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…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
Damper ApplicationsDamper Applications
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
Damper ApplicationsDamper Applications
Smoke (leakage-rated)
■ Actuator and damper must be UL approvedas a MATCHED SET for smoke control
You cannot use just any actuator!!
ULULULULcc
Damper ApplicationsDamper Applications
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
Damper ApplicationsDamper Applications
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
% Damper Blade Rotation
100100
5050
00
Factorsaffecting
performance
100100
5050
0000 5050100100
%Flow
Determined in a certifiedtesting laboratory
% Damper Blade Rotation
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
Static PressureControl ApplicationStatic PressureControl Application
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
Static PressureControl ApplicationStatic PressureControl Application
(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
Static PressureControl ApplicationStatic PressureControl 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
Mixed Air ControlApplicationMixed Air ControlApplication
■ 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
Mixed Air ControlApplicationMixed Air ControlApplication
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