[Passive-house schools--a tool for improving indoor air quality in schools?]

In Germany, some schools have already been built according to the passive-house standard as an answer to the discussion of climate change and energy saving. For European passive construction, a prerequisite is an annual heating requirement of less than 15 kWh/(m2a) (4755 Btu/ft2/yr). Efficient heat recovery from exhaust air using an air-to-air heat exchanger reduces energy consumption and is considered to improve indoor air quality as well. However, data on indoor air quality have been lacking up to now. Here, the data on indoor air quality in a passive house school are presented.

In the passive-house school in Frankfurt/M in summer time ventilation is performed by opening the windows. In winter time a mechanical ventilation system provides air at 14-16 m3/person h, with the incoming air being heated by an air-to-air heat exchanger. CO2 levels were obtained during 3 school days in one classroom in summer time, and during 5 days in two classrooms in winter time. In 5-minute intervals a continuous documentation of the number of persons present in the room, their activity and ventilation was done parallel to the measurements.

Mean CO2 levels in summer time were 1127 ppm, and 946 ppm in winter time. Regarding only those measurements with people present in the classroom, the air quality standard of 1000 ppm (Pettenkofer's level) was exceeded in two thirds of the measurements in summer and in winter, with 5% (summer) and 10% (winter) of the levels exceeding the guideline value (DIN 1946) of 1500 ppm. Considering the guideline values of the "new" DIN EN 13779, 9-21% of the measurements exceeded 1400 ppm, i.e., "low air quality".

Mean CO2 levels in the passive-house school were comparable to those in conventionally ventilated schools, i.e., ventilation via opening the windows, whereas maximal levels were lower in the passive-house school than in other schools. The guideline value of 1500 ppm was exceeded on 33% of the measurement days, the level of 1400 ppm was exceeded in 92% of the days. According to these data, indoor air quality should be improved not only in conventionally ventilated schools but also in passive-house schools. In addition to the mechanical ventilation, ventilation by opening the windows during breaks is necessary. Therefore, sufficient capacity for opening the windows should be available. This is mandatory not only for summer time ventilation but also in case of problems with the mechanical ventilation system. As a result air quality should be an important issue in passive houses as well, in addition to the focus on energy saving.