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Solar-Driven Humidification Dehumidification
Desalination for Potable Use in Haiti by Shannon Omari Liburd
Bachelor of Science in Aerospace Engineering
MIT, 2008
Submitted to the Engineering Systems Division
in Partial Fulfillment of the Requirements for the Degree of
Solar-Driven Humidification DehumidificationDesalination for Potable Use in Haiti
by Shannon O. Liburd
Submitted to the Engineering Systems Division
on May 7, 2010 in Partial Fulfillment of the
Requirements for the Degree of Master of Science in Technology and Policy
Abstract
Worldwide water scarcity, especially in the developing world, provides the impe-tus for utilizing inexpensive desalination technologies on a wider scale to contribute tofreshwater supply. Small-scale desalination technologies, such as solar-driven humidi-fication dehumidification (HDH), are needed to help provide clean drinking water topeople living in coastal areas. This thesis explores the question of whether the fills usedin the humidifier of the HDH system, which allow for increased contact area betweenthe water and air streams, can be made of locally available materials such as charcoal,bamboo, and lou!a found in Haiti. It also addresses how the institutional, economic,social and technological barriers to successful deployment of renewable energy (RE)desalination technologies such as HDH can be overcome.
Charcoal, lou!a and bamboo custom fills were experimentally tested in a benchtopcooling tower to determine their suitability for use in the humidifier of a HDH system.The fills’ transfer characteristics and pressure drop data were obtained and analyzedto determine the overall fill performance in terms of fan power consumption. Thelower the fan power consumption required by the fill, the better the fill performance.The performances of the custom fills were compared with each other and with twocommercial thin film fills. The lou!a fill performed the best among the custom fills,having power consumption 2.9 and 4.4 times less than the charcoal and bamboo fills,respectively. The lou!a fill is therefore recommended for use in the humidifier.
To help overcome the barriers facing RE desalination policy and implementation,several strategies are recommended: a decentralized regulatory system for water sup-ply, public-private financial arrangements and supporting policies; market analysis ofprospective RE desalination systems, targeted R&D to make improved system compo-nents and a community platform for the various stakeholders to work together. Mostimportantly, the general public must be engaged throughout the entire process to fostertransparency, community trust and public acceptance of the desalination technology.
Thesis Supervisor: John H. Lienhard VTitle: Collins Professor of Mechanical EngineeringProject Supervisor: Amy B. SmithTitle: Senior Lecturer of Mechanical Engineering
vices not depicted) [24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2113 Schematic diagram of electrodialysis desalination process [24] . . . . . . . . . 2314 Characteristics of the two main thermal desalination technologies and the two
main mechanical desalination technology options [30] . . . . . . . . . . . . . 2515 Possible combinations of renewable energy systems with desalination tech-
driven plants [50] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7712 Comparison of HDH process (with waste heat) with other processes [50] . . . 7813 Cost comparison for small-scale desalination methods [52] . . . . . . . . . . 7914 Four solutions used to remineralize desalinated water [62] . . . . . . . . . . 9115 Water remineralization process comparison [62] . . . . . . . . . . . . . . . . 9116 Concentrate characteristics for various desalination technologies [63] . . . . 94
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1 Introduction
1.1 Project Motivation
Water scarcity is a serious problem that will increase in the coming decades and dispropor-
tionately impact those in developing countries. While functional desalination technologies
exist, currently there are no cost-e!ective, high e"ciency desalination systems for people
living on less than $2/day. Solar-driven humidification dehumidification (HDH) desalination
has the potential to be an appropriate technology for this market. It has the flexibility to
provide decentralized clean water, it uses a renewable energy source, it has moderate installa-
tion and operating costs and it does not require skilled operators to maintain it. The purpose
of this study is to examine the feasibility of the implementation of small-scale (100 m3/day
<), solar-driven HDH desalination in the developing world, particularly in conjunction with
an ongoing project in Pestel, Haiti. A technical, policy, environmental and socio-economic
assessment of the application of such technology will be made in the context of impoverished,
remote and potentially o!-grid areas.
1.2 The Central QuestionsThe central questions that will be examined in this thesis are:
1. Are small-scale (100 m3/day <) solar-driven HDH desalination systems made from low-cost, locally available materials in Pestel, Haiti technically and economically feasible?
2. What mechanisms are needed to sustainably implement small-scale remote HDH de-salination systems in Pestel, Haiti?
3. What are the barriers with respect to small-scale, renewable energy desalination im-plementation in coastal areas and how can they be addressed for successful technologydeployment?
These questions will be addressed through technical experimentation and thorough literature
review.
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1.3 Thesis Outline
The thesis is divided into five parts that address di!erent components of the central ques-
tions. Section two gives background on worldwide water scarcity, discusses how desalination
plays an important role in reducing water scarcity and o!ers an overview of di!erent de-
salination technologies with an emphasis on HDH desalination. Section three discusses the
potential for HDH application in developing countries by using local materials to reduce
the cost of system components. It provides an overview of cooling tower theory, which is
important for understanding how the humidifier in the HDH system works. It also provides
the results of the experimental investigation into the use of di!erent locally available fill
materials in Haiti for use in the system’s humidifier. Section four examines the technical,
economic, social, environmental and policy issues relevant to the successful implementation
of HDH desalination in developing countries. It also outlines recommendations on how to
overcome the existing barriers. Section five discusses the roles that stakeholders, the mar-
ket, research and development (R&D) and the public play concerning seawater desalination
policy and implementation. The summary, conclusion and recommendations for future work
are provided in section six.
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2 Desalination Background
2.1 Worldwide Water Scarcity
Water scarcity means that the annual water supply of a region is below 1,000 m3/person.
Water stress is defined as between 1,000 m3 and 1,700 m3/person [1]. 1,000 m3 is the
annual amount of water deemed necessary to satisfy basic human needs [2]. Figure 1 is an
indicator map of worldwide water scarcity in 2003. According to the 1997 Population Action
International estimate, in 2050 the world’s relative freshwater su"ciency will be 58% while
water stress and scarcity will account for 24% and 18% respectively [3]. Figure 2 illustrates
global water stress in 1995 and in 2025.
People use four thousand cubic kilometers of water each year around the world, for domes-
tic, agricultural and other industrial purposes. This water use does not include consumptive
uses such as energy generation, mining and recreation [2]. However, there is great disparity
between water consumption in developed and developing regions. For example, in 2004 the
average water use per capita in the U.S. (2,026 m3/p/yr) was approximately three times
higher than that in India (641 m3/p/yr) [6]. Figure 3 shows the great disparity in average
water use per person per day in 2006 between developed and developing countries. From
Figure 3 it appears that the average water use per person per day in the U.S. is approxi-
mately 30 times greater than that of a person in Haiti. In Haiti in the year 2000 the total
freshwater withdrawal was 0.99 km3/yr with the industrial, domestic and agricultural sectors
accounting for 1%, 5% and 94% respectively. (1 km3 of water is 1 billion m3 or 264 billion
gallons of water.) The global per capita freshwater withdrawal in the year 2000 was 116
m3/yr (30,644 gal/yr) [8]. World water demand, approximately 4,200 km3 in 2000, has more
than tripled over the past half century and is estimated to be about 30% of the world’s total
accessible fresh water supply. That fraction may reach 70% by 2025 [2].
In addition to the overall scarcity of freshwater in the world, there is the added problem
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Figure 1: Global water stress indicator map [4]
Figure 2: Worldwide freshwater stress in 1995 and 2025 [5]
11
Figure 3: Daily per capita water use by country [7]
of the lack of clean drinking-water. UNICEF/WHO estimate that globally 884 million people
do not use improved sources of drinking-water, almost all of them in developing regions [9].
Sub-Saharan Africa accounts for a third of that number with only 60% of the population
using improved sources of drinking-water [9]. Improved sources of drinking water include a
household connection, a public standpipe, a borehole, a protected spring, a protected dug
well and rainwater [10]. Figure 4 shows the worldwide use of improved drinking water in
2008.
Population growth and climate change will bring new water supply challenges. By 2050
the world population is projected to grow to at least 9.4 billion and the great majority of the
people will live in developing countries [2]. Climate change will cause places that were once
habitable to be uninhabitable. This phenomenon will result in mass migration of refugees
to neighboring locations, placing strains on the available water supply and causing conflict.
It is estimated that more than 2.7 billion people will face severe water shortages by the year
2025 if the world continues consuming water at the same rate per capita, and if the real
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Figure 4: Worldwide use of improved drinking-water sources in 2008 [9]
population growth fits the forecasted trend [11].
2.1.1 Water Issues in Haiti
More than 60% percent of Haiti’s total population of approximately nine million people does
not have access to clean water [12]. In the Western Hemisphere the country is ranked last on
the International Water Poverty Index. The country’s continued political instability and the
7.0 magnitude earthquake that struck 25 km west of Port-Au-Prince, the capital of Haiti, on
January 12, 2010 have only worsened the water situation [13]. An estimated three million
people were a!ected by the earthquake, and Haiti’s main infrastructure was demolished [14].
Prime Minister Jean-Max Bellerive estimated that 250,000 residences and 30,000 commercial
buildings had collapsed or were severely damaged [15]. Before the earthquake nearly a third
of the population resided in urban areas [12]. Since the earthquake, around 600,000 people
have fled the capital for cities like Cap Haitien, in the north, and Hinche, in the central
plateau. The population of Gonaïves, a port city on the west coast roughly midway between
the country’s two major fault lines, has swollen to 300,000 from 200,000 in less than three
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months [16]. There has also been reverse migration from hard hit cities and towns to rural
areas. This shift is putting further pressure on rural households, a!ecting the socio-economic
stability in areas already grappling with meager resources. Haiti’s Ministry of Agriculture
estimates the number of people leaving cities for rural areas could reach 1.5 million [17].
Even when a public water system is available, getting water is a daily struggle. Many
Haitians have to travel long distances to collect water for drinking, washing, cooking, clean-
ing, and bathing and it still has to be purified prior to drinking. In addition, potable water
is not free. For the 80% of Haitians who live in poverty, the cost of clean drinking water
can be a significant challenge [19]. This fact may force them to consume water from unclean
sources. See Figure 5.
Depletion and contamination of resources supplying water is a major issue. Haiti’s
aquifers are being depleted. Aquifers are replenished by the absorption of rainwater. As a
result of soil erosion due to deforestation, there is limited topsoil to absorb su"cient amounts
of rainwater and much of the rainwater runs o! into the sea. The aquifer in the capital of
Haiti, the Port-au-Prince aquifer, currently is so low that a lack of pressure has begun to
allow saltwater to seep in. In four to nine years Port-au-Prince will have to tap into another
aquifer farther away from the city [12]. Additionally, nearly every water source in Haiti is
contaminated by human waste: there are no public sewage treatment or disposal systems
anywhere in the country [20]. The lack of clean drinking water contributes to the highest in-
fant and child mortality rate in the Western Hemisphere. In developing countries like Haiti,
up to 90% of diarrheal illness, a leading cause of death, can be attributed to unsafe water
and poor sanitation [19]. Therefore, there is a clear need for decentralized, cost-e!ective
water technologies for providing clean drinking-water. Haiti is the western one-third of the
island Hispaniola and is surrounded by the Caribbean Sea and the North Atlantic Ocean.
See Figure 6. It has a coastline of 1,771 km [8]. Thus, appropriate desalination technologies
can be used to help alleviate water stress in Haiti.
14
Figure 5: Haitian girl collecting water from an open water source [18]
Figure 6: Map of Haiti [8]
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2.2 Why Desalination?
Three-quarters of the earth is covered by water. The oceans represent the earth’s largest
water reservoir, accounting for 97.5%. Only 2.5% of the earth’s water is freshwater and less
than 1% of the freshwater is available for use since the rest is frozen in ice caps and glaciers
[21]. Figure 7 illustrates the world’s water supply graphically.
The abundance of saltwater presents great potential for seawater desalination to help
increase the world’s potable freshwater supply. Worldwide, only 1% of drinking water is
produced by desalination, supplied by more than 12,500 plants in more than 120 countries.
Considering that almost one quarter of the world’s population lives less than 25 km from
the coast, seawater could become one of the main sources of freshwater in the near future.
Additionally, conventional seawater desalination technologies produce relatively inexpensive
freshwater that costs between $0.5/m3-$1.0/m3. In terms of the geographical breakdown of
the desalination market, the regions of the Middle East clearly dominate the demand with
over 50% of the market share, followed by Asia-Pacific, America and Europe, which each
Nature uses solar energy to desalinate ocean water through the water cycle, as shown in
Figure 18. In the water cycle, the sun’s solar irradiation evaporates a portion of the ocean’s
surface water and the water vapor rises humidifying the surrounding air which acts as a
carrier gas. The humidified air rises, convects and condenses forming clouds. The clouds
then “dehumidify” in the form of rain. The manufactured version of this natural process is
known as the humidification dehumidification (HDH) desalination cycle.
Figure 18: Water cycle [26]
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The predecessor of the HDH cycle is the simple solar still. The solar still is similar to a
greenhouse system in the manner in which it captures the solar energy. The incident solar
radiation is transmitted through the glass cover or similar transparent material having the
property of transmitting incident short-wave solar radiation and it is absorbed as heat by
a black surface in contact with the salt water in the basin of the still. Some of the water
evaporates and the water vapor condenses on the surface of the solar still, which is at a lower
temperature because it is in contact with the ambient air, and is collected for use. See Figure
19. Well-designed units can produce 2.5 - 4 L/m2 per day [29]. Solar stills have the advantage
of ease of construction and maintenance. However, they have several disadvantages. The
most prohibitive drawback of a solar still is low e"ciency. For a solar still the GOR is less
than 0.5. Thus, large areas of land are required to produce relatively small amounts of water.
Another disadvantage of the solar still is that the various functional processes (solar ab-
sorption, evaporation, condensation and heat recovery) all occur within a single component,
reducing its thermal e"ciency. A major improvement in solar still design is possible through
the multiple use of the latent heat of condensation in the still [34]. Some multi-e!ect still
designs recover and reuse the heat of condensation, increasing the still e"ciency but the
overall performance is still relatively low [26]. By separating these functions into distinct
components, thermal ine"ciencies may be reduced and overall performance can be increased.
The HDH process is the most promising recent development in solar desalination. The
Figure 19: Solar still [26]
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HDH process is based on the fact that air can be mixed with large quantities of water
vapor. The vapor carrying capability of air increases with temperature. The HDH technique
is especially suited for seawater desalination when the demand for water is decentralized.
Several advantages of this technique include flexibility in capacity, moderate installation
and operating costs, the possibility of using low-grade thermal energy (solar, geothermal,
recovered energy or cogeneration) and simplicity [34]. The process is easy to operate and
it does not require skilled operators. Another advantage is that the recovery ratio, the
amount of water produced per kilogram (kg) of seawater feed, tends to be lower for HDH
than conventional systems. This feature reduces the need for brine pre-treatment or brine
disposal processes. Some pre-treatment or bleeding of the water leaving the humidifier in
closed water cycles is needed, however, to prevent accumulation of salt and fouling of the
heat exchangers in the HDH unit. The HDH process consists of three subsystems: (a) the
air and/or water heater, which can use various sources of heat like solar thermal, (b) the
humidifier or the evaporator and (c) the dehumidifier or condenser [26]. In this process, air
is heated and humidified by hot water received from a solar collector. It is then dehumidified
in a large surface condenser using relatively cold saline feed. Most of the latent heat of
condensation is used for preheating the feed. The simplest form of HDH is illustrated in
Figure 20.
2.3.5 Types of HDH Systems
HDH systems are classified into three broad categories. One category is based on the source
of energy used, such as renewable energy. For example, solar thermal HDH or hybrid HDH.
The second classification is based on the cycle configuration. There are two main types of
HDH cycles: closed-water, open-air (CWOA) cycle and closed-air, open-water (CAOW). An
open-water, open-air cycle is also possible but since it has a lower thermal e"ciency than the
other two cycles, it will not be discussed. The air in these systems is circulated by natural
or forced convection (fans). Figure 21 illustrates these two types of cycles.
34
Figure 20: HDH desalination (air heated, open cycle) [26]
In a CWOA cycle (Figure 22) the closed-water circulation is in contact with a continuous
flow of cold outside air in the evaporation chamber. The air is heated and loaded with
moisture as it passes upwards through the falling hot water in the evaporation chamber.
After passing through a condenser cooled with cold seawater, the partially dehumidified
air leaves the unit, while the condensate (distillate) is collected. The water is recycled or
recirculated. Incoming cold air provides a cooling source for the circulating water before it
re-enters the condenser. The productivity of units working on this principle is high, but the
power required for air circulation is also very high [34]. One disadvantage of the CWOA
cycle is that when the humidification process does not cool the water su"ciently, the water
temperature to the inlet of the condenser is higher, resulting in lower air dehumidification
and lower water production [26]. However, in the case where e"cient humidifiers are used,
cooling the water as low as possible up to the limit of the ambient wet-bulb temperature,
the closed water system yields more water than the open-water system.
35
Figure 21: HDH cycles [26]
In a CAOW cycle (Figure 23) the humidifier is irrigated with hot water and the air stream
is heated and humidified using the energy from the hot water stream. The humidified air is
cooled in a heat exchanger using seawater as the coolant. The seawater gets preheated in
the process and is further heated by a heat source before it returns to the humidifier. The
dehumidified air stream from the condenser is then circulated back to the humidifier. Exper-
imental evidence has shown that for the closed-air, water-heated cycle, natural circulation
of air yields better e"ciency than forced circulation of air [26].
36
Figure 22: HDH unit with closed water cycle/open-air [34]
It is of critical importance to understand the relative technical advantages of each of
these cycles and to choose the one that best meets the user specifications in terms of thermal
e"ciency and water production cost.
The third classification of HDH system is based on whether the air or the water is heated.
The performance of the system heavily depends on whether the air or water is heated. There
is extensive knowledge of solar water heating devices but relatively little work has been done
on air heating solar collectors. Typically, air-heated systems have higher energy consumption
than water-heated systems because in the air-heated cycle the air heats up the water in the
humidifier and this energy is not subsequently recovered from the water [26]. On the other
hand, in the water-heated cycle, the water stream is cooled in the humidifier and the energy
is transferred or recovered in the air stream. Enhanced latent heat recovery is needed to
minimize the energy consumption and the resulting cost of these cycles. Figure 21 shows the
di!erent HDH cycle combinations discussed above.
37
Figure 23: HDH unit with closed-air/open-water cycle [26]
2.3.6 Possible Improvements to the HDH Cycle
A couple of methods can be used to improve the solar HDH desalination technology. These
methods include sub-atmospheric pressure operations through the use of a vacuum and using
thermal storage for sustained system operation even when the solar or RES is unavailable.
Operating the HDH unit at pressures below atmospheric increases the humidity ratio, re-
sulting in an increase in water production [26]. Adding thermal energy storage to the HDH
system can result in an improvement of the overall system e"ciency by enabling 24-hour
operation of the unit [35]. Installing thermal storage equipment such as hot water tanks
is one way to improve the system e"ciency. A major factor prompting 24-hour per day
operation of these HDH units is the realization that the major capital cost of these units is
due to the humidifier and condenser [34]. Continuous (24 hour/day) operation and distillate
production of these HDH units helps reduce the cost of water, making HDH an economically
feasible option relative to small-scale (5-100 m3/day) RO desalination systems.
38
3 Application of Solar HDH Desalination in the Devel-oping World
3.1 Overview
Solar-driven HDH has potential to help meet the water needs of people in remote, coastal
areas without su"cient access to freshwater. Concerning the application of solar HDH in the
developing world, the challenge for the near future seems to be the development of small,
autonomous, modular, flexible and reliable units, o!ering O&M at reasonable cost, in order
to serve the segment of isolated users [28]. Although more research is needed on HDH and
its system costs, once the technology is further developed and proven on a larger scale, it
can play a significant role in increasing freshwater supply in coastal areas. Sections 3.2 and
3.3 discuss cooling towers and cooling tower fills respectively.
3.2 Cooling Tower Principles
A cooling tower is a heat rejection device, which rejects waste heat to the atmosphere through
the cooling of a water stream to a lower temperature [36]. The type of heat rejection
in a cooling tower is termed "evaporative" in that water is evaporated into a moving air
stream with the objective of cooling the water stream [37]. The heat from the water stream
transferred to the air stream raises the air’s temperature and its relative humidity (usually
to 100%), and this air is discharged to the atmosphere. Evaporative heat rejection devices
such as cooling towers are commonly used to provide significantly lower water temperatures
than are achievable with non-direct contact heat rejection devices like conventional heat
exchangers [36].
Common applications for cooling towers are providing cooled water for refrigeration, air-
conditioning, industrial processes and electric power generation. The smallest cooling towers
are designed to handle water streams of only a few gallons of water per minute, while the
largest cool hundreds of thousands of gallons per minute for large power plants [36].
39
There are two principal types of cooling towers: counter-flow and cross-flow. Each has
the same fundamental components, but the configuration of these components di!ers to
accommodate the di!erence in the air stream direction. In a counter-flow cooling tower,
Figure 24, air travels upward through the fill or tube bundles, opposite to the downward
motion of the hot water sprayed from above [36]. Heat and mass are transferred and the
water enthalpy decreases while that of air increases [38].
In a cross-flow cooling tower, Figure 25, air enters through the side of the fill and leaves
from the top as the water moves downward [36]. Crossflow towers have a smaller footprint
than counter-flow towers of the same capacity. This feature can be an advantage for sites
where space is limited [39].
Counter-flow towers are the more common tower type and have the advantage of lower
pumping costs (because the water is generally pumped to a lower elevation than in cross-
flow towers of similar size) [39]. Thermodynamically, the counter-flow arrangement is more
e"cient, since the air-water enthalpy potential di!erence is held approximately constant
throughout the process, resulting in a higher thermodynamic e"ciency. Ultimately, the
economic choice between a counter-flow and cross-flow cooling tower is determined by the
e!ectiveness of the fill, design conditions and the costs of tower manufacture [41].
Cooling towers are also characterized by the means by which air is moved. Mechanical-
draft towers rely on power-driven fans to draw or force the air through the tower [36]. The
two types of mechanical-draft towers are forced-draft and induced-draft. In the induced-draft
tower, the fan is located internally, at the top of the tower and air is drawn or induced from
the bottom of the tower. In the forced-draft tower, the fan is mounted at the base and air is
forced in at the bottom and discharged at low velocity through the top. This arrangement
has the advantage of locating the fan and drive outside the tower. However, because of the
low exit-air velocity, the forced-draft tower is often subjected to excessive recirculation of the
humid exhaust vapors back into the air intake, reducing tower performance. The induced-
draft tower is better than the forced-draft tower because the induced draft tower eliminates
40
Figure 24: Counter-flow cooling tower [40]
Figure 25: Cross-flow cooling tower [40]
41
the poor air distribution that occurs from the high velocity fan discharge into the base of
the tower. On the other hand, the induced-draft tower has the problem of the hot, humid
exit air corroding the fan. The induced-draft tower is the most common type used in the
United States [41].
Natural-draft cooling towers use the buoyancy of the exhaust air rising in a tall chimney
to provide the draft. Natural-draft towers can be either counter-flow or cross-flow types and
operate using those same principles. The heat removed from the water and transferred to
the air causes the warm, moist air, leaving the top of the fill to rise naturally (induces a
draft), creating a continual air stream upward through the tower [39]. Since the air inlet
temperature is usually lower than that of the water inlet temperature, the water is cooled
both by evaporation and sensible heat loss or heat that is removed without phase change
[37]. Natural-draft towers have extremely high construction costs but low operating cost,
since there is no mechanical equipment needed to move the air. This high initial cost makes
them practical only for applications having very large water volumes, such as large power
plants [39]. A fan-assisted natural-draft cooling tower employs mechanical draft to augment
the buoyancy e!ect [36].
The set of experiments reported in this thesis use a counter-flow cooling tower and so
counter-flow cooling towers will be the focus of the remainder of this section. As mentioned
above, the counter-flow tower cools water by spraying hot water from above into an air
stream from below. The heat-transfer process involves (1) latent heat transfer owing to
vaporization of a small portion of the water and (2) sensible heat transfer due to the di!erence
in temperature of water and air. Approximately 80% of the heat transfer in a standard
cooling tower is due to latent heat and 20 percent to sensible heat [41].
An indication of the moisture of the air is its wet-bulb temperature. Practically, the cold
water or exit water temperature approaches but does not equal the ambient air wet-bulb
temperature in a cooling tower. This is because it is impossible to contact all the water with
fresh air as the water drops through the wetted fill surface to the basin. The approach of the
42
cooling tower is the di!erence between the cold water temperature and the ambient or inlet
wet-bulb temperature. In practice, cooling towers are seldom designed for approaches less
than 2.8°C. Important cooling tower performance factors include air-to-water contact time
or water retention time, amount of fill surface, fill height, air and water mass flow rates and
breakup of water into droplets [41].
In order to increase the cooling rate, the interface area between air and water is increased
by providing packed beds or ba#es which are also known as fills. Cooling tower fills play
an important role in increasing the e!ective surface contact area between air and water to
promote better heat and mass transfer. Fills are discussed in greater detail in section 3.3.
3.3 Fills
There are two general categories of cooling tower fills: structured or systematically-arranged
and random or dumped. Splash fills and film fills fall under the category of structured
packings. Random packings are elements with a given form dumped randomly in the column
over its supporting grid. The advantages of random packings are easy production and easy
dumping. Their main disadvantages are poor distribution of the phases over the cross-
section of the apparatus and often higher pressure drop relative to structured packings [42].
Structured packings are packings with regular shape and are used when it is important to
have a low gas-flow pressure drop. They are usually crimped layers of corrugated sheets or
wire mesh and sections of these packings are stacked in the column [41].
The most commonly used cooling tower fills are film fills. They form a thin layer of
water over the fill surface and drive cooling performance by having a large surface area of
water film in contact with the cooling tower air. This arrangement reduces the problem of
carryover of water droplets into the atmosphere and allows higher air velocities to be used
[43]. Film fills also typically have a lower air-side pressure drop as compared to splash fills,
where a large water surface area is achieved by forming droplets [44]. However, water quality
43
must be good for film fills to be used; otherwise, fill clogging and fouling will result.
Splash fills typically are used where water quality is poor and where fill fouling occurs.
Splash fills work by breaking up the hot circulating water into small droplets that create
an increased surface area, which allows for both convective and evaporative cooling. Splash
fill designs can be grouped into two categories: profile designs and grid packs [44]. Grids
are systematically arranged packings with an open-lattice structure [41]. Typical splash fills
have about half the thermal performance of film fills. The lower thermal performance is due
to the splash fill’s inability to equal the surface area of film fills coupled with the higher
air-side pressure drop of splash fills [44].
The objective of any packing is to maximize e"ciency for a given capacity, at an economic
cost. To achieve these goals, packings are shaped to maximize the specific surface area (
i.e. surface area/unit volume), spread the surface area uniformly, maximize the porosity per
unit column volume, minimize friction and pressure drop, and minimize cost. An additional
packing functional requirement for the particular experiment in this thesis is ease of packing
construction from locally available materials in Haiti. A tradeo! exists when determining
the ideal packing size because maximizing packing e"ciency (specific area) and maximizing
capacity (void fraction) are in direct conflict [41]. Thus, the selection of the dimensions
of the packing can be made only through an optimization procedure. The geometrical
characteristics that must be measured for the packing are the packing nominal size (Dp), the
specific surface area (a) in m2/m3 and the void fraction (E) in m3/m3 [42].
The polyvinyl chloride (PVC) CF-1200 and CF-1900 Brentwood film fills and lou!a,
charcoal and bamboo custom fills that were tested using the benchtop cooling tower are
shown in Figures 26, 27, 28, 29 and 30 respectively.
The void fraction of the CF-1200 and CF-1900 fills is approximately 97%. The specific
surface area of the CF-1200 and CF-1900 fills is 226 m2/m3 and 157.5 m2/m3 respectively.
The individual lou!a and bamboo pieces both had heights of 0.152 m. The approximate
diameter of the lou!a and bamboo pieces was 0.07 m and 0.013 m respectively. The car-
44
Figure 26: CF-1200 fill
Figure 27: CF-1900 fill
45
Figure 28: Lou!a fill
Figure 29: Charcoal fill
46
Figure 30: Bamboo fill
bonized corn cob pieces had an upper limit of length and an upper limit of diameter of 0.068
m and 0.011 m respectively.
3.4 Cooling Tower Theory
Merkel [45] developed a method for the performance evaluation of cooling towers in the 1920s.
The Merkel method of the cooling tower heat transfer process is the most generally accepted
and its employment is recommended by international standards [46]. Merkel analysis is based
on enthalpy potential di!erence. Each particle of water is assumed to be surrounded by a
film of air, and the enthalpy di!erence between the film and the surrounding air provides the
driving force for the cooling process [41]. Merkel analysis relies on several critical assumptions
to simplify the solution of the complex process of heat and mass transfer in wet-cooling
towers: namely, that the Lewis number (Lef ) is equal to unity, the exiting air is saturated
and the reduction of the water flow rate due to evaporation is neglected in the energy balance
[46]. Lewis number is a dimensionless number defined as the ratio of thermal di!usivity to
mass di!usivity. It is used to characterize fluid flows where there is simultaneous heat and
47
mass transfer by convection. Kröger [43] gives a detailed derivation from first principles of
what is referred to as Merkel’s number for a counter-flow configuration. Merkel’s equation
is given by Equation 2:
Me =KaV
L=
Twiˆ
Two
cpwdTw
(h! ! h)(2)
where K= mass transfer coe"cient, kg/m2s; a=surface area per unit volume m"1; V =active
cooling volume, m3; h!= enthalpy of saturated air at bulk water temperature, J/kg; h=
enthalpy of air-water mixture at wet-bulb temperature, J/kg; and Twi and Two are the
entering and leaving water temperatures respectively, °C; L= water flow rate, kg/s; and
Me is the Merkel number, or transfer characteristic according to the Merkel method. The
right-hand side of Equation 2 is expressed entirely in terms of air and water properties
and is independent of tower dimensions [41]. It can be solved if the water inlet and outlet
temperatures, air inlet dry bulb and wet bulb temperatures, air outlet dry and wet bulb
temperatures, water mass flow rate, and air mass flow rate are known [46]. Equation 2 was
solved using the 4-point Chebyshev numerical integration method as shown in Equation 3:
KaV
L=
Twiˆ
Two
cpwdTw
(h! ! h)! Twi ! Two
4(
1
!h1+
1
!h2+
1
!h3+
1
!h4) (3)
where!h1= value of (h! ! h) at Two + 0.1(Twi ! Two)!h2= value of (h! ! h) at Two + 0.4(Twi ! Two)!h3= value of (h! ! h) at Twi ! 0.4(Twi ! Two)!h4= value of (h! ! h) at Twi ! 0.1(Twi ! Two) [41].
It is important to note that if the transfer characteristic of a wet-cooling tower fill is
determined by a particular method, like the Merkel method, the same method must be used
in the subsequent wet-cooling tower design calculations [46].
Figure 31 provides a graphical representation of the water and air relationships and
the driving potential which exist in a wet, counter-flow cooling tower process. The water
operating line or enthalpy of saturated air at a given water temperature is shown by line AB
48
Figure 31: Cooling tower process heat balance [41]
and is fixed by the inlet and outlet tower water temperatures.
The air operating line or enthalpy of air stream begins at C, vertically below B and at
a point having an enthalpy corresponding to that of the entering wet bulb temperature.
Line BC represents the initial driving force (h! ! h). The coordinates refer directly to the
temperature and enthalpy of any point on the water operating line but refer directly only
to the enthalpy of a point on the air operating line. The liquid-gas mass flow rate ratio
L/G is the slope of the operating line. The air leaving the tower is represented by point D.
The cooling range is the projected length of line CD on the temperature scale and is the
di!erence between the hot-water temperature entering the tower and cold-water temperature
leaving the tower. The cooling tower approach is shown on the diagram as the di!erence
between the cold-water temperature and the ambient wet bulb temperature. The integral in
Equation 2 is represented by the area ABCD in Figure 31 [41]. This value is known as the
The objective of the experiments was to determine the packing performance characteristics,
heat transfer and pressure drop of several packings made using local materials (bamboo,
carbonized corn cobs or charcoal and lou!a) available in Haiti. The performance of the
fills was assessed using the Merkel method of analysis and the following correlations were
determined:
• The fill transfer characteristic (i.e. Me) correlations as a function of water-air massflow ratio (L/G)
• The fill pressure drop empirical correlations as a function of air velocity and watermass flux (L/A).
3.5.2 Experimental Setup
Apparatus Overview
Experiments were carried out to determine the thermal performance characteristics of
custom-made packings under steady state conditions. The apparatus can be considered in
terms of the column, water circuit, air circuit and the measuring devices. The air circuit
consists of the fan, the air distribution chamber and the orifice. The water circuit consists of
the water distribution system, the droplet arrester or drift eliminator and the basin. Refer
to Figure 32 for the schematic of the benchtop cooling tower. The cooling tower column
dimensions are 150 mm x 150 mm x 600 mm high. To facilitate observation of the bed, the
column was constructed with transparent PVC.
For Figure 32 the temperature measurement descriptions are given in Table 2.
A picture of the apparatus is provided in Figure 33.
50
Figure 32: HC891 benchtop forced-draft cooling tower unit
Table 2: Benchtop cooling tower temperature measurementsTemperature Description
Tai Inlet air dry bulb temperatureTwbi Inlet air wet bulb temperatureTao Exit air dry bulb temperatureTwbo Exit air wet bulb temperatureTwi Inlet water temperatureTwo Exit water temperature
51
Refer to Appendix A for the experimental apparatus limitations, specifications and the
desired experimental parameter ranges.
Water Circuit
The water circuit is an open water loop, taking warm water from the sink, to the water
flow meter or control valve, to the column cap where its temperature is measured before it
is sprayed over the packing through the water nozzle. The water is uniformly distributed
over the top of the packing and as it spreads over the packing, a large thin film of water is
exposed to the air stream. During its downward passage through the packing, the water is
cooled, largely by the evaporation of a small portion of the total flow. The cooled water falls
from beneath the packing into the basin, from where it flows past a thermocouple and into
the load tank, where it exits to the drain. A Dwyer rotameter is used to measure the water
flow rate.
Air Circuit
Air from the atmosphere enters the fan at a rate that is controlled by the intake damper
setting. The ambient air conditions have a significant e!ect on the cooling tower performance.
The fan forces the air into the distribution chamber and the air passes wet and dry bulb
thermocouples before it enters the packed column. As the air stream flows through the fill,
its moisture content increases and the water is cooled. On leaving the top of the column,
the air passes through the drift eliminator, which traps most of the entrained droplets and
returns them to the fill. The air is then discharged to the atmosphere via the air-measuring
orifice at the tower outlet. The air passes wet and dry bulb thermocouples before it exits the
tower. The air mass flow rate (G) is measured by a pressure di!erential across the air exit
orifice, connected to an inclined manometer. The air flow rate may be calculated according
to Equation (4), where Y is a constant equal to 0.00438 m2 and !G is the density of moist
air (kg moist air/m3):
G = Y!
!G!Porifice. (4)
Measurements
52
Figure 33: Actual benchtop cooling tower apparatus
The quantities measured in the experiments are given in Table 3. The outlet orifice
pressure drop is measured in order to calculate the air mass flow rate, the pressure drop
across the fill is measured using an inclined manometer and the water flow rate is based
on the Dwyer rotameter reading. The air dry and wet bulb temperatures at the fan inlet
(base of column) and outlet (exit from column), in addition to the temperatures of the water
at inlet and outlet, are measured with a digital temperature indicator with a thermocouple
selector switch.
Instrumentation
Temperatures: Two pairs of wet and dry-bulb Omega type “T” thermocouples for air
entry and exit from the tower respectively. Two type “T” Omega thermocouples for water
entry and exit to tower. Thermocouples have an ambient reference temperature connected
to the interface directly. Refer to Figure 32 for thermocouple locations.
Air flow measurement: Sharp-edged orifice with pressure tapping at tower outlet con-
nected to an inclined manometer to determine the orifice pressure drop. Refer to Figure 32
for the location of the connection of the orifice di!erential pressure tap.
Fill pressure drop: Pressure tap above and below the fill to determine the fill pressure
53
drop using an inclined manometer. Refer to Figure 32 for the locations of the fill static
pressure taps.
Water flow rate: The Dwyer rotameter indicates and controls the water flow rate.
3.5.3 Experimental Procedure
Inlet Water Temperature
The inlet water temperature was held fixed at 39°C, which was the temperature of the
water exiting the sink. Brentwood Industries, a manufacturer of commercial fills, tests at
37.8°C since it has been shown by many experiments that the Merkel analysis overestimates
the heat transfer at higher hot water temperatures [47].
Air Wet Bulb and Dry Bulb Temperatures
The experimental lab’s ambient air wet bulb and dry bulb temperatures were used. The
temperature variations were held within ± 2°C.
Data Collection
All measurements were conducted in steady state. The system took between 5-10 minutes
to reach steady state. A data set for nine water-air loading (L/G) conditions at a given fill
height (H) were manually recorded. At least one data point from the set was randomly
picked and repeated to determine the repeatability of the results. A complete test on a fill
was completed when it was tested for three distinct fill heights of 152.4 mm, 304.8 mm and
457.2 mm respectively. These fill heights were chosen in order for the fills to fit well inside
the cooling tower column and for ease of cutting the fills. Data collection was done quickly
once the system was stable. Experimental measurements were taken for the parameters in
Table 3.
Test Point Matrix
For a full fill test for a given fill height, nine L/G water-air loadings were tested. The nine
water-air loads for the proposed experiment were experimentally determined. For uniform
54
Table 3: Cooling tower test measurementsParameter Name Parameter Symbol Units
Water mass flow rate L kg/sAir mass flow rate G kg/s
Inlet water temperature Twi °CWater outlet temperature Two °C
Air inlet dry bulb temperature Tai °CAir inlet wet bulb temperature Twbi °CAir inlet wet bulb temperature Twbi °CAir outlet dry bulb temperature Tao °CAir outlet wet bulb temperature Twbo °C
Fill di!erential pressure !Pfill PaAmbient barometric pressure Pa PaOrifice di!erential pressure !Porifice Pa
water distribution it was important for the water flux or water loading (L/A) to be between
0.8 and 4.2 kg/m2s [40]. Brentwood noted that it gets incomplete wetting of packings with
water loadings less than 2.7 kg/m2s. Since the test was done in steady state, the air-water
mass flow rate ratio was never high enough to flood the fills. These water-air loading set
points were in the range 0.25 < L/G < 5. The variation of the mass flow rate ratio (L/G)
was obtained by appropriately varying the air and water mass flow rates respectively. The
measurements were taken starting from the lowest L/G ratio to the highest. The test was
repeated for the given packing three times at the three di!erent fill heights. Table 4 displays
the chosen L/G test conditions for the CF-1200 fill for the three di!erent fill heights as an
example of how the L/G measurements were recorded for each fill.
Transfer Characteristic Dependencies
The transfer characteristic (Me) correlations for wet, countercurrent cooling tower fills are
functions of L/G and the fill height. Inlet air dry bulb and wet bulb temperatures and inlet
water temperature do not have a significant e!ect on the cooling tower fill loss coe"cient
once corrected for density. Therefore, the loss coe"cient was determined by measuring the
pressure drop across the fill [48].
Data Analysis
55
Table 4: CF-1200 L/G test conditions for H=0.152 m, 0.305 m, 0.457 mFill Height (m) L (kg/s) G (kg/s) L/G
From the collected data for a given fill, the Merkel number (Me) was calculated for each
of the nine L/G ratios and for each of the three fill heights. From this data the transfer
characteristic correlation for the fill was determined. From the pressure drop measurements
(!Pfi) empirical pressure drop correlations were determined for the fill height of 457.2 mm.
Pressure drop data for the other two fill heights was not obtained and so correlations were
not made for those heights.
System Issues
It is important to manage the wall water or water diverted to the wall to mitigate the
issues associated with scaling up the size of the cooling tower. The same water spray system
was employed in the fill test and subsequent cooling tower application of the fill to eliminate
the e!ects of droplet size and distribution on the transfer coe"cient [46].
3.5.4 Experimental Results
Validation of Cooling Tower Results
Before the custom (bamboo, lou!a, and charcoal) fills were tested using the benchtop
cooling tower, the cooling tower apparatus had to be validated. Two methods were used to
ensure data validity using the apparatus:
1. The Omega T-type thermocouples were tested to ensure that they provided consistent,reliable data.
2. Data was taken for two Brentwood cooling tower fills, the CF-1900 and CF-1200, usingthe benchtop cooling tower. The transfer characteristic for each fill was compared withthe transfer characteristic data that Brentwood published for those fills.
The experimental fill transfer characteristic obtained using the CF-1200 and CF-1900 fills
in the benchtop cooling tower varied by at most 32.6% from the transfer characteristic data
that Brentwood published. For the CF-1200 fill, the water to air mass flow ratio ranged
between 1 and 3 (1 < L/G < 3). Brentwood tested the CF-1200 fill for heights of 0.61 m,
0.91 m and 1.2 m respectively. Brentwood’s CF-1200 transfer characteristic correlation was
57
KaV/L = 0.967(L
G
"0.779
) · H0.632. (5)
Figures 34, 35 and 36 compare the plots for the CF-1200 transfer characteristic versus L/G
for the Brentwood correlation and benchtop cooling tower experimental results for fill heights
of 0.152 m, 0.305 m and 0.457 m respectively.
For the CF-1900 fill, the water to air mass flow ratio ranged between 0.5 and 3 (0.5 <
L/G < 3). Brentwood tested the CF-1900 fill for heights of 0.61 m, 0.91 m, 1.2 m, 1.5 m
and 1.8 m respectively. Brentwood’s CF-1900 transfer characteristic correlation was
KaV/L = 0.696(L
G
"0.707
) · H0.714. (6)
Figures 37, 38 and 39 compare the plots for the CF-1900 transfer characteristic versus L/G
for the Brentwood correlation and the benchtop cooling tower experimental results for fill
heights of 0.152 m, 0.305 m and 0.457 m respectively.
Fill Transfer Characteristics
A summary of the fill transfer characteristic correlations, according to the Merkel ap-
proach, is shown in Table 5 for a fill height of 0.152 m, in Table 6 for a fill height of 0.305
m and in Table 7 for a fill height of 0.457 m. The plots of the Brentwood and custom fill
transfer characteristic correlations for the fill heights of 0.152 m, 0.305 m, and 0.457 m are
Figure 34: Me comparison CF-1200 (H=0.152 m)
58
Figure 35: Me comparison CF-1200 (H=0.305 m)
Figure 36: Me comparison CF-1200 (H=0.457 m)
Figure 37: Me comparison CF-1900 (H=0.152 m)
59
Figure 38: Me comparison CF-1900 (H=0.305 m)
Figure 39: Me comparison CF-1900 (H=0.457 m)
60
shown in Figures 40, 41, 42, 43 and 44.
Fill Pressure Drop
Pressure drop is an important fill characteristic. The lower the fill pressure drop, the
better because this results in a lower pumping power requirement and thus less power con-
sumption. The pressure drop for each fill was measured in Pascals at an air density of 1.1
kg/m3 with an inclined manometer while the fan air velocity and water mass flow rate were
varied. The fan air velocity was gradually increased between 0.5 m/s and 3.0 m/s and the
water mass flow rate was changed to three di!erent set points of 0 kg/s, 0.091 kg/s and
0.126 kg/s. These water mass flow rates correspond to water fluxes of 0 kg/m2s, 4.1 kg/m2s
and 5.6 kg/m2s respectively. The pressure drop data was recorded for each setting and for
each fill at a height of 0.457 m. Figures 45, 46, 47, 48 and 49 plot the pressure drop for
the CF-1200, CF-1900, lou!a, charcoal and bamboo fills respectively. Table 8 displays the
pressure drop correlations for each fill in the form:
!P = (B + C · vDair) + L/A(E + F · vI
air) (7)
where B, C, D, E, F, and I are constants, vair is the air velocity and L/A is the water flux.
For the water flux of 5.6 kg/m2s the fill pressure drop in order from highest to lowest was
the bamboo, charcoal, lou!a, CF-1900 and CF-1200 fill. For the water flux of 4.1 kg/m2s in
order of highest fill pressure drop to lowest: bamboo and charcoal were tied for the highest
pressure drop, followed by lou!a, CF-1900 and CF-1200. For the water flux of 0 kg/m2s the
Table 5: Transfer characteristic correlations according to Merkel approach (H=0.152)Fill Merkel Empirical Relation Correlation
Drinking water is considered a basic human right. Given this fact, water price structures
are such that the cost of water production is not represented by the price that consumers
pay for their water. In many cases the price paid is much less than the cost of the water
production, with subsidies e!ectively provided by central government or local authorities.
(The costs of water provided by traditional systems is approximately $1/m3.) This situation
is further complicated because the costs of water distribution are also generally di"cult
to isolate [29]. These factors make it hard for commercial RE-desalination technologies to
compete because, relative to the subsidized public resources, the water from RE-desalination
plants is too expensive. Therefore, there needs to be coordination between the local water
authority and the SME to work out a water allocation and distribution plan for villagers
along the coast that cannot be reached by the centralized public water system. This kind of
coordination will provide the SME with a long-term market and the country’s government
with another option to supply its’ population’s drinking water needs.
In Haiti water sachets or packets containing about seven ounces of water typically sell for
about one gourde or approximately three cents. Water trucks have become one of the main
water distributors in Haiti. A truck of water can cost anywhere from $30 to well over $100
for the consumer, depending on location within the city. Those that have cisterns buy the
water from the water trucks, then resell it by the bucket at eight gourdes, about 25 cents,
79
for a big bucket and four gourdes for a small bucket. These prices are expensive relative to
the cost of government supplied water, which costs about a gourde per bucket [12].
The community that this project focuses on is the town of Pestel, which has a popu-
lation of approximately 3,000. People are most likely to buy water during the dry season
from November to January. Most people in the village earn between $1-$2/day, which is
approximately 40 gourdes. They spend five gourdes per five gallon bucket of water and use
between four to ten buckets per day. (This water may not be clean.) Usage depends on the
size of the household and on average ranges between two and five gallons per person per day.
There are also 20 fluid ounce water bottles that cost twenty gourdes but most villagers do
not purchase these because they are too expensive [53].
Given the low price of water in Haiti and in many other developing countries, for a HDH
water plant provider to make a significant profit, the water produced will have to be low cost
and will have to be demanded by thousands of people having large economies of scale. The
HDH water plant distributor should also target schools, hospitals, central water districts
and other large institutions or populated areas that may be better able than individual
consumers to pay higher prices for clean water. Alternatively, if the price of the water
produced is to be subsidized, the water plant operator will need to establish a payment plan
with the government or local NGOs for providing a valued public service. This situation
leads to the question of the value of water and how to supply it while taking the concepts
of equity, e"ciency and sustainability into consideration.
Water is both a social and an economic good. Although access to clean drinking water is
a basic human right, it should not be freely distributed. In the past, most cities and utilities
in the world have provided water to their customers almost free of charge because water was
a relatively cheap and abundant resource and because it is considered a basic necessity. Now
with much larger communities requiring water service due to increased population size and
decreased freshwater availability, the only way to ensure that everyone has access to water
is to ration it in some way.
80
One way to promote equity, e"ciency and sustainability in the water sector is through
water pricing. Studies have shown that if water resources are managed in an integrated
fashion where the economics, legal and environmental aspects complement each other, in-
creased water prices do improve equity, e"ciency and sustainability. It is basic economic
theory that an increase in price reduces demand and increases supply. However, the less
obvious benefits of increased water price policy include improved managerial e"ciency due
to increased revenues, water conservation and environmental sustainability and an extension
of water services. Low-priced water encourages excessive consumption by those connected
to the supply system, which limits the water utility’s coverage. The poor are left to pur-
chase higher priced water from vendors. Consequently, the poor are able to a!ord only small
quantities of water enough for bare necessities but not hygienic needs. Higher water rates
encourage water conservation and allow utilities to extend improved water services to those
currently not served and forced to purchase water from vendors at very high prices. This
results in more equitable water distribution and a reduction in the per unit cost of water to
poor people. Additionally, when the price of water reflects its true cost, the resource will be
put to its most valuable uses, where value depends on individual preference [54].
In order to adequately price water, its full cost and value must be determined. The full
cost includes O&M costs, capital costs, opportunity costs and economic and environmental
externalities. The full value of water includes benefits to users, benefits from returned flows,
indirect benefits and intrinsic values. Figure 52 and Figure 53 provide a visual breakdown of
the full water cost and full water value respectively and an illustration of how the components
relate to each other. Rogers et al. (1998) in “Water as a Social and Economic Good: How
to Put the Principle into Practice” gives detailed definitions of each of these water cost and
value components. For economic equilibrium, the value of water should equal the full cost
of water. From the full cost and value of water, the price can be set by the relevant political
and social stakeholders to ensure cost recovery, equity and sustainability. Water prices must
also reflect supply characteristics like water quality, reliability and frequency of supply. The
81
Figure 52: General principles for cost of water [54]
price may or may not include subsidies. It is important to note that the prices for water
are not determined solely by cost. Using pricing policies still requires significant government
intervention to ensure that equity and public goods issues are su"ciently addressed [54].
Several water pricing strategies can be considered for providing quality drinking water
to villagers in Pestel, Haiti from a solar-driven HDH system. Since most of the villagers
in Pestel live on $1-$2/day, an appropriate tari! structure is needed to meet the di!erent
social, political and economic goals of supplying clean drinking water during the dry season.
Consumers want quality water at an a!ordable and stable price. Suppliers prefer to cover all
costs and to have a stable revenue base. A two-part tari! system for water use in Pestel is one
option to meet these objectives. The two-part tari! structure has fixed and variable elements.
The fixed element varies according to some characteristic of the user and the variable part
charges the consumer according to consumption level and encourages conservation [54].
The two-part tari! will provide the supplier with a stabilized revenue base. The fixed
82
Figure 53: General principles for value of water [54]
83
element will protect the water supplier from demand fluctuations and reduces financial risks.
For Pestel, the variable element could operate using an increasing block tari! (IBT) system.
IBT is a progressive tari! that provides di!erent prices for two or more pre-specified blocks
of water. The price rises with each successive block. When designing the IBT structure the
utility must decide on the number of blocks, volume of water use associated with each block
and the price to be charged for each block. This system allows the utility to provide a lifeline
to the poor at below-cost rate and to charge higher prices beyond this minimum volume.
Under this system the poorer households get access to low-rate water since they possess
fewer water consuming appliances. The system also allows for rich-to-poor and industrial-
to-domestic subsidies. If the two-tari! structure is insu"cient for providing water to the
villagers in Pestel, then tari! structures such as lifeline rates, IBT’s or lump sum credits can
be used to equitably supply water [54].
It is important to note that governments have many rationales for providing subsidized
water beyond notions of human rights. In recent decades there has been increased debate
around the status of water as a “human right,” a resource which cannot be owned and which
all should have access to for their own use and survival. Serious problems can result if
the water supply to a given poor population is fully privatized by an unscrupulous water
company that has no regard for equitable water distribution. Governments may provide
subsidized water to obviate these fears.
At the heart of colonial theory is the idea of the core being served by the periphery,
whereby a resource rich area lacking the technology or capital to exploit its own resources
is thus exploited “for its own benefit” by another group with the power and means to do so.
In the case of water, this is called a “hydraulic empire” or a water monopoly. In a “hydraulic
civilization” an entity maintains power over a population through exclusive control of access
to water. For example, control over water emerged as a major issue in Latin America in the
1990’s following World Bank loans to Bolivia to modernize and later privatize the municipal
water systems of La Paz-El Alto and Cochabamba. The Bolivian government auctioned
84
the public utilities in charge of water and sold them to Aguas del Tunari, a subsidiary of
Bechtel Corporation, the largest engineering company in the U.S. The terms of this contract
stipulated that control over all water in Cochabamba was the property of Aguas del Tunari.
This became a major clashing point, as almost 40% of the city was receiving its water
from informal systems not linked to the city’s water supply [55]. Water control by Aguas
del Tunari e!ectively signaled the end of local control of water and meant that the new
corporate owners would have the right to place Bolivian water on the international market.
This situation e!ectively led to hydraulic control over the cities involved [56]. In these type
of situations, government intervention and regulation is needed to ensure that water access
equity is enforced.
4.3 Socio-economic Issues4.3.1 Social Barrier
Typically there has been a negative perception of desalination by the population and some-
times opposition of local communities to installation of desalination plants. A major mis-
perception is that desalinated water is not suitable for drinking, either because of individual
prejudice or cultural issues. Other negative perceptions of desalination technologies are that
they are uneconomic, unreliable, environmentally damaging and/or aesthetically unpleas-
ing. Some of these negative perceptions will have arisen because of failures of prototype
renewable energy or desalination technologies and some due to a misunderstanding of the
technologies. For example, people in developing countries might have a negative perception
of RE-desalination technologies because of intermittent water supply based on the availabil-
ity of the RE resource. They may also have concerns that the technology will fail quickly
because it is complex and will not be properly maintained. These negative perceptions will
result in limited community support where the system is installed and a lack of popular
support from institutions and politicians because of perceived rather than actual deficiencies
85
[29].
Public acceptance is crucial for application of a RE-desalination technology and wide-
scale implementation. The public’s attitude towards the technology must be monitored
throughout the life of its operation. Often it is not about the engineering, although this fac-
tor is important, but about building community trust and ownership of the project. There
is often a cultural gap between project developers and the end-users. This gap may result
in the project failing for non-technical reasons such as the installation of the desalination
system being viewed as something foreign or there is conflict about who controls the system
[29]. To build community trust and ownership, it is important that the local community is
involved with the implementation of the technology and is trained to maintain the system.
Establishment of a community water-board to maintain the system and to monitor proper
distribution of the water produced will help ensure that the community takes shared owner-
ship of the consequent outcomes of the system. The local water board must take su"cient
e!orts to understand the public’s underlying beliefs or perceptions behind their response to
the desalination technology in order to address their concerns through an education program
or alternative method.
The objective of an education program about RE-desalination is to enlighten and per-
suade the general public about the safety and positive benefits associated with the adoption
of RE-desalination technology. The information campaign should aim to convince the com-
munity that the proposed use of desalination technology for producing potable water will
1) not threaten the health of those consuming it, 2) will produce economic benefits to the
community, 3) is favored by people in the community, and 4) will combat future or present
water supply shortage [57]. The best way to communicate that the desalinated water will
not threaten the health of those consuming it is to learn what people already believe, tailor
the communication to this knowledge and to the decisions people face and then subject the
resulting message to careful empirical evaluation [58]. Once the community feels a sense of
ownership of the RE-desalination technology and is well-informed about how it functions
86
and how to maintain it, it will have a larger positive impact on meeting the community’s
water demands.
4.3.2 Water Quality and Public Perception
Desalinated waters or highly soft waters produced by desalination plants cannot be directly
used as they are unpalatable, unhealthy and corrosive [59]. Desalinated or demineralized
water is water that is almost or completely free of dissolved minerals as a result of distillation,
deionization, membrane filtration, electrodialysis or other technology. The TDS in such water
varies but it can be as low as 1 mg/L. Desalinated or demineralized water without further
mineral enrichment is inappropriate for consumption for three reasons:
1. Demineralized water is highly corrosive and, if untreated, it will attack the waterdistribution piping and storage tanks leaching metals and other materials from thepipes.
2. There are health risks from consumption of demineralized or low-mineral water as aresult of dietary deficiency.
3. Distilled and low mineral content water (TDS < 50 mg/L) can have poor taste char-acteristics and the water is reported to be less thirst quenching [60].
Su"cient experimental evidence confirms the health risks from drinking low-mineral water.
Results from both animal and human volunteer studies were in agreement and showed that
low-mineral water markedly: 1) increased diuresis (almost by 20% on average), body water
volume and serum sodium concentrations, 2) decreased serum potassium concentration, and
3) increased the elimination of sodium, potassium, chloride, calcium and magnesium ions
from the body [60]. The body needs an adequate intake of electrolytes and ingestion of
distilled water leads to the dilution of the electrolytes dissolved in the body’s water.
There is a low level of essential elements in low-mineral water. The modern diet of many
people, especially in developing countries, may not be an adequate source of minerals and
microelements. Although drinking water is not the major source of essential elements for
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humans, in the case of people with mineral deficient diets, even the relatively low intake of
some essential elements may play a relevant protective role. This is because elements are
usually present in water as free ions and are more readily absorbed from water compared
to food, where they are mostly bound to other substances. Additionally, when used for
cooking, soft water was found to cause substantial losses of all essential elements from food
(vegetables, meats, cereals). These losses may reach up to 60% for magnesium and calcium
or even more for some other microelements [60]. In contrast, when hard water is used for
cooking, the loss of these elements is much lower.
There is practically zero calcium and magnesium intake from low mineral water. Calcium
and magnesium are both essential elements. Numerous international studies have reported
that soft water (i.e. water low in calcium and magnesium) and water low in magnesium
is associated with increased morbidity and mortality from cardiovascular disease (CVD)
compared to hard water and water high in magnesium. It has also been suggested that
intake of low-magnesium water may be associated with a higher risk of bone fracture in
children, motor neuronal disease, pregnancy disorders such as pre-term birth and low weight
at birth and some types of cancers. [60].
The corrosive nature of demineralized water and potential health risks related to the dis-
tribution and consumption of low TDS water have led to recommendations for the minimum
and optimum mineral content in drinking water. Based on the currently available data,
various researchers have recommended the following levels of calcium, magnesium, specific
ion content and water hardness in drinking water:
• For magnesium, a minimum of 10 mg/L and an optimum of about 20-30 mg/L
• For calcium, a minimum of 20 mg/L and an optimum of about 50 (40-80) mg/L
• For total water hardness, the sum of calcium and magnesium should be 2 to 4 mmol/L
• For TDS an optimum of 200-400 mg/L
• For Na an optimum of 0-100 mg/L
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• For Cl an optimum of 30-150 mg/L
• For sulfate an optimum of 0-200 mg/L
• The bicarbonate recommendation is to have a concentration equivalent to the hardnesscontent [59].
Remineralization is used to overcome these deficiencies. A commonly used operation in
the remineralization process is to place CO2 acidified desalinated water in contact with
a bed of domestic limestone or calcium carbonate. Limestone dissolution is a slow rate-
controlling step that adds two essential ingredients to the water, bicarbonate alkalinity and
calcium content: CaCO3 + CO2 + H2O = Ca2+2HCO"3 [59]. Alternatively, blending the
desalinated water with small volumes of more mineral-rich waters to improve its taste and
reduce its corrosiveness to the distribution network is also suitable. The procedure for adding
minerals to water is not complex. A remineralization solution can be prepared in a clean
reservoir under constant stirring using the same water that will be in the product. The
remineralization solution can also be pasteurized. A pump can be used to inject a portion
of the remineralization solution either directly or to a feed tank maintained under agitation
to avoid precipitation of salts [61]. Table 14 shows four solutions that are widely used to
remineralize desalinated water and Table 15 qualitatively compares these processes.
When desalinated water needs to be remineralized, the key considerations in supplement-
ing minerals are:
• potential health benefits;
• taste;
• product stability;
• quality of the salts;
• industrial procedures; and
• cost [61].
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As discussed previously the health benefits of remineralizing desalinated water are clear but
acceptable water taste is a more subtle issue. Consumer taste preferences are crucial because
upon consumption the consumer may immediately accept or reject the water. If the taste of
the desalinated remineralized water is unacceptable, the consumers may opt for a di!erent
source of drinking water that tastes good but is unclean, despite the higher water quality
of the remineralized water. Therefore, it is crucial that the water producer seeks feedback
from the consumers about the acceptability of the water attributes (i.e. taste, smell and
appearance or color) and responds appropriately.
Concerning product stability and quality of the salts, the salt concentrations that can be
added without exceeding the solubility of the salts in the water at 20°C must be calculated
to prevent precipitation. Solubility can be improved if the water is carbonated since lower
pH usually enhances solubility. With respect to cost, to add 20 mg of calcium to water, the
cost would rise by U.S. $0.00222/L of product (U.S. $2.2 per 1000 liters) if prepared from
calcium sulfate and magnesium chloride or by U.S. $0.00198/L of product (U.S. $1.98 per
1000 liters) if prepared from calcium chloride and magnesium sulfate. These costs exclude
the costs of electricity and mixers/pasteurizers [61].
4.4 Environmental Issues4.4.1 Possible Environmental E!ects
Environmental issues related to desalination are a major factor in the design and implementa-
tion of desalination technologies. Some major environmental concerns include issues related
to location of desalination plants and water intake structures, and concentrate management
and disposal [63]. The desalination plant location is important for several reasons: proximity
to the population center, distance from the saltwater source to the plant and availability of
the needed infrastructure.
If the proposed desalination plant is being constructed next to a population center, land
use and noise pollution from the construction must be considered. If planners place a desali-
90
Table 14: Four solutions used to remineralize desalinated water [62]Remineralization
gies near the coastlines where saline or brackish environments are located which have the
greatest feasibility for use in disposal options [64].
4.4.3 Concentrate Disposal Methods and Mitigation
Concentrate disposal methods include surface disposal (surface water and submerged dis-
posal), deep well injection, land application, evaporation ponds, brine concentrators and zero
liquid discharge (ZLD) technologies. Since surface disposal is the most common method of
concentrate disposal it, will be the focus here. Surface water disposal includes disposal into
freshwater, tidal rivers and streams; coastal waters such as oceans, estuaries and bays; and
freshwater lakes or ponds [63].
Surface water disposal takes place immediately at the coastline and its appropriateness
depends on the surroundings and properties of the receiving water. If the area is highly
populated, disposal may be a problem because of the interference of the mixing zone with
recreation on the beach. In this case submerged disposal, disposing the concentrate under-
water using long pipes stretched out into the ocean, may be more appropriate. However, this
method places benthic marine organisms living at the sea bottom at risk. As concentrate
enters the receiving water, it creates a high salinity plume which either sinks, floats or sta-
bilizes in the seawater based on its relative density. The radius of the plume impact varies;
without proper dilution, the plume may extend for hundreds of meters, beyond the mixing
94
zone, harming the ecosystem along the way. The type of dispersion and natural dilution of
the concentrate plume that may occur depends on the discharge pipe’s location. Factors such
as waves, tides, currents and water depth are all important aspects that determine natural
dilution and the amount of mixing that may occur at the concentrate mixing point [63].
If natural dilution is not enough to properly di!use the concentrate, then desalination
plants use artificial dilution methods including e"cient blending and di!users or utilize mix-
ing zones prior to surface disposal. Mixing zones are quantified limits within the receiving
waters where the law allows surface water to exceed water quality standards due to the exis-
tence of point source disposal. Blending involves mixing the concentrate with cooling water,
feedwater or other low TDS waters before disposal. Di!users are jets that dilute the concen-
trate at the concentrate disposal outlet for maximum mixing. Mitigation e!orts related to
chemical use in the desalination plant include using non-toxic additives and de-chlorination
techniques which limit the toxic chemical concentrations that enter the environment. Using
materials in the desalination process that are less likely to corrode can limit the occurrence
of corrosion products in the water [63]. Figure 54 shows the main concerns with surface
water disposal, as well as mitigation methods to reduce those concerns.
Figure 54: Surface water disposal problems and mitigation [63]
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4.5 Political Issues4.5.1 Institutional Barrier
In general, water authorities have been found to be reluctant to commission RE-desalination
technologies because of their confidence with conventional water technologies and a culture of
risk avoidance [29]. Water authorities prefer to install technology that they are familiar with
and that is well understood. RE-desalination technologies like HDH are perceived as risky
since they have not been commercially proven and because of a relative lack of knowledge
and experience with the technologies.
In addition to the perceived risk of the newness of RE-desalination technology, given the
technologies decentralized nature, water authorities may also perceive them as a political
risk. The provision of water supplies has typically been provided using a centralized ap-
proach, where water supply and quality can most easily be controlled. Many RE-desalination
technologies are generally small-scale and suitable for community-led water provision. This
situation might result in a perceived loss of control by the water providers, making it unlikely
for them to adopt RE-desalination technologies. This institutional aversion is compounded
by the fact that local rural communities might not trust water supplies powered by RE and
would in some cases prefer to rely on traditional fresh water supplied even in cases where
the supply is of low quality [29].
The legal structures required to ensure specific water quality standards typically favor
the centralized approach of water provision. Consequently, the legal structures are often
highly bureaucratic, not tailored for small-scale independent water production, and require
a large investment of time and e!ort for each source of water supplied. Many RE-desalination
plants are developed by independent water suppliers and have only a small capacity. Thus,
the legal overhead is relatively large, making the installation potentially uneconomic. The
issue is further complicated by the fact that in many countries the management of energy
is totally separated from the management of water, so the coordinated organization and
provision of these two services is di"cult. The separation of the management of energy and
96
water means that the benefits of RE-desalination are not always fully recognized because
decision-makers focus on either the supply of water or the supply of energy [29].
The institutional barrier of lack of training and infrastructure can also be problematic.
Many developing countries lack the materials and infrastructure needed to construct and sus-
tain the required RE-desalination technology. As a result, the materials must be imported
at a high price. If a component in the system fails, unless the technology was built appro-
priately using locally available materials, the replacement parts will need to be imported,
reducing the overall system sustainability. These factors result in reduced plant availability,
reluctance to o!er service contracts and reluctance to purchase the system without service
contracts [29]. It is important that the RE-desalination system is an appropriate technology
built using local materials, expertise and input to ensure system practicality and sustain-
ability. It is also essential that a group of people in the village be trained to maintain the
system regardless of whether the system is purchased with a service contract.
4.5.2 Water Regulatory Framework in Haiti
In terms of both water supply and sanitation Haiti’s coverage levels in urban and rural areas
are the lowest in the Western Hemisphere [65]. The quality is also inadequate. In rural
areas, systems have often fallen into disrepair, either not providing any service water at all
or providing service only to those close to the source. In almost all urban areas, water supply
is intermittent. Sewer systems and wastewater treatment are nonexistent and there is no
legislation concerning desalination. Foreign and Haitian NGOs play an important role in the
sector given the weakness of the public institutions.
The main public sectors in the Haitian water sector are two state owned enterprises:
CAMEP (Centrale Autonome Métropolitaine d’Eau Potable), responsible for providing wa-
ter in the Port-au-Prince metropolitan area, and SNEP (Service National d’Eau Potable),
responsible for providing water nationally (secondary cities and, in theory, for rural areas).
The absence of management, regulations and funding has crippled the two government-owned
97
water services, leaving the country’s water resources polluted and severely depleted. Nei-
ther agency has been able to maintain or update their equipment and water lines, adapt to
changes in population or respond to the country’s growing environmental crisis. Estimates
on the percentage of metropolitan Port-Au-Prince that is being serviced by CAMEP vary
from 20 percent to 30 percent. However, these figures are uncertain because CAMEP’s ser-
vice is intermittent, their metering system is inconstant and people often break their pipes
and steal the water to sell for a profit. According to the Haitian Institute of Statistics and
Information, SNEP is servicing only 16 percent to 24 percent of the population [12].
There is no institutional responsibility for sanitation in Haiti, since the mandates of
CAMEP and SNEP currently do not include sanitation. Both entities theoretically operate
under the authority of boards, including representatives of several ministries. Since these
boards have not met for more than a decade, both entities are de facto under the sole
control of the Ministry of Public Works, Transport and Communications (MTPTC). MTPTC
currently does not have a water and sanitation directorate, although its creation is foreseen
[65]. MTPTC now envisages creating a water and sanitation directorate as part of a draft
framework law for the sector.
A fundamental problem for Haiti is that there is no Water Ministry. The responsibilities
for ensuring delivery of safe water are spread throughout government agencies, including
those related to agriculture, public works and public health. “It is very di"cult to control
because there are so many people involved and nobody is in control exactly,” said Benoit
Frantz, the general secretary of CAMEP [12]. There are hundreds of water committees,
called CAEPs (Comités d’Aprovisionnement en Eau Potable) or simply Comités d’Eau,
in charge of water systems in rural areas and small towns. Their degree of formalization
and e!ectiveness varies considerably. The best water committees meet regularly, closely
interact with the community, regularly collect revenues, hire a plumber who performs routine
repairs, have a bank account and are registered and approved by SNEP. However, many
water committees fall short of these expectations. There is no national or regional registry
98
of water committees or water systems and there are no associations of water committees at
the municipal, departmental or national level. The Ministry of Public Works now refers to
these committees o"cially as water and sanitation committees (Comité d’Approvisionnement
en Eau Potable et Assainissement—CAEPA) to reflect the broader role the committees are
expected to play in the future [65].
4.5.3 Desalination Regulatory Framework in the U.S.
The legal and institutional structure of the U.S. has ensured that the states and localities
have the main burden of regulation and decision-making on desalination. Although under
the constitution, U.S. federalism has decisive power over local governments at the state level,
federal constitutional provisions have remained almost entirely in the background. States
usually oversee special districts concerned with water issues and the regulation of private
and public utilities. It is at the level of localities and sub-state regions that most provision of
infrastructure like water and electricity gets decided. The local politics of desalination is often
the most decisive for approval even when the processes take place at higher levels. In some
states, like California, the requirements that states impose in coastal areas can decisively
influence the prospects and character of desalination processes. This circumstance is largely
due to the fact that companies or local governments seeking to develop desalination plants
are responsible for obtaining the numerous required overlapping permits for implementation
[66]. Limited cooperation between the energy and water authorities often results in small
producers having to go to many di!erent organizations that deal with water, energy and the
environment for securing all the permits needed to construct the desalination plant [29]. For
example, in California up to 24 separate permits from an array of agencies, at multiple levels
of government, may be required. Consequently, much of the expertise on these projects goes
into filing permit applications [66].
99
4.5.4 Policy Gaps, Links and Recommendations for Increasing Desalination
Despite a more centralized context of desalination policy-making in developing countries
relative to the U.S., the U.S. desalination regulatory framework is likely to have far-reaching
consequences for other regions of the world. Several lessons that can be learned from the
U.S. regulatory experience with desalination are the importance of fostering public-private
financial desalination arrangements, creating decentralized water producers that can abide
by the local regulations of the water authority and reducing the bureaucracy of the legal
structures.
Public-private financial arrangements and policy sources of support are crucial for the
success of a desalination project. Even before the cost of desalination has decreased enough
to make itself marketable, it can be widely cost-e!ective with a combination of private in-
vestment and public subsidy. Private investment by itself may be too unreliable to provide
the basis for investment in desalination. Local or national regulation may ultimately be
necessary for market investments and the reliability of desalination projects. Private invest-
ment is needed for desalination to be carried out in developing countries. To make privatized
arrangements accountable, protections through regulation at multiple levels, including local
review, are critical. RE has been largely supported in the U.S. through support policies
like feed in tari!s, quota schemes, tax incentives, investment grants and cap and trade [29].
An investigation into how these policies can be applied and enforced for RE-desalination in
a given country must be conducted. In the U.S. the placement of desalination plants has
proceeded according to the logic of private investment rather than policy guidance. Investors
tend to focus on communities with greater ability to pay for investments in plants and in-
frastructure for desalination technology. Only in heavily subsidized states like California has
the implementation of desalination plants followed patterns of public investment. From an
equity standpoint and not in terms of economic e"ciency, in order to equitably supply and
distribute desalinated water, it is important to have the proper balance of public and private
interest, support and investment.
100
Decentralized regulation for water supply is important for RE-desalination. As observed
in the U.S., having a centralized desalination regulation is problematic for states. While there
can be centralized general oversight and an overaching desalination regulatory framework,
decentralized local water authorities are the most e!ective at regulating local desalination
plants and holding them accountable. However, there are several drawbacks to the localized
desalination regulatory approach. One problem is that the localized nature of regulation
means that little attention is given uniformly to social and environmental equity among
di!erent places. Additionally, there are concerns of a fragmented regulatory desalination
framework that will be di"cult for water plant operators and desalination investors alike to
navigate. Non-uniformity also presents the issue of investors going to local areas that have
a regulatory climate favorable to their business interests which might have negative social
and/or environmental impacts for the local community [29]. Thus, an overaching centralized
framework is needed to help ensure social equity and justice to help prevent business abuse
and exploitation from happening due to a lack of adequate local standards.
The extensive regulatory and procedural requirements that surround desalination of-
fer numerous opportunities for debate over the strengths and weaknesses of a desalination
project and are a significant barrier to the successful development of desalination plants [66].
The knowledge debate over desalination projects is good because it allows for constructive
criticism that makes the proposed desalination project stronger and more environmentally
responsible. To address the issue of extensive regulatory and procedural requirements there
needs to be more coordination between the energy and water authorities. In every coun-
try the RE-desalination community must lobby for greater cooperation between the power
and water sectors in governmental and non-governmental institutions and work with local
authorities to identify the bottlenecks in licensing and eliminate them. This cooperation
will dramatically reduce the legal bureaucracy. It will enable decentralized supply of desali-
nated water similar to how the U.S. legal framework has allowed for decentralized electricity
production and subsequent sale at the central market level via the national grid [29].
101
5 The E!ect of Stakeholders on Seawater DesalinationPolicy and Implementation
5.1 Role of Market in Overcoming Barriers
The development of reliable and detailed market analysis for RE-systems is one of the most
important but also most challenging tasks. The main requirements of this type of market
analysis include identifying and analyzing in detail the main target groups for each kind of
di!erent available RE-desalination combination and quantifying the demand by these groups
for the water desalination technology. RE-desalination product developers who decided to
enter a market outside their home country must collaborate with the appropriate local com-
panies in order to identify niche markets where the users are willing and able to pay for
the technology. In order for a SME to overcome barriers associated with the local legal
system, currency and political developments, it needs to get as much external support as
possible. The SME will need a good network to establish a local presence with sales, mar-
keting and technical sta!. If the SME works together with local companies, agencies and/or
missions and obtains support from international development organizations, it can develop
this network. Additionally, the RE-desalination community can get organized, collect rele-
vant information and make it available to its members to help them expand to new markets
[29].
The desalination industries need to lobby the water authorities in countries to develop
a suitable water pricing structure. Introducing water pricing that accounts for full cost
recovery of the “real cost” of water is crucial. The real cost of water is based on the cost of
water supply, maintenance and new infrastructure, environmental and resource costs, and
the volume of water used. Successful water pricing will require a good understanding of the
relationship between price and use for each sector and needs to account for local conditions.
The challenge is to define water pricing that reflects the costs but allows equitable access to
safe water. Traditionally public subsidies have been used to accomplish this aim, especially in
places where real water costs are much higher than the income of the local people. However,
102
the structure and mechanism of the subsidies has to be incorporated in a pricing system
that still lets the market choose the most e"cient water supply solution, while encouraging
e"ciency in the use of the water [29].
5.2 Role of R&D in Overcoming Barriers
Targeted R&D is needed to substantially increase the market for and worldwide application
of RE-desalination. R&D priorities include focused e!orts on developing the components
necessary for the smooth and e"cient coupling of the existing desalination and RE tech-
nologies and development of the elements that will make RE-desalination robust for stand-
alone operation in harsh environments. Some issues that RE-desalination developers have
to address and that need more R&D are adaptation of pumps and energy recovery systems
for e"cient operation in small-scale plants, suitable small-scale electric and thermal energy
storage, use of seawater resistant materials, automated and environmentally friendly pre and
post-treatment technologies and control systems that optimize the system performance and
minimize maintenance requirements. With respect to the latter issue, doing R&D on how
to minimize the impacts on the desalination plant due to energy variability is one possibil-
ity. The desalination process and its components should be reassessed and designed towards
a new desalination technology able to operate under variable energy supply. Research is
needed on improved control algorithms that result in control software that can ensure the
best use of the available energy and that protect the system from energy supply fluctuations
[29].
Other areas of research that must be conducted are R&D that supports the development
of hybrid systems with more than one source of energy and cogeneration plants that produce
water and power. Hybridization with the electricity grid, together with a tailor-made control
system, can guarantee continuous plant operation. Cogeneration of electricity with the
desalination of water will enable optimal utilization of the desalination plant and make
103
the desalination process diverse and more economically attractive. The management of
the available electricity and water produced would depend on the needs and on the tari!
structures of both commodities in the area of operation [29].
5.3 Stakeholder Activities for Desalination Awareness and Growth
Wide-scale growth of RE-desalination requires a worldwide RE-desalination community with
an e!ective communication platform. Companies that produce and sell RE-desalination
plants, academics who research desalination technology, country-specific relevant water reg-
ulatory bodies and the general public should be members of this community. The barriers
and problems associated with RE-desalination could be discussed and addressed by this
community, making it easier for the RE-desalination producers and sellers to gain market
share. More specifically, the community can work to convince manufacturers to produce
equipment tailored to the RE-desalination industry, complete a thorough market analysis
and remove bureaucratic barriers with respect to plant installation. The community can
also convince water authorities and policy makers to adjust the water pricing system to an
acceptable metric. It can also share experiences or best methods on what has worked and
failed concerning overcoming social barriers or public resistance [29]. Transparency is key
to further increasing the general public’s understanding of and trust in RE-desalination.
To foster greater transparency and understanding, university classes concerning the topic
should be expanded and continued, more workshops for professionals should be developed
and local community water boards should be established to clarify misunderstandings and
remove misconceptions about the technology.
This RE-desalination community and communication platform will not develop on its
own but must be established. Either the European Union (E.U.), the U.S., the International
Energy Agency (IEA), a large RE-desalination company or some other entity must initiate
it. All interested companies have to be found and integrated. A website has to be created
104
where all the information and questions can be stored and exchanged. To ensure that the
RE-desalination community can function for a long time, funding must be guaranteed either
from E.U. or U.S. projects and collecting member fees. A model for this community could be
SolarPaces, which has facilitated the market entry of CSP for over 30 years. It is managed
under the umbrella of the IEA to help find solutions to the worldwide energy problems [29].
105
6 Summary and Conclusions
RE-desalination generally, and HDH in particular, have a critical role to play in meeting the
world’s rapidly increasing water demands. For RE-desalination to become widely spread,
it must overcome technological, social, economic, political and environmental barriers. Key
factors to surmount these barriers are RE-desalination R&D, market signals that reduce
the perceived risks associated with RE-desalination and e!ective action by the appropriate
stakeholders for raising RE-desalination awareness and growth.
Since a large portion of the future water need will be in developing countries, appropriate
desalination technologies that can increase water are critical. Solar-driven HDH desalination
has a crucial role to play in producing potable water for people in coastal regions of developing
countries. Solar-driven HDH is an appropriate technology for coastal regions of developing
countries because it has the potential to be made using local materials, it uses a renewable
energy source, it does not require skilled labor for O&M and it is a source of decentralized
water production. Making the necessary trade-o!s to reduce the overall system cost, such
as using local manual labor and materials, in the HDH system will make it more a!ordable
for people living on $1-$2/day. By experimentally determining the thermal performance
and pressure drop of custom cooling tower fills such as bamboo, lou!a and charcoal, it was
concluded that the lou!a fill had the highest overall performance. The tested custom fills
are locally available in Haiti and can be easily replaced at no cost. Using a lou!a fill in
the humidifier of the HDH desalination unit is one way to reduce the system cost while still
maintaining adequate thermal performance relative to PVC commercial fills.
The next steps to further the successful implementation of a HDH desalination system
in a developing country such as Haiti are to design several prototype HDH systems that can
meet both user requirements and the price target for the clean water produced. To minimize
HDH system cost, it is important to identify and design around each of the key contributors
to cost such as the condenser, the solar heater, the water pump and the fan. These design
trade-o!s can be satisfied by finding acceptable substitutes from locally available materials
106
as well as from local input and expertise in building the prototype. Then the prototype
performance must be tested in the field in order to acquire data and user feedback that can
be used to improve the system. In addition to the technical next steps there are also political
issues that must be resolved. The RE-desalination community and platform must be created
in order to raise RE-desalination awareness and to increase the growth of this field through
political lobbying and knowledge sharing. With an e!ective RE-desalination platform the
barriers associated with RE-desalination can be targeted and overcome. With successful
implementation of HDH, developing countries will have another water supply option to meet
their rapidly increasing water demand.
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A AppendixApparatus Limitations
The following restrictions apply:
Maximum water stream temperature: 40°CMaximum water mass flow rate: 0.139 kg/sMaximum airflow rate: 119 L/sMaximum fan speed: 4,000 rpm
Desired Experimental Parameter Ranges
Experiments are to be conducted in steady state for the following conditions.
L/G ratio (mass flow rate water/mass flow rate air): 0.25-5Inlet water temperature (Twi): 39°CThree fill heights (H): 152.4 mm (0.5 feet), 304.8 mm (1.0 foot), and 457.2 mm (1.5 feet)
All components are mounted on a robust base plate. The cooling tower components
include:
(i) Air distribution chamber.(ii) A centrifugal fan with intake damper.(iii) A 3/8 MP125N 316 stainless steel BETE spray nozzle.(iv) A water-collecting basin.(v) A column cap which fits on top of the column and includes a 80 mm diameter sharp
edged orifice and pressure tapping, and a droplet arrester.(vi) A Dwyer (0.2-2.2 GPM) rotameter catalogue no. RMC-142-SSV