Is it possible to create an acute elbow?

Question

Suppose I have two ducts, and the angle between them is less than 90 deg. Is is possible to create ONE SINGLE elbow that is less than 90 deg?

Let's first define ACUTE and OBTUSE: For a common duct elbow, it is usually generated by a SWEEP model. If the angle between 2 ducts is obtuse, the sweeping angle of the elbow fitting is less that 90 deg. But we still call it an OBTUSE elbow, because there is an OBTUSE angle between 2 ducts, OK?

I tested this issue in Revit UI, and as we all know, in Revit UI user CANNOT create an acute elbow fitting. It will be a perpendicular elbow, following by a short straight MEPCurve element, then an obtuse elbow fitting. So, there will be 2 elbow fittings and a short MEPCurve created in document.

Questions are:

1. A typical elbow family is based on a sweep model, and the sweep model based on an ARC. If I have an elbow family that supports a SWEEP greater than 90 deg, can I create an acute elbow fitting? (I am just a Revit API developer, not so professional at Revit. And we don't have such families. In standard Revit tempolates, they don't provide such elbow families)
2. If I pass 2 Connectors into the method NewElbowFitting, it throws an exeption which reads: Fitting cannot be created between the input connectors becuase the angle between them is too small or to large.. So, no other way to create an acute elbow fitting connection except "2 elbow fittings & a short MEPCurve" solution?

Answer 1

Yes, with some caveats.

Please see attached screenshot - I did this with the default Revit UI - no code or weird fitting magic required. I didn't need to edit the family either.

The key is to draw the fitting first, then set the angle of the fitting greater than 90 degrees (in this case greater than 90 degrees means an acute fitting - the angle is measured as a deflection from a straight line). Once the fitting is acute, you can attach ductwork to it.

In this example, it is at 135. The maximum is probably just under 180 (which would fold the fitting back on itself). I did this with fittings in the Mechanical Template that is installed alongside Revit.

The first caveat is that it is unlikely this would be built in practice - fittings always restrict airflow somewhat - the tighter the bend, the more the restriction. Sharp bends can make the duct system noisy or cause so much friction loss that you need to upsize the fan.

The second caveat is that Revit doesn't produce fittings like this by default because of the first caveat - the product would be less useful if it created fittings like the below instead of segmenting them into several different fittings.