulations. They are further evaluated across cold regions over a full year using conduction transfer function models. Results indicate that building components in different spatial locations exhibit highly diverse and sometimes counterintuitive thermal characteristics. For example, increasing thermal mass does not always reduce energy demand. We propose reducing the internal wall thermal mass and, for southern rooms, increasing depth, narrowing width, and lowering floor height. Each adjustment saves 0.15–0.24 kWh/m2. When combined, they achieve 6.8–21.2 % energy savings in cold regions, particularly those with high solar radiation. These findings reveal a promising direction for passive energy harvesting by leveraging the inherent thermal mass.