How to Calculate Volumetric Flow Rate and Pressure Drop in Fans

Static pressure drop is determined using the appropriate performance curve, based on the duct dimensions and total length.

Example 1:

Consider a workshop that requires an exhaust airflow rate of 8,495 m³/h. The installed duct is 35 meters long with a diameter of 20 inches. The static pressure drop for this system is calculated as follows:

Note:

If the duct route includes any elbows, tees, filters, or other obstructions, the equivalent length of each fitting must be added to the total duct length.

Example 2:

For a highly contaminated workshop environment—such as a foundry—with dimensions of 24 m (length) × 12 m (width) × 5.5 m (height), the standard air exchange rate for this type of application is 15 to 20 air changes per hour. Based on this, the required airflow capacity is estimated as follows:

To improve overall system efficiency, enhance performance, and allow for better airflow distribution, a total of 5 exhaust fan units are selected for this project.