The Scientific Basis About Efficient Shutters And Hoods For Natural Ventilation

Recently, natural ventilation is generally adopted in today's ecological buildings, which has the advantages of cleanness and economy compared with mechanical ventilation.Natural ventilation is produced by thermal or wind pressure. Now researches mostly focus themselves on calculational methods, only a few studies emphasize on the performance of inlets or outlets. This paper will pay attention to inlets and outlets to improve the efficiency of natural ventilation. Shutter is one kind of inlets used widely in natural ventilation, therefore, the study for shutters may be a breakthrough for using natural ventilation more effectively. Firstly, this paper will study the performance of shutters in single side by CFD. Secondly, we will work at hoods with shutters in four sides. Finally, this paper will make a pilot study for the shelters from rain.For shutters, the results show:1) According to the formula p = , the theoretical value of is calculated by theeffective velocity of the flow, and its engineering value is calculated by the arriving velocityof the flow, the relationship between the theoretical value of and its engineering value is2) The smaller value of declining angle will result in the smaller pressure loss and smaller outlet velocities. As a result, the declining angle of 30掳 or less is recommended in some places which need small wind velocity, such as broadcasting studio and library, and the declining angle of 45 掳 or less is recommended in places which need big wind velocity, such as cinema and office;3) The larger value of ratio between the wide of the shutter b and the space between two boards h (b/h) will result in the larger pressure loss and smaller outlet velocities. The range of b/hfrom 0.8 to 2.0 and the optimum value 1.2 is recommended;4) The range of b from 10 mm to 50 nun and the optimum value 40 mm is recommended;5) The proper thickness of the boards 8 of the shutters is 1.5 mm;6) Cuneiform boards should replace the rectangle inlet boards of the shutters in order to obtain better ventilation.For hoods with shutters in four sides, the results show:1) The hoods positively placed boards are called hoods used for venting airflow; hoods negatively placed boards are called hoods used for leading airflow;2) Among the hoods used for venting airflow, the most effective hoods should have positive declining angle value of 30 , the ratio 4 of areas between the four windward faces and the gular section (Fy/Fj=4), the value of b range from 70 mm to 120 mm and the value of b/h range from 0.5 to 0.6;3) The most effective hoods should have negative declining angle value of 60 , the ratio 4 of areas between the four windward faces and the gular section(Fy/Fj=4), the value of b range from 100 mm to 170 mm(the optimum value is 120 mm) and the value of b/h range from 1.4 to 2.2(the optimum value is 2.0).For shelters, the results show:1) To reduce the raining drops entering into the inlet and to decrease the influence of the vortex, the declining angle of 45 is recommended for the shelters;2) It is better to choose those shelters which are longer 100 mm~200 mm than the height of the inlets, as they may protect the room from rain.