Research On Influencing Factors Of Central Shafts For High-rise Residential Buildings

Currently,high-rise residential buildings accounts for 68%of urban residence in China.The central cooking exhaust shaft is the main form for excluding fumes in high-rise residential buildings.Due to the large height of buildings and the large amount of fume,the static pressure in the main duct of the central shaft is large.Users even need to provide more power to exhaust fumes.Therefore,fumes can’t exhaust efficiently,which decrease the indoor air quality.In this Paper,Computational Fluid Dynamics（CFD）was used to study the effect of central shaft structure Parameters and pressure deflector on the performance of the exhaust system.In addition,the fumes in the inlet of the exhausting hood were tested to study the influence of the thermal buoyancy on efficiency of shaft.Finally,the usage rates of the exhausting hoods were analyzed through theoretical calculation.The results show that the cross-sectional area of the main duct,the wall roughness,and the usage rates of the exhausting hoods affect the efficiency of the whole exhaust shaft.If the cross-sectional area of the main duct increases or wall roughness decreases,the performance of the shaft is better.However,the former has more influence on the shaft than the latter.When the dimensionless cross-sectional area of the main duct A^*increases by 46%,imbalance rateβdecreases by 62.3%,the average amount of fumes in all branch pipe_（60）increases by 74.6%,and the minimum amount of fumes in all branch pipe Q_minin increases by nearly 4 times.As for the usage rates of the exhausting hoods,the higher opening rate,the smaller the amount of fumes.When the opened hoods are concentrated in the upper floors,the amount of fumes exhausted are the largest,followed by the condition of opened hoods randomly distributed in the entire shaft.Under the condition of opened hoods concentrated in the lower floors,the amount of fumes are the smallest.Pressure deflectors and thermal buoyancy can only affect the performance of the shaft Partially.For a pressure deflector,it mainly affects the shaft which are in themiddle or lower floors.Lower floors can be influenced by thermal buoyancy.As for the performance of the shaft,the installation location of the pressure deflector has greater influence than the height of deflectors and thermal buoyancy.When the pressure deflectors are installed in the middle and lower Part of the shaft,the performance of the shaft is improved,especially in the lower Part-the minimum amount of fumes in all branch pipes Q_min increased by 25.5%,and the average amount of fumes in all branch pipes Q_ave increased 3.9%,the imbalance rateβdecreased by 7.4%.ComPared to the installation location of the pressure deflector,the influence of thermal buoyancy on shaft efficiency is 20%of the installation location of the pressure deflector.