a office building conditioned through the use of the following systems:

System 1 is a ventilation only system that conditions the OA to 72 degree F.
System 2 is a cooling only VAV air handling system that cools the building's return air to 55 degree F (This system has an economizer mode).

THE TRICKY PART: The two ducted air streams supplied by System 1&2 discharged separately to condition the same room..
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In addition, a floor mounted 4-pipe fan coil unit system is used for the building's parameter heating and cooling.

So, i wonder if it's valid if i model the system as follow:

create three different zones within the boundary of the room and have them assigned to System 1, System 2 and the 4-pipe fan coil system respectively (Also specify the internal wall that separates the three zones to U=1 ) ?

Thank you.
Guo Hong Ho