3ducts bs11 lect
TRANSCRIPT
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A.C . DUCTS A.C . DUCTS
Aparna ParateAparna Parate
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AIR CONDITIONERS
NON DUCTABLE DUCTABLE
WINDOW SPLIT
FLOOR
MOUNTED
WALL
MOUNTED
CEILING
MOUNTED
EXPOSED HIDEAWAY CASSATTE
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INTRODUCTIONINTRODUCTION Ducts divert the air from the fan to theDucts divert the air from the fan to the
room.room.
They are insulated passages for treatedThey are insulated passages for treatedair with diffusers at the end.air with diffusers at the end.
They can be placed on the floor ,wall orThey can be placed on the floor ,wall orceilingceiling..
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GENERAL GUIDELINESGENERAL GUIDELINES
The duct layout should be orderly andThe duct layout should be orderly andsystematic, like the structural system.systematic, like the structural system.
Avoid crisscrossing air ductsAvoid crisscrossing air ducts
Provide adequate access to largeProvide adequate access to largeequipment that might have to be replaced.equipment that might have to be replaced.
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DUCT SIZESDUCT SIZES
Duct sizes depend on the amount of air toDuct sizes depend on the amount of air totreated and the size of the room to be airtreated and the size of the room to be airconditioned.conditioned.
Formula: A =Formula: A = Delivery rateDelivery rate
VV
Where A = cross sectional area in sq.m.Where A = cross sectional area in sq.m.
D.R=delivery rate in m^3/sec.D.R=delivery rate in m^3/sec.
V =air velocity in m/s.V =air velocity in m/s.
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SHAPES OFSHAPES OF DUCTSDUCTS
Circular ductsCircular ducts
Rectangular ductsRectangular ducts
Flat oval ductsFlat oval ducts
Square ductsSquare ducts
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CIRCULAR DUCTSCIRCULAR DUCTS
These ducts provide more flexibility in layout.These ducts provide more flexibility in layout.
Although round ducts are preferable they requireAlthough round ducts are preferable they requireclearances that are not always available.clearances that are not always available.
These ducts requireThese ducts requireleast volume andleast volume and
material but has thematerial but has thegreatest depthgreatest depth
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RECTANGULAR DUCTSRECTANGULAR DUCTS
Ratio of short to longRatio of short to longside should not exceedside should not exceed
1:51:5because the resultingbecause the resultinghigh air flow friction airhigh air flow friction airflow requires the ductflow requires the duct
to have excessivelyto have excessivelylarge areas andlarge areas andperimetersperimeters
Most popular.Most popular.
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FLAT OVAL DUCTSFLAT OVAL DUCTS
These ducts are forThese ducts are forpositive pressurepositive pressureapplications onlyapplications onlyunless special designsunless special designsare used.are used.
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MATERIALS FOR DUCTSMATERIALS FOR DUCTS
The different materials used for ductsThe different materials used for ductssystems can substantially affect the overallsystems can substantially affect the overall
performance of the systems.performance of the systems. Galvanized steelGalvanized steel
Uncoated carbon steelUncoated carbon steel
AluminumAluminum
Fiber glass reinforced plasticFiber glass reinforced plastic coppercopper
polyvinyl steelpolyvinyl steel
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METMETAL DUCTSAL DUCTS
These ducts areThese ducts areinherently strong &inherently strong &
rigid.rigid. They are the mostThey are the most
efficient & economicalefficient & economicalducts.ducts.
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FLEXIBLE DUCTSFLEXIBLE DUCTS
Unnecessary length, offsetting and compression ofUnnecessary length, offsetting and compression ofthese ducts significantly increase airflow resistance.these ducts significantly increase airflow resistance.
These should be kept as short and straight asThese should be kept as short and straight aspossible, fully extended and supported to minimizepossible, fully extended and supported to minimizesagging.sagging.
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DUCT CONSTRUCTIONDUCT CONSTRUCTION
The operating pressure conveyed in the airThe operating pressure conveyed in the airstream is the primary parameter that determinesstream is the primary parameter that determinesa duct system's construction method anda duct system's construction method andmaterial.material.
Ductwork ranges from light gauge galvanizedDuctwork ranges from light gauge galvanizedsteel for low pressure,steel for low pressure,
thickthick--walled stainless steel for high negativewalled stainless steel for high negative
pressure,pressure, minus 30 water gauge and more, to conveyminus 30 water gauge and more, to convey
corrosive gases and abrasive materials.corrosive gases and abrasive materials.
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POSITIONING OF DUCTSPOSITIONING OF DUCTS
To minimize the space required ducts should beTo minimize the space required ducts should be
coco--ordinated with beamsordinated with beams
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DUCT SYSTEM LAYOUTDUCT SYSTEM LAYOUT
The overall design of the building and structuralThe overall design of the building and structuraland mechanical system elements govern theand mechanical system elements govern the
ultimate layout of each duct system.ultimate layout of each duct system. Generally, ductwork is concealed above dropGenerally, ductwork is concealed above drop--
down ceilings, in mechanical rooms, and indown ceilings, in mechanical rooms, and invertical cases that allow duct and othervertical cases that allow duct and other
mechanical systems to pass unseen through wallmechanical systems to pass unseen through walldivisions and between floors.divisions and between floors.
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VIEW OF COMPONENTSVIEW OF COMPONENTS
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DUCTCLEANINGDUCTCLEANING
Ducts may collect moisture , which can harbor orDucts may collect moisture , which can harbor ortransport microbial contaminants.transport microbial contaminants.
Ducts should be designed, constructed andDucts should be designed, constructed andmaintained to minimize growth and dissemination ofmaintained to minimize growth and dissemination ofmicromicro--organisms.organisms.
Control measures:Control measures: Providing access for cleaningProviding access for cleaning
Providing proper filtrationProviding proper filtration
Preventing moisture and dirt accumulationPreventing moisture and dirt accumulation
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DUCT LEAKAGEDUCT LEAKAGE
The impact of duct leakage depends onThe impact of duct leakage depends onduct location, length, design, andduct location, length, design, and
pressure.pressure.
When duct is located in the conditionedWhen duct is located in the conditionedspace leakage is less than when duct isspace leakage is less than when duct is
located outside of conditioned areas.located outside of conditioned areas.
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JOINERY IN DUCTSJOINERY IN DUCTS
Connection byConnection byboltingbolting
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Right angle turnRight angle turn
ConnectionConnectionbetween primarybetween primary
and secondary ductand secondary duct
ConnectingConnectingpiecepiece
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HANGERSHANGERS
To hang & support ductsTo hang & support ducts
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LEVER USED TO CONTROLLEVER USED TO CONTROL
AIR FLOWAIR FLOW
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FLEXIBLE MATERIALFLEXIBLE MATERIAL
IS USED TO REDUSEIS USED TO REDUSETHE VIBRATIONSTHE VIBRATIONSCOMING FROM A.H.UCOMING FROM A.H.U
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DUCT INSULATIONDUCT INSULATION
Such insulation must be vapor sealed, i.e. sealedSuch insulation must be vapor sealed, i.e. sealedagainst ingress of atmospheric air otherwise theagainst ingress of atmospheric air otherwise the
insulation will become water logged and useless.insulation will become water logged and useless. Transmission of heat through bare metal duct wallsTransmission of heat through bare metal duct walls
varies according to air velocity.varies according to air velocity.
Materials for duct insulation, internal and external toMaterials for duct insulation, internal and external to
the duct must not support fire.the duct must not support fire. Some suitable materials are glass fiber, mineral woolSome suitable materials are glass fiber, mineral wool
and polyurethane.and polyurethane.
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DUCT INSULATIONDUCT INSULATION
To prevent condensation, a vapor barrier mustTo prevent condensation, a vapor barrier mustbe on the outside of the insulation.be on the outside of the insulation.
For noise control, the insulation must beFor noise control, the insulation must beexposed to the air stream.exposed to the air stream.
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DUCT INSULATIONDUCT INSULATION
At least 2 inches must be added to theAt least 2 inches must be added to theheight and width when duct insulation isheight and width when duct insulation is
used.used.
It is required for 3 reasons;It is required for 3 reasons;
11-- to reduce heat gain or loss.to reduce heat gain or loss.
22-- to prevent condensation.to prevent condensation.
33-- to control noise.to control noise.
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The effect of insulation is to reduce the loss suchThe effect of insulation is to reduce the loss suchthat air velocity in the duct affects thethat air velocity in the duct affects the UU value onlyvalue only
to a minor extent.to a minor extent.
The gain or loss of temperature in air conveyed in aThe gain or loss of temperature in air conveyed in alength of duct may for practical purpose be calculatedlength of duct may for practical purpose be calculatedfrom the following:from the following:
HH--=PLU delta t=PLU delta t
Where,Where,
HH= heat loss or gain= heat loss or gain
PP= perimeter of duct= perimeter of ductLL= length of duct= length of duct
UU= thermal transmittance of bare/insulated duct= thermal transmittance of bare/insulated duct
deltadelta tt= mean temperature differences between= mean temperature differences between
inside/outside of ductinside/outside of duct
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DUCT INSULATIONDUCT INSULATION
Ducts can be sealed using a variety ofDucts can be sealed using a variety oftechniques and materials including tapes,techniques and materials including tapes,
mastics and aerosols.mastics and aerosols. Standard cloth tapes should never be used toStandard cloth tapes should never be used to
seal due to their poor durabilityseal due to their poor durability
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ACOUSTIC TREATMENTACOUSTIC TREATMENT
Duct systems, unless properly designed,Duct systems, unless properly designed,
will act as large speaker tubes andwill act as large speaker tubes andtransmit noise throughout the building.transmit noise throughout the building.
The direction of airflow has little effectThe direction of airflow has little effect
on the transmission of noise.on the transmission of noise.
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ACKNOWLEDGEMENTACKNOWLEDGEMENT
SYMBIOSIS COLLEGE.SYMBIOSIS COLLEGE.
Thank youThank you