Human exposure to respiratory aerosols: Impact of ventilation rates, mixing ventilation configuration, and breathing patterns

This study investigates airborne transmission dynamics between occupants in office rooms equipped with mixing ventilation (MV). The primary aim was to assess how different ventilation configurations, air change rates (ACH), breathing patterns, and supply air temperatures influence cross-exposure and infection risks. The experimental setup involved two thermal manikins simulating an infected and an exposed occupant within a climate chamber. The investigated parameters included four ACH levels (1.2, 2, 4 and 6.6 h⁻ 1 , representing four EN 16798–1 ventilation categories), two MV configurations (near-ceiling and near-floor inlets), two breathing patterns (nose and mouth breathing), and two supply air temperatures (19 °C and 21 °C). Carbon dioxide (CO₂) was used as a tracer gas to simulate exhaled aerosols, enabling precise measurements of effectiveness ( ε v ), intake fraction ( IF ), and infection probability ( P ). The findings indicate that higher ACH do not uniformly improve ε v but are linked to reduced cross-exposure risk. The near-floor inlet MV configuration significantly outperformed the near-ceiling configuration in reducing IF and P by 15–41 % under most investigated scenarios. Additionally, mouth breathing increased IF and P compared to nose breathing, especially at higher ACH (2, 4, and 6.6 h⁻ 1 ). The results also showed that lower supply temperatures do not always correlate with higher IF and P , as MV configuration and breathing patterns significantly influence outcomes. This research provides insights into optimizing ventilation strategies for safer indoor environments, emphasizing the importance of airflow dynamics, breathing patterns, and supply temperature in ventilation design. • Thermal manikins were used to simulate airborne transmission dynamics. • Increasing the ACH from 1.2 h −1 to 6.6 h −1 reduced IF by 69–89 %. • Switching from near-ceiling to near-floor MV inlets reduced IF by 15–41 %. • Mouth-breathing raised IF by 4.2–65.3 % compared to nose-breathing. • The effect of supply temperature on IF varied with ventilation and breathing modes.