Indoor air temperatures, CO2 concentrations and ventilation rates: Long-term measurements in newly built low-energy schools in Sweden

Within a period of ten years a large number of schools need to be built in Sweden and these new schools need to be nearly zero energy buildings. School classrooms are required to provide healthy learning environments to help children perceive and process information. This means that classrooms must provide adequate levels of indoor air quality and thermal comfort. This article investigates CO2 concentration levels and indoor air temperatures in several recently built, low-energy schools in Sweden, and compares them with design criteria stipulated in specific international standards and Swedish regulations to provide feedback to the building construction industry. Field measurements of CO2 concentrations, indoor air temperatures and ventilation rates in seven low-energy schools, with a total of 145 classrooms, taken during several months spanning both summer and winter periods, are analysed in this article. All the schools in the study have mechanical supply and exhaust ventilation systems with demand control devices in the classrooms. The study shows that all the classrooms, in general, comply with the design criteria regarding indoor air temperatures and CO2 concentrations in EN15251, ASHRAE 62.1 and the Swedish national regulations and recommendations. Median values of indoor air temperatures were between 19 and 23.5 degrees C in all classrooms during school hours. The 90-percentile levels of CO2 concentrations were below 1000 ppm in 60 of 61 classrooms in which these measurements could take place. It is concluded that during this long-term measurements in the studied seven low-energy schools, modern HVAC systems with demand control and heat recovery, in general, provided satisfactory indoor climates in terms of CO2 levels and indoor air temperatures.