Fix documentation of VRF Heat Pump Total Heating Rate, should equal the sum of coil heating rate, not air terminal heating rate #10627

yujiex · 2024-07-26T23:59:47Z

Pull request overview

Fixes VRF FluidTCtrl heat pump total heating rate doesn't match zone VRF air terminal total heating rate #10625
Previously the documentation says total heating rate is the sum of air terminal heating rate (which includes supplemental heating coil heating rate). This is wrong for both the curve-based model and FluidTCtrl model. This PR fixes the documentation issue.
Also fixes the fact that heat pump heating rate doesn't match total heating coil heating rate

Details on the fix of heat pump heating rate not matching total heating coil heating rate

The issue of heat pump heating rate not matching total heating coil heating rate, is caused by three factors

In function ControlVRFIUCoil, the capacity calculation method in FanSpdResidualHeat uses temperature difference (TotCap = FanSpdRto * Garate * 1005.0 * (Tout - Tin)) rather enthalpy difference (TotCap = FanSpdRto * RatedAirMassFlowRate * (PsyHFnTdbW(Tout, Wout) - PsyHFnTdbW(Tin, Win))). This is different from the coil heating rate calculation, causing some mismatches. So a function FanSpdResidualHeatUsingH is used to compute the capacity instead.
The piping correction value used in the coil calculation is different from the one used in heat pump heating rate calculation, causing some mismatches. So the piping loss adjustment to the coil heating rate is moved to the end of the VRF simulation to make sure the piping correction factor is up-to-date.
The heat pump capacity gets value here: TotalCondHeatingCapacity = this->HeatingCapacity;, its value is then passed to TotalTUHeatingCapacity and used in function LimitTUCapacity to compute an upper bound on coil heating output, when the flag FirstHVACIteration is true. So a check on this flag is added, to ensure that the update of this->HeatingCapacity syncs with the coil side.

before fixing

eplusout_develop.csv

after fixing

eplusout_feature.csv

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

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previously it says HP total heating rate is the sum of air terminal heating rate (which includes supplemental heating coil heating rate). This is wrong for both the curve-based model and FluidTCtrl model. FluidTCtrl model doesn't have an entry to this output field, so one is added.

coil heating rate calculation is like the following AirMassFlow * (OutletAirEnthalpy - InletAirEnthalpy) * PartLoadRatio In the computation of fan speed ratio, the coil heating capacity is FanSpdRto * Garate * 1005.0 * (Tout - Tin) The difference between 1005.0 * (Tout - Tin) and (OutletAirEnthalpy - InletAirEnthalpy) can cause mismatches between coil heating rate and heating demand Here we change the fan speed ratio caculation to also use the enthalpy difference way to compute its heating capacity to match the demand

mjwitte · 2024-08-16T15:09:37Z

doc/input-output-reference/src/overview/group-variable-refrigerant-flow-equipment.tex

@@ -619,7 +619,7 @@ \subsubsection{Outputs}\label{outputs-039}

 \paragraph{VRF Heat Pump Total Heating Rate {[}W{]}}\label{vrf-heat-pump-total-heating-rate-w}

-This output field is the operating total heating capacity of the variable refrigerant flow heat pump in Watts. The capacity includes any degradation due to defrost mode. This value is calculated for each HVAC system time step being simulated, and the results are averaged for the time step being reported. This value should match the sum of the individual zone terminal unit output variables for Zone VRF Air Terminal Total Heating Rate.
+This output field is the operating total heating capacity of the variable refrigerant flow heat pump in Watts. The capacity includes any degradation due to defrost mode. This value is calculated for each HVAC system time step being simulated, and the results are averaged for the time step being reported. This value should match the sum of the individual zone terminal unit heating coil output variables for Heating Coil Heating Rate.


It thought this should say "sum of the individual zone terminal unit heating coil output variables for Heating Coil Heating Rate less any piping loss."

It might just be the total of heating coil heating rate rather than total coil heating rate - piping loss.

in CalcVRFCondenser, vrf.TotalHeatingCapacity (VRF Heat Pump Total Heating Rate output variable) is computed like this

vrf.TotalHeatingCapacity = TotalCondHeatingCapacity * HeatingPLR * CyclingRatio;

And in HeatingPLR is like this

if (TotalCondHeatingCapacity > 0.0) { HeatingPLR = min(1.0, (TUHeatingLoad / vrf.PipingCorrectionHeating) / TotalCondHeatingCapacity); } else { HeatingPLR = 0.0; }

For normal cases where TotalCondHeatingCapacity > 0.0,

vrf.TotalHeatingCapacity would just be

TotalCondHeatingCapacity * ((TUHeatingLoad / vrf.PipingCorrectionHeating) / TotalCondHeatingCapacity) * CyclingRatio = TUHeatingLoad / vrf.PipingCorrectionHeating * CyclingRatio

TUHeatingLoad / vrf.PipingCorrectionHeating would be coil heating rate plus the piping loss.

Right, I meant coil heating rates plus piping loss is the output from the outdoor unit.

I see. Sorry I misunderstood earlier. I will modify the description.

mjwitte · 2024-08-16T15:10:21Z

doc/input-output-reference/src/overview/group-variable-refrigerant-flow-equipment.tex

@@ -1153,6 +1153,10 @@ \subsubsection{Outputs}

 Note: refer to the rdd file after a simulation for exact output variable names

+\paragraph{VRF Heat Pump Total Heating Rate {[}W{]}}\label{vrf-heat-pump-total-heating-rate-w}


This needs a unique label (there are duplicate label warnings when file changes are viewed in github).

Good catch. I'll add a suffix to it

mjwitte · 2024-08-16T15:11:53Z

src/EnergyPlus/DXCoils.cc

@@ -17346,7 +17346,7 @@ void ControlVRFIUCoil(EnergyPlusData &state,
    MaxSC = 20;
    Garate = state.dataDXCoils->DXCoil(CoilIndex).RatedAirMassFlowRate(1);
    // why always limit the minimum fan speed ratio to 0.65?
-    FanSpdRatioMin = min(max(OAMassFlow / Garate, 0.65), 1.0); // ensure that coil flow rate is higher than OA flow rate
+    FanSpdRatioMin = min(max(OAMassFlow / Garate, 0.0), 1.0); // ensure that coil flow rate is higher than OA flow rate


This seems like a big change, unrelated to the heating rate outputs. Does this branch include some changes from another branch?

I might have left it in by accident. Just reverted it.

…eatRate

yujiex · 2024-08-26T21:53:49Z

@mjwitte @rraustad would you mind taking another look at this PR? Thanks. I was wondering whether the type of adjustment in HVACVariableRefrigerantFlow.cc look Okay.

rraustad · 2024-08-26T22:40:50Z

src/EnergyPlus/DXCoils.cc

+    if (std::abs(ZnSenLoad) < 100.0) ZnSenLoad = sign(100.0, ZnSenLoad);
+    Real64 Wout = Win;
+    Real64 TotCap = FanSpdRto * RatedAirMassFlowRate * (PsyHFnTdbW(Tout, Wout) - PsyHFnTdbW(Tin, Win));
+    return (TotCap - ZnSenLoad) / ZnSenLoad;


Do you really need to iterate on this? There's only 1 unknown.., FanSpdRto.

I guess not. I will change it to directly calculate FanSpdRto

rraustad · 2024-08-26T22:46:00Z

src/EnergyPlus/DXCoils.cc

+            Tout = Tin + (Ts_1 - Tin) * (1 - BF);
+            Real64 RatedAirMassFlowRate = state.dataDXCoils->DXCoil(CoilIndex).RatedAirMassFlowRate[0];
+            auto f = [QCoilSenHeatingLoad, RatedAirMassFlowRate, Tout, Tin, Win](Real64 FanSpdRto) {
+                return FanSpdResidualHeatUsingH(FanSpdRto, QCoilSenHeatingLoad, RatedAirMassFlowRate, Tout, Tin, Win);


I am not saying to change this but it just seems odd to me when meeting a load to modulate the fan based on suction temperature (which meets the load using air flow) instead of modulating the compressor at some known fan speed. I guess this is an artifact of using VS fan. I would hope in the case of a VS fan that the refrigerant suction T is relatively constant.

It seems that modulating the compressor is at the next step after the calculation of the TU's are finished. In this function, I don't think refrigerant suction temperature changes

rraustad · 2024-08-26T23:05:10Z

src/EnergyPlus/HVACVariableRefrigerantFlow.cc

+    }
+    if (this->TUHeatingLoad / this->PipingCorrectionHeating > TotalCondHeatingCapacity) {
+        this->TotalHeatingCapacity = this->HeatingCapacityPrev * HeatingPLR * this->PipingCorrectionHeatingPrev;
+    }


TotalHeatingCapacity should match the sum of the TU capacity + piping losses. So isn't it just that? TotalHeatingCapacity = Q_h_TU_PL = TU_HeatingLoad + Pipe_Q_h?

yes, it is matching this.

rraustad · 2024-08-26T23:07:00Z

testfiles/US+SF+CZ4A+hp+crawlspace+IECC_2006_VRF.idf

-    autosize,                !- Cooling Outdoor Air Flow Rate {m3/s}
-    autosize,                !- Heating Outdoor Air Flow Rate {m3/s}
+    0,                !- Cooling Outdoor Air Flow Rate {m3/s}
+    0,                !- Heating Outdoor Air Flow Rate {m3/s}


Does including OA flow cause a difference between the sum of TU heating capacity + piping losses and condenser total heating capacity?

it does cause some more difference

@rraustad Here is the output file when the heating cooling air flow rate is autosize
eplusout_when heating cooling air flow rate autosize.xlsx

The following is a snapshot sorted with column O in descending order

If L x M = 9083.83288 * 0.98793126 = 8974.2, which closely matches column K at 8973.19993, then why is the TU heating coil "allowed" to provide more than that "max" heating rate? Is the TU heating coil capacity getting limited by the MaxHeatingCapacity variable? I recall discussing that function LimitTUCapacity should include piping losses.

Coil capacity should have been limited. Maybe there's some lingering issues there. I will check on that.

@rraustad I've changed to just using TU_HeatingLoad for this->TotalHeatingCapacity. Now the total "Heating Coil Heating Rate" and the "VRF Heat Pump Total Heating Rate" equals (regardless of whether the "Heating/Cooling Outdoor Air Flow Rate" is autosize or 0). The following are the outputs for these two cases.

eplusout_0 heating cooling air flow.csv
eplusout_autosize heating cooling air flow.csv

The coil capacity is indeed limited. I set the OU evaporative capacity to 5000W (coil capacity is 10023W). Coil heating rate is less than OU capacity at max speed.

…eatRate

github-actions · 2024-09-03T20:58:01Z

⚠️ Regressions detected on macos-14 for commit `b9a481a`

Regression Summary

EIO: 3
ESO Big Diffs: 3
Table Small Diffs: 1
MTR Small Diffs: 1
Table Big Diffs: 2
Table String Diffs: 1
ESO Small Diffs: 1

dareumnam · 2024-09-10T21:05:29Z

@rraustad @mjwitte Do you have any further comments on this? If this PR needs more time for discussion, we can move it to the 25.1 bug freeze milestone, as we're planning to tag the first RC for 24.2 tomorrow.

rraustad · 2024-09-11T18:29:55Z

doc/input-output-reference/src/overview/group-variable-refrigerant-flow-equipment.tex

@@ -619,7 +619,7 @@ \subsubsection{Outputs}\label{outputs-039}

 \paragraph{VRF Heat Pump Total Heating Rate {[}W{]}}\label{vrf-heat-pump-total-heating-rate-w}

-This output field is the operating total heating capacity of the variable refrigerant flow heat pump in Watts. The capacity includes any degradation due to defrost mode. This value is calculated for each HVAC system time step being simulated, and the results are averaged for the time step being reported. This value should match the sum of the individual zone terminal unit output variables for Zone VRF Air Terminal Total Heating Rate.
+This output field is the operating total heating capacity of the variable refrigerant flow heat pump in Watts. The capacity includes any degradation due to defrost mode. This value is calculated for each HVAC system time step being simulated, and the results are averaged for the time step being reported. This value should match the sum of the individual zone terminal unit heating coil output variables for Heating Coil Heating Rate plus any piping loss.


This does seem like the correct definition for the VRF heating capacity.

rraustad · 2024-09-11T18:40:48Z

src/EnergyPlus/HVACVariableRefrigerantFlow.cc

@@ -12219,7 +12221,8 @@ void VRFCondenserEquipment::CalcVRFCondenser_FluidTCtrl(EnergyPlusData &state)
    }

    this->TotalCoolingCapacity = TotalCondCoolingCapacity * CoolingPLR;
-    this->TotalHeatingCapacity = TotalCondHeatingCapacity * HeatingPLR;
+    // adjustment for matching HP heating rate and coil heating rate
+    this->TotalHeatingCapacity = TU_HeatingLoad;


This is not actually correct. The TU_HeatingLoad is the target (coil load + piping loss) that the model will iterate on to find a solution. The TotalHeatingCapacity is the result. With a tolerance on the iterations these 2 variables should not match. They should be very close (like within 0.001%), but not match. How far off TotalHeatingCapacity is from TU_HeatingLoad tells you how well the model did to calculate the final result. To equate these at the end will hide any issues with the model. TU_HeatingLoad should match exactly with the coil loads + piping loss. TotalHeatingCapacity should represent the refrigerant side heating capacity. Since this model has refrigerant properties could TotalHeatingCapacity = Mdot deltaH on the refrigerant side? Then you would know how well the model did to meet the load.

I see.

I think the piping correction is not consistent in the IU and OU calculation, which might have partly caused the discrepancy. See comment here: #10625 (comment)

There might be other places contributing to it as well. I've been playing around with adjusting stuff but so far I've not been able to figure out how to effectively resolve the discrepancy.

Maybe just revert this one change and revisit how different these 2 results are. TotalHeatingCapacity versus TU_HeatingLoad. Maybe also add another report for refrigerant side capacity?

I will do that

Myoldmopar · 2024-09-11T19:43:00Z

Thank you both for the comments this afternoon. I'm going to mark, for now, that this is not going into 24.2. If things get resolved and we agree, we can certainly go ahead and drop it in. But I'm going to change it to focus on other things.

yujiex · 2024-09-11T22:34:57Z

Thanks, @Myoldmopar. I will investigate this more and hope to resolve it in the next round

nrel-bot-2c · 2024-09-20T19:04:55Z

@yujiex it has been 8 days since this pull request was last updated.

nrel-bot-2c · 2024-09-28T00:21:58Z

@yujiex it has been 7 days since this pull request was last updated.

nrel-bot-2c · 2024-10-05T00:20:36Z

@yujiex it has been 7 days since this pull request was last updated.

…eatRate

This reverts commit 94e3c1f.

This reverts commit 098e584.

github-actions · 2024-10-10T01:40:55Z

⚠️ Regressions detected on macos-14 for commit `4735f12`

Regression Summary

EIO: 4
ERR: 2
ESO Big Diffs: 4
Table Big Diffs: 4
Table String Diffs: 4
MTR Big Diffs: 2

github-actions · 2024-10-10T02:00:16Z

⚠️ Regressions detected on macos-14 for commit `6c6c059`

Regression Summary

EIO: 4
ERR: 1
ESO Big Diffs: 4
Table Big Diffs: 4
Table String Diffs: 4
MTR Big Diffs: 2

github-actions · 2024-10-10T02:25:56Z

⚠️ Regressions detected on macos-14 for commit `8ace59e`

Regression Summary

EIO: 4
ESO Big Diffs: 4
Table Big Diffs: 3
MTR Small Diffs: 1
Table String Diffs: 2
Table Small Diffs: 1

yujiex · 2024-10-10T17:50:59Z

@mjwitte and @rraustad I have modified the code fixing the mismatch between the coil total heating rate and heat pump total heating rate. Some details are added in the PR description to explain the contributing factors to the issue and how they're addressed. Please see if they make sense.

I tried using Chicago weather, there's still noticeable difference between the heating coil heating rate and the heat pump heating rate. So there might be other things to change to make them agree. I'll look into it.

nrel-bot-2c · 2024-11-12T19:29:01Z

@yujiex @Myoldmopar it has been 29 days since this pull request was last updated.

yujiex added Defect Includes code to repair a defect in EnergyPlus Documentation Related primarily on the LaTeX-based EnergyPlus documentation labels Jul 26, 2024

yujiex added this to the EnergyPlus 24.2 milestone Jul 26, 2024

yujiex self-assigned this Jul 26, 2024

yujiex mentioned this pull request Aug 9, 2024

VRF FluidTCtrl heat pump total heating rate doesn't match zone VRF air terminal total heating rate #10625

Open

3 tasks

Fix non-matching HP heating rate and coil total heating rate

098e584

yujiex requested review from Myoldmopar, mjwitte and rraustad August 15, 2024 18:28

mjwitte reviewed Aug 16, 2024

View reviewed changes

Yujie Xu added 3 commits August 16, 2024 10:08

latex label add suffix, revert FanSpdRatioMin change

a75d23a

Doc update, HP heating rate is coil + piping loss

6379fdc

Merge remote-tracking branch 'origin/develop' into fixDocVRFheatpumpH…

f306890

…eatRate

rraustad reviewed Aug 26, 2024

View reviewed changes

dareumnam self-requested a review August 28, 2024 17:39

Yujie Xu added 3 commits August 28, 2024 17:54

change to directly use limited TU_HeatingLoad

94e3c1f

revert test idf back to autosize heating cooling air flow TU1

ac4911c

Merge remote-tracking branch 'origin/develop' into fixDocVRFheatpumpH…

c9fb07f

…eatRate

rraustad reviewed Sep 11, 2024

View reviewed changes

Myoldmopar removed this from the EnergyPlus 24.2 milestone Sep 11, 2024

Myoldmopar added this to the EnergyPlus 25.1 milestone Sep 11, 2024

yujiex mentioned this pull request Sep 12, 2024

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

Merged

20 tasks

Yujie Xu added 8 commits October 7, 2024 17:03

Merge remote-tracking branch 'origin/develop' into fixDocVRFheatpumpH…

94fbca7

…eatRate

Revert "change to directly use limited TU_HeatingLoad"

3ba669a

This reverts commit 94e3c1f.

Revert "Fix non-matching HP heating rate and coil total heating rate"

303a572

This reverts commit 098e584.

put back check on whether endpoints both positive or negative

0ca1aa3

remov piping loss in coil heating calculation for now

fbcb90c

Wrongly removed a line, add back

bc5d7c9

add back piping correction to heating coil heating rate

6161f8d

revert back the FanSpdRatioMin bound as in develop

e1db7ed

		@@ -1153,6 +1153,10 @@ \subsubsection{Outputs}

		Note: refer to the rdd file after a simulation for exact output variable names

		\paragraph{VRF Heat Pump Total Heating Rate {[}W{]}}\label{vrf-heat-pump-total-heating-rate-w}

Fix documentation of VRF Heat Pump Total Heating Rate, should equal the sum of coil heating rate, not air terminal heating rate #10627

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Fix documentation of VRF Heat Pump Total Heating Rate, should equal the sum of coil heating rate, not air terminal heating rate #10627

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yujiex commented Jul 26, 2024 • edited Loading

Pull request overview

Details on the fix of heat pump heating rate not matching total heating coil heating rate

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yujiex commented Aug 26, 2024

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yujiex Aug 29, 2024 • edited Loading

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github-actions bot commented Sep 3, 2024

⚠️ Regressions detected on macos-14 for commit b9a481a

dareumnam commented Sep 10, 2024

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Myoldmopar commented Sep 11, 2024

yujiex commented Sep 11, 2024

nrel-bot-2c commented Sep 20, 2024

nrel-bot-2c commented Sep 28, 2024

nrel-bot-2c commented Oct 5, 2024

github-actions bot commented Oct 10, 2024

⚠️ Regressions detected on macos-14 for commit 4735f12

github-actions bot commented Oct 10, 2024

⚠️ Regressions detected on macos-14 for commit 6c6c059

github-actions bot commented Oct 10, 2024

⚠️ Regressions detected on macos-14 for commit 8ace59e

yujiex commented Oct 10, 2024 • edited Loading

nrel-bot-2c commented Nov 12, 2024

yujiex commented Jul 26, 2024 •

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⚠️ Regressions detected on macos-14 for commit `b9a481a`

⚠️ Regressions detected on macos-14 for commit `4735f12`

⚠️ Regressions detected on macos-14 for commit `6c6c059`

⚠️ Regressions detected on macos-14 for commit `8ace59e`

yujiex commented Oct 10, 2024 •

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