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same procedure of normal ducting but check the size of VAV Box. During VAV Open the cfm in the other branches will be standard required CFM but if the fan of unit is not with VSD then on closing VAV the CFM will be increased in other branches so they have to be designed on that cfm during VAV is closed but it is better to have VSD on the unit fan
friction factor to be set at0. to 1" WC/ ft
duct sizing will be done at maximum CFM indicated
friction0.08 to1" WC/100 ft , watch the velocity limits
read well manufacturer recommendation
normal duct sizing >>>then use one piece round to square to connect to the VAV
