ANSI/ASHRAE Standard 62-2001, Ventilation for Acceptable IndoorAir Quality, as modified by Addendum 62n, prescribes newminimum breathing-zone ventilation rates and new calculation proceduresto find intake airflow for different ventilation systems. Previousarticles discussed the design of “simple” ventilation systems (singlezone,100% outdoor-air, and changeover-bypass VAV) in compliancewith Addendum 62n requirements. Here, we examine the design of amore complex set of ventilation systems, namely single-path, multiplezonerecirculating systems.