| Under the general background of global warming and energy shortage,the passive application of natural ventilation in contemporary architecture have become more and more valued by people.Some practical and specific passive technologies of natural ventilation emerge and are favored by many architects and engineers.As a kind of typical passive equipment of natural ventilation,windcatchers capture the wind outside and sink it down into the interior under insufficient ventilation conditions for strengthening air movement.Because of its feature of light structure,simple installation,wind independent and good in fire protection,windcatcher shows obvious advantages among various natural ventilation technology.Whatsmore,although it has a long history applying in foreign countries and proven technology has been developed abroad,it is still rarely used in China,“bank zone” of the basic researchment still exist and there is no guidance on the design of windcatcher based on the characteristics of China's various climates,relevant research needs to be carried out urgently.An experimental investigation and CFD simulations have been carried out to evaluate the performance of three(i.e.circular,rectangle and square)four-sided wind-catchers with different section types but equivalent inlet diameter.It has been performed under four incremental wind speeds(1-7m/s)and five angles(0°-90°).Practical and functioning wind-catcher systems operated in real conditions was connected to the top of a roof to a room with dimensions 3.5m by 4m by 3 m(height,width and length)respectively.60 working condition scenarios were designed in total in terms of cross section,wind velocities and incident angles in the city of Chongqing.Tracer gas methods using CO2 concentration was employed to calculate the air change rate of the room considering the air exchange from the wind-catcher.The results show that the section type,wind speed and incident angles are main contributing factors in the performance of the wind-catcher systems.Notably,comparing with round section,the rectangle and square systems provide higher efficiencies.The ventilation rate increase with wind speeds,while differences among various angles are only distinctive when outdoor velocity is above 4m/s in this paper,indicating that the importance as influence factor of incident angle for ventilation performance depends on outdoor wind sources to a great extent.In addition,direction and cross section had a coupling influence on the ventilation performance,from which angles 0°and 90° always provided significant results.Moreover,streamline and velocity vectors were visualized by CFD simulations,which shows a good agreement with experimental results,and explains the reason behind the phenomenon.Based on the ventilation characteristics of the top-windcatcher,this paper designs a new type of wind-catcher structure which can be used for lateral wind capture in order to orientating the high-rise buildings tendency in China.As a typical city of Hot summer and cold winter area,Hangzhou has been chosen for further case study and a high-rise building named “Liubo” was applied by this two kind of windcatchers under real transition season period.The results show that this two kinds of windcatcher both can promote a certain air change rates,the flow patteren of the top-windcatcher greatly depends on the the outdoor wind field and the opening position of the building,indoor air change rate can be increased by 22.34% when the windcatcher act as a wind capture machine.The lateral windcatcher can be designed under the situation that the opening of the building is parallel to the main wind direction,which leads to insufficient ventilation.Its ventilation effect is directly related to the outdoor wind speed,generally,higher wind velocity showing in the higher position of the building lead to better air change rate. |
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