All, I have an ASHRAE 90.1-2007 question that I've run into while completing an energy model.

ASHRAE 90.1-2007 section 6.4.3.9 is a mandatory provision for demand control ventilation in densely occupied zones.

Exception 9.4.3.9(a) reads, "Systems with energy recovery complying with Section 6.5.6.1."

6.5.6.1. Exhaust Air Energy Recovery. Individual fan systems that have both a design supply air capacity of 5000 cfm or greater and have a minimum outdoor air supply of 70% or greater of the design supply air quantity shall have an energy recovery system with at least 50% recovery effectiveness. Fifty percent energy recovery effectiveness shall mean a change in the enthalpy of the outdoor air supply equal to 50% of the difference between the outdoor air and the return air at design conditions. Provision shall be made to bypass or control the heat recovery system to permit air economizer operation as required by Section 6.5.1.1.

My question: If I have a system that's only 20% outside air but complies with the remainder of 6.5.6.1, can I still use exception 9.4.3.9(a) to avoid DCV in densely occupied zones? Or does that exception only apply to those systems with 70% OA or more?

Thank you!

Stormy L. Shanks, PE