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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
Distribution SystemDistribution System
Plans SymbolsPlans Symbols
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Distribution SystemDistribution System
Plans SymbolsPlans Symbols
'low !atterns
()way
*)way
+)way
,)way
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-%ermostat
Smoke.'ire
Dam!er
Distribution SystemDistribution System
Plans SymbolsPlans Symbols
-
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Double Line
Single Line
Distribution SystemDistribution System
Plans SymbolsPlans Symbols
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Plan
Section
Distribution SystemDistribution System
Plans SymbolsPlans Symbols
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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Difuser SeletionDifuser Seletion
Air 'low
-%row
#C Level
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-%row1
Distance o0 air movement
Avoid 2a!s and overla!
3bstructions.deectors
Difuser SeletionDifuser Seletion
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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Difuser !ayoutDifuser !ayout
+6 De@ne Su!!ly Air tem!eratures
Heating1
-sa range is 5)((5B'
-ra;/
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Difuser !ayoutDifuser !ayout
,6 De@ne >-
Heating1
>-;?((5)/
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Difuser !ayoutDifuser !ayout
*6 Determine Air 'low C'="
C'=%tg; :s
(65< " >-%tg"
C'=clg; :s (65< " >-clg"
Larger result determines air ow
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Difuser !ayoutDifuser !ayout
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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Difuser !ayoutDifuser !ayout
/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$le
3Gce s!ace wit%over%ead %eatingand cooling su!!ly
#C level ,4
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Difuser !ayout #"am$leDifuser !ayout #"am$le
Heating :s; ((9
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Difuser !ayout #"am$leDifuser !ayout #"am$le
8evise Heating -sa
C'=!eak ; :s
(65< " >-"
;,*/;((9
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Difuser !ayout #"am$leDifuser !ayout #"am$le
De@ne Pattern
,*/ C0m
8ound u! to 5 or 4 c0m
(J,45 c0m
+J(4;,45 c0m,J((4;,*4 c0m
*J5;,/5 c0m
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De@ne Pattern
,*/ C0m
8ound u! to 5 or 4 c0m
(J,45 c0m +)way
+J(4;,45 c0m *)way,J((4;,*4 c0m ,)way
*J5;,/5 c0m +)way
Difuser !ayout #"am$leDifuser !ayout #"am$le
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Difuser SeletionDifuser Seletion
#C ,4
Air 'low
-%row
Select
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De@ne Pattern
,*/ C0m
+J(4;,45 c0m *)way
Difuser !ayout #"am$leDifuser !ayout #"am$le
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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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#,ual (rition 'et+o.#,ual (rition 'et+o.
(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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#,ual (rition 'et+o.#,ual (rition 'et+o.
#"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$8
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#,ual (rition 'et+o.#,ual (rition 'et+o.
#"am$le#"am$leSu!!ly Difuser !ressure loss1 565,
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#,ual (rition 'et+o.#,ual (rition 'et+o.
(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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#,ual (rition 'et+o.#,ual (rition 'et+o.
+6 Nstablis% allowed static !ressure loss.(55
'an SP1 564,,F
)Su!!ly Dif1 565,
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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 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$8
234
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#,ual (rition 'et+o.#,ual (rition 'et+o.
,6 Size ducts
88)/
#,ual (rition 'et+o.#,ual (rition 'et+o.,6 Size ducts
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#,ual (rition 'et+o.#,ual (rition 'et+o.( (4c0m F diam J /+5 0!m
+ (4c0mF diam J /+5 0!m
, ,45 c0m F diam J
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9or&s+eet9or&s+eet
Duct Actual Nuiv Nfective Air >P Duct Air
SectionLengt% Lengt% Lengt% Vol6 F.(55 Diam Velocity
60 10 60 7 12 7: 621 5$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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