Hybrid passive cooling strategies for low-rise Indian residential buildings: whole-life carbon assessment under present and CMIP6 future climates in Bengaluru and Chennai

Residential cooling demand is increasing in India due to urbanisation, rising air-conditioner ownership, and climate change, creating a need for passive cooling strategies that prioritise building-envelope (fabric-first) measures and operational controls such as night ventilation before electrification or renewable energy integration. This study develops an integrated simulation framework combining CMIP6-based future climate projections, hybrid passive cooling assessment, and whole-life carbon accounting for low-rise residential buildings. Six passive cooling configurations were evaluated for climatically contrasting Bengaluru and Chennai under present-day and projected 2050 SSP2-4.5 conditions using EnergyPlus. Whole-life carbon integrates operational carbon, derived from cooling energy using air-conditioning efficiency and grid emission factors, with embodied carbon over a 50-year service life. The configuration combining cool roof coating, roof insulation, external shading, high-performance glazing, and temperature-controlled night ventilation achieved the best performance, reducing annual cooling energy by 82.0%, peak cooling demand by 68.1%, and whole-life carbon by 69.3% under constant grid emissions and 62.5% under declining grid emissions. It eliminated overheating across simulated cities and climate scenarios. Future climate increased baseline cooling demand by 58.2% in Bengaluru and 39.8% in Chennai. Embodied carbon increased from 14.7 to 22.6% to 50.0–63.0% of whole-life carbon, highlighting material selection as operational emissions decline in low-carbon buildings.