Efficiency is an important consideration when selecting a fan. There are two types of fan efficiency-fan static efficiency and fan total efficiency.

Fan efficiency is a measure of how effectively a fan moves air. The more efficient a fan is, the less it will cost to operate throughout its lifetime. Fan efficiency is the ratios of the amount of air moved at a given pressure, divided by the power required, expressed as a percentage. Fan static efficiency is calculated using the formula shown, which required CFM, pressure and brake horsepower. Efficiencies for fans can be calculated two ways-static efficiency, which is generally used in commercial applications and require the use of static pressure in the formula and total efficiency, which is used in industrial installations and requires total pressure.

Motor efficiency is a measure of how effectively a motor converts electricity to mechanical rotation. Motor efficiency is the ratio of the output to input power. There are several factors that affect motor efficiency. Motor designs – standard, high and premium – have different efficiencies. There are also voltage considerations. In general, the higher the voltage the higher the efficiency. The phase of the motor will also affect efficiencies. Typically a 3-phase motor is more efficient than single-phase motor. The size and speed of the motor will affect the efficiency. Fractional horse power motors, categorized as less than one horsepower, are typically less efficient. Integral horsepower motors greater than one horsepower are more efficient.

In this section, we learned that there are two types of efficiency to consider when selecting fans; fan efficiency, which is the measure of how effectively a fan moves air and motor efficiency, which is a measure of how effectively a motor converts electricity to mechanical rotation.