I am working for a client who has a variable refrigerant HVAC system with a separate fully condition ventilator supplying fresh air. They are over budget and the contractor is proposing ducting the air into the back of the units in lieu of separate ducts for the ventilation system. We are worried that this would lead to them not meeting the LEED IEQ prerequisite. Would they not meet the prerequisite because it is already fully conditioned and not just a heat exchanger?

I am trying to understand how outside air loses effectiveness and would require more. In an effort to maximize the potential energy savings and minimize first costs (reduced unit size and main ductwork sizes as part of the shell package) the outdoor airflow quantity was based on a ventilation effectiveness of 1.0.

In this case that meant space delivered neutral air. If the air were ducted to the back of each unit it would be heated to a temperature that reduces the effectiveness to 0.8, thus requiring more total outdoor air.

Would this change of effectiveness hurt our chances of obtaining the LEED IEQ prerequisite related to ASHRAE 62.1?