States that HVAC system outdoor air flow rates are usually measured and set at the air handling unit. The effectiveness of a HVAC system in delivering the outdoor air to the occupied space of a building is varied and often disputed. Reports that to investigate the delivery of outdoor air to the occupied spaces of a variable air volume system, ASHRAE Technical Committee 9.1, large Buildings Air Conditioning Systems, funded Project 687-TRP, Minimum Ventilation Airflow Rates with VAV Systems. Presents some of the information collected from tests during the project. Concludes that following Standard 62-1989 guidance on calculating ventilation for multiple spaces can reduce the outdoor air requirements for many systems. In addition, increasing the supply air flow to a zone can improve the ventilation effectiveness of a zone so that the outdoor air requirements could be reduced for some zones. Innovative control strategies could be incorporated in some situations to reduce the outdoor air brought into the air handling unit as the supply airflow increases.