Calculating fan pressure means determining how much pressure the fan adds to the air as it passes through the machine. This value is fundamental for matching a fan to a duct system, mine airway or process. In practice, engineers distinguish between static pressure, velocity pressure and total pressure when evaluating fan performance.
Static pressure is the pressure that pushes equally in all directions on the duct walls. It is measured with a pressure tap facing perpendicular to the flow. Velocity pressure is related to the kinetic energy of the moving air and depends on air velocity; it is often calculated from measured velocity using the formula pv = 0.5 × ρ × v², where ρ is air density and v is velocity. Total pressure is the sum of static and velocity pressure: pt = ps + pv.
To calculate the fan pressure rise, you measure or estimate total pressure at the fan outlet and at the fan inlet. The fan total pressure (FTP) is the difference: FTP = pt,outlet − pt,inlet. Similarly, the fan static pressure (FSP) is based on static pressure difference: FSP = ps,outlet − ps,inlet. Which one you use depends on the definition adopted in your standards and on how system resistance is expressed, but the method is the same—compare inlet and outlet conditions.
In a field situation, you may not have detailed velocity data at both sides of the fan. In that case, static pressure taps and typical duct velocities are used to estimate velocity pressure and thus total pressure. Standard fan test methods (such as those used in laboratories) use carefully designed inlet and outlet chambers, flow measuring nozzles and correction factors to obtain accurate fan pressure curves. For most industrial and mining ventilation design work, manufacturer-supplied fan curves of pressure versus airflow are used instead of performing full tests on site.
Once you know fan pressure, you can relate it to system resistance. Ducts, filters, bends, regulators and mine roadways all create pressure loss that usually increases with the square of airflow. By plotting fan pressure and system pressure on the same graph, you find the operating point where the two curves intersect. If the calculated fan pressure is insufficient at the desired airflow, you may need a larger fan, higher speed or reduced system resistance.
In summary, calculating fan pressure involves understanding static, velocity and total pressure, measuring or estimating these quantities at the inlet and outlet, and taking the difference to find the fan’s pressure rise. This value is essential for checking whether a fan can overcome the resistance of industrial or mining ventilation systems.
