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Water Side Economizer (HeatExchanger:FluidToFluid) Override Will Not Activate

asked 2016-03-31 15:49:52 -0500

updated 2016-03-31 15:50:20 -0500


I am attempting to simulate a Water Side Economizer (WSE) in EnergyPlus 8.4. I am using a HeatExchanger:FluidToFluid with the CoolingSetpointOnOffWithComponentOverride option to override the chiller when possible. The simulation runs without any errors but the WSE never turns on.

I have looked at the FreeCoolingChiller.idf file in the EnergyPlus example files but have not been able to distill any solutions to my current problem.

The branches, splitters, mixers, and branchlists appear to be working correctly. I believe it is a problem with using the control scheme/setpoints and the Loop option for the Component Override Cooling Control Temperature Mode. I am using Loop because my condenser loop is actually connected to a river. I have allowed the condenser loop to go to 0.005 C and checked that the river temperature is below the 6.7 C set for the free cooling.

Is there a SetpointManager/Control Scheme I need to incorporate that I have missed? I was going to implement an EMS control scheme but figured I should get a simple configuration working first before dynamically adjusting the Condenser Loop.

Thank you,


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answered 2016-04-01 06:57:34 -0500

updated 2016-04-01 06:58:01 -0500

Make sure you have defined a zero offset temperature: see this

Also, you need to add a setpoint manager to the outlet of the HX on the chilled water side, or create your own plant loop equipment operation scheme (see this)

Here's how the chilled water loop should look like (unless you choose to define your own plant equip operation scheme)

Chilled water loop

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Thank you very much for your help! I had the Minimum Temperature Difference to Activate Heat Exchanger=0 but I also had the Operation Minimum Temperature Limit=0.005. After deleting the optional input fields for the Operation Min/Max Temperature Limits the simulation ran and the WSE was activated!

It appears that providing a minimum and maximum operative temperature limits the WSE from overriding the Chiller. Thank you for your help and the examples.

JustinShultz's avatar JustinShultz  ( 2016-04-01 10:45:54 -0500 )edit

What is the hourly node temperature difference before and after the HX ? Is it close to your design Delta T? I created a similar model with HX but my delta T across the HX never gets close to my design Delta T in peak day.

BL's avatar BL  ( 2016-04-04 13:33:14 -0500 )edit

I also have some troubles to get my favored design DeltaT (supply side inlet temperature - demand side outlet temperature) when I'am using a HX for waterside economiser (integrated). Does anyone have some experience?

nielex's avatar nielex  ( 2016-06-07 06:24:16 -0500 )edit

answered 2016-06-19 17:45:26 -0500

updated 2016-06-20 00:21:57 -0500

Using this setup along with some EMS logic to reset the condenser temperature I can get the WSE to be activated whenever ambient wetbulb conditions allow. However, the chiller doesn't always turn off when it should and stays on with a very low PLR at times because the HX is supplying most of the cooling. I believe this is because the operation schemes that OS is defaulting to.

See timeseries below:

image description

Here are the default schemes that OS translates to E+:

  Chilled Water Loop Operation Schemes,   !- Name
  PlantEquipmentOperation:CoolingLoad,    !- Control Scheme Object Type 1
  Chilled Water Loop Cooling Operation Scheme, !- Control Scheme Name 1
  Always On Discrete,                     !- Control Scheme Schedule Name 1
  PlantEquipmentOperation:Uncontrolled,   !- Control Scheme Object Type 2
  Chilled Water Loop Uncontrolled Operation Scheme, !- Control Scheme Name 2
  Always On Discrete,                     !- Control Scheme Schedule Name 2
  PlantEquipmentOperation:ComponentSetpoint, !- Control Scheme Object Type 3
  Chilled Water Loop Setpoint Operation Scheme, !- Control Scheme Name 3
  Always On Discrete;                     !- Control Scheme Schedule Name 3

  Chilled Water Loop Cooling Operation Scheme, !- Name
  0,                                      !- Load Range Lower Limit 1 {W}
  1000000000,                             !- Load Range Upper Limit 1 {W}
  Chilled Water Loop Cooling Equipment List; !- Range Equipment List Name 1

  Chilled Water Loop Cooling Equipment List, !- Name
  Chiller:Electric:EIR,                   !- Equipment Object Type 1
  Chiller -2;                             !- Equipment Name 1

  Chilled Water Loop Uncontrolled Operation Scheme, !- Name
  Chilled Water Loop Uncontrolled Equipment List; !- Equipment List Name

  Chilled Water Loop Uncontrolled Equipment List, !- Name
  HeatExchanger:FluidToFluid,             !- Equipment Object Type 1
  Non-Integrated Waterside Economizer HX; !- Equipment Name 1

  Chilled Water Loop Setpoint Operation Scheme, !- Name
  HeatExchanger:FluidToFluid,             !- Equipment Object Type 1
  Non-Integrated Waterside Economizer HX, !- Equipment Name 1
  Node 118,                               !- Demand Calculation Node Name 1
  Node 122,                               !- Setpoint Node Name 1
  Autosize,                               !- Component Flow Rate 1 {m3/s}
  Dual;                                   !- Operation Type 1

Ideally, I would like to use only a 'PlantEquipmentOperation:ComponentSetpoint' scheme and have both pieces of equipment listed in the scheme with the HX having priority. I don't believe this scheme is supported by OS directly. Does anyone have any ideas on how to create this configuration without manipulating the IDF via measure?

Update: I performed a test where the other two operating schemes were disabled and only the 'PlantEquipmentOperation:ComponentSetpoint' scheme was operational. This resulted in no change at all and the WSE and chiller were staged just like before. Given this disregard my previous question. This was surprising for me as I thought the priority of the other operation schemes would impact how equipment was staged.

I thought it maybe had something to do with the min. PLR and min. unloading ratio for the chiller so I ran another test where these were both set to zero instead of 0.1 and 0.2 respectively. To my surprise, this resulted in quite a large penalty as the chiller's baseload increase by over 100 kW. I'm thoroughly confused now...

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I had a lot of issues where using the HX in economizer mode didn't actually save any energy for the building, which was strange based on the source being a very cold river. I had to change setpoints to force the condenser loop to stay colder so that it wouldn't bypass the HX and activate the chiller.

In other words, I set the condenser loop temp to 0.5 degC higher than the source temperature for the time frame in which I knew the economizer should be operational. I had wished that E+ would have known to keep the loop temperature low to optimize the economizer but that was not the case.

JustinShultz's avatar JustinShultz  ( 2016-06-20 10:19:17 -0500 )edit

@Lincoln, my two cents are..since all the three control schemes in PlantEquipmentOperationSchemes use Always On Discrete schedule, they will all be on and off at the same time. If you apply different schedules to Uncontrolled and CompSetPoint schemes above, adding/removing them should make difference in results. Not sure about OpenStudio, but E+ example files such as FreeCoolingChiller.idf, WaterSideEconomizer_Integrated.idf and WaterSideEconomizer_NonIntegrated.idf only add Heat exchanger either in series with pump or in parallel branch of chiller. And not in PlantEquipmentList.

Chandan Sharma's avatar Chandan Sharma  ( 2016-06-30 04:24:01 -0500 )edit

regarding the original question, there is an issue with CoolingSetpointOnOffWithComponentOverride in EnergyPlus as outlined here. I am not sure EMS can offer any work around to address this issue.

Chandan Sharma's avatar Chandan Sharma  ( 2016-06-30 04:26:44 -0500 )edit

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Asked: 2016-03-31 15:49:52 -0500

Seen: 930 times

Last updated: Jun 20 '16