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NBS TECHNICAL NOTE 1115

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U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

A Report on the Relevance

of the Second Law of

Thermodynamics to

Energy Conservation

QC

100

.115753

NO. 1115

1980

c.2
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

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'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234.

2 Some divisions within the center are located at Boulder, CO 80303.
National Bureati of StatHtorfc

Library, E-01 Admin. Bldg.

A Report on the Relevance Aug2 7 198o

of the Second Law of Thermodynamics

n

"aa T

L

to Energy Conservation -usiss

" no. /i /f

David Didion 1 David Garvin

Jack Snell

National Bureau of Standards

Washington, D.C. 20234

'Center for Building Technology

National Engineering Laboratory

2 Center for Thermodynamics and Molecular Science

National Measurement Laboratory

3 Office of Energy Programs

National Engineering Laboratory

Sponsored by:

Department of Energy

Office of Industrial Programs

1000 Independence Avenue, SW.

Washington, D.C. 20585

'ethnical note

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Luther H. Hodges, Jr., Deputy Secretary

Jordan J. Baruch, Assistant Secretary for Productivity, Technology and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued August 1980
National Bureau of Standards Technical Note 1115

Nat. Bur. Stand. (U.S.), Tech. Note 1115, 51 pages (Aug. 1980) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1980

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

Price $3.25

(Add 25 percent for other than U.S. mailing)
ABSTRACT

This is a study of the relevance to Federal energy conservation

programs of the use of the concept of energy efficiency as being

the ratio of the minimum available work necessary for accomplishing a given task to the available work in the actual fuel used to

accomplish this task. Included within the study is a review of

selected elements of thermodynamics and efficiency concepts, and

identification of the technology pertinent to energy conservation

programs. The study examines the potential benefits, if any, that

would accrue from the application of Second Law of Thermodynamics

principles to these technologies. Results indicate the positive

value of the Second Law analytical techniques in the planning

and design stages of system development, and the rather limited

value of its use during the performance monitoring stage. Needs

for advancing the acceptance and use of the Second Law analytical

techniques are identified.

Key words: Availability analysis; energy conservation; energy;

process efficiency, Second Law of Thermodynamics;

system efficiency

iii
Table of Contents

Page

I . Introduction 1

II . Methodology 4

III . Background 7

A. Technical 7 B. Energy Conservation Programs 23

IV. Relevance of Second Law Analysis to Energy Conservation

Programs 31

V. Conclusions and Recommendations 43

VI . References 46

iv
I. INTRODUCTION

Section 683 of the National Energy Conservation Policy Act (NECPA) , Pub. L. 95-619,

directed the Secretary of Energy to conduct a study of the "relevance to energy

conservation programs of the use of the concept of energy efficiency as being

the ratio of the minimum available work necessary for accomplishing a given

task to the available work in the actual fuel used to accomplish that task"

(hereinafter referred to as the "study" or the "Second Law Study") . This concept of energy efficiency is based on the First and Second Laws of Thermodynamics.

The National Bureau of Standards (NBS) conducted this study for the Department

of Energy (DoE) . Staff members at NBS carried out a qualitative assessment of

the benefits of applying the Second Law of Thermodynamics concepts to the

various energy technologies which comprise the energy conservation programs

that are specified in Section 683 of NECPA. The discussion and results of this

effort are covered in Volume 1 of the the DoE report to Congress (DoE/CS/40178. 000-01)

of January 1980. NBS also contracted with a private firm specializing in

Second Law analyses to conduct detailed technical analyses. The contractor's

report consisting of a quantitative analyses of selected technology systems

and generalized conclusions are presented in Volume 2 of the same DoE report.

This NBS report is a rewrite of Volume 1. It contains a modest elaboration

of the thermodynamics background and is oriented towards a slightly more

technical audience. Although the conclusions are generally identical to

those in the DoE report, it is hoped that the technical discussion is more

precise and explicit. (A format identical to Volume 1 has been maintained

for ease of comparison.)

The energy conservation programs addressed in this study include (1) those

authorized in the Energy Policy and Conservation Act (EPCA) , Pub. L. 94-163;

the Energy Conservation and Production Act (ECPA) , Pub. L. 94-385; and NECPA;

1
and (2) appropriate Federal programs in energy research, development and demonstration.

The process of establishing the relevance of the Second Law of Thermodynamics

to these energy conservation programs includes reviewing the elements of

thermodynamics and efficiency concepts, identifying the technologies pertinent

to energy conservation programs* and finally establishing what particular

benefits, if any, would accrue from application of Second Law principles to

these technologies.

In particular, consideration has been given as to how the analytical techniques

based on the Second Law of Thermodynamics might be useful in:

(1) planning and setting of research priorities (i.e. the assessment of

technologies for investment, management, regulatory, or policy purposes)

(2) design, analysis and testing of components or systems

(3) monitoring or rating of operating systems

With reference to each of these questions, sample energy systems from the

following five major energy technology groups were considered:

(1) industrial processes which involve the generation of process steam as

applied to the manufacture of chemical products, paper, and allied

products, food products, transportation equipment, machinery and

textiles;

(2) industrial systems which involve direct heating as applied to the

processing of primary metals, fabricated metals, stone, glass and

clay products, petroleum and coal products;

(3) transportation;

(4) generation of electrical power; and

(5) building, heating, ventilating and air conditioning systems.

* Only those aspects of energy conservation programs that deal with "more

efficient use" have been considered. The curtailment aspects of the

programs were not considered relevant to this study.

2
The methodology utilized in conducting this study is presented in Section 2.

Section 3 presents the technical background of the pertinent elements of

thermodynamics and the legislative background of Federal energy conservation

programs. The analyses and conclusions of the study are the topics of Sections

4 and 5

.
II . METHODOLOGY

This section addresses the methodology employed in assessing the relevance of

Second Law analyses to the research, development and demonstration programs

of the Federal Government that are related to energy conservation. The

study methodology involved examining actual examples of the use of Second Law

analysis and hypothetical applications of its use in Federal energy conservation

programs. Its relevance was assessed using a simple evaluation scheme.

In principle, analyses based on the Laws of Thermodynamics are relevant to all

systems in which energy is an important factor. But this does not mean that

those analyses always will be useful. Relevance must be defined in a more

limited sense for the purpose of this study.

Typically, the criterion used to establish the relevance of an analytical tool

to application in a particular area is that its benefit-cost ratio is

favorable relative to other available tools. This may mean providing the same information that other tools do but more quickly, with less effort or at a lower cost; or,

it may mean the tool in question provides new or additional information, the

value of which is greater than the costs associated with its use. Energy

analyses based on the Second Law of Thermodynamics clearly must fall within

the latter of these categories if they are to be practical. (This assertion

will become clearer on review of the next section of this report.) Therefore,

the criterion used in this study for assessing the relevance of Second Law

analyses to energy conservation programs is the following:

Will Second Law analysis provide data, information, or insights

of sufficient value or benefit beyond those obtained using

"conventional" energy analysis techniques in relation to its

cost to warrant its use?
This general question is answered and the rationale for the different answers

for various energy conservation programs and generic classes of potential use

is presented. In each case, one of three alternative levels of relevancy

is given; i.e., Second Law analysis is useful, or is of limited applicability,

or is not beneficial when considered in light of the above question.

As part of this study, an advisory team of in-house thermodynamicists was

formed of which the authors of this report were a part. A literature

survey was conducted to obtain a cross-section of the various applications

of these analytical techniques . Close liaison was maintained with the

staff of General Energy Associates who conducted the study presented in

Volume 2 of the DoE report. NBS staff members also discussed the subject

with several authorities on the application of the Second Law and with

representatives of various sectors of industry including an ad hoc technical

committee of the Chemical Manufacturers Association. During the period this

study was conducted, two professional meetings specifically oriented toward

Second Law analytical techniques were held. In December 1978, one of the

team members organized and chaired a panel of experts from industry and

the university sector to discuss the practical value of using Second Law

techniques. This discussion was conducted at the Winter Annual Meeting of

the American Society of Mechanical Engineers. In August 1979, several team

members attended a Workshop on the Second Law of Thermodynamics held at

George Washington University in Washington, D.C. Over twenty-five experts

from the United States and Europe presented technical papers of various

2 systems analyses based on Second Law techniques . Dr. Frederick Costello,

a private consultant who had previously conducted a study using Second Law

1. Dr. Max Klein, Senior Scientist of the Thermophysics Division,

Dr. Kenneth Kreider, Chief of the Thermal Processes Division,

Dr. Preston McNall, Chief of the Building Thermal Performance Division,

and the authors.

2. The proceedings of that meeting may be obtained from Dr. Ali Cambel,

School of Engineering, George Washington University, Washington, D.C.

5
analysis for the American Gas Association, participated in the early stages

of this study. Professor Richard A. Gaggioli, Marquette University made

a detailed review of a draft of this report and offered many useful suggestions,
Ill, BACKGROUND

A. Technical

In this section several terms used throughout the report are described.

The first few are technology terms: energy conservation, energy consumption,

sources of energy and feedstocks. These apply to conventional materials

used in industrial systems. Then, the thermodynamic basis for quantifying the

use of energy sources is explained in terms of internal energy, useful

work (availability) and entropy. Next, measures of efficiency are described.

Finally, the scope, application and limitations of energy analysis are treated

in the context of what is practical and the broader analysis that includes

cost, limitations imposed by materials and social factors.

A.l Energy Sources

Energy conservation , as the term is commonly used and as it is used in this

report, has as its goal the more efficient use of sources of energy. This

means (a) using less of a source of energy to do a particular job, (b) doing

several tasks (concurrently or sequentially) with the same portion of the

source, or, (c) using a different source, one more closely matched to the

task. An example of (a) is savings resulting from the use of better insulation.

Use of process steam both for the generation of electricity or work and then

for heating illustrates (b) . Use of a low temperature heat source for space

heating is an example of (c)

.

Energy consumption means using the energy stored in a source. More correctly,

it means converting the stored energy (chemical, gravitational, magnetic, etc.)

to some other, desired form (often heat or work). Neither of these definitions

of conservation or consumption should be confused with thermodynamic statements

about the conservation of energy, discussed below.
The sources of energy of principal concern here are fossil fuels, biomass,

nuclear reactions, geothermal reservoirs, falling water, wind and solar

radiation. Sources of energy are rated (and bought and sold) in terms of the

energy released by them in certain common standardized processes, for example,

the heat released during the combustion of fossil fuels when burned in a

constant volume calorimeter at 25°C. Most of the energy from these sources is

provided indirectly through conversion to provide heat (thermal energy)

work (mechanical energy) or electricity. The nearly direct production of

electricity is a special case (fuel cells, photoelectric cells); most electrical

generation is done in a secondary process by application of heat to a fluid

that produces work (as in a turbine) to drive a generator.

Feedstocks are the raw materials converted to desired products by the processing

industries. Often they are distinct from fuels, as for example, iron ore used

to make steel. But occasionally they are not, as in coal gasification where

part of the coal is reacted with water to produce low BTU gas at a high

temperature maintained by burning the rest of the coal. The petrochemical

industry is based on converting a fuel, oil, to a variety of chemicals.

A. 2 Thermodynamic Quantities

The science of thermodynamics is a rigorous, mathematically consistent treatment of energy changes. It is the technical field which encompasses the

laws that describe the nature of energy, its behavior and its associated

properties of materials. Two thermodynamic properties of materials, internal

energy and entropy, are essential to the understanding of energy analyses.

Only changes in these properties are pertinent to energy analysis. Changes

in internal energy of a system are directly related to the heat and work

produced or absorbed. Internal energy changes are specified by the First Law

of Thermodynamics. Changes in the entropy are directly related to the

extent to which a process will run under specified external constraints.
Entropy is defined by the Second Law of Thermodynamics. Measures of useful

work are obtained when the changes in internal energy and entropy are

combined. These combinations are meant when the term "second law analysis"

is used.

The energy , or more precisely the internal energy of a system is a thermodynamic

property upon which all analyses discussed later depend. This property

cannot be measured. However, changes in the energy of a system are

measurable. (A system is any microcosm of interest, ranging from a

simple laboratory experiment to an industrial plant to the universe.)

The change in energy of a system, AU, when that system goes from one

physical state to another is defined by the First Law of Thermodynamics as

AU = Q - W

change heat work

in energy absorbed done

Energy has two important properties. First, the energy of a system is a

function of the present state of the system and does not depend upon how the

system got there. If the temperature, pressure, material composition and,

if need be, gravitational potential, etc., are specified, then the internal

energy is fixed. This means that the change of energy of a system accompanying

a process can be determined without knowing the details of the process. Only

the properties of the system before and after the process need to be known.

For example, the change in internal energy of one kilogram of water when

heated from 20°C and one atmosphere pressure to 350°C and 165 atmospheres

(where it is steam) depends only on the properties of the initial water and

the final steam. This change can then be compared to the amount of an

energy source used to produce the change, in order to calculate the efficiency

of the actual process.
The second important property of energy is that it can be converted from

one form (chemical, mechanical, thermal, etc.) to another but it cannot be

destroyed. This is the thermodynamic statement of conservation of energy.

This leads to an accounting principle used in energy analysis. The total

energy in a system before a process begins is equal to the total energy

present afterwards. Energy conservation measures aim at maximizing the

energy in useful products of the process. Consider the production of

electricity. Fossil fuel is burned to produce hot gases which convert

water to steam at high temperature and pressure. The steam drives a turbine

(mechanical work) coupled to a generator that produces electricity. The

initial store of energy that was in the fuel is present afterwards in the

electricity, waste heat and the combustion products. Contrast this statement

to the energy conservation question: how much fuel must be burned to produce

a certain amount of electricity? This question implies that the only

useful output of the process is the electricity, which, of course, is

correct if electricity is the only desired output. The electricity is only

a fraction («35%) of the input energy and thus the efficiency of the process

is less than 100 percent.

Heat and work are energy in transit from one material to another. Heat flows

from a hotter body to a cooler one, raising the internal energy of the latter.

Work causes a mechanical change, seen most easily in the raising of a weight,

winding of a spring, or deformation of a material.

Useful work . An accounting of the energy changes accompanying a process

does not reveal the maximum useful work that can be done by a system. This

can be appreciably smaller than the total energy change, particularly if

there are steps in the process driven by the application of heat. The

thermodynamic limiting value for the maximum useful work is controlled jointly

by energy and entropy changes. (Entropy is further described below. It, like energy

is a function of only the present state of the system. But, unlike energy,

the total entropy is not conserved in natural processes. It tends to increase).

10
Various terms are used in engineering practice to describe this maximum

useful work concept and to calculate a value. Common ones are availability,

exergy, essergy, lost work, potential work and potential energy (1, 2). Their

definitions differ but their essential content is the same. Availability

is the term used in this report. It is defined as the maximum work that

can be done by a system when it changes from its initial state to complete

equilibrium with the terrestrial environment. In terms of thermodynamic

quantities the availability of a system, B, is defined as

B = (U - U ) + P (V. - it oilVf ) - Toir (S. - S.)

where U, V, and S are the internal energy, volume and entropy of the system

in the initial and final states. T and P are the temperature and pressure

of some standardized terrestrial environment, as for example, 25°C and one

atmosphere pressure. Unlike energy, the availability is not conserved. It

decreases in any natural process.

The importance of this thermodynamic property, B, is that the thermodynamic

limiting value for the work that a system could do can be calculated from

the properties of the system itself. Because B involves entropy and because

entropy is defined by the Second Law of Thermodynamics (see below) , it

provides a recipe for the quantitative application of the Second Law of

Thermodynamics to industrial systems.

Although this discussion is in the context of the maximum work that a system

could do, exactly the same limit is reached when one calculates the minimum

work required to produce the reverse of the process considered. This is the

basis of the statement in the Introduction quoted from the National Energy

Conservation Policy Act.

11
Entropy is a property that specifies the feasibility of a process: the

direction in which it will run spontaneously and how far it will run before

reaching equilibrium. It is a quantitative statement about the tendency of

liquids to mix, solids to dissolve, gases to expand and fill the available

volume. In a very general sense, the change of entropy measures the change

of randomness in the system—both mixing of materials and spreading of thermal

energy. For a natural, spontaneous process in a closed system, entropy

and randomness increase.

Entropy is defined by the Second Law of Thermodynamics as being a function

of the state of the system. Entropy change is defined in terms of the most

efficient, reversible process as dS = (dq/T) here dq is the infinitesimal

absorption of heat at temperature T in the process. When no heat is absorbed,

dS is zero for a reversible process and is greater than zero in a natural

process (as for a chemical reaction occuring in an insulated bottle).

There are two classical statements of the Second Law of Thermodynamics which

are a generalization of experiences with the heat engine and its exact opposite

the refrigeration machine (i.e. heat pump). These statements may be written

as:

(1) It is impossible to construct a machine, operating in cycles, which

will produce no effect other than the absorption of heat from a

reservoir and the conversion of that heat to an equivalent amount

of work.

(2) It is impossible to construct a machine, operating in cycles, which

will produce no effect other than the transfer of heat from a cooler

to a hotter body.

12
A. 3 Measures of Efficiency

The energy efficiency based on the First Law of Thermodynamics, n, is the

ratio of the energy transferred to the desired products to the energy

applied. For example:

heat transferred to a material

change in internal energy in the fuel

_ work done

change in internal energy

or, more generally, with a very broad interpretation of the terms

useful energy in the desired products

energy applied to do the task.

For example, n answers the question: what fraction of the heat released

by burning a known quantity of coal is transferred to the steam produced

in a boiler.

Energy efficiencies based on the Second Law of Thermodynamics take two

forms. The first answers the question: what is the maximum achievable

value of r\ for a specified process. This question is most pertinent to a

component of an industrial process. The answers are particularly simple

for the large class of processes that can be considered to be either heat

engines or heat pumps (steam and gas driven turbines, diesel and gasoline

engines, air conditioners, refrigerators, etc.). For the case of high

pressure steam at a temperature T , driving an engine producing work with

the waste steam being exhausted to the atmosphere at a temperature T„, the

maximum or Carnot efficiency is

n = (T, - T„)/T1

. max 1 2 1

This maximum efficiency is necessarily less than unity.

Similarily, for a refrigerator operating between temperatures T and T~

the maximum efficiency is

n = T_/(T, - T 9

) max J j I

13
The numerical value for this ideal heat pump efficiency (usually called

coefficienct of performance) is necessarily greater than 1. Thus,

n = 1 is not the measure of 100% efficiency for either of these traditional

efficiency scales. A comparison of n .. with r\ is a comparison of actual max v

what has been achieved to what is achievable in a particular type of

system. It shows how much room there is for improvement. An effective

comparison for nine types of such heat and work systems is given in reference

(13).

The second question answered by application of Second Law analysis is

more general. It is: how does the theoretical least work required to

accomplish the task compare with the maximum work that could have been

extracted from the input energies. This comparison, often called effectiveness, £ , is

_ minimum work required to do the task

potential work available in the inputs

or, for simple heating of a material

minimum heat required to do the task . heat available from the inputs

This measure, effectiveness, is the one of primary concern in this report.

Two features should be noted. First, effectiveness is independent of the

way the task is actually done. Second, the inputs are rated in terms of

the maximum effect they could produce, not what they could produce in

the actual process were it to be run with maximum efficiency. At times

this generalization leads to different answers than does n , particularly

max

for complex systems.

In short, effectiveness is task oriented. The other measures are process

oriented. Because effectiveness gives the ultimate thermodynamic limit,

it has been recommended as a rational approach to the measurement of the

14
utilization of sources of energy (4, 13). The thermodynamic function,

availability, B, defined earlier, can be used to determine both the

numerator and denominator of the expressions for

B . _ mm

Bactual

This general formulation is applicable to any process (13) . It is particularly

appropriate for complex systems that have several inputs and outputs.

Variations on this definition of effectiveness do exist and are often

used for system analysis, depending on what information is desired. For

example, the fact that in the theoretical limit the availability associated

with the total input can be completely transferred to the total output can

also be used to define an effectiveness measure (4)

:

available energy in useful products , available energy supplied

This definition relates to the actual process specifically in that both

the numerator and the denominator refer to the actual system's properties

and not to an idealized system. The denominator exceeds the numerator

in value by the amount of availability consumed in the conversion. This

definition, therefore, is particularly convenient for a basis of determining

operating costs, as will be discussed later.

A. 4 Energy Analysis

Energy analysis utilizing measures such as those found above treats the

changes of energy and entropy in a process. It is a study of efficiency

and is a major tool in developing energy conservation strategies.

The analysis of energy and materials processing is carried out on several

levels of complexity in engineering practice and is used at various stages

of operation in industry. Typical complexity levels are:

15
(a) Energy accounting based on the First Law of Thermodynamics,

(b) First Law energy accounting supplemented with a qualitative, intuitive

application of the Second Law,

(c) Quantitative analysis of the availability (potential work) based

on a combination of the principles of the First and Second Laws of

Thermodynamics

,

(d) Analysis of the dynamics of a system, combining principles of

equilibrium thermodynamics, irreversible thermodynamics, physical

and chemical kinetics and fluid mechanics,

(e) Any or all of the above combined with other technical considerations

(e.g. reliability, safety, etc.)> economic analysis and consideration

of social impacts.

The first three items are of principal concern here. These energy analyses

may be applied at the following stages of an energy system's life:

(a) Research and development on a new concept,

(b) Selection between different conceptual methods for performing a

task,

(c) Design of an operating system to perform the task,

(d) Optimization of new or existing equipment - usually applied to

specific components,

(e) Operation and control of existing systems

(f) Monitoring of performance, and

(g) Reporting of energy utilization.

All of these stages are of interest when methods of energy analysis are being

compared; but the value of a specific analysis method may vary for the different

stages as well as for different systems.

16
Many efficiency analyses conducted today are done on a First Law basis with

a qualitative awareness of the Second Law concepts. This awareness means

that it is understood not only the quantity of energy but also its quality

(potential level) are important. For instance, in order to achieve high

Second Law efficiency one should match the temperature of heat source to

that of the heated material as closely as possible. Also, one should arrange

that the inevitable heat rejection from the system should be done at a

temperature as close to ambient as possible. Lack of an understanding of this

principle is responsible for some of the misconceptions held by the general

public about the everyday energy systems. For example, it is commonly believed

that home heating is an efficient use of fossil fuel combustion and that

fossil fuel fired electric power plants are relatively wasteful because they

reject large amounts of energy to the atmosphere. In the first case, the

large difference between the furnace combustion temperature (*3500°F) and the temperature of the hot air (~120°F) means that there is an ineffective use of the fuel since

the energy of the high temperature of combustion could be used to produce some

mechanical work before delivering the heat (cogeneration) . In the latter

case, the fact that power plants reject large amounts of heat is inevitable

because they are producing large amounts of electric power from a high

temperature heat source. What is important is that the temperature level

at which the heat is rejected is relatively low and therefore the heat is

virtually useless except for applications at even lower temperatures (e.g.

space heating) . The inefficiency that the power plant does have is again a result

of the large difference (although not as large as the home furnace) between

the combustion and utilization (steam) temperatures.

17
Availability analysis, which is based on both the first and second laws, is

a formal energy accounting procedure which considers the potential level of

each energy stream as well as the quantity. It is concerned with the work

that can be done by a perfectly efficient process. For every system there

is a maximum fraction of the input energy that can be converted theoretically

to work. Anytime there is a decrease in the quality of thermal energy (e.g.

that due to the difference between a furnace's combustion temperature and

the house heating system's supply air temperature) without an extraction of

useful work there is a net loss of availability for the system. Whereas

energy is always conserved, availability is destroyed in a natural process.

The amount of availability destruction is used as a basis for measuring the

processes efficiency.

A. 5 Applicability and Limitations of Energy Analysis Methods

Both simple energy accounting and availability analysis can be applied to

a complex process, treating the process as a "black box" and considering

only inputs and outputs. Thus both can be used for monitoring at a plant

or industry level. Both methods can be applied to individual steps in a

complex process. Availability analysis gives a better guide to where improvements are possible. It is particularly applicable to the design (or redesign)

phase of an industrial process. However, for some cases both methods give

substantially the same result. This must be determined by detailed analyses

of typical processes. When this has been determined for test cases the

simplicity of First Law analysis is to be preferred. Although both methods

can be used to assess the needs for developing new processes or to select

among possibilities, the Second Law approach provides a better comparison

in this application. In one form or another it is essential to understand the

Second Law implications in planning stage of an industrial system [3, 4].

18
When applying any of the energy analysis techniques it is imperative that

the system be well defined and the thermodynamic properties of the inputs

and outputs be known. For application of a First Law analysis this means

that the thermodynamic property, internal energy, must be known for the fuels,

feedstocks and products. For the Second Law application another property,

entropy, must be known. This property is more difficult to obtain. There

are larger gaps in the data bank of this property than for internal energy.

This is a practical limitation, one that should become less important in the

future. This is not a limitation today for the most significant industrial

case, the generation and use of steam, simply because an immense amount of

careful work has been done to establish the properties of steam [5], There

also is a large body of data for metallurgical systems. However, for many

chemicals neither of these properties is known and for others the energy

is known but the entropy is not. Where these essential properties are not

known the technique either can not be applied or estimates of their values

must be made. There is a need for better methodologies for predicting thermochemical properties and an even greater need for making them widely known in

the engineering comnunity.

Efficiency analysis, based on the First Law only, may usually be used for

comparing the relative performance of similar systems that are producing an

identical product or energy output. Energy analyses of different systems,

which are producing different products, are more difficult to intercompare

[6]. Usually a Second Law analysis of some form must be used to establish

a maximum performance limit. It is then possible to compare the respective

ratios of theoretical to actual performance for each system and determine

which is closer to ideal performance.

19
However, comparison of different systems on the basis of energy efficiency

can be misleading. Energy efficiency is only part of the story. Improving

the performance of a comparatively poor system may be impractical for various

technical reasons: process technology, strength of materials, requirements

for high rates of production, inability to control combustion temperatures,

corrosion, pollution, etc. In addition, energy performance is often subordinate

to economic and social considerations [7],

Much of what has been said above can be understood fairly easily if one

restricts consideration to power generation systems: work out, thermal energy

in. But it is much more difficult to develop a feeling for the idea of

efficiency in systems where several things are happening at the same time.

A case in point is materials processing. Aluminum is made from bauxite.

During this process there are two streams that suffer changes in availability.

The feedstock stream changes (bauxite to aluminum) , with the product having

a higher availability than the raw materials. At the same time the source

of energy applied to the task suffers a decrease in availability. Over all,

availability decreases for the combined streams. The efficiency of the

process can be calculated. However, there are procedural questions that

are very difficult to answer. It is possible that they can be settled only

by agreement. For example, from a strict energy conservation point of view

it may be immaterial that aluminum metal has a high availability that could

be released by reacting it with acid to produce hydrogen. How should this

availability be counted? Another ultimate disposal of fabricated aluminum

is recycling it - back to the melting pot. How should account of this

preservation of availability be counted in assessing the original processing?

These conceptual difficulties abound, particularly for cross-industry

comparisons.

20
In spite of these caveats, availability analysis remains important. It

is availability (potential energy) not energy for which we pay. Availability

is consumed in the combustion of a fuel, not energy. Therefore, everywhere

that availability is destroyed in a system, due to inefficiency, the

decrease in availability is a measure of what that particular inefficiency,

costs the operator of the system.

An important use of availability analysis techniques has been in the quantification of life cycle costs for a system (capital and operating costs)

[8, 9]. At least two types of costing applications are becoming more prevalent

in engineering studies. The first is the prorating of charges for different

types of energy or different potential levels of energy [14] . For example,

a total energy plant, whose primary product is electric power, but also sells

"waste" steam for industrial processes or building heating, has to determine

the relative costs of fuel consumption and equipment amortization. One

advantage (increased fairness in pricing) to using availability, as opposed

to energy, is that it takes into account the by-product's temperature and

pressure level. Clearly the higher these are the potentially more useful the

steam is. That is, it is either able to produce more work or be used to

create a higher temperature environment.

In Figure 1 (from reference [14]), the results of an analysis of a total energy

plant are presented. Here "waste" steam is available at various temperatures

and pressures. The energy costing line shows a price for 100°F saturated

steam that is 80% of the price for steam at 250°F. In contrast the available

energy costing shows that 100°F steam is worth less than 1/3 that at 250°F.

Available energy costing shows the customer the value of what he is buying

even if all of this value cannot be used in the immediate application.

21
0.18 0.43 0.95

0.25-

co 0.15 O

u

0.10

0.05

Energy Costing

PRESSURE, psia

1.95 3.72 6.70 11.5 19.0 296 45.8 67.0

Available-Energy Costing

75 100 125 150 175 200 225

TURBINE EXHAUST TEMPERATURE, °F

250 275

Figure 1. Cost of Cogenerated Steam

(as presented in reference [14])

Another costing application is one that may be utilized during the design

phase of most any complex manufacturing systenu Typically a trade-off between

first cost expenditures and operating costs may be optimized so that minimum

life cycle costs result. Attempts to utilize operations research techniques

in conjunction with availability analysis are presently under development

[10] . This combined analysis of the availability of an energy stream and its

cost (in dollars) may well prove to be the most valuable contribution of the

Second Law techniques.

22
B. Energy Conservation Programs

The purpose of this section is to describe briefly the energy conservation

programs covered by this study and to note in each case the aspect of the

program, if any, for which the concept of energy efficiency deriving from the

second law of thermodynamics may be relevant. Section 683 of P.L. 95-619,

the National Energy Conservation Policy Act, requires specifically that the

following energy conservation programs be considered:

1. Those authorized in . . .

a- Pub.L. 94-163, the 1975 Energy Policy and Conservation Act (EPCA)

:

b. Pub.L. 94-385, the 1976 Energy Conservation and Production Act

(ECPA)

;

c. Pub.L. 95-619, the 1978 National Energy Conservation Policy

Act (NECPA); and

2. Appropriate Federal programs in energy research, development and

demonstration. (Principal authority in this area is Pub.L. 93-577

the 1974 Federal Nonnuclear Energy Research and Development Act.)

In general, all of these programs fall under the responsibility of the Assistant

Secretary, Conservation and Solar Energy, Department of Energy, with important

related roles played by other offices in DOE, other government agencies including

State and local governments, and private sector organizations as well.

A number of the programs authorized by these statutes are concerned with

related aspects of the same technologies within the various sectors of the

energy economy. This is particularly true for DOE research, development and

demonstration programs. Therefore, in the analysis (Section IV) the principal

techniques associated with each sector are discussed instead of the individual

programs. For example, in the area of building energy conservation, the technologies of appliances; building heating, ventilating and air conditioning

23
systems; and total energy or cogeneration are considered instead of each of

the numerous specific programs described below.

Finally, the general topic of solar energy is not explicitly addressed in this

study although it is mentioned in a number of these statutes. Solar is not usually

considered as an energy conservation technology, but as an alternative source.

Also, as yet, no clear advantage for applying Second Law techniques to solar

systems has been established. Furthermore, difficulties exist in defining

an appropriate solar source temperature that will provide an equitable

comparison with fossil fuel systems.

Since the technologies involved in the DOE energy conservation research,

development and demonstration (RD&D) programs are essentially the same as

those affected by the mandated programs, the RD&D programs are not

described in the following paragraphs. What follows is a brief summary of

Federal energy conservation programs by major energy-using sectors of the

economy (buildings, industry, transportation, and utilities).

B.l Energy Conservation in Buildings

Buildings account for approximately 1/3 of energy use. Thus, programs and

technologies aimed at improving efficiency of energy use in new and existing

buildings and associated appliances and equipment offer important contributions

to the total national energy conservation effort. Legislated programs in this

area include the following:

Energy Conservation Standards for New Buildings (Pub.L. 94-385 sections

301-311). This program involves the development and implementation, 'as

soon as practicable, of performance standards to which new residential and

commercial buildings will be designed to achieve the maximum practicable,

improvements in energy efficiency and increases in the use of nondepletable

24
sources of energy." DOE's proposed standards were issued for public

comment on November 14, 1979 (44 FR 68120 [November 28, 1979]). Tbe

standards will require new buildings to meet specific design energy

budget levels measured in terms of thousands of Btu's per square foot per year.

Because they are performance, instead of component standards,

designers and builders will retain flexibility in choosing designs

which achieve significant energy savings. In developing these

standards, DOE is carrying out extensive research and technology

development efforts which will significantly advance the state-of-the

art for the energy efficient design of new buildings.

° State Energy Conservation Plans (Pub.L. 94-163, sections 361-366;

Pub.L. 94-385, sections 431-432; Pub.L. 95-619, sections 621-623).

This program lays out the requirements that State energy conservation

plans must meet to be eligible for Federal assistance. They include

mandatory lighting efficiency standards for public buildings,

mandatory standards and policies relating to energy efficiency in

procurement practices, and mandatory thermal efficiency standards

and insulation requirements for new and renovated buildings. The

mandatory lighting efficiency standards which have been developed

by DOE are expressed in terms of illumination requirements for various

types of activities within buildings. Thermal efficiency standards and

insulation requirements are expressed in engineering units in a form

consistent with the building energy conservation standards described

above and other standards widely used in current practice (for example,

the American Society for Heating, Refrigerating and Air-Conditioning

Engineers' Standard 90-75).

25
° Weatherization Assistance for Low-Income Persons /Families (Pub.L. 94-385

sections 411-422; Pub.L. 95-619, sections 231-233). The purpose of this

program is to develop and implement procedures to assist low- income persons

in achieving the prescribed level of insulation in the dwellings. This

is a financial assistance program. DoE's regulations for this program

are required "to achieve a balance of a healthy dwelling environment and

maximum practicable energy conservation." The weatherization materials

eligible under this program include, for example, caulking and weatherstripping, certain furnace modifications, clock thermostats, ceiling/

attic/wall/floor /duct insulation, and "such other insulating or energyconserving devices or technologies as the Administrator may determine by

rule." DoE and others have conducted a series of analyses to determine

the energy conservation effects of such weatherization measures.

' Residential Conservation Service Program (Pub.L. 95-619, sections 210-

225, 10 CFR Part 456 [1979]). This program requires large electric and

gas utilities and, on a voluntary basis, urges oil dealers to inform customers

of suggested measures for energy conservation and uses of renewable resources and

to provide estimates of the energy savings and costs of such measures.

These measures include insulation, storm windows and doors, caulking

and weatherstripping, replacement air conditioners, furnace efficiency

modifications, clock thermostats, solar hot water heaters, and solar

space heating systems. These programs are to be initiated in 1980.

Here again, the principal technical issues include identifying the appropriate standards necessary for safe and effective installation of the

program measures and determining which measures are appropriate for use

for a given location and category of building.

26
Energy Conservation in Schools and Hospitals (Pub.L. 95-619, sections

301-312) . This program involves grants "to States and to public and nonprofit schools and hospitals to assist them in identifying and implementing energy conservation maintenance and operating procedures and

in evaluating, acquiring, and installing energy conservation measures

to reduce the energy use and anticipated energy costs of schools and

hospitals." As with the Residential Conservation Service, this program

involves explicitly defined energy conservation measures. These include

insulation, storm windows and doors, automatic energy control systems,

furnace or utility plant and distribution system modifications , energy

recovery systems, cogeneration systems, "such other measures as the

Secretary identifies by rule," and "such other measures as a grant

applicant shows will save a substantial amount of energy and are

identified in an energy audit."

' Energy Conservation and Measurement in Federal Buildings (Pub.L. 94-163,

section 318, Pub.L. 95-619, sections 501-551). These programs involve

efforts to improve efficiency of energy use in new and existing Federal

buildings and facilities and to encourage the use of renewable resource systems

in them. In particular, it is the purpose of these programs to promote

the use of commonly accepted methods to establish and compare the lifecycle costs of operating Federal buildings and the life-cycle fuel

and energy requirements of such buildings with and without special features

for energy conservation and "... the use of solar heating and cooling

and other renewable energy sources in Federal buildings."

° Appliance Labeling and Minimum Efficiency Standards (Pub.L. 94-163

sections 321-339, Pub.L. 95-619, sections 421-427). This program is

aimed at improving the efficiency of a variety of home appliances

27
including refrigerators and refrigerator-freezers, freezers, dishwashers,

clothes dryers, water heaters, room air conditioners, home heating

equipment, kitchen ranges and ovens, clothes washers, central air

conditioners, furnaces, etc. DOE has developed test methods presently

used for the energy efficiency labeling of appliances under regulations

of the Federal Trade Commission. "Energy efficiency" is defined in terms

of the "ratio of the useful output of services from a consumer product

to the energy use of such product." DOE, prior to NECPA enactment,

developed efficiency improvement targets for these appliances. The

National Energy Conservation Policy Act presently requires the development of energy efficiency standards for 13 categories of appliances.

Further, the Department of Energy has the authority to expand the list

to cover other major appliances meeting statutory criteria.

B.2 Industrial Energy Conservation

Industry accounts for over 40 percent of energy used in the U.S. The effect

of increased fuel prices and altered patterns of fuel availability has

stimulated many commercial and industrial firms to improve the efficiency with

which they use energy. Mandated programs in this area include the following:

Industrial Energy Conservation (Pub.L. 94-163> sections 371-376:

Pub.L. 95-619, section 601). This program is designed to "promote

increased energy efficiency by American industry." This program

requires each corporation which consumes at least 1 trillion British

Thermal Units (one terajoule) of energy per year and is within one

of the twenty major energy-consuming industries identified by DoE

to report annually to the Secretary of Energy on the progress made

28
by that corporation in improving its energy efficiency. Further,

this program requires the Secretary to establish energy efficiency

improvement targets for at least the most energy-consuming industries

and to apprise the Congress of the progress made toward meeting such

targets.

° Industrial Equipment Energy Efficiency Pub.L. 95-619, section 441),

quoted as "The purpose of this part is to improve the efficiency of

electric motors and pumps and certain other industrial equipment in

order to conserve the energy resources of the Nation." The types

of equipment covered include compressors, fans, blowers, air conditioning

and refrigeration equipment, electrolytic and electric arc equipment,

steam boilers, ovens, furnaces, kilns, evaporators and dryers. This

program authorizes a study to determine the practicability of requiring

electric motors and pumps to meet performance standards establishing

minimum levels of energy efficiency. Further, it authorizes the

Secretary of Energy to conduct similar evaluations of other types of

industrial equipment. It further authorizes DOE to propose test

procedures and labeling requirements for any equipment for which such

standards are determined to be practicable.

Recovered Materials (Pub.L. 95-619, section 461). The purpose of this

program is to conserve valuable energy in scarce natural resources by

establishing targets for increased industrial utilization of recovered

materials and to establish voluntary goals and incentives for this

purpose. Materials explicitly covered by this program as energy-saving

recovered materials include aluminum, lead, copper, zinc, iron, steel,

paper and allied paper products, textiles, and rubber. In establishing

these voluntary goals or targets, the technological and economic ability

29
of each affected industry to increase progressively use of energy-saving

recovered materials is to be considered.

B.3 Transportation

Transportation accounts for approximately 25 percent of energy end use. A

major energy conservation program of interest in this study in this area

involves

:

Automotive Fuel Economy (Pub.L. 94-163, section 301; Pub.L. 95-619,

sections 401-404). This program involves the establishment of average

fuel economy standards applicable to each of a number of designated

automobile manufacturers. Average fuel economy is defined in terms of

a fleet-weighted average for all the vehicles produced by a manufacturer

in a given model year. The standards range from an average fuel economy

standard in miles per gallon of 18 in 1979 to 27.5 in 1985 and thereafter,

B.4 Utilities

Efficiency of energy use in energy utilities, particularly electric power

generation, but also in those producing and selling heat, is also an important

element of the national energy conservation effort. A major mandated program

in this area involves:

° Rate Designed Initiatives for Electric Utilities (Pub.L. 94-385,

section 204) . The purpose of this program is to fund regulatory

rate reform initiatives. In addition, under the Public Utility

Regulatory Policies Act of 1978, Pub.L. 95-617, State regulatory bodies

and nonregulated utilities are required to consider 11 ratemaking and

regulatory policy standards with respect to, among other things, the

conservation and efficient use of resources.

30
IV. RELEVANCE OF SECOND LAW ANALYSIS TO ENERGY CONSERVATION PROGRAMS

The purpose of this section is to present an analysis of the relevance of

analytical techniques based on the Second Law of Thermodynamics to energy

conservation programs. This analysis was carried out using the methodology

described in Section II, draws on the materials presented in the previous

sections, on the results of the contract study carried out by General

Energy Associates (Vol. 2 of DoE's report to Congress) , the state-of-the

art as reflected in the literature, and the judgment of the NBS reviewers.

This analysis has of necessity been limited both in scope and depth by

the resources available for this study. Nonetheless, it is believed that

the most important and potentially relevant applications of Second Law

analysis have been considered in this process. Since availability analysis

and other forms of application of Second Law principles are constantly

evolving and finding broader use, it should be expected that new techniques

and applications will emerge in the future.

Before describing the results of the study they must be put into context.

Energy analyses based on the Second Law of Thermodynamics are relevant,

in principle, to the understanding, designing and optimizations for all

systems in which the use of energy is important. However for some

applications they may not be sufficient, for others they may be irrelevant

and in some cases they may be impractical today.

Capital costs and social goals may be overriding factors. Energy analysis may

be only tenuously connected to programs emphasizing financial assistance.

Current technology and the lack of thermodynamic properties data may inhibit

the use of Second Law based analyses. All of these factors are reflected

in the judgments presented below.

31
A summary of the results of the analysis of the relevance to energy

conservation programs of the Second Law of Thermodynamics is presented on

Table 1. An account of the basis for this assessment constitutes the balance

of this section. The rows of Table 1 represent the various groups of

Federal energy conservation programs outlined in Section III. The titles

of the various elements of each of these programs are also presented in

Column 1. The second column of this table identifies potentially relevant

existing energy technologies or systems considered in examining each of the

major energy conservation program areas. Major technical systems or

components not particularly affected by Second Law analysis are not shown.

(For example, consider the area of building energy conservation. The thermal

resistance of a building envelope and its design are largely functions of

weather, indoor-outdoor temperature differentials, and materials properties.

In this instance, Second Law analysis is of little relevance since it provides

no additional useful information. Similarly, in the transportation area,

transportation network configuration, traffic generation and density distributions are affected by a wide range of socioeconomic as well as technical

factors and are beyond the scope of Second Law analysis techniques).

The third column of Table 1 presents the principal results of this study. This

column contains three subcolumns representing the three generic situations for

which the potential relevance of Second Law analysis has been considered; that

is, in general planning or establishing research priorities; as a tool for

system or component design, analysis, evaluation, or testing; and, finally,

in the monitoring and/or reporting of system operational performance. The first

of these subcolumns is analogous to the general planning stage during which

background research on various technologies might be conducted to determine

whether a commitment for investing in a particular technology should be made.

32
It also represents the type of activity in which research priorities are established for overcoming existing barriers to further development of a given technology.

The second subcolumn represents situations analogous to the detailed design

process which generally follows conceptual design. It includes analyses,

evaluation, and testing of new or existing systems where energy optimization is

one of the major criteria of a successful design. It also includes assessment of the effect of improvement of components on the overall performance

of a system. The third subcolumn is concerned with existing functioning

systems and their operation performance and control. Obviously,

information gathered from monitoring! or reporting on operating systems

is used by decision makers in the other two subgroups as well as by system

operators, technicians, etc. Also, measures of system operational performance generally involve a number of parameters in addition to efficiency

of energy use.

The symbols inserted under each of these three headings represent judgments

on the potential relevance of Second Law analyses to the general types of

Federal energy conservation programs indicated. Obviously, there are many

aspects of each of these energy conservation program areas for which Second Law

analysis is of little or no immediate relevance—for example, in developing

State energy conservation plans or in developing innovative utility rates.

(In the long run there may be relevance in these areas) . The energy conservation programs involving technologies of potential interest here are

highlighted with an asterisk in column 1 on Table 1. The symbols shown on

Table 1 relate only to those technologies such as the examples listed in

column 2 for which it is appropriate to consider Second Law analysis.

33
Three symbols are used in this table. They are defined as follows: The

Second Law analysis is . . .

Z\: useful . It is effective for the general purpose indicated and

merits consideration for use.

[_J, [XJ : of limited applicability . It is generally useful and could

provide some new information, but may not be practicable or practical

problems may now exist in implementing the Second Law technique.

(These may include institutional political, economic, or technological

constraints.) Two cases are distinguished. Lx' means that Second

Law analysis is applicable in a limited number of particular cases;

whereas I I means there may be a broad range of cases where Second

Law analysis is useful but for which it offers at best marginal benefits,

(/}: not beneficial . It would reveal no new information of practical value

beyond what is revealed from conventional analysis.

Rationale

The methodology outlined in Section II was used in assigning the symbols in

column 3 of Table 1. This involved first identifying the potentially relevant

existing energy technologies or systems arising in the context of the various

energy conservation programs listed in column 1. This produced the list of

technologies or systems which follows: *

Household appliances

Building heating, ventilating and air conditioning systems

The general topic of solar has not been explicitly addressed. Solar is

generally not considered an energy conservation technology. Also, lack

of agreement on a definition of a meaningful reference temperature for

the solar source makes availability analysis difficult to apply in a manner possible to make performance comparisons with fossil fuel

systems

.

34
Total energy or cogeneration systems

° The automobile

Generation and use of process steam

Direct heating of materials in industrial manufacturing processes

Materials processing, including extractive, recovery, refining, chemical,

reforming, and fabrication, etc.

Generation of electric power.

The potential relevance of Second Law analysis to each of these technologies

as they arise in the context of the Federal energy conservation programs was

reviewed in light of the contractor study report (DoE report to Congress

Vol. 2) and other relevant information as discussed in the following paragraphs.

It may be apparent from Table 1 that the rationale for the potential relevance

of Second Law analyses to energy conservation programs is similar for

each of the technologies listed under the three subheadings of column 3. For

this reason, and to avoid needless repetition, the bases for the assignment of

the symbols on Table 1 is discussed in terms of each subcolumn.

Planning and Setting Research Priorities

General planning and research priority setting involve generalized analyses

and decisions relating to choice of technologies, to conceptual approaches and

to basic decisions affecting resource allocation. Formalized availability

analyses appear to be most useful in this context. Vol. 2 of the DoE report

to Congress and literature surveys have identified a number of specific

examples of appropriate and effective use of Second Law analyses in conceptual

design of industrial processes. For example, analytical studies have been

made of the application of availability analysis to residential water heating,

35
automobile performance, coal gasification, petroleum refining, polymerization,

paper making, the glass industry, aluminum production, steel production,

total energy systems, heating and air conditioning, electric power. Various

authors have provided summary tables showing approximate efficiencies for

industries and technologies. One study uses the results of Second Law

anslyses in the formulation of energy conservation policy proposals. Also,

the Office of Industrial Energy Conservation, DoE, has made use of Second Law

analyses in establishing its research program priorities and in identifying

areas of particular promise for potential efficiency improvement in the ten

most energy-intensive industries. Historically, Second Law analysis has

found its most widespread use in the system conceptual design stage. Principal

examples arise in the context of total energy or cogeneration strategies which

make effective use of the rather large amounts of heat that are rejected.

Second Law analyses are also particularly useful in analyzing industrial

heating and materials processing technologies. Chemical processing industries

have utilized Second Law analyses in this context for many years.

Obviously, this is but one of a number of tools used in the planning stage,

but with increasing energy prices and with looming constraints on available

supplies of energy, it is one that will only increase in importance. One

practical constraint on more widespread use of availability analyses in this

context is the lack of thermodynamic data directly applicable to the actual

conditions used in materials processing. Another is a lack of agreement on

the reference states that should be used in the analysis of various types

of processes. Also, it is not clear how the changes of availability in

feedstocks should be handled in analyses that are concerned with the conservation of energy sources, that is, how narrowly the systems should be

defined.

36
Also, it should be obvious that all heat rejected in one process is not

equally useful in others. In many industrial systems, particularly

those involving complex processes with many different energy requirements tools

such as Second Law analysis are virtually essential in achieving optimization

of natural resource use.

Although Second Law analysis is somewhat less directly relevant to residential

appliances and heating, ventilating and air conditioning systems, it is useful

in identifying areas for potential improvement in these systems and for

identifying possible practical combinations of traditionally independent

functions. Current developments in heat pump technology and applications are a good case in point. Potentially beneficial technology combinations

include solar energy heat pumps, ground water heat pumps, hot water heater heat

pumps, and heat recovery from refrigeration for water pre-heating. Second Law

analysis of overall building energy use will, in fact, point out the relative

importance of the energy conversion equipment inefficiency (typically e < 10%)

as compared to the more popular area of reducing building loads [13, 14],

Obviously, improved automobile efficiency is an important national goal.

Considerable Federal as well as industry effort is being directed toward

identification of potentially more efficient forms of automotive transport

than that provided by state-of-the-art internal combustion engines. Economy in

the use of transportable fuels is just one factor of concern in personal

transport system design. Second Law analysis appears to be limited usefulness

in pinpointing immediate targets of opportunity in various areas of automotive

engine research, but could easily become more important in the future. On

this basis, all areas have been assigned the symbol JL\ except for automotive

which has been labeled Uu .

37
Design, Analysis, and Testing of Components or Systems

Assessments of the potential relevance of Second Law analyses to design

analysis or testing of energy systems and their components range from useful

(i.e., Z\) to limited applicability (i.e., I I) for the technologies and programs

considered.

These assessments are consistent with the findings of the contractor's study. The

contractor notes that "the second law is most appropriate in the process and

system design and modification area and for component design." Detailed

examples are presented in Volume 2 of DoE's report to Congress which

address heat exchangers, petroleum heaters, multi-effect evaporators, and

distillation processes. Examples in the area of process design include

pulp mills (the Kraft process), processes for producing alkalies and chlorine,

ethylene production, a number of petroleum refining processes, and primary

aluminum productions are also presented. Further, the use of Second Law

concepts by engineers in process design and modification has been widespread

in industry for years. Thus, a / \ is assigned for the industry programs.

The potential relevance of application in the areas of building mechanical

systems, appliances, and automobiles is somewhat limited because of the often

overriding importance of user requirements vis-a-vis energy efficiency in

the design of such systems. Also once the user requirement are defined many

of the First Law figures of merit serve quite adequately for determining the

relative efficiency of a component or system (i.e. miles per gallon, energv

efficiency ratio). Therefore, the limited applicability symbol, GO, is assigned.

38
As with any analytical tool, the applicability of Second Law analysis is highly

situation-specific. Thus, it is difficult to generalize and, indeed, it would

be inappropriate to specify its use industry-wide. The potential benefits

derivable from its application depend in large part on the state of development

and quality of the analytical or computerized models and basic data available

to the system or component design engineer and, of course, his ability to use

these tools. Indeed, increased efforts on the part of the Federal Government

to help industry produce needed data and models and to develop appropriate

training materials may be most effective in stimulating more widespread use

of this important analytical tool.

Monitoring or Rating of Operating Systems

The essential requirement in monitoring or rating of operating system performance

is to characterize performance in useful terms. The principal use of such

information is in tracking the overall performance of a system or in providing

essential feedback on the operation and maintenance costs of an existing system

to designers of new and retrofit systems.

For a particular plant this can be done on the basis of measurements of

energy consumption, products produced and operating variables. The optimum

conditions can be set partially on the basis of Second Law analyses made

during the design phase, but they must also consider pilot plant performance

and studies made during the run-in phase of the actual system. This means

that currently used measures of energy efficiency often can be considered

adequate for comparing performance now with that achieved in the past for the

same system. A switch to Second Law based methods would not be warranted

for the purposes described above, unless more useful or important new

information resulted.

39
When the broader picture was considered, comparison of similar systems,

the conclusion in Volume 2 of DoE's report to Congress was "where the

product or function is the same, present efficiency measures are adequate."

In addition a warning was given that "it is inappropriate to use an availability

measure to compare products or systems whose products or end functions are

different." This is because more than energy efficiency is involved in such

comparisons. It should be noted that these conclusions apply only to existing

systems and that an entirely different conclusion has been reached for the

conceptual and design phases.

Some of the diverse, situation specific efficiency measures now being used

include, for example, miles per gallon for automobiles, energy efficiency

ratio for appliances, measures such as Btu's per hour for HVAC systems,

Btu's per pound of product in a number of industrial processes, etc. The

study in Volume 2 of the DoE report to Congress reviewed 20 diverse industrial

processes to examine various availability measures. The conclusion was,

"We have been unable to distinguish any inherent advantages afforded by any

of these measures relative to others and have been unable to observe any

intrinsic insights these measures afforded in comparing different processes.

As a result, the not beneficial symbol, \J , usuallv has been assigned.

The exceptions in Table 1 all involve the case of multiple output systems.

Total energy and cogeneration systems are examples of this class. In this

case, system output is partly thermal and partly mechanical or electrical.

Here, Second Law efficiency is useful, particularly for pricing the various outputs.

A strong argument has been presented for the need to use Second Law based

energy price schemes for steam and electricity from the same plant [15]

for customer equity. It is even suggested [14] that the inequities of

First Law based energy pricing schemes have been a principal factor in the

continuing unsuccessful attempts to make total energy plants viable in the

40
U.S.A. Thus, it is noted in column 3 of Table 1 that Second Law analyses

may offer some benefit in programs involving analyses of cogeneration and

similar energy systems. Thus, the symbol, | | , has been assigned.

41
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42
V. CONCLUSIONS AND RECOMMENDATIONS

This study has presented an analysis of the potential relevance of the use of

analytical tools based on the Second Law of thermodynamics to existing Federal

energy conservation programs. It is believed to have addressed the most

significant of potential applications and programs. However, this is a rapidly

developing field with new applications continually arising that could change

in detail the assessment provided herein. Despite this, it is not expected that

foreseeable developments will alter substantially the major conclusions of this

effort.

The principal conclusions of this study are the following:

General

Energy analysis techniques are commonly used in current engineering

practice. Both First Law and Second Law analysis techniques are used.

Second Law availability analysis is a useful tool, but only one of a

number of directly pertinent planning and analysis tools.

° Second Law analyses provide useful information and insights about

energy systems, i.e., where various energy losses of different types

may occur, but do not determine what to do about such losses. The

latter requires insight and invention.

In engineering analysis, the relative importance of Second Law analysis

varies considerably between applications.

Application

Planning :

Second Law analysis is highly pertinent to planning and research

priority setting and is already being used widely in this context.

43
Second Law analysis very often is appropriate for conceptual design

and assessment of new ideas.

Design ;

° Energy analysis is only one of a number of performance measures that

can be used in designing or evaluating energy conservation programs.

Second Law analysis can be useful in the detailed design of a system.

The more complex a system, the greater chance that it will be useful.

Monitoring :

In most cases, both First and Second Law analyses are not sufficient

to establish practical efficiency goals. Other technical factors such

as strength of materials, speeds of chemical reaction, needed rates of

production, corrosion and pollution control must be considered.

° There is little or no advantage to using Second Law analyses as

opposed to energy accounting in monitoring the performance of an

existing plant or system.

° In most cases examined, including those involving intra-industry

comparisons, existing monitoring and reporting measures appear

adequate. Exceptions involve complex processes with multiple energy

streams. Second Law analysis does not resolve difficulties in making

inter-industry comparisons; for example, comparing the efficiency

of aluminum with steel-making processes.

In cases where different energy streams (i.e. steam and electricity)

are being sold to the public, an availability based pricing structure

should be considered for customer equity purposes.

Needs :

° The potential applicability of Second Law analysis to the long-term

policy realm of optimal resource allocation remains to be established.

Research on this point is desirable.

44
Increased use of Second Law analysis, where appropriate, is dependent

upon development of better data, models, and further generalized

education and training.

-Appropriate intercomparisons require data for common reference

states to be developed and defined.

-Fundamental research and applications are needed to further develop

Second Law-based analytical tools and computer models. There will be

some need to expand the data base of thermodynamic properties of

materials widely used in commerce and industry.

-Specialized reference and course materials are required for education

and training in many engineering disciplines particularly on

(a) fundamentals of thermodynamics

(b) calculation of thermodynamic properties applicable to conditions

found in industrial processes

(c) estimation of thermodynamic properties, and

(d) application of availability analysis.

In the final analysis, Second Law analysis techniques must be viewed in the

context of a broader range of engineering tools and along with economic,

institutional, political, and social factors in making important decisions in

the energy conservation arena. The above conclusions establish no basis

for requiring Second Law efficiency analysis as a mandatory factor in controlling

any particular facet of government or industrial activities in energy conservation. This report has pointed out in a general way the potential relevance of

Second Law analyses. These are neither simple nor routinely used techniques. It

is characteristic of the state-of-the-art of development of these tools that the

relative benefit/cost of their use should be considered on a case-by-case basis.

45
VI . REFERENCES

[1]. Evans, Robert, A Proof that Essergy is the Only Consistent Measure of

Potential Work (for Chemical Systems). Ph.D Thesis, Dartmouth College,

1969.

[2], Haywood, R. W. , A Critical Review of the Theorems of Thermodynamic

Availability, with Concise Formulations—Part 1. Availability, J. Mech. Engrg. Science, Vol. 16, No. 3, 1974. Part 2. Irreversibility,

ibid, Vol. 16, No. 4, 1974.

[3], Keenan, Jos. H. , Availability and Irreversibility in Thermodynamics.

British J. of Appl. Physics, Vol. 2, p. 183-192, July 1951.

[4]. Gagglioli, Richard A., and Petit, Peter J., Use THE SECOND LAW, first,

CHEMTECH, Aug. 1977.

[5]. Keenan, J. H. , A Steam Chart for Second-Law Analysis—A Study of Thermodynamic

Availability in the Steam Power Plant. Steam Table Session, Annl. Mtg.

1931, American Society of Mechanical Engineers, N. Y. , March 1932.

[6]. Hall, E. H. , Hanna, W.T., et al, Evaluation of the Theoretical Potential

for Energy Conservation in Seven Basic Industries, Report to Federal

Energy Admin., July 1975, by Battelle, Columbus Laboratories. FEA/D-75/CE1.

(PB # PB-244 772).

[7]. Weinberg, Alvin M. , Reflections on the Energy Wars. American Scientist , Vol. 66, pp. 153-158, Mar. -Apr. 1978.

[8]. Gyftopoulos, Elias P., and Widmer, Thomas F. , Benefit-Cost of Energy

Conservation. Sympos. on Theoretical and Applied Thermodynamics; Am.

Chem. Soc, Sept. 1978, Miami, Fla.

[9]. Reistad, Gordon M. , and Gaggioli, Richard A., Available Energy Costing,

Sympos. on Theoretical and Applied Thermodynamics; Am. Chem. Soc, Sept. 1978,

Miami, Fla.

[10]. Evans, R.B., Thermoeconomic Isolation and Essergy Analysis, Workshop

Second Law of Thermodynamics, U.S. Dept. of Energy and Geo. Washington U.

Washington, D.C. August 1979.

[11]. Gyftopoulos, Elias P., Availability Analysis: The Combined Energy and

Entropy Balance. Sympos. on Theoretical and Applied Thermodynamics;

Am. Chem. Soc, Sept. 1978, Miami, Fla.

[12]. Hatsopoulos, G. N. , Gyftopoulos, E. P., Santi, R. W. , and Widner, T. F. , Capital investment to save energy. Harvard Business Review , Vol. 56, No. 2,

pp. 111-122, Mar. -Apr. 1978.

[13]. "Efficient Use of Energy", American Institute of Physics

Conference Proceedings No. 25, American Institute of Physics, New York,

Part I, Chapter 2.

[14]. Gaggioli, Richard A. and Wepfer, William J., Exergy Economics,

Presented at the DoE/George Washington University Workshop on the

Second Law, Washington, D.C, August 1979.

[15]. Kennan, J. H. , A Steam Chart for Second Law Analysis: A Study of

Thermodynamic Availability in the Steam Power Plant, ASME Transactions 1931.

46

ft U. S. GOVERNMENT PRINTING OFFICE : 1980 31 1-046/197 (265)
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1. PUBLICATION OR REPORT NO. NBS TN 1115

2. Gov't Accession No, 3. Recipient's Accession No.

4. TITLE AND SUBTITLE

A Report on the Relevance of the Second Law of Thermodynamics to Energy Conservation

5. Publication Date August 1980

$. Performing Organization Code Ml 7. AUTHOR(S)

David Didion, Dave Garvin, Jack Snell

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, DC 20234

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Final

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^} Document describes a computer program; SF-185, FIPS Software Summary, is attached.

16. ABSTRACT (A 200-word or less [actual summary of most significant information. If document includes a significant bibliography or

literature survey, mention it here.)

This is a study of the relevance to Federal energy conservation programs of

the use of the concept of energy efficiency as being the ratio of the minimum

available work necessary for accomplishing a given task to the available work

in the actual fuel used to accomplish this task. Included within the study is

a review of selected elements of thermodynamics and efficiency concepts, and

identification of the technology pertinent to energy conservation programs.

The study examines the potential benefits, if any, that would accrue from the

application of Second Law of Thermodynamics principles to these technologies.

Results indicate the positive value of the Second Law analytical techniques in

the planning and design stages of system development, and the rather limited

value of its use during the performance monitoring stage. Needs for advancing

the acceptance and use of the Second Law analytical techniques are identified.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name;

separated by semicolons) Availability analysis; energy, energy conservation; process efficiency,

Second Law of Thermodynamics; system efficiency

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