Which design parameters impact the resilience to overheating in a typical apartment building?

Airtight, highly insulated, and passively cooled buildings in the EU are designed under typical outdoor and indoor thermal conditions. With increasing risk and uncertainty with regards to climate change and associated heatwaves(HW), the design thermal performance of these buildings is not guaranteed. It is crucial to focus on improving thermal resilience to overheating and futureproof these buildings. “Thermal resilience to overheating” is the characteristic that describes the extent to which buildings and their cooling strategies can maintain habitable conditions during or post shocks. Thus, a new design approach to improve the thermal resilience to overheating of existing and newly built buildings is a growing need in the building sector. Within the framework of IEA EBC Annex 80-Resilient Cooling of Buildings, the aim of this study is to determine the most influential building and system design parameters that impact the thermal resilience to overheating. To achieve this aim, building energy simulation (BES), is conducted on a reference typical apartment building in Belgium. A 2 bedroom apartment for 3 occupants is simulated in Open Studio and EnergyPlus during summer (April-September) of typical meteorological year (TMY). The apartment is evaluated with its default design (very heavy thermal mass, window to wall ratio (WWR) 10% and with no shading and no passive cooling strategy (in this case natural night ventilation -NNV). Apart from the default design, design parameters were altered such as thermal mass (very heavy-medium-light),WWR (10-30%), implementation of solar shading and NNV. The impact of the worst, improved and the optimized designs are also evaluated during a 6 day intense heatwave period. Overheating are most likely to occur in current buildings with higher WWR (>30%), no shading and with lighter thermal mass. WWR has highest impact on the thermal resilience followed by thermal mass. Apartment with very heavy thermal mass,WWR 10%, with NNV and solar shading shows the best result (80% reduction in the percentage of occupied hours above 25℃ threshold). However, in buildings with higher WWR (>30%) and lighter thermal mass, thermal resilience can be improved with implementation of solar shading and passive cooling strategies such as NNV. Even during heatwave, an apartment without NNV has better ( 45%) thermal resilience to overheating than an apartment with NNV if the WWR is < 30%) and has a medium thermal mass rather than a light thermal mass.