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INVESTIGATION OF AIR FLOW IN CHAMBER USING

AIR-CONDITIONING UNIT FOR THERMAL COMFORT

TEO YIN YIN

This report is submitted as partial requirement for the completion of the

Bachelor of Mechanical Engineering (Thermal Fluids) Degree Programme

Faculty of Mechanical Engineering

Universiti Teknikal Malaysia Melaka

MAY 2009

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DECLARATION

“I hereby, declare this thesis is result of my own research except as cited in the

references”

Signature : ………………………….

Author Name : Teo Yin Yin

Date : ………………………….

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DEDICATION

To

My Beloved Family

Jenny

Sonia

Ivan

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ACKNOWLEDGEMENT

First and foremost, I wish to extend my heartfelt thanks to Mr. Shamsul

Bahari Bin Azraai as the final year project supervisor who has gracefully offered his

time, attention, experience and guidance throughout the completion of the

investigation thus far. I would also like to extend my thanks to Mr. Asjufri Bin

Muhajir, technician of Combustion Lab for his assistance and provision of

information on the Air-Conditioning facilities at UTeM (industry campus). Thanks to

the university library for providing lots of sources which assist to complete the report.

I would like to thank each and every individual who have either directly or

indirectly helped me throughout the efforts of this report be it in the form of

encouragement, advice or kind reminders. Finally kudos goes out to family and

parents who endured this long process which gave me love and support all the way.

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ABSTRACT

Control of relative humidity is an essential aspect of maintaining indoor air

quality in an air-conditioned. The aim of using air-conditioning is to provide thermal

comfort and control the quality of air. Humans feel comfort when air temperature is

between 220C to 270C with the relative humidity of 40% to 60% when the air speed

is about 0.25 m/s. This project focuses on both temperature and humidity control of

air in order to achieve thermal comfort zone. The experiments were based on the

acceptable thermal comfort conditions in a chamber by referring to the ASHRAE

standard and the thermal comfort standard from Building Regulations of Singapore.

Experiments were conducted using Air-Conditioning Unit. Several parameters has

considered in this study are air velocity, Pre-heater, and damper. The results reveal

that the suitable setting is achieved at 2.75 m/s air velocity with 100% fresh air

intake at the condition of operates a Pre-heater. In addition to the above work,

Computational Fluid Dynamics with using ANSYS CFX software is used to

investigate the air flow pattern and the temperature distribution in chamber.

Simulation results is validated the experimental data.

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ABSTRAK

Mengawal kelembapan relatif adalah satu aspek penting memelihara kualiti

udara dalam sebuah tempat yang berhawa dingin. Tujuan penggunaan sistem

penyaman udara adalah untuk keselesaan terma dan mengawal kualiti udara.

Manusia berasa selesa pada suhu antara 220C hingga 270C dengan kelembapan

relative antara 40% dan 60% dengan kelajuan udara adalah lebih kurang 0.25 m/s.

Objectif projek ini adalah mengawal suhu udara dan kelembapan udara supaya

mencapai zon selesa. Eksperimen adalah diasaskan keselesaan terma yang boleh

diterima syarat-syarat di dalam sebuah bilik dengan merujuk kepada tahap ASHRAE

dan tahap keselesaan terma daripada Peraturan Bangunan Singapura. Eksperimen-

eksperimen telah dijalankan dengan menggunakan Unit Penyaman Udara. Beberapa

parameter dalam kajian ini adalah halaju udara, Pra-pemanas, dan peredam.

Keputusan menunjukkan parameter yang sesuai adalah dicapai pada 2.75m/s halaju

udara dan 100% udara luar dengan satu Pra-pemanas dihidupkan. Kaedah

Computational fluid Dynamic dengan perisian ANSYS CFX digunakan untuk

simulasi corak aliran udara dan taburan suhu dalam kebuk. Hasil simulasi telah

disahkan oleh hasil eksperimen.

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TABLE OF CONTENT

CHAPTER TOPIC PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENT vii

LIST OF TABLES x

LIST OF FIGRUES xi

LIST OF SYMBOLS xiii

LIST OF ABBREVIATIONS xiv

LIST OF APPENDIX A xv

LIST OF APPENDIX B xvi

LIST OF APPENDIX C xvii

CHAPTER 1 INTRODUCTION 1

1.1 Background Study 1

1.2 Problem Statement 2

1.3 Objectives 3

1.4 Scope 3

CHAPTER 2 LITERATURE REVIEW 5

2.1 Background of Air-conditioning System 5

due to Thermal Comfort

2.2 Studies on Air Flow Pattern and Thermal 6

Comfort on Air-conditioning Unit

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2.3 Definition of Computation Fluid Dynamic 8

2.3.1 Application of Computation Fluid 9

Dynamic

2.3.2 Advantages of Computation 9

Fluid Dynamic

2.3.3 Disadvantages of Computation 11

Fluid Dynamic

2.4 Psychrometric Chart 11

2.4.1 Psychrometric Properties 11

CHAPTER 3 METHODOLOGY 13

3.1 Introduction 13

3.2 Air-Conditioning Unit Test 13

3.2.1 Air Flow in Air-Conditioning Unit 14

3.2.2 Air Conditioning Unit 18

Experimentation Set-up

3.3. Computation Fluid Dynamic Simulation 21

3.3.1 Geometrical Construction in ANSYS 23

Workbench

3.3.2 Generate Meshing in CFX Mesh 23

3.3.3 Defining a Simulation in ANSYS 24

CFX-Pre

3.3.4 Obtaining a Solution using ANSYS 25

CFX - Solver Manager

3.3.5 Results in ANSYS CFX-Post 25

CHAPTER 4 RESULTS AND ANALYSIS 26

4.1 Introduction 26

4.2 Data Analysis of Experimental Result 26

4.2.1 Analysis of Case A 27

4.2.2 Analysis of Case B and C 27

4.2.3 Analysis of Case D and E 28

4.2.4 Final Experimental Setting 30

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4.2.5 Investigation on Air Properties 31

4.3 Simulation Result of Air Properties in 32

Chamber using ANSYS CFX

4.3.1 Simulation Result of Temperature 32

Contour

4.3.2 Simulation Result of Air Flow Pattern 34

4.3.3 Simulation Result of Air Properties 36

Variation with Time

4.4 Validation of Simulation Result 40

4.4.1 Validation for Air Temperature 40

4.4.2 Validation for Air Flow Speed 41

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 43

5.1 Conclusion 43

5.2 Recommendations for future works 43

REFERENCES 45

BIBLIOGRAPHY 47

APPENDIX A 49

A1 Isometric View of Chamber (a) 50

A2 Isometric View of Chamber (b) 51

A3 Simulation Part of Chamber 52

APPENDIX B 53

B1 ASHRAE Psychrometric Chart No. 1 (SI) 54

APPENDIX C 55

C1 Schematic Diagram of Air- Conditioning Unit 56

C2 Air-Conditioning Laboratory Unit 58

A660 Specification

C3 Apparatus 58

C4 Control Part at Air Conditioning Unit 59

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LIST OF TABLES

NO. TITLE PAGE

2.1 Comparison of Experiments Techniques with CFD 10

Simulations

3.1 Chosen range of values for variable factors 19

3.2 Increment levels of each Experimental Setting 19

3.3 Experimental Setting for Air Properties Test 20

4.1 Experimental Results 27

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LIST OF FIGURES

NO. TITLE PAGE

3.1 Air-conditioning Units at Faculty of Mechanical 14

Engineering Laboratory, UTeM

3.2 Schematic Diagram of Air-Conditioning Unit A660 15

(Source: P. A. Hilton (2003))

3.3 Air volume control on damper of Air-conditioning Units 17

at Faculty of Mechanical Engineering Laboratory, UTeM

3.4 Directions of air flow in chamber 17

3.5 Flow Chart of Air Conditioning Simulations using 22

ANSYS CFX

3.6 CFX Geometry Surface Mesh and Volume Mesh 23

3.7 Direction of air flow and boundary condition at chamber. 24

3.8 Convergence criterion and iteration process 25

4.1 Air Properties of each case at Psychrometric Chart 29

4.2 Air Properties at Inlet and Outlet of Chamber 30

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4.3 (a) Temperature profile in chamber 33

(b) Temperature profile in chamber at plane view 33

4.4 Simulation of temperature profile at inlet and outlet 34

part of chamber

4.5 (a) Air flow pattern in chamber (Isometric View) 35

(b) Air flow pattern in chamber (Front View) 35

4.6 (a) Temperature Profile at Various Time Intervals 36

(t = 10seconds)

(b) Temperature Profile at Various Time Intervals 37

(t = 1.0 minutes)

(c) Temperature Profile at Various Time Intervals 38

(t = 5.0minutes)

4.7 (a) Air Flow Pattern at Various Time Intervals 39

(t = 10seconds)

(b) Air Flow Pattern at Various Time Intervals 39

(t = 1.0minutes)

(c) Air Flow Pattern at Various Time Intervals 39

(t = 5.0minutes)

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LIST OF SYMBOLS

Cp = Specific heat capacity

mw = Mass of water vapor (kg, lb)

ma = Mass of dry air (kg, lb)

= Partial pressure of water vapour in the mixture

= The saturated vapour pressure of water at the temperature of

the mixture. RH = Relative humidity of the mixture being considered

t1 = Dry-bulb temperature of air at fan inlet

t2 = Wet-bulb temperature of air at fan inlet

t3 = Dry-bulb temperature of air after leaving Pre-heater

t4 = Wet-bulb temperature of air after leaving Pre-heater

t5 = Dry-bulb temperature of air after cooling

t6 = Wet-bulb temperature of air after cooling

t7 = Dry-bulb temperature of air after Re-heating

t8 = Wet-bulb temperature of air after Re-heating

x = Humidity ratio (kgwater/kgair, lbwater/lbdry_air)

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LIST OF ABBREVIATIONS

3D = Three Dimensional

ASHRAE = American Society of Heating, Refrigeration and Air

conditioning Engineers

CAD = Computer-Aided Design

CFD = Computational Fluid Dynamics

HVAC = Heating, Ventilation and Air-conditioning

IAQ = Indoor Air Quality

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LIST OF APPENDIX A

NO. TITLE PAGE

A1 Isometric View of Chamber (a) 49

A2 Isometric View of Chamber (b) 50

A3 Simulation Part of Chamber 51

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LIST OF 1APPENDIX B

NO. TITLE PAGE

B1 ASHRAE Psychrometric Chart No. 1 (SI) 53

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LIST OF APPENDIX C

NO. TITLE PAGE

C1 Schematic Diagram of Air-Conditioning Unit 55

C2 Air-Conditioning Laboratory Unit A660 Specification 57

C3 Apparatus 57

C4 Control Part at Air Conditioning Unit 58

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CHAPTER 1

INTRODUCTION

1.1 Background Study

The variation in temperature, humidity, and wind occurring throughout the world

provides the climates which vary with season of the year and with geographical

locations. Hence, in very few places the natural environment is comfortable for human

beings or suitable for a specific product or process throughout the year. Since the

principal purpose of air-conditioning systems is to provide conditions for humans to stay

with thermal comfort, air conditioning that based on the climatic considerations been

suggested to provide conditions for human thermal comfort.

According to the comfort standard from Building Regulation Singapore, a space

air-conditioned temperature had specified between 23 and 27 0C, relative humidity not

exceeding 75% and maximum air movement (relative velocity) of 1.25 m/s. The air

motion also plays an important role to determine the human comfort. It removes the

warm, moisture air that builds up around body and replaces it with fresh air. Air speed of

about 0.25m/s will make people feel comfortable. Beside human thermal comfort, air

conditioning is also widely used for the efficiency and effectiveness of manufacturing

process, or to maintain the quality and life of a stored product.

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Air-conditioning not just as simple the cooling of air, furthermore it includes

some processes in some way to improve the quality of air. More formally, air-

conditioning maybe defined as a form of air treatment which controls simultaneously the

temperature, humidity, cleanliness and distribution of air to meet the requirements of the

conditioned space. To provide these functions with most natural atmospheres, heating,

cooling and regulation of thermal radiation was required for temperature control.

Humidification and dehumidification was required for humidity control and introduction

of outside ventilation air.

The air flow rate was affect the air flow pattern and humidity inside a room to

achieve thermal comfort. Data on the effect of air motion and temperature to the

humidity of the air in the chamber was go for determine the system thermal comfort.

1.2 Problem Statement

In fact of hostile environment, the design specification for a comfort

conditioning system is intended to be the framework for providing a comfortable

environment for human being throughout the year. The comfort zones are intended to

provide acceptable thermal environment for occupants wearing typical indoor clothing

and at a near sedentary activity. To be comfortable, people require a certain amount of

ambient humidity that not too high, and not too low.

Poor air quality in homes can cause asthma in children, and that poor air quality

in workplaces decreases productivity. One of the basic requirements creating a

comfortable environment is to maintain thermal conditions comfortable for occupants as

these have a direct effect on their health, productivity and morale. Low humidities, with

dew points less than 20C, tend to give a dry nose and throat, and eye irritation. A dusty

environment can exacerbate low humidity skin conditions. High humidities support the

growth of pathogenic and allergenic organisms, certain fungi, mycotoxins and house

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mites. Factors that influence thermal comfort are air temperature (dry-bulb), relative

humidity, air velocity, radiation (mean radiant temperature), metabolic rate, and clothing

insulation.

An investigation was done for this project to control the level of air temperature

and humidity in a chamber using Air-Conditioning Unit. Humidification and

dehumidification were control by varying the amount of moisture and quantity of return

air with other fix experimental setting. The corresponding range of experimental setting

that give relative humidity lie on the comfort zone was determined through the

psychrometric chart. For CFD (Computational Fluid Dynamics) simulation, the ANSYS

CFX software is used to simulate the air flow pattern in a chamber. Simulation of

temperature distribution was done by using ANSYS CFX software. Experimental results

was use to validate the simulation result.

1.3 Objectives

The objectives of this project are to study the comfort zone of air characteristic

and investigate the characteristic of the air flow in chamber. The simulation result was

validated with experimental data.

1.4 Scope

The investigation was based on study the comfort zone of air characteristic using

Air-Conditioning Unit. A simulation system was used from the condition of real air

conditioning system in a chamber. CFD simulation was used to simulate the temperature

profile of air in chamber. Experiment was set-up based on the control of water heater

and quantity of return air to get the suitable relative humidity in chamber. Relative

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humidity which achieved thermal comfort was determined by using the psychrometric

chart. Furthermore, the wet-bulb and dry-bulb temperature at the inlet and outlet of

chamber was obtained. Analysis was done based on the air-conditioning testing results

to get the suitable settings which give comfort condition. The air flow in a chamber was

examined and simulate by using CFD simulation.

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CHAPTER 2

LITERATURE REVIEW

2.1 Background of Air-conditioning System due to Thermal Comfort

Air-conditioning systems is used in many parts of the world. The purpose of

most systems is to provide thermal comfort and an acceptable indoor air quality (IAQ)

for occupants. With the improvement of standard of living, occupants require more and

more comfortable and healthful indoor environment. People spend 80 to 90% of their

time in indoors, and indoor environment has important effects on human health and

work efficiency. A comfortable and healthy indoor air environment is favourable to

occupants. In recent years, indoor thermal comfort has been improved greatly due to the

development of air-conditioning systems. However, health problems related to poor IAQ

appear more frequently, and it is the indoor pollutants that lead to poor IAQ. Control of

relative humidity is an essential aspect of maintaining indoor air quality in an air-

conditioned space.

Thermal-comfort is attained when a thermal balance is achieved in which no heat

storage occurs in the body. Although this can be achieved over a wide range of thermal-

environment conditions, thermal-comfort is associated with conditions to which the

body can readily adjust. It is defined as ‘‘that state of mind which expresses satisfaction

with the thermal environment’’. The thermal-environment parameters involved are all

those affecting body heat gains and losses. Air temperature, air humidity, air velocity,

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mean radiant temperature as well as human clothing and activity levels are factors that

determine the heat balance of a human body in a given thermal environment. Several

models are available in literature to relate the human sensation of comfort to those

factors. In one basic form, the human body has been considered as an inert object

exchanging energy with its environment through radiation, convection and conduction

and capable of losing heat by evaporation and adapting to conditions through the body

regulatory system. Prediction of thermal-comfort has been of substantial interest to

ASHRAE (American Society of Heating Refrigeration and Air-conditioning Engineers),

which developed the original comfort index based on effective temperature.

The sensations of warmth or cold experienced by human body depend not only

on the dry-bulb temperature but also on the moisture content of the air. Cooling

applications remove only the sensible heat fall short of establishing comfortable

conditions if the latent heat gain is particularly high. The air will be cooler under these

conditions, but it will feel damp and uncomfortable. In order to meet minimal standards

of comfort, both sensible and latent heat must be reduced to and acceptable level.

2.2 Studies on Air Flow Pattern and Thermal Comfort on Air-conditioning Unit

Thermal comfort encompasses environmental parameters such as air-temperature,

radiation, humidity and air-movement and personal parameters such as clothing and

activity. The combined influence of all the parameters was quantified with the

introduction of the 'comfort equation', subsequently resulting in the presentation of

ASHRAE thermal comfort standards as performance criteria for buildings.

Human beings want to live in comfort environment that neither hot nor cold,

neither humid nor dry. The comfort of the human body depends primarily on three of the

main factors which are dry-bulb temperature, relative humidity, and air motion. Most

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people feel comfortable when the environment temperature is between 220C and 270C

with relative humidity of 40% to 60% at air speed about 0.25m/s.

From the study by S.C. Sekhar (1995), acceptability of such space conditions

from thermal comfort considerations has been discussed with reference to comfort

diagrams and it has been shown that higher space temperatures of about 26 °C with

relative humidity levels around 60% are quite acceptable from thermal comfort

considerations in the tropics. The ASHRAE upper limit on relative humidity is 60% and

the average summer air movement should not exceed 0.25 m/s. In tropical buildings, it is

not common to find low space temperature around 230C and high relative humidity

levels in order of about 70 to 75%. Building in the Asian rim countries typically does not

employ humidity control as part of the air-conditioning system. According to Building

Regulation of Singapore specify a space air-conditioned temperature between 23 and

270C, relative humidity not exceeding 75% and maximum air movement (relative

velocity) of 1.25m/s.

J. W. Wan, Kunli Yang, W.J. Zhang and J. L. Zhang (2008) had investigated a

new method of determination of indoor temperature and relative humidity with

consideration of human thermal comfort. From the viewpoint of indoor thermal

environment design, effective temperature represents the human thermal comfort level.

It should be noted that surely there are many other factors that influence human thermal

comfort, notably air velocity. However, as far as air velocity, its effect may be replaced

by humidity. It is common sense that for a given human thermal comfort level, increase

in indoor temperature needs to be accompanied with decrease in indoor humidity. It

seems to be such that indoor temperature and indoor relative humidity are two major

important parameters to be chosen. Their sensitivity analysis of the six comfort factors

showed that the clothing worn by occupants, the activity level, air temperature, and

mean radiant temperature all have significant effects on human thermal comfort.

Humidity and air velocity play rather small roles in comparison, but they seem to

regulate the sensitivity of the other four factors and are therefore important. Humans are

more sensitive to variations in temperature than those of relative humidity.