Reordering `PlantLoop` objects give different results

[lymereJ]

Issue overview

Three models are included with this ticket. The only difference between these models is the order in which the three plant loops are specified. All three cases give different results, see below. The EIO files are pretty much identical, the only difference are in the convergence values (6th decimal place).

Case 1:

Case 2:

Case 3:

Details

Some additional details for this issue (if relevant):

• Platform: Windows
• Version of EnergyPlus: 24.1

Checklist

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

• [x] Defect files: defect_files.zip
• [ ] Ticket added to EnergyPlus Defect Complexity (Github Project)
• [ ] Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[lymereJ]

The models have an EMS program, commenting out the program reduces the differences but they're still there.

[mjwitte]

Try increasing " Minimum Plant Iterations" in ConvergenceLimits to see if that reduces the differences (without EMS).

[lymereJ]

Increasing the Minimum Plant Iterations (without EMS) seems to increase the energy use differences:

Minimum Plant Iterations = 2:

• Case 1:

• Case 2:
  

• Case 3:

Minimum Plant Iterations = 5:

• Case 1:

• Case 2:
  

• Case 3:

Case 1 and Case 3 see to always have similar results.

PlantLoop objects order: (CWH is chilled water loop, CW is condenser water loop)

• Case 1: CW, CWH secondary, CWH primary
• Case 2: CWH primary, CWH secondary, CW
• Case 3: CWH secondary, CW, CWH primary

[rraustad]

@EnergyArchmage any insight? I do know that HeatExchanger:FluidToFluid may have some issues with how node conditions are passed through in the plant.

[EnergyArchmage]

I think the cool tools cooling tower model is suspect, be interesting to try with the Merkel version.

I would try a test to reorder the Sizing:Plant objects to match the order of the PlantLoop objects. I keep finding places where the plant sizing index and plant loop index are mixed up. But if the eio's are the same then that probably isn't it.