Air ducts desgin

Air ducts design

How to design air ducts design


Method of designing and calculating that weigh of the air duct


Now i will explain briefly the design of Air ducts and calculate its weight by example .

Air duct uses air conditioning systems to transfer cold air from the internal unit to the place to be conditioning .



The duct is divided into 



  • Supply Air Duct ( S.A.D)
  • Return Air Duct ( R.A.D)
  • Fresh Air Duct (F.A.D)
  • Exhaust Air Duct (EX.A.D)

The Material from which the duct is made
  • Galvanized steel 
  • stainless steel 
  • textile (Fabric )
  • Aluminum Cladding 


Several factors must be considered when designing a duct system . Generally in order of importance , they are as follows :

  • Space availability 
  • Installation cost
  • Air friction loss
  • Noise level
  • Duct heat transfer and air flow leakage 
  • Codes and standards requirements 
Suppose That 
1 T.R Take from (300 CFM TO 400 CFM ) but these number are appreciated .
Example 
Assume that after calculation ( space area ) its needed to :
  •  3 T.R 
  • 1200 CFM ( Assume 1 T.R take  400 cfm )
  • Velocity = 600 fpm this value from velocity tables ( SMACNA code )





Velocity Table






This part is pass it air flow rate (1200 cfm) . and the velocity it 600 fpm
Enter the program 
  • Enter air flow rate = 1200 cfm.
  • Enter the velocity = 600 fpm




Click here ( on calculation ) to know friction



Aspect ratio ( Width / high less than or equal 1 : 4)


Choose any value or according to aspect ratio 
I choose 550 * 350 mm 

1200 cfm divided to 600 cfm in first branch and 600 cfm in second branch 


Enter the program the new value 
  • Air flow rate = 600 cfm
  • Air velocity = 800 fpm


choose 550 * 200 mm


Assume that ( duct thickness 1 mm )


Vibration isolators (canves )

Its used to prevent vibrations resulting from the indoor unit  to the related duct with indoor unit ( FCU or AHU 



Volume control dampers (VCD )

Volume damper is used to control the amount of air outside from the outlet air 

Type of Volume damper : 
  • Manual Volume damper .
  • Motorized Volume damper .


Fir damper (F.D)

Fire Damper is installed on return duct . to prevent smoke from entering the AHU and passing smoke from place to place during Fire .

Plenum box
Plenum box is installed on diffuser


Flexible duct
Its a flexible duct used to connected the outlet air and the duct and easy move the outlet air 
Type of flexible duct
  • Air connector 
  • Air duct 

Duct leakage Test
  • Smoke Test .
  • Light Test. 
  • Pressure Test .

Duct Wight

Wight = 2 * ( W + H ) * L * T * density 

  • W : duct wight 
  • H : duct depth 
  • L : duct Length 
  • Duct thickness 
  • Density = 7850 kg / kg3


Air Terminal Outlet 
Advantages of uses Air Terminal outlet
  • Distribute the air place well
  • Give an aesthetic shape to the place 

Type and shape of Air Terminal outlet : 
  • Square diffuser 
  • Round diffuser 
  • Swirl diffuser 
  • Slot diffuser 
  •  Jet diffuser
  • Perforated diffuser 
  • Air grille and register
  • Fresh air lover 
  • Disk Valve
  • Door grille and under cut 

Factors that influence the selection of air outlet
  • Ceiling Type and Decoration 
  • Ceiling high 
  • Construction 

Square Diffuser

Square diffuser : two size ( neck size and face size ) .


Factors influencing the determination of output size
  • Air flow Rate ( CFM)
  • Noise Criteria (NC)
  • Throw
To determine the nick size (from catalogue or equation) .

Q = A * V
Q : air flow rate cfm
A :diffuser area ( X * Y )
V: velocity 






To download the program Ductulator

DOWNLOAD

Thank You