Ok, this prereq, in my mind, is more of a design-based item. And this is a long comment for a particularly fuzzy issue in my mind. Apologies ahead of time.

As critical zones are used for design purposes, the 62MZ calculator and this prerequisite require calculations to go down to the zone level. Therefore, critical zones would be required to be balanced and checked for ASHRAE 62.1‐2007 requirements. However, the intent of this prereq states: “Modify or maintain each outside air intake, supply air fan and/or ventilation distribution system to supply at least the outdoor air ventilation rate required by ASHRAE Standard 62.1‐2007…” and not to balance each zone to ensure the correct amount of airflow is meeting each zone’s requirements, based on occupancy count and spacetype.

And, regardless, the critical zones in question (conference rooms, office space, breakrooms,etc) all have the same requirements per ASHRAE 62.1‐2007 Table 6‐1 (5 OA CFM / Person and 0.06 OA CFM / Sq. Ft.).

So, what does this all mean, then? Why do we need to look at the critical zones if all zones served by a AHU require the same amount of OA?

Then, furthermore, lets say heat pumps are being used. These units are all served by a dedicated outside air fan. One outside air fan serves the entire building’s ventilation needs, based on ASHRAE 62.1‐2007
requirements. Also, each heat pump is not directly ducted from the OA chase. The OA chase distributes air to each floor in the RA plenum, dilutes, and mixes with the RA at each heat pump to serve the zone/space.

So, while the OA fan meets the requirements of ASHRAE, how should compliance be demonstrated for potentially critical zones (which is at the heat pump level) to determine how they affect overall system efficiency, and therefore the OA required to be brought into the AHU?