A Numerical Study On High-speed Elevator Piston Effect

With the development of urban buildings in recent years,multi-functional ultra-tall buildings have been established.The ultra-tall buildings have many stories and large occupants.Traditional evacuation strategy under fire conditions cannot meet the requirements for safe evacuation.This paper reviews previous experiments and numerical simulations to study the piston effect of elevator on building pressure and smoke distribution.The elevator piston effect causes a certain pressure difference between the elevator lobby and the building,thereby affecting the spread of fire smoke.Based on piston effect theory,this paper set up a ultra-tall building model with single car shaft elevator using CFD tool,ANSYS FLUENT15.Numerical simulations are conducted to investigate the impact of elevator piston effect to the pressure of elevator lobby and the shaft.In this paper,the elevator velocities of 5m/s,8m/s and 10m/s are mainly selected.With the simulation of several conditions,building pressure difference and smoke distribution were compared and analyzed.The conditions are elevator lobby under the condition of 32 Pa pressurization or no-pressurization,elevator shaft under the condition of 40 Pa pressurization or no-pressurization,and elevator shaft with an extra pressure relief well connected with 0.5m×0.5m,1.0m×1.0m and 1.5m×1.5m three sizes of relief vent,and the following conclusions were obtained:(1)Moving elevator car promote the spread of smoke.(2)Higher elevator velocity causes greater influence on elevator lobby pressure difference,and with a same elevator velocity,the higher the height of the elevator lobby,the greater the pressure change in the elevator shaft.With an activated smoke control system to pressurized lobby to32 Pa can keep the lobby still maintain a certain pressure to stop the smoke while the operating velocity is lower than 10m/s.(3)The pressurization in elevator lobby causes lobby pressure always greater than the corresponding elevator shaft pressure after the upward-moving elevator passes through the lobby.If the smoke control system fails,the smoke enters the lobby,and the smoke can enters the shaft after the elevator passed through.And smoke can enter the shaft anytime if it can enter into the lobby when lobby pressurization is 32 Pa and elevator velocity is 5m/s.(4)The pressurization in shaft can reduce the pressure difference range of the low floor shaft,but at the same time it will increase the peak value of the high floor pressure increase,and slow down the high floor pressure recover after the elevator moving downward.The pressurization of the shaft is not as good as the pressurization of the elevator lobby.(5)Greater pressure relief vent size leads to better the pressure relief effect.Noticed that this condition cause a large amount of smoke enters the pressure relief well,which expanding the spread area of smoke.