We tag systems as 'SA', 'RA' (Supply Air, Return Air). 'HW', 'CW' (Hot Water, Cold Water), etc. It would be nice to be able to:
1) Define additional System Types. Like Exhaust Air, many piping system types are necessary
2) Be able to have an Abbreviation for those System Types that can be reported in a Tag (all the current 'work arounds' are not in the true spirit of BIM.
My other CAD is a Cadillac and I like to Revit to the Max!