Evaluating thermal resilience to overheating in a Belgian apartment in shock scenarios

Building designs to be in line with energy efficient and carbon reduction goals, often focus on energy efficient techniques like high insulation, airtightness. However, these buildings are often subjected to overheating risks due to unforeseeable events like frequent heatwaves and power outages even in moderate climate zones like Belgium. Overheating risks in residential buildings have negative impact on the health of the building occupants (especially on the vulnerable occupants like elderly, infants and sick persons), causing sleep deprivation, heat stress and even mortality. In future climate scenarios, measures to reduce overheating risk in buildings while limiting the energy use of space cooling are gaining importance. This calls for a new design approach where thermal resilience (ability of the building and system to withstand shocks, adapt and maintain its normal function) is taken into account. The focus of this research is to evaluate existing resilience indicators (thermal autonomy, passive survivability, absorptive capacity, recovery capacities, etc.) for a typical Belgian apartment, by dynamic Building Energy Simulations (BES). A parametric study was conducted by implementing passive (night cooling) and active cooling technologies (air conditioning) and by changing building parameters (glazing ratio and shading) to check which building parameters and passive cooling strategies have the biggest impact on the overheating risk. Thermal resilience will be evaluated by subjecting the case study building to different shocks like heat waves (varying intensity, duration and severity) and power outages (varying duration and time of occurrence). The heatwave files, used for the BES are developed adopting the methodology of the ‘Weather Data Task Force of IEA EBC Annex 80 “Resilient Cooling of Buildings”. Finally, the evaluation of the thermal resilience for different shocks (heatwaves, power outages etc.), will indicate the most influencing design parameters (system’s + building’s) contributing to the resilience to overheating. Results show that the recovery time of the apartment building is shortened from more than 2 weeks to 28 hours during an intense heatwave. Implementing solar shading can improve the thermal comfort during an intense heatwave by approximately 30% of the occupied hours. When changing the window-to-wall ratio in combination with night cooling, it was found important to find a balance between window opening and solar heat gains.