1. Lecture 16: Zone Air Paths and Air Distribution Units
Notes: __________________________________________________________________
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Material prepared by GARD Analytics, Inc. and University of Illinois
at Urbana-Champaign under contract to the National Renewable Energy
Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2. 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

3. Keywords Covered in this Lecture
Fan:Simple:VariableVolume
Zone Air Supply Path
Zone Air Return Path
Zone Splitter and Zone Mixer (review)
Direct Air
Air Distribution Unit
Single Duct:VAV:Reheat

4. 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
, !- FanCoefficient 1
, !- FanCoefficient 2
, !- FanCoefficient 3
, !- FanCoefficient 4
0.000, !- FanCoefficient 5
Main Heating Coil 1 Outlet Node, !- Fan_Inlet_Node
VAV Sys 1 Outlet Node; !- Fan_Outlet_Node

5. Zone Equipment Syntax Map

6. Air Path
Zone Supply Air Path
Zone Return Air Path

7. Zone Supply Air Path Zone splitter Zone supply plenum
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

8. Zone Supply Air Path -Example
ZONE 3 ATU
In Node
ZONE3
ZONE2 ATU
ZONE2
ZONE1 ATU
ZONE1
Zone Eq
Zone Supply Air Splitter 1
Zone Supply Air Path 1
Supply
Fan
Exhaust

9. Zone Supply Air Path - Example (cont’d)
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;

10. Zone Return Air Path Zone Mixer Zone return plenum
Mixes the return air streams returning to the main air handler from individual zones
Zone 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)

11. Zone Return Air Path - Example
Outlet Node
ZONE3
ZONE2
ZONE1
Return Air
Mixer Outlet
Zone Return Air Mixer
Zone Return Air Path
Supply
Fan
Exhaust

12. Zone Return Air Path – Example with Return Plenum

13. Zone Return Air Path - Example (cont’d)
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

14. Air Loop Zone Equipment
Direct Air
Air Distribution Units

15. Zone Equipment Schematic
Local
Con -
vective
Units
Air HP
Unit
Heater/
Vent
ilator
Fan Coil
Window AC
High
Temp
Radiant/
Low
Radiant
Base b
oards
Radiators
Panels
Select
One
Select One
Return Air
Path
Zone Exhaust Branch (Opt.)
None
Dual
Duct
Constant
Volume
(CV)
Single
Duct CV
Reheat
VAV
VAV:
Loca
l Conv. Unit Alternatives
Hi Temp Rad/Conv
Alternatives
Low Temp Rad
Distribution
Options
Zone
Supply Air
Splitter
Water
HP &
Ground
Source

16. 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

17. Direct Air - Example DIRECT AIR, Zone1DirectAir, !- Direct Air Name
Inlet Node
ZONE2
Inlet Node
Supply
Fan
ZONE1
Node
ZONE2
Node
ZONE1
ZONE2
ZONE1
Out Node
ZONE2
Out Node
Control Zone with thermostat
Slave Zone
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}

18. 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

19. Air Distribution Units (cont’d)
Single Duct Constant Volume Reheat
Single Duct VAV Reheat
Dual Duct Constant Volume
Dual Duct VAV
Powered Induction Units (Series and Parallel)

20. Air Distribution Units (cont’d)
Zone 1
None
Dual
Duct
Constant
Volume
(CV)
Single
Duct CV
Reheat
VAV
VAV:
Select One
Air
Distribution
Unit
Options

21. Air Distribution Unit - Example
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

22. Single Duct:VAV:Reheat - Example
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

23. 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