I would like to get some feedback on how you all are interpreting Exceptions (c) and (d) under 90.1-2007 G3.1.1 Baseline HVAC System Type and Description. I have heard and seen differing standpoints from within my office, reviewing other energy models through the commissioning process, and looking through the CIR database.

Exception (c) allows certain zones to be modeled as contant volume even though the primary baseline system type is VAV. These zones are "having special pressurizaiton relationships, cross-contamination requirements, or code-required minimum circulation rates." I see this exception as being intended for mainly hospital and laboratory spaces.

If I have a lab with fume hoods or other hazardous materials that require a negative pressure relationship to adjacent spaces (and also a minimum circulation rate), does this exception apply?

Or if a lab has no fume hoods and no hazardous materials, but the Authority Having Jurisdiction mandates a specific air-change requirement, does this exception apply?

For labs with no air-change requirement, then I can see sticking with the 0.4 cfm/SF minimum or minimum ventilation rate and maintaining the VAV system type.

I also previously posted the question on Exception (d) about how to treat laboratory spaces with a minimum of 5000 cfm of exhaust. How are you applying this exception? Are you assuming this is the sum of lab spaces or individual lab spaces?