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Implementation of Pump-as-Turbines as Energy Recovery

Solutions within Water Distribution and Supply Systems

Case Study of Funchal Water Distribution System Pilot Zone

Manuel Amorim de Oliveira Perdigão

Thesis to obtain the Master of Science Degree in

Civil Engineering

Supervisor: Professor Helena Margarida Machado da Silva Ramos

Examination Committee

Chairperson: Professor Rodrigo De Almada Cardoso Proença de Oliveira

Supervisor: Professor: Helena Margarida Machado da Silva Ramos

Members of the Committee: Professor Maria Manuela Portela Correia dos Santos

Ramos da Silva

October 2018

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Declaration

I declare that this document is an original work of my own and that it fulfills all requirements of the Code of

Conduct and Best Practices of the University of Lisbon.

ACKNOWLEDGEMENTS

First of all, I would like to express my gratitude to Engineer Rui Silva Santos for the enormous help provided

in the development of this thesis. Without his expertise on the field and most of all, his patience and support,

this work wouldn’t have been possible. Our frequent meetings kept me interested and motivated throughout

every stage of the research, greatly contributing to my knowledge on the subject.

I would also like to thank Professor Helena Ramos, my advisor in the dissertation, for her guidance on the

writing itself and structure of the thesis. Being an expert on the matter, her assistance was vital to complete

this work.

The Instituto Superior Técnico deserve my recognition and appreciation as well, especially the teachers

who lectured my classes over the years and helped me develop the foundations for scientific knowledge

much required in the world of engineering.

Also a big thanks to my family and friends who directly or indirectly helped me get through this challenge

and contributed to my well-being during this important period of my academic life.

i

ABSTRACT

Water distribution systems worldwide are characterized by significant levels of energy consumption and

excessive amounts of water losses, which are caused primarily by the inadequate management of water

utilities. In fact, the occurrence of ruptures and leakages within water networks is often associated with the

poor regulation of water pressures, which significantly hinders the system’s efficiency by requiring greater

amounts of water and energy to provide the same level of service.

This ineffective management exerts a tremendous pressure on available water and energy resources,

whose preservation has become increasingly important to our present-day society and ecosystem. Indeed,

the alarming consequences of climate change and the high rates of population growth can only aggravate

the serious problem of water scarcity and further complexify the interconnectedness of water and energy

in human activities. Therefore, it is of the utmost importance to address the issue of water losses and energy

waste in order to attain a sustainable development which does not compromise the quality of life of future

generations.

A relatively recent approach to this problem is the implementation of a micro hydro power plant within the

water distribution system itself, through the use of pump-as-turbines (PATs). By replacing valves originally

intended to control water pressures in the network with PATs, energy could be generated from a clean

source while pressure levels are kept within the established limits.

In this dissertation, this alternative has been investigated for the case study of the Funchal water network,

which presents optimal conditions for the implementation of this energy recovery method. Several pressure

reducing valve (PRV) locations have been selected for the application of PATs, and different hydraulic and

electrical configurations have been analyzed with the purpose of evaluating the economic feasibility of this

investment.

Key-words – water distribution system (WDS); water losses; water-energy nexus; sustainable

development; micro hydro power plant; pressure reducing valve (PRV); pump-as-turbines (PATs).

ii

RESUMO

As redes de distribuição de água em todo o mundo são frequentemente caracterizadas por significativos

consumos energéticos e excessivas perdas de água, o que em grande parte resulta da inadequada gestão

por parte das entidades responsáveis. De facto, a ocorrência de roturas e fugas de água nos sistemas de

distribuição é geralmente associada à regulação deficiente de pressões na rede, o que provoca um impacto

bastante significativo na sua eficiência ao exigir maiores quantidades de água e energia para fornecer o

mesmo nível de serviço.

Esta ineficaz gestão causa uma enorme pressão sobre os recursos hídricos e energéticos disponíveis,

cuja preservação é cada vez mais importante para a sociedade e para o ecossistema. Na verdade, as

alterações climáticas e elevadas taxas de crescimento populacional apresentam inúmeras consequências

relacionadas com o agravamento da escassez de água no mundo, além de acentuarem a complexa

interligação entre a água e energia nas atividades humanas. Deste modo, é de grande importância abordar

a questão das perdas de água e do desperdício energético de forma a alcançar um desenvolvimento

sustentável que não comprometa a qualidade de vida das gerações futuras.

Uma abordagem relativamente recente para este problema é a implementação de centrais micro-hídricas

no próprio sistema de distribuição de água, através do uso de bombas-como-turbinas (BTs). Ao substituir

as válvulas originalmente destinadas a controlar as pressões de água por BTs, é possível manter os níveis

de pressão na rede enquanto se produz energia a partir de uma fonte renovável.

Para o trabalho desenvolvido nesta dissertação, esta alternativa foi investigada recorrendo ao caso de

estudo da rede de distribuição de água do Funchal, que apresenta condições ótimas para a implementação

deste método de recuperação de energia. De forma a avaliar a viabilidade económica do investimento,

diversas configurações hidráulicas e elétricas foram analisadas para a aplicação das BTs, considerando

os diferentes locais de implantação correspondentes a localização das válvulas redutoras de pressão

(VRPs).

Palavras-chave – sistemas de distribuição de água; perdas de água; nexo água-energia; desenvolvimento

sustentável; micro-hídrica; válvula redutora de pressão (VRP); bomba-como-turbina (BT).

iii

TABLE OF CONTENTS

ABSTRACT .............................................................................................................................................. i

RESUMO ................................................................................................................................................ ii

TABLE OF CONTENTS ...........................................................................................................................iii

LIST OF FIGURES ................................................................................................................................. vi

LIST OF TABLES .................................................................................................................................... x

ABBREVIATIONS AND SYMBOLS........................................................................................................ xiii

1 INTRODUCTION .................................................................................................................................. 1

1.1 Scope ............................................................................................................................................ 1

1.2 Objectives ...................................................................................................................................... 2

1.3 Thesis Structure ............................................................................................................................. 3

2 WATER ENERGY NEXUS.................................................................................................................... 4

2.1 The state of global water resources ................................................................................................ 4

2.2 Water energy nexus ....................................................................................................................... 5

2.3 Energy recovery in the water sector ............................................................................................... 7

3 WATER DISTRIBUTION SYSTEMS AND LEAKAGE CONTROL .......................................................... 9

3.1 Water balance................................................................................................................................ 9

3.2 Active leakage control .................................................................................................................. 10

3.3 Pressure management ................................................................................................................. 11

3.4 Water loss indicators .................................................................................................................... 12

3.5 District Metered Areas (DMAs) ..................................................................................................... 13

3.6 PRV operation modes .................................................................................................................. 14

3.7 Mathematical simulation ............................................................................................................... 15

3.8 Energy recovery and PAT implementation .................................................................................... 15

3.9 Implementation of PATs in the supply system .............................................................................. 16

4 PATS AS ENERGY RECOVERY SOLUTIONS ................................................................................... 17

4.1 Introduction .................................................................................................................................. 17

4.1.1 Best Efficiency Point (BEP)………………..………………………………………………………….18

4.1.2 Computational Fluid Dynamics (CFD) .................................................................................... 19

iv

4.1.3 Variable Operating Strategy (VOS) ........................................................................................ 19

4.1.4 PATs in the water supply system ........................................................................................... 22

4.2 Real cases of PAT application ...................................................................................................... 23

4.2.1 Malecòn, Spain ..................................................................................................................... 23

4.2.2 Conejeras and Cartuja, Spain ................................................................................................ 25

4.2.3 San Antonio, Chile ................................................................................................................ 26

5 FUNCHAL WATER NETWORK CASE STUDY ................................................................................... 27

5.1 RSS leakage control study ........................................................................................................... 27

5.1.1 Current situation .................................................................................................................... 28

5.1.2 Objectives ............................................................................................................................. 29

5.1.3 Characteristics of the network ............................................................................................... 29

5.1.4 Consumptions ....................................................................................................................... 30

5.1.5 Current situation model ......................................................................................................... 31

5.1.6 “Short-term future” situation model ........................................................................................ 32

5.1.7 Water loss analysis ............................................................................................................... 34

5.2 PAT implementation ..................................................................................................................... 36

5.2.1 PRV selection ....................................................................................................................... 36

5.2.2 Hydraulic models................................................................................................................... 39

5.2.3 No Regulation (NR)/fixed Electrical Regulation (fixed ER) PAT modes .................................. 43

5.2.4 Variable Electric Regulation (variable ER) PAT mode ............................................................ 47

5.2.5 Energy production results ...................................................................................................... 52

5.2.6 Automatous algorithm method ............................................................................................... 56

5.2.7 Fixed rotational speed Electric Regulation energy results ...................................................... 57

5.2.8 Variable rotational speed Electric Regulation energy results .................................................. 60

5.2.9 Energy recovery within the supply system ............................................................................. 62

5.3 Group set elements and electrical installation ............................................................................... 65

5.3.1 Characteristics of the group ................................................................................................... 65

5.3.2. Main components ................................................................................................................. 67

5.3.2 Additional components .......................................................................................................... 68

v

6 DISCUSSION ..................................................................................................................................... 69

6.1 Economic analysis ....................................................................................................................... 69

6.2 Sensitivity analysis ....................................................................................................................... 73

6.3 Final conclusions ......................................................................................................................... 74

6.4 Future work .................................................................................................................................. 75

REFERENCES ...................................................................................................................................... 76

APPENDIX ............................................................................................................................................ 83

APPENDIX I – “MEDIUM-TERM FUTURE” (2033) EPANET MODEL WITH SELECTED PRVS ............. 84

APPENDIX II – SELECTED PRVS OPERATING CONDITIONS FOR MEAN AND PEAK DISCHARGE . 85

APPENDIX III – FIXED ER MODE ENERGY RESULTS ........................................................................ 86

APPENDIX IV – VARIABLE ER MODE ENERGY RESULTS ................................................................. 88

APPENDIX V – WATER DISTRIBUTION SYSTEM OPTIMAL INVESTMENT CASH FLOW STATEMENT

REPORT ............................................................................................................................................... 89

APPENDIX VI - WATER SUPPLY SYSTEM OPTIMAL INVESTMENT CASH FLOW STATEMENT

REPORT ............................................................................................................................................... 90

APPENDIX VII – EXAMPLE OF EMITTER COEFFICENTS (K) ITERATION TABLE FOR THE YEAR

2026 (LIMITED NUMBER OF JUNCTIONS DISPLAYED) ...................................................................... 91

APPENDIX VIII – HYDRAULIC SCHEME OF THE PROPOSED WATER DISTRIBUTION SYSTEM

HYDRO POWER PLANT ....................................................................................................................... 92

APPENDIX IX – PAT 100-200 WATER DISTRIBUTION SYSTEM HYDRO POWER PLANT PLAN ....... 93

APPENDIX X – PAT 100-200 WATER DISTRIBUTION SYSTEM HYDRO POWER PLANT

LONGITUDINAL SECTION ................................................................................................................... 94

APPENDIX XI – PAT 100-200 WATER DISTRIBUTION SYSTEM HYDRO POWER PLANT CROSS

SECTION .............................................................................................................................................. 95

APPENDIX XII – DIGITAL ALGORITHM FLOW CHART - MAIN PROGRAM ......................................... 96

APPENDIX XIII – DIGITAL ALGORITHM FLOW CHART - PRV SUBROUTINE ..................................... 97

APPENDIX XIV – DIGITAL ALGORITHM FLOW CHART - PAT SUBROUTINE ..................................... 98

APPENDIX XV – ESTABLISHED AREAS OF INFLUENCE…………………………………………………..100

vi

LIST OF FIGURES

Figure 1 – Total water (left) and freshwater (right) distribution in the world (Cassardo et al., 2011; Lui et

al., 2011). ................................................................................................................................................ 4

Figure 2 - Hybrid Sankey diagram of 2011 U.S. interconnected water and energy flows (DOE, 2014)....... 6

Figure 3 - Electricity consumption in the water sector by world region (left) and its evolution in the world

for the next 22 years (right) (IEA, 2016). Notes: Supply includes water extraction from groundwater and

surface water, as well as water treatment. Transfer refers to large-scale inter-basin transfers. ................. 7

Figure 4 - Distribution of water losses by world region in 2014 (IEA, 2016). .............................................. 8

Figure 5 - Graphic representation of the ELL; Figure 6 - Diagram illustrating the UARL. ......................... 12

Figure 7 - Implementation of DMAs in a distribution network with flow monitoring points (Farley, 2001). . 14

Figure 8 - Different PRV modes of operation. ......................................................................................... 15

Figure 9 - Hydraulic Regulation (HR) configuration scheme (left) and graphical representation of its

operation (right) (Carraveta, A., et al., 2014). ......................................................................................... 20

Figure 10 - Electric Regulation (ER) configuration (left) and graphic representation (right) (Carraveta, A.,

et al., 2014). .......................................................................................................................................... 21

Figure 11 - Hydraulic and Electric Regulation (HER) configuration (left) and graphic representation (right)

(Carravetta, A., et al., 2013). .................................................................................................................. 21

Figure 12 - The Malecón hydro power plant. .......................................................................................... 23

Figure 13 - Working conditions in the Malecón hydro power plant on 4/9/2014. ...................................... 24

Figure 14 - Working conditions in the Malecón hydro power plant on 20/10/2014 (left) and measured

working conditions with PAT characteristic curves (right)........................................................................ 24

Figure 15 - Conejeras power plant (left) and Cartuja power plant (right). ................................................ 25

Figure 16 - Scheme of the San Antonio power plant. .............................................................................. 26

Figure 17 - Funchal municipality (dark blue) and pilot zone (light blue). .................................................. 27

Figure 18 – Water losses evolution from 2012 to 2016. .......................................................................... 28

Figure 19 - Water volumes in the network. ............................................................................................. 28

Figure 20 – Current and future proposed scenarios. ............................................................................... 29

Figure 21 - Terrain elevation; Figure 22 - Current regulation of existing PRVs. ....................................... 30

vii

Figure 23 - Hourly discretization of water consumption; Figure 24 - Distribution of water consumption in

the network. ........................................................................................................................................... 31

Figure 25 – “Current” situation spatial pressure distribution at 13H00; Figure 26 – Pressure distribution at

13H00. .................................................................................................................................................. 32

Figure 27 – “Short-term future” situation network spatial pressure distribution at 13H00; Figure 28 –

“Current” and “short-term future” situation network pressure distribution at 13H00. ................................. 34

Figure 29 - Predictable evolution of water losses; Figure 30 - Economic savings on losses (annual and

cumulative). ........................................................................................................................................... 35

Figure 31 - Characteristic curves (left) and efficiency curves (right) of available PATs (KSB Etanorm

models); In the PAT legend (below), the first number corresponds to the PAT inflow diameter and the last

its rotational speed. ............................................................................................................................... 38

Figure 32 - 2018 EPANET model – pressure levels in network junctions; Figure 33 – 2018 EPANET

model – consumption demand on network junctions. ............................................................................. 39

Figure 34 – Demand multiplier. .............................................................................................................. 40

Figure 35 - Reservoirs outflow at 13h00. ................................................................................................ 40

Figure 36 - Generic valve (red) upstream PRV TR08B (blue) (left); Figure 37 - PAT 150-200 at 1500 rpm

characteristic curve for generic valve (center); Figure 38 - Established demand pattern (right). .............. 42

Figure 39 - Flow and Head values for each hour relative to PAT 150-200 in PRV TR08B for 2019 (left)

and 2020 (right) extracted from EPANET ............................................................................................... 42

Figure 40 – NR (left) and fixed ER (right) configuration schemes............................................................ 43

Figure 41 – Characteristic curves for PATs KSB Etanorm 150-200 and 100-200 at 1500 rpm, and PRVs

TR07.5F and TR08B operational mean and peak values for 2018, 2021, 2025 and 2033 (from left to right

respectively). ......................................................................................................................................... 44

Figure 42 - Characteristic curves for PATs 100-200 and 150-200 (color red corresponds to nominal speed

NR mode). ............................................................................................................................................. 45

Figure 43 – Variable ER configuration scheme....................................................................................... 47

Figure 44 - Characteristic curves for the variable ER mode for PATs 100-200 and 150-200. .................. 49

viii

Figure 45 - Energy produced with PAT 150-200 throughout the analysis period for NR mode (left) and

variable ER mode (right). ....................................................................................................................... 52

Figure 46 - Energy produced with PAT 100-200 throughout the analysis period for NR mode (left) and


Figure 47 - Accumulated energy for each PRV site for the NR mode (left) and ER mode (right). ............. 54

Figure 48 - NR and ER total accumulated energy................................................................................... 55

Figure 49 – Evolution of accumulated energy over the years. ................................................................. 57

Figure 50 – PRV TR08B and TR07.5F total accumulated energy production for every PAT analyzed as a

function of its rotational speed (above) and the annual production throughout the years for its optimal

rotational speed (below)......................................................................................................................... 58

Figure 51 - Evolution of accumulated energy over the years. ................................................................. 60

Figure 52 – Annual energy production for each tested PAT in PRV TR08B and TR07.5F and rotational

speed variation throughout the day over the years for PAT 100-200 and 150-200 in PRV TR08B and PAT

80-200 and 100-200 in PRV TR07.5F. ................................................................................................... 61

Figure 53 – Location of Terça mini hydro power plant (red) and Alegria WT facility (yellow); Figure 54 –

Supply transmission pipeline system curve ............................................................................................ 62

Figure 55 –System characteristic curve (left), QH curve as a function of Q (center) and QH as a function

of H (right). ............................................................................................................................................ 63

Figure 56 – Graphic representation of the total accumulated energy production with respective restrictions

and optimal QH point ............................................................................................................................. 64

Figure 57 – Group set elements. ............................................................................................................ 65

Figure 58 - Electric configuration for the NR and ER modes in battery, grid and local connection variants.

.............................................................................................................................................................. 66

Figure 59 – Respective cumulative cash flows. ...................................................................................... 71

Figure 60 – Respective cumulative cash flows. ...................................................................................... 71

Figure 61 - Ribeira Grande (green) and Alegria Reservoirs (blue), along with PRVs TR08B (red) and

TR07.5F (black) ..................................................................................................................................... 72

ix

Figure 62 - Terrain slope (Hasenack, H. et al., 2010), density of inhabitants (INE, 2011), water

consumption rates (ERSAR, 2018), real water losses within water distribution systems (ERSAR, 2018) by

region .................................................................................................................................................... 73

Figure 63 - Potential for energy recovery in water distribution systems by region (right)...........................73

x

LIST OF TABLES

Table 1 - Standard water balance in a water distribution network as proposed by IWA (Hirner et al., 2000;

Alegre et al., 2000). ............................................................................................................................... 10

Table 2 – Respective power plant costs. ................................................................................................ 23

Table 3 – Respective power plant costs. ................................................................................................ 25

Table 4 – Conejeras and Cartuja power plant characteristics. ................................................................ 25

Table 5 - Respective power plant costs. ................................................................................................. 26

Table 6 - San Antonio power plant characteristics. ................................................................................. 26

Table 7 - Water losses evolution from 2012 to 2016.. ............................................................................. 28

Table 8 - Water components in the network. .......................................................................................... 28

Table 9 – DMAs established in the “short-term future” situation (areas of influence displayed in

APPENDIX XV. ..................................................................................................................................... 33

Table 10 - Water losses for each scenario. ............................................................................................ 35

Table 11 - Expenses and revenue from 2016 (current scenario) to 2033 (“medium-term future” scenario).

.............................................................................................................................................................. 35

Table 12 - Current definitions for implemented PRVs; PRVs with highest QH product highlighted in grey;

Pressure levels correspond to the dynamic situation. ............................................................................. 37

Table 13 - PRVs selected for PAT implementation. ................................................................................ 38

Table 14 - Evolution of water components throughout the period in analysis. ......................................... 40

Table 15 - Ratios utilized for the 2026 model iterations. ......................................................................... 41

Table 16 - NR mode operating conditions for PAT 100-200 (left) and PAT 150-200 (right) for 2018. ....... 46

Table 17 - Simplified version of tables used for the calculation of the variable ER curve for PAT 100-200

relative to PRV TR07.5F; The maximum generated power is highlighted in yellow and selected entries are

highlighted in green. .............................................................................................................................. 48

Table 18 – Variable ER characteristic and power curves for PAT 100-200 and PAT 150-200 ................. 48

Table 19 - ER mode operating conditions for PAT 100-200 (left) and PAT 150-200 (right) for 2018. ....... 51

Table 20 - Energy produced with PAT 150-200 throughout the analysis period for NR mode (left) and


xi

Table 21 - Energy produced with PAT 100-200 throughout the analysis period for NR mode (left) and


Table 22 - Accumulated energy for each PRV in NR and ER mode ........................................................ 54

Table 23 - Accumulated energy for each PRV in NR and ER mode by 2033........................................... 54

Table 24 – Total accumulated energy for each PAT.. ............................................................................. 57

Table 25 – Optimal rotational speeds for each PAT in PRV TR08B (left) and PRV TR07.5F (right) and

respective total accumulated energy production. .................................................................................... 58

Table 26 - Total accumulated energy for each PAT. ............................................................................... 60

Table 27 - Total accumulated energy production for each tested PAT in PRV TR08B (left) and PRV

TR07.5F (right). ..................................................................................................................................... 60

Table 28 - Transmission pipeline system characteristic values. .............................................................. 62

Table 29 – Total accumulated energy production according to flow rate with restrictions highlighted in

grey ....................................................................................................................................................... 64

Table 30 – Energy production of a simulated hydro power plant in the adduction system of Funchal. ..... 64

Table 31 – Initial Investment for every analyzed PAT and respective mode of operation. ........................ 69

Table 32 – Economic measurements of the proposed solutions (grid connection). ................................. 70

Table 33 – Economic measurements of the proposed solutions (local and battery connection) ............... 70

Table 34 – Economic measurements for the optimal investment. ........................................................... 71

Table 35 - Economic measurements for the hydro power plant located in the main transmission pipeline

supplied by the Alegria water treatment station. ..................................................................................... 71

xii

ABBREVIATIONS AND SYMBOLS

AC - Alternating Current

AC/DC - Rectifier

ARM - Águas Regionais da Madeira

B/C - Benefit/Cost Ratio

BEP - Best Efficiency Point

c – Manning Roughness Coefficient

CARL - Calculated Annual Real Losses

CFD - Computational Fluid Dynamics

CMF - Câmara Municipal do Funchal

D - Diameter

DC - Direct Current

DIN - German Institute for Standardization

DMA - District Metered Area

DN - Diameter Nominal

E - Energy Generated

ELL - Economic Level of Leakage

EPA - United States Environmental Protection Agency

EPANET - Environmental Protection Agency Network

ER - Electrical Regulation

g - Gravitational Acceleration

HWC - Hazen-Williams Coefficient

ɣ - Specific weight of a fluid

H - Hydraulic Head

HDPE - High Density Polyethylene

HER - Hydraulic and Electrical Regulation

xiii

HR - Hydraulic Regulation

ILI - Infrastructure Leakage Index

IP - Ingress Protection

IPCC - Intergovernmental Panel on Climate Change

IRAR – Instituto Regulador de Águas e Resíduos

IRR - Internal Rate of Return

IWA – International Water Association

L - Length

LPS – Liters per second

MNF - Minimum Night Flow

NPV - Net Present Value

NR - No Regulation

NRW - Non-Revenue Water

P - Power

p - Pressure

PAT - Pump-as-Turbine

PEAASAR - Plano Estratégico de Abastecimento de Água e de Abastecimento de Águas Residuais

PN - Pressure Nominal

PRV - Pressure Reduction Valve

PVC - Polymerizing Vinyl Chloride

Q - Flow Rate

Qcalc - Calculated Flow Rate

rpm – Rotations per minute

RSS - Redes e Sistemas de Saneamento lda.

T - Payback Period

UAC - Unbilled Authorized Consumption

UARL - Unavoidable Annual Real Losses

UPS - Uninterruptible Power Supply

xiv

V - Voltage

v - Water Velocity

VFD - Variable Frequency Drive

VSD – Variable Speed Drive

VOS - Variable Operating Strategy

VSD - Variable Speed Driver

WDS - Water Distribution System

η - PAT effciency

1

1 INTRODUCTION

1.1 Scope

The present thesis is part of the specialized field of Hydraulic and Water Resources and focuses on the

exploitation of energy recovery solutions within water distribution systems through the use of Pump-as-

turbines (PATs). To investigate this solution, an in-depth analysis was carried out to evaluate the possibility

of installing a micro hydro power plant within the water distribution network of Funchal (Portugal),

characterized by significant water losses and considerable topographical gradients. The reason behind this

work is to provide water utilities with financially appealing alternatives which can hopefully improve their

system’s efficiency, while at the same time contribute to lessen the impacts of poor water and energy

management in a world increasingly marked by evident climatic changes.

Also referred to as Global Warming, climate change is one of the greatest challenges of modern society,

with serious implications for the environment and human communities worldwide. Although some minorities

still refuse to accept it, an overwhelming scientific consensus supports that climate change is a real

phenomenon, caused primarily by the human activity. In fact, without serious efforts to mitigate the impacts

caused by our activities we could be compromising the quality of life of future generations, not to mention

the perfect and invaluable equilibrium of the Earth’s ecosystem. It is important to note that the drastic

change in weather patterns and rapid increase of average global temperatures are not the only

consequences of climate change, with water scarcity being one of the most alarming aspects of this global

crisis.

Indeed, considering the importance of water resources and its close connection with energy, a great deal

of attention has been addressed to water distribution management over the world. As stated by

Intergovernmental Panel on Climate Change (IPCC, 2008) – “global warming will lead to changes in all

components of the freshwater system” and “water and its availability and quality will be the main pressures

on, and issues for, societies and the environment under climate change”. Aware of the impact water has

on food security, Nestlé’s chairman Peter Brabeck-Letmathe (2008) exposes his concern about water

scarcity and the dangers it may present to the largest food company in the world: - “I am convinced that,

under present conditions and with the way water is being managed, we will run out of water long before we

run out of fuel.”

An important contributor to the problem of water scarcity around the world are the water losses caused by

leakages within distribution systems. The excessive pressures under which many water distribution

networks operate often lead to ruptures in pipes, causing a tremendous waste of freshwater which could

be saved with an adequate pressure management. Although it is not economically feasible to reduce water

losses completely, urgent action should be taken to keep them at acceptable levels.

2

As a global average, it is estimated that water losses represent 35% of the total water entering the system,

rising to 50-60% in developing countries, which demonstrates the deteriorated state of most distribution

systems in the world (Fields, 2015). The Funchal water distribution network is no exception, presenting an

excessive level of water losses before any intervention had been made to improve its efficiency. However,

fortunately for the municipality of Funchal, the portuguese company RSS – Redes e Sistemas de

Saneamento – conducted a study to reduce its losses and reverse this unsustainable situation.

Only after a minimal amount of lost water is guaranteed, can additional energy concerns be addressed.

Despite the considerable amount of energy savings directly caused by the leakage control – less water

enters the system to meet the same consumer demands – a lot of energy is dissipated within the distribution

network to maintain satisfactory pressure levels. For that reason, the integration of energy recovery

solutions in water distribution systems has recently gained increasing relevance, particularly within the

context of renewable and sustainable sources of energy.

1.2 Objectives

The purpose of this thesis is to analyze the energy recovery potential of the water distribution system of

Funchal (Portugal) through the replacement of pressure reducing valves (PRVs) by PATs, ensuring both

an adequate pressure management and valuable energy savings. Only a section of the Funchal water

distribution system was studied – the pilot zone selected for the study of leakage reduction carried out by

the Hydraulic Engineering company RSS – which comprises of roughly 40% of the entire municipality of

Funchal and corresponds to the area of influence of the reservoirs of Terça, S. Martinho, Penteada, Ribeira

Grande and Nazaré.

Currently, almost 70% of the total water entering the water network of Funchal is lost within the system,

mostly as a result of inadequate pressure regulation. This poses a serious threat to the environment and

presents a significant economic impact for the involved water utilities. However, RSS estimated these

losses may be reduced to 15% if the correct measures are taken, particularly the creation of control zones

in the water distribution network and the correct placement of PRVs.

After these modifications, the installation of micro hydro power plants within the system through the use of

PATs can further improve the efficiency of the system. Indeed, the recovered energy which would otherwise

be dissipated in PRVs to control the pressure, could then be converted into electricity and stored in three

different ways: the energy output can be connected to the grid; the energy can be stored in batteries; or it

can directly supply electrical equipment/devices. Different PAT configurations were analyzed for each of

these variants with the purpose of identifying the one which minimized the payback period for every PAT

location in the distribution system.

These alternatives were tested using the flow conditions provided by the digital software EPANET, which

models pressurized water networks and allows the simulation of hydraulic behavior and pressure

3

distribution. The EPANET models utilized to perform these simulations were based on the models RSS had

previously developed to analyze and control the level of water losses, and the time period used in the

analysis was the same RSS adopted - from 2018 to 2033.

1.3 Thesis Structure

This document is composed of 6 different chapters: introduction (chapter 1 previously presented); water

energy nexus; water distribution systems and leakage control; PATs as energy recovery solutions; Funchal

water network case study; discussion.

Chapter 2 focuses on the problem of water scarcity and its complex relationship with energy in a context

of evident climatic changes. The water sector was analyzed as well, namely in terms of energy consumption

and water losses, addressing particular attention to its distribution over the world.

In Chapter 3, the main components of water distribution systems are presented, as well as fundamental

aspects of leakage control. The essential steps to solve the problem of water losses are explained,

providing the background over which energy recovery solutions can be adequately understood.

The scientific findings and published information regarding the use of PATs in water distribution systems

are included in the Chapter 4. This comprises the most relevant investigations and researches conducted

by several different authors in this area, along with some of the key elements and concepts related to the

PAT application as energy recovery solutions.

Chapter 5 presents the case study of the Funchal water distribution system. In the first part of the chapter,

the water loss control study developed by RSS is explained in detail, and the basic characteristics of the

network are analyzed. The second part comprises developments of the integration of a micro-hydro power

plant within the system, by replacing pressure reducing valves with PATs. This power generation method

was also tested in the water supply system, upstream of the network’s reservoirs.

The Chapter 6 concludes about to the economic feasibility and other relevant impacts of implementing the

energy recovery solutions.

4

2 WATER ENERGY NEXUS

2.1 The state of global water resources

The abundant presence of liquid water on earth provided the necessary requirements for life to begin

flourishing billions of years ago. From the most elementary lifeforms to complex organisms, water plays an

essential role, acting as a delivery mechanism for nutrient exchange between cells and aiding in vital

metabolic processes. It is also a critical factor for climate regulation and heat transfer between the oceans

and continents, not to mention the weather patterns created by the water cycle. Historically, it has greatly

contributed for the rise of human civilization, leading the first large scale communities to emerge along large

river valleys. Indeed, the widespread use of irrigation techniques and water transport were key elements in

the establishment and development of modern societies, which eventually shaped the world as we know it.

Although there is no doubt that our growing population and ever more demanding lifestyle have been

creating a great pressure on water resources, it is tempting to think that there is plenty for future human

generations, since it covers roughly 71% of our planet’s surface. However, only a minute amount of that

water is available and suitable for consumption, as saline water makes up about 97% of global resources.

Furthermore, most of the remaining 3% freshwater is almost inaccessible or improper, 69% being locked

away in the form of icecaps and glaciers, and approximately 30% in contaminated or deep underground

aquifers (Cassardo et al., 2011; Lui et al., 2011), as illustrated in Figure 1. It is important to note that despite

the recent development in desalinization techniques to transform water from the oceans into drinking water,

these are still very expensive methods which require enormous amounts of energy (Marshad, 2014).

Figure 1 – Total water (left) and freshwater (right) distribution in the world (Cassardo et al., 2011; Lui et al., 2011).

Therefore, water has become a scarce commodity in present-day society, with over 844 million people

lacking access to clear drinking water and 4.5 billion suffering from inadequate sanitation (WHO, 2017).

This is partly responsible for the mortality rates and disease transmission in developing countries, not to

mention the ongoing economic and political crisis. Although developed countries do not undergo such

hardships, they are the biggest contributors to this global scale environmental threat, with alarmingly high

consumption levels required to support their modern industry.

97%

3%

Seawater Freshwater

68,7%

30,1%

0,9% 0,3%

Ice caps and glaciers Ground water

Other Surface water

5

The arising problem of freshwater shortage has two major variants: physical water scarcity and economic

water scarcity. Physical water scarcity occurs when there are no sufficient water supply resources to meet

its demand, a phenomenon mostly prevalent in arid regions. Economic water scarcity is related to the lack

of proper technology and financial resources, as well as a poor water management, which prevents people

from having access to safe water (Schmitz et al., 2013). This happens frequently despite the

overabundance of freshwater resources, which is a typical issue in central Africa.

Since most world regions have enough water to satisfy their demand, and many fail to provide the necessary

means for its easy access, economic water scarcity is often considered to be the main cause of water

scarcity in the world (UNDP, 2006). For this reason, water management has become a critical matter, with

the ability to reverse this tendency and ensure a sustainable development, granting future generations an

acceptable quality of life. Indeed, if no action is taken to prevent it, it is expected by 2025 about two thirds

of the world’s population could experience water shortages, along with unpredictable environmental

consequences caused by the gradual depletion of this invaluable resource (WWF, 2017). Adequate water

management is therefore a major concern to many countries and governments around the world and should

be addressed with the utmost urgency.

2.2 Water energy nexus

Water and energy are fundamentally intertwined, and their interconnectedness is central for a sustainable

development. It takes a significant amount of water to generate electricity and it is needed for every phase

of energy production, from cooling steam electric power plants to fuel extraction, not to mention hydropower.

Energy is also essential for a variety of water related operations, like water distribution and disposal of

wastewater (IEA, 2016). A general awareness of this inter-dependence has been increasing for the last

decade, leading to a growing concern over natural events which make this close connection very evident.

For instance, the devastating damages caused by natural disasters may cause temporary interruptions in

electric power distribution, which in turn might disturb the correct functioning of water delivery systems. In

the same way, any water shortage caused by those events, can significantly restrain electricity generation

for a significant period of time (DOE, 2014).

All these linkages have been accentuated by the recently changing patterns of water and energy

consumption needs. On the one hand, the global population has been expanding very rapidly, creating

additional pressure on freshwater resources and electricity generation, while also further complicating its

already complex relationship and difficult management (Hoff, 2011). On the other hand, climate change

and the fast-rising average surface temperatures on Earth are responsible for significant changes in the

large-scale hydrological cycle, resulting in exacerbated water shortage issues. As an example, sea level

rise due to melting ice sheets and glaciers is expected to have major consequences in freshwater resources

in coastal areas, like rivers and lakes. Equally alarming, the projected precipitation variability patterns in the

6

near future will likely provoke an increased risk of flooding and droughts in many regions, limiting the water

availability and thus hindering energy production activities (Bates et al., 2008). Another relevant aspect is

the technological development of power generation methods and adoption of new cooling techniques, which

could lead to increased water consumption. The predictable rise in alternative green sources whose energy

production processes demand significant amounts of water, like biofuel, should also be taken in

consideration. Finally, the expected improvement of living standards in developing countries and the

gradual eradication of water scarcity are likely to have a tremendous impact in freshwater resources (IEA,

2016).

In order to provide a better understanding of this intricate relation, the Department of Energy of the United

States of America created a Sankey Diagram for water and energy flows in the United States on a national

scale, as illustrated in Figure 2.

Figure 2 - Hybrid Sankey diagram of 2011 U.S. interconnected water and energy flows (DOE, 2014).

By observing this illustration, several conclusions can be drawn, particularly regarding the interdependency

between water and energy: thermoelectric cooling for electricity production is the most water demanding

operation, while also being largely responsible for energy dissipation levels; agricultural activities need vast

water resources as well and display the highest levels of water consumption, but support the energy sector

indirectly by producing biofuel; oil is the biggest source of energy used mainly for transportation, requiring

water to be able to generate power, however much less than agriculture or thermoelectric cooling; water

treatment and distribution systems also require energy to operate. There are other important elements to

consider beyond the scope of this diagram, mainly the fact that water/energy flows do not stay constant.

https://en.wikipedia.org/wiki/Sankey_diagram

7

2.3 Energy recovery in the water sector

Freshwater supply and wastewater treatment services are energy intensive operations which often require

pumping stations to transport water from the water source to treatment facilities and consumers. Whenever

gravity is insufficient to ensure an adequate flow, pumps are necessary to maintain positive pressures

throughout the water distribution network and to aid the treatment process in wastewater facilities. Only

rarely can these services rely solely on power-free gravitational flow, where the height difference is sufficient

to overcome energy losses due to friction in pipes. For this reason, water extraction from either groundwater

or surface water, comprise the most energy demanding component within the water sector, followed by

wastewater treatment (GAPS, 2015).

It is estimated that the global energy demand within the water sector accounts for roughly 820 TWh, which

is the equivalent to 4% of the world’s energy consumption, while water distribution alone is currently

estimated to consume about 180 TWh, representing 22% of the energy spent for the entire sector. There

are however, significant global consumption inequities which heavily depend on each region’s

topographical conditions and water supply infrastructures, as well as the country’s population and standards

of living. Another relevant aspect is the expected increase of energy consumption for the entire water sector

in the next 25 years, whereas water distribution energy demands are likely to remain constant over time

(IEA, 2016), as displayed in Figure 3. In the specific case of Portugal, water distribution systems accounted

for roughly 406GWh in 2015, making up 0.86% of the country’s energy consumption (Mendes, 2016).

Figure 3 - Electricity consumption in the water sector by world region (left) and its evolution in the world for the next

22 years (right) (IEA, 2016). Notes: Supply includes water extraction from groundwater and surface water, as well as water treatment. Transfer refers to large-scale inter-basin transfers.

In addition to the noticeable impact on global electricity consumption, there are also considerable water

withdrawals related to water supply, accounting 13% of the total in 2014 and predicting to rise to 17% in

2040 (IEA, 2016). Even though this increase is perfectly justifiable since water consumption is expected to

rise significantly, a considerable portion of those withdrawals is lost through the water network systems and

never reaches the customers. Indeed, water leakages and pipe bursts along with water theft are responsible

for tremendous water losses worldwide, which could be reduced significantly with an adequate loss control

strategy (Lambert, 2002). Although several measures are usually necessary to maintain acceptable levels

of operation, such as managing water pressures, controlling leaks and rehabilitating infrastructures, most

http://www.isq.pt/EN/tag/energy/

8

water utilities fail upon taking action to mitigate this problem. This ineffective management is often times

motivated by the significant initial investment required to improve the water system’s efficiency, despite the

evident long-term financial benefits of water loss control (Garcia et al., 2001).

The estimation of these losses accounted for 12% in the United States, 19% in China, 24% in the European

Union and 48% in India, in 2014. Although most water losses are attributed to developing countries in Asia,

the European Union displays substantial levels as well, mostly a result of poor maintenance and ageing

infrastructures (IEA, 2016). This is illustrated in Figure 4.

Figure 4 - Distribution of water losses by world region in 2014 (IEA, 2016).

Since energy is fundamentally dependent on the water usage, it should therefore come as no surprise that

water losses also imply a considerable waste of energy, which could be used for water extraction, treatment

and distribution. Indeed, if every country presented a degree of water losses equal to those currently

observed in the most developed countries – 6% of water losses, e.g., as seen in Japan and Denmark – the

entire energy needs of Poland could be saved. The estimation of these water losses consists of 50-60% of

the total water entering the system for developing countries, dropping to 35% as a global average. This

means 45 million cubic meters of freshwater are lost every day, which could meet the needs of almost 200

million people with currently no access to drinking water. Hence, there is a great potential to minimize water

losses within water networks, and therefore to save substantial amounts of energy as well. In fact, the

projection of the overall energy demands in the water sector could be reduced by 15% in 2040, based on

the exploitation of energy recovery alternatives (IEA, 2016).

To conclude, water scarcity worldwide is mostly a result of ineffective management of water resources,

coupled with the poor economic conditions prevalent in third world countries. In order to reverse this

unfavorable scenario and attain a healthy coexistence of mankind and the environment, a major political,

social and economic shift is necessary to ensure universal access to drinking water without compromising

the protection of water resources. It is in this context, that alternative energy recovery solutions within water

distribution systems were studied for the purpose of this thesis, while also adopting a mindful attitude

towards managing water losses as efficiently as possible with the hope of contributing to strengthen this

yet widely misunderstood connection between water and energy.

Q (

10^9 m

³/s)

9

3 WATER DISTRIBUTION SYSTEMS AND LEAKAGE CONTROL

For a large number of water companies, the service sustainability is a major aim which can only be attained

through the reduction of losses in water distribution systems to levels considered economically viable and

technically acceptable. Indeed, due to its extensive impact in water distribution networks, water losses have

been a matter of discussion worldwide. Although they can never be completely eliminated from a water

distribution system, they can be controlled through the implementation of programs which help to identify

and correct inefficiencies. These programs include leakage control, meter accuracy assessment and

detection of unauthorized consumption of water. Indeed, by reconfiguring the water network operation

conditions, particularly in terms of pressure management and the definition of control zones, water losses

can be dramatically reduced to acceptable levels, which may help to substantially improve the system

energetic efficiency (Lambert et al., 2000). Additionally, energy recovery measures, such as the

implementation of turbomachines within the distribution system have shown promising results when

complemented with the aforementioned procedures. In essence, with a clear understanding of the

underlying causes that lead to these problems, and by developing the ability to act and invest in sustainable

solutions, environmental goals can be met without sacrificing consumption needs and economic stability.

The key components necessary to analyze the state of a distribution system will be described in this chapter

and will hopefully provide the clarity required to comprehend the work developed in this thesis.

3.1 Water balance

In every water distribution network, there is a portion of the volume entering the system which won’t

generate any revenue. This is referred to as Non-Revenue Water (NRW) and consists of the difference

between the amount of water entering the distribution system and the amount of water billed to consumers.

While its presence is inevitable to some extent, high NRW levels are generally associated with considerable

water losses and inefficient hydraulic control. Thus, minimizing this component has been one of the most

challenging and persistent problems that municipal water utilities must face to improve the efficiency of the

system, mainly from an economic perspective. Additionally, since considerable levels of NRW are

frequently associated with higher water input volumes to maintain consumption demands, environmental

concerns should also be a priority (Petroulias et al., 2016; Kingdom et al., 2006).

In order to perform an assessment of Non-Revenue Water volumes, an annual water balance is usually

required. Being aware of the multiple formats frequently adopted to define its components, the International

Water Association (IWA) created an international standard approach for Water Balance calculations which

enables national and international comparisons of NRW management performances. According to IWA,

the clarification of all components involved should be the essential first step in the practical management

of water losses. This approach and respective definitions of all terms involved are displayed in Table 1.

10

Table 1 - Standard water balance in a water distribution network as proposed by IWA (Hirner et al., 2000; Alegre et

al., 2000).

3.2 Active leakage control

Active Leakage Control consists of any activity related to detection and repair of leaks and ruptures in the

distribution system. Such occurrences are generally driven by excessive pressure and usually lead to

substantial water losses, causing considerable changes in the water network operation. A typical approach

for detection of newly emerging anomalies that may arise is the observation of changes in night inlet volume

over time. This procedure is called MNF – minimum night flow – and operates by calculating mean values

over a certain period of time, disregarding momentary fluctuations in the measured flow (Berardi et al.,

2016). Other methods proposed by various authors consist of correlating flow measurements and expected

hydraulic behavior calculated by mathematical models which simulate these leakages. A distinct strategy

System

Input

Volume

Authorized

Consumption

Billed Authorized

Consumption

Billed Metered Consumption Revenue Water

Billed Unmetered Consumption

Unbilled

Authorized

Consumption

Unbilled Metered Consumption

Non-Revenue Water

(NRW)

Unbilled Unmetered Consumption

Water Losses

Apparent Losses Unauthorized Consumption

Customer Metering Inaccuracies

Real Losses

Leakage on Transmission and /or

Distribution Mains

Leakage and Overflows at Utility’s

Storage Tanks

Leakage on Service Connections up to

point of Customer metering

Component Definition

System Input Volume Annual input to the whole water supply system

Authorized Consumption

Annual volume of metered and/or non-metered water taken by registered consumers,

the water supplier and others implicitly or explicitly authorized to do so. It includes

water exported, and leaks and overflows after the point of customer metering

Non-Revenue Water (NRW) Difference between System Input Volume and Billed Authorized Consumption; NRW

consists of Unbilled Authorized Consumption and Water Losses

Water Losses Difference between System Input Volume and Authorized Consumption, consisting of

Apparent Losses and Real Losses

Apparent Losses Composed of Unauthorized Consumption and metering inaccuracies

Real Losses

Annual volumes lost through all types of leaks, bursts and overflows on mains, service

reservoirs and service connections, up to the point of customer metering. It is widely

assumed Real losses account for the largest portion of NRW in a distribution system,

and thus should be tackled proactively for the benefit of all parts involved

11

requires field operations, which generally demands specialized equipment and the temporary isolation of

the pipeline. These procedures are usually based on automated leak noise monitoring, which relates sonic

impulses to detected leakages (Martini et al., 2016). Once new leaks are reported, water utilities must be

able to respond promptly, and repairs must be carried out efficiently and with lasting results.

3.3 Pressure management

The correct management of water pressures is considered of paramount importance by the European

Commission, highlighted in the European Union reference document “Good Practices on Leakage

Management”, adopted by EU Water Directors in their final meeting of 2014. In fact, its inadequate

regulation is unquestionably the major cause of water losses in distribution networks and often leads to

substantial avoidable leakage and bursts. Although it is becoming increasingly clear how to overcome this

challenge, most water utilities still struggle to address the underlying issues generally due to poor

management and financial limitations, which is evident as they tend to focus solely on replacing and

repairing aging and inefficient distribution networks and fail to realize its inability to solve long term

problems.

Worldwide, water network systems are designed to provide the minimum pressure required to supply its

consumers at a specified level of service, which is usually guaranteed in most developed countries.

However, certain areas of the network require higher pressure levels than others, mostly as a result of their

terrain topography or respective distance from the supply reservoir, which causes some areas to operate

at substantially higher pressures than needed. This phenomenon is aggravated when the periods of peak

demand are taken into account, forcing the whole system to operate at an excessive pressure throughout

the year solely to provide appropriate supply volumes and pressures for a very short period of time. In

conclusion, managing water pressures in a distribution system is a challenging task with many aspects to

take into consideration.

Therefore, to avoid these occurrences, the network pressure should be reduced during times of low demand

and district metered areas with a specified baseline pressure should be created for monitor and control

purposes. This can be accomplished with several different pressure reduction procedures, which range

from the simple use of pressure regulation valves to advanced pressure control devices, also called

electronic controllers. These devices have become increasingly sophisticated with integration of artificial

intelligence, allowing a pressure manipulation according to demand levels which can be particularly

advantageous in aged infrastructures, offering the opportunity to extend their life (FAPESP, 2018).

Nevertheless, even with plenty of access to cutting edge technology, water utilities should never disregard

the importance of a properly designed network and well managed pressures.

Other additional benefits of pressure reduction include the following: less consumption and more efficient

use of water; better service provided to consumers, with more stable pressure levels throughout the day;

preservation of the network by reducing the occurrence of new bursts and leakages, which mean reduced

12

costs of Active Leakage Control; reduction of water supply interruptions guaranteed by an increased

network preservation. Despite these considerable advantages, some issues may arise without an adequate

regulation, such as: decreased billed consumption; deficient reservoir filling at night; inadequate PRVs

operation; supply limitations for tall buildings. In conclusion, pressure management is now recognized as

the foundation of any well managed water distribution system, with its wide array of benefits far surpassing

the financial interests of water utilities involved.

3.4 Water loss indicators

Although water utilities should always act on the principle of minimizing water losses within the system, it

is actually uneconomic to reduce them beyond a certain limit – The Economic Level of Leakage (ELL) –

which occurs when reducing losses by one unit of volume equals the cost of production of that unit of water

volume. In other words, “That level of leakage where the marginal cost of active leakage control equals the

marginal cost of the leaking water” (EOC, 1994). In Figure 5, shown below, the ELL is the point at which

the “cost of lost water” and “cost of leakage control” curves intersect each other. It is clear that by reducing

water losses, the costs of leakage control increase exponentially while the costs of lost water decrease,

making it increasingly unfavorable to control leakages once this limit is reached. At the same time though,

it is also evident that there is an economic limit to the loss of water that should be tolerated through leakage.

Thus, the operation of a water distribution system at the economic level should result in the lowest possible

combination between the cost of loss control actions and the price of lost water (minimum point), and any

further reduction wouldn’t be worth the water savings (FM, 2016) The vertical line in the graphic in Figure

5 represents the water losses which can’t be eliminated from a distribution system and remain as a residual

background leakage, commonly referred to as Unavoidable Annual Real Losses (UARL) (Vermersch et al.,

2016). This is an important indicator of water distribution efficiency and consists of the lowest possible water

loss level of reduction, which is represented in the diagram in Figure 6 as well.

Figure 5 - Graphic representation of the ELL. Figure 6 - Diagram illustrating the UARL.

13

Another relevant indicator is the Potentially Recoverable Real Losses, which is defined by the difference

between the Current Annual Real Losses (CARL) and Unavoidable Annual Real Losses (UARL),

comprising the volume of water losses that can be avoided through technically viable methods of loss

reduction. As demonstrated in Figure 6, although no reduction is possible beyond the limit established by

the Unavoidable Real Water Losses, water loss control strategies can be adopted with the purpose of

reducing them to an optimal level – the Economic Level of Leakage. These strategies consist of pressure

management, active leakage control, pipeline management and quality of repairs. A similar indicator is the

Infrastructure Leakage Index (ILI), which is the ratio between the Current Annual Real Losses (CARL) and

Unavoidable Annual Real Losses (UARL), indicating not only the level of existing water losses but also the

potential for its reduction. Like most water loss indicators, the selection for the most adequate ILI for any

given distribution network is fundamentally related with economic aspects (costs associated with water

production and leakage control) and environmental concerns of water utilities involved (their strategy

towards sustainability). Another important indicator which provides the level of water losses according with

pressure is the Index of Losses (IL). The IL formula was essential to compare and verify the water loss

results calculated through the hydraulic models in the case study of Funchal water distribution system, as

shown later in this work.

It should be noted that since both apparent and real water losses have distinct origins and reduction

procedures associated, there is frequently different indicators defined for each one. This means its control

strategy should be handled accordingly, usually involving a much more complex approach in the case of

real losses. In fact, these depend on an extensive number of factors like the cost of water production,

deterioration level of the infrastructure, methods used for leakage control, cost of labor, or the network area.

3.5 District Metered Areas (DMAs)

The subdivision of a distribution system into smaller sections is one of the most effective tools for water

loss control. Through the establishment of hydraulic isolated sub-zones, known as District Metered Areas

(DMAs), water consumption and pressure management can be monitored much more efficiently as they

enable a faster detection and control of water leakages by decreasing the complexity of each subdivision

(Ilicic et al., 2009). To carry out this procedure, a prior knowledge of the topological conditions of the network

and the overall behavior of the system is required, since that is critical to ensure each DMA is designed to

operate at maximum and minimum working pressures, as well as to maintain stable pressure levels. Thus,

the first step should be the creation of larger major districts according to the similarity of consumption

demand patterns, hydraulic behavior, state of preservation of the infrastructures and water quality. By

following these criteria, baseline pressure levels and/or areas associated with different supply locations can

be established, providing a high degree of organization within the system and minimizing the probability for

errors in flow measurement. The water utility should proceed to further subdivide the network and create

sub districts, based on topographical difference, levels of reservoir operation and density of branches

(Gomes, 2011). This sectorization strategy is illustrated in Figure 7.

14

Figure 7 - Implementation of DMAs in a distribution network with flow monitoring points (Farley, 2001).

Despite the inherent advantages of the sectorization of water networks, the lack of financial availability from

management entities can hamper its implementation. In fact, an excessive subdivision requires a greater

number of border valves and flow metering stations which results in greater expenses, while larger DMAs

tend to be more complex and less efficient at detecting water leakages, thus becoming costlier as the size

increases. Therefore, to conclude about the feasibility of alternative proposed solutions, a cost-benefit

analysis must be performed (Gomes, 2011).

3.6 PRV operation modes

The use of pressure reducing valves is absolutely essential for an adequate pressure management. They

work by reducing upstream inlet pressures to desired values set by operators, thus controlling the flow of

water downstream. This outlet pressure remains stable regardless of fluctuations in upstream flow

rate/pressure, ensuring a reliable supply for water demand and providing acceptable levels of service. To

accomplish that, PRVs are usually regulated for the minimum pressure required at peak consumption, also

taking into account the fire protection design requirements (WW, 2010). In addition, it is of the utmost

importance to carefully choose the optimal PRV locations within the network (Nicolini et al., 2009). There

are three possible modes of operation for any PRV (Ramos et al., 2005):

Active state - if the downstream pressure is excessive, the valve shut-off device is activated by reducing

the downstream pressure value up to the pressure reducing valve setting load, otherwise it opens;

Passive state - if the upstream pressure is insufficient and lower than the PRV setting load, the valve

opens fully while maintaining the same pressure level;

Closed state - if the downstream pressure is higher than the upstream pressure the valve closes fully,

operating as a check valve.

The Figure 8 illustrates the three distinct modes of operation.

http://www.processindustryforum.com/article/singers-versatile-water-control-valves-controlling-pressure-level-flow

15

Figure 8 - Different PRV modes of operation.

3.7 Mathematical simulation

To perform an adequate pressure management and to accurately define the optimal architecture and

hydraulic behavior of a specific water network, a mathematical modelling software is usually required. By

performing hydraulic simulations with computational algorithms, detailed analyses can be carried out with

the intention of providing a complete understanding of a distribution system operation. For this purpose, the

software EPANET was chosen to support the work developed in this thesis. This program is a public domain

of a water distribution system modeling software package developed by the United States Environmental

Protection Agency's (EPA), which allows the creation of models for drinking water distribution systems and

performs extended-period simulations within pressurized pipe networks (Rossman, 2000). One of the major

features of this software regarding water losses, is the use of emitter coefficients to describe water leakages

through nodes. After entering all the necessary data relative to the piping system and reservoir levels, the

emitter coefficients are automatically calculated, expressing the amount of water lost in each node. This

enables the development of a calibration process, which helps to minimize these coefficients, i.e. the water

losses (Parra et al., 2017).

3.8 Energy recovery and PAT implementation

Being aware of the severe impact that water supply has on the ecosystem, managing entities have become

ever more concerned with reducing the energy consumption implicated in this activity. As said by Jenerette

& Larssen, 2006 - ‘The sustainability of the water supply process and its interaction with climate change

has been shown to be of concern on a global scale for large urban centers. Thus, extensive research has

been carried out in order to investigate alternative methods and renewable energy sources which could

help to improve this situation.

As mentioned previously, a considerable amount of energy is dissipated within the distribution system,

mainly as a consequence of friction in pipes and the head drop imposed in pressure reducing valves. With

the purpose of recovering some of that energy, a cost-effective and environmentally friendly solution is the

implementation of hydraulic turbomachines in the distribution network, which would replace or work in

conjunction with pressure reducing valves. These turbines generate energy by converting the water’s kinetic

https://en.wikipedia.org/wiki/Public_domainhttps://en.wikipedia.org/wiki/Water_supply_networkhttps://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agencyhttps://en.wikipedia.org/wiki/United_States_Environmental_Protection_Agency

16

energy into electricity, always taking into account the maximum head drop defined for that specific PRV.

The installation of a small-scale hydroelectric power system represents an interesting technical solution,

with several studies and experimental data revealing promising results. However, one should not forget

pressure reducing valves consist of a much simpler and cheaper alternative, and an economic analysis is

required to evaluate the plausibility of such investment. Indeed, even though hydropower is widely regarded

as one of the most mature renewable power generation technologies (traditional turbine efficiency rates

reach 85% for small power plants), it is sometimes very expensive to implement, which may imply long

payback periods. For that reason, centrifugal pumps operating as turbines – pumps-as-turbines (PATs) –

have appeared as an interesting solution, despite having lower efficiencies than traditional turbines. In fact,

these reverse-operating pumps are able to generate electricity simply by reversing the direction of the

power flow, without having to apply any modifications to the impeller geometry or casing design.

It is worth mentioning that PATs have been creating great interest to water utilities and environmentally

friendly companies worldwide, due to its easy and cheap implementation, and significant energy recovery

potential. Not only is this an economically feasible approach with particular interest to rural communities in

developing countries, but also an appealing alternative to large water distribution infrastructures with the

purpose of increasing their overall revenue.

3.9 Implementation of PATs in the supply system

Instead of taking advantage of the energy dissipation occurring in pressure reducing valves within the

distribution system to generate power, turbomachines can also be installed within the adduction supply

system as an alternative. Indeed, several factors suggest promising results with this approach, mainly the

considerable flow rates and head drop values which occur in transmission pipelines upstream the network’s

reservoirs.

While turbines designed for distribution systems are usually best suited for low flow rate and head drop

values, which often results in limited energy outputs, supply systems allow for much more favorable energy

recovery conditions since the supply water isn’t yet distributed in the distribution system and is still being

transported at a much higher flow rate. Additionally, depending on the topography, there may be an

appreciable head drop in the supply system to take advantage of, which could be a further improvement in

relation to the power generation within the network.

Another important aspect relevant to energy production using turbomachines is the fluctuating flow rates

which constantly hinder the power generated by water distribution turbines. This is a typical occurrence in

distribution systems due to changes in consumption patterns, and often results in less than ideal energy

recovery solutions of less economical interest for water utilities. Contrarily, water supply usually displays a

constant flow of water, providing optimal recovery conditions in which turbine solutions can easily become

worthwhile investments.

17

4 PATS AS ENERGY RECOVERY SOLUTIONS

4.1 Introduction

Water loss control is the most important step to save energy (and water) within the water distribution

network, evidently implying a tremendous financial impact for water utilities worldwide. However, once that

is achieved to an optimal degree, additional measures can be taken to further reduce energy consumption

and operational costs in water distribution systems. For this purpose, various studies were carried out to

explore and investigate the feasibility of energy recovery solutions within the distribution system, such as

the implementation of micro-hydropower plants especially designed for the low and variable flow rates

which occur within the pipe system of water distribution networks (Sammartano et al. 2013; Carravetta and

Giugni, 2009; Paish, 2002). In such micro hydro power plants (MHP), the power output is expected to range

from a few kilowatts to a maximum of one hundred kilowatts (Carravetta et al., 2018).

Small-scale hydropower presents innumerous advantages over many other sources of renewable energy,

mainly that it impo

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