Effect of ventilation strategies on particle decay rates indoors: An experimental and modelling study

A cubic experimental chamber of 2.5 m×2.5 m×2.5 m was designed to study the impact of ventilation strategies on the indoor particle concentration. Particles of 0.3-15 μm aerodynamic diameter were used. The combined effects of the ventilation rate (0.5 and 1.0 ach) and the inlet and outlet locations (six different strategies) were tested. Results show that the ventilation acts differently according to the particle size. For small particles (particle diameter lower than 5 μm in diameter), deposition is increased by a factor 2 when the airflow was changed from the Top-Top to the Bottom-Top inlet/outlet configuration. Increasing the ventilation rate from 0.5 to 1.0 h−1 does not modify deposition for the Top-Top configuration but decreases it by 2.8 for the Bottom-Top. The effect of the inlet and outlet locations is less notable for coarse particles. This experimental study reveals that the ventilation strategy has to be well adapted to the particle size in order to improve its effectiveness. We show that the locations of the inlet and the outlet can be a very important parameter and have to be taken into account to predict particle indoor air quality. In addition, a numerical model of particle dispersion was developed. The program calculates instantaneous distributions of air velocity, using the large eddy simulation (LES) method. Trajectories of particles are obtained by implementing a Lagrangian particle model into the LES program. We simulated the experimental conditions in the three-dimensional numerical model and results show that ventilation strategy influences particle deposition in the room. A comparison of numerical and experimental results is given for 5 and 10μm particles. Particle behaviour is well predicted and this model seems to be adapted to predict indoor particle air quality in buildings. More experimental results are needed for a better validation of the numerical model, essentially for small particles.