I am revisiting this model and never received a response, and I see
another has run into the same warnings. Reposting/rephrasing for any
suggestions/input:

In hindsight perhaps I can phrase a simpler set of questions:

1. True or False: Is it simply impossible in eQuest to
simultaneously use OA-FROM-SYSTEM and either of the DCV ventilation
control methods with the same system. This appears to be the case.

2. Based on #1, I seem to be stuck being unable to modeling the
savings from DCV at the zonal level (instead forced to use fraction of
design or the like for my min-OA method)...

But I've got a crazy idea: For an alternative way to force DCV
behavior, might I define a set of MIN-AIR-SCHEDULE's, using the zonal
occupancy schedules as a template, and multiply each fractional
occupancy rate by the designed OA ratio? This would be tied to an
assumption that the C02 levels rise and fall instantaneously with the
occupancy, which I know is not true but may be an acceptable
approximation given #1.

Example: A classroom has a daily schedule that looks like this (this is
for evening classes, if this looks odd):

"General Classroom Occup Mon-Thu" = DAY-SCHEDULE-PD

TYPE = FRACTION

VALUES = ( 0, &D, &D, &D, &D, &D, 0.2, &D, &D, &D, &D, &D,
&D,

&D, &D, &D, 0.6, 1, &D, &D, &D, &D, 0.5, 0 )

..

With the design OA flow being 60% of the design Supply Air flow for that
terminal unit, I create a new MIN-AIR-SCHEDULE multiplying through:

"General Classroom MinAir Mon-Thu" = DAY-SCHEDULE-PD

TYPE = FRACTION

VALUES = ( 0, &D, &D, &D, &D, &D, 0.12, &D, &D, &D, &D, &D,
&D,

&D, &D, &D, 0.36, 0.60, &D, &D, &D, &D, 0.30, 0 )

..

For this approach I would tightly control the OA present at each zone
specifying MIN-OUTSIDE-AIR and clearing out the zonal-level OA inputs.

For reference - The system I am trying to model is:

* Dedicated outside air unit - HW/CHW coils, enthalpy recovery
wheel, variable supply which effectively sums the terminal fan coil's
call for OA over time. Conditioned OA is supplied to VAV's which
modulate based on the terminal fan-coil's DCV sensor.

* Terminal units of widely varying size: 4-pipe HW/CHW coils
which handle essentially all the internal/envelope loads, constant
volume, local thermostat controlled, conditioned OA from dedicated OA
units ties into supply ductwork (not seen by the terminal fan coil
units). OA is modulated down to zero based on a CO2 sensor in return
path.

For reference - I'm trying to model the above using:

* Single Zone Reheat (SZRH) for the DOAS, tied to a dummy zone

* 4-pipe Fan Coil (FC) for the terminal units, system per zone,
OA-FROM-SYSTEM

NICK CATON, E.I.T.