I'm working on a LEED project with the following conditions:

1) The proposed system is a 4 pipe Fan Coil system. Outside air is
brought into the space through an central ERV and independently ducted
to each Zone.

2) Appendix G requires the Baseline case to be Packaged VAV for
each floor, with terminal re-heat for each zone

In my simulation, I have the outside air being calculated based on the
"critical" zone for the baseline case. In order to meet the needs of the
critical zone, outside air for each floor is increased to meet the
critical zone needs. Outside air for the proposed system is simply the
sum of all the zones, because each zone is supplied individually.

The net result is that the OA in the baseline and proposed simulation
are different, because the PVAV system has to adjust the OA upward for
the critical zone.

The reviewer has commented that the outside air must be the same for
both simulations.

This seems like a paradox to me. It is physically impossible to make
15% OA go to one zone and 20% OA go to another zone in a PVAV system,
where the OA is mixed in the AHU prior to distribution through a common
duct. Forcing my simulation to do this in order to meet the reviewers
comments seems to violate the spirit of LEED. Why would we purposefully
compare a proposed system to baseline which cannot be built?

Likewise, artificially raising the OA used in the proposed system
simulation, to match that of the baseline system makes no since.

Has anyone else run into this before? Do you have suggestions?

All help greatly appreciated!

Regards,

Chris D. Mullinax, P.E., LEED AP, CEM