Duct Mounted Diffusers

[cwade.109269]

Ok, I have posted this before on various boards (including this one) and didn't get any response, but every time that I mention Duct Mounted Diffusers and that you can't create them in Revit MEP, I get told that you can and to ask on Augi. So, once again, I ask, how do I create and use duct mounted diffusers in Revit MEP 2009?

[JoelLondenberg]

The best we've been able to come up with is here---

http://forums.augi.com/showthread.php?t=74320

[cwade.109269]

Yeah, I think that's what we used last time and it was close, but not quite right unfortunately.

[Andrew.Bagnall]

Its quite simple.
Don't try and mount them directly to the ducts or by creating a duct fitting type air terminal - the former is not possible and the latter will look ok but will not let you assign flows to the terminals and let systems work properly - you don't want to start "if it looks right it is right" habits with Revit MEP, if so go back to cad.
The best way is to use tap fittings to create a takeoff the main duct then override the tap fitting instance parameters to reduce the takeoff length down to a very small value, say 2mm or so and then add a section of duct - again very short, and then a very thin sideblow register family. This way you have the air gille connected to the main duct via a length of duct and a tap, which is the way revit likes it, and your systems will work etc.

See the image attached for an example. This setup lets me use the inspect tool and check pressure drops etc and flow propagates along the system correctly, all other workarounds to my knowledge will not.

Tip - get everything working, connected and in the right place first before trying to override the takeoff lengths and making the short duct sections - Revit gets a bit touchy with them after that is done in my experience.

Whilst we're kindof on the subject - can someone please shed some light on how to get tap fittings to be pependicular only and not adjustable angles - I know there is a parameter in the family settings which should enable this, but I change it to be perpendicular and they still are adjustable - weird... A bug perhaps? Anyone from Autodesk listening???
I'm fed up of my flexes coming off at slight angles and manually having to straighten them.

[Andrew.Bagnall]

One more, this time showing plan view of the duct and diffusers and proof that the flow propagates etc...

Also - to change the takeoff lengths you have to override the automatic takeoff length projection instance parameter - to do you have to first set the 'takeoff fixed length' parameter to say 2mm, and then you change the 'takeoff length' parameter to the same value and the tap will reduct to next to nothing making it look like your register is connected straight to the duct.

[martin.schmid]

I know there is a parameter in the family settings which should enable this, but I change it to be perpendicular and they still are adjustable - weird... A bug perhaps? Anyone from Autodesk listening???
I'm fed up of my flexes coming off at slight angles and manually having to straighten them.

Hmm... this does seem to be a bug... i.e., if the Flex Duct Type's specified tap is 'Tap - Perpendicular' it doesn't 'force' the tap to be perpenduclar...However, the same tap when using rigid duct is forced Perpendicular.

[Andrew.Bagnall]

Yeah it's quite infuriating - I've tried everything I can think of and can't get it to force to being perpendicular. But I don't remember it being this hard originally?
This would be a good thing to get fixed as it wastes a lot of time trying to straighten them up one by one.

[cwade.109269]

Ok, let me try to simplify this, I want something that is easy and fast, as well as accurate, what I want is to simply be able to click where I want the diffuser to mount on the duct and have it mount accordingly as I am placing the diffusers and still be able to provide appropriate calculations. We wouldn't add duct in the real world to accomplish this, so we shouldn't have to add duct in Revit to accomplish this.

[JoelLondenberg]

Ok, let me try to simplify this, I want something that is easy and fast, as well as accurate, what I want is to simply be able to click where I want the diffuser to mount on the duct and have it mount accordingly as I am placing the diffusers and still be able to provide appropriate calculations. We wouldn't add duct in the real world to accomplish this, so we shouldn't have to add duct in Revit to accomplish this.

No - Revit MEP cannot do this with a single click.