CO2 tracer gas concentration decay method for measuring air change rate

• In-situ CO2 sensors are tested to measure air change rate by tracer gas technique.
• Measured ACR by in-situ CO sensors are in good agreement with reference values.
• Multiple sensors in different positions allow to assess the ventilation efficiency.
• Multi-points calculation method gives more accurate results than two-points method.

The measure of air change rate (ACR) in building is a difficult and usually expensive task. The tracer gas method is the reference technique but its implementation is difficult and the interpretation of results is not straightforward. In the present work, the concentration decay method by multiple CO2 transmitters is experimentally validated in the case of cross-ventilation. It is observed that in-situ CO2 transmitters lead to ACR values in good agreement with reference measurements obtained from mechanically controlled values. Whereas multiple transmitters in different sampling positions show the imperfect mixing, a sensor located at the outlet or an averaged value of all sensors can provide an accurate measure of the ACR. Moreover, the spatial variation of CO2 concentration can be used to assess the ventilation efficiency in the test chamber. Different measures and calculation methods are discussed, and the uncertainty analysis of each method is carried out.