Return Fan:VariableVolume Fan Power Minimum Flow Fraction imposes air loop flow

[ecoeficiente]

Issue overview

Return Fan:VariableVolume imposes air loop flow to Fan Power Minimum Flow Fraction despite E+I/O states the opposite:

This field does not enforce the system air flow rate during simulation

Details

It seems to happen with return fan but not with supply fan.

[Nigusse]

Looking at the source code confirms that the input field Fan Power Minimum Flow Fraction value is used for fan power calculation only. @ecoeficiente Do you have idf file that shows the defect?

[Nigusse]

@mjwitte There is no defect file to confirm the defect and looking at the source code the value of Fan Power Minimum Flow Fraction is used for fan power calculation only. I labeled the issue to unconfirmed defect.

[ecoeficiente]

So sorry I did not notice your request for example files. I attatched 2 idf files, everything identical but Fan Power Minimum Flow Fraction in AHU return fan.
You will see that the one with 0.3 fraction imposes the flow (the one with 0 fraction gets no flow).

FlowFractionBug.zip

[jmarrec]

I took the files from @ecoeficiente , updated them to E+ 9.4 and I can reproduce the issue : Here I am plotting the ('CIRCUITO DE AIRE SUPPLY SIDE OUTLET 1', 'System Node Mass Flow Rate', 'kg/s') variable

Interestingly I created a MCVE test case using OpenStudio with a simple AirLoopHVAC that has two Fan:VariableVolume, and changing the Min Flow Fraction on the return fan from 0 to 0.3 has no effect there...

[jmarrec]

Ok, I found it, it's becasue my VAV:NoReheat terminal had a Constant Minimum Air Flow Fraction = 0.3... Switching it to 0 like in the defect files exhibits the defect.