Impact of zero energy buildings and houses on urban thermal environment and heat-related mortality risk

Zero-Energy Buildings (ZEB) and Zero-Energy Houses (ZEH) are designed to reduce energy consumption using high-efficiency equipment and highly insulated envelopes. ZEHs are expected to enhance the indoor thermal conditions in winter, reducing the health risks associated with low temperatures. On a larger scale, ZEB/ZEH implementations in urban areas can influence outdoor temperatures by reducing building exhaust heat and heat retention in the building structures. Despite these potential benefits, few epidemiological studies have evaluated the effect of temperature on heat-related health risks. This study aimed to quantify temperature changes and their impact on heat-related mortality risk when ZEB/ZEH is adopted city-wide in 23 wards of Tokyo. Using an urban meteorological model and an environmental epidemiological model, the study set ZEB/ZEH performance to government benchmarks. Findings indicated that the average urban temperature in August remained stable during the day but decreased by 0.1–0.3 °C from night to early morning. This decrease was largely due to reduced air-conditioning exhaust heat, decreased heat storage in building frame, and the emission of cold heat from heat pump water heaters. When these results were applied to an epidemiological mortality risk prediction model, the risk of heat-related deaths in August was reduced by over 8 % across all 23 wards. This reduction is comparable to the effect of a significantly increasing green coverage in the area. Approximately half of the risk reduction was attributed to the cold heat from the heat pump water heaters.