Research On The Influence Of Ventilation On Indoor/outdoor Particle Concentration Relationship

Airborne particles are the main atmospheric pollutant in China and have seriously harmful effect on human health. Since people spend most of their time in the rooms, the relationship between the indoor and outdoor particle concentration can be established to evaluate the harm of atmospheric particles on human health. The study on relationship between indoor and outdoor particle concentration is through establishment of indoor and outdoor particle concentration ratio (I/O Ratio). Factors affecting I/O Ratio include penetration ratio of building envelop, ventilation, indoor source, deposition rate and particle resuspension. This thesis focuses mainly on influence of ventilation on I/O Ratio.Under steady and unsteady ventilation conditions and different airflow organization, increasing of indoor particle concentration during entrance of particle from outdoor to indoor through ventilation is investigated. Indoor particle concentration distribution is found to have important influence on I/O Ratio, and a concept of particle age is brought forward herein; particle distribution characterization of different diameter is investigated through numerical simulation, standard k ?εmodel and drift flux model (DFM) are recommended for simulation of turbulence and particle concentration distribution, respectively. Applicability of Eulerian model and Lagrangian model is analyzed.The I/O Ratio can be greater than 1 with absence of indoor source, and particle age is greater than air age of the same position due to slip velocity between airflow and particle. In the process of particle concentration increase caused by ventilation, concentration increasing curve is different from theoretical curve, mass balance equation is thus revised to be more accordant with test value. Steady and unsteady ventilation have the same effect on increasing rate of I/O Ratio on occupant area. A longer time is needed for the particle concentration to reach the outdoor value around the air inlet under unsteady than steady ventilation, decreasing the influence of outdoor particle concentration variation on indoor.Gravity and slip velocity between airflow and particle can not be neglected for particles with diameter larger than 5μm through the result of numerical simulation by DFM, and I/O Ratio near floor of a room can be greater than 1 without indoor source due to gravity. Gravity and slip velocity between airflow and particles are negligible and have no effect on concentration distribution for particles with diameter smaller than 1μm. For particles with diameter 1μm-5μm, gravity and slip velocity between airflow and particles are only negligible under certain circumstance.Airflow organization has great effect on relationship between indoor and outdoor particle concentration. Airflow organization of downward supply and upward discharge is more effective in decreasing influence of outdoor larger particles on indoor.Research on the influence of ventilation on I/O Ratio and moving characterization of particles with different diameter can provide guideline for air conditioning system design to minimize the harmful effect of outdoor particle concentration on indoor.