Integration test file ASHRAE9012016_Hospital_Denver problem with hard size of zone exhaust and outdoor air ventilation

[EnergyArchmage]

Issue overview

The integration test file ASHRAE9012016_Hospital_Denver has two zones with exhaust fans with airflow rates that exceed the outdoor air requirements for the zone. This causes problems in modeling make up air and return air flows in the central air handler. The file is often an outlier in integration testing outcomes and this issue is a likely cause.

A custom warning message created to help catch these sorts of input problems generates these errors for this file.

    ** Warning ** checkZoneOutdoorAirFlowDesignBalanceForExhaustFan Zone Exhaust Fan is starved by minimum ventilation requirements.  Ventilation should be increased to match that required to balance the exhaust fans in the zone. 
   **   ~~~   ** Zone name =CORRIDOR_FLR_5
   **   ~~~   ** Zone exhaust fan flow for air system design = 0.152911 [m3/s] 
   **   ~~~   ** Minimum ventilation requirement for zone = 0.152901 [m3/s] = 
   **   ~~~   ** Input for outdoor air requirements should be increased to larger flow needed for exhaust fan(s).  Check DesignSpecification:OutdoorAir and Fan:ZoneExhaust for this zone.  Simulation continues.
   ** Warning ** checkZoneOutdoorAirFlowDesignBalanceForExhaustFan Zone Exhaust Fan is starved by minimum ventilation requirements.  Ventilation should be increased to match that required to balance the exhaust fans in the zone. 
   **   ~~~   ** Zone name =KITCHEN_FLR_5
   **   ~~~   ** Zone exhaust fan flow for air system design = 3.398022 [m3/s] 
   **   ~~~   ** Minimum ventilation requirement for zone = 1.883542 [m3/s] = 
   **   ~~~   ** Input for outdoor air requirements should be increased to larger flow needed for exhaust fan(s).  Check DesignSpecification:OutdoorAir and Fan:ZoneExhaust for this zone.  Simulation continues.

Details

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• Platform (Operating system, version)
• Version of EnergyPlus (if using an intermediate build, include SHA)
• Unmethours link or helpdesk ticket number

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[EnergyArchmage]

@JasonGlazer I wanted to point this out during 10x call today. I suspect it is why that file is an outlier in testing.

[mjwitte]

Note that these files are getting updated in #8686. I have not looked to see if this issue is addressed there.

[JasonGlazer]

Very interesting @EnergyArchmage. So we randomly picked a poor file to do the 10x testing.

[EnergyArchmage]

I just ran the new version of the file from #8686 with my custom e+ and get the same error message. The kitchen zone is severely starved and the air loop serving it is going to operate erratically.

[lymereJ]

@EnergyArchmage - Would you mind sharing the name of the branch that you are using to generate these warnings?

[EnergyArchmage]

Sorry, it isn't a public repo. I'll see if client wants to contribute that bit of code.

[lymereJ]

@EnergyArchmage - Thanks for sharing the branch that you are using to generate this new warning messages!

I took a look at the code changes and at the model. It appears that, for this particular file, what the warning shows will never occur because the kitchen exhaust fan is off between midnight and 7am.

The code in the PR shows that its retrieving the minimum value of the schedule used to represent the hourly balanced exhaust fraction and use it to determine the balanced air flow fraction. For that model, the schedule is 0 between midnight and 7am so it is assumed that none of the exhaust flow is actually balanced. However, this is not really true because the fan will never operate during these hours.

I changed the fraction from 0 to 1 for that period and the warning changes to the following which shows that the exhaust and ventilation requirement are virtually the same. Let me know if I'm missing something here, otherwise we'll modify #8686 to make sure that the exhaust flow and requirements are exactly the same (I believe that the same warning for the corridor is due to a rounding error in the input file) so the warning does not pop up.

   ** Warning ** checkZoneOutdoorAirFlowDesignBalanceForExhaustFan Zone Exhaust Fan is starved by minimum ventilation requirements.  Ventilation should be increased to match that required to balance the exhaust fans in the zone. 
   **   ~~~   ** Zone name =KITCHEN_FLR_5
   **   ~~~   ** Zone exhaust fan flow for air system design = 1.883542 [m3/s] 
   **   ~~~   ** Minimum ventilation requirement for zone = 1.883542 [m3/s] = 
   **   ~~~   ** Input for outdoor air requirements should be increased to larger flow needed for exhaust fan(s).  Check DesignSpecification:OutdoorAir and Fan:ZoneExhaust for this zone.  Simulation continues.

[lymereJ]

@jungwyoungs made some changes to the models in #8686 to address the warnings generated by #8886. The balanced air flow fraction schedules that were using a fraction of 0 when the exhaust fans are scheduled to be off were changed to 1. This removed most of the warnings. The remaining were due to some very small discrepancies in inputs (one example is the warning for the corridor shown above) and were also addressed.