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Controlling a hydronic economizer in EnergyPlus

asked 2015-04-23 21:22:08 -0500

updated 2017-05-17 12:48:11 -0500

I have a design which has a very specific sequence of operation on its waterside economizer. In short there is an outdoor dry bulb temperature when the hydronic economizer can active (anything below 38°F) and when the economizer is operating the chiller is off. Also when the hydronic economizer is working the cooling tower condenser water temperature is allowed to go below its specific boundary for chiller operation.

Does anyone know:

  1. If there is a control to turn the chiller off in EnergyPlus when the economizer is working?
  2. if there is a control that will allow me to control the condenser water temperature when the chiller is operating and a completely different set of controls on the condenser water temperature when the hydronic cooling tower is working?

I am assuming if these controls do not exist then I will need to write some EMS. If this is the case and anyone has experience with writing these I would certainly appreciate pointers for this case.

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answered 2015-04-24 07:33:53 -0500

Chandan Sharma's avatar

updated 2016-06-28 22:40:58 -0500

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.

    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
    Condenser Loop Setpoint Manager, !- Name
    Temperature,             !- Control Variable
    Cond Loop Temp Schedule,  !- Schedule Name
    Condenser Supply Outlet Node; !- Setpoint Node or NodeList Name
    Set_CondLoopTemp_Sched, !- Name
    Cond Loop Temp Schedule, !- Actuated Component Unique Name
    Schedule:Compact,            !- Actuated Component Type
    Schedule Value;             !- Actuated Component Control Type
    My Setpoint Schedule Calculator Example,
    OutdoorTemp,                          !- Name
    Environment,                          !- Output:Variable Index Key Name
    Site Outdoor Air Drybulb Temperature; !- Output:Variable Name
    IF (OutdoorTemp >= 3.33),
     Set Set_CondLoopTemp_Sched = 35 ,
     Set Set_CondLoopTemp_Sched = 3 ,
 Output:Variable,Cond Loop Temp Schedule,Schedule Value,timestep;
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Also, check out the example file WaterSideEconomizer_Integrated.idf

aparker's avatar aparker  ( 2015-04-25 17:08:48 -0500 )edit

Thanks so much @chandanshama the override seems to be working using this so I am very happy! I have been battling with the economizer to make it work and this helped for sure. I also made the control node on the condenser loop which helped the flow go through the economizer when necessary.

Annie Marston's avatar Annie Marston  ( 2015-04-28 09:29:52 -0500 )edit

Did anyone use a integrated waterside economiser (based to WaterSideEonomizer_Integrated.idf) with a 'SetpointManager:FollowOutdoorAirTemperature' and without EMS? There are any problems? Using this application I have still the following topic:

nielex's avatar nielex  ( 2016-06-07 06:50:33 -0500 )edit

That should work.

Chandan Sharma's avatar Chandan Sharma  ( 2016-06-09 22:22:01 -0500 )edit

I also tried to implemente a EMS programm based on the above-mentioned example. But I got an error message like " ** Severe ** GetSetPointManagerInputs:SetpointManager:Scheduled="CONDENSER_LOOP_SETPOINT_MANAGER", invalid field. ** ~~~ ** ..invalid Schedule Name="CONDENSER_LOOP_TEMP_SCHEDULE"." Does anyone know, what does it mean?

Is it necessary to create also a "Schedule:Compact" in the schedules tab? Should that be the case I have to set a value. Does it mean, that the defined value is always override by the EMS program?

nielex's avatar nielex  ( 2016-06-28 07:32:05 -0500 )edit

answered 2015-04-24 01:39:04 -0500

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.

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This is a very good point. I am actually going to put a schedule on the condensor water temperature because it is easier. Thanks so much for the answer.

Annie Marston's avatar Annie Marston  ( 2015-04-28 09:30:59 -0500 )edit

I was having trouble implementing the EMS scheme above. I saw your comment and found it to be very straight forward and helpful, thank you!

JustinShultz's avatar JustinShultz  ( 2016-04-04 15:13:40 -0500 )edit

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Asked: 2015-04-23 21:22:08 -0500

Seen: 964 times

Last updated: Jun 28 '16