New to Revit MEP 2012 are system families for systems. These can be found in the Project Browser.
System families can have additional types created in the same way as other loadable families, by right-clicking on any one of the existing types in the Project Browser and duplicating. It is important that you choose carefully—duplicating a Domestic Hot Water piping system cannot be changed later to a Domestic Cold Water piping system.
With these new system families come new parameters: System Abbreviation and System Classification. New to Revit MEP 2012 is the ability to tag any pipe (or duct) and refer to the system type of what may be a system with no equipment assigned. You could not achieve this in previous
releases without manual workarounds. Additionally, you can utilize these parameters in display filters. Display filters can be used to assign a color, linetype, and line weight to a particular system