High Or Variable Velocity Duct System

air design

Can anybody tell me about these systems or if there is such thing as a variable velocity system.I will tel you why I am asking.I did a duct design for a guy last year and I used the furnace and a/c unit that he told me to use.Now he is telling me that the unit in the house is different than I designed.He told me that the manufacterer suggested to use 8" round for the trunks and 5" round for the branches.He first told me that it is a high velocity duct system and when I told him I don't have the software for that type of system he told me it was a variable velocity system.Does this system sound like a high velocity system to you guys.
Any input would be greatly appreciated.

22rifle

What brand was the equipment?

westernhvac

I'm not sure if that sounds like a high velocity system necessarily. How large is this job?

playsinmud

Sounds like high velocity to me

air design

Its not a very big job ,what it is is they are adding a business to the back of their home,about 1000 sq ft.I dont know the make of the unit he is not telling me everything because he is hoping that I will just design it the way he wants to install it.I dont do work for him anymore because he is cheap and seems he dosent care about his customers.I would like to get some info about high velocity anyways because I have never designed one before because there is not a big demand for them here.