I tried running your model and actually had a different error terminate the
run:

***ERROR***********************************************************************
Loop: Hot Water Loop has zero design flow.
Check input for consistency, or specify design loads.

It looks like your VAV systems are setup with no reheat coils, which may or
may not be accurate to what you're trying to model. Based on your inputs
though, the only time the system would ever go into heating is when ALL the
zones need heating which is rather unlikely for a VAV system serving 20
zones.

I was able to get your model to simulate properly by using reheat coils and
giving it a delta T on the reheat temperature. If you don't actually have
reheat, then maybe consider using a preheat coil, not a heating coil, to
model the heating being done at the central air handler.

See attached for the .inp with my edits so you can see it running.

Again - I wasn't able to replicate your chilled water primary equipment
error so I apologize if this doesn't solve your issue!

[image: Inline image 1]