Effects of an extreme heat event on indoor conditions of social heritage housing in Mediterranean climate

Social heritage housing in Mediterranean historic cities is particularly vulnerable to climate change hazards as protection policies lead to its exclusion from energy retrofitting programmes, leaving their residents - at higher risk of fuel poverty and the heat-island effect – defenceless. Increasingly frequent heatwaves can potentially produce “overheating” in these buildings, a thermal state that impedes people's comfort with harmful consequences to their health. Other indoor air quality factors, like humidity and CO₂ levels, also affect residents' health. The objective of this research is to evaluate the actual indoor environmental quality of three occupied dwellings in social buildings of high heritage value located in two historic cities in Andalusia (Spain) during the extreme heat events that occurred in 2022. A monitoring campaign was conducted and the data collected over the summer was analysed and evaluated using existing metrics. Our results show that the CO2 concentration rates generally remained below the upper limit of 1000 ppm in all cases, probably due to the high air infiltration rates measured (5.83 h−1, 4.39 h−1 and 14.65 h−1). On the contrary, the relative humidity rates were outside the acceptable range (45–60 %) for 90 % of the occupied hours in all cases. In the warmest city, overheating was continuous and severe in all rooms, according to the metric adopted (CIBSE standards TM52 and TM59 under the adaptive thermal comfort model). The situation was particularly critical in the free-running bedroom, but the overheating index values in the living rooms, where air conditioning was installed and used about 50 % of the occupied time, also deviated significantly from the acceptable limits.