Fixes source side sizing calculation for HeatPump:PlantLoop:EIR:Heating issue by Nigusse · Pull Request #10382 · NatLabRockies/EnergyPlus

Nigusse · 2024-01-26T19:39:19Z

Pull request overview

Fixes Source side sizing calculation for HeatPump:PlantLoop:EIR:Heating is incorrect #10381
Corrected the source-side flow rate sizing calculation for HeatPump:PlantLoop:EIR:Heating Coils. This change impacts the Source Side Reference Flow Rate field only when it is auto-sized. The fix results in lower source side flow rate for AirSource and WaterSource condenser types.

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

Pull Request Author

Add to this list or remove from it as applicable. This is a simple templated set of guidelines.

Reviewer

This will not be exhaustively relevant to every PR.

Nigusse

Code changes walk through:

source side capacity and fluid flow rate calc changed for the heating coil only
cleaned up function names as an argument in several places

Nigusse · 2024-01-26T19:57:01Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                           state.dataLoopNodes->Node(this->loadSideNodes.inlet).Temp,
                                                           thisLoadPlantLoop.FluidIndex,
-                                                           "PLHPEIR::simulate()");
+                                                           "EIRPlantLoopHeatPump::doPhysics()");


Updated function names used as an argument in several places.

Good catch.

Nigusse · 2024-01-26T19:57:08Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

        auto &thisSourcePlantLoop = state.dataPlnt->PlantLoop(this->sourceSidePlantLoc.loopNum);
        CpSrc = FluidProperties::GetSpecificHeatGlycol(
-            state, thisSourcePlantLoop.FluidName, this->sourceSideInletTemp, thisSourcePlantLoop.FluidIndex, "PLHPEIR::simulate()");
+            state, thisSourcePlantLoop.FluidName, this->sourceSideInletTemp, thisSourcePlantLoop.FluidIndex, "EIRPlantLoopHeatPump::doPhysics()");


Updated function names used as an argument.

Nigusse · 2024-01-26T19:58:05Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                       loadSideInitTemp,
                                                       state.dataPlnt->PlantLoop(this->loadSidePlantLoc.loopNum).FluidIndex,
-                                                       "EIRPlantLoopHeatPump::size()");
+                                                       "EIRPlantLoopHeatPump::sizeLoadSide()");


The same change here.

Nigusse · 2024-01-26T19:58:11Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                        this->EIRHPType == DataPlant::PlantEquipmentType::HeatPumpEIRCooling ? Constant::HWInitConvTemp : Constant::CWInitConvTemp,
                        state.dataPlnt->PlantLoop(compLoopNum).FluidIndex,
-                        "EIRPlantLoopHeatPump::size()");
+                        "EIRPlantLoopHeatPump::sizeLoadSide()");


The same change here.

Nigusse · 2024-01-26T19:58:16Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                        this->EIRHPType == DataPlant::PlantEquipmentType::HeatPumpEIRCooling ? Constant::HWInitConvTemp : Constant::CWInitConvTemp,
                        state.dataPlnt->PlantLoop(compLoopNum).FluidIndex,
-                        "EIRPlantLoopHeatPump::size()");
+                        "EIRPlantLoopHeatPump::sizeLoadSide()");


The same change here.

Nigusse · 2024-01-26T19:58:26Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                                                 Constant::CWInitConvTemp,
                                                                                 state.dataPlnt->PlantLoop(compLoopNum).FluidIndex,
-                                                                                 "EIRPlantLoopHeatPump::size()");
+                                                                                 "EIRPlantLoopHeatPump::sizeLoadSide()");


The same change here.

Nigusse · 2024-01-26T19:58:32Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                            sourceSideInitTemp,
                                                            state.dataPlnt->PlantLoop(this->loadSidePlantLoc.loopNum).FluidIndex,
-                                                            "EIRPlantLoopHeatPump::size()");
+                                                            "EIRPlantLoopHeatPump::sizeSrcSideWSHP()");


The same change here.

Nigusse · 2024-01-26T19:58:36Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                                sourceSideInitTemp,
                                                                state.dataPlnt->PlantLoop(this->loadSidePlantLoc.loopNum).FluidIndex,
-                                                                "EIRPlantLoopHeatPump::size()");
+                                                                "EIRPlantLoopHeatPump::sizeSrcSideWSHP()");


The same change here.

Nigusse · 2024-01-26T20:03:23Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

+            designSourceSideHeatTransfer = tmpCapacity * (1 - 1 / this->referenceCOP);
+        } else {
+            designSourceSideHeatTransfer = tmpCapacity * (1 + 1 / this->referenceCOP);
+        }


For the heating coil, the source side design capacity is basically the evaporator capacity (heat transfer). Derivation of the above equation for heating coil leads to minus sign. The previous equation is valid for cooling coil only. This fix is for water-source HP.

Nigusse · 2024-01-26T20:04:19Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

+            designSourceSideHeatTransfer = tmpCapacity * (1 - 1 / this->referenceCOP);
+        } else {
+            designSourceSideHeatTransfer = tmpCapacity * (1 + 1 / this->referenceCOP);
+        }


This change is the same as the previous, but for the air-source HP.

Nigusse · 2024-01-26T20:06:54Z

Sample diffs. Only the heating coil source side flow rate was impacted as expected.

Component Sizing Information, Pump:VariableSpeed, HEATSYS1 PUMP, Design Power Consumption [W], 12547.22436
  Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Nominal Capacity [W], 3583772.55507
  Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Load Side Volume Flow Rate [m3/s], 0.11637
- Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 408.24654
+ Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 198.35115
  Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_2 HEATING SIDE, Design Size Nominal Capacity [W], 3583772.55507
  Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_2 HEATING SIDE, Design Size Load Side Volume Flow Rate [m3/s], 0.11637
- Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_2 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 408.24654
+ Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_2 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 198.35115

rraustad · 2024-01-26T20:07:51Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

+            designSourceSideHeatTransfer = tmpCapacity * (1 - 1 / this->referenceCOP);
+        } else {
+            designSourceSideHeatTransfer = tmpCapacity * (1 + 1 / this->referenceCOP);
+        }


This should be tmpCapacity / (1 + 1 / this->referenceCOP) for heating. I tried both ways and don't get the same answer.

designSourceSideHeatTransfer = Hcap * (1 - 1/COP) = 1000 * (1 - 1/3) = 667
designSourceSideHeatTransfer = Hcap / (1 + 1/COP) = 1000 / (1 + 1/3) = 750

And as a test, if the cooling and heating EIR HP capacity is hardsized and the heating capacity is 1 + 1/COP the size of the cooling capacity (and the COPs are the same), then the autosized load side water flow rate on the cooling EIR HP should be the same size as the autosized source side water flow rate of the heating EIR HP.

The above formulations are based on the first-law energy balance equations and COP definition as shown below:

Qcond = Qevap + Power; COPc = Qevap / Power; COPh = Qcond / Power

You can derive them from these three equations. The heat transfer should not be the same even if the COP are equal because the heat transfer at the condenser includes the power input while the heat transfer at the evaporator doesn't.

Ah, that's what I was missing, the COPs are different:

COPh = COPc * (1 + 1/COPc) = 3 * (1 + 1/3) = 4 <-- is this COP conversion correct?

designSourceSideHeatTransfer = Hcap * (1 - 1/COPh) = 1000 * (1 - 1/4) = 750
designSourceSideHeatTransfer = Ccap * (1 + 1/COPc) = 750 * (1 + 1/3) = 1000

I think there are places where the divide by (1 + 1/COP) is used. Maybe those are wrong also.

The correct relationship is COPh = COPc + 1.

The only places that needed to be changed were in source side sizing calculation functions: sizeSrcSideASHP() and sizeSrcSideWSHP().

@rraustad I searched for (1 + 1/COP) and (1.0 + 1.0 / this->referenceCOP) but did not find any.

Thanks for working through this description, it's helpful.

Nigusse · 2024-01-26T21:12:49Z

Diffs are expected only if the HeatPump:PlantLoop:EIR:Heating has its Source Side Reference Flow Rate input field set to autosize.

Nigusse · 2024-01-26T21:16:01Z

The two example files shown below are expected to have diffs:

 PlantLoopHeatPump_EIR_LargeOffice-2-AWHP-AuxBoiler-Pri-Sec-4PipeBeam.idf
 PlantLoopHeatPump_EIR_Large-Office-2-AWHP-DedHR-AuxBoiler-Pri-Sec-HW.idf

Nigusse · 2024-01-29T15:03:57Z

Modified three unit tests failed due to this fix.

Nigusse

Modified failed unit tests.

Nigusse · 2024-01-29T15:13:24Z

tst/EnergyPlus/unit/PlantLoopHeatPumpEIR.unit.cc

    thisCoolingPLHP->sourceSideDesignVolFlowRate = expectedSourceFlow;
    thisCoolingPLHP->referenceCapacity = expectedCapacity;
-    Real64 const designSourceSideHeatTransfer = expectedCapacity * (1 + 1 / thisHeatingPLHP->referenceCOP);
+    Real64 const designSourceSideHeatTransfer = expectedCapacity * (1 - 1 / thisHeatingPLHP->referenceCOP);


For heating coil, the source side heat transfer calc expression updated to match the correct expression in the code.

Nigusse · 2024-01-29T15:14:52Z

tst/EnergyPlus/unit/PlantLoopHeatPumpEIR.unit.cc

-    Real64 expectedSourceCp = 1004.0;
-    Real64 expectedSourceRho = 1.2;
+    Real64 expectedSourceCp = Psychrometrics::PsyCpAirFnW(sourceSideHumRat);
+    Real64 expectedSourceRho = Psychrometrics::PsyRhoAirFnPbTdbW(*state, state->dataEnvrn->StdBaroPress, sourceSideInitTemp, sourceSideHumRat);


Needed to match the sizing calculation assumptions to remove diffs.

Nigusse · 2024-01-29T15:15:39Z

tst/EnergyPlus/unit/PlantLoopHeatPumpEIR.unit.cc

    thisCoolingPLHP->referenceCapacity = expectedCapacity;
    expectedCapacity = expectedLoadRho * expectedLoadFlow * expectedLoadCp * plantSizingLoadDeltaT;
-    expectedSourceLoad = expectedCapacity * (1 + 1 / COP);
+    expectedSourceLoad = expectedCapacity * (1 - 1 / thisHeatingPLHP->referenceCOP);


For heating coil, the source side heat transfer calc expression updated to match the correct expression in the code.

Nigusse · 2024-01-29T15:17:12Z

tst/EnergyPlus/unit/PlantLoopHeatPumpEIR.unit.cc

                                                      "  Autosize,",
                                                      "  Autosize,",
-                                                      "  1.0,",
+                                                      "  2.0,",


Changed the heating coil COP to 2.0 from 1.0 to avoid zero source side flow rate.

I have seen users set COP=1 on DX equipment for various reasons, mostly for ideal simulations. If a user sets COPh = 1 the new equation calculates 0 source heat transfer. If COPh < 1 then there is negative source side heat transfer and there would be heating on the load and source side. I'm not sure what that means or what the limit of COPh=1 represents other than non-DX equipment. If COPc = 1 you get twice the source heat transfer as the load side. It seems for an ideal run then COPh=2, as you have shown here. I am tempted to change all these COP limits in the idd to >=1 for cooling or >=2 for heating. Not for this issue but for clarity of operation for users.

HeatPump:PlantLoop:EIR:Heating, N4, \field Reference Coefficient of Performance \type real \minimum> 0.0 \units W/W \default 3.0

If the heating coil (heating mode) design COPh is 1.0, it means the source side COPc is 0.0, i.e., there is no heat transfer at the evaporator coil. Also, it means the heat dissipated at the condenser is the same as the power input at the system (compressor). Can this operating condition be possible in the actual machine? To me, this implies the refrigeration cycle will not be complete; hence, it is not possible.

Nigusse · 2024-01-29T15:19:03Z

tst/EnergyPlus/unit/PlantLoopHeatPumpEIR.unit.cc


    Real64 expectedClgSourceFlow = 86.71;
-    Real64 expectedHtgSourceFlow = 86.71;
+    Real64 expectedHtgSourceFlow = 21.68; // changed from 86.71 due to issue#10381;


The source side flow rate is now divided by 4 because of this fix and COP value assumption change.

Nigusse · 2024-01-29T16:10:43Z

Uploaded defect file.
PLHP_EIR_AirSource_Issue10381.idf.txt

Nigusse · 2024-01-29T16:36:06Z

Demonstration of change in Source Side Reference Flow Rate sizing calculation based on the attached defect file.

Develop:
Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, HEATING COIL, Design Size Source Side Volume Flow Rate [m3/s], 8.69352

Branch:
Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, HEATING COIL, Design Size Source Side Volume Flow Rate [m3/s], 4.82974

The ratio between these flow rates is 1.8 (= 8.69352/4.82974) or (= (1+1/COPh) / (1-1/COPh) = (1+1/3.5) / (1-1/3.5) ).

rraustad · 2024-01-29T22:50:44Z

In the eio diffs I see that the source side volume flow rate did change due to your code correction so that's good. This is an air-source HP so the volume flow rates on the load and source side seem resonable (rho different by about 1000). I don't see any other issues.

  Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Load Side Volume Flow Rate [m3/s], 0.11637
- Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 408.24654
+ Component Sizing Information, HeatPump:PlantLoop:EIR:Heating, AWHP_1 HEATING SIDE, Design Size Source Side Volume Flow Rate [m3/s], 198.35115

rraustad

This change seems straight-forward and correct.

Myoldmopar

This seems like a fine change. I'll build and test locally.

Myoldmopar · 2024-02-08T15:40:29Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

                                                           state.dataLoopNodes->Node(this->loadSideNodes.inlet).Temp,
                                                           thisLoadPlantLoop.FluidIndex,
-                                                           "PLHPEIR::simulate()");
+                                                           "EIRPlantLoopHeatPump::doPhysics()");


Good catch.

Myoldmopar · 2024-02-08T15:42:00Z

src/EnergyPlus/PlantLoopHeatPumpEIR.cc

+            designSourceSideHeatTransfer = tmpCapacity * (1 - 1 / this->referenceCOP);
+        } else {
+            designSourceSideHeatTransfer = tmpCapacity * (1 + 1 / this->referenceCOP);
+        }


Thanks for working through this description, it's helpful.

Myoldmopar · 2024-02-08T17:00:00Z

I'm seeing only the same two regression diffs locally, and otherwise things are happy. Merging this. Thanks @Nigusse

Nigusse added 2 commits January 26, 2024 13:59

Fixed the source side sizing calculation

ec36492

Updated function names as an argument to FluidProperties function

8d45679

Nigusse added the Defect Includes code to repair a defect in EnergyPlus label Jan 26, 2024

Nigusse added this to the EnergyPlus 24.1 milestone Jan 26, 2024

Nigusse commented Jan 26, 2024

View reviewed changes

rraustad reviewed Jan 26, 2024

View reviewed changes

modified three failed unit tests

6aee0a2

Nigusse commented Jan 29, 2024

View reviewed changes

converted const to constexpr

09c37e4

Merge branch 'develop' into plhp_eir_sourceSide_sizing

c7270cf

Nigusse requested a review from rraustad January 29, 2024 21:19

rraustad approved these changes Jan 30, 2024

View reviewed changes

Myoldmopar approved these changes Feb 8, 2024

View reviewed changes

Myoldmopar merged commit a509560 into develop Feb 8, 2024

Myoldmopar deleted the plhp_eir_sourceSide_sizing branch February 8, 2024 17:00

yujiex mentioned this pull request Jan 24, 2025

WaterSource HeatPump:PlantLoop:EIR:Heating heat imbalance #10854

Open

3 tasks

rraustad mentioned this pull request Apr 3, 2025

Use condenser capacity instead of evaporator capacity to determine water flow rate of WAHP coils #11019

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