Controlling a hydronic economizer in EnergyPlus

edit

FreeCoolingChiller.idf may help you with what you are looking for. Override Cooling Control Temperature Mode' in HeatExchanger:FluidToFluid should probably be set to 'DryBulbTemperature' and 'Free Cooler Outlet Node' should have different setpoint. For chilled water loop, everything else is probably fine. But for condenser loop you may also need EMS. Instead of 'SetpointManager:FollowOutdoorAirTemperature', condenser supply outlet node should have setpoint schedule which is modified based on outdoor air temperature something like below.

 Schedule:Compact,
    Cond Loop Temp Schedule, !- Name
    Any Number,              !- Schedule Type Limits Name
    Through: 12/31,          !- Field 1
    For: Alldays,            !- Field 2
    Until: 24:00,1;          !- Field 3
 SetpointManager:Scheduled,
    Condenser Loop Setpoint Manager, !- Name
    Temperature,             !- Control Variable
    Cond Loop Temp Schedule,  !- Schedule Name
    Condenser Supply Outlet Node; !- Setpoint Node or NodeList Name
 EnergyManagementSystem:Actuator,
    Set_CondLoopTemp_Sched, !- Name
    Cond Loop Temp Schedule, !- Actuated Component Unique Name
    Schedule:Compact,            !- Actuated Component Type
    Schedule Value;             !- Actuated Component Control Type
 EnergyManagementSystem:ProgramCallingManager,
    My Setpoint Schedule Calculator Example,
    EndOfZoneTimestepBeforeZoneReporting,
    Set_CondLoopTemp_Sched_Prog;
 EnergyManagementSystem:Sensor,
    OutdoorTemp,                          !- Name
    Environment,                          !- Output:Variable Index Key Name
    Site Outdoor Air Drybulb Temperature; !- Output:Variable Name
 EnergyManagementSystem:Program,
    Set_CondLoopTemp_Sched_Prog,
    IF (OutdoorTemp >= 3.33),
     Set Set_CondLoopTemp_Sched = 35 ,
    ELSE,
     Set Set_CondLoopTemp_Sched = 3 ,
    ENDIF;
 Output:Variable,Cond Loop Temp Schedule,Schedule Value,timestep;

I'll defer to some people who might have ran into similar situations. But my gut feeling is that you might need the EMS...

I just wanted to mention something that might get overlooked, as it's easy when you don't know how to do something to just say the catchphrase "Write your own program using EMS":

You could look into creating 8760-hourly schedules. Extract the EPW, use the drybulb temperature in your case, and build schedules with your own logic based on that. That might not work for everything as you have to be able to input a schedule in whatever object you're trying to use, but it's worth a shot.