Abstract
In an air-conditioned office building, the ventilation air is normally mixed with the return air from the room within an air-handling unit. In this system, the fresh air is distributed also into the non-breathing zone. If only the fresh air is supplied into the breathing zone directly, the indoor air quality in the breathing zone will be improved and the requirement of the fresh air will be reduced in comparison with conventional air-conditioning systems. The CFD simulation for isothermal conditions was carried out to compare the age of air and the concentration of contaminant between two types of ventilation systems mentioned earlier. (1) The age of air at the breathing point (5cm ahead from the mouth of the occupant, 0.6m from the fresh air outlet, FL+1.1m) of the ventilation system by supplying the fresh air directly to the breathing zone is shorter than that of the conventional one to about 55-65%. (2) The concentration of contaminant at the breathing point of the ventilation system by supplying the fresh air directly to the breathing zone is smaller than that of the conventional one about to 60%.