R E S E A R C H A N D A N A LY S I S
The Sankey Diagram in
Energy and Material Flow
Management
Part I: History
Mario Schmidt
Keywords:
efficiency
energy use
industrial ecology
industrial engineering
material flow analysis (MFA)
scarcity
Address correspondence to:
Mario Schmidt
Institute of Applied Sciences IAF
Pforzheim University
Tiefenbronner Str. 65
D-75175 Pforzheim, Germany
mario.schmidt@hs-pforzheim.de
http://umwelt.hs-pforzheim.de
Summary
The Sankey diagram is an important aid in identifying inefficiencies and potential for savings when dealing with resources.
It was developed over 100 years ago by the Irish engineer Riall Sankey to analyze the thermal efficiency of steam engines
and has since been applied to depict the energy and material
balances of complex systems. The Sankey diagram is the main
tool for visualizing industrial metabolism and hence is widely
used in industrial ecology. In the history of the early 20th century, it played a major role when raw materials were scarce
and expensive and engineers were making great efforts to improve technical systems. Sankey diagrams can also be used to
map value flows in systems at the operational level or along
global value chains. The article charts the historical development of the diagrams. After the First World War the diagrams
were used to produce thermal balances of production plants
for glass and cement and to optimize the energy input. In
the 1930s, steel and iron ore played a strategic role in Nazi
Germany. Their efficient use was highlighted with Sankey diagrams. Since the 1990s, these diagrams have become common
for displaying data in life cycle assessments (LCAs) of products. Sankey diagrams can also be used to map value flows in
systems at the operational level or along global value added
chains. This article, the first of a pair, charts the historical development. The companion article discusses the methodology
and the implicit assumptions of such Sankey diagrams.
c 2008 by Yale University
DOI: 10.1111/j.1530-9290.2008.00004.x
Volume 12, Number 1
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Journal of Industrial Ecology
www.blackwellpublishing.com/jie
R E S E A R C H A N D A N A LY S I S
Introduction
The use of Sankey diagrams has long been
standard practice in science and engineering. The
diagrams are described as graphical heat balances
(Minister of Fuel and Power 1944, 709), heat balance diagrams (Christensen 1990, 394), energy
flow charts (Schnitzer 1991), or simply Sankey
diagrams (Pople 2001, 138). The diagrams frequently focus on energy flow and its distribution
to various sources or sinks, represented by arrows, the width of which indicates the amount
of energy flow. Material flows are also frequently
displayed with Sankey diagrams, and these are
described, for example, as material flow charts
(Koelbel and Schulze 1960).
If one looks at basic articles on industrial
ecology or life cycle assessment (LCA), it becomes apparent that they frequently use Sankey
diagrams to show the complexity of industrial “metabolism.” For instance, Frosch and
Gallopoulos (1989, 100) used a Sankey diagram
showing the production, use, and subsequent
whereabouts of platinum metals. Saur and colleagues (1996) produced an LCA with a Sankey
diagram tracking the main material flow for the
production of aluminum sheet parts in the automotive industry. Graedel (1996, 72) applied
Sankey diagrams to compare material flows in biological and industrial ecology.
One could almost believe that Sankey diagrams are the visual language of industrial ecology. At least since Edward Tufte, the noted
scholar of visual representation, we know how
important it is to visualize quantitative information in order to understand it. It is interesting to note that Tufte described Charles Joseph
Minard’s map showing the losses sustained by
Napoleon’s army during the Russia campaign of
1812–1813 as possibly the best statistical graphic
ever drawn (Tufte, 2001, 40). It has much in
common with a Sankey representation and can
be found today in nearly every good book on European history. With just a few strokes, it shows
the whole tragedy of the war in Russia. Industrial
ecology, conversely, aims to show (and prevent)
the tragedy resulting from human disregard of
natural substance cycles.
Graedel (1996, 73) pointed out that industrial
ecology addresses the budgets and cycles of input
and output streams and tries to optimize them. He
went on to say that the key concepts of industrial
ecology include conservation of mass and conservation of energy. This is exactly what Sankey
diagrams do, as the present article shows. With
their intuitive readability and transparency, they
are ideal for interpreting complicated sets of resource flows. It is therefore not surprising that
such diagrams were repeatedly used in the past to
explain significant findings to a broad public and
to launch technical or social measures. This is
illustrated below with the aid of a historical incident closely connected with scarcity of resources.
The article also traces the history of the Sankey
diagram for the first time.
It is not commonly known that the introduction of the Sankey diagram over 100 years ago,
by the Irishman Riall Sankey, was initially connected with a call for efficiency, in this case for
steam engines. Whether to help produce more
economical cars or more productive steel plants,
the Sankey diagram was subsequently used to
understand and tackle consumption of scarce
resources.
Thermal Efficiency and Riall
Sankey
In the late 19th century, engineers in the upand-coming industrialized countries tried applying scientific methods to further improve steam
engines and optimize them for their respective applications. The theory of thermodynamics, which
was completed during these years, was a great
help to the engineers. They discussed the question of what an ideal steam engine might look
like with particular intensity. The best thermodynamic cycle, the Carnot process, was too abstract for practical application. Instead, William
J. M. Rankine and Rudolf Clausius proposed
the Rankine–Clausius process, named after them,
with which real machines could be compared
(Cardwell 1994, 123).
In the 1870s, Willard Gibbs introduced the
temperature-entropy diagram. This made it possible to show the efficiency with which a
machine transfers thermal energy into work
(Cardwell, 1995, 360). Sankey also examined the
question of how an ideal practical steam engine
could be defined and how the efficiency could be
Schmidt, The Sankey Diagram in Energy and Material Flow Management, Par t I: Histor y
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measured. In this context, in a committee report
of the Institution of Civil Engineers, he first used
the diagram later named after him. The diagram
was published in 1898 (Sankey 1898, Plate 5).
Captain Matthew Henry Phineas Riall Sankey
was born on 9 November 1853, the son of a
general in Menagh, County Tipperary, Ireland
(Anonymous 1926a, 1926b). He joined the Royal
Military Academy in Woolwich, near Greenwich, at that time one of the best technical
schools in the United Kingdom. Subsequently,
he went on to the School of Military Engineering in Chatham, in the county of Kent. He was
one of the best students, had a profound knowledge of theory, received his certificate as Royal
Engineer in 1873, and then served in England, in
Gibraltar, and later as an instructor at the New
Royal Military College in Kingston, Canada. In
1882 he was appointed to the Ordnance Survey in
Southampton.
In connection with the technical printing
of maps, he learned about copperplate printing.
Electricity was necessary for this, which at that
time was being supplied by expensive batteries.
Sankey sought an alternative method using dynamos driven by constantly running steam engines. He tested several for their suitability and
came across machines designed by Peter Willans,
one of the leading inventors in the field of steam
engines (Cardwell 1994, 122). Willans’s engines
were used in the United Kingdom in most power
stations. During the subsequent period, Sankey
conducted various investigations, the results of
which he published. Like Willans, he had an interest in the economic improvement of steam
engines.
At Willans’s suggestion, Sankey resigned his
commission in 1889 and became a director of the
firm Robinson & Willans. There he conducted
various experiments, including thermodynamic
tests on steam engines, and after the death of
Willans in 1892 he assumed responsibility for
the design of steam engines and turbines for the
company.
It was Sankey who, in the course of technical
discussions on steam engine efficiency, declared
that a standard was necessary to compare actual
steam engines with a perfect steam engine and
that the Rankine–Clausius engine was best suited
for this purpose (Sankey 1896). The diagram used
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for these analyses, with its important content,
was not the subsequent “Sankey diagram” but instead the temperature-entropy diagram. When a
commission appointed by the Institution of Civil
Engineers essentially confirmed Sankey’s ideas 2
years later, he prefaced this report with an introduction that he—rather casually—supplemented
with a chart in the annex (Sankey 1898). In this
introduction, he compared a practicable steam
engine with an idealized steam engine whose
thermal flows were represented in the diagram
(figure 1). He did not use this mode of representation again later. It was a by-product of the
discussion of steam engine efficiency and simply
served to illustrate the matter.
Later, Sankey worked as a consultant and was
on the boards of various firms. In his later years,
from 1920 to 1921, he was president of the Institution of Mechanical Engineers. In the course of
his scientific life, he published various books and
technical articles, including “The Energy Chart.
Practical Applications to Reciprocating SteamEngines.” Sankey died on 3 October 1925.
The top chart in figure 1 shows an American
steam engine (Louisville Leavitt Pumping Engine). The steam leaves the boiler with a quantity of 159,250 B.T.U./min (B.T.U. = British
thermal unit, an old energy unit: 1 B.T.U. =
1.055 kiloJoules [kJ]). If the refluxes are taken
into account, the net supply to the steam engine
is 142,150 B.T.U. After all losses are deducted,
27,260 B.T.U. remain for the mechanical work.
In the report, the thermal efficiency of the engine
is given as 27,260 / 142,150 = 0.19.
The bottom diagram represents an ideal steam
engine with an assumed Rankine cycle. The losses
cease to apply. The thermal efficiency here is
quantified at 0.285.
Sankey (1898) explained descriptively how
the diagram was to be interpreted:
No portion of a steam plant is perfect, and
each is the seat of losses more or less serious. If therefore it is desired to improve the
steam plant as a whole, it is first of all necessary to ascertain separately the nature of
the losses due to its various portions; and in
this connection the diagrams in Plate 5 have
been prepared, which it is hoped may assist
to a clearer understanding of the nature and
extent of the various losses.
R E S E A R C H A N D A N A LY S I S
Figure 1 The first two energy flow diagrams of Captain Sankey (1898). They represent two steam
engines—a real one (top) and an ideal one (bottom). The figures are stated in British thermal units (B.T.U.)
per minute. The graphics were designed in such a way that a flow of 100,000 B.T.U./min corresponded to 1
in. in the drawing. Source: Sankey 1898, Plate 5.
The boiler; the engine; the condenser and
air-pump; the feedpump and the economiser,
are indicated by rectangles upon the diagram.
The flow of heat is shown as a stream, the
width of which gives the amount of heat entering and leaving each part of the plant per
unit of time; the losses are shown by the many
waste branches of the stream. Special attention is called to the one (unfortunately small)
branch which represents the work done upon
the pistons of the engine (Sankey 1898, 279).
Accordingly, the flow of heat is represented as
a stream, the width of which shows the amount of
heat fed into the factory and leaving it again per
unit of time. The heat losses are indicated by the
branches. Consequently, the useful energy, in this
case the mechanically performed work, is shown
very graphically in comparison with the original
input. The figures are given in absolute quantities. Furthermore, the representation shows the
processes involved, the boiler and the engine.
Schmidt, The Sankey Diagram in Energy and Material Flow Management, Par t I: Histor y
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The diagram is immediately clear. It can be
adapted flexibly to various needs and to empirical
conditions. There are thus many possible ways of
preparing such charts. The essential feature is the
representation of flow sizes by quantified arrows—
in other words, correspondingly wide arrows.
The Use of Sankey Diagrams in
Germany
A decade later, Sankey’s diagrams were already being used internationally. In 1908, a whole
series of different “heat balances” was printed
in a review in the Journal of the Association of
German Engineers of a blast furnace, a coke furnace, and a comparison between a steam engine and a gas engine (VDl 1908). Attention
was drawn to the great superiority of the gas engine in heat utilization and to the fact that the
diagram “did not need any further explanation”
(VD1 1908, 2017).
One of the first German-speaking engineers
to use Sankey diagrams on a large scale was
Alois Riedler (1850–1936), who became professor of mechanical engineering at the Technical
University (TH) Berlin in 1888 and later president of the TH Berlin. Riedler traveled abroad
extensively, visiting the World Expositions in
Philadelphia (1876), Paris (1878), and Chicago
(1893) as well as many technical teaching institutes in, for example, the United States. As
a result, he was familiar with developments
abroad.
Riedler was very practice-driven and called for
mechanical engineering laboratories to be set up
at the technical universities. He also busied himself with matters such as the development of internal combustion engines, and, starting in 1903,
he built up a laboratory for internal combustion
engines and motor vehicles at the TH Berlin.
There he developed the first roller dynamometer
for motor vehicles and was the first to start scientific measurements of such vehicles. At that time,
he was particularly opposed to assessing motor
vehicles on the basis of the then-customary races
oriented toward maximum performance parameters, such as speed. Those results were commonly
used for marketing purposes in the advertisements
of automobile firms. According to Riedler, however, this practice was not expedient for assessing
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the economics of motor vehicles in practical operation. For this purpose he sought objective and
plausible criteria with which he could compare
vehicles, and he introduced measurements of typical driving situations on a roller dynamometer.
He wanted to measure more appropriate measures
of performance and loss in vehicles and engines.
He can thus be considered as one of the founders
of the automobile tests that are today indispensable for every car buyer.
In 1911, Riedler published Wissenschaftliche
Automobil-Wertung (Scientific Automobile Assessment), in which he presented his first measurements, including those of a 30 horsepower (hp)
Renault, a 100 hp Benz, and a 75 hp Adler.
The reasons he gave for conducting these investigations included fuel scarcity and the need
to import fuel from other countries. “A vital issue for all motor vehicles: their dependence on
certain fuels, especially those from foreign countries” (Riedler 1911, Report 1, 18). The results
were amazing for that time. Riedler was able to
show that the losses due to the driving unit were
lower than generally assumed. Instead, the tires
and the thermal losses of the engines had a crucial
influence on the engines’ efficiency.
As the rolling losses in motor vehicles consume a very large portion of the available
engine output, complete clarification . . . is
extremely important. . . . A slight fraction of
the costs spent on the greatly flourishing advertising for pneumatics and automobiles, or
a small portion of the sums that automobile
clubs and even towns and cities spend on racing events would suffice for thorough investigation of this important question. (Riedler
1911, Report V, 13)
The energy flow diagrams were an important
medium that helped Riedler to illustrate the results clearly (see figure 2). In this concrete case,
he quantified the vehicle’s effective output for
overcoming air resistance, for accelerating, and
for climbing gradients at ultimately only 12.5%
of the fuel energy fed in.
Riedler (1911) wrote,
Energy diagrams graphically represent the intake, output and losses, as well as the energy amount then still available and thus
provide a characteristic picture of the fuel
R E S E A R C H A N D A N A LY S I S
Figure 2 The energy diagram of the 20/30 hp Renault car for 60 km/h driving speed. Source: Riedler 1911,
figure 12.
utilization of the vehicles examined. The
findings gained from the energy diagrams of
energy distribution in the motor vehicle are
one of the means for assessing its economic
perfection. It shows the expert the points
where essential improvements are possible.
(Riedler 1911, Report I, 9)
The systematic analyses and the representation of the results in energy flow diagrams made
it possible, above all, to explain relevant characteristics. Riedler (1911, Report V, 25) scornfully
remarked that among German engineers there
was “no agreement of views on the meaning of
the concept of efficiency” and that this led to
misunderstandings and misinterpretations in the
question of economic efficiency.
Riedler’s work Das Maschinen-Zeichnen (Machine Drawing) in 1896 was of great significance
for engine building and design. In this work he
called for exact, dimensioned, black-and-white
drawings adapted to the relevant purpose, and
with that he became one of the founders of modern technical draftsmanship. As early as the 1913
issue, he presented an “energy diagram” alongside
the entropy diagrams, showing the energy flow
of a steam engine. In the textbook Das Entwer-
fen und Berechnen der Verbrennungskraftmaschinen
und Kraftgas-Anlagen (Designing and Calculating
Internal Combustion Engines and Gas Power Plant),
Gueldner (1913, 13) too presented the “special
nature of a heat plan,” called the “Sankey diagram.” However, he complained that although
this representation provided clarity, it was not
easily and accurately drawn and was therefore
more suitable for general illustration purposes
than for technical use.
Despite this criticism, Sankey diagrams played
an important role in technical analyses of plants
in Germany during the following years. As a result of the demand for reparation payments following the First World War, Germany had to
handle its resources economically. The goal was
to improve the yield of energy-intensive processes
such as cement production, glass manufacturing,
or steelmaking. Plants were measured in detail
in a series of experiments, and thermal balances
were drawn up to identify inefficiency and scope
for improvements. This work was largely carried
out by cross-company commissions serving the
individual branches of industry. The importance
of such savings for the national economy was often pointed out.
Schmidt, The Sankey Diagram in Energy and Material Flow Management, Par t I: Histor y
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For example, in 1920 a heat-specific advisory
center was set up for the German glass industry
(WBG; Trier 1992). The membership dues were
assessed on the basis of the fuel consumption of
the firms. Thermal measurements were carried
out on real plants belonging to the members in
order to improve, for example, the gas generators
or the smelting furnaces. Accordingly, the first
known heat balance was drawn up for a whole
glass smelting plant. The results were compiled
in the WBG publication series and made a major
contribution to the progress of thermal engineering in the glass industry.
Within the cement industry, PortlandZementwerke Heidelberg-Mannheim had been
conducting experiments since 1904 to utilize
waste gases for steam production. In the 1920s,
a furnace commission of the association of German Portland cement factories conducted comprehensive measurements and produced systematic heat balances of various cement kilns. The
first Sankey diagrams for firing cement were presented in 1927 (Schott 1954) and then became
an indispensable graphical instrument. The results of the analysis were used to compare various furnace types, to propose improvements
in process engineering, and ultimately to compare the theoretically optimal heat balance with
the real, empirical heat balance. Depending on
the type of furnace, manufacturing procedure,
and combustion facility, the thermal consumption of cement production in the 1920s fluctuated between twice and five times the theoret-
ically necessary heat input (see figure 3, Schott
1933).
Material Flow Management in
the Steel Industry
After the First World War, supplies of raw
materials for the German steel industry were critical. There was a lack of fuels. That is why the
main tasks in the 1920s and 1930s were grouped
around the concepts of operating economically
and improving product quality (Spingorum 1936,
1043). Today one would talk about improving
efficiency and quality management. Energy expenditures accounted for about one quarter of
total product production costs, which is why the
Heating Center Duesseldorf of the association of
German ore smelting works was set up at the beginning of the 1920s as a joint enterprise for all
German smelting plants. It developed and expanded measuring systems to obtain reliable data
on the production and consumption of energy
resources, and its reports provided plant managers with guiding values and reference points
for improvements, for more uniform use of energy, and for ongoing cost monitoring. Thanks to
scheduled heat management, it became possible
to lower the heat consumption needed per ton of
steel by more than one quarter within the space
of just 10 years.
Furthermore, as of 1923, data had been collected on total “material management,” as it was
called in those days—in other words, on the use
Figure 3 Theoretical heat outlay (left) and practical heat consumption (right) in cement production. Source:
Schott 1954, figures 3 and 4, page 154.
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R E S E A R C H A N D A N A LY S I S
Figure 4 Iron flow chart for the German iron industry. Figures related to 100% iron content in ore. Source:
Reichardt 1937, figure 2.
of raw and auxiliary materials and of finished and
semifinished products. At the time, this was done
for purposes of cost monitoring and was essentially promoted by a new species of expert—the
business economist.
There was also another reason for material
management. Iron ore had become a scarce commodity in Germany after the country had been
forced to cede the rich ore mines in Lorraine
back to France after the First World War. Many
iron resources in Germany were of lower quality,
which made it more difficult to process them in
blast furnaces. Thanks to the intelligent combination of the various processes for obtaining pig
iron, it proved possible to increase the yield considerably. The use of scrap and the closing of material cycle loops (Reichardt 1937, 1104) played
a key role here, as figure 4 shows with average
values for the entire German economy.
Whereas using Sankey diagrams became standard practice for the energy and heat industry
as of 1931 (Waermestelle Duesseldorf 1931, 9),
their use for quantity-related material management took off in the mid-1930s. In a lecture at
an engineering conference in Breslau in 1935,
Professor Paul Goerens (1935) talked about raw
material management issues. In line with the
times, the lecture was all about state-forced management and national autonomy. He referred to
the “material flow chart” as a valuable aid that
can contain quantity-based information about
the origin, production, processing, and purpose
of a material. He presented national balances for
iron, copper, and lubricating oil.
Figure 5 shows the general arrangement of
a material flow chart by Goerens (H. Schmidt
1936, 14). The accompanying explanation is interesting:
A raw material, R, comes from within the
country, 1, or from abroad, 2, and, up to consumption, runs through a series of stages, C,
D, E, F, covering selection, conversion, processing and shaping. At each stage, starting
with the domestic raw material, export, 3,
can take place. In addition, a part of the material is eliminated from the work flow at each
stage. If it can be saved in value terms in any
form and be returned to one of the preceding
stages, it appears as material recirculation in
various forms, 4a, 4b, 4c. If recovery does not
enter into consideration either technically or
economically, then the loss, sub-flow 5, appears. A loss of the material also occurs if it
is used up completely during the processing
stage. Also, export represents a material loss
for the material economy of a country. . . .
The plotting of the individual flows to scale
results in a precise overview of the management of a material.
Schmidt, The Sankey Diagram in Energy and Material Flow Management, Par t I: Histor y
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Figure 5 The diagram of a flow
chart according to Goerens (1935).
Source: Schmidt 1936, figure 1.
The reflux of a part of the material to the work
process resulting from circulation triggers the
additional demand for new raw material. . . .
Depending on the type of consumption, it is
possible to make a sub-division into different
material groups whereby the flow chart has a
particularly descriptive form.
The first group comprises all materials that
are consumed completely. Examples of this
are liquid fuels, solid fuels and foods. The
flow pattern of such materials is characterized by the fact that it lacks the material
circulation. . . .
A second group consists of those materials
that do not lose their material value, but
of which the form of use is devalued, such
as metal, rubber, lubricating oil, and paper.
Apart from the case of exports, material loss
only occurs as a result of wear. As wastes result
from each processing stage that can be processed again, the scrap generated is not very
significant for material management as long
as the conversion does not cause any notable
loss of material. However, the economic viability is influenced. The level of the reflux
alone determines the replacement with fresh
material.
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The third group is made up of materials that
serve as auxiliaries, e.g., as solvents or bonding agents in the chemical conversion of
other materials. Managing these is intended
to form a cycle with no loss, as far as is
possible.
Once the need for management has been ascertained by a material balance and material
flow pattern, it will be necessary to seek ways
of limiting the imports of foreign materials
without harming the national economy. This
includes savings measures, consulting science
and research, as well as progress in technology. Furthermore, all means of reducing losses
and recycling wastes are to be considered. (H.
Schmidt 1936, 14)
The article thus states important aspects of
modern material flow management and closed cycle management—but for the purpose of a developing war economy. The special type of diagram
was then taken up in many ways by the steel
industry engineers to analyze the raw material
situation (Bansen 1936, 1937). The seriousness
with which material management was pursued in
those days is really quite amazing. For instance,
consider that cleaning rags were recycled in the
smelting industry (Heinrich 1937).
R E S E A R C H A N D A N A LY S I S
It is remarkable that this “material management” in the steel industry was chiefly propagated
and implemented by business economists. Altogether, these new business economists had to justify their existence in dealings with classic commercial and engineering staff. Business administration had been first introduced as an academic
subject in Germany in 1898, with the first higher
commercial college in Leipzig, initially under the
title Private Economics or the Science of Trade
(Schneider 1999, 16). Kurt Rummel, chairman of
the Committee of Business Administration of the
Association of German Metallurgy, pointed out
the advantages and mode of operation of business
administration in an article, saying that they
consist in planning, planning not on the
grounds of any “sensing” through fingertips,
but on the basis of very carefully collected
statistical and experimental findings on the
passage of the material through the plants
over time. All major influences are ascertained and the effects of these influences are
identified with special auxiliary means and
formed into a system. Thinking in terms of
balances makes the sources of losses appear
more clearly; calculating with carefully evaluated quantities helps to select the suitable
material, the most expedient process and the
correct plant. (Rummel 1936, 228)
Rummel ascertained that the demand for material management personnel and a distinct material management system was very high. In the
steel industry this was understandable, as that
branch is based on materials (i.e., raw materials and auxiliary materials—not including fuel)
that constitute 35% to 45% of costs (Rummel
1936, 222). The required investigations, therefore, track the passage of the material over time,
on the basis of quantity and quality. The strict
division of costs into two constituent parts, consumption in quantity units and price in money
units, was said to be important:
The purely quantity-based consideration is
particularly important today in view of the
scarcity of raw materials and the necessary
careful treatment of the few raw material resources that our country is able to supply itself. (Rummel 1936, 224)
In this connection, Rummel talked of a “material budget”—a concept that was taken up again
in detail 60 years later in environmental science (Baccini and Bader 1996)—that explored
the material balance in detail. Rummel (1936,
225) stated,
Thinking in terms of balances must increasingly replace the crude term “outputs in percent.” In the heat industry the output is set
against the “efficiency.” . . . However, often
enough, it is not at all certain what the denominator is and what the numerator is as
regards either efficiency or output.
By way of example, he cited recycled scrap,
which was simply left out of many net considerations, which then led to misinterpretations of the overall performance of a plant.
This is, by the way, an error that is still (or
once again) found in production sites that
apply internal recycling today.
Naturally, Rummel also continued his considerations further to obtain a value-based analysis.
We must of course be clear that the quantityspecific saving that can be achieved by all
these measures is only slight. In terms of
value, though, as in every balance, the single percentage point saved is of key importance for the final calculation; this only becomes apparent in the profit and loss account.
(Rummel 1936, 226)
He then went on to consider relevant issues
such as how inventories can be evaluated—for
example, on the basis of purchase price, book
price, or replacement price—and how capital servicing of plant installations should be taken into
account. He adopted the position that existing
installations, irrespective of whether they have
been written off, should not be included in comparative costing.
The first Sankey diagram with value flows
was suggested in this connection by Warczewski
(1937; figure 6). What is remarkable in this representation is that it divides input and output
sides on the basis of differing criteria—according
to material group and type of use—and also attempts to include the initial and final inventory.
In the example, these do, after all, amount to
21% of annual turnover. This is because the question of inventory becomes relevant if the subject
Schmidt, The Sankey Diagram in Energy and Material Flow Management, Par t I: Histor y
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Figure 6 Schematic annual value flow of the materials in an iron and steel works. Source: Warczewski 1937,
figure 1.
of the flow is no longer heat or energy but instead concrete objects that can be stored and that
are subject to mass balance maintenance. These
analyses were used to reduce the stock quantities
as the speed of turnover increased—that is, to
optimize procurement.
Conclusions
In the 1930s, the difficult framework conditions in the steel production sector, characterized by high prices and a scarcity of raw materials, led to what later came to be called “material
management,” thus practically forcing the application of material balances or Sankey diagrams.
The graphics played a major role in explaining
the complicated situation to a broad public and
in obtaining the necessary policy.
The circumstance of this having been
directly connected with Germany’s war preparations should not mask the insight that the specific concern was to achieve efficiency in raw
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materials. One can pick up this concern again today, though for different reasons—that is, because
raw materials are scarce and expensive throughout the world and their use represents a burden
for the environment. Sankey diagrams might be
a helpful tool to illustrate and optimize complex
material flow systems again—but now with an actual view of the industrial metabolism and with
the new goal of reducing the ecological impact.
In this context, methodological improvements
and new application areas of the Sankey diagram
could be useful for practical purposes in companies. This will be the topic of part II (M. Schmidt
2008), the sequel to this article.
Acknowledgements
I should like to thank the three unknown reviewers for their suggestions and Linda Golding
and Clayton Macdonald for their support with
the language.
R E S E A R C H A N D A N A LY S I S
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About the Author
Mario Schmidt is professor of environmental management at Pforzheim University in
Pforzheim, Germany, and director of the Institute of Applied Sciences IAF.