Convergence problem with Controller:WaterCoil and TemperatureAndHumidity control - need more plant iterations?

[mjwitte]

Issue overview

Work on changing the order of the internal surface data (#7575) has tripped over some surprising diffs. For example, here's the cooling coil load and chiller load for the summer design day in 5ZoneWaterCooled_Baseboard, with develop and with ManageSurfaceHeatBal2. Similar behavior has been observed in 5ZoneCoolingPanelBaseboardAuto (both files have baseboard with a radiant fraction, but I'm not sure that's relevant) or maybe it is. The cooling coil loads a differ some, but the chiller load shows big diversions at night when the load is smaller.

On a wild guess (or goose chase), I tried increasing the minimum plant iterations to 10 (from the default of 2).

  ConvergenceLimits,
    1,                       !- Minimum System Timestep {minutes}
    20,                      !- Maximum HVAC Iterations
    10,                       !- Minimum Plant Iterations
    20;                       !- Maximum Plant Iterations

This alters the chiller load significantly in both branches.

Looking at just develop with the change in ConvergenceLimits:

Details

Some additional details for this issue (if relevant):

• Platform Win64
• Version of EnergyPlus 9.3.0-d0361cca92
• Reference ManageSurfaceHeatBal2 #7575

Checklist

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

• Defect file: testfiles\5ZoneWaterCooled_Baseboard.idf
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[mjwitte]

Here's a comparison of versions back to v8.9. The chiller behavior started in v9.1, changed again in v9.2.

[mjwitte]

Lovely. This got broken in #7215 which was a fix for chilled water coils with humidity control which potentially affects 20 test files.