Energy Efficiency: What it is, Why it is Important, and How to Assess it

Abstract

Faced with increasing production costs and with high prices of industrial energies such as crude oil, of which market price has risen from about 20perbarrelatthestartof2000s−even10 per barrel at the start of 2000s - even 10 /b in 1998 - to about 100 $/b as of end of 2013, our one important means of action is the energy efficiency of industrial processes.

This is nothing new as show all the engineering and fundamental works done to reduce the steam engine coal consumption in the early industrial revolution.

The book deals with this large topic first by defining exactly what is the energy efficiency of a system. Even if its boundary and flows are well-defined the value(s) of its efficiency depends on the indicator choice. The typical agro-ethanol factory in Brazil is the most or least efficient relative to the American factories, depending on the definition of the indicator.

Because modern economy and population have thrived owing to cheap and abundant useful energies (and products derived from them like ammonia) efficiency of processes is important, even vital, to maintain these flows. However, it may encounter some fundamental limitations.
It is also crucial to convert large natural resource into these useful flows.

The book suggests a methodology to assess the efficiency at the system level from the data - flows and established knowledge - found at the process level. This analysis determines the dependence of the system efficiency on some physical characteristics of its processes. It permits to avoid large errors and to fix the range of actions for improvement.

Finally the book deals with the energy conservation and its consequences. Historic exploitation of underground coal could not run for its operations a steam engine which requires more coal than it can lift. Can the agro-ethanol industry operate without external energies, i.e. it is more than self-reliant?

Full text

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Book
ENERGY EFFICIENCY: WHAT IT IS,WHY IT IS
IMPORTANT,AND HOW TO ASSESS IT
Xavier Chavanne1
Equipe Dynamique des Fluides Géologiques.
Institut de Physique du Globe de Paris, Univ. Paris Diderot,
Sorbonne Paris Cité, UMR 7154 CNRS.
Case postale 7011 - F75205 Paris cedex 13, France
September 2013
1E-mail address: chavanne@ipgp.fr

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Energy efficiency: What it is, why it is important, and how to assess it 1
PACS 05.45-a, 52.35.Mw, 96.50.Fm. Keywords: Energy efficiency, industrial processes,
consumption rate, dissipation rate, steam engine, energy intensive economic units, demog-
raphy and energy, consumer behavior, energy resources.

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Contents
1 Preface 3
2 Introduction 9
1. First Mentions of Energy Efficiency . . . . . . . . . . . . . . . . . . . . . 9
2. Structure of the Present Book . . . . . . . . . . . . . . . . . . . . . . . . . 10
1

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Chapter 1
Preface
The topic of this book is the energy efficiency in industry, i.e. the potential reduction of
the energy dissipated along a chain of processes from the natural resources extracted by
humans, or primary energy, to the useful forms of energy such as electricity, transport fuels,
mechanical energy, heat or even ammonia. It also deals with the energy required to pro-
duce consumer goods like phones and capital items like tractors, or to provide services like
freight shipments, and information and communication technologies.
The search on better energy efficiency of processes started even before the very notion
of energy, or the equivalence of heat and work, was established. Indeed the first improve-
ments on the steam engine to reduce its coal requirement at identical work took place before
the foundation of the thermodynamic theory.
The present study does not cover new developments in the field of energy conversion,
as was the fundamental understanding of work production from heat in the steam engine
(which was at the origin of the thermodynamic theory). Instead, it gathers and analyzes
critically established knowledge and data in both fundamental and engineering sciences to
determine the efficiency of any industrial system (from coal exploitation to phone manufac-
turing), and to compare between possible designs for potential gains.
The book aims equally to bridge a growing gap between this specialized and complex
information about processes, and questions about energy efficiency at the economy or soci-
ety level. Consequently it intends to address a large audience from physicists and engineers
to economists, executives and teachers, i.e. anyone with an interest in energy.
What is Energy Efficiency?
The chapter of the book following the introduction shows that, even for a well-defined
system and its materials and energy flows, the assessment of energy efficiency is not as
simple as it may appear at first.
Within the book the efficiency/inefficiency of the system is defined by the energy re-
quired per unit of its resource input or its production output. However, the rate changes with
the choice for the denominator and with what are considered energy requirements. Is the
energy consumed to manufacture the equipments and materials, or to produce the electricity
and fuels used by the system, included in the requirements? Must we count all the energy
consumed or only that dissipated in the processes? Are the requirements limited to external
3

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4 Xavier Chavanne
primary energy?
Moreover, a practical rate like the energy consumed per unit of joule J of ethanol pro-
duced can give a value higher than one. It does not mean that there is any violation of the
energy conservation, or the system dissipates more energy than it extracts. A more funda-
mental rate can be established based on the thermodynamic laws. It leads to the notion of
the self-reliant energy system, which uses only the energy resource it extracts and processes
to meet all its requirements, both fuel and feedstock. By its mere existence our whole en-
ergy system, from petroleum industry to hydroelectric production, is self-reliant. But not
each of its components is necessarily self-reliant. The notion is important not only in terms
of the fundamental significance of the efficiency of a system, but also for the viability of
entire societies and their thriving economies, as the example of an ancient coal exploitation
demonstrates.
Why is Energy Efficiency Important?
Because of the importance of the energy - and subsequently of energy efficiency in terms of
energy savings - for the activities of our own society and for our personal life, the book in
the third chapter also deals with these connections between industrial efficiencies and the
economy or the human well-being.
The energy efficiency issue has gained renewed importance with the recent rise of hy-
drocarbon prices. France, the author’s country, imported roughly 85 G$ - billion dollars
- worth of crude oil, refined petroleum products and gas in 2012. At the end of 90s the
annual trade bill amounted to a mere 20 G$ (in constant $ value). This rise represents 2 to
3% of the annual France Gross Domestic Product GDP, small as a percentage but with a
staggering impact on economic growth and national debt levels. Further improvements in
efficiency in the transport sector or in the thermal insulation of buildings could significantly
alleviate this financial burden.
The objective of the third chapter is equally to distinguish among the various energy
related notions in economic and social themes those that are not relevant to the energy
efficiency in its strict definition.
Thus an economic system is judged efficient if it generates a large added value. The
latter represents the sales of the system outputs less the cost of its inputs. The added value
is distributed in salaries, taxes and surplus capital. In the long run, especially for basic
industries such as electricity generation and ammonia industry, the value benefited from the
improvements of the manufacturing processes and the lowering of their energy and material
consumption rates. Along with rising productivities in labor and capital investments, these
gains in the basic industries permitted to decrease the unit price of their products, on which
the whole economic activity has drawn to thrive. The price reached such a low level that
it reduced the weight of the economic value of these industries in the GDP, less than 10
percent in developed countries.
However, the unit price can equally be driven by the balance, or imbalance, between
demand and supply, or, in the short term, by government ill-defined regulations or by spec-
ulative markets, as observed in the case of the industry and market of the photovoltaic
modules since 2000. Mechanisms of price fixing add another layer of complexity, which
may well hide fundamental trends in the efficiency of processes and so in the long-term cost

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Energy efficiency: What it is, why it is important, and how to assess it 5
of products.
Thermodynamic theory, which has explained and guided the 250 fold efficiency gains
of the steam engine since its inception, also determines the limit to these gains, as seen
in the last chapter of the book. For the last decades the extraction and transformation of
each barrel of crude oil have required increasing amounts of physical resources - energy,
equipment...-, despite evident progress in the specific efficiencies of the processes involved.
Because of the oil high demand - except during crises - due to its essential function in
running nearly all economic activities, its prices have definitely followed the physical
trend. Only the thorough technical study of extraction processes and their improvements
as well as that of the characteristics of the deposits to be developed to maintain production
can reveal future developments. In summary, not only "it’s the economy, stupid", but also
"it’s thermodynamics and engineering, stupid".
At the consumer level energy saving can also be obtained by the decision to drive less, to
buy a smaller car, or to reduce the heating temperature in his/her house·· · , which is in fact
independent of efficiency. It is more often than not motivated by the final price of the useful
energies like electricity and transport fuel, as the behavior of the typical American drivers
proves. They are essential consumer costs which governments try to control to deflect the
social pressure.
Moreover, the price paid by the consumer for other goods and services such as cars
and insurances has little relationship to the energy costs to produce them. As a result of
productivity and efficiency gains of basic industries the energy cost component is generally
similar to the one in the country GDP. At the personal level incentives for saving energy
are thus reduced.
At first glance the abundance of the energy resources on Earth surface, or close to it, is
independent of the efficiency of the processes employed to extract and make them useful.
The resource base is actually huge compared with the human demand, either in terms of
energy of flows, like solar radiation, or energy stores such as fossil organic carbon in the
crust of Earth. However, only a very tiny fraction of this energy resource is amendable to
exploitation. Its characteristics - concentration, accessibility, state... - do allow the use of
efficient process. Other portions of the resource can require more energy to extract and
transform them than they actually contain, making their extraction physically non-viable.
How to Assess Energy Efficiency?
The fourth chapter describes a methodology to assess the rate of energy consumption of a
complex system and the dependence of this indicator on a variety of physical and technical
quantities.
The methodology rests on the decomposition of the system on its much simpler parts
for which a local consumption rate - a priori independent of the system one - is defined and
calculated from available and accurate information (flow data and established relationships
at process level). Thus is isolated the mechanized operations at the farm in an agro-ethanol
industry. Its efficiency is expressed with the volume of diesel required per unit of cultivated
surface. From the local rate of the operation is determined the operation contribution to the

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6 Xavier Chavanne
global rate of consumption. The relation between both rates provides some of the variables
of the system efficiency. The conversion from the consumption of diesel per ha of crop
acreage to the consumption per joule of ethanol requires the yield of crops per hectare, the
mass of sugar or starch in the harvest and the fraction of sugar converted into ethanol. The
physical analyses of these variables and others from different operations define possible
future gains or limitations on the final efficiency of the agro-ethanol industry.
The fifth and last chapter dwells on the self-sufficiency of energy systems, or in other
words, whether systems can only rely on the resource they extract for their operations. Coal
extraction from underground mines necessitated efficient steam engines to lift the coal and
pump the excess water. These engines had to consume only a fraction of the coal lifted at
the surface for coal exploitation to be viable and self-reliant.
Agro-ethanol industry is a more complex energy system as it requires the outputs of
other energy systems - diesel, electricity, ammoniac... -, and consequently depends on
their efficiency. From the industry actual direct consumptions (electricity, fuels...) and by
replacing existing processes to produce internally these requirements, the system can be
made self-reliant, consuming its own production and/or resource. Hence its real efficiency
can be determined. It may well be possible that the industry does not produce enough
energy to fuel its own processes.
And More
The reader is invited to learn more about the agro-ethanol industry and its efficiency
throughout the book. Other examples like steam engines, the ammonia industry, phone
manufacture... are also used to illustrate and support the various arguments developed in
this book about energy efficiency.
Feedbacks on this study are welcome. Oversights on such a complex matter cannot be
ruled out.
The author thanks the prof. J.-P. Frangi, director of the Institut Universitaire Profession-
nel Génie de l’Environnement at the university of Paris Diderot for his help and remarks.
Without him this work would not have been possible.
He is also grateful to P. Brocorens, P. Alba and B. Durand for their thorough review. P.
Brocorens is a young researcher on advanced chemistry at the University of Mons working
on the properties of new materials like conjugated polymers and composites. P. Alba is a
retired engineer of Elf Aquitaine where among various positions he had been in charge of
the economic studies of the company. B. Durand is an expert of petroleum geochemistry
and had been responsible of the geology-geochemistry department at Institut Français du
Pétrole (IFP). He had been also director of Ecole Nationale Supérieure de Géologie in
Nancy.
This book also benefited from the review of J. Heissner, promoter of a novel project of
a self-sustainable village in New-Zealand. I wish him success in his project.
X. Chavanne
Physicist (PhD, member of Société Française de Physique) and research engineer. He

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Energy efficiency: What it is, why it is important, and how to assess it 7
worked on various topics in academic and applied areas: study of the turbulent natural
convection both experimentally and theoretically, modeling of the convection in glass
furnaces at St Gobain company (with physical models and theory), development of
soil moisture sensors for both fundamental and industrial objectives (use of a dielectric
principle). Since 2004 study of the efficiencies of different industrial systems in areas from
the telecommunications to basic industries and to transport.
September 2013

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Chapter 2
Introduction
1. First Mentions of Energy Efficiency
The first evocations of the efficiency of an industrial system in modern terms can be associ-
ated with the improvements of the steam engine by J. Watt, and with the work of S. Carnot
to establish a theory of fire machines at the turn of the nineteenth century. Both J. Watt and
S. Carnot used as an indicator of efficiency the quantity of coal burnt, or its calories, per unit
of the product of mass of water lifted by the height. Indeed, the notion of energy itself was
introduced later by the experiments of J. Joule and the establishment of the thermodynamic
theory by R. Clausius and W. Thomson.
The steam engine was first developed successfully in Great Britain in 1712 by T. New-
comen to access water filled coal mines [1, 2]. Because of the wood disappearance and the
easy access at the surface or shallow depths of peat and coal in some regions of Europe
(Holland, Great Britain, Wallonie region in Belgium, the basin of la Loire in France...), the
fossil resources were exploited as early as the thirteenth century. Due to a rising demand
the production had to be increased.
The Newcomen machine had a very low yield in terms of conversion of coal heat into
work (less than 0.3% as established later; see the details in the chapter ??). Successors of
T. Newcomen managed to increase this efficiency, most notably J. Watt after 1769 (sepa-
rate condenser among various modifications). One of Watt’s sale pitches was that his new
machine was able to save 75% of coal by comparison with the previous design [3]. The ef-
ficiency was all the more important as J. Watt’s improvements and modifications allow the
use of the steam engine in other industries (textile, iron...) to provide mechanical energy.
Thanks to Watt and other inventors the steam engine became more efficient - still less than
5% in 1824 - while more available and reliable to produce energy than other means such
as muscular work, windmill or even water mill. After 1830 with the locomotive the steam
engine was used in the transportation of freight and people.
Around 1820 the aim of the physicist S. Carnot was to determine the ideal transforma-
tions along a cycle in a "fire" machine (not only a steam engine) to produce a maximum
of work from a fixed amount of heat [4]. It was equivalent to solving an efficiency
problem with the deduction of the fundamental factors, chiefly the temperature difference
between the hot and cold sources rather than the level of gas pressure as believed at that
time, to be most important (at least for an ideal cycle). His study founded the theory
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10 Xavier Chavanne
of thermodynamics with notions like thermodynamic cycles, reversible transformations,
adiabatic and isothermal compressions or dilatations of a perfect gas... Thanks to his
work large and fast improvements were made possible with the existing machines (the
steam engine benefited of the theory as shown in the chapter ??), and new machines were
conceived (internal combustion engine, gas turbine). Some modern steam engines in
power plants can reach a yield of 45% and gas fired plants can surpass 55% owing to two
combined cycles.
2. Structure of the Present Book
In the early industrial revolution energy efficiency of processes was one of the major preoc-
cupations of engineers to save expensive coal or to increase the outputs of an industry with
the same amount of coal. Energy efficiency has always been a priority when the supply of
energy is restricted resulting in high prices, as observed in the beginning of 19th century for
coal and nowadays for crude oil. Obviously, as it was also the case in the nineteenth century,
energy efficiency is not the only factor to consider when developing a process or a system
at the industrial scale. They must also fulfill economic or environmental constraints such as
labor and equipment productivity, which can further impact the energy consumptions.
The purpose of the book is not to present new developments on energy conversion, as
was the understanding of work production from heat in the steam engine. But rather it
will show how to gather and analyze critically already established knowledge and data of
both fundamental and engineering sciences to determine the efficiency of a large range of
industrial systems.
It also deals with the role of the energy efficiency in the economy and human societies.
The book in the second chapter establishes first a definition of the efficiency for any
system. It is expressed with an indicator based on the rate of consumption of the system,
i.e. its energy consumed per unit of its output. It turns out that different indicators for a
system and its flows are possible. A practical rate is estimated from the direct inputs and
outputs of the industry, like coal and lift work in the case of the steam engine. Its scope
can be enlarged to include indirect consumptions like those to extract and clean the coal
used by the steam engine. However, in the case of energy systems like steam engine or
coal exploitation, the application of the energy conservation suggests a different and more
fundamental rate based in the energy dissipated.
The third chapter shows how the efficiency gains and its limitations still play an impor-
tant role in our societies, its economy, human well-being and comfort, and our extraction
of natural resources although it is not as apparent as it was in the times of Watt and Carnot
due to the very progresses of efficiency since then. Other factors have also to be considered
like the cost of production in monetary value, the prices of energies and products, energy
conservation by end consumers, as well as the abundance and characteristics of the energy
resources.
The fourth chapter is dedicated to a methodology and its mathematical tools to derive
a rate for the system under study and the dependences of this rate. Energy efficiency can
be studied for quite simple systems like the steam engine as well as for more complex ones

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Energy efficiency: What it is, why it is important, and how to assess it 11
such as the production of ethanol from agriculture - agro-ethanol - or the phone manu-
facture. The main principles of the analysis are the decomposition of the system towards
simpler operations of few processes or even just one, and the determination of the natural
rates of consumption of these operations. These local rates, deduced only from data at op-
eration level, are much less variable than the rate of the whole system. A reverse process
allows to derive from the local rates the latter rate. As a result of the process, the physical
and technical variables on which the system rate depends are identified. In the process, and
thanks to different sources and/or established knowledge in sciences and technologies, large
errors on data and on assumptions are tracked. The suggested methodology also provides
tools to propagate the remaining uncertainties from the raw data to the system rate. This
allows to quantify the compromise between the accuracy on the rates and the time required
for data gathering and analysis.
The last chapter deals more specifically with the energy systems. Among them are ex-
amined self-reliant systems. The resource they use must provide both the fuel consumed
in their processes and their feedstock. Historic industries such as the exploitation of a coal
basin offer examples of autonomy due to the necessity themselves to use local resources
for production. Significantly, in industrial times only fossils fuels show their ability to ap-
proach self-sufficiency. If they are to be substituted for conventional and dominant systems,
alternatives systems like the agro-ethanol production must also demonstrate this capability.
This can be achieved thanks to modifications of present systems with existing processes.
However, the resulting rate of dissipation expressed as the energy dissipated per unit of to-
tal input of the system must be lower than one in order for the self-reliant system to produce
a surplus output.
Note about Unit Symbols Due to the difficulty to define an equivalence between the
different forms of energy such as between final and primary energies, the unit of each form
of energy is accompanied by a subscript informing about the form.
Thus the subscript LHV in JLHV stands for the low heat value of a fuel, HHV in JHHV
for its high heat value, ein Jefor electricity, min Jmfor the mechanical energy, th in Jth
for the thermal energy, ph in Jph for the energy of photons, EF in JEF for the final energy -
part of the direct requirements ED- consumed by the system under study, EP in JEP for the
overall primary energy EEP used to produce EDby the system aux...
The subscripts of units are also used for other quantities if necessary. For instance the
volume of water lifted over a fixed height is measured by m3
w.mh.
The use of subscripts for the symbol of units is not recommended by the Comité In-
ternational des Poids et Mesures (CIPM) in charge of defining the Système international
d’unités (SI) [52]. All energies have a unique (derived) SI unit, joule, based on their equiv-
alence in terms of heat value. But, as we have seen, the different forms are not equivalent
in terms of usefulness for the consumer. Otherwise the notion of efficiency itself can be
questioned.
Notations like J of electricity or J of primary energy could be used. But for concision
we prefer to use the convention introduced above. We follow the rest of the norms enacted
by the CIPM.

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Energy efficiency: What it is, why it is important, and how to assess it 15
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