How to calculate duct size?

[blati]

Hi Everyone

I need some help.

How to calculate duct size & friction loss at elbow ?

2 straight ducts & one 90 degree duct elbow.

Ceiling Mounted Duct Type fan coil 23Kw,78499btu/h & 58/50 meter cubic & 2047/1765 CFM

What is the air outlet m/s ?

Thank you.