AirloopHVAC:UnitarySystem control type = SingleZoneVAV crashes with autosized water coils by rraustad · Pull Request #7258 · NatLabRockies/EnergyPlus

rraustad · 2019-04-08T16:01:08Z

Pull request overview

This fixes #7085 where autosized waters coils were not sizing correctly and caused a divide by 0 crash. The water coils do not have a capacity input field and capacity is used to calculate water volume flow rate. The result was water flow = 0 and the divide by 0 problem surfaced. It is also possible that the water coil could size to 0 flow and protection was added to ensure the model would run successfully.

Work Checklist

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

Title of PR should be user-synopsis style (clearly understandable in a standalone changelog context)
At least one of the following appropriate labels must be added to this PR to be consumed into the changelog:
- Defect: This pull request repairs a github defect issue. The github issue should be referenced in the PR description
- Refactoring: This pull request includes code changes that don't change the functionality of the program, just perform refactoring
- NewFeature: This pull request includes code to add a new feature to EnergyPlus
- Performance: This pull request includes code changes that are directed at improving the runtime performance of EnergyPlus
- DoNoPublish: This pull request includes changes that shouldn't be included in the changelog

Review Checklist

This will not be exhaustively relevant to every PR.

rraustad · 2019-04-08T16:54:45Z

Defect file: 7085-HVACTemplate-5ZoneUnitarySystem-SinglZoneVAV-exp-DXandChW.idf. Not sure why cooling doesn't respond same as heating. Although this is Chicago Ohare weather and maybe cooling air flow rarely needed to increase above minimum.

AirLoopHVAC:UnitarySystem,
  Sys 5 HW ChW System Unitary System,                      !- Name
  SingleZoneVAV,                                           !- Control Type
  SPACE5-1,                                                !- Controlling Zone or Thermostat Location
  None,                                                    !- Dehumidification Control Type
  ,                                                        !- Availability Schedule Name
  Sys 5 HW ChW System Mixed Air Outlet,                    !- Air Inlet Node Name
  Sys 5 HW ChW System Heating Coil Outlet,                 !- Air Outlet Node Name
  Fan:SystemModel,                                         !- Supply Fan Object Type
  Sys 5 HW ChW System Supply Fan,                          !- Supply Fan Name
  BlowThrough,                                             !- Fan Placement
  FanAvailSched,                                           !- Supply Air Fan Operating Mode Schedule Name
  Coil:Heating:Water,                                      !- Heating Coil Object Type
  Sys 5 HW ChW System Heating Coil,                        !- Heating Coil Name
  1.0,                                                     !- DX Heating Coil Sizing Ratio
  Coil:Cooling:Water,                                      !- Cooling Coil Object Type
  Sys 5 HW ChW System Cooling Coil,                        !- Cooling Coil Name

rraustad · 2019-04-08T16:57:46Z

@Myoldmopar looks like a CI problem with finding necessary files (e.g., ReadVars)

Myoldmopar · 2019-04-08T16:59:27Z

Yes, CI is currently undergoing a major overhaul (vastly improved Decent CI codebase, new CI machine, updated E+ CI related stuff), so I'm expecting some speedbumps this week. Let me get the machines rolling out some results today and tomorrow and then we'll see where we stand. Thanks!

nrel-bot · 2019-04-19T00:34:23Z

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

nrel-bot · 2019-04-27T00:34:53Z

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

nrel-bot · 2019-05-04T00:33:10Z

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

…-with-SingleZoneVAV-control-crashes

Myoldmopar · 2019-05-14T02:05:39Z

src/EnergyPlus/UnitarySystem.cc

+                        if (thisSys.MaxHeatCoilFluidFlow == DataSizing::AutoSize) {
+                            thisSys.m_RequestAutoSize = true;
+                            thisSys.m_DesignHeatingCapacity = DataSizing::AutoSize;
+                        }


OK, so just setting the heating capacity to autosize everywhere in this setup function, not just setting the autosize flag. Fine.

Well, the intent was to set thisSys.m_DesignHeatingCapacity = DataSizing::AutoSize; only for coils that did not have a Capacity input, otherwise thisSys.m_DesignHeatingCapacity is initialized to =0 and there is a problem when sizing. The Coil:Heating:Water does have a capacity input field, although it's hard for water coils to know the design capacity for the alternate sizing method of UA and water flow rate (during GetInput). I wonder if this is why the diff's file has differences?

Myoldmopar · 2019-05-14T02:06:13Z

tst/EnergyPlus/unit/UnitarySystem.unit.cc

                0.0001);                                                          // fan PLR at minimum speed
    EXPECT_LT(DataLoopNode::Node(OutletNode).Temp, thisSys->DesignMaxOutletTemp); // outlet temperature does not exceed max limit

+    // test with 0 water flow rate to ensure divide by 0 does not happen (plant off, size = 0, etc.)


Great, heating coil unit test for this condition. 👍

Myoldmopar · 2019-05-14T02:06:24Z

tst/EnergyPlus/unit/UnitarySystem.unit.cc

    EXPECT_NEAR(thisSys->FanPartLoadRatio, 0.5117, 0.0001);                               // fan PLR above minimum speed
    EXPECT_NEAR(DataLoopNode::Node(OutletNode).Temp, thisSys->DesignMinOutletTemp, 0.01); // outlet temperature modulated to meet max limit

+    // test with 0 water flow rate to ensure divide by 0 does not happen (plant off, size = 0, etc.)


And the cooling coil test. 👍

Myoldmopar · 2019-05-14T02:07:46Z

src/EnergyPlus/SZVAVModel.cc

            if (HeatingLoad) { // Function UnitarySystems::calcUnitarySystemToLoad, 4th and 5th arguments are CoolPLR and HeatPLR
                // set the water flow ratio so water coil gets proper flow
-                SZVAVModel.HeatCoilWaterFlowRatio = maxCoilFluidFlow / SZVAVModel.MaxHeatCoilFluidFlow;
+                if (SZVAVModel.MaxHeatCoilFluidFlow > 0.0) SZVAVModel.HeatCoilWaterFlowRatio = maxCoilFluidFlow / SZVAVModel.MaxHeatCoilFluidFlow;


It would be nice if these checks could be done in one location ahead of calling this function, but I see that each case has different evaluations, so unless things were significantly refactored (out of scope for this defect), I don't think it would be feasible here.

Agreed. I am considering condensing SZVAVModel.cc into one function and also making this type of change.

Myoldmopar · 2019-05-14T02:08:38Z

src/EnergyPlus/SZVAVModel.cc

            if (!coilActive) { // if the coil is schedule off or the plant cannot provide water
-                DataLoopNode::Node(coilFluidInletNode).MassFlowRate = 0.0;
-                if (coilLoopNum > 0)
+                if (coilLoopNum > 0) {


I wasn't really expecting this change, but it's reasonable to protect the node mass flow rate evaluation to only cases where the coil has a loop number.

Myoldmopar · 2019-05-14T02:32:03Z

Merged with develop locally and rebuilt. Verified that the defect file crashes with current develop branch. Verified the file runs to completion with this branch. Code changes look good. Weird CI issues are unrelated to your changes, but there are CI diffs. I'm investigating them now.

CHW LOOP CHILLER:Chiller Condenser Heat Transfer Rate [W] (Hourly) has absolute differences of nearly 200 W. That's significant. I'm wondering if it is because of the mass flow rate being set to zero differently here? Or maybe this branch was just behind develop when CI hit here? I don't recall any other branches causing that though. I am running the branch through my regression tool with the two diff files and we'll see.

Sure enough, there are still diffs. The chiller condenser rate really isn't off by that much as a percentage, but it's still pretty significant in absolute terms. Since I wasn't really expecting any diffs, this is too much:

I did try to revert the mass flow reset to zero changes you made in SZVAVModel.cc, and put the reset back outside the coil loop num block. Just for fun. I reran the diffs and they were still the same. I think I'm giving in for tonight. I'm going to push the branch back up now with develop merged in just to get shiny CI results. If we can resolve the diffs, this can go right in.

rraustad · 2019-05-14T17:25:20Z

Condenser heat transfer diff's may be due to a change in false loading that happens at minimum unloading ratio. The chiller capacity changed by -4%. In your figure, 4200W is well below 25% of design capacity so false loading is definitely a possibility. These diff's don't appear to happen at higher heat transfer rates (chiller PLRs). If the chiller now runs at a higher PLR (because design capacity is lower) then false loading would be reduced.

HVACTemplate-5ZoneUnitarySystem.expidf (the only one with condenser heat transfer rate report variable)

Chiller:Electric:EIR,
ChW Loop Chiller, !- Name
0.0, !- Minimum Part Load Ratio
0.25, !- Minimum Unloading Ratio

Output:Variable,*,Chiller False Load Heat Transfer Rate,hourly; !- HVAC Average [W] (could add to investigate)

    MinPartLoadRat = ElectricEIRChiller(EIRChillNum).MinPartLoadRat;
    MinUnloadRat = ElectricEIRChiller(EIRChillNum).MinUnloadRat;
    FRAC = 1.0;

    // Chiller cycles below minimum part load ratio, FRAC = amount of time chiller is ON during this time step
    if (PartLoadRat < MinPartLoadRat) FRAC = min(1.0, (PartLoadRat / MinPartLoadRat));
    PartLoadRat = max(PartLoadRat, MinUnloadRat);

    // calculate the load due to false loading on chiller over and above water side load
    ChillerFalseLoadRate = (AvailChillerCap * PartLoadRat * FRAC) - QEvaporator;

    QCondenser = Power * ElectricEIRChiller(EIRChillNum).CompPowerToCondenserFrac + QEvaporator + ChillerFalseLoadRate;

Myoldmopar · 2019-05-16T02:34:54Z

OK, I accept the justification. Merging this now.

Correct SZVAV crash and sizing for water coils

61ac448

Add unit test.

0212524

Merge remote-tracking branch 'origin/develop' into 7085-UnitarySystem…

216b4c0

…-with-SingleZoneVAV-control-crashes

Myoldmopar mentioned this pull request May 14, 2019

UnitarySystem with SingleZoneVAV control crashes #7085

Closed

3 tasks

Myoldmopar approved these changes May 14, 2019

View reviewed changes

Myoldmopar added the Defect Includes code to repair a defect in EnergyPlus label May 16, 2019

Myoldmopar merged commit ff12a8d into develop May 16, 2019

Myoldmopar deleted the 7085-UnitarySystem-with-SingleZoneVAV-control-crashes branch May 16, 2019 02:35

rraustad mentioned this pull request May 16, 2019

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

Merged

18 tasks

Comments

Conversation

rraustad commented Apr 8, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Pull request overview

Work Checklist

Review Checklist

Uh oh!

rraustad commented Apr 8, 2019

Uh oh!

rraustad commented Apr 8, 2019

Uh oh!

Myoldmopar commented Apr 8, 2019

Uh oh!

nrel-bot commented Apr 19, 2019

Uh oh!

nrel-bot commented Apr 27, 2019

Uh oh!

nrel-bot commented May 4, 2019

Uh oh!

Myoldmopar May 14, 2019

Choose a reason for hiding this comment

Uh oh!

rraustad May 14, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Myoldmopar May 14, 2019

Choose a reason for hiding this comment

Uh oh!

Myoldmopar May 14, 2019

Choose a reason for hiding this comment

Uh oh!

Myoldmopar May 14, 2019

Choose a reason for hiding this comment

Uh oh!

rraustad May 14, 2019

Choose a reason for hiding this comment

Uh oh!

Myoldmopar May 14, 2019

Choose a reason for hiding this comment

Uh oh!

Myoldmopar commented May 14, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

rraustad commented May 14, 2019 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Myoldmopar commented May 16, 2019

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

7 participants

rraustad commented Apr 8, 2019 •

edited

Loading

rraustad May 14, 2019 •

edited

Loading

Myoldmopar commented May 14, 2019 •

edited

Loading

rraustad commented May 14, 2019 •

edited

Loading