Determination on Carbon Dioxide Levels in School Buildings: the Effect of Thermal Efficiency Improvement

Indoor air quality (IAQ) in schools is an important public health concern. Particular attention should be paid to children, because they are more vulnerable to air pollution than adults. Although carbon dioxide is not considered a toxic air pollutant, its concentrations inside buildings may have a negative impact on users. The most commonly described health problems include tiredness and its effects (headaches, bad mood, poor attentiveness). Carbon dioxide concentrations are often used as a surrogate for the rate of outside supply air per occupant. Permissible concentration of carbon dioxide in confined spaces is 1,000 ppm. This minimum sanitary requirement is recommended by the European Office of the WHO and ASHRAE. The Polish Committee for Standardization has established general guidelines concerning the quality of air inside non-residential buildings. This standard was drawn up based on EU directives, through classification of IAQ, as it is influenced by the CO2 concentrations above the outdoor level (∆CO2). Based on the above regulations, the increase in indoor CO2 concentrations in relation to CO2 concentrations in outdoor air (∆CO2) were measured along with physical parameters (temperature and relative humidity) to evaluate IAQ in the classrooms of two primary schools built in the nineteenth century in Poland. More than 100-year-old buildings built of bricks before World War II are a frequent occurrence in rural schools in the area of Upper Silesia, Poland. One of the school buildings underwent thermal effectiveness improvement while the other has not been modernized in these terms yet. The aim of the research was to check the extent to which thermal modernization of an old public building influences indoor air quality in the context of concentrations of carbon dioxide. The measurement period was chosen for late spring in order to avoid the impact of municipal emissions (so-called low emissions) common in rural areas. The average concentration of carbon dioxide in school rooms after thermal modernization (WTM) were higher than the concentrations observed in the school not subjected to thermal modernization (NTM). The CO2 concentrations ranged from 1,287 ±333 ppm to 2,146 ±386 ppm and from 936 ±196 ppm to 1,878 ±567 ppm in WTM and NTM school buildings, respectively. The results clearly indicate a higher occurrence of poor air quality (up to 70% of time during the school days) in the thermally improved school building compared to the one without thermal improvement (up to 52% of the time). The measurements also showed that the exposure of school children to elevated carbon dioxide concentrations during classes was higher in thermally improved primary school buildings, which in turn may represent a health concern.