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Correct physics based VRF model to align inlet and outlet air flow rates #7295

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merged 12 commits into from
May 17, 2019
Merged

Correct physics based VRF model to align inlet and outlet air flow rates #7295

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3aa02d6
Adjust cryptic model to align inlet/outlet air flow rates
rraustad May 9, 2019
63442e6
Merge remote-tracking branch 'origin/develop' into 6301-VRF-Terminal-…
Myoldmopar May 13, 2019
03f4064
Add a few comments
rraustad May 13, 2019
ac463cb
Mimic new VRF model calculations
rraustad May 14, 2019
a674053
Merge branch 'develop' of https://github.com/NREL/EnergyPlus into 630…
rraustad May 14, 2019
1b8245c
Merge branch '6301-VRF-Terminal-unit-flow-balance-problems' of https:…
rraustad May 14, 2019
69211ef
Clean up and add unit test
rraustad May 15, 2019
ce7d093
A bit more clean up to fix formatting and delete unnecessary code
rraustad May 15, 2019
b2f4106
Delete unused variable
rraustad May 15, 2019
5bd6ae1
Remove more unused variables
rraustad May 16, 2019
2ec3bcf
Merge remote-tracking branch 'origin/develop' into 6301-VRF-Terminal-…
Myoldmopar May 17, 2019
9792e73
Fix unused variable issue
Myoldmopar May 17, 2019
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41 changes: 22 additions & 19 deletions src/EnergyPlus/HVACVariableRefrigerantFlow.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -8663,34 +8663,35 @@ namespace HVACVariableRefrigerantFlow {
}

// Set inlet air mass flow rate based on PLR and compressor on/off air flow rates
SetAverageAirFlow(VRFTUNum, 1.0, temp);
//SetAverageAirFlow(VRFTUNum, 1.0, temp);
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The TUs have already been simulated. At this point it appears the model want to know what the evap T and cond T are for use during the next time step. Anything that tried to resimulate the TUs is now commented out.

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Note here that the original model did not set OA flow rate and therefore used the OA flow for the last TU simulated when SetAverageAirFlow was called. When I corrected this (lines 8671 and 8676), my new method matched the old method results.

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Also note that any calls to this and other functions updates the node flow rates. So data set when the TU was actually modelled is used here instead.

VRFInletNode = this->VRFTUInletNodeNum;
T_TU_in = Node(VRFInletNode).Temp;
W_TU_in = Node(VRFInletNode).HumRat;
T_coil_in = T_TU_in;
W_coil_in = W_TU_in;

// Simulation the OAMixer if there is any
if (this->OAMixerUsed) {
SimOAMixer(this->OAMixerName, false, this->OAMixerIndex);
//SimOAMixer(this->OAMixerName, false, this->OAMixerIndex);
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Mixer has already been simulated.


OAMixerNum = UtilityRoutines::FindItemInList(this->OAMixerName, OAMixer);
OAMixNode = OAMixer(OAMixerNum).MixNode;
T_coil_in = Node(OAMixNode).Temp;
W_coil_in = Node(OAMixNode).HumRat;
} else {
T_coil_in = T_TU_in;
W_coil_in = W_TU_in;
}
// Simulate the blow-through fan if there is any
if (this->FanPlace == BlowThru) {
if (this->fanType_Num == DataHVACGlobals::FanType_SystemModelObject) {
HVACFan::fanObjs[this->FanIndex]->simulate(1.0 / temp, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
FanOutletNode = HVACFan::fanObjs[this->FanIndex]->outletNodeNum;
} else {
Fans::SimulateFanComponents("", false, this->FanIndex, FanSpeedRatio, ZoneCompTurnFansOn, ZoneCompTurnFansOff);
FanOutletNode = Fans::Fan(this->FanIndex).OutletNodeNum;
}
T_coil_in = Node(FanOutletNode).Temp;
W_coil_in = Node(FanOutletNode).HumRat;
}
//if (this->FanPlace == BlowThru) {
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@rraustad rraustad May 9, 2019 •
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Fan has already been simulated. If the intent here is to simulate at full flow then why weren't the coils simulated again?

// if (this->fanType_Num == DataHVACGlobals::FanType_SystemModelObject) {
// HVACFan::fanObjs[this->FanIndex]->simulate(1.0 / temp, ZoneCompTurnFansOn, ZoneCompTurnFansOff, _);
// FanOutletNode = HVACFan::fanObjs[this->FanIndex]->outletNodeNum;
// } else {
// Fans::SimulateFanComponents("", false, this->FanIndex, FanSpeedRatio, ZoneCompTurnFansOn, ZoneCompTurnFansOff);
// FanOutletNode = Fans::Fan(this->FanIndex).OutletNodeNum;
// }
// T_coil_in = Node(FanOutletNode).Temp;
// W_coil_in = Node(FanOutletNode).HumRat;
//}

Garate = CompOnMassFlow;
H_coil_in = PsyHFnTdbW(T_coil_in, W_coil_in);
Expand All @@ -8702,8 +8703,9 @@ namespace HVACVariableRefrigerantFlow {
if ((Garate > 0.0) && ((!VRF(VRFNum).HeatRecoveryUsed && CoolingLoad(VRFNum)) ||
(VRF(VRFNum).HeatRecoveryUsed && TerminalUnitList(TUListIndex).HRCoolRequest(IndexToTUInTUList)))) {
// 1.1) Cooling coil is running
QZnReqSenCoolingLoad = max(0.0, -1.0 * ZoneSysEnergyDemand(ZoneIndex).OutputRequiredToCoolingSP);
Tout = T_TU_in - QZnReqSenCoolingLoad * 1.2 / Garate / 1005;
//QZnReqSenCoolingLoad = max(0.0, -1.0 * ZoneSysEnergyDemand(ZoneIndex).OutputRequiredToCoolingSP);
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@rraustad rraustad May 9, 2019 •
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Here's the big question. What Tout is needed here? The Tout when the coil is operating I assume. Line 8706 is wrong since for that zone, the TU operated and probably met the load, so OutputRequiredToCoolingSP is probably 0. Instead I use the actual coil outlet temp, but this is premised on needing actual Tout.

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I guess I should read the Eng. Ref. to get better acquainted.
@nealkruis @mbadams5 @mjwitte @Myoldmopar @jasondegraw @kbenne this will need some serious thought and review because I don't know this model. What the heck should it do? Does it need full output conditions while coils are operating? Yet the coils can have different PLR's so how to average correctly to get condenser performance? Anyone recognize old line 8706 above? Q*1.2/Mdot/1005 ? Figuring out what this function needs will probably correct this issue. If Tout at full air flow is really needed then the coils will need to be simulated again, or better yet that information needs to be saved when the TUs model full flow and then used here. Is Xiufeng Pang or RP Zhang or anyone at LBNL available for consult on this model?

//Tout = T_TU_in - QZnReqSenCoolingLoad * 1.2 / Garate / 1005;
Tout = DXCoils::DXCoilOutletTemp(CoolCoilNum);
Th2 = T_coil_in - (T_coil_in - Tout) / (1 - BFC);
DeltaT = C3Tevap * SH * SH + C2Tevap * SH + C1Tevap;
EvapTemp = max(min((Th2 - DeltaT), EvapTempMax), EvapTempMin);
Expand All @@ -8717,8 +8719,9 @@ namespace HVACVariableRefrigerantFlow {
if ((Garate > 0.0) && ((!VRF(VRFNum).HeatRecoveryUsed && HeatingLoad(VRFNum)) ||
(VRF(VRFNum).HeatRecoveryUsed && TerminalUnitList(TUListIndex).HRHeatRequest(IndexToTUInTUList)))) {
// 2.1) Heating coil is running
QZnReqSenHeatingLoad = max(0.0, ZoneSysEnergyDemand(ZoneIndex).OutputRequiredToHeatingSP);
Tout = T_TU_in + QZnReqSenHeatingLoad / Garate / 1005;
//QZnReqSenHeatingLoad = max(0.0, ZoneSysEnergyDemand(ZoneIndex).OutputRequiredToHeatingSP);
//Tout = T_TU_in + QZnReqSenHeatingLoad / Garate / 1005;
Tout = DXCoils::DXCoilOutletTemp(HeatCoilNum);
Th2 = T_coil_in + (Tout - T_coil_in) / (1 - BFH);
DeltaT = C3Tcond * SC * SC + C2Tcond * SC + C1Tcond;
CondTemp = max(min((Th2 + DeltaT), CondTempMax), CondTempMin);
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