A4372_HVAC_DistributionSystemsSizing.ppt

8/20/2019 A4372_HVAC_DistributionSystemsSizing.ppt

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ARCH-4372/6372ARCH-4372/6372

HVAC Distribution & Sizing

HVAC Distribution Systems

Difuser Selection and Layout

Ductwork Sizing


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HVAC Distribution

Systems


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Positive Pressure su!!ly"

#egative Pressure return or

e$%aust"

Distribution SystemDistribution System

Plans SymbolsPlans Symbols


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Arrow indicates

air ow direction




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'low !atterns

()way

*)way

+)way

,)way


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-%ermostat

Smoke.'ire

Dam!er



-


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Double Line

Single Line




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Plan

Section



z z

z z

(+ $ (/

(/ $ (+


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DistributionDistribution

SystemSystem

PlansPlansDouble Line

Single Line


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DistributionDistribution

SystemSystem

PlansPlansDouble LineSingle Line


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CeilingCeiling

PlenumPlenumPlansPlans

S%ows duct !at%0rom distribution

network to su!!lydifuser or returnregister


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Difuser Selection and

Layout


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Difuser SeletionDifuser Seletion

Difuser Selection Criteria

Air ow

-%row #oise Criteria #C" Level

A!!earance


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Air 'low

-%row

#C Level


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-%row1

Distance o0 air movement

Avoid 2a!s and overla!

3bstructions.deectors


Velocity 0!m"

(45 (55

45


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Difuser !ayoutDifuser !ayout

(6 7se 8oom Sensible Load no latent9 noventilation" to determine air ow

:s;(65< " C'= " >-

w%ere

-;?-sa)-ra?

t%us

C'=; :s

(65<" >-"


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+6 De@ne Su!!ly Air tem!eratures

Heating1

-sa range is 5)((5B'

-ra;/


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,6 De@ne >-

Heating1

>-;?((5)/


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*6 Determine Air 'low C'="

C'=%tg; :s

(65< " >-%tg"

C'=clg; :s (65< " >-clg"

Larger result determines air ow


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46 8evise disc%arge air tem!erature to matc% reuired air ow

C'=!eak ; :s (65< " ?-sa)-ra?"

solve 0or -sa


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/6 Select difuser layout

8egular !attern

7ni0orm coverage

Avoid Es%ort circuitingF wit%

e$%aust.return registers


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Difuser !ayout #"am$leDifuser !ayout #"am$le

3Gce s!ace wit%over%ead %eatingand cooling su!!ly

#C level ,4


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Heating :s; ((9


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8evise Heating -sa

C'=!eak ; :s

(65< " >-"

;,*/;((9


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De@ne Pattern

,*/ C0m

8ound u! to 5 or 4 c0m

(J,45 c0m

+J(4;,45 c0m,J((4;,*4 c0m

*J5;,/5 c0m


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De@ne Pattern

,*/ C0m

8ound u! to 5 or 4 c0m

(J,45 c0m +)way

+J(4;,45 c0m *)way,J((4;,*4 c0m ,)way

*J5;,/5 c0m +)way



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#C ,4

Air 'low

-%row

Select


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De@ne Pattern

,*/ C0m

+J(4;,45 c0m *)way



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Return Register SeletionReturn Register Seletion

Selection Criteria

Air ow

#oise Criteria #C" Level A!!earance


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Return Register SeletionReturn Register Seletion

Air 'low

#C Level


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Avoid S%ort circuiting wit% su!!ly difusers Locating in visually obtrusive location

Return Register !ayoutReturn Register !ayout


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De@ne Pattern

Su!!ly;,45 c0m

8eturn

(J,45;,45 c0m

Return Register !ayoutReturn Register !ayout


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Return Register SeletionReturn Register SeletionAir 'low ,45 c0m#C Level ,4

Select(5F "


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De@ne Pattern

Su!!ly;,45 c0m

8eturn

(J,45;,45 c0m(5F $


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Ductwork Sizing


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Dut%or& SizingDut%or& Sizing

Volume :" is a 0unction o0 cross sectional

area A" and velocity V"

:;AV

%owever9 momentum9 0riction and turbulence

must also be accounted 0or in t%e sizingmet%od


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'omentum'omentum

As air leaves 0an9 centri0ugal motioncreates momentum

(A)


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(rition(rition

As air moves along aduct9 0riction slowst%e velocity at t%eedges

(A)


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*urbulene *urbulene

As ducts c%ange direction or cross)sectional dimensions9 turbulence iscreated

(A)


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Stati PressureStati Pressure

'orce reuired to overcome 0riction andloss o0 momentum due to turbulence

As air encounters 0riction or turbulence9static !ressure is reduced

'ans add static !ressure


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Pressure 'easurementPressure 'easurement

Static !ressure is measured in inc%es o00orce against a water column

Knc%es)water gauge

Positive !ressure !us%es air

#egative !ressure draws air


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Pressure 'easurementPressure 'easurement

Straig%t ducts %ave a !ressure loss o0

Ew6g6.(55

based on diameter and velocity

% t i t%


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(rition(rition

!oss C+art!oss C+art

%at is t%e !ressureloss.(55 0t in a (+F diameter duct

delivering (555 c0m o0airM VelocityM

56+F.(55 '-

(,+4 0!m


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#,uialent !engt+#,uialent !engt+

Describes t%e amount o0 static !ressurelost in a @tting t%at would becom!arable to a lengt% o0 straig%t duct


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Dut%or& Com$arisonDut%or& Com$arison

8ound ductwork is t%e most eGcient butreuires greater de!t%

8ectangular ductwork is t%e leasteGcient but can be reduced in de!t% toaccommodate smaller clearances

Avoid as!ect ratios greater t%an 41(


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#,ual (rition 'et+o.#,ual (rition 'et+o.

Presumes t%at 0riction in ductwork canbe balanced to allow uni0orm 0rictionloss t%roug% all branc%es


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(6 'ind efective lengt% NL" o0 longest run

+6 Nstablis% allowed static !ressure loss.(55

>P;(55SP".NL,6 Size ducts

*6 8e!eat 0or eac% branc%

#ote1 velocity must be %ig%er in eac%u!stream section


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#"am$le#"am$leSize ductwork serving oGce difusers0rom earlier e$am!le

Nlbow euivalent lengt%1 (5

Straig%t @tting euiv6 lengt%1 4

AH7 connection1 45

AH

40 40

60 60

310 20 0

60

7 5m ty$8


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#"am$le#"am$leSu!!ly Difuser !ressure loss1 565,


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(6 'ind efective lengt% o0 longest run

Kdenti0y longest runLabel duct sections

AH

40 40

60 60

310 20 0

60

7 5m ty$8

234


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9or&s+eet9or&s+eet

Duct Actual Nuiv Nfective Air >P Duct Air

SectionLengt% Lengt% Lengt% Vol6 F.(55 Diam Velocity

60 10 60 7

2 0 0 30 7

3 20 0 70 31

4 310 10 10 711

60 710 260

AH

40 40

60 60

310 20 0

60

7 5m ty$8

234


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+6 Nstablis% allowed static !ressure loss.(55

'an SP1 564,,F

)Su!!ly Dif1 565,


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9or&s+eet9or&s+eet



60 10 60 7 12

2 0 0 30 7 12

3 20 0 70 31 12

4 310 10 10 711 12

60 710 260

AH

40 40

60 60

310 20 0

60

7 5m ty$8

234


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,6 Size ducts

88)/

#,ual (rition 'et+o.#,ual (rition 'et+o.,6 Size ducts


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#,ual (rition 'et+o.#,ual (rition 'et+o.( (4c0m F diam J /+5 0!m

+ (4c0mF diam J /+5 0!m

, ,45 c0m F diam J


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9or&s+eet9or&s+eet



60 10 60 7 12 7: 621 5$m

2 0 0 30 7 12 7: 621 5$m

3 20 0 70 31 12 ;: 11 5$m

4 310 10 10 711 12 2: ;11 5$m

60 710 260

AH

40 40

60 60

310 20 0

60

7 5m ty$8

234


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A4372_HVAC_DistributionSystemsSizing.ppt

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