United States
Environmental Protection
Agency
Office of Atmospheric
and Indoor Air
Programs
EPA-430-R-93-008
June 1993
vvEPA
Multiple Pathways to
Super-Efficient Refrigerators
Recycled/Recyclable
Printed on paper that contains
at least 50% recycled fiber
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Multiple Pathways to
Super-Efficient Refrigerators
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Acknowledgments
ACKNOWLEDGMENTS
This report has been compiled by an EPA-assembled technical team led by Jean
Lupinacci and Alan Fine with technical assistance from Dick Merriam and con-
sisting of the following researchers in government, academia, and the private
sector:
Richard Merriam, Arthur D. Little, Inc.
Taghi Alereza, ADM
Jane Bare, EPA
Ray Bohman, Consultant
John Dieckman, Arthur D. Little, Inc.
John Hoffman, EPA
William Kopko, EPA
Michael L'Ecuyer, EPA
Reinhard Radermacher, University of Maryland
James Waldron
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Multiple Pathways to Super-Efficient Refrigerators
CONTENTS
Acknowledgments
Major Findings iii
Part 1: Results 1
1.1 The Impetus for Change 1
1.2 Analytical Approach 6
1.3 Incremental Cost Estimates 24
1.4 Pathways to Achieving Energy-Efficient Refrigerators 31
1.5 Attributes for Evaluating Technologies 58
1.6 Key Uncertainties and Research Agenda 61
1.7 How Reliable Are the Results Reported in This Document? 62
1.8 Conclusions 62
Part 2: Supporting Documentation 67
2.1 Technical Options Support Sheets 67
2.2 EPA Refrigerator Analysis Program (ERA) 108
2.3 Market Analysis of Double-Insulated Refrigerators 119
2.4 The Sears Energy Story 122
Appendix A 143
Appendix B 150
References 159
Notice
Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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Multiple Pathways to Super-Efficient Refrigerators
MAJOR FINDINGS v
I. There are,many5 pathways or combinations p'f technologies available *
- >/i for producing super-efficient refrigerator/freezers (R/Fs);> ~k * / !l , *
Modifications can be made to the hermetic system, to the
;; , cabinet or to auxiliary systems to increase the efficiency of/ '*\
i?*: £* refrigerators sufficiently to improve performance to inbre rc
|| :^ than 30 percent better than 1993 DOE standards. - "'-'
^ Z^Thereikre many, pathways, using different technologies, to achieve 4 ,
1; *'f ''superefficiency"; so lacker" success in implementing a "'new" technol-:,'-..
ty- ASJ S * ^. ! .. *' ff~- ^ "V -'" \ ' .._.>< %§j8&, * f v "fr &§ *J "% "'J-^ t ^ " ' ' ff '
'"-', <>-i f °SJ, ^^ ^°^ 'l?^?^^1* ^BS^I^?111 P^&fc*8 H^X^^PS deyelbped^, * |r*
S IS;; 3001 to 400-kilowatt-hour ,{kWh) energy consumption fpr an 18-$?, R/F >ff ;
! rt can-be developed and Manufactured withbiil,major technological *
; -'breakthroughs. ,-,,"- : ,- ; - : -,-.-,' r - .- ^ ; -< , -
4. It may be possible to prodtice a super^efficient R/F with energy cori-
'" sun>ption*aii low as 200 kWh/year, However, this would require the :
^'';'§."'^^^^fec^fl«e|t£o%^^ar3[ing!s~up^-emderitl;elri|eratoirs is^not' ,;^,,;
l^ ^ ''to:'chio6se tie^pafh with" the'highest value' an^dVthe, Jea'st:am6unFof,' \
4$p * Tiie^ughest-value.cost path will depend q^mdivicjual man- 4i,,,., ,x
tf ^ irfac^rers^ product'Hnes/s^cnire/and;iec|ra
;§1 Itis possible^develop"a <3FC-free, supe
- ..-' -* /SfriracaiMy?grea'tei(.efficiency-gains are*possible'by usiog-^ ~-,^i>
I, &/'wy^i|i^ ai ti Sv ;#
^',*il'"!;-1!T^.i^i'_^.;twi» '-!"- '" ' , '>* *" .:"* - c--
..jg, ^J^pren|t:ycie. _ v^ ,,,,f , f.. t,
^f'-.'i * fZyfi't''i'-. t !-" ''''.'^"""ftf ";*" :J- '"*' ' ^'' ' s ' * *'' ''
,7. Commercializatiori of^super-efficient refrigeratorsvvyifl,require dedicat-
^ ed efforts; to assemble technologies and,perfect;technblpgical improve- '
C'\ 'i?ientsrNo "exotic" breakthfbughs are needed. f.
1U
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Part 1. Results
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Multiple Pathways to Super-Efficient Refrigerators
PART 1. RESULTS
1.1 The Impetus for Change
Energy efficiency and environmental protection are rapidly becoming more
important in making investment decisions in the United States and around the
world. Concern with such global environmental issues as global warming and
ozone depletion has prompted the need for technological advancement.
Refrigerators and freezers (R/Fs) currently consume roughly 7 percent of the
total residential demand for energy. Consequently, they indirectly cause emis-
sion of carbon dioxide (CO2). They also use chlorofluorocarbons (CFCs), chemi-
cals linked to global warming and ozone depletion. The need to increase efficien-
cy and eliminate CFCs creates an opportunity and challenge for manufacturers
ofR/Fs.
The impetus to advance current R/F technology is driven by various factors:
Montreal Protocol to Eliminate CFCs
Regulations under the Montreal Protocol and the Clean Air
Act of 1990 to eliminate CFCs at the end of 1995 necessitate
change in the current R/F design. This creates an opportuni-
ty to make significant advances in technology and to consid-
er new cycles and systems (Exhibit 1.1).
Rio Treaty on Climate Change
The world conference in June 1992 in Brazil moved the
nations of the world forward in addressing the problems of
increasing greenhouse gas emissions. The Rio Treaty on
Climate Change and President Clinton's announcement to
commit the United States to stabilize greenhouse gas emis-
sions strengthen the need for energy efficiency and use of
low-global-warming chemicals (Exhibit 1.2).
"Golden Carrot " Refrigerator Program
The utility-pooled $30 million to request bids for delivery of
energy-efficient refrigerators in 1996 creates an opportunity
for the profitable development of super-efficient products, m
June 1993, one manufacturer will win the bid to deliver super-
efficient refrigerators to the service territory of 25 utilities.
Utility Integrated Resource Planning
Additional utility programs for demand-side management,
including rebates, trade-in programs, and other energy-sav-
ing programs, create a market and incentive for energy-effi-
cient products.
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Part 1. Results
EXHIBIT 1.1
Montreal Protocol Will Eliminate CFCs
1974
1976
1978
1985
1987
1990
1992
Drs. Molina and Rowland theorize that chlorofluorocarbons
deplete the stratospheric ozone layer, increasing ultraviolet-B
(UV-B) radiation, which could increase skin cancers and
cataracts, suppress the human immune system, harm crops and
natural ecosystems, and damage plastics.
First National Academy of Sciences report on ozone depletion is
published.
United States bans the use of CFCs in nonessential aerosol prod-
ucts due to growing public concern of ozone depletion.
Vienna Convention on the Ozone Layer is adopted.
British scientists publish data on the "ozone hole" over
Antarctica.
Scientists discover a 95 percent ozone loss over Antarctica.
The Montreal Protocol on Substances That Deplete the Ozone
Layer is signed by 23 nations. CFC production is reduced by 50
percent by 1998.
Scientists measure an average 3 percent ozone depletion in
northern mid-latitudes.
London Amendments to the Montreal Protocol call for a full
phase-out of CFCs and halons by the year 2000. China and India
pledge to join the Protocol as mechanisms to transfer technology
and financial resources are established.
The Clean Air Act Amendments (CAA) of 1990 require the
phase-out of CFCs, halons, and carbon tetrachloride by 2000,
methyl chloroform by 2002, and HCFCs by 2030. The amend-
ments also contain provisions for National Recycling and
Emissions Reduction, Labeling, and Safe Alternatives Policy.
Over 70 countries representing 90 percent of the world's CFC
production ratified the London Amendments to the Montreal
Protocol.
Parties meet in November 1992 in Copenhagen to strengthen the
Protocol. CFCs will be phased out January 1, 1996, and HCFCs
will be phased out in stages: 995 percent by 2020 and 100 per-
cent by 2030.
Satellite data confirm global ozone depletion on average of 5
percent. Scientists report increased CIO levels over populated
Northern Hemisphere.
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.2
Events Building Toward a World Conference on Climate
June 1988 At the Toronto Conference on the Changing Atmosphere,
46 countries were represented. Recommendations includ-
ed a comprehensive global convention, technology trans-
fer from industrialized countries to developing countries,
and a reduction in CO2 emissions by 20 percent of 1988
levels by the year 2005.
November 1988 The Intergovernmental Panel on Climate Change (IPCQ
was created under the auspices of the United Nations
Environment Programme (UNEP) and the World
Meteorological Organization (WMO). It is divided into
three working groups: a science working group, a work-
ing group studying the social and environmental impacts
of climate change, and a response strategies working
group.
March 1989 Representing 24 countries, the Declaration of Hague calls
for establishing an institutional authority charged with
"combating any further global wanning of the atmos-
phere."
May 1989 The Governing Council of UNEP requested the heads of
UNEP and WMO to begin preparation for negotiations on
a framework convention on climate.
November 1989 At the Noordwjik Ministerial Conference on Atmospheric
Pollution and Climate Change, 68 environment ministers
endorsed the ambitious goal of reversing deforestation to
make forests a sink of carbon by early in the next century.
December 1991 Japan, the European community, the Nordic nations,
Australia, and New Zealand all call for stabilizing CO2
emissions during negotiations.
June 1992 The United Nations (UN) Conference on Environment
and Development (Earth Summit) was held in Brazil. A
Treaty on Climate Change aimed at stabilizing green-
house gas emissions in 2000 was signed by the United
States.
April 1993 President Clinton announced in an Earth Day speech to
commit the United States to stabilize greenhouse gases by
2000. The President committed the U.S. Government to
develop an Action Plan on how to stabilize greenhouse
gases by August 1993.
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Part I. Results
Department of Energy Appliance Efficiency Standards
Revisions in the energy-efficiency standards for 1998 will cre-
ate a climate for development of more efficient technologies
(Exhibit 1.3).
Customer Awareness of Environmental Issues
Consumers are becoming increasingly aware of environmen-
tal issues and are demanding more environmentally superior
products. Acting upon this consumer awareness, Sears
recently introduced a successful marketing campaign to train
its sales force and advertise the "Energy Story" when selling
the more efficient 1993 refrigerator models (see Section 2.4).
These converging factors will continue to intensify and drive technology
toward CFC-free, super-efficient R/Fs.
This report analyzes the existing, emerging, and long-term technologies that
can be used to achieve energy-efficient, environmentally superior refrigerators.
By combining and evaluating each of the technologies, this analysis shows that
there are multiple pathways and large benefits for achieving efficient refrigera-
tors. For this reason, the failure of any single option or pathway does not elimi-
nate the potential to actually achieve cost-effective superefficiency.
Each refrigerator manufacturer will decide on the most cost-effective set of
options based on its current product's energy efficiency, design, and cost structure.
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.3
Evolution of Energy- Efficiency Standards
1975
1976
1978
1979
1987
1990
1993
1998
Energy Policy and Conservation Act - Federal Trade
Commission required to consider efficiency labeling for 13 cate-
gories of home appliances.
California establishes energy-use restrictions on refrigerators.
Congress orders DOE to establish energy-efficiency standards
stricter than the California standards.
FTC promulgates labeling rules for seven appliance categories,
including refrigerators.
Congress enacts the National Appliance Energy Conservation
Act to take effect January 1, 1990.
DOE establishes 1993 energy-efficiency standards. A 25 percent
greater efficiency level (on a sales-weighted average) over 1990
was imposed on models to be sold in 1993 for household R/Fs.
Manufacturers will produce 18-ft3, top-mount R/Fs that con-
sume less than 690 kWh/year. Costs are much less than antici-
pated when setting standards. Technological progress (such as
high EER compressor) exceeds expectations.
Next round of energy-efficiency standards.
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Part I. Results
1.2 Analytical Approach
STEPS IN THE ANALYSIS
As illustrated in Exhibit 1.4, the analytical approach followed three steps:
1. definition of baseline refrigerator/freezers;
2. development of assumptions concerning each technology option and
specification of specific pathways; and
3. analysis of the potential energy savings associated with each path
using the EPA Refrigerator Analysis (ERA) computer model [1].
Step 1: Define Baseline Models
Baseline descriptions of three pre-1993 18-ft3, top-mount R/Fs (Models A, B,
and C) were obtained directly from the manufacturers, from which ERA model
inputs were prepared. Information about changes made to these models to meet
the 1993 energy-consumption standards was not available at the time of the writ-
ing of this report. As a consequence, sample designs for Models A, B, and C that
meet the 1993 energy-efficiency standards have been developed, starting from the
pre-1993 baseline designs. These sample 1993 designs, shown in Exhibit 1.5, are
listed as "typical" rather than "actual." It is noted that the manufacturers will
have modified their existing products to meet the 1993 efficiency standards
according to their own criteria, which is not to be construed as the typical design.
Refrigerator/freezer Model D input data specifications were prepared by a
refrigerator/freezer design engineer. Model D does not represent an actual
design, but is intended to be "typical" of an advanced design.
The inputs for Models E, (a 20-ft3, bottom-mount R/F) and F (a 27-ft3, side-by-
side R/F), were prepared by the manufacturers of these units. The specific units
represented by these inputs have not been identified; however, they are "actual"
1993 designs.
The insulation levels listed in Exhibit 1.5 are defined as the total volume of
insulation normalized to the refrigerator/freezer food storage volume in order to
account for differences in the relative sizes of the appliances. Refrigerator/freez-
er Model B used the lowest level of insulation of the top-mount units. This was
partially compensated by its higher foam resistivity.
Also shown in the exhibit are the relative sizes of the evaporators and con-
densers (normalized according to the total storage volume of the refrigerator)
and the electrical inputs for the fans and anti-sweat heat. It is noted that the six
designs show a wide variation in these parameters.
The "system COP" is the calculated compressor COP at the operating condi-
tions, taking into consideration cycling losses. System COP, defined as the refrig-
erator evaporator capacity divided by the compressor power input, is generally
lower than the compressor-calorimeter-rated COP (EER/3.413). The compressor-
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.4
Analytical Approach for Multiple Pathways Study
1991 models
Step 1-A: Choose
actual R/F baseline
models
Step 1-B: Develop
possible 1993 baseline
models that meet
DOE standards
Step 2: Develop path-
ways of technical
options for creating
super-efficient refrig-
erators
Step 3: Use model
and experimental
results (in some cases)
to evaluate each path
kWh/year:
770-860
kWh/year:
640-680*
o a
Prototype
o
a
kWh/year:
230-430*
^S-ft3 models
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Part 1. Results
EXHIBIT 1.5
Design of Model A (Top-Mount)
1991 Model (Actual)
Design Changes
Storage Volume (ft3):
17.7
Compressor Design:
Recip 4.55 EER
Insulation R/lnch:
8.0 Walls
7.4 Doors
Insulation Volume (ft/Vft3):
0.51 of Storage Volume
Width (in.):
32.0
Evaporator Area (tfVft3):
1.42
Condenser Area (f^/ft3):
0.51
Fans (w):
28.0
Anti-Sweat Heaters (w):
11.5
Refrigerant Line Heat:
None
System COP:
1.16
5.28 EER
Compressor
Add 3/4 Inch
to Doors
Vapor Line
Cabinet Door
Range Anti-Sweaty
Total kWh/yr:
807
1990 Standard (kWh/yr):
954
1993 Model (Typical)
Storage Volume (ft3):
17.7
Compressor Design:
Recip 5.28 EER
Insulation R/lnch:
8.0 Walls
7.4 Doors
Insulation Volume (ftrVft3):
0.56 of Storage Volume
Width (in.):
32.0
Evaporator Area (ft/Vft3):
1.42
Condenser Area (ftW):
0.51
Fans(w):
28.0
Anti-Sweat Heaters (w):
5.5
Refrigerant Line Heat:
Vapor Line
System COP:
1.36
Total kWh/yr:
650
1993 Standard (kWh/yr):
684
8
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.5 (continued)
Design of Model B (Top-Mount)
1991 Model (Actual)
Design Changes 1993 Model (Typical)
Storage Volume (ft3):
18.0
Compressor Design:
Rotary 4.57 EER
Insulation R/lnch:
9.1 Walls
9.1 Doors
Insulation Volume (f^/ft3):
0.44 of Storage Volume
Width (in.):
29.3
Evaporator Area (f^/ft3):
0.67
Condenser Area (tf/ft3):
0.33
Fans (w):
20.7
Anti-Sweat Heaters (w):
6.4
Refrigerant Line Heat:
Liquid Line
System COP:
1.13
5.0 EER
Compressor
\
/
Low Watt Defrost
Timer and Move
Out of Cabinet
Add 1/2 Inch
of Insualtion
Add 1/2 Inch
to Doors
Total kWh/yr:
837
1990 Standard (kWh/yr):
970
Storage Volume (ft3):
18.0
Compressor Design:
Rotary 5.00 EER
Insulation R/lnch:
9.1 Walls
9.1 Doors
Insulation Volume (ff/ft3):
0.61 of Storage Volume
Width (in.):
30.3
Evaporator Area (f^/ft3):
0.67
Condenser Area (f^/ft3):
0.33
Fans (w):
20.7
Anti-Sweat Heaters (w):
6.4
Refrigerant Line Heat:
Liquid Line
System COP:
1.27
Total kWh/yr:
643
1993 Standard (kWh/yr):
694
9
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Part 1. Results
EXHIBIT 1.5 (continued)
Design of Model C (Top-Mount)
1991 Model (Actual)
Design Changes
Storage Volume (ft3):
18.1
Compressor Design:
Rotary 4.85 EER
Insulation R/lnch:
8.0 Walls
8.0 Doors
Insulation Volume (tfVfl3):
0.44 of Storage Volume
Width (in.):
29.1
Evaporator Area (ffrft3):
1.14
Condenser Area (ftVft3):
0.44
Fans (w):
21.0
Anti-Sweat Heaters (w):
16.3
Refrigerant Line Heat:
None
System COP:
1.28
Liquid Line
Flange Heat
5.0 EER
Compressor
ECM Evaporator
Fan
Add 1/2 Inch
to Doors
Total kWh/yr:
812
1990 Standard (kWh/yr):
967
1993 Model (Typical)
Storage Volume (ft3):
18.1
Compressor Design:
Rotary 5.00 EER
Insulation R/lnch:
8.0 Walls
8.0 Doors
Insulation Volume (rfVfl3):
0.47 of Storage Volume
Width (in.):
29.1
Evaporator Area (ffrft3):
1.14
Condenser Area (ffrft3):
0.44
Fans (w):
15.6
Anti-Sweat Heaters (w):
9.6
Refrigerant Line Heat:
Liquid Line
System COP:
1.38
Total kWh/yr:
672
1993 Standard (kWh/yr):
693
10
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.5 (continued)
Design of Model D (Top-Mount)
1993 Model (Typical)
Storage Volume (ft3):
18.0
Compressor Design:
Recip 5.28 EER
Insulation R/lnch:
8.0 Walls
8.0 Doors
Insulation Volu me (ffVft3):
0.49 of Storage Volume
Width (in.):
30.0
Evaporator Area (f^/ft3):
1.39
Condenser Area (frVft3):
0.51
Fans (w):
21.4
Anti-Sweat Heaters (w):
5.5
Refrigerant Line Heat:
Liquid Line
System COP:
1.37
Total kWh/yr:
647
1993 Standard (kWh/yr):
689
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Part 1. Results
EXHIBIT 1.5 (continued)
Design of Model E (Bottom-Mount)
1993 Model (Actual)
Storage Volume (ft3):
20.2
Compressor Design:
Recip 5.1 SEER
Insulation R/lnch:
8.0 Walls
8.0 Doors
Insulation Volume (ftVft3):
0.57 of Storage Volume
Width (in.):
32.6
Evaporator Area (ffrft3):
1.92
Condenser Area (ft2/^):
1.82
Fans (w):
20.5
Anti-Sweat Heaters (w):
2.0
Refrigerant Line Heat:
Liquid Line
System COP:
1.42
Total kWh/yr:
619
1993 Standard (kWh/yr):
703
12
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.5 (continued)
Design of Model F (Side by Side)
1993 Model (Actual)
Storage Volume (ft3):
26.6
Compressor Design:
Recip 5.27 EER
Insulation R/lnch:
7.6 Walls
7.6 Doors
Insulation Volume (tfVft3):
0.39 of Storage Volume
Width (in.):
35.5
Evaporator Area (f^/ft3):
0.85
Condenser Area (frVft3):
0.36
Fans(w):
20.6
Anti-Sweat Heaters (w):
3.6
Refrigerant Line Heat:
Liquid Line
System COP:
1.43
Total kWh/yr:
829
1993 Standard (kWh/yr):
890
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Parti. Results
calorimeter-rated COP is defined as the refrigerant mass-flow-enthalpy differ-
ence at the 90 °F vapor and liquid states at the evaporator and condenser pres-
sures divided by the compressor work input. Because of these definition differ-
ences, the system COP is generally about 90 percent of the compressor calorime-
ter COP.
Specific information about each model refrigerator/freezer is given in Section
2.2, where comparisons are made between manufacturers' reported energy con-
sumption and those calculated by ERA. The energy consumption values listed in
Exhibit 1.5 were calculated by ERA.
Step 2: Develop Multiple Pathways
The refrigerator options defined in this report are combinations of various
technologies applicable to the following major subsystems:
Hermetic System: The hermetic system includes the refrigeration cycle
and all of its components. The baseline system consists of a single fan-
forced evaporator, condenser, compressor, and flow control device.
Cabinet: The cabinet system includes insulated walls and doors, and
door gaskets.
Auxiliaries: Auxiliary functions include automatic defrost, controls,
and anti-sweat devices.
Table 1.1 shows the major technical options available to the appliance manu-
facturer. These technical options range in commercial availability and cost to
implement. Some options are currently used in refrigerator designs, and others
are in the experimental stage.
Eighteen sample pathways for increasing the energy efficiency of current
refrigerator/freezers were defined from this list of options. The pathways con-
sisted of individual steps, where a candidate technology is added to the refriger-
ator/freezer design represented by the previous steps. Analyses were carried out
at each step in the pathway.
Table 1.2 summarizes the specific component design features considered in the
various paths. The table lists the assumptions made in applying each technology,
along with references upon which the assumptions were based. These assump-
tions were followed rigorously at each step to ensure a consistent analysis.
Additional details about the assumptions made for each of the technologies are
presented in Appendix A.
Step 3: Use Model to Evaluate Each Path
The analysis uses the ERA computer model to simulate the energy perfor-
mance of each refrigerator pathway. ERA predicts the performance (energy con-
sumption) of household R/Fs and is capable of simulating various cabinet, auxil-
iary, and cycle configurations.
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Multiple Pathways to Super-Efficient Refrigerators
15
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Part 1. Results
16
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Multipk Pathways to Super-Efficient Refrigerators
17
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Part I. Results
18
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Multiple Pathways to Super-Evident Refrigerators
ERA is a micro-computer-based program consisting of four major components
that combine to simulate the performance of a domestic refrigerator:
1. A menu-driven input processor
2. Estimation of the cabinet loads
3. Thermodynamic cycle simulation
4. Energy-consumption calculations
An important capability of the model is its ability to consider the interactive
effects between different savings measures. Savings predicted for individual
measures are not simply additive, but depend upon those design options previ-
ously considered and made part of the current design. Each case represents a
new design where the interactions of all components are taken into considera-
tion. As a consequence, the apparent benefit of a design option depends upon
where it is introduced into the path.
As an example, the net reduction in anti-sweat heat available from a con-
denser liquid line will be dependent upon the compressor run-time and con-
denser heat load, which are themselves dependent on the cabinet heat load and
on the fan and compressor efficiencies. In certain instances, additional electrical
anti-sweat heat is required to supplement the liquid-line anti-sweat heat. This is
particularly necessary near the end of a path where significant reductions in cab-
inet loads occur. As a general rule, improvements in one part of the design will
lessen the apparent benefit of other options.
As cabinet loads and fan energies are reduced, the compressor capacity may
need to be reduced to maintain a reasonable run-time and acceptable cycling
losses. This condition is noted by the model and is taken into account when cal-
culating the cycling losses (see Appendix B of the ERA User's Manual for the spe-
cific algorithms). If the compressor size is substantially reduced, the reduced effi-
ciencies currently available for smaller sizes may raise the overall energy use.
However, in the larger-size range of current compressors, the drop-off in efficien-
cy with reduced capacity is small.
A brief discussion of the ERA model is provided in Section 2.2 of this report.
Additional details are provided in the ERA User's Manual [1].
BASELINE TEST RESULTS
The baseline refrigerators served to calibrate the model. Using the manufac-
turer's supplied information on baseline refrigerators A, B, and C (pre-1993 top-
mounts), ERA inputs were prepared, and the model results were compared with
the manufacturer's reported energy consumption. The differences ranged from
-3.0 percent to +4.7 percent. The only data available for Model E (1993 bottom-
mount) and F (1993 side-by-side) were ERA model inputs developed by the
manufacturers; specific design data from which ERA model inputs can be devel-
oped were not available. The differences between reported energy consumption
19
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Part 1. Results
and ERA output values were +9.0 for model E and +2.3 percent for the side-by-
side units (ERA predicted energies were higher). This information is summa-
rized in Table 2.3 in Section 2.2.
PROTOTYPE TEST RESULTS
Several pathways are no longer theoretical. In cooperation with individual
companies and academic research labs, EPA has built and tested prototype
refrigerator designs to evaluate the performance of new technologies.
Vacuum Insulation
Two recent tests on R/Fs and freezers using vacuum insulation show mea-
sured energy improvements of 10 percent or greater by using evacuated powder-
filled panels. DOE 90 °F closed-door test procedures were followed.
Four 19-ft3 R/Fs having 63 percent panel coverage consistently measured 10
percent or higher energy efficiency. Freezers tested with 50 percent panel cover-
age measured energy-efficiency gains of over 10 percent [10,11].
By using ERA and modeling the same conditions, the computer simulated
within 2 percent, or one standard deviation, of the measured test results.
Refrigerators with vacuum-panel insulation were introduced in early 1993 in
limited product lines in the European refrigerator market.
Double Insulation
The insulation thickness of a 20-ft3 R/F cabinet was increased by an average of
1.5 inches by putting the liner of a 20-ft3 unit into a 25-ft3 outer cabinet. No other
modifications to the R/F system were made.
The measured energy performance (using the standard DOE 90 °F closed-door
test) was 25 percent less than for the standard 20-ft3 model. By modeling the
same conditions, ERA estimated the energy performance within 3 percent, or
one standard deviation [12]. (See the market analysis in Section 2.3 on the poten-
tial to successfully market double-insulated products.)
Cycle Modifications: Lorenz-Cycle Refrigerators
Lorenz-cyde refrigerators tested at the University of Maryland have consis-
tently achieved net energy savings of 8 percent to 16 percent, depending upon
the refrigerant combination being used [13,14]. ERA analysis of similar systems
have predicted energy savings of 9 to 18 percent.
Energy-Efficient Compressors
More efficient refrigerator compressors than those used in the current produc-
tion models are available on the market. For instance, Americold currently
advertises 5.5 HER compressors in the 500 to 1^00 Btu/h range for use with
CFC-12, HFC-134a, and HCFC-22. These compressors show a trend in manufac-
turing to more efficient designs (see Exhibit 1.6).
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Multiple Pathways to Super-Efficient Refrigerators
A breakthrough in compressor technology is the linear compressor developed
by Sunpower, Inc., with initial funding by EPA to evaluate the concept and veri-
fy the energy-saving potential of the new compressor. Americold assisted
Sunpower during this evaluation process.
The linear compressor has measured 6.0 EER on compressor-calorimeter tests,
and measured energy savings of 10-15 percent on refrigerator tests (see Exhibit
1.7). When in full production, the manufactured cost of the linear compressor is
expected to be the same or less than existing compressors. The compressor
requires no lubricating oils and can inherently achieve variable capacity. A
detailed cost analysis is under way.
Provided testing continues to show favorable results, the compressor may be
available on the market in a couple of years.
Carbon Black
Celotex Corp. has commercialized insulation products with carbon black filler.
The filler reduces heat transfer and improves the foam efficiency by about 10
percent [15]. While this product is only commercially available in foam-sheath-
ing products used for building insulation, trials of this technology with
polyurethane foam used in appliances have been completed, indicating favor-
able efficiency improvements and foam characteristics.
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Part 1, Results
EXHIBIT 1.6
More Efficient Compressors Are Available
AMERICOLD CONTINUES TO OFFER THE
HIGHEST EFFICIENCY REFRIGERATION COM-
PRESSORS IN THE WORLD!
5.5 EER WITH R12/R134A/R22
Mention of trade names or commercial products does not constitute endorsement or recommendation for use
22
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.7
Compressor Efficiency Comparison
6--
5--
4--
3--
2--
1--
New Linear Compressor
Potentjanjriear _
Compressor" '
Performance
* Conventional
Compressors
200 400 600 800
Cooling Capacity (Btu's per hour)
Source: Arthur D. Little, Inc. 1993. State ol the Ait of Hermetic Compressor
Technology Applicable to Domestic ftetrigentor/Freezem. Prepared for the
U.S. EPA.
1000
The new linear compressor design has a measured EER (energy-efficiency ratio)
of 6.0 or better at standard rating conditions. The best efficiencies for conven-
tional refrigerator compressors range from 5.5 to less than 4.0 EER for small
units. The smaller compressors tend to have lower efficiency because friction
and motor losses become more important at these sizes. The new linear design
greatly reduces these losses, which means its efficiency should not change sig-
nificantly with compressor size. Future improvements to the linear compressor
could further boost its efficiency to as high as 6.8 EER.
23
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Part 1. Results
i .3 Incremental Cost Estimates
METHODOLOGY
Incremental manufacturer's cost estimates for each design were determined
by contacting component manufacturers, residential refrigerator manufacturers,
and refrigeration consultants for estimates and feedback.
A list of component manufacturers who could supply all or part of each fea-
ture to the refrigerator manufacturers was developed based on the list of design
features. All of the component manufacturers were then contacted to elicit their
participation in the project. Those agreeing to participate were then sent a list of
the design features applicable to their product lines.
Using the descriptions of the design features, the component manufacturers
estimated the cost to supply components for the different options. Follow-up
calls were made to determine if additional information was needed to complete
the estimates. In some cases, sketches of the different parts of the refrigerator
were provided to properly cost out the various features.
The incremental costs associated with the additional assembly required were
estimated by ADM using labor-hour estimates and rates for each of the features.
The rates included direct and overhead costs. Overhead costs included plant
retooling, depreciation, profit, and other indirect costs. Labor estimates were
finalized into a first-cost estimate as well.
The raw data were then formalized into a questionnaire that was sent to
refrigerator manufacturers who expressed interest in participating in the project.
The questionnaire contained the estimated component and labor costs for each of
the design features. The R/F manufacturers were asked to comment on the ini-
tial cost estimates, provide new estimates as needed, and assign confidence fac-
tors to the estimates.
The ADM and manufacturer's average cost and confidence factors were sub-
mitted to EPA. As a final check, these numbers were given to expert consultants
in the refrigeration field, checked against EPA research reports, or verified by
further contacts with component and/or refrigerator manufacturers.
RESULTS
The design features, manufacturer's average cost increments and confidence
factors, ADM costs, and EPA costs are summarized in Table 1.3. Instances where
entries are missing resulted from: (1) manufacturers not pricing a particular
design feature, (2) insufficient data to develop an accurate estimate, or (3) the
design feature being changed after the ADM contract expired.
Manufacturers' and EPA estimates agreed within the confidence levels set by
the manufacturers 9 out of 27 times. The EPA estimate was lower 12 out of 27
24
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Multiple Pathways to Super-Efficient Refrigerators
times. The manufacturer's number was lower 6 out of 27 times. The ADM esti-
mates were within the confidence levels of the manufacturer's estimates 6 out of
24 times, and below the other 18 times.
The EPA estimates will be used in further analyses in this report, except for
the three cases where they were not available. In these cases, the manufacturer's
estimates are used.
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Part 1. Results
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Multiple Pathways to Super-Efficient Refrigerators
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Part 1. Results
28
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Multiple Pathways to Super-Efficient Refrigerators
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Part I. Results
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Multiple Pathioays to Super-Efficient Refrigerators
1.4 Pathways to Achieving Energy-Efficient
Refrigerators
DEFINITION OF PATHWAYS
The refrigerator options presented in this section reflect potential combina-
tions of various technologies. Manufacturers will develop their own paths,
depending upon the unique characteristics of their existing products, cost struc-
ture, and research agenda.
The paths were constructed to examine some particular design theme (e.g.,
additional insulation as a means of load reduction). They reflect existing and
emerging technological options, along with longer-term or potential technolo-
gies that will require additional research and development. The order of features
examined in each path was determined from an estimation of the cost-benefit of
the measure and status of the technology, with consideration given to the poten-
tial effect of the particular measure on the benefits of later measures.
The Multiple Pathways analysis does not represent an attempt to establish
optimized designs. For example, the cost-benefit of a measure will depend upon
the design features incorporated earlier in the path. The best set of technical
options and the order in which they are implemented will depend on individual
manufacturers' product lines, production facilities, technical capabilities, and
cost structure.
PRACTICAL CONSIDERATIONS
The Multiple Pathways analysis focuses on the prediction of the effects of
design alternatives on energy consumption as measured under the DOE 90 °F
closed-door test conditions. It is recognized that a practical design will require
testing and evaluation at other usage conditions, such as in high-humidity envi-
ronments, and high- or low-temperature environments. Other criteria that will be
considered by individual manufacturers will be the impact on the manufacturing
methods used for current products, the characteristics of the market served by the
manufacturer, and the risks associated with introduction of new technologies.
Certain design features may directly affect other characteristics of the R/F,
such as the small loss of storage volume from the use of a larger evaporator, or
the requirement for a second evaporator in the fresh-food section in a Lorenz or
dual-loop cycle. Those design features may also add value to the R/F, for exam-
ple, by reducing smells in ice cubes and dehydration in vegetables in two evapo-
rator designs. These are some of the many design issues that would have to be
weighed in creating a practical design. Some of the issues relating to the imple-
mentation of each of the design features are described in detail in Section 2.1.
Experience in marketing suggests a wide variation of design options that con-
sumers find attractive, with most consumers concerned about general size, not
very small differences in cubic capacity.
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Part I. Results
Although algorithms for estimating the effects of door openings on energy
consumption have been included in the model, all analyses performed as part of
the Multiple Pathways analysis were carried out for the 90 °F DOE closed-door
conditions. This rating may have to be modified to adequately evaluate future
designs where annual energy reductions in the 50 percent to 70 percent range are
targeted. In situations where the cabinet loads have been significantly reduced
by increased or more effective insulation, the effects of door openings will domi-
nate the total loads in actual use. This subject is beyond the scope of this report.
However, the ERA model used to perform the Multiple Pathways analyses can
be utilized to explore the value of design options under conditions with door
openings taken into account [1].
SUMMARY OF RESULTS
The pathways are organized into four groups:
Single-Evaporator-Cyde Refrigerators.
Lorenz-Cyde Refrigerators.
Dual-Loop Refrigerators.
Most Cost-Effective Technologies With No Impact on Cabinet Size or
Capacity.
The results are shown in Exhibit 1.8, with the annual energy consumptions
rounded to the nearest 10 kWh/year (0.03 kWh/day). Additional details on each
pathway are presented in Appendix B. The incremental costs associated with
adding design features beyond the 1993 non-CFC step in each pathway are also
indicated in the exhibit. These numbers are rounded to the nearest U.S. dollar.
The energy change and incremental cost from the 1993 non-CFC step to the end
of the pathway are summarized for the 18 paths in Table 1.4. Cost-increment data
were not established for Models E and F and are therefore not induded. The future
value of the avoided costs for the energy saved and the benefit-cost ratio are also
presented. A 6-percent annual rate of return and 19-year R/F life were assumed
for these calculations. A 3-percent escalation rate was assumed for electricity, and
an initial cost of $0.08/kWh was assumed for the benefit-cost calculation. The pre-
sent value of the avoided cost is about one-third (1 /1.0619) of the future value.
As noted previously, the cost-benefit of the various features will depend on
where they are placed in the pathway. A measure of the cost-effectiveness of
individual design features can be estimated from the cost of the feature per per-
centage reduction in energy consumption. The average, standard deviation, min-
imum and maximum percentage energy reduction, mean and standard deviation
of the cost per percent energy reduction, and the present value of the avoided
electricity costs are presented in Table 1.5 for each of the design features. With
the exception of a few design features which must follow other features, the
design features are ordered from most to least cost-effective in Table 1.6.
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8
Path 1: Model D "Prototype" Single-Evaporator Cycle
Current Technologies With Increased Insulation
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
Switch to HCFC foam at r=
0.544 m2*K/(W»cm) and
HFC-134a refrigerant
Dl 02G50 Reduce gasket loads
second 25%
Dl 04CMP Switch to 5.5 HER
compressor
Dl 06MCI Switch HCFC foam to
microcell foam at r=0.590
m2*K/(W»cm)
Dl 08ADF Add adaptive defrost and
0.25W controller
Dl 10DCC Switch condenser fan to
3.6WDCfan
Key Characteristics of Pathway
The pathway emphasizes the use of existing technologies to achieve
super efficiency.
Key Uncertainties
All technologies have been demonstrated in practice, except for demonstra-
tion of 50% gasket-load reduction in production.
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Parti. Results
EXHIBIT 1.8 (continued)
Path 1 A: Model D "Prototype" Single-Evaporator Cycle
Current Technologies With Thick-Wall Cabinet
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
Switch to HCFC foam
atr=0.544m2*K/(W*cm)
and HFC-134a refrieerant
Reduce gasket loads
second 25%
D104CMP Switch to 55 HER compressor 500
Switch HCFC foam to
microcell foam at
r=0.590m2*K/(W»cm)
Dl A08IN2 Add 5.08 cm of insulation
everywhere
Dl A10DCC Switch condenser fan to
3.6WDCfan
Key Characteristics of Pathway
The pathway emphasizes the use of existing technologies.
Key Uncertainties
Demonstration of 50% gasket-load reduction in production
Market analysis by individual manufacturers on thick-wall cabinet
34
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 2: Model B Single-Evaporator Cycle
Improved Components and Auxiliaries
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
B201CMP Switch to 5.0 HER rotaiy 770
compressor
B2 03INO Add 1.27 cm of insulation
everywhere
B2 04DRI Add 1.27 cm of insulation
to doors
B206LLM Replace electric-mullion
heater with equivalent
liquid-line heater
B2 08SHV Add shutoff valve
B210ADF Add adaptive defrost
B212DCF Switch fans (2) to 3.6W
DC fans
45
Key Characteristics of Pathway
All technologies in this pathway have been demonstrated in practice.
Key Uncertainties
Availability of 5.3 HER rotary compressors
35
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 3: Model C Single-Evaporator Cycle
Improved Compressor and Cabinet
Step
Modification
Energy,
kWh/yr
C3 01LLF Replace electric FZ-flange 760
heaters with equivalent
liauid-line heater
Switch evaporator
fanto3.6WDCfan
Switch to HCFC foam at
r=0.544 m2*K/ (W*cm) and
HFC-134a refrigerant
C307CMP Switch to 5.3 HER
rotary compressor
Add 234 cm of insulation
everywhere except doors
C311ADF Add adaptive defrost
Key Characteristics of Pathway
All technologies in this pathway have been demonstrated in practice.
Key Uncertainties
Availability of 5.3 HER rotary compressors
36
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 3A: Model C Single-Evaporator Cycle
Improved Compressor and Cabinet With Better Refrigerant
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
C3 01LLF Replace electric FZ-flange 760
heaters with equivalent
liquid-line heater
C3 03DCE Switch evaporator
fanto3.6WDCfan
C31993 Switch to HCFC foam at 670
r=0.544 m2*K/(W*cm)
and HFC-134a refrigerant
C3A07CCP Switch refrigerant to
cyclopropane
C3A09MCI Switch HCFC foam to
microcell foam at
r=0.590m2*K/(W*cm)
C3A11ADF Add adaptive defrost
Key Characteristics of Pathway
All technologies in this pathway have been demonstrated in practice except for
the use of cyclopropane refrigerant.
Key Uncertainties
Safe use, commercial availability, and material compatibility of cyclopropane
Availability of 5.3 HER rotary compressors
37
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 4: Model A Single-Evaporator Cycle
Current Technologies With Advanced Insulation
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
A4 01CMP Switch compressor to 720
Americold model
SSG108-1 (5.28 HER)
A403VLF Replace electric FZ-flange 650
heaters with equivalent
vapor-line heaters
A405G50 Reduce gasket loads 50%
A4 07DCE Switch evaporator fan
to3.6WDCfan
A4 09HRI Add 50% coverage
of2.54-cm-thick
high-R gas insulation
Key Characteristics of Pathway
The pathway uses advanced insulation technology that has been demonstrated
in prototypes. More applied research is required.
Key Uncertainties
Life and cost of high-R gas insulation
Demonstration of 50% gasket-load reduction in production
38
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 4A: Model A Single-Evaporator Cycle
Current Technologies With Improved Insulation
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
A4 01CMP Switch compressor to
Americold model
SSG108-1 (5.28 HER)
A4 03VLF Replace electric FZ-flange 650
heaters with equivalent
vapor-line heaters
A4 05G50 Reduce gasket loads 50%
A4A07REF Change refrigerant to
HFC-152a
A4A09CBI Switch microcell foam
to carbon black foam
at r=0.630 m2*K/(W*cm)
A4A11DCF Switch fans (2)
to3.6WDCfans
Key Characteristics of Pathway
The pathway uses advanced technologies. Some have been demonstrated in pro-
totypes; however, more applied research is required.
Key Uncertainties
Safe use of HFC-152a refrigerant
Demonstration of 50% gasket-load reduction in production
Carbon black insulation in appliance applications
39
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 5: Model D "Prototype" Single-Evaporator Cycle
Advanced-Cycle and Insulation Technologies
Step
Modification
Energy,
kWh/yr
D1993
Switch to HCFC
foam at r=0.544 m^K/
(W*cm)andHFC-134a
refrigerant
D502CMP Switch to 5.5 HER
compressor
D504VCC Switch to 65 HER linear
compressor with
variable capacity
D5 06VCM Add 50% coverage of
254-cm-thickr=1.60
vacuum-panel insulation
Key Characteristics of Pathway
The pathway uses advanced technologies. Some have been demonstrated in pro-
totypes; however, more applied research is required.
Key Uncertainties
* Life and cost of vacuum insulation
Demonstration of 50% gasket-load reduction in production
Commercialization of 6.5 HER linear compressor
40
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 6: Model B Lorenz Cycle
Improved Technologies
Modification
Energy,
kWh/yr
B201CMP Switch to 5.0 HER
rotary compressor
B2 03INO Add 1.27 cm of insulation 660
everywhere
Switch to microcell HCFC 660
foam at r=0.590 and
HFC-134a refrigerant
B6 07G25 Reduce gasket loads 25%
B6 09SH V Add shutoff valve
B611ADF Add adaptive defrost
B613DCC Switch condenser fan
to3.6WDCfan
Key Characteristics of Pathway
This pathway uses the Lorenz cycle with other existing technologies. The Lorenz
has been successfully demonstrated in the laboratory.
Key Uncertainties
Availability of 5.3 EER rotary compressors
Carbon black insulation in appliance applications
Choice of refrigerant blend
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 7: Model C Lorenz Cycle
Improved Components and Advanced Insulation
Energy,
kWh/yr
C301LLF Replace electric FZ-flange 760
heaters with equivalent
liauid-line heater
C3 03DCE Switch evaporator fan
to3.6WDCfan
C31993 Switch to HCFC foam 670
atr=0-544m2*K/(W*cm)
and HFC-134a refrigerant
C707G50 Reduce gasket loads 50%
C709DCC Switch condenser fan to
3.6WDCfan
C711VCM Increase vacuum-panel
insulation coverage to 80%
Key Characteristics of Pathway
This pathway uses the Lorenz cycle with other advanced technologies. More
applied research is required.
Key Uncertainties
Life and cost of vacuum insulation
Demonstration of 50% gasket-load reduction in production
Choice of refrigerant blend
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 8: Model A Lorenz Cycle
Best Cycle Components and Auxiliaries
Step
Modification
Energy,
kWh/yr
A8 09ADF Add adaptive defrost and
0.25W controller
Cost,
S/unit
A401CMP Switch compressor to 720
Americold model SSG108-1
(5.28 HER)
A4 03VLF Replace electric FZ-flange
heaters with equivalent
vapor-line heaters
A8 05LRZ Add Lorenz with free
conv. evap. and 20%-22/
50%-152a/30%-123 blend
A807CMP Switch to 6.0 HER
compressor
Key Characteristics of Pathway
This pathway uses the Lorenz cycle with the best-available compressor
and auxiliaries.
Key Uncertainties
Control strategies
Choice of refrigerant blend
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 8A: Model A Lorenz Cycle
Current Technologies With Thick-Wall Cabinet
Step
Modification
Energy,
kWh/yr
A4 01CMP Switch compressor
Americold model
SSG108-1 (5.28 HER)
A4 03VLF Replace electric FZ-flange
heaters with equivalent
vapor-line heaters
A8 05LRZ Add Lorenz with free
conv. evap. and 20%-22/
50%-152a/30%-123 blend
A8A07CMP Switch to 5.5
EER compressor
A8A09IN2 Add 5.08 cm of
insulation everywhere
Cost,
S/unit
Key Characteristics of Pathway
This pathway uses the Lorenz cycle with other existing technologies.
Key Uncertainties
Control strategies
Choice of refrigerant blend
Market analysis by individual manufacturers on thick-wall cabinet
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 9: Model D "Prototype" Dual-Loop Cycle
Improved Components With Thick-Wall Cabinet
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
Switch to HCFC foam 640
at r=0544 m2*K/(W*cm)
and HFC-134a refrigerant
D9 02FSC Switch to 5.1 HER (FZ) 560
and 4.6 HER (FF) compressors
D904DLR Switch refrigerants to
152a (FZ) and 142b (FF)
D906MCI Switch HCFC foam to
microcell foam at r=0590
m2*K/(W*cm)
D908IN1 Add 2.54 cm of insulation
everywhere
D910IN2 Add second 2.54 cm of
insulation everywhere
Key Characteristics of Pathway
This pathway uses enhanced technologies to achieve super efficiency.
Key Uncertainties
Development of efficient small compressors
Safe use of flammable refrigerants
Demonstration of 50% gasket-load reduction in production
Full market analysis of thick-wall cabinet
Carbon black insulation in appliance applications
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Parti. Results
EXHIBIT 1.8 (continued)
Path 10: Model A Dual-Loop Cycle
Improved Components With Advanced Insulation
Energy,
kWh/yr
Modification
A401CMP Switch compressor to
Americold model
SSG108-1 (5.28 HER)
A4 03VLF Replace electric FZ-flange 650
heaters with equivalent
vapor-line heaters
A1005FSC Add dual-loop with
HFC-152a (FZ) & HCFC-
142b (FF) & future
small comp.
A1007ADF Add adaptive defrost 5
and 0.25W controller
A1009DCC Switch condenser fans
(2)to3.6WDCfans
A1011HRI Increase high-R gas
insulation coverage
to 80%
201
Key Characteristics of Pathway
This pathway uses advanced technologies. More applied research is required.
Key Uncertainties
Development of efficient small compressors
Safe use of flammable refrigerants
Demonstration of 50% gasket-load reduction in production
Life and cost of high-R gas insulation
46
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 11: Model D "Prototype" Single-Evaporator Cycle
Most Cost-Effective Conventional Technologies
Step
Modification
Energy,
kWh/yr
Cost,
$/unit
Switch to HCFC foam at
r=0544m2*K/(W*cm)
and HFC-134a refrigerant
D1102LLM Replace electric-mullion
heaters with equivalent
liquid-line heater
D1104MCI Switch HCFC foam to
microcell foam at
r=0.590m2*K/(W*cm)
D1106DCE Switch evaporator
fan to 3.6W DC fan
Key Characteristics of Pathway
This pathway uses the most cost-effective existing technologies that will not
affect cabinet dimensions or utility.
Key Uncertainties
Carbon black insulation in appliance applications
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Part 1. Results
EXHIBIT 1.8 (continued)
Path 12: Model D "Prototype" Lorenz Cycle
Most Cost-Effective Advanced Technologies
Step Modification
Energy,
kWh/yr
Cost,
$/unit
D1993 Switch to HCFC foam 640
atr=0544m2*K/(W*cm)
and HFC-134a refrigerant
D1202CMP Switch to 55
HER compressor
D1204ADF Add adaptive defrost
and 0.25W controller
D1206G50 Reduce gasket loads 50%
D1208VCC Switch to 65 EER linear
compressor with variable
capacity control
Key Characteristics of Pathway
This pathway uses the most cost-effective advanced technologies. More applied
research is required.
Key Uncertainties
Safe use of flammable refrigerants
Demonstration of 50% gasket-load reduction in production
Life and cost of vacuum insulation
Commercialization of linear compressors
Lorenz control strategies
48
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 1.8 (continued)
Path 13: Model E 20' Bottom Freezer, Single-Evap. Cycle
Most Cost-Effective Conventional Technologies
Step
E1303MCI
Modification
Energy, kWh/yr
1993 baseline 20'
refrigerator
E1301G25 Reduce gasket loads 25%
Switch HCFC foam to
microcell foam at r=
0590m2*K/(W*cm)
E1305DCE Switch evaporator
fanto3.6WDCfan
Key Characteristics of Pathway
This pathway uses the most cost-effective existing technologies that will not
affect cabinet dimensions or utility.
Key Uncertainties
Carbon black insulation in appliance applications
49
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Part 1. ResH/fe
EXHIBIT 1.8 (continued)
Path 14: Model F 27' Side-by-Side, Single-Evaporator Cycle
Most Cost-Effective Conventional Technologies
Step
Modification
Energy, kWh/yr
Model F3 1993 baseline 27' refrigerator
F1401G25 Reduce gasket loads 25%
F1403MCI Switch HCFC foam to
microcell foam at
r=0.590m2*K/(W*cm)
F1405DCE Switch evaporator fan
to3.6WDCfan
Key Characteristics of Pathway
This pathway uses the most cost-effective existing technologies that will not
affect cabinet dimensions or utility.
Key Uncertainties
Carbon black insulation in appliance applications
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Part I. Results
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Part 1. Results
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Multiple Pathways to Super-Efficient Refrigerators
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Part 1. Results
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Part 1. Results
1.5 Attributes for Evaluating Technologies
The preceding exhibits show that there are multiple technologies that can cre-
ate an energy-efficient refrigerator. In choosing the optimum pathway for an
individual manufacturer, managers need to look beyond measures of simple
energy efficiency to determine the ultimate performance and value of a technolo-
gy. Some of the attributes of a technology can be established quantitatively, such
as the value of reduced energy. Other performance attributes are valued by con-
sumer preference and are subject to qualitative measurements.
Each of the following attributes needs to be considered when evaluating the
performance and benefits associated with a technological change.
REDUCTION IN ENERGY
Some technologies lead to a measured reduction in energy consumption,
which can be valued by the cost of energy per kWh.
Test procedures to measure the exact energy consumption of the R/F as a full
system can lead to different results. Each test procedure has advantages and dis-
advantages.
Some prototypes using the Lorenz cycle, thick-walled insulation, and vacuum
insulation have been tested under a variety of ambient conditions. Energy sav-
ings were consistent with the 90 °F tests. For instance, the Lorenz cycle achieved
8-16 percent savings over the baseline at different ambient temperatures,
depending upon the refrigerant mixture. Further testing by manufacturers
would be necessary.
PULL-DOWN CAPACITY
The ability and speed of the refrigerator system to eliminate a heat gain in the
cabinet are important attributes, particularly for customer satisfaction and food
preservation.
FREEZER AND FRESH-FOOD TEMPERATURES
The ability to set and maintain temperature in each compartment with the
least variability is important. For instance, with appropriate control strategies,
the Lorenz cycle can achieve proper temperature requirements at reduced energy.
TEMPERATURE UNIFORMITY IN COMPARTMENTS
Temperature uniformity is critical to ensuring that all food stays fresh and that
consumers can place food where they wish.
HUMIDITY IN LOWER BOX
Humidity affects the freshness and crispness of food in the refrigerator compart-
ment Technologies that increase humidity and preserve food longer will have an
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Multiple Pathways to Super-Efficient Refrigerators
advantage in the market. In addition, sufficient compressor capacity must be avail-
able to meet high humidity loads associated with frequent door openings.
DEFROST SYSTEM
Automatic, semi-automatic, and manual defrost imply different degrees of
work for the consumer to maintain the R/F. In evaluating the various defrost
options, manufacturers are still likely to maintain a reliable defrost system at
reduced energy.
WATER CONDENSATION AND ANTI-SWEAT DEVICES
Anti-sweat devices determine whether condensate forms on external parts of
the box. There are a number of anti-sweat devices that can be considered for
energy reduction, which will maintain reliable control of water condensation.
RELIABILITY
Consumers expect to turn refrigerators on and forget them, sometimes for
over 20 years. To maintain long-term reliability, manufacturers engage in extend-
ed applied research, accelerated aging tests, and field tests, before delivering
products to full-scale market. The length of these test requirements makes it dif-
ficult to judge the timing of commercialization for new technologies.
RISK OF FIRE
Consumers want safe products. Some of the refrigerants that can be used to
replace CFC-12 are flammable, but offer other attractive characteristics, such as:
low global warming potential; increased energy efficiency; compatibility with
existing, lower-cost lubricants; and lower refrigerant costs.
Balancing these factors is necessary, and risk analysis can be used to deter-
mine the ability to safely use flammable refrigerants. Analysis conducted by EPA
in conjunction with Underwriters Laboratories indicates that there is a de minimis
risk associated with using roughly 8 ounces of refrigerant HFC-152a (the charge
for an average-size U.S. refrigerator/freezer) in the product.
FIRST COST
Consumers have limited budgets. First cost has dominated consumer purchas-
ing decisions. However, consumers will pay for added-value features. Energy
efficiency can be one of those features.
OPERATING COSTS
Consumers have limited budgets, but life-cycle operating costs are not often
calculated when consumers are making purchasing decisions. New marketing
techniques, led by Sears, have been successful in focusing consumers on the eco-
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Part 1. Results
nomic benefits, the environmental benefits, and rate of return for "investing" in
energy-efficient products. (See Section 2.4 for more details.)
REFRIGERATOR SMELLS
Ice and frozen food can absorb smells that are transferred with air exchange
between the fresh- and frozen-food compartments. Cycles, such as many of the
two-evaporator configurations, avoid such air exchange and, when controlled
properly, will have value to consumers.
ACCESS TO COMPARTMENTS
Consumers like specialized access.
APPEARANCE
Consumers like refrigerators that look good. Energy-efficiency changes are not
expected to adversely affect the product's appearance. Manufacturers are con-
cerned that double-insulated refrigerators, an existing and reliable technology
option, will have a negative impact on the appearance of the refrigerator.
Provided the refrigerator fits in the void in a kitchen, market research indicates
that consumers can desire a thicker-walled cabinet, without negative impact on
their purchasing decisions.
CONVENIENCES AND OTHER ADDED FEATURES
Consumers want attractive and functional controls, door handles, lights, and
glass shelves, which will not be affected by energy-efficiency upgrades.
NOISE
Consumers dislike noise, and refrigerator manufacturers have been designing
their products over the years to reduce noise levels in refrigerators. One emerg-
ing technology that can help reduce noise levels is variable-speed drives, when
applied to compressors and fans.
ENVIRONMENTAL SOUNDNESS
Consumers want products that do not harm the environment. An important
factor in their purchasing decisions is the degree to which R/Fs contribute to
global warming and ozone depletion.
All of these attributes need to be valued when determining the benefits of the
technical alternatives. Trade-offs will be made in decision making. It is also
important to remember that marketing can influence customer choices, and cus-
tomer values can shift (e.g., safety now sells cars).
To assist manufacturers, EPA commissioned a consumer survey that evaluated
consumer responses to one pathwaydouble-insulated refrigerators. The results
are shown in Section 2.3.
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1.6 Key Uncertainties and Research Agenda
The key characteristics and uncertainties for each pathway have been high-
lighted in Exhibit 1.8. Some emerging technologies used in this analysis, includ-
ing the Lorenz cycle, linear compressor, gasket improvements, carbon black
foam insulation, and new refrigerants have shown significant energy-efficiency
increases using computer modeling and prototype testing.
These technologies require further applied research, and manufacturability
and cost analyses by individual manufacturers. With the appropriate research,
these technologies can contribute significantly to advances in energy efficiency.
Determining the commercial potential of emerging technology will be depen-
dent upon each manufacturer's cost structure and other technologies under con-
sideration in the company.
The following technologies can make significant impacts on the energy effi-
ciency potential of refrigerators, and deserve continued research to implement or
reduce the cost.
SMALL, EFFICIENT COMPRESSORS
A recent analysis by Arthur D. Little, Inc. [4] concluded that small compres-
sors in the range of 400 to 600 Btu's can be developed to reach 5.0 EER. The
development of such technology is critical to success of dual-loop refrigerators.
Early developments with the linear compressor indicate that the performance
does not degrade with size, as with reciprocating compressors. If further testing
confirms that there is no significant performance loss associated with down-scal-
ing the compressor, the linear compressor may be a cost-effective breakthrough
in small compressor technology.
GASKETS
The pathway analysis shows that 50 percent gasket savings would contribute
to significant energy reductions. The prediction of such savings has been report-
ed by modeling results. Initial experimental testing appears to reinforce the
potential savings. Detailed laboratory studies are currently under way to test dif-
ferent approaches to reducing gasket loss by 50 percent [7]. If successful, gasket
improvements can be the most cost-effective energy-saving technology.
ADVANCED INSULATION
Various types of vacuum insulation panels are under consideration. Research
indicates that there are plastic laminate materials available to provide reliability.
Major outstanding issues are to find a cost-effective filler material, and the man-
ufacturability and lifetime of the panels. Some manufacturers have committed to
large-scale production of vacuum panels in 1994 and have introduced limited
production refrigerators in 1993.
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High-R gas panels can also provide significant energy benefits; however, the
cost, manufacturability, and lifetime are still major issues to be resolved.
LORENZ CYCLE
Prototype testing has consistently achieved 8-16 percent energy savings using
the Lorenz cycle. Refrigerator manufacturers in other countries, such as China,
have been evaluating the Lorenz cycle for their domestic products. Research
issues still being addressed include optimal refrigerant mixture choice and con-
trol strategies.
1.7 How Reliable Are the Results Reported in
This Document?
The results reported for different pathways in this document depend upon
modeling projections and their comparison with prototypes and existing sys-
tems. However, since many of these pathways have never been built, it is not
possible to state with certainty that the results will, in practice, and after an engi-
neering effort, be exactly the same as the model predicts.
Experience shows computer models can under- or over-predict energy use.
Experience also shows that experimental testing cannot always indicate true
potential. For example, early tests of HFC-134a in refrigerators showed very
poor energy results, while models predicted results much more in line with what
has ultimately become practicable. Early efforts to realize gains in building
Lorenz-cycle refrigerators fell far short of model predictions. More recently,
experimental prototypes tested in China exceeded the energy savings estimated
by modeling.
The bottom line is that there is no perfect way to assess the future perfor-
mance of a R/F design. R/F performance will be found through a combination
of models/prototypes and testing. However, the ERA model does a very good
job of approximating the energy efficiency of R/F designs and has significant
utility as an evaluation and design tool.
1.8 Conclusions
It may be possible to produce a super-efficient 18-cubic-foot refrigerator/
freezer, consuming less than 250 kWh/year, by using different approaches and
technological alternatives. Similar savings are possible for other configurations
and sizes.
For roughly $3Q-$35, (manufacturer's cost) reductions to the 400-kWh/year
range are dearly possible with existing technologies. To achieve reductions below
250-300 kWh/year, development of various key future technologies is necessary.
Some of the emerging technologies that can lead to significant reductions in
energy consumption will have a high degree of likely success, provided the
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proper research priorities are developed and resources in applications research
are expended in these areas.
Other potential technologies are very encouraging and, if successful, have the
ability to achieve substantial energy reductions. These technologies may be
longer term and riskier. However, accelerated research agendas and commitment
of resources could bring some of these to market within several years.
Given the large number of system components that affect energy performance
and that can be modified in an R/F, there are multiple pathways that can be adopt-
ed to achieve a super-efficient product. The Multiple Pathways analysis indicates
that there are many combinations of options possible, even in the face of accelerat-
ed CFC regulations that eliminate CFC refrigerants and blowing agents.
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Multiple Pathways to Super-Efficient Refrigerators
PART 2. SUPPORTING DOCUMENTATION
2.1 Technical Options Support Sheets
CYCLES
Conventional, Single-Evaporator Cycle
In the United States, refrigerator/freezers use the basic vapor compression
cycle to move heat from the R/F cabinet to the surroundings. The appliances are
typically manufactured with a single compressor and condenser, and a single
evaporator, which is usually located in the freezer compartment. There is air
exchange between the freezer and fresh-food compartment to cool both compart-
ments to the necessary temperatures. A single refrigerant is used in this cycle.
Description of Technology
Evaporates refrigerant at low pressure within the evaporator, which
produces cooling.
Refrigerant passes from the evaporator through suction heat exchanger
to the compressor.
Refrigerant is compressed to a high pressure level under input of
work
Refrigerant condenses in the condenser, which releases heat to the sur-
roundings.
Liquid refrigerant flows back to the evaporator. One evaporator locat-
ed in freezer. Fresh-food compartment cooling is accomplished with
air exchange.
Status of Development
Well developed.
State of the art and mass produced.
Technical Issues
Refrigerant must evaporate at temperature level lower than that of the
freezer.
Large amount of energy is wasted by cooling fresh food, which is at a
relatively higher temperature, with freezer air.
Simple method of automatic defrost.
Relatively simple to produce.
Cost Issues
Retooling.
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Research and development for new designs.
Potential Performance
Cycle improvements possible with cabinet improvements, more effi-
cient compressor motors or compressors, the introduction of thermal
mass and of low-power fan motors.
Conventional Two-Evaporator Cycles
A conventional, two-evaporator appliance uses the same basic vapor compres-
sion cycle; however, instead of having just one evaporator in the freezer com-
partment and air exchange to the fresh-food compartment, there are two evapo-
rators servicing each compartment individually. This type of system is mass pro-
duced in foreign markets, such as China.
Description of Technology
Separate evaporators for fresh-food and freezer compartments.
Status of Development
Well developed.
Mass produced in foreign countries.
Technical Issues
Less frequent defrosting (energy savings possible).
Evaporator fan not normally used in fresh-food compartment.
Temperature control.
Reduced inner volume.
Refrigerant must evaporate at a temperature level that is lower than
the freezer temperature.
Cost Issues
Retooling.
Research and development for new designs.
Potential Performance
Reduction in energy consumption with thicker or advanced insulation,
introduction of thermal mass, larger heat exchangers, more efficient
working fluids, and more efficient compressors and motors.
Dual-Loop System With Two Compressors
Dual-loop systems with two compressors are the same as the conventional
single evaporator/compressor models, except for duplication of components.
These models currently exist in the marketplace, both in the United States and in
foreign markets. The largest disadvantage of these models is that smaller com-
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Multiple Pathways to Super-Efficient Refrigerators
SCHEMATIC OF TWO-EVAPORATOR-CYCLE SYSTEMS
Compressor
Heat Exchanger #1
& Capillary
Condenser
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SCHEMATIC OF DUAL-LOOP SYSTEM WITH TWO COMPRESSORS
Evaporator #2
Evaporator #1
Heat
Exchanger #1
& Capillary
Condenser #1
Compressor #1
Heat Exchanger
#2 & Capillary
Condenser #2
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Multiple Pathways to Super-Efficient Refrigerators
pressor sizes are required, which with today's technology are less efficient than
the larger compressors used in single-evaporator models.
Description of Technology
Cools fresh-food and freezer compartments by independent refrigerant
cycles.
Uses optimized fluids or mixtures in each cycle.
Two compressors, condensers, and evaporators are required.
Increase in heat-exchange area expected.
Status of Development
Well developed and mass produced, especially in foreign countries.
Comparable to single-evaporator model, except for duplication of
components.
Technical Issues
Compressor sizes are smaller, and compressors are less energy-effi-
cient.
Excellent flexibility in selection of operating temperatures.
Reduced inner volume.
Trade-off between matching temperature levels and smaller compres-
sor.
Cost Issues
Number of components and labor cost in production are increased.
Increase in production costs due to larger heat exchanger area and two
compressors.
Potential Performance
Energy efficient with fresh-food compartment cooled at appropriate
temperature.
Dual-Loop System With One Compressor
This dual-loop model has just one compressor that serves alternately either
the fresh-food compartment or the freezer compartment. This concept could be
more efficient with advances in small compressor technology and more sophisti-
cated control of cycling losses.
Description of Technology
One compressor that serves alternately either the fresh-food compart-
ment or the freezer compartment.
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Condensing unit (compressor-condenser unit) can be switched to serve
either evaporator.
Same refrigerant must be used in each evaporator.
Status of Development
Mass produced in Europe.
Technical Issues
Each evaporator uses appropriate expansion device (own capillary
tube).
Complex temperature control. Control has to decide what compart-
ment should have priority and may have different tasks and character-
istics during pull-down versus other modes of operation.
Reduced inner volume.
Temperature uniformity in the food compartment.
Compressor run time must not be excessively long for either compart-
ment.
One three-way valve in the system contributing to additional power
consumption and reliability concerns.
Charge management problems.
Cost Issues
First cost less compared to dual-loop system with two compressors.
Three-way valve will offset some of the savings.
Potential Performance
Comparable with dual-loop system with two compressors.
Temperature control more complex.
Two-Stage System
A two-stage refrigerator/freezer cycle has been patented by the General
Electric Company [33]. This cycle operates with three pressure levels and two
compressors. While this technology is well established in large-scale refrigeration
plants, its successful adaptation to small systems has not been demonstrated.
Description of Technology
One patented cycle operates with three pressure levels and two com-
pressors.
Performance potential similar to dual-loop cycle using same refrigerant
Control problem similar to dual-loop with one compressor.
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SCHEMATIC OF TWO-STAGE SYSTEM
(GE Patent)
1st
Expansion
Valve
Condenser
2d
Compressor
Phase
Separator
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Active expansion valves may be required (as opposed to capillary
tubes).
Allows higher-efficiency compressors, as they operate over a small
pressure ratio of about 2.
Both compressors could be housed in same unit and driven by a single
motor.
Status of Development
Well established and extensively used in large refrigeration plants.
Application of staging in small capacity is new.
No commercial product available.
Work is proceeding in at least one research laboratory.
Technical Issues
Two compressors of different capacities are required in one refrigera-
tion cycle.
* Oil management.
Controls.
Reduced inner volume.
Complexity of system.
Small compressors are needed.
Charge management.
Cost Issues
Comparable to dual-loop version.
Two compressors required, although one may be a lower-cost version.
Slightly higher costs for piping system and controls than dual-loop
with one compressor.
Potential Performance
Energy savings beyond dual-loop are possible with cooling of vapor
during compression and subcooling of the liquid stream to the freezer.
Experiments necessary to gauge performance gains under typical oper-
ating conditions.
This R/F design, while potentially viable, was not considered in the multiple
pathways options analysis.
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Multiple Pathways to Super-Efficient Refrigerators
Lorenz Cycle
Laboratory tests have recently proven the energy-efficiency advantages possi-
ble with a Lorenz-cycle configuration. Energy savings of 8-16 percent have been
achieved using various refrigerant mixtures [13,14]. The advantage of a Lorenz
cycle is that it is the simplest among the advanced cycles in that only two addi-
tional components are added to the conventional single-evaporator model. The
Lorenz design uses the boiling-point differences between the components of the
refrigerant mixture to achieve energy savings.
Description of Technology
Option to provide cooling in the fresh-food compartment at the appro-
priate temperature level.
One compressor, two evaporators (one each for fresh food and freezer
compartments).
Uses a nonazeotropic refrigerant mixture that evaporates over a tem-
perature glide of about 40 °F. The low temperature range of the glide is
used to cool the freezer compartment and the high temperature range
to cool the fresh-food compartment.
Intercooler used between the two evaporators to better utilize temper-
ature glide by precooling the liquid stream on the way to the expan-
sion device.
Status of Development
Energy savings of nearly 20 percent in steady-state operation reported
in mid-seventies [13,14].
Four refrigerators show savings of 8-16 percent [13,14].
Technical Issues
Simplest among advanced cycles.
Only two components added to conventional R/F.
Need to address the following in design and development efforts:
-Load distribution between freezer and fresh food compartment.
-Sizing of evaporators and expansion devices.
-Location and size of internal heat exchangers.
-Percent on-time and cycling losses.
-Selection of a suitable refrigerant mixture.
-Implementation of controls.
No charge management issues.
Charging procedure in field.
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Refrigerant availability, toxicity, flammability.
Material compatibility.
Reduced inner volume.
Cost Issues
Expected to be lowest-cost advanced cycle with only one additional
evaporator and intercooler.
Potential Performance
Energy savings of 16 percent confirmed in laboratory tests [13,14].
Low-cost, advanced-cycle alternative when implemented together
with a super-insulated freezer with potential energy savings reaching
beyond 20 percent in certain designs.
REFRIGERANTS
CFC-12 has been the conventionally used refrigerant for R/Fs. With the man-
dated phase-out of CFCs, a number of new replacements are being evaluated,
including HFC-134a, HFC-l52a, cyclopropane, hydrocarbons, and refrigerant
mixtures.
HFC-134a
HFC-134a is the fluid that has received the most consideration as a replace-
ment refrigerant for R/Fs. There is concern over its global warming potential.
Status of Development
Currently being mass produced.
Preferred fluid in the automobile.
Toxicology testing completed.
Technical Issues
Available.
Extensive material compatibility studies are close to being completed.
A satisfactory compressor oil seems to be available.
Compressor redesign is required.
Cost Issues
Increases first cost of R/F slightly.
Potential Performance
Effect on energy savings dependent largely on product and compres-
sor design. Work recently completed at the University of Maryland
indicates that the performance is roughly comparable to CFC-12 [17].
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Multiple Pathways to Super-Efficient Refrigerators
HFC-152a
HFC-152a is a flammable refrigerant. Fault-tree analysis has shown that the
additional risk associated with using this refrigerant is minimal [18].
Status of Development
Currently being mass produced.
Is used as a component in an azeotropic refrigerant mixture, as a blow-
ing agent for extruded polystyrene foam, and as an aerosol propellant.
Toxicology testing completed.
Technical Issues
Available.
Material compatibility studies may be required; however, HFC-152a
has been used for over 20 years as a component of R-500 in dehumidi-
fiers.
Existing oils are expected to be satisfactory.
Flammability and safety issues have been addressed by EPA and UL.
EPA has proposed that 152a is an acceptable alternative for CFC-12 in
refrigerator/freezers under Section 612 of the Clean Air Act.
Good heat transfer coefficients are expected.
Compressor redesign is required.
Cost Issues
Increases first cost of R/F slightly.
Potential Performance
Effect on energy savings dependent largely on product and compres-
sor design. Current work indicates that the performance is roughly 2
percent better than CFC-12 and HFC-134a [17].
Cyclopropane
Cyclopropane, C-270, is a promising refrigerant. However, its physical behav-
ior and flammability need to be further evaluated.
Status of Development
Was mass produced in the past as an anesthetic
Uncertain about completeness of toxicology testing and its thermal sta-
bility under compressor conditions
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Technical Issues
Available in small quantities.
Extensive material compatibility studies are necessary.
A satisfactory oil seems to be available.
Flammability and safety issues need to be addressed.
Good heat transfer coefficients are expected.
Compressor redesign is required.
Cost Issues
Increases first cost of R/F slightly; cost increase would be higher if risk
analysis identifies the need for additional safety mitigation measures.
Potential Performance
Effect on energy savings dependent largely on product and compres-
sor design. Current work indicates that the energy savings can be 6
percent over CFC-12 [17].
Hydrocarbons
Hydrocarbons are being considered as refrigerants by Greenpeace and
German refrigerator manufacturers.
Status of Development
Refrigerators in Europe are currently being introduced with hydrocar-
bons.
Toxicology testing completed.
Used as refrigerants historically and currently in industrial applica-
tions.
Technical Issues
Available.
Material compatibility studies have been conducted.
Existing oils are compatible with hydrocarbons.
Flammability and safety issues need to be addressed by manufacturers.
Good heat transfer coefficients are expected.
Compressor redesign is required.
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Multiple Pathways to Super-Efficient Refrigerators
Cost Issues
Increases first cost of R/F slightly, unless extensive safety measures are
applied.
Potential Performance
Effect on energy savings dependent largely on product and compres-
sor design. Current work indicates that the performance is at least
comparable to CFC-12 [17].
Refrigerant Mixtures
Refrigerant mixtures are considered as replacements for CFC-12. They offer
more flexibility in the selection of properties, but at the same time, more chal-
lenges in material compatibility and service. U.S. manufacturers offer a number
of mixtures as short- or long-term alternatives.
Status of Development
Most of the constituents of mixtures are currently being mass produced.
Often, but not always, one of the constituents lacks safety, toxicology,
or materials compatibility testing.
Technical Issues
Mixtures are available, some only in research quantities.
Extensive material compatibility studies are necessary.
Compressor oil compatibility has to be considered carefully; however,
often a mixture constituent may enhance mixing.
For some mixtures, flammability and safety issues need to be
addressed.
Heat-transfer coefficients may be graded compared to pure fluids.
Compressor redesign may be required for some mixtures.
Cost Issues
Increases first cost of R/F slightly.
Potential Performance
Effect on energy savings dependent largely on product and compres-
sor design. Current work indicates that the performance is significant-
ly better than CFC-12 in properly designed R/Fs [40].
COMPRESSORS
Today's U.S. refrigerator/freezers typically use two types of compressors-
reciprocating and rotary. The compressor is the largest energy-consuming com-
ponent in a refrigerator, so advances in compressor efficiency have a significant
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effect on overall refrigerator efficiency. Efficiencies have been increasing as the
manufacturers have incorporated higher-quality materials and closer tolerances
in the compressor designs. A significant current need is the development of effi-
cient, small-capacity compressors. Efforts in this area are under way.
Rotary
Description of Technology
Rolling-piston, stationary-vane-type compressor for R/Fs.
Cylindrical piston rolling on wall of a cylinder capped at both ends.
Reciprocating vane ensures variable-pressure compression.
Contains motor and pump in a welded hermetically sealed shell.
Suction gas flows directly to suction port, minimizing superheating.
Discharge gas ported directly into shell at discharge pressure.
Includes a suction accumulator and strainer closely coupled to the
inlet.
High volumetric efficiency because of its inherently low clearance vol-
ume and unrestricted suction port.
Cycling losses can be reduced with a check valve and pressure valve
on the condenser discharge side.
Rotaries are more compact and lightweight than reciprocating com-
pressors of comparable capacities.
Sound damping and/or vibration isolation is normally required.
Status of Development
Well developed and commercialized.
Technical Issues
Close clearances between piston and cylinder, crankshaft, and cylinder
caps require dose machining tolerance over a much greater total sur-
face area than a reciprocating compressor and make the pump less tol-
erant of wear.
Cost Issues
Inherently simple, low-cost machines.
Close tolerance requires some added cost.
Potential Performance
Large rotaries (>600 Btu/hr) currently have EERs of approximately 4.7
to 5.0 using high-efficiency PSC motors. Incremental improvement, at
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Multiple Pathways to Super-Efficient Refrigerators
added cost, through the use of higher-efficiency ECM motors, with 5.3
to 5.5 EER as a target range [4].
In smaller capacities (<400 Btu/hr) the efficiency potential is more lim-
ited as mechanical losses, gas blow-by, and motor inefficiencies are
more significant. Potential EER level is approximately 4.5 [4].
Reciprocating
Description of Technology
Single-cylinder device with a piston driven by a crankshaft that is an
integral extension of the driving motor shaft.
Piston reciprocates in a stationary cylinder secured to the motor stator.
Two reed valves attached to cylinder head open to suction into the
cylinder and discharge outward from cylinder.
Gas drawn from evaporator cools motor and pump.
High-efficiency compressors may provide for direct suction path from
inlet into muffler assembly, reducing superheating.
Liquid refrigerant slugged into canister at start-up is vaporized by heat
dissipated from suction gas and returned to the cycle.
Small energy penalty associated with liquid being vaporized in the
crank case.
Status of Development
Most common type used.
High state of development and is mechanically efficient and reliable.
Technical Issues
Unavoidable discharge gas to suction gas heat transfer paths in cylin-
der body and cylinder head inherently leads to higher suction port
temperatures than in a rotary.
Cost Issues
Less expensive than rotary compressor because of lower overall sensi-
tivity to manufacturing tolerances and highly-automated manufactur-
ing processes.
Potential Performance
Best current large compressor (above 650 Btu/hr) has energy-efficiency
rating (EER) of 5.3 to 5.5 Btu/watt-hr.
6.0-EER unit now being evaluated by refrigerator manufacturers
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6.3-EER large compressor feasible with ECM, improved lubrication,
reduced suction gas heating, and reduced mechanical losses [4].
Current small compressor (200-400 Btu/hr), HER level is 3.0 to 3.5.
5.7-EER small compressors are technically feasible [4].
Scroll
Description of Technology
Developed in 1970's.
Introduced into markets for automobile, residential central, and com-
mercial air conditioning in the 1980's.
In automobile and commercial A/C (capacity range is 18,000-180,000
Btu/hr), scroll compressors are highest-efficiency compressors available.
Scroll compressors, unlike rotary compressors, have radially and axial-
ly compliant drives.
Sealing tolerant of particulate contamination and liquid slugs.
Compliant sealing allows some relaxation of machining tolerances rel-
ative to those required for notaries.
Status of Development
Well developed and commercialized for larger applications indicated
above.
Little, if any, development has been carried out for smaller capacities
Technical Issues
R/F applications have lower mass and volume flow rates and a pres-
sure ratio 2 to 3 times higher.
Design studies indicate potential to operate at high efficiencies with
development of solutions to high-pressure ratio and internal sealing
requirements [19].
Same sealing considerations that limit utility of notaries for small appli-
cations apply.
Cost Issues
Noncircular scroll involute contours are costlier to machine (an NC
milling process is used) than the cylindrical or flat surfaces of rotary or
reciprocating compressors.
Potential Performance
Potential EER level not readily quantified due to above-mentioned lack
of development to date.
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Compliant designs potentially combine the low pressure loss, low-suc-
tion gas heating of a rotary with the mechanical efficiency and internal
gas sealing of a reciprocating unit.
Best efficiency potential in larger capacities (>600 Btu/hr).
Linear Compressor
Description of Technology
Piston device, driven by electronically controlled, linear, permanent-
magnet motor.
Constant speed, variable displacement device.
Piston sprung with natural frequency close to operating frequency.
Oil-free, self-lubricating.
Uses high-efficiency (94 percent) linear motor.
Status of Development
Prototype units in early tests.
HER of 6.2 achieved in bench tests [20,21],
Technical Issues
Demonstration of reliability and long operating life (40,000 hours).
light control over piston location to prevent contact with compressor
body.
Reduction of leakage past piston seal.
Electronics losses.
Cost Issues
Costs of high-energy, permanent-magnet materials and electronic
drive.
Costs estimated by developers to be similar to conventional compres-
sor [21].
Potential Performance
Potential EER of 6.5 to 7.0.
Variable capacity control, with nearly flat efficiency versus capacity.
Variable-Speed Capacity Control
Description of Technology
Variable-speed operation of the compressor and, optionally, the fans, to
match the cooling output to the instantaneous loads.
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Reduces on-off cycling and associated losses.
Utilizes heat exchangers more efficiently by reducing thermal loading.
Provides opportunity to match capacity to instantaneous load.
Status of Development
Electronically driven, variable-speed-motor technology is developed
and commercialized for appliance applications, such as variable-speed
residential heat pumps.
In the United States, production levels for appliance application are
modest (tens of thousands of units annually). Inverter drivers are mass
produced in Japan for heat pump applications.
Technical Issues
Electronic drives inject noise onto the AC line.
Increased levels of integration of the electronics would produce some
cost savings.
Incorporation of variable capacity control will require automatic air
baffle operation to ensure proper distribution of cold air to the fresh
food and freezer compartments.
Cost Issues
The current OEM cost for a variable-speed, permanent-magnet rotor,
brushless DC motor and the associated drive electronics, for an 800
Btu/hr compressor, is approximately $100.
In large-scale mass production, OEM unit costs could fall to $50 to $55
The variable-speed drive and motor can operate at higher speeds,
allowing reduced compressor cost, and replaces the existing compres-
sor motor, for offsetting cost reductions of approximately $20. The net
increase in OEM component costs, then, would be approximately $30
to $35 [22].
Potential Performance
With the standard efficiency (shaded pole induction) fan/motor, the
variable-speed drive operating at steady state results in increased total
energy, with the energy associated with the increased fan run-time
more than offsetting compressor power savings.
With efficient fans, variable-speed compressor operation can achieve
energy savings.
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Motor Efficiency
Description of Technology
All current U.S. domestic R/F compressors use single-phase induction
motors.
Subject to physical limitations due to material properties, motor effi-
ciency is essentially a cost and size trade-off.
Permanent magnet rotor, brushless DC motor/drive system efficiency
is comparable to the best induction motor, with approximately half of
the losses occurring outside the compressor shell and variable-speed
capability.
Compressors using ECM motors are currently under evaluation.
Status of Development
Induction motor for R/F compressors are fully developed, commer-
cialized, and mass produced.
Highest efficiency requires higher-grade lamination materials, but can
be manufactured with existing production tooling.
Permanent magnet rotor brushless DC motors are fully developed and
commercialized for appliance applications, but are not in mass production.
Technical Issues
No major technical issues relative to induction motors; simply cost/effi-
ciency trade-offs with other requirements, such as starting torque to be
taken into account.
Electronically driven brushless DC motors inject electrical noise onto
utility lines.
FANS
Fans are applied to the evaporators in automatic defrost units and to the con-
densers for units which have bottom-mount condensers. The condenser fan also
provides cooling of the compressor shell, thereby contributing to a significantly
higher compressor HER. By increasing the efficiency of the fan motors, the ener-
gy use of the refrigerator/freezer can be reduced.
Single-Speed Fans
Description of Technology
Fans in R/Fs require 2 to 3 watts of shaft power at speeds of approxi-
mately 1,500 rpm (condensers) and 3,000 rpm (evaporators).
Inexpensive, low-efficiency (20-24 percent), 115V AC-shaded pole-
induction motors are generally used.
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115V AC PSC type induction motor efficiencies up to approximately 37
percent are available, at a significant cost premium [5].
Small DC motor efficiencies up to 72 percent are available [5].
Brushless DC motors are needed for long life requirements
Limited, but improving, mass production for small brushless DC
motors operating at 115V AC exists.
Lower voltage small brushless DC motors are mass produced, but
115V to lower voltage energy conversion increases costs and losses.
Status of Development
Inductive motors with efficiencies up to 30 percent are developed, and
technology is well known.
DC motors having higher efficiency (72 percent) are available.
Mass production of low-voltage (12 and 24 volt), brushless DC motors.
ECM evaporator fans currently used as standard equipment by at least
one manufacturer.
Technical Issues
Protection of electronic circuit boards and components to ensure relia-
bility for long service life is essential.
Cost Issues
115V AC induction motors with efficiencies up to 30 percent are avail-
able for a significant cost premium, almost double the cost.
115V DC motors significantly higher cost than AC motors.
Low-voltage DC motors are low in cost, except for the high cost of
energy conversion from 115V AC to low voltage DC.
Potential Performance
Efficient single-speed PSC fan motor consumes 6-8 watts.
Efficient single-speed ECM fan motor consumes 3-4 watts.
Annual energy savings obtained by ECM fans in place of shaded pole
induction fans range from 30 to 60 kWh, including effects of reduced
cabinet heat load [22].
Variable-Speed Control
Description of Technology
Shaft power consumption of fan in a system of fixed air flow restric-
tions is proportional to cube of fan speed.
Air flow is directly proportional to speed.
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Variable-speed controls needed to operate over range of fan speeds.
Pulse-width modulated (PWM), brushless, DC motorthe most likely
for fan applications.
Status of Development
Technology well known.
Variable-speed drives not integrated with mass-produced, low-volt-
age, brushless DC motors.
Two-speed ECM fans currently available, with second speed at 83 per-
cent of nominal and 45 percent reduction in fan power [5].
Technical Issues
Effective use with variable-capacity compressor, where the fan speed
and air flow rate are reduced in tandem with compressor speed.
Cost Issues
High cost due to lack of electronics integration and mass production.
Potential Performance
Annual savings of 15-25 kWh per year obtained with variable-speed
ECM fans and compressor compared to a variable-speed compressor
with ECM constant-speed fans (in an 18-ft3, high-performance cabinet),
including effect of reduced cabinet loads [22].
HEAT EXCHANGERS
Fan-Forced
Fans are used for air circulation across the evaporator coil to ensure homoge-
nous temperature distribution within the refrigerator compartments and to
increase the heat-transfer coefficients. Fans are also used for the condenser.
This allows the condenser to be located underneath the refrigerator compart-
ments and removes this heat exchanger from sight and provides a "plain" back
on the refrigerator.
Description of Technology
Three basic types: cross-flow, counter-flow, or parallel-flow.
Most fan-forced heat exchangers are cross-flow for simplicity of con-
struction and compactness, as large gains using counter-flow are not
expected with pure refrigerants like CFC-12.
Allows heat exchanger to be partitioned from interior of the cabinet, to
eliminate unnecessary heating during defrosting.
Increased air flow compared to natural convection, allowing greater
heat transfer or increased UA.
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Operates at a higher efficiency due to less compressor work, but
requires additional fan power.
Reduces temperature variation in the cabinet.
Additional energy is necessary to power fans.
Status of Development
Many proposed refrigerants are NARMs, which have a theoretical
advantage (and practical challenges) in the counter-flow design, as
they allow two streams to operate at closer approach temperatures and
higher efficiency.
Evaporators and condensers are available as cross-flow units and
designs that approach counter-flow from at least one major evaporator
supplier have been tested in prototypes in a laboratory setting.
Condensers approaching counter-flow can be built from existing con-
densers in a laboratory setting.
No gains expected with parallel-flow heat exchangers with any refrig-
erant type. No testing in R/Fs.
Technical Issues
Energy gains with use of fan-forced heat exchangers have to be bal-
anced with additional power for operation of fans.
Only heat exchangers that approach counter-flow (as opposed to pure
counter-flow) can be manufactured within space constraints of R/Fs.
Cost Issues
Counter-flow heat exchangers currently available; and cost the same as
cross-flow.
Potential Performance
Modeled performance of NARMs with counter-flow condenser has
shown improvement over same NARM in cross-flow [23].
No experimental numbers available for counter-flow design alone.
Natural Convection
Natural-convection heat exchangers evaporate or condense the refrigerant
without the use of fans. Natural convection has been used for many years.
Description of Technology
Can be used in evaporators and condensers.
Common in cycle-defrost R/Fs.
Evaporators located within cabinet.
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Multiple Pathways to Super-Efficient Refrigerators
Fresh-food evaporator defrosts during the "off cycle of the compres-
sor, but the freezer evaporator should not exceed 32 °F at any time
other than when manual defrost is performed.
No fan power required.
Larger space needed to accommodate evaporators and condensers,
since natural-convection heat exchangers must be larger (unless wrap-
around design is used).
Options that maximize internal volume and evaporator surface area
include: a wrap-around design located in walls, a hanging design from
top or back wall, or an evaporator shelf design.
Can approximate counter-flow if exchanger orientation is correct, but
not as well as fan-forced heat exchangers.
No parallel designs have been investigated, as no potential gains are
expected.
Significant temperature gradients throughout compartment are possible.
Lack of fan significantly reduces compressor performance.
Status of Development
Used for many years.
Cross-flow and designs approaching counter-flow are available for
fresh-food section and for the condenser.
Technical Issues
Enlarged evaporator surface area requires more space within the cabinet
Cost Issues
More materials of construction needed with natural convection for
counter-flow or cross-flow designs than fan-forced designs (although
cost of fan is not required).
Potential Performance
Generally, compressor power is higher, but partially offset by absence
of fan power.
Location
The location of the evaporator and condenser can affect the energy perfor-
mance of the system.
Description of Technology
Locating condenser above instead of beneath the cabinet may reduce
undesirable heat transfer between the condenser and the cabinet due to
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conduction through the floor of the R/F, especially when the less-used
freezer compartment is a drawer underneath the food compartment.
Evaporator location is important, especially for natural convection
evaporators, to allow adequate mixing with natural air-flow patterns.
Options that maximize internal volume and evaporator surface area
include: a wraparound design located in the walls, a hanging design
from the top or back wall, or an evaporator shelf design.
Status of Development
Most fan-forced condensers are located on the bottom of the R/F, and
most natural-convection condensers are located on the back of the R/F.
Most fan-forced evaporators are located either behind the freezer com-
partment or in the mullion.
Most natural-convection evaporators are wrap-around or hanging.
A few manufacturers locate condensers on top of cabinet.
Some manufacturers locate condensers or portions of condenser within
the outer shell of the cabinet, eliminating the need for anti-sweat
heaters or space requirements of a natural-convection condenser.
Technical Issues
Condensers on top of cabinet may be more energy efficient but may be
inconvenient for consumers. One manufacturer hides the top-mounted
condensers. Manufacturers are reluctant to change because of possible
loss of consumer acceptance, and higher manufacturing costs.
Hanging evaporators or shelf evaporators are two ways to maximize
the internal cabinet space while maintaining surface areas, but may
make it difficult to clean compared to evaporators located within the
walls of the cabinet.
Top-heavy refrigerators may tend to tip over.
Cost Issues
Evaporators or condensers integrated into the walls of the cabinet may
make the R/F more expensive to manufacture than external condensers.
Slightly higher manufacturing costs are associated with the trim neces-
sary to conceal top-mounted condensers.
Enhanced Surface Area
Enhanced surface areas increase the heat-transfer coefficient by disrupting the
boundary layer of the fluid flowing across such a surface. However, any such
improvement is usually accompanied by an increased pressure drop. Good
designs of enhanced surface areas improve the heat-transfer coefficient signifi-
cantly with only a minimum effect on pressure drop.
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Description of Technology
Heat exchangers with greater surface area increase the amount of heat
transfer between the streams, allowing the approach temperature of
the two streams to be reduced and the system to operate at greater effi-
ciency. Effects of greater area are more evident in natural-convection
systems.
Increasing both the internal heat-transfer coefficients and the external
heat-transfer coefficient is theoretically beneficial. The largest contribu-
tion is, however, expected from outside enhancements.
Status of Development
Enhanced surface areas include the current fan-forced designs (e.g.,
fin-tube, spiny fin, glued fin).
Natural-convection heat exchangers often enhance surface area by
using a plate or roll-bond design, as opposed to a single coil of refriger-
ant piping. Attempts have been made to maximize natural-convection
evaporators by adding short fins to natural-convection evaporators.
Technical Issues
Enhanced designs that significantly increase original charge of refriger-
ant may have negative impact on cycling losses and overall efficiency
of the system.
In general, more fins/inch increase the surface area and should
increase performance of heat exchanger. In reality, performance is lim-
ited by increasing pressure drop through the fin spacing, which
increases with frost buildup.
The effect of enhancements in heat transfer has always to be weighted
against any increase in pressure drop.
Cost Issues
Increased material cost is proportional to the amount of additional
material necessary for enhanced surfaces and the increased complexity
of the manufacturing process.
Potential Performance
Increased performance expected with enhanced surface areas, if
cycling losses or pressure drop losses or defrost losses do not cancel
the benefits of modifications.
High Thermal Mass
A certain loss of energy efficiency is associated with the compressor cycling on
and off. A reduction of the number of cycles leads to increased overall efficiency.
One way of reducing the number of cycles without affecting the temperature
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swing is to increase the thermal mass in the cabinet. It is important that this mass
is in a good heat-transfer relationship with the air passing across the evaporator.
Description of Technology
May reduce cycling by allowing a "cold storage or heat storage" location.
Allowing high-thermal-mass evaporators to act as a cold storage loca-
tion may lengthen the "off" time of the system, but it will also lengthen
the time necessary to cool the evaporator; reduced cycling losses; simi-
lar reasoning holds for condensers.
* May be more effective with natural-convection heat exchangers, which
already have large surface areas.
Increased power requirements for defrosting likely.
Status of Development
At least two researchers have attempted to use high-thermal-mass
evaporators to reduce cycling in R/Fs [24,25].
Performance improvements could not be attributed to this design
change alone.
Technical Issues
Adds weight and bulk to the R/F.
Most manufacturers attempt to maximize the internal cabinet volume.
Cost Issues
Additional cost for additional materials and complexity of manufac-
turing process.
Potential Performance
Some experimental performance gain estimates are available [24,25].
Any gains will be associated with cycling, but are very difficult to esti-
mate at this time.
Suction Line
Suction-line heat exchangers located in the refrigerant loop may provide
changes in efficiency; however, it is entirely dependent upon the refrigerant used
and for some refrigerants, there may be a decrease in performance. Suction line
heat exchanger may increase compressor life.
Description of Technology
In current R/Fs, the suction-line heat exchanger acts as a flow con-
troller (capillary tube) and heat exchanger.
In some prototypes, these two functions have been separated.
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Suction-line heat exchangers ensure that no liquid will enter the compres-
sor, while at the same time subcool the refrigerant before the evaporator.
Status of Development
Consists of capillary tubes bound to the refrigerant line.
Currently available.
Cost Issues
The presence and size of the suction-line heat exchanger will affect the
cost of the R/F only slightly.
Potential Performance
May increase or decrease the performance of the cycle, depending on
the individual refrigerant.
EXPANSION DEVICES
Expansion devices are used in vapor compression cycles to control the flow of
the refrigerant and provide a pressure drop into the evaporator. Different type of
controls can be used. The optimization of this component is critical when chang-
ing refrigerants and oils.
Capillary Tlibe
A capillary tube is the simplest device to meter the refrigerant flow into the
evaporator.
Description of Technology
Causes pressure drop to restrict refrigerant flow (to the evaporator)
with its small diameter and long length.
Tube length is optimized for certain operating conditions. Under other
conditions, the evaporator surface is not well utilized.
Advantages compared to other expansion devices include low cost,
ease of manufacturing and installation, and high reliability (usually no
clogging).
Status of Development
Extensively used in mass-produced appliances.
Technical Issues
No active control of refrigerant flow is possible.
Cost Issues
Lowest-cost expansion device.
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Potential Performance
As a passive control device, performance is less than ideal in many
applications, especially when operating conditions, such as cycling,
and the temperature of the surrounding compartments change.
Mechanical Thermostatic
Thermostatic expansion valves are designed to maintain a constant superheat
at the evaporator outlet.
Description of Technology
Keeps superheat temperature at the evaporator outlet constant.
Needle valve operated by pressure difference between small refriger-
ant charge in a bulb that senses temperature at evaporator outlet and
evaporator and condenser pressure.
Status of Development
Used extensively in air conditioners, heat pumps, and large-scale
refrigeration systems.
Not used in any mass-produced refrigerator.
Technical Issues
Orifices are small, as thermostatic expansion valves have to control
very small flow rates. Clogging of orifices by compressor oil is a possi-
bility. The "on" time of a typical R/F is short compared to other appli-
ances, such as A/Cs, and the transients are rather fast.
Do not adjust sufficiently to changing operating conditions, so benefits
in R/Fs are rather limited.
Performance is estimated based on analysis of losses during compres-
sor "on" time.
Valve has to act as shutoff valve during compressor "off" time.
Cost Issues
Low-cost and readily available devices.
May increase the cost of R/F by $3-$10.
Potential Performance
Use with desired operating conditions potentially decreases the energy
consumption due to constant superheat leaving the condenser.
Electronic Thermostatic
Electronic thermostatic expansion valves use electronic circuitry to maintain a
constant superheat at the evaporator outlet
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Description of Technology
Needle valves are motor controlled or pulsed by sophisticated elec-
tronic devices.
Status of Development
No operating experience.
No device available for R/R
Technical Issues
Reliability.
No experience in R/Fs.
Can be activated by "smart" microprocessor-based controls.
Cost Issues
Expected to be at least several dollars up to several tens of dollars.
Potential Performance
Expected to lead to energy savings more reliably than mechanical ther-
mostatic-expansion devices.
Shutoff Valve
A shutoff valve prevents refrigerant migration from the high-pressure side
(where most of the refrigerant charge is located during the "on" time) to the
low-pressure side and prevents flooding the evaporator. This reduces cycling
losses considerably.
Description of Technology
Separates condenser outlet from evaporator inlet.
Located just upstream of the capillary tube.
Closed during the compressor "off time.
Operated by a solenoid or acts similar to an overpressure relief valve.
Status of Development
Used in large refrigeration, air-conditioning, and heat-pump systems.
Function usually taken over by expansion device.
Some mass-produced R/Fs with rotary compressors use shutoff valves.
Technical Issues
Available.
Not introduced in every product.
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Application limited to rotary compressors due to high starting torque
requirements.
No major technical hurdles.
Cost Issues
Increases first cost of R/F slightly.
Potential Performance
Effect on energy savings dependent largely on product, its design fea-
tures (especially on the high-pressure side of the refrigeration cycle),
the geometry and location of heat exchangers and their connections,
and the compressors used.
Expected energy savings of several percent in certain R/F models.
CABINETS
Increased Foam Thickness
Energy efficiency can be improved by adding insulation to the cabinet, there-
by decreasing the amount of heat flow into the cabinet. The greatest concern
regarding the thickness of the insulation has been the size constraints of the
kitchen void, the ability to get the refrigerator through doors in the home, and
the ultimate consumer acceptance of thicker walls.
Recent market analysis studies, described in Section 2.3, indicate that con-
sumers will both accept and desire double-insulated refrigerators. Prototypes
have demonstrated energy savings of over 25 percent.
Description of Technology
* Cabinet (or door) assembled.
Liquid chemicals injected between liner and case.
Reaction in situ produces foam that fills void.
Foam solidifies and cures.
Status of Development
State-of-the-art, mass-production process.
Thick walls now employed in some freezer models and several super-
efficient refrigerator models produced in Europe and Asia.
Technical Issues
CFC-11 blowing agent replacement must be found.
Foam-density modification may be required.
Increased demold time may affect production rate and cost.
Larger cabinet size may affect market served.
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Cost Issues
Materials costs: $7 for adding 0.5" to $30 for adding 2" to an 18' refrigerator.
Transportation: $5 to $8.
Equipment and retooling: $10.8 to $14.8 million.
Other expenses: $5.8 to 7.7 million.
Manufacturer's cost impact analysis completed [26].
Potential Performance
Energy savings of greater than 25 percent achieved in prototype tests
(see Section 2.2.).
Energy savings greater than 25 percent predicted [27].
Alternatives to Blowing Agents
Various alternatives are under consideration to replace CFC-11 as the foam
blowing agent in polyurethane foam insulation. The most promising liquid
blowing agent options include: HCFC-141b and cyclopentane. HCFC-123 is no
longer being actively pursued by refrigerator manufacturers. The most promis-
ing gaseous blowing agents include: HCFC-22 with or without HCFC-142b, and
HFC-134a. The HCFC options are considered "transitional/' due to their ozone-
depleting potential. Due to toxicity concerns, global warming potential, energy-
efficiency implications, and other environmental factors, the final blowing agent
choice has not yet been determined, and may not be a single solution, but rather
a number of options introduced in different refrigerator markets.
Most of the alternatives have been extensively tested for their energy perfor-
mance. Initially, HCFC-123 and HCFC-141b had been expected to increase the k-
factor by 5-10 percent. With changes in foam formulation, HCFC-141b is now
able to provide equivalent performance to typical foams produced in the United
Statesi.e., k-factor of 0.125 Btu*in/(h*ft2*F) or 0.018 w/(m*K) [28]. This analy-
sis, however, assumes the k-factor of HCFC-141b foam insulation is 2 percent
higher than the typical CFC-11 foam [9].
Longer-term options under consideration include fluorinated ethers and hexa-
fluorobutane.
Description of Technology
Blowing agent fills cells in foam insulation.
Low-conductivity blowing agent yields excellent thermal performance
of foam.
Status of Development
Near-term options extensively tested.
Thermal performance over timei.e., aginguncertain for some options.
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Technical Issues
HCFC-141b (and HCFC-123) are near-drop-in replacements.
Explosion proofing of foaming equipment required for cyclopentane.
High-pressure tanks, etc., required for gaseous blowing agents.
Poorer thermal performance of all foams, except with HCFC-141b.
Toxicity of decomposition products of some alternatives needs to be
evaluated but is not expected to be an uncontrollable problem.
Work-place exposure levels for HCFC-123 are 10 ppm.
Cost Issues
Materials costs higher: approximately 20 percent higher for HCFC-
141b blown foam [3].
Capital costs: explosion proofing for use of cyclopentane or high-pres-
sure equipment for use of gaseous-blowing agents.
Potential Performance
Equivalent thermal performance to typical U.S. CFC-11 blown foams
attained with HCFC-141b.
Five percent or more poorer thermal performance with other near-
term options.
Microcell Foam
Microcell foam results from modifications to the foam formulation to provide
a finer cell structure, thereby reducing the radiative transport within the foam
and decreasing the net thermal transport. Microcell foams are under develop-
ment to use with alternative blowing agents.
Development of Technology
Formulation modifications and/or additives produce finer cell structure.
Smaller cell size reduces radiative transport within foam and improves
thermal performance.
Status of Development
Used in CFC-11 foams in Japan.
Under development for alternate blowing agents.
Technical Issues
Some nucleating agents currently employed have very long atmos-
pheric lifetimes and are a global warming concern.
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Cost Issues
Higher materials cost and density: approximately a 20 percent
increased cost for microcell HCFC-141b foam over typical HCFC-141b
foam [3].
Potential Performance
Six to eight percent improvement in thermal performance typical [3].
Greater than 10 percent improvement possible.
Carbon Black
Carbon black particles distributed into the foam reduce the radiative heat
transfer within the foam and therefore can improve the thermal performance of
foam by 10 to 20 percent. Currently this technology is being introduced into the
building insulation market in polyisocyanurate foam products and tested in
appliance insulation applications.
Description of Technology
Particles distributed in chemicals before foaming.
Particles reduce radiative heat transfer within foam and improve ther-
mal performance.
Status of Development
Commercial production of construction materials.
Trials of pour-in-place formulations for R/Fs completed.
Technical Issues
Development of optimized pour-in-place formulations.
Cost Issues
Carbon black replaces more expensive foam chemicals.
Higher materials costs and density may result in 10 to 20 percent
increase in foam cost [3].
Capital for possible foaming equipment modifications.
Potential Performance
Up to 10 percent improvement in thermal performance.
Up to 15 percent improvement in combination with microcell formula-
tion [3].
Gasket Region
A significant portion of the heat gain to R/Fs occurs through the gaskets and
the door and cabinet flangesi.e., the gasket region. By improving the design of
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the gasket region, heat leakage into the cabinet can be greatly reduced, and the
efficiency of the refrigerator significantly improved. Removing the thermal
shunting on either side of the gasket results in more than a 50 percent reduction
in heat leakage through the gasket region [7].
Description of Technology
Plastic extrusion with complex cross section containing many small air
pockets.
Flexible magnet inserted.
Cut and joined to appropriate dimensions.
Fastened to R/F door(s).
Flexible magnetic seal to cabinet.
Status of Development
Significant R/F energy-consumption reductions achieved in laboratory
tests [7].
Modified door flange incorporated into some 1993 products.
Technical Issues
Redesign of cabinet flange maintaining rigidity, while reducing ther-
mal short.
Minor redesign of door flange to obtain maximum possible improvement.
Cost Issues
Capital for retooling.
Potential Performance
Fifty percent reduction in heat leakage through gasket region [7].
Advanced Insulations
Advanced insulation technologies, typically in the form of evacuated panels,
are being evaluated for R/F insulation. These technologies have provided resis-
tivity of greater than R-20 per inch for powder-filled panels and R-40 per inch
for fiber-filled panels. When incorporated into the walls of an R/F, this can sig-
nificantly affect the energy performance. The largest uncertainty is their long-
term reliability.
Description of Technology
Evacuated systems
-Powder, fiber or ceramic spacer filler materials.
-Plastic, glass, or metal containment materials.
-Modest to high vacuum.
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Gas-filled systems
-Low-conductivity gas.
-Polymer radiation barrier and containment materials.
Container formed, filled, and sealed
Elements combined with foam to produce composite wall
Status of Development
Pilot production of panels.
R/F prototype tested.
Lower-cost filler and barrier materials under development.
Production facility announced for 1994.
Limited product introduced in the European refrigerator market in 1993.
Technical Issues
Life.
Thermal performance over time.
Mechanical performance.
Production and installation technology.
Cost Issues
Materials cost: $1.40 per board foot [26].
Capital costs: $23.6 million [26].
Performance Potential
Ten to twenty percent energy reductions obtained in prototype units
[29,30].
Twenty percent or more reduction predicted [9,27].
DEFROST HEATERS
Gal Rod Heaters
Description of Technology
Cal Rod, or similar, metal-jacketed, electric-resistance heating elements
are integral with the evaporator.
During the defrost cycle, with the evaporator fan off, the heaters are
powered, typically 400 to 500 watts, heating the evaporator and melt-
ing the frost.
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Typical defrosting time is about 10 minutes with light frost loads.
Longer periods when heavy usage is encountered.
Status of Development
Fully developed and commercialized for several decades.
Used, along with other types of electric-resistance heating elements, in
virtually all automatically defrosted domestic R/Fs.
Technical Issues
Heater element occupies a portion of the evaporator air-flow cross section.
Heat input is not well distributed; as a result some areas of the evapo-
rators become warmer than necessary to melt the frost.
Cost Issues
Low-cost method of defrosting.
Potential Performance
A timed, electric resistance defrost system in a single-evaporator,
1993 standards R/F uses approximately 4 to 7 percent of the total
energy input in the DOE closed-door test (total of electric-resistance
heat input and refrigeration energy to return evaporator to normal
operating temperature).
Reductions can be achieved through improved controls e.g., adap-
tive defrost (see below).
Glass-Enclosed Heater Element
Description of Technology
Radiant tube-type heater (metal-jacketed, electric-resistance heaters
can also be operated as radiant heaters).
Originally used in helical spine-fin evaporators, where a single radiant
tube in the center could heat the entire evaporator.
Also used in fin-tube evaporators due to lower cost. Located at the bot-
tom, heat is distributed over the entire evaporator via a combination of
radiation, conduction, and natural convection.
Status of Development
Fully developed and commercialized.
Used, along with other types of electric-resistance heating elements, in
virtually all automatically defrosted domestic R/Fs.
Technical Issues
Heat input is not well distributed; as a result, some areas of the evapo-
rator become warmer than necessary to melt the frost.
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Cost Issues
Least-cost method of defrosting, lower cost than nonradiant Cal Rod
heaters, because power density is higher and the length is correspond-
ingly shorter.
Potential Performance
No significant difference in energy consumption compared to non-
radiant Cal Rod.
Reductions can be achieved through improved controlse.g., adaptive
defrost (see below).
Hot-Gas Bypass (Condenser Gas)
Description of Technology
With hot gas defrosting, the heat input to melt the frost from the evap-
orator is supplied by compressor discharge gas.
To defrost, a hot gas bypass valve opens, allowing the compressor dis-
charge gas to bypass the condenser and capillary tube. The hot gas
enters the normal inlet end of the evaporator, passes through and heats
the evaporator, and then returns to the compressor.
Heat to the hot gas is provided by a combination of the real-time
power input to the compressor, plus heat stored in the compressor
motor and cylinder parts from the preceding run cycle.
Status of Development
Hot-gas defrosting is widely used in supermarket refrigeration sys-
tems and commercial ice machines.
The technology has been applied to domestic R/F in the past but was
discontinued due to reliability problems.
Technical Issues
The hot-gas bypass valve is less reliable than electric-resistance heaters.
The sealed refrigeration system must be opened to replace a failed valve.
Compressor power input typically rises during a hot-gas defrost cycle,
potentially overloading a low back pressure-type compressor.
The heat input supplied by the hot gas will be less than the heat input
supplied by an electric-resistance element, especially at low room
ambients, requiring longer defrost times.
Hot-gas defrost does not melt ice chunks that fall off the evaporator,
requiring supplemental heat to complete melting.
Valve leakage in the closed position cannot be tolerated. Even a small
leak will reduce the efficiency of the cycle for normal cooling operation.
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Cost Issues
A hot-gas valve and the extra tubing would cost $5-$10 more than an
electric-resistance element.
Potential Performance
Hot-gas defrost is unlikely to be adopted in future designs due to reli-
ability problems in the past.
Adaptive Defrost
Description of Technology
The most common defrost control is an electromechanical timer that
initiates defrosting after a fixed period of compressor run time, with
defrost termination determined by coil temperature/ as sensed by a
bimetallic disc temperature sensor.
Commercial adaptive defrosts adjust the interval of compressor run
time between defrosts, based on the time required to reach defrost ter-
mination temperature (e.g., less time to termination is indicative of a
light frost load, so the compressor run time between defrosts would be
increased).
Status of Development
Timed defrosting, using an electromechanical defrost timer based on a
fixed compressor run time, has been standard practice for several
decades.
Adaptive defrost systems have been developed and commercialized
and are used in current, top-end domestic R/Fs having microproces-
sor-based controls.
Technical Issues
None.
Cost Issues
Electromechanical defrost timers are very low in cost at the OEM level
(approximately $4-$5).
Adaptive defrost will be more expensive than timed defrost (addition-
al cost on the order of $8-$10) for R/Fs not already having micro-
processor-based controls and displays. The major cost elements
include a microprocessor (and DC power supply), and a contactor for
switching the compressor off and the defrost heater on (or otherwise
activating the defrosting system).
Mass production can be expected to lower the cost, if more widespread
use is made of adaptive defrost.
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Potential Performance
As noted above, conventional, timed, electric-resistance heated defrost-
ing (heat input plus refrigeration to remove the defrost heat) accounts
for 4-7 percent of the total input power of a typical 1993 top-mount
refrigerator/freezer at DOE closed-door test conditions.
Across the range of U.S. climate and usage patterns, adaptive defrost
could reduce defrosting power consumption significantly.
ANTI-SWEAT HEATERS AND THERMAL BREAK
Anti-Sweat Electric Heaters
Description of Technology
Low-cost, electric-resistance wire traces the perimeter of freezer door,
sometimes the refrigerator door as well, outside the gasket and ther-
mal break, maintains cabinet exterior surface temperature above room
dew point.
As anti-sweat heat input is usually not needed, an energy saver switch
is usually provided, allowing consumer to shut off power to heaters.
Status of Development
Fully developed; have been used for decades.
Technical Issues
Electric-resistance heat input adds to cabinet load as well as direct
power consumption.
Cost Issues
Least-cost means of providing anti-sweat function.
Potential Performance
Performance is not limited by electric heater performances, but rather
by the performance of the thermal break (see brief treatment, below).
Anti-Sweat, Post-Condenser Loop (Liquid-Line Heat)
Domestic refrigerators commonly have small electric-resistance heaters in the
door mullion and door flange to prevent condensation. These heaters could be
replaced by the liquid line from the condenser. This would require additional
piping within the cabinet, but would reduce the need for these small heaters.
Description of Technology
Utilization of heat in refrigerant leaving condenser.
Additional liquid subcooling improves cycle efficiency.
Conduct the condenser liquid line around the door flange and mullion.
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Status of Development
Liquid line heating around door flange currently used in refrig-
erator/freezer models by several manufacturers.
Technical Issues
More complex circuiting.
Not reliable in preventing condensation of moisture and buildup of
mildew, as heat is only available during compressor run times.
Post-condenser, anti-sweat heat may not be adequate in cold, humid
climates.
For some products, electric heaters may still be required, either to sup-
plement the anti-sweat capability or to cover sweat areas that cannot
be reached with liquid lines.
Application to mullion area would require a two-tub design for refrig-
erator/freezers.
Reduction of refrigerant charge inventory may require completion of
condensation in the post-condenser loop.
Heat leak to cabinet from post-condenser loop occurs whenever com-
pressor runs; electric heaters are switchable, with no heat leak while in
the "off position.
Cost Issues
Electric heaters are installed at lower cost. In some units, electric heaters
are installed in pairs for reliability, thereby reducing cost difference.
Installation requires more brazed connections, increasing the potential
for future system leaks.
Potential Performance
May increase liquid subcooling, providing increased evaporator capacity.
Choose suitable compressor run times to prevent mildew formation.
Risk in humid climates that liquid-line heat is not sufficient to prevent
mildew formation.
Cabinet design improvements may result in shortened run times, with
reduced post-condenser heat available to meet the anti-sweat needs.
Anti-Sweat, Pre-Condenser Loop (Vapor-Line Heat)
Description of Technology
Instead of electric-resistance heating wire, copper tubing with con-
denser discharge gas used to trace the freezer-door perimeter.
As with electric-resistance, anti-sweat heaters, the purpose is to main-
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Multiple Pathways to Super-Efficient Refrigerators
tain the temperature of the flange and mullion external surface areas
above the room air dew point.
Some increased gasket-area heat leak into the cabinet may result (com-
pared to no anti-sweat heater), but additional condenser capacity is
also provided.
Status of Development
Hot-gas, anti-sweat loops are well developed and understood.
Technical Issues
This form of anti-sweat heater cannot be shut off when not needed;
some additional heat leak results from maintaining higher mullion and
flange temperatures.
The internal volume and heat transfer of the loop interact with the rest
of the refrigeration system, particularly affecting the optimum charge
level and capillary sizing.
Anti-sweat effectiveness drops in low-room ambient (low-compressor
run time), high-humidity conditions.
Control of hot spots along the cabinet exterior may be difficult with
pre-condenser loop.
Cost Issues
Minimal overall cost impact, more expensive loop cost partially offset
by elimination of electric heaters, energy-saver switch, and wiring.
Potential Performance
Eliminates power consumption of electric heater.
Heat leaks to cabinet occur whenever compressor operates, whereas
heat leaks from electric anti-sweat heaters occur only when heater is
activated.
Anti-Sweat, Thermal Break/Energy-Saving Options
Description of Technology
The thermal break provides a low heat-gain transition zone at the door
gasket areas between the room ambient temperature and the cabinet
interior temperature.
The heat gain through the thermal break to the cabinet interior can be
reduced by increasing the length of the conduction path through the
break area.
Magnetized plastic gasket contact areas are being introduced.
Reducing the heat leak reduces the total cabinet loads and also reduces the
heat input to the door-perimeter area that is needed to prevent condensation.
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Status of Development
Conventional, narrow-door, gasket-thermal breaks have been used in
production R/Fs, meeting the 1990 energy-efficiency standards.
There is ongoing work relating to improved thermal breaks to reduce
gasket heat leaks. Improved thermal breaks are probably being used in
1993 standard models.
Technical Issues
Geometric considerations (wall and mullion thickness, door-swing
radius, door-shelf depth) limit the length of the thermal-break conduc-
tion path.
Cost Issues
Within the geometric constraints noted above, the cost impact of an
improved break configuration is minimal.
Potential Performance
Substantial reductions in both gasket-area heat leak and anti-sweat
heater heat input can be realized.
2.2 EPA Refrigerator Analysis Program (ERA)
MODEL DESCRIPTION
Background
The computer model used in this report to compare R/F design choices and to
project energy efficiency evolved over a 10-year period, beginning with the
development of a public-domain model for the DOE Appliance Efficiency
Standards effort [35]. At that time, the refrigerant choice was essentially limited
to CFC-12, and the single-evaporator cycle was the refrigeration system design
most widely used.
This early public-domain model was used by DOE in subsequent evaluations
of energy-savings options and served as a partial basis for setting the 1990 and
1993 energy-efficiency standards.
Beginning in 1989, as part of an effort undertaken by EPA to facilitate the
development of CFC-free, energy-efficient appliances, a series of important
enhancements to the model was initiated. The model evolved substantially over
this time to meet the broad needs for evaluating advanced cabinet designs, new
refrigerants, and alternative-cycle design choices.
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Multiple Pathways to Super-Efficient Refrigerators
Model Overview
The EPA Refrigerator Analysis (ERA) model consists of four major compo-
nents that combine to simulate the performance of a domestic refrigerator: (1) a
menu-driven input processor, (2) a cabinet-loads simulation; (3) a thermodynam-
ic-cycle simulation, and (4) an energy-consumption calculation [1].
ERA determines the daily energy consumption assuming quasi-steady cabinet
heat flow and cycle-averaged operating efficiencies. The underlying assumption
is that the effects of cabinet-load dynamics and the uncertainties associated with
corrections to describe the refrigeration cycling behavior are small relative to the
difference between alternative cabinet and cycle designs.
Most of the common refrigerator classes are represented within ERA.
Refrigeration cycles commonly used in the United States, Europe, and Asia are
simulated, along with most of the advanced cycles of recent interest.
Simulation of the energy consumption considers the major interactions that
appear in a working refrigerator. A change in one area of the design will affect
the performance of a number of other components. As an illustration, specifica-
tion of the application of a post-condenser loop around the freezer door flange
will affect the heat leak into the cabinet, the need for supplemental electric-resis-
tance, anti-sweat heat, and the refrigerant subcooling prior to entering the
expansion device (cap-tube); for this same example, a change in the compressor
capacity or efficiency will affect the heat available to a post-condenser loop, since
it is related to the compressor run time and the condenser heat load.
ERA treats the refrigerator cabinet, cycle, and controls as a system, rather than
as a sum of isolated components. As a consequence, the effects of the use of dif-
ferent technologies will be dependent upon which prior technologies have been
adopted into the conceptual design.
Table 2.1 summarizes the R/F design parameters considered by this program.
Cabinet Loads Model
Five basic R/F configurations can be simulated by ERA: (1) top-mount refrig-
erator/freezer, (2) side-by-side refrigerator/freezer, (3) bottom-mount refrigera-
tor/freezer, (4) chest freezer, and (5) upright freezer. Design parameters consid-
ered include: external dimensions, internal volumes, insulation system geometry
and resistivities, mullion dimensions and resistivity, compressor cabinet dimen-
sions and insulation design, gasket heat leaks, cabinet-section control tempera-
tures, environmental conditions, door-opening schedules, defrost strategies, anti-
sweat heater design, and penetrations. The cabinet-loads program breaks down
the steady-state heat loads by component as well as by compartment.
A door-opening model has been incorporated into ERA, based on published
research data [36] and a description of time-dependent air exchanges. The sensi-
ble and latent heat loads are estimated for assumed door-opening schedules. The
moisture exchange may result in additional defrost loads, depending on the tem-
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Multiple Pathways to Super-Efficient Refrigerators
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Part 2. Supporting Documentation
gerator/i-reezer ues
*» i«*«V.7t * V.. , ". , T"..\\N.»lA'frvaS\i T
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Multiple Pathways to Super-Efficient Refrigerators
perature of the evaporator. Although the Multiple Pathways analyses have
focused on the DOE 90 °F closed-door test conditions, ERA can be used to explore
a given refrigerator/freezer performance at other ambient and use conditions.
Cycle Model
The cycle model is a derivative of the NIST CYCLE7 program [37]. Changes to
the original model include: (1) incorporation of an ability to deal with R/F cycle
designs, (2) addition of interchangers (including the suction-line heat exchang-
er), (3) specification of the evaporator and condenser heat-exchanger design in
terms of area and U-value parameters (e.g., in terms of the parameters that con-
trol the net heat transfer, rather than in terms of the results of the heat transfer),
and (4) determination of mass flow and motor power consumption from a com-
pressor model.
Four cycle configurations are included in ERA: (1) standard single evaporator
cycle; (2) Lorenz cycle with refrigerant mixtures; (3) dual-loop system employing
two independent refrigeration cycles, one for each compartment; and (4) dual-
evaporator cycle, with two evaporators connected in series, normally employing
a pure refrigerant.
Heat-exchanger conductance (UA) values can be specified. Or, as an option, the
heat exchanger may be described in terms of its design parameters (tube size and
length., configuration, fins, materials, air-flow rate, refrigerant flow, entering and
leaving refrigerant quality, etc.) and models built into ERA will calculate the refrig-
erant-side and air-side heat-transfer UAs and the refrigerant pressure drops. As
the refrigerant-flow rate changes (from a compressor substitution, for example), or
as refrigerant properties change (from substitution of an alternate refrigerant or
refrigerant blends), updated values for the heat-exchanger UA can be calculated.
Models for single-stage reciprocating and rotary-compressor designs are
included in ERA. Three means of describing compressor performance are provid-
ed: (1) input of the full map data, (2) specification of compressor capacity and EER
at the calorimeter rating point conditions, and (3) definition of the physical para-
meters comprising the compressor (displacement, speed, clearance volume, etc.).
Energy-Consumption Model
The relationship between: (1) the hourly total cabinet heat loads (the refrigera-
tion requirement at the evaporators) and (2) the instantaneous capacity of the
refrigeration cycle establishes the compressor run time. Once the duty cycle is
determined, the energy-consumption terms are easily calculated.
Integration of the loads and cycle through the calculated duty cycle leads to
natural trade-offs associated with design choices that result in a low evaporator
capacity (with the thermodynamic advantage of reduced thermal loads on the
evaporator and condenser) and increased fan energy use due to the longer run
times. For example, the trade-off of a low-speed fan that uses less energy but
provides reduced air flow for heat exchange can be evaluated using the heat-
exchanger algorithms discussed above.
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Part 2. Supporting Documentation
Once the quasi-steady compressor power has been established, a correction
for cycling losses is made, where the cycling rate is a controlling parameter.
Hence, although the analysis is based on cycle-average conditions, approximate
corrections for nonsteady effects are made.
Additional details about the simulation model and its underlying assump-
tions are provided in the ERA User's Manua.1 [I].
Comparison of ERA Predictions and Measured Data
The baseline models used in the Multiple Pathways analysis span the range of
designs for large U.S. refrigerator/freezers. Specific design details for these
refrigerator/freezers (Models A, B, C, E, and F) are summarized in Table 2.2. As
noted earlier, Model D does not represent actual hardware, whereas the remain-
ing models do. In particular, all the data entered in Table 2.2 either were sup-
plied directly by the manufacturers (Models A, B, and C) or were prepared as
input data to a developmental version of ERA by the manufacturers.
The additional Models G and H represent smaller refrigerator/freezers cur-
rently marketed in China. Model G is a bottom-mount unit, whereas Model H is
a small top-mount. Both of the modeled Chinese appliances utilize the dual-
evaporator cycle (two evaporators in series, with a single compressor), and uti-
lize cold-wall evaporators and natural-convection condensers. Design data as
well as test measurements for these models were supplied by the Beijing
Household Electric Appliance Research Institute [38].
A very wide range of cabinet designs, cycle components, and control strate-
gies is represented by the seven actual units. The large U.S. refrigerator/freezers
all use the standard single-evaporator cycle with fan-forced evaporator and con-
denser. Anti-sweat is supplied by a mix of electric heaters and liquid-line heaters.
Both rotary and reciprocating-type compressors are present. Temperature control
of the U.S. designs (Models A-C, E, F) is provided by a temperature sensor in one
of the cabinets to control compressor and fan operation, with a manually set baf-
fle to control the distribution of refrigerated air to the two cabinets. The U.S. bot-
tom-mount (E) and side-by-side (F) use liquid-line, anti-sweat and electric heat
for the freezer door flange and the mullion region.
The Chinese designs are smaller units, with manual defrost and completely
different control methods. A solenoid-controlled valve is used in the Chinese
bottom-mount unit to bypass refrigerant around the fresh-food section for a por-
tion of the cycle to balance the cabinet loads to the individual evaporator capaci-
ties. No active means of matching the evaporator capacities to the cabinet loads
is provided in the Chinese top-mount Model H. However, since these units must
operate satisfactorily in cool environments, an electric heater can be activated to
create an artificial fresh-food cabinet load to force compressor operation and sat-
isfactory freezer temperature.
ERA is capable of modelling each of these designs. Table 2.3 compares test
results against model predictions for each of the models (other than Model D,
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Multiple Pathways to Super-Efficient Refrigerators
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Multiple Pathways to Super-Efficient Refrigerators
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Multiple Pathways to Super-Efficient Refrigerators
which is only conceptual). The first three comparisons in the table are for pre-
1993 top mounts in the DOE closed-door test condition. The range of variation
between the reported DOE test results and ERA simulations is 2 to 5 percent. The
results for Models E and F are for 1993 designs/ which were specified by the
manufacturers in the form of ERA input rather than in the detailed descriptive
form obtained for Models A, B, and C. The error range is 2 to 9 percent for these
two cases.
Four sets of results are listed for the Chinese bottom-mount unit G: current
equipment and thick-wall prototypes at two room temperatures. The error over
this range of conditions is 0 to 9 percent, with the largest error for the thick-
walled prototype at low room temperature.
Current equipment and thick-wall prototype (closed-door) test results for the
Chinese top-mount were obtained at a single room temperature. The ERA model
predictions vary from the test data by 1 to 6 percent.
While the ERA validation is by no means definitive, the program seems capa-
ble of representing a wide range of cabinet and cycle designs with a reasonable
degree of accuracy. The comparison for the Chinese designs shows that the pro-
gram can capture the major effects associated with the changes in the environ-
ment temperature and the level of cabinet insulation. It is noted that the report-
ed daily energy consumptions for the different models range from 0.69 kWh to
2.36 kWh.
2.3 Market Analysis of Double-Insulated
Refrigerators
In recent years, utilities in the United States and Canada have steadily
increased the amount of conservation and load management services they offer
to their customers. To date, over 500 utilities have offered over 1,000 "demand-
side management" (DSM) programs. In 1991 alone, utilities budgeted some $2
billion for DSM investments. Utility conservation incentives increase the attrac-
tiveness of more efficient products by reducing their first cost to consumers.
They respond to the recognition that, even with the presence of energy labels,
most consumers give higher precedence to first cost and other product attributes
than to minimizing product life-cycle costs. By reducing first cost, many utility
appliance rebate programs have been successful in shifting consumer awareness
and preference toward more efficient products.
As refrigerator companies respond to DSM and other programs to enhance
refrigerator efficiency, they need to consider alternative technological pathways
for achieving super efficiency. The characteristics that will determine the sales of
their products are cost, reliability, energy efficiency, and consumer acceptability.
By increasing the insulation thickness of refrigerators, manufacturers have an
opportunity to make significant gains in the energy efficiency of their products.
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Part 2. Supporting Documentation
"Double-insulated" or thick-wall refrigerators offer manufacturers a cost-effec-
tive and reliable way to increase efficiency. While vacuum panel insulation may
provide greater efficiency per inch, the technology is more expensive.
This section reviews the findings of three consumer surveys that indicated that
double-insulated refrigerators will be both accepted and desired by consumers.
FRAMEWORK FOR EVALUATION
Double-insulated refrigerators will be competing to fill kitchen voids (Exhibit
2.1) that become available in the replacement market or are planned in new con-
struction. For example, the typical 18-ft3 refrigerator:
1. Fails to fit in the current void,
2. Just fits,
3. Has very limited expansion room for height or width,
4. Has essentially unlimited room for added height or width but not
both, or
5. Would fit without problem.
Clearly a double-insulated unit, because it is higher, wider, deeper, or all
these, would lose some potential customers, since it will not fit into all potential
customers' voids. In addition, fitting through doorways may further limit the
potential market.
Thus, in evaluating the desirability of using double insulation, it is necessary
to consider how well these units will compete for the remaining markets based
on other desirable attributes. Consideration of these other attributes will deter-
mine whether sales gained because of perceived desirable attributes are greater than
sales lost to competitors for consumers who cannot buy the double-insulated refrigerator
because it is too big for their void.
If sales gained exceed sales lost, the change will prove beneficial. Of course, a
company with a thick-wall model may reposition other products to compete for
the "lost voids" or continue with a product that can fill them.
Increasing thickness by increasing depthespecially of doorsmay also
prove a promising avenue to avoid potential market loss, because of refrigera-
tors that exceed the void size for some consumers.
In the final analysis, the success of double-insulated refrigerators will depend
upon the value consumers place on environmental attributes, on operating-cost
savings, on appearance, on capacity, and on other salient features.
METHOD FOR COLLECTING EVIDENCE
EPA's contractor engaged a professional assessment firm, Richard Saunders
International, to use paid consumer consultants to evaluate double-insulated
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Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 2.1
Prototypical Voids
Voidl
Void 3
Void 2
Void 4
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Part 2. Supporting Documentation
refrigerator concepts. Saunders used focus groups consisting of 100 female head
of households. Groups were selected to yield a socioeconomic profile similar to
that of the country. Sessions were held in Cincinnati, Ohio, in July, August, and
November of 1991 (see Exhibits 2.2-2.4).
Each member of the focus group was given a booklet containing concepts and
questions at the beginning of the session. Consumers were then led through the
concepts by an "emcee," who read the questions out loud and kept things flow-
ing. Concepts were shown and questions were asked about a number of new
product concepts in each session. All consumers responded to each question
simultaneously by electronic device. Responses were tabulated by a computer,
and missing responses were identifiable. The emcee ensured cooperation with
humor and by stressing the importance of each participants' response.
The concepts used in the July and November sessions are shown in the follow-
ing exhibits. The questions asked after each concept was presented and the mean
value of the consumer responses, follow each exhibit. Additional questions that
were asked during a session are organized by their relevance to specific issues
and are listed at the end of this section.
In gathering participant profiles, consumers were also asked to look up the
capacity of their refrigerator and to measure the dimensions of their refrigerator
and kitchen void. The results of these questions, as well as detailed person-by-
person responses to each of the questions, are available at cost upon request.
2.4 The Sears Energy Story
In December 1992, just prior to the delivery of the energy-efficient 1993 mod-
els that comply with the DOE efficiency standards, Sears Brand Central institut-
ed a new marketing techniqueto sell consumers on the benefits of more energy
efficient refrigerators.
Sears introduced both its sales personnel and its customers to the benefits of
the new "Energy-Saving" 1993 refrigerators. Their program includes both inter-
nal training and external advertising. The guidance to sales personnel stresses
selling the environmental benefits of energy efficiency and working with cus-
tomers to calculate the economic benefits of reduced operating costs to make a
cost- effective decision. The advertising and store placards stress the life-cycle
cost advantage to buying more efficient refrigerators (see Exhibit 2.5).
According to Associate Buyer W.F. Cody, "The initial feedback from the Sears
sales organization has been terrific. Through the combination of training, adver-
tising, point-of-sale identification, and a chart that quickly and clearly shows
that customer the tangible benefits of buying an energy-saving refrigerator, we
have proven that energy sells. Many of our customers are asking for the new
models and are often willing to wait and pay more for them" [39].
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The energy labeling applies to all 1993 models, which have lower energy use
because of the DOE energy-efficiency laws. The labeling does not distinguish
those refrigerators that may even be below the 1993 standards. A potential future
marketing strategy that may be evaluated is to differentiate those models that
just meet the 1993 standard from those that exceed the standard.
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EXHIBIT 2.2
Focus Group Concept 1July 1991
Refrigerator A:
TT1 I I
Refrigerator B:
Refrigerator B has thicker walls than refrigerator A. Assume that
both units have the same interior storage space, all the features/
options of importance to you (color, ice maker, etc.), would fit into the
space that you currently have for a refrigerator, and both cost $500.00.
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If you were going to purchase a refrigerator, which would you prefer?
Strongly Prefer Strongly Prefer
Refrigerator A Refrigerator B
I 1 1 1 1 1 I I L_ I I
01 234567 8A 9 10
8.3
If refrigerator B produces less pollution and the Environmental Protection Agency (EPA)
certifies that it is earth-friendly, which would you prefer?
Strongly Prefer Strongly Prefer
Refrigerator A Refrigerator B
I I I I I I I I I I I
0 1 2 3 4 5 6 7 8 X 10
9.2
If refrigerator B had an EPA certification stating that it would save you $360 on your
electric bill over its lifetime (about 15 years), which would you prefer?
Strongly Prefer Strongly Prefer
Refrigerator A Refrigerator B
I I I I I I I I I I I
10
9.3
If refrigerator B produces less pollution and the EPA certifies that it is earth-friendly,
how much more would you be willing to pay for B?
$0 $20 $40 $60 $80 $100 $120 $140 $160 $180 $200
I I l» I _L I i 1 1 1
01 2 A 3 4 5678910
$50
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Part 2. Supporting Documentation
EXHIBIT 2.3
Focus Group Concept 2November 1991
Choice A:
Double-Insulated Refrigerator
Purchase Price: $490
First-Year Energy Cost: $43
Interior volume same as
your current refrigerator
Choice B:
Single-Insulated Refrigerator
Purchase Price: $500
First-Year Energy Cost: $55
Interior volume 1 cubic more
than your current refrigerator
Assume both refrigerators would fit where you put your current refrigerator.
Assume that a new super-efficient, 18-cubic-foot refrigerator (A) costs you $10 less ($490)
than an 18-cubic-foot refrigerator (B) with the same features ($500), since the local utility
is now offering a rebate on the purchase price, and refrigerator A has an energy cost of
$43 per year. Which would you prefer?
Strongly Prefer
Refrigerator A
0 1
A
1.5
|
2
I I
3 4
I
5
I
6
I
7
Strongly Prefer
Refrigerator B
I I I
8 9 10
126
-------
Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 2.4
Focus Group Concept 3November 1991
Assume your current refrigerator has broken. You enter an appliance store prepared
to purchase a refrigerator with the same interior volume as you now own for $500
(most people own an 18-ft3 refrigerator).
The store manager offers you a special gift certificate for $60, which you can apply to
one of two choices:
Choice A:
Double-Insulated Refrigerator
Purchase Price: $560
First-Year Energy Cost: $43
Interior volume same as
your current refrigerator
Choice B:
Single-Insulated Refrigerator
Purchase Price: $560
First-Year Energy Cost: $57
Interior volume 1 cubic foot more
than your current refrigerator
Assume both refrigerators would fit where you put your current refrigerator.
127
-------
Part 2. Supporting Documentation
Which would you prefer?
Strongly Prefer
Refrigerator A
|
0
1
1 A :
I I
2 3
I
4
I
5
I
6
I
7
I
8
Strongly Prefer
Refrigerator B
I
9
|
10
1.6
Now assume that you can double your energy savings with a new super-efficient, 18-
cubic-foot refrigerator (A) that saves you $28 per year, instead of $14 over the 19-cubic-
foot-refrigerator, and costs you the same as a 19-cubic-foot refrigerator (B). Both cost
$560, and refrigerator (A) has an energy cost of $29 per year while refrigerator (B) has an
energy cost of $57 per year. Which would you prefer?
Strongly Prefer Strongly Prefer
Refrigerator A Refrigerator B
I II I I I I I I I I
0 1 A 23 4 5 6 7 8 910
1.5
128
-------
Multiple Pathways to Super-Effident Refrigerators
How important is it to you to purchase a refrigerator that would prevent the pollution
caused by burning 2,900 Ibs. of coal?
Not Important
I I
Very Important
I I I
8.2
9
10
How important is it to you to purchase a refrigerator that would help prevent global
warming?
Not Important
I
B~K 9
8.4
Very Important
J I
10
Would the knowledge that 15% of the air pollution caused by your home electric use is
due to refrigerators lead you to choose an energy-efficient model over a standard model?
Would Not
Influence Decision
Would Strongly
Influence Decision
1
0
1
1
I
2
|
3
I
4
I
5
I
6
I
7
I
8
_L-
19
8.8
I
10
I believe that my buying decisions:
Make no difference to
the environment
I L_
Can, combined with other people's
decisions, make a significant
environmental difference
IT
8.8
10
129
-------
Part 2. Supporting Documentation
;r*x^«^riWis;ssE^«M%r
would different gram
......
,- -v .
environmental s
Consumer Reports
Important
I 1 I I
Very Important
I I I
0123
Good Housekeeping
Important
I I I I
7.9
9 10
Very Important
I I I
0 1 2
EPA
Important
I I I
0 1 2
Ralph Nader
Important
I I I
3 4
I I
3 4
I I
01234
A Citizen's Action Group
Important
I I I I I
0 1 2
Greenpeace
Important
I I I
012
National Park Service
Important
I I I
0 1 2
Nature Conservancy
Important
I I I
3 A*
3.8
I I
3 A 4
3.5
I I
3A 4
3.2
I I
s eA 7
6.3
I I I
5 A 7
5.9
I I I
5 A6 7
5.7
I I I
567
I I I
567
I I I
567
I I I
8
I
8
I
8
I
8
I
8
I
8
9 10
Very Important
I I
9 10
Very Important
I I
9 10
Very Important
I I
9 10
Very Important
9 10
Very Important
9 10
Very Important
012A345678910
2.8
In purchasing a refrigerator, how important to you is it that your refrigerator be certified
by the US. Environmental Protection Agency as "environmentally superior"?
Important Very Important
I I I I I I I I I I I
130
&A 9
8.2
10
-------
Multiple Pathways to Super-Efficient Refrigerators
How important is it to you to purchase a refrigerator that would keep your ice cream
fresher for longer with fewer ice crystals?
Not Important Very Important
I I I I I I I I I I I
9 10
7.8
How much more would you be willing to pay for a refrigerator that kept your ice cream
fresher for longer with fewer ice crystals?
$0 $10 $20 $30 $40 $50 $60 $70 $80 $90 $100
I I I _ I _ I _ J _ I _ I _ I _ I - 1
0 1 2A 3456789 10
$22
How important is it to you to purchase a refrigerator that would keep your vegetables
fresher and crisper for a longer time?
Not Important Very Important
I I I I I _ I _ I - 1 - L_-J - 1
0 1 2 3 4 5 6 7 8 A 9 10
8.6
How much more would you be willing to pay for a refrigerator that kept your vegetables
fresher and crisper for a longer time?
$0 $10 $20 $30 $40 $50 $60 $70 $80 $90 $100
I I I I _ I _ J _ I - 1 - 1 - 1 - 1
012^456789 10
$29
How important is it to you to purchase a refrigerator that makes less starting and stop-
ping noise?
Not Important Very Important
I I I I _ I _ I - 1 - 1 - L_ - 1 - 1
012345678A910
8.2
How much more would you be willing to pay for a refrigerator that made less starting
and stopping noise?
$0 $10 $20 $30 $40 $50 $60 $70 $80 $90 $100
I I I I _ I _ J - 1 - 1 - 1 - 1 - *
8 9 10
$22
131
-------
Part 2. Supporting Documentation
What is the importance of the following features in your decision to purchase a refrigerator?
Initial Cost
Not Important
1 1 1 1 1 1
01 2345
Better Seals
Not Important
I I I I I I
01 2345
Storage Space/Interior Volume
Not Important
I I I I I I
01 2345
Width of Available Kitchen Space
Not Important
I I I I I I
012345
Energy Efficiency
Not Important
I I I I I I
01 2345
More Easily Moved
Not Important
I I I I I I
01 2345
Interior Volume
Not Important
I I I I I I
01 2345
Very Important
I I I I I
678 9A 10
9.2
Very Important
I I I I I
6 7 8 A 10
9.1
Very Important
I I I I I
6 7 8 A 10
9.0
Very Important
I I I I I
6 7 8 AQ 10
8.8
Very Important
I I I I I
678 A9 10
8.7
Very Important
I I I I I
678 Ag 10
8.7
Very Important
I I I I I
6 7 8 A 9 10
8.6
132
-------
Multiple Pathways to Super-Efficient Refrigerators
What is the importance of the following features in your decision to purchase a refrigerator?
Movable Shelves
Not Important Very Important
1 1 1 1 1 1 1 1 1 1 1
0123456
Operating Cost
Not Important
1 1 1 1 1 1 1
01 23456
Height of Available Kitchen Space
Not Important
I I I I I I I
01 23456
Depth of Available Kitchen Space
Not Important
I I I I I I I
0123456
Freezer Location (Top, Bottom, or Side)
Not Important
I I I I I I I
0123456
Doesn't Break Easily
Not Important
I I I I I I I
0123456
Sturdier Doors
Not Important
| | I I I I I
0123456
Easier to Clean Underneath
Not Important
1 I I I I I I
0123456
Easier to Clean Seals
Not Important
1 I I I I I I
0123456
7 8 A
8.5
I I
7 SA
8.4
I I
7 8 A
8.4
I I
7 8A
8.4
I I
7 8A
8.4
I I
7 8 A
8.4
I I
7 &A
8.2
I I
7 A
8.1
I 1
7 A
8.0
9 10
Very Important
I I
9 10
Very Important
I |
9 10
Very Important
I I
9 10
Very Important
I I
9 10
Very Important
1 1
9 10
Very Important
I I
9 10
Very Important
I I
9 10
Very Important
I I
9 10
133
-------
Part 2. Supporting Documentation
What is the importance of the following features in your decision to purchase a refrigerator?
Deep Door Shelves
Not Important
I I I
8.0
Very Important
I I
9
10
Type of Shelves
Not Important
I I I
I
B
7.8
Very Important
I I
10
Kick Plate That Doesn't Fall Off
Not Important
I I I I
Very Important
I I
0
1
2
3
4
5
6
7
As
7.7
9
10
Environmental Impact
Not Important
I I I I
Freezer Room
Not Important
I [_
7 A 8
7.4
6.9
Very Important
I I
10
Very Important
I I
10
Larger Crispers
Not Important
I I
6.7
Very Important
I I
9
10
Make More Ice
Not important
I I I
I
5 A 6
5.4
Very Important
I I
9
10
134
-------
Multiple Pathways to Super-Efficient Refrigerators
What is the importance of the following features in your decision to purchase a refrigerator?
Controls Odors
Not Important
1 1 1
012
I I I I I
3 4 5 A 6 7
5.4
Very Important
II I
8 9 10
Changeable Color Panels
Not Important
I I I
0 1 2
Ice/Water Service
Not Important
I I I
012
Bottom Freezer
Not Important
I I I
0 1 2
Make Different Shape
Not Important
I I I
0 1 A
1.9
I I I I I
3 4 A 5 6 7
4.4
I I I I I
3 4A 567
4.2
il I I I
4567
3.0
Ice
I I I I I
34567
Very Important
I I I
8 9 10
Very Important
I I I
8 9 10
Very Important
I I I
8 9 10
Very Important
I I I
8 9 10
135
-------
Part 2. Supporting Documentation
What average interest rate do you think you got on your savings accounts, CDs, or other
investments over the last 15 years?
0% 1.5% 3% 4.5% 6% 7.5% 9% 10.5% 12% 13.5% 15%
I I I I I I I I I I I
4 s
7.05%
8
9
10
What rate do you think you will get over the next 15 years?
0% 1.5% 3% 4.5% 6% 7.5% 9% 10.5% 12% 13.5% 15%
I I I I I I I I I I I
4 A 5
6.9%
8
10
Which would you prefer? A $60 increase in your annual salary, or a $60 decrease in your
annual electric bill?
Strongly Prefer $60 Increase
In Annual Salary
I
I
I
Strongly Prefer $60 Decrease In
Annual Electricity Bill
I I I
6 A7
6.6
8
9
10
What inflation rate do you think will take place over the next 18 years?
0% 1.5% 3% 4.5% 6% 7.5% 9% 10.5% 12% 13.5% 15%
I I I I I I I I I I I
s e
8.55%
8
9
10
How much do you pay for your electric, gas, and oil bills every year?
$0 $500 $1,000 $1,500 $2,000 $2,500 $3,000 $3,500 $4,000 $4,500 $5,000
I I I I I I I I I I I
1
$1,650
8
9
10
136
-------
Multiple Pathways to Super-Efficient Refrigerators
How much do you expect your rate of electricity to inflate per year in the future?
0%
1
0
1.5%
I
1
3%
I
2
4.5%
I
3
6%
I
4
7.5% 9%
I I
5 A 6
7.95%
10.5%
I
7
12%
|
8
13.5%
I
9
15%
I
10
What percentage of your income do you think you pay to federal income, Social
Security, and state or local income taxes?
0% 5%
I I
0 1
10% 15% 20% 25% 30%
I I I I I
234 sA 6
26.5%
35% 40% 45% 50%
I I I I
7 8 9 10
Which would you prefer:
Strongly Prefer $152 U.S. Savings Strongly Prefer $60
Bond Redeemable in 17 years No Preference Cash Now
I I I I I i I II i I
0 1 2 3 4 5 6 7 A 8 9 10
7.3
If you were in the market to purchase a refrigerator, how likely would you be to finance
that purchase with a credit card that you pay interest on?
Very Unlikely Very Likely
I I I I I I I I I I I
0 1 A 3 4 5 6 7 8 9 10
2.0
Which is the larger cost of owning a refrigeratorthe purchase price, or the cost of pay-
ing for the electricity to operate the refrigerator over the 17-year life?
Refrigerator Cost Cost of Electricity to Operate
I I I I I I I I II I
0 1 2 3 4 5 6 7 8 A 9 10
8.4
Consider the fact that the energy-efficient refrigerator could save you $14 on your elec-
tricity bill this year. Now suppose you could bank the yearly savings on your energy bill
throughout the 17-year life of your new energy-efficient refrigerator. How much money
do you think you would have to put in the bank today in order to have the same amount
of money at the end of the 17 years as you would have if you were banking your energy
savings?
$0 $34 $68 $102 $136 $170 $204 $238 $272 $306 $340
'I''' JL 1 i 1 1 1
0123456A8910
$238
137
-------
Part 2. Supporting Documentation
EXHIBIT 2.5
Sears Brand Central Labeling
Becoming the Energy Leader
138
-------
Multiple Pathways to Super-Efficient Refrigerators
EXHIBIT 2.5 (continued)
Sears Brand Central Labeling
Becoming the Energy Leader
139
-------
Part 2. Supporting Documentation
EXHIBIT 2.6
Sears Brand Central Energy Sales Training
The Energy Stay
wwuwmein
mm
$40peryoar
x S years
$200 Total
$40p«ry»ar
x IQyeofs
$400 Total Savings
Estimated Annual Consumer Energy Savings
12
Actual household savings vary according to appliance use, geographic area
and uflRly rates.
Environmental Benefits
The second major benefit of the new energy saving refriger-
ators is environmental. We must communicate that buying a new
energy saving refrigerator...
Reduces consumption of natural resources
(coal, oil, gas)
» Reduces harmful power plant emissions
Hetps offset the need to build new power
plants
Being pro-active and knowledgeable on the environmental
benefits is more important than ever. Today, eight out of ten Brand
Central customers consider themselves environmentally conscious.
140
-------
Appendices
-------
Multiple Pathways to Super-Efficient Refrigerators
APPENDIX A
ERA Design Feature Assumptions
Table 1.2 summarizes the specific component design features considered in the
various paths. More detailed descriptions of the assumptions made in applying
each technology follow. These assumptions were followed rigorously at each
step to ensure a consistent analysis.
ADAPTIVE DEFROST
In most instances, the closed-door test condition defrost heat was determined
from an algorithm relating defrost operation to compressor run-time (with a typ-
ical compressor on-time interval of 10 hours). The adaptive defrost algorithm
assumed that the on-time interval could be lengthened to 38 hours (a savings of
74 percent). In addition, it was assumed that the defrost controller used 0.25
watts power when the compressor was running, and that the controller was
located outside the cabinet.
In some of the models the baseline defrost controller used over 1 watt of energy,
and was located inside the fresh food section. Hence, the application of adaptive
defrost results in the additional savings associated with removal of the controller
heat from the cabinet and the reduction in electrical energy.
Assuming that defrost operation is proportional to the compressor on-time
results in a lower defrost requirement when the duty cycle is decreased. Hence,
as the cabinet load is reduced due to increased insulation, or higher resistivity
insulation, the compressor run-time and defrost heat will be likewise reduced.
As a consequence, the savings predicted for adaptive defrost near the end of a
path will be lower than at the beginning when the compressor run-time is longer.
ADVANCED FOAM INSULATION (M1CROCELL AND CARBON
BLACK)
The assumed resistivities for microcell and carbon black HCFC insulation
were 0.590 and 0.630 m2-°C/W-cm, respectively (compared to 0.555 for CFC-11
blown foam). When these options were considered, it was assumed that all the
foam in the cabinet and doors were of the same formulation. Carbon black insu-
lation was always applied following the assumption of microcell insulation.
ALTERNATE REFRIGERANTS
The built-in CSD equation of state [31] was used to determine the thermodynam-
ic properties of all refrigerants. Heat exchanger UA values were calculated for the
new refrigerant using the thermophysical properties for the refrigerant, including
the effects of a change in the refrigerant mass flow rate.
143
-------
Appendix A
Since compressor map data was unavailable for the alternate refrigerants, the
compressor rating point model [1] was used to account for the difference in
refrigerants. As described in the ERA User's Manual [I], the refrigerant density at
the suction port was calculated using the CSD equation of state to adjust the
mass flow rate. The compressor displacement was reduced 25 percent when
cyclopropane was specified as the refrigerant to reduce heat exchanger loading.
The thermophysical properties of alternate refrigerants may dictate the need
for changes in the heat exchanger designs (tube dimensions, etc.) to optimize the
tradeoffs between heat exchanger effectiveness and pressure drops. Such opti-
mizations might make significant impacts on overall performance. They are, how-
ever, beyond the scope of the present study
COMPRESSORS
To the extent feasible, the analysis has been based on the data reported for actu-
al compressors. Inputs needed to describe the compressor performance are the dis-
placement, speed (rpm), type of cooling (fan or static), capacity, and HER as mea-
sured in a calorimeter at the standard -10/90/130 test condition using CFC-12
refrigerant. Corrections were made for other refrigerants and for different operat-
ing conditions [1].
Each path started with the baseline compressor used in the modeled refrigera-
tor. Typical duty cycles were in the range of 40-50 percent. As higher EER com-
pressors were substituted at various points in the paths, the models selected gen-
erally required a smaller displacement to achieve the same capacity as the mod-
els they replaced.
Several of the paths, in particular the dual-loop cycle, assumed the availability of
(future) efficient small compressors. Limiting efficiencies for these components
were based on the analysis presented in References 4 and 22, and on information
obtained in discussions with compressor manufacturers [6].
Designs involving reduced cabinet loads will probably require smaller compres-
sors (with resultant longer compressor run-times). However, selection of the
appropriate design must take into consideration pull-down requirements, which
will place constraints on the allowable reduction in capacity. In addition, fre-
quent door openings, even with a more efficient cabinet, will require that suffi-
cient capacity be retained. For these reasons each pathway analysis was conduct-
ed at a constant compressor capacity. The effects of cycling losses, due to short-
ened duty cycles, were taken into account (cycling losses typically amounted to 2
percent of compressor energy).
CONDENSER AREA
The condenser air flow was held constant with condenser area increases. Only
the number of tubes and the total length of wire fins were increased. The frontal
area for air flow was considered unchanged.
144
-------
Multiple Pathways to Super-Efficient Refrigerators
Increases in condenser area resulted in a lowered refrigerant temperature,
which in turn lowered the heat available for liquid-line heating. Hence, in
some instances the interactive effects resulted in the need for increased electric
anti-sweat heat.
DUAL-LOOP CYCLE
The modeled dual-loop cycle essentially doubled the refrigeration cycle com-
ponents of the baseline units. Evaporator and condenser areas, and fan capaci-
ties, were assumed to be the same in both loops. Capacities, displacements, and
EERs of the "current small compressors" were taken from manufacturer's data.
In general, the compressor EERs (3.6 and 4.7) were significantly below those for
current large compressors (5 to 5.5).
Values for the efficiency of "future small compressors" were obtained from
discussions with a compressor manufacturer. Achievement of these EERs (4.6
and 5.1) does not require any technological breakthroughs.
The compressor behavior with alternate refrigerants (HFC-152a and HCFC-
142b) was determined using the compressor rating point model algorithm [I] as
discussed above for Alternate Refrigerants.
ELECTRIC ANTI-SWEAT HEATERS
Electric anti-sweat heater capacities were defined by the manufacturer's data
obtained for the base case analyses. According to the DOE test protocol, the units
are tested separately with the anti-sweat heaters on and off and the results aver-
aged. The Multiple Pathways analyses were carried out assuming constant oper-
ation of the heaters at half power condition (e.g., if the switchable mullion heater
were 5 watts, the analysis assumed 3 watts constant heater power).
Approximations were made to determine the leakage of the applied anti-
sweat heat back into the cabinet. Based on calculations reported in Reference 32,
and on conversations with industry personnel, it was assumed that 0.30 of the
anti-sweat applied along the freezer cabinet door flange re-entered that cabinet
as an additional heat load. Of the heat applied in the mullion area, it was
assumed that 0.50 contributed to the freezer load and 0.25 contributed to the
fresh food load (0.75 in total re-entered the cabinet). These fractions were held
constant throughout the multiple paths even for cases with increased wall insu-
lation thickness and reduced gasket heat losses. Hence, the analysis was consid-
ered conservative in this area.
EVAPORATOR AREA
An increase in the evaporator area was made by raising the number of tubes
in the direction of the air flow (increase in the evaporator depth). No change was
made in the air flow rate. The ERA model heat exchanger algorithms were used
to determine the change in the net UA of the evaporator as well as the pressure
drop increase.
145
-------
Appendix A
The area increase resulted in a higher refrigerant mass flow rate, which in turn
affected both heat exchanger UAs and pressure drops.
The addition of evaporator area will increase the total refrigerant charge, some-
thing that may be undesirable in terms of oil control or compressor start-up con-
ditions. An optimized design will consider the tradeoffs associated with reduced
tube diameters (which will result in higher pressure losses) and refrigerant
charge. This is beyond the scope of what is intended in this study, where the
objective is primarily to review the potential for energy-efficiency improvements.
FANS
As summarized in Table 1.2, specific fan powers were associated with the vari-
ous categories of fans. The baseline fan energies were unchanged from the refrig-
erator manufacturer's data. "High-efficiency" fans (PSC type) were assigned a fan
power of 6.8 watts for both the evaporator and condenser. ECM fan energy was
assumed to equal 3.6 watts at full speed, and 2.0 watts at 83 percent speed [5].
Systems that required multiple fans (Lorenz and dual-loop cycles) were assumed to
use the same sized fans for both the freezer and fresh food evaporators.
GASKET LOSSES
Gasket heat leaks were specified as door perimeter heat leaks. They were
assumed uncorrelated to other parameters, such as the insulation thickness.
Where refrigerator manufacturers' data were available, they were used for the
baseline units.
Reductions of 25 percent and 50 percent of the gasket loads were considered
as design options. These assumptions were based on recent studies performed at
the University of Kentucky and on laboratory experiments [7]. As discussed in
detail in Reference 7, significant reductions in the heat flow in the gasket region
can be realized by substitution of low conductivity (plastic) materials for the
metallic door flange in current designs.
HEAT EXCHANGER UA VALUES
Specific design information was available for the heat exchangers for most of the
refrigerator/freezer models. This information was used to determine the heat
exchanger UA values.
Updates to the heat exchanger UAs were made at each step in a path using
heat exchanger algorithms built into the ERA model. For example, the substitu-
tion of a different compressor, or a different refrigerant, will affect the refriger-
ant-side heat transfer, thereby affecting the overall heat transfer rate. The effects
of refrigerant mass flow rate and properties on the pressure drops was also eval-
uated at each step using the built-in heat exchanger algorithms [1].
146
-------
Multiple Pathways to Super-Efficient Refrigerators
The built-in heat exchanger algorithms allowed the effects of reduced air flow
to be taken into account. For example, with a two-speed (ECM) fan, fan energy
savings would be offset somewhat by the reduced heat exchanger effectiveness
at the lower air flow rate.
HIGH-RESISTIVITY INSULATION PANELS
High-resistivity panels, such as high-R gas or vacuum panels, were assumed
foamed into the walls containing the panels. Parameters affecting the overall
heat resistance of the walls included: the center resistivity of the panel, the thick-
ness and thermal conductivity of the enclosure about the high resistivity core
(e.g., 0.1 mm plastic wrap), and the position of the panel within the wall itself. In
all cases, the high resistivity panel was assumed placed inside the wall, against
the cabinet skin, with foam separating it from the inner liner.
Two generic cases were considered: (1) 50 percent coverage of the outer wall,
and (2) 80 percent coverage. Since the coverage was less than complete, the pan-
els were foamed along the outer four edges.
Calculation of the net resistivity of the wall included the effects of heat trans-
fer through the enclosure and the foamed portions. A discussion of the method
for determining the net resistivity of a wall containing a high resistivity panel is
given in the ERA User's Manual [I].
INCREASED INSULATION THICKNESS
Increased insulation thickness was assumed to affect only the outer dimensions
of the cabinet; the inner dimensions and food storage volumes were held fixed.
The foam resistivity was assumed to be equal to that used in the previous step
in the path. For example, if the cabinet used microcell insulation, the added insu-
lation was also assumed to be microcell type with the same resistivity.
The wedge dimensions were changed as needed to maintain the same door
dyke dimensions as in the base case. No changes to the anti-sweat heat require-
ments or to the leakage of heat into the cabinet from the anti-sweat heaters or liq-
uid-line heaters were assumed. However, as noted elsewhere, the reduced cabi-
net loads and consequently the reduced compressor run time might require
additional electric anti-sweat heat to supplement liquid-line heat.
LIQUID-LINE OR VAPOR-LINE ANTI-SWEAT HEAT
The advantages of using available heat from the condenser liquid line for
anti-sweat heat come from: (1) removal (or reduction) of electric heat, and (2)
additional sub-cooling achieved prior to entering the cap-tube. Reduction of the
needs for electric heat result in a direct electrical energy savings. Additional sub-
cooling of the refrigerant results in a thermodynamic improvement due to the
increased latent heat available in the evaporator (which will raise the evaporator
temperature and pressure) and the slightly reduced expansion irreversibilities.
147
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Appendix A
In effect, the cabinet flange and mullion act as additional condenser surface. In
practice, the designer may size the components to achieve completion of the con-
densation in the liquid line, rather than in the condenser, to minimize the refrig-
erant charge. The ERA model cannot simulate this condition; however, the con-
denser subcooling was set to zero for all designs involving liquid-line heating.
In situations where the condenser area is increased, or where a higher EER
compressor is used, the heat available for liquid-line anti-sweat is lessened.
Electric anti-sweat heat may need to be added to compensate. Generally, the
requirement for electric anti-sweat heat is highest near the end of a path. The
condition defining the need for electric anti-sweat heat is the refrigerant temper-
ature at the exit of the liquid-line. The amount of switchable heat (when the anti-
sweat control is in the on-position) added was sufficient to meet the net anti-
sweat heat requirements. The analysis of potential savings from using liquid-line
heat was actually conservative since it assumed that the refrigerant leaving the
condenser was fully condensed.
Vapor-line anti-sweat heat was another alternative considered. Because of the
high superheat of the vapor leaving the compressor, the available heat was nor-
mally sufficient to fully replace the need for electric heaters. In effect, the vapor-
line anti-sweat heater acted as a precondenser, resulting in reduced superheat
entering the condenser.
LINEAR (VARIABLE CAPACITY) COMPRESSOR
The linear compressor is a variable capacity device running at a constant
speed [20,21]. It was assumed to be running at half the capacity of the compres-
sor it replaced in the path, and was assigned an EER of 6.5. This option clearly
falls within the realm of technology not immediately available, although early
prototype units have achieved EERs slightly greater than 6 [21] at full capacity.
In a practical system employing variable capacity control, some means must
be incorporated for controlling the distribution of cooled air to each cabinet (baf-
fle control). At low capacities, a smaller fraction of the air must be directed
towards the fresh food section. ERA model predictions for the fraction sent to the
fresh food section by the baffle were 10-16 percent for the baseline units, and
approximately half that with operation at low capacity (high-duty cycle). Some
sort of active baffle control will be required in a system employing variable
capacity control.
LORENZ CYCLES
Two types of Lorenz cycles were simulated: (1) fan-controlled fresh food evap-
orator (Paths 6 and 7); and (2) natural convection fresh food evaporators (Paths 8,
8A, and 12). At each step in Paths 8, 8A, and 12, the evaporator was resized to
achieve a balance between the fresh food and freezer section loads with the evap-
orator capacities. Each step represented a new design point, where the evapora-
tor area was one of the design variables. A complete evaluation of such a design
148
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Multiple Pathways to Super-Efficient Refrigerators
would require analysis of its behavior (with a fixed evaporator size) in various
environmental conditions and usage scenarios (door-opening schedules).
Several criteria were followed when defining the Lorenz cycles: (1) the refrig-
erant blends consisted of HFCs and HCFCs; (2) blends must not result in sub-
atmospheric evaporator operation; (3) only refrigerants whose properties could
be reliably predicted by the CSD equation of state algorithms were used (this
excluded HFC-32 from the analysis); and (4), in fan-forced systems, the evapora-
tor fans were the same size in both compartments (this ensured that assigned
fresh food evaporator fan properties were realistic).
In the fan-forced system, one of the evaporator fans would normally be off dur-
ing a portion of the compressor run-time. During this (small) portion of the cycle,
the particular evaporator was assumed to be effectively absent from the cycle.
NON-CFC DESIGNS
The predicted energy efficiencies for HCFC-blown cabinets and refrigeration
cycles using HFC-134a are nearly the same as, or slightly higher than, the 1993
designs using CFC-11 as the blowing agent and CFC-12 as the refrigerant. As
noted in Table 1.2, the resistivity assumed for HCFC-blown foam is 98 percent of
that for CFC-11 foam. Because the model assumes no degradation in perfor-
mance due to lubricant problems, the predicted system COP when using HFC-
134a is about 1-2 percent higher than for CFC-12. Recent studies, with improved
lubricants, have shown essentially equal performance in a compressor calorime-
ter with the two fluids. The total difference in efficiency of 1-2 percent associated
with the non-CFC design is well within the accuracy of ERA model calculations.
SHUTOFF VALVE
The shutoff valve option can only be applied to the rotary compressor. As
indicated in Reference 34, prevention of the flow of refrigerant from the con-
denser to the evaporator, accompanied by pressure ratio loss during the com-
pressor off-cycle, can overcome cycling losses and can even yield slight increases
in efficiency. The degree to which the shutoff valve improves operation is depen-
dent on the number of compressor cycles per hour, with the largest effect for sys-
tems that have a high cycling rate.
Data supplied by the manufacturers for the baseline systems were used
throughout each path (1 to 1.4 cycles/hour). At these nominal rates, the net change
in compressor power was on the order of 2-3 percent. In practice, as the cabinet
loads are reduced the cycling rates are expected to increase. Hence, the assump-
tions used for the Multiple Pathways analysis may have been conservative.
149
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Appendix B
APPENDIX B
Detailed Pathway Descriptions
PATHWAY 1: MODEL D, CURRENT TECHNOLOGIES WITH
INCREASED INSULATION
Model D is a conceptual design for a refrigerator intended to represent a "typi-
cal" top-mount refrigerator/freezer that meets the 1993 energy standards. The
pathway studies the effects of the application of current technology, with empha-
sis on increased insulation to the doors and to the entire cabinet.
Model D represents the 1993 baseline using CFCs. D 1993 assumes the substi-
tution for CFC-11-blown insulation by an HCFC-blown foam of nearly the same
resistivity (a 2 percent loss in resistivity was assumed). As noted earlier, the
model predicts a modest energy-efficiency gain (about 2 percent) when HFC-
134a is substituted for CFC-12 refrigerant (the gain results from reduced heat-
exchanger thermodynamic losses at the reduced pumping rate).
The first two steps assume a reduction in gasket heat loads of up to 50 percent.
A means for achieving this is described in Reference 7.
A liquid-line mullion heater is introduced as the third step in the pathway,
where 5.5 watts of switchable electric heat is replaced by post-condenser heat. In
practice, this would require a two-tub design.
The fourth step involved the substitution of a commercially available 5.5 HER
compressor to replace the baseline 5.28 EER unit. A reduction in the displace-
ment (from 6.57 cc to 5.92 cc) was required to maintain a similar capacity.
The remaining steps in the path use readily available technologies. The additions
of insulation to the cabinet and the door result in an overall width of 32 inches and
a depth of 31 inches.
With decreased cabinet loads, some electric anti-sweat heating was required in
the mullion area to supplement the available post-condenser heat. At the end of
the path, the required electric anti-sweat heat was 1.5 watts of switchable heat
(0.75 watts average in the DOE test).
The net predicted reduction in annual energy at the end of the path from
the non-CFC 1993 baseline is 52 percent. The most uncertain step in the path is
the achievement of an additional 25 percent gasket heat leak reduction (50
percent total).
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Multiple Pathways to Super-Efficient Refrigerators
PATHWAY 1A: MODEL D, CURRENT TECHNOLOGIES WITH
THICK-WALL CABINET
Pathway 1A is the same as Pathway 1, with 1 inch additional cabinet insula-
tion, raising the overall width to 34 inches. Use of the additional insulation
resulted in a predicted additional savings of 50 kWh/yr, for an overall net reduc-
tion at the end of the path of 59 percent from the non-CFC 1993 baseline.
PATHWAY 2: MODEL B, IMPROVED COMPONENTS AND
AUXILIARIES
Pathway 2 examines potential improvements to Model B, where the focus is on
improved components and auxiliaries. The pre-1993 baseline unit uses a 4.57 HER
rotary compressor, and a post-condenser cabinet flange heater. The defrost timer
consumes 2 watts of energy and is located in the fresh-food section. The manufac-
turer specified insulation resistivity is 0.63 m2-K/W-cm. Steps 1 through 4 are
sample improvements assumed to reach the 1993 energy standards.
Use of a post-condenser loop to replace the 6.4-watt switchable electric anti-
sweat heater in the mullion is assumed in Step 6 (recognizing the need for a two-
tub design). Step 7 assumes the availability of a 5.3 EER rotary compressor. This is
a "future" technology, since the maximum reported EER for current rotaries is
slightly above 5.0. Use of a shutoff valve (applicable to rotaries only) saves about 2
percent energy (the manufacturer-specified cycling rate is only 1 cycle per hour).
With an increase in condenser area, 3 watts of switchable electric heat are
required in the mullion to supplement the post-condenser loop heat. Application
of adaptive defrost assumes the replacement of the 2-watt controller with a 0.25-
watt controller outside the cabinet.
Following the assumed increase in evaporator area and use of ECM evaporator
and condenser fans, the predicted net annual energy reduction is 48 percent from
the pre-1993 design, and 35 percent from the 1993 non-CFC sample design. Four
watts of switchable electric heat were needed in the mullion at Step 9 in the path-
way. If this option were looked at as the last step, rather than the ninth step, in the
pathway, it would most likely not appear attractive due to limited available heat.
PATHWAYS: MODEL C, IMPROVED COMPRESSOR AND
COMPARTMENT
Model C also uses a rotary compressor, specified by the manufacturer as hav-
ing a 4.85 EER. Pathway 3 examines the effects of a higher EER compressor and
the use of thick-wall cabinet insulation.
Steps 1 through 4 are sample changes from the manufacturer-defined pre-1993
refrigerator/freezer to a unit that would meet the 1993 energy standards. Use of
post-condenser heat is limited to the cabinet flange in this pathway.
All changes to the sample 1993 unit employ available technology other than
the 5.3 EER rotary compressor. Although this is a "future" technology, it could be
replaced by a high-efficiency reciprocating unit.
-------
Appendix B
Addition of the cabinet insulation at the end of Step 9 increases the cabinet
width to 31 inches. The net energy reduction at the end of the path is 48 percent
from the pre-1993 model, and 37 percent from the sample non-CFC 1993 model.
PATHWAY 3A: MODEL C, IMPROVED COMPRESSOR AND
CABINET WITH BETTER REFRIGERANT
Pathway 3A is similar to Pathway 3, with the exception of the use of cyclo-
propane refrigerant. Because of the significantly increased capacity with this
refrigerant, the assumed compressor displacement was reduced by 25 percent.
The predicted net energy consumption difference at the end of the pathways,
from the use of cyclopropane refrigerant, is 18 kWh/yr (shown is lOkWh in
Exhibit 1.8 because of the rounding process).
PATHWAY 4: MODEL A, CURRENT TECHNOLOGIES WITH
ADVANCED INSULATION
The pre-1993 Model A refrigerator uses a 4.55 HER compressor. The first three
steps of Pathway 4 are sample design changes to reduce the annual energy con-
sumption below the 1993 standard. These changes combine a high EER compres-
sor (commercially available), a post-condenser loop along the freezer cabinet
flange, and 3/4 inch additional door insulation.
The remainder of the path examines the effects of using state-of-the-art tech-
nology in the cabinet: reduced gasket loads (50 percent), and incorporation of
high-R gas insulation panels into the cabinet walls and doors. State-of-the-art
fans (ECM) and compressor are included. Hence, the sample pathway looks at
the effects from pushing the state of the art in all areas. The net predicted energy
savings is 52 percent from the pre-1993 design, and 40 percent from the sample
non-CFC 1993 unit.
PATHWAY 4A: MODEL A, CURRENT TECHNOLOGIES WITH
IMPROVED INSULATION
Pathway 4A is similar to Pathway 4, with a focus on current technologies, an
alternate refrigerant (HFC-152a), and improved foams. HFC-152a is predicted to
provide a modest efficiency gain (1-2 percent). Combined with high-resistivity
foams, the predicted net annual energy savings at the end of the path is 49 percent
from the pre-1993 design, and 37 percent from the non-CFC 1993 prototype design.
PATHWAYS: MODEL D, ADVANCED-CYCLE AND INSULATION
TECHNOLOGIES
Pathway 5 looks at the potential energy savings from advanced cycle compo-
nents and vacuum panels foamed into the cabinet walls and doors, applied to
the Model D refrigerator/freezer. Step 4 assumes the availability of a 6.5 EER lin-
ear compressor operating at 50 percent capacity of the baseline compressor.
152
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Multiple Pathways to Super-Efficient Refrigerators
The lengthened duty cycle resulted in reduced thermodynamic loadings of the
heat exchangers, but increased fan energies. Combined with the use of ECM fans,
the linear compressor achieved a predicted 31 percent energy saving over the sys-
tem with a 5.5 EER compressor and baseline fans.
The predicted net annual energy savings with foamed-in vacuum panels is
59 percent over the non-CFC 1993 unit.
Technical viability for the pathway requires development and commercializa-
tion of a high-efficiency, variable-capacity compressor and of reliable high-resis-
tivity vacuum panels.
PATHWAY 6: MODEL B, LORENZ CYCLE WITH IMPROVED
TECHNOLOGIES
Pathway 6 explores the application of a fan-controlled Lorenz cycle using
a ternary blend (HCFC-22, HFC-152a, and HCFC-123). The fresh-food evapora-
tor was sized at 40 percent of the freezer evaporator (which was unchanged from
the baseline unit), with the same fan and air flow rate as the freezer. The net
reduction in compressor power in Step 6 was 17 percent; including the energy
from the additional fan, the predicted net energy saving associated with the
Lorenz cycle was 9 percent.
The remaining steps in the path employ current or near-term technologies (a
5.3 EER reciprocating compressor can be substituted for the rotary compres-
sor). The predicted net energy savings at the end of the path is 55 percent from
the pre-1993 baseline design, and 42 percent from the prototype non-CFC 1993
design.
PATHWAY 7: MODEL C, LORENZ CYCLE, IMPROVED
COMPONENTS, AND ADVANCED INSULATION
A second fan-controlled Lorenz cycle with a slightly different blend was simu-
lated for Model C. The fresh-food evaporator was 30 percent of the size of the
freezer evaporator, but with the same fan, both using ECM fan motors. Because
of the low fan energies, the predicted net energy savings from introduction of the
Lorenz cycle was 14 percent (the compressor power reduction was 19 percent).
The remainder of the path assumed a gasket heat leak reduction of 50 percent
and the availability of vacuum panels foamed into the cabinet walls and doors.
Electric anti-sweat heat (3 watts switchable power) was required to supplement
the post-condenser loop heat in the flange area due to the reduced cabinet loads
and the reduced compressor run time. The predicted annual energy savings for
this advanced technology path was 48 percent from the non-CFC 1993 model
153
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Appendix B
PATHWAY 8: MODEL A, LORENZ CYCLE, BEST COMPONENTS,
AND AUXILIARIES
Pathway 8 examined the potential savings from a Lorenz cycle with a natural-
convection, fresh-food evaporator and with a ternary blend. At each step in the
path following the introduction of the Lorenz cycle, the fresh-food evaporator
size was adjusted to balance the cabinet loads to the evaporator capacities (the
required area was 0.90 m2 at Step 5 and 0.95 m2 at the end of the path). Although
possible with the ERA model, off-design conditions were not looked at.
The remainder of the path examined energy savings from high-efficiency fans
and compressors. A 6.0 HER compressor, using an ECM motor, is currently under
evaluation by various manufacturers.
The predicted net annual energy saving for this path is 43 percent compared
to the non-CFC 1993 prototype design.
PATHWAY 8A: MODEL A, LORENZ CYCLE, CURRENT
TECHNOLOGIES
Pathway 8A combines the same Lorenz cycle with a thick-walled cabinet.
Adding 2 inches of insulation to all surfaces and doors of the cabinet increases
the width to 36 inches. This would result in its applicability to a smaller market
segment, and the issue of control of the natural-convection Lorenz cycle remains.
Nevertheless, the pathway, which uses entirely available technology, yields an
overall energy savings of 66 percent over the pre-1993 model, and 58 percent
over the non-CFC 1993 prototype design.
PATHWAYS: MODEL D, DUAL-LOOP CYCLE, IMPROVED
COMPONENTS WITH THICK-WALL CABINET
The potential energy savings from a dual-loop system is explored here. With
the best of current small compressors, and an essential doubling of the cycle com-
ponents, the energy savings is only 2 percent. However, assuming the availability
of efficient small compressors and utilizing ECM fans everywhere, the predicted
net savings at Step 3 in the path is 27 percent. Use of the two flammable refriger-
ants HFC-152a and HCFC-142b in the separate loops results in an additional pre-
dicted 4 percent savings. Finally, combined with an assumed 50 percent gasket-
leak reduction and a thick-walled cabinet using high-resistivity foam, the predict-
ed net annual savings over the non-CFC 1993 model is 63 percent.
PATHWAY 10: MODEL A, DUAL-LOOP CYCLE, IMPROVED
COMPONENTS WITH ADVANCED INSULATION
Step 5 of Pathway 10 assumes the availability of "future small compressors"
and the use of the alternate refrigerants in the dual-loop cycle. Since the fans' ener-
gies are high (56 watts) at this point in the path, the net predicted energy savings is
154
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Multiple Pathways to Super-Efficient Refrigerators
only 3 percent. Replacing the current fans with ECM motor-driven fans, combined
with gasket-leak reduction and adaptive defrost (Step 9), reduces the predicted
annual energy consumption to 360 kWha savings of 45 percent from the non-
CFC 1993 prototype design. The final two stepsuse of foamed-in, high-R gas
panelsreduce the predicted net annual energy to 46 percent of the non-CFC 1993
prototype design, a 54% savings.
PATHWAY 11: MODEL D, MOST COST-EFFECTIVE
CONVENTIONAL TECHNOLOGIES
A set of moderately low-cost options is used to create Pathway 11. Each of the
steps uses very feasible technology and would not result in any dimension or stor-
age capacity changes.
The predicted net annual energy savings is 33 percent from the non-CFC 1993 base-
line design.
PATHWAY 12: MODEL D, LORENZ CYCLE, MOST COST-
EFFECTIVE ADVANCED TECHNOLOGIES
Pathway 12 is an extension of the previous pathway that assumes the avail-
ability of advanced technology, including high-resistance vacuum panel (foamed
into the cabinet walls and doors), and a 6.5 HER linear compressor with variable
capacity control. The Lorenz cycle adopted in Step 1 uses a binary refrigerant
blend of propane and HCFC-123. The predicted savings achieved with this nat-
ural-convection Lorenz cycle is 16 percent, in agreement with measurements at
the University of Maryland.
Use of a currently available high-efficiency compressor, adaptive defrost, post-
condenser-loop, mullion, anti-sweat heat, and ECM fans (Step 5) reduced the
predicted annual energy consumption to 410 kWh/yr, a savings of 36 percent
from the non-CFC 1993 baseline design. Combining these steps with reduced
gasket heat leakage, foamed-in vacuum panels, and a 6.5 EER linear compressor
yields a predicted annual energy consumption of 230 kWh, a savings of 64 per-
cent from the non-CFC 1993 baseline design.
Additional component development will be required to bring the final steps
into the marketplace. However, all steps have been shown to be feasible.
PATHWAY 13: MODEL E, MOST COST-EFFECTIVE
TECHNOLOGIES
A 20-ft3 bottom-mount unit is simulated in Pathway 13, where the focus is on
the application of least-cost current technologies that will not affect the size or
volume of the unit. The baseline refrigerator/freezer (1993 design) already uti-
lizes a two-tub design and a post-condenser-loop, anti-sweat heater (supple-
mented with a 2-watt, switchable, electric anti-sweat heater).
The pathway is essentially identical with the "Most Cost- Effective Conventional
Technologies" pathway followed for the Model D top-mount design (Pathway 11),
155
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Appendix B
where essentially all technologies have been demonstrated. The predicted net
annual energy savings is 31 percent from the non-CFC 1993 baseline design.
PATHWAY 14: MODEL F, MOST COST-EFFECTIVE
CONVENTIONAL TECHNOLOGIES
Cost-effective technologies that will not affect the size or volume are simulat-
ed for a 27-ft3, side-by-side unit in this pathway. The refrigerator/freezer, which
is an actual unit, uses a post-condenser loop around the freezer door flange and
across the mullion, supplemented by 3.6 watts of switchable anti-sweat heat. The
predicted net annual energy savings at the end of the path is 25 percent from the
non-CFC 1993 baseline design.
156
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References
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Multiple Pathways to Super-Efficient Refrigerators
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