How to calculate the CFM vs HP or KW of any air handling unit.
You could try doing things the way most engineers learn their trade. You could go to school and apply yourself in your schooling. This schooling does not have to be a formal academic institution, although this will be easier.
Look on the nameplate. Read the specifications.
The HP depends on the CFM, but also on the SP (static pressure) differences both through the AHU and through any ductwork and stored product. HP = k(CFM)( SP), where k is a constant depending on which measurement units are used. The hard part of this is figuring out what SP to use.
"Perplexity is the beginning of knowledge." -- Kahlil Gibran