Air Duct Design

# Air Duct Design

Air Duct DesignThis post will talk about for the Design of Air Duct (Size of Duct ) also will talk about for Air Outlet with example .

 Air Duct Design

## Air Duct design

### How to Calculat Air Duct Design

Method of designing and calculating that weigh of the Air Duct.

This post will talk about for the Design of Air Duct(Size of Duct ) with 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 )

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 )
• Assume that ( duct thickness 1 mm )

 Velocity Table

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

• Enter the velocity = 600 fpm

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

 Aspect Ratio

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 = 600 fpm

 Choose 550 * 200 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 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 .

 Volume  Dampers

### 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 .

 Fire Damper

 Plenum box

### Flexible duct

Its a flexible duct used to connected the outlet air and the duct and easy move the outlet air
 Flexible Duct

### 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

 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