David,
Where there are two systems serving a single zone, see if you can model
the zone as two separate zones. For example, something I have done to
handle a spot cooler in a hot room is to create a "dummy" room of
negligible floor area that has only the sensible cooling load (computers
or whatever) and nothing else. Perhaps you could make it a tiny interior
corner of the "real" room. Then I assign this "dummy" room to the spot
cooler. The "real" room has all the other loads (envelope exposure,
people, etc.) and is on the main air system. I keep the thermostat
settings the same in both. This approach works well if you can easily
separate loads within the room.
Sincerely,
Keith Swartz, PE, LEED(r) AP