Fluid power and advanced fluid mechanics

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FLUID POWER

AND ADVANCED

FLUID

MECHANICS Assignment 2: REDESIGN A VENTILATION SYSTEM

Submitted By

Sreeshob Sindhu Anand 19485180

Muhammed Fajir TK 19485649

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Contents

1. Aim...................................................................................................................................... 5

2. Introduction ....................................................................................................................... 6

3. Method ............................................................................................................................... 7

3.1 Formulas Used: ................................................................................................................. 7

3.2 Velocity Reduction Method ............................................................................................. 8

3.3 Constant Friction Gradient Method ................................................................................. 8

3.4 Current Design and Issues ................................................................................................ 9

3.4.1 Description of current Design .................................................................................... 9

3.4.2 Issues in Current design ............................................................................................. 9

4. Results .............................................................................................................................. 11

4.1 Initial Calculations without Dampers ............................................................................. 11

4.2 With Dampers ................................................................................................................ 15

4.3 Velocity Reduction Method ........................................................................................... 16

4.4 Constant Friction Gradient Method ............................................................................... 19

5. Improved Design ............................................................................................................... 23

5.1 Velocity Reduction Method ...................................................................................... 23

5.2 Constant Friction Factor Method ................................................................................... 24

6. Discussion ......................................................................................................................... 25

6.1 Limitations of the current and modified design ............................................................ 26

7. Reference ......................................................................................................................... 27

8. Appendix .......................................................................................................................... 28

9. Student Declaration ......................................................................................................... 30

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List of figures

Figure 1 Initial Design ................................................................................................................. 5

Figure 2 Improved design using Velocity Reduction Method .................................................. 23

Figure 3 Improved Design (Constant Friction Factor Method) ................................................ 24

Figure 4 Chart to calculate friction loss, velocity and size of ducts. ........................................ 28

Figure 5 Rectangular duct dimensions ..................................................................................... 29

Figure 6 Dynamic loss cpffecient for fittings ........................................................................... 29

List of Tables

Number Table name Page number

1 Velocity in different systems 8

2 Initial design flow rate and dimension in each duct 9

3 Calculations for the initial design without Damper 11

4 T section Calculations 13

5 Elbow calculations 13

6 Grill calculations 13

7 Intake louvers Calculation 14

8 Path 1 total loss calculation 14




12 Path 1 total loss calculations 15




16 Losses in each duct (Velocity reduction method) 16

17 Path 1 total loss 18



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21 Losses in each duct (Constant friction method) 19

22 Losses in damper (Positions changed) 21





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1. Aim The objective of this assignment is to redesign the ventilation system shown in figure 1 to

achieve a balanced air flow by choosing appropriate duct sizes for each section.

Figure 1 Initial Design

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2. Introduction

The use of ventilation systems in buildings are to supply continuous fresh air supply from

outside, for maintaining humidity and temperature at comfortable levels. The critical part in

the ventilation systems are the ductworks. The duct acts as the pathway to deliver or remove

the air in the buildings. The planning and designing are the important part in the installation

of ventilation systems.

Sheet Metal and Air Conditioning Contractors National Association (SMACNA) is the

international association which provides various standards for duct fabrication, balancing of

air for industrial, commercial, and residential purpose. The different types of materials used

for ducting includes galvanised mild steel, aluminium, polyurethane, flexible ducts. The

material and its thickness are chosen depending upon the area to be ventilated.

The ventilation in buildings are achieved by mechanical, natural and mixed means. The

ventilation in Sustainable building make use of natural method where the outdoor air directed

to the required area by physical phenomenon like wind pressure or stack pressure and the

flow can be controlled through openings like window or doors. Using supply and exhaust fans,

the air flow is directed into the building in mechanical ventilation systems.

The amount of air flow inside the ducts depends upon the area of cross section and

velocity of air. Lesser velocity inside the duct will cause settling and accumulation of dust

particles and thereby eventually causing clog in the duct. As the velocity increases, it causes

more power loss and noise problems. So, the duct systems should be designed by reducing

the possibility of arising resistance and considering recommended speed. This report details

the design of duct system by choosing the appropriate size of duct for each section and thus

achieving a balanced system.

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3. Method

There are several ways for designing a duct. The main three methods used to simplify the

steps are:

• Equal Friction Factor (Constant Friction Gradient) Method

• Velocity Reduction Method

• Static pressure regains

In some cases, a combination of these methods is also used. The design of the duct

varies with the requirements of the place where it is designed for. For instance, there are

comfort systems which is used in offices and residential buildings and there are industrial

and high-speed systems used in factories and laboratories. The main difference between

these systems are the noise levels, the velocity of air flow will be high in the industrial

systems which results in high noise levels.

To design the duct system for the given requirements (Figure 1) we are using the

velocity reduction method and constant friction factor method.

3.1 Formulas Used:

The total energy loss in a duct:

𝐻𝐿 = ℎ𝐿 ∗ 𝐿

Equivalent Diameter of rectangular ducts:

𝐷𝑒 =1.3(𝑎𝑏)5/8

(𝑎 + 𝑏)1/4

Dynamic Losses

𝐻𝑣 =𝛾𝑎𝑖𝑟𝑣

2

2𝑔𝛾𝑤𝑎𝑡𝑒𝑟=

𝛾𝑎𝑖𝑟𝑣2

2𝑔 ➔ 𝐻𝑣 = (

𝑣

1.289)2

𝐻𝐿 = 𝐶(𝐻𝑣)

C= Dynamic loss coefficient

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3.2 Velocity Reduction Method

In this method the flow velocity is assumed according to the type of system and type of

ducts, Table 1 shows the different velocities for different ducts.

Table 1 Velocity in different systems

Type of Duct Velocity (m/s)

Comfort Systems Industrial/High speed

Systems

Main Ducts 4-8 8-18

Main Branch Ducts 3-5 5-12

Branch Ducts 1-3 3-8

• Suitable duct velocities are selected as per the table 1 for each type of duct.

• As the flow rate in each section is given, we can use the chart (Figure 4) to determine

the values of friction factor and equivalent diameter of the duct.

• The diameter from the chart is the equivalent circular diameter, the rectangular duct

dimension can be obtained from the table from textbook (Figure 5).

• The next step is to calculate the total loss and the losses due to fittings. Then total

losses in each path is calculated.

• The pressure difference is equalised by increasing or decreasing the velocities in

each ducts and smaller difference is adjusted by changing the position of dampers.

3.3 Constant Friction Gradient Method

Constant friction factor method is used by most of the HVAC design companies. This

method reduces the iterations and steps in the design of ducts. In this method friction factor

will be always constant throughout the design.

Velocity in each duct is obtained from the chart by using the flow rate and friction

factor values. By using this method most of the similar branches will have same dimensions

and loss, so the design becomes much simple and easy to install.

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For comfort system the friction factor value is taken to be 1.25 in most of the

designs. And for Industrial and high-speed systems the friction factor value can be much

higher. The total loss is then balanced by the introducing dampers in ducts and adjusting the

position of the dampers.

3.4 Current Design and Issues

3.4.1 Description of current Design

For the given duct shown in figure 1, the total flow rate in the system is 2.28 m3/s. The

system equipped with four grills for the outlet of air and each of the outlet have a flow of 0.57

m3/s. The flow rate and length for each duct is shown in table x. The fan is fixed in between

duct A and B and is connected by using a plenum duct. The connection between the duct and

the grill is achieved using 90-degree elbow. A total of four number of tee and eight elbows

are used in the duct. There are four path of air flow in the system namely B to D, B to F, B to

I, B to K.

Table 2 Initial design flow rate and dimension in each duct

Duct Flow Rate (m3/s) Length (m)

A 2.28 15.2

B 2.28 10.7

C 1.14 6.1

D 0.57 5.5

E 0.57 9.1

F 0.57 5.5

G 1.14 12.2

H 1.14 6.1

I 0.57 5.5

J 0.57 9.1

K 0.57 5.5

3.4.2 Issues in Current design

The major issues with the given design shown in figure 1 are:

• The dimensions for the ducts are not specified

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• The calculations carried out shows that system is not balanced

• There is no volume control dampers (VCD) included in the system. So, the flow of air

through each branch cannot be controlled manually.

• The dimensions for the plenum duct used for fixing the fan are not given in the

design

• The grill size used are not mentioned.

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4. Results

4.1 Initial Calculations without Dampers

Table 3 Calculations for the initial design without Damper

Section Length

(m) Velocity

(m/s) Flow Rate

(m3/s) hl

(Pa/m) Hv (Pa) HI (Pa) De

(mm) Possible rectangular

dimensions(mm/inch)

A 15.2 4.3 2.28 0.23 11.12835769 3.496 795

• 775 (30.5) → (30in X 26in)

• 805 (31.7) → (30in X 28in)

• 777 (30.6) → (28in X 28in)

• 833 (32.8) → (30in X 30in)

B 10.7 6.1 2.28 0.58 22.39514276 6.206 688

• 676 (26.6) → (30in X 20in)

• 688 (27.1) → (28in X 22in)

• 693 (27.3) → (26in X 24in)

C 6.1 4.9 1.14 0.55 14.45061483 3.355 525

• 526 (20.7) → (30in X 12in)

• 526 (20.7) → (20in X 18in)

• 523 (20.6) → (26in X 14in)

• 518 (20.4) → (22in X 16in)

D 5.5 4 0.57 0.45 9.629730831 2.475 420

• 409 (16.1) → (30in X 8in)

• 419 (16.5) → (24in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) → (16in X 14in)

E 9.1 4.9 0.57 0.78 14.45061483 7.098 375

• 384 (15.1) → (26in X 8in)

• 371 (14.6) → (24in X 8in)

• 368 (14.5) → (18in X 10in)

• 386 (15.2) → (20in X 10in)

• 361 (14.2) → (14in X 12in)

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• 384 (15.1) → (16in X 12in)

• 389 (15.3) → (14in X 14in)

F 5.5 4 0.57 0.45 9.629730831 2.475 420

• 409 (16.1) → (30in X 8in)

• 419 (16.5) → (24in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) → (16in X 14in)

G 12.2 6.1 1.14 0.93 22.39514276 11.346 465

• 465 (18.3) → (30in X 10in)

• 465 (18.3) → (24in X 12in)

• 462 (18.2) → (20in X 14in)

• 470 (18.5) → (18in X 16in)

H 6.1 4.9 1.14 0.55 14.45061483 3.355 525

• 526 (20.7) → (30in X 12in)

• 526 (20.7) → (20in X 18in)

• 523 (20.6) → (26in X 14in)

• 518 (20.4) → (22in X 16in)

I 5.5 4 0.57 0.45 9.629730831 2.475 420

• 409 (16.1) → (30in X 8in)

• 419 (16.5) → (24in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) → (16in X 14in)

J 9.1 4.9 0.57 0.78 14.45061483 7.098 375

• 384 (15.1) → (26in X 8in)

• 371 (14.6) → (24in X 8in)

• 368 (14.5) → (18in X 10in)

• 386 (15.2) → (20in X 10in)

• 361 (14.2) → (14in X 12in)

• 384 (15.1) → (16in X 12in)

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• 389 (15.3) → (14in X 14in)

K 5.5 4 0.57 0.45 9.629730831 2.475 420

• 409 (16.1) → (30in X 8in)

• 419 (16.5) → (24in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) → (16in X 14in)

Table 4 T section Calculations

T Section Velocity C Hv HL

T to duct C from B (Branch) 6.1 1 22.39514276 22.39514276

T to duct D from C (branch) 4.9 1 14.45061483 14.45061483

T to duct G from B (flow through Mains) 6.1 0.1 22.39514276 2.239514276

T to duct I from H (Branch) 4.9 1 14.45061483 14.45061483

Table 5 Elbow calculations

Elbow Velocity C Hv HL

Elbow in C 4.9 0.18 14.45061483 2.601110669

Elbow in F 4 0.18 9.629730831 1.73335155

Elbow in H 4.9 0.18 14.45061483 2.601110669

Elbow in K 4 0.18 9.629730831 1.73335155

Elbow to grille (D) 4 0.18 9.629730831 1.73335155

Elbow to grille (F) 4 0.18 9.629730831 1.73335155

Elbow to grille (I) 4 0.18 9.629730831 1.73335155

Elbow to grille (K) 4 0.18 9.629730831 1.73335155

Table 6 Grill calculations

Grill HL

Duct D 15

Duct F 15

Duct I 15

Duct K 15

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Table 7 Intake louvers Calculation

Table 8 Path 1 total loss calculation Table 9 Path 2 total loss calculation

Table 10 Path 3 total loss calculations Table 11 Path 4 total loss calculations

Intake Size (m) K (Well Rounded) Flow Rate

Velocity (m/s)

HL (Pressure drop) (Kpa) hl

Gradual Contraction 1 x 1 0.04 2.28 4.3 17 0.037696

Path 1

Section Loss (Pa)

B 6.206

Elbow in C 2.601110669

T to duct C from B (Branch) 22.39514276

C 3.355

T to duct D from C (branch) 14.45061483

Elbow to grille (D) 1.73335155

D 2.475

Grill in D 15

Total Loss 68.21621981

Path 2

Section Loss (Pa)

B 6.206

Elbow in C 2.601110669

C 3.355


E 7.098

Elbow to grille (F) 1.73335155

Elbow in F 1.73335155

Grill in F 15

F 2.475


Path 3

Section Loss (Pa)

B 6.206

T to duct G from B (flow through Mains) 2.239514276

G 11.346

Elbow in H 2.601110669

H 3.355

T to duct I from H (Branch) 14.45061483

Elbow to grille (I) 1.73335155

I 2.475

Grill in I 15


Path 4

Section Loss

B 6.206


G 11.346

Elbow in H 2.601110669

H 3.355

J 7.098

Elbow to grille (K) 1.73335155

Elbow in K 1.73335155

K 2.475

Grill in K 15


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4.2 With Dampers

Table 11 Losses due to damper

Damper Velocity C Hv HL

Damper in duct A 4.3 0.2 11.12835769 2.225671538

Damper in duct D 4 0.2 9.629730831 1.925946166

Damper in duct F 4 0.2 9.629730831 1.925946166

Damper in duct I 4 0.2 9.629730831 1.925946166

Damper in duct K 4 0.2 9.629730831 1.925946166

Table 12 Path 1 total loss calculations Table 13 Path 2 total loss calculations

Table 14 Path 3 total loss Table 15 Path 4 total loss

Path 1

Section Loss (Pa)

B 6.206

Elbow in C 2.601110669


C 3.355


D 2.475

Damper in duct D 1.925946166


Grill in D 15


Path 2

Section Loss (Pa)

B 6.206

Elbow in C 2.601110669

C 3.355


E 7.098

Elbow in F 1.73335155

Damper in duct F 1.925946166


Grill in F 15

F 2.475


Path 3

Section Loss (Pa)

B 6.206


G 11.346

Elbow in H 2.601110669

H 3.355


Damper in duct I 1.925946166


I 2.475

Grill in I 15


Path 4

Section Loss

B 6.206


G 11.346

Elbow in H 2.601110669

H 3.355

J 7.098

Damper in duct K 1.925946166


Elbow in K 1.73335155

K 2.475

Grill in K 15


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Table 16 Losses in each duct (Velocity reduction method)

Section Length

(m) Velocity

(m/s) Flow Rate

(m3/s) hl (Pa/m) Hv (Pa) HI (Pa) De

(mm) Available duct size

A 15.2 4.3 2.28 0.23 11.12835769 3.496 800

• 805 (31.7) → (30in X 28in)

• 833 (32.8) → (30in X 30in)

• 777 (30.6) → (28in X 28in)

B 10.7 8 2.28 1.25 38.51892332 13.375 600

• 600 (23.7) → (30in X 16in)

• 597 (23.5) → (26in X 18in)

• 620 (24.4) → (28in X 18in)

• 607 (23.4) → (24in X 20in)

• 610 (24) → (22in X 22in)

C 6.1 4 1.14 0.29 9.629730831 1.769 580

• 582 (22.9) → (28in X 16in)

• 577 (22.7) → (24in X 18in)

• 562 (22.9) → (22in X 20in)

• 561 (22.1) → (26in X 16in)

D 5.5 3.3 0.57 0.28 6.554235547 1.54 475

• 465 (18.3) → (30in X 10in)

• 465 (18.3) → (24in X 12in)

• 483 (19) → (26in X 12in)

• 462 (18.2) → (20in X 14in)

• 485 (19.1) → (22in X 14in)

• 470 (18.5) → (18in X 16in)

E 9.1 3.9 0.57 0.41 9.154262871 3.731 430

• 434 (17.1) → (26in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) →

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(16in X 14in) • 439 (17.3) → (18in X 14in)

F 5.5 3.9 0.57 0.41 9.154262871 2.255 430

• 434 (17.1) → (26in X 10in)

• 426 (16.8) → (20in X 12in)

• 417 (16.4) → (16in X 14in)

• 439 (17.3) → (18in X 14in)

G 12.2 6.1 1.14 0.89 22.39514276 10.858 580

• 582 (22.9) → (28in X 16in)

• 577 (22.7) → (24in X 18in)

• 562 (22.9) → (22in X 20in)

• 561 (22.1) → (26in X 16in)

H 6.1 6.1 1.14 0.89 22.39514276 5.429 580

• 582 (22.9) → (28in X 16in)

• 577 (22.7) → (24in X 18in)

• 562 (22.9) → (22in X 20in)

• 561 (22.1) → (26in X 16in)

I 5.5 5 0.57 0.75 15.04645442 4.125 375

• 371 (14.6) → (24in X 8in)

• 384 (15.1) → (26in X 8in)

• 368 (14.5) → (18in X 10in)

• 386 (15.2) → (20in X 10in)

• 361 (14.2) → (14in X 12in)

• 384 (15.1) → (16in X 12in)

• 389 (15.3) → (14in X 14in)

J 9.1 5.4 0.57 1.1 17.55018444 10.01 360

• 358 (14.1) → (22in X 8in)

• 371 (14.6) → (24in X 8in)

• 368 (14.5) → (18in X 10in)

• 361 (14.2) → (20in X 14in)

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• 361 (14.2) → (14in X 12in)

K 5.5 5.4 0.57 1.1 17.55018444 6.05 360

• 358 (14.1) → (22in X 8in)

• 371 (14.6) → (24in X 8in)

• 368 (14.5) → (18in X 10in)

• 361 (14.2) → (20in X 14in)

• 361 (14.2) → (14in X 12in)

Table 17 Path 1 total loss Table 18 Path2 total loss

Path 1

Section Loss (Pa)

B 13.375

Elbow in C 1.73335155


C 1.769


D 1.54


Damper in duct D 1.310847109

Grill in D 15


Path 2

Section Loss (Pa)

B 13.375

Elbow in C 1.73335155

C 1.769


E 3.731

Elbow in F 1.647767317



Grill in F 15

F 2.255


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4.4 Constant Friction Gradient Method

Table 21 Losses in each ducts (Constant friction method)

Section Length

(m) Velocity

(m/s)

Flow Rate

(m3/s) hl (Pa/m) Hv (Pa) HI (Pa) De

(mm) Available Duct

Size

A 15.2 8 2.28 1.25 38.51892332 19 600

• 600 (23.7) → (30in X 16in)

• 597 (23.5) → (26in X 18in)

• 620 (24.4) → (28in X 18in)

• 607 (23.4) → (24in X 20in)

• 610 (24) → (22in X 22in)

B 10.7 8 2.28 1.25 38.51892332 13.375 600

• 600 (23.7) → (30in X 16in)

• 597 (23.5) → (26in X 18in)

• 620 (24.4) → (28in X 18in)

• 607 (23.4) → (24in X 20in)

• 610 (24) → (22in X 22in)

Path 3

Section Loss (Pa)

B 13.375


G 10.858

Elbow in H 4.031125697

H 5.429




I 4.125

Grill in I 15


Path 4

Section Loss

B 13.375


G 10.858

Elbow in H 4.031125697

H 5.429

J 10.01



Elbow in K 3.159033199

K 6.05

Grill in K 15


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C 6.1 7 1.14 1.25 29.49105067 7.625 450

• 450 (17.7) → (28in X 10in)

• 447 (17.6) → (22in X 12in)

• 445 (17.5) → (16in X 16in)

D 5.5 5.8 0.57 1.25 20.24650907 6.875 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

E 9.1 5.6 0.57 1.1 18.87427243 10.01 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

F 5.5 5.6 0.57 1.1 18.87427243 6.05 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

G 12.2 7 1.14 1.25 29.49105067 15.25 450

• 450 (17.7) → (28in X 10in)

• 447 (17.6) → (22in X 12in)

• 445 (17.5) → (16in X 16in)

H 6.1 7 1.14 1.25 29.49105067 7.625 450

• 450 (17.7) → (28in X 10in)

• 447 (17.6) → (22in X 12in)

• 445 (17.5) → (16in X 16in)

I 5.5 5.8 0.57 1.25 20.24650907 6.875 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

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J 9.1 6 0.57 1.3 21.66689437 11.83 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

K 5.5 6 0.57 1.3 21.66689437 7.15 350

• 345 (13.6) → (30in X 6in)

• 342 (13.5) → (20in X 8in)

• 358 (14.1) → (22in X 8in)

• 348 (13.7) → (16in X 10in)

Table 22 Losses in damper (Positions changed)


Damper Velocity C Hv HL

Damper in duct A 8 0.2 38.51892332 7.703784665

Damper in duct D 5.8 0.52 20.24650907 10.52818472

Damper in duct F 5.6 1.5 18.87427243 28.31140864

Damper in duct I 5.8 1.5 20.24650907 30.36976361

Damper in duct K 6 1.5 21.66689437 32.50034155

Damper in duct J 6 0.52 21.66689437 11.26678507

Path 1

Section Loss (Pa)

B 13.375

Elbow in C 5.308389121


C 7.625


D 6.875

Damper in Duct D 10.52818472


Grill in D 15


Path 2

Section Loss (Pa)

B 13.375

Elbow in C 5.308389121

C 7.625


E 10.01

Elbow in F 3.397369037



Grill in F 15

F 6.05


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Path 3

Section Loss (Pa)

B 13.375


G 15.25

Elbow in H 5.308389121

H 7.625



I 6.875


Grill in I 15


Path 4

Section Loss

B 13.375


G 15.25

Elbow in H 5.308389121

H 7.625

J 11.83


Elbow in K 3.900040987


K 7.15

Grill in K 15

Damper in Duct J 11.26678507


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5. Improved Design

After all the calculations and determining the dimensions of the ducts two designs are

proposed by using two different methods. In both the cases the pressure drop is balanced

which increases the comfort.


The designing of duct done in such a way that the velocity of air flow inside the duct

decreased as the flow proceeds. The velocity in the improved design varied from 8m/s to 4

m/s.

Figure 2 Improved design using Velocity Reduction Method

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5.2 Constant Friction Factor Method

Usually in his method the friction factor value is constant, but in this case for most of

the cases we took the friction factor value as 1.25. But in four ducts the friction factor value

is different (1.1 and 1.3). In normal case the pressure drop in this method is balanced by

adjusting the dampers. But as we have only 0,10,20,30,40 and 50, it’s not possible to balance

the pressure drop. So, we have taken a slightly lesser friction factor to balance the air flow.

The damper can be set to 15 degrees, but the value of dynamic coefficient is not available, so

the only way was to reduce the velocity.

Figure 3 Improved Design (Constant Friction Factor Method)

Page | 25

6. Discussion

In the initial design there is higher possibility of power loss and the system is not efficient.

The dimensions for the duct are not specified in the design. Based on the calculations carried

out using standard values taken from table shown in appendix, it shows that the system is not

balanced. The specification of fittings like elbows, tees, dampers, reducers used in the design

are not mentioned in the drawing. Thus, using improper connections increases the resistance

in the path of air flow. Even though the design shown in figure 1 shows each outlet has a flow

rate of 0.57 m3/sec, since there are no dampers for controlling the air flow, the system cannot

provide the equal outlet flow rate as shown in the design.

The calculations done based on the given parameters in the initial design shows that the

system is not balanced. The air flow path from duct B to outlet in duct D shows a higher

friction loss value of 68 Pa while in path B to K shows a value of 53Pa. This difference in value

shows that outlet flow through the grill is not the same in every branch in the duct. In the

modified design, this imbalance is corrected by using excel calculations and the friction loss

occurring in four paths are made equal and hence the outlet flow through each grill will be

the same.

The type of elbows and tees used in the design are not mentioned in the drawing. There

are several types of elbows and tees used in the ventilations systems. Choosing the right type

of fittings depends upon the type of air flow and design. In the initial drawing there is no such

details are not mentioned. So, there will be errors in the calculation of friction loss in the

system. In the modified design developed using AutoCAD software, the type of fittings is

chosen based in the standards used in the industry. So, while calculating the various

parameters related with those fittings and duct, the chances of error is reduced.

In order to regulate the flow of air through each branch and balance the system, volume

control dampers are required. There are no dampers included in the drawing and thus the

system is not efficient. In the improved designed a total of five dampers are included in the

drawing in order to regulate the flow. To avoid errors, the positions of each dampers are also

specified. The balancing of the modified drawing is achieved by adjusting the position of

damper.

Page | 26

6.1 Limitations of the current and modified design

The main design limitation for this design is the application of this design. Normally when

a HVAC duct system is designed, the main parameters determining the final design are:

• Application (Comfort /Industrial systems): The flow velocity is determined

• Location/Plan of the place the system is installed:

The proposed design is just focused on a balanced air flow. There will be several issues like:

• Clogging of the ducts

Depending on the area where the duct is erected, there is chances of dust particles

entering inside the duct. The long-term usage will cause the particles to settle down

and eventually leads to block in the ducts. There should be proper filters used in the

systems to avoid this condition.

• Installation

The ceiling height in the buildings need to be considered while designing a ventilation

system. There are other utility services passing through the same area where the duct

needed to be hanged. So before planning and designing the dimensions of duct, the

clearance should the made clear. This factor is not considered in the modified design.

Normally the selection of the shape of the ducts depends on the architecture and ceiling

height of the building where the duct is installed. In the proposed design all the ducts are

rectangular. This is because rectangular ducts are much cheaper and easy to install. But the

design can only be finalised by the ceiling height of the place where it is installed.

Page | 27

7. Reference

Mott, R. L., & Untener, J. A. (2015). Applied fluid mechanics : Global edition.

ProQuest Ebook Central https://ebookcentral.proquest.com

Engineering ToolBox, (2003). Ducts Sizing - Velocity Reduction Method. [online]

Available at: https://www.engineeringtoolbox.com/sizing-ducts-d_207.html

Engineering ToolBox, (2008). Duct Sizing - Equal Friction Method. [online] Available

at: https://www.engineeringtoolbox.com/equal-friction-method-d_1028.html

https://ebookcentral.proquest.com/

https://www.engineeringtoolbox.com/sizing-ducts-d_207.html

https://www.engineeringtoolbox.com/equal-friction-method-d_1028.html

Page | 28

8. Appendix

Figure 4 Chart to calculate friction loss, velocity and size of ducts.

Page | 29

Figure 5 Rectangular duct dimensions

Figure 6 Dynamic loss coefficient for fittings

Page | 30

9. Student Declaration

I have not copied any part of this report from any other person's work, except as correctly

referenced. No other person has written any part of this report for me.

1. Student Name: Sreeshob Sindhu Anand

Student declaration of the above ___________________________________ signed.

2. Student Name: Muhammed Fajir TK

Student declaration of the above ___________ ________________________ signed.

Date post:	14-Apr-2022
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