Design Of A Noise Enclosure For Portable Generator.

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SUPERVISOR DECLARATION

“I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of

Bachelor of Mechanical Engineering (Structure & Materials)”

Signature :... Supervisor :... Date :...

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DESIGN OF A NOISE ENCLOSURE FOR PORTABLE GENERATOR

MOHD FAIZ BIN MOHD MOKHTAR

This report is submitted as partial fulfillment of requirement for the award Bachelor of Mechanical Engineering (Structure & Materials)

Fakulti Kejuruteraan Mekanikal Universiti Teknikal Malaysia Melaka

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DECLARATION

“I hereby declare that the work in this report is my own except for summaries and quotations which have been duly acknowledged.”

Signature: Author : Date :

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iii

Special to my beloved Father and Mother

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ACKNOWLEDGEMENT

First and foremost, thank Allah the Almighty for blessing me to complete my Final Year Project 1 Report. I would like to take this opportunity to record my utmost and sincere gratitude to my supervisor, Dr. Azma Putra Without him, I can never start work on my project and report and to proceed until this point of development. He has shown me knowledge, important advice, guidance and inspiration throughout the project time period. I also would like to thank my examiner, Pn. Siti Norbaya for his commitment and kindness throughout the project time period.

Besides that, I would like to show my appreciation to all of my previous lectures, who have taught me over the years in UTeM. They have taught me the basic of Mechanical Engineering, and this invaluable knowledge has provided me a firm foundation for doing this report. Most importantly, the knowledge I required from them has prepared me for my career in the future.

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Furthermore, I would like to thank my friends and beloved classmates for sharing and discussing, knowledge with me. Their support, opinion, and advised will be not forgotten. To my beloved family, I would like to forward my obliged to them for their continuous support during my study period, their patience and benevolence. Lastly, I would like to thank everyone who has contributed during the time of finishing this project report. Their kindness and cooperation of my report is much appreciated.

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ABSTRACT

A portable generator is a one of sources that affect the environmental noise. Although the noise level might not harm the human hearing, the noise emitted by a portable generator causes disturbance to the environment. In practice, most people do not cover the portable generator to reduce its noise emission. In this project a simple box-shaped, for portable generators For this project, the sound power level emitted by a portable generator was measured according to ISO 3746. From this, a single partition of noise enclosure was design using mild steel panel having thickness 4 mm. It is found that the sound power level can be reduced by 13dBA. However this is not agree well with the theory due to compromised situation in the design, such as the introduction of holes for air intake and exhaust.

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ABSTRAK

Sebuah penjana kuasa mudah alih adalah merupakan salah satu sumber yang mempengaruhi pencemaran bunyi. Walaupun tahap bunyi yang dipancarkan oleh penjana kuasa mudah alih mungkin tidak membahayakan pendengaran manusia, namun ia menyebabkan gangguan bunyi kepada persekitaran. Dalam aplikasi seharian, kebanyakan orang tidak menutupi penjana kuasa mudah alih ini dengan penyerap bunyi untuk mengurangkan bunyi yang dipancarkan. Didalam projek ini, sebuah penyerap bunyi yang berbentuk kotak direka untuk penjana mudah alih. Tahap bunyi yang dipancarkan oleh penjana kuasa mudah alih diukur mengikut piawaian ISO 3746. Daripada itu, sebuah penyerap bunyi telah direka mengunakan besi ringan. Didapati bahawa tahap bunyi dapat dikurangkan sebanyak 13 dBA. Namun ia tidak sama dengan teori kerana pada rekaan penyerap bunyi terdapat lubang udara untuk pengaliran udara keluar masuk dan juga ekzos.

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TABLE OF CONTENTS

CHAPTER TITLE PAGE

SUPERVISOR DECLARATION i

STUDENT DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENT v

ABSTRACT vii

ABSTRAK viii

TABLE OF CONTENT ix

LIST OF TABLES xii

LIST OF FIGURES xiii

NOMENCLATURE xv

CHAPTER I INTRODUCTION 1

1.1Background 1.1.1 Environmental Noise 1

1.1.2 Noise Standard 3

1.1.3 Environmental Noise From Portable Generator 6

1.2 Problem Statement 7

1.3 Objective of the Project 7

1.4 Methodology 8

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1.5 Scope of the Project 10

CHAPTER II LITERATURE REVIEW 11

2.1 Decibel and A-Weighting 11

2.2 Sound Power Level 16

2.3 Measurement of Sound Power Level 19

2.4 Sound Transmission Loss 20

2.4.1 Introduction 20

2.4.2 Single Panel Transmission Loss 21

CHAPTER III EXPERIMENT 24

3.1 Measurement of Sound Power Level 24

3.1.1 Microphone Positions 25

3.1.2 Calculation of surface sound pressure level and sound power level 27

3.2 Experimental Setup 27

3.3 Fabricating the Enclosure 31

CHAPTER IV RESULT AND ANALYSIS 34

4.1 Introduction 34

4.2 Results without an enclosure 35

4.2.1 Incident Sound Power Level (L_Wi) 38

4.2.2 Transmitted Sound Power Level (LWtc) 40

4.2.3 Calculation of dBA values 43

4.3 With an Enclosure 45

4.3.1 Transmitted Sound Power Level (LWtmea) 46

CHAPTER V CONCLUSION AND RECOMMENDATION 51

5.1 Conclusion 51

5.2 Recommendation 52

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LIST OF TABLES

NO TITLE PAGE

1.1 Guideline for Occupational and Non-occupational

Noise Exposure Time Limit 4

2.1 A-Weighting for 1/3 Octave Frequency 13

2.2 Sources, Sound Power and Sound Power Level 18

3.1 International Standard (ISO 3746) specification

for determining the sound power levels

of machine and equipment 25

3.2 The coordinates of microphones position in terms

of distance from centre of hemisphere along three

mutually perpendicular axes (x, y, z) 26

3.3 The material and thickness 28

3.4 Apparatus used for the experiment 30

4.1 Values of Wtotaland LWfor incident energy

and transmitted energy for aluminium 43

4.2 Values of Wtotal and LW for incident energy and

transmitted energy for steel 44

4.3 Comparison between aluminium and steel 44

4.4 Values of Wtotaland LWfor transmitted energy

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xii

LIST OF FIGURES

NO TITLE PAGE

1.1 Environmental Noise Effect Schemas 3

1.2 Typical sound level in sound pressure level (decibels)

and PSI 6

1.3 Portable Generators 6

2.1 International standards A-, B-, C- and D-weighting

curves for sound level meter 12

2.2 A-Weighting Frequencies 12

2.3 Measuring Sound Power Level according to

ISO 3745 in the anechoic room 20

2.4 Sound Transmission Loss of Partition 21

2.5 Comparison of theory and measurement for

homogeneous and isotropic materials 23

3.1 The microphones array on the hemisphere 26

3.2 Equipment diagram for the experiment 29

3.3 Holes at the roof of the enclosure 32

3.4 Air intake holes 32

3.5 Flexible exhaust pipe 33

4.1 Graph of sound power level versus frequency

of four measurement points at radius 1 m 35

4.2 Graph of Transmission Loss versus Frequency of

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xiii

4.3 Graph of Transmission Loss versus Frequency for

Steel for different thickness 37

4.4 Graph of surface sound power level versus frequency 38

4.5 Graph of incident sound power level (L_Wi)

versus Frequency 39

4.6 Comparison between calculated incident sound power

level with calculated transmitted sound power level

versus frequency for aluminium 41

4.7 Comparison between calculated incident sound

power level with calculated transmitted sound

power level versus frequency for steel 42

4.8 Graph of sound power level versus frequency of four

measurement points at radius 1 m 45

4.9 Graph of surface sound power level versus frequency 46

4.10 Graph of transmitted sound power level (LWtmea)

versus Frequency 47

4.11 The comparison of calculated incident sound power

level with measurement transmitted sound power level

versus frequency 48

4.12 The comparison of calculated incident sound power

level with calculated transmitted sound power level and also with measured transmitted sound power

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NOMENCLATURE

L Equivalent sound level

max

L Maximum equivalent sound level

min

L Minimum equivalent sound level

L p Sound power level

ref

p

_{Reference acoustic pressure}

p

_{Acoustic pressure}

L Sound power

DI Directivity Index

r _{Radial distance between receivers to the source}

f Frequency (Hz)

f Critical frequency (Hz)

pc Characteristic impedance in air

T Sound transmission coefficient

W Transmitted sound power

W Incident sound power

W The 0 dB reference level

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xv pA

L The A-weighted surface sound pressure level in decibels

pAi

L The A-weighted sound pressure level at the _ith _measurement

position

N The total number of the measurement position

L Sound pressure level of the source

K The environmental correction to account for the influence of

reflected sound Wtc

L Calculated transmitted sound power level

L Incident sound power level

total

W _{Total of sound power level}

Wtmea

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CHAPTER I

INTRODUCTION

1.1 BACKGROUND

1.1.1 Environmental Noise

Noise means any unwanted sound that we are exposed everyday without any

consideration. Noise defined as a sound or sounds at such amplitude as to cause

annoyance or to interfere with communication and it was mentioned that noise was psychological and subjective feeling. It can be block, change or interfere with the meaning of a message in human, animal and electronic communication. Noise can cause a physical problem such as permanent hearing loss and also the psychological problem, like stress.

Environmental noise is unpleasant or unwanted outdoor sound that disrupts the human life activity. This unwanted and unpleasant outdoor sound mostly generated by traffic and industry. Road traffic is the most widespread source. It has a lower priority than other environmental pollution such as air pollution and water pollution. It also recognised that, despite significant reduction in the noise produced by individual source, total exposure to environmental noise has not change significantly.

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2 Most people are affected by noise exposure more than any other environmental stimulus. The most widespread problem created by noise is nuisance. Noise has been known as stressor which can cause a several serious health effect. Environmental noise affects us in the following areas:

a) Hearing Loss

The most notable effect of environmental noise is hearing loss. It affected if the noise is loud enough and the exposure long enough. Noise induced hearing loss is usually gradual and painless, but unfortunately, hearing loss is a permanent effect. Once destroyed, the hearing nerve and it sensory nerve cell do not regenerate.

b) Cardiovascular Effect

Exposure to environmental noise during sleep bring to a number of physiological effect such as increased of blood pressure, increased heart rate and an increase in body movements. Environmental noise probably affects the cardiovascular system through the stimulation of hormones in our body such as cortisol, noradrenaline and also adrenaline.

c) Annoyance and Quality of Life

Environmental noise is a subjective experience and feelings of annoyance are profoundly affected by personal attitudes and also belief. It is because environmental noise is commonly perceived to be an avoidable form of harm and an intrusion into personal privacy that creates such unhappiness. Road traffic is the main effect that causes environmental noise. The noise from the transport is associated with productivity losses by an inability to concentrate at work and tiredness caused by disturbed sleep.

d) Sleep Disturbance

Insomnia and sleep disturbance caused by environmental noise can affect the quality and quantity of sleep. Difficult to falling asleep, awakenings and alternations of sleep stages or depth, especially a reduction in the proportion of REM-sleep (REM = Rapid Eye Movement) are examples. Road traffic is the largest cause that affects sleep quality and quantity.

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Figure 1.1: Environmental Noise Effect Schemas

1.1.2 Noise Standard

According to the Occupational Safety and Healthy Administration OSHA, exposure to high level of noise for long durations may lead to hearing loss, create physical and psychological stress, reduce productivity, interfere with communication and contribute to accidents and injuries by making it difficult to hear warning signals. The maximum permissible occupational noise exposure limit in the range of 90-85 dB(A) Leq for 8 hour per day (40 hour per week) have been recommended by the International Standards Organization (ISO).

The OSHA of the U.S Department of Labor regulation sets the limits of exposure to workplace noise. Based on the noise exposure criteria that were verified in 1983 by OSHA, continuous exposure to noise level greater than 115 dB(A) is not permitted for any duration. Occupational and no occupational permissible noise exposure standards based on the durations of exposure are given in Table 1.1The maximum exposure noise level in workplace for duration of 16 hours should not

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4 exceed 85 dB(A). For non-occupational areas, the maximum level for a duration of 16 to 24 hours is 70 dB(A). Figure 1.2 illustrates typical sound levels for several conditions.

Table 1.1:Guideline for Occupational and Non-occupational Noise Exposure Time Limit

Maximum exposure noise level dB(A)

Exposure Time Limit (hours per day) Occupational(OSHA)

Non-occupational 70 75 80 85 90 95 100 105 110 115 - - - 16 8 4 2 1 0.5 0.25 16-24 8 4 2 1 0.5 0.25 0.13 0.07 0.03

ECMA Standard specifies procedures for measuring and reporting the noise emission of information technology and telecommunications equipment. This

Standard is considered part of a noise test code for this type of equipment, and is

based on basic noise emission standards ISO 3741:1999 , ISO 3744:1994 , ISO

3745:2003 and ISO 11201:1995 . The basic emission quantity is the A-weighted sound power level which may be used for comparing equipment of the same type but from different manufacturers, or for comparing different equipment.

Three basic noise emission standards for determining the sound power levels are specified in ECMA Standard in order to avoid undue restriction on existing facilities and experience. The first basic standard (ISO 3741) specifies comparison

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5 measurements in a reverberation room; the other two (ISO 3744 and ISO 3745) specify measurements in an essentially free field over a reflecting plane. Any one of these three basic noise emission standards may be selected and shall then be used exclusively according to this Standard when determining sound power levels of a machine.

The A-weighted sound power level is supplemented by the A-weighted emission sound pressure level measured at the operator position(s) or the bystander positions, based on the basic noise emission standard ISO 11201. This sound pressure level is not a worker's emissions rating level, but it may assist in identifying any potential problems that could cause annoyance, activity interference, or hearing damage to operators and bystanders.

The ECMA Standard is suitable for type tests and provides methods for manufacturers and testing laboratories to obtain comparable results. The methods specified in ECMA Standard allow the determination of noise emission levels for a unit tested individually.

The procedures may be applied to equipment which emits broad-band noise, narrow-band noise and noise which contains discrete-frequency components, or impulsive noise.

The sound power and emission sound pressure levels obtained may serve noise emission declaration and comparison purposes and if sound power levels obtained are determined for a number of units of the same production series, they can be used to determine a statistical value for that production series (ECMA-109).

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Figure 1.2:Typical sound level in sound pressure level (decibels) and PSi

1.1.3 Environmental Noise From Portable Generator

Portable generators are used very commonly in construction, shops, offices and homes today in order to supply and maintain power during power shutdowns or in an emergency power outage. The generator needed to be both mobile and quiet since it would often be used near commercial or residential areas. These generators emitted very high levels of noise, in addition to noxious air emissions. The noise may be generated by aerodynamic effects or due to forces that result from combustion process or may result from mechanical excitation by rotating or reciprocating engine components.

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1.2 PROBLEM STATEMENT

A portable generator is a one of sources that affect the environmental noise. Although the noise level might not harm the human hearing, the noise emit by a portable generator cause disturbance to the environmental. Moreover, in practice, most people do not cover the portable generator to reduce its noise emission.

1.3 OBJECTIVES OF THE PROJECT The objectives of this project are:

a) To measure the sound power level that emitted from a portable electric

generator.

b) To design and manufacture a simple enclosure for reducing

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1.4 METHODOLOGY

This project begins with a literature review, particularly related to theory of the sound transmission loss and also the theory of sound power level measurement. Literature review consists of studying the previous research established journal, articles, academic book and other related references to obtain the theory.

After obtaining all the theory related, the next step is to measure the sound power level that emit by the portable generator. The measurement of the sound power level will conduct outdoor which is with minimum background noise and reflecting surface. The sound power level that emit by portable generator will be measure by using acoustic microphones.

Once the sound power level is obtained, this becomes ‘an input’ to design an enclosure to meet the target of noise reduction. Theoretical formula will be used to calculate the dimensions and type of material for the enclosure. This involved the sound and structural vibration analysis. The nest step, the measurement of the sound power level from the portable generator with the noise enclosure which has been designed will be conducted. The result will be compared with the acceptable noise standard.

The final step is to summarize the study in the final report. Suggestion and recommendation for the future work will also given.

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Figure 1.1: Environmental Noise Effect Schemas 1.1.2 Noise Standard

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exceed 85 dB(A). For non-occupational areas, the maximum level for a duration of 16 to 24 hours is 70 dB(A). Figure 1.2 illustrates typical sound levels for several conditions.

Table 1.1:Guideline for Occupational and Non-occupational Noise Exposure Time Limit

Maximum exposure noise level dB(A)

Exposure Time Limit (hours per day) Occupational(OSHA)

Non-occupational 70 75 80 85 90 95 100 105 110 115 - - - 16 8 4 2 1 0.5 0.25 16-24 8 4 2 1 0.5 0.25 0.13 0.07 0.03

ECMA Standard specifies procedures for measuring and reporting the noise emission of information technology and telecommunications equipment. This Standard is considered part of a noise test code for this type of equipment, and is based on basic noise emission standards ISO 3741:1999 , ISO 3744:1994 , ISO 3745:2003 and ISO 11201:1995 . The basic emission quantity is the A-weighted sound power level which may be used for comparing equipment of the same type but from different manufacturers, or for comparing different equipment.

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measurements in a reverberation room; the other two (ISO 3744 and ISO 3745) specify measurements in an essentially free field over a reflecting plane. Any one of these three basic noise emission standards may be selected and shall then be used exclusively according to this Standard when determining sound power levels of a machine.

The procedures may be applied to equipment which emits broad-band noise, narrow-band noise and noise which contains discrete-frequency components, or impulsive noise.

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Figure 1.2:Typical sound level in sound pressure level (decibels) and PSi 1.1.3 Environmental Noise From Portable Generator

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1.2 PROBLEM STATEMENT

1.3 OBJECTIVES OF THE PROJECT

The objectives of this project are:

a) To measure the sound power level that emitted from a portable electric generator.

b) To design and manufacture a simple enclosure for reducing environmental noise from a portable electric generator.

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1.4 METHODOLOGY

The final step is to summarize the study in the final report. Suggestion and recommendation for the future work will also given.

Design Of A Noise Enclosure For Portable Generator.

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