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

Master of Science in Technology and Policy

at the

Massachusetts Institute of Technology

June 2010

© 2010 Massachusetts Institute of Technology. All rights reserved.

Signature of Author…………………………………………………………………………………………………

Technology and Policy Program, Engineering Systems Division

May 7, 2010

Certified by…………………………………………………………………………………………………………

John H. Lienhard V

Collins Professor of Mechanical Engineering

Thesis Supervisor

Accepted by………………………………………………………………………………………………………...

Dava J. Newman

ProfessorofAeronauticsandAstronauticsandEngineeringSystems

Director,TechnologyandPolicyProgram

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

3

Contents1 Introduction 8

1.1 Project Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.2 The Central Questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.3 Thesis Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2 Desalination Background 102.1 Worldwide Water Scarcity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.1.1 Water Issues in Haiti . . . . . . . . . . . . . . . . . . . . . . . . . . 132.2 Why Desalination? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.3 Desalination Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.3.1 Conventional Desalination Technologies . . . . . . . . . . . . . . . . . 172.3.2 Limitations of Conventional Technologies . . . . . . . . . . . . . . . . 242.3.3 Renewable Energy Desalination . . . . . . . . . . . . . . . . . . . . . 252.3.4 Humidification Dehumidification (HDH) Desalination . . . . . . . . . 322.3.5 Types of HDH Systems . . . . . . . . . . . . . . . . . . . . . . . . . . 342.3.6 Possible Improvements to the HDH Cycle . . . . . . . . . . . . . . . 38

3 Application of Solar HDH Desalination in the Developing World 393.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.2 Cooling Tower Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.3 Fills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.4 Cooling Tower Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473.5 Experimental Cooling Tower Test . . . . . . . . . . . . . . . . . . . . . . . . 50

3.5.1 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.5.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . 503.5.3 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . 543.5.4 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 573.5.5 Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 703.5.6 Implications for Fills Made of Local Materials . . . . . . . . . . . . . 72

4 Issues Relevant to HDH Desalination 734.1 Technical Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

4.1.1 Technological Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . 734.2 Economics of desalination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74

4.2.1 Economical Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . 744.2.2 Economics of HDH System . . . . . . . . . . . . . . . . . . . . . . . . 754.2.3 Water Price in Haiti . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.3 Socio-economic Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.3.1 Social Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.3.2 Water Quality and Public Perception . . . . . . . . . . . . . . . . . . 87

4.4 Environmental Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904.4.1 Possible Environmental E!ects . . . . . . . . . . . . . . . . . . . . . 904.4.2 Brine Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

4

4.4.3 Concentrate Disposal Methods and Mitigation . . . . . . . . . . . . . 944.5 Political Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

4.5.1 Institutional Barrier . . . . . . . . . . . . . . . . . . . . . . . . . . . 964.5.2 Water Regulatory Framework in Haiti . . . . . . . . . . . . . . . . . 974.5.3 Desalination Regulatory Framework in the U.S. . . . . . . . . . . . . 994.5.4 Policy Gaps, Links and Recommendations for Increasing Desalination 100

5 The E!ect of Stakeholders on Seawater Desalination Policy and Imple-mentation 1025.1 Role of Market in Overcoming Barriers . . . . . . . . . . . . . . . . . . . . . 1025.2 Role of R&D in Overcoming Barriers . . . . . . . . . . . . . . . . . . . . . . 1035.3 Stakeholder Activities for Desalination Awareness and Growth . . . . . . . . 104

6 Summary and Conclusions 106

References 108

A Appendix 112

5

List of Figures1 Global water stress indicator map [4] . . . . . . . . . . . . . . . . . . . . . . 112 Worldwide freshwater stress in 1995 and 2025 [5] . . . . . . . . . . . . . . . 113 Daily per capita water use by country [7] . . . . . . . . . . . . . . . . . . . . 124 Worldwide use of improved drinking-water sources in 2008 [9] . . . . . . . . 135 Haitian girl collecting water from an open water source [18] . . . . . . . . . 156 Map of Haiti [8] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 The world’s water supply [22] . . . . . . . . . . . . . . . . . . . . . . . . . . 168 U.S. and global desalination sources and process distribution [25] . . . . . . 189 Schematic diagram of multi-stage flash desalination process [24] . . . . . . . 1810 Schematic diagram of multi-e!ect evaporator desalination process (horizontal

tube-parallel feed configuration) [24] . . . . . . . . . . . . . . . . . . . . . . 2011 Schematic diagram of single stage mechanical vapor compression desalination

process [24] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2112 Block diagram of reverse osmosis operations (optimal pressure recovery de-

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-

nologies [29] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2716 Renewable energy-driven desalination processes and energy sources [29] . . . 2717 Recommended renewable-energy desalination combinations [28] . . . . . . . 2818 Water cycle [26] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3219 Solar still [26] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3320 HDH desalination (air heated, open cycle) [26] . . . . . . . . . . . . . . . . 3521 HDH cycles [26] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3622 HDH unit with closed water cycle/open-air [34] . . . . . . . . . . . . . . . . 3723 HDH unit with closed-air/open-water cycle [26] . . . . . . . . . . . . . . . . 3824 Counter-flow cooling tower [40] . . . . . . . . . . . . . . . . . . . . . . . . . 4125 Cross-flow cooling tower [40] . . . . . . . . . . . . . . . . . . . . . . . . . . . 4126 CF-1200 fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4527 CF-1900 fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4528 Lou!a fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4629 Charcoal fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4630 Bamboo fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4731 Cooling tower process heat balance [41] . . . . . . . . . . . . . . . . . . . . . 4932 HC891 benchtop forced-draft cooling tower unit . . . . . . . . . . . . . . . . 5133 Actual benchtop cooling tower apparatus . . . . . . . . . . . . . . . . . . . 5334 Me comparison CF-1200 (H=0.152 m) . . . . . . . . . . . . . . . . . . . . . 5835 Me comparison CF-1200 (H=0.305 m) . . . . . . . . . . . . . . . . . . . . . 5936 Me comparison CF-1200 (H=0.457 m) . . . . . . . . . . . . . . . . . . . . . 5937 Me comparison CF-1900 (H=0.152 m) . . . . . . . . . . . . . . . . . . . . . 5938 Me comparison CF-1900 (H=0.305 m) . . . . . . . . . . . . . . . . . . . . . 60

6

39 Me comparison CF-1900 (H=0.457 m) . . . . . . . . . . . . . . . . . . . . . 6040 CF-1200 transfer characteristic plots . . . . . . . . . . . . . . . . . . . . . . 6241 CF-1900 transfer characteristic plots . . . . . . . . . . . . . . . . . . . . . . 6342 Custom fill transfer characteristic plots (H=0.152 m) . . . . . . . . . . . . . 6443 Custom fill transfer characteristic plots (H=0.305 m) . . . . . . . . . . . . . 6544 Custom fill transfer characteristic plots (H=0.457 m) . . . . . . . . . . . . . 6645 CF-1200 fill pressure drop (H=0.457 m) . . . . . . . . . . . . . . . . . . . . 6646 CF-1900 fill pressure drop (H=0.457 m) . . . . . . . . . . . . . . . . . . . . 6747 Lou!a fill pressure drop (H=0.457 m) . . . . . . . . . . . . . . . . . . . . . 6848 Charcoal fill pressure drop (H=0.457m) . . . . . . . . . . . . . . . . . . . . 6849 Bamboo fill pressure drop (H=0.457 m) . . . . . . . . . . . . . . . . . . . . 6950 Fan power consumption for tested custom fills . . . . . . . . . . . . . . . . . 7051 Fan power consumption for tested fills (H=0.457 m) . . . . . . . . . . . . . 7152 General principles for cost of water [54] . . . . . . . . . . . . . . . . . . . . 8253 General principles for value of water [54] . . . . . . . . . . . . . . . . . . . . 8354 Surface water disposal problems and mitigation [63] . . . . . . . . . . . . . . 95

List of Tables1 GOR of the main thermal desalination technologies [27] . . . . . . . . . . . . 192 Benchtop cooling tower temperature measurements . . . . . . . . . . . . . . 513 Cooling tower test measurements . . . . . . . . . . . . . . . . . . . . . . . . 554 CF-1200 L/G test conditions for H=0.152 m, 0.305 m, 0.457 m . . . . . . . . 565 Transfer characteristic correlations according to Merkel approach (H=0.152) 616 Transfer characteristic correlations according to Merkel approach (H=0.305

m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627 Transfer characteristic correlations according to Merkel approach (H=0.457

m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 628 Fill Pressure Drop Correlations (H=0.457 m) . . . . . . . . . . . . . . . . . 639 Uncertainties of measured variables . . . . . . . . . . . . . . . . . . . . . . . 7110 Uncertainty contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7211 Distribution of costs for conventional (RO and MSF) and renewable energy

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

7

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.

8

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.

9

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

10

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

12

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

13

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]

15

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

share about 10% of the market [23].

Figure 7: The world’s water supply [22]

16

2.3 Desalination Technologies2.3.1 Conventional Desalination Technologies

There are three main processes for the desalination of seawater or brackish water: thermal

distillation, use of a semi-permeable membrane to separate fresh water from concentrate and

chemical approaches to desalination. The first approach involves using thermal means to

e!ect a phase change of the water (i.e. to vapor) and to separate the new phase from the

remaining salt solution. The heat source may be obtained from a conventional fossil-fuel or

from a renewable energy source (RES). These thermal distillation processes account for a

large portion of the world’s desalination capacity [24], as shown in Figure 8. In the mem-

brane processes, electricity is used either for driving high pressure pumps or for establishing

electric fields to separate ions [26]. Chemical approaches to desalination are more varied

than the other two and include processes such as ion exchange, liquid-liquid extraction, and

gas hydrate or other precipitation schemes. Ion exchange is used to soften brackish water.

With the exception of ion-exchange, it is generally found that chemical processes are too

expensive to produce fresh water. Even ion exchange is impractical for treating water with

higher levels of total dissolved solids (TDS) [24].

The most important commercial thermal distillation processes are multi-stage flash (MSF),

Multi-E!ect Evaporation (MEE) and Vapor Compression (Thermal and Mechanical). MSF

is widely used in the Middle East and accounts for over 40% of the world’s seawater de-

salination capacity. MSF is a distillation (thermal) process that involves evaporation and

condensation of water. The evaporation and condensation steps are coupled in MSF so that

the latent heat of evaporation is recovered for reuse by preheating the incoming water. Each

stage of an MSF unit operates at a successively lower pressure in order to maximize water

recovery. Another key design feature of MSF systems is bulk liquid boiling, which alleviates

problems with scale formation on heat transfer tubes [24]. See Figure 9.

The gained output ratio (GOR) is a performance ratio often applied to thermal desali-

17

Figure 8: U.S. and global desalination sources and process distribution [25]

Figure 9: Schematic diagram of multi-stage flash desalination process [24]

18

nation processes. GOR is essentially the e!ectiveness of water production and an index of

the amount of heat recovery e!ected in the system [26]. The higher the GOR, the better

the thermal desalination technology. GOR is defined as the ratio of the latent heat of evap-

oration (hfg) of the pure water produced (·mpw) to the heat input (

·Qin) to the cycle [27], as

shown in Equation 1.

GOR =·mpwhfg

·Qin

(1)

Table 1 shows the range of GOR for typical thermal desalination systems.

Multi-E!ect Evaporation (MEE) or Multi-E!ect Distillation (MED) is a distillation pro-

cess related to MSF. MEE is not widely used because of problems with scaling on the heat

transfer tubes, but it has gained attention due to its better thermal performance compared

to MSF. In MEE, vapor from each stage is condensed in the next successive stage, giving

up its heat to drive more evaporation. To increase MEE performance, each stage is run at

a successively lower pressure. This technique gives the plant the flexibility to be configured

for high or low temperature operation. The low temperature setting allows the use of low-

grade waste heat and helps reduce corrosion and scaling [24]. See Figure 10. The di!erence

between MEE and MSF is that in MEE the evaporation of salt water occurs by boiling,

causing scale to form on the heat exchanger surface. In MSF, the saline feed is first heated

in tubes without being allowed to boil with little precipitation of scale on the inside of the

tubes; it is then made to evaporate in chambers by successive flashing to lower pressures

[21].

Table 1: GOR of the main thermal desalination technologies [27]Thermal Desalination System GOR

Solar Still < 0.5Existing HDH 0.2 - 4.5

MSF 8 -12MED 12 -16

19

Figure 10: Schematic diagram of multi-e!ect evaporator desalination process (horizontaltube-parallel feed configuration) [24]

Vapor compression (VC) processes rely on reduced pressure operation to drive evapo-

ration. The heat for the evaporation is supplied by the compression of the vapor, either

with a mechanical compressor (mechanical vapor compression, MVC, Figure 11) or a steam

ejector (thermal vapor compression, TVC). After the vapor is compressed, it is condensed

to generate potable water.

Vapor compression processes are particularly useful for small to medium installations.

MVC systems generally only have a single stage, while TVC systems usually have several

stages. The thermal e"ciency of TVC systems is increased by adding additional stages but

in MVC adding stages or e!ects increases only capacity [24].

Membrane processes are the second important class of industrial desalination technology.

These are primarily reverse osmosis (RO) and electrodialysis (ED). RO works by applying

pressure to force a solution through a membrane, retaining the solute on one side and allowing

the pure solvent to pass to the other side. See Figure 12.

This process is the reverse of the normal osmosis process, which is the natural movement

of solvent from an area of low solute concentration, through a membrane, to an area of

20

Figure 11: Schematic diagram of single stage mechanical vapor compression desalinationprocess [24]

Figure 12: Block diagram of reverse osmosis operations (optimal pressure recovery devicesnot depicted) [24]

21

high solute concentration when no external pressure is applied. Pressurizing the saline water

accounts for most of the energy consumed by RO. The higher the salinity of the solution,

the larger the pressure required to perform the separation and the greater the amount of

energy consumed. Consequently, RO is often the method of choice for brackish water, where

only low to intermediate pressures are required. The operating pressure for brackish water

systems ranges from 15-25 bar and for seawater systems from 54-80 bar (the osmotic pressure

of seawater is about 25 bar). The water recovery of seawater RO systems tends to be low,

typically 40%, since the pressure required to recover additional water increases as the brine

stream increases. RO membranes are sensitive to pH, oxidizers, organics, particulates and

other foulants. Pretreatment of all the feed water, even the 60% that will eventually be

discharged, is required before it enters the membrane. Pretreatment of feed water is an

important system consideration since it can have a significant impact on the cost of RO [24].

Electrodialysis (ED) is used to transport salt ions from one solution, through ion-exchange

membranes, to another solution under the influence of an applied electric potential di!erence.

ED utilizes a direct current source and a number of flow channels separated by alternating

anion (negatively charged) and cation (positively charged) selective membranes to achieve

the separation of water and dissolved salts (Figure 13) [24].

This process is done in a configuration called an electrodialysis cell. The cell consists of

a feed (diluate) compartment and a concentrate (brine) compartment formed by an anion

exchange membrane and a cation exchange membrane placed between two electrodes. Typi-

cally, multiple electrodialysis cells are arranged into a configuration called an electrodialysis

stack, with alternating anion and cation exchange membranes forming the multiple electro-

dialysis cells. Since the driving force for the separation is an electric field, ED is capable of

removing only ionic components from solution, unlike RO or distillation. Electrodialysis pro-

cesses are unique compared to distillation techniques and other membrane based processes,

such as reverse osmosis, in that dissolved species are moved away from the feed stream rather

than the reverse. The energy required to separate the ions from solution increases with con-

22

Figure 13: Schematic diagram of electrodialysis desalination process [24]

centration and so ED is generally limited to brackish water. The ED membrane units are

subject to fouling and some pretreatment of the feed water is usually necessary. The electro-

dialysis reversal (EDR) process was developed to help eliminate membrane fouling. In the

EDR process, the membrane polarity is reversed several times an hour. This technique has

the e!ect of switching the brine channels to freshwater channels, and the freshwater channels

to brine channels, thus breaking up and flushing out deposits [24].

With respect to process selection between RO and ED, the choice of the most relevant

technology mostly depends on the feed water quality, level of technical infrastructure (avail-

ability of skilled operators and of chemical and membrane supplies) and user requirements.

For example, both RO and ED can be used for brackish water, but RO is better for seawater

desalination given its higher energy e"ciency at feed water salinity higher than 2,000 parts

per million (ppm). ED is preferable for brackish water desalination given its relatively higher

e"ciency and robustness. Pretreatment is usually more strict in the case of RO since RO

membranes are very susceptible to fouling. On the other hand, since ED removes only ions

from water, additional measures like disinfection or removal of particles may be required

23

[28].

2.3.2 Limitations of Conventional Technologies

Conventional desalination units are centralized due to their large size and required energy

input. They are driven with waste heat or conventional generated power and are mainly

operated in or near urban centers at relatively huge capacities. These complex and mostly

standardized technologies are di"cult to downscale to sizes smaller than 500 m!/day or to

adapt for use within decentralized applications like rural villages that are desperately in

need of clean, potable water [29]. Decentralized water production is important for remote

regions, which have neither the infrastructure nor the economic resources to run conventional

desalination plants [26]. Generally, water must be transported via pipes or trucks to remote

regions that need it. Water transport can be prohibitively expensive, limiting the quantity

of freshwater that reaches the people in rural areas. It is important to have a decentralized

water supply to meet the immediate water needs of people living in those areas.

Another limitation of conventional desalination technologies is that they require expertise

to operate and maintain. People in remote, rural areas would have to be trained in operating

and maintaining any conventional desalination technology in order to mitigate scaling and

increase system life. Trained labor for technical support of the technology is a serious

issue that needs to be adequately addressed for sustainable use of small-scale desalination

applications in less developed areas.

Water and energy are intrinsically connected because conventional desalination processes

consume large amounts of energy to produce potable water. Figure 14 shows the energy

use estimates for the saltwater desalination technologies described above. The range shown

for MED/TVC covers simple MED as well as combined MED/TVC plants. It should be

noted that power consumption does not include power losses induced by cogneration due to

increasing outlet temperature at the turbine. Furthermore, plant cost increases with product

water quality and energy e"ciency [30].

24

Figure 14: Characteristics of the two main thermal desalination technologies and the twomain mechanical desalination technology options [30]

In addition to the issue of massive energy consumption, most desalination plants using

these technologies are fossil-fuel driven. This results in green house gas emissions and a large

carbon footprint, which have detrimental e!ects on the environment. Fossil-fuel powered

desalination plants are also subject to the price volatility and availability of oil, which can

make energy use quite expensive. Desalination technologies based on renewable energy

are desirable to reduce the scarcity of energy, high cost and environmental impact issues

associated with conventional desalination technologies.

2.3.3 Renewable Energy Desalination

Renewable energy desalination is increasingly being considered for wider scale implemen-

tation, especially in developing regions, given the limitations of conventional desalination

technologies. Remote regions like inland rural villages, coastal areas and little islands tend

to have available renewable energy sources (RES). Since conventional energy supply is not al-

ways possible or easily implemented in these isolated regions, RES represent the best energy

supply option for autonomous desalination systems. Renewable energy (RE) driven desali-

25

nation promotes self-su"ciency. The operation and maintenance (O&M) of these systems in

remote areas is often easier than that of conventional desalination units. Furthermore, the

implementation of RE-desalination systems enforces sustainable socioeconomic development

by utilizing local resources. Given the fact that seawater desalination processes are highly

energy-consuming, RE provides an unlimited source of energy, allowing for diversification of

energy resources. This situation helps to avoid dependence on external energy supply.

Over the last two decades, numerous desalination systems utilizing RE have been con-

structed [29]. Most of these plants have been installed as small capacity research or demon-

stration projects. Renewable energies and desalination technologies can be combined in

various configurations. Figure 15 shows some possible combinations where SD stands for di-

rect solar distillation, MEH is Multi-E!ect Humidification and MD are membrane distillation

systems.

Figure 16 presents the installations of several desalination processes in conjunction with

renewables, regarding small-scale systems up to 50 m3/day. As seen in Figure 16, the most

popular combination is Photovoltaic (PV) with Reverse Osmosis followed by wind. How-

ever, all RE-desalination systems combined represent less than 1% of the total desalination

capacity [29]. Figure 17 shows recommended RE-desalination systems based on the system

size, the RE source available and the product water.

Photovoltaic (PV) Desalination

Since RO and ED require electricity to power their membrane processes, PV is typically

the most applicable RE source. PV as well as RO and ED are mature and commercially

available technologies. The feasibility of PV-powered RO or ED systems, as valid options for

desalination at remote sites, has been proven and there are commercially-available, stand-

alone, PV-powered desalination systems. The main problems of these technologies are the

high system cost, availability of PV cells in remote regions and membrane fouling [28].

Accelerated membrane fouling may occur due to variable operation of the desalination system

based on the intermittency of the RES. Fouling can result in frequent membrane cleaning

26

Figure 15: Possible combinations of renewable energy systems with desalination technologies[29]

Figure 16: Renewable energy-driven desalination processes and energy sources [29]

27

Figure 17: Recommended renewable-energy desalination combinations [28]

and increased membrane replacement. The repetitive starting due to RES intermittency can

also cause other problems like inverter overload and the need to flush the membranes after

each stop of the RO [31].

Given solar intermittency, energy storage is an important issue for PV desalination. Bat-

teries are used for energy storage for PV cells because they provide backup power when

there is no available solar resource, thereby prolonging operation of the desalination sys-

tem. However, non-sealed deep cycle batteries require careful maintenance and consequently

higher skill levels for sustainable operation. These higher skill levels do not tend to be locally

available in remote areas and so technology training is needed. Battery replacement can also

be expensive: while they must be replaced every five to seven years or longer if properly

maintained, without proper maintenance they will only last one year. Technically feasible

alternatives are batteryless, energy recovery PV desalination systems, and there has been

successful operation of batteryless PV desalination systems. With energy recovery, a tested

batteryless PV desalination system was able to use its energy very e"ciently, making up for

the absence of batteries [31].

Wind Desalination

The electrical or mechanical power generated by a wind turbine can be used to power

desalination plants. Like PV, wind turbines are mature, commercially available technologies.

28

Wind turbines have great potential for seawater desalination along coastal areas that have

a high availability of wind energy resources. Wind turbines may be coupled with RO and

ED desalination units [28]. A number of units have been designed and tested with regard

to the coupling of wind turbines and RO [31]. Most of them have been installed at the

Canary Islands, Spain: a 200 m3/day wind–RO plant for brackish water desalination, a 56

m3/day hybrid diesel–wind–RO plant providing fresh water and electricity for local people,

a battery-less wind–RO and a wind–ED experimental plant [28]. There have also been a

few applications of mechanical VC installations powered by wind turbines. For example,

a wind MVC plant was installed in Gran Canaria in 1999. The main conclusion from this

installation was that the start-up process took too long and that conventional MVC was

not compatible with intermittent operation, as a hard layer of scale developed within a few

weeks time [31].

Hybrid Desalination

Desalination hybrid units have also been implemented. A hybrid desalination system can

be a combination of fossil-fuel and RES or of multiple RES. For example, in Loughborough,

UK in 2003, a 0.5 m3/hour PV-wind turbine-RO system was commissioned without batteries.

It was demonstrated that this system is technically possible and that high energy e"ciency

can be achieved [31]. In a recent paper, Carta et al. presented a fully autonomous, batteryless

system, which consists of a wind farm supplying a group of eight RO modules and in the

Canary Islands, Spain there is a hybrid diesel-wind RO plant providing potable water. Some

hybrid wind-solar desalination systems are used to capture the two forms of renewable energy

based on the fact that for some locations, according to metrological data simulations, the

wind and solar time profiles do not coincide [28].

Nuclear Desalination

Nuclear desalination can be employed for producing pure water. Cogeneration nuclear

plants that produce thermal energy, electricity and pure water can help to reduce the cost

of desalinated water. Recent studies have shown that only RO and MED are compatible for

29

combination with nuclear desalination. The modular high temperature gas cooled reactor

(MHTGR) and the liquid metal fast breeder reactor (LMFBR) can be employed in the new

design of water and energy cogeneration plants because of their small size and compatibility

with desalination applications. The average annual cost of water production consists of

annual production charges, operation and maintenance cost and fuel cost. Nuclear plants

are very capital intensive. It was reported that the annual capital charges represent more

than 70% of the total annual average production cost. Despite the cost, nuclear energy is

used for desalination purposes in the city of Skeichenko in Russia. The complex is a large

multi-purpose plant and it has been supplying the city with fresh water, electricity and

thermal energy. It provides 0.14 million m3 of fresh water per day and generates 150MW of

electric power [32].

Ocean Power Desalination

Wave energy and wave-powered desalination technologies are in the prototype stage and

are not yet commercially available. Wave-power desalination has high potential because the

two main ingredients of (wave) energy and (sea) water are both available in abundance and

at the same location. The wave-powered desalination plant prototypes built have all used

reverse osmosis for the desalination process. The RO plants have either been powered by

electricity generated by a wave energy plant or directly by using sea-water pressurized by

the action of the waves. Current wave-powered desalination technologies are large-scale and

typically with unit capacities in the range of 500–5,000 m3/day. Smaller desalination units

(less than 500 m3/day) are technically feasible but the development e!ort for this size of

unit is currently small. Wave-powered desalination can be done in three ways: 1) direct

pressurization of sea-water (avoiding the generation of electricity) that is then fed into a RO

desalination plant to produce fresh water 2) creating a temperature di!erence between the

water surface and deep sea-layers through a process called Ocean Thermal Energy Conversion

(OTEC), which provides low grade thermal energy suitable for distillation processes and 3)

tidal energy, which can be extracted using tidal barrages or tidal turbines to provide energy

30

as a rotating shaft similar to wind turbine desalination [29].

Geothermal Desalination

Geothermal energy is a mature technology that can be used to provide energy for desali-

nation at a competitive cost. Geothermal desalination may be appropriate at sites where

drinking water is scarce and geothermal resources with temperatures of 80-100°C can be

developed at acceptable costs ( < $11.2/GJ and < $3.3/m3 respectively). For reservoirs

with higher temperatures there is also the option to generate geothermal power for use in a

desalination plant [29].

Geothermal energy sources may be classified in terms of the measured temperature as low

( < 100°C), medium (100°C - 150°C) and high temperature (> 150°C). The main advantage

of geothermal energy relative to other renewable energy technologies is that thermal storage

is unnecessary since it is both continuous and predictable. Geothermal energy can be utilized

in a variety of di!erent ways for desalination. Geothermal energy can be directly used in

combination with thermal desalination technologies like MED, MEH, TVC and MD (low

temperature) or with MSF (medium temperature). Moreover, the thermal energy of high

temperature geothermal fluids can be converted into electricity or shaft power, permitting

the coupling with other desalination systems like RO, ED and MVC [29].

It is recognized that there is significant potential to improve desalination systems based

on geothermal energy. In the 1970’s, the first geothermal energy powered desalination plants

were installed in the U.S., testing various potential configurations for the desalination tech-

nologies, including MSF and ED [28]. During the 1990’s a research project on Milos Island in

Greece demonstrated that it is technically feasible to utilize low enthalpy geothermal energy

for electricity generation and seawater desalination [29].

Solar thermal Desalination

Megawatt scale solar power generation using Concentrating Solar Power (CSP) technol-

ogy can be achieved by using any one of the three main types of concentrating solar power

systems: linear concentrator, dish/engine and power tower systems. All of these configu-

31

rations are based on glass mirrors that continuously track the position of the sun, using

the reflected sunlight to heat a fluid flowing through the tubes. The hot fluid then is used

to boil water, producing high-pressure, high-temperature steam, for use in a conventional

steam-turbine generator to produce electricity [33].

Several configurations are possible for CSP-desalination plants: (i) MSF distillation units

operating with steam extracted from steam turbines or supplied directly from boilers; (ii)

low-temperature MED using steam extracted from a turbine and; (iii) seawater RO desalting

units supplied with electricity from a steam power plant or from a combined gas/steam power

cycle. Currently, no commercial or even demonstration installations of CSP combined with

desalination exist [29].

2.3.4 Humidification Dehumidification (HDH) Desalination

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]

32

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]

33

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

tower characteristic, varying with the L/G ratio.

49

3.5 Experimental Cooling Tower Test3.5.1 Objective

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

CF-1200 0.152 0.038 0.072 0.5CF-1200 0.152 0.057 0.067 0.8CF-1200 0.152 0.132 0.070 1.9CF-1200 0.152 0.132 0.052 2.6CF-1200 0.152 0.132 0.043 3.1CF-1200 0.152 0.132 0.037 3.6CF-1200 0.152 0.132 0.032 4.1CF-1200 0.152 0.132 0.028 4.7CF-1200 0.152 0.132 0.025 5.2CF-1200 0.305 0.038 0.069 0.5CF-1200 0.305 0.057 0.072 0.8CF-1200 0.305 0.126 0.067 1.9CF-1200 0.305 0.126 0.052 2.4CF-1200 0.305 0.126 0.044 2.9CF-1200 0.305 0.126 0.038 3.3CF-1200 0.305 0.126 0.032 3.9CF-1200 0.305 0.126 0.029 4.3CF-1200 0.305 0.126 0.026 4.8CF-1200 0.457 0.038 0.071 0.5CF-1200 0.457 0.057 0.071 0.8CF-1200 0.457 0.126 0.069 1.8CF-1200 0.457 0.126 0.052 2.4CF-1200 0.457 0.126 0.044 2.9CF-1200 0.457 0.126 0.038 3.4CF-1200 0.457 0.126 0.032 3.9CF-1200 0.457 0.126 0.029 4.3CF-1200 0.457 0.126 0.026 4.8

56

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

Coe"cient(R2)

CorrelationAverage %Uncertainty

CorrelationMax %

UncertaintyCF-1200 Me=0.9327(L/G)"0.914 0.9801 9.4 13.3CF-1900 Me=0.5126(L/G)"0.625 0.9912 3.3 5.2Charcoal Me=0.8466(L/G)"0.594 0.9421 5.8 23.8Lou!a Me=1.1481(L/G)"0.966 0.9948 5.0 8.3

Bamboo Me=0.7311(L/G)"0.687 0.9779 4.0 6.6

61

Table 6: Transfer characteristic correlations according to Merkel approach (H=0.305 m)Fill Merkel Empirical Relation Correlation

Coe"cient(R2)

CorrelationAverage %Uncertainty

CorrelationMax %

UncertaintyCF-1200 Me=1.0723(L/G)"0.885 0.9928 3.7 7.4CF-1900 Me=0.6377(L/G)"0.633 0.9945 2.6 6.4Charcoal Me=1.623(L/G)"0.889 0.9806 8.2 31.0Lou!a Me=1.2363(L/G)"1.012 0.9933 9.64 22.5

Bamboo Me=1.4202(L/G)"1.000 0.9694 4.4 8.5

Table 7: Transfer characteristic correlations according to Merkel approach (H=0.457 m)Fill Merkel Empirical Relation Correlation

Coe"cient(R2)

CorrelationAverage %Uncertainty

CorrelationMax %

UncertaintyCF-1200 Me=1.0347(L/G)"0.848 0.9659 4.1 8.3CF-1900 Me=0.8067(L/G)"0.677 0.9953 3.1 5.0Charcoal Me=3.9702(L/G)"1.723 0.9824 5.6 13.9Lou!a Me=1.2354(L/G)"0.854 0.9934 4.8 8.8

Bamboo Me=1.4426(L/G)"0.724 0.9000 4.7 9.9

Figure 40: CF-1200 transfer characteristic plots

62

Figure 41: CF-1900 transfer characteristic plots

fill pressure drop in order from highest to lowest was charcoal, bamboo, lou!a, CF-1200 and

CF-1900.

Fill Comparison

To compare the overall performance of the fills, their transfer characteristic and pressure

drop had to be combined into the metric of fan power consumption. The data from the

expressions for Me vs L/G and !P vs air velocity with water loading (flux) as a parameter

Table 8: Fill Pressure Drop Correlations (H=0.457 m)Equation: !P = (B + C · vD

air) + L/A(E + F · vIair)

Constant CF-1200(R2=0.9790)

CF-1900(R2=0.9107)

Charcoal(R2=0.9687)

Lou!a(R2=0.9614)

Bamboo(R2=0.9431)

B 0.3992 -222.7662 3.0298 -20.7525 -1.3329C 3.2498 230.2587 81.2022 26.0532 25.2751D 2.1851 -0.0679 1.9405 1.5815 1.8033E 1.4459 1.2088 -4.6872 0.4448 8.74027F 1.7931 0.1074 17.4330 5.5351 34.9581I 0.1070 3.3738 5.1459 1.2926 1.9898

63

Figure 42: Custom fill transfer characteristic plots (H=0.152 m)

64

Figure 43: Custom fill transfer characteristic plots (H=0.305 m)

65

Figure 44: Custom fill transfer characteristic plots (H=0.457 m)

Figure 45: CF-1200 fill pressure drop (H=0.457 m)

66

Figure 46: CF-1900 fill pressure drop (H=0.457 m)

were entered into the CTI 3.1 Toolkit software package created by the Cooling Tower Institute

(CTI) to facilitate cooling tower design [49]. The Toolkit analysis program enabled the

calculation of the power required for each fill to meet a cooling tower approach of 4°K.

In order to complete this analysis in Toolkit, a cooling tower range of 5°C, a wet bulb

temperature of 26°C, a relative humidity of 100% and the intercept (c) and the slope (m) of

the Merkel number correlation (Me = c(L/G)m) for a fill of a given height were input. The

L/G value was adjusted until the desired approach of 4°K was attained. From this L/G,

the air mass flow rate (G) was calculated for a fixed water mass flow rate of 0.126 kg/s.

The centrifugal fan power, in units of Watts, was then calculated according to Equation 8

where V = specific volume of air (m3/kg dry air), G = air mass flow rate (kg dry air/s),

" = centrifugal fan e"ciency (30%) and !Pfill = the fill pressure drop (Pa) at a given air

velocity.

P =V · G · !Pfill

"(8)

67

Figure 47: Lou!a fill pressure drop (H=0.457 m)

Figure 48: Charcoal fill pressure drop (H=0.457m)

68

Figure 49: Bamboo fill pressure drop (H=0.457 m)

In this way the e!ects of the fill thermal performance (Me) and pressure drop (!P ) were

combined. The lower the required fan power, the better the fill performance. As shown

in Figure 50 the lou!a was the best custom packing because it had the lowest fan power

consumption for all three fill heights. The absolute uncertainty or error displayed on the bar

graphs of Figure 50 is 2.477 Watts (W). For fill heights of 0.305 m and 0.457 m the charcoal

fill performed better than the bamboo fill. The fan power required for the charcoal fill was

8% and 50% less power than the bamboo fill for heights of 0.305 m and 0.457 m respectively.

However, for the fill height of 0.152 m the bamboo fill consumed 24% less power than the

charcoal fill. Figure 51 displays the fan power consumption for all five of the fills that were

tested for a fill height of 0.457 m. As a base for comparison, for a fill height of 0.457 m, the

fan power consumption for the CF-1900 and CF-1200 was 7.8 W and 9.6 W respectively.

For the same fill height the lou!a fan power consumption was 20.8 W, or approximately

2.7 times the fan power consumption of the CF-1900 fill, which had the lowest fan power

consumption of all the fills tested. In order to potentially lower the pressure drop of the

69

Figure 50: Fan power consumption for tested custom fills

lou!a fill, it can be cut vertically in half and the halves stacked front to back in the cooling

tower column.

3.5.5 Error Analysis

The errors, in terms of absolute uncertainty, associated with each of the observed mea-

surements are tabulated in Table 9. These uncertainties represent the manufacturer er-

ror associated with the actual instrument (thermocouples, inclined manometer, flow meter,

barometer).

These errors were used to calculate the overall uncertainty in the Merkel number for each

trial. The majority of the uncertainty is due to the Two and the Twi thermocouple readings

since the Merkel number is most sensitive to these parameters. The percent uncertainty

70

Figure 51: Fan power consumption for tested fills (H=0.457 m)

Table 9: Uncertainties of measured variablesVariable Units Absolute Uncertainty!Porifice Pa 3.74!Pfill Pa 4.98

L kg/s 0.0028Tai °C 0.50Tao °C 0.50Twi °C 0.50Two °C 0.50Twbi °C 0.50Twbo °C 0.50

71

associated with each of the measurements is in Table 10. As a result of these uncertainties,

the overall uncertainty in the Merkel number was approximately 10.3%.

3.5.6 Implications for Fills Made of Local Materials

As expected, fills made of local materials such as bamboo, charcoal and lou!a have a lower

performance than high-e"ciency, industrial PVC packings (CF-1200, CF-1900). However,

of the three custom fills tested, lou!a had the best overall (combined thermal and pressure

drop) performance. Although its performance, measured in terms of fan power consumption,

was 2.7 times worse than the Brentwood CF-1900 fill, it still has the most potential as a

locally available, inexpensive fill for use in the humidifier of the HDH system. For a fill

height of 0.457 m, the charcoal and bamboo fills performed 2.9 and 4.4 times worse than

the lou!a fill respectively. As backup, if lou!a is not available, the charcoal and then the

bamboo fill could be used in the humidifier.

Table 10: Uncertainty contributionsPartial Derivative % Uncertainty

#Me/#!Porifice 3.57%#Me/#L 0.53%#Me/#Tai 0.00%#Me/#Tao 0.00%#Me/#Twi 32.84%#Me/#Two 62.46%#Me/#Twbi 0.59%#Me/#Twbo 0.00%

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4 Issues Relevant to HDH Desalination

In this chapter the obstacles related to the development of RE-desalination generally and

HDH desalination in particular are identified and categorized along technical, economic,

social, environmental and political lines. Where relevant, this chapter also addresses these

issues in the specific context of Haiti.

4.1 Technical Issues4.1.1 Technological Barrier

Conventional desalination technology is considered mature, although there are still significant

margins that can be gained regarding e"ciency increase, as well as volume and costs decrease.

Concerning RE-desalination generally, and HDH in particular, there tends to be a lack

of suitable design guidelines and tools to implement these technologies on a large-scale.

Worldwide, there are only a few specialists in solar desalination installations [29]. More

people must be trained in this technology. There is also a demand for standardization

and performance validation in order to make these RE-desalination systems comparable.

The installation of solar thermal desalination systems needs to be as easy as possible. Some

possible ideas to achieve ease of operation are self-explanatory modular components, low-tech

components that can be easily and economically replaced (i.e. fills made from local materials

in the humidifier of the HDH system) and having experienced water plant operators available

to help with training locals in the operation and maintenance of the technology.

For many desalination technologies, the focus has been on the development of relatively

large plants, so there is a lack of technologies appropriate for small-scale applications. These

undeveloped technologies include small capacity pumps and control systems for decentralized

desalination systems, suitable pre- and post-treatments of the water, suitable energy recovery

technologies, energy storage and methods for safe and e"cient disposal of the brine in inland

plants [29]. Furthermore, complementary components such as energy storage equipment,

73

anti-fouling materials and control systems are needed for autonomous operation of the small-

scale desalination plants.

The variability of energy supply from RES is a major technical issue for RE-desalination.

There is typically a mismatch between the energy supply and demand. The designs of

conventional desalination plants are based on a constant supply of energy. The HDH tech-

nology is appropriate for small-scale, decentralized use but it also has the problem of in-

termittent operation due to the variability of solar radiation intensity. The fluctuation of

the energy supply can have negative e!ects on the HDH system, including biological foul-

ing that can cause contaminated product water, increased maintenance requirements and

under-utilization. Under-utilization typically leads to higher specific costs of water, which

results in the plant being less commercially attractive. Energy storage can be used to in-

crease the HDH plant operation time and to stabilize water production. However, storage

options are limited. Typically for thermal energy storage, the main option today is storing

it in a tank of a thermal fluid (i.e. water, oil) depending on the operation temperature.

Additionally, specific control software to guarantee stable, autonomous operation during the

common oscillations of solar supply is also lacking [29].

4.2 Economics of desalination4.2.1 Economical Barrier

Market and risk uncertainty are the primary obstacles to wide-scale deployment of RE-

desalination. RE-desalination is a relatively new area and little is known about its market

potential. There is a lack of comprehensive market analysis as to the size, locations and

segments of the market. Without such analysis, it is di"cult to determine where and how

to enter the market and how long it may take to receive a return on investments. Given the

uncertainty associated with the return on the investment, the magnitude of risk associated

with investment in the technology is unclear. Consequently, investors are hesitant to invest

74

and if they do decide to invest, they require high rates of return on their investment [29].

Development of a clear and reliable market and risk analysis is needed to help correct this

issue.

RE-desalination small-to-medium enterprises (SME) lack the financial resources and lo-

cal knowledge needed to promote their technologies and penetrate the most promising niche

markets. RE-desalination has the greatest potential in developing countries, where there

is a lack of infrastructure and need for decentralized, o!-grid potable water supply. Un-

fortunately, these markets are typically relatively far away with di"cult access, inadequate

currency, political risks and di!erent cultural norms concerning business and utility services.

It is also crucial that the water produced from the technology be a!ordable because the

customers in this market typically live o! on less than $2/day. However, if the technology is

a!ordable enough and impacts numerous people, then with economies of scale the SME can

make a profit. The SME should also utilize the resources available from NGO water sup-

port programs, microfinance and financial aid (i.e. World Bank) available for installations

in developing countries. All of these issues make it important for SME with appropriate

desalination technologies to collaborate with local companies where the technology is to be

deployed. It is also important for the SME to collect and disseminate relevant experiences

and information obtained in the region to the RE-desalination community [29].

4.2.2 Economics of HDH System

The principal components of the HDH system are the solar collector, the humidifier and the

dehumidifier. The solar collector is the main component of a solar desalination unit and any

improvement in its e"ciency will have a direct bearing on the water production rate and the

product cost. The solar collector is a crucial component in the HDH system because it is the

majority of the system’s capital cost: 40-45% for air heated systems and 20-35% for water

heated systems. Therefore, it is important to ensure the reliability of the solar collector

and to have a high specific water production. Specific water production is the amount of

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water produced per m2 of solar collector area per day and is an indicator of the solar energy

e"ciency of the HDH cycle. At present there are no commercial systems that utilize a solar

air heater for solar desalination. Representative values for air temperature rise and solar

irradiation are 50°C and 1 kW/m2 respectively. The best performing air-heating collector

under these conditions has an e"ciency of only 32%, where solar collector e"ciency is defined

as the heat gained by air divided by solar incident radiation [26]. Currently, the prices of the

collectors are relatively high. Only a reduction in these prices through increased collector

e"ciency and cost-e!ective materials will enable the cost of the desalinated water to drop

to economical levels, allowing solar–thermal units to compete with conventional desalination

techniques [50].

The share of the fill in the total cost of the cooling tower or humidifier is normally only

10-20% depending on the type and size of the cooling tower. There is a direct relationship

between the e"ciency of the fill and the size of the tower. A low e"ciency fill will increase

the cross-sectional area of the tower and the required pumping head. To compensate, a

larger fill height is required to bring the cross-sectional area of the tower to an acceptable

figure. The problem is that this increases the cooling tower height, the amount of material

needed for construction and the resulting cooling tower cost. A high e"ciency fill, such as

the film fill, will considerably reduce the required cross-section and the first year cost of a

counter-flow cooling tower [51]. However, as mentioned in section 3.3, the problem with film

fills is that they are more prone to fouling compared to lower e"ciency splash type fills.

Energy costs can determine whether a desalination system is successful or not. If the en-

ergy costs are too high, especially in developing countries with limited energy infrastructure,

the desalination system may not be feasible. For HDH systems, the energy costs associated

with the condensers and pump operation, as well as the energy savings associated with the

fill choice and coupling the system to waste heat energy sources, may end up being crucial

in developing a commercially viable system.

For desalination, the balance between investment and operational costs is one of the main

76

aspects for fundamental decisions regarding two possible strategies to minimize lifetime water

costs: low investment or low operational costs [52]. There is evidence that the HDH process

can economically compete with conventional desalination processes. The HDH system costs

are site-specific based on local material costs and the availability of solar insolation. However,

there is not su"cient data to estimate the costs of HDH given that no commercial HDH

system has been analyzed for cost data in a specific region. The data in Table 11 is illustrative

for displaying comparative cost trends between solar desalination and conventional RO and

MSF systems. The comparison shows that investment costs are the highest, but energy costs

are the lowest in the case of RE-desalination because the energy is “ free ” and renewable.

The “ free ” energy is partially o!set by increased amortization costs [50]. It is worth noting

that the data in Table 11 is almost 20 years old and might no longer be valid, but the cost

trends are still valid. As solar RE technology improves, the investment costs will be driven

down to comparable levels to the investment costs of conventional desalination systems.

Table 12 shows a comparison of equipment capital cost for the HDH process with other

conventional techniques made by El-Dessouky in a study utilizing waste heat from a gas-

turbine powered HDH desalination unit [50]. The main take-away from Table 12 is that the

HDH process powered by waste heat has the lowest specific cost compared to other conven-

tional processes based on waste heat. Thus, the HDH process appears to be economically

attractive, making it a suitable replacement for all other forms of solar desalination in the

smaller capacity range.

For small-scale installations in the range from 500 up to 5,000 m3/day, water costs in

Table 11: Distribution of costs for conventional (RO and MSF) and renewable energy drivenplants [50]

Type of Process Investment costs (%) Operational costs (%) Energy costs (%)Conventional (RO) 22-27 14-15 59-63Conventional (MSF) 25-30 38-40 33-35

Renewable 30-90 10-30 0-10

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Table 12: Comparison of HDH process (with waste heat) with other processes [50]

Parameter ProcessSpecificCost

($/m3d)

SpecificPower(kJ/kg)

Water to PowerRatio (kg/kWh)

HDH 287 61.26 3.9772Single MSF 1451.18 294.21 -Dual MSF 3647.4 96.519 23.919

Single RO without energy recovery 1022.8 50.420 -Single RO with energy recovery 1127.4 33.619 -

Dual RO without energy recovery 1906.3 36.20 36.819Dual RO with energy recovery 2225.8 27.20 49.19

the range of $1.0/m3- $4.6/m3 are reported. Very small installations of capacities from 5-

100 m3/day are currently mainly served by small, brackish RO installations. Operation and

maintenance costs are high for installations of this size. Regarding seawater RO, maintenance

companies report maintenance and energy costs between $1.3/m3 - $4.2/m3 including labor

costs. These costs result in water prices ranging from $2.1/m3 up to $6.3/m3. The main

advantage of HDH relative to small-scale RO is its low maintenance demand and no need of

chemical pretreatment. Additionally, the use of low temperature heat as a main energy source

for HDH allows the application of waste heat from small diesel or gas electrical generators

(combined heat and power, CHP) for supplying relatively inexpensive heat where the grid

is nonexistent or unreliable. This development makes HDH appropriate for remote villages.

Savings in thermal to mechanical conversion losses allow HDH to compete economically with

the RO process for such decentralized applications [52].

The main conclusion drawn from Table 13 is that RO has light cost advantages at small-

scale operations over 5 m3/day in installations where standard electrical grid connection is

available and electricity prices are at or below $0.22/kWh. In all other cases when comparing

costs and ease of operation, the use of thermal desalination units such as HDH should be

considered [52].

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Table 13: Cost comparison for small-scale desalination methods [52]Costs in $/m3

(operation/total)Heat

SourceElectricity

Source1 m3/day 5 m3/day 10 m3/day

HDH waste heat CHP CHP $4.5/$9.25 $4.27/$5.88 $3.58/$4.98HDH solar thermal solar

collectorGrid $10.77/$13.23 $7.71/$9.32 $7.11/$8.52

HDH autonomous solarcollector

PV $13.12/$15.21 $8.86/$10.11 $7.65/$8.55

RO grid connected - Grid - $1.3/$4.18 $2.09/$6.26RO-genset - Generator - $1.49/$4.03 $4.18/$8.35RO-PV - PV - $1.04/$3.88 $6.26/$10.44

4.2.3 Water Price in Haiti

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.

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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

87

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

88

• 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].

89

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

ProcessDescription Minerals

1 Blend with 1%clarified seawater

+pH neutralization

15 mg/L Mg + 5 mg/LCa +125mg/L Na + 220

mg/L Cl + 25 mg/LSO4, pH 7-7.5

2 CO2

addition+CalciteLimestone (CaCo3,MgO) percolation +

Na2CO3

80 mg/L CaCO3, pH7-7.5

3 CO2 addition+Dolomite

Limestone (CaCO3,MgCO3) percolation

+ Na2CO3

80 mg/L CaCO3, pH7-7.5

4 Addition of CaCl2 +NaHCO3

100 mg/L CaCO3, 100mg/L Na + 50 mg/L Cl,pH 7-7.5

Table 15: Water remineralization process comparison [62]Process Investment Operation Water Quality Ease of

Operation1 Very Low Low Medium water

quality- highsodium chloride

content

Easy

2 High High Good water quality(very small sodium

increase)

Easy

3 High High Very good waterquality (very smallsodium increase,more magnesium)

Easy

4 Very Low Low Medium waterquality- high

sodium chloridecontent

Timeconsuming(chemical

dissolution)

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nation plant in densely populated areas, it may impact the residential environment. Some

desalination plants generate noise due to the use of high-pressure pumps. Noise pollution

can be mitigated by using canopies or acoustical planning. Since construction can be time-

consuming, inconvenient, noisy and disruptive to the environment, it is ideal to have as little

construction as necessary. If the fuel resources, electricity connection and water connections

are near the proposed plant site, then there will be less construction. After construction

begins, planners should develop an environmental monitoring plan to ensure the project

meets established environmental guidelines. Management plans are also important during

the plant’s operation to ensure consistent environmental acceptability [63].

Construction of water intake structures and pipelines to carry feedwater and concen-

trate discharge may cause disturbances to environmentally sensitive areas. The water intake

structures, unless properly designed, may kill fish. There is also a risk of polluting the

groundwater from the drilling process when installing feedwater pumps. Leakage from pipes

that carry feedwater into the desalination plant and concentrated brine out of the plant can

cause damage to groundwater aquifers. To help prevent this damage, plants should have

sensors to detect this leakage and workers to notify plant operators if leaks develop in the

pipes [63].

Concerning infrastructure, if the plant is obtaining the needed electricity from the grid

or other fossil fuel sources, the gas emissions and air pollution must be addressed. The

burning of fossil fuels for energy use will lead to increased air pollution, which can have a

serious e!ect on public health. There is also concern regarding the quantity of chemicals

stored at the plants. Chemical spill risks require storing the chemicals away from residential

areas [63]. It should be noted, however, that in developing countries, emissions and other

environmental issues are secondary to economic development and survival.

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4.4.2 Brine Discharge

Desalination plants generate two products: fresh water and concentrate (reject or residual

stream) byproduct. Brine concentrate is high in salinity (i.e. contains a TDS concentration

> 36,000 mg/L) and may contain low concentrations of certain chemicals used during pre-

treatment and post-treatment cleaning processes as well as elevated temperatures. These

concentrate properties can lead to problems for the marine habitats and the receiving water

environments. Critical concentrate parameters are TDS, temperature, and specific weight

(density). The amount of concentrate produced from a desalination plant is a factor of the

desalination process’ recovery rate (product water/feedwater). Generally, membrane plants

have a higher recovery rate than distillation plants, resulting in a higher amount of salt in

the concentrate. This trend is observed in Table 16, which shows concentrate characteristics

for RO and MSF/MED desalination technologies. The solar-driven HDH desalination plant

typically has a low recovery rate of 5% so brine disposal is not a significant issue. Distillation

desalination plants usually can reduce the concentrate density by diluting it with cooling

water before it is discharged into receiving water. Table 16 also shows that concentrate from

distillation processes is generally warmer than concentrate from membrane processes. Many

desalination plants dispose of brine in surface water. Compared to freshwater, concentrate

has a higher density due to the higher salt concentration [63]. The concentrate tends to sink

in water with lower salinity (lower density). This tendency for the concentrate to sink in the

receiving water has negative e!ects on the marine environment.

The disposal of desalination concentrate is often a leading factor in determining the cost-

e!ectiveness of a project. If brine disposal regulations are in place and the desalination plant

has di"culty satisfying them, then fees can accrue against the plant. The U.S. Environmen-

tal Protection Agency (EPA) has initiated the classification of membrane concentrate as an

industrial wastewater. This regulatory classification has made it essential that the desali-

nation plants in the U.S. be able to properly dispose of the concentrate that they produce.

Regulation of concentrate disposal will tend to keep the application of desalination technolo-

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Table 16: Concentrate characteristics for various desalination technologies [63]Process RO RO MSF/MEDFeedwater Brackish Seawater Seawater

Recovery Rate 60-85% 30-50% 15-50%Temperature Ambient Ambient 10-15°F above

ambientConcentrate

BlendingPossible, not

typicalPossible, not

typicalTypical, withcooling water

FinalConcentration

Factor

2.5-6.7 1.25-2.0 <1.15

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

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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

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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].

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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.

107

References[1] Engelman, R., People in the Balance. Washington, D.C.: Population Action Interna-

tional, 2000. <www.populationaction.org>.

[2] Vigotti, R., Ho!man, A., Workshop on Renewable Energy and Water. IEA WorkingParty on Renewable Energy Technologies, 2009.

[3] Gardener-Outlaw, T., Engelman, R., Sustaining Water, Easing Scarcity: ASecond Update. Washington, D.C.: Population International, 1997. <http://www.populationaction.org/Publications/Reports/Sustaining_Water_Easing_Scarcity/Sustaining_Water_Easing_Scarcity_-_Full_Report.pdf>.

[4] World Resources Institute 2003. Accessed 10 April 2010. <http://www.wri.org/>.

[5] Global Environment Outlook 2000. UNEP, Earthscan, London, 1999. <http://www.unep.org/geo/geo2000/>.

[6] Gleick, P. The World’s Water 2006. Accessed 10 April 2010. <http://www.worldwater.org/>.

[7] UNDP 2006. Accessed 10 April 2010. <http://www.data.360.org/temp/dsg757990600.jpg>.

[8] CIA, The World Factbook: Central America and Caribbean: Haiti. Accessed 10April 2010. <https://www.cia.gov/library/publications/the-world-factbook/geos/ha.html>.

[9] WHO/UNICEF Joint Monitoring Program for Water Supply and Sanitation. Accessed3 April 2010. <http://www.wssinfo.org/download.php?id_document=1289>.

[10] WHO, Water Sanitation and Health (WSH) 2010. Accessed 10 April 2010. <http://www.who.int/water_sanitation_health/mdg1/en/index.html>.

[11] Fiorenza, G., Sharma, V., and Braccio, G., Techno-economic evaluation of a solar pow-ered water desalination plant. Energy Conversion and Management 44, 2217–2240,2003.

[12] Guy, S., Haiti: The Struggle for Water. Frontline World. October 2004. Accessed 10April 2010.<http://www.pbs.org/frontlineworld/fellows/haiti/indexb.html>.

[13] USGS, Earthquake Hazards Program. Magnitude 7.0-Haiti Region. Accessed10 April 2010. <http://earthquake.usgs.gov/earthquakes/eqinthenews/2010/us2010rja6/>.

[14] CBS News, Red Cross: 3M Haitians A!ected by Quake. 13 January 2010. Accessed 10April 2010. <http://www.cbsnews.com/stories/2010/01/13/world/main6090601.shtml?tag=cbsnewsSectionContent.4>.

108

[15] Renois, C., Haitians angry over slow aid. The Age. 5 February2010. Accessed 10 April 2010. <http://www.theage.com.au/world/haitians-angry-over-slow-aid-20100204-ng2g.html>.

[16] Ourousso!, N., A Plan to Spur Growth Away from Haiti’s Capital. The New YorkTimes. 30 March 2010. Accessed 10 April 2010. <http://www.nytimes.com/2010/03/31/arts/design/31planning.html?pagewanted=1&hp>.

[17] IFAD, Haiti: Turning a nation’s misfortune to hope for its people. 29 January 2010.Accessed 10 April 2010. <http://www.ifad.org/operations/projects/regions/pl/haiti/rural.htm>.

[18] Water.org, Haiti Challenge Launches at CGI. Accessed 10 April 2010. <http://water.org/2009/09/haiti-challenge-launches-at-cgi/>.

[19] Clean Water: International Child Care, Inc. 2009. Accessed 10 April 2010. <http://www.intlchildcare.org/haiti_health_water.php>.

[20] Schaaf, B., International Action’s Campaign for Clean Water in Haiti. 1 Dec.2008. Accessed 10 April 2010. <http://www.haitiinnovation.org/en/2008/12/02/international-actions-campaign-clean-water-haiti>.

[21] Spiegler, K., El-Sayed, Y., A Desalination Primer. Italy: Balaban Desalination Publi-cations, 1994.

[22] United Nations Environment Programme. Accessed 10 April 2010. <http://www.unep.org/>.

[23] Environmental Technologies Action Plan: Water Desalination Market Acceleration.Accessed 10 April 2010. <http://ec.europa.eu/environment/etap/inaction/pdfs/watedesalination.pdf>.

[24] Miller, J., Review of Water Resources and Desalination Technologies. New Mexico:Sandia National Laboratories, 2003.

[25] Lienhard V, J., Balaban, M., 2.500 Desalination and Water Pu-rification. Spring 2009. Accessed 19 April 2010. <http://ocw.mit.edu/NR/rdonlyres/Mechanical-Engineering/2-500Spring-2009/21389582-02BE-41AB-9028-4061652FDADF/0/MIT2_500s09_lec01.pdf>

[26] Narayan, G., Sharqawy, M., Lienhard V, J., Zubair, S., and Antar, M., The potential ofsolar-driven humidification-dehumidification desalination for small-scale decentralizedwater production. Renewable and Sustainable Energy Reviews 14 (4), 1187-1201, 2010.

[27] Narayan, G., Sharqawy, M., Lienhard V, J., and Zubair, S., Thermodynamic analysis ofhumidification dehumidification desalination cycles. Desalination and Water Treatment16, 339-353, 2010.

109

[28] Mathioulakis, E., Belessiotis, V., and Delyannis, E., Desalination by using alternativeenergy: Review and state-of-the-art. Desalination 203, 346–365, 2007.

[29] Intelligent Energy for Europe programme, Roadmap for the development of desalinationpowered by renewable energy. ProDes project. 19 Sept. 2009.

[30] Trieb, F., AQUA-CSP: Concentrating Solar Power for Seawater Desalina-tion. Stuttgart, Germany: DLR, 2007. Accessed 19 April 2010. <http://www.dlr.de/tt/Portaldata/41/Resources/dokumente/institut/system/projects/aqua-csp/AQUA-CSP-Full-Report-Final.pdf>.

[31] Papapetrou, M., Epp, C., and Tzen, E., Autonomous Desalination Units based onRenewable Energy Systems - A Review of Representative Installations Worldwide.Springer, Solar Desalination for the 21st Century, 343–353, 2007.

[32] Akash, A., AI-Jayyousi, O., and Mohsen, S., Multi-criteria analysis of non-conventionalenergy technologies for water desalination in Jordan. Desalination 114, 1-12, 1997.

[33] National Renewable Energy Lab, Learning about Renewable Energy: ConcentratingSolar Power. 29 Sept. 2009. Accessed 21 Oct. 2009. <http://www.nrel.gov/learning/re_csp.html>.

[34] Parekh, S., Solar desalination with humidification-dehumidification technique- a com-prehensive technical review. Desalination 160, 167-186, 2004.

[35] Summers, E., Lienhard V, J., Design and Optimization of an Air Heating Solar Collec-tor with Integrated Phase Change Material Energy Storage for Use in Humidification-Dehumidification Desalination. Solar Energy. Submitted for publication.

[36] Cooling Tower Institute, What is a cooling tower? Accessed 10 Oct. 2009. <http://www.cti.org/whatis/coolingtowerdetail.shtml>.

[37] Mills, A., Heat and Mass Transfer. Chicago: Irwin, 1086-1119, 1995.

[38] Bedekar, S., Nithiarasu, P. and Seetharamu, K., Experimental Investigation of the Per-formance of Counter-Flow, Packed-Bed Mechanical Cooling Tower. Energy 23 (11),943-947, 1998.

[39] Brentwood Industries, What is a Cooling Tower? Cooling Tower Basics. 2006. Accessed10 Oct. 2009. <http://www.brentwood-ind.com/cool/basics.htm>.

[40] Kloppers, J., A Critical Evaluation and Refinement of the Performance Predictionof Wet-Cooling Towers, Ph.D. thesis, University of Stellenbosch, Stellenbosch, SouthAfrica, 2003.

[41] Perry, R., Green, D., Perry’s Chemical Engineers’ Handbook. McGraw Hill, 1997. Ac-cessed 10 Oct. 2009. <http://www.knovel.com/web/portal/basic_search/display?_EXT_KNOVEL_DISPLAY_bookid=48&_EXT_KNOVEL_DISPLAY_fromSearch=true&_EXT_KNOVEL_DISPLAY_searchType=basic&_EXT_KNOVEL_DISPLAY_showSearchTOC=true>>.

110

[42] Kolev, N., Chapter 3 - Industrial Packing, Packed Bed Columns: For absorption, des-orption, rectification and direct heat transfer, 1st edition. Elsevier, 154-157, 2006.

[43] Kröger, D., Chapter 4 - Mass Transfer and Evaporative Cooling, Air-Cooled HeatExchangers and Cooling Towers: Thermal-Flow Performance Evaluation and De-sign, volume 1. Tulsa, Oklahoma: PennWell Corporation, 2004. Books24x7. Ac-cessed 11 Sept. 2009. <http://common.books24x7.com.libproxy.mit.edu/book/id_17327/book.asp>.

[44] Wallis, J., Aull, R., Getting Your Fill. Process Cooling, 2005. Ac-cessed 10 Oct. 2009. <http://www.process-cooling.com/CDA/Archives/988aa774bc5b7010VgnVCM100000f932a8c0____>.

[45] Merkel, F., Verdunstungskühlung, VDI-Zeitchrift, 70, 123-128, 1925.

[46] Kloppers, J., Kröger, D., Refinement of the Transfer Characteristic Correlation of Wet-Cooling Tower Fills. Applied Thermal Engineering 26 (4), 35-41, 2005.

[47] Aull, R., Personal communication, December 2009.

[48] Kloppers, J., Kröger, D., Loss Coe"cient Correlation for Wet-Cooling Tower Fills.Applied Thermal Engineering 23 (17), 2201-2211, 2003.

[49] Cooling Tower Institute (CTI) Toolkit, Version 3.1. Accessed 10 April 2010. <http://www.cti.org/toolkit.shtml>.

[50] Al-Hallaj, S., Parekh, S., Farid, M., and Selman, J., Solar Desalination withHumidification-Dehumidification Cycle: Review of Economics. Desalination 195, 169-186, 2006.

[51] Skold, J., Energy Savings in Cooling Tower Packings, CEP, 48-53, 1981.

[52] Müller-Holst, H., Solar Thermal Desalination Using the Multiple E!ect Humidification(MEH)-Method. Solar Desalination for the 21st Century, 215-225, 2007.

[53] Smith, A., Personal communication, April 2009.

[54] Rogers, P., de Silva, R., and Bhatia, R., Water is an economic good: How to use pricesto promote equity, e"ciency, and sustainability. Water Policy 4, 1-17, 2002.

[55] Gallaher, C., Shirlow, P., Gilmartin, M., Mountz, A., and Dahlman, C., Key Conceptsin Political Geography, Sage Publications Ltd. Neoliberalism, 159-160, 2008.

[56] Lawson, V., Making Development Geography, Hodder Education: Geographies of Marx-ist Feminist Development. 147, 2007.

[57] Bruvold, W., Obtaining Public Support for Innovative Reuse Projects. Colorado:AWWA Research Foundation. Future of Wastewater Reuse 1, 122-128, 1984.

111

[58] Morgan, G., Risk Analysis and Management. Scientific American, 24-30, 1993.Accessed 1 Nov. 2009. <https://stellar.mit.edu/S/course/17/fa09/17.310/courseMaterial/topics/topic7/readings/R-Morgan-RiskAnalysis-SA-19931/R-Morgan-RiskAnalysis-SA-1993.pdf>.

[59] Hasson, D., Bendrihem, O., Modeling remineralization of desalinated water by limestonedissolution, Desalination 190, 189-200, 2006.

[60] World Health Organization, WHO (1980) Guidelines on health aspects of water desali-nation. ETS/80.4. Geneva, 1980.

[61] World Health Organization, Calcium and Magnesium in Drinking-Water: Public HealthSignificance. Geneva, 2009. Accessed 28 Feb. 2010. <http://whqlibdoc.who.int/publications/2009/9789241563550_eng.pdf>.

[62] Lenntech, Water Treatment Solutions. Accessed 28 Feb. 2010. <http://www.lenntech.com/processes/desalination/post-treatment/post-treatments/remineralization.htm>.

[63] Younos, T., Environmental Issues of Desalination. Journal of Contemporary Water Re-search & Education (132), 11-18, 2005.

[64] Kimes, K., The regulation of concentrate disposal in Florida. Desalination 102, 87-92,1995.

[65] Wikipedia, Water Supply and Sanitation in Haiti. Accessed 10 Oct. 2009. <http://en.wikipedia.org/wiki/Water_supply_and_sanitation_in_Haiti>.

[66] Sellers, J., Desalination Policy in a Multilevel Regulatory State. 173-188.

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)

respectively

112

No. of packings tested: 5 1) lou!a 2) charcoal 3) bamboo 4) CF-1200 5) CF-1900

Specifications

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

113