Experimental Evaluation of CO

Reliable evaluation of ventilation effectiveness is essential to ensuring healthy, energy-efficient indoor environments. Tracer gas methods are widely used to assess air distribution performance and contaminant removal. However, little attention has been given to how the tracer gas should be released to describe a human point source and how the tracer gas flow rate influences the reliability of these measurements. This study experimentally investigates the effect of CO2 dosing method and concentration level on the measured contaminant removal effectiveness (CRE) under mixing ventilation. Experiments were conducted in a mock-up classroom using several tracer gas dosing methods, including human metabolic CO2, and controlled injection approaches such as thermal dummies, a table tennis ball and a heated manikin. A range of dosing flow rates was applied to achieve different steady-state CO2 concentrations. The results show that CRE values depend on the achieved CO2 steady-state concentration. Low dosing rates, including human metabolic CO2, produce concentrations close to outdoor levels, resulting in large variability and systematically lower CRE values. In contrast, higher dosing rates lead to more stable and reproducible CRE values. These findings demonstrate that tracer gas steady-state concentration above the outdoor concentration level plays a key role in determining the reliability of CO2-based ventilation effectiveness measurements and highlight the importance of selecting dosing strategies and rates.