| A well-designed underfloor air distribution system can provide such benefits as improving thermal comfort, ventilation efficiency and indoor air quality, reducing energy use, life cycle building costs and floor-to-floor height in new constructions. Although many project experiences have been done at present at home and abroad, some probles need to be sloved. For example, the calculation method of air-condition load and air volume, the theory of thermal stratification need to be verified and lack of corresponding design standard and design code, inlet airflow characteristics and how to avoiding the draught sensation, cold sensation and the resuspension of particle.At first, the development, application range and research status of UFAD systems are summerized. The wind incidence angle between the direction of velocity and the ground is defined to beα. The airflow characteristics thatαis 0°, 30°, 45°, 60°and 90°was studied using computational fluid dynamics in an office with an UFAD system which has the dimensions of 3m×3m×3m. The influence of different inlet wind directions on airflow characteristics for underfloor air distribution system was analized. Numerical simulation results were verified by model experiment. The frequency of inhalable particulate matter was measured whenαis 90°. The surface area and mass concentration were calculated. The relationship between frequency, surface area, mass concentration and particle size were shown in foumula. The effect of human activities and smoking to the characteristics of size distribution was also studied. The results are as follows:(1)The airflow patterns are similar whenαare 0°, 30°and 45°, the maximum velocities are close to the floor. The dust in the ground is easliy to move and resuspension when the wind incidence angle is 0°because ground velocities are the fastest. People feel uncomfortable by draught sensation in this case. More vortices are formed when the angle between the floor and inlet air are 30°and 45°, so air exchange efficiency were poor.(2)The airflow characteristics are similar whenαare 60°and 90°, the maximum velocities are in the center of the room. The indoor air was more-mixed when the wind incidence angle is 60°compared with 90°. So indoor air temperature difference is smaller. (3)The logarithm of cumulative frequency and the logarithm of diameter was a linear relation, the logarithm of cumulative total surface area and diameter was a linear relation and the logarithm of cumulative total mass and diameter was a linear relation.(4)Particle of no less than 1 micron increased due to human activities, total mass concentration were two times the concentration of no human activities. The particle of no larger than 1 micron may increase due to smoking.
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