局部通风设计

局部通风系统

Source

Path WorkerLocalExhaustVentilation局部排风

(Ref.ACGIH-IndustrialVentilationManual)GeneralVentilation全面通风

(Ref.ASHRAE-62)ENGINEERINGCONTROLSVENTILATION通风GeneralandLocalVentilationGeneralVentilation

全面通风LocalExhaustVentilation

局部通风全面通风LOCALEXHAUSTVENTILATION(LEV)局部排风January12,20237SOMECOMMONMYTH常见问题LEVSYSTEMS

局部排风系统

1.Fans风机 2.Hoods排风罩 3.Ducts风管 4.Stacks排气筒 5.AirCleaners空气净化器

LOCALEXHAUSTSYSTEM

局部排风系统TypesofHood

排风罩的类型Totalenclosures全密闭罩Partialenclosures局部密闭罩Captorhoods收集式吸气罩Receptorhoods接受式排风罩TYPESOFHOODS

排风罩类型密闭罩半密闭罩January12,202316捕集罩TypesofLocalExhaustHoodandtheEffectiveness收集罩半密闭罩全密闭罩DESIGNINGHOODS

排风罩设计1.Enclosedtheprocessasmuchaspossiblewhilenotinterferingwithworker.

在不影响工人操作的情况下，排风罩尽可能包括整个操作范围。2.Placethehoodsothatcontaminantsaredrawnawayfromthebreathingzoneoftheworker.

排风罩的位置适当，应能将有害物从工人呼吸带处排出。3.Locatethehoodascloseaspossibletothepointofgenerationofcontamination(tominimizeairvolumeandforeffectivecapture).

排风罩应尽可能靠近有害物的产生点，可以减少所需风量、提高捕集效率。WORKERPOSITIONEFFECT

工人位置的影响VelocityTerms风速CaptureVelocity控制风速FaceVelocity面风速DuctVelocity风管风速CAPTUREVELOCITY

控制风速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排风罩外部的污染源处，捕集逸散污染物的气流速度。CAPTUREVELOCITY控制风速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排风罩外部的污染源处，捕集逸散污染物的气流速度。Notfacevelocity!罩口风速这种情况下有意义吗?HowtoAssessitsEffectiveness?有害物发散的状态举例控制风速要求(m/s)无速度的挥发到静止的空气中溶剂从容器内挥发；涂料干燥0.3–0.5低速度的发散到基本静止的空气中电焊；锡焊；液体转移0.5-

1.0中等速度的发散到运动的空气中粉碎；喷漆1.0-

2.5高速度的发散到的运动的空气中切割；打磨；喷砂2.5-

10January12,202324控制风速要求CaptureVelocity不同形状排风罩的风量计算January12,202328不同形状排风罩的风量计算MaximumCaptureDistanceShouldNotBeMoreThan1.5TimestheDuctDiameter

最大捕集距离不超过风罩直径的1.5倍。RuleofThumbforSimpleCaptureHoods排风罩的基本规则

RelationshipBetweenCapture,Working&BreathingZones

排风罩的有效区域

DUCTVELOCITY

风管风速

Airvelocitythroughtheductcross-section.

风管横截面的风速Whensolidmaterialispresentintheairstream,ductvelocitymustbeequaltoorgreaterthantheminimumairvelocityrequiredtomovetheparticlesintheairstream.

当风管气流中存在固体颗粒时，风管风速应不小于能将颗粒物移动的最小风速。RANGEOFMINIMUMDUCTDESIGNVELOCITIES

风管最小设计风速的范围

SHORTCIRCUITING短路MinimumStackHeightinRelationtoImmediateRoofLineorCenterofAnyAirIntakeontheSameRoof

屋顶进风口与屋顶排气口的高度要求ENERGYLOSSESINTHELEVSYSTEM

局部排风系统能力损失HOODENTRYLOSS排风罩进口阻力ELBOWLOSS弯头阻力BRANCHENTRYLOSS支管入口阻力WEATHERCAPLOSS风帽阻力FRICTIONLOSS摩擦阻力DUCTCONTRACTLOSS

管径改变导致的阻力排风罩进口阻力(hoodentryloss)January12,202336弯头阻力January12,202337支管入口阻力January12,202338摩擦阻力January12,202339选择合适的风管风速通风系统的阻力与风管风速的平方成正比高风速：风道截面积较小，系统造价低；

但系统阻力大，设备能耗大；

设备内部易受磨损低风速：系统阻力小，设备能耗小；

风道截面积较大，系统造价高；

风速过低易导致粉尘沉积，堵塞风道

January12,202340FANLAWS

风机定律WHAT

DO

THE

FAN

LAWS

TELL

US?

风机定律告诉了我们什么？TherelationshipbetweenvolumetricairflowandHPiscubic风量和风机功率的关系是三次方的关系Therefore,todoubletheairflowyoumustincreasethehorsepowerby

因此，为了让风量增加一倍，风机功率要变为原来的8倍CostforelectricityisproportionaltofanHP.

所需电费与风机功率成比例Illustratesimportanceofproperdesignandlowlosses说明优化设计和低能量损失的重要性Pressure

压力Forairtoflowtheremustbeapressuredifferenceandairwillflowfromthehigherpressuretothelowerpressure空气的流动需要有压力差,空气从压力高的位点移向压力低的位点

Pressureisconsideredtohavetwoforms:压力通常分为两种:staticpressure(Ps)静压

velocitypressure(Pv)动压Withthesumofthesebeingtotalpressure(Pt).

静压和动压之和为全压StaticPressure

静压Staticpressureisdefinedasthepressureexertedinalldirectionsbyafluidthatisstationary静压定义为静止气流向各个方向施加的压力

Ifthefluidisinmotion(asisthecaseinaventilationsystem),staticpressureismeasuredat90°tothedirectionoftheflowsoastoeliminatetheinfluenceofmovement(ie:

velocity)如果气流是运动的(如在通风系统中），静压为垂直于气流运动方向测得的压力，以消除气流运动的影响（如风速）StaticPressure(Cont)

静压FAN(-)SUCTIONSIDE(+)PRESSURESIDECanbebothpositiveandnegativedependingifitismeasuredonthedischargeorsuctionsideofafan在风机的进风侧为负压，出风侧为正压。January12,202346VelocityPressure

动压Definedasthatpressurerequiredtoaccelerateairfromzerovelocitytosomevelocityandisproportionaltothekineticenergyoftheairstream定义为将气流速度从零加速到一定流速所需要的压力，与气流的动能成正比。

Insimpleterms,velocitypressureisthekineticenergygeneratedinaventilationsystemasaresultofairmovement简单的说，动压就是通风系统中气流运动的能量的动能。VelocityPressure(cont)

动压 =Densityofair(kgm-3)

v

=Airvelocityms-1 Pv=Velocitypressure(PaieNm-2)VelocityPressure(cont) Ifstandardtemperatureandpressureconditionsareinexistence,ie:

= 1.2kgm-3 Then Pv = 0.6v2Relationshipis:Pt=Ps+Pv

总压=静压+动压

全压测定局部通风系统效果评估January12,202352

SmokeTubesIndicatingAirMovement

发烟管显示气流的运动

SmokeTubes

发烟管测量控制风速（非罩口风速）January12,202355MeasuringFaceVelocity

测量罩口风速（仅适用于密闭罩、半密闭罩）Hot-wireAnemometer

热线风速仪

PitotTubes

皮托管（风管风速，动压、静压测量）PitotTubeandManometerwithDigitalReadout

皮托管和压力计

1.

Blockingoffhoodorinlet

排风罩或进气口阻塞

2.Leakage(discolorationatseamand

turns)接合处或转弯处漏风

3.Fanswiredincorrectly风机连接不当

4.Slippingdrivebelts传动带松弛

5.Burnedoutmotors电机烧毁IDENTIFYINGLEVPROBLEMS

识别局部排风系统存在的问题ReducedFlowRate风量降低的可能原因Pluggedordentedducts风管阻塞或管壁有凹陷Slippingfanbelts风机传动带松弛Openaccessdoors检查门未关闭Holesinducts,elbows管道、弯道有漏洞Closedblastgatetobranch,oropenblastgatestootherbranches,orcorrodedandstuckblastgates调风阀关闭,或调风阀指向其它支道,或调风阀被腐蚀或受阻Fa