室外风对高层建筑竖井内烟气运动影响的数值模拟

采用火灾模拟专业软件FDS对不同火源位置、不同风向条件下火灾烟气的运动进行模拟,测定典型位置处温度、速度、CO及CO2体积分数变化情况。实验结果表明:在近地风场中,风向对竖井内烟气蔓延的影响大小顺序为迎风>背风>侧风,竖井开口位于迎风面时,外界风对竖井内烟气运动影响最大:火源位于中性面以上时,烟气通过竖井与前室的开口向竖井内蔓延,并向下运动;而火源位于中性面以下时,前室内烟气向外部运动,竖井内无烟气流入。     

Characterization of Stack Effect in High-Rise Buildings Under Winter Conditions,Including the Impact of Stairwell Pressurization

To characterize the magnitude of stack effect within stairwells and elevator shafts, differential pressure measurements were taken in fifteen (15) high-rise buildings in four (4) different cities (Cleveland, Baltimore, Minneapolis, and Philadelphia) during the winter months of January–March, 2013. Test buildings ranged in height from 44 m to 150 m (143 ft–492 ft). Outside temperatures during testing ranged from ?12°C to 15°C (10°F–59°F). Based on the differential pressures measured, there was evidence of winter stack effect in all buildings tested. On the lower levels of all buildings, air was observed flowing from the building into the stairwells and elevator hoistways with pressure differential magnitudes ranging from ?2.7 Pa to ?24.9 Pa, ?12.0 Pa average (?0.011 in. w.g. to ?0.100 in. w.g., ?0.048 in. w.g. average). Similarly, in most buildings (excluding Buildings 6 and 7) air was observed flowing from the stair and elevator hoistways into the building on the upper levels with pressure differential magnitudes ranging from 0.5 Pa to 34.9 Pa, 11.2 Pa average (0.002 in. w.g. to 0.140 in. w.g., 0.045 in. w.g. average). Under winter conditions, the data suggests that large quantities of air can migrate, floor-to-floor, via unprotected elevator shafts. Data further suggests activation of the stairwell pressurization system can increase vertical air movement via unprotected elevator shafts. This behavior is expected to impact the movement of smoke floor-to-floor during a fire, as airflow is indicative of smoke migration. The exterior stack force on the building’s envelope (governed by the building’s height and temperature differential between the building interior and exterior) does not always translate proportionally to shaft-to-building differential pressures (i.e., “stack effect”), as each building is unique. Although a building’s height and outside temperature play important roles in determining vertical airflow movement within a building, height alone was not found to be a good predictor of vertical airflow (or smoke movement) within the building due to stack effect. Other variables, such as architectural layout, architectural leakage, wind effects, and ventilation systems should all be considered. Simplified algebraic calculations (i.e. hand calculations) do not treat the building as a complete system, and do not account for all variables involved. Therefore, simplified algebraic calculations may result in inaccurate shaft-to-building differential pressure predictions. Based on this analysis, unless conservative leakage values are used, the simplified algebraic calculations may underpredict the shaft-to-building differential pressures. Using simplified algebraic calculations may be suitable for preliminary approximations, however, for design purposes a more complex analysis is recommended. The more complex analysis should consider other variables that affect pressure differentials such as changes in architectural layout and envelope leakage from floor-to-floor, HVAC systems, and wind.     

Study of FDS simulations of buoyant fire-induced smoke movement in a high-rise building stairwell

Numerical simulations of fire-induced smoke movement in the stairwell of a high-rise building are conducted using FDS, version 6.0.1, with default settings. Twelve scenarios are considered. The required fineness of the grid has been determined in earlier work by considering both the fire source and the vent flow, and by assessing the velocity profile at the bottom opening and the vertical distribution of temperature in the stairwell. In the present study, the results including the airflow velocity at the bottom opening, vertical distribution of temperature, the temperature at the middle opening, pressure distribution, and neutral plane height in the stairwell, are compared to experimental data. For the average velocity through the bottom opening, a maximum deviation of 16.23% is obtained. Good agreement is achieved for the vertical temperature inside the stairwell (maximum relative deviation of 12.3%). By analyzing the temperature at the middle opening, it is found that the smoke moves faster than in the experiment. The influence of the staircase on the pressure distribution is demonstrated by comparing two cases: one with and one without staircase. The difference between the pressure inside the stairwell and the pressure outside increases with height, due to fire-induced buoyancy. However, the pressure difference evolution is non-monotonic when there are staircases inside the stairwell. The neutral plane height value, as obtained by post-processing the simulation results, is too high in the simulations, compared to experimental data and the corresponding analytical expression. Finally, the influence of the turbulence model is shown to be negligible.     

Development of CAU_USCOP,a network-based unsteady smoke simulation program for high-rise buildings

In this study, a new network-based unsteady smoke control program, CAU_USCOP (Chung-Ang University, Unsteady Smoke Control Program), was developed for use in high-rise buildings. This program solves the unsteady conservation of mass and energy equation. Using CAU_USCOP, we then analyze the movement of smoke in a high-rise building according to the existence of a natural smoke release unit. Moreover, the strength of the stack effect is estimated using the movement of a neutral plane in a stairwell over time. The neutral plane in the case with the natural smoke release unit descends 90% less than the case without the unit, and the natural exhaust in the fire room should be helpful in reducing the risk from fire.     

耦合电梯门狭缝流动的高层竖井火灾烟气模拟

利用FDS 建立17 层高层办公楼数值模型,考虑狭缝的小开口流动,耦合了基于开口流动理论的HVAC 模型,研究高层建筑内烟气通过电梯竖井的蔓延过程,得到了高层建筑内烟囱效应诱导的火灾烟气蔓延规律。高层建筑内较低层发生的火灾会显著加热电梯竖井中的气体,形成烟囱效应,高层建筑内部会形成中性面。通过将HVAC 模型与基于标准流量系数的模型进行比较,可以发现这两种方法计算的质量流量相差约1.5 倍。这是由于采用的HVAC 模型并没有考虑狭缝处的开口流动损失。通过进一步修正,取开口损失系数K 值为3.56 能得到较好的模拟结果。     

A computational study on the use of balconies to reduce flame spread in high-rise apartment fires

High-rise apartment fires are perhaps the most dangerous residential fires. Within high-rise buildings, flames and smoke can travel through ductwork, between interior walls, and up elevator shafts and stairwells. One of the fastest ways a fire spreads to other floors is along the exterior of the building due to open windows. Flame spread up vertical walls has been studied experimentally and computationally for years in the US and abroad. A numerical study has been undertaken to examine the reduction of vertical flame spread due to the presence of a balcony. The depth and geometry of the balcony greatly affects the vertical movement of fire. By varying the balcony depth and geometry, the aim of this study is to find an optimum configuration that reduces vertical fire spread on the external wall.     

Smoke movement in elevator shafts during a high-rise structural fire

In high-rise fires, smoke is often the leading cause of fatalities. Therefore, in the event of a fire, the ability to predict the movement of smoke throughout a tall structure is of vital importance. Smoke moves depending on a number of interacting and complex factors including weather conditions, building construction, operation of HVAC equipment, as well as the location and intensity of the fire. Smoke often travels long distances from the fire floor, and in the particular case of a high-rise fire, smoke frequently moves to upper floors via open passages such as elevator shafts and stairwells.     

高层建筑电梯活塞效应对电锑井及其前室烟气运动影响的数值模拟

通过对电梯运动产生的活塞效应的理论进行相关分析,采用CFD工具FDS5.4.1建立高层建筑典型的竖向疏散通道物理模型,选择大涡模拟方法进行数值模拟,研究电梯在不同运行过程中竖向疏散通道中的烟气运动规律,分析前室与建筑空间的压力差及烟气运动路径、速度的变化。模拟结果显示:电梯活塞效应会使电梯井及其前室的压力发生变化,电梯运动使得前室与建筑空间之间的压力差呈现先升后降的趋势;电梯向下运动一定程度上可以减缓烟气的扩散,而电梯向上运动会加速烟气通过前室向其它楼层地扩散。     

COSMO—Software for designing smoke control systems in high-rise buildings

A differential computer model specifically designed to quantify smoke movement during a fire in a high-rise structure is described. The basic conservation equations are transformed into a computer code which can be used to determine the paths that smoke will take during a fire. The program is a tool for fire protection engineers to design a smoke management plan with the ultimate goal of improving occupant safety in the event of a fire. The computer code is based on a modified and improved differential smoke control model for the conditions in the floor spaces, stairwells and elevator shafts and it considers a complete set of variables that influence the motion of smoke throughout the building. Program output suggests ways to alter the pressure distribution within the building by using air handling equipment, so that occupants will have smoke-free areas on the floors and inside of the fire escape stairwells. Results for several example cases are provided, and the results are used to illustrate how smoke movement can be managed in order to mitigate dangerous conditions within the building.     

Comparison of FDS Prediction of Smoke Movement in a 10-Storey Building with Experimental Data

In this study, the Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) model developed by National Institute of Standards and Technology (NIST) is used to simulate fire tests conducted at the National Research Council of Canada (CNRC). These tests were conducted in an experimental 10-storey tower to generate realistic smoke movement data. A full size FDS model of the tower was developed to predict smoke movement from fires that originate on the second floor. Three propane fire tests were modelled, and predictions of O₂, CO₂ concentrations and temperature on each floor are compared with the experimental data. This paper provides details of the tests, and the numerical modelling, and discusses the comparisons between the model results and the experiments. The 10-storey experimental tower was designed to simulate the centre core of high-rise buildings. It includes a compartment and corridor on each floor, a stair shaft, elevator shaft and service shafts. Three propane fire tests were conducted in 2006 and 2007 to study smoke movement through the stair shaft to the upper floors of the building. The fire was set in the compartment of the 2nd floor. Thermocouples and gas analyzers were placed on each floor to measure temperature and O₂, CO₂ and CO concentrations. Comparisons in the fire compartment and floor of fire show that the FDS model gives a good prediction of temperature and O₂ and CO₂ concentrations. In the stair shaft and upper floors there are some small differences which are due to the effect of heat transfer to the stairs that was not considered in the model. Overall the study demonstrates that FDS is capable of modelling fire development and smoke movement in a high rise building for well ventilated fires.     

A study on the development and application of the E/V shaft cooling system to reduce stack effect in high-rise buildings

This study suggests the E/V(Elevator) shaft cooling system as a new approach to reduce the stack effect and the related problems in high-rise buildings. The basic characteristics on its application were analyzed with some simulations in this study. Moreover, the system was applied to an actual building and its performance was evaluated through the measurements.The system can reduce the stack effect itself and the related problems simultaneously and it can reduce the pressure and the air flow rate in each part of a building in the same ratio. These features were shown in the results of the simulations; for the examples, when all the E/V shafts were cooled from 22 °C to 12 °C, the stack effect and the pressure in each part of the modeled building were decreased by about 27%.In the field measurements, the wind velocity through the E/V door was decreased effectively in the whole building; its reduction ratio at the lobby floor was about 25% and at the upper floors (37F, 38F) about 10% respectively. But, the neutral pressure level at the E/V shaft was moved by the vertical temperature difference in the E/V shaft because of the inflow ducts concentrated in the lower part of the E/V shaft. This movement was also shown in another simulation on the same conditions as the measured ones. It is very important to minimize the vertical temperature difference in the E/V shaft to maximize the reduction effects on the problems.     

On stairwell and elevator shaft pressurization for smoke control in tall buildings

Elevator shaft and stairwell shaft-pressurization systems are studied as means of smoke migration prevention through the stack effect in tall buildings using the CONTAM simulation software. A thirty story building model is considered with exterior leakages calibrated to experimental data for both a residential and a commercial building. Stairwell pressurization is found to be completely feasible in the absence of elevator shaft pressurization. In contrast, coupled elevator shaft-pressurization systems are found to produce prohibitively large pressure differences across both the elevator and stairwell doors if (1) minimum pressure differences must be maintained at both open and closed elevator doors and (2) if the system must function properly when the ground floor exterior building doors are closed. Even in these cases situations arise in which smoke may enter the shaft and be actively distributed throughout the building by the fan system. These differences between stairwell and elevator shaft pressurization are directly attributable to the much larger leakage areas associated with elevator doors. Relatively large flow rates through the open elevator doors act to pressurize the ground floor of the building, indirectly causing large pressure differences across upper floor elevator doors. Furthermore, the results show that there is a strong coupling between the fan speed requirements of the stairwell and elevator shaft-pressurization systems. Fan requirements are also found to be sensitive to the ambient temperature. Effects of the fan location, louvers, vents, the building height, and the number of elevator cars and/or shafts are also addressed.     

高层综合体育训练馆消防设计有关问题探析

高层综合体育训练馆是一种新型体育建筑，针对该类建筑的特点，文章探析了建筑分类、耐火等极、防火分区、安全疏散、消防电梯、排烟、灭火设施等消防设计中的有关问题。     

Distribution of wind- and temperature-induced pressure differences across the walls of a twenty-storey compartmentalised building

An experimental investigation has been made of the distribution of pressure differences across the walls of a 20-storey student residence building at the University of Ottawa. The wind velocity at the test building as well as the temperature distributions both inside and outside the building were measured simultaneously.

While pressure differences are caused by all three of the factors investigated, namely the temperature gradient (stack effect), the wind and the mechanical ventilation system installed in the building, the first two effects are predominant for this particular building during the winter season.

The stack effect is found to be linearly proportional to the difference of the reciprocal outside and inside (absolute) temperatures, and varies almost linearly with height. The neutral pressure level occurs at a height of 40 m, or 70% of the height of the building.

The wind-induced pressure difference under relatively strong wind shows a good conformity with previous knowledge for typical bluff sections such as a rectangular prism.     

Driving Forces for Smoke Movement and Management

The movement of smoke in buildings and tunnels is governed by a number of driving forces, including fire-induced buoyancy and expansion, stack effect, wind effect and mechanical ventilation. To manage smoke movement in buildings and tunnels, these driving forces need to be considered individually and collectively so that appropriate strategies and systems can be implemented to achieve desired smoke control objectives. This paper provides an overview of the driving forces for smoke movement in buildings and tunnels and for the current methods used to manage smoke movement in structures.     

Smoke control based on a solar-assisted natural ventilation system

The possibility of using the same system for natural ventilation and smoke control is examined. As an example, a prototype building is proposed. The proposed prototype is an eight-storey building with a solar chimney on top of the atrium. Reduced scale model experiments and Computational fluid dynamics analysis are conducted. As a result, when the area ratio of outlet to inlet is greater than 2, air change rate of the utility space reaches over 2 times per hour and in an event of a fire breaking out in the atrium, the neutral pressure plane of the smoke layer stays inside the chimney. Smoke infiltration into adjacent spaces used for evacuation is prevented.     

室内烟气运动影响因素模拟研究

运用FDS模拟室内火灾烟气的运动规律,分析烟气层稳定性,以及门的尺寸、火源位置和火源面积对烟气温度及高度的影响。结果表明,具有稳定热释放速率的火源,燃烧一段时间后烟气层高度不会随时间发生变化;烟气层高度随门的高度和宽度增加而升高;火源处于房间中心时,烟气层高度随着门宽度增加迅速升高,与门高度的关系较小;随着火源面积增加,烟气层高度下降,温度升高。     

关于高层住宅设计的思考

从平面设计、交通核设计、立面设计、空间设计等方面对高层住宅的设计内容及有关要素进行了探讨,分析了高层住宅建筑设计中存在的有关问题及相应的解决方法,并提出了有益的建议,以创造出更多更好的优秀住宅。     

高层建筑竖井内烟气流动特性及控制方法

竖井火灾烟气流动特性和控制是与高层建筑火灾安全紧密相关的问题。从竖井烟气流动作用因素、烟气参数分布特性与烟气上升速度3个方面论述了对于高层建筑竖井烟气流动特性的研究现状。总结了目前常用的竖井烟气控制方法及工程实践中存在的问题,提出了改善烟气控制效果的方法和思路。     

Characteristics of pressure distribution and solution to the problems caused by stack effect in high-rise residential buildings

This paper shows the characteristics of pressure distribution caused by stack effect in high-rise residential buildings and proposes solutions for stack effect problems during the cold season. First, field measurements were conducted in two high-rise residential buildings in Korea to understand the characteristics of pressure difference and problems due to stack effect. Next, several high-rise residential buildings were simulated to confirm these characteristics and problems. From the field measurements and simulation results, the Thermal Draft Coefficients varied from 0.20 to 0.49. These values meant that most of the stack pressure difference in high-rise residential buildings acted on interior partitions rather than on exterior walls, so that serious problems due to large pressure differentials can occur on the inside of the building. The separation method which includes installing ‘air-lock doors’ between the elevator core area and residential area, is proposed to solve the pressure difference problems.