Xiaohua Xia and Jiangfeng Zhang
Energy Efficiency and Energy
Optimization
Centre of New Energy Systems,
Department of Electrical, Electronic, and Computer Engineering,
University of Pretoria
December 2007
1
Energy Efficiency
Energy efficiency has come under increasing scrutiny as a result of the world­
wide increase in the demand for energy. Energy suppliers could employ several
strategies in their attempts to cater for this increased demand.
The first would be to simply expand conventional power plants. It is un­
derstood that the expansion of conventional power plants will need to take
place for a couple more years in order to sustain research and development of
cleaner energy generation technologies. However, a move away from the use
of fossil fuels and conventional coal burning power generation is a pressing
matter on the world agenda.
Generating energy in a renewable and more sustainable manner is the
second strategy. This would include the development and use of technologies
such as solar, wind and hydrogen energy as well as the conversion of biogas
into liquid fuel.
The third strategy is energy management of which the main aim is to
increase the effective use of available energy or energy efficiency. This may
decrease the immediate demand for the generation of energy, as some of the
demand is met through the efficient use of already generated electricity. En­
ergy efficiency in industry, transportation and residential sectors is seriously
encouraged. Also, energy efficiency is applicable whether the energy is gener­
ated conventionally or through sustainable methods.
Since the energy crisis in the 1970’s, academia, government and indus­
try progressively focussed more on both the research and development of re­
newable/sustainable technologies and the development of energy management
programmes. This book will argue for a specific framework to address energy
efficiency.
1.0.1 The need for a unifying framework
Literature provides ample views on energy efficiency. Varying aspects within
the broad category of energy efficiency such as management efficiency, oper­
ational efficiency, carrier efficiency, information and control efficiency, billing
2
1 Energy Efficiency
efficiency, maintenance efficiency, performance efficiency, equipment efficiency,
conversion efficiency, fuel efficiency, thermal efficiency, luminous efficiency and
mechanical efficiency are discussed. These views however, are not clearly clas­
sified and they encompass different points of departure on the components of
energy efficiency. A unifying classification system could add significant value
to the field.
Energy efficiency is defined as the ratio between energy output and energy
input. Energy efficiency is the key factor in rationalising energy use. Consider
Fig. 1.0.1 below. Energy saved per capital investment is compared in terms
of different measures that could be employed to increase energy efficiency.
Fig. 1.1. EE Components
Part 1 represents energy saving measures that achieve significant energy
efficiency per investment. Energy saving measures that achieve this level of
energy efficiency usually includes simple activities such as switching off an
air-conditioner when leaving the office or detecting and fixing the leakage in
a compressed air system. These actions would result in large reductions in
energy wastage per investment and is the most cost effective way to improve
energy efficiency.
For the same investment as in Part 1, Part 2 activities will achieve sig­
nificant energy efficiency, however the improvements are not as drastic as in
Part 1. Part 2 activities may include skills training and improved operation
and control of any given energy system.
1.1 POET–Four components of energy efficiency
3
In Part 3, achieved energy efficiency per investment is much lower. Retrofitting
more efficient equipment to existing technology such as motors or even build­
ings will only slightly improve energy efficiency when the same investment is
made.
Lastly, the least energy efficiency is achieved per investment through ac­
tions such as technology research and development as represented in Part 4.
Although Part 4 has the lowest energy savings per investment rate, technology
research and development is very important since the progress of technology
may give rise to important changes in the previous three parts.
A unifying classification system for energy efficiency would lead to suc­
cessful demarcation of the measures described above, enabling a systematic
approach toward energy efficiency improvement programmes. A comprehen­
sive classification system is proposed in the subsequent section.
1.1 POET–Four components of energy efficiency
Energy efficiency is a measure of the efficient use of available energy. It can
be divided into four components: Performance efficiency, Operation efficiency,
Equipment efficiency, and Technology efficiency (or POET in short).
These components will be discussed in detail below. The discussion will
start with technology efficiency, as technology dictates the possible efficiency
rates in all other components. In each section, key characteristics and the
places where research is done is discussed in order to enable the reader to
identify the energy efficiency components.
1.1.1 Technology efficiency
Technology efficiency can be defined as the measure of efficiency of en­
ergy conversion, processing, transmission and usage. A key characteristic of
technology efficiency is its novelty, where no baseline exists with which the
technology could be compared. When a ground-breaking technology is truly
feasible it would defeat peer technologies and establish a market share swiftly.
The use of a new technology in the market is called a ”greenfield” project.
Another key characteristic is the search for optimality. This pursuit of
scientific limits and the drive toward development previously undiscovered or
thought to be impossible, is essential in establishing a new technology. This
pursuit for technology efficiency and improvement are usually carried out in
controlled research spaces such as laboratories and research centres.
Natural laws predictably impede technological development. Evaluation
criteria for technology efficiency include feasibility, life-cycle cost and return
on investment and coefficients in the energy conversion/process/transmission
rates. These criteria are discussed below:
(i) Feasibility: A fundamental criterion for the evaluation of a new tech­
nology is its feasibility. The energy output of a motor could never, according
4
1 Energy Efficiency
to the natural laws, exceed the energy consumed. The aspiration for changing
water into fuel is thus ludicrous.
(ii) Life-cycle cost ([1]) and return on investment ([Vanek and Albright(2008)]):
A technology efficiency programme typically stretches over a number of years.
Decision makers should analyse the profitability of the project by taking the
running cost and the life span of the new technology or a green project into
consideration.
(iii) Coefficients in the conversing/processing/transmitting rate ([56]):
During the energy conversion, processing or transmission the output energy
can often be written as a constant energy loss plus the production coefficient
and the input energy. The technology efficiency increases as the coefficient in­
crease. Some examples of this relationship is the relevant coefficient in energy
conversion which is used to evaluate the clean coal technology in coal-fired
power generation; the coefficient in energy processing rate of a transformer
which has non-negligible heat losses; and the coefficient in energy transmission
lines which use high voltage to reduce line losses. Table 1.1.1 provides some
more examples:
As with most components of energy efficiency, technical, human and time
influences cannot be ignored. Their influences on the success of technology
efficient improvement projects are discussed below:
(i) Technical factors: A strong correlation exists between technical charac­
teristics and the possible resulting technology efficiency. These characteristics
predetermine the new technology’s possible efficiency. Below are some exam­
ples that illustrate this point.
• Technologies in smart grid are investigated to improve energy efficiency in
power generation, transmission and distribution;
• Electrical vehicle technology is developed to improve vehicle energy effi­
ciency and to reduce carbon emissions;
• Wave and solar energies are studied to improve their energy conversion
ratios, and;
• In order to improve the overall technology efficiency of underground mines
and to save energy, the Three Chamber Pipe Displacement Feeder [55] was
invented to take advantage of potential energy to hoist water.
As is clear from the examples, improvements made to the technical char­
acteristics of part of a system could increase the technology efficiency of the
system as a whole.
(ii) Human factors: Technology efficiency improvement projects will al­
ways be influenced by humans. Decision making by stakeholders throughout
the improvement programme will influence the eventual success thereof. Any
efficiency improvement project will require adequate financial aid and politi­
1.1 POET–Four components of energy efficiency
5
Fig. 1.2. Equipment efficiency [79]
cal will at more than one level. These aspects might even be deterministic in
the success of efficiency improvement programmes.
(iii) Time factors: When an efficiency improvement project is started, the
life cycle of equipment should be analysed. A number of aspects could change
during the project and will need to be taken into consideration in order to
ensure the success of the project. A technology efficiency improvement pro­
gramme typically stretches over 10 or more years.
The technical, human and time factors that influence the success of a tech­
nology efficiency improvement programme are generally unavoidable. There­
6
1 Energy Efficiency
fore they need to be regarded throughout the project. These factors also in­
fluence equipment, operation and performance efficiencies.
1.1.2 Equipment efficiency
Equipment efficiency is a measure of the energy output of isolated individ­
ual energy equipment with respect to given technology design specifications.
The equipment is usually considered being separated from the system and hav­
ing little interactive effect to other equipment or system components. Energy
efficiency of equipment is measured under ideal and controlled conditions. The
equipment could be an isolated energy sub-system in a bigger energy system,
for example a wind turbine in a wind energy system.
Standardization and constant improvement are key characteristics of equip­
ment efficiency. Technical standards for stand alone equipment are generally
developed through research in a laboratory or research centre with the goal
to optimally use that particular piece of equipment. Manufacturers are ex­
pected to ensure that equipment is manufactured in accordance with these
standards, with as little deviation as possible. This would result in the most
efficient use of any particular piece of equipment. Changes to different parts of
a system or the availability of new technology could necessitate improvements
and changes to the standards. A continued effort to improve efficiency using
the latest technology available should be upheld.
The distinction between equipment efficiency and technology efficiency is
important. It is well illustrated in the following example: The study on the
improvement of compact fluorescent lights (CFLs) technology to provide more
efficient lighting facilities is technology efficiency improvement. Replacing in­
candescent bulbs, on the other hand, with CFLs would improve the efficiency
of the lighting equipment and is thus classified as equipment efficiency im­
provement.
Evaluation criteria for the improvement of equipment efficiency include
specifications, capacity, constraints, standards and maintenance indicators.
These are discussed separately in the following section:
(i) Specifications: The most important aim of equipment efficiency is to
minimize the deviation of the equipment from the technical design speci­
fications. Manufacturers should adhere to specifications applicable to their
products to ensure optimal equipment efficiency. It is, however possible for
equipment manufactured by different producers under the same specifications
to differ slightly because of varying technical and manufacturing processes
among producers.
(Ii) Capacity: Equipment operating at equal energy consumption levels
may have different capacities. The type of equipment with the higher capac­
ity, operating at the same energy consumption level as the first, would be more
efficient. This could be illustrated by the following example: When transport­
ing fruit from one city to another, the transportation tool could be a truck
or a train. It is clear that the train would be able to transport much more
1.1 POET–Four components of energy efficiency
7
fruit that the truck when consuming the same amount of energy. That is, as a
transportation tool, the train has higher equipment efficiency than the truck.
(iii) Constraints: Specifications of energy equipment may include certain
constraints promoting optimal use of the equipment. A specified range of
current and voltage for instance would accompany electrical wires. The output
of equipment is sometimes limited by the technology efficiency. An example
of this is the theoretical upper bound 59% of a wind turbine (see Table 1.1.1).
(iv) Standards: Standards from different fields of research such as electrical,
mechanical and chemical engineering amongst others are important regulators
to ensure equipment efficiency. For example, the standards in CFLs specify
the portion of the emitted electromagnetic radiation which is should be used
for human vision and thus ensures the equipment efficiency of CFLs.
(v) Maintenance: A well planned maintenance programme is of paramount
importance, in aiming to minimise the deviation of equipment from its des­
ignated specifications ([22]). A simple example is the maintenance done on a
car. If oil is changed and filters are replaced at the correct times, then energy
conversion from fuel to mobility would happen as efficiently as the equipment
would allow.
As is the case with technology efficiency, equipment efficiency is also im­
pacted by technical, human, and time factors. These are discussed below:
(i) Technical factors: Technology dictates the possible energy efficiency of
every other type of efficiency. Thus technological advancements would enable
increased or decreased efficiency of equipment. In recent years, motors with
Variable Speed Drive (VSD) have been developed. VSD’s has a much better
equipment efficiency than the older style fixed power motors.
(ii) Human factors: In order to maintain equipment efficiency, humans
need to intervene quite often. Interventions would include proper maintenance,
retrofitting more efficient equipment and drawing on expertise to ensure that
specification standards are met.
(iii) Time factor: Equipment efficiency could be upheld or improved by
proper maintenance and retrofitting more efficient equipment. These actions
both need to be timed well, in order to reduce the losses caused by a mainte­
nance backlogs and the use of old equipment. The following serves as illustra­
tion: the maintenance of a conveyor belt system can be done when the produc­
tion demand is lower and/or the electricity price is expensive; and retrofitting
an efficient water supply system is better to be done at lower water demand
seasons.
The human, technical and time factors that influence equipment efficiency
could all be mitigated through good management of the equipment. They also
play a role in operation efficiency as will be discussed in the following section.
1.1.3 Operation efficiency
Operation efficiency is a system wide measure which is evaluated by con­
sidering the proper coordination of different system components. Operation
8
1 Energy Efficiency
efficiency is achieved when three system components are coordinated; these
include the physical parts of the system, time and human operators. Firstly,
the physical parts of the systems should fit optimally by means of sizing and
matching. Secondly, time coordination is done by controlling time when en­
ergy should best be used. Thirdly, operation efficiency is highly dependent on
the skill levels of human operators.
(i) Physical coordination: Operation efficiency can often be measured by
considering whether the physical coordination of system components is op­
timal. The physical coordination consists of the sizing of particular physical
components. Sizing is the coordination of one physical part with the rest of
the system. Component sizing is an operational issue, because this is a mea­
sure of the coordination of the components with respect to the rest of the
system. This aspect should be distinguished from the capacity discussion in
equipment efficiency.
Another aspect of the physical coordination is matching different physical
components. Matching is done when one physical part in relation to two or
more system components is coordinated. An example of matching is when the
load on a conveyor belt is coordinated with the speed at which the load is
transported. In order to maintain the highest operation efficiency, a decrease
in the loading rate would require a decrease in the speed and vice versa so that
the belt is maximally loaded. The speed of the conveyor belt is matched with
the load. See [44] for more process ‘matching’ energy optimization examples.
(ii) Time coordination: Time coordination includes time scheduling of dif­
ferent system components. In a conveyor belt system of a colliery studied in
([38]), coal is transported to a stock silo, and then by conveyor belt to a rail­
way terminal where trains further transport the coal to other destinations.
The objective of the study was to minimize the energy consumption of the
conveyor belt connecting the stock silo and the railway terminal. The train
usually has more than 200 wagons and is more than 2.5Km in length. It takes
about 4 hours to fully load the train. The conveyor belt must be optimally
controlled so that there is enough coal to load the train on arrival. The eco­
nomic loss caused by the train waiting to be loaded is much higher than the
energy cost of the conveyor belts. Therefore the switching on or off timetable
of the conveyor belt is determined by the train timetable when the total ca­
pacity of the up stream coal supply and the stock silo is enough to supply
the train. The time coordination of the conveyor belt and the train will thus
determine the operation efficiency of this belt system.
(iii) Human coordination: The skills of human operators could increase
operation efficiency. For instance, a car driven by an experienced driver, as
apposed to being automatically steered, will use fuel more efficiently than
when it is driven by an inexperienced driver.
With suitable coordination between physical components of a system and
appropriate scheduling of use and maintenance, the operation efficiency will
undoubtedly increase. As with technology efficiency and equipment efficiency,
operation efficiency is affected by technical, human and time factors:
1.1 POET–Four components of energy efficiency
9
(i) Technical factors: Energy needs for a specific task must be technically
determined in order to achieve optimal energy efficiency. An example is in
motor sizing. For a given load, the size of the corresponding motor should be
properly chosen; the power of the motor should not be too big or too small.
The motor size and load must match in order to reach the maximum operation
efficiency. This required the motor size to be technically determined in order
to match the load and consequently achieve better performance efficiency.
(ii) Human factors: Coordination between different systems components is
a prerequisite for operation efficiency. A well trained person or an automated
control system could manage the system in a coordinated way thus increasing
operation efficiency. For example, the speed and the braking system of a train
must be suitably controlled in order to be most energy efficient when the train
is climbing or running down a hill. Only a well trained driver, or a state of
the art auto driver, can control the train as expected.
(iii) Time factors: As mentioned above, time coordination of different sys­
tem components is an indicator for operation efficiency. Furthermore, the op­
eration of an energy system is often routine, and other time related factors
will also give rise to the change of operation efficiency. For example, the tem­
perature set point of a refrigerator can be optimally set to achieve energy
efficiency under normal working conditions, say, fixed temperature and food
stored. However, when time changes from noon to midnight, the ambient tem­
perature drops too, and the previously optimal temperature set point may not
be optimal in terms of energy efficiency. As time factors change the efficiency
of a setting on an appliance may change as well. Another example is the en­
ergy minimization of a crusher in a colliery. The crusher crushes coal from a
conveyor belt into smaller size and then transports it into a stock silo. The
performance efficiency of the crusher is poor if there is not enough coal supply
from the conveyor belt. To achieve better performance efficiency, the conveyor
belt must be switched on before the crusher in order to provide enough coal
to the crusher. By synchronising the ’switch on times’ of the conveyor belt
and the crusher, the efficiency of both the crusher and the conveyor belt is
increased.
An operation efficiency improvement project is often a short to medium
term project that may last from several months to 3or 5 years. Operation
efficiency improvements and studies of a plant could be conducted within the
plant. In the following section, performance efficiency will be looked at.
1.1.4 Performance efficiency
Performance efficiency of energy systems is a measure of energy efficiency
which is determined by external but deterministic system indicators. These
deterministic indicators that play a role in performance efficiency could be
compiled into two groups: Engineering Indices (EI) and Social and Environ­
mental Indices (SEI). These system indicators that impact on the performance
10
1 Energy Efficiency
efficiency are energy security (EI), production (SEI), cost (SEI), environmen­
tal impact (SEI), energy sources (EI) and technical indicators (EI), amongst
others.
(i) Energy Security: Energy security means the secure supply of energy to
meet the energy demand. It is the basis of energy efficiency: without a secured
energy supply, it is meaningless to talk about energy efficiency. Energy security
can be threatened by many factors: tremendously high end user demand,
accidents of power generations, natural disasters, increase of international
energy prices, wars and many political issues.
(ii) Production: Production is a SEI and is often determined by mar­
ket, and the performance efficiency can change whenever market conditions
change. For example, a plant runs most energy efficient when it produces 1 ton
of a product per day however, the market demands much more than 1 ton of
that product everyday. Therefore the plant has to produce more products and
its performance efficiency will be reduced. Another example of how produc­
tion influences performance efficiency is when season changes cause changes
in the market demand. The production in the clothing industry will increase
during winter, when demand for clothes is high. This will ultimately change
the performance efficiency during winters in the clothing industry.
(iii) Cost: Cost is also a SEI, and when the cost of a process is changed, it
will give rise to the change of the performance efficiency of the energy system.
For example, when a TOU electricity tariff is introduced, an end-user often
tries to shift their energy consumption from the peak time to off-peak time
period, and the corresponding electricity cost to the end-user will then be
reduced. This implies that the end-user still uses the same amount of energy
however, the energy cost is reduced, and thus the performance efficiency in
terms of cost is improved. This cost indicator also includes aspects such as
energy intensity, energy per GDP, fuel intensity and heat use per square meter
([35]).
(iv) Environmental impact: The last of the SEI are the environmental con­
cerns. Performance efficiency could be evaluated by considering environmen­
tally responsible production. Emission problems and waste generated through
production should be addressed and may influence performance efficiency. For
example, a paper plant will release poisonous waste water at the end of the
production process. If the waste water is retreated, there will be little or no
pollution to the environment, thus performance efficiency in terms of environ­
mental concerns is increased. Another example is that emission constraints is
included in the modeling of the economic dispatch of electricity generation in
[42].
(v) Energy sources: Different energy sources are EI and energy systems
often consist of different forms of energy sources like electricity, gas, coal, fuel
and wood. The performance efficiency of the system could be evaluated by
considering using these different sources. For instance, an end-user in a rural
area may use coal or gas for cooking. The energy efficiencies of the two sources
differ with gas having a higher efficiency than coal. Therefore using gas will
1.1 POET–Four components of energy efficiency
11
improve the performance efficiency in terms of energy sources. It is interesting
to note that gas is often more expensive than coal, thus the switching to gas
from coal increases the performance efficiency in terms of energy sources, but
decreases the performance efficiency in terms of cost. This indicates that the
cost and the energy source indicators may sometimes be contradicting.
(vi) Technical indicators: Some technical indicators are used as a means
to measure aspects of performance. At other times, technical indicators are
built into a performance objective to drive the design process. For example,
the maximum in-train force, which is a technical indicator, is combined with
energy consumption and traveling time, in the control of heavy haul trains to
avoid collisions of wagons, minimizing energy consumption and traveling time
([11]).
One process or energy system may be evaluated by one or more of the
above four indicators, and sometimes other indicators may be needed for the
evaluation. It is worth noting that these performance efficiency indicators are
sometimes contradictory or in competition with each other. If there were no
cost and no emissions, there would be no production, which in itself would not
be sustainable either. Any given energy system could be managed to maximise
production and at the same time minimize cost and emission. Therefore the
performance efficiency could only be improved when certain trade-offs among
different indicators are made. Energy efficiency aims to optimally coordinate
all contributing factors in such a way that the least energy is lost, thus making
the production process more sustainable. True sustainability, taking environ­
mental cost into consideration, will require more than just energy efficiency
but also efficiency in terms of natural and human resources used to achieve
a worthwhile outcome. Establishing a balance where all indicators are ad­
dressed, would be to achieve a sustainable solution. Sustainability requires
in the first instance that an EI does not compete with an SEI. So the first
criterion for sustainability is that the solution makes financial and technical
sense.
The technical, human and time factors that influence performance effi­
ciency will be discussed below.
(i) Technical factors: Performance efficiency could be improved by means
of technical aspects such as energy efficiency tools. The use of these tools could
aid in finding the optimal energy source combination and ultimately improve
performance efficiency.
(ii) Human factors: Human behaviour is another important factor affecting
performance efficiency. Increased public awareness of the benefits of switching
off air conditioners and lights when leaving the office, may lead to significant
energy efficiency in their office building. Energy waste, leakage and theft are
all aspects where human behaviour could play a significant role.
(iii) Time factors: Time plays an incredibly important role in performance
efficiency. For example, a new TOU electricity tariff would stimulate perfor­
mance efficiency improvement; or market demand will fluctuate and affect the
production in the plant, consequently affecting also the performance efficiency.
12
1 Energy Efficiency
We have discussed the technology, equipment, operation and performance
efficiencies in detail. In the subsequent section, the application and relation­
ships between the various components will be explored.
1.1.5 Remarks on POET
In the preceding section, the four components of energy efficiency components
along with their indicators, relations with technical factors, human behaviours
and time factors were discussed. The differences between the four POET com­
ponents could also be described by investigating factors such as places, people,
and outputs. These provide some insight into the differences between the four
components of energy efficiency.
(i) Places: The place of an energy efficiency project is less important than
other factors such as technical and time factors; however, it still provides some
insight into the differences among the four POET components. Performance
efficiency improvements of a plant are carried out, outside the plant; operation
efficiency improvements are within the plant, while equipment efficiency is
often improved in testing centers, laboratories, and research centres. New
technology is developed and technology efficiency is investigated at research
institutions.
(ii) People: People involved in performance efficiency includes administra­
tive management personnel and the general public; while the kinds of people
involved in operation, equipment and technology efficiency usually include
technicians, engineers, and scientists respectively.
(iii) Output: Performance efficiency aim at establishing targets and oper­
ation efficiency at developing systems. Equipment efficiency focuses on devel­
oping equipment that could be patented. The output of technology efficiency
could be research papers or intellectual property.
We have listed differences among POET components above, in order to
help classify the type of efficiency in any given scenario. It is however, impor­
tant to take note that the four POET efficiency components may not have
clear-cut boundaries, and they may also exist at micro-level underneath a more
visible macro-level, exhibiting a multi-layer structure. In practice, equipment,
operation and performance efficiencies are often measured in energy improve­
ment projects or the so-called brown field projects. The overlap between these
components, for example, could be the simple strategy to switch off water sup­
ply pumps during peak hours. This will save energy cost in terms of a TOU
tariff and thus improve performance efficiency. On the other hand, an opti­
mized control of these pumps will minimize electricity cost while maintaining
water supply and thus improve operation efficiency.
There are no strict distinctions between ‘simple strategy’ and ‘optimized
control’. A simple peak shifting strategy provided by an experienced system
operator may yield quite similar results as a control strategy obtained through
the mathematical solution of an optimization model.
1.1 POET–Four components of energy efficiency
13
A multi-layer system exists where a piece of equipment could be a technol­
ogy on one level and a piece of equipment on another level. Each of the four
components may also be treated as an energy sub-system and has its own four
POET sub-components, which eventually exhibits a multi-layer structure.
The Multi-layer System
An energy system may have different layers of energy subsystems. Each of
these subsystems could be classified according to the four POET components.
The following multi-layer example on a wind energy system illustrates this.
Fig. 1.3. A Wind Energy System
In a wind energy system, such as in Fig. 1.1.5, mobility energy from the
wind is transferred into electricity. This energy transfer efficiency is depen­
dant on the corresponding technology efficiency. The wind energy system falls
into the technology efficiency category. However, a wind system can be further
divided into several components such as the wind turbine, power processing
component and operation control system. The wind turbine’s efficiency is cate­
gorized as equipment efficiency; while the power processing component could
be technology efficiency and the operation control system in the operation
efficiency category.
The multi-layer nature of this system would allow a further breakdown
into smaller parts of the system. The power processing component could be
treated as another energy sub-system. This sub-system consists of the power
processing component, the aped regulator and the AC/DC converters. The
power quality of the output of the wind system, for instance, is determined
by the power processing component and thus can be improved by studying
the performance efficiency of the power processing component; the optimal
14
1 Energy Efficiency
wind turbine speed regulation improves the operation efficiency; and the op­
timal design of the AC/DC and DC/AC converters improves the equipment
efficiency.
In this way, every system could be broken down into smaller parts and opti­
mally gauged in order to improve efficiency at multiple levels. The boundaries
between these different methods of energy efficiency are flexible. The relations
between these different components will be discussed in the following section.
1.1.6 Relationships between POET efficiencies
The POET efficiency components relate to one another in a number of ways.
Two ways of interaction between different components in energy efficient
strategies have already been discussed in the previous subsections. Another
method of interaction exists. The relationships between these four components
are explored in this section.
In every system that uses energy, some energy is lost. Reasons for the
loss of energy may include theft, leakage or energy wastage. This ’loss’ is
due to non-technical aspects, and it has neither relation to the technology or
equipment used nor the operation of the system. It is simply considered gone.
Conversion (usually from mobility energy into electricity) takes place by
means of a certain technology. Technology efficiency is deterministic for all
other components of efficiency as it prescribes the system in which energy
efficiency is strived for. In the attempt to achieve optimum energy efficiency,
the equipment that forms part of that particular technology should comply
with specifications and should be properly maintained. Similarly, operation
efficiency could be achieved when the system is well coordinated physically
as well as in terms of timing. The person in control of the system should also
have the necessary skills enabling maximum operation efficiency. Performance
efficiency consists of four factors that contribute to an overall performance ef­
ficient system: Energy performance, time performance and skills performance
all of which contribute to a high achieved level of performance efficiency. The
inevitable loss discussed previously also forms part of performance efficiency.
Consider the following diagram in which the relationships among these aspects
of the efficiency components are illustrated in Fig. 1.4.
The top layer of the pyramid represents technology efficiency, where the
other layers sequentially denote equipment efficiency and operation efficiency,
with performance efficiency forming the base.
Technology efficiency is primarily concerned with the conversion, process­
ing and transmission of electricity. In every conversion/process/transmission
process some energy is lost. This loss is represented in the most right block in
the performance efficiency base (P4).
The useful output of generated energy would be the total input energy
minus the energy lost. Consider an energy system which convert, process, or
transmit n energy sources into either the same form of energy or a different
form of energy. ET denotes the useful output energy by technology efficiency,
1.1 POET–Four components of energy efficiency
15
Fig. 1.4. Triangle Structure of POET
Ei denotes the i-th kind of input energy; ETi := αi Ei + βi , αi Ei denotes the
valid converted, processed or transmitted energy; while βi denotes the wasted
energy during conversion, procession or transmission.
ET =
n
n
i=1
ETi =
n
n
(αi Ei + βi ),
(1.1)
i=1
The aim of technology efficiency is to increase the ratio between the total
usable energy and the input energy, thus making more energy available for
use by decreasing loss. It could be expressed as:
ET
ηT := _n
i=1
Ei
.
Let us examine the relationship between equipment specification and the
energy output attained by a specific technology. Equipment efficiency endeav­
ours to minimise the difference between the output energy as obtained by
technology efficiency and the specification of equipment for a certain amount
of input into an energy system. For the i-th kind of input energy in an energy
16
1 Energy Efficiency
system, the relationship between equipment specification SPi and the output
energy achieved through technology efficiency ETi could be expressed in the
following way:
ηE :=
n
n
(ETi − SPi )2 .
(1.2)
i=1
This is then represented in the pyramid diagram where technology ef­
ficiency (T1) relates to equipment specification (E1). The maintenance of
equipment (E2) would assist in attaining optimal efficiency between technol­
ogy efficiency (T1) and equipment specification and compensation (E1) thus
keeping its efficiency indicator ηE . Equipment maintenance (E2) is not di­
rectly related to technology efficiency (T1). These relations are shown in the
pyramid diagram by the dashed line.
The coordination of different components in an energy system would in­
crease its operation efficiency. As noted previously, the technology used is
deterministic of the efficiency that could be attained through equipment and
operation efficiency. Thus, system coordination (O1) is determined by technol­
ogy efficiency (T1). Leading from the explanation of the relationship between
the technologies used (T1) and the equipment specifications (E1) above, E1
inevitably then influences the way in which the system in coordinated (O1)
as well.
An example of system coordination (O1) could be found in the design of
the size of a motor needed to power a conveyor belt. The power of the motor
should be determined by technical issues such as the geometric position of the
two ends of the conveyor belt, the maximum the conveyor belt is expected to
transport and the length and width of the belt.
Assume that the energy system consists of m components which will be
coordinated to improve operation efficiency. The j-th system component has
also n forms of input energy sources denoted by Eji . The useful output energy
of the j-th component with respect to the i-th input energy form, and this
Eji can be written as a function Eji (OP1 , OP2 , OPm , ETi , SPi ). OPk denotes
the operating condition of the k-th system component, where i = 1, · · · , n,
k = 1, · · · , m. The purpose of operation efficiency is thus to maximize the
following ratio:
_m _n
j=1
i=1 Eji (OP1 , OP2 , · · · , OPm , ETi , SPi )
_n
ηO :=
.
(1.3)
i=1 Ei
Note that during the maximization of operation efficiency, ETi , SPi are
fixed and OP1 , OP2 , · · · , OPm are variables. This enables us to consider the
operations only to improve operation efficiency.
Time coordination and plant wide automation (O2), is affected by the
maintenance done on the system equipment (E2) (again delineated by the
dashed line in Fig. 1.4). Time-related operational strategies and component
coordination for equipment maintenance are some of the equipment efficiency
1.1 POET–Four components of energy efficiency
17
factors that influence time coordination and automation within the plant.
The skills, education level and level of experience of a human operator could
increase the operation efficiency. This is represented by O3 in Fig. 1.4. As is
visible from the figure, skills, experience or educational qualifications are not
directly influenced by the type of equipment or technologies that are used.
Performance efficiency is rather more complex. Energy performance (P1),
time performance (P2), and skills performance (P3) form part of performance
efficiency. As explained earlier, loss, theft or leakage in an energy system would
impact upon its performance and is therefore represented in P4.
A practical example of energy performance (P1) could illustrate the rela­
tion of energy performance to system coordination (O1), equipment specifica­
tion (E1) and the type of technology (T1) used. Consider a pump driven by
a variable speed motor. The energy performance (P1) of the pump would be
its average energy consumption when it is operating at capacity. This energy
consumption would be determined by the theoretical technology efficiency
(T1) of the variable speed motor, the equipment specifications (E1) for that
particular pump and the correct operation of the pump (O1).
Time performance (P2) relates with maintenance efficiency of equipment
(E2) and the time coordination (O2) within a plant or energy system. It
could further be explained using the following example: If E2 represents the
maintenance efficiency of a pumping system and O2 the optimal scheduling
of existing pumps for a maintenance plan. P2 could then be the resulting
maintenance timetable which would imply the relevant cost for maintenance
and possible benefits brought by the maintenance activity.
Skills performance (P3) would be determined by the operation skills (O3)
of an energy manager. Operation skills, as represented by O3, could include
education level and experience. For instance, if the operation skill (O3) of one
person working as an energy manager exceeds that of another, the resulting
energy savings will be represented by skills performance (P3).
Presenting performance efficiency as a formula, is rather complex. It could
be written as a function
ηP := φ(ηT , ηE , ηO , ηN ),
where ηN is the non-technical energy losses in the performance efficiency irrel­
evant to technology, equipment, and performance efficiencies. The φ function
can be simplified as
ηP := α1 ηT + α2 ηE + α3 ηO + α4 ηN ,
where α1 , α2 , α3 , α4 are nonnegative constants. A zero αi , say, i = 3 will
imply the corresponding equipment efficiency does not affect the performance
efficiency; while α4 = 0 implies that there is no non-technical losses in this
energy system.
It is evident from the discussion above that some parts of the efficiency
components could be regrouped. Possible efficiency levels is determined by
18
1 Energy Efficiency
the technology, and these aspects could be grouped together: technology effi­
ciency (T1), equipment specification (E1), system coordination (O1) and the
performance of the energy system (P1). These parts form the energy group
since they are all likewise influenced by the specific energy technology and
energy efficiency needs to be obtained in the realm of the technology used.
Energy efficiency could also be improved through time planning. This
group, named as time planning group, consists of equipment maintenance
(E2), time coordination (02) and time performance (P2) all of which are time
related.
Maintenance (E2), skills (O3) and theft/loss (P4) often denote the behavior
changes of end users in the energy system. Consider the following: energy
efficiency could be improved through behaviour changes such as developing
and sustaining a maintenance plan (E2), improving skills through development
programmes and training (O3) and creating awareness about energy loss (P4).
P1 and P2 are determined by technical factors such as the technology in
an energy equipment and advanced optimization of system component coor­
dination. P3 and P4 are determined by non-technical factors such as the skill
training for energy system operations, energy waste/loss reduction, etc. In
the following section we will take a look at how energy management plans are
developed.
The POET decomposition and grouping become extremely interesting and
useful when they are used to plan and prioritize energy management activities,
projects, programmes and human support and interventions. For instance, a
“quick win” in detecting the non-technical losses is usually the first target.
“Low hanging fruits” are normally picked up in addressing behavior change.
Some existing DSM policy programmes quantify energy saving potentials in
different categories and groups ([18]), thus offer strategies directions for dif­
ferent stages of energy efficiency and DSM projects.
1.2 Energy Management using POET
In the previous section, the relationships among the efficiency components
were explored. These gave insight into the technical and non-technical meth­
ods that could be used to improve energy efficiency in a plant or any other
energy generating or consuming system. In this section, the development of
an energy management plan, the activities involved in energy management
and the research and development of energy management will be discussed
using the POET components of energy efficiency as foundation.
1.2.1 Decisive and Driving Methods in approaching energy
management
The method in which energy efficiency is approached is important as it may,
in itself, affect the ultimate efficiency of an energy system. There are two ways
1.3 Extensions of POET
19
in which energy efficiency could be approached, although it should be kept in
mind that these are not separate methods, mere different ways in which to
address the same problem. They are however distinct enough in their approach
to be discussed separately.
First, an energy efficiency problem could be approached from the technol­
ogy side. This would entail taking available technology, developing appropriate
equipment and looking for suitable operation methods that would maintain
a certain level of performance. Let us call it the Decisive Method, in which
the available technology is the decisive factor in all other energy efficiency
activities. The Decisive Method would entail the existing energy system to be
analysed, through the use of energy audits and modelling. Energy efficiency
improvement and saving opportunities would be identified through the audits
and energy modelling. Clear objectives, in the form of possible percentages
on energy saving could be obtained from these results.
The second way in which energy efficiency could be approached is by look­
ing at the performance of any given energy system. From the practical demand
for energy or the market analysis of performance efficiency, the operations and
design of equipment could be analysed in a search for energy saving oppor­
tunities. As these opportunities are identified and equipment is improved,
the technology might start to change. This method would result in markets
driving the development in technology and we would thus call it the Driving
Method. Often, energy system design is done involving systems planning and
optimisation.
Once the Driving Method is complete, one may start again, using the
Decisive Method, and vice versa. This cyclical improvement from technology
to performance and from performance to technology would ultimately lead to
an increasingly efficient energy system.
The energy management activity is a human intervention aimed at steering
the EI and the SEI in the same direction if the EI and SEI are working against
eath other. Good energy management would make both technical and finan­
cial sense. Attaining a sustainable solution is a complex task. It may require a
change in lifestyle, a change in the method in which goods are manufactured
and in extreme cases may even require certain actions to cease completely. The
drive toward renewable energy has the ultimate goal of maintaining produc­
tion while decreasing the environmental impact, thus being able to produce
sustainable. Buy-in from top management and the organisational structure
are determintal. So a second criterion for sustainability is that the solution is
support by an organisational structure to the success of a project.
1.3 Extensions of POET
The four POET components can be further understood from their extensions
in energy management (EM) activities and the research and development of
EM.
20
1 Energy Efficiency
1.3.1 Energy Management Activities
In this section the four POET components will be used to discuss the activ­
ities undertaken in energy management. Energy management activities are
impacted by technology and human influences. These will be discussed sepa­
rately in the following section.
Strategic EM activities
The strategic EM activities are put together by a full cycle of actions: Energy
audit, Energy planning ,and Monitoring and Assessment.
(i) Energy audit:
Energy audit is a process to identify energy efficiency improvement and
energy saving opportunities. This energy audit process can be divided into
three layers: conceptual layer, active layer, and technical layer.
In the conceptual layer, conceptual design of the energy audit is done to
determine the focus and content of the energy audit. For example, the focus
of the conceptual energy audit can be performance efficiency and operation
efficiency, or all the four POET components. The relevant methods to conduct
conceptual energy audit can be questionnaires and existing various auditing
checklists can be adopted in the designing of the questionnaires.
The active layer involves further investigations on the energy system to be
audited, and a work-in site visit is needed to collect necessary information.
Again, this active energy audit can be done in any of the POET components
of this energy system.
The technical layer needs technical aids such as exact meter reading,
daily/monthly electricity bills, on line monitoring, etc. This kind of audit
can be done for any part of the POET components.
The application of the POET classification in the identification of energy
efficiency improvement opportunities are illustrated below. Consider Fig. 4:
Fig. 4 lists the production and the corresponding energy consumption of
a production plant. The energy consumptions have three clusters A, B, and
C. There are a few points out of these three clusters which are scattered here
and there, these are called outliers. The outliers are ignored because from a
statistical point of view they do not provide reliable information.
In each cluster there are points which have the same production but differ­
ent energy consumption, and points which have the same energy consumption
but different production. These points indicate that energy consumption may
increase or decrease while the same level of production is maintained. The un­
derlying reason for this might be very complicated. Consider the following: if
it is already known that there were neither new technology introduced nor new
equipment purchased, then there will be performance efficiency improvement
opportunities at these points
Points at cluster B, quite clearly has a higher production-to-energy ratio
that the points in clusters A and C. Therefore, cluster B has the highest
1.3 Extensions of POET
21
Fig. 1.5. Energy Consumption v.s. Production
operation efficiency compared to clusters A and C. In order to make optimal
use of energy in production, the energy consumption and production range
should be around cluster B. Production outside of this range will have a lower
energy efficiency.
(ii) Energy Planning
Energy planning consists of putting together energy efficiency projects and
programmes, and soliciting the human support.
(ii.1) Projects and Programmes:
The extensions of POET in EM projects and programmes can be analyzed
through three aspects: General issues, actions, and classifications of projects
and programmes.
The general issues include the awareness arising to promote performance
efficiency, peaking shifting to increase operation efficiency, motor efficiency to
improve equipment efficiency, and the relevant research to support technology
efficiency. This may include information of technological nature about energy
conservation products, process and programmes, as well as their fiancial via­
bility and social acceptability.
The actions in projects and programmes also correspond to POET effi­
ciencies. DSM activities such as simple peak shifting and time management,
the use of energy saving lamps, etc, correspond to performance efficiency; op­
22
1 Energy Efficiency
eration optimization and skill training correspond to performance efficiency;
retrofitting of existing facilities corresponds to equipment efficiency; and cap­
ital investment and the relevant research on energy efficiency improvement
correspond to technology efficiency.
The classifications of existing energy management projects and programmes
according to the POET components will further help to understand energy
efficiency improvement. For example, it is important to understand the es­
sential differences between a load shifting project and other EE improvement
projects such as the replacement of incandescent lights into CFLs. In South
Africa,there are more than 500 DSM projects which have been finished and
supported by the main electricity supplier. We are currently leading the clas­
sifications of these projects according to the four POET components.
(ii.2) Human Support to EM activities
There are many human supports to EM activities such as policies and
regulations; incentives, competitions, awards, or penalties; and human sensi­
tizations.
Human support at the policy or regulation level plays a fundamental role
in EE activities. For example, green rating image of electrical appliances,
energy saving lamps (e.g., CFL) and geysers (e.g., solar water heaters), and
electricity tariff (e.g., TOU tariff and maximum demand charges) have greatly
stimulated the interest, research, and investment on energy efficiency projects
and activities; the voluntary load shedding policy and dynamic market par­
ticipation policy are provided by the main electricity supplier in South Africa
([17]) to support the operation efficiency; controlled list of new energy efficient
products and governmental procurement have promoted equipment efficiency;
deregulated market, feed-in tariff for electricity generated by renewable re­
sources or other distributed generators, EE Act, etc, have greatly improved
technology efficiency.
Supports such as incentives, competitions, awards and penalties are also
important in EE improvement. For example, TOU tariff encourages the perfor­
mance efficiency by stimulating energy use at off-peak time while penalizing
energy use at peak time; the Power Conservation Programme ([48]) of the
Department of Minerals and Energy of South Africa adds compulsory power
saving aims to end users to improve operation efficiency; controlled list of
inefficient products and appliance labeling focuses on equipment efficiency;
judge criteria of EE awards and competitions include the EE improvement
at all the four POET components; and the tax incentive in South Africa also
rewards the EE improvement in any of the POET components.
POET can also be considered from the viewpoint of human sensitizations.
For example, performance efficiency is usually improved by alerting the gen­
eral public and carrying on an awareness campaign; operation efficiency can
be increased by providing human resource training on procedural guidance of
work flow; equipment efficiency is enhanced by purchasing new energy effi­
cient equipments from product exhibitions and operating the equipments by
accredited professionals; while technology efficiency improvement opportuni­
1.3 Extensions of POET
23
ties are generally found in technology road shows and relies on formal higher
education.
(iii) Monitoring and Assessment
The POET components can also be understood from the energy system
monitoring and assessment (MA) aspects which include measures of MA, MA
contents, MA timeline, and governing of MA.
The MA measures consists of the following parts: the verification of perfor­
mance efficiency of an energy system; the measurement of operation efficiency;
the specifications of equipment; and the evaluation of technology efficiency.
Note that equipment specifications can often be treated as an indicator of en­
ergy efficiency of an equipment, thus it is an important part of MA measures.
The evaluation of technology efficiency is particularly important for MA when
a new greenfield energy efficiency project is proposed since a greenfield project
has no a direct object to be compared with and the evaluation can only be
based on the feasibility of a project proposal and the maximum amount of
energy efficiency improvement or energy saving claimed in the proposal.
The contents of MA for an energy system include the energy protocols
for performance efficiency, the operational procedures for operation efficiency,
the standards for equipment efficiency; and potential and feasibility of new
technologies to improve technology efficiency. These contents help much the
monitoring and assessment of the energy efficiency of an energy system.
The timeline of MA is obvious: the MA of performance efficiency happens
after the implementation of an energy efficiency project; the MA of operation
efficiency needs information on real current conditions; the MA of equipment
efficiency relies on the controlled current conditions; and the MA of technology
efficiency depends on the controlled predictions of the energy system.
The governing of MA is as follows: performance efficiency is governed by
Measurement and Verification (M&V) bodies; operation efficiency is under the
control of engineering councils; equipment efficiency is determined by specifi­
cations released by government organizations such as bureau of statistics; and
technology efficiency is financially supported and thus constrained by banks,
research foundations, etc.
The MA of performance efficiency is often conservative–a project is moni­
tored and assessed according to its averaged or worst efficiency under normal
operating conditions. The MA of operation efficiency is real–the MA results
are based on real measured information. Equipment efficiency is often mon­
itored and assessed under ideal real conditions, for example, the equipment
specifications are often given under laboratory conditions, while the same con­
ditions may not be satisfied in a practical application. Technology efficiency
is assessed optimistically since its assessment is often based on a project pro­
posal and the project is often approved by the proposal feasibility and the
maximum possible percentages of energy efficiency improvement and energy
savings.
It is worthy to note the MA measures mentioned above are actually the
Measurement and Verifications (M&V) of energy projects. According to the
24
1 Energy Efficiency
International Protocols on Measurement and Verification ([15]), there are four
methods for any M & V project: Options A, B, C, and D.
Option A is called Partially Measured Retrofit Isolation, and the savings
are determined by partial field measurement of the energy use of the system,
i.e., the energy use of the isolated equipment, which is affected by an energy
management programme, is measured. The partial measurement means that
some but not all parameter may be stipulated, if the total impact of possible
stipulation errors is not significant to the savings. Option A is applicable
if interactive effects between energy management innovations or with other
facility equipment can be measured or assumed to be not significant. This
Option A corresponds to equipment efficiency in the sense that the equipment
under consideration is isolated and often has less interactive effects with the
rest of the energy system.
Option B is called Retrofit Isolation, and the savings are determined by
field measurement of the energy use of the systems to which the energy man­
agement programme was applied. The savings determination techniques of
Option B are identical to those of Option A except that no stipulations are
allowed under Option B. Option B is applied to the case that interactive ef­
fects between different energy management innovations or with other facility
equipment can be measured or assumed to be immaterial. This option corre­
sponds exactly to operation efficiency in the sense that Option B measures
savings of different components of a whole energy system.
Option C is named as Whole Facility, and the savings are determined by
measuring energy use at the whole facility level. It corresponds to performance
efficiency in the sense that Option C measures the total energy savings of the
whole energy system and does not consider energy savings of subsystems,
which implies that Option C cares only the total performance of the whole
facility.
Option D is termed as Calibrated Simulation, and the savings are deter­
mined through simulation of the energy use of components or the whole fa­
cility. It corresponds exactly to technology efficiency in the sense that Option
D requires the modelling of the energy system and the calibrated computer
simulation of the energy usage in which advanced technologies involved in the
energy procession, transmission, and conversion in the system are needed for
the energy usage modeling process.
1.3.2 Engineering EM activities
The extensions of POET components in the Research and Development of
EM can be analyzed on the applications of this POET classification to other
research fields and the other engineering examples.
Research fields
In the research fields of chemical engineering, mechanical engineering, elec­
trical engineering, etc, classifications similar to POET can also be made in
1.3 Extensions of POET
25
some branches of these fields. For example, in the automatic control branch
in electrical engineering, a POET-like classification can be done as below, and
thus one can use a control system approach to investigate energy efficiency
problems.
In a control system, there are four important components which are used to
obtain an optimal control for a system. In fact, the purpose of control theory
is to find a good controller for a physical system, therefore the first important
component in a control system is to identify the objectives of control. The
objective functions are usually determined by external factors to be controlled,
thus the objectives can be used as indicators to measure the performance
efficiency.
The second component is to model the system dynamics. This is to model
the physical interactions and constraints of different system components by
deep understanding on the technical phenomenon. This component is therefore
correlated to the basic features of technology efficiency.
The third component is trajectory planning or operating point identifica­
tion which is often determined by the relations and coordinations of internal
system components. This can be done in an open loop nature such as trajec­
tory planning, plant wide automation, as well as a closed-loop nature such as
system integration and coordination. Both of these open loop and closed-loop
strategies are essential issues in operation efficiency.
The fourth component is the implementation of controllers or embedded
systems. These are expected to be done as specified in the physical realizations
via actuator devices and the corresponding lower level controllers. It follows
that equipment efficiency corresponds to the fourth component of the system.
Engineering examples
The POET components are comprehensible from their applications in en­
gineering examples. In the example of a conveyor belt energy system, the
optimized on/off scheduling in terms of a TOU tariff can reduce the electric­
ity cost and thus improve its performance efficiency; the optimized belt speed
and feeding rate control will increase the operation efficiency; the replacement
by new motors is a booster for equipment efficiency; and the installation of
a motor with a variable speed drive can enhance the technology efficiency.
All these efficiency improvement activities can be guided by proper research
work: the optimized on/off scheduling and the optimized belt speed and feed­
ing rate control can be obtained through solving the corresponding global
optimization problems; and the design of new energy efficient motors, includ­
ing motors with variable speed drives, depends largely on the corresponding
research advancement.
Another engineering example is the control of a train. The shortest route
planning, the minimum time planning problem, or the least energy cost prob­
lem, for the train will correspond to the performance efficiency as these prob­
lems are determined by external factors. The differential equations which gov­
26
1 Energy Efficiency
erns system dynamics belongs to the technology efficiency of the train system;
the coordinating of the forces to run up or down an incline, and open or closed
loop trajectory or speed planning correspond to the operation efficiency. The
electronic control of the pneumatic brake corresponds to the equipment effi­
ciency.
The above two sections are best summarized in the following tables.
Fig. 1.6. EE Components
1.3 Extensions of POET
Fig. 1.7. EE Extensions
27
28
1 Energy Efficiency
Fig. 1.8. EE Extensions (continued)
1.3 Extensions of POET
29
Fig. 1.9. EE Extensions (continued)
Note that in the above two tables, there are different colours in the
columns. The green color denotes that a technology efficiency improvement
project needs often capital investment, and is often a new project; thus often
called a “greenfield” project. The other three columns for POE efficiencies cor­
respond to the energy efficiency improvement on existing old projects, there­
fore these projects are called ‘brownfield’ projects, and thus the tree columns
are colored in colors similar to brown.
The column to the left of performance efficiency is coloured in black and
represents existing part in energy efficiency which can not be explained by the
science and engineering today, but perhaps can be well explained in the future.
There are many examples in energy efficiency which are obviously explained
nowadays but were mysterious to people living a thousand years ago.
The column to the right of Technology efficiency is in white colour and
represents things (such as EE indicators) in energy efficiency which are clear
at the moment but may be changed in the future and yet we still do not
know which things will possibly be changed in the future. For example, to
protect the environment the reduction of carbon emission is an important EE
indicator. However, it is not know if it is still an important EE indicator in
the future if we do not have any environmental problem then.