What is CFM ? How to measure it ?

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What is CFM?







-CFM is short for cubic feet per minute (cu ft/min).

- CFM determines how much Volume(cubic feet) can be moved or exchanged each minute.

-In HVAC we use CFM to represent the capacity of equipment like Air Handling Unit.

-It is measured by Anemometer.




 


Anemometer


-An anemometer is a device used for measuring wind speed and direction.

-It provides Velocity of air in M/s or FPM.

-It does not provide air quantity directly.

Formula

Air Quantity   =   The velocity of Air (FPM)  X  Area(Through which air is passing)

                                                  …… Area will be in Sq. feet









How to measure CFM across coil/Filter


AVG Velocity across filter = (A+B+C+D+E)/5

Total CFM = Area(LxW) X Avg Velocity

Ex.

AVG Velocity=60 FPM

Area =2*2=4 SqFt

Total CFM=4*60

                   =240 Cubic Feet per Minute


Eg.


AVG Velocity across filter = (A+B+C+D+E+F+G+H)/8

Total CFM = Area(LxW) X Avg Velocity



How to measure CFM across Grill/Diffuser


For Grill 


A                                      B                                           C





AVG Velocity across filter = (A+B+C)/3

Total CFM = Area(LxW) X Avg Velocity




                              
Square Diffuser


AVG Velocity across filter = (A+B+C+D)/4

Total CFM = Area(LxW) X Avg Velocity



 

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