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PERFORMANCE STUDY OF AN ABSORPTION COOLING SYSTEM UNDER DIFFERENT ENERGY SOURCES
Tang Chung Hieng
Master of Engineering 2010
o~1
P.KHIDMAT MAKLUMAT AKADEMIK
111111111 IIi'WIIIIIIIIII 1000246351
PERFORMANCE STUDY OF AN ABSORPTION COOLING SYSTEM UNDER DIFFERENT ENERGY SOURCES
Tang Chung Hieng
A thesis submitted in fulfillment of the requirements for Degree of Master of Engineering
Faculty of Engineering
UNIVERSITI MALAYSIA SARA W AK
2009
ACKNOWLEDGEMENT
First of all, I would like to give the highest thanks to my supervisor Dr.
Mohammad Omar Bin Abdullah, who had given me some guidelines, valuable
advices and in formation to complete this thesis. I also did not forget to give thanks
to Mechanical Laboratory Technicians like En Masri Zaini, En Rhyier Juen and staff
of Faculty engineering in UNlMAS for their cooperation and allow me to use
facilities that have been provided in UNlMAS.
Secondly, I would to express appreciation to PhD student; Mr Standly Leo for
his motivated support, valuable advices and guidelines in driving a way to complete
this thesis. Beside that, thanks also will be given to my parents for their fuB support
and offer me the immediate helps when I needed.
Lastly I would like to thank those who are directly or indirectly help me in
completing this thesis. Thank you for all of your helps and advices.
ABSTRAK
Dalam kajian ini, ammonia/air dengan penambahan gas hidrogen (~O-NH3-
H2) bagi penerapan pendinging udara telah disediakan untuk mengaji ciri-ciri
termodinamik. Objektif kajian pertama ialah mengaji suhu dalam enam bahagian
dalam penerapan pendinging udara semasa dihidupkan dengan menggunakan
sumber tenaga yang berlainan, seperti eletrik dan Gas Petroleum Cecair yang
senang digabung dengan penerapan pendingin udara tersebut. Kajian dijalankan
dalam tempoh masa dua jam dalam keadaan suhu makamal, 27°C dan data suhu
dicatatkan pada setiap minit. Lima kumpulan data akan dikumpulkan untuk
membuat kajian. Mean dan standard deviation akan digunakan untuk mengaji
kejituan keputusan. Graf suhu lawan Illasa akan diplotkan untuk dianalisi. Melalui
kajian ini, keputusan yang didapati bagi kedua-dua jenis sumber tenaga yang
berlainan adalah hampir sarna. Perbezaan yang wujud adalah antara masa
permulaan dan minimum suhu yang dicapai. Sistem yang menggunakan tenaga
eletrik mempunyai masa permulaan yang lebih awal, iaitu .6 minit lebih awal
daripada system yang menggunakan Gas Petroleum Cecair. Akan tetapi, sistem
yang menggunakan Gas Petroleum Cecair dap~t mencapai suhu yang lebih rendah,
iaitu _9°C, system yang menggunakan tenaga eletrik hanya mencapai _7°C. Objektif
kedua ialah menggunakan Program Matlab 7.0 untuk menghasilkan satu
'simulation program' dengan rumusan persamaan ODE. Tujuaannya ialah simulate
keadaan suhu pada setiap bahagian dalam penerapan pendingin udara semasa
dihidupkan. Keputusan yang diperolehi perlu digabung dengan nilai-k supaya
ii
keputusannya lebih hampir sarna dengan keputusan eksperimen yang dijalankan.
Setiap bahagian mempunyai nilai-k yang berbeza, generator menunjukkan
keputusan yang paling memuaskan dan hampir sarna dengan keputusan
eksperimen. Nilai-knya ialah 2. Bahagian lain-lain seperti condenser, evaporator,
absorber, titik kedua dan titik ketiga mempunyai nilai-k masing-masing, iaitu 0.05,
0.05, 0.01, 2.5 and 0.15. Julat keputusan COP antara eksperimen (system yang
menggunakan tenaga electric) dengan 'simulation program' ialah 2.25%.
iii
I
ABSTRACT
In the present study, a H20-NHa -H2 cooling machine, which used ammonia
(NH) as refrigerant, water as adsorbent and Hydrogen as equalizer for pressure,
had been employed and investigated. The first objective of this work is to assess the
transient temperature of the system's components under the two types of energy
sources: Electric from Grid and Liquid Petroleum Gas which can be easily obtained
and integrated to the absorption refrigeration for residential usage. Five sets of
experiments were done under the lab environment at 27°C. In the experiments, the
data was recorded every minute within two hours. Five sets of data were collected
and analyzed with statistical analyses. In these analyses, the standard deviation
and mean were estimated. The mean for transient temperature was plotted against
time. Results obtained have shown that performance of the components under
different type of energy sources is almost coherent. For the evaporator, the system
with Common Electricity Supply has the shorter and better starting time which is 6
minutes earlier than the system with Liquid Petroleum Gas. Meanwhile, the system
with Liquid Petroleum Gas produced a lower cooling temperature which is _9°C,
compared with the system with Common Electricity Supply, which produced a
cooling temperature of _7°C. Then, the second 'objective is to model the transient
temperature of the components using Mathlab 7.0. A mathematical model, Runge
Kutta method had been developed herewith to simulate the transient temperature
behavior at each main components of the system. In the simulation process, the
coefficient factor, k-factor was estimated to asses the goodness of fitting between the
experiment and simulated data. A high k-factor represents a good fitting, where it
iv
I
was found that the simulated data for the generator fit the experimental data well,
shown by the high k-factor of 2.The k-factors for condenser, evaporator, absorber,
point 2 and point 3 are 0.05, 0.05, 0.01, 2.5 and 0.15 respectively. The Coefficient of
Performance (COP) of the simulated result was also estimated. Then, the
comparison between the simulation COP result and the experimental (system with
Common Electricity Supply) COP result was done. The COP values obtained from
simulation are found quite agree to the experimental values with an error
percentage of 2.25%.
Keywords: Absorption, refrigeration, energy scheme, simulation
v
Posat Khidmat Maklumat Abdemik UN1VERS1TI MALAY IA SARAWAK
TABLE OF CONTENTS
Content Page
Acknowledgement i
Abstrak ii
Abstract iv
Table of Contents vi
List of Table
List of Figure
Nomenclature
Chapter 1
1.1
1.2
,' ,
1.3
1.4
1.5
1.6
Chapter 2
2.1
2.2
Chapter 3
ix
x
xiii
INTRODUCTION
General Introduction . 1
Energy Schemes 3
1.2.1 Electric from grid 3
1.2.2 .Liquid Petroleum Gas (LPG) 4
Performance Study 4
Modeling and Simulation 5
The Objectives and the Aims Of The Project: 5
Scope and Goal of research 5
LITERATURE REVIEW
System Performance, Modeling and Simulation 7
Aspect of the Absorption Systems
Main Observations from the Review 22
BACKGROUND STUDY
vi
r
3.1 Refrigerator 24
3.1.1 The structure of the Refrigerator and the 25
Associated Components.
3.1.2 The Working Principle 25
3.1.3 Temperature- Entropy (T-s) Diagram for 26
the Refrigeration Cycle
3.2 Absorption System 28
3.2.1 The Components and Refrigerant 28
3.2.2 Refrigerant and Transfer Medium 30
3.2.2.1 Lithium BromideJWater 30
3.2.2.2 AmmonialWater 31
3.2.3 Working Principle of the Absorption 31
System
3.2.4 T-sDiagram 33
3.2.5 Advantage and Disadvantages of the 34
Absorption System
3.3 Energy Source 34
3.3.1 Liquid Petroleum Gas, (LPG) 35
3.3.2 Conventional Electrical Supply 35
Chapter 4 METHODOLOGY
4.1 Experimental study: Performance of the 37
Absorption Refrigeration
4.2 Numerical Simulation Modeling 39 ..
4.2.1 Flowchart of Numerical Simulation 47
Modeling
Chapter 5 RESULT AND DISCUSSION
5.1 Performance of Absorption Refrigerator 50
Powered By Electrical Grid (Case 1)
5.1.1 Cooling Temperature and Humidity vs. 53
vii
Generator Temperature and Evaporator I,'
Temperature.
5.2 Performance of Absorption Refrigerator 55
Powered By LPG ( Case 2 )
5.2.1 Cooling Temperature and Humidity vs. 57
Generator Temperature and Evaporator
Temperature.
II
5.3 Comparison Performance of Energy Resources 58
5.4 Simulation Work 61
5.4.1 The Comparison between Simulated COP 65
with Experiment COP
Chapter 6 CONCLUSION AND RECOMMENDATION
6.1 Conclusion 67
6.2 Recommendation 68
REFERENCES 69
APPENDIXES 73
viii
I"
I
LIST OF TABLES
II Table Title Page
3.1 The function of refrigerator components 25
(Mechanical type)
3.2 The function of the refrigerator components 29
(Absorption type)
3.3 The Properties of LPG 35
5.1 The k-factor 65
5.2 Comparison between experiment work and 66
simulation work.
6.1 The k-factor 67
ix
.,
Figure
2.1 a-b
2.2 a-b
2.3 a-d
2.4a-b
2.5
2.6
2.7 a-b
3.1
3.2
3.3 a-b
3.4
3.5
r'
LIST OF FIGURE
Title Page
Hourly variation of temperature and Coefficient of 8
Performance.( Source: Muneer and Uppal, 1985)
Maximum COP as a function of evaporator 10
temperature at differ condenser and absorber
temperature.( Source: Bulgan, 1995)
Comparison of effect of COP values on generator, 13
evaporator and condenser temperature.( Source:
Da,1998)
The COP of the VAR system against the generator 16
and condenser temperature (Source: Horuz, 1998)
The COP of the VAR system against the evaporator 17 . temperature (Source: Horuz, 1998)
Temperature variation (Source: De Francisco et al., 18
2002)
COP against chilled water inlet temperature and 19
energy input.( Source: Horuz and Callander, 2004)
The typical common refrigerator(Photo by: C.H. 24
Tang)
The working principle of the refrigerator(Modified 25
by: C.H. Tang)
T -s diagram for vapor compression refrigeration 26
cycle (Sources: <;engal and Boles,1998)
The components of absorption air conditioning 29
(Modified by: C.H. Tang)
Absorption refrigeration Cycle(Modified by: C.H. 31
Tang)
x
I
3.6 T-s diagram for absorption refrigeration cycle 33
(Sources: Rogers & Mayhew, 1992).
3.7 Schematic Diagram of A Typical Electricity 36
Generating Method
4.1 The photo of the absorption refrigerator 38
4.2 Schematics diagram of absorption trainer 38
(Source: ElettronicaVeneta, Anon)
4.3 a-b The location of point(Photo by: C.H. Tang) 40
4.4 Schematic diagram of the absorption refrigerator 41
with location point
4.5 Flow Char.t of Thermodynamic Analysis 49
5.1 Plots of time Vs component temperature (with 51
electrical grid)(Case 1)
5.2 The relation between the time with temperature of 54
generator, evaporator, cooling space and humidity
(Case 1)
5.3 Plots of time Vs component temperature (with 56
LPG)(Case 2)
5.4 The relation between the time with temperature of 58
generator, evaporator, cooling space and humidity
(Case 2)
5.5 The generator temperature profile for LPG and 59
Electric
5.6 The evaporator temperature 'profile for LPG and 60
Electric
5.7 The comparison of LPG and Electric (Temperature 61
of cooling space and humidity)
5.8 The comparison between the experiment work with 62
simulation result (generator).
5.9 The comparison between the experiment work with 62
simulation result (condenser).
XI
5.10 The comparison between the experiment work with 63
simulation result (evaporator).
5.11 The comparison between the experiment work with 63
simulation result (absorber).
5.12 The comparison between the experiment work with 64
simulation result (Point 2).
5.13 The comparison between the experiment work with 64
simulation result (Point 3).
5.14 The comparison between the experiment work and 66
simulation work.
xii
I
Nomenclature H M P Q T h U A
X
T"
q in
Cp•w
Cp.Cl
C Cm
C.. F,. CLS
C, C OP
CM
F F.
Abbreviation COP NPV LPG NAT ANAT RT P 1 N S R RRI lRR ARR
Enthalpy (kJIKg) Mass flow rate (ms·') Pressure (Pa) Heat (kW) Temperature(O C) Enthalpy Overall heat transfer coefficient ( cal /sec cm2 K) Area oftube (cm2
)
Percentage of ammonia Temperature of ambient (K)
Mass of ammonia
Mass of water (g) Supply Heat (callsec) Tube fluid heat capacity for water ( cal /g K)
Tube fluid heat capacity for ammonia ( cal /g K)
Capital Cost Cost of Machine Cost of Supplying Energy Annual fuel cost of the machine Life cycle cost Cost of Fuel Annual operating cost· Cost of maintenance Fuel cost Fuel cost of the electrical grid system
Coefficient of Performance Net Present Value Liquid Petroleum Gas Net Annual Saving
. Average Net Annual Saving Running tools Present Value Interest rate earned at the end of each inters period Number of interest period Future value Uniform future value Real rate of interest Internal Rate of Return Accounting rate of Return
xiii
c
,
Greek Letters p Density,kg/m3
Subscripts e Evaporator
Condenser g Generator a Absorber
xiv
CHAPTER ONE
INTRODUCTION
1.1 General Introduction
Refrigeration is the technology that cannot be separated from the modern daily life.
It has been widely used in the commercial cooling activities, as we]! as the residential
activities. According to Kuehn (1998), refrigeration is the removal heat process in the
specific space for producing the environmental temperature which is lower than the natural
surroundings. So, any methods that are used for lowering temperature, in the range from
the ambient temperature to absolute zero ca'n be categorized as refrigeration processes.
There are two common types of refrigeration system_s: mechanical vapor compression system
and absorption system.
Mechanical vapor compression system is used in the majority of refrigeration system.
The cooling effect is provided by the evaporation of a liquid refrigerant. The mechanical
compression is needed to elevate the vapor refrigerant for rejecting heat to the environment
through the condensation process. It has many favQrable characteristics, such as high
Coefficient of Performance which is 2.5 to 3.0 (under ASHERAE standard condition) and low
capital cost. But, the typical compressor refrigerator just can be driven by electricity .. The
large amount of work is needed to compress the vapor that undergoes a large change in
specific volume. Besides, the CFC, refrigerant used in compression system is main factor for
1
,
the ozone layer depletion (Whitman et aI., 2005). Nowadays, the Hybrid refrigerant, R-410A
is developed, to replace CFC.,
Absorption refrigeration system, which uses the binary-mixture of ammonia-water or
Lithium Bromide-water, is increasing in popularity and developing gradually to replace the
mechanical vapor compression system. It is a simpler physical-chemical process. In the
evaporator, the liquid refrigerant is flashed off and the heat is absorbed from the cooling
space. Then, the vapor refrigerant is dissolved and reacted with the transfer medium in the
absorber and the heat release. Next, the solution is sent to the generator for vaporation.
After the generator, the refrigerant goes to the condenser for condensing the vapor to be
liquid and the transfer medium is sent back to the absorber. Lastly, the liquid from the
condenser back to evaporator to continue the cycle. Horuz (2003) pointed out that it has the
advantage of being environmentally friendly, having zero potential in ozone layer depletion
and reducing global warming. It is also attractive for quiet operation, low-maintenance and
low energy consumption as there is no moving part. According to Qengel & Boles (1998), an
absorption refrigeration system has a lower Coefficient of Performance (COP) and higher
capital cost. However, the advantage is that it can be driven by many type of energy source.
The present study aims to study the performance of absorption system, which uses
ammonia (NH3) as refrigerant, water as absorbent and Hydrogen as equalizer for pressure,
under various conventional energy schemes.
2
,..
I"
1.2 Energy Schemes
The present work is devoted to study the alternatives of energy schemes that can be
integrated into the absorption refrigerator which could be easily found in the market. The
different alternatives that can be conveniently used and considered in this study for
powering this absorption refrigerator are conventional electric from grid and liquid
petroleum gas (LPG), as far as the present location i.e. Sarawak is concerned.
1.2.1 Electric From Grid
Using the power from grid to drive the absorption refrigeration machines is the most
convenient alternative. It has lowest capital cost and with simple technology. The electric is
used to drive the heater for heating purpose. The heater is installed inside the generator for
heating. The heat is used to evaporate the refrigerant participant from the strong solution
which has higher content of refrigerant. Then, the steam goes to the condenser and weak
solution which has low content of refrigerant goes back to the absorber. In the condenser,
the refrigerant vapor will be condensed to be liquid. The energy of condensation will be
released through the heat coil. The liquid refrigerant will be evaporated in the evaporator to
absorb the heat in the cooling environment. Electric energy is attractive for its simple
standard installation, low capital and convenience, but it leads to higher fuel cost.
3
1.2.2 Liquid Petroleum Gas (LPG)
There are two type of Liquid Petroleum Gas (LPG) heating technology, liquid
petroleum gas flame (direct-fired) or hot water or steam heating. The hot water or steam
heating needs a higher capital because piping is needed for running the transfer medium.
So, for tills project the direct-fired is chosen because it is simple and suitable for low
powered absorption refrigeration. A liquid petroleum gas burner is needed for burning
process. The burner is used to heat the generator. Hot combustion gas flows around the
finned part of the body inside the generator and provides the heat energy to the generator.
It is installed directly under the generator that its, position is normally vertically. So, the
heat can flow through the whole generator to heat up the strong refrigerant.
1.3 Performance Study
Performance study is done to investigate and analyze the performance of the
absorption refrigeration under two different energy sources. The transient temperature of
each component is recorded and analyzed.
Beside the transient temperature of components is analyzed, the temperature and
the humidity of cooling space are also recorded and ana1yzed.
4
Pu t idma 1aklumat Akademik UNlVERSm MALAYSIA SARAWAK
1.4 Modeling and Simulation
In the present study, a detailed numerical model for the absorption refrigerator is
developed with Mathlab 7.0. The Runge-Kutta method is chosen for the numerical analysis
because according to Plybon(1992), Runge Kutta method can obtain the better accuracy for
higher-order ordinary differential equation by using a computational procedure that does no
require computation of the partial derivatives.
1.5 The Objectives and the Aims of the Project:
The objectives of the projects are as follows:
1. To evaluate the performance of the absorption refrigeration using two types of energy.
(i) electric from grid and (ii) heating by LPG.
2. To develop a numerical simulation model for the absorption refrigerator
1.6 Scope and Goal of Research
In this research, an ammoniaiwaterlhydrogen absorption refrigerator is used for the
experimental work. Research works using ammoniaJwaterlhydrogen type of absorption
refrigeration are extremely rare reported in literature because it is not the common type of
absorption refrigerator. For the present study, the performance parameter, such as
temperature of the absorption machine was collected and analyzed. Subsequently, a
numerical simulation model was developed to simulate on the system performance. Runge
5
Kutta method was used for numerical modeling of the system. In final, some environmental
study in relation to the energy resources was also briefly discussed.
6
CHAPTER 2
LITERATURE REVIEW
2.1 System Performance, Modeling and Simulation Aspect of the Absorption
Systems
Many research projects in absorption refrigeration were carried out since 1950s. The
researchers were concentrated on dual working fluids notably ammonia-water or lithium
bromide-water.
Muneer and Uppal (1985) had conduct~d modeling and simulation of solar absorption
cooling system. The authors described the modeling and simulation of a commercially
available, solar operated lithium bromide absorption cooler for residential application. The
simulation approach was based on an empirical 'black box' representation of cooler wherein
the system is modeled on the performances. The system consists of absorption chiller,
cooling tower, solar collectors and storage tank.
The results are shown in Figure 2.1.
Their result shows that the temperature of storage tank temperature was higher
than the generator. The system is reported to be able to handle the full load at considerably
lower generator temperature (70-800 C). The COP of the system is between 0.57 and 0.64.
This result concluded that the optimum temperature for generator is 70-80oC. The
temperature which higher than this range is not contributes to the COP of system.
7
100
'\:. ~ 20 mt 90
60
70 -'"' : 60 0: ::>
:; 50
" '" la~ '.0 ~
]0 Ie
10
10
6 7 B 9 ,10 11 12 I) H. 1') I£, n 18 T ~ '0 ] ' 2 2 ~) 0 1 J , 5 11M £ f ttOUM)
(a)
0 7
0 6'
'"u
..i z
f?.. '"0. 0& ~ . o
QS>
6 7 8 9 10 11 12 13 14 1-;' 16 17 18 19 20 21 22 23 0 " 2 J " 5 TIME' (HOURI
(b)
Figure 2.1 a-b: Hourly variation of temperature and Coefficient of Performance versus time ( Sources: Muneer and Uppal ,1985). (ta=Ambient temperature (oC), tc=Cooling water temperature leaving cooling tower(oC), ts=Storage water temperature at the beginning of an hour(oC), tg= temperature of generator(oC), tw=wet-bulb temperature(oC), Ac= collector area).
8
