| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 104 === Abstract
Most of Taiwan's small and medium sized factories rely on natural ventilation. During the summer time, heat generated gathers near the roof ceiling and causes a sultry environment with poor ventilation. Traditional natural ventilation architectural designs or devices have many problems on maintenance, lighting, and water leaking during rainy day. Therefore, the main purpose of this study is to confirm the performance of a new commercial natural ventilation system that can resolve all the aforementioned problems, and assess the feasibility of improving its effectiveness. In the study, ANSYS CFX was used for simulation of a 1:1 model in order to understand the impact of the heat source wattage, wind speed and direction on the ventilation system’s performance.
The simulation results show that, in the absence of wind, the efficiency of the ventilation system will increase with increasing indoor/outdoor temperature difference, and the ambient temperature has no impact on its performance. When the wind direction is parallel to the system outlets, system performance only changes a little at low wind speed, which represents the thermal buoyancy effect still plays a very important role. But as the wind speed increases, the air flow will interfere with the stack effect and produce unexpected consequences. On the other hand, when the wind direction is perpendicular to the system outlets, different amount of air depending on the wind speed will pour into the building through system’s windward openings and affect the indoor flow field. Apparently, the relative orientation of the wind has a great relevance to the ventilation system’s performance, therefore, the seasonal changes in wind direction should be properly considered before installation of the ventilation system in order to maximize its efficiency.
As the design improvement is concerned, although reducing the number of louvers at the outlet can significantly increase the efficiency of the ventilation system due to reduced flow impedance, but considering its purpose of preventing the wind and the rain from entering the building, a best balance between that and the system ventilation efficiency should be sought out. As for the employment of the concept of venture tube by adding a sheet to the outlet to create a negative pressure area, simulation results show that overall performance has been increased dramatically, and the higher the wind speed, the more obvious the degree of improvement.
Key word: Natural Ventilation, ANSYS CFX, Venturi Tube
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