Sorry about my initial reply - what I described is accurate, BUT not for the R1 released version . It seems that a limitation of R1 is that the ceiling grid is not recognized as an eligible face to host a face-based diffuser. This may be addressed in the next release.
As far as the problem with the diffuser being upside down, it seems that when the face-based diffuser is hosted by a ceiling (or a by a work-plane that is defined by a ceiling) the orientation of the diffuser is rotated upside down from it's defined orientation within the family - which is apparently why the diffuser is defined "upside down" within the family editor. It appears that when the diffuser is placed on any surface or plane not related to a ceiling, it will come in upside down in the project (which is "right-side" up in the family editor).
I looked at this a bit in R1 now and found a potential solution to the problem using R1 content.
Open ceilng plan mech view
Tools>Work Plane>Set Work Plane...
Pick a Plane -> select the ceiling grid
Insert the diffuser using the placement mode "Place on Work Plane".
This should insert the diffuser at the the elevation of the ceiling. When the ceiling elevation is changed, the diffuser will stay connected to the work-plane, which stays connected to the ceiling.
This solution requires one extra step (setting the work plane to the the ceiling grid prior to placement of diffusers), but all should be good after that, and the diffuser content that shipped with R1 should (hopefully) be able to do what you are trying to accomplish.
Please let us know if you still are having troubles.
Jason Bishop, PE
Building Solutions Division
Revit Systems QA
You were right. The ceiling grid is an eligible face, IF you are working in the 3d view. My main concern isn't with change in the grid elevation. I'm more interested in the diffuser aligning with the grid, which this particular family won't do. So I will just have to create my own diffusers for now. Thanks for your input, you've given me a better understanding of hosted families.
Thanks for looking into that. It's no trouble, I'm learning a lot here. Bob asked me to mention to you that this may be a good interoperability point. Looking at how the software is used by multi-discipline firms (like ours) as opposed to consultants. We are preparing a project template that will utilize worksets across the disciplines so that is what started my exploration of how the mechanical systems function.
Have you tried using the align command and locking the diffusers to the vertical and horizontal grid lines? I did this and am able to use the R1 content and product to maintian the diffuser's alignment with the grid.
By the way, I actually was NOT able to have the ceiling as an eligible face in R1, even in 3D view (not sure how you were able to accomplish this?). My initial reply was regarding working with a current in-house build - I am able to place the diffuser on the ceiling in PLAN view (something which cannot be done in release 1).
...another interesting nuance... if you actually select the entire ceiling grid and move it (use tab key until entire ceiling grid is red - not just one grid line) then the diffusers will maintain their location with respect to the grid, i.e they will remain "attached" to the grid, even if you have not locked them