I have a school which will be served by ground source heat pumps.
Outside air will be provided to the classrooms with a Dedicated Outside
Air Unit/ ERV with a VAV fan which operates based on CO2 sensors within
the spaces. The heat pumps won't have any outside air provided to them.

My question is what's the best way to model this? Since you can't apply
more than one HVAC system to a particular space, do I create a fake
space and apply the outside air unit/ERV to that? If so, how do I model
the fake space such that there is no heat loss and only people to
require outside air?

I tried to just model the dedicated outside air system by way of the
heat pumps, but I run into problems when trying to specify when the
dedicated outside air unit would operate. I would want it to operate
independently from just when the heat pump is operating and I can't find
a way to do this.

Has anyone had any luck modeling something similar to this?

Thanks.

David B. Everhart, P.E. LEED AP