VAV design minimum cooling air flow fraction > 1.0 when system adjusts zone flows

[mjwitte]

Issue overview

• Defect file for VRF:FluidTemperatureControl crashes with Fan:SystemModel #6218 shows new warnings. Not sure if this is the result of Add air terminal unit sizing option, allow air loops with no return path, and partially allow multiple air loops serving the same zone #6248 or Fix and clarify VAV minimum flow sizing, especially when VRP calculations adjust the min flow #6140 . Should this warning even be happening. And if so, do fractions >1.0 make any sense? And in any case, the units are wrong.

   ************* SizeHVACSingleDuct: Potential issue with equipment sizing for AirTerminal:SingleDuct:VAV:NoReheat = "CORE_BOTTOM ATU".
   **   ~~~   ** User-Specified Minimum Cooling Air Flow Fraction of 1.00000 [m3/s]
   **   ~~~   ** differs from Design Size Minimum Cooling Air Flow Fraction of 1.47043 [m3/s]
   **   ~~~   ** This may, or may not, indicate mismatched component sizes.

Pretty sure this came is as a result of #6140.

Preliminary look at this says it's because system sizing is using ventilation requirement so the original cooling vol flow rate has been reduced. But then why is the DesCoolVolFlowMin > the OA requirement which should result in a 1.0 min frac.
One solution is in SingleDuct::SizeSys around line 2116, MinAirFlowFracDes should be limited to no more that 1.0.
That's probably useful, but either DesCoolVolFlowMin or Sys.MaxAirVolFlowRate is wrong at this point.

• Also, noticed there are twice as many TermUnitSizing objects as zones when debugging.
  That's correct. There is one TermUnitsizing object for each zone inlet node, so if there is zone equipment there will be extra instances of TermUnitSizing.

Details

Some additional details for this issue (if relevant):

• Platform (Operating system, version)
• Version of EnergyPlus 8.8.0 9bd43c6

Checklist

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

• Defect file added use the defect file for VRF:FluidTemperatureControl crashes with Fan:SystemModel #6218
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)

[Myoldmopar]

Closed via #6338