Richard J.A.M. Stevens

Professor at the University of Twente

Wind energy · Turbulence · Environmental flows

Publication 108 · Cross-cutting research

Effect of airflow rate on CO2 concentration in downflow indoor ventilation

G.S. Yerragolam, C.J. Howland, R. Yang, R.J.A.M. Stevens, R. Verzicco, D. Lohse, Indoor Environments 1(2), 100012 (2024).

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Main finding

Ventilation layout and mixing change how lower-layer, volume-average and outlet CO2 concentrations relate in the sampled cases. Absolute CO2 decreases as airflow increases in Equation (4) and Figure 4; no infection-risk conclusion is supported.

Carbon dioxide concentration against airflow rate for two ventilation layouts
How to read the figure. Carbon dioxide concentration in a downflow-ventilated room against the airflow rate, for two layouts, measured in the lower occupied layer, as a volume average, and at the outlet. The three measures do not move together as layout and mixing change, which is the paper's point. Absolute concentration falls as airflow rate rises - the opposite of an increase - and no infection-risk conclusion follows from this figure. Open the full-resolution figure. Figure 4. G.S. Yerragolam et al. (2024). No separate licence is stated here; consult the original publication and credited source before reuse.

Why this matters

More mixing does not automatically mean a cleaner breathing zone.

Research context

Occupant and inlet plumes establish two scalar layers. Downflow ventilation recirculates upper-layer contaminant downward, whereas displacement ventilation replaces the lower layer with clean supply air; the model does not extend to infection dose or a multi-occupant non-adiabatic room.

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