3ducts bs11 lect

8/8/2019 3Ducts Bs11 Lect

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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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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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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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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

3ducts bs11 lect

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