United States
Environmental Protection
Agency
Air and bnergy bngmeering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-95/066
May 1995
& EPA Project Summary
Alternative Technologies for
Refrigeration and
Air-Conditioning Applications
D.C. Gauger, H.N. Shapiro, and M.B. Pate
A study was conducted to assess
refrigeration technologies which are
alternatives to vapor compression re-
frigeration for use in five application
categories: domestic air conditioning,
commercial air conditioning, mobile air
conditioning, domestic refrigeration,
and commercial refrigeration. A funda-
mental criterion for the selection of the
alternative refrigeration technologies to
be assessed was that they be environ-
mentally safe.
The study was conducted in three
phases: a survey of U.S. patents, sys-
tem modeling, and a technology as-
sessment. Each refrigeration applica-
tion was defined by a set of thermal
source and sink temperatures. The U.S.
patent survey was conducted from 1918
to the present. A method was devel-
oped for classifying refrigeration tech-
nologies found during the survey.
Thermodynamic models were devel-
oped for the alternative refrigeration
cycles. A computer program was writ-
ten using these thermodynamic mod-
els to conduct a parametric study of
the cycle efficiency of the alternative
refrigeration technologies.
A method for assessing and compar-
ing the refrigeration technologies was
developed. Six technical assessment
criteria were identified: state-of-the-art,
complexity, size and weight, mainte-
nance, useful life, and efficiency.
It was concluded that the most prom-
ising alternative refrigeration technolo-
gies to vapor compression were ab-
sorption and solid sorption. From en-
vironmental and economic standpoints,
none of the alternative refrigeration
technologies were as attractive as
adapting vapor compression refrigera-
tion to non-chlorofluorocarbon refrig-
erants.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings of the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
The vapor compression cycle is pres-
ently the most widely used method of cool-
ing for domestic, commercial, and mobile
air conditioning and refrigeration. Vapor
compression technology has been devel-
oped to its present level of maturity by
using chlorofluorocarbon (CFC) and
hydrochlorofluorocarbon (HCFC) refriger-
ants. These refrigerants have excellent
thermodynamic properties for cooling
cycles. They are inexpensive, stable, non-
toxic, and (until 1974) were thought to be
environmentally safe. In 1974, a paper
was published hypothesizing the poten-
tial destruction of upper atmosphere
ozone due to the release of chlorofluo-
romethanes. This naturally occurring
ozone in the upper atmosphere shields
the Earth's surface from ultraviolet (UV)
radiation emitted from the sun. Depletion
of ozone results in the additional transmit-
tance of UV band electromagnetic radia-
tion to the Earth. Overexposure to UV
radiation has been linked to skin cancer
and other medical problems in humans
and other animals.
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Refrigeration equipment utilizing the va-
por compression cycle is capable of cool-
ing performance which has been consid-
ered acceptable in areas where a ready
supply of low-cost electricity is available.
Vapor compression machinery also has
the advantages of low first cost and high
reliability, compared to other existing re-
frigeration methods. This is due to its high
level of development.
Recently, two global problems have
caused the engineering community to ex-
plore alternatives to vapor compression
refrigeration:
• Global environmental changes brought
about by ozone depletion in the up-
per atmosphere and global warming.
• The continuing need and an increased
desire for refrigeration in parts of the
world where electricity is not readily
available or economical.
Global warming is caused by the re-
lease of greenhouse gases into the atmo-
sphere. Of all carbon dioxide (CO2) emis-
sions, 75% are from fossil fuel combus-
tion. The release of HCFC and CFC re-
frigerants also contributes to the green-
house effect. Some of these gases have
a longer atmospheric lifetime and a much
higher global warming potential (GWP)
than CO2.
Refrigeration systems can make two
potential contributions to the greenhouse
effect: (1) The direct GWP contribution
results from the release of refrigerants
with a high GWP into the atmosphere,
and (2) The indirect GWP results from the
creation of CO2 during the combustion of
fossil fuels to produce work to drive me-
chanical systems or to convert the fossil
fuel energy to thermal energy to drive
heat-driven systems.
Project Objective
The objective of this project was to iden-
tify, analyze, and assess refrigeration tech-
nologies which could serve as alterna-
tives to vapor compression refrigeration.
Project Description
This project was conducted in three
phases: (1) Identification and classifica-
tion of refrigeration technologies, (2) Ther-
modynamic analysis of some of the more
promising cycles, and (3) Technical as-
sessment of the alternative technologies.
The U.S. patents and the technical lit-
erature were used as sources for identify-
ing the different means of refrigeration.
Once a representative group of refrigera-
tion method concepts had been identified,
a method of classifying them for thermo-
dynamic analysis was developed.
The reversed Brayton, reversed Stirling,
magnetic, thermoacoustic, thermoelectric,
and pulse-tube refrigeration thermody-
namic cycles were analyzed in detail. A
computer model was developed for each
of these cycles, and computer subrou-
tines were written for each model. An in-
teractive program was written to allow us-
ers to choose cycles they wished to con-
sider and to vary specific parameters on a
case-by-case basis. The program was
used to provide an estimate of both the
coefficient of performance (COP) and the
thermodynamic (Second Law) efficiency
for the cycles.
The final phase of this project was a
technical assessment of refrigeration con-
cepts. Criteria which were common to all
refrigeration systems were identified.
These criteria were rated on a scale of 1
(very low) to 5 (very high) for each tech-
nology and application category. A com-
puter program was written to rank the
refrigeration technologies from best to
worst for each application area.
Discussion
Identification of Refrigeration
Technologies
Phase 1 of this study involved identify-
ing refrigeration technologies for the pur-
poses of further analysis and technical
assessment. U.S. patents and literature
were surveyed to identify refrigeration
methods known to the technical commu-
nity from 1918 to the present. The litera-
ture survey was conducted in parallel with
the patent survey.
The initial search for refrigeration pat-
ents was conducted manually for patents
granted between 1918 and 1950. A list
was compiled of U.S. patent classes and
subclasses related to refrigeration and air
conditioning. The patent classes and sub-
classes were used to locate patent num-
bers in the U.S. Patent Index for each
calendar year being surveyed. The patent
number was used to locate the abstract
for the patent abstract in the Official Ga-
zette of the United States Patent Office.
Databases are available which contain
a complete listing of all U.S. patent titles
and abstracts granted from 1950 to the
present. The patents relating to a particu-
lar technology can be located in the data-
base by supplying the computer with a list
of the appropriate class and subclass num-
bers. Class and subclass numbers which
had been identified during the manual
patent search were used to locate refrig-
eration patent abstracts within the data-
base. The abstracts were reviewed to de-
termine the nature of the patents. Patents
were accepted or rejected based on ab-
stract information.
Approximately 2140 patent titles and
abstracts were surveyed. Approximately
800 of these were from 1918 to 1950, and
the remainder were for the post-1950 pe-
riod. Since many of the refrigeration con-
cepts found during the patent survey were
similar, patents that were representative
of those found in the survey were se-
lected to avoid redundancy.
Once a representative sample of refrig-
eration technologies was found, they were
classified into categories which had simi-
lar thermodynamic cycles.
Classification of Refrigeration
Technologies and Applications
Two classification systems were devel-
oped for this study: the first to classify
refrigeration technologies which had been
identified during the U.S. patent and lit-
erature survey, and the second to define
the types of applications in which the re-
frigeration technologies would be used with
a set of thermodynamic source and sink
temperatures.
During the review of the U.S. patents
found during the patent survey, it was
determined that the technologies fell into
groups that could be defined by the ther-
modynamic cycle used for refrigeration.
These cycles were used to categorize the
refrigeration technologies for the thermo-
dynamic analysis and technical assess-
ment phases of the project (Phases 2 and
3).
The refrigeration technology categories
considered during this project were ab-
sorption, adsorption, pulse-tube and
thermoacoustic, magnetic, reversed
Brayton, reversed Stirling, thermoelectric,
and vapor compression.
The temperatures of the thermodynamic
source (from which heat is accepted) and
sink (to which heat is rejected) were es-
tablished for each application. A search of
refrigeration industry standards and other
technical literature was conducted to de-
termine a practical set of source and sink
temperatures for each application area.
Based upon this survey, a set of source
and sink temperatures was established
for each of the five application categories.
Table 1 summarizes the five refrigeration
categories and the source and sink tem-
peratures used for comparing refrigera-
tion technologies in each category. Four
source temperatures were used for com-
mercial refrigeration. These source tem-
peratures are for Refrigeration Groups I
through IV in the Air-Conditioning and Re-
frigeration Institute (ARI) Standard 420-
1977, Standard for Unit Coolers for Re-
frigeration.
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Table 1. Thermal Source and Sink Temperatures for Five Refrigeration Categories
Refrigeration Category
Source Temperature (°C)
Sink Temperature (°C)
Domestic Air Conditioning
Commercial Air Conditioning
Mobile Air Conditioning
Domestic Refrigeration
Commercial Refrigeration:
ARI Group 1
ARI Group II
ARI Group III
ARI Group IV
25.0
25.0
25.0
-18.0
2.8
1.7
-2.2
-23.3
35.0
35.0
35.0
35.0
35.0
35.0
35.0
35.0
Refrigeration Technology
Modeling
An interactive computer program was
written in FORTRAN to analyze the re-
generative and non-regenerative reversed
Brayton, reversed Stirling, thermoelectric,
pulse-tube, thermoacoustic, and magnetic
refrigeration cycles. The program calcu-
lates the COP and cycle efficiency for
source temperatures from -24 to 28°C and
a fixed sink temperature of 35°C (or
changed to another value by the user).
Thermodynamic property routines were
developed for air, helium, and gadolinium
(a magnetic solid used as the working
material in magnetic refrigerators).
Technical Assessment of
Refrigeration Technologies
The assessment of refrigeration tech-
nologies involved the evaluation of two
fundamental criteria common to all refrig-
eration and air-conditioning applications:
environmental acceptability and system
cost.
Environmental Acceptability
Environmental acceptability consider-
ations include:
1 Ozone depletion potential (OOP) of
the working material
2 Global warming potential of the re-
frigeration technology.
3 Toxicity of the working material.
4 Flammability of the working material.
5 Noise generated by the refrigeration
system hardware.
Only refrigeration technologies capable
of using working materials which are not
ozone depleting were considered in this
study.
Cost-Related Technology
Assessment
Cost-related technology assessment
considerations include:
1 State-of-the-art. Some alternative re-
frigeration technologies are more ma-
ture than others. Research and de-
velopment were considered in two
broad areas: basic technology devel-
opment and system development. For
this study, a basic technology was
defined as one which is not unique to
refrigeration and would have many
potential applications in other areas.
Generally, improving a basic technol-
ogy is extremely expensive and there
are no guarantees of success. Sys-
tem development refers to refining a
refrigeration technology until it is mar-
ket-ready.
2 Size and weight. Size and weight con-
siderations are important for many
refrigeration applications. Larger,
heavier systems with the same cool-
ing capacity as smaller, lighter sys-
tems contain more raw material, which
increases the capital costs of the sys-
tem. Increased size and weight cre-
ate higher capital costs for structures
in which they are used or reduce the
usable space within the structures,
this is particularly true in transporta-
tion applications.
3 System complexity. Assessment of
system complexity includes consider-
ations regarding the number and sim-
plicity of subsystems, number of mov-
ing parts, and uncommon materials
used in a refrigeration system. The
difficulty in manufacturing the system,
including likely manufacturing tech-
niques and precision, and the cost of
the working material and controls were
also considered. These issues relate
directly to the capital cost of the re-
frigeration system.
4 Useful life. Useful life of the refrigera-
tion system is defined as the length
of time during which the major com-
ponents remain functional while oper-
ating with a nominal duty cycle and
receiving normal maintenance. For ex-
ample, the useful life of a domestic
central air conditioner would be the
life of the compressor, the major sys-
tem component expected to have the
shortest useful life.
5 Maintenance. Maintenance cost con-
siderations include the amount of re-
pair and preventive maintenance re-
quired, skill level of maintenance per-
sonnel, portion of time an operator
would need to attend to the system,
likelihood of component failure, and
recurring costs (such as recharging a
refrigeration system with working ma-
terial as needed over the life of the
system) for normal system operation.
6 Efficiency. Two factors are affected
by the efficiency of the system: the
cost to operate the refrigeration sys-
tem and the indirect GWP. It was
assumed for this study that all heat or
electricity required to operate the re-
frigeration systems originated from the
combustion of fossil fuels. The effi-
ciency criterion rating is based on the
cycle efficiency (fraction of the Carnot
COP) at which the refrigeration sys-
tem would operate for a particular
application. This rating is based on
what is technically feasible in the
1990s. As technology advances, the
cycle efficiency of some less mature
technologies may improve. Therefore,
some of these technologies may be-
come more attractive in the future.
Rating Factors
Numerical rating factors were assigned
to assess the individual technical assess-
ment criteria for each refrigeration tech-
nology. Each rating factor is the
investigator's best estimate, on a scale of
1 (very low) to 5 (very high), of the merit
of a particular technology for a technical
assessment criterion. A rating of 5 for a
criterion would indicate that it is particu-
larly attractive for a technology. A rating
of 1 would indicate that it is very unattrac-
tive with respect to the criterion being
considered. Table 2 summarizes the lin-
guistic interpretation of the extreme rat-
ings (1 and 5) for each criterion. The rat-
ing numbers for the efficiency criteria are
listed in Table 3.
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Table 2. Literal Definition of the Numerical Ratings for Technology Assessment Criteria
Tech. Assessment Criterion Rating of 1 Rating of 5
State-of-the-Art
Complexity
Size and Weight
Maintenance
Use Life
Efficiency
Theory Only
Very Complex
High
High
Short
0.0 to 0.12
Fully Matured
Very Simple
Low
Low
Long
Above 0.50
Table 3. Numerical Definition of the Efficiency
Criteria Rating Scale
Efficiency
Rating No.
Cycle Efficiency
Range
0.000 < 0.125
> 0.125 < 0.250
> 0.250 < 0.375
> 0.357 < 0.500
>0.50
Technical Assessment Ratings
for the Refrigeration
Technologies
To rate suitability of refrigeration tech-
nologies for domestic, commercial, and
mobile air conditioning and domestic and
commercial refrigeration, an algebraic ex-
pression was developed:
Q = £ wfi x i
i = A
(1)
where
Q = the overall technology rating, di
mensionless
wf. = the technical assessment weight-
ing factor for each criterion, frac-
tion
A, B,...,F = the individual technical as-
sessment criterion rating for
each technology.
The individual weighting factors, wf: ,
are chosen so that their sum equals 1;
i.e.,
wfi= 1.0
(2)
Weighting factors were developed for
each application to rank the relative im-
portance of each of the six criteria for
each type of application.
A computer program using Equation (1)
was developed to calculate the overall
technology rating, Q, and rank the refrig-
eration technologies from high to low
based on the value of Q for each technol-
ogy.
Results of Technology
Assessment and Summary of
Conclusions
The alternative refrigeration technolo-
gies considered during this project were
rated using the computer program apply-
ing Equation (1), the numerical technol-
ogy assessment rating data presented for
each technology, and the weighting fac-
tors. The data in the computer program
are a numerical summary of the patent
search, numerical modeling, and technol-
ogy assessment information developed
during this project.
Technology Assessment
Criteria Weighting Factors
Technology assessment criteria weight-
ing factors were developed for each of the
five applications areas. The value of each
of these weighting factors was chosen to
reflect the relative importance of the six
criteria (state-of-the-art, complexity, size
and weight, maintenance, useful life, and
efficiency) for each application (Table 4).
Results
Domestic Refrigeration
Table 5 contains the technology ratings
for domestic refrigeration. The technology
ratings are distributed into four groups:
1 High (Rating of 4.60) Vapor com-
pression was the most suitable tech-
nology for domestic air conditioning.
2 Medium (Rating of 3.70 to 3.25) Ab-
sorption received a medium rating.
Absorption systems are characterized
by a high cycle efficiency; however,
the absorption refrigeration technol-
ogy was penalized for use in domes-
tic refrigeration because of additional
complexity increased size, increased
maintenance, and shorter useful life
than vapor compression systems. The
hardware for the reversed Stirling re-
frigeration cycle is compact. However,
additional heat transfer loops are re-
quired so that the heat exchangers
used in the reversed Stirling system
can be in communication with the ther-
mal source and sink. These additional
heat transfer loops add to the com-
plexity (and capital cost) of the refrig-
erator and reduce the cycle efficiency
which is already low when compared
to the cycle efficiency of domestic
refrigeration systems using vapor
compression.
3 Low (Rating of 3.05 to 2.60) The
solid sorption, reversed Brayton, and
pulse-tube/thermoacoustic technolo-
gies received low ratings. Presently,
solid sorption refrigeration and the
pulse tube/thermoacoustic technolo-
gies are immature. Therefore, the cost
to develop these refrigeration tech-
nologies into marketable domestic re-
frigeration systems probably will be
high.
4 Very Low (Rating of 2.20 to 1.95)
Two technologies (thermoelectric re-
frigeration and magnetic refrigeration)
received the lowest rating for domes-
tic refrigeration. Both technologies
have very low cycle efficiencies. An-
other limiting feature of thermoelec-
tric refrigeration is the small amount
of tellurium-based material which is
available for producing the semicon-
ductors used in thermoelectric cool-
ing modules. Furthermore, the maxi-
mum temperature lift for a single stage
of thermoelectric refrigeration is ap-
proximately 22°C which is insufficient
for refrigeration, making it necessary
to cascade thermoelectric systems in
order to achieve the required source
temperatures. This would further re-
duce the already low cycle efficiency.
Magnetic refrigeration technology is
immature. The principal technical area
which must be developed to achieve
higher cycle efficiencies is regenera-
tive heat transfer with a very high
effectiveness.
Domestic Air Conditioning
Table 6 contains the refrigeration tech-
nology ratings for domestic air condition-
ing. Four rating groups were observed for
domestic air conditioning.
1 High (Rating of 4.80) Vapor com-
pression received the highest rating
for use in domestic air conditioning.
2 Medium (Rating of 3.80) Absorption
received a medium rating. Absorption
systems used in air conditioning are
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Table 4. Technology Assessment Criteria Weighting Factors by Refrigeration Application
Assessment
Criterion
State-of-the-Art
Complexity
Size and Weight
Maintenance
Useful Life
Efficiency
Domestic
AC
0.20
0.15
0.05
0.15
0.15
0.30
Commercial
AC
0.20
0.10
0.05
0.15
0.20
0.30
Mobile
AC
0.15
0.20
0.30
0.20
0.05
0.10
Domestic
Refrif.
0.20
0.20
0.10
0.10
0.15
0.25
Commercial
Refrig.
0.20
0.10
0.05
0.15
0.20
0.30
Table 5. Ranking of Domes/to Refrigeration Technologies from Most to Least Favored
Ranking Refrigeration Technology
Rating
1
2
3
4
5
6
7
8
Vapor Compression
Absorption
Reversed Stirling
Solid Sorption
Reversed Brayton
Pulse-Tube/Thermoacoustic
Thermoelectric
Magnetic Refrigeration
4.60
3.70
3.25
3.05
2.65
2.60
2.20
1.95
Table 6. Ranking of Domestic Air-Conditioning Technologies from Most to Least Favored
Ranking Refrigeration Technology Rating
Vapor Compression
Absorption
Pulse-Tube/Thermoacoustic
Reversed Stirling
Solid Sorption
Reversed Brayton
Thermoelectric
Magnetic Refrigeration
4.80
3.80
2.95
2.90
2.80
2.35
2.05
1.95
characterized by high cycle efficien-
cies and long useful lifetimes in air
conditioning. However, the absorption
refrigeration technology rating was
penalized for domestic air condition-
ing because of additional complexity,
increased size, and increased main-
tenance.
3 Low (Rating of 2.95 to 2.80) The
pulse-tube/thermoacoustic, reversed
Stirling, and solid sorption technolo-
gies received a low rating for domes-
tic air conditioning. The pulse-tube/
thermoacoustic technology is imma-
ture, and has low cycle efficiencies at
source temperatures of 20°C and
above. The most promising technol-
ogy in this group for domestic air con-
ditioning is solid sorption. The cycle
efficiency of solid sorption systems
should be high in the temperature lift
range used for air conditioning.
4 Very Low (Rating of 2.35 to 1.95)
The reversed Brayton, thermoelectric
refrigeration, and magnetic refrigera-
tion were rated as having very low
suitability for domestic air condition-
ing. The principal reasons for the very
low rating of the reversed Brayton
technology are: a large physical size
per ton of cooling effect of the hard-
ware (compressor, expander, and
ducts), high complexity (and there-
fore high capital cost) of the turbine
and expander, and a low cycle effi-
ciency.
Mobile Air Conditioning
Table 7 contains the refrigeration tech-
nology ratings for mobile air conditioning.
The technologies are ranked from the most
to least favored. The size and weight cri-
teria were given a high relative impor-
tance and the efficiency criterion weight-
ing was reduced for mobile air condition-
ing (Table 3). The useful life of mobile air
conditioning systems is also shorter than
for the other four application areas (a 10-
year average life was used as an esti-
mated life of mobile air conditioners for
this study). The refrigeration technology
ratings in Table 7 were considered to be
in four groups of suitability for mobile air
conditioning:
1 High (Rating of 4.30) Vapor com-
pression was rated highest. The pri-
mary reasons for rating were a rela-
tively low weight and small hardware
size per ton of cooling effect in mo-
bile cooling. Mobile vapor compres-
sion cooling systems also require little
maintenance and are relatively inex-
pensive to produce.
2 Medium (Rating of 3.25) The re-
versed Stirling technology was rated
as medium for mobile cooling. The
important attributes of reversed Stirling
technology for mobile cooling are com-
pactness and low maintenance of the
refrigeration system. The low cycle
efficiency, particularly at higher source
temperatures, was the principal rea-
son that reversed Stirling did not re-
ceive a high rating for mobile cooling.
3 Low (Rating of 2.65 to 2.30) The
pulse-tube/thermoacoustic, solid sorp-
tion, reversed Brayton, and absorp-
tion technologies received low ratings
for mobile air conditioning. The pri-
mary reasons for the low rating was
the large size and high weight per ton
of cooling capacity as compared to
vapor compression systems.
4 Very Low (Rating below 2.15) Ther-
moelectric cooling and magnetic re-
frigeration were rated lowest for mo-
bile air conditioning. The reasons for
the very low rating were a low cycle
efficiency and the need for a large
electrical generation system aboard
the vehicle for both technologies.
Commercial Air Conditioning
Table 8 contains the refrigeration tech-
nology ratings for commercial air condi-
tioning. The suitability ratings are distrib-
uted into three groups:
1 High (Rating of 4.85 to 4.45) Vapor
compression was the most suitable
technology for commercial air condi-
tioning. Absorption was also rated
high. Since commercial air-condition-
ing systems generally have a larger
cooling capacity and longer life ex-
pectancy than domestic systems, they
were not penalized as heavily for ad-
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Table 7. Ranking of Mobile Air-Conditioning Technologies from Most to Least Favored
Rankng Refrigeration Technology Rating
Vapor Compression
Reversed Stirling
Pulse-Tube/Thermoacoustic
Solid Sorption
Reversed Brayton
Absorption
Thermoelectric
Magnetic Refrigeration
4.30
3.25
2.65
2.55
2.50
2.30
2.15
1.25
Table 8. Ranking of Commercial Air-Conditioning Technologies from Most to Least Favored
Ranking Refrigeration Technology Rating
1
2
3
4
5
6
7
8
Vapor Compression
Absorption
Pulse-Tube/Thermoacoustic
Solid Sorption
Reversed Stirling
Reversed Brayton
Magnetic Refrigeration
Thermoelectric
4.85
4.45
3.10
2.80
2.75
2.35
2.05
1.95
ditional complexity and increased
maintenance. Emphasis was placed
on the efficiency of commercial air
conditioning systems.
2 Medium (Rating of 3.10 to 2.75) The
pulse-tube/thermoacoustic, solid sorp-
tion, reversed Stirling, and reversed
Brayton technologies were in the me-
dium suitability rating group. These
gas cycle refrigeration technologies
have low cycle efficiencies at the
higher source temperatures used in
air conditioning. Solid sorption refrig-
eration technology has the highest
cycle efficiency in the medium group.
3 Low (Rating of 2.35 to 1.95) Ther-
moelectric and magnetic refrigeration
have very low cycle efficiencies. Pres-
ently, the amount of tellurium-based
material for semiconductors is limited.
Therefore, the first cost of thermo-
electric systems will be high. Mag-
netic refrigeration technology is im-
mature. Highly effective regenerative
heat transfer is the principal technical
area which must be developed to im-
prove the cycle efficiency of magnetic
air conditioning.
Commercial Refrigeration
Table 9 contains the refrigeration tech-
nology ratings for commercial refrigera-
tion. The suitability ratings are distributed
into four groups:
1 High (Rating of 4.70) Vapor com-
pression received the highest rating
for commercial refrigeration.
2 Medium (Rating of 3.80) Absorption
refrigeration was rated next highest.
Although absorption refrigeration is
capable of high cycle efficiencies, it is
not as attractive as vapor compres-
sion from the perspective of complex-
ity, size and weight, and maintenance
(particularly for supermarkets).
3 Low (Rating of 3.10 to 2.80) The
gas cycle refrigeration technologies
(reversed Stirling, reversed Brayton,
and pulse-tube/thermoacoustic refrig-
eration) were in the low suitability rat-
ing group. The cycle efficiencies of
refrigeration systems using these tech-
nologies increase with decreasing
source temperature. All of these tech-
nologies are best suited for cryogenic
and low-temperature industrial refrig-
eration.
4 Very Low (Rating of 2.05) Thermo-
electric and magnetic refrigeration
were in the lowest suitability rating
group for commercial refrigeration .
Both of these technologies have very
low cycle efficiencies.
Conclusions
• Vapor compression refrigeration us-
ing non-CFC refrigerants is the most
desirable technology of those consid-
ered for use in the five application
areas considered in this study (do-
mestic, commercial, and mobile air
conditioning; and domestic and com-
mercial refrigeration). This conclusion
is supported by the first place ranking
that vapor compression received in
the technical assessment of each
technology (Tables 5 through 9).
• Absorption refrigeration is attractive
for commercial refrigeration and air
conditioning. If the complexity and
maintenance levels can be reduced,
it could also be attractive for domes-
tic applications.
• Solid sorption refrigeration technology
is immature. This technology may
have some advantages over absorp-
tion systems using liquid absorbents,
particularly for domestic refrigeration
and air conditioning. Canister sorp-
tion and heat transfer efficiencies must
be improved above present levels.
Complete systems must be developed
to demonstrate a reasonable useful
life and acceptable maintenance lev-
els. Solid sorption is the most promis-
ing new refrigeration technology in
terms of technical feasibility, particu-
larly for air conditioning and refrigera-
tion, where batch processes can be
used.
• The highest cycle efficiencies for the
gas cycle refrigeration technologies
(reversed Stirling, reversed Brayton,
and pulse-tube/thermoacoustic) occur
Table 9. Ranking of Commercial Refrigeration Technologies from Most to Least Favored
Ranking Refrigeration Technology Rating
1
2
3
4
5
6
7
8
Vapor Compression
Absorption
Reversed Stirling
Solid Sorption
Reversed Brayton
Pulse-Tube/Thermoacoustic
Magnetic Refrigeration
Thermoelectric
4.70
3.80
3.15
3.10
3.00
2.80
2.05
2.05
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at source temperatures below the low- • The thermoelectric and magnetic re-
est temperature considered in this frigeration technologies are impracti-
study (-24°C). These technologies are cal for normal refrigeration and air
best suited to low temperature refrig- conditioning at this time.
eration.
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D. Gauger, H. Shapiro, and M. Pate are with Iowa State University, Ames, IA 50011.
Theodore G. Brna is the EPA Project Officer (see below).
The complete report, entitled "Alternative Technologies for Refrigeration and Air-
Conditioning Applications," (Order No. PB95-224531; Cost $44.50, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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EPA
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