When the installation distance of the air conditioning fresh air duct on the ceiling is short, it is

You mean the duct is placed directly on the horizontal bracket without needing to be fixed, right? Yes, there is no need to fix it, because one section of the air duct is connected to the air conditioning equipment, and the other end is connected to the air outlet, which is equivalent to limiting the movement of the air duct. And the canvas soft connection is set at the connection between the equipment and the air duct, and the air duct itself does not produce vibration, so it does not need to be fixed.

I don't understand why you will be involved in the problem of fixed or not, the air duct installation has always been customary, not to say that it must not be fixed (I think you drill the horns), if you have to be fixed, there is no specific fixing method (the construction specification does not mention the problem of fixing), you like how to fix it, as long as it does not affect the use, but since it can be fixed or not, why spend time and materials and manpower to fix? Therefore, the habit is not to fix it, just rest on the horizontal support, I repeat it, the air duct itself has no vibration source, and will not vibrate.

Conclusion: There is no specification that must be fixed or must not be fixed, and the customary practice is not fixed (except for special circumstances that cause the instability of the air duct, of course), and the specification does not mention or give a method of how to fix it.

If it's unstable, you'd better root the boom and stabilize it.

It doesn't matter that you can rest assured later.