Learning, our way DUCT DESIGN (material to be checked with local legislation) Daikin Europe,...

D a i k i n E u r o p e A c a d e m y

Learning, our way

DUCT DESIGN

(material to be checked with local legislation)

Daikin Europe, Consulting sales section


Learning, our waySummary

1. Introduction

2. Ducts classification

3. Pressure losses in ducts

4. Air diffusers and resisters

5. Methods for duct calculation

6. Daikin ductmeter


Learning, our way1. 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


Learning, our way1. 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.

– …


Learning, our way

• 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.

2. Duct classificationBy size


Learning, our way2. 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.


Learning, our way2. 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


Learning, our way

3. Pressure losses in ductsIntroduction

• Duct system losses are the irreversible transformation of mechanical energy into heat.

• These losses can be divided into friction losses

and dynamic (local) losses.


Learning, our way

3. Pressure losses in ducts

• 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.)

Friction loss (mmH2O/m)

Friction loss in the Zn Iron Plate duct

Air

volu

me

(m³/

h) Diameter (mm)

Air velocity (m

/s

Charts for friction losses in round ducts


Learning, our way3. 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.


Learning, our way4. Air diffusers & resisters- Types

Adjustable flush with hidden pattern control for horizontal draftless air distribution to vertical projection plan

Deep outer cone reduces smudging.

Inner cone is a plaque.

Flange outer cone. Adjustable square diffuser for directional control from horizontal to vertical pattern. Extruded aluminium construction

Adjustable square diffuser with a plaque. Extruded aluminium construction

Extruded aluminium linear slot diffuser for directional control from horizontal to vertical position

Extruded aluminium linear grilles with fixed bars

Double direction supplying grilles with front louvers vertical behind louvers horizontal

C2

E2

VTL

VHS

ACP

EP

KL


Learning, our way

Cylindrical air diffuser with a long throw and low noise

Diffusers with unrestricted swivel type inner assembly

Return air grilles with fixed bars

Return air grilles with filters. Cores are hinged for easy removal and replacement of filter

Return air grilles with punching plates

Grilles for exhaust air or intake air with slant louvers

Return air grilles with a sight ploof core

NOZZLE

PK

SLIT

PG

DG

RF

GL

4. Air diffusers & resisters- Types


Learning, our way4. 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



• 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

W=

9 m

H= 3m

L=7,5 m L=7,5 m

Variant 1 Variant 2

Design procedure for supply/return grilles



Design procedure for supply/return grilles

• Outlet velocityThe 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 235 Cinema – hospital – library 340 Office – school – hotel 446 Bank – public hall 550 Store – post office 670 Factory 10


Learning, our way5. 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


Learning, our way

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


Learning, our way5. 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.

Friction loss (mmH2O/m)

Friction loss in the Zn Iron Plate duct

Air

volu

me

(m³/

h) Diameter (mm)

Air velocity (m

/s


Learning, our way5. 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


Learning, our way6. Duct calculation by equal friction method

The Daikin ductmeter


Learning, our way6. Duct calculation with the Daikin

ductmeter• Assume that one packaged air conditioner is used to cool 4 rooms of a public building

• Given data:

1. Total air volume: 84 m³/min

2. Discharged air flow volume from each universal resister: 21 m³/min

3. Passing air velocity through supply and return grille: aprox. 4 m/s


Learning, our way

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)

STEP 2

• Find the static pressure loss of the main duct route

•Select the corresponding air velocity and duct size

21 m³/min 21 m³/min 21 m³/min

21

m³/

min

B

C

A

D E

F

K

G3,5 m 3,5 m

1 m

1 m

1 m

2 m

1 m

1,5 m

2,5

m

6. Duct calculation with the Daikin ductmeter


Learning, our way

• Select the air velocity for the main duct in accordance with the desirable air velocity, mentioned in the table:



Learning, our way

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

Long side length < 7 x short side length

Friction loss

Round duct

Rectangular duct

Air volume

Air velocity

Long side length

Short side length



Learning, our way

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 0,4 mm H2O friction loss in the elbow

w

“W“shows the diameter of the round duct or the long side of the rectangular duct



Learning, our way

Equivalent length of main duct (A K)

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



Learning, our way

Table for main duct calculation

Mai

n du

ctin

g ro

ute

Part of duct Discharged Duct size Discharged Equivalent Local friction loss

air volume air velocity length of part Friction loss Fittings Lossm³/min cm m/s m mm H2O mm H2O

A-B 42x 2 35x30 6 ~ 10 1B 84 75x35 6 Branch 0,8B 84 75x35 6 Elbow 0,4

B-C 84 75x35 6 4,5C 63 58x35 6 Branch 0

C-D 63 58x35 5,7 3D 42 42x35 5,7 Standard Branch 0

D-E 42 42x35 5,05 1,5 Friction lossE 21 25x35 5,05 =0,07 mmH2O/m Branch 0,8

E-F 21 25x35 4,3 2,5F 21 25x35 4,3 Elbow 0,2

F-K 21 45x20 4,3 1 Reducer 0,2K 21 Register grille 4 Register 1,5P 84 Gallery or 4 Gallery or 0,5

Louver LouverTotal 13,5 m 0,07 x 13,5 = 1 mm 4,4 mm H2O

Required effective external static pressure H= 1+4,4+1 (Discharged air velocity) = 6,4 mm H2O

Static pressure loss

Ducting

Reducer


Learning, our way

Table for branch duct calculation

Part of duct Discharged Duct size Discharged Equivalent Local friction loss

air volume air velocity length of part Friction loss Fittings Loss

m³/min cm m/s m mm H2O mm H2O

C - H C - H 21 45 x 20 4,3 1

route H 21

D - I D - I 21 45 x 20 4,3 1

route I 21

E - G E - G 21 25 x 35 4,3 2- J G - J 21 45 x 20 4,3 1

route J 21

Static pressure loss

Ducting


Learning, our wayRemember 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


Learning, our way

THANK YOU FOR YOUR ATTENTION !

Learning, our way DUCT DESIGN (material to be checked with local legislation) Daikin Europe,...

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