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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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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 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.