Numerical Simulation On Ventilation And Smoke Extraction System In An Underground Garage

With the rapid development of China's economy and a substantial increase in per capita income,more and more people have private cars,and followed by more parking spaces.In the first and second tier cities,the land is very tight and very expensive,and "parking difficult" phenomenon can be seen everywhere.In order to solve this problem,developers begin to build underground parking garages.However,the underground space is generally in a closed or semi-closed state,it is difficult to carry out ventilation,coupled with the car generating a large number of pollutants in the underground garage,which need to choose the appropriate ventilation to improve the garage of the air quality and accompanied by the consumption of electricity and a lot of ventilation heat loss.In addition,due to the relatively closed underground garage,once in the event of fire,the consequences are very serious.So,a good smoke control system is very necessary.When the car is in the idling state of the underground garage,the ratio of CO.HC and NOx emission is about 7:1.5:0.2.Therefore,the indoor allowable limit of CO and the CO emission of the car affect the ventilation volume of the garage.When the car is in the start and idle state,the amount of CO produced by the impact of environmental temperature is great.So in winter and summer,we should adopt different ventilation strategies.Specific work is as follows:(1)The numerical simulation on the natural ventilation of the underground parking garage is carried out.The temperature,CO concentration,air age and velocity distribution of the air in typical garage sections in winter and summer are simulated.As can be seen:In winter,because the heat gain of the underground garage is very large,the air temperature rises to form the hot-pressing.Besides,the air entrances by the lanes and pedestrian and emit by four stairs.Because lane equip with hot air curtain,the minimum temperature is in the lane and pedestrian enterance and the highest temperature is located in the hot air curtain at the exit.With uneven distribution of CO concentration,the CO concentration far away from the air inlet shaft is higher than that in closer from the air inlet shaft.The natural ventilation of wind speed closer from the intake shaft is greater than the far from intake shaft.In addition to that,the stair shaft tuyere wind speed is larger,the air flow velocity near the air curtain is larger,too.The wind speed is synthesized from natural ventilation air curtain air supply and lanes.The distribution of air age is consistent with velocity and CO concentration distribution.At the position of the CO concentration with less air speed,the air age is big,and vice versa.In summer,the hot direction of the garage is in contrast to the winter.The pedestrian and lane change from winter natural air inlet to outlet.The stairs passage changes the ventilation system of winter into air inlet.The flow rate of the stairs formation is less than the winter and the summer air age is greater than that in winter.CO concentration and air age in summer are greater than that in winter.The natural ventilation rate in summer is far less than that in winter.But for the garage CO concentration,summer is not very big difference from winter.(2)The numerical simulation on different types of mechanical ventilation system,we reach the distribution of temperature field and concentration field,air age nephogram and speed distribution of cloud about the typical surfaces.From the result,we can see that induction ventilation system has no advantage compared with other good ventilation types.(3)According to the CFD simulation,we analyze which method is more favorable for fire smoke.We reach the distribution of gas and temperature in a garage.When the fire is located at the center of 500m2 smoke partitions,the temperature and concentration distribution is more close.When the fire is located at the center of 2000m2 smoke partitions,the 2000m2 is better than the 500m2.