Derivation of equations necessary for primary airflow redistribution in VAV systems to reduce outdoor air intake while meeting ventilation requirements.

The multiple spaces equation of ASHRAE Standard 62-1989 makes it possible to bring in a smaller fraction of outdoor air than that dictated by the critical space. This paper develops an analytical proof that increasing the primary airflow rate to t e critical space reduces the outdoor airflow rate required to meet ventilation requirements. For systems employing fan-powered boxes, where more than one box is critical, a systematic procedure for incrementally increasing the primary air is currently required. Also presented are equations necessary to undertake such a systematic procedure of incrementally increasing the primary air for situations typically encountered in the operation of fan-powered variable-air-volume systems.