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Ducting Design: " Add Your Company Slogan "

This document provides an example calculation for the duct design of an office building HVAC system with 5400 CFM of air and 18 air terminals. It determines: 1) The initial duct velocity of 1700 FPM, cross-sectional area of 3.18 sqft, and size of 22x22 inches with a friction rate of 0.145 inches water gauge per 100 feet of duct. 2) The total equivalent duct run length from the fan to terminal 18 of 229 feet, which has the highest resistance of 0.332 inches water gauge. 3) The total static pressure required at the fan discharge of 0.482 inches water gauge, which is the sum of the terminal operating pressure and ductwork

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153 views30 pages

Ducting Design: " Add Your Company Slogan "

This document provides an example calculation for the duct design of an office building HVAC system with 5400 CFM of air and 18 air terminals. It determines: 1) The initial duct velocity of 1700 FPM, cross-sectional area of 3.18 sqft, and size of 22x22 inches with a friction rate of 0.145 inches water gauge per 100 feet of duct. 2) The total equivalent duct run length from the fan to terminal 18 of 229 feet, which has the highest resistance of 0.332 inches water gauge. 3) The total static pressure required at the fan discharge of 0.482 inches water gauge, which is the sum of the terminal operating pressure and ductwork

Uploaded by

Arga Benny
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PPT, PDF, TXT or read online on Scribd
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Add your company slogan

DUCTING DESIGN

LOGO

EQUAL FRICTION METHOD EXAMPLE

Duct system for general office ;


Total air quantity
18 air terminals
Operating pressure for all terminals
Radius elbows

5400 cfm
300 cfm each
-0.15 in.wg
R/D = 1.25

Find ;
1. Initial duct velocity, area, size and friction rate in the duct
2. Total equivalent length of duct run, with highest resistance
3. Total static pressure required at Fan discharge

DUCT LAYOUT

SELECT AN INITIAL VELOCITY

RECOMMENDED MAX DUCT VELOCITIES FOR LOW VELOCITY SYSTEMS

Velocity dipilih 1700 fpm

Duct area : 5400 cfm/1700 fpm

= 3.18 sq.ft

Duct size (TABLE 6)

Duct size : 22 in x 22 in

Circular equiv. diameter

Initial friction rate

Friction rate ; 0.145 in wg per 100 ft of


eauivalent length

Percent section area in branches

Percent of cfm = air quantity in duct


section/ total air quantity

It appears that the duct run from the Fan


to terminal 18 has the highest resistance

Friction of rectangular Elbow

The total friction loss in the ductwork frfom


the Fan to terminal 18 :

Loss

= total equiv length x friction rate


= 229 ft x (0.145/100 ft)
= 0.332 in. wg

Total pressure at Fan Discharge

The sum of the terminal operating


pressure and the loss in the ductwork

0.332 in. wg + 0.15 in.wg = 0.482 in.wg

Friction losses

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