AN EXPLORATORY STUDY OF A LIQUID DESICCANT WATERFALL SYSTEM FOR THE
MALAYSIAN HUMID CLIMATE
BY
IHAB FAISAL IBRAHIM AHMED
A dissertation submitted in fulfilment of the requirement for the degree of Master of Science in Building Services
Engineering
Kulliyyah of Architecture and Environmental Design International Islamic University Malaysia
DECEMBER 2013
ii
ABSTRACT
An exploratory study of a liquid desiccant waterfall (LDW) system was conducted as a means of achieving air dehumidification of an internal air environment. The aim is to explore an alternative technology which can reduce energy consumption, while still achieving acceptable thermal comfort conditions and achieving specific advantages when compared with conventional air conditioning systems. Some of these advantages include the pleasing aesthetics and appearance of a waterfall feature, the efficient functionality behind desiccant dehumidication technologies of the LDW system. This study and research proposed a system which harnesses hygroscopic salt of lithium chloride (desiccant) in its liquid form (45% concentration). This naturally attracts and absorbs moisture from an internal environment. Having absorbed the moist indoor air into the system, the lithium chloride then converts into a diluted form (30% concentration) and this requires the solution to be reactivated. A further advantage of the LDW system is explored representing significant potential in saving energy through the harvesting of solar thermal energy in order to expel moisture out of the system, as well as to efficiently reactivate the saline solution of lithium chloride to undertake its the cyclic nature of new dehumidification processes. To further quantify the amount of moisture to be absorbed by the LDW system and to some extent verify this exploratory study, a case study of a hypothetical space of an open plan office building in Kuala Lumpur city was proposed. The study then calculates the total amount of moisture to be eliminated by the LWD system (as specified by the common standard) was 25.4 kg/hr based on standards of thermal comfort for an office environment. Life cycle costs and energy savings were estimated. The results demonstrate and suggest a high prospect in creating an attractive financial return-on investment (ROI) including energy savings. When design optimally, this technology or system can save up to 92% of energy consumption and offer an investment rate of return of 34% per year. This was considered an attractive investment because it could offer reasonable payback period of 3 years.
iii
ملخص البحث
شلال صورة في السائلة اففات لنظام تفصيلية تصميم دراسة العلمي البحث اهذ يتضمن الرطوبة لازالة تحكم كوسيلة ليستخدم النظام هذا تصميم الي الوصل تم وقد. داخلي مائي
استخدام من المتسببة المشاكل على والتغلب لازالة المثلى الحلول من ويعتبر ,بالجو العالقة واستهلاك هدر من عالية نسبة تشمل التي و التقليدية التبريد اجهزة او الهواء تكيف انظمة الهواء جودة مستوى علي السلبي والتاثير الكهربائية الطاقة خصوصا والموارد للطاقة
أحدث كأحد النظام هذا في المميز الجمالي والشكل الحديثة التقنية بين الجمع تم .الداخلي الذي المائي الشلال صورة في النظام هذا طرح. المطورة سائلةال اففات تكنولوجيا اساليب مما %45 تركيز بنسبة كلوريد اليثيوم محلول في متمثلة اففة الكيميائية المادة علي يحتوي داخل في استيعاا و به المحيط الهواء في الموجودة الرطوبة طبيعية بصورة يمتص و يجذب يجعله نسبة الى كلوريد الليثيوم محلول تركيز ينخفض حتي النظام يعمل. داخليا لمعالجتها النظام
صورة في البديلة الطاقة باستخدام وذلك المحلول تفعيل لاعادة النظام يخول مما 30% توضيحي شرح تقديم تم كما . فاعلة و منتظمة بصورة عمله دورة ليواصل الشمسية الطاقة
مدينة في التصميم حديثة مكاتب علي يشتمل مبنى في النظام هذا عمل طريقة و لاستخدام تحقق بنسبة الجو من ازالتها المراد الرطوبة كمية لتحديد مربع متر 320 بمساحة لمبور كوالا والمواصفات المقاييس، المعايير كل الاعتبار في وضعا المساحة لمستخدمي الحرارية الراحة
25,4 بمقدار ازالتها المراد الرطوبة ةكمي تحديد و قياس تم قد و.عالميا عليها المتعارف و. عليها المتعارف المقاييس حسب الحرارية الراحة ظروف على للحفاظ ساعة / كيلوجرام
يضمن كما %92 بنسبة للطاقة توفيرا يحقق انه بما عالية مالية فاعلية النظام هذا اثبت قد فى منه الاستثمار اعادة يعنى مما سنويا % 34 بنسبة الاستثمار اعادة معدل النظام هذا
. فقط سنوات ثلاث فترة خلال
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APPROVAL PAGE
I certify that I have supervised and read this study and that in my opinion, it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science in Building Services Engineering.
................................................. Puteri Shireen Jahn kassim Supervisor
I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Master of Science in Building Services Engineering.
................................................. Noor Aziah Mohd Ariffin Examiner
This dissertation was submitted to the Kulliyyah of Architecture and Environmental Design and is accepted as a fulfilment of the requirement for the degree of Master of Science in Building Services Engineering.
…............................................. Nurul Hamiruddin Salleh Head, Department of Architecture
This dissertation was submitted to the Kulliyyah of Architecture and Environmental Design and is accepted as a fulfilment of the requirement for the degree of Master of Science in Building Services Engineering.
…............................................. Khairuddin Abdul Rashid Dean, Kulliyyah of Architecture and Environmental Design
v
DECLARATION
I hereby declare that this dissertation is the result of my own investigations, except
where otherwise stated. I also declare that it has not been previously or concurrently
submitted as a whole for any other degrees at IIUM or other institutions.
Ihab Faisal Ibrahim Ahmed
Signature …………………………………… Date ……………………..
vi
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
DECLARATION OF COPYRIGHT AND AFFIRMATION OF FAIR USE OF UNPUBLISHED RESEARCH
Copyright © 2013 by Ihab Fasial Ibrahim Ahmed. All rights reserved.
AN EXPLORATORY STUDY OF A LIQUID DESICCANT WATERFALL SYSTEM FOR THE MALAYSIAN HUMID CLIMATE
No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below.
1. Any material contained in or derived from this unpublished research may only be used by others in their writing with due acknowledgement.
2. IIUM or its library will have the right to make and transmit copies print or electronic) for institutional and academic purposes.
3. The IIUM library will have the right to make, store in a retrieval system and supply copies of this unpublished research if requested by other universities and research libraries.
Affirmed by Ihab Faisal Ibrahim Ahmed.
……………………………. ……………….. Signature Date
vii
ACKNOWLEDGEMENTS
First and foremost, i would like to express my sincere and grateful appreciation to my supervisor, Dr. Puteri Shireen Jahnkassim whom i am profoundly indebted to her support, encouragement, guidance and insightful discussions on this research. Her joy and enthusiasm in conducting this research were my supportive motivations and I will be forever thankful for being her student. Beside my supervisor, accomplishing this research would not have been possible without the assistance from Dr. Yousif Abakr, his valuable comments and remark which were my guidance to expand my knowledge in this research area.
Finally and most importantly, there are no words to convey my sincere acknowledgement to my precious mother, father and siblings for their unconditional love and spiritual support throughout my study. Ihab Faisal Ibrahim Ahmed
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TABLE OF CONTENTS
Abstract ............................................................................................................... ii Abstract in Arabic ................................................................................................ iii Approval Page ..................................................................................................... iv Declaration Page ................................................................................................. v Declaration of Copyright ..................................................................................... vi Acknowledgements ............................................................................................. vii List of Tables ....................................................................................................... x List of Figures ..................................................................................................... xii List of Abbreviations ........................................................................................... xiv CHAPTER ONE: INTRODUCTION .............................................................. 1
1.1 Introduction ....................................................................................... 1 1.2 Desiccant Dehumidification Technology ......................................... 2 1.3 The Liquid Desiccant Waterfall (LDW) System .............................. 3 1.4 Problem Statement............................................................................ 4 1.5 Research Aim and Objectives ......................................................... 4 1.6 Research Structure ............................................................................ 5
CHAPTER TWO: LITERATURE REVIEW ................................................. 9
2.1 Introduction ........................................................................................ 9 2.2 Desiccant Materials in Perspective...................................................... 9 2.3 Desiccant Material Studies ................................................................. 12
2.3.1 Background Studies on Solid Desiccant Materials ..................... 13 2.3.2 Background Studies on Liquid Desiccant Materials ................. 14 2.3.3 Previous Studies on Desiccant Mixtures .................................... 16
2.4 Practicability and Applications for Desiccants Technology ................. 16 2.5 Desiccant Performance ....................................................................... 17 2.6 Liquid Desiccant Waterfall Systems .................................................. 20 2.7 Summary ........................................................................................... 21
CHAPTER THREE: AIR VENTILATION REQUIREMENTS IN A HUMID CLIMATE .......................................................................................................... 23
3.1 Introduction ........................................................................................ 23 3.2 Malaysia’s Actual Weather Condition ................................................ 23 3.3 Malaysian Standards for Thermal Comfort ......................................... 26 3.4 Moisture Sources ............................................................................... 27
3.4.1 Permeation and Infiltration through the Building Materials ....... 28 3.4.2 Infiltration through Miscellaneous Openings ............................. 30 3.4.3 Moisture from Occupants .......................................................... 31 3.4.4 Ventilation and Makeup Air ...................................................... 32
3.5 Moisture Load Quantifications ........................................................... 32 3.6 Summary ............................................................................................ 35
ix
CHAPTER FOUR: SELECTION OF THE OPTIMUM DESICCANT SOLUTION ........................................................................................................ 36
4.1 Introduction ........................................................................................ 36 4.2 Investigation of the Liquid Desiccant Solutions .................................. 36
4.2.1 Equilibrium Vapor Pressure of the Liquid Desiccants ............... 38 4.2.2 Thermal Conductivities of the Liquid Desiccants ...................... 42 4.2.3 Dynamic Viscosity of the Liquid Desiccants ............................. 44 4.2.4 Specific Heat Capacity of the Liquid Desiccants ....................... 46 4.2.5 Safety Criteria of Liquid Desiccants .......................................... 49 4.2.6 Corrosion of the Liquid Desiccants ........................................... 50 4.2.7 Cost of Liquid Desiccants ......................................................... 51
4.3 Summary ............................................................................................ 52 CHAPTER FIVE: THE DEVELOPMENT OF THE LDW SYSTEM DESIGN ............................................................................................................. 54
5.1 Introduction ........................................................................................ 54 5.2 Quantification of Liquid Desiccant for the LDW System .................... 54 5.3 Development of the LDW System Components .................................. 62
5.3.1 The Waterfall Dehumidifier Feature.......................................... 64 5.3.2 Flat Desiccant Solar Collector System ...................................... 66 5.3.3 The Cooling Tower System ....................................................... 69 5.3.4 The Pumping System ................................................................ 71 Determining the Pump Power ............................................................ 77 5.3.5 The Control Panel System ......................................................... 78 5.3.6 Storage Tanks System ............................................................... 79
5.4 Air Circulation System ....................................................................... 79 5.5 Summary ........................................................................................... 81
CHAPTER SIX: ECONOMICAL VALUE AND LIFE CYCLE COST ANALYSIS......................................................................................................... 83
6.1 Introduction ........................................................................................ 83 6.2 Economical Value of the LDW System............................................... 83 6.3 Life Cycle Cost Analysis of the LDW System .................................... 84 6.4 Cost Analysis Comparison of the LDW System & AC System ........... 85
6.4.1 The Capital Costs ...................................................................... 86 6.4.2 The Operation Costs ................................................................. 86 6.4.3 The Maintenance Costs ............................................................. 86 6.4.4 The Disposal Costs .................................................................. 87
6.5 Summary ............................................................................................ 88 CHAPTER SEVEN: CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK ............................................................................................... 89
7.1 Main Achievements of this Work and Discussion ............................... 89 7.3 Recommendations and Future Work ................................................... 92
BIBLIOGRAPHY .............................................................................................. 94
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LIST OF TABLES
Table No. Page No. 3.1 The mean surface wind speed for 34 Years (1969–2003) 26
3.2 F1 Factor for Grain Difference 29
3.3 Evaporation Rates of People 31
4.1 Weighting Factor & Figures Of Merit for the proposed properties 37
4.2 The vapor pressure at the surface of proposed desiccant solutions at 25 oC and 30% concentration. 40
4.3 Equilibrium humidity ratio at the surface of some saturated solutions at 40oC 41
4.4 Thermal conductivities of the selected desiccant solutions at 25% concentration and 30 oC 44
4.5 Dynamic viscosity of the selected desiccants at 30% concentration and 25oC 46
4.6 Table 4.6: Specific heat capacity of the selected desiccant at 30% concentration and 25 oC 48
4.7 Safety criteria of the selected desiccant solutions 50
4.8 Corrosion rate of the proposed liquid desiccants 51
4.9 The cost of the selected desiccants per USD per kilogram of solution 51
4.10 The selection of the optimum desiccant solutions 53
5.1 The Vapor Pressure Of LiCl Based On Different Temperature & Concentration Level 59
5.2 The Vapor Pressure Of Specified Indoor Conditions 60
5.3 The Vapor Pressure Of Actual Outdoor Conditions 60
5.4 Sizing Of Suction Pipe 74
5.5 Equivalent Feet of Straight Pipe for Fittings 75
5.6 Friction Loss Multipliers 75
6.1 The Initial Cost Of The LDW System’s Components 85
xi
6.2 Cost Analysis Comparison For LDWS & AC System 87
xii
LIST OF FIGURES
Figure No. Page No. 1.1 Air dehumidification in conventional air conditioning system 2
1.2 The research’s structure 6
2.1 Diagrammatic representations of the vapor pressure role in desiccant cycle (Lewis and Harriman, 2002) 10
2.2 A schematic of Liquid Spray – Tower system (Bhatia, 2012 And Lewis, 2002) 12
2.3 Liquid desiccant waterfall of the University of Maryland (2011) 20
3.1 The average, minimum and maximum dry bulb temperature 24
3.2 The average, minimum and maximum wet bulb temperature 25
3.3 The average, minimum and maximum relative humidity 25
3.4 F2 Factor For Space Permation 30
4.1 Vapor pressure at the surface of (A) lithium bromide and (B) lithium chloride solutions for different temperature and concentrations (Mohammad, 2010) 39
4.2 Vapor pressure at the surface of (A) calcium chloride and (B) magnesium chloride solutions for different temperature and concentrations, (Mohammad, 2010) 39
4.3 Equilibrium humidity ratio at the surface of some saturated solutions (Linke, 1965 and Stephen, 1963) 41
4.4 Thermal conductivities of (a) lithium chloride and (b) calcium chloride under different concentration conditions (Mohammad, 2010). 42
4.5 Thermal conductivities of (a) magnesium chloride and (b) lithium bromide under different concentration conditions, (Mohammad, 2010). 43
4.6 Viscosity of (a) lithium chloride and (b) calcium chloride, (Mohammad, 2010). 45
4.7 Viscosity of (a) magnesium chloride and (b) lithium bromide, (Mohammad, 2010) 45
xiii
4.8 Specific heat capacity of (A) lithium chloride and (B) calcium chloride solution under different temperature and concentration (Mohammad, 2010). 47
4.9 Specific heat capacity of (A) lithium bromide and (B) magnesium chloride solutions under different temperature and concentration (Mohammad, 2010). 48
5.1 Actual Condition In Kuala Lumpur city, ( ) Feasible Thermal Comfort Condition ( ) and ( ) the amount of moisture to be removed 55
5.2 ASHRAE Desiccant Comparison Chart, Fundamentals Handbook - Chapter 22 56
5.3 The Vapour Pressure Of Lithium Chloride At Different Temperature and Concentration, (M.Conde, 2004) 58
5.4 The Mass Balance of the Proposed Lithium Chloride 61
5.5 Schematic drawing of the LDW System Cycle 62
5.6 The waterfall dehumidifier feature at the proposed open plan office 64
5.7 The flat Desiccant Solar Collector, (Shuli, 2008) 66
5.8 The Average Global, Direct and Diffuse Solar Radiation for the Kuala Lumpur City. 67
5.9 The Average Global Solar Radiation for Kuala Lumpur City 68
5.10 Solar Collector Efficiency, (Viridian solar, 2013) 69
5.11 The schematic diagram of natural draft counter flow cooling tower (Viska, 2011) 70
5.12 Schematic Drawing Of Air Circulation Methods 80
xiv
LIST OF ABBREVIATIONS
ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers. CaCl2 Calcium chloride. CFM Cubic feet per minute. COP Coefficient of performance. DH-5 Molecular sieve. DH-7 Molecular sieve. KCOOH Potassium formate. LCIX Artificial silicate. LDW Liquid desiccant waterfall. LiBr Lithium bromide. LiCl Lithium chloride. MgCl2 Magnesium chloride. MS Malaysian Standard. MSDS Material safety data sheet. TEG Triethylene glycol. TRY Test reference year. 13X Zeolite molecular sieve.
1
CHAPTER ONE
INTRODUCTION
1.1 INTRODUCTION
For the past decades, conventional air conditioning systems have ensured thermal
comfort in hot humid regions. However, this enhancement does not come without a
high amount of energy consumption. From a luxury to a necessity, the air conditioning
system has increased air pollution levels, mainly because of higher carbon dioxide
levels of fossil fuels used to generate energy for the system. In the long run, this can
influence global warming and climate change.
Traditional air conditioning system is ideally required to counterbalance
between two load components termed as latent loads and sensible loads in order to
attain feasible thermal comfort condition. For instance, to handle a latent load and
dehumidify moist air, the system must initially cool the humid air down to its
saturation point in order to condense the moisture out of the atmospheric air. This
cooling is more than what is necessary for human thermal comfort. The dry air is then
reheated to a feasible room temperature for comfort. These processes of overcooling
and reheating consume a large sum of energy and this can only be fulfilled by an
excessive use of electricity. Figure 1.1 indicates the complete dehumidification
process in a conventional air cooling system.
2
Figure 1.1 Air dehumidification in conventional air conditioning system
In humid climate regions, the conventional air conditioning system is no longer
sufficient to meet the requirements of occupants, who are concerned about indoor air
quality. One such example is the Sick Building Syndrome phenomenon. Adequate
ventilation can eliminate such occurrence, but it will increase indoor moisture to a
level unhealthy and uncomfortable to the occupants.
1.2 DESICCANT DEHUMIDIFICATION TECHNOLOGY
In order to eradicate shortcomings of the traditional air cooling systems, more energy
saving technologies were innovated. This causes the emergence of various
dehumidification techniques and applications, which are becoming the main part of
the air conditioning system’s function in buildings and spaces that require humidity
control.
In recent years, dehumidification technology applications based on desiccant
materials have attracted considerable public attention with regards to their energy
Dehumidification due to further cooling
Sensible heating to meet a desired temperature
Air is cooled to saturation
3
saving characteristics and precise humidity control. These features prevent major
problems faced by industrial applications such as moisture regimes, protection against
condensation and protection against corrosion.
In contrast to the conventional air conditioning systems, a desiccant
dehumidification system utilizes a highly absorbent material called desiccant to
capture and absorb water vapor naturally from the ambient air, due to the difference of
water vapor pressure between the desiccant - air interfaces. Expelling the absorbed
moisture out of the desiccant as well as reactivating the desiccant material can be
accomplished by introducing heat from any energy source, such as solar thermal
energy, natural gas, electricity or wasted heat source.
For dehumidification task, generating heat is much easier and less costly than
consuming electricity for sophisticated machineries. Therefore, the desiccant
dehumidification system is particularly functional in the case where a latent load is
high since such system can eliminate moisture more economically than the traditional
air conditioning system.
1.3 THE LIQUID DESICCANT WATERFALL (LDW) SYSTEM
The liquid desiccant waterfall (LDW) system aids in removing water vapor from the
air without the burden of conventional air conditioning system’s excessive energy
consumption. The functionality behind desiccant dehumidification technologies along
with the aesthetic appearance of the waterfall feature are combined to create the LDW
system.
The critical notion that drives the LDW system’s operation is the harnessing of
hygroscopic salt of lithium chloride (desiccant) in its liquid form (45% concentration).
This naturally attracts and absorbs moisture from the atmosphere. Subsequent to
4
having the indoor moist air absorbed in the LDW, the working fluid of the lithium
chloride converts to be diluted (30% concentration). Another advantageous
characteristic of the LDW system is in harvesting solar thermal energy to expel
moisture; this efficiently reactivates the saline solution of the lithium chloride to
undertake new dehumidification tasks.
The LDW system proposes a variety of advantages — dehumidification,
cooling, particle elimination, purifying, energy conservation — over the conventional
air conditioning system. Hence, it can be implemented and adapted to numerous
applications such as in residential, healthcare, office, and commercial buildings.
1.4 PROBLEM STATEMENT
The liquid desiccant waterfall (LDW) system eradicates moisture out of the air with
an extremely low energy consumption. It can also eliminate the necessity of
conventional air-conditioner in humid climate. There is a lack of research on the
applications and energy saving impacts of the combination between this waterfall
feature and the desiccant dehumidification technologies. Most previous studies
harnessed the desiccant dehumidification technology to solely the air conditioning
system applications.
1.5 RESEARCH AIM AND OBJECTIVES
The research aims to explore, using variable standards and design assumptions, the
liquid desiccant waterfall (LDW) system as a mean of space dehumidification, which
aids to eliminate the potential pitfalls associated with conventional an air conditioning
system.
The following are the objectives of the study:
5
1- To review related aspects and concepts of liquid desiccant waterfall
(LDW) system and recent advancement of the dehumidification
technologies applied.
2- To identify and analyze air ventilation requirements in order to accomplish
feasible thermal comfort conditions according to the air conditioning
standards related to the subject in applicable climates.
3- To apply the standard environmental parameters to a proposed case study
space in Malaysia in order to quantify the total amount of moisture to be
removed from the space.
4- To investigate the optimum properties of desiccant materials in order to
select the best desiccant solution to the LDW system.
5- To establish the selection and sizing of the proposed system components
to demonstrate maximum efficiency with respect to air ventilation
requirements.
6- To conduct a life cycle cost analysis of the LDW system with a
corresponding air conditioning system at the specific space.
1.6 RESEARCH STRUCTURE
The thesis outlines the premises and methodological approach adopted to explore the
proposed system as a dehumidification means under a humid and tropical climate.
This thesis is structured in seven main chapters in order to meet the problem
statement, objectives and the aims presented. The research structure of this research is
illustrated n Figure 1.2.
6
Figure 1.2 The research’s structure
The second chapter highlights related literature on desiccant dehumidification
technologies. This includes desiccant materials classification, their performance, the
applicable climate to adapt such technology and the potential of cost and energy
saving obtainable from applying the dehumidification technology. The literatures are
sources from both international and national. Relevant books, scientific papers,
journals and websites were also extensively reviewed to obtain an understanding of
this technology.
In Chapter Three, air ventilation and humidity removal requirements were
identified and presented as the foundation for developing the exploratory study. It will
also be determined and calculated, the total amount of moisture to be absorbed by the
Literature Review
Air Ventilation Requirements & Moisture Loads
Investigating of Desiccants
Developing LDWS Components
Checking Standards & Specification
Selecting & Sizing System Components
Quantifying Liquid Desiccant Amount
Life Cost Analysis
Results Optimization & Analysis
Comparison With Corresponding Air-Conditioning System
Data Collection, Review & Filtration
Exploratory Study
Conclusions & Recommendations
Moisture To Be Removed
7
LWD system in order to attain a feasible thermal comfort condition in the Malaysian
climate.
To achieve such goals, this thesis proposes a hypothetical case study of an open
plan office located in Kuala Lumpur. The office has an area of 320 m2. Secondly, the
building comfort set points specified by the Malaysian Standards (MS1525-2009)
along with the extreme and actual Malaysian weather data conditions were obtained.
Lastly, all the sources of moisture were identified in the proposed space.
Chapter Four presents a comparative study of the desiccant material
specification in order to select the optimum desiccant solution for the LDW system
based on the desired properties and the advance performance. Lithium chloride,
lithium bromide, calcium chloride and magnesium chloride were the four proposed
desiccant solutions.
Each candidate saline solution was investigated through a screening process
based on the eight properties required to be satisfied such as vapor pressure, corrosion
rate, safety and cost. Whereas, the importance of the properties to the LDW system
was assigned as the maximum weight factor and the relative weight was assigned as
the objective of merits for the properties that were investigated. The optimum
desiccant solution is then to be chosen as the one with the highest weight factor.
After obtaining the exact amount of moisture to be removed with the optimum
desiccant solution, the configuration and sizing of the system components were
addressed in Chapter Five. The sizing was a reflection of the system requirement to
operate efficiently in the proposed space. Each component was sized separately to
accomplish maximum clearance on its different parts, functions and roles in the LDW
system’s operation.
8
Chapter Six provides the development of life cycle cost analysis for the LDW
system’s different components, as well as clarifies the economical value this system
can offer in the long run. The engineering estimation method was taken as the most
appropriate approach for the cost analysis of the proposed system. This is because an
exact system specification does not exist in the current markets, and this study was
established based on design guidelines for the system’s potential implementation.
The pricing process of the system component was assigned based on a search
for the component’s supplying company in local and international markets. After the
capital cost of the proposed system was determined, a simple comparative life cycle
analysis was conducted for the LDW system with a corresponding air conditioning
system at the proposed open plan office. In addition, investment rate of return for the
system was presented to confirm the system value economically and environmentally,
as well as proving that it gives much more room for additional improvements,
depending on flexible adjustments possible for the components of the system.
Chapter Seven concludes the results optimization and analysis throughout the
thesis both theoretically and technically. It also provides the reader with a vision of
how this system can be improved, modified and implemented in order to achieve
maximum efficiency.
Furthermore, this chapter summarizes all results from a different set of
calculations which lead to the presenting of the LDW system to ensure the flexibility,
simplicity and user-friendliness of the system. Alongside the above, it will show a
great prospect for implementing the proposed system in residential, commercial and
health care buildings.
9
CHAPTER TWO
LITERATURE REVIEW
2.1 INTRODUCTION
This chapter outlines a background literature on the development of desiccant
dehumidification technologies throughout the last two decades including a study on
the suitable criteria for the selection of the most proper desiccant for the LDW system.
Furthermore, it reviews various studies on different types of desiccant materials,
determining their advantages and disadvantages and how they are applied in the
dehumidification technology industry. It also reviews their developments and
performances under different conditions of temperature and concentration levels.
This also includes current case studies on innovative feature of the desiccant
waterfall dehumidification established by the team from University of Maryland
(2011), one of the most attractive ideas that leads to the concept of the LDW system’s
design development.
2.2 DESICCANT MATERIALS IN PERSPECTIVE
Since the early 1920’s, the notion of water absorption and adsorption was initially
explored as dehumidification’s means of cooling, focusing on their applications in
residential, commercial and industrial buildings (Anon, 1996). With respect to
advanced technologies, the interest of desiccant dehumidification was renewed in the
early 1990’s, having the solution perceived as an alternative to eliminate new
challenges associated with the conventional air cooling and heating system (Jurinak,
10
Mitchell and Beckman, 1984). Such challenges include the significant depletion of
energy resources along with escalating energy demands.
Desiccants are either natural or synthetic substances with high affinity for
water vapor within the air due to the differences in vapor pressure of water between
the exposed surface of the desiccant and the surrounding air. The capability of
desiccant materials to capture moisture out of the air is termed as Sorption, while the
process of transferring and extracting moisture from the desiccants to the surrounding
environment is called Desorption (ASHRAE, 2005).
Vapor pressure is the crucial driver for transferring moisture from desiccant
materials to the atmosphere and vice versa. For instance, desiccants with lower vapor
pressure than that of the surrounding air will absorb moisture from the latter. In
contrast, substances with higher vapor pressure will always expel moisture out to the
ambient air. Figure 2.1 represents the diagram of vapor pressure role in a desiccant
cycle.
Figure 2.1 Diagrammatic representations of the vapor pressure role in desiccant cycle (Lewis and Harriman, 2002)
