A novel indicator to assess thermal resilience of buildings to overheating

The increasing frequency and intensity of heatwaves highlight the necessity for resilient building design to reduce heat-stress-related discomfort and mortality among occupants. "Thermal resilience" refers to a building's capacity to endure thermal disruptions, maintain habitable conditions, and return to its intended state. This study aims to develop a thermal resilience indicator to make resilience an actionable concept for architects and HVAC engineers to assess and improve thermal resilience of buildings to overheating. To do this, different building types such as mid-sized offices, schools and apartments were evaluated during 3 different type of heatwaves (severe, intense and long) conducting building energy simulations. Building and system design parameters such as building orientation, envelope and glazing properties, occupancy pattern, airtightness, operation of solar shading and natural night ventilation, cooling capacity and cooling set-points were varied within standard design ranges. This study utilised global sensitivity analysis to identify the most influential design parameters affecting shock impact on heat stress of occupants i.e. degree hours above Standard Effective Temperature (SET-Dh) of 28℃. Sensitivity analysis revealed that for all three increasing shocks, and two cooling systems (convective and radiant), parameters such as window-to-wall ratio (WWR), cooling capacity, and the operation of passive strategies like natural night ventilation (NNV) and solar shading had twice the influence compared to building orientation, envelope and glazing properties, occupancy pattern, airtightness, and cooling set-point. Based on the results of the sensitivity analysis, regression models/thermal resilience indicators were developed to predict SET-Dh for each type of buildings- office, apartments and classrooms during 3 increasing shocks. The indicator is based on the most influential design parameters and the impact of overheating on the occupants health during increasing degree of shock (in this case, different types of heatwaves). The performance of the developed indicators are tested on two case study building type-(a) office and (b) residential buildings during 2 heatwaves.  This research aims to guide architects, engineers, and policymakers in assessing and enhancing buildings' ability to withstand and recover from overheating risk.