1. 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

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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

9. 9 Air Loop Layout (cont’d)

10. 10 Air Loop Syntax Map

11. 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

12. 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

13. 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

14. 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

15. 15 System Control (cont’d)  Plant: component sequencing & load management  Control is ideal PI/PID control is not modeled – would require shorter time steps

16. 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

17. 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

18. 18 System Availability Manager:Scheduled  Simple on/off schedule SYSTEM AVAILABILITY MANAGER:SCHEDULED, Furnace- Avail, !- Name FanAndCoilAvailSched; !- Schedule name

19. 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

20. 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}

21. 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

22. 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

23. 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

24. 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

25. 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

26. 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

27. 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.

28. 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