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.
III
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
variable ER mode (right). ....................................................................................................................... 53
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
variable ER mode (right). ....................................................................................................................... 52
xi
Table 21 - Energy produced with PAT 100-200 throughout the analysis period for NR mode (left) and
variable ER mode (right). ....................................................................................................................... 53
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.
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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