Address variable speed DX cooling Coil does not run on latent only load #11135

Nigusse · 2025-07-28T12:51:48Z

Pull request overview

Fixes Coil:Cooling:DX:VariableSpeed does not run on latent only load #10765

Description of the purpose of this PR

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Nigusse

Variable DX cooling coil is turned off when there is latent load but no sensible load. Need to modify a logic to avoid turning off the VS dx cooling when there is latent load only.

Nigusse · 2025-07-28T13:06:03Z

src/EnergyPlus/UnitarySystem.cc

+                if ((PartLoadRatio > 0.0) || (PartLoadRatio == 0.0 && this->m_CoolingSpeedRatio > 0.0)) {
                    CompressorOn = HVAC::CompressorOp::On;
                    this->m_LastMode = CoolingMode;
                }


When there is latent load only (i.e., when there is no sensible load), then the above logic if (PartLoadRatio > 0.0) holds true for single speed DX coil only. For variable speed DX cooling coil, the PLR can be zero when the speed ratio is greater than zero. Thus, it needs to add a second logic to avoid turning off a variable DX cooling coil when there is latent load only.

At the bottom of controlCoolingSystemToSP is:

this->m_CoolingPartLoadFrac = PartLoadFrac; this->m_CoolingSpeedRatio = SpeedRatio; this->m_CoolingCycRatio = CycRatio; this->m_DehumidificationMode = DehumidMode;

I wonder if it would be better to correct this issue here because you would want the UnitarySystem to know what the PartLoadRaio is for control and reporting of m_PartLoadFrac. There is also the calcUnitarySystemToLoad function which may need review to see if an update is needed there as well.

this->m_CoolingPartLoadFrac = std::max(PartLoadFrac, SpeedRatio);

this->m_CoolingPartLoadFrac = std::max(PartLoadFrac, SpeedRatio);

This logic may work but we will be mixing up two variables. The m_CoolingPartLoadFrac and SpeedRatio have a different meaning and resetting the m_CoolingPartLoadFrac that may have un-intended consequence elsewhere.

May be use a local variable that does not affect the m_CoolingPartLoadFrac member variable.

If I understand correctly, for variable speed DX coil, the m_CoolingPartLoadFrac value is set 0.0 whenever the SpeedRatio is > 0.0. @rraustad Do you agree?

I think it's CycRatio that gets set to 0 when SpeedRatio > 0. The VS coil is tricky. I suggest plotting Unitary System Part Load Ratio to see what that shows during latent only operation. Also, CycRatio > 0 at speed = 1 and SpeedRatio > 0 at speed > 1 so my suggestion was not quite right.

I see on one place where the PLR is set to SpeedRatio this->m_CoolingPartLoadFrac = SpeedRatio; for VS DX cooling coil. Let me examine the report variables (PLR, CyclingRatio and SpeedRatio).

That could be a mistake. this->m_CoolingPartLoadFrac is similar to CycRatio and both should be 1 at speed > 1.

Nigusse · 2025-07-28T13:06:23Z

src/EnergyPlus/UnitarySystem.cc

                PartLoadRatio = this->m_CoolingPartLoadFrac;
                CompressorOn = HVAC::CompressorOp::Off;
-                if (PartLoadRatio > 0.0) {
+                if ((PartLoadRatio > 0.0) || (PartLoadRatio == 0.0 && this->m_CoolingSpeedRatio > 0.0)) {


The same change as the above.

Nigusse · 2025-07-28T13:52:38Z

The plots below show a DX cooling coil outlet node humidity ratio for a single speed and a variable speed DX coil when the Run on Latent Load input field in CoilSystem:Cooling:DX object is set to Yes. For the variable speed coil, the results are before and after the fix. Before, the fix the VS DX cooling coil is Off when there is latent load only or it is On when there are sensible and latent loads. Whereas the after-fix results show that the VS DX cooling coil is On whenever there is latent load regardless of the presence of a sensible load.

Nigusse · 2025-07-28T14:12:14Z

The plots below show similar results trend for Total Cooling Rate report variable as well. The after the fix, the variable speed DX cooling coil is On whenever there is latent load regardless of the sensible load. Before the fix, the VS DX cooling coil is On only when there are sensible and latent loads.

Nigusse · 2025-07-28T18:04:04Z

See the PLR, CyclingRatio and SpeedNumber before and after the fix. In this test case, the SpeedNumber is always > 1 and the cycling ratio in both cases is 1. Note that the PLR is always 1.0 before and after the fix.

Nigusse · 2025-07-28T18:06:04Z

src/EnergyPlus/UnitarySystem.cc

                                    General::SolveRoot(state, HumRatAcc, MaxIte, SolFla, SpeedRatio, f, 0.0, 1.0);
+                                    CycRatio = 0.0;
                                }
+                                PartLoadFrac = SpeedRatio;


Now I reset the PRL in one place using the SpeedRatio and removed the previous code changes.

Nigusse · 2025-07-28T18:09:12Z

src/EnergyPlus/UnitarySystem.cc

                                                                                        HVAC::CompressorOp::On);
                                    };
                                    General::SolveRoot(state, HumRatAcc, MaxIte, SolFla, SpeedRatio, f, 0.0, 1.0);
+                                    CycRatio = 0.0;


The CycRatio is reset to 0.0 when the SpeedNumber is = 1.

The CycRatio should be set 1.0 when the SpeedNumber is >1. I will remove the CycRatio = 0.0; statement that added above.

Nigusse · 2025-07-28T18:11:00Z

src/EnergyPlus/UnitarySystem.cc

                this->controlCoolingSystemToSP(state, AirLoopNum, FirstHVACIteration, HXUnitOn, CompressorOn);
                PartLoadRatio = this->m_CoolingPartLoadFrac;
                CompressorOn = HVAC::CompressorOp::Off;
+                // if ((PartLoadRatio > 0.0) || (PartLoadRatio == 0.0 && this->m_CoolingSpeedRatio > 0.0)) {


This commented out line will be removed.

github-actions · 2025-07-28T19:17:04Z

⚠️ Regressions detected on macos-14 for commit `549dd90`

Regression Summary

EIO: 1
ERR: 1
ESO Big Diffs: 1
Table Big Diffs: 1
Table String Diffs: 1

Nigusse · 2025-07-29T18:58:01Z

tst/EnergyPlus/unit/UnitarySystem.unit.cc

+    EXPECT_NEAR(0.112564, CoilSys.m_CoolingSpeedRatio, 0.000001);
+    EXPECT_NEAR(0.008917, CoilSys.m_DesiredOutletHumRat, 0.000001);
+    EXPECT_NEAR(0.008917, state->dataLoopNodes->Node(CoilSys.AirOutNode).HumRat, 0.000001);
+}


Added a unit test to demonstrate the fix.

Nigusse · 2025-07-29T19:27:57Z

src/EnergyPlus/UnitarySystem.cc

                                    };
                                    General::SolveRoot(state, HumRatAcc, MaxIte, SolFla, SpeedRatio, f, 0.0, 1.0);
                                }
+                                PartLoadFrac = SpeedRatio;


The SpeedRatio is saved in a local variable which is then assigned to this->m_CoolingPartLoadFrac.

Not sure where this->m_CoolingPartLoadFrac = SpeedRatio is ever used. If the speedNum > 1 then the coil never turns off during the time step and this->m_CoolingPartLoadFrac = 1. So this line should be:

PartLoadRatio = CycRatio;

At the bottom of this function:

this->m_CoolingPartLoadFrac = PartLoadFrac; this->m_CoolingSpeedRatio = SpeedRatio; this->m_CoolingCycRatio = CycRatio; this->m_DehumidificationMode = DehumidMode;

Oh, I see it now. It's used a lot in the MuiltStage electric heater. I think that's a mistake. Here speedNum > 1 so the heating coil never turns off during the time step.

case HVAC::Coil_HeatingElectric_MultiStage: { if (this->m_SuppHeatingSpeedNum > 1) { auto f = [&state, this, DesOutTemp, CycRatio](Real64 const SpeedRatio) { return UnitarySys::heatingCoilVarSpeedResidual(state, SpeedRatio, this->m_SuppHeatCoilIndex, DesOutTemp, this->m_UnitarySysNum, CycRatio, this->m_SuppHeatingSpeedNum, this->m_FanOpMode, HVAC::CompressorOp::On, true); }; General::SolveRoot(state, Acc, MaxIte, SolFla, SpeedRatio, f, 0.0, 1.0); PartLoadFrac = SpeedRatio; this->m_SuppHeatPartLoadFrac = PartLoadFrac; this->m_SuppHeatingCycRatio = CycRatio; this->m_SuppHeatingSpeedRatio = SpeedRatio;

github-actions · 2025-07-29T20:01:32Z

⚠️ Regressions detected on macos-14 for commit `9d2cbf2`

Regression Summary

EIO: 1
ERR: 1
ESO Big Diffs: 1
Table Big Diffs: 1
Table String Diffs: 1

nrel-bot-2c · 2025-08-30T00:55:22Z

@Nigusse @Myoldmopar it has been 30 days since this pull request was last updated.

mitchute · 2025-09-26T21:55:26Z

This looks OK to me. @rraustad any final comments?

github-actions · 2025-09-26T22:34:46Z

⚠️ Regressions detected on macos-14 for commit `9946d93`

Regression Summary

EIO: 1
ERR: 1
ESO Big Diffs: 1
Table Big Diffs: 1
Table String Diffs: 1

rraustad · 2025-09-29T12:44:57Z

@mitchute the code change appears to correct the issue. CI failures are unrelated. OK to merge.

Initial fix for VS CCoil latent load only operation

49e2e4a

Nigusse added the Defect Includes code to repair a defect in EnergyPlus label Jul 28, 2025

Nigusse added this to the EnergyPlus 25.2 milestone Jul 28, 2025

Nigusse commented Jul 28, 2025

View reviewed changes

Modified the initial fix my resetting the cooling plr

6a9ff7d

Nigusse commented Jul 28, 2025

View reviewed changes

Cleanup code changes

4b0905c

Nigusse added 2 commits July 29, 2025 14:52

Added a Unit test

a42ec74

Merge branch 'develop' into Issue10765_vs_dx_cooling_coil

0b04f25

Nigusse commented Jul 29, 2025

View reviewed changes

mitchute self-requested a review September 24, 2025 18:38

Merge branch 'develop' into Issue10765_vs_dx_cooling_coil

24d5ff0

mitchute merged commit 8fc445e into develop Sep 29, 2025
10 of 11 checks passed

mitchute deleted the Issue10765_vs_dx_cooling_coil branch September 29, 2025 14:34

Address variable speed DX cooling Coil does not run on latent only load #11135

Address variable speed DX cooling Coil does not run on latent only load #11135

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Nigusse commented Jul 28, 2025

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Nigusse commented Jul 28, 2025

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github-actions bot commented Jul 28, 2025

⚠️ Regressions detected on macos-14 for commit 549dd90

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github-actions bot commented Jul 29, 2025

⚠️ Regressions detected on macos-14 for commit 9d2cbf2

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nrel-bot-2c commented Aug 30, 2025

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mitchute commented Sep 26, 2025

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github-actions bot commented Sep 26, 2025

⚠️ Regressions detected on macos-14 for commit 9946d93

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rraustad commented Sep 29, 2025

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Nigusse Jul 28, 2025 •

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Nigusse commented Jul 28, 2025 •

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Nigusse Jul 28, 2025 •

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⚠️ Regressions detected on macos-14 for commit `549dd90`

rraustad Jul 30, 2025 •

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⚠️ Regressions detected on macos-14 for commit `9d2cbf2`

⚠️ Regressions detected on macos-14 for commit `9946d93`