Mixing and ventilation in a living laboratory due to fast and slow response modes

Abstract: We present and analyse observational data from a highly instrumented classroom computer laboratory and develop a multizone model to describe its mechanical ventilation and mixing regime. The laboratory houses 70 workstations that are used heterogeneously in time and space, in a manner similar to a generic office environment. Our model predicts CO2 concentration in the laboratory, accounting for air exchange between the occupied classroom and its ceiling plenum and by parametrising irreversible mixing in each zone. Applying the model to our measurements helps identify critical components in the ventilation network, as highlighted by a strong separation of the time scales characterising the flow response. On the one hand, this time scale separation leads to a simplified model describing the CO2 transport. On the other hand, it suggests that the forced exchange of volume between the room and the plenum is 'overdriven' in that reduced energy operation could be achieved without compromising air quality. More generally, our modelling approach offers a systematic method to enhance energy efficient ventilation of multi-zone systems.