Prospects of Improving the Indoor Air Quality in Classrooms by Reactivating Historic Ventilation Stacks

Stack ventilation systems were installed in German schools constructed around 1900 and are no longer in operation. The aim of this study was to show how reactivating these systems could improve the indoor air quality in classrooms. Ventilation stacks were reactivated in three classrooms in a school while a fourth classroom, which was naturally ventilated via openable windows, served as the reference case. All classrooms were measured for carbon dioxide levels, air temperature and relative humidity. During winter, 50% of all measured carbon dioxide values in the classroom with natural ventilation using windows were higher than 1800 ppm. All classrooms with stack ventilation showed median values of 1600 and 1350 ppm. In these classrooms, the volumetric flow rate per person in winter (14 m³/(h.pers)) was approximately seven times higher compared to the classroom with window ventilation (2 m³/(h.pers)). The supply stacks provided a preheating effect of 0.5 to 0.7 K/m. Effects of summer flow reversal were found in both of the classrooms with exhaust and supply ventilation stacks. Reactivating ventilation stacks provides the potential to improve indoor air quality in classrooms. Some adjustment of the systems, such as adding automated dampers to close the stacks at night and during flow reversal in summer, could allow the systems to meet today’s hygienic and comfort requirements and turn them into modern low energy consuming systems.