TecKnow of the day
Rule Of Thumb Air Velocity.
Air velocities (fpm):
700 to 750 fpm are needed for disposable filters; 250 fpm for HEPA filters; and 500 fpm for electronic air cleaners.
These are the recommended air speeds for filters. Speeds higher than these will decrease filtering efficiency.
550 to 600 fpm maximum and 400 fpm minimum are needed for evaporators; 1,000 fpm for condensers; and 700 fpm for hot water coils.
These are the recommended velocities for coils. Speeds faster than these may cause condensation to be blown off of the evaporator fins and down the duct. Speeds slower than 400 fpm may cause the evaporator to freeze over.
Terminal velocities are the velocities at the end of the run, such as registers or diffusers, where the air enters a room.
Bypass air should be at a rate of 0.1 to 0.35, or 10% to 35%.
This is the average percentage of air that bypasses or fails to come into contact with the evaporator as it passes through the evaporator. The higher the air speed in fpm, the higher the bypass factor. High bypass factors are normally found on heat pumps in the heating cycle, and on high sensible heat applications like computer room systems. Low bypass factors are found on high latent heat applications, such as those found in restaurants (especially cooking areas) and bowling alleys.