Fan Selection Flashcards
What is CFM?
Cubic Feet Per Minute. It’s a measure of volume of air over a time period
What is SP?
Static Pressure is a resistance to flow (energy added by the fan) measured in inches of water gauge in.wg.)
How is a fan selected?
A fan is selected based on CFM and ESP
What is BHP?
Brake Horse Power is a measurement of power consumption
What is HP?
Horse Power is used to indicate fan’s motor size
What is RPM?
Revolutions per minute is a measurement of motor speed
What is FRPM?
Revolutions per minute measuring fan speed
What is TS?
Tip speed is the speed of the fan impeller tip measured in feet per minute
How is Tip Speed Caluculated?
3.14 x RPM x impeller diameter / 720
What is a decibel?
A logarithmic measurement of magnitude
What is a Sone? What is considered quiet or loud?
A linear measurement of sound
1-2 is quiet. 5 is loud.
What are the three basic types of fans?
Axial, Centrifugal, and Mixed Flow
Describe Axial fans
airflow is parallel to the fan impeller. High CFM, most economical impeller. higher efficiencies at lower SP. Louder than centrifugal, mostly unducted applications
Describe Centrifugal fans
inline, utility set, plenum/plug fans, or dome. More expense than axial. Takes up more physical space. Lower sound levels. Moves air perpendicular to air inlet
Describe Mixed Flow fans
Hybrid between axial and centrifugal. Efficient air movement. High Volume or CFM flow. Lower sound levels
What are the two types of fan motor configuration?
Direct Drive and Belt Drive
What are pros of Direct Drive fan motors?
Low maintenance and compact design
What are the cons of Direct Drive fan motors?
Limited motor availability. Limited motor access and less performance flexibility.
What are the pros of Belt Driven fan motors?
Performance flexibility. Easy access to motors. Work with VFDs. Motors are readily available.
What are the cons of Belt Driven fan motors?
More maintenance. Takes up more space.
How do you adjust the CFM flow on a belt driven motor?
Opening the pulley will decrease fan RPM and closing it will increase fan RPM.
What is the rule of thumb for Belt Drive?
Normally above 2,000 CFM with a SP above .5” wg
What is the rule of thumb for Direct Drive?
Normally below 2,000 CFM with a SP less than .5” wg
