Lecture 15: Air Primary Loops and Controls

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 primary air loops in EnergyPlus Control their operation and

availability for conditioning thermal zones

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Keywords Covered in this Lecture

Air Primary LoopSystem Availability Manager ListSystem Availability

Manager:ScheduledSystem Availability Manager:Night

CycleController ListController:Simple

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Describing a Central Forced Air System

Can be thought of as an “Air Loop” with 2 “sides”: Supply side: air primary loop and its

associated objects central fans, coils, etc.

Demand side: controlled zone equip configuration and its associated objects air terminal units, fan coils, etc.

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Describing a Central Forced Air System (cont’d)When we say “Air Loop” we will

normally mean the supply side of the overall air loop

“Zone Equipment” will mean the demand side: all the stuff specific to a zone

If no central air system, then there will be only zone equipment

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Describing a Central Forced Air System (cont’d)

North

Zone

East

Zone

Resistive

Zone

Supply Fan

Ret

urn

Air

Mix

er

Zo

ne A

ir Sp

litter

Cooling CoilCC

VAV Box:ReHeat

VAV Box:ReHeat

Mixed OutsideAir Box

Relief Air

Outside Air

VAV Box:ReHeat

Supply Side/AirPrimary Loop

Demand Side/ZoneEquipment

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Air Loop Simulation

Simulates central air distribution, mixing, and conditioning Equipment: supply & return fans,

central heating and cooling coils, heat recovery, mixed air box

Control: supply air temperature, outside air economizer

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Hot Branch

Cold Branch

Air Loop Layout

Main Supply Branch

Splitter

Zone Equipment Group

Zone Splitter

Zones

Zone Splitter

Zone Mixer

Zone Equipment

Group Inlets

Zone EquipGroup Outlet

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Air Loop Layout (cont’d)

Supply Fan

Mixed OutsideAir Box

Relief Air

Outside Air

Heating/CoolingCoil

Supply Fan

Relief Air

Outside Air

Heating/CoolingCoil

Air Loop Outlet NodeAir Loop Inlet Node

Zone Equip Inlet NodeZone Equip Outlet Node

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Air Loop Syntax Map Air Loop Input Structure/Map

Air Primary Loop

data

Controller List System Availability Manager List Branch List Supply Air Controller List

component controllers in order of priority; defined by CONTROL:... syntax

System Availability Manager List managers such as:

System Availability Manager:Scheduled

etc.

Branch List

branch name 1, branch name 2, …..

Connector List

Connector List

Connector type, connector name

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Air Primary Loop

Controller ListSystem Availability Manager ListBranch ListConnector ListConnection to Zone Equipment

ReturnAir AirLoop Inlet Node ZoneEquipGroup Outlet Node SupplyAirPath ZoneEquipGroup Inlet Nodes AirLoop Outlet Nodes

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Air Primary Loop - Example

AIR PRIMARY LOOP,

Unitary System, !- Primary Air Loop Name

, !- Name: Controller List

Avail List, !- Name: System Availability Manager List

autosize, !- Primary air design flow rate {m3/s}

Air Loop Branches, !- Air Loop Branch List Name

, !- Air Loop Connector List Name

Air Loop Inlet Node, !- ReturnAir AirLoop Inlet Node

ZONE EQUIP OUTLET NODE, !- ZoneEquipGroup Outlet Node

Zone Equipment Inlet Node,!- SupplyAirPath ZoneEquipGroup In Nodes

Air Loop Outlet Node; !- AirLoop Outlet Nodes

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System Control

High Level Similar to an energy management

system Set Point Managers

algorithms establish fluid loop set points Availability Managers

make global on/off decisions

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System Control (cont’d)

Component Control Controllers

sense state at one point in system control flow at another point to match set

point Integrated control

control integrated within component

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System Control (cont’d)

Plant: component sequencing & load management

Control is ideal PI/PID control is not modeled – would

require shorter time steps

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System Availability Managers

Scheduled System availability determined by an

on/off schedule

Night Cycle Used to cycle an air system on when

one or more zones becomes too hot or too cold

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System Availability Manager List

Lists all of the applicable system availability managers for a given air loop

SYSTEM AVAILABILITY MANAGER LIST,

Furnace- Avail List, !- Name

SYSTEM AVAILABILITY MANAGER:SCHEDULED, !- Type

Furnace- Avail; !- System Availability Manager Name 1

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System Availability Manager:Scheduled

Simple on/off schedule

SYSTEM AVAILABILITY MANAGER:SCHEDULED,

Furnace- Avail, !- Name

FanAndCoilAvailSched; !- Schedule name

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System Availability Manager:Night Cycle

Applicability schedule nameFan schedule nameControl type

Stay Off, Cycle On Any, Cycle On Control Zone, Cycle On Any - Zone Fans Only

Thermostat on/off toleranceCycling run timeControl zone name

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System Availability Manager:Night Cycle-

Example SYSTEM AVAILABILITY MANAGER:NIGHT CYCLE, VAV Sys 1 Avail, !- Name SysAvailApplicSch, !- Applicability schedule name FanAvailSched, !- Fan schedule name Cycle On Any, !- Control type 4.0, !- thermostat on/off tolerance {deltaC} 7200.; !- Cycling run time {s}

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Set Point Managers

Scheduled Uses a schedule to determine one or more

set points

Outside Air Sets the supply air temperature according

to the outside air temperature using a reset rule

Reset schedule determined by the supply air set point temperature at the outside high and low temperature

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Set Point Managers (cont’d)

Single Zone Reheat Calculates a set point temperature for

the supply air that will satisfy the load of a controlled zone

Single Zone Minimum Humidity Calculates the supply air humidity

ratio needed to maintain the zone relative humidity at or above a given set point

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Set Point Managers (cont’d)

Mixed Air Used to establish a temperature set

point at the mixed air node Set point must take into account any

downstream system fan heat Outside air controller operates the

outside air damper to meet this set point for economizer

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Controllers

Simple Controls variable at one node based on the

condition at another node For a cooling coil, the control node might be

the outlet air temperature while the actuated variable is the flow rate through the coil

Outside Air Controls mixed air box to use outside air for

free cooling whenever possible

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Controller List

Repeat for each controller

CONTROLLER LIST,

VAV Sys 1 Controllers, !- Name

Controller:Simple, !- Controller Type 1

Central Cooling Coil Controller 1, !- Controller Name 1

Controller:Simple, !- Controller Type 2

Central Heating Coil Controller 1; !- Controller Name 2

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Controller:Simple

Control_Node really the sensed node

Actuator_NodeController convergence toleranceMax actuated flowMin actuated flowAction

Reverse for cooling Normal for heating

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Controller:Simple - Example

CONTROLLER:SIMPLE,

Central Heating Coil Controller 1, !- Name

TEMP, !- Control variable

Normal, !- Action

FLOW, !- Actuator variable

VAV Sys 1 Outlet Node, !- Control_Node

Main Heating Coil 1 Water Inlet Node, !- Actuator_Node

0.002, !- Controller Convergence Tolerance: delta from setpoint

autosize, !- Max Actuated Flow {m3/s}

0.0; !- Min Actuated Flow {m3/s}

Action is “Normal” for heating, “Reverse” for cooling.

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Summary

Central forced air systems in EnergyPlus consist of an “air loop” (supply side) and a “zone equipment loop” (demand side)

Primary air loop description contains: controller list, availability manager, branch list, and connection information

Setpoint manager used by controllers to calculate current setpoint for various HVAC components