  Indoor air quality in schools and classrooms is paramount for the health and
well-being of pupils and staff. CO2 monitors offer a cost-effective way to
assess and manage ventilation provision. However, often only a single point
measurement is available which might not be representative of the CO2
distribution within the room. A relatively generic UK classroom in wintertime
is simulated using CFD. The natural ventilation provision is driven by buoyancy
through high- and low-level openings in both an opposite-ended or single-ended
configuration, in which only the horizontal location of the high-level vent is
modified. CO2 is modelled as a passive scalar and is shown not to be
`well-mixed' within the space. Perhaps surprisingly, the single-ended
configuration leads to a `more efficient' ventilation, with lower average CO2
concentration. Measurements taken near the walls, often the location of CO2
monitors, are compared with those made throughout the classroom and found to be
more representative of the ventilation rate if made above the breathing zone.
These findings are robust with respect to ventilation flow rates and to the
flow patterns observed, which were tested by varying the effective vent areas
and the ratio of the vent areas.
