高层建筑底层大门及底层房间外窗渗透风量的计算——高层建筑内部隔断对空气渗透的影响(续一)

本文就冬季在热压作用下高层建筑内部的前室和楼梯间的隔断门对底层大门、底层房间空气渗透的影响进行了理论分析,推导出了几种不同情况下计算底层大门及房间外窗空气渗透公式。对于改进高层建筑设计、正确计算高层建筑中的渗透风量和冷热负荷具有实际意义。     

高层建筑烟囱效应分析

烟囱的主要作用是拔火拔烟，排走烟气，改善燃烧条件。高层建筑内部一般设置数量不等的楼梯间、排风道、送风道、排烟道、电梯井及管道井等竖向井道，当室内温度高于室外温度时，室内热空气因密度小，便沿着这些垂直通道自然上升，透过门窗缝隙及各种孔洞从高层部分渗出，室外冷空气因密度大，由低层渗入补充，这就形成烟囱效应。烟囱效应是室内外温差形成的热压及室外风压共同作用的结果，通常以前者为主，而热压值与室内外温差产生的空气密度差及进排风口的高度差成正比。这说明，室内温度越是高于室外温度，建筑物越高，烟囱效应也越明显，同时也说明，民用建筑的烟囱效应一般只是发生在冬季。就一栋建筑物而言，理论上视建筑物的一半高度位置为中和画，认为中和面以下房间从室外渗入空气，中和面以上房间从室内渗出空气。     

高层建筑火灾时的“烟囱效应”

“烟囱效应”是高楼火灾时特有的，是燃烧产物（包括烟气）快速向上窜的现象。热烟和毒气的流动速度为3—5米／秒，这是由于建筑物内外空气温度的不同，造成密度差异，使建筑物内受热烟气产生一种被加速往上拉升的现象。高楼内部的楼梯间、电梯间、通讯管道及电源系统管道等都会发生“烟囱效应”。楼的高度愈高，火灾时内外温差愈大，越易产生“烟囱效应”，加速火灾纵向蔓延，增加了受灾和抢险人员的生命危险。“烟囱效应”给救人救生带来了诸多困难。高层建筑火灾中容易造成众多人员伤亡，这是一个重要原因。高层建筑火灾时的“烟囱效应”…     

高层建筑自然通风对内部竖向压差分布的影响

为了研究应用窗式通风器进行高层建筑自然通风时建筑内部的竖向压差分布,对一栋高层办公建筑窗式通风器开启和关闭的工况进行了垂直热压分布实地测量。研究发现:大楼开启窗式通风器进行自然通风后,在"烟囱效应"影响最大的首层位置,开启自然通风后,热压绝对值增大,对电梯门开启影响加大;而在"烟囱效应"影响仅次于首层的地下车库位置,热压值减小,"烟囱效应"得到缓解,开启自然通风未对高层部分的压差分布起到较大影响。研究结果能为高层建筑利用自然通风进行节能过程中如何缓解"烟囱效应"以保证首层电梯安全提供参考。     

烟囱效应在生态建筑中的应用

该文介绍了生态建筑中自然通风的重要性,阐述了生态建筑中通常采用的烟囱效应的四种方式：热压作用下的烟囱效应;风压作用下的烟囱效应;风压、热压同时作用的烟囱效应;机械辅助的烟囱效应。以具体的实例说明四种方式的设计和应用,对人们进行生态建筑设计给予启迪和参考。     

高层建筑火灾中电梯竖井烟气流动特性的模拟研究

高层建筑中诸多竖井,比如楼梯间、电梯竖井,是建筑火灾中烟气竖向蔓延的主要通道。在烟囱效应的作用下,若高层建筑竖井设计合理,利用电梯竖井进行自然排烟具有一定的可行性。本文利用正交实验的方法对"典型建筑"在"标准火源"条件下的烟气流动特性进行场-网模拟,电梯竖井作为场区域,其它空间作为网络区域,采用CONTAM软件实现了两区域之间的耦合计算。模拟计算得到了竖井顶部开口面积、各楼层送风量、电梯门密封性以及不同着火楼层对电梯竖井内烟气流动的影响。计算结果表明,竖井顶部开口面积对自然排烟量与中和面位置影响程度均最大。     

寒区高层建筑设计减少渗风能耗有效措施

分析了建筑内部隔断对渗风能耗的影响，指出在多层建筑与高层建筑设计中，如果采取封闭楼梯间或封闭前室等措施，切断建筑内渗透空气流动的竖向通道就能有效地抑制热压的作用，使建筑渗风耗能量显着减少。在本文列举的七层办公楼实例中，当采用封闭楼梯间时，建筑外窗的渗风耗能量仅为开敞型建筑的８２％，节能率达９１８％；当楼梯间与前室同时封闭时，渗风耗能量节省了９４８％。     

热压及室外风压对高层建筑楼梯间加压送风系统影响的网络模拟分析

以两幢高度不同的高层建筑为例,利用网络模拟软件CONTAM3.0模拟分析了热压及室外风压单独作用和二者耦合作用对楼梯间加压送风效果的影响。结果显示:建筑高度、建筑内外温差、室外风的风向和风速都会影响楼梯间加压送风效果;由建筑内外温差产生的热压作用会导致楼梯间压力重新分布,冬季的热压作用极可能导致楼梯间的压力小于安全阈值,使加压送风系统失效;当热压和室外风压耦合作用时,最不利情况是夏季建筑上部迎风面房间着火和冬季建筑下部迎风面房间着火,这两种情况下着火层前室门处的压差均降至6Pa左右,远低于规范规定的25Pa,导致楼梯间加压送风系统失效。     

风对高层建筑空气渗透的总体效应

探讨单纯热压作用和风压与热压联合作用两种情况下高层建筑总渗风量之间的关系，由此得出风对高层建筑空气渗透的总体效应。     

高层建筑空调讲座之（7）高层建筑空调设计

高层建筑空调讲座之（７）高层建筑空调设计同济大学钱以明第六讲高层建筑防排烟６．１概述高层建筑功能复杂，着火源和可燃物多，一旦发生火灾，由于楼梯间、电梯井、管道井等竖向管井的烟囱效应和风力的影响，将使火势迅速蔓延，容易造成大的损失和伤亡事故。为使因火灾...     

Investigation of indoor air pollutant dispersion and cross-contamination around a typical high-rise residential building: Wind tunnel tests

The dispersion of air pollutant in complex building environment has become of great concern as more and more people live in large and crowded cities. The present work is aimed at investigating the indoor air pollutant dispersion and possible cross-unit contamination with typical high-rise residential building design in Hong Kong. Experiments were performed in a boundary layer wind tunnel for a 1:30 scale model that represented a 10-story residential building in prototype. Tracer gas, simulating exhausted room air, was continuously released from three different floor levels, and its concentrations on the adjacent and opposite envelope surfaces were measured using fast flame ionization detectors, while the pressure distributions along building facade were also measured and examined under a typical incoming wind profile. By analyzing the pressure and concentration distribution, the risk of air cross-contamination was evaluated under two wind directions. The experiment results illustrated that, in the so-called re-entrance spaces, the pollutant can spread in both vertical directions, not only in the upward direction that was found under buoyancy effect, but also in the downward direction. Furthermore, dispersion can also occur in the horizontal direction, indicating a potential risk of cross-contamination in the horizontal adjacent flats could not be overlooked as well. The study on this physical process is directly useful for the purpose of prevention and control of infectious diseases outbreak in the residential environment. In the long run, the wind tunnel test data will serve to develop computational tools to assist natural ventilation design for high-rise buildings.     

The optimum azimuth for a solar chimney in hot climates

In a solar-heated chimney, used to promote air movement within a building, stored heat is the main source for warming air within the chimney. This creates a buoyancy pressure which draws air through the building. It is therefore important to study the effect of the orientation upon the amount of heat that can be collected by the chimney for better performance. A theoretical study was conducted using a finite difference technique which showed that the amount of heat that can be collected by a solar chimney is strongly dependent upon its azimuth.     

防烟空气幕二维数学模型

通过分析高层建筑火灾时引起烟气流动的因素 ,建立了烟气流动的二维流场数学模型 ,运用流函数的叠加原理 ,在实验研究的基础上 ,推导了高层建筑火灾时防烟空气幕流量、吹风口宽度和吹风口的射流速度的计算模型     

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。     

高层写字楼火灾混合疏散策略研究

选取某高层写字楼进行实例研究,利用PyroSim进行火灾模拟,计算25层走廊着火时的可用安全疏散时间,运用Pathfinder建立人员紧急疏散模型,分析混合疏散策略对疏散效率的影响。结果表明：相比温度、CO体积分数,能见度到达人员安全疏散界限的时间更短。25层走廊着火时,最不利条件下着火层可用安全疏散时间为319.1 s。楼梯疏散、楼梯电梯混合疏散所需安全疏散时间分别为526.3、427.9 s,均不满足安全疏散条件。楼梯、电梯及避难层混合疏散所需安全疏散时间为294.2 s。楼梯、楼梯电梯混合疏散整栋楼分别用时2 618、2 289 s。楼梯、电梯与避难层混合疏散整栋楼用时1 796 s。因此,高层建筑火灾时,楼梯、电梯与避难层混合疏散效率更高,更安全。研究结果为制定高层写字楼火灾应急疏散预案提供依据。     

任意排列两方形断面高层建筑风致干扰机理研究

风致干扰效应是高层建筑群抗风设计中的常见难点问题之一。采用刚性模型测压试验,研究了均匀层流和两种大气边界层风场条件下任意排列两方形断面高层建筑的风致干扰效应,通过平均和脉动基底弯矩系数的干扰因子、风力系数、风压系数分布以及风荷载功率谱的研究,解释了其风致干扰效应的机理。结果表明,任意排列的两方形断面高层建筑风致干扰中,至少存在横风向静力干扰、顺风向静力干扰和横风向动力干扰三个值得注意的干扰区域。 窄道形成的加速效应使受扰结构上形成指向施扰建筑横风向平均吸力和阻塞形成的受扰建筑的横风向平均推力;遮挡效应使得受扰建筑承受指向位于上游的施扰建筑的顺风向风力;漩涡叠加增强位于尾流区受扰建筑上的横风向脉动荷载。不同风场的试验结果表明,提高来流的紊流度有助于减弱上述干扰效应。     

基于风洞试验的高层建筑钢结构风致加速度研究

对钢结构高层建筑群中的典型狭长形建筑进行了表面风压的风洞模型试验,分别考虑了建筑为单体和群体的情况。利用试验获得的风荷载时程对该高层结构进行风振响应的动力时程分析,并着重对得到的与风致舒适度关联的加速度响应进行分析和讨论,对比群体效应对顺风向、横风向和扭转向峰值加速度的不同影响。结果表明,对于平面为狭长形的住宅钢结构高层建筑,扭转效应引起的风致峰值加速度不容忽略;而群体效应一般对结构的加速度呈增大趋势,而且对横风向及扭转向的增大程度通常大于对顺风向的程度。     

Experimental and numerical studies of flows through and within high-rise building arrays and their link to ventilation strategy

Urban ventilation implies that wind from rural areas may supply relatively clean air into urban canopies and distribute rural air within them to help air exchange and pollutant dilution. This paper experimentally and numerically studied such flows through high-rise square building arrays as the approaching rural wind is parallel to the main streets. The street aspect ratio (building height/street width, H/W) is from 2 to 5.3 and the building area (or packing) density (λ_p) is 0.25 or 0.4. Wind speed is found to decrease quickly through high-rise building arrays. For neighbourhood-scale building arrays (1-2 km at full scale), the velocity may stop decreasing near leeward street entries due to vertical downward mixing induced by the wake. Strong shear layer exists near canopy roof levels producing three-dimensional (3D) vortexes in the secondary streets and considerable air exchanges across the boundaries with their surroundings. Building height variations may destroy or deviate 3D canyon vortexes and induced downward mean flow in front of taller buildings and upward flow behind taller buildings. With a power-law approaching wind profile, taller building arrays capture more rural air and experience a stronger wind within the urban canopy if the total street length is effectively limited. Wider streets (or smaller λ_p), and suitable arrangements of building height variations may be good choices to improve the ventilation in high-rise urban areas.     

A study of natural ventilation in a refuge floor

Under the Building Codes of Hong Kong Special Administration Region, the provision of refuge floors has been an indispensable element in high-rise building design since 1996. Wind-induced cross natural ventilation is an important design criterion of a refuge floor since it helps to prevent any smoke entering to become persistent state remained (logging) on the refuge floor. This paper reports a study of refuge floor natural ventilation induced by wind flow around a high-rise building with a refuge floor arriving from different wind incidence angles. The study is based on CFD simulations which are validated by wind tunnel measurements. The refuge floor under investigation has a main services core at the centre and support walls flush with the building walls along two opposite sides. The results reveal that at all wind angles, wind is able to enter the refuge space from the windward side and escape from the leeward side. At some wind angles, wind is found to re-enter the refuge space from the leeward opening and accumulate behind the main services core. Based on the results, we suggest that stairs connecting to the refuge space should be located inside the side corridors formed by the internal and external side walls.     

The fluid mechanics of natural ventilation—displacement ventilation by buoyancy-driven flows assisted by wind

This paper describes the fluid mechanics of natural ventilation by the combined effects of buoyancy and wind. Attention is restricted to transient draining flows in a space containing buoyant fluid, when the wind and buoyancy forces reinforce one another. The flows have been studied theoretically and the results compared with small-scale laboratory experiments. Connections between the enclosure and the surrounding fluid are with high-level and low-level openings on both windward and leeward faces. Dense fluid enters through windward openings at low levels and displaces the lighter fluid within the enclosure through high-level, leeward openings. A strong, stable stratification develops in this case and a displacement flow is maintained for a range of Froude numbers. The rate at which the enclosure drains increases as the wind-induced pressure drop between the inlet and outlet is increased and as the density difference between the exterior and interior environment is increased. A major result of this work is the identification of the form of the nonlinear relationship between the buoyancy and wind effects. It is shown that there is a Pythagorean relationship between the combined buoyancy and wind-driven velocity and the velocities which are produced by buoyancy and wind forces acting in isolation. This study has particular relevance to understanding and predicting the air flow in a building which is night cooled by natural ventilation, and to the flushing of gas from a building after a leak.