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

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:VariableVolumeZone Air Supply PathZone Air Return PathZone Splitter and Zone Mixer (review)Direct AirAir Distribution UnitSingle 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 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

5

Zone Equipment Syntax Map

6

Air Path

Zone Supply Air Path

Zone Return Air Path

7

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

8

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

9

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;

10

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)

11

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

12

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

13

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

14

Air Loop Zone Equipment

Direct Air

Air Distribution Units

15

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

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

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

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)

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)

20

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

21

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

22

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

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