Turning Vanes in 45 Degree Elbows

The cases where intalling turning vanes in 45 degree elbows are justified are fairly rare.

Think of it as a cost versus benefit analysis:

Turning vanes cost both in terms of material and labor. However, in a 90 degree elbow,they impart a significant measurable benefit (a reduction in air turbulence far exceeding the turbulence they create by being placed in the air stream in the first place) that makes it cost effective and practical to use them.

Turbulence from the mere presence of a turning vane in an airstream? Of course!! Any obstruction placed in an air stream creates turbulence. What about "straightening" guides/grids/vanes etc.? Those too. Keep in mind such devices are placed in streams that are already extremely turbulent. Their purpose is to break-up and control turbulence that would otherwise be present (and felt) if they were not installed.

A square 90 degree elbow without vanes has much more turbulence associated with it than a 45 degree elbow. The available benefit gained from using turning vanes in a 45 degree elbow are correspondingly reduced. The net benefit (fitting turbulence reduction versus turbulence of turnig vane installation) becomes very small.

The benefit versus cost ratio drops. (Less benefit versus same cost).

In most cases, turning vanes in 45 degree elbows just isn't worth the effort.

That doesn't mean they can't be used. There are applications using different fluids, pressures, and air velocities where using the vanes would be a benefit (high sub-sonic to supersonic range wind-tunnels or vacuum systems come to mind), but these are outside the realm of conventional (HVAC) air moving systems and account for only a small percentage (say 2 percent?) of cases.

If using turning vanes in 45 degree elbows provides a significant difference in the design of a conventional system, that system is not being designed properly.

Take care and may good fortune and health be yours.

Rifle 47