# Robustness of point measurements of carbon dioxide concentration for the inference of ventilation rates in a wintertime classroom

## TL;DR

This study uses CFD simulations to evaluate how well single-point CO2 measurements in classrooms reflect actual ventilation rates, highlighting the importance of measurement location and flow patterns for indoor air quality assessment.

## Contribution

It demonstrates that CO2 measurements above the breathing zone provide more accurate ventilation estimates and shows the robustness of these findings across different flow conditions.

## Key findings

- Single-ended ventilation can be more efficient than opposite-ended configurations.
- Measurements above the breathing zone better represent overall ventilation rates.
- Results are consistent across various flow rates and vent configurations.

## Abstract

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.