&EPA
United States
Enviromental Protection
Agency
Office of Atmospheric
and Indoor Air
Programs
EPA-430-R-94-011
June 1994
Energy-Efficient Refrigerator
Prototype Test Results
United Stales Office o! Atmospheric EPA-430-R-93-OC8
Emiromenlal Projection and Indoor Air June 1993
Agency Programs
Multiple Pathways to
Super-Efficient Refrigerators
Uriled Slates Offico of Atmospheric EPAM30/R-92/OQ9
EfM/wnental Protection andlndoorAir Odober1992
Agency Programs
S C P A Finite Element Analysis of Heat
\S La r M Transfer Through the Gasket
Region of Refrigerator / Freezer
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled liber
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ACKNOWLEDGMENTS
This report has been compiled by H. Alan Fine and Jean Lupinacci. of the Global Change
Division of the U.S. Environmental Protection Agency and Professor Reinhard
Radermacher of the Center for Environmental Energy Engineering at the University of
Maryland. The authors wish to thank the many students at the University and
technicians and engineers at the many companies who worked to develop the prototypes
tested in this report. Particular thanks must go to Admiral Company, Frigidaire
Company, GE Appliances, Haier Group, ShangLing Refrigerator Company, W.C. Wood
Coppany Ltd., and Whirlpool Corporation for their donation of refrigerators and/or
help in the manufacture of the prototypes. Many component suppliers, including
Aladdin Industries, Inc., AMERICOLD, Degussa AG, Owens-Corning, and Thermalux,
are also gratefully acknowledged for their donations and help on this project.
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CONTENTS
Page
Findings 1
I. Introduction 3
LA. Purpose of Report 4
I.B. Energy Test Procedure 5
I.C. ERA Energy Calculations 7
II. Cabinet Modifications 9
II.A. Foam Insulation Enhancements 10
II.A.1. Thick-Wall Foam Insulation 10
II.A.2. Lower-Thermal Conductivity Foam Insulation—Carbon Black .... 12
ILB. Vacuum Insulation 14
II.B.l. VIP Insulation 15
ILB.l.a. VIP Insulation—Chest Freezers 15
II.B.l.b. VIP Insulation—Upright Freezers 17
II.B.l.c. VIP Insulation—Top-Freezer Refrigerators 18
II.B.l.d. VIP Insulation—Side-by-Side Refrigerators 20
II.B.2. Aerogel Insulation 22
ILB.3. Owens-Corning Evacuated Insulation 24
II.B.4. Aladdin Insulation 26
II.C. Improved Gaskets 27
II.C.l. Improved Gasket—VIP Insulated Refrigerator 28
III. Cycle Improvements 31
III.A. Improved Components 32
III.A.l. Linear Compressor 33
III.A.2. Inverter 34
III.A.3. Voltage Regulator 35
III.A.S.a. Green-Plug—New Top-Freezer Refrigerator 35
III.A.S.b. Green-Plug—Side-by-Side Refrigerator 36
III.A.4. Hot Water Refrigerator 37
III.B. Improved Refrigerants 38
III.B.l. Improved Refrigerants-Hydrocarbon Blends 38
III.B.2. Improved Refrigerators—Cyclopropane 39
III.B.3. Improved Refrigerators—HFC-134a and HFC-152a 40
III.B.4. Improved Refrigerants—HCFC-22 and HFC-152a Blends 41
11
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III.C. Improved Cycle . : 42
I III.C.1. Lorenz-Meutzner Cycle 42
IILC.l.a. Lorenz-Meutzner Cycle—Zeotropic Refrigerant Mixtures 42
III.C.l.b. Lorenz-Meutzner Cycle—Hydrocarbon Blends 43
III.C.l.c. Lorenz-Meutzner Cycle 45
; III.C.2. Modified Lorenz-Meutzner Cycle 46
1 III.C.2.a. Modified Lorenz-Meutzner Cycle—U.S. Refrigerators ... 46
| III.C.2.b. Modified Lorenz-Meutzner Cycle—Chinese Refrigerator . 47
, III.C.3. Dual-Loop System . 48
III.C.4. Two-Stage Refrigerator 50
m.C.5. Kopko Cycle | 51
IV. System and Cabinet Modifications 59
ly.A. Double Insulation and Lorenz-Meutzner Cycle 60
I IV.A.1. Double Insulation 61
i IV.A.2. High-Efficiency Compressor 61
; IV.A.3. Modified Lorenz-Meutzner Cycle 62
! IV.A.4. Improved Gasket 63
I
ly.B. Double Insulation and Kopko Cycle 64
i !
IV.C. Double Insulation and Alternate Refrigerants 67
IV.C.1. HFC-152a 67
i IV.C.2. Hydrocarbon Mixtures 68
V. References . 69
in
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TABLES AND FIGURES
Page
TABLES
I.I University of Maryland and Manufacturer Test Results 6
II. 1 Double-Insulated Refrigerators 11
II.2 Carbon-Black Foam Refrigerators 12
II.3 Typical Vacuum Insulation Thermal Conductivities 14
II.4 VIP Insulated Chest Freezers 15
II.5 VIP Insulated Upright Freezers 17
II.6 VIP Insulated Top-Freezer Refrigerators 18
II.7 VIP Insulated Side-by-Side Refrigerators 20
II.8 Aerogel Insulated Top-Freezer Refrigerators 22
II.9 OC Insulated Top-Freezer Refrigerators 24
11.10 Aladdin Insulated Top-Freezer Refrigerators 26
11.11 VIP Insulated Refrigerator with Improved Gasket 28
III.l Linear Compressor 32
III.2 Inverter 34
III.3 Green Plug—New Top-Freezer Refrigerator 35
III.4 Green Plug—Side-by-Side Refrigerator 36
III.5 Hot Water Refrigerator 37
III.6 Hydrocarbon Blends 7 38
III.7 Cyclopropane 39
III.8 Minimum Energy Consumption of the Optimized Systems 40
III.9 Calorimeter Data for the Two Compressors 40
111.10 HCFC-22 and HFC-152a Blends 41
III.ll Lorenz-Meutzner Cycle—Zeotropic Refrigerant Mixture 42
III. 12 Lorenz-Meutzner Cycle—Hydrocarbon Blends 43
III. 13 Lorenz-Meutzner Cycle 45
111.14 Modified Lorenz-Meutzner Cycle—U.S. Refrigerator 46
111.15 Modified Lorenz-Meutzner Cycle—Chinese Refrigerator 47
111.16 Dual Loop System 48
111.17 Two-Stage System 50
IH.18 Kopko Cycle 51
111.19 Kopko Cycle—First Modiacation 52
111.20 Kopko Cycle—First Modification Test Results 53
111.21 Kopko Cycle—Second Modification 54
111.22 Kopko Cycle—Second Modification Test Results 55
111.23 Kopko Cycle—Third Modification and Test Results 56
111.24 Kopko Cycle—Fourth Modification and Test Results 57
IV
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I V.I Double-Insulated, Lorenz-Cycle Refrigerator
IV.2 High-Efficiency Compressor
IV.3 Modified Lorenz-Meutzner Cycle
IV.4 Double-Insulated, Kopko-Cycle Refrigerator
IV.5 Specifications for the First Modification
IV.6 Test Result for the First Modification
IV. 7 Compressor Comparison for Kopko Modifications .
IV.8 Increased Insulation with Refrigerant HFC-152a . . .
IV.9 Increased Insulation with Hydrocarbon Refrigerants
60
61
62
64
65
66
66
67
68
FIGURES
11.1 Cross Section of Gasket Region
II.2 Front View of Gasket Region . .
29
30
I V.I Schematic Representation of Improved Gasket 63
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VI
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Prototype Test, Results
May 1994
FINDINGS
Working prototype refrigerator/freezers demonstrating a wide variety of existing and
emerging technologies for energy conservation have been built and tested.
Energy-efficiency gains resulting from improvements to individual components can be
grouped as follows:
n
o Energy Reduction
5-10
10-15
15-20
25-30
, Improvement
improved gasket region design
inverter
hydrocarbon refrigerants
50% coverage advanced insulation
linear compressor
Lorenz cycle in side-by-side R/F
Lorenz cycle in top-freezer R/F
Kopko Cycle
Adding 1.5 inches of foam insulation
Substantial energy-efficiency gains resulting from a combination of improvements can be
grouped as follows:
% Energy Reduction
30-40
40-50
>50
Improvements
Adding 1.5 inches of insulation and Kopko cycle
Adding 1.5 inches of insulation, better compressor, Lorenz
cycle, and improved gasket
Adding insulation, better compressor, and HFC-152a
refrigerant to a Chinese R/F
Adding insulation, better compressor, and hydrocarbon
refrigerants to a Chinese R/F
The EPA Refrigerator Analysis (ERA) model predictions agree with measurements made
on the prototypes.
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Energy-Efficient Refrigerators
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Prototype Test Results
May 1994
I. INTRODUCTION
Many factors have driven industry to implement energy-efficiency improvements in
household refrigerator/freezers (R/Fs). The 1993 DOE Energy Efficiency Standards have
been in effect for a little more than one year, and many manufacturers have models on
the market that exceed this standard. In fact, the winner of The Golden Carrot
Competition for $30 million, Whirlpool Corporation, will be selling R/Fs in 1994 that
exceed the standard by more than 25 percent, without using ozone-depleting CFCs.
Other manufacturers are expected to offer similar energy efficient products in the near
future.
There appears to be dramatic changes occurring in consumer buying preferences.
Consumer acceptability is an important factor to selling refrigerators. Based on the
marketing perception that consumers are only first cost driven and place high value on
internal volume, manufacturers were reluctant to explore cost-effective design changes to
increase energy efficiency, particularly by adding more insulation to the refrigerator
walls.
The recent success of Sears's program to prominently market the "Energy Efficient" 1993
moldels may change the idea that energy efficiency would not drive the sale of
refrigerators. The Sears program consisted of training, advertising, point-of-sale
identification, and charts that helped customers understand the substantial savings and
environmental benefits from purchasing energy-efficient refrigerators. Early indications
from Sears showed that many customers would ask for the new models and were even
willing to wait and pay more for them.
There is not just one path or design approach that leads to super-efficient refrigerators
but rather multiple pathways to achieve large energy savings. Each refrigerator
manufacturer will decide on the most cost-effective set of options emd technologies based
on tits current products' energy efficiency, design, size class, cost-structure, and other
factors.
In evaluating the potential energy savings in R/Fs, EPA has conducted a wide variety of
analyses, including technical evaluations, model development and analysis, cost analyses,
marketing and consumer preference analysis, and prototype development and testing.
All are necessary to determine the ultimate acceptability of the various options.
Manufacturers will conduct similar analyses pertaining to their own product lines and
circumstances as they commercialize new energy-efficient products.
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Energy-Efficient Refrigerators
LA PURPOSE OF REPORT
This report will summarize the test results for the numerous R/Fs built by EPA and our
partners to evaluate a wide variety of technologies to increase energy efficiency and to
eliminate the use of CFCs. The results for many of the prototypes represent the joint
efforts of EPA, the University of Maryland, and various equipment and refrigerator
manufacturers. In many cases, the prototypes were tested at both the University and the
individual companies. The partnerships were a critical component of the success of the
prototypes. The interaction between the various experts was useful to define realistic
parameters, resolve problems, and make modifications to the prototypes on the
production line.
The prototypes were developed to test technologies that increase energy efficiency and
eliminate CFCs. The refrigerators that were built and tested are not meant to showcase
all combinations of technologies, but rather to demonstrate significant energy savings
that could be achieved with existing and emerging technologies.
Some of the prototypes were built to test the performance of a single technology. Other
prototypes combined technologies that demonstrated substantial energy savings to
identify any interactive effects between the different technologies and different systems.
The report is divided into four sections.
• The Introduction describes the purpose of the report, the testing methodology, and
comparison with ERA energy calculations.
• The Cabinet Improvements section summarizes the test results from refrigerator/
freezers that demonstrate improvements to the thermal envelope of the unit.
• The Cycle Improvements section summarizes the test results from refrigerator/freezers
that demonstrate improved components, alternate refrigerants, and alternate cycles.
• The System and Cabinet Modifications section provides a summary of test results
from units that combined both improvements to the cycle and the cabinet.
Many technologies have shown great promise for future development, but further
evaluation will need to be conducted for commercialization. Continued applied research,
manufacturability, long-term reliability, and cost analyses may be required by the
manufacturers.
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Prototype Test Results
May 1994
I.B ENERGY TEST PROCEDURE
Except as noted, refrigerator energy tests were performed at the University of Maryland
(Ul Md.) according to the DOE test procedure, with some minor modifications. The
modifications were necessary to arrive at well optimized refrigeration cycles in a short
period of time. For those tests that included a defrost cycle and the anti-sweat heaters,
the outcome is the same as for the DOE procedure.
During testing at U. Md., all compartment temperatures and the room temperature are
measured and maintained as prescribed by DOE. The compartment temperatures,
however, are maintained with an independent temperature controller, not the original
refrigerator thermostat. Generally, the temperature controller controls the freezer
temperature, while the food compartment temperature is adjusted by either a second
controller (Kopko and dual loop systems) or by adjusting charge and capillary tube
length. The instantaneous power and energy consumption are measured with watt and
watt-hour transducers, respectively.
i
The defrost is normally deactivated during testing at U. Md. and tests are conducted for
one day (24h). The system, however, is defrosted regularly to maintain system
performance. When a defrost cycle is included in the measurement at U. Md., the energy
consumption is measured from the onset of one defrost cycle to the onset of the next.
The energy consumption is then extrapolated to 24h. When defrost cycles and anti-sweat
heaters in the on and off positions are included, the U. Md. method is the same as the
DOE method, except it is faster and more accurate. The refrigerator performance is
determined at a freezer temperature of 5°F rather than measuring above and below this
temperature and then interpolating to it.
Modifications to the defrost cycle were not tested. In certain instances, such as the
incorporation of either the Lorenz or Kopko cycle into the R/F, additional energy savings
could be achieved by modifying the defrost cycle.
Table LI reports refrigerator tests that were repeatable within ±1 percent when repeated
under the same conditions and at the same laboratory, and within +. 5 percent when
compared to other laboratories. The table also shows a comparison of the U. Md. test
results and the test results of the manufacturers conducted according to the DOE
standard.
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Energy-Efficient Refrigerators
Table I.I University of Maryland and Manufacturer Test Results
: : . -• Energy !
Test Location land FF Temperature I|Z Temperature Consumption ;
ModeJ Tested Conditions • (°F) . (°F) (kWh/24h) ;
t ; • i
Admiral
RB19xx
with vacuum
insulation
Whirlpool
ET20ZK
Thick-wall 20
ft3 Whirlpool
U. Md. w/o defrost
U. Md. with defrost
Admiral DOE Test
U. Md. with anti-sweat
heaters on
Whirlpool with anti-
sweat heaters on
U. Md. with anti-sweat
heaters on
Whirlpool with anti-
sweat heaters on
U. Md. with anti-sweat
heaters off
Whirlpool with anti-
sweat heaters off
5.3
4.9
5
5.0
5.0
5.0
5.0
5.0
5.0
38.5
38.3
38
41.9
40.0
37.4
38.1
37.1
36.6
1.96
2.16
2.12
2.17
2.31
1.91
1.85
1.38
1.44
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Prototype Test Results
May 1994
I.C ERA ENERGY CALCULATIONS
The EPA Refrigerator Analysis (ERA) computer model can be used to estimate the
impact on energy consumption of a wide variety of modifications to the refrigerator
cabinet and components. ERA predicts the performance (energy consumption) of
household R/Fs and is capable of simulating various cabinet, auxiliary, and cycle
configurations. It consists of four major components:
1. j^. menu-driven input processor;
2. Estimation of the cabinet loads;
3. Thermodynamic cycle simulation; and
i
4. Energy-consumption calculations.
I ;
Additional details are provided in the ERA User's Manual. [1]
The results of a variety of ERA calculations have been presented in. Multiple Pathways to
Super-Efficient Refrigerators. [2] These results have been compared to the test results of
applicable prototype models.
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Energy-Efficient Refrigerators
8
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Prototype Test Results
May 1994
II. i CABINET MODIFICATIONS
A series of prototype refrigerator/freezers (R/Fs) were produced that contained
improvements to the thermal envelope of the units. These improvements included:
• Improvements to the foam insulation system,
• The addition of vacuum insulation, and/or
i
• Improvements to the gasket system.
l
Details of the prototypes and the resulting energy savings are presented in the following
section.
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Energy-Efficient Refrigerators
II.A FOAM INSULATION ENHANCEMENTS
The overall thermal performance of the cabinets was improved by increasing the
thickness of the R/F cabinet or by reducing the thermal conductivity of the foam., The
results of these tests are described next. ••>•.,
II.A.1 Thick-Wall Foam Insulation
Polyurethane foam insulation was added to the walls of a refrigerator to reduce heat:
flow into the refrigerated volume. The internal volume was maintained by adding the
insulation to the exterior of the. unit, at the expense of slightly larger exterior dimensions.
Alternatively, insulation can be added to the interior surfaces, but at the expense of
internal volume.
Baseline Unit
The baseline unit was a standard 20 ft3 automatic-defrost top-freezer
refrigerator, Whirlpool model number ET20DK. Dimensions and
daily energy consumption are presented in Table 11.1.
Thick-Wall Unit The "double-insulated" refrigerator was manufactured by installing
the liner for the" standard 20 ft3 model into the shell of a standard
25 ft3 unit, model ET25DK. The unit was then foamed and completed
with components identical to those for the standard ET20DK. Special
doors did, however, have to be manufactured to fit the unit.
Two units were built and tested at Whirlpool.
10
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Prototype Test Results
May 1994
Table H.l Double-Insulated Refrigerators
Baseline Thick- Wall
Unit Unit
Volume (ft3)
Freezer
Fresh Food
Exterior Dimensions (in)
Height
Width
Depth
Insulation Thickness (in)
Doors
FF Sides
FF Back
FF Bottom
FZ Sides
FZBack
FZTop
Mullion
Energy Consumption Whirlpool
(kWh/24h) U.Md.
EPA-RTP
5.5
14.4
66
32
28
1.5
1.8
1.8
1.8
•2.2
2.2
2.2
2.5
2.33
5.5
14.4
69
35
31
2.8
3.3
3.6
3.3
3.6
4.0
3.6
2.5
1.63 + 0.03
1.73
1.72
Discussion As can be seen from the above table, approximately 1.5 inches of foam
• were added to all exterior surfaces of trie unit. Interior volume was
i maintained, while exterior dimensions were increased by 3 inches on each
i dimension.
A measured 27 percent decrease in energy consumption was achieved. The
ERA model predicts a 19 percent energy reduction for the addition of
1 inch of insulation to the exterior of 18 ft3 R/Fs and 29 percent for the
addition of 2 inches. ,[2] ERA is thus in good agreement with the
measurements.
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Energy-Efficient Refrigerators
II.A.2 Lower Thermal Conductivity Foam Insulation—Carbon Black
The thermal performance of foam insulation is a complex function of three modes of heat
transfer that occur within the insulation: heat conduction in the solid and vapor phases
and thermal radiation through the composite. Reducing the amount of heat transferred
by any of these mechanisms should reduce the thermal conductivity of the foam and the
rate of heat flow through the foam for a given set of conditions.
The addition of carbon black particles to polyurethane foam reduces thermal radiation
transport and the thermal conductivity of the foam. Black foams have been developed
for the construction industry and are under development for appliance applications by
Miles Inc. and the Center for Applied Energy Research Inc. [3]
Baseline Unit
Black-Foam
Units
The baseline model was a standard 17 ft3 automatic-defrost top-freezer
model, Admiral Co. model number RB17OPW. Foaming of pre-
assembled empty cabinets with an HCFC-141b-blown foam was done at
Miles Inc. The foam formulation was developed by Miles for this trial.
After foaming, the units were returned to Admiral for final build-up and
testing. Foam properties and energy test results are shown in
Table 11.2. [3]
Foam with the same formulation but containing 6.3 percent carbon black
was used for these units. All other processing and testing protocols
were identical.
Table IL.1 Carbon-Black Foam Refrigerators
i ' i ' 1 Baseline Black-Foam
" ' ; Units ! Units .
• : ; : -:1 " • : -. , - -r ! r
Foam Thermal Conductivity
(BTU*in/(h*ft?*0F))
Foam Density (Ib/ft3)
Energy Consumption (kWh/24h)
0.129
1.75
1.84 + 0.03
0.12
1.87
1.83 + 0.01
Discussion The thermal conductivity of the carbon-black loaded foam was eight
percent lower than the baseline HCFC-141b foam. Computer model
simulations made by Admiral predicted a 3.2 percent lower energy
consumption for the refrigerator. ERA predictions for 18 ft3 models [2]
show energy reductions ranging from 3.4 to 4.3 percent with an average
of 4.0 percent.
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Prototype Test Results
May 1994
The actual energy consumption of the black-foam prototype refrigerator
was less than one percent lower than the baseline. Tests, including
reverse heat flow measurements, are being performed to determine why
larger energy savings were not observed. One hypothesis for why the
eight percent lower thermal conductivity black-foam did not reduce the
energy consumption of the unit was that the black-foam units were
made in February 1993 and the baseline models in May. Small
improvements in components over this period may have lowered the
energy consumption of the baseline models and masked the effect of the
improved foam.
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Energy-Efficient Refrigerators
II.B VACUUM INSULATION
A number of advanced insulation systems are currently under development. These
systems generally consist of a filler material contained in a gas-tight barrier. All of the
concepts, except for gas-filled panels, attain their lower thermal conductivity at reduced
pressure (under vacuum). Filler materials incorporated into these advanced insulations
include ceramic spacers, precipitated silica or other powders, fiberglass, aerogel tiles, and
open-cell foams. Barrier materials range from laminated polymer structures to stainless
steel.
High thermal resistance (low thermal conductivity) elements can be combined with foam
insulation in the walls of R/Fs to improve their thermal performance, without effecting
their structural integrity. Four types of advanced insulation systems were tested in R/Fs
and/or freezers. Typical center-of-panel properties for the vacuum insulations employed
in the prototypes are summarized in Table II.3. It is important to note that the
conductivities of panels used in the prototypes may be substantially higher than those
given in the table, as edge effects may substantially change the thermal performance of
small panels, especially those fabricated with metallic barriers.
Table II.3 Typical Vacuum Insulation Thermal Conductivities
* 1 ; :' 1 ' : ; '
; : ! Thermal Conductivity ;
Description \ ' Manufacturer (BTU*in/(h*ft2*°F)) 1
• • i . - i
Precipitated Silica in Plastic
Laminate (VIPs)
Aerogel Tiles in Plastic Laminate
Fiberglass in Stainless Steel
Precipitated Silica and Carbon
Black in Stainless Steel
Degussa AG
Thermalux
Owens-Corning
Aladdin Industries, Inc.
0.050 ±0.0031
0.051+ 0.0011
0.018 + 0.0022
0.0421
Measurements made by Materials Thermal Analyses Group at Oak Ridge National Laboratory.
1 Measurements made by Owens-Corning.
14
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Prototype Test Results
May 1994
II.B.1. VIP Insulation
j
WB.l.a VIP Insulation—Chest Freezers
Vacuum insulation panels (VIPs) consisting of precipitated silica filler in a plastic-
laminate barrier/container were installed in three chest freezers at W. C. Wood Co. Ltd.
injNovember 1991. The balance of the composite insulation system consisted of W. C.
Wood's standard foam formulation blown with CFC-11.
Baseline Units Two production model chest freezers were employed as baseline units:
i WC42-xx and WE46-xx. Storage capacity, insulation thickness, and
; energy consumption data for these models are listed in Table II.4.
\
VIP Units VIPs were mounted on styrofoam inserts adjacent to the cold-wall
I evaporators on the sides and bottom of the three prototype units. The
i cabinets were then assembled, foamed, and built-up on the production
} line without any additional modifications. The percentages of area
i covered by VIPs and energy consumption results are presented in the
j following table. Additional details on panel sizes and locations are
i available in reference [4].
i ' I
i
Table HA VIP Insulated Chest Freezers
WC42-XX
• ; . ' ; ; #1
Capacity (ft3)
Insulation Thickness (in)
Baseline Energy Consumption
(kWh/24h)
% Area Covered by VIPs
Energy Consumption (kWh/24h)
% Energy Reduction
14.8
2.5
1.16
54
1.04
11
WC42-Jx ; WE46-XX
•U.1
14.8
2.5
1.16
54
0.99
15
16.5
3.0
1.24
44
1.08
13
Discussion An average 13 percent reduction in energy consumption for an average
I 50 percent area of coverage was obtained. The baseline models were
i relatively high-efficiency models incorporating thick insulation walls.
j The impact of VIPs on energy consumption would thus be less than that
1 for freezers or R/Fs with thinner walls.
15
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Energy-Efficient Refrigerators
Measurements performed, on the WC42-xx units approximately 18
months after production showed 13 and 16 percent increases in energy
consumption with 12 and. 7 percent increases in run time for units 1 and
2, respectively. The increase for unit one is much higher than that
which would be expected from the aging of the foam alone. Either a
panel failure or aging of the panels must have occurred. The increase in
run time for unit two would be consistent with foam aging. The
significant increase in energy consumption, as compared to the increase
in run time, has not been explained.
16
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Prototype Test Results
May 1994
II.B.l.b VIP Insulation—Upright Freezers
VIPs were installed in upright freezers at W. G. Wood Co. Ltd. in February 1992. The
balance of the composite insulation system consisted of W. C. Wood's standard CFC-11
blown foam insulation formulation, with the exception of fiberglass doors.
Baseline Units Two production model upright freezers were used as baseline models:
WVF47-xx and WV58-xx, Data on these models are presented in
Table 71.5.
Vllf Units VIPs were mounted on the sides, back, and top of the smaller unit and
! on the sides, back, top, and bottom, of the larger model. Cabinets were
I then assembled, foamed, and built-up on the production line without
j any other modifications. Percentages of area covered and test results
follow. Additional details on panel sizes and locations can be found in
reference [4].
Table IL5 VIP Insulated Upright Freezers
_ • . " ' : : . WVF47-XX . WV58-xx
Capacity (ft3)
Insulation Thickness, (in)
Baseline Energy Consumption (kWh/24h)
% Area Covered by VIPs
Energy Consumption (kWh/24h)
% Energy Reduction
16.7
2.5
2.15 ,
56 '
2.02
6
20.3
2
•2.34 ,-=.-:
53 .
2.05
12
Discussion The approximately 10 percent energy reduction is lower than that
achieved for the chest freezers even though the walls are thinner. This
probably results from the fiberglass insulated door, which allow a
disproportionate amount of heat to flow into the cabinet.
Retests on the prototypes performed approximately 14 months after
production showed a 5 percent increase in energy consumption and
compressor run time. This is consistent with aging of the foam
insulation, alone/over this period.
17
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Energy-Efficient Refrigerators
IJ.B.2.C VIP Insulation—Top-Freezer Refrigerators
VIPs were installed in 19 ft3 automatic-defrost top-freezer refrigerators produced by the
Admiral Company in 1991 and 1992. The balance of the insulation system was either
Admiral's standard foam formulation blown with CFC-11 or a special CO2-blown
formulation.
Baseline Units The 1991 baseline units were standard Model RB19xx production units
built during the last quarter of the year. The 1992 baseline models were
RB19K2A production models, modified with a flat back to accommodate
larger VIPs. Foam insulated doors also replaced the standard fiberglass
insulation in all baseline models. DOE energy test results for the
various units are presented in Table 11.6.
VIP Units VIPs were mounted on the sides and top adjacent to the steel cabinet
and on the back adjacent to the plastic liner on all prototype units.
Panels were also mounted adjacent to the steel cabinet bottom on the
1992 units. Cabinets were then assembled, foamed, and built-up without
any additional modifications. Three sets of cabinets and doors were
generally produced. These components were tested together or in
combination with doors or cabinets from the baseline models to generate
the data presented below. Additional information on the panel sizes
and locations can be found in references [5] and [6}.
Table 11.6 VIP Insulated Top-Freezer Refrigerators
\ : ! ' - " 1 : : -1 ..---.
Year ; 1991 j 1992 1992
Foam Blowing Agent
Baseline DOE Energy Consumption
(kWh/24h)
VIPs in Cabinet and Doors
% Area
DOE Energy
% Reduction
VIPS in Cabinet only
DOE Energy
% Reduction
VIPs in Doors Only
DOE Energy
% Reduction
CFC-11
2.36 + 0.12
47
2.12 + 0.05
10
2.27 + 0.06
4
2.23 + 0.07
5
CFC-11
2.26 + 0.06
68
2.08 + 0.06
8
2.15 + 0.06
5
2.21 + 0.01
2
C02
2.58 + 0.10
68
2.26 + 0.09
13
18
-------
Prototype Test Results
May 1994
Discussion The energy reduction results for the 1992 prototypes were less than
i expected. The results for the units made with CFC-11 foam are based
on only two sets of cabinets and doors. Two additional sets were made
| but found to have very poor energy performance. These units were
I disassembled after testing and found to have punctured panels. The
i percentage reduction for the poorer insulating CO2-blown foam was as
' expected. Measurements were not made for the cabinet-only and door-
1 only configurations, as rapid aging of these foams would have produced
' confusing results.
I The average 10 percent energy reduction is smaller than the 14 to 16
percent predicted by ERA for 50 percent area of coverage of several
! 18 ft3 refrigerators. [2] The ERA calculations were based on 1-inch thick
' panels, while the tests were performed with 0.5- and 0.75-inch thick
' panels. Linear extrapolation of the test results for the 1991 prototypes to
1-inch thick panels yields a 14 percent energy reduction. Similar
i calculations for the 1992 prototypes yields 12 and 19 percent reductions
for the CFC-11 and CO2 foams, respectively. Only the results for the
i 1992 prototypes with CFC-11 foam are not in good agreement with ERA.
As mentioned previously, there may have been problems with
; punctured panels in these tests.
19
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Energy-Efficient Refrigerators
ILB.l.d VIP Insulation—Side-by-Side Refrigerators
A set of 22 ft3 side-by-side refrigerators were built at Admiral Co. in 1991. The insulation
system in these units consisted of VIPs and Admiral's standard CFC-11 foam
formulation.
Baseline Units The baseline units were standard production models built in late 1991,
model CNS22V8A. All walls and doors of the baseline units contained
foam insulation.
VIP Units VIPs were mounted on the top, sides, and doors of the prototype units.
All panels were attached to the steel case, except the back panels that
were attached to the liner. Cabinets were then assembled, foamed, and
completed without any additional modifications on the production line.
Additional details on panel sizes and location can be found in reference
[5]. Test data are presented in the following table.
Table IL7 VIP Insulated Side-by-Side Refrigerators
Baseline DOE Energy Consumption (kWh/24h)
2.98 + 0.08
VIPs in Cabinet and Doors
% Area Covered by VIPs
DOE Energy
% Energy Reduction
49
2.96 ± 0.07
1
VIPS in Cabinet only
DOE Energy
% Energy Reduction
2.82 ± 0.07
5
VIPs in Doors Only
DOE Energy
% Energy Reduction
3.06 + 0.15
-3
Discussion The presence of the VIPs in the long slender doors of the side-by-side units
resulted in warpage and poor sealing. Thus the energy consumption went
up for the doors-only case and only went down one percent for the cabinet
and doors case. Foam voids were also observed in the cabinet. These were
patched prior to energy testing but may have contributed to the small
reduction in energy that resulted for the cabinet-only tests.
20
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Prototype Test Results
May 1994
Similar vacuum panels at approximately 55 percent area of coverage have
been installed in a 25 ft3 side-by-side model. [7] These panels resulted in a
17 percent reduction in energy consumption.
21
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Energy-Efficient Refrigerators
II.6.2 Aerogel Insulation
Panels consisting of aerogel tiles encapsulated in a plastic laminate barrier/container
were installed in top-freezer automatic-defrost refrigerators. The panels were
manufactured by Thermalux from 12 in. by 12 in. by 0.5 in. silica aerogel tiles, which
were cut and assembled into the desired panel sizes. The refrigerators were made at
Admiral Co., and the remainder of the insulation composite was their standard foam
formulation blown with CFC-11.
Baseline Units The baseline units were standard Admiral production models
manufactured in 1992, model RB19K2A. Several indentations in the
backs of the units were eliminated to allow a higher coverage of vacuum
panels. Foam-insulated doors were also used to replace the standard
fiberglass insulation. All other dimensions and components were
unchanged from the standard production models.
Aerogel Units Three prototype units containing aerogel panels were fabricated.
Aerogel panels were attached to all surfaces of the prototypes, including
the bottom. All panels except those on the back were attached to the
steel case. The panels were 1-inch thick, except those on the fresh food
compartment sides, bottom, and back, which were 0.5 inches thick. The
units were assembled, foamed, and completed on the normal production
line without any additional modifications. Additional details on panel
sizes and locations can be found in reference [6]. Test results follow.
Table II.8 Aerogel Insulated Top-Freezer Refrigerators
Baseline DOE Energy Consumption (kWh/24h)
Panels in Cabinet and Doors
% Area Covered by Aerogel
DOE Energy
% Energy Reduction
Panels in Cabinet only
DOE Energy
% Energy Reduction
Panels in Doors Only
DOE Energy
% Energy Reduction
2.26 + 0.06
67
2.10 + 0.09
7
2.12 + 0.07
6
2.24 + 0.05
1
22
-------
Prototype Test Results
May 1994
Discussion The aerogel panels were very fragile, and several were broken during
i shipment. After energy testing, one prototype was disassembled and
! also found to have panels that had lost their vacuum. The panels
j located on the bottom of the units also blocked foam flow, resulting in
; voids that had to be patched. These two problems account for the poor
performance of these prototypes.
| Additional tests of this insulation are not currently possible, as
• Thermalux has gone out of business, and they were the only known
; supplier of large aerogel tiles.
23
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Energy-Efficient Refrigerators
II.B.3 Owens-Corning Evacuated Insulation
Vacuum panels consisting of fiberglass in a stainless steel container are produced by
Owens-Corning (OC). As noted earlier, these panels may have center-of-panels thermal
resistivities higher than 50 h*ft2*°F/(BTU*in), but edge effects may substantially lower
their performance in refrigerators.
Baseline Units Baseline units were 1992 Admiral RB19K2A models with flat backs and
foamed doors as described in section II.B.l.c.
OC Units Four prototypes were built with OC panels. Panels were 0.75 inches
thick, except for the fresh food back, which was 0.5 inches thick. Small
panels were used in two of the prototypes to cover the machine
compartment. All four units had panels on the other five sides. After
mounting the panels, the cabinets were assembled, foamed with
Admiral's standard CFC-11 foam formulation, and completed on the
production line. Test results follow.
Table II.9 OC Insulated Top-Freezer Refrigerators
Baseline DOE Energy Consumption (kWh/24h)
Panels in Cabinet and Doors
% Area Covered
DOE Energy
% Energy Reduction
Panels in Cabinet only
DOE Energy
% Energy Reduction
Panels in Doors Only
DOE Energy
% Energy Reduction
2.26 + 0.06
69
1.92 + 0.05
15
1.99 + 0.05
12
2.18 ± 0.04
4
Discussion The energy reduction results were the best of the advanced insulations
tested. This is probably reflective of the higher thermal resistances of
the panels, measured by Owens-Corning to average almost R-40 per inch
including edge effects.
The two units with panels over the machine compartments did not have
significantly different energy consumption than those without these
24
-------
Prototype Test Results
May 1994
panels. This is indicative of the fact that small panels will not have an
improved performance over foam, especially for panels with metallic
edges. ,
One unit was also known to have a panel that had lost its vacuum.
Again, the performance was not significantly different than that of the
other units. This is probably indicative of the small number of
prototypes and the variability in the other components of the refrigerator
masking the effect of one bad panel.
25
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Energy-Efficient Refrigerators
II.B.4 Aladdin Insulation
Evacuated panels containing a blend of precipitated silica and carbon black contained in
stainless steel are produced by Aladdin Industries. These panels have slightly higher
center-of-panel thermal resistance than the panels contained in plastic, but edge effects
may substantially lower their effectiveness.
Baseline Units The baseline models were 1993 RB193PW refrigerators produced by
Admiral. The only modification to the standard units was the use of
2-inch thick doors. At the request of Admiral, only percentage changes
from the baseline are presented in this report.
Aladdin Units Three prototype units were built with Aladdin panels. All panels were
1-inch thick, except for 0.5 in. panels on the fresh food back. Panels
were not placed over the machine compartment. Except for the panels
and 2-inch thick doors, the prototypes were identical to standard
production models. Foam blown with CFC-11 was used for the balance
of the insulation system. [6]
Table 11.10 Aladdin Insulated Top-Freezer Refrigerators
Baseline DOE Energy Consumption
Panels in Cabinet and Doors
% Area Covered
% Energy Reduction
Panels in Cabinet only
% Energy Reduction
100%
57
6
5
Discussion The Aladdin panels had approximately 15 percent higher areas of
coverage and 25 percent higher center-of-panel thermal resistances than
the panels contained in plastic. The energy reductions were, however,
lower. Edge effects are clearly very important. Higher center-of-panel
thermal resistances and larger panels can overcome this problem, as
demonstrated by the Owens-Corning insulation results.
26
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Prototype Test Results
May 1994
ILC Improved Gaskets
Heat flow through the gasket region of the cabinet contributes significantly to the total
load. Finite element analysis (PEA) of this region of the refrigerator cabinet has shown
that heat flow in this region can be reduced by 50 percent by minor changes to the
design of the flanges on the door and cabinet. [8] Test results for two prototype units
with gasket modifications are presented in the next section and section IV.A.
27
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Energy-Efficient Refrigerators
II.C.1 Improved Gasket—VIP Insulated Refrigerator
Heat flow in the gasket region occurs by conduction down the flanges and then by
convection from the ends of the flanges and the gasket. Replacing a portion of the
flanges on the inside of the refrigerator with plastic can reduce the total amount of heat
flow in this region by one-half. In many cases, the cabinet flange does not extend into
the cabinet as far as the gasket. Unless the small gap between the gasket and interior
liner is sealed, convection from the end of the flange will still occur as if the flange
extended into the refrigerated volume.
Baseline Unit One of the Admiral RG19xx prototype units built in 1991 and containing
VIPs was used in this test program (see II.B.l.c.). The energy tests were
performed at U. Md. with the anti-sweet heaters off (one portion of the
standard DOE test).
Modified Unit A cross section of the gasket region is shown in Figure ILL The cabinet
flange was modified by adding a piece of foam insulating tape adjacent
to the flange on the inside of the refrigerated volume. The door flange
was modified by removing the metal that protruded through the flange
region. A front view of these modifications is shown in Figure 11.2.
Table 11.11 VIP Insulated Refrigerator with Improved Gasket
Baseline Energy Consumption (kWh/24h)
Energy consumption with door flange modification
% Reduction
Energy consumption with both flanges modified
% Reduction
2.18 + 0.02
2.11
3
2.01 + 0.01
8
Discussion Slightly greater energy reductions could be achieved by redesigning the
door flange, as opposed to removing the flange from between the screw
holes.
ERA predicted energy reduction of 7 and 11 percent for 25 percent and
50 percent reductions in heat flow through the gasket region,
respectively. The FEA results indicate that an approximately 40 percent
reduction in heat flow should have occurred, with the modifications
performed. Thus agreement between ERA and the test results is very
good.
28
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Prototype Test Results
May 1994
Figure II.l Cross Section of Gasket Region
Door
Door Flange
Foam Insulation
Cabinet Flange
Gasket
Removal Metal
Insulating Tape
Foam
Inner
29
-------
Energy-Efficient Refrigerators
Figure 11.2 Front View of Gasket Region
|
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30
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Prototype Test Results
May 1994
III. Cycle Improvements
t
i
Aj series of prototype refrigerators was also produced with improved cycle components.
Improvements included:
• i Improved components, i
• Alternate refrigerants, and
i
• j Alternate cycles.
The results of tests on these prototypes are presented in this section.
31
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Energy-Efficient Refrigerators
III.A. IMPROVED COMPONENTS
III.A.l Linear Compressor
A linear compressor differs from a conventional reciprocating compressor in that the
motor drives the piston directly. This feature eliminates the crank mechanism and
simplifies the design. In the linear compressor developed by SunPower Inc., gas
bearings guide the piston as it resonates on a spring. Use of gas bearings and
elimination of the crank greatly reduces friction losses and eliminates the need for
lubricating oil. The resonant piston reduces motor size and improves motor efficiency.
Reducing the input voltage to the linear motor reduces the stroke of the piston and
allows for easy capacity control. The net result of these improvements is a simple,
efficient, oil-free, variable-capacity design. Compressor calorimeter tests with the
SunPower compressor have shown a 15 percent improvement in design efficiency
compared to a conventional reciprocating design. [9]
Baseline Unit
The baseline unit was an 18.6 ft3 top-freezer automatic-defrost
refrigerator produced by Frigidaire, model number FPGS19TSWO.
Prototype Unit The compressor was replaced with the linear compressor. The capillary
tube and refrigerant charge were optimized for minimum energy
consumption. Thermocouples were installed. The remainder of the
baseline unit remained unchanged.
Table 111.1 Linear Compressor
••..'<:• .1 • . 1- T. • • .!.
:i ; Linear .
\ Baseline , Compressor
1 • ! I1' r . ! "
Compressor EER
Charge (g)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
5.5
156
1.94
45.2/4.6
0.52
6.2
200
1.73
46.1/4.4
0.48
11
32
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Prototype Test Results
May 1994
Discussion
The linear compressor was more efficient than the original compressor
and produced an 11 percent energy savings. The savings were smaller
than expected when compared on an HER basis because the fans also
consume electricity.
ERA predicted a 10 percent energy savings when the linear compressor
replaced a 6.0 EER reciprocating compressor in an 18 ft3 R/F. [2] The
linear compressor in the ERA analysis was assumed to have an EER of
6.5 and variable capacity control. The test did not include capacity
control, and the linear compressor had an EER of 6.2 and replaced the
Frigidaire unit, which had a 5.5 EER.
33
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Energy-Efficient Refrigerators
III.A.2 Inverter
An inverter is a variable-frequency power source that can be used to vary the speed of
electric motors. The inverter used in the experiments is a proprietary design. It works
with conventional permanent split capacitor (psc) motors such as those used in
refrigerator compressors.
Baseline Unit
The baseline unit was an 18 ft3 top-freezer automatic-defrost refrigerator
manufactured by Whirlpool.
Prototype Unit A 90 V inverter was added to the power supply to the compressor. The
fan voltage and frequency was not changed.
Table III.2 Inverter
— . _ _ . — . — . ,— : 1
: Baseline Inverter
FF/FZ Temperature (°F)
Energy Consumption (kWh/24h)
Duty Cycle
% Energy Reduction
42.3/4.4
2.49
0.57
42.3/4.8
2.36
0.69
5
Discussion The best result with the inverter was achieved at an inverter frequency
of 45 Hz. The test results demonstrate that there may exist an optimum
duty cycle, which is not 100 percent, when an inverter is used. In
addition to using the inverter, the supply voltage was optimized and
found to be 90V.
34
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Prototype Test Results
May 1994
III.A.3. Voltage Regulator
i
III.A.3.O. Green Plug—New Top-Freezer Refrigerator
The "Green Plug" is a commercially available voltage regulator. '
t
Baselinfe Unit The baseline unit was a 20 ft3 top-freezer automatic-defrost R/F
! manufactured by Whirlpool in 1992, model number ET20ZKXZW.
Prototype Unit Baseline R/F was connected to a 115V and 120V power supply via the
! Green Plug.
t .
; Table III.3 Green Plug—New Top-Freezer Refrigerator
i Green
; Baseline Plug
Input Voltage (V)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
115
2.47
37.1/4.0
0.54
115
2.37
35.2/4.9
0.54
4
; . • '• . - ' - - *
i - ; V "
i Green
i Baseline Plug
i . o
Input Voltage (V)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
120
2.41
38.2/8.4
0.48
120 ,
2.40
38.7/8.6
0.45
0
Discussion Generally, test results with this refrigerator showed performance
i changes of about 2+3 percent when the Green Plug was used. Similar
results have been found by Consumers Union. [10]
35
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Energy-Efficient Refrigerators
IILA.3.b Green Plug—Side-by-Side Refrigerator
The Green Plug is a commercially available voltage regulator.
Baseline Unit The baseline unit was a 1975 Sears 19 ft3 side-by-side R/F, model
number 106-7650511.
Prototype Unit The baseline unit was connected to a 115V and 120V power supply via
the Green Plug.
Table ILIA Green Plug—Side-by-Side Refrigerator
... ' v i : •! * .'(•••-.••.
'.' : ' : ,| • I i Green ;
: ' ; ; 1 Baseline r Plug
Input Voltage (V)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
120
5.34
34.1/8.2
0.67
120
5.35
34.4/8.4
0.69
0
! -.{ '. ! ! - l
: : - | ; ' Green;
j -j 'j ' Baseline Plug
Input Voltage (V)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
120
6.11
30.1/3.8
0.75
120
5.75
30.9/4.2
0.68
6
Discussion Generally, test results with this refrigerator showed performance
changes of about minus two to six percent when the Green Plug was
used. Only at 120V and under severe operating conditions (high
temperature lift) were savings of 6 percent found. These results are also
consistent with results found by Consumers Union. [10]
36
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.Prototype Test Results
May 1994
III.A.4 Hot Water Refrigerator
Baseline Unit
The baseline R/F was an 18 ft3 top-freezer automatic-defrost unit
produced by Whirlpool, model number ET18ZKXZWOO.
Prototype Unit A water-cooled condenser was added before and in series with the
condenser of the baseline R/F. The water loop for the water-cooled
i condenser was equipped with a 5-gallon water tank and a circulation
I pump. Whenever the refrigerator was in operation, the pump operated
! and the condenser fan was turned off. If the water temperature in the
I tank rose above the set point, the pump would turn off, and the
t condenser fan would come on. The water-cooled condenser was a tube-
j in-tube, counter-flow heat exchanger with refrigerant in the inside tube.
j Outside and inside tubes were 0.375" and 0.125" in diameter, and the
I condenser was about 120" long.
Table III.5 Hot Water Refrigerator
i Baseline Prototype
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Water Flow Rate (g/s)
Initial Temperature in Water Tank (°F)
Final Temperature in Water Tank (°F)
Heat Recovered to Water Tank
(kWh/24h)
Duty Cycle
1.86
38.9/3.5
n/a
n/a
n/a
n/a
0.46
2.09
36.0/4.1
14.5
: 72
118
1.26
0.33
Discussion While the energy consumption of the prototype R/F was higher than for
; the baseline, the heat recovered by the water-cooled condenser reduced
j the energy requirement of the water heater. Results of a simulation of a
domestic water heater combined with the measured refrigerator
performance show net energy savings of 10 to 15 percent for the
! combined system.
37
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Energy-Efficient Refrigerators
III.B. IMPROVED REFRIGERANTS
III.B.1 Improved Refrigerants—Hydrocarbon Blends
Baseline Unit
The baseline unit was a 20 ft3 top-freezer automatic-defrost R/F
produced by Whirlpool, model number ET20ZKXZW.
Prototype Unit A mixture of n-butane (R-600) and propane (R-290) was used as a
refrigerant in the original refrigerator. The capillary tube length and
charge were optimized. A sight glass at the condenser outlet and two
pressure transducers were also added. The additional capillary tube had
a diameter of 0.026".
Table III.6 Hydrocarbon Blends
Baseline R-600 and R-290
1 ' i i . " i - -i
Charge (g)
Extra Cap. Tube (ft)
Energy Consumption (kWh/24h)
FF/FZ Temperature (F)
Duty Cycle
% Energy Reduction
240
0
2.47
37.1/4.0
0.54
80 (30/70)
5
2.30
39.4/3.3
0.33
7
Discussion There are a number of advantages that result from hydrocarbon use:
energy savings up to seven percent compared to R-12 as the refrigerant,
charge reduction to a third of that of R-12, and a lower pressure ratio
than that of R-12. The energy savings can be improved by taking
advantage of the temperature glide (which was not done here). The
charge can also be reduced further with better designs, thereby reducing
the flammability risk. It should be noted that the mixture concentration
may vary considerably due to preferential oil solubility and storage
effects in components. [11]
38
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Prototype Test Results
May 1994
III.B.2 Improved Refrigerants—Cyclopropane
Baseline Unit The baseline R/F was an 18.0 ft3 top-freezer automatic-defrost unit
i manufactured by Whirlpool.
Prototype Unit Only the refrigerant, amount of charge, and the length of the capillary
i tube were changed.
j Table IIL7 Cyclopropane
Baseline Cyclopropane
Charge (g)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
156
2.20
38.5/4.4
0.52
100
2.05
38.9/4.4
0.47
7
Discussion Cyclopropane showed a seven percent decrease iri energy consumption
compared to the baseline with R-12. The volummetric capacity of
cyclopropane is 17 percent higher than that of R-12. Since the
j compressor remained unchanged, the higher volummetric capacity
i resulted in a reduction of the compressor run time. The discharge
pressure of cyclopropane increased by 10 percent, while the suction
, pressure was similar to that of R-12. [12]
! ERA predicted a four percent energy reduction when HFC-134a was
replaced by cyclopropane. [2]
39
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Energy-Efficient Refrigerators
III.B.3 Improved Refrigerants—HFC-134a and HFC-152a
Original Unit The original unit was an 18.0 ft3 top-mounted automatic-defrost R/F
built by GE, model number TBX18P.
Prototype Unit The original compressor was replaced with a RG108-1 compressor for
HFC-134a tests. It was then replaced with a TG108-1 compressor for
HFC-152a tests. Both compressors came from AMERICOLD. •
Table HL8 Minimum Energy Consumption of the Optimized Systems
System bfype . '. \ HFC-134a HFC-152a
Min. energy consumption (kWh/day)
Avg. instantaneous power (on time) (W)
Compressor on-time (min)
Total cycle time (min)
Additional capillary tube length (ft)
Refrigerant charge (g)
Avg. freezer comp. temperature (°F)
Avg. food comp. temperature (°F)
Avg. evap. pressure during on time (psia)
Avg. cond. pressure during on time (psia)
1.83
172.4
23.0
52.0
7.0
200
5.6
40.8
15.1
174.0
1.79
174.0
21.0
49.0
18.0
120.
5.1
40.3
13.3
163.3
Table III.9 Calorimeter Data for the Two Compressors
' ;- .:•!;. I . . ' ! '• : :.
Refrigerant i HFC-134a HFC-152a
' : ' [ ! i
Compressor model #
Oil type
Evaporation teinperature (°F)
Evaporation pressure (psia)
Condensing temperature (°F)
Condensing pressure (psia)
Capacity (BTU/h)
EER
RG108-1
RL212B (Ester)
-10.4
16.5
129.9
213.4
759.9
4.78
TG108-1
100DL (alkylbenzene)
-9.4
15.4
129.8
190.3
824.7
4.93
Discussion The HFC-152a R/F test has two percent lower energy consumption than
the HFC-134a R/F test. The calorimeter tests show a three percent lower
EER and an eight percent lower capacity for the HFC-134a compressor.
The lower capacity of the compressor is reflected in the longer run time
for the HFC-134a R/F. When the lower EER of the HFC-134a
compressor is considered, both systems have the same performance. [13]
40
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Prototype Test Results
Mai/1994
III.B.4 Improved Refrigerants—HCFC-22 and HFC-152a Blends
Baseline Unit The baseline R/F was a GE 18 ft3 top-freezer automatic-defrost unit.
i
Prototype Unit There were essentially no changes made to the refrigerator, except
i changes to the capillary and the addition of measurement probes (two
pressure transducers and one sight-glass).
Table 111.10 HCFC-22 and HFC-152a Blends
' 1 ' :
i Babeline 13% HCFC-22 and 87% HFC-152a
Charge (g)
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
1
I
Duty Cycle
% Energy Reduction
350
2.11
44.3/5.0
0.48
207 (27&180)
2.03
43.7/4.8
0.48
4
Discussion Several mixture compositions were tried to find the mixture of 13
percent HCFC-22 and 87 percent HFC-152a. This best mixture led to an
optimum energy savings of four percent. [12]
41
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Energy-Efficient Refrigerators
m.C. IMPROVED CYCLE
IH.C.l Lorenz-Meutzner Cycle
IILC.l.a Lorenz-Meutzner Cycle—Zeotropic Refrigerant Mixtures
Baseline Unit The baseline R/F was a 20.0 ft3 side-by-side unit produced by Whirlpool.
Prototype Unit The original evaporator was replaced by a counter-cross-flow evaporator, and
a natural convection evaporator was added to the fresh food compartment.
The total internal volume of the two evaporators was 72 percent of the original
evaporator volume, resulting in a reduction of the charge. The original 10W
freezer evaporator fan was replaced with a 7W unit, and a small 1W DC fan
was placed in the fresh food cabinet to eliminate temperature gradients. A
combination of two counter-current tube-to-tube heat exchangers (high and
low temperature) and an adiabatic capillary tube replaced the conventional
suction line heat exchanger. The original reciprocating compressor and
condenser were used. The original compressor oil, a 150 SSU mineral oil
(naphthenic), was used for tests involving R-12. A synthetic oil (alkylbenzene)
was used with the zeotropic refrigerant mixture. A commercial filter dryer
was installed in the liquid line after the condenser. Additional details on the
various components can be found in reference [14].
Table III.ll Lorenz-Meutzner Cycle—Zeotropic Refrigerant Mixtures
Baseline
' (R-12)
:. 65% HCFC-22 •-
and
35%HCFC-123
71% HqFC-22
and
29% HCFC-141b
60% HCFC-22
and
40% HCI-C-123
Energy Consumption
(kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
2.44
36.6/4.5
0.57
2.17
36.2/5.0
0.53
11
2.20
40.0/4.9
0.51
10
2.26
38.0/4.9
0.58
7
Discussion This prototype demonstrates that the Lorenz-Meutzner cycle works well in a
side-by-side refrigerator/freezer. The natural-convection food-compartment
evaporator caused significant temperature stratification that could be
eliminated with a 1W fan. Consequently, a forced-convection evaporator is
recommended for the food compartment in a side-by-side unit.
42
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Prototype Test Results
May 1994
IILC.l.b Lorenz-Meutzner Cycle—Hydrocarbon Blends
Baseline Unit The baseline unit was an 18.0 ft3 top-freezer automatic-defrost R/F built
: by Whirlpool, model number WT18NKYO.
Prototype Unit A natural convection food compartment evaporator, a counter-flow
| freezer evaporator, and a suction line heat exchanger were added to the
1 baseline R/F.
1
Table IIL12 Lorenz-Meutzner Cycle—Hydrocarbon Blends
Baseline Baseline
Cycle Baseline LM 1 ,LM 2 L-M L-M L-M L-M
! i
; '
Refrigerant
Charge (g)
Energy Consumption
(kWh/24h)
f
FF/FZ T
emperature
% F^nergy Reduction
Test Date
R-12
300
1.83
38.1 /
4.7
10/91
original
R-12
310
1.69
38.5/
5.0
8
* 09/92
R-12
360
1.84
38.1/
4.7
-1
* 05/93
R-290/
C5H12
180
(50/50)
1.54
40.4/
4.8
16
R-290/
HCFC-123
180
(50/50)
1
1.52
38.9/
4.7
17
:
R-290/
R-600
145
(48/52)
1.52
38.8/
5.1
17
R-290/
R-600/
157
(42/S9/
19)
1.50
40.2/5.1
18
* After conversion to Lorenz-Meutzner cycle
Discussion Hydrocarbon mixtures in the Lorenz cycle save energy in the range from
I 16 to 18 percent as compared to R-12 in a top-freezer automatic-defrost
I refrigerator. If it is considered that the refrigerator insulation tends to
! age over time (increasing of thermal conductivity), which may be
t indicated by the difference in the baseline tests LM1 and LM2 with
j otherwise identical hardware, then the savings will reach 23 to 25
I percent.
43
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Energy-Efficient Refrigerators
ERA predicted 18 percent energy reductions for similar R/Fs with
natural convection evaporators in the fresh food compartment. This is
in agreement with the test results.
44
-------
Prototype Test Results
May 1994
III.C.l.c Lorenz-Meutzner Cycle
Baseline Unit The baseline R/F was a 19.8 ft3 top-freezer automatic-defrost unit
I produced by Whirlpool, model number ET20ZKXZW.
i
Prototype Unit A counter-cross-flow condenser (forced convection), counter-flow freezer
| evaporator (forced convection), counter-flow food compartment
I evaporator (natural convection) were added. An inter-cooler between
1 the freezer and fresh food evaporators was not used.
1 Table IIL13 Lorenz-Meutzner Cycle
I 1
Heater On Off Off Off On On
Refrigerant
FF/FZ Temperature
(PF)
Energy
Consumption
(kWh/24h)
% Energy
Reduction**
R-12
41.9/5
2.17
R-12
38.6/5
2.05
Mixture 1*
38.5/4.5
1.74
15
Mixture 2*
42.0/5.2
1.66
19
R-12
41.8/4.8
!- 2.28
Mixture 2*
42.3/4.8
1.92
16
Mixture 1 is HFC-134a (56%)/HCFC-123 (31%)/R-290 (4%)/HFC-32 (9%), and (Mixture) 2 is R-290
(65 %)/HCFC-123 (35%). • • - ;
i |
Compared •with the test result using R-12.
Discussion The R-12 test was repeated (second to last column) to account for the
! aging of the cabinet and any other deterioration of the insulation that
may have occurred during the numerous modifications. The energy
1 savings are calculated based on the respective baseline test (either with
I the heater on or off). The savings of the last test are based on the latest
: baseline. Test results show that at least 15 percent energy savings can
i be achieved with this version of the Lorenz-Meutzner cycle.
45
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Energy-Efficient Refrigerators
III.C.2 Modified Lorenz-Meutzner Cycle
III.C.2.a Modified Lorenz-Meutzner Cycle—U.S. Refrigerator
The modified Lorenz-Meutzner cycle has three-way internal heat exchangers in the food
and freezer compartments, where heat is mutually exchanged between the compartment
air, refrigerant condensate, and evaporating refrigerant. In the original Lorenz-Meutzner
Cycle, heat is internally exchanged between the compartment air and refrigerant vapor,
while the refrigerant condensate line is bypassed.
Baseline Unit
The baseline R/F was a 19.8 ft3 top-freezer automatic-defrost Whirlpool
(Kitchen Aid) unit, model number KTRS20KXWH10.
Prototype Unit A modified Lorenz-Meutzner cycle with internal heat exchange in the
evaporators, counter-cross-flow condenser and freezer evaporator,
natural-convection food evaporator, and intercooler added. The
refrigerator/freezer was equipped with the original rotary compressor
and energy-saving valve.
Table IIL14 Modified Lorenz-Meutzner Cycle—IT.S. Refrigerator
''.'•: : ;; Baseline - i Prototype
Refrigerant
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
% Energy Reduction
R-12
1.86
38.1/5.1
R-290/HCFC-123
1.55
38.6/4.1
17
Discussion The results indicate that the daily energy consumption decreased by up
to 17 percent without considering the defrost cycle. Many other CFC-free
refrigerant mixtures were also tested with significant energy savings, in
the same 17 percent savings range.
46
-------
Prototype Test Results
May 1994
III.C.2.b Modified Lorenz-Meutzner Cycle—Chinese Refrigerator
Baseline Unit
The baseline R/F was a top-freezer 6.4 ft3 automatic-defrost model
produced by the ShangLing Refrigerator Co., model number BCD-180.
Prototype Unit Modification similar to those described in Section IH.C.2.a were made.
The evaporator was constructed of 5/16 inch O.D. aluminum/copper
! tubing in a cross-counter-flow pattern with 40-45 plate fins. The
! resulting heat exchanger was 9 inches deep in the direction of air flow
I with 12.5 inch x 2 inch cross-sectional area.
f
: Table 111.15 Modified Lorenz-Meutzner Cycle—Chinese Refrigerator
Refrigerant
Baseline
R-12
Prototype
R-290/
HCFC-123
Energy Consumption (kWh/24h)
1.29
1.16
FF/FZ Temperature (°F)
38.7/5.0
38.1/5.0
' % Energy Reduction
10
Discussion The results indicate that the daily energy consumption decreased by up
, to 10 percent. Since this Chinese refrigerator had much smaller internal
j volume, there was not much room for optimizing the evaporators. Also,
I the condenser was located in the foam insulation and was not a counter-
flow design. Considering these limitations, the energy savings were
quite good, although not as high as found in the American R/F. [15]
47
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Energy-Efficient Refrigerators
III.C.3 Dual-Loop System
Baseline Unit
Prototype Unit
The baseline R/F was a 19.8 ft3 top-freezer automatic-defrost unit
manufactured by Whirlpool.
A dual-loop system with two separate vapor compression cycles, one
for the freezer and one for the food compartment, were added. The
freezer compartment cycle included a 4.0 EER reciprocating
compressor, which was placed at the left outside of the cabinet, the
original evaporator and fan, mounted in the original position, and a
natural convection condenser located on the back of tine cabinet.
The food compartment cycle consisted of a 3.65 EER reciprocating
compressor, located in the original compressor compartment, a new
counter-flow heat exchanger with a 6 W fan, and a new natural
convection condenser.
To reduce heat transfer between the two compartments, the top side
of the food and the bottom side of the freezer compartments were
insulated with a 1-inch thick glass wool mat. The compressor oil was
changed from a mineral oil with 3GS viscosity to a 1GS mineral oil to
compensate for the lower operating temperatures. Additional details
can be found in reference [16].
Table 111.16 Dual Loop System
I ! Baseline ' DuallLoop
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
% Energy Reduction
1.98
40.5/3.7
0.47
1.87
(1.3.0 in FF + 0.57 in FZ)
39.6/3.7
0.51 for FZ/0.22 for FF
4
Discussion The best result achieved with the dual loop system showed a four
percent improvement of the total energy consumption over the baseline.
The compressors used in both cycles were smaller and lower EER than
the original rotary compressor (EER = 4.9). Energy savings of more than
20 percent could be possible, if compressors with the same EER as the
original compressor were available. The reported savings exclude
defrost. Higher energy savings can be expected when defrost is
included. This effort continued for an additional 12 months with the
48
-------
Prototype Test Results
May 1994
best result being a 4 percent reduction in energy consumption.
Accounting for foam aging, the result would have been higher.
ERA calculations for the dual loop have predicted a two percent energy
reduction. The savings were smaller because forced convection
evaporators and condensers were used. [2]
49
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Energy-Efficient Refrigerators
III.C.4 Two-Stage Refrigerator
Baseline Unit
The baseline model was built at U. Md. It consisted of an approximately
20 ft3 top-freezer refrigerator that was housed in an insulated wooden
box.
Prototype Unit A forced convection food compartment evaporator, forced convection
freezer evaporator, and condenser were used. Two compressors were
used in series. The first pumped refrigerant from the freezer evaporator
to the food compartment evaporator pressure level, the second from the
fresh food pressure level to the condenser pressure level.
Table 111.17 Two-Stage System
•i^MMl
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
FF/FZ Compressor EER
Charge (g)
% Energy Reduction
r - "
Baseline j pfwo-Stage
3.30
43.9/5.2
0.72
4.4
480
3.20
38.3/5.3
0.62
4.2/3.4
316
3
Discussion The test results show a three percent energy savings over the single
stage configuration. Considering that the food compartment
temperature was considerably lower than in the baseline test, another
three percent could have been gained. Finally, accounting for the lower
compressor EER would result in a total energy savings of about 20
percent.
50
-------
Prototype Test Results
May 1994
III.C.5 Kopko Cycle
The Kopko cycle represents a method of achieving energy savings with two evaporators
in 3 single circuit without the use of mixtures or special control valves. The basic set-up
uses a freezer evaporator and fresh-food evaporator connected in series, each with its
own fan. The controls run one evaporator fan at a time. Only the freezer fan operates
when cooling the freezer; and only the fresh-food compartment fan operates when
cooling the fresh-food compartment. The evaporators are installed to minimize natural
convection of air when the fans are off. The normal sequence is to cool the fresh-food
compartment first, then the freezer. This set-up uses the higher evaporator pressures
that normally occur at the beginning of the compressor on time to cool the fresh-food
compartment.
Baseline Unit
The baseline unit was an 18 ft3 top-freezer automatic-defrost R/F
manufactured by Whirlpool, model number ET18NKXYW.
Prototype Unit A forced convection food compartment evaporator was added to the
• system. Capillary tube length was optimized and measurement probes
j were added. The control logic was changed. Lastly, the compressor
I was exchanged as indicated in the table below. [17]
; Table 111.18 Kopko Cycle
Baseline Kopko
i
Energy Consumption (kWh/24h)
FF/FZ Temperature (°F)
Duty Cycle
Compressor
HER
Charge (g)
% Energy Reduction
1.78
38.4/4.9
0.45
FGV80AW(SINGLE)
4.91
177
1.24
39.0/5.1
0.43
AMERICOLD HG107
5.52
360
30
Discussion The use of the Kopko configuration leads to considerable energy
i savings. When the higher compressor EER is excluded, the new
configuration produces an 18 percent increase in performance.
, The following six tables describe all of the intermediate modifications to
i the Kopko system and the respective test results.
51
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Energy-Efficient Refrigerators
Table IIL19 Kopko Cycle—First Modification
' Baseline First Modification '-.
> 1 i i i . 1
Size
Compressor
Freezer Evaporator
Type
Total Area
Flow
Fan
Food Evaporator
Type
Total Area
Flow
Fan
Condenser
Capillary Tube
SLHX
Fan Control
R-12 Flow Path Direction
R-12 Charge (g)
Two-Way Switch
Model #
Power
On-time Delay Relay
Model #
Power
Filter Dryer
Sight-glass
18ft3
FGV80AW
Forced Convection
Plate Fin and Tube
2,500 in2
Cross-Flow
40 - 50 cfm, 8 - 12 W
N/A
Natural Convection
~8' (0.026" ID)
6'8"
0.026" ID by 0.313" OD
N/A
N/A
177
N/A
N/A
Original
N/A
Same as Baseline
Same as Baseline
Forced Convection
Spiny Fin and Tube
1,457 in2(0.94 m2)
Counter-Flow
Same as Baseline
Forced Convection
Plate Fin and Tube
2,500m2
Cross-Flow
65cfm, 7W
Pewee Boxer
Model* 4715PS-12T-B10
Same as Baseline
9'6" (0.026" ID) in FZ
10' (4' located in FF)
0.125" by 0.313"OD
FZ Fan First with Timer ,
FZ to FF Evaporator
230
Potter-Brumfield
KUP-5A15-120
2W
Dayton Elect. MFG. Co.
6X601F (Range 9-900sec)
3 W
ALCO
EK - 032
Installed
52
-------
Prototype Test Results
May 1994
Table 111.20 Kopko Cycle—First Modification Test Results
Energy Consumption
,(kWh/24h)
Baseline
1.78
First Modification
1.67
^Z/FF Temperature (°F)
4.9/38.4
4.7/38.2
kTD Controller
Set Point, FZ/FF (°F)
jHysterisis, FZ/FF
5.5/-
1.4/-
4.5/38.55
0.4/0.3
Puty Cycle
0.45
0.42
% Energy Reduction
53
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Energy-Efficient Refrigerators
Table 111.21 Kopko Cycle—Second Modification
First Modification Second Modification :
Compressor
Freezer Evaporator
Type
Total Area
Flow
Fan
Food Evaporator
Type
Total Area
Flow
Fan
Condenser
Capillary Tube
SLHX
Fan Control
R12 Flow Path
Direction
R12 Charge (g)
Two-Way Switch
On-time Delay Relay
Filter Dryer
Sight-glass
Special Insulation
Mullion
FZ Evaporator Cover
FGV80AW
Forced Convection
Spiny Fin and Tube
1,457 in2
Counter-Flow
40 - 50 cfm, 8 - 12 W
Forced Convection
Plate Fin and Tube
2,500 in2
Cross-Flow
65 cfm, 7 W
Pewee Boxer
Model* 4715PS-12T-B10
Natural Convection
9'6" (0.026" ID) in FZ
10' (4' located in FF)
0.125" by 0.313"OD
FZ Fan First with Timer
FZ to FF Evaporator
230
Installed
Installed
Installed
Installed
N/A
FGV80AW .'
Forced Convection
Spiny Fin and Tube
2,853 in2 (1.84 m2)
Counter-Flow
26 cfm, 4 W
Forced Convection
Plate Fin and Tube
3,661 in2 (2.36 m2)
Cross-Flow
65 cfm, 7 W
Pewee Boxer
Model* 4715PS-12T-B10
Natural Convection
8'0" (0.026" ID) in FZ
6'8"
0.026'TD by 0.313"OD
FF Fan First
FZ to FF Evaporator
300
Installed
N/A
Installed
Installed
1" Foam
Glass Wool
54
-------
Prototype Test Results
"May~1994
Table 111.22 Kopko Cycle—Second Modification Test Results
: " =: 1-
Eirst Second
; i ,
Modification . Modification
Energy Consumption (kWh/d)
FZ/FF Temperature (°F)
RTD Controller
Set Point, FZ/FF (°F)
Hysterisis, FZ/FF ;
Pressure (psia)
High Side-
Low Side
Temperature (°F)
Condenser
FZ Evaporator
FF Evaporator
On/Off-Time (min)
FF On-Time (min)
Duty Cycle
% Energy Reduction from
Baseline
1.67
4.7/38.2
4.5/38.55
0.4/0.3 .
161.6
15.5
105.2
-21.3
9.5
12.8/18.0
- (Fan on once)
0.42
6
1.56
5.0/38.3
5.9/36.9
1.0/0.2
158.1
16.2
113.0
-15.8
-3.9
13.5/19.7
4.5 (Fan on twice)
0.41
1
12
55
-------
Energy-Efficient Refrigerators
Table 111.23 Kopko Cycle—Third Modification and Test Results
: • - : • ' 1 . .' ' 1 • ' ' •
• Second Modification Third Modification
Energy Consumption
(kWh/d)
FZ/FF Temperature
RTD Controller
Set Point, FZ/FF (°F)
Hysterisis, FZ/FF
Pressure (psia)
HigltySide
Low Side
Temperature (°F)
Condenser
FZ Evaporator
FF Evaporator
Compressor
Model*
Capacity
EER
Oil
R12 Charge (g)
On/Off-Time (min)
FF On-Time (min)
Duty Ctcle
% Energy Reduction
from Baseline
1.56
5.0/38.3
5.9/36.9
1.0/0.2
158.1
16.2
113.0
-15.8
-3.9
Reciprocating
FGV80AW
(EMBRACO)
820
4.91
Mineral, 3GS
300
13.5/19.7
4.5
0.41
12
1.29
5.1/ 39.2 .
5.35/36.25
0.7/0.7
152.2
15.5
97.5
-17.5
12.3
Reciprocating
HG-107
(AMERICOLD)
700
5.5
Mineral, 1GS
320
13.3/16.3
5.5 ,
45
28
56
-------
Prototype Test Results
May1994
Table 111.24 Kopko Cycle—Fourth Modification and Test Results
I 1
Third Modification Fourth Modification
; -
Energy Consumption
(kWh/24h)
FZ/FF Temperature
! (°F)
! RTD Controller
| Set Point, FZ/FD (°F)
! Hysterisis, FZ/FD
Pressure (psia)
High /Low Side
Temperature (°F)
Condenser
FZ/FF Evaporator
Compressor
1 Model*
[ Capacity
EER
Oil
: R12 Charge (g)
Filter Dryer
Sight-glass
On/Off-Time (min)
FF On-Time (min)
Duty Cycle
% Energy Reduction
from Baseline
1.29
5.1/39.2
5.35/36.25
0.7/0.7
152.2/15.5
97.5
-17.5/12.3
Reciprocating
HG-107 (AMERICOLD)
700
5.5
Mineral, 1GS
320
Installed
Installed
13.3/16.3
5.5
0.45
28
1.24
5.1/39.0
4.0/35.2
1.5/0.6
150.1/16.2
95.0
-15.2/42.8
Reciprocating
HG-107 (AMERICOLD)
700
5.5
Mineral, 1GS
320
Removed
Removed
20.8/28.0
7
0.43
30
57
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Energy-Efficient Refrigerators
58
-------
Prototype Test Results
May 1994
IV. SYSTEM AND CABINET MODIFICATIONS
Several super-efficient prototype units have been built and tested combining
modifications to both the system and cabinet. These units are described in this section.
59
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Energy-Efficient Refrigerators
IV.A DOUBLE INSULATION AND LORENZ-MEUTZNER CYCLE
Baseline Unit The baseline model was a 20 ft3 top-freezer automatic-defrost R/F
produced by Whirlpool. This was the same unit described in
Section II.A.1.
Prototype Unit A series of modifications were made to the prototype unit. These
included adding double insulation (see II.A.1), adding a high-efficiency
compressor, adding a modified Lorenz-Meutzner cycle with a HCFC-123
and R-290 refrigerant blend, and reducing the gasket region heat leak.
The results of each step in the path follow. Details of individual steps
are then presented. [18]
Table W.l Double-Insulated, Lorenz-Cycle Refrigerator
In$ulatlon Standard Double Double Double Double DOUBLE
Compressor*
Cycle
Door Seal
Refrigerant
Charge (g)
FF/FZ Temp. (°F)
Duty Cycle
Energy Consump.
(kWh/24h)
Energy Consump.
including defrost
% Energy
Reduction
Total % Energy
Reduction
Standard
Standard
Standard
R-12
38/5
1.86
Standard
Standard
Standard
R-12
220
37.0/5.3
0.36
1.36
1.47
27
27
High Eff.
Standard
Standard
R-12
220
37.2/5.4
0.39
1.26
1.38
7
32
High Eff.
Lorenz
Standard
R-12
410
36.4/5.9
0.39
1.25
N/A
1
33
High Eff.
Lorenz
Standard
HCFC-123
and R-290
210
38.6/5.4
0.26
1.05
1.20
16
44
High Eff.
Lorenz
Improved
HCFC-123 and
R-290
210
38.5/5.5
0.25
1.01
1.14
4
46
*Sce Table IV.2. for additional information.
Discussion The next four sections provide design details
Detailed comparison of the test results and a
improved door seal are also attached.
of the prototypes tested.
drawing showing the
60
-------
Prototype Test Results
May 1994
IV.A.1 Double Insulation
These modifications are described in Section II.A.I.
IV.A.2 High-Efficiency Compressor
The calorimeter test data for the high-efficiency compressor were provided by the
manufacturer. Table IV.2 compares the original rotary compressor with the high
efficiency reciprocating compressor. The EER of the new compressor was about 12
percent higher than that of the conventional compressor used in the original thick wall
unit. [18]
, Table IV.2 High-Efficiency Compressor
' \
Original High Efficiency
Compressor Compressor
Model
Type
Oil
Oil Viscosity
EER (BTU/W-h)
Capacity (BTU/h)
Power (W)
RA53L11RA
Rotary
Alkylbenzene
3GS
4.80-4.86
850-867
177
HG107
Reciprocating
Mineral Oil
1GS
5.50-5.54 ,
703.2-713.4
129
61
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Energy-Efficient Refrigerators
IV.A.3 Modified Lorenz-Meutzner Cycle
A modified Lorenz-Meutzner cycle was incorporated into the R/F. See section III.C.l.c
for additional details. Table IV.3 compares the specifications of the standard and new
cycles.
Table IV.3 ModifiedTLorenz-Meutzner Cycle
Double Insulated with
High Efficiency
Compressor
Modified
Lorenz-Meutzner
Cycle
Size
Compressor
Compressor Oil
Freezer
evaporator
Cabinet
evaporator
Condenser
Suction line HX
Low temp. HX
19.9 cubic feet
HG107
Alkylbenzene
Forced convection tube and fin,
18 tube passes, 26" each pass,
3/8" OD, 77 fins, cross-flow
type
None
Forced convection
0.026" ID capillary tube
soldered to 5/16" OD suction
line
None
Less than 19.9 cubic feet
(considering space of cabinet
evaporator)
HG107
Mineral oil
Forced convection tube and fin,
18 tube passes, 25". each pass,
3/8" OD counter-cross flow
Natural convection copper flat-
plate, 28" by 26", copper plate
two side with thickness 1/32",
total surface area 1456 in2
Forced convection, modified to
counter flow
1/8" OD soldered to 5/16" OD
suction tube, same length as the
original length
25" long 3/8" OD and 1/8" OD
tube soldered together, two
passes
62
-------
; , Prototype Test Results
: May 1994
IV.A.4 Improved Gasket
t
The cabinet flange was modified to reduce heat leakage into the cab:inet as described in
Section II.C.l. A drawing of the modified gasket region follows.
Figure IV.l Schematic Representation of Improved Gasket
insulation tape
2 inches in width
1/8 inch in thickness
Freezer Compartment
Fresh Food Compartment
Front View
63
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Energy-Efficient Refrigerators
IV.B DOUBLE INSULATION AND KOPKO CYCLE
Baseline Unit The baseline model was the 20 ft3 R/F described in Section II.A.1.
Prototype Unit Double insulation (section II.A.I) and the Kopko cycle (Sectidn III.C.5)
were added to the baseline model.
Table IV.4 Double-Insulated, Kopko-Cycle Refrigerator
\ : :
; Baseline Double Insulation ; Kopko
Energy
Consumption
(kWh/24h)
FF/FZ
Temperature (°F)
Duty Cycle
Compressor
EER
% Energy
Savings
Total % Energy
Savings
1.86
38.1/5.1
0.45
RA53L11RA(SINGLE)
4.9
1.43
38.7/5.2
0.34
RA53L11RA(SINGLE)
4.9
23 ...
23
1.29
38.2/5.0
0.34
FN45R80T
4.5
10
31
Discussion Accounting for the change in the compressor EER, the total energy
savings based on the Kopko concept amounts to 19 percent. This would
result in nearly a 40 percent reduction for the total modification. The
following four tables describe all of the intermediate modifications to the
system and the respective test results.
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Prototype Test Results
May 1994
Table IV.5 Specifications for the First Modification
Baseline First Modification
Size
Wall Insulation
Compressor
Model*
Capacity
EER
Oil
Freezer Evaporator
Type
Total Area
Flow
Fan
Food Evaporator
Type
Total Area
Flow
Fan
Condenser
; Capillary Tube
SLHX
Fan Control
I R-12 Flow Path
; Direction
R-12 Charge
Two- Way Switch
Model #
Power
Filter Dryer
Sight-glass
20ft3
Thick wall
Rotary
RA53L11RA
870.7 BTU/h(255.2 W)
4.91
Mineral, 4GS
Forced convection
Plate fin and tube
3,661in2
Cross-flow
40 - 50 cfm, 6 - 10 W
N/A
Forced convection
~ 8 ' (0.026" ID)
0.026" ID by 0.313" OD
N/A
N/A
205.5 g
N/A
Original
N/A
Same as baseline
Same as baseline
Rotary
RA48L83TE
787 Btu/h(230.7 W)
5.01
Mineral, 4GS
Forced convection
Plate fill and tube
4,265 in2(3.96 m2)
Counter-flow
65 cfm, 7W
Forced convection
Plate fin and tube
4,168 in2(3.87 m2)
Counter-flow
65 cfm, 7 W
Same as baseline
7'0" (0.026" ID) in FZ
0.125" by 0.313"OD
FF fan first
FZ to FF evaporator
410 g
Potter-Brumfield
KUP-5A15-120
2 W
Same as baseline
N/A
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Energy-Efficient Refrigerators
Table JV.6 Test Result for the First Modification
: 1 - - j 1 • i
. , : ! • i
j Double Insulation j: First Modification
Energy Consumption
(kWh/d)
FZ/FF Temperature (°F)
Total Savings (%)
Net Saving
On/Off Time (min)
FF On-Time (min)
On-Time Ratio (%)
RTD Controller
Set Point, FZ/FF (°F)
Hysterisis, FZ/FF
1.43
5.2/38.7
-
18.1/35.5
-
33.8
5.857 -
1.27-
1.24
5.2/38.2
12.8
10.8
17.0/32.0
5.6
34.7
4.5/39.0
1.5/0.2
Table IV.7 Compressor Comparison for Kopko Modifications
: ! : ! : 1
' •; ! ; First ; , Second
Baseline Modification Modification
Compressor
Model #
Capacity (BTU/h)
EER (%)
Oil
Rotary
Matsushita
RA53L11RA
870.7(255.2 W)
4.91
Mineral, 4GS
Rotary
Matsushita
RA48L83TE
787.0(230.7 W)
5.01 (+ 2.0)
Mineral, 4GS
Rotary
Matsushita
FN45R80T
715.0(209.5 W)
4.5 (- 8.4)
Mineral, 4GS
66
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_"-"••' Prototype Test Resutis
Way'1994
IV.C DOUBLE INSULATION AND ALTERNATE REFRIGERANTS
IV.C.1 HFC-152a
Baseline Unit The baseline model was an 8.5 ft3 bottom-freezer R/F produced by
i Qingdao Haier in China, model number BCD-220. The standard cycle
, includes two evaporators and a single compressor with a switching
j valve to control refrigerant flow.
I
Prototype Unit Double insulation and cycle modifications were made to the unit.
I Added insulation was 0.8 inches on the sides, back, and bottom and 0.6
; inches to the doors. Cycle improvements included, adding a counter-
{ flow condenser (natural convection), a counter-flow freezer evaporator
j (three-way heat exchanger, natural convection), and a food compartment
j evaporator (natural convection). An inter-cooler was not added between
s the freezer and food compartment evaporators. A high-efficiency
| compressor obtained from AMERICOLD (TG105-12) was also used.
; Table IV.8 Increased Insulation with Refrigerants HFC-152a
Refrigerant R-12 HFC-152a
Energy Consumption (kWh/24h)
Compressor EER
FF/FZ Temperature (°F)
% Energy Reduction
1.70
3.62
38.0/5.0
0.96
4.48
38.0/5.1
44
Discussion The results show that the combination of modifications reduced the
energy consumption by about 44 percent.
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Energy-Efficient,Refrigerators
IV.C.2 Hydrocarbon Mixtures
Baseline Unit The baseline unit was the same as described in the previous section.
Prototype Unit The modifications were the same as above except hydrocarbon
refrigerants were used.
Table IV.9 Increased Insulation with Hydrocarbon Refrigerants
Refrigerant
Energy Consumption (kWh/24h)
R-290 (68i%) and R-2^0 (63%) and
R-600 (32%) R-600 (37%)
1.70
0.80
0.83
FF/FZ Temperature (°F)
38.0/5.0
37.5/4.8
38.1/5.0
% Energy Reduction
53
51
Discussion Test results show that an additional 10 percent energy savings can be
achieved using hydrocarbon mixtures as compared to the system using
HFC-152a.
68
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Prototype Test Results
May 1994
V. REFERENCES
1. EPA Refrigerator Analysis Program (ERA): User's Manual, Report Number EPA-430-R-93-
007, U.S. Environmental Protection Agency, June 1993.
2. Multiple Pathways to Super-Efficient Refrigerators, Report Number EPA-430-R-93-008,
U.JS. Environmental Protection Agency, June 1993.
i
3. Carbon Black in Appliance Foam Insulation, }. S. Pisipati et al., in Proceedings of the 1993
Polyurethanes World Congress, Society of the Plastics Industries, New York, October
1993, 146-53. !
4. Performance Test Results for Freezers Containing Vacuum Insulation Panels, H. A. Fine and
S. R. Griffin, Proceedings of the International Conference on Alternatives to CFCs and
Hdlons, FGU, Berlin, Germany, 1992, 317-22.
! I
I I
5. Test Results for Refrigerator/Freezers Containing Vacuum Insulation Panels, H. A. Fine, G.
J. Haworth and R. Srikanth, Proceedings of the International Conference on Alternatives to
CFCs and Halons, FGU, Berlin, Germany, 1992, 305-15.
t i
6. Evaluation of Advanced Insulations for Refrigerators, G. J. Haworth, R, Srikanth, and H. A.
Fine, Proceedings of the 44th. Annual International Appliance Technical Conference, Ohio
State University, Columbus, Ohio, May 1993, 1-12
7. Development and Application of Vacuum Insulation Technology to Refrigerators, G.A.
Mellinger and K. L. Downs, presented at International Conference on CFC and Halon
Alternatives, Washington, DC, September 1992.
8. Finite Element Analysis of Heat Transfer Through the Gasket Region of Refrigerator/Freezers,
Report Number EPA-430-R-92-009, U.S. Environmental Protection Agency,
October 1992.
9. Linear Compressors—A Maturing Technology, N.R. van der Walt and R. Unger, presented
at 45th International Appliance Technical Conference, University of Wisconsin, May
1994.
10. "Can a Fancy Plug Cut Energy Costs?," Consumer Reports, November 1993, 694.
11. Experimental Results with Hydrocarbon Mixtures in Domestic Refrigerator/Freezers, B.Y. Lin,
M4-L. Tomask and R. Radermacher, paper sumitted to ASHRAE, April 1994.
t
12. R22/R152a Mixtures and Cyclopropane (RC 270) as Substitute for R12 in Single-Evaporator
Refrigerators: Simulation and Experiments, K. Kim, U. Spindler, D.S. Jung,
R. jRadermacher, ASHRAE Trans., Vol. 99, Part 1, Paper #3655.
69
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Energy-Efficient Refrigerators
13. Evahiation ofHFC-134a and HFC-152a as Working Fluids in a Domestic Refrigerator/Freezer,
J. Pannock, Z. Liu, K. Yu, R. Radermacher, ASHRAE Transactions, Vol. 100, Part 1.
14. Testing of Domestic Two-evaporator Refrigerators with Zeotropic Refrigerant Mixtures, Bob
Rose, Dong Soo Jung, R. Radermacher, ASHRAE Transactions 1992, Vol. 98, Pt. 2,
Paper #3620.
15. R. Radermacher, "Progress Report to EPA," 1/12/93.
16. An Experimental Study of the Performance of a Dual-Loop Refrigerator/Freezer System,
S. Won, D. Jung, R. Radermacher, Submitted to International Journal of Refrigeration.
17. Experimental Research and Development of a Tandem System Domestic Refrigerator, K. Kim,
B. Kopko and R. Radermacher, Paper submitted to ASHRAE Transactions.
18. Development and Testing of a High Efficiency Refrigerator, Q. Zhou, J. Pannock,
R. Radermacher, ASHRAE Transactions, Vol. 100, Part 1.
70
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