A System Thinking Approach to Enhance Building Thermal Resilience Through Integrated Envelope and Mechanical SystemPaneru, Suman Thermal resilienceSystem thinkingEnvelopeMechanical systemIntegrated envelope-mechanical systemExtreme heatwavesPower outagesBuilding upgrades.Architectural EngineeringPHDThermal resilience in buildings has become critical as extreme heatwaves grow more frequent, intense, and prolonged, increasing reliance on mechanical cooling systems while elevating the risk of power outages. In the United States, approximately 60% of residential buildings were constructed before 1990 and therefore predate modern energy codes; many of these buildings contain inefficient envelopes and outdated mechanical systems that exacerbate indoor thermal stress during extreme heat events and power disruptions. These risks are unevenly distributed, as socially vulnerable populations are more likely to reside in buildings with poor thermal performance, intensifying inequities in heat exposure and associated health outcomes. While building envelope and mechanical system upgrades are widely recognized as strategies for improving thermal resilience, critical gaps remain in understanding how building thermal characteristics vary across levels of social vulnerability, how envelope performance drives disparities in indoor thermal resilience across income groups, and how integrated retrofit strategies perform relative to mechanically focused, single-measure interventions during extreme heatwaves and power outages. This dissertation addresses these gaps using Philadelphia, Pennsylvania, as a case study due to its increasing exposure to extreme heat, a housing stock largely designed for cold climates, and high levels of social vulnerability. The research is structured around three objectives. First, residential building characteristics from Zillow are integrated with detailed thermal attributes from ResStock using a Gaussian Naïve Bayes model, and the resulting model is analyzed alongside indicators from the Centers for Disease Control and Prevention’s Social Vulnerability Index to assess thermal resilience disparities. Statistical analyses reveal significant differences in building thermal attributes, such as insulation levels, infiltration rates, and system types, across social vulnerability groups, with highly vulnerable populations disproportionately residing in thermally inefficient buildings. Second, the impact of building envelope performance on indoor thermal resilience is quantified across low-, medium-, and high-income housing units under historical, mid-term, and future climate scenarios. EnergyPlus simulations, validated through controlled thermal chamber experiments, show that low-income units experience peak cooling loads up to 15.45 kW, exceeding those of middle- and high-income units by approximately 35% and 53%, respectively. During power outages, low-income units reach the ‘Danger’ heat index threshold (≥ 41 °C) in less than 4 hours, compared to approximately 6 hours for middle-income units and 8 hours for high-income units, highlighting substantial inequalities in indoor thermal resilience. Third, the current state of practice in residential retrofits is examined through semi-structured expert interviews and complementary simulation-based analyses to evaluate interactions between envelope and mechanical system upgrades under a systems-thinking framework. The optimization results showed that the optimal solution can be achieved by combining high-performance glazing (U = 0.25 W/m²K), wall insulation (R-18), high mechanical efficiency (C)OP = 4.24), and moderate infiltration control (ELA = 0.060 m²). Furthermore, the EnergyPlus simulation results indicate that integrated envelope–mechanical retrofit strategies reduce peak cooling loads by 50–66%, delay the onset of dangerous indoor heat exposure during outages by approximately one hour, and reduce total energy use by 41–45% relative to mechanical-only upgrades under extreme heatwave and power-outage conditions. This dissertation advances understanding of thermal resilience by integrates building thermal characteristics with social vulnerability indicators, quantifies envelope-driven inequalities in indoor thermal performance through validated simulations and demonstrates that integrated envelope and mechanical system upgrades are essential for enhancing indoor thermal resilience during extreme heatwaves and power outages.Guangqing Chi, Outside Field MemberLisa Iulo, Outside Unit MemberJulian Wang, Professor in Charge/Director of Graduate StudiesYuqing Hu, Chair & Co-Dissertation AdvisrJulian Wang, Dissertation Co-Advisoropen_access2026-05-11T22:10:11Zhttps://etda.libraries.psu.edu/catalog/30816sbp5863