Unable to determine fan air flow rate Error

hvac-template
fan
pthp
energyplus
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Hello,

I've created an EnergyPlus model for my apartment and want to conduct some analysis on that. I get results when I set the setpoint to 23C, but when I change the setpoint to 25C, it gives me this error:

* Fatal * Unable to determine fan air flow rate.

I have used HVACTempleta:Zone: PTHP in my model. Does anyone know why I get this error?

You can find both files in this link.

Thanks for your help in advance!

Thanks, Mostafa

217

Mostafa Meimand

asked 2024-03-07 11:54:06 -0500

14.1k

Aaron Boranian

updated 2024-03-08 07:19:59 -0500

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I suggest opening an issue at https://github.com/NREL/EnergyPlus/is.... I'm not seeing any other users that have hit this issue, and since EnergyPlus isn't providing any suggestions in the error message about how to resolve it, it may be an unexpected error that an EnergyPlus developer needs to look into.

shorowit (2024-03-08 14:19:25 -0500) edit

Sure, I will do that!

Thanks

Mostafa Meimand (2024-03-13 07:16:24 -0500) edit

Hi Mostafa, were you able to solve this? I'm getting the same error using different types of templates in my model.

MatteoMerli (2024-03-25 10:53:24 -0500) edit

Hi Matt,

No, I couldn't solve the problem

Mostafa Meimand (2024-05-16 11:56:37 -0500) edit

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There is a clue in the warnings above the fatal error:

* Warning * Calculated design cooling load for zone=THERMAL ZONE 1 is zero. * ~~~ * Check Sizing:Zone and ZoneControl:Thermostat inputs. * Warning * Calculated design heating load for zone=THERMAL ZONE 1 is zero. * ~~~ * Check Sizing:Zone and ZoneControl:Thermostat inputs. * Warning * SizeUnitarySystem: ZoneHVAC:PackagedTerminalHeatPump = THERMAL ZONE 1 PTHP * Fatal * Unable to determine fan air flow rate.

The sizing results for the 23C file show no heating load, and a small cooling load (from the eio output):

! <Zone Sizing Information>, Zone Name, Load Type, Calc Des Load {W}, User Des Load {W}, Calc Des Air Flow Rate {m3/s}, User Des Air Flow Rate {m3/s}, Design Day Name, Date/Time of Peak, Temperature at Peak {C}, Humidity Ratio at Peak {kgWater/kgDryAir}, Floor Area {m2}, # Occupants, Calc Outdoor Air Flow Rate {m3/s}, Calc DOAS Heat Addition Rate {W}
 Zone Sizing Information, THERMAL ZONE 1, Cooling, 366.58315, 366.58315, 3.58480E-002, 3.58480E-002, TESTDESIGNDAY, 7/20 19:00:00, 33.37000, 1.05960E-002, 60.00000, 0.00000, 0.00000, 0.00000

With the 25C setpoint, there is no load, and there is zero outdoor air, so there is nothing to calculate a flow rate from. The PTHP flow rates are zero:

! <Component Sizing Information>, Component Type, Component Name, Input Field Description, Value
Component Sizing Information, ZoneHVAC:PackagedTerminalHeatPump, THERMAL ZONE 1 PTHP, Design Size Cooling Supply Air Flow Rate [m3/s], 0.00000
Component Sizing Information, ZoneHVAC:PackagedTerminalHeatPump, THERMAL ZONE 1 PTHP, Design Size Heating Supply Air Flow Rate [m3/s], 0.00000