Fan Efficiency Grade (FEG) is a numerical rating that classifies fans by their aerodynamic ability to convert mechanical shaft power to air power. In case of direct driven fan, it indicates fan’s aerodynamic ability to convert impeller power to air power.
Hence, essentially, FEG reflects fan energy efficiency, allowing engineers to more easily differentiate between fan models.
Therefore, FEGs, as defined in AMCA 205, are designed to be a simple system to indicate the aerodynamic quality of the fan and are based on the fan’s peak total efficiency.
The total efficiency is calculated using the traditional airflow, pressure, and input power as measured per AMCA Standard 210. Fan efficiency does not take into effect the efficiency of the drive (belt drive) or the motor.
Efficiency is defined as the air power divided by the fan input power.
Both static and total efficiency can be calculated from fan performance data as follows:
CFM = Fan flow rate, ft3/min
Ps = Static pressure, in. wg
Pt = Total pressure, in. wg
BHP = Fan power input, hp
FEG Curve :Pressure Vs Airflow – Total Fan Efficiency
In Figure 2, fan static pressure and total efficiency is plotted along with the fan pressure curves. The peak total efficiency occurs at the top of the “bell” shaped efficiency curve. Hence, this peak total efficiency is used to determine the FEG value.