Airtightness and indoor air quality in subsidised housing in Spain

Over three million subsidised dwellings were built in Spain between 1940 and 1980. Most of these buildings are now obsolete and fail to comply with thermal comfort and ventilation standards. A building's existing energy performance, including its airtightness, should be determined prior to conducting low-energy refurbishment, for those factors, particularly the latter, impact thermal comfort, energy demand and indoor air quality (IAQ) fairly heavily.
This paper introduces a study on airtightness and IAQ in subsidised housing built in Spain in the aforementioned 40-year period. Airtightness and CO2 measurements taken in 2014-2015 in six units in multi-dwelling buildings, three each in Seville and Madrid, are described.
The results show that in a building in Madrid, the number of air changes per hour at a pressure of 50 Pa (n50) ranges from 3.2 to 8.3. The winter time CO2 concentration in bedrooms is 1900 ppm and in living rooms 1400 ppm, with peaks of 5000 ppm and 4700 ppm, respectively. The number of air changes per hour at 50 Pa (n50) in Seville, ranges from 5.0 to 9.5. The winter time CO2 concentration in bedrooms is 1500 ppm and in living rooms 800 ppm, with peaks of 6000ppm and 4000 ppm, respectively. In the summer, however, when users tend to open windows at night primarily to let in cooler air, the CO2 concentration values observed in Seville drop to 700 ppm and in Madrid to 1100 ppm.
As those values are much higher than recommended in the standards on good indoor air quality, the inference is that winter time housing ventilation must not be allowed to rest solely on users’ voluntary opening of windows.