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SMACNA HVAC Duct Design

(1)SMACNA Duct Design

Publications include HVAC Duct Construction Standards - Metal and Flexible, HVAC Systems Duct Design, HVAC Duct Systems Inspection Guide,
HVAC Air Duct Leakage Test Manual, HVAC Systems Commissioning Manual, HVAC Systems Applications,  Fibrous Glass Duct Construction Standards, Fire,
Smoke and Radiation Damper Standard, and more. Istallation Guide for HVAC, System Air Leakage Test Fire, Smoke and Radiation.

(2)SMACNA Duct Design Literature

(3)SMACNA Duct Design Calculation

SI - Units (Air density : 1.2(kg/m3)

Section Length
(m)		 Airflow
(m3/s)		 Diameter
(mm)		 Velocity
(m/s)		 Friction
Loss
(Pa/m)		 Friction
Loss
Section
(Pa)		 Minor
Dynamic
Loss
Coeff. (e)		 Minor
Dyanamic
Loss
Section
(Pa)		 Pressure
Loss
Damper
(Pa)		 Total
Pressure
Loss (Pa)		 Pressure
Loss Path
0-1-2 (Pa)		 Pressure
Loss Path
0-1-3-4
(Pa)		 Pressure
Loss Path
0-1-3-5
(Pa)
0-1 20 3 800 6.0 0.45 9 2.6 56 65 65 65
1-2 20 1 500 5.1 0.59 12 1.3 20 18 50 50
1-3 10 2 800 4.0 0.21 2 1 10 12 12 12
3-4 10 1 500 5.1 0.59 6 2 31 37 37
3-5 15 1 500 5.1 0.59 9 2 31 40 40
115 113 116

Imperial - Units

Section Length
(f5)		 Airflow
(cfm)		 Diameter
(in)		 Velocity
(ft/min)		 Friction
Loss
(in H2O/ft)		 Friction
Loss
Section
(in H2O)		 Minor
Dynamic
Loss
Coeff. (e)		 Minor
Dyanamic
Loss
Section
(in H2O)		 Pressure
Loss
Damper
(in H2O)		 Total
Pressure
Loss (in H2O)		 Pressure
Loss Path
0-1-2 (in H2O)		 Pressure
Loss Path
0-1-3-4
(in H2O)		 Pressure
Loss Path
0-1-3-5
(in H2O)
0-1 66 6360 30 1296 0.000707 0.047 2.6 0.27 0.32 0.32 0.32 0.32
1-2 66 2120 20 972 0.000671 0.044 1.3 0.08 0.09 0.21 0.21
1-3 33 4240 30 864 0.000327 0.011 1 0.05 0.06 0.06 0.06
3-4 33 2120 20 972 0.000671 0.022 2 0.12 0.14 0.14
3-5 50 2120 20 972 0.000671 0.034 2 0.12 0.15 0.15
0.53 0.52 0.53

(4)Air Duct Sizing - SI & Imperial Units

This spreadsheet template can be helpful when calculating dimensions and pressure loss in air duct systems.

How to use :
  • 1.

    Use "File" menu above to make your own editable copy of this document. You are free to use the copy as you want!

  • 2.

    Select the table with the units you want to use - delete the lines with the other table.

  • 3.

    Make a simplified sketch for the system you want to calculate.

  • 4.

    Add the sections to the table - insert new lines by selecting similar lines - right click and copy the lines right click and insert the lines above/below where you want it - paste in the copied line.

  • 5.

    Add volume flows for terminals - add sumarized formulas for the volume flows in the main sections.

  • 6.

    Add duct diameters.

  • 7.

    Add sumarized minor dynamic loss coefficients for each seaction.

  • 8.

    Add the pressure loss paths from node 0 to the end of all terminals - connect the pressure drops in each section - summarize the pressure drops for each path.

  • 9.

    Evaluate the velocities and pressure losses for each section and for the total system to your criteria - modify duct sizes if necessary.

  • 10.

    Add pressure loss in dampers to balance the system - the total pressure drop for all paths should be close.

(5)SMACNA Duct Size Calculation Program

(6)SMACNA Duct Size Calculation Program

  • Schematic Drawing

  • 3-D drawings

  • 2-D Drawings