Linking outdoor thermal comfort and residential cooling demand under climate change: an energy sensitivity index

Rising outdoor temperatures and more frequent heatwaves are degrading outdoor thermal comfort and increasing building cooling demand, calling for quantitative metrics linking both processes under climate change. This study introduces and applies an energy sensitivity index (ESI), defined as the change in building energy demand per degree increase in outdoor air temperature (ΔE/ΔT). A multifamily residential building was modelled in EnergyPlus, validated according to ASHRAE (2023). ASHRAE Guideline 14-2023: Measurement of energy, demand, and water savings, and simulated using CMIP6 climate projections (SSP3-7.0 and SSP5-8.5) for mid- and late-century horizons across four cities: Mendoza, Madrid, Barcelona and Rome. Results show a strong linear relationship between monthly mean outdoor temperature and energy demand (R > 0.94). Under SSP5-8.5 (2080), annual maximum temperatures increase by 6.0–8.3°C, reducing heating demand by 55–65% and increasing cooling demand. Cooling energy use increases by approximately 3.3–5.6 kWh/m2 per 1°C rise in summer mean temperature. These findings highlight the growing sensitivity of residential cooling demand to outdoor warming and establish the ESI as a tool for climate-responsive building and urban design.