Fix load dispatch for variable-flow chillers with a low leaving temperature limit

[dareumnam]

Pull request overview

• Fixes Variable CHW Flow Chillers Operate unexpectedly #10965

Description of the purpose of this PR

• Multiple chillers on a SequentialLoad / SequentialUniformPLR scheme all run at an identical PLR instead of staging up, when they use LeavingSetpointModulated flow mode, sit on pumped branches, and have a Leaving Chilled Water Lower Temperature Limit at or near the loop setpoint.
• AdjustChangeInLoadByHowServed() truncates the dispatched load for a ByNominalCapLowOutLimit component using the flow present at its inlet node:
  QdotTmp = CurMassFlowRate * Cp * (Tinlet - ToutLowLimit)
• The branch pump runs before the chiller, so that flow is still the pump minimum. But a LeavingSetpointModulated chiller sets its own flow rate, so this understates its capacity. Chiller 1 is capped well below what it can do and the remainder cascades down the equipment list. The chiller model already enforces the low outlet limit internally, so this outer truncation is redundant for variable-flow machines.
• So I added CompData::ModulatedFlow, set by each chiller in LeavingSetpointModulated mode. When set, capacity is evaluated at MassFlowRateMaxAvail instead of the current flow. Constant-flow behavior is unchanged.
• Also updated both truncation branches in PlantCondLoopOperation.cc and the chiller modules that register a low outlet limit (ChillerElectricEIR, ChillerReformulatedEIR, ChillerIndirectAbsorption, PlantChillers).
• Defect idf file: I ran the file from the original issue (HVACTemplate-5ZoneVAVWaterCooled_V2420_rev_exp_CHWLimit7.22.idf), which has four Chiller:Electric:EIR on parallel pumped branches, SequentialUniformPLR, and both the loop setpoint and the low limit at 7.22C. (RunPeriod: May).

- On develop the load splits into exact quarters every hour. With the fix, chiller 1 carries the base load and chiller 4 runs only 16 hours on the hottest days. Equal PLR among running chillers is expected under `SequentialUniformPLR`. Chiller 1 peaks at 0.78 rather than 1.0 because the low limit equals the setpoint, capping usable delta T at about half the design value.

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[github-actions]

⚠️ Regressions detected on macos-14 for commit 9a48904

Regression Summary

• EIO: 85
• ESO Small Diffs: 92
• MTR Small Diffs: 105
• Table Small Diffs: 55
• ESO Big Diffs: 32
• Table Big Diffs: 25
• Table String Diffs: 11
• JSON Big Diffs: 1
• MTR Big Diffs: 13
• ERR: 6

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit 9a48904

Regression Summary

• EIO: 85
• ESO Small Diffs: 92
• MTR Small Diffs: 104
• Table Small Diffs: 56
• ESO Big Diffs: 32
• Table Big Diffs: 25
• JSON Big Diffs: 1
• Table String Diffs: 11
• MTR Big Diffs: 13
• ERR: 6

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on macos-14 for commit acaf7b0

Regression Summary

• EIO: 85
• ESO Small Diffs: 92
• MTR Small Diffs: 105
• Table Small Diffs: 55
• ESO Big Diffs: 32
• Table Big Diffs: 25
• Table String Diffs: 11
• JSON Big Diffs: 1
• MTR Big Diffs: 13
• ERR: 6

• View Results
• Download Regressions

[github-actions]

⚠️ Regressions detected on ubuntu-24.04 for commit acaf7b0

Regression Summary

• EIO: 85
• ESO Small Diffs: 92
• MTR Small Diffs: 104
• Table Small Diffs: 56
• ESO Big Diffs: 32
• Table Big Diffs: 25
• JSON Big Diffs: 1
• Table String Diffs: 11
• MTR Big Diffs: 13
• ERR: 6

• View Results
• Download Regressions