Quantifying the Impact of Over-Cladding Energy Retrofits on Thermal Resilience Using DesignBuilder and TRNSYS Simulations

Over-cladding retrofit solutions are increasingly becoming a more common method to reduce the energy consumption of buildings in Canada. Simultaneously, extreme weather events, which can induce power outages, are becoming more frequent in an already stressed infrastructure. This paper aims to explore the impact of an over-cladding retrofit on a building’s vulnerability and thermal resilience during a weather-induced power outage. The study provides new evidence that thermal resilience predictions are highly sensitive to simulation engine assumptions, even when calibrated models are developed from the same building and operating data, by comparing DesignBuilder and TRNSYS. The thermal resilience and behavior of each model are analyzed during a power outage. The results of both models are analyzed and compared independently. For this study’s purposes, novel methods for quantifying the passive survivability and thermal resilience of the building energy models (BEMs) were developed. The findings show that over-cladding improved short-term passive survivability during the 48-h outage but did not consistently improve annual thermal autonomy. For example, in DesignBuilder, the retrofit reduced the percentage of annual hours below the NOAA Caution threshold in Vancouver by 4.4% under historical TMY conditions and by 17.2% under the EWY +3.5 °C scenario. The daily-outage analysis further showed that summer overheating, assessed using indoor heat index above 26.7 °C, reached up to 19 h/day, while winter underheating, assessed using indoor air temperature below 15 °C, reached up to 24 h/day. These findings demonstrate the strong seasonal dependence of thermal vulnerability on outage timing. Furthermore, the modeling process in DesignBuilder and TRNSYS reveals differences in how these tools handle outputs, particularly occupancy density. The comparison further revealed tool-sensitive resilience predictions: TRNSYS generally produced higher cumulative heat-stress exposure than DesignBuilder. The novelty of this work lies in combining calibrated cross-platform comparison, future-weather resilience assessment across multiple Canadian climate zones, and a daily-outage framework to quantify how retrofit decisions and modeling assumptions jointly affect predicted thermal resilience.