Summer overheating in a prefabricated concrete panel building: Are passive measures sufficient in a warming climate?

The rising frequency and intensity of heatwaves due to climate change have amplified concerns about summertime overheating in residential buildings, particularly in regions historically characterized by mild summers. This study investigates the overheating risk and adaptation potential in a typical prefabricated concrete panel apartment in Budapest, Hungary. A calibrated multi-zone dynamic building energy model was developed based on long-term in-situ measurements, including indoor temperatures and occupant-controlled window operation. Using this model, various passive adaptation strategies, including glazing upgrades, external shading, increased natural ventilation, and facade thermal insulation, were assessed under current and future climate scenarios based on Representative Concentration Pathways (RCP 2.6, 4.5, and 8.5). Simulation results show that natural ventilation is the most effective single intervention, but its cooling potential declines under warmer conditions. Summer overheating, quantified by the ODH 26 indicator, is projected to increase up to sixfold by 2100 (RCP 8.5), highlighting the urgency of intervention. While combined passive strategies can reduce overheating by up to 66.6% under present conditions, their effectiveness drops to 21% in late-century scenarios. The study highlights the critical interaction between thermal insulation and ventilation, where insulation can worsen overheating without sufficient airflow. The novelty of this study lies in using a measurement-calibrated, multi-zone dynamic model as the foundation for all further analyses, ensuring high reliability of the results. This research builds on real-world data from an occupied apartment and systematically explores the performance of passive strategies under current and future climate conditions. The findings emphasize that passive measures alone may not guarantee thermal resilience in future climates, particularly for dense, urban housing stock prevalent across Central and Eastern Europe.