Experimental Study On Mechanism And System Performance Of Displacement Ventilation With Up-fixing Diffusers

In our country, along with people increasingly attatch importance to indoor air quality, displacement ventilation (DV) are being recognized and used gradually by designers as a means of ventilation to provide good IAQ and thermal comfort compared with mixing ventilation, and it has been extensively used in industrial, civil and pubic buildings.As a rule, DV system concludes three types: displacement ventilation with low sidewall diffusers; upward air supply; displacement ventilation with up-fixing diffusers. We can call the two former types as traditional displacement ventilation. There is lots of research on traditional displacement ventilation, but the research is very poor on displacement ventilation with up-fixing diffusers. Our group took the lead in researching the theory and experimental study of displacement ventilation with up-fixing diffusers which has a special structure form. We acquired some cognition on characteristics of diffusers and thermal comfort, but we need to do some further study on displacement ventilation with up-fixing diffusers of the mechanism, ventilation efficiency, heat removal capacity and so on.In this paper, the up-fixing diffusers which was devised by us is still facing-wall diffuser slatted which the velocity distribution is ladder figure. In the test room of displacement ventilation with up-fixing diffusers, the writer did some in-depth study on the mechanism, ventilation efficiency, heat removal capacity of displacement ventilation with up-fixing diffusers. Through the analyzing of the experimental datas, the paper find the temperature field of displacement ventilation with up-fixing diffusers is similar with traditional displacement ventilation. The air flow of displacement ventilation with up-fixing diffusers is generated by the coupling between thermal plumes which comes from the indoor heat sources and the cold jet current which comes from the supply air outlet. The writer analyses the mechanism of the coupling. The thermal comfort includes the vertical temperture gradient and indoor velocity at the 0.1 meter is analyzed. The fitting formulas of jet current developing at 0.1 meter is given. The writer calculates and forecasts the location of maximum velocity at the 0.1 meter. The displacement ventilation with up-fixing diffusers can remove more heat loads and gain higher ventilation efficiency comparing with mixing ventilation which the system can maintain acceptable comfort. Through comparing the diffusers which the velocity distribution is ladder figure with the diffusers which the velocity distribution is even, the paper find that in the close range along the jet current, the inflow of the former diffusers is fewer than the latter, and the former diffuers which gain the better ventilation efficiency is suit for the displacement ventilation with up-fixing diffusers. The fitting formulas of the wall jet which comes from the two air supply air outlet are given.