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Issue Warning Error on negative coil capacity sizing #11197

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42c437e
Add severe error to indicate negative capacity calculation.
tanaya-mankad Aug 22, 2025
fd1df60
Test for too-cold entering air on design day.
tanaya-mankad Sep 4, 2025
1884a53
Add Unitary test with a VSCoil for capacity error verification.
tanaya-mankad Sep 5, 2025
3592a72
Merge branch 'develop' of https://github.com/NREL/EnergyPlus into neg…
tanaya-mankad Sep 5, 2025
9a097d9
Correct formatting.
tanaya-mankad Sep 5, 2025
237e68e
Recreate failing conditions in test after warning change.
tanaya-mankad Sep 12, 2025
a678190
Add design day name to error.
tanaya-mankad Sep 18, 2025
ff8edfd
Merge branch 'develop' of https://github.com/NREL/EnergyPlus into neg…
tanaya-mankad Sep 22, 2025
78dd547
Add diagnostic information to WarningError.
tanaya-mankad Oct 2, 2025
ecbc41a
Add test to be enabled at a later time.
tanaya-mankad Oct 2, 2025
49fc066
Updated warning message and test.
tanaya-mankad Oct 8, 2025
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14 changes: 7 additions & 7 deletions src/EnergyPlus/VariableSpeedCoils.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -4749,18 +4749,18 @@ namespace VariableSpeedCoils {
TotCapTempModFac =
Curve::CurveValue(state, varSpeedCoil.MSCCapFTemp(varSpeedCoil.NormSpedLevel), MixWetBulb, RatedSourceTempCool);

if (MixTemp < SupTemp) {
ShowSevereError(
state,
"On design day, cooling coil entering air temperature is less than design outlet air temperature. This will "
"yield negative coil capacity sizing.");
ShowContinueError(state, "Cooling capacity is set to zero during sizing; simulation continues.");
}
if (MixEnth > SupEnth) {
CoolCapAtPeak = (rhoair * VolFlowRate * (MixEnth - SupEnth)) + FanCoolLoad;
} else {
CoolCapAtPeak = (rhoair * VolFlowRate * (48000.0 - SupEnth)) + FanCoolLoad;
}
if ((CoolCapAtPeak < 0) && (MixTemp < SupTemp)) {
ShowWarningError(
state,
format("On design day {}, cooling coil entering air temperature {:.2R} is less than design supply air temperature {:.2R}. This would "
"yield negative coil capacity sizing for {}.", state.dataSize->FinalSysSizing(state.dataSize->CurSysNum).CoolDesDay, MixTemp, SupTemp, varSpeedCoil.Name));
ShowContinueError(state, "Cooling capacity is set to zero during sizing; simulation continues.");
}
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Coil sizing is based on enthalpy. Given the sneaky use of a standard capacity if enthalpies are not correct CoilCapAtPeak should never be negative here. I would like to see the 48000 removed (i.e., delete the else) since it just forces a non-zero coil capacity. There is nothing wrong with the coil sizing to 0 if FinalSysSizing conditions warrant that result.

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Yes! Not knowing where it came from, I was reticent to touch a "magic number."

CoolCapAtPeak = max(0.0, CoolCapAtPeak);
if (TotCapTempModFac > 0.0) {
RatedCapCoolTotalDes = CoolCapAtPeak / TotCapTempModFac;
Expand Down
32 changes: 16 additions & 16 deletions tst/EnergyPlus/unit/UnitarySystem.unit.cc
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Expand Up @@ -5953,18 +5953,18 @@ TEST_F(EnergyPlusFixture, VSCoilUnitary_NoNegativeCapacity)

"Sizing:System,",
"Heat Pump Sys 1, !- AirLoop Name",
"sensible, !- Type of Load to Size On",
"VentilationRequirement, !- Type of Load to Size On",
"autosize, !- Design Outdoor Air Flow Rate {m3/s}",
"0.0, !- Central Heating Maximum System Air Flow Ratio",
"7.0, !- Preheat Design Temperature {C}",
"1.0, !- Central Heating Maximum System Air Flow Ratio",
"27.0, !- Preheat Design Temperature {C}",
"0.008, !- Preheat Design Humidity Ratio {kgWater/kgDryAir}",
"25.0, !- Precool Design Temperature {C}",
"32.222, !- Precool Design Temperature {C}",
"0.008, !- Precool Design Humidity Ratio {kgWater/kgDryAir}",
"25., !- Central Cooling Design Supply Air Temperature {C}",
"50., !- Central Heating Design Supply Air Temperature {C}",
"32.222, !- Central Cooling Design Supply Air Temperature {C}",
"12.777, !- Central Heating Design Supply Air Temperature {C}",
"noncoincident, !- Type of Zone Sum to Use",
"no, !- 100% Outdoor Air in Cooling",
"no, !- 100% Outdoor Air in Heating",
"yes, !- 100% Outdoor Air in Cooling",
"yes, !- 100% Outdoor Air in Heating",
"0.008, !- Central Cooling Design Supply Air Humidity Ratio {kgWater/kgDryAir}",
"0.008, !- Central Heating Design Supply Air Humidity Ratio {kgWater/kgDryAir}",
"DesignDay, !- Cooling Supply Air Flow Rate Method",
Expand All @@ -5978,17 +5978,17 @@ TEST_F(EnergyPlusFixture, VSCoilUnitary_NoNegativeCapacity)
", !- Heating Fraction of Autosized Heating Supply Air Flow Rate",
", !- Heating Fraction of Autosized Cooling Supply Air Flow Rate",
", !- Heating Supply Air Flow Rate Per Unit Heating Capacity {m3/s-W}",
", !- System Outdoor Air Method",
"1.0, !- Zone Maximum Outdoor Air Fraction {dimensionless}",
"CoolingDesignCapacity, !- Cooling Design Capacity Method",
"autosize, !- Cooling Design Capacity {W}",
"ZoneSum, !- System Outdoor Air Method",
", !- Zone Maximum Outdoor Air Fraction {dimensionless}",
", !- Cooling Design Capacity Method",
", !- Cooling Design Capacity {W}",
", !- Cooling Design Capacity Per Floor Area {W/m2}",
", !- Fraction of Autosized Cooling Design Capacity",
"HeatingDesignCapacity, !- Heating Design Capacity Method",
"autosize, !- Heating Design Capacity {W}",
", !- Heating Design Capacity Method",
", !- Heating Design Capacity {W}",
", !- Heating Design Capacity Per Floor Area {W/m2}",
", !- Fraction of Autosized Heating Design Capacity",
"VAV; !- Central Cooling Capacity Control Method",
"; !- Central Cooling Capacity Control Method",

"Curve:Cubic,",
"HPACHeatCapFT, !- Name",
Expand Down Expand Up @@ -6767,7 +6767,7 @@ TEST_F(EnergyPlusFixture, VSCoilUnitary_NoNegativeCapacity)
Real64 constexpr SpeedRatio{0.0};
int constexpr SpeedCal{1};
VariableSpeedCoils::InitVarSpeedCoil(*state, DXCoilNum, SensLoad, LatentLoad, fanOp, OnOffAirFlowRatio, SpeedRatio, SpeedCal);
EXPECT_TRUE(compare_err_stream_substring("entering air temperature is less than design outlet air temperature", true));
EXPECT_TRUE(compare_err_stream_substring("This will yield negative coil capacity sizing", true));
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This unit test should fail. The old message used "will" and the new warning message above uses:

This would yield negative coil capacity sizing

}

TEST_F(EnergyPlusFixture, UnitarySystemModel_SetOnOffMassFlowRateTest)
Expand Down