ASHRAE美国采暖、制冷与空调工程师学会汉语版

ASHRAE美国采暖、制冷与空调 工程 路基工程安全技术交底工程项目施工成本控制工程量增项单年度零星工程技术标正投影法基本原理 师学会汉语版 相关的商业资源 29 通风设计原则..................................................................... 29.1 一般舒适性与稀释通风...................................................... 29.2 ............................................ ................................ 29.4 加热控制 节能与回收............................ ... ... ....................................29.6 工业环境需要通风以降低在工作场所中生成的余热和污染物；在某些的情况下可能还需要制冷。通 风主要用于控制余热、气味以及有害的颗粒物和化学污染物，在某些情况下，当积累超过它们的允许可 燃下限时就会自燃或燃烧，它们会影响工人健康和安全。通过使用局部引风系统可以尽可能最好的控制 余热和污染物。局部引风系统把热和污染物从热源和污染物源抽出，需要比一般 (稀释) 通风更低的气 流量。更多的信息请参阅第30章。 全面通风可通过机械（风扇）系统或自然通风系统实现，或由两者相结合。组合系统包括机械驱动 和机械引风，带空气减压阀的机械驱动(风扇驱动) 通过天窗或其他类型的通风孔来供应空气，机械引风带换气天窗进口或换气门。 机械 (风扇驱动) 送风系统提供最佳的控制和最舒适、最一致的环境，尤其是在本地的气候条件有 异常时。该系统通常由一个入口部分、过滤器、加热和/或冷却设备、风扇、管道和空气分散器组成，空气分散器用来把空气分散到各工作场合。在一般的引风系统中，当空气清洁或自由悬挂得过滤装置中 没有有毒气体或蒸气时，可以通过回风管实现空气再循环。空气循环可降低加热和冷却的成本。 一个全面排气系统，通常包括一个或多个风扇，多个入口、管道和一个空气滤清器或过滤器，它能 消除气体、蒸汽或局部排气不能捕捉的粒子引起的污染。空气通过过滤器后，可以排到外面或部分循环 到建筑场所。空气过滤系统的清洁效率应符合环保规定，它取决于诸如建筑位置、大气中的污染物浓度、 污染物的种类、建筑物废气排放的高度和速度这些因素。 很多工业通风系统必须能同时处理排放的热和有害物质。在这种情况下，一个由局部引风，全面送 风、全面引风系统的组合可以提供所需的通风。通风工程师必须仔细分析送风和引风要求来确定不利的 工况。例如，送风排气罩可能不足以控制热暴露。考虑季节气候对通风系统尤其是对自然通风系统的性 能的影响是很重要的。 工业卫生员或工业卫生工程师必须查阅相应的规管 标准 excel标准偏差excel标准偏差函数exl标准差函数国标检验抽样标准表免费下载红头文件格式标准下载 与准则，确定可接受的化学污染物和热暴露 水平。大多数的化学和热暴露标准级别是在工作日内时间保持平衡的允许超过上限区间和下限制区间的 加权平均值。但是，热和污染物暴露级别标准不是安全与不安全暴露的分界线，而是几乎所有的工人可 能会天天接触而无不良影响的条件。由于一小部分工人承受的最大暴露水平可能会低于标准水平，此时 设计的暴露水平低于暴露界限是很明智的。 在暴露于有毒化学品的情况下， 污染物源的数量、 衍生率和排气罩的排效果可能是未知的。因此， 通风工程师在设计有毒污染控制时必须依靠常用工业通风卫生经验，工业卫生员、工艺工程师和通风工 程师之间的密切合作是必需的。 在暴露于易燃或可燃化学品的情况下，为了防止可能发生的生命危险或重大伤害，必须仔细考虑污 染源的比重、浓度，空间内所有电器设备以及任何余热源和点的额定值。如使用有毒化学物质时，就需 要知识专家包括电气的工程师的的合作。 本章介绍了通风实践的原则，以及在工业环境中包括对卫生的其他信息。英国职业卫生协会 (1987)和国家安全委员会 (2002 年) ，美国国家职业安全及健康研究所 (NIOSH 2005) 与卫生和人类服务部（1986）的出版书都进一步提供了工业卫生原则及其应用的 资料 新概念英语资料下载李居明饿命改运学pdf成本会计期末资料社会工作导论资料工程结算所需资料清单 。 全面送风或引风用来提供用来散热、稀释污染物到健康水平和更新排气的空气，可通过自然或机械 送风和引风来实现通风。工业区必须符合美国国家标准协会 / 美国采暖、制冷与空调工程师学会标 准62.1-2004和其他标准要求[如，美国防火协会标准（NFPA）]。如果室外空气含有任何污染物浓度在美国国家标准协会 / 美国采暖、制冷与空调工程师学会标准62.1给出以上的对于通风是不能接受的。如果空气包含的污染物没有在标准中列出，可接受的暴露水平应依据美国职业安全与健康局/职 业安全与健康法案标准（美国政府及工业卫生协会标准2006 a）获得。全面的通风量必须足够高，以 便稀释居民产生的二氧化碳。对于复杂工业通风的问题，除了现场试验，还通常用相似实验模型与计算 流体动力学 （CFD） 模型。 为安全、有效的生产，工厂需要补风用来更换大量的废气，为工作人员提供舒适、安全环境以及 过程操作的合格状况。补风，持续提供良好的空气分布，适合在夏季高效率的降温和冬季高效率加热。 安装窗户或其他入口由于不能在暴风雨天起作用是很让人丧气的。补风设计一些要考虑因素包括以下内 容： ?局部和全面引风系统或处理设备补风必须足以补充排出的空气或燃烧过程的消耗（请参阅第 30 章）。（大型空气压缩机可能会消耗大量的空气，应考虑空气是否来自该建筑物内。） ?补风系统应通过正确安排送风口的设计来消除不舒服的交叉通风，防止通过门、窗口和类似开口 的入渗，它可能导致排气罩不安全或不能正常工作、破坏环境控制、引起或挑起灰尘、或通过冷却或干 扰对进程产生负面影响。设计工程师需要考虑侧面通风和靠近局部排气罩的工作区域内空气流动的其他 来源。卡普兰和克努森（1977年，1978年）发现，在实验室空气罩前的气流可以逃离空气罩进入工作 人员的呼吸区域导致污染物。在工业应用中，通常可以看到在空气罩的前面大功率风扇向工人输送空气， 这可能导致局部排气罩不能正常工作的状态，以至于不能为工人提供任何保护。 ?补风应从最干净的风源获得，供风可以被过滤而渗透风却不能。更多传输空气的应用请参阅美 国国家标准协会 / 美国采暖、制冷与空调工程师学会标准62.1。 ?对于被有毒，易燃，可燃或化学品污染的空间，补风可能要通过严格封闭的管网从一个已知不 受任何污染的区域获得，并提供给它足够速率和压力 (1) 以能够用来排除所有的污染和(2) 防止从周围地区或邻近的区域渗透的类似污染物。 ?补风应该用于控制建筑物的压力和气流，（1)以避免正压或负压导致的开门的困难或不安全、(2) 减少通风量以及 (3) 防止渗透。 ?补风应该用来隔离污染物，减少其浓度，控制其温度、湿度和气流流动。 ?补风系统应该被设计用作于回收热量和节省能源（请参见节能与回收部分）。 美国政府及工业卫生协会标准(2006b) 提供关于从建筑物中的特定负压级别可能会导致不利的条 件的信息。 通风房间内良好的空气扩散和适当的空调数量，是创建一个合格的的工作环境、移除污垢和减少 通风系统的初始和运行成本的必要条件。通风系统必须提供合适的送风速度和温度空气使污染物浓度在 允许的范围内。在大多数的情况下，通风目标是提供带有很小误差的 (可接受的) 工作条件，而不是舒适性的（最佳的）条件。 全面通风系统的设计是基于局部排气通风、辐射屏蔽和已选定的保温及密闭设备的假设来将工作 场所中的热负荷和污染（见工业工作区热控制部分）减到最小。在寒冷的气候中，通过维护结构的渗透 和热损失，可以通过加厚建筑物将其最大程度减到最小。稀释通风的更多信息请参阅美国政府及工业卫 生协会标准(2006b)。 必须提供足够的空气来更换工艺通风和局部排出的空气，以用来稀释局部排气不能捕捉的污染物 （气体、蒸气或空气中的颗粒）和提供所需的热环境。供气量应该是温度控制、稀释和换气所需要的风 量的最大者。 可以通过自然或机械通风系统对工业场所送风。尽管自然通风系统是用重力和/或风力效果驱动，但仍然广泛应用在工业领域（尤其是在冷热交替的气候前提下)，但是，在大型建筑物中自然通风系统 效率是很低的，它可能造成穿堂风，还可能因为没有采用实际有效的过滤方法而不能解决空气污染问题。 因此，工业领域中的大多数通风系统不是机械送风（风扇驱动）就是机械送风和自然排风相结合，自然 排风利用百叶通风窗或门进行空气减压（或排气系统的换气）。 最常用的对工业厂房的送气方法是混合送风、置换送风和局部送风。 在混合系统中，送风速度通常远远超过工作场所所能接受的速度，送风温度根据加热/冷却负荷可以高于、低于或等于工作场所的空气温度。送风射流与室内空气混合的夹带扩散，降低了空气流速和空 气温度平衡。工作场所的通风不是直接通过喷射器的空气射流或反向射流。正确选择和设计混合气流分 布使得在工作场所和在房间高度上的空气流速、温度、湿度和空气质量状况相对的均匀分布。 调节的空气以较低的速度大约0.5 m/s 或更小从出风口送出，其温度应比工作场所目标房间的空气 温度稍低。由于浮力，较冷的空气沿地板扩散进而充满房间较低的区域，接近热源的空气被加热作为一 对流上升气流向上运动，而在上层，热气流沿着天花板蔓延。中下区的高度取决于供给工作场所的送风 风量和温度以及控制对流传热热源的数量。 通常，出口放置在地板或贴近地板的位置，送风直接被引入工作场所。在某些应用中（如，在机 房或或温暖的工业建筑)，可以通过夹层地板向工作场所供应空气。排气或回气位于或接近天花板或屋 顶上。 置换通风常见于北欧并在欧洲其他国家越来越受欢迎。当被释放的污染物伴有余热，污染空气的 温度高于 (或浮力大于) 环境空气，置换通风是一种选择。置换空气分布系统的更多信息可以在 Goodfellow 和 Tahti （2001 年）里找。 空气被局部地提供给工作场所或几个固定的工作区 （图 1）。调节的空气被直接供应到工作场所 的呼吸区域，以提供舒适性的工作环境和减小污染物的浓度。这些区域的空气可能比周围空气高5至10倍的洁净。在局部通风系统中，送风通过下列设备之一： ?专门设计的低速/低湍流喷嘴或格栅 (例如，用于局部冷却)设备。 ?悬挂在垂直淋浴导管上位置靠近工作站的多孔板。 1 Fig. 1 Localized Ventilation Systems 在工作领域中炎热热的作业场所很少，在整个工作空间中保持一个舒适的环境很可能是不现实和能 源效率低下的。所以，空调、单独冷却和局部冷却可以提高工作场所的工作条件。空调房间可提供热舒 适性，监测生产和制造过程的控制室可以使用这种技术。 局部冷却可通过辐射（更改平均辐射温度）或通过对流（改变风速和/或送风温度）或两者兼而有之提供冷量，它可能是改善热环境最受欢迎的方法。局部冷却设备被固定在工作站，而单独冷却却需要 工人穿着冷却设备。 在工业设施中，更衣室、卫生间和浴室的通风是很重要的，用来清除气味和降低湿度。一些的行业 中，足够的工作室污染的控制要求从饮食和呼吸两方面来预防。所以，在衣帽间、更衣室、淋浴室、餐 厅和休息室就需要足够的卫生设施包括适当的通风。国家和地方法规，应尽早提供这方面的设计咨询。 送风可能会通过门或墙格栅。在某些的情况下，工厂空气可能因为受污染以至于需要过滤器或 (最 好是) 机械通气。当对工作室污染物的控制不足或不可行时，应通过加压送风尽量减少更衣室、餐厅和 休息室的污染的水平，来减少员工暴露。 当使用机械通风时，供风系统应该有足够的管道和空气分流的设备如分流器或格栅，把空气分散到 所有区域。 在更衣室，废气大部分是从卫生间和淋浴室的排出，其余部分从储物柜和房间的天花板排出。美 国采暖、制冷与空调工程师学会标准 62.1 提供这方面的要求。 屋顶通风设备是热排气口位于一座建筑物的高位置，并应妥善防风雨（Goodfellow1985）。对于重力(浮力) 驱动的连续与圆形的通风设备的运行，拔风作用和气流诱导器就是它的原动力。圆形通风设 备可配备风扇圆筒和电机，允许自然或机械通风运行。 许多通风设备的设计都可用，包括百叶窗式通风器，它带有一个雨罩的折叠风扇和一个分立式蝴蝶 档板，蝴蝶档板它可以浮动开排放空气并通过一个平衡锤关闭，两者都使用最小罩壳并具有很小甚至没 有阻尼容量。分立式蝴蝶气流调节器有增加风扇噪音的趋势，并且在强气流条件时会随着猛然关闭而损 坏。因为噪音往往是电力驱动的屋顶通风设备中常见的问题，所以制造商的噪声等级应予重新考虑。应 安装消声器，以满足设计所需的噪声等级。 连续通风控制器最有效地移除大量的集中热负荷。一种类型，流线型连续通风器效率高、防风雨， 旨在阻止回流；它通常带有调节风门，冬天可以关闭来节约建筑耗能，它的功率仅受有效的屋顶面积和 低进气口适当的位置与尺寸的限制。为了得到一个高于环境空气（全国消防保护协会定义的压力）的轻 微压力，连续通风也可用来降低或消除封闭空间电的的等级。通常，通过美国防火协会标准 496 的建议，能够得到从1级1区的减少量、1至1级、2区或第2分部的标度。这允许使用通用电气设备替代 2 区或第 2 分部设备或使用 2 区或第 2 分部的电气设备替代1 区或第1部分的设备，这(1) 大大降低了电器设备的成本，并且 (2) 当特定的设备对于较高（较为波动) 电器区域等级不可用时 ，它也提供一种正确的替代 方案 气瓶 现场处置方案 .pdf气瓶 现场处置方案 .doc见习基地管理方案.doc关于群访事件的化解方案建筑工地扬尘治理专项方案下载 。 重力式通风器，也是非常高效的，成本低、不会产生噪音、并能自我调节（增加通风器气流得到高 散热效果）。必须重视和保证通风器正压运行，特别是在供暖季节。否则，外部空气将进入通风器。 接下来，根据除热容量选具有风扇和电机圆形重力或管式通风器、(3) 低柜电动通风器及 (4) 垂直上吹电动通风器。垂直上吹保护罩设计带有有偏转空气向上的而不是向下的外围挡板。垂直排出对于减 少由于热空气包含凝油或溶剂蒸气对屋顶造成的破坏是非常理想的。要避免皮带在困难的场所保持一个 整体，直接连接马达的通风器是可行的。圆形重力通风器适用于轻型热负荷的仓库和制造领域高屋顶及 轻负荷的地方。 流线型连续通风器必须在没有机械动力的情况下正常地运行。为确保通风器的性能，进气必须提供 足够的低位开口；不适当的入口区和大量的空间气流是最常见重力屋顶通风器故障的原因。在一个外墙 入口远离热设备的大建筑物内，可能需要一个向热设备周围的正供风。2005 美国采暖、制冷与空调工程师学会标准手册-基础第 27 章有通风与入渗的其他信息。 机械通风器高于屋顶通风器多消耗的电能可以用其气流稳定的优点来补偿。机械通气还可以为良好 的空气流通建立所需的压力差，并且带有小的进风口。进气口的尺寸应该正确地选择以避免渗透和由于 建筑物内高负压造成的其他问题。通常，一个机械系统以供应足够的清新空气保持工作区处于正压力状 态来判断是否合理。 屋顶通风器由机械操作窗口或机械式电动排气风扇组成。操作辅助窗口或调节风门通常用在高天花 板的商店和利用自然通风向空间通风时。 通风控制经常不足以满足工业工作区热应力的标准。最佳解决方案应包括其他控制如现场冷却、工 作/休息模式的切换和辐射屏蔽的控制。 许多工业过程向环境中释放大量的热量和水分。在这样的环境中，在经济上可行的条件下保持舒适 性是不可能的（美国采暖、制冷与空调工程师学会标准55），尤其是在夏天。舒适的条件不是生理需要：身体必须处在与环境的热平衡中，尽管是发生在远高于舒适区域的温度和湿度状况下。如果是不经常接 触和暂时的人员处在伴有生产过程产生的热量和水分的区域，可以不必提供温和舒适环境。在这种情况 下，为防止过度的生理热应力，唯一可能需要的是通风调节。 工程师必须区分炎热/干燥工业区和温暖/潮湿工况的控制需求。在炎热/干燥地区，可以感受到工序放出不带水分的（主要对流和辐射） 热到空气中。由汗水蒸发的冷量不可能使其大大减少，所以这会 增加接触工人的热负荷。可以保持人体热平衡，但也会时汗水流的过多。炎热/干燥环境多发生在炉膛、锻造、金属挤压和轧制厂、玻璃成型机等周围。 在温暖/潮湿条件下，湿法加工可能会生成大量潜热负载。对于工人，显热负荷的升幅可能是微不 足道的，但水分含量增加的空气可以严重减少排汗降温， 这使温暖/潮湿的条件比炎热/干燥更具有潜 在的危险。我们发现纺织厂、洗衣店、染房和深矿井都是典型的温暖/潮湿作业场所，在矿井中水广泛用于粉尘治理。 工业热负荷也受到当地气候的影响。日照得热量和室外温度的升高增加的工作场所的热负荷，与工 艺生成的热负荷对比，可能是微不足道。室外空气中的水分是一个重要因素，它可以通过限制人体的排 汗蒸发冷却来影响炎热/干燥工作环境。对于温暖/潮湿的状况，因为由室外空气散发的湿度相对于工艺 产生的是微不足道，所以日照得热量和提高室外温度对工业热负荷更为重要。 美国采暖、制冷与空调工程师学会标准55和（ISO）国际标准化组织7730指定了人类的热舒适性条件。 无论是在舒适性条件还是存在热和冷应力下，身体全面热力学状态的评估方法都是基于对人体的热 平衡的分析，正如2005 美国采暖、制冷与空调工程师学会标准手册-基础第8章所讨论的。由于非对称辐射、风速、气温垂直差异、热或冷的表面（地板、机器、工具等）对身体接触造成的局部影响，我 们会发现这样的热环境是不可接受和不能容忍的。 另一个评估环境的潜热应力的热应力指标是湿球黑球温度（WBGT），定义如下： 有日照的户外负荷： WBGTttt,，，0.70.20.1 （1） mwbgdb 室内或没有日照的室外负荷： WBGTtt,，0.70.3 （2） mwbg 这里 t=自然通风湿球温度（没有定义空气流速的范围；饱和温度或焓湿球温度不同 ；），?C mwb t =地球温度（弗农球温度计，直径150毫米），?C g t =干球温度（太阳辐射传感器），?C db (1) 及 (2) 方程中的系数表示组成的温度的分数比重。 不同级别体育活动的热应力的暴露限制如图2所示 (美国国家职业安全与卫生研究所 2005)，它通过一系列湿球黑球温度的为不同级别的工作描绘了允许的工作状态（根据每小时休息时间和工作时 间）。当应用图2的时，假定休息区和工作区拥有相同的湿球黑球温度。曲线表示工人适应热的有效 值。美国采暖、制冷与空调工程师学会标准62.1-2004为不同的运动提供了与图2中相同的新陈代谢速率。参照美国国家职业安全与卫生研究所（2005）为不适应暑热的工作者建议湿球黑球温度限制。 湿球黑球温度指标是热环境评价的国际标准 (ISO标准7243和7730)。湿球黑球温度指标和功率水平应以1小时的平均值来评估；即湿球黑球温度和功率是在1小时连续工作时间或间歇接触时的2 小时的基础上的加权平均数进行测量和估计。虽然湿球黑球温度被美国国家职业安全与卫生研究所推 荐，但是已经不被职业安全及健康管理（OSHA）接受作为法定标准。它通常结合其他方法来确定热 应力。 虽然图 2 对评估热应力暴露的限制很有用，但是，对于控制目标或舒适性评价是受限制的。气 流速度和温湿空气湿球测量值通常需要特殊与恰当的操作，和仅通过间接测量确定湿球黑球温度。其 他有用的工具包括热应力指数（HSI）信息，可以2005 美国采暖、制冷与空调工程师学会标准手册-基础第8章和国际标准化组织标准7243，7730和7933找到。 人与环境的热力学关系由四个独立变量确定： ?气温 ?辐射温度 ?空气中的水分含量 ?空气流速 连同内部热量产生的速率 （代谢率)，这些因素可以结合起来用不同的方法表示不同程度的热应力。 热应力指数通过排汗润湿皮肤的百分数来定义： 图 2 对热水土不服人员热应力暴露限制的推荐标准[改编自美国国家职业安全与卫生研究所（1986 年）] Fig. 2 Recommended Heat Stress Exposure Limits for Heat-Acclimatized Workers [Adapted from NIOSH (1986)] HSIEE,，/100 （3） skmax 这里 2E =从皮肤的蒸发热损失 ， Wm/sk 2E=从皮肤蒸发最大可能的热损失， Wm/max 并结合代谢、辐射得热量（或损失）、对流换热得热量（或损失）、蒸发（出汗）得热量（或损失）的相 对比重。关于使用诸如减少辐射、转变工作/休息模式、局部冷却、冷却背心和西装的热应力的评估和 控制的方法的补充信息，参考美国政府及工业卫生协会标准（2006年b）、概要等（1983年）、综合（1980） 和美国国家职业安全与卫生研究所（2005年）。 从源头控制。通过热绝缘设备、所在区域具有良好通风、在户外覆盖蒸汽水箱，提供直接清理热水 的有盖疏水渠、保持蒸汽可能逃跑的接头和阀门紧固等措施可降低热暴露。 局部排气通风。局部排气通风移除通过热加工工艺和/或工艺设备排放的上升气体产生的热空气，同时从环境空间中移除一部分空气。局部排气系统在第30章进行了详细讨论。 辐射屏蔽。在某些工业，环境的大部分热负荷是热物体及表面如炉膛、烤炉、炉膛烟道和烟囱、锅 炉、熔融金属、热锭、铸件、和锻件的辐射热。由于气温对辐射热流量并没有显著的影响，所以通风对 控制此类暴露的帮助不大。唯一有效的控制就是减少辐射对工人的冲击热量。通过隔热或在辐射源周围 放置辐射屏蔽可降低辐射热暴露。 有效的辐射屏蔽形式如下： ?反射屏蔽。反光材料表或绝缘板临时的连接到热设备或一半移动的地板上。 ?吸收屏蔽（水冷）。这些屏蔽吸收和移除热设备产生的热。 ?透明屏蔽。热反射钢化玻璃板、反光金属链窗帘和密网筛铁丝网屏幕的适当辐射不妨碍设备的热 辐射。 ?柔性屏蔽。铝制纤维能够产生高度的辐射屏蔽。 ?防护服。反射服装如围裙、长手套和提供适当辐射屏蔽面罩。对于极端的辐射暴露，可能需要带 涡管冷却的成套西装。 如果屏蔽是一个很好的反射器，但它仍然在严重辐射热的地方保持相对的凉爽。明亮或光洁度高的 镀锡铁、不锈钢和普通的平的或波纹状的铝板是耐久高效的。箔面的石膏板，虽然较不耐久，但反射很 好。然而，为了提高效率，反射屏蔽物必须保持明亮。当多层使用时，辐射屏蔽更为有效; 它们应该把辐射热反射回到辐射源，然后在那里被局部排气带走。然而，除非屏蔽完全包围主要辐射源源，一些红 外线能量被反射进入到较凉爽的环境，也可能反射到一个工作场所。为保证适当的屏蔽设施，应该去研 究直接辐射热。 现场冷却。如果工作场所位于辐射热源的附近，以至于不能完全通过辐射屏蔽来控制，现场冷却就 派上了用场。现场冷却扩散器制造商的进一步的信息和资料见2005年美国采暖、制冷与空调工程师学 会手册-基础第33章。 由于大的空气容积要求通风工业车间，所以应该实行节约能源和回收措施以得到实质的节约。能 源回收应该包括在一个工厂的初步设计中。在选择能源回收设备时，要确保所选用的材料与所有可能 排出烟雾的相容。用当地标准核实能源回收的可行性。 在某些情况下，它可以向建筑物提供不加热或部分加热的清洁空气。虽然在本部分大多数节能和 回收方法适用于加热，但是冷却系统的节能的可能是相似的。以下是节约能源和回收的一些方法： ?在原始的设计阶段，应提供工艺和设备隔热层和热屏蔽以把热负荷减到最小。可能需要对玻璃区域气 密处理和减少玻璃区域面积。应当对排气罩和工艺的排气要求进行复核使其保持在一个最低安全的实用 性。更多的局部排气系统，见第30章。 ?通过整一年对全面通风系统供风及排气最优化运行进行设计。应该尽可能近的向工作场所提供空气。 再循环的空气应该用于冬天补风，并且应该带给通风厨和工艺未加热或部分加热的空气(美国政府及工业卫生协会标准 2006b)。 ?送风可以通过空气-空气、液体-空气或热气体-空气的热交换器来恢复建筑物或工艺的热量。旋转的、 可再生的能量回收盘管（操作现场）和空气-空气热交换器的更多讨论在2004年美国采暖、制冷与空调工程师学会手册-暖通空调系统及设备第44章。能量回收在美国政府及工业卫生协会标准 (2006b)第7章也被谈论到。 ?经济的操作系统。只要能使补风与通风厨和工艺设备的需求达到平衡，就可以在夜间或周末关闭通风 系统。保持热送风在最低温度和冷送风在最高温度，这与工艺和员工舒适的需要是一致的。保持建筑物 处在压力平衡状态，以使过热状态不需要令人不舒服的引风。 ?一定要测定所有再循环空气中的污染物浓度，以使其没有超出在场所允许的极限。当再循环的空气回 到场地，部分被过滤的回气中污染物含量就增加了已经存在于场地的污染物等级。必须确定浓度的增加 是否在工作人员暴露期间的时间加权平均(TWA)允许的范围内。这个期间通常被假定为一个8小时轮班制，但也可以是任何的暴露期间。 工人呼吸区的时间加权平均（美国政府及工业卫生协会标准2006b） QB(1),KC()(1)()CCCfCCfKC,,,，,，， (4) BGMOMBRBMQA 这里 C=工人呼吸区再循污染物浓度时间加权平均值, ppm B 3Q=无再循环的通风总气流, ms/B 3Q=有再循环的通风总气流, ms/A C=无再循环的空间平均浓度 , ppm G =工人在工作站的时间系数 f C=呼吸区域无再循环工作站污染物浓度的时间加权平均值, ppm O K=有再循环工人呼吸区域系数, 0 ～1.0 B C=再循环空气(在空气过滤器后)排除的污染物浓度, ppm, 或者 R (1)(),,,CKCERM C, (5) R1(1),,,KR =污染物空气净化效率系数 , C= 无再循环的(局部)排气的污染物浓度, ppm E K=再循环空气排除的污染物浓度系数, 0～1.0 R C=新风含有的污染物浓度, ppm M 其他再循环系统参考Goodfellow第8章和Tahti (2001)。 333例1、一工业区域通风量为4.7 ，由全面排风2.35和局部排风2.35构成(美国政府及ms/ms/ms/ 工业卫生协会标准2006b)。局部排气通过一个效率0.8的清洁器实现再循环。再循环空气直接送到工 作场所，这里KK = 0.5， = 0.8 (再循环空气大多是被局部排除而不是进入工人呼吸区). 工作人BR 员在工作站为100%的时间(Cf= 1)。 补风的污染物浓度为5 ppm (), 局部排气污染物浓度为500 M ppm (CC), 空间内污染物的平均浓度为20 ppm (),无再循环工人呼吸区域污染物的浓度为ppm EG(C)。 O 解：带再循环的呼吸区域污染物的浓度C由下得到： B (1)[5000.8(5)],,,,,,Cppm,,155 R,,,,,,1(1)(0.8) 所以 10.000Cppm,,,，,，，,,(205)(11)(355)(1)0.5(155)(10.5)5110 B5000 这是否会超过工作场所污染物浓度的时间加权平均值或极限值，取决于具体的污染物。 CHAPTER 29 Related Commercial Resources VENTILATION OF THE INDUSTRIAL ENVIRONMENT Ventilation Design Principles..................................................................... 29.1 General Comfort and Dilution Ventilation................................................ 29.2 Heat Control................................................................................................ 29.4 Energy Conservation and Recovery.............................................................29.6 INDUSTRIAL environments require ventilation to reduce exposure to excess heat and contaminants that are generated in the workplace; in some situations, cooling may also be required. Ventilation is primarily used to control excess heat, odors, and hazardous particulate and chemical contaminants that could affect the health and safety of industrial workers or, in some cases, be ignited or become combustible when allowed to accumulate beyond their lower flammable limit (LFL). Excess heat and contaminants can best be controlled by using local exhaust systems whenever possible. Local exhaust systems exhaust heated air and contaminants at the source of the heat and contaminants and may require lower airflows than general (dilution) ventilation. For more information, see Chapter 30. General ventilation can be provided by mechanical (fan) systems, by natural draft, or by a combination of the two. Combination systems could include mechanically driven (fan-driven) supply air with air pressure relief through louvers or other types of vents, and mechanical exhaust with air replacement inlet louvers and/or doors. Mechanical (fan-driven) supply systems provide the best control and the most comfortable and uniform environment, especially when there are extremes in local climatic conditions. The systems typically consist of an inlet section, a filter, heating and/or cooling equipment, fans, ductwork, and air diffusers for distributing air within the workplace. When toxic gases or vapors are not present, air cleaned in the general exhaust system or in free-hanging filter units can be recirculated via a return duct. Air recirculation may reduce heating and cooling costs. A general exhaust system, which removes air contaminated by gases, vapors, or particulates not captured by local exhausts, usually consists of one or more fans, plus inlets, ductwork, and an air cleaner or filters. After air passes through the filters, it is either discharged outside or partially recirculated to the building workplace.The air filter system’s cleaning efficiency should conform to environmental regulations and depends on factors such as building location, background contaminant concentrations in the atmosphere，type of contaminants, and height and velocity of the building exhaust discharge. Many industrial ventilation systems must handle simultaneous exposures to heat and hazardous substances. In these cases, the required ventilation can be provided by a combination of local exhaust, general ventilation air supply, and general exhaust systems.The ventilation engineer must carefully analyze supply and exhaust air requirements to determine the worst case. For example, air supply makeup for hood exhaust may be insufficient to control heat exposure. It is also important to consider seasonal climatic effects on ventilation system performance, especially for natural ventilation systems. In specifying acceptable chemical contaminant and heat exposure levels, the industrial hygienist or industrial hygiene engineer must consult the appropriate governing stand ards and guidelines. The standard levels for most chemical and heat exposures are time-weighted averages that allow excursions above the limit as long as they are balanced by equivalent excursions below the limit during the workday. However, exposure level standards for heat and contaminants are not lines of demarcation between safe and unsafe exposures. Rather, they represent conditions to which it is believed nearly all workers may be exposed day after day without adverse effects (ACGIH 2006a). Because a small percentage of workers may be overly stressed at exposure levels below the standards, it is prudent to design for exposure levels below the limits. In the case of exposure to toxic chemicals, the number of contaminant sources, their generation rates, and the effectiveness of exhaust hoods may not be known. Consequently, the ventilation engineer must rely on common ventilation industrial hygiene practice when designing toxic chemical controls. Close cooperation among the industrial hygienist, process engineer, and ventilation engineer is required. In the case of exposure to flammable or ignitable chemicals, the specific gravity of the contaminant source(s), their concentration,and the rating of all electrical devices within the space, along with any source or point of excessive heat, must be carefully considered to prevent possible loss of life or severe injury. As with toxic chemicals, cooperation of knowledgeable experts, including electrical engineers, is required. This chapter describes principles of ventilation practice and includes other information on hygiene in the industrial environment. Publications from the British Occupational Hygiene Society(1987), National Safety Council (2002), U.S. National Institute for Occupational Safety and Health (NIOSH 2005), and the U.S. Department of Health and Human Services (1986) provide further information on industrial hygiene principles and their application. VENTILATION DESIGN PRINCIPLES General Ventilation General ventilation supplies and/or exhausts air to provide heat relief, dilute contaminants to an acceptable level, and replace exhaust air. Ventilation can be provided by natural or mechanical supply and/or exhaust systems. Industrial areas must comply with ANSI/ASHRAE Standard 62.1-2004 and other standards as required [e.g., by the National Fire Protection Association (NFPA)]. Outdoor air is unacceptable for ventilation if it is known to contain any contaminant at a concentration above that given in ANSI/ASHRAE Standard 62.1. If air is thought to contain any contaminant not listed in the standard, guidance on acceptable exposure levels should be obtained from OSHA standards (ACGIH 2006a). General ventilation rates must be high enough to dilute the carbon dioxide produced by occupants. For complex industrial ventilation problems, experimental scale models and computational fluid dynamics (CFD) models are often used in addition to field testing. Makeup Air For safe, effective operation, most industrial plants require makeup air to replace the large volumes of air exhausted to provide acceptable comfort and safety for personnel and acceptable conditions for process operations. Makeup air, consistently provided by good air distribution, allows more effective cooling in the summer and more efficient and effective heating in the winter. Installing windows or other inlets that cannot function in stormy weather is discouraged. Some factors to consider in makeup air design include the following: ?Makeup air must be sufficient to replace air being exhausted or consumed by combustion processes, local and general exhaust systems (see Chapter 30), or process equipment. (Large air compressors can consume a large amount of air and should be considered if air is drawn from within the building.) ?Makeup air systems should be designed to eliminate uncomfortable crossdrafts by properly arranging supply air outlets, and to prevent infiltration (through doors, windows, and similar openings) that may make hoods unsafe or ineffective, defeat environmental control, bring in or stir up dust, or adversely affect processes by cooling or disturbances. The design engineer needs to consider side drafts, and other sources of air movement close to the capture area of a local exhaust hood. Caplan and Knutson (1977, 1978) found that air movement in front of laboratory hoods can cause contaminants to escape from the hood and into the operator’s breathing zone. In industrial applications, it is common to see large fans blowing air on workers in front of the hood. This can render the local exhaust hood ineffective to the point that no protection is provided for the worker. ?Makeup air should be obtained from the cleanest source. Supply air can be filtered, but infiltration air cannot. For transfer air use, see ANSI/ASHRAE Standard 62.1. ?Makeup air for spaces contaminated by toxic, ignitable, or combustible chemicals may have to be acquired through carefully sealed ductwork from an area know to be free of any contamination and be supplied at sufficient rates and pressures to (1) remove all contamination, and (2) prevent infiltration of similar contaminants from surrounding areas or adjacent spaces. ?Makeup air should be used to control building pressure and airflow from space to space to (1) avoid positive or negative pressures that make it difficult or unsafe to open doors, (2) minimize drafts, and (3) prevent infiltration. ?Makeup air should be used to confine contaminants and reduce their concentration and to control temperature, humidity, and air movement. ?Makeup air systems should be designed to recover heat and conserve energy (see the section on Energy Conservation and Recovery). ACGIH (2006b) provides information on adverse conditions that may result from specific negative pressure levels in buildings. GENERAL COMFORT AND DILUTION VENTILATION Effective air diffusion in ventilated rooms and the proper quantity of conditioned air are essential for creating an acceptable working environment, removing contaminants, and reducing initial and operating costs of a ventilation system. Ventilation systems must supply air at the proper velocity and temperature, with contaminant concentrations within permissible limits. In most cases, the objective is to provide tolerable (acceptable) working conditions rather than com-fort (optimal) conditions. General ventilation system design is based on the assumption that local exhaust ventilation, radiation shielding, and equipment insulation and encapsulation have been selected to minimize both heat load and contamination in the workplace (see the section on Heat Control in Industrial Work Areas). In cold climates, infiltration and heat loss through the building envelope may need to be minimized by pressurizing buildings. For more information on dilution ventilation, see ACGIH (2006b). Quantity of Supplied Air Sufficient air must be supplied to replace air exhausted by process ventilation and local exhausts, to dilute contaminants (gases, vapors, or airborne particles) not captured by local exhausts, and to provide the required thermal environment. The amount of supplied air should be the largest of the amounts needed for temperature control, dilution, and replacement. Air Supply Methods Air supply to industrial spaces can be by natural or mechanical ventilation systems. Although natural ventilation systems driven by gravity forces and/or wind effect are still widely used in industrial spaces (especially in hot premises in cold and moderate climates), they are inefficient in large buildings, may cause drafts, and may not solve air pollution problems because there is no practical filtration method available. Thus, most ventilation systems in industrial spaces are either mechanical (fan-driven) or a combination of mechanical supply with natural exhaust, using louvers or doors for air pressure relief (or for air replacement in exhaust systems). The most common methods of air supply to industrial spaces are mixing, displacement, and localized. Mixing Air Distribution. In mixing systems, air is normally supplied at velocities much greater than those acceptable in the occupied zone. Supply air temperature can be above, below, or equal to the air temperature in the occupied zone, depending on the heating/cooling load. The supply air diffuser jet mixes with room air by entrainment, which reduces air velocities and equalizes the air temperature. The occupied zone is ventilated either directly by the air jet or by reverse flow created by the jet. Properly selected and designed mixing air distribution creates relatively uniform air velocity, temperature, humidity, and air quality conditions in theoccupied zone and over the room height. Displacement Ventilation Systems. Conditioned air slightly cooler than the desired room air temperature in the occupied zone is supplied from air outlets at low air velocities (~0.5 m/s or less). Because of buoyancy, the cooler air spreads along the floor and floods the room’s lower zone. Air close to the heat source is heated and rises upward as a convective air stream; in the upper zone, this stream spreads along the ceiling. The height of the lower zone depends on the air volume and temperature supplied to the occupied zone and on the amount of convective heat discharged by the sources. Typically, outlets are located at or near the floor, and supply air is introduced directly into the occupied zone. In some applications (e.g., in computer rooms or hot industrial buildings), air may be supplied to the occupied zone through a false floor. Exhaust or air returns are located at or close to the ceiling or roof. Displacement ventilation is common in Scandinavia and is becoming popular in other European countries. It is an option when contaminants are released in combination with surplus heat, and contaminated air is warmer (more buoyant) than the surrounding air. Further information on displacement air distribution systems can be found in Goodfellow and Tahti (2001). Localized Ventilation. Air is supplied locally for occupied regions or a few permanent work areas (Figure 1). Conditioned air is supplied toward the breathing zone of the occupants to create comfortable conditions and/or to reduce the concentration of pollutants. These zones may have air 5 to 10 times cleaner than the surrounding air. In localized ventilation systems, air is supplied through one of the following devices: Fig. 1 Localized Ventilation Systems ? Nozzles or grilles (e.g., for spot cooling), specially designed lowvelocity/low-turbulence devices ?Perforated panels suspended on vertical duct drops and positioned close to the workstation Local Area and Spot Cooling In hot workplaces that have only few work areas, it is likely impractical and energy-inefficient to maintain a comfortable environment in the entire space. However, air-conditioned cabins, individual cooling, and spot cooling can improve working conditions in occupied areas. Air-conditioned cabins can provide thermal comfort. Control rooms for monitoring production and manufacturing processes can use this technology. Spot cooling, probably the most popular method of improving the thermal environment, can be provided by radiation (changing mean radiant temperature), by convection (changing air velocity and/or air supply temperatures), or both. Spot-cooling equipment is fixed at the workstation, whereas in individual cooling, the worker wears the equipment. Locker Room, Toilet, and Shower Space Ventilation Ventilation of locker rooms, toilets, and shower spaces is important in industrial facilities to remove odor and reduce humidity. In some industries, adequate control of workroom contamination requires prevention of both ingestion and inhalation, so adequate hygienic facilities, including appropriate ventilation, may be required in locker rooms, changing rooms, showers, lunchrooms, and break rooms. State and local regulations should be consulted early in design. Supply air may be introduced through doors or wall grilles. In some cases, plant air may be so contaminated that filtration or (preferably) mechanical ventilation may be required. When control of workroom contaminants is inadequate or not feasible, minimizing the level of contamination in the locker rooms, lunchrooms, and break rooms by pressurizing these areas with excess supply air can reduce employee exposure. When mechanical ventilation is used, the supply system should have adequate ducting and air distribution devices, such as diffusers or grilles, to distribute air throughout the area. In locker rooms, exhaust should be taken primarily from the toilet and shower spaces as needed, and the Roof Ventilators remainder from the lockers and the room ceiling. ASHRAE Standard 62.1 provides requirements in this area. Roof ventilators are heat escape ports located high in a building and should be properly enclosed for weathertightness (Goodfellow 1985). Stack effect and some wind induction are the motive forces for gravity- (buoyancy-) driven operation of continuous and round ventilators. Round ventilators can be equipped with a fan barrel and motor, allowing gravity or forced ventilation operation. Many ventilator designs are available, including the low ventilator, which consists of a stack fan with a rain hood, and a ventilator with a split butterfly closure that floats open to discharge air and closes by a counterweight. Both use minimum enclosures and have little or no gravity capacity. Split butterfly dampers tend to increase fan airflow noise and are subject to damage from slamming during strong wind conditions. Because noise is frequently a problem in powered roof ventilators, the manufacturer’s sound rating should be reviewed. Sound attenuators should be installed where required to meet the design sound ratings. Continuous ventilation monitors remove substantial, concentrated heat loads most effectively. One type, the streamlined continuous ventilator, is efficient, weathertight, and designed to prevent backdraft; it usually has dampers that may be closed in winter to conserve building heat. Its capacity is limited only by the available roof area and the proper location and sizing of low-level air inlets. Continuous ventilation to achieve a slight pressure above he surrounding atmosphere (referred to as pressurization by the National Fire Protection Association) can also be used to reduce or declassify the electrical classification of enclosed spaces. Typically, reductions from Class I, Zone 1 or Division 1 to Class I, Zone 2 or Division 2 can be achieved by following the recommendations of NFPA Standard 496. This allows using general-purpose electrical devices instead of Zone 2 or Division 2 devices or using Zone 2 or Division 2 electrical devices instead of Zone 1 or Division 1 devices, which (1) greatly reduces the cost of electrical equipment and (2) provides a sound alternative when particular devices are not available for the higher (more volatile) electrical area classificaions. Gravity ventilators, also highly effective, have low operating costs, do not generate noise, and are self-regulating (i.e., higher heat release increases airflow through the ventilators). Care must be taken to ensure positive pressure at the ventilators, particularly during the heating season. Otherwise, outside air will enter the ventilators. Next according to their heat removal capacity are (1) round gravty or windband ventilators, (2) round gravity ventilators with fan and motor added, (3) low-hood powered ventilators, and (4) vertical upblast powered ventilators. The shroud for the vertical upblast design has a peripheral baffle to deflect air upward instead of downward. Vertical discharge is highly desirable to reduce roof damage caused by hot air if it contains condensable oil or solvent vapor. Venilators with direct-connected motors are desirable to avoid belt maintenance on units in difficult locations. Round gravity ventilaors are applicable for warehouses with light heat loads and for manufacturing areas with high roofs and light loads. Streamlined continuous ventilators must operate effectively without mechanical power. To ensure ventilator performance, sufficient low-level openings must be provided for incoming air; insufficient inlet area and significant space air currents are the most common reasons gravity roof ventilators malfunction. A positive supply of air around hot equipment may be necessary in large buildngs where external wall inlets are remote from the equipment. Chapter 27 of the 2005 ASHRAE Handbook—Fundamentals has additional information on ventilation and infiltration. The cost of electrical power for mechanical ventilation over that of roof ventilators can be offset by the advantage of constant airflow. Mechanical ventilation can also create the pressure differential necessary for good airflow, even with small inlets. Inlets should be sized correctly to avoid infiltration and other problems caused by high negative pressure in the building. Often, a mechanical system is justified to supply enough makeup air to maintain the work area under positive pressure. Roof ventilators can comprise either mechanically operated openngs or fan-powered mechanical exhaust. Operator-assisted openings or dampers are usually used in shops with high ceilings, and must be nstalled when natural ventilation is used to provide air to the space. HEAT CONTROL Ventilation control alone may frequently be inadequate for meeting heat stress standards for industrial work areas. Optimum solutions may involve additional controls such as spot cooling, changes in work/rest patterns, and radiation shielding. Ventilation for Heat Relief Many industrial processes release large amounts of heat and moisture to the environment. In such environments, it may not be economically feasible to maintain comfort conditions (ASHRAE Standard 55), particularly during summer. Comfortable conditions are not physiologically necessary: the body must be in thermal balance with the environment, but this can occur at temperature and humidity conditions well above the comfort zone. In areas where heat and moisture generated by a process are low to moderate, comfort conditions may not have to be provided if personnel exposures are infrequent and brief. In such cases, ventilation may be the only control necessary to prevent excessive physiological heat stress. The engineer must distinguish between control needs for hot/dry industrial areas and warm/moist conditions. In hot/dry areas, a process gives off only sensible (primarily convective and radiant) heat without adding moisture to the air. This increases the heat load on exposed workers, but the rate of cooling by evaporation of perspiration may not be significantly reduced. Body heat equilibrium may be maintained, but could cause excessive perspiration. Hot/dry work situations occur around furnaces, forges, metal-extruding and rolling mills, glass-forming machines, etc. In warm/moist conditions, a wet process may generate a significant latent heat load. The rise in sensible heat load on workers may be insignificant, but the increased moisture content of the air can seriously reduce cooling by evaporation of perspiration, making warm/moist conditions potentially more hazardous than hot/dry. Typical warm/moist operations are found in textile mills, laundries, dye houses, and deep mines, where water is used extensively for dust control. Industrial heat load is also affected by local climate. Solar heat gain and elevated outdoor temperatures increase the heat load at the workplace, but may be insignificant compared to process heat generated locally. The moisture content of outdoor air is an important factor that can affect hot/dry work situations by restricting an individual’s evaporative cooling. For warm/moist conditions, solar heat gain and elevated outdoor temperatures are more important because moisture contributed by outdoor air is insignificant compared to that released by the process. Both ASHRAE Standard 55 and International Organization for Standardization (ISO) Standard 7730 specify thermal comfort conditions for humans. Methods for evaluating the general thermal state of the body both in comfort conditions and under heat and cold stress are based on analysis of the heat balance for the human body, as discussed in Chapter 8 of the 2005 ASHRAE Handbook—Fundamentals. A person may find the thermal environment unacceptable or intolerable because of local effects on the body caused by asymmetric radiation, air velocity, vertical air temperature differences, or contact with hot or cold surfaces (floors, machinery, tools, etc.). Heat Stress—Thermal Standards Another heat stress indicator for evaluating an environment’s heat stress potential is the wet-bulb globe temperature (WBGT), defined as follows: Outdoors with solar load WBGTttt,，，0.70.20.1 （1） mwbgdb Indoors, or outdoors with no solar load WBGTtt,，0.70.3 （2） mwbg where t =naturally ventilated wet-bulb temperature (no defined range of air velocity; different from saturation mwb temperature or psychrometric wet bulb temperature), ?C t = globe temperature (Vernon bulb thermometer, 150 mm diameter), ?C g t = dry-bulb temperature (sensor shaded from solar radiation), ?C db Coefficients in Equations (1) and (2) represent the fractional contributions of the component temperatures. Exposure limits for heat stress for different levels of physical activity are shown in Figure 2 (NIOSH 2005), which depicts the allowable work regime (in terms of rest periods and work periods each hour) for different levels of work over a range of WBGT. When applying Figure 2, assume that the rest area has the same WBGT as the work area. The curves are valid for workers acclimatized to heat. ASHRAE Standard 62.1-2004 provides some metabolic rates for different activities that can be used with Figure 2. Refer to NIOSH (2005) for recommended WBGT limits for nonacclimatized workers. Ventilation of the Industrial Environment The WBGT index is an international standard (ISO Standards 7243 and 7730) for evaluating hot environments. The WBGT index and activity levels should be evaluated on 1 h mean values; that is, WBGT and activity are measured and estimated as time-weighted averages on a 1 h basis for continuous work, or on a 2 h basis when exposure is intermittent. Although recommended by NIOSH, the WBGT has not been accepted as a legal standard by the Occupational Safety and Health Administration (OSHA). It is generally used in conjunction with other methods to determine heat stress. Although Figure 2 is useful for evaluating heat stress exposure limits, it is of limited use for control purposes or for evaluation of comfort. Air velocity and psychrometric wet-bulb measurements are usually needed to specify proper controls, and are only measured indirectly in WBGT determinations. Information on other useful tools, including the heat stress index (HSI), can be found in Chapter 8 of the 2005 ASHRAE Handbook—Fundamentals and in ISO Standards 7243, 7730, and 7933. The thermal relationship between humans and their environment is determined by four independent variables: ?Air temperature ?Radiant temperatures ?Moisture content of the air ?Air velocity Together with the rate of internal heat production (metabolic rate), these factors may combine in various ways to create different degrees of heat stress. The HSI is defined as the percent of the skin that is wetted by perspiration: Fig. 2 Recommended Heat Stress Exposure Limits for Heat-Acclimatized Workers [Adapted from NIOSH (1986)] HSIEE,，/100 （3） skmax Where 2E = evaporative heat loss from the skin， Wm/sk 2E= maximum possible evaporative heat loss from the skin, Wm/max and incorporates relative contributions of metabolism, radiant heat gain (or loss), convective heat gain (or loss), and evaporative (perspiration) heat gain (or loss). For supplemental information on evaluation and control of heat stress using methods such as reduction of radiation, changes in work/rest pattern, spot cooling, and cooling vests and suits, refer to ACGIH (2006b), Brief et al. (1983), Caplan (1980), and NIOSH (2005). Heat Exposure Control Control at Source. Heat exposure can be reduced by insulating hot equipment or locating it in zones with good general ventilation or outdoors, covering steaming water tanks, providing covered drains for direct removal of hot water, and maintaining tight joints and valves where steam may escape. Local Exhaust Ventilation. Local exhaust ventilation removes heated air generated by a hot process and/or nonbuoyant gases emit- ted by process equipment, while removing a minimum of air from the surrounding space. Local exhaust systems are discussed in detail in Chapter 30. Radiation Shielding. In some industries, the major environmental heat load is radiant heat from hot objects and surfaces, such as furnaces, ovens, furnace flues and stacks, boilers, molten metal, hot ingots, castings, and forgings. Because air temperature has no significant effect on radiant heat flow, ventilation is of little help in controlling such exposure. The only effective control is to reduce the amount of radiant heat impinging on the workers. Radiant heat exposure can be reduced by insulating or placing radiation shields around the source. Radiation shields are effective in the following froms： ? Reflective shielding. Sheets of reflective material or insulating board are temporarily attached to the hot equipment or arranged in a semiportable floor stand. ? Absorptive shielding (water-cooled). These shields absorb and remove heat from hot equipment. ? Transparent shields. Heat-reflective tempered plate glass, reflective metal chain curtains, and close-mesh wire screens moderate radiation without obstructing the view of hot equipment. ? Flexible shielding. Aluminum-treated fabrics give a high degree of radiation shielding. ? Protective clothing. Reflective garments such as aprons, gauntlet gloves, and face shields provide moderate radiation shielding. For extreme radiation exposures, complete suits with vortex tube cooling may be required. If the shield is a good reflector, it remains relatively cool in severe radiant heat. Bright or highly polished tinplate, stainless steel, and ordinary flat or corrugated aluminum sheets are efficient and durable. Foil-faced plasterboard, although less durable, reflects well on one side. To be efficient, however, the reflective shield must remain bright. Radiation shields are much more efficient when used in multiple layers; they should reflect the radiant heat back to the primary source, where it can be removed by local exhaust. However, unless the shield completely surrounds the primary source, some infrared energy is reflected into the cooler surroundings and possibly into an occupied area. The direction of the reflected heat should be studied to ensure proper shielding installation. Spot Cooling. If the workplace is located near a source of radiant heat that cannot be entirely controlled by radiation shielding, spot cooling can be used. See Chapter 33 in the 2005 ASHRAE Handbook—Fundamentals and data from spot-cooling diffuser manufacturers for further information. ENERGY CONSERVATION AND RECOVERY Because of the large air volumes required to ventilate industrial plants, energy conservation and recovery should be practiced, and provides substantial savings. Energy recovery should be incorpoated into preliminary planning for an industrial plant. When selecting energy recovery equipment, ensure that materials are compatible with all fumes that may be exhausted. Verify the acceptability of energy recovery with local codes. In some cases, it is possible to provide unheated or partially heated makeup air to the building. Although most energy conservation and recovery methods in this section apply to heating, the savings possible with cooling systems are similar. The following aresome methods of energy conservation and recovery: ? In the original design phase, process and equipment insulation and heat shields should be provided to minimize heat loads. Vaporproofing and reducing the glass area may be required. Exhaust requirements for hoods and processes should be reviewed and kept to a practical, safe minimum; for more on local exhaust systems, see Chapter 30. ? Design the supply and exhaust general ventilation systems for optimal operation throughout the year. Air should be supplied as close to the occupied zone as possible. Recirculated air should be used in winter makeup, and unheated or partially heated air should be brought to hoods and processes (ACGIH 2006b). ? Supply air can be passed through air-to-air, liquid-to-air, or hot-gas-to-air heat exchangers to recover building or process heat. Rotary, regenerative, coil energy recovery (runaround), and air-to-air heat exchangers are discussed extensively in Chapter 44 of the 2004 ASHRAE Handbook—HVAC Systems and Equipment. Energy recovery is also discussed in Chapter 7 of ACGIH (2006b). ? Operate the system for economy. Shut systems down at night or on weekends whenever possible, and operate makeup air in balance with the needs of process equipment and hoods. Keep heating supply air temperatures at the minimum, and cooling supply temperatures at the maximum, consistent with process needs and employee comfort. Keep the building in pressure balance so that uncomfortable drafts do not necessitate excessive heating. ? Contaminant concentrations in any recirculated air must be determined so that allowable limits in the space are not exceeded. As recirculated air returns to the space, the concentration of contaminants in the partially filtered return air adds to the contaminant levels already existing in the space. It must be determined whether the concentration increases beyond the allowable time-weighted average (TWA) during the period for which the worker is exposed. This period is usually assumed to be 8 h for an 8 h work shift, but could be any period of exposure. The TWA at the workers breathing zone is (ACGIH 2006b) QB(1),KC()(1)() (4) CCCfCCfKC,,,，,，，BGMOMBRBMQA where C= TWA worker breathing zone contaminant concentration with recirculation, ppm B 3Q= total ventilation airflow without recirculation, ms/B 3Q= total ventilation airflow with recirculation, ms/A C= average space concentration without recirculation, ppm G f=fraction of time worker spends at workstation C=TWA contaminant concentration at breathing zone of workstation without recirculation, ppm O K=fraction of worker breathing zone that consists of recirculated air, 0 to 1.0 B C=recirculated air (after air cleaner) discharge concentration, ppm, or R (1)(),,,CKCERM C, (5) R1(1),,,KR =fractional air cleaner efficiency for contaminant , C=(local) exhaust concentration without recirculation, ppm E K=fraction of exhaust that that is recirculated air, 0 to 1.0 R C=replacement air contaminant concentration, ppm M Other recirculation systems are given in Chapter 8 of Goodfellow and Tahti (2001). 33Example 1. An industrial space uses 4.7 for ventilation, of which 2.35 is general exhaust and ms/ms/ 32.35 local exhaust (ACGIH2006b). Local exhaust is recirculated through an air cleaner with an ms/ efficiency of 0.8. Recirculated air is directed toward the worker spaces, such that KK = 0.5 and = BR 0.8 (more of the recirculated air is locally exhausted than enters the worker’s breathing zone). The worker is at the workstation 100% of the time (C= 1). The makeup air has a concentration of 5 ppm (), the local fM exhaust has a concentration of 500 ppm (CC), the space has an average concentration of 20 ppm (), and EG without recirculation the worker’s breathing zone is 35 ppm (C). OSolution: The concentration C at the breathing zone with recirculation is determined from B (1)[5000.8(5)],,,,,,Cppm,,155 R,,,,,,1(1)(0.8) And 10.000 Cppm,,,，,，，,,(205)(11)(355)(1)0.5(155)(10.5)5110B5000 which may or may not exceed the TWA or threshold limit value (TLV) of the worker space, depending on the specific contaminant. REFERENCES ACGIH. 2006a. Guide to occupational exposure values, 2006. American Conference of v Governmental Industrial Hygienists, Cincinnati, OH. ACGIH. 2006b. Industrial ventilation: A manual of recommended practice, 26th ed. American Conference of Governmental Industrial Hygienists, Cincinnati, OH. ASHRAE. 2004. Thermal environmental conditions for human occupancy. ANSI/ASHRAE Standard 55-2004. ASHRAE. 2004. Ventilation for acceptable indoor air quality. ANSI/ASHRAE Standard 62.1-2004. Brief, R.S., S. Lipton, S. Amamnani, and R.W. Powell. 1983. Development of exposure control strategy for process equipment. Annals of the American Conference of Governmental Industrial Hygienists (5). British Occupational Hygiene Society (BOHS). 1987. Controlling airborne contaminants in the workplace. Technical Guide 7. Science Review Ltd. and H&H Scientific Consultants, Leeds, U.K. Caplan, K.J. 1980. Heat stress measurements. Heating, Piping and Air Conditioning (February):55-62. Caplan, K.J. and G.W. Knutson. 1977. The effect of room air challenge on the efficiency of laboratory fume hoods. ASHRAE Transactions 83(1): 141-156. Caplan, K.J. and G.W. Knutson. 1978. Laboratory fume hoods: Influence of room air supply. ASHRAE Transactions 84(1):522-537. Goodfellow, H.D. 1985. Advanced design of ventilation systems for contaminant control. Elsevier Science B.V., Amsterdam. Goodfellow, H. and E. Tahti, eds. 2001. Industrial ventilation design guide- book. Academic Press, New York. ISO. 1989. Hot environments—Estimation of the heat stress on workingman, based on the WBGT-index (wet bulb globe temperature). Standard 7243. International Organization for Standardization, Geneva. ISO. 2005. Ergonomics of the thermal environment—Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. Standard 7730. International Organization for Standardization, Geneva. ISO. 2004. Ergonomics of the environment—Analytical determination and interpretation of heat stress using calculation of the predicted heat strain. Standard 7933. International Organization for Standardization, Geneva. National Safety Council. 2002. Fundamentals of industrial hygiene, 5th ed.Chicago. NFPA. 2003. Purged and pressurized enclosures for electrical equipment. Standard 496-2003. National Fire Protection Association, Quincy, MA. NIOSH. 2005. Criteria for a recommended standard: Occupational exposure to hot environments. CDC/NIOSH Publication 72-10269. National Institute for Occupational Safety and Health, Washington, D.C. Available from www.cdc.gov/NIOSH/72-10269.html. U.S. Department of Health and Human Services. 1986. Advanced industrial hygiene engineering. PB87-229621. Cincinnati, OH. BIBLIOGRAPHY Alden, J.L. and J.M. Kane. 1982. Design of industrial ventilation systems, 5th ed. Industrial Press, New York. Anderson, R. and M. Mehos. 1988. Evaluation of indoor air pollutant control techniques using scale experiments. ASHRAE Indoor Air Quality Conference. Balchin, N.C., ed. 1991. Health and safety in welding and allied processes, 4th ed. Abington Publishing, Cambridge. Bartknecht, W. 1989. Dust explosions: Course, prevention, protection. Springer-Verlag, Berlin. Burgess, W.A., M.J. Ellenbecker, and R.D. Treitman. 1989. Ventilation for control of the work environment. John Wiley & Sons, New York. Cawkwell, G.C. and H.D. Goodfellow. 1990. Multiple cell ventilation model with time-dependent emission sources. Proceedings of the 2nd International Conference on Engineering Aero- and Thermodynamics of Ventilated Rooms, Al-9, Oslo. Chamberlin, L.A. 1988. Use of controlled low velocity air patterns to improve operator environment at industrial work stations. M.A. thesis,University of Massachusetts. Cole, J.P. 1995. Ventilation systems to accommodate the industrial process. Heating, Piping, Air Conditioning (May). Constance, J.D. 1983. Controlling in-plant airborne contaminants. Marcel Dekker, New York. Cralley, L.V. and L.J. Cralley, eds. 1986. Patty’s industrial hygiene and toxicology, vol. 3: Industrial hygiene aspects of plant operations. John Wiley & Sons, New York. Fanger, P.O. 1982. Thermal comfort. Robert E. Krieger, Malabar, FL. Flagan, R.C. and J.H. Seinfeld. 1988. Fundamentals of air pollution engineering. Prentice-Hall, Englewood Cliffs, NJ. Godish, T. 1989. Indoor air pollution control. Lewis Publishers, Chelsea, MI. Goldfield, J. 1980. Contaminant concentration reduction: General ventilation versus local exhaust ventilation. American Industrial Hygienists Association Journal 41(November). Goodfellow, H.D. 1986. Proceedings of Ventilation ’85. Elsevier Science B.V., Amsterdam. Goodfellow, H.D. 1987. Encyclopedia of physical science and technology, vol. 14: Ventilation, industrial. Academic Press, San Diego, CA. Goodfellow, H.D. and J.W. Smith. 1982. Industrial ventilation—A review and update. American Industrial Hygiene Association Journal 43 (March):175-184. Harris, R.L. 1988. Design of dilution ventilation for sensible and latent heat. Applied Industrial Hygiene 3(1). Hayashi, T, R.H. Howell, M. Shibata, and K. Tsuji. 1987. Industrial ventilation and air conditioning. CRC, Boca Raton, FL. Heinsohn, R.J. 1991. Industrial ventilation engineering principles. John Wiley & Sons, New York. Holcomb, M.L. and J.T. Radia. 1986. An engineering approach to feasibility assessment and design of recirculating exhaust systems. Proceedings of Ventilation ’85. Elsevier Science B.V., Amsterdam. Jackman, R. 1991. Displacement ventilation. CIBSE National Conference (April), University of Kent, Canterbury. Laurikainen, J. 1995. Displacement ventilation system design method. Seminar presentations, Part 2. INVENT Report 46. FIMET, Helsinki. Licht, W. 1988. Air pollution control engineering, 2nd ed. Marcel Dekker, New York. McDermott, H.J. 1985. Handbook of ventilation for contaminant control, 2nd ed. Ann Arbor Science Publishers, Ann Arbor, MI. Mehta, M.P., H.E. Ayer, B.E. Saltzman, and R. Ronk. 1988. Predicting concentration for indoor chemical spills. ASHRAE Indoor Air Quality Conference.(R) NFPA. [Annual.] National fire codes . National Fire Protection Association, Quincy, MA Olesen, B.W. and A.M. Zhivov. 1994. Evaluation of thermal environment in industrial work spaces. ASHRAE Transactions 100(2):623-635. Pozin, G.M. 1993. Determination of the ventilating effectiveness in mechanically ventilated spaces. Proceedings of the 6th International Conference on Indoor Air Quality (IAQ ’93), Helsinki. RoomVent ’90. 1990. Proceedings of the 2nd International Conference on Engineering Aero- and Thermodynamics of Ventilated Rooms, Oslo. RoomVent ’92. 1992. Proceedings of the 3rd International Conference on Engineering Aero- and Thermodynamics of Ventilated Rooms, Aalborg, Denmark. RoomVent ’94. 1994. Proceedings of the 4th International Conference on Engineering Aero- and Thermodynamics of Ventilated Rooms, Krakow. RoomVent ’96. Proceedings of the 5th International Conference on Air Distribution in Rooms, Yokohama. Schroy, J.M. 1986. A philosophy on engineering controls for workplace protection. Annals of Occupational Hygiene 30(2):231-236. Shilkrot, E.O. and A.M. Zhivov. 1996. Zonal model for displacement ventilation design. RoomVent ’96, Proceedings of the 5th International Conference on Air Distribution in Rooms, vol. 2. Yokohama. Skaret, E. 1985. Ventilation by displacement—Characterization and design applications. Elsevier Science B.V., Amsterdam. Skaret, E. and H.M. Mathisen. 1989. Ventilation efficiency—A guide to efficient ventilation. ASHRAE Transactions 89(2B):480-495. Skistad, H. 1994. Displacement ventilation. Research Studies Press, John Wiley & Sons, West Sussex, U.K. Stephanov, S.P. 1986. Investigation and optimization of air exchange in industrial halls ventilation. Proceedings of Ventilation ’85. Elsevier Science B.V., Amsterdam. Vincent, J.H. 1989. Aerosol sampling, science and practice. John Wiley & Sons, Oxford, U.K. Volkavein, J.C., M.R. Engle, and T.D. Raether 1988. Dust control with clean air from an overhead air supply island (oasis). Applied Industrial Hygiene 3(August):8. Wadden, R.A. and P.A. Scheff 1982. Indoor air pollution: Characterization, prediction, and control. John Wiley & Sons, New York. Wilson, D.J. 1982. A design procedure for estimating air intake contamination from nearby exhaust vents. ASHRAE Transactions 89(2A):136-152. Zhivov, A.M. and B.W. Olesen. 1993. Extending existing thermal comfort standards to work spaces. Proceedings of the 6th International Conference on Indoor Air Quality (IAQ ’93), Helsinki. Zhivov, A.M. E.O. Shilkrot, P.V. Nielsen, and G.L. Riskowski. 1997. Displacement ventilation design. Proceedings of the 5th International Symposium on Ventilation for Contaminant Control (Ventilation ’97), vol. I, Ottawa.