Three-dimensional numerical simulation of a hybrid fresh air and recirculated air diffuser for decoupled ventilation strategy

In conventional mixing ventilation air conditioning system, fresh air which has been polluted by recirculated air is supplied to occupied zone. Therefore, more fresh air which results in energy penalty needs to be supplied in order to keep good indoor air quality (IAQ) and thermal comfort. Some alternatives such as personalized ventilation air conditioning system can address this problem effectively by supplying fresh air directly into occupied zone. However, room layouts and visual effects will be influenced deeply because of extended air ducts. A new approach supplying fresh air directly by utilizing high velocity circular air jet without mixing with recirculated air is introduced. Objective measurements and computational fluid dynamics (CFD) tool are used to evaluate corresponding indoor parameters to verify that it can both supply fresh air into occupied zone effectively and avoid draught rating. It is found that the measured air velocities are within the limits (0.25 m/s) of thermal comfort standards, although they are close to the limits. Higher air change rate can be obtained in breathing zone than that in ambient air in the background area. The predicted results show unique distributions of airflow characteristics and are in fair agreement with empirical measurements. Different angles of recirculated air diffuser blades, different lengths and directions of protruding fresh air jets and different inlet velocities of fresh air are adopted for comparing the effectiveness and efficiency of this new ventilation strategy numerically.