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Adjust low flow warning for w2a coil in cycling fan mode #11485

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Adjust low flow warning for w2a coil in cycling fan mode #11485

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ed5a7fa
Adjust low flow warning for cycling fan.
joseph-robertson Mar 27, 2026
e0be50a
Formatting.
joseph-robertson Mar 27, 2026
dcb96e7
Pass PartLoadRation into InitSimpleWatertoAirHP.
joseph-robertson Mar 27, 2026
cca85cb
Update unit tests for update to InitSimpleWatertoAirHP.
joseph-robertson Mar 27, 2026
9ec1457
Formatting.
joseph-robertson Mar 27, 2026
0a5be8c
Merge branch 'develop' into coil-w2a-cycling-fan
joseph-robertson Apr 8, 2026
e8f0d32
Merge branch 'develop' into coil-w2a-cycling-fan
mitchute Apr 9, 2026
1ced44d
Move low flow flag to conditions struct so each coil can report the w…
joseph-robertson Apr 9, 2026
dfd83ab
Coil in cycling fan mode with PLR=0 should throw the low flow warning.
joseph-robertson Apr 9, 2026
db02101
Update unit test to check for recurring warning with continuous fan.
joseph-robertson Apr 9, 2026
8639482
Coil is off when PLR=0 for cycling fan.
joseph-robertson Apr 13, 2026
0590663
Add unit test for cycling fan low flow.
joseph-robertson Apr 13, 2026
550577d
Merge branch 'develop' into coil-w2a-cycling-fan
joseph-robertson Apr 13, 2026
ad69260
Formatting.
joseph-robertson Apr 13, 2026
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37 changes: 27 additions & 10 deletions src/EnergyPlus/WaterToAirHeatPumpSimple.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -181,12 +181,13 @@ namespace WaterToAirHeatPumpSimple {

if (simpleWAHP.WAHPPlantType == DataPlant::PlantEquipmentType::CoilWAHPCoolingEquationFit) {
// Cooling mode
InitSimpleWatertoAirHP(state, HPNum, SensLoad, LatentLoad, fanOp, OnOffAirFlowRatio, FirstHVACIteration);
InitSimpleWatertoAirHP(state, HPNum, SensLoad, LatentLoad, fanOp, OnOffAirFlowRatio, FirstHVACIteration, PartLoadRatio);
CalcHPCoolingSimple(state, HPNum, fanOp, SensLoad, LatentLoad, compressorOp, PartLoadRatio, OnOffAirFlowRatio);
UpdateSimpleWatertoAirHP(state, HPNum);
} else if (simpleWAHP.WAHPPlantType == DataPlant::PlantEquipmentType::CoilWAHPHeatingEquationFit) {
// Heating mode
InitSimpleWatertoAirHP(state, HPNum, SensLoad, DataPrecisionGlobals::constant_zero, fanOp, OnOffAirFlowRatio, FirstHVACIteration);
InitSimpleWatertoAirHP(
state, HPNum, SensLoad, DataPrecisionGlobals::constant_zero, fanOp, OnOffAirFlowRatio, FirstHVACIteration, PartLoadRatio);
CalcHPHeatingSimple(state, HPNum, fanOp, SensLoad, compressorOp, PartLoadRatio, OnOffAirFlowRatio);
UpdateSimpleWatertoAirHP(state, HPNum);
} else {
Expand Down Expand Up @@ -914,9 +915,10 @@ namespace WaterToAirHeatPumpSimple {
int const HPNum, // Current HPNum under simulation
Real64 const SensLoad, // Control zone sensible load[W]
Real64 const LatentLoad, // Control zone latent load[W]
[[maybe_unused]] HVAC::FanOp const fanOp, // fan operating mode
HVAC::FanOp const fanOp, // fan operating mode
[[maybe_unused]] Real64 const OnOffAirFlowRatio, // ratio of compressor on flow to average flow over time step
bool const FirstHVACIteration // Iteration flag
bool const FirstHVACIteration, // Iteration flag
Real64 const PartLoadRatio // compressor part load ratio
)
{

Expand Down Expand Up @@ -1103,12 +1105,27 @@ namespace WaterToAirHeatPumpSimple {
state.dataLoopNodes->Node(AirInletNode).Temp,
state.dataLoopNodes->Node(AirInletNode).HumRat,
RoutineName);
if (simpleWAHP.AirMassFlowRate < 0.25 * RatedAirMassFlowRate) {
ShowRecurringWarningErrorAtEnd(state,
"Actual air mass flow rate is smaller than 25% of water-to-air heat pump coil rated air flow rate.",
state.dataWaterToAirHeatPumpSimple->AirflowErrPointer,
simpleWAHP.AirMassFlowRate,
simpleWAHP.AirMassFlowRate);
if (fanOp != HVAC::FanOp::Cycling) {
if (simpleWAHP.AirMassFlowRate < 0.25 * RatedAirMassFlowRate) {
ShowRecurringWarningErrorAtEnd(
state,
"Actual air mass flow rate is smaller than 25% of water-to-air heat pump coil rated air flow rate.",
state.dataWaterToAirHeatPumpSimple->AirflowErrPointer,
simpleWAHP.AirMassFlowRate,
simpleWAHP.AirMassFlowRate);
}
} else {
if ((PartLoadRatio == 0.0) || (simpleWAHP.AirMassFlowRate / PartLoadRatio) < 0.25 * RatedAirMassFlowRate) {
if (simpleWAHP.LowFlowFlag) {
ShowWarningError(
state,
EnergyPlus::format(
"{}: Actual air mass flow rate is smaller than 25% of water-to-air heat pump coil ({}) rated air flow rate.",
RoutineName,
simpleWAHP.Name));
simpleWAHP.LowFlowFlag = false;
}
}
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@rraustad rraustad Apr 8, 2026

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This is the same thing that is done in the calc function so this is correct.

void CalcHPCooling(Heating)Simple:

    if (fanOp == HVAC::FanOp::Continuous) {
        LoadSideFullMassFlowRate = simpleWatertoAirHP.AirMassFlowRate;
    } else {
        // default to cycling fan, cycling compressor, full load air flow
        if (PartLoadRatio > 0.0) {
            LoadSideFullMassFlowRate = simpleWatertoAirHP.AirMassFlowRate / PartLoadRatio;
        } else {
            LoadSideFullMassFlowRate = 0.0;
        }
    }

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@rraustad rraustad Apr 8, 2026

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@joseph-robertson I see the recurring removed from the err file, but where is the 1-time warning? In this diff, shouldn't there be a new warning that wasn't there before ? ASHRAE901_ApartmentHighRise_STD2019_Denver

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@rraustad rraustad Apr 8, 2026 •
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Also, this should be a SimpleWatertoAirHPConditions struct variable so each coil can report the warning.

if (state.dataWaterToAirHeatPumpSimple->LowFlowFlag) {

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@joseph-robertson joseph-robertson Apr 9, 2026

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@rraustad I think previously the recurring warning was being thrown on this testfile for coils in cycling fan mode. With the new / PartLoadRatio, the warning goes away. It's possible there are no testfiles (with coils in continuous fan mode) where we should expect the 1-time warning to be thrown. Perhaps I should look into writing a couple new unit tests for showing that both warning types get thrown under the right conditions; one for coil in continuous fan mode and one for coil in cycling fan mode.

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@rraustad rraustad Apr 9, 2026

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Duh, your right.

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@joseph-robertson joseph-robertson Apr 9, 2026 •
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After the divide by zero fix in dfd83ab, the testfile DOAToWaterToAirHPInlet_MultispeedFan.idf does throw the 1-time warning.

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@rraustad rraustad Apr 10, 2026

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What is the node air flow rate when that warning is hit? If it's 0 then that warning should not be reported. Even if the flow rate is > 0 the coil will be off. Why report a warning for a time step when the coil is off? Eventually the coil will be on and that check will throw if necessary. For cycling fan if PLR = 0 then the coil will be off and the fan will be off. A parent can still call the coil with PLR = 0 when there is actually a load and the result will be capacity = 0. A parent will call the coil model with PLR = 0 and PLR = 1 to test whether either of these can meet the load. For continuous fan and PLR = 0 there will be a non-zero capacity because of fan heat and also if OA is provided and that result could meet the load so the parent will not turn on the coil. The check should be testing for if the coil is on, which also protects the divide by 0 but that's a different thing.

if (PartLoadRatio > 0.0 && (simpleWAHP.AirMassFlowRate / PartLoadRatio) < 0.25 * RatedAirMassFlowRate)

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@joseph-robertson joseph-robertson Apr 13, 2026

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I will make this change. (I do see that the node air flow rate > 0 when PLR = 0.)

Since we'll now have no testfiles throwing this warning, I'll see if I can add a unit test for demonstrating it.

}
simpleWAHP.WaterFlowMode = true;
} else { // heat pump is off
Expand Down
4 changes: 3 additions & 1 deletion src/EnergyPlus/WaterToAirHeatPumpSimple.hh
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Expand Up @@ -162,6 +162,7 @@ namespace WaterToAirHeatPumpSimple {
Real64 LatentCapacityTimeConstant = 0.0; // Latent capcacity time constant [s]
Real64 FanDelayTime = 0.0; // Fan delay time, time delay for the HP's fan to
bool reportCoilFinalSizes = true; // one time report of sizes to coil report
bool LowFlowFlag = true; // one time low flow warning for coil in cycling fan mode
};

void SimWatertoAirHPSimple(EnergyPlusData &state,
Expand Down Expand Up @@ -190,7 +191,8 @@ namespace WaterToAirHeatPumpSimple {
Real64 const LatentLoad, // Control zone latent load[W]
HVAC::FanOp const fanOp, // fan operating mode
Real64 const OnOffAirFlowRatio, // ratio of compressor on flow to average flow over time step
bool const FirstHVACIteration // Iteration flag
bool const FirstHVACIteration, // Iteration flag
Real64 const PartLoadRatio // compressor part load ratio
);

void SizeHVACWaterToAir(EnergyPlusData &state, int const HPNum);
Expand Down
2 changes: 1 addition & 1 deletion tst/EnergyPlus/unit/WaterThermalTanks.unit.cc
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Expand Up @@ -3151,7 +3151,7 @@ TEST_F(EnergyPlusFixture, StratifiedTank_GSHP_DesuperheaterSourceHeat)
CoilBranch.Comp(CompNum).Name = "GSHP_COIL1";

state->dataGlobal->BeginEnvrnFlag = true;
WaterToAirHeatPumpSimple::InitSimpleWatertoAirHP(*state, HPNum, 10.0, 10.0, fanOp, 1.0, true);
WaterToAirHeatPumpSimple::InitSimpleWatertoAirHP(*state, HPNum, 10.0, 10.0, fanOp, 1.0, true, 1.0);
WaterToAirHeatPumpSimple::CalcHPCoolingSimple(*state, HPNum, fanOp, 10.0, 10.0, HVAC::CompressorOp::On, PLR, 1.0);
// Coil source side heat successfully passed to HeatReclaimSimple_WAHPCoil(1).AvailCapacity
EXPECT_EQ(state->dataHeatBal->HeatReclaimSimple_WAHPCoil(1).AvailCapacity, state->dataWaterToAirHeatPumpSimple->SimpleWatertoAirHP(1).QSource);
Expand Down
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