Anthropogenic Heat Emissions and Energy Use in Buildings at the Block Scale: Differences across Local Climate Zones and Component Contributions

Under global warming and rapid urbanization, anthropogenic heat emission from buildings (AHEb) has become a key driver of urban thermal environments. However, most studies approximate AHEb using building energy consumption, which limits the accurate representation of block-scale heat release and its variability across urban forms. This study examines typical urban blocks representing different Local Climate Zone (LCZ) types in Xi’an, China. Using building energy simulations, we quantify the spatiotemporal characteristics of AHEb and their component mechanisms across LCZs. Results show that in summer, compact high-density blocks (LCZ 1–2) exhibit daily mean heat emission intensities of 134.2–230.0 W/m2, significantly higher than those of open blocks (LCZ 4–6-II; 72.7–202.7 W/m2). Peak heat emissions lag solar radiation by approximately 3 h and are 1.7–4.5 times higher than building energy use intensity. In winter, overall heat emissions decrease markedly, with peak values of 101.5–243.9 W/m2 in compact blocks and 39.4–98.3 W/m2 in open blocks, while inter-block differences are more strongly influenced by dominant building functions. Component analysis indicates that in summer, HVAC systems and building envelopes contribute 43–68% and 17–53% of total heat emissions, respectively. In winter, relief air dominates heat emissions in commercial and office blocks (29–80%), whereas residential blocks are mainly governed by envelope heat release and air infiltration. These findings demonstrate that equating building energy consumption with heat emissions substantially underestimates actual urban heat release. Integrating the LCZ framework enables more refined and function-sensitive assessments of urban thermal environments.