Table of Contents
How do you assess the performance of fans?
The fans are tested for field performance by measurement of flow, head, temperature on the fan side and electrical motor kW input on the motor side. Static pressure Static pressure is the potential energy put into the system by the fan.
How do you calculate the flow rate of a fan?
To calculate air flow capacity of a fan in cubic feet per minute (cfm): multiply the average air speed you measured in feet/minute (fpm) by the area of the fan face in square feet. (Area of circle =þ d2/4; where d = diameter in feet).
How do you calculate CFM from RPM for fans?
Define the terms in the general centrifugal fan formula and rearrange them to use the formula to solve for the higher air flow: CFM 1/CFM 2 = RPM 1/RPM 2 x (D1/D2)^3 (cubed). The (D1/D2)^3 is 1, since the impeller diameter stays the same, so CFM 2 = CFM 1 x (RPM 2/RPM 1).
How do you calculate fan velocity and pressure?
V = CFM ÷ Area (Sq. Ft.). VP. – Velocity Pressure, is equal to the kinetic energy per unit volume of the flowing air.
What is fan performance?
Fan performance is typically defined by a plot of developed pressure and power required over a range of fan-generated airflow. Understanding this relationship is essential to designing, sourcing, and operating a fan system and is the key to optimum fan selection.
What makes a fan efficient?
Fans move air most efficiently when they have a cowling. Cowlings prevent air around the tip of the blades from circling about outside the blades, instead forcing that air forward, yielding much more air for the same power draw. A cowling on a fan directs airflow and improves efficiency.
What is airflow rate?
Air velocity (distance traveled per unit of time) is most often expressed in feet per minute (FPM). Multiplying air velocity by the area of a duct allows you to determine the air volume flowing past a point in the duct per unit of time. Volume flow is generally measured in cubic feet per minute (CFM).
What is CFM for a fan?
A fan’s ability to move air is measured in cubic feet per minute (CFM). The bigger your bathroom, the higher the CFM rating you’ll need. A fan should have a CFM rating high enough to replace the air in your bathroom at a rate of eight times per hour.
How is fan pressure calculated?
Multiply the specified operating static pressure by the correction factor to determine the standard air density equivalent static pressure. (Corrected static pressure = 3.0 x 2.00 = 6”. The fan must be selected for 6 inches of static pressure.)…
| Distance between Riser and Elbow | System Effect Coefficient (K) |
|---|---|
| 5 feet | 1.2 |
What are fan curves?
Fan curves are simply graphs showing fan performance, normally with air volume on the horizontal “x” axis, and pressure on the vertical “y” axis. For a fan driven by an electric motor, the input voltage remains the same throughout the test.