The Reliability of CO2 Measurements Using Low-Cost Sensors: A Study of Sensor Positioning and Ventilation Strategies in Classrooms

The COVID-19 emergency evidenced the value of keeping indoor spaces properly ventilated, which increased the interest in CO2 loggers. However, when monitoring, many significant variables are often overlooked, such as sensor specifications, the position of the system with respect to the airflow path (or occupants), and the relationship between these variables and the ventilation system of the room. With the purpose of properly standardizing future indoor air quality measurements in classroom settings, this study evaluated the results of a measurement campaign consisting of 33 individual measurements performed on site during 5 months in primary schools and university classrooms. This work uses dCO(2)/dt to identify CO2 tendencies while taking into account classroom topology and ventilation. Results show that variables such as their position and the ventilation strategy of the room often outweigh the sensor specifications, causing spatial discrepancies beyond 100 ppm. Along with the results, recommendations for future measurements are discussed in order to avoid nonrepresentative estimations of the CO2 level of indoor spaces.