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Fix VRFFluidCtrl heating cycling issue by moving cycling ratio calc in compressor spd calc #10416

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Fix VRFFluidCtrl heating cycling issue by moving cycling ratio calc in compressor spd calc #10416

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yujiex
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@yujiex yujiex commented Feb 28, 2024 •
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Pull request overview

The PR fixes the cycling ratio calculation of the VRF model in heating mode.

image

It also enforces a lower bound on the outdoor unit's evaporating temperature. The older version uses the refrigerant lowest saturation temperature as the lower bound, which might not be realistically reachable.

        this->VRFOU_CalcCompH(state,
                              TU_HeatingLoad,
                              this->EvaporatingTemp,
                              Tdischarge,
                              h_IU_cond_out_ave,
                              this->IUCondensingTemp,
                              this->IUEvapTempLow,           // <-- lower bound enforced here
                              Tfs,
                              Pipe_Q_h,
                              Q_c_OU,
                              CompSpdActual,
                              Ncomp_new,
                              CyclingRatio);

NOTE: ENHANCEMENTS MUST FOLLOW A SUBMISSION PROCESS INCLUDING A FEATURE PROPOSAL AND DESIGN DOCUMENT PRIOR TO SUBMITTING CODE

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@yujiex yujiex added the Defect Includes code to repair a defect in EnergyPlus label Feb 28, 2024
@yujiex yujiex self-assigned this Feb 28, 2024
@yujiex yujiex marked this pull request as draft February 28, 2024 00:49
yujiex
yujiex commented Mar 6, 2024
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src/EnergyPlus/HVACVariableRefrigerantFlow.cc
if (CapDiff > (Tolerance * Cap_Eva0)) NumIteCcap = 999;

Ncomp = this->RatedCompPower * CurveValue(state, this->OUCoolingPWRFT(CounterCompSpdTemp), T_discharge, T_suction);
if (CapDiff > (Tolerance * Cap_Eva0)) {
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cycling ratio calculation is moved to here

yujiex
yujiex commented Mar 6, 2024
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src/EnergyPlus/HVACVariableRefrigerantFlow.cc
@@ -11856,80 +11856,60 @@ void VRFCondenserEquipment::CalcVRFCondenser_FluidTCtrl(EnergyPlusData &state)
CapMinTe + 8,
this->IUCondensingTemp - 5);

if ((Q_c_OU * C_cap_operation) <= CompEvaporatingCAPSpdMin) {
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The cycling ratio calculation is removed here

yujiex
yujiex commented Mar 6, 2024
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src/EnergyPlus/HVACVariableRefrigerantFlow.cc
Tdischarge,
h_IU_cond_out_ave,
this->IUCondensingTemp,
this->IUEvapTempLow,
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enforces a lower bound to the outdoor unit evaporating temperature

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I know the goto Label20 was present in the original code but we should try to eliminate goto statements when possible. This does not need to change in this branch and is a suggestion for future code. I moved out of the loop any code that does not need to be calculated each iteration.

Counter = 1;
m_air = this->OUAirFlowRate * RhoAir;
Ncomp_new = Ncomp;
while (std::abs(Ncomp_new - Ncomp) > (Tolerance * Ncomp)) && (Counter < 30)) {
}

@yujiex yujiex added this to the EnergyPlus 24.2 milestone Mar 11, 2024
@yujiex yujiex marked this pull request as ready for review March 13, 2024 17:52
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@yujiex @Myoldmopar it has been 28 days since this pull request was last updated.

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@yujiex @Myoldmopar it has been 28 days since this pull request was last updated.

rraustad
rraustad reviewed May 6, 2024
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src/EnergyPlus/HVACVariableRefrigerantFlow.cc
NumIteCcap = 999;
CyclingRatio = min(1.0, (TU_load + Pipe_Q) * C_cap_operation / Cap_Eva1);
} else {
CyclingRatio = 1.0;
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This looks odd. This appears to say if the calculation converged set CyclingRatio = 1 ?

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@rraustad rraustad rraustad left review comments

@Myoldmopar Myoldmopar Awaiting requested review from Myoldmopar

@mjwitte mjwitte Awaiting requested review from mjwitte

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@yujiex yujiex

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EnergyPlus 24.2
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Successfully merging this pull request may close these issues.

VRF heating issue: same heating power with different compressor speed at low heating load
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