External Statis Pressure Calculation

[nidhincletus]

Can anyone please tell me how to calculate the external static pressure of an AHU to get the required cfm.

[frank]

You are going about it the wrong way.

You calculate the required CFM from the work you want it to do,(design intent) i.e. number of air changes per hour in the ventilated space or extraction rate from a machine or cooking room.

Once you have the air volume calculated, you then design the ductwork system, possibly using the constant velocity method, and from this you can calculate the total system external static pressure drop.

The AHU can then be sized and the correct fan selected based on the relevant fan curve.

It is not a simple task for someone that does not understand the principles.

Do a Google search for 'Designing Ductwork' for more information.