某船舶涂装厂房两种通风方式的通风效果

为了探讨某船舶涂装厂两种通风方式(上送下回和侧送侧回)的通风效果,设计了不同换气次数下的模拟案例。以瞬时捕集效率、平均污染物浓度和排污效率为评价指标。结果表明,换气次数越大,瞬时捕集效率越高,且捕集效率达到稳定的时间越早。随着换气次数的增加,平均污染物浓度会减小,但是换气次数的增加量和平均污染物浓度的减小量不是线性关系。总体来说侧送侧回的通风效果优于上送下回。     

关于地下车库的通风设计

本文分析了汽车污染物的危害及散发有害物的四个来源，提出了地下车库污染物的计算式，介绍了稀释污染物所需要的排风量计算方法；分析并指出间歇通风方法可满足车库洋稳定通风状态的有害物浓度要求，最后分析了气流组织形式及系统运行和控制方法。     

控制室内建材散发挥发性有机物浓度分布的空调系统提前开启时间研究

提前开启通风或空调系统可保证室内空气品质或温度在人员进入室内时达到可接受的水平。基于污染源可及性和数值模拟,分别研究了等温和非等温通风条件下污染物浓度分布达到稳定所需的时间与提前开启时间。结果显示:在等温通风条件下,当换气次数为1h-1时,8种典型通风方式下污染源可及性达到稳定的时间为6~16h;在非等温通风条件下,空调系统提前开启时间可由污染物浓度分布达到稳定的时间来决定;而在较高的换气次数(≥4h-1)下,空调环境室内平均温度和呼吸区挥发性有机物(VOC)平均浓度达到稳定所需的时间接近,为1~3h,为控制污染物浓度分布设计的空调通风系统提前开启时间仍可根据为加热或冷却房间空气温度设计的提前开启时间来确定。     

特大型圆筒式尾水调压室穹顶施工通风技术

施工通风是影响地下洞室开挖施工安全和设备效率的重要因素。白鹤滩水电站特大型圆筒式尾水调压室规模大,埋深深,无通风竖井,穹顶施工通风十分困难。为确定穹顶施工通风关键因素,制定针对性的通风方案,采用流体数值软件构建了地下洞室三维非稳态湍流模型,分析了压入、压出和混合式通风的特点,提出了一套适用于穹顶施工期的高效循环置换通风技术;研究了穹顶开挖爆破污染物时空分布特点和逸散规律,并进行了现场污染物测试。数值计算和测试结果证明:洞室群内气流组织顺畅,污染物能及时排至排风洞内,通风10 min后污染物浓度可达到规范要求,循环置换通风技术高效可行。     

组合通风在住宅中的数值研究和分析

本文基于雷诺平均的n-s方程和RNG的k-着方程,采用数值模拟方法,分别对同一住宅在单独运行空调系统时与组合通风和空调系统联合运行时的室内空气质量进行了研究。研究结果表明,空调系统与组合通风系统联合运行对降低室内污染物浓度,提高室内空气质量具有较好的效果。     

置换通风的原理及应用

在过去的十多年中，置换通风系统在北欧国家得到了大量应用并显示出极大的优势。本文介绍了置换通风的原理及其在工业民用建筑中的应用实例，用通风效率、换气效率和热舒适性指标比较了置换通风与混合式通风的优缺点，最后指出置换通风系统在控制污染物、改善空气品质方面极强的生命力。     

排除人员活动区内人体释放污染物的有效通风方式--置换通风

分析了置换通风和混合通风的原理。基于气流分布特性和双层模型理论，比较了这两种通风方式的排污能力。对办公室、会议室及体育馆置换通风系统的通风效率进行了实测。结合人体释放污染物的气流运动特性，指出以排除人员活动区内人体释放污染物为目的时，置换通风较混合通风更为有效。     

严寒地区住宅冬季置换通风测试分析

为研究严寒地区住宅冬季有组织通风效果,对哈尔滨市某住宅小区的通风系统进行了现场实测。通过测试数据分析结果表明:采用置换通风方式时,室内空气温度能够满足采暖热舒适度要求;室内空气品质达到标准规定;该通风系统的通风效率较高,能够有效地排除室内污染物,同时可减少新风量需求,降低空气的处理、输送能耗。     

地下车库污染物浓度的数值模拟

本文主要结合某地下车库通风系统某一天的实测数据，根据地下车库室内环境的特殊性建立数学模型，介绍采用计算流体力学软件Fluent对地下车库通风时的气流组织作数值模拟，对CO浓度场作进一步的模拟计算，并和实测数据进行对比，发现数值模拟所得结果和该地下车库的实测数据较为吻合，从而说明本文提出的用CFD方法来模拟地下车库空间内污染物平均浓度的正确性，为预测地下车库空间内污染物平均浓度，实现通风系统的实时控制提供了一种较为简便、形象的方法。     

复合空调室内气态污染物对流输运模拟

利用CFD数值模拟方法分析了复合窗式空调系统对建筑室内气态污染物输运过程的影响.采用雷诺应力模型(RSM)描述了室内空气和污染物对流输运过程,并详细探讨了复合窗式空调系统的送风速度、新风比、净化效率和室内热源强度等对室内气态污染物对流输运过程的影响.计算结果表明,提高送风速度、新风比以及净化效率都能有效降低室内气态污染物平均浓度.值得注意的是,当送风速度超过0.75 m/s后,室内气态污染物浓度水平维持恒定;空调系统即使按全新风模式运行,也不能彻底排除室内污染物.     

Influence of the floor-based obstructions on contaminant removal efficiency and effectiveness

Dimensioning of dilution ventilation is often made using the perfect mixing approximation, assuming uniform contaminant concentration throughout the room space. However, the contaminant removal efficiency and effectiveness of air conditioning system should be accounted for during design. The effectiveness is in this context used as a measure of the contaminant distribution uniformity within the occupied zone. Influence of an occupied zone obstruction level, air distribution method, air change rate, cooling load and contaminant source non-uniformity on the contaminant removal efficiency and occupied zone contaminant concentration uniformity were studied in scale model. The room air distribution method results in contaminant concentration non-uniformity inside the occupied zone. A method was developed to take this into account during the design of air distribution system. Contaminant supply non-uniformity was found to have great influence on the concentration non-uniformity with two tested air distribution methods.     

通风的有效性与室内空气品质

指出了通风有效性对改善室内空气品质的重要性,比较了不同送风方式的换气与通风效率,分析了通风效率与室内污染度的关系,最后提出了关于如何提高通风效率的建议。     

Comparison of gaseous contaminant diffusion under stratum ventilation and under displacement ventilation

The gaseous contaminant diffusion under stratum ventilation is investigated by numerical method which is validated by experiments carried out. The concentration of gaseous contaminants along the supply air jet is found to be lower than the other parts of the room. Compared with displacement ventilation, the formaldehyde concentration in breathing zone is lower when a contaminant source locates close to the occupant. The concentration is at the same level when the contaminant source locates up-steam to the occupant. The concentration in the occupied zone (<1.9 m from the floor) is also lower when the contaminant source locates on the floor. At supply air temperature optimized for displacement ventilation, the toluene concentration in breathing zone for stratum ventilation is higher than that for displacement ventilation when the area source locates on the four surrounding walls of the room.     

Analysis of visitation frequency through particle tracking method based on LES and model experiment

As ventilation efficiency in a room is not always uniformly distributed, an index for measuring ventilation efficiency at a concerned point or in a concerned local domain is required. Local ventilation efficiency is often represented by the rate of the averaged concentration of the local domain to that of exhausted air from the room. From the age theory of air, it is well known that the averaged concentration in a room corresponds to the mean staying time of contaminant. Evaluating the domain-averaged concentration (Cdomain) means evaluating the average staying time of the contaminant in the domain. It can be only one part of the whole room and can be considered as an occupied zone. Visitation frequency (VF) and the average staying time of the contaminant for one visitation in the local domain (Tp) are introduced to analyze the average staying time of the contaminant in the local domain. The value of VF is strongly affected by the position of the local domain in the room; that is, the position of the local domain in the whole flow field of the room. Tp represents the property of the flow pattern in the local domain. As the indication of VF and Tp represent the mechanism for forming the domain-averaged concentration, they are deeply related to local purging flow rate, which represents the airflow rate for defining the domain-averaged concentration. As VF and Tp are related to the contaminant transportation property, it is effective to analyze them by particle tracking method. A CFD method of large eddy simulation (LES) was thereby carried out in this study. The prediction result by LES is also validated by a precise model experiment. In this paper, the detailed analysis of VF and Tp is carried out on the basis of the particle tracking method utilizing the LES result in order to clarify the mechanism of the domain-averaged concentration. The analyzed room has one supply inlet and one exhaust outlet. A clear re-circulating flow, generated by the forced ventilation, is observed in the room. The value of VF is examined with three types of local domains in the room model. In the room model, VF shows a value of 5.70 when the local domain occupies half of the room. It becomes smaller when the size of the local domain is reduced.     

Vertical profiles of temperature and contaminant concentration in rooms ventilated by displacement with heat loss through room envelopes

The purpose of this study is to examine the effect of heat loss through walls upon the gradients of temperature and contaminant concentration in room with displacement ventilation. It is known that conduction heat loss is governed by outside temperature, heat load inside the room, supply air temperature and overall heat transfer coefficient of walls. Experiments were conducted to measure the temperature gradient and the ventilation efficiency in the room ventilated by displacement ventilation with various combinations of heat load and temperature difference between supply air and outside air. In order to simulate the change of seasons, the supply air temperature was changed instead of the outside air temperature. The effect of supply air temperature and heat generation inside the room on the temperature gradient and the concentration of tracer gas were investigated through the experiments. As a result, it turned out that the higher the heat generation rate and the lower the supply temperature, the stronger the temperature stratification and the lower the concentration in the lower zone. Additionally, ventilation heat loss turned out to be a good index for assessing the concentration in the lower zone. Temperature differences of around 3 degrees C between supply air temperature and exhaust temperature are at least needed for displacement ventilation under the conditions of the experiment presented in this paper.     

Concentration Distribution in the Centre Plane of a Ventilated Room Under Isothermal Conditions

This paper presents a series of fill-scale measurements of the concentration distribution in the centre plane of a room with isothermaI mixing ventilation. Vertical projiles of the concentration in the middle of the room have been measured under different conditions. With the contamination source in the middle of the room the vertical profiles were changed radically with an increase of the air change rate from n = 1.5h^?1 to n = 6h^?1 due to a change in the flow structure in the room. With a constant air change rate, the location of the contamination source in the room showed a great influence on the vertical profile. A high velocity around the contamination source resulted in a uniform contaminant distribution in the room, while a low velocity resulted in considerable differences. Contours of concentration in the centre plane of the room have been measured using different contaminant densities. The densities were low, neutral and high in relation to the density of air. The results showed that the contaminant distribution in the room with the chosen flow conditions depended strongly on the contaminant density, and that the high density case gave the highest concentrations in the occupied zone.     

The effect of source motion on contaminant distribution in the cleanrooms

In the recent decades, cleanrooms have found growing applications in broad range of industries such as pharmacy and microelectronics. Concerns about negative effects of the contaminant exposure on the human health and product quality motivate many researchers towards understanding of the airflow and contaminant distribution though these environments. With an improvement in computational capacity of the computers, computational fluid dynamics (CFD) technique has become a powerful tool to study the engineering problems including indoor air quality (IAQ). In this research, indoor airflow in a full-scale cleanroom is investigated numerically using Eulerian-Eulerian approach. To evaluate the ventilation system effectiveness, a new index, called final efficiency, is introduced which takes all aspects of the problem into account. The results show that the contaminant source motion and its path have a great influence on the contaminant dispersion through the room. Based on the results, the contaminant distribution indexes, e.g. final efficiency and spreading radius, are improved when the source motion path is in the dominant direction of the ventilation airflow. Consequently, the efficiency of an air distribution system which provides a directional airflow pattern shows the least source path dependency. This study and its results may be useful to gain better understanding of the source motion effects on the indoor air quality (IAQ) and to design more effective ventilation systems.     

Distribution of exhaled contaminants and personal exposure in a room using three different air distribution strategies

The level of exposure to human exhaled contaminants in a room depends not only on the air distribution system but also on people's different positions, the distance between them, people's activity level and height, direction of exhalation, and the surrounding temperature and temperature gradient. Human exhalation is studied in detail for different distribution systems: displacement and mixing ventilation as well as a system without mechanical ventilation. Two thermal manikins breathing through the mouth are used to simulate the exposure to human exhaled contaminants. The position and distance between the manikins are changed to study the influence on the level of exposure. The results show that the air exhaled by a manikin flows a longer distance with a higher concentration in case of displacement ventilation than in the other two cases, indicating a significant exposure to the contaminants for one person positioned in front of another. However, in all three cases, the exhalation flow of the source penetrates the thermal plume, causing an increase in the concentration of contaminants in front of the target person. The results are significantly dependent on the distance and position between the two manikins in all three cases. PRACTICAL IMPLICATIONS: Indoor environments are susceptible to contaminant exposure, as contaminants can easily spread in the air. Human breathing is one of the most important biological contaminant sources, as the exhaled air can contain different pathogens such as viruses and bacteria. This paper addresses the human exhalation flow and its behavior in connection with different ventilation strategies, as well as the interaction between two people in a room. This is a key factor for studying the airborne infection risk when the room is occupied by several persons. The paper only takes into account the airborne part of the infection risk.     

空气传播的生化袭击与建筑环境安全(5):有效因子——以人为本的通风效果评价新指标

为了合理评价突发事件中的通风效果,从以人为本的角度提出了有效因子概念。定义了污染源有效因子EFCS和送风有效因子EFSA两个系列指标,每个系列均包括3个指标。EFCS和EFSA分别用于度量任意时段内污染源和送风对室内人员的影响。通过三维房间的算例,说明了指标的特点和应用。结果表明,系列指标能定量地反映任意时段内室内污染源和送风对人员的影响,可用于指导突发事件中应急通风和疏散策略的制定。