Most electronic enclosures have a static pressure of between 0.05 and 0.15 in. Assuming a dense package, the fan in the previous example should be capable of delivering 80cfm in free air, instead of 32cfm. An AMCA Standard 210 double chamber is used to accurately measure air volume and static pressure. The pressure difference Ps represents the maximum static pressure achievable by the fan. The maximum air volume can then be calculated using Pn, D and the air volume equation above.
Q represents the maximum achievable airflow with the fan in free air.
The performance of a fan in a specific application is determined by the intersection of the Device Characteristic Curve and the Fan Characteristic Curve. The Device Characteristic Curve is a property inherent to an individual electronics enclosure. It describes how air will flow through the enclosure given its particular obstacles and internal resistance. Resistance can be turns in the airflow or chambers that the air must flow through. The flow resistance is roughly proportional to the square of the volumetric flow rate.