Effect of airflow rate on CO2 concentration in downflow indoor ventilation

Yerragolam, G.S.; Howland, C.J.; Yang, R.; Stevens, R.J.A.M.; Verzicco, R.; Lohse, D.

doi:10.1016/j.indenv.2024.100012

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).

Main finding

The sampled layout and mixing changes alter how lower-layer, volume-average, and outlet concentrations relate. They do not show absolute CO2 increasing with airflow: Equation (4) and Figure 4 give the opposite trend. 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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