1. (material to be checked with local legislation)
DUCT DESIGN
(material to be checked with local legislation)
Daikin Europe, Consulting sales section

2. Summary Introduction Ducts classification Pressure losses in ducts
Air diffusers and resisters
Methods for duct calculation
Daikin ductmeter

3. 1. Introduction Needs to be considered
Space availability
Space air diffusion
Noise level
Duct leakage
Duct heat gains and losses
Balancing
Fire and smoke control
Investment costs
Operating cost of the system
When designing a duct system, the following items need to be considered to meet the requirements of the customer:

4. 1. Introduction Needs to be considered
Poor or excessive air distribution can cause discomfort, loss of productivity and even adverse health problems.
Lack of sound attenuators may permit objectionable noise levels. …
Poor duct design can lead to many problems

5. 2. Duct classification By size
Main duct system:
each branch is connected to the main duct
most widely used
Separate ducting system:
“-” more ducting material required
more ducting space necessary.
“+” economical solution if:
mass produced
round ducts are used.
In a main duct system is each branch duct connected to the main duct. The main duct system is the most widely used system from an economical point of view.
The separate ducting system needs more ducting material and requires more ducting space. It could prove to be an economical solution if only mass produced round ducts are used.

6. 2. Duct classification By purpose
Air supply duct
Cool or warm air coming out of the air-conditioner, is delivered to the room through the air supply duct.
The air supply duct is generally insulated to prevent heat losses and dew formation.
Return air duct
The air is returned from the room to the air-conditioner through the return air duct.
If the resistance inside the duct is big, pressure inside the duct goes down, leading to a lower efficiency.
Air supply duct
Cool or warm air coming out of the air-conditioner, is delivered to the room through the air supply duct.
The air supply duct is generally insulated to prevent heat losses and dew formation.
Return air duct.
The air is returned from the room to the air-conditioner through the return air duct.
If the resistance inside the duct is big, pressure inside the duct goes down and more fresh air gets into the air-conditioner leading to a lower efficiency.

7. 2. Duct classification By purpose
Fresh air intake duct.
The fresh air intake duct is connected to the suction side of the machine
Location of the fresh air intake port should prevent sucking in bad smells or dust.
Insulation might be necessary
Separate fresh air system id recommended
Air exhaust duct.
Polluted air is released to the outside through the air exhaust duct.
The material and paint of the air exhaust duct should be selected in function of the composition of the polluted air
Fresh air intake duct.
The fresh air intake duct is connected to the suction side of the machine and provides ventilation to the room.
Special attention needs to be paid to the location of the fresh air intake port in order to prevent sucking in bad smells or dust.
Insulation might be necessary to prevent heat losses and dew formation.
The fresh air intake duct needs to be designed taking into consideration the ventilation needs during times that the air-conditioner is stopped.
Air exhaust duct.
Polluted air is released to the outside through the air exhaust duct.
The material and paint of the air exhaust duct should be selected in function of the composition of the polluted air

8. 3. Pressure losses in ducts Introduction
Duct system losses are the irreversible transformation of mechanical energy into heat.
These losses can be divided into friction losses and dynamic (local) losses.
Duct system losses are the irreversible transformation of mechanical energy into heat. These losses can be divided into friction losses and dynamic losses.

9. 3. Pressure losses in ducts
Friction loss in the Zn Iron Plate duct
3. Pressure losses in ducts
Diameter (mm)
Charts for friction losses in
round ducts
Air volume (m³/h)
Fluid resistance caused by friction in round ducts can be determined by use of the friction chart (based on an absolute roughness of 0.09 mm.)
Air velocity (m/s
Fluid resistance caused by friction in round ducts can be determined by use of the friction chart (Fig …). This chart is based on standard air flowing through round galvanized ducts with beaded slip couplings on 1200 mm centers, equivalent to an absolute roughness of 0.09 mm.
Changes in barometric pressure, temperature and humidity have an impact on the air density, air viscosity and Reynolds number. No corrections to Fig. … are needed for:
duct materials with a medium smooth roughness factor
temperature variations in the order of +/- 15 K from 20°C
elevations to 500 m
duct pressures +/- 5 kPa relative to the ambient pressure
For duct materials other than those categorized as medium smooth in table … , and for variations in temperature, barometric pressure (elevation), and duct pressures (outside the range listed), calculate the friction loss in a duct by the Altshul-Tsal and Darcy equations.
Friction loss (mmH2O/m)

10. 3. Pressure losses in ducts: dynamic losses
Dynamic losses are the result of flow disturbances caused by duct mounted equipment and fittings.
These fittings include entries, exits, elbows, transitions and junctions.
The dynamic losses due to these fittings can be derived from tables, curves and equations.

11. 4. Air diffusers & resisters- Types
Adjustable flush with hidden pattern control for horizontal draftless air distribution to vertical projection plan C2
Deep outer cone reduces smudging.
Inner cone is a plaque.
ACP
Flange outer cone. Adjustable square diffuser for directional control from horizontal to vertical pattern. Extruded aluminium construction E2
Adjustable square diffuser with a plaque. Extruded aluminium construction EP
Extruded aluminium linear slot diffuser for directional control from horizontal to vertical position
VTL
Extruded aluminium linear grilles with fixed bars KL
Double direction supplying grilles with front louvers vertical behind louvers horizontal
VHS

12. 4. Air diffusers & resisters- Types
Cylindrical air diffuser with a long throw and low noise
NOZZLE
Diffusers with unrestricted swivel type inner assembly PK
SLIT
Return air grilles with fixed bars
Return air grilles with filters. Cores are hinged for easy removal and replacement of filter RF PG
Return air grilles with punching plates
Grilles for exhaust air or intake air with slant louvers GL
Return air grilles with a sight ploof core DG

13. 4. Air diffusers & resisters
Location
needs to be determined with care.
to avoid drafts for the people, the diffuser should be positioned high enough.
care to avoid dew generation on the ceiling surface.
position of the lights, structural beams, etc., needs to be considered
Location
The resister needs to be positioned with care.
In order to avoid drafts for the people, the resister should be positioned high enough.
Special care needs to be taken to avoid dew generation on the ceiling surface.
In addition, the position of the resister needs to be considered in function of the lights, structural beams, … .

14. 4. Air diffusers & resisters
Design procedure for supply/return grilles
Divide the room into squares or rectangles
Each sq./rectangle to be served by one grille
Rules of thumb:
H= height of room
W and L: dimensions of Sq/rectangle
W or L ≤ 3 * H
L ≤ 1.5 * W
L=15 m
L=7,5 m
L=7,5 m
Divide the room into squares or rectangles to be served by one grille respecting the following rules of thumb:
W or L ≤ 3 * H
W ≤ 1.5 * L
W=9 m
Variant 2
H= 3m
Variant 1

15. 4. Air diffusers & resisters Design procedure for supply/return grilles
Outlet velocity
The permissible sound level, and as a consequence the maximum air velocity, is determined by the application.
dB(A) Application Max. velocity (m/s)
25 Studio – recording room 2
35 Cinema – hospital – library 3
40 Office – school – hotel 4
46 Bank – public hall 5
50 Store – post office 6
70 Factory
Select the diffusers by the maximum allowable air velocity for the room (Table …):
Make sure that the maximum spreading radius covers the complete square / rectangle.
Make sure that the nearest minimum spreading radiuses do not overlap each other to prevent drafts (Fig. …)

16. 5. Duct calculation Main steps
Draw schematically the duct network
Establish the airflows for each section of the duct
Calculate dimensions of ducts, based on airflow velocities (see following 4 methods)
Draw on scale the duct network, mentioning the special fittings (elbows, junctions, regulating flaps, etc.)
Calculate the total pressure loss, to choose the corect ventilator (the correct ESP)
The velocities are decreasing from the ventilator to the far end of duct

17. 5. Methods for duct calculation
4 main methods related to the selection of air velocities along the main duct sections:
The method of equal air velocities
The method of reducing the air velocities
The method of equal frictions
The method of static pressure regain

18. 5. Methods for duct calculation
The method of equal velocities:
Uses the same air velocity along the main duct
“+” simple
easy equilibration of duct branches
“-” big and expensive installation
noisy in case of big air velocities
Conclusion: recommendable for industrial applications

19. 5. Methods for duct calculation
The method of reducing the air velocities:
Establish a maximum air velocity next to the fan
Choose an air velocity for each section of the main duct. The velocities are decreasing gradually to the end of the main duct.
“+” Provides simple calculation of each section
Gives the possibility to choose velocities according to the required level of comfort
“-” Arbitrary selection of velocities
Conclusion: requires personal experience

20. 5. Methods for duct calculation
Friction loss in the Zn Iron Plate duct
5. Methods for duct calculation
The method of equal friction:
Establish a maximum air velocity next to the fan
Determine the friction loss by using the chart
Use the same friction loss along the whole duct system
Determin the duct dimensions and the speed by inputing the friction loss and the airflow into the chart.
Diameter (mm)
Air volume (m³/h)
Air velocity (m/s
Friction loss (mmH2O/m)

21. 5. Methods for duct calculation
Advantages/difficulties of the equal friction method:
“+” The velocities resulting from charts are already decreasing along the duct- no arbitrary selection in this case
“-” Calculation may become difficult in case of many dynamic losses (elbows, etc.):
Dynamic losses are determined from charts
Add dynamic losses and divide the sum to the total duct length
Add the result to the constant value of the friction loss
Use the new value to determin the duct dimensions and air velocity from charts
Difficulty: the dynamic losses have to be recalculated by using several attempts (velocities)
Conclusion: precise method, easy to use for straight ducts

22. 6. Duct calculation by equal friction method The Daikin ductmeter

23. 6. Duct calculation with the Daikin ductmeter
Assume that one packaged air conditioner is used to cool 4 rooms of a public building
Given data:
Total air volume: 84 m³/min
Discharged air flow volume from each universal resister: 21 m³/min
Passing air velocity through supply and return grille: aprox. 4 m/s

24. 6. Duct calculation with the Daikin ductmeter
STEP 1
Draw schematic view of the duct system
Make notes for air volume, air velocity, etc
Mark clearly the elbow, the branch parts, the air discharge outlet
Select one main ducting route (where the maximum static pressure loss occures) K F
1 m
21 m³/min
2,5 m C D E
3,5 m
3,5 m
1,5 m
2 m G
STEP 2
Find the static pressure loss of the main duct route
Select the corresponding air velocity and duct size
1 m
1 m B
1 m A
21 m³/min
21 m³/min
21 m³/min

25. 6. Duct calculation with the Daikin ductmeter
Select the air velocity for the main duct in accordance with the desirable air velocity, mentioned in the table:

26. 6. Duct calculation with the Daikin ductmeter
INPUT:
the total air flow is 84 m³/min
select the velocity 6 m/s for the source section (B-C) of the main duct
OUTPUT from the ductmeter:
friction loss: 0,07 mm H2O/m
size of round duct: ǿ 53 cm or,
size of rectangular duct: Lxl=75 cm x 35 cm
Friction loss
Air volume
Air velocity
Round duct
Long side length
Rectangular duct
Short side length
Long side length < 7 x short side length

27. 6. Duct calculation with the Daikin ductmeter
STEP 3: Find the local friction loss of the main duct
Find the total friction loss at the elbow or branch parts:
Input the velocity into the local friction loss calculation table
In our case, to v=6 m/s corresponds ,4 mm H2O friction loss in the elbow
“W“shows the diameter of the round duct
or the long side of the rectangular duct w

28. Equivalent length of main duct (A K)
6. Duct calculation with the Daikin ductmeter
STEP 4: Calculate the required external static pressure
ESP > total friction loss main duct + local friction loss + 1 mm H2O
In our example: ESP > (0,07 x 13,5) + 4,4 + 1= 6,4 mm
Necessary ESP = 7 mm H2O
STEP 5: Dimensioning of the branch ducts
Obtain the duct size of each branch duct based on the same standard friction loss as for the main duct:0,07 mm H2O/m
Input standard friction loss and airflow and use the ductmeter to find velocity and duct size
Complete the calculation tables for main ducts and branch ducts
Equivalent length of main duct (A K)

29. Table for main duct calculation
Reducer
Main ducting route

30. Table for branch duct calculation

31. Remember the main steps of duct calculation !
Draw schematically the duct network
Establish the airflows for each section of the duct
Calculate dimensions of ducts, based on airflow velocities
Draw on scale the duct network, mentioning the special fittings (elbows, junctions, regulating flaps, etc.)
Calculate the total pressure loss, to choose the corect ventilator (the correct ESP)
The velocities are decreasing from the ventilator to the far end of duct

32. THANK YOU FOR YOUR ATTENTION !