dampers - applications

…essential componentsof an HVAC system

…essential componentsof an HVAC system

DampersDampers

Volume

Pressure

Temperature

Dampers –Part of a SystemDampers –Part of a System

Control Air Flow

DampersDampers

■ Volume (Air) Control––Regulate air flowRegulate air flow

■ Temperature Control––Maintain constant temperatureMaintain constant temperature

Damperregulates

air tobranch

Typical Volume ControlApplicationTypical Volume ControlApplication

Volume ControlDampersVolume ControlDampers

■ Isolating Dampers––Regulate or stop flow of air in branchesRegulate or stop flow of air in branchesof a duct systemof a duct system

■ Balancing Dampers––Limit air flow by holding damper bladesLimit air flow by holding damper bladesat a specified positionat a specified position

■ Fan Inlet Vane Dampers––Used to control air flow rate to a fanUsed to control air flow rate to a fan

■ Fan Outlet Dampers(or Terminal Unit VAV Type Dampers)

––Used to control air flow rate from a fanUsed to control air flow rate from a fan

Air Flow atTemp B

Air Flow atTemp A

Typical TemperatureControl ApplicationsTypical TemperatureControl Applications

Face & bypass for discharge air temp

Mixed air control

Temp C

TemperatureControl DampersTemperatureControl Dampers

■ Operate as pairs to maintain apredetermined set point

■ Simultaneously regulate two differentair streams, each having a differenttemperature

■ Can control the temperature as wellas maintain a constant volume of air

Typical Temperature &Volume Control ApplicationTypical Temperature &Volume Control Application

Outside air

Exhaust airReturn airReturn air

Supply airSupply air

Conditionedspace

Damper ApplicationsDamper Applications

Barometric / Gravity

Balancing

Control

Fire

Smoke

Combination Fire / Smoke


Barometric / Gravity

■ Automatically open and close tomaintain predetermineddifferential pressure

■ Insures proper air flow in boilerflue exhausts

■ Safely limits high static pressurein ductwork

Balancing■ Used for air balancing applications

Control■ Most commonly specified for

environmental control

■ Rectangular dampers have 2 types ofoperation

ParallelAll blades move together at same rate and same direction

OpposedAdjacent blades turn in oppositedirections

Damper ApplicationsDamper Applicationsfor round orrectangular

ducts


Smoke (leakage-rated)

■ Actuator and damper must be UL approvedas a MATCHED SET for smoke control

You cannot use just any actuator!!

ULULULULcc


Fire

■ Normally open

■ Closes with a spring loaded mechanism(fusible link) at a predeterminedtemperature or in a fire condition

ULULULULcc

When FUSIBLE LINKtemperaturereaches 165°F(74°C) or 212°F(100°C) linkreleases high-torquespring, & BLADESSLAM SHUT


Combination Fire / Smoke

■ Provide both smoke and fire functionsin a SINGLE damper

■ Driven with an actuator during smokecontrol

■ Permanently close via a fusible linkduring fire conditions

Factors AffectingDamper PerformanceFactors AffectingDamper Performance

■ Inlet and Outlet Conditions

■ Location

■ Damper Authority

■ Damper Flow Characteristic

■ In-duct Obstructions

Air currents causedAir currents causedby these conditionsby these conditionscan adversely affectcan adversely affectdamper performancedamper performance

Inlet and OutletConditionsInlet and OutletConditions

■ Overhangs

■ Projections

■ Obstructions

■ Adjacent walls

■ Turbulencefrom nearbydischarge fan

Factorsaffecting

performance

Damper LocationDamper Location

■ Entering air should be evenlydistributed across damper face

■ Air outlet should not be restricted

■ Nearness of duct elbows,upstream and downstream

■ Location of next damper

Factorsaffecting

performance

Damper FlowCharacteristicDamper FlowCharacteristic

The relationship betweenflow rate through the damperand the position of thedamper blades

100100

5050

00

% Damper Blade Rotation

Damper FlowCharacteristic (Opposed)Damper FlowCharacteristic (Opposed)

Use damper authority to determine installeddamper flow characteristic

00 5050 100 100

%Flow

A=5%A=5%

A=10%A=10%

A=20%A=20%

A=50%A=50%A=1%A=1%

InherentInherent

Factorsaffecting

performance

00 5050 100100

A=5%A=5%

A=10%A=10%

A=20%A=20%

A=50%A=50%

InherentInherent

A=1%A=1%

Damper FlowCharacteristic (Parallel)Damper FlowCharacteristic (Parallel)Use damper authority to determine installeddamper flow characteristic

%Flow


100100

5050

00

Factorsaffecting

performance

100100

5050

0000 5050100100

%Flow

Determined in a certifiedtesting laboratory


OpposedBlade

ParallelBlade

Johnson ControlsInherent Flow CharacteristicJohnson ControlsInherent Flow Characteristic

Valid when differential pressure is heldconstant regardless of damper blade position

Factorsaffecting

performance

■ Impact of the damper ontotal system

■ The ratio of wide openpressure drop through thedamper to the total ductsystem pressure drop at thedesign flow

% Damper Authority% Damper AuthorityFactors

affectingperformance

= ( 0.1= ( 0.1÷ 2 ) x 100 = 5%÷ 2 ) x 100 = 5%

= (= ( P Pdd ÷ ÷ PPt t ) x 100) x 100

Fan Static = 2 in. W.G. P Damper = 0.1 in. W.G

GrillGrill

Fire Fire DamperDamper

CCCC

RoomRoom

Pd = Pressuredrop acrosswide opendamper

Pt = Totalpressuredrop in thatportion ofthe systemin whichthe damperis to beinstalled

% Damper Authority% Damper AuthorityFactors

affectingperformance

In-duct ObstructionsIn-duct Obstructions

■ Actuators

■ Jackshaft assemblies

■ Sensing devices

■ Structural supports

■ Filters

Factorsaffecting

performance

AdditionalConsiderationsAdditionalConsiderations

■ Pressure drop

■ Leakage

■ Maximum torquerequired to movedamper blades

Factorsaffecting

performance

Selecting theCorrect DamperSelecting theCorrect Damper

■ Determine which installed damperflow characteristic will provide thebest control

■ Use the value of the damperauthority which best matches thesystem characteristics to determinethe wide open pressure drop throughthe damper

Factorsaffecting

performance

DamperApplications

2-PositionStatic Pressure ControlTemperature Control

Face and BypassMixed Air Control

2-PositionStatic Pressure ControlTemperature Control

Face and BypassMixed Air Control

2-Position Application2-Position Application

■ Fully open or fully closed

■ Not a modulated device

■ Must obtain wide open design flowrate through damper with apressure drop less than or equal toa value specified

■ Size to duct to provide lowestpossible wide open pressure drop

EXAMPLESEXAMPLES

•• 100%100%Flow Flow oror

•• 100%100%Shut OffShut Off

DamperApplications

DamperApplications

Static PressureControl ApplicationStatic PressureControl Application

■ Less common today with the use ofVariable Air Volume systems and useof inlet vanes to control fan capacity

■ Damper modulated to maintain astatic pressure set point at somedownstream point in ductwork

■ Generally installed near the fandischarge

■ The damper pressure drop must beincluded in the overall systemresistance

Damper fully openDamper fully open

Fan curve

System resistance curve forductwork, filters, coils(excluding damper)

Percent of System Flow

Pressure(In. WG)

2.62.62.42.42.22.22.02.01.81.81.61.61.41.41.21.21.01.00.80.80.60.60.40.40.20.2

0000 5050100100

At 25% of theAt 25% of thesystem flow ratesystem flow rate(vertical line Y),(vertical line Y),

the pressure dropthe pressure dropacross theacross the

damper must bedamper must beequal to 2.4 -equal to 2.4 -(0.05 + 0.5) =(0.05 + 0.5) =

1.85 in. WG to1.85 in. WG tomaintain set pointmaintain set point

Point APoint ASet Point 0.5Set Point 0.5

in. WG*in. WG**Set Point at “A” is*Set Point at “A” iswhat the VAV boxeswhat the VAV boxesrequire at MAX CFMrequire at MAX CFM

PPdamperdamper = = PPfanfan – ( – ( PPsystemsystem + P + Pset pointset point))

XX


YY

DamperApplications

Damper Pressure Drop Requirement

22

11

00

Percent of System Flow

DamperPressure

DropInch WC

% Damper Authority = ( Pd ÷ Pt) x 100

00 2525 5050 7575 100100

1.851.85


(Necessary to maintain(Necessary to maintainset point)set point)

DamperApplications

Note: The damper flow characteristic for thestatic pressure application would be anauthority of 100%.

But damper authorities over 50% are notrecommended due to excessive pressuredrops and potential noise problems.

AUTHORITY RECOMMENDATIONS

Opposed Blade Dampers –Size for an authority of 20 to 50%

Parallel Blade Dampers –Not recommended for this application

AUTHORITY RECOMMENDATIONSAUTHORITY RECOMMENDATIONS

Opposed Blade Dampers –Opposed Blade Dampers –Size for an authority of 20 to 50%Size for an authority of 20 to 50%

Parallel Blade Dampers –Parallel Blade Dampers –Not recommended for this applicationNot recommended for this application


DamperApplications

SensibleHeat Transfer (BTUH) = (1.08) (CFM) (Tsa – Tr)

CFM = Flow rate through damper

Tsa = Temperature of supply air

Tr = Temperature of room air

TemperatureControl ApplicationTemperatureControl Application

■ Used to regulated amount ofconditioned (supply) air to compensatefor heat gain / loss within a space

■ Determine amount of heat gain / lossrequired from supply air by usingequation

DamperApplications

AUTHORITY RECOMMENDATIONSAUTHORITY RECOMMENDATIONSSize for a linear damper flow characteristicSize for a linear damper flow characteristic

Opposed Blade Dampers –

Use an authority of 8 to 10%

Parallel Blade Dampers –

Use an authority of 20 to 25%Others –

Refer to product data sheets

Opposed Blade Dampers –

Use an authority of 8 to 10%

Parallel Blade Dampers –

Use an authority of 20 to 25%Others –

Refer to product data sheets

TemperatureControl ApplicationTemperatureControl Application

DamperApplications

Face & Bypass orMulti-Zone ApplicationFace & Bypass orMulti-Zone Application■ Size the face and bypass dampers so combined

flow rate is relatively constant

■ Use parallel blade dampers to enhancedownstream air mixing

Face

Bypass

T

Air Flow

DamperApplications

Face &Face &BypassBypassDamperDamper

Ratios forRatios forVariousVarious

Coil DropsCoil Drops

“A” - Coil Face Vel. = 500 fpm“B” - Coil Face Vel. = 400 fpm“C” - Coil Face Vel. = 300 fpm

“A” - Coil Face Vel. = 500 fpm“B” - Coil Face Vel. = 400 fpm“C” - Coil Face Vel. = 300 fpm

“A”

“B”

“C”

“A”

“B”

“C”

.01 .02 .03 .05 .1 .2 .3 .5 1

Pressure Drop Through Coil, in. WG

BypassDamperSize %of Coil

100

80

60

40

20

0

Face & BypassApplicationFace & BypassApplication■ Use same full flow resistance to achieve constant flow

rate through both face and bypass sections

■ Size bypass damper so full flow resistance equalssum of full flow resistance of coil and coil face damper

DamperApplications

Example:Example: Economizer cycle control Economizer cycle control

Mixed Air ControlApplicationMixed Air ControlApplication■ Used to regulate flow rate of two air streams so

mixed air stream can be maintained at apredetermined temperature

Outside airOutside air

Exhaust airExhaust airReturn airReturn air

Supply airSupply air

Conditionedspace

DamperApplications

MatchMatchdampersdampersso theirso their

combinedcombinedflow rateflow rate

is constantis constantregardlessregardlessof positionof position

100

50

00 50100% Actuator Stroke or Rotation

%Flow

Authority O.A. + R.A. = 7%

Poorly Matched Dampers

CombinedCombinedR.A. FlowR.A. FlowO.A. FlowO.A. Flow

100

50

00 50100% Actuator Stroke or Rotation

Authority O.A. + R.A. = 7%

Well Matched Dampers

%Flow

Mixed Air ControlApplicationMixed Air ControlApplication

Dampers are adequately matched ifthe combined flow characteristic doesnot deviate more than 15%

DamperApplications

“hunting and cycling”“hunting and cycling”

Mixed AirControl ApplicationMixed AirControl Application

Instability in both temperature andstatic pressure control loops occursif variations in combined flowcharacteristics are excessive

■ Large variations cause mixing plenum pressureto fluctuate significantly as dampers aremodulated

■ In turn, the flow rate of each air streamunpredictably varies so set point is difficult tomaintain

■ This instability causes oscillation in supply fanstatic pressure

DamperApplications

Mixed AirControl ApplicationMixed AirControl Application

00 55 1010 1515 2020 2525 3030

% Authority ofSecond Damper

7070

6060

5050

4040

3030

2020

1010

00

% Authority of First Damper

Parallel Blade

Opposed Blade

Constant Flow DamperMatching Chart(i.e. for Mixing Plenums)

DamperApplications

Tm = [(T1)(Flow1)+(T2(Flow2)] ÷ (Flow1 + Flow2)

Tm = Temperature of mixed air streamT1 = Temperature of air stream #1T2 = Temperature of air stream #2Flow1 = Flow rate of air stream #1Flow2 = Flow rate of air stream #2


■ Select mixing dampers to havea linear flow characteristic

■ When two air streams are mixed,resulting mixed air temperature can bedetermined with equation

DamperApplications

AUTHORITY RECOMMENDATIONSAUTHORITY RECOMMENDATIONS


Outdoor air damper installed in duct

■ Size for an authority of…–– 8-10% for opposed linkage8-10% for opposed linkage

–– 20-25% for parallel linkage20-25% for parallel linkage

■ Select return and exhaust airdampers for an authority of:

–– 8-10% for opposed linkage8-10% for opposed linkage

–– 20-25% for parallel linkage20-25% for parallel linkage

Outdoor air damper installed at louver face

■ Its size may match the louver

■ Determine the authority for design flow rate(assume 400FPM) and damper size

■ Use constant flow damper matching chart todetermine authority of return air damper

■ Select exhaust air damper for same authority asoutdoor air damper

Opposed Opposedor Parallelor Parallel

BladeBladeDampersDampers

DamperApplications

DAMPERS Made RIGHT,

Right AwayDAMPERS Made RIGHT,

Right Away

FAN 268.1FAN 268.1

dampers - applications

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