different between suply and return sistems

[konticv]

I have two completely identical systems, one supply and the other return. With the return system, everything is ok, while with the supply system, it reports an error to check the flow direction. With both systems, the air is taken from all the grates behind the machine and introduced into the space through two grates on the "T" arms of the channel. Why does it report an error with the supply system.

[RobDraw]

Hard to say for sure but I'd be willing to bet that you used the same grates on both sides. You may also have open ended ductwork. 

[konticv]

I didn't understand you very well. Of course, the bars are not the same on both sides. On the suction side there are grates with connector orientation out and on the discharge side there are grates with connector orientation in. Look at the picture I attached and you will see that everything works when the system is declared as return, while it does not work if everything is the same only the system is declared as supply.

[konticv]

Obviously there is a difference between the supply and return system properties in Revit

[RobDraw]

With only the two images and an inadequate description, nothing is obvious. I was only able to guess.

Share the file EXACTLY as you have it there. I think I know what it is but I'm done guessing if you're going to react like that. 

[konticv]

Here is the attached file.
So, I repeat, everything is exactly the same, but exactly the same, only it works when the system is declared as return air and it doesn't work when the same system is declared as supply

[konticv]

Try to make a system like this yourself, just let one be the return air system and the other the supply. the connectors on the suction grids are "present", both connectors on the machine are "calculated" and the connectors on the discharge grids are "system" with a coefficient of 0.5. When the system is declared as return, everything is ok, but if you create the same system and declare it as supply, it reports an error.

[RobDraw]

It's the connectors in the equipment family. They have flow direction assigned so the air can only flow in one direction.