Comparison of two ventilation control strategies in the first Norwegian school with passive house standard

The Marienlyst School is the first educational building in Norway built according to the passive house standard. This building benefits from a super-insulated and airtight envelope. While this reduces the heating demand largely, it also enhances the risk for poor indoor air quality and overheating compared to conventional buildings. It is therefore particularly important to implement an efficient ventilation strategy in order to avoid adverse effects on the health, well-being and productivity of the pupils.

In this context, the perceived indoor climate resulting from two different ventilation control strategies was evaluated in one classroom of the building. Both strategies consisted in varying the ventilation rate according to room demand, ie. Demand Controlled Ventilation (DCV). The existing strategy consisted in varying the ventilation rate in order to maintain a constant carbon dioxide concentration of 800 ppm in the classroom. A new strategy was implemented which consisted in a combined CO2 and temperature DCV, ie. to control towards a proportionally lower CO2 concentration when the indoor temperature increased. The aim with this strategy was to address both overheating and the fact that perceived indoor air quality decreases when temperature rises.

Indoor climate measurements, as well as questionnaires on the perceived indoor air quality and thermal comfort filled up by the pupils were used to compare both strategies. The data from the questionnaires were then analyzed using a random effect linear regression model. The regression analysis revealed that the initial ventilation strategy was responsible for discomfort resulting from too high variations in the indoor temperature. The new combined CO2 and temperature DCV strategy provided a perceived indoor climate which was significantly better than the existing strategy. Therefore, the developed ventilation strategy appears to be a relevant solution in order to address the problem of overheating and perceived indoor air quality in educational buildings with passive house standard.