Nonlinear Cooling Benefits of Natural Ventilation Under Different Climatic Conditions in Japan

Natural ventilation (NV) is an effective passive strategy for reducing building cooling demand, yet its performance varies substantially with climate and may not increase proportionally with larger openings. This study examines the nonlinear cooling benefits of NV in detached residential buildings under different climatic conditions in Japan using dynamic building energy simulation. Eight representative cities were selected to evaluate how regional temperature and humidity influence NV availability, indoor thermal response, and cooling-energy demand under multiple window-opening scenarios. The results reveal strong climate dependence. In temperate regions, NV provides the greatest cooling benefits by enhancing nighttime heat dissipation and reducing multi-day indoor heat accumulation. In cold regions, cooling demand is relatively low, resulting in limited or negligible net cooling-energy benefits from NV. In warm-humid regions, high moisture conditions significantly weaken the cooling effect of larger openings. Across all climates, the relationship between window opening area and cooling-energy savings is nonlinear and not universally monotonic. In seven of the eight cities, the 5% opening scenario provides the best annual cooling-energy performance among the examined non-zero opening conditions. These findings indicate that NV design should be climate-responsive rather than based on uniform opening assumptions and provide practical guidance for region-specific residential cooling strategies.