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Lecture 16: Zone Air Paths and Air Distribution Units
Material prepared by GARD Analytics, Inc. and University of Illinoisat Urbana-Champaign under contract to the National Renewable Energy
Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved
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Purpose of this Lecture
Gain an understanding of how to: Define the Zone Equipment (Demand
Side) of an Air Loop Zone Air Supply and Return Paths Air Distribution Units Examples of Zone Equipment
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Keywords Covered in this Lecture
Fan:Simple:VariableVolumeZone Air Supply PathZone Air Return PathZone Splitter and Zone Mixer (review)Direct AirAir Distribution UnitSingle Duct:VAV:Reheat
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Air Loop Components: Simple Example
FAN:SIMPLE:VariableVolume, Supply Fan 1, !- Fan Name FanAvailSched, !- Available Schedule 0.7, !- Fan Total Efficiency 600.0, !- Delta Pressure {Pa} 1.56, !- Max Flow Rate {m3/s} 0.45, !- Min Flow Rate {m3/s} 0.9, !- Motor Efficiency 1.0, !- Motor In Airstream Fraction 0.35071223, !- FanCoefficient 1 0.30850535, !- FanCoefficient 2 -0.54137364, !- FanCoefficient 3 0.87198823, !- FanCoefficient 4 0.000, !- FanCoefficient 5 Main Heating Coil 1 Outlet Node, !- Fan_Inlet_Node VAV Sys 1 Outlet Node; !- Fan_Outlet_Node
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Zone Equipment Syntax Map
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Air Path
Zone Supply Air Path
Zone Return Air Path
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Zone Supply Air Path
Zone splitter Splits the supply air from the main air
handler to serve individual zones Dual duct systems require splitters for both
the cold and hot air ducts
Zone supply plenum Allows system air to flow through a zone
before it reaches the zone(s) to be served One supply plenum per air handler supply
duct
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Zone Supply Air Path -Example
ZONE 3 ATUIn Node
ZONE3
ZONE2 ATUIn Node
ZONE2
ZONE1 ATUIn Node
ZONE1
Zone EqIn Node
Zone Supply Air Splitter 1
Zone Supply Air Path 1
SupplyFan
ExhaustFan
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Zone Supply Air Path - Example (cont’d)
ZONE SUPPLY AIR PATH,
Zone Supply Air Path 1, !- name of object
Zone Eq In Node, !- supply path inlet node
Zone Splitter, Zone Supply Air Splitter 1; !- type and name of component
ZONE SPLITTER,
Zone Supply Air Splitter 1, !- name
Zone Eq In Node, !- inlet node
ZONE1 ATU In Node, !- outlet nodes
ZONE2 ATU In Node,
ZONE3 ATU In Node;
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Zone Return Air Path
Zone Mixer Mixes the return air streams returning to the
main air handler from individual zonesZone return plenum
Allows system air to flow through a zone before it reaches the main return duct
Allows system air to be mixed from multiple zones, can eliminate the need for a zone mixer
Can mix plenum and ducted returns Plenums may be in series or parallel (series
temperatures lag by a zone time step)
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Zone Return Air Path - Example
ZONE 3Outlet Node
ZONE3
ZONE2Outlet Node
ZONE2
ZONE1Outlet Node
ZONE1
Return AirMixer Outlet
Zone Return Air Mixer
Zone Return Air Path
SupplyFan
ExhaustFan
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Zone Return Air Path – Example with Return
Plenum
Space2-1
Space1-1
Supply Fan
Zo
ne
Air S
plitte
r
CC
VAV
Box:ReHeat
VAV
Box:ReHeat
Mixed OutsideAir Box
Relief Air
Outside Air HC
Return AirPlenum Zone
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Zone Return Air Path - Example (cont’d)
ZONE RETURN AIR PATH,
TermReheatReturnPath, !- Return Air Path Name
Return Air Mixer Outlet, !- Return Air Path Outlet Node
Zone Mixer, !- KEY--System Component Type 1
Zone Return Air Mixer; !- Component Name 1
ZONE MIXER,
Zone Return Air Mixer, !- Mixer Name
Return Air Mixer Outlet, !- Outlet_Node
Zone 1 Outlet Node, !- Inlet_Node_1
Zone 2 Outlet Node, !- Inlet_Node_2
Zone 3 Outlet Node; !- Inlet_Node_3
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Air Loop Zone Equipment
Direct Air
Air Distribution Units
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Zone Equipment Schematic
Zone 1
Local Con-
vective Units
Air-Air HP
Unit Heater/ Vent- ilator
Fan Coil Window AC
High Temp
Radiant/ Con-
vective
Low Temp
Radiant
Base- boards Radiators High
Temp Radiators
Low Temp
Radiant Panels
Select One
Select One
Return Air Path
Zone Exhaust Branch (Opt.)
None Dual Duct
Constant Volume
(CV)
Single Duct CV Reheat
Dual Duct VAV
Single Duct VAV:
Reheat
Local Conv. Unit Alternatives Hi Temp Rad/Conv Alternatives
Low Temp Rad Alternatives
Select One
Air
Distribution Unit
Options
Zone Supply Air
Splitter
Air Distribution
Unit
Water-Air HP &
Ground Source
HP
Select One
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Direct Air
Used to model systems in which central system air is supplied directly to a zone Furnace Heat pump
Central supply air may be controlled to meet setpoints in a “control zone”
“Slave zones” typically have no individual control
“Slave zones” may have baseboards or other equipment to allow individual control
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Direct Air - Example
ZONE1Node
Supply Fan
ZONE1DirectAir
ZONE1
ZONE1Inlet Node
ZONE1Out Node
DIRECT AIR,
Zone1DirectAir, !- Direct Air Name
FanAndCoilAvailSched, !- Schedule name for on/off schedule
Zone 1 Inlet Node, !- Zone Supply Air Node Name
0.47; !- Maximum air flow rate {m3/s}
ZONE2Node
ZONE2DirectAir
ZONE2
ZONE2Inlet Node
ZONE2Out Node
Control Zone with thermostat
Slave Zone
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Air Distribution Units
Allows equipment within the zone inlet duct-work to be attached to the supply air stream
Includes equipment that controls or tempers the air going into a zone such as dampers, reheat coils, etc.
Only one ADU allowed per zone on a given air loop
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Air Distribution Units (cont’d)
Air Distribution Units Single Duct Constant Volume Reheat Single Duct VAV Reheat Dual Duct Constant Volume Dual Duct VAV Powered Induction Units
(Series and Parallel)
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Air Distribution Units (cont’d)
Zone 1
None Dual
Duct
Constant
Volume
(CV)
Single
Duct CV
Reheat
Dual
Duct
VAV
Single
Duct
VAV:
Reheat
Select One
Air
Distribution
Unit
Options
Air
Distribution
Unit
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Air Distribution Unit - Example
AIR DISTRIBUTION UNIT,
SPACE1-1 ATU, ! Name of air distribution unit
SPACE1-1 In Node, ! unit outlet node
SINGLE DUCT:VAV:REHEAT, ! type of component
SPACE1-1 VAV Reheat; ! name of component
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Single Duct:VAV:Reheat - Example
SINGLE DUCT:VAV:REHEAT,
SPACE1-1 VAV Reheat, ! object name
ReheatCoilAvailSched, ! availability schedule
SPACE1-1 Zone Coil Air In Node, ! zone heating coil inlet node
SPACE1-1 ATU In Node, ! terminal unit inlet node
0.33, ! max air flow rate m3/s
0.3, ! min air flow as decimal fraction of max air flow
SPACE1-1 Zone Coil Water In Node, ! water flow control node
COIL:Water:SimpleHeating, ! heating component type
SPACE1-1 Zone Coil, ! heating component name
0.0003, ! max water flow rate m3/s
0.0, ! min water flow rate m3/s
SPACE1-1 In Node, ! terminal unit outlet node
0.001, ! convergence tolerance
REVERSE ACTION; ! Damper Heating Action
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Summary
Zone Equipment loop is the “demand side” of a forced air system
Main parts of the zone equipment loop include: Supply and Return paths Thermostats Air Distribution Unit
Can also add local radiative or convective systems that serve the zone apart from the air loop