局部通風(fēng)設(shè)計(jì)

局部通風(fēng)系統(tǒng)

Source

Path WorkerLocalExhaustVentilation局部排風(fēng)

(Ref.ACGIH-IndustrialVentilationManual)GeneralVentilation全面通風(fēng)

(Ref.ASHRAE-62)ENGINEERINGCONTROLSVENTILATION通風(fēng)GeneralandLocalVentilationGeneralVentilation

全面通風(fēng)LocalExhaustVentilation

局部通風(fēng)全面通風(fēng)LOCALEXHAUSTVENTILATION(LEV)局部排風(fēng)January12,20237SOMECOMMONMYTH常見問題LEVSYSTEMS

局部排風(fēng)系統(tǒng)

1.Fans風(fēng)機(jī) 2.Hoods排風(fēng)罩 3.Ducts風(fēng)管 4.Stacks排氣筒 5.AirCleaners空氣凈化器

LOCALEXHAUSTSYSTEM

局部排風(fēng)系統(tǒng)TypesofHood

排風(fēng)罩的類型Totalenclosures全密閉罩Partialenclosures局部密閉罩Captorhoods收集式吸氣罩Receptorhoods接受式排風(fēng)罩TYPESOFHOODS

排風(fēng)罩類型密閉罩半密閉罩January12,202316捕集罩TypesofLocalExhaustHoodandtheEffectiveness收集罩半密閉罩全密閉罩DESIGNINGHOODS

排風(fēng)罩設(shè)計(jì)1.Enclosedtheprocessasmuchaspossiblewhilenotinterferingwithworker.

在不影響工人操作的情況下，排風(fēng)罩盡可能包括整個(gè)操作范圍。2.Placethehoodsothatcontaminantsaredrawnawayfromthebreathingzoneoftheworker.

排風(fēng)罩的位置適當(dāng)，應(yīng)能將有害物從工人呼吸帶處排出。3.Locatethehoodascloseaspossibletothepointofgenerationofcontamination(tominimizeairvolumeandforeffectivecapture).

排風(fēng)罩應(yīng)盡可能靠近有害物的產(chǎn)生點(diǎn)，可以減少所需風(fēng)量、提高捕集效率。WORKERPOSITIONEFFECT

工人位置的影響VelocityTerms風(fēng)速CaptureVelocity控制風(fēng)速FaceVelocity面風(fēng)速DuctVelocity風(fēng)管風(fēng)速CAPTUREVELOCITY

控制風(fēng)速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排風(fēng)罩外部的污染源處，捕集逸散污染物的氣流速度。CAPTUREVELOCITY控制風(fēng)速Thevelocityofairinducedbyahoodtocaptureemittedcontaminantsfromthesourceexternaltothehood.在排風(fēng)罩外部的污染源處，捕集逸散污染物的氣流速度。Notfacevelocity!罩口風(fēng)速這種情況下有意義嗎?HowtoAssessitsEffectiveness?有害物發(fā)散的狀態(tài)舉例控制風(fēng)速要求(m/s)無速度的揮發(fā)到靜止的空氣中溶劑從容器內(nèi)揮發(fā)；涂料干燥0.3–0.5低速度的發(fā)散到基本靜止的空氣中電焊；錫焊；液體轉(zhuǎn)移0.5-

1.0中等速度的發(fā)散到運(yùn)動的空氣中粉碎；噴漆1.0-

2.5高速度的發(fā)散到的運(yùn)動的空氣中切割；打磨；噴砂2.5-

10January12,202324控制風(fēng)速要求CaptureVelocity不同形狀排風(fēng)罩的風(fēng)量計(jì)算January12,202328不同形狀排風(fēng)罩的風(fēng)量計(jì)算MaximumCaptureDistanceShouldNotBeMoreThan1.5TimestheDuctDiameter

最大捕集距離不超過風(fēng)罩直徑的1.5倍。RuleofThumbforSimpleCaptureHoods排風(fēng)罩的基本規(guī)則

RelationshipBetweenCapture,Working&BreathingZones

排風(fēng)罩的有效區(qū)域

DUCTVELOCITY

風(fēng)管風(fēng)速

Airvelocitythroughtheductcross-section.

風(fēng)管橫截面的風(fēng)速Whensolidmaterialispresentintheairstream,ductvelocitymustbeequaltoorgreaterthantheminimumairvelocityrequiredtomovetheparticlesintheairstream.

當(dāng)風(fēng)管氣流中存在固體顆粒時(shí)，風(fēng)管風(fēng)速應(yīng)不小于能將顆粒物移動的最小風(fēng)速。RANGEOFMINIMUMDUCTDESIGNVELOCITIES

風(fēng)管最小設(shè)計(jì)風(fēng)速的范圍

SHORTCIRCUITING短路MinimumStackHeightinRelationtoImmediateRoofLineorCenterofAnyAirIntakeontheSameRoof

屋頂進(jìn)風(fēng)口與屋頂排氣口的高度要求ENERGYLOSSESINTHELEVSYSTEM

局部排風(fēng)系統(tǒng)能力損失HOODENTRYLOSS排風(fēng)罩進(jìn)口阻力ELBOWLOSS彎頭阻力BRANCHENTRYLOSS支管入口阻力WEATHERCAPLOSS風(fēng)帽阻力FRICTIONLOSS摩擦阻力DUCTCONTRACTLOSS

管徑改變導(dǎo)致的阻力排風(fēng)罩進(jìn)口阻力(hoodentryloss)January12,202336彎頭阻力January12,202337支管入口阻力January12,202338摩擦阻力January12,202339選擇合適的風(fēng)管風(fēng)速通風(fēng)系統(tǒng)的阻力與風(fēng)管風(fēng)速的平方成正比高風(fēng)速：風(fēng)道截面積較小，系統(tǒng)造價(jià)低；

但系統(tǒng)阻力大，設(shè)備能耗大；

設(shè)備內(nèi)部易受磨損低風(fēng)速：系統(tǒng)阻力小，設(shè)備能耗??；

風(fēng)道截面積較大，系統(tǒng)造價(jià)高；

風(fēng)速過低易導(dǎo)致粉塵沉積，堵塞風(fēng)道

January12,202340FANLAWS

風(fēng)機(jī)定律WHAT

DO

THE

FAN

LAWS

TELL

US?

風(fēng)機(jī)定律告訴了我們什么？TherelationshipbetweenvolumetricairflowandHPiscubic風(fēng)量和風(fēng)機(jī)功率的關(guān)系是三次方的關(guān)系Therefore,todoubletheairflowyoumustincreasethehorsepowerby

因此，為了讓風(fēng)量增加一倍，風(fēng)機(jī)功率要變?yōu)樵瓉淼?倍CostforelectricityisproportionaltofanHP.

所需電費(fèi)與風(fēng)機(jī)功率成比例Illustratesimportanceofproperdesignandlowlosses說明優(yōu)化設(shè)計(jì)和低能量損失的重要性Pressure

壓力Forairtoflowtheremustbeapressuredifferenceandairwillflowfromthehigherpressuretothelowerpressure空氣的流動需要有壓力差,空氣從壓力高的位點(diǎn)移向壓力低的位點(diǎn)

Pressureisconsideredtohavetwoforms:壓力通常分為兩種:staticpressure(Ps)靜壓

velocitypressure(Pv)動壓Withthesumofthesebeingtotalpressure(Pt).

靜壓和動壓之和為全壓StaticPressure

靜壓Staticpressureisdefinedasthepressureexertedinalldirectionsbyafluidthatisstationary靜壓定義為靜止氣流向各個(gè)方向施加的壓力

Ifthefluidisinmotion(asisthecaseinaventilationsystem),staticpressureismeasuredat90°tothedirectionoftheflowsoastoeliminatetheinfluenceofmovement(ie:

velocity)如果氣流是運(yùn)動的(如在通風(fēng)系統(tǒng)中），靜壓為垂直于氣流運(yùn)動方向測得的壓力，以消除氣流運(yùn)動的影響（如風(fēng)速）StaticPressure(Cont)

靜壓FAN(-)SUCTIONSIDE(+)PRESSURESIDECanbebothpositiveandnegativedependingifitismeasuredonthedischargeorsuctionsideofafan在風(fēng)機(jī)的進(jìn)風(fēng)側(cè)為負(fù)壓，出風(fēng)側(cè)為正壓。January12,202346VelocityPressure

動壓Definedasthatpressurerequiredtoaccelerateairfromzerovelocitytosomevelocityandisproportionaltothekineticenergyoftheairstream定義為將氣流速度從零加速到一定流速所需要的壓力，與氣流的動能成正比。

Insimpleterms,velocitypressureisthekineticenergygeneratedinaventilationsystemasaresultofairmovement簡單的說，動壓就是通風(fēng)系統(tǒng)中氣流運(yùn)動的能量的動能。VelocityPressure(cont)

動壓 =Densityofair(kgm-3)

v

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

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

總壓=靜壓+動壓

全壓測定局部通風(fēng)系統(tǒng)效果評估January12,202352

SmokeTubesIndicatingAirMovement

發(fā)煙管顯示氣流的運(yùn)動

SmokeTubes

發(fā)煙管測量控制風(fēng)速（非罩口風(fēng)速）January12,202355MeasuringFaceVelocity

測量罩口風(fēng)速（僅適用于密閉罩、半密閉罩）Hot-wireAnemometer

熱線風(fēng)速儀

PitotTubes

皮托管（風(fēng)管風(fēng)速，動壓、靜壓測量）PitotTubeandManometerwithDigitalReadout

皮托管和壓力計(jì)

1.

Blockingoffhoodorinlet

排風(fēng)罩或進(jìn)氣口阻塞

2.Leakage(discolorationatseamand

turns)接合處或轉(zhuǎn)彎處漏風(fēng)

3.Fanswiredincorrectly風(fēng)機(jī)連接不當(dāng)

4.Slippingdrivebelts傳動帶松弛

5.Burnedoutmotors電機(jī)燒毀IDENTIFYINGLEVPROBLEMS

識別局部排風(fēng)系統(tǒng)存在的問題ReducedFlowRate風(fēng)量降低的可能原因Pluggedordentedducts風(fēng)管阻塞或管壁有凹陷Slippingfanbelts風(fēng)機(jī)傳動帶松弛Openaccessdoors檢查門未關(guān)閉Holesinducts,elbows管道、彎道有漏洞Closedblastgatetobranch,oropenblastgatestootherbranches,orcorrodedandstuckblastgates調(diào)風(fēng)閥關(guān)閉,或調(diào)風(fēng)閥指向其它支道,或調(diào)風(fēng)閥被腐蝕或受阻Fa