New Phase Change Material (PCM) Thermal Storage #11113

rohitj0204 · 2025-07-02T20:11:53Z

Pull request overview

Description of the purpose of this PR

This PR adds a new Phase Change Material (PCM) Thermal Storage model in EnergyPlus. The PCM storage object allows simulation of latent heat storage using encapsulated or bulk PCM, which can smooth thermal loads, reduce peak demand, and integrate with CHP or renewable systems.

Pull Request Author

Reviewer

…ragePCM_V2

…ce folder

…ransfer properties

Updated IDD File to reflect the added PCM Material Object Input

…EnergyPlus into ThermalStoragePCM_V3

…lStoragePCM_V3

nrel-bot-2 · 2025-09-24T16:01:07Z

@Myoldmopar @rohitj0204 @Myoldmopar it has been 28 days since this pull request was last updated.

src/EnergyPlus/PCMThermalStorage.cc

rraustad · 2025-10-01T00:09:21Z

doc/input-output-reference/src/overview/group-water-heaters.tex

+\item
+  Thermal Energy Storage Heat Loss Rate~~~~~~~~~~ !- HVAC Average [W]
+\item
+  Thermal Energy Storage Energy Stored~~~~~~~~~~~~ !- HVAC Average [J]


This would also show !- HVAC Sum [J]

Same response as above. The energy can go up and down, so average would be a right method

rraustad · 2025-10-01T00:11:35Z

tst/EnergyPlus/unit/PCMThermalTank.unit.cc

+
+    // Stop here — WH minimal tests end after input parsing & sanity asserts.
+    // (No Init/Calculate: that would require plant context and is outside this simple parse test.)
+}


I don't see a new example file. Could a new example file be added please? Include the example file name and weather file in \testfiles\CMakeLists.txt

Added the example file and pushing it to the branch now

rraustad · 2025-10-01T00:27:03Z

src/EnergyPlus/PCMThermalStorage.cc

+            EnergyPlus::PCMStorage::RegisterPCMStorageOutputVariables(state);
+            this->MyPlantScanFlag = false;
+        }
+        Real64 rho = 998.2;


Shouldn't this come from the PCM material properties?

This is the density value of water. PCM material properties are mostly obtained from the PCM object connected

But you should be getting the properties of plant loop fluid itself. It could be something other than water.

rraustad · 2025-10-01T00:32:54Z

src/EnergyPlus/PCMThermalStorage.cc

+        if (mUseReq > 0.0) {
+            useOutlet.Temp = useOutletTemp;
+        } else if (mPlantReq > 0.0) {
+            plantOutlet.Temp = std::min(plantOutletTemp, state.dataPlnt->PlantLoop[this->sourcePlantLoc.loopNum].MaxTemp);


If the plant outlet temp gets clipped here then the calculation for plantheatTransfer_req, netPowerW and EnergyStored above are inaccurate. I suggest moving those calculations below this if/else if.

Thanks for the suggestion. Made the changes.

…lStoragePCM_V3

… modified unit test to resolve build errors

rraustad · 2025-10-07T23:38:25Z

src/EnergyPlus/PCMThermalStorage.cc

+        }
+        if (soc >= cutOutSOC) {
+            chargingMode = false;
+        }


If there is ever more than 1 storage tank then the chargingMode variable should be a member variable to control a specific tank.

Thanks Richard for your feedback. I can work on this and maybe have it as another update for future release.

rraustad · 2025-10-07T23:47:18Z

@mitchute I'm a little less critical of new models since they need time for user testing and feedback. This looks pretty sound without that feedback.

rraustad

Looks like a good new model.

rraustad · 2025-10-07T23:48:35Z

@rohitj0204 if you want to make some last minute changes then now is the time.

mitchute

Some nitpicks, but this is generally OK. Unless there's justification, I think we ought to clean up the fluid prop issues noted.

mitchute · 2025-10-08T15:23:59Z

src/EnergyPlus/PCMThermalStorage.cc

+
+// PCM Thermal Storage Module - PCMThermalStorage.cc
+
+#include "PCMThermalStorage.hh"


This import syntax is inconsistent with the rest of E+.

Updated and will push it through a new branch

mitchute · 2025-10-08T15:25:29Z

src/EnergyPlus/PCMThermalStorage.cc

+            EnergyPlus::PCMStorage::RegisterPCMStorageOutputVariables(state);
+            this->MyPlantScanFlag = false;
+        }
+        Real64 rho = 998.2;


But you should be getting the properties of plant loop fluid itself. It could be something other than water.

mitchute · 2025-10-08T15:30:32Z

src/EnergyPlus/PCMThermalStorage.cc

+            // If the tank capacity has been set to zero or negative (autosize request), estimate a capacity.
+            // The estimate here is based on storing one hour of flow on the larger of the use side or plant side.
+            // This provides a reasonable latent mass storage size without relying on external sizing objects.
+            if (this->TankCapacity <= 0.0) {


Fine to leave, but I don't see how this would be hit.

Updated Plant Loop Fluid Properties

mitchute · 2025-10-08T15:34:56Z

src/EnergyPlus/PCMThermalStorage.hh

+        Real64 PCM_TankTemp = 0.0;       // C, estimated from enthalpy
+        Real64 EnergyStored = 0.0;       // J
+        Real64 PercentCapacity = 0.0;    // %
+        Real64 HeatLossRate_W = 0.0;     // W
+        Real64 useheatTransfer = 0.0;    // W
+        Real64 plantheatTransfer = 0.0;  // W
+        Real64 DesignMassFlowRate = 0.0; // kg/s
+        Real64 UseSideDesignFlowRate = 0.0;
+        Real64 PlantSideDesignFlowRate = 0.0;
+        Real64 UseSideMassFlowRate = 0.0;
+        Real64 PlantSideMassFlowRate = 0.0;


Variable naming convention isn't consistent. Not a big deal, just noting in case any other quick fixes are made.

mitchute · 2025-10-08T15:54:36Z

src/EnergyPlus/PCMThermalStorage.cc

+#include <EnergyPlus/ScheduleManager.hh>
+#include <EnergyPlus/UtilityRoutines.hh>
+
+#include <algorithm> // for std::max used in autosizing


Convention in E+ is to group C++ imports first, then any Objexx imports, then the E+ imports.

When I use Visual Studio's Format Document option it automatically is rearranging everything. I hope this is not a major issue

When I use Visual Studio's Format Document option it automatically is rearranging everything. I hope this is not a major issue

If you follow this pattern (e.g. PlantManager.cc), it will stay at the top even with VS formatting.

license text.... // POSSIBILITY OF SUCH DAMAGE. // C++ Headers #include <algorithm> #include <cassert> // ObjexxFCL Headers

mitchute · 2025-10-08T16:08:10Z

src/EnergyPlus/PCMThermalStorage.hh

+        Real64 FreezingTemp = 0.0;                       // C
+        Real64 LatentHeat = 0.0;                         // J/kg (typically from PCMmat)
+        Real64 SpecificHeat = 0.0;                       // J/kg-K (backup if needed)
+        Real64 Effectiveness = 0.9;                      // HX effectiveness (optional input)


Should make this constexpr since you are not exposing it to the user (contrary to the comment).

mitchute · 2025-10-08T16:08:57Z

src/EnergyPlus/PCMThermalStorage.hh

+#include <EnergyPlus/PlantComponent.hh>
+#include <string>


See https://github.com/NREL/EnergyPlus/pull/11113/files#r2414338207

mitchute · 2025-10-08T16:10:30Z

src/EnergyPlus/PCMThermalStorage.cc

+        // Hysteresis thresholds (tune as needed)
+        constexpr Real64 cutInSOC = 0.40;  // start charging when SOC <= 40%
+        constexpr Real64 cutOutSOC = 0.95; // stop charging when SOC >= 95%


Maybe expose these to the users at some point? Are these described in the docs?

Will do so as a future update. However, the current limits seem to be a good starting point and current fit for the industry works

mitchute · 2025-10-08T16:11:26Z

src/EnergyPlus/PCMThermalStorage.cc

+        // Real64 avail = this->AvailabilitySchedule->getCurrentVal();
+        Real64 dt_seconds = state.dataHVACGlobal->TimeStepSys * 3600.0;
+
+        Real64 CpWater = 4180.0; // J/kg-C


Another water property that should be pulled from the actual plant loop fluid props.

mitchute · 2025-10-08T16:15:39Z

src/EnergyPlus/PCMThermalStorage.cc

+
+        // Real64 useheatTransfer = massFlowUse * CpWater * deltaTUse;       // Heat to Water Heater
+        // Real64 plantheatTransfer = massFlowPlant * CpWater * deltaTPlant; // Heat to PCM Tank
+        HeatLossRate_W = HeatLossRate;


Why two variables? There's no difference between how they are used.

Thanks for pointing it out. Fixed this issue

mitchute · 2025-10-08T20:18:52Z

As I stated on the call, if you all are good with the current state of the inputs, we can merge this and handle any lingering cleanups after IO Freeze.

mjwitte · 2025-10-08T20:57:35Z

As I stated on the call, if you all are good with the current state of the inputs, we can merge this and handle any lingering cleanups after IO Freeze.

@mitchute Code cleanup should be ready by Friday. If you want to merge this now, then those can be done in a follow-up PR. It's up to you.

mitchute · 2025-10-09T01:57:44Z

This is ready, so I'll just merge now and you can follow up when ready.

rohitj0204 added 20 commits January 21, 2025 11:18

New IDD Object

7b9a5f7

Merge branch 'ThermalStoragePCM' into ThermalStoragePCM_V2

6818ef1

Fixed Units

109ad16

Fixed syntax error and changed alpha numbering

fff714f

Added component to the Plant Manager and Branch Node Connections

2e409d4

Moved the PCM inclusion to stay along with the Ice:Simple model

457bde1

Merge remote-tracking branch 'remotes/origin/develop' into ThermalSto…

0df681e

…ragePCM_V2

Added to Component.hh

7f14cc6

Added PCMThermalStorage.cc and PCMThermalStorage.hh files to the Sour…

564d9e7

…ce folder

Modified the code to replace the outlet temperatures using PCM heat t…

b01df5c

…ransfer properties

Added the license information

ebe0872

Formatted the .hh file

e42d2c2

Connected PCM Material Property and Added PCM Tank Temp calculations

cc34c42

Updated IDD File to reflect the added PCM Material Object Input

Added Percent Capacity and Energy Storage Calcualtions

8e07d66

Corrected the units in the comments

131e102

Corrected units

ba673f4

Added license file in .hh file

4e32bf9

Modified the PlantManager Code for ThermalStorage:PCM

05387a6

Updated IDD and HH Files

6706ed3

IDD Format Update

2699cc6

mjwitte mentioned this pull request Jul 2, 2025

Thermal Storage PCM - v2 #10906

Closed

20 tasks

mjwitte added NewFeature Includes code to add a new feature to EnergyPlus IDDChange Code changes impact the IDD file (cannot be merged after IO freeze) labels Jul 2, 2025

mjwitte marked this pull request as draft July 2, 2025 20:22

rohitj0204 added 6 commits July 3, 2025 16:01

Modified CC File to include PhaseChange Material Properties

0c5521b

PCM Field - IDD Update

b61661d

PCM Field - IDD Update

c591a62

Fixed Errors

94071d2

Merge branch 'ThermalStoragePCM_V3' of https://github.com/rohitj0204/…

5dc8088

…EnergyPlus into ThermalStoragePCM_V3

Updates to Flow Rates

72c9bf9

mjwitte and others added 5 commits August 18, 2025 12:51

Fix custom check

d3cdeaa

Make clang-format happy (hopefully)

2022fa8

Merge remote-tracking branch 'remotes/NRELorigin/develop' into Therma…

3ade46b

…lStoragePCM_V3

Added unit test

fdd060e

Fixed the code formatting

77d5970

mjwitte added this to the EnergyPlus 25.2 IO Freeze milestone Aug 20, 2025

Unit test repairs

0265a32

Myoldmopar self-assigned this Aug 27, 2025

mitchute self-requested a review September 24, 2025 18:19

mjwitte changed the title ~~Thermal Storage PCM V3~~ New Phase Change Material (PCM) Thermal Storage Sep 24, 2025

rraustad reviewed Sep 30, 2025

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src/EnergyPlus/PCMThermalStorage.cc Show resolved Hide resolved

rraustad reviewed Oct 1, 2025

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mjwitte and others added 4 commits October 1, 2025 16:27

Merge remote-tracking branch 'remotes/NRELorigin/develop' into Therma…

89f4ae8

…lStoragePCM_V3

Added example file, modified to code addressing reviewer comments and…

9af61bf

… modified unit test to resolve build errors

Fixed errors

27691da

Fixed Errors

4f6658b

rraustad reviewed Oct 7, 2025

View reviewed changes

rraustad approved these changes Oct 7, 2025

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mitchute reviewed Oct 8, 2025

View reviewed changes

mitchute merged commit eb45bfa into NREL:develop Oct 9, 2025
11 checks passed

mitchute mentioned this pull request Oct 21, 2025

PCM Thermal Storage Use Fluid Properties from Plant Loop #11277

Merged

20 tasks


		// PCM Thermal Storage Module - PCMThermalStorage.cc

		#include "PCMThermalStorage.hh"

New Phase Change Material (PCM) Thermal Storage #11113

New Phase Change Material (PCM) Thermal Storage #11113

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rohitj0204 commented Jul 2, 2025 • edited by mjwitte Loading Uh oh! There was an error while loading. Please reload this page.

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Pull request overview

Description of the purpose of this PR

Pull Request Author

Reviewer

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nrel-bot-2 commented Sep 24, 2025

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rohitj0204 commented Jul 2, 2025 •

edited by mjwitte

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