Study Of Fire-Smoke Extraction System Utilizing Elevator Shaft In High-Rise Buildings

Smoke is the main cause of casualties in building fire, and characteristics of smoke movement have become hotspot in building fire safety design. After building fire, "Chimney effect" of many shafts in high-rise buildings is the main driving force of the vertical smoke movement. When smoke enters into the vertical shaft, it invades floor area by opening or gap, and this makes smoke spread. Considering the effect of chimney and combined with smoke numerical simulation, the analysis for smoke exhausting by elevator shafts in high-rise buildings is made.Smoke flows from high pressure zone to low pressure area. Since elevator shafts and stair shafts are set separately in some high-rise buildings, the method smoke exhausting through elevator shafts is proposed in this paper. The vertical shafts are used to exhaust smoke naturally, which is declined in Codes for Fire Protection Design of Tall Buildings (GB50045-2005) in section 8.1. As a result of large area of vertical shaft, designers usually don’t accept it and it has been rarely used recently. Elevator shaft with large cross-sectional area is a channel connected the whole building up and down, and it can be regarded as smoke exhausting shaft. In practice, it is considered to set smoke vents on the top of elevator shafts for exhausting, if fire stairs and elevator stairs are separated on the plane and used as the ways for people escaping and smoke exhausting respectively. Specific methods of elevator shaft smoke exhausting are not clearly defined in the codes. In this paper, smoke exhausting through elevator shaft is mainly researched in high-rise buildings.In terms of the mathematical model study, network model is mainly used for smoke movement numerical calculation in high-rise building fire. The treatment of fire is very easy in traditional network model, considering no heat transfer with the wall and ignoring friction loss of smoke movement. So the results are inevitably different with actual smoke movement pattern. Based on traditional network, an improved network is proposed in this article. Two-layer zone model is used in fire rooms. Heat transfer by convection and radiation between smoke and elevator shaft walls is also considered. Friction loss is not ignored in vertical shaft when smoke movement is calculated in order to correct smoke rising resistance and capability of smoke exhausting in shafts. The results show that two-layer zone model considered fire in fire rooms and heat transfer model in shafts have great impacts on calculation.In terms of model validation, first, results of a high-rise building smoke control system are compared, which are respectively achieved through CONTAM software and traditional network model written in this article, and the accuracy of traditional network model written in this article in calculation has been verified. The results of fire rooms are also compared, which are respectively received through two-layer zone model and FDS (Fire Dynamic Simulator) software, and the accuracy of two-layer zone model in calculation has been verified. Smoke temperature distribution inside shaft is obtained through scale model experiment for smoke movement form antechamber to shaft, and heat transfer model between smoke and walls has been verified effectively. Smoke movement in shafts is demonstrated by model experiment. Based on each sub-model above, mathematical model and method of an improved network is developed in order to research smoke movement law in vertical shafts.In terms of application research, numerical calculation of smoke exhausting naturally in elevator shaft has been made through improved network model. Factors that affect smoke exhausting in elevator shaft are also analyzed in detail, such as opening area of the elevator shaft top, the smoke vent sizes of fire floor, gaps of elevator door and friction coefficient on shaft wall surface. In the process of numerical simulation, the stairwells are pressurized with supply air flow system to keep the positive pressure, for the consideration of preventing hot smoke. The smoke extracting via mechanical fans are not concluded. Considering the position of neutral pressure plane, the volume of smoke exhausting and the smoke volume into elevator shaft from fire floor, the concept of elevator shaft comprehensive smoke coefficient are proposed in order to compare smoke exhausting under different conditions. The importance of each factors in the ranges of calculation data have been verified by orthogonal experiment, and natural smoke exhausting effect in elevator shaft has been also analyzed for different fire floors. Pressurizing air flow to floors above the fire floor through HVAC equipment is also considered. And numerical calculation for smoke exhausting in elevator shaft is also made using improved network model. So that effects of different volume pressurizing air flow can be achieved. Effects of smoke exhausting in elevator shaft have been also calculated when pressurize air flow to elevator antechamber above the fire floor individually, so that the effects of different volume pressurizing air flow to elevator antechamber are achieved. Effects of pressurizing air flow to floors above the fire floor through HVAC equipment on different fire floors have been analyzed. Finally, optimized calculations on smoke exhausting through elevator shafts are calculated by genetic algorithm, and this can make us learn how to set factors values in the calculation ranges in order to make smoke exhaust better in elevator shaft, such as opening area ratio of elevator top vent, the volume of pressurizing air flow, slit width of elevator door and the vent sizes located on the fire floor.