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Lecture 15: Air Primary Loops and Controls Material prepared by GARD Analytics, Inc. and University of Illinois at 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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2 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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3 Keywords Covered in this Lecture Air Primary Loop System Availability Manager List System Availability Manager:Scheduled System Availability Manager:Night Cycle Controller List Controller:Simple
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4 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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5 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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6 Describing a Central Forced Air System (cont’d) North Zone East Zone Resistive Zone Supply Fan Return Air Mixer Zone Air Splitter Cooling Coil CC VAV Box:ReHeat Mixed Outside Air Box Relief Air Outside Air VAV Box:ReHeat Supply Side/Air Primary Loop Demand Side/Zone Equipment
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7 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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8 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 Equip Group Outlet
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9 Air Loop Layout (cont’d)
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10 Air Loop Syntax Map
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11 Air Primary Loop Controller List System Availability Manager List Branch List Connector List Connection to Zone Equipment ReturnAir AirLoop Inlet Node ZoneEquipGroup Outlet Node SupplyAirPath ZoneEquipGroup Inlet Nodes AirLoop Outlet Nodes
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12 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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13 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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14 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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15 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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16 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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17 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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18 System Availability Manager:Scheduled Simple on/off schedule SYSTEM AVAILABILITY MANAGER:SCHEDULED, Furnace- Avail, !- Name FanAndCoilAvailSched; !- Schedule name
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19 System Availability Manager:Night Cycle Applicability schedule name Fan schedule name Control type Stay Off, Cycle On Any, Cycle On Control Zone, Cycle On Any - Zone Fans Only Thermostat on/off tolerance Cycling run time Control zone name
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20 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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21 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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22 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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23 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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24 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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25 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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26 Controller:Simple Control_Node really the sensed node Actuator_Node Controller convergence tolerance Max actuated flow Min actuated flow Action Reverse for cooling Normal for heating
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27 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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28 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
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