How do high-insulation buildings influence cooling energy consumption and the outdoor thermal environment? A multi-scale analysis in China's severe cold regions

Climate change is intensifying summer overheating and cooling energy demand, even in China's severe cold regions, where residential building design has historically prioritized winter thermal insulation. This study investigates how envelope insulation levels affect indoor overheating, cooling energy consumption, and neighbourhood-scale outdoor thermal conditions during summer. Twelve residential buildings and 12 residential areas in Yichun, Harbin, Changchun, and Shenyang were analysed through field indoor-temperature monitoring, EnergyPlus-based building energy simulation, and ANSYS Fluent-based neighbourhood-scale CFD modelling. Monitored data showed that south-facing living rooms exceeded the CIBSE TM59 overheating threshold for 6.68% to 12.32% of occupied hours across all cities. Simulation results indicated that enhanced insulation prolonged overheating duration by 2.11% to 67.74% and increased cooling energy consumption by 3.66% to 28.53%. At the neighbourhood scale, lower envelope U -values raised maximum outdoor air temperature by 0.55 to 1.98°C, whereas average temperature increases were limited to 0.00 to 0.40°C. Dynamic simulations using meteorological data from 2005 to 2050 projected a continued rise in cooling demand, further amplified by stricter insulation requirements. These results demonstrate that winter-oriented high-insulation strategies may unintentionally increase summer overheating, cooling energy demand, and outdoor thermal stress, highlighting the need for climate-adaptive envelope standards that balance seasonal performance in severe cold regions.