Exploring indoor thermal comfort and CO₂ concentrations observations in Amsterdam

Climate change is projected to raise the frequency of heat events, triggering also enhanced indoor heat loads for urban dwellers. However, understanding of the climatology of indoor environments in existing residences remains limited. Establishing and maintaining long-term and systematic networks recording indoor temperatures is both challenging and costly, making such networks scarce. This study uses a unique dataset collected through weather stations that we placed in 93 residences in Amsterdam, the Netherlands, since 2022 as part of a citizen science project. We aim to observe and analyse indoor air temperature, humidity and CO₂ concentrations through indoor placed Netatmo weather stations in bed and living rooms. From these observations, we also estimate the thermal comfort indices PMV (predicted mean vote) and the Dutch GTO (weighted temperature threshold exceedance hours). We report on the climatology, variability and exceedance of limit values for these observed and estimated variables during the summer seasons May-September of 2023 and 2024.

During a warm period from 1 to 15 September 2023, which included a regional heatwave, the median and 95^th percentile (P95) of the daily maximum indoor air temperatures observed in both the bedrooms and living rooms within this professional network were 25.4 °C and 27.8 °C, respectively. For comparison, the WHO recommends a comfortable indoor air temperature range of 18-24 °C. The corresponding median and P95 of the daily maximum CO₂ concentrations observed in the bedrooms were 882.9 ppm and 1223.6 ppm, respectively. Ideally, indoor CO₂ concentrations should remain close to the outdoor CO₂ concentration of 420 ppm. Regarding thermal comfort, the corresponding median and P95 of the estimated PMV in the living room were 1.10 and 1.30, respectively, indicating a slightly warm thermal sensation. Similarly, the corresponding median and P95 of the estimated GTO in the living room were 2.3 hours and 879.1 hours, respectively. That means that 5% of the residences exceeded the annual 900-hour threshold for GTO within just 2 weeks.

Additionally, we will also present preliminary findings on how house characteristics (e.g., energy label, window orientation, room volume, etc.) may explain indoor air temperature characteristics. This study contributes to understanding the health risks and cooling demands faced by residents of Amsterdam in their homes.