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Addressed FanCoil with CyclingFan control using Fan:SystemModel has different fan power than Fan:OnOff #7380

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Aug 26, 2019
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Addressed FanCoil with CyclingFan control using Fan:SystemModel has different fan power than Fan:OnOff #7380

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18bd3ae
Addressed FanCoil System Model Fan Cycling Issue
Nigusse Jul 9, 2019
5103ffc
Added unit test
Nigusse Jul 9, 2019
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18 changes: 12 additions & 6 deletions src/EnergyPlus/FanCoilUnits.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -3594,8 +3594,7 @@ namespace FanCoilUnits {
ZoneCompTurnFansOn,
ZoneCompTurnFansOff);
} else {
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(
FanCoil(FanCoilNum).LowSpeedRatio, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(_, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
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Can you walk me through this change? By not passing a speed ratio, does this force the fan object to operate at a single discrete mode? Is that what fixes the fan to operate just like the Fan:OnOff?

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@Nigusse Nigusse Aug 26, 2019 •
edited
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We do not want to pass the fan speed ratio for cycling operating mode. FanCoilUnits cycling mode are designed such that the fan coil unit cycles at each speed level. Thus passing speed ratio will result incorrect fan power calculation. By not passing the fan speed ratio, the fansystem model locally calculates average flow fraction instead, for the fan power calculation.

}
} else if (FanCoil(FanCoilNum).SpeedFanSel == 2) {

Expand All @@ -3607,15 +3606,22 @@ namespace FanCoilUnits {
ZoneCompTurnFansOn,
ZoneCompTurnFansOff);
} else {
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(
FanCoil(FanCoilNum).MedSpeedRatio, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(_, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
}
} else { // using 1.0 here for fan speed ratio seems wrong if FCU max flow rate is different than the fan maximum flow rate
} else if (FanCoil(FanCoilNum).SpeedFanSel == 3) {

if (FanCoil(FanCoilNum).FanType_Num != DataHVACGlobals::FanType_SystemModelObject) {
Fans::SimulateFanComponents(
FanCoil(FanCoilNum).FanName, FirstHVACIteration, FanCoil(FanCoilNum).FanIndex, 1.0, ZoneCompTurnFansOn, ZoneCompTurnFansOff);
} else {
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(1.0, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(_, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
}
} else { // using 1.0 here for fan speed ratio seems wrong if FCU max flow rate is different than the fan maximum flow rate
if (FanCoil(FanCoilNum).FanType_Num != DataHVACGlobals::FanType_SystemModelObject) {
Fans::SimulateFanComponents(
FanCoil(FanCoilNum).FanName, FirstHVACIteration, FanCoil(FanCoilNum).FanIndex, 0.0, ZoneCompTurnFansOn, ZoneCompTurnFansOff);
} else {
HVACFan::fanObjs[FanCoil(FanCoilNum).FanIndex]->simulate(0.0, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
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Is this change required for fixing this defect or is this an unrelated change?

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@Nigusse Nigusse Aug 26, 2019 •
edited
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If you referring to the last line where I set 0.0 for speed ratio, is to turn off the fan. Simple because the unit is off if no fan speed is specified.

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The fancoil unit is expected to operate at one of the three fan speed levels, if the fan speed is not set yet, then the fan coil unit must be off. Otherwise, what does the fancoil unit do if no fan speed set yet? I observed such a case when I was debugging the defect.

}
}
if (FanCoil(FanCoilNum).CCoilType_Num == CCoil_HXAssist) {
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