A guide to CO2 monitoring and using CO2 data loggers to measure indoor air quality.

One obstacle in IAQ management is that air quality is not visible. While building occupants easily recognise uncomfortable temperatures, indoor air quality is difficult to detect by sensation alone.

CO₂ monitoring is a simple means of making the indoor air visible. Using carbon dioxide data loggers, building owners and managers can 'see' the levels of CO₂ in the environment. Identifying consistent levels of CO₂ below 800ppm in an indoor space, for example, will indicate that the space is well ventilated. An average of over 1500ppm for the occupied period, on the other hand, indicates that the space is receiving inadequate ventilation.

How to use CO₂ data loggers to measure indoor air quality

CO₂ data loggers should be placed at head height and away from windows, doors and vents. A sampling location that is representative of overall conditions should be chosen. If CO₂ levels are extremely low or high, this may indicate that your data logger is in an unsuitable location. It is good practice to sample CO₂ measurements in different areas so that a sufficiently representative monitoring location is used.

Using data loggers with non-dispersive infrared (NDIR) sensors is recommended, as these sensors directly measure the volume of CO₂ in the air. It is also recommended that the device has an accuracy of +/- 50ppm and is routinely calibrated. Alarms or other visual indicators of excess CO₂ levels are helpful for enabling occupants to improve ventilation when necessary.

After an initial monitoring period, data should be assessed to understand patterns in indoor air quality: for example, whether CO₂ levels are elevated at a particular time of day, or whether levels are consistently above the recommended limits. Targeted action can then be taken based on this data.

Data loggers should also be used to assess the efficacy of ventilation strategies. Data from continuous monitoring of CO₂ levels can be used to justify investment in mechanical solutions for ventilation in areas where natural ventilation is shown to be ineffective, or where natural ventilation should not be utilised due to high levels of outdoor pollution.

Long-term indoor air quality monitoring with CO₂ data loggers can ensure consistent efforts are taken to improve indoor air quality on a daily basis and for the future. Occupants can make use of alarm indications by opening windows or vents, or alerting building managers of the need for increased mechanical ventilation. Long-term data can be used to assess environmental patterns, such as seasonal variations in ventilation rates and IAQ, enabling pre-emptive action to be taken to improve indoor air quality.

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References and further reading