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DonPenn,PE,CGDImageEngineering Group,Ltd
DESIGNING FOR SUCCESSWHAT ABOUT PURGING AND
FLUSHING
Commercial Applications
Learning Objectives• Discuss the importance of proper piping
design to accommodate purging and flushing.
• Discuss design considerations to facilitate flushing and purging.
• Discuss the potential benefits of different design features.
• Introduce new IGSHPA Inspectors Course
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Outline/Agenda
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q ImproperFlushingandPurgingandpipedesign/sizingcanbreakanotherwisepotentiallysuccessfulproject……..
q Designphilosophyforflushingandpurging
q Pipesizingconsiderations.
q Valvelocationandlocationpreferencesandlimitations….
q Header/manifoldconsiderations
Protection/Purging of Piping
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• Duringallphasesoftheinstallationitiscriticalthatallpipingisprotectedfromdebrisandforeignobjectsenteringthepipe.
• Aftertheheatexchangeriscompletedthesystemshouldbepurgedofallairanddebris.
• Debriscanclogorfoultheheatexchanger• Entrainedaircancorrodemetalliccomponents,causenoise,andcanpossiblypreventflowinsectionsofthesystem.
• Trappedaircanbeseparatedfromwaterandthereforeremovedbypowerflushingthesystemataminimumflowvelocityof2feetpersecond(FPS).
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• Therearetwobasicflowregimesdefinedinfluidmechanicstodescribethenatureoffluidflowinanysituation:laminarandturbulent.Inthelow-velocitylaminarregime,fluidflowisstreamlinedandsmooth.Oncethefluidvelocityhasbeenincreasedaboveacriticalvalue,flowbecomeschaoticanddisorderedandentersintotheturbulentregime.
• Themixingoffluidinturbulentflowmaximizestheheattransfercapability.
• Ground-looppipingshouldbesizedsuchthatfluidflowthrougheachloopisturbulenttoensuremaximumheattransfer.
• Turbulentflowcanalsoproducehigherlevelsoffrictionbetweenthefluidandpipewalls,pressuredropneedstobeevaluatedtominimizepumpHP.
Sizing Considerations
FLUSHING, PURGING AND FLOW TESTING
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Ø Beforethesystemisplacedinoperation,flushingofallheatexchangerpipingshallbeperformedtoremovedebrisandair.
Ø Flushingshallbeperformedat135%ofdesignflow,butinnocaselessthan2FPS.
ØEachsubfieldshallbeseparatelyflushedandpurgedØLaststageofflushingandpurgingshouldbethrutheunitheatexchanger;heatexchangersshouldbebypasseduntilpipingsystemisflushedandpurged.
ØAclosedloop-flushingunitwithavolumetankfiltersshallbeutilized.ØTheflushingvolumeshallbeatleast3xthe systemvolume