Investigation of airborne particle exposure in an office with mixing and displacement ventilation

Effective ventilation could reduce COVID-19 infection in buildings. By using a computational fluid dynamics technique and advanced experimental measurement methods, this investigation studied the air velocity, air temperature, and particle number concentration in an office under a mixing ventilation (MV) system and a displacement ventilation (DV) system with different ventilation rates. The results show reasonably good agreement between the computed results and measured data. The air temperature and particle number concentration under the MV system were uniform, while the DV system generated a vertical stratification of the air temperature and particle number concentration. Because of the vertical stratification of the particle number concentration, the DV system provided better indoor air quality than the MV system. An increase in ventilation rate can reduce the particle concentration under the two systems. However, the improvement was not proportional to the ventilation rate. The increase in ventilation rate from 2 ACH to 4 ACH and 6 ACH for MV system reduced the particle concentration by 20% and 60%, respectively. While for the DV system, increasing the ventilation rate from 2 ACH to 4 ACH and 6 ACH reduced the particle concentration by only 10% and 40%, respectively. The ventilation effectiveness of the MV system was close to 1.0, but it was much higher for the DV system. Therefore, the DV system was better than the MV system.