Assessment of UHI mitigation strategies on indoor and outdoor thermal comfort under future extreme heat and power outage conditions, case study: educational building in Shahrood, Iran

• South-facing green walls reduce indoor PET by up to 1.7 °C during heatwaves. • Low-albedo facades decrease outdoor PET by 1.52 °C, enhancing pedestrian comfort. • Integrated UMM-BEM approach improves accuracy in thermal comfort predictions. • Strategies offer resilience during power outages, supporting sustainable cities. • Multi-scale simulation framework provides actionable insights for urban planning under future climate scenarios. The combination of climate change and urbanization can intensify extreme heat events, compromising human comfort by worsening the Urban Heat Island (UHI) effect. This leads to increased demand on the power grid and more frequent power outages. Therefore, it is crucial to explore UHI mitigation strategies (UHIMS) and assess their potential to improve thermal comfort, especially in future conditions and during a power outage. To achieve this goal, the present study investigates the effectiveness of UHIMSs that can be applied to the envelope of a building, which serves as a critical interface between indoor and outdoor environments. Given the boundary nature of these interventions, they influence both indoor and outdoor thermal conditions. The study introduces an integrated simulation approach, combining a Building Energy Model (BEM) for indoor assessments, with an Urban Microclimate Model (UMM) to evaluate outdoor microclimate changes. All simulations were conducted under future climate scenarios and power outage during a summer heatwave. The Physiological Equivalent Temperature (PET) index was used to assess thermal comfort consistently across indoor and outdoor settings. Based on results, the low-albedo facade proved to be the most effective strategy for reducing outdoor PET, while the south-facing green wall had the greatest impact on lowering indoor temperatures. Unlike outdoor conditions, the high-albedo facade performed better indoors. Across all strategies, surface radiative properties had a stronger impact than thermal mass in enhancing thermal comfort. The findings highlight vertical greenery on the southern facade as a particularly effective solution, offering benefits for both indoor and outdoor comfort.