What is the methode calculating duct size asper cfm

Question

in middleast there are many projects for hvac afew contractors with experience and knowledge about the actual calculation a of duct designing asper cfm that means velocity of duct nd heat load&cooling capacity calculation

Answer 1

The amounts of (total) cooling or (sensible) heating required and also the temperatures involved will determine the quantity of air to be delivered in a particular HVAC duct.

The nominal (round) size of the duct can be determined by one of three methods; equal velocity; equal friction; static regain. Equal friction is commonly used; however, some programs are set- up on static regain which is more accurate, but also more tedious. There are tables and nomographs showing the various rectangular duct shapes which will have the same (aerodynamically) equivalent round diameter.

The Trane Co. has offered a "Ductulator" nomograph several years ago that was an invaluable tool for ductwork sizing before the broad use of computer programs. They may still be available to purhase.

Equal velocity is mostly used when material transfer is a concern as would be the case in a sawdust or other conveying exhaust duct. Tables show what the conveying velocities need to be for the various materials.