Geometric optimization on active chilled beam terminal unit to achieve high entrainment efficiency.

In this paper, a novel structure of terminal unit is investigated to achieve high entrainment of room air. The energy efficiency of the whole system can thus be increased. Firstly, entrainment ratio of a commercial terminal unit is tested with a series of experiments. An innovative method of acquiring entrainment ratio is also proposed and validated throughout our experimental studies. Secondly, a computational fluid dynamics (CFD) model of this terminal unit is established for simulation study. It is verified that the model accords with the experimental data and is thus proved valid. Thirdly, the geometry of the terminal unit based on the CFD model is modified in CFD software to achieve higher entrainment ratio. It is found that, by changing the geometry of the mixing chamber and lengthening the nozzle, the modified structure can increase entrainment ratio by 30% with the same working condition and primary air volume flow rate. The height of the terminal unit is also suppressed to fit a tighter space. This study proves that the entrainment ratio of a terminal unit, as well as the efficiency of the whole air conditioning system, can be effectively increased by proper modification on its geometry. The findings about the nozzle can also guide the adjustment of other geometric characters of the terminal unit.