Experimental study on airflow-induced particle resuspension from carpet under floor-supply displacement ventilation

Application of floor-supply displacement ventilation (FSDV) in medical facilities remains limited due to concerns about particle resuspension, including infectious droplets and dust from shoes. However, research data on this phenomenon under FSDV airflow are scarce. This study aimed to quantitatively evaluate particle resuspension under FSDV conditions and compare it with a circular ceiling diffuser (CCD) system. Experiments were conducted in a cleanroom chamber. For FSDV, the floor supply velocity (vf = 0.040, 0.030, and 0.010 m/s) and relative humidity (20%, 50%, and 80%) were varied. For CCD, the airflow rate (850, 750, and 250 m³/h) was varied at 50% relative humidity. Particle concentrations were measured using particle counters to calculate resuspension rates. Microscopic observations of carpet fibers above perforations were also performed to assess microscale resuspension behavior. Both supply velocity and humidity significantly affected resuspension under FSDV. The resuspension rate ranged from 10⁻⁷–10⁻⁴ h⁻¹ ( v f = 0.040 m/s, 50 ACH) and 10⁻⁸–10⁻⁵ h⁻¹ ( v f = 0.010 m/s, 12 ACH), showing that higher velocity and lower humidity enhanced resuspension. The resuspension rate increased with particle size, and large agglomerates (>10 μm) observed microscopically were more likely to detach due to greater exposed surface area to upward airflow. Under CCD, rates ranged from 10⁻⁵–10⁻³ h⁻¹ for 0.3–3 μm particles but were near zero for ≥10 μm. Airflow-induced resuspension under FSDV was smaller than that reported for walking-induced resuspension, even under high air exchange rates. This indicates that FSDV does not inherently increase resuspension risk under the tested conditions.