United States Office of Atmospheric E PA-430-R-93-009

Environmental Protection

Agency

and Indoor Air

Programs

June 1993

Recycled/Recyclable

Z^aJ Printed on paper that contains

at least 50% recycled fiber

EE-RM-93-801 COMMENT OR3

United States 

Environmental Protection 

Agency 

tate 

t 

!i!I 

I 

Office of Atmospheric 

and Indoor Air 

Programs 

re 

EPA-430-R-93-009 

June 1993 

ress 

ers 

I 

W Recycled/Recyclable 

TI 1:) Printed on paper that contains 

D<,J at least 50% recycled fiber 
State Of eArtSurvey

Motor Tec hnology App E!o©lb^9 1u 7-71 Yc eti c

Compressors For DomestL

Prepared for

Environmental Protection Agency

Division of Global Change

Revised : March, 1993

Reference 64128

64122

67986

 EE-RM-93-801 COMMENT OR3

State Of The Art Survey 

Of Motor Technology Applicable To Hermetic 

Compressors For Domestic Refrigerator/Freezers 

Prepared for 

Environmental Protection Agency 

Division of Global Change 

Revised: March, 1993 

Reference 64128 

64122 

67986 
Prologue

Motor technology can play an important role in allowing potential efficiency

improvements of various refrigerator/freezer design alternatives. This review of the

motor technology applicable to small hermetic refrigeration compressors was

undertaken as part of a larger study to evaluate the options for maximizing the

efficiency of domestic refrigerators. The motor characteristics documented in the report

are being used in the overall study as part of the input database for modeling and

evaluating design options.

Findings

1. Two kinds of approaches are possible for compressor motors.

Constant speed, 2 pole, 115 VAC, 60 HZ, single phase, squirrel cage induction

motors are current practice in all refrigerators and freezers; motor speed is close to

3500 RPM;

® Variable speed alternatives are:

- 2 speed (1750/3500 RPM) squirrel cage induction motors; and

- Continuously variable speed, electronically driven motors.

2. Smaller compressors will be needed in future refrigerators.

® super insulation (either vacuum panels or thicker walls) is likely to reduce loads.

® Dual loop (or staged) systems using two compressors may replace single

compressor/evaporator designs to gain theoretical energy efficiency advantages.

3. Small compressors are inefficient because of inefficient motors; these can be

improved with currently available technology.

® Current small compressors are relatively inefficient, mainly due to inefficient

motors.

® Current technology exists to make efficient motors for small compressors at a

reasonable price.

4. Variable speed technology can provide an additional and/or alternative means

to achieve superior energy efficiency

® Variable speed compressor operation has the potential to reduce compressor power

requirements by virtue of more efficient heat exchanger utilization and elimination of

cycling losses.

® Two speed induction motors area low first cost, relative to electronically. driven

variable speed motors, means of reducing compressor on/off cycling.

i

 EE-RM-93-801 COMMENT OR3

Prologue 

Motor technology can play an important role in allowing potential efficiency 

improvements of various refrigerator/freezer design alternatives. This review of the 

motor technology applicable to small hermetic refrigeration compressors was 

undertaken as part of a larger study to evaluate the options for maximizing the 

efficiency of domestic refrigerators. The motor characteristics documented in the report 

are being used in the overall study as part of the input database for modeling and 

evaluating design options. 

Findings 

1. Two kinds of approaches are possible for compressor motors. 

.. Constant speed, 2 pole, 115 V AC, 60 HZ, single phase, squirrel cage induction 

motors are current practice in all refrigerators and freezers; motor speed is close to 

3500 RPM; 

.. Variable speed alternatives are: 

2 speed (1750/3500 RPM) squirrel cage induction motors; and 

- Continuously variable speed, electronically driven motors. 

2. Smaller compressors will be needed in future refrigerators. 

.. super insulation (either vacuum panels or thicker walls) is likely to reduce loads. 

.. Dual loop (or staged) systems using two compressors may replace single 

compressor/evaporator designs to gain theoretical energy efficiency advantages. 

3. Small compressors are inefficient because of inefficient motors; these can be 

improved with currently available technology. 

.. Current small compressors are relatively inefficient, mainly due to inefficient 

motors. 

.. Current technology exists to make efficient motors for small compressors at a 

reasonable price. 

4. Variable speed technology can provide an additional and/or alternative means 

to achieve superior energy efficiency 

.. Variable speed compressor operation has the potential to reduce compressor power 

requirements by virtue of more efficient heat exchanger utilization and elimination of 

cycling losses. 

.. Two speed induction motors are a low first cost, relative to electronically. driven 

variable speed motors, means of reducing compressor on/off cycling. 
® Two speed motors, though not currently produced for or used in domestic

refrigerator compressor applications, could be produced for this application, at a cost

approximating that of premium efficiency single speed motors, but at an efficiency

reduction of 5% at full speed and close to 15% at half speed. At these reduced motor

efficiency levels, no net improvement in RJF energy consumption can be expected to

result from their use.

® The most efficient small variable speed motor/drive system alternative is an

electronically commutated permanent magnet rotor DC motor, with full speed

system efficiency comparable to the best single speed induction motor, and half

speed efficiency within a few percent of full speed. There is some uncertainty with

respect to the cost level that would be reached after a few years of mass production,

but one quarter horsepower ECM motor/drive systems are currently being produced

and sold on a modest scale OEM basis for approximately $100.

® OEM unit costs of these variable speed drives could fall to $50-$55 (or less) in large

scale (hundreds of thousands of units annually) mass production.

® The variable speed drive and motor can operate at higher speeds, allowing reduced

compressor cost, and replaces the existing compressor motor, for offsetting cost

reductions of approximately $20. The net increase in OEM component costs, then,

would be approximately $30-$35.

® Modeled results of R/F performance with a variable speed compressor show

improvements in performance over a single speed compressor.

® A substantial energy saving (10%) can be obtained by replacing the inefficient

fan/motor of typical current practice with a modest efficiency fan and motor.

® With the standard efficiency fan/motor, the variable speed drive operating at steady

state results in increased total energy, with the energy associated with 100% fan run

time more than offsetting compressor power savings.

• With efficient fans, the VSD compressor shows energy savings.

® With variable speed fans added to the VSD, substantial energy savings are obtained.

® A limitation on the compressor energy savings is the declining variable speed motor

system efficiency below half speed.

• The same general observations apply to the application of VSD to a high

performance cabinet, with increased sensitivity of the variable speed options to the

fan efficiency.

ii

 EE-RM-93-801 COMMENT OR3

.. Two speed motors, though not currently produced for or used in domestic 

refrigerator compressor applications, could be produced for this application, at a cost 

approximating that of premium efficiency single speed motors, but at an efficiency 

reduction of 5% at full speed and close to 15% at half speed. At these reduced motor 

efficiency levels, no net improvement in RlF energy consumption can be expected to 

result from their use. 

.. The most efficient small variable speed motor/drive system alternative is an 

electronically commutated permanent magnet rotor DC motor, with full speed 

system efficiency comparable to the best single speed induction motor, and half 

speed efficiency within a few percent of full speed. There is some uncertainty with 

respect to the cost level that would be reached after a few years of mass production, 

but one quarter horsepower ECM motor/drive systems are currently being produced 

and sold on a modest scale OEM basis for approximately $100. 

.. OEM unit costs of these variable speed drives could fall to $50-$55 (or less) in large 

scale (hundreds of thousands of units annually) mass production. 

.. The variable speed drive and motor can operate at higher speeds, allowing reduced 

compressor cost, and replaces the existing compressor motor, for offsetting cost 

reductions of approximately $20. The net increase in OEM component costs, then, 

would be approximately $30-$35. 

.. Modeled results of RlF performance with a variable speed compressor show 

improvements in performance over a single speed compressor. 

" A substantial energy saving (10%) can be obtained by replacing the inefficient 

fan/motor of typical CutTent practice with a modest efficiency fan and motor. 

II With the standard efficiency fan/motor, the variable speed drive operating at steady 

state results in increased total energy, with the energy associated with 100% fan run 

time more than offsetting compressor power savings. 

" With efficient fans, the VSD compressor shows energy savings. 

.. With variable speed fans added to the VSD, substantial energy savings are obtained. 

II A limitation on the compressor energy savings is the declining variable speed motor 

system efficiency below half speed. 

.. The same general observations apply to the application of VSD to a high 

performance cabinet, with increased sensitivity of the variable speed options to the 

fan efficiency. 

ii 
® The value of these energy savings was calculated. Assuming an electric energy cost

of 80 per kWh, for real discount rates less than 10% the real, present value of the

saved energy is on the order of $75, over the projected 15 year life of the

refrigerator, greater than the incremental cost, of the variable drive.

5. Energy improvements from improved compressor performance, especially

small compressors, are possible with improved motors and variable speed

technology. Dual loop and super-insulation systems should be economically

viable with this currently available (but as of yet) unmanufactured technology.

® Motors for small compressors can be improved to efficiency levels within a few

percent of large compresors for $15, while the energy gain they would produce

would be worth $75.

® Variable speed technology could add $35 (costs) to refrigerators, but save more than

$10 per year in electricity.

® Research and improved manufacturing could improve the benefit/cost calculations

used in this report.

Hi

 EE-RM-93-801 COMMENT OR3

.. The value of these energy savings was calculated. Assuming an electric energy cost 

of 8¢ per kWh, for real discount rates less than 10% the real, present value of the 

saved energy is on the order of $75, over the projected 15 year life of the 

refrigerator, greater than the incremental cost, of the variable drive. 

5. Energy improvements from improved compressor performance, especially 

small compressors, are possible with improved motors and variable speed 

technology. Dual loop and super-insulation systems should be economically 

viable with this currently available (but as of yet) unmanufactured technology. 

.. Motors for small compressors can be improved to efficiency levels within a few 

percent of large compresors for $15, while the energy gain they would produce 

would be worth $75. 

" Variable speed technology could add $35 (costs) to refrigerators, but save more than 

$10 per year in electricity. 

" Research and improved manufacturing could improve the benefit/cost calculations 

used in this report. 

iii 
Table of Contents

1.0 Introduction ................................................................................................. 1-1

1.1 Stratospheric Ozone Depletion and the CFC Phase Out .......................... 1-1

1.2 Global Warming ....................................................................................... 1-2

1.3 DOE Appliance Energy Efficiency Standard Setting ............................... 1-2

1.4 Other Regulatory and Policy Initiatives ................................................... 1-2

2.0 Issues in Compressor and Motor Selection ............................................... 2-1

2.1 Motor Technology Options ...................................................................... 2-3

3.0 Single Speed Induction Motors - Current Practices in

Refrigerator/Freezer Compressors ............................................................ 3-1

4.0 Two Speed Motors ... .................................................................................... 4-1

5.0 Variable Speed Drives ................................................................................. 5-1

5.1 Efficiency ................................................................................................. 5-4

5.2 Variable Speed Motor/Drive Costs .......................................................... 5-5

5.3 Variable Speed Drives - Life, Reliability ................................................. 5-7

5.4 Description of Specific Variable Speed Motor/Drive Types ................... 5-8

5.4.1 Electronically Commutated Permanent Magnet Rotor DC

Motors .............................................................................................. 5-8

5.4.2 Pulse Width Modulation Inverter/3 Phase Induction Motor ........... 5-9

5.4.3 Six Step Inverter - 3 Phase Induction Motor Drives ....................... 5-11

5.4.4 Switched Reluctance Motors ........................................................... 5-13

6.0 Potential Value of Improvements ............................................................... 6-1

7.0 Areas forR& D ........................................................................................... 7-1

8.0 Conclusions ................................................................................................... 8-1

8.1 One Speed Motors (Present Practice) ....................................................... 8-1

8.2 Two Speed Motors ................................................................................... 8-1

8.3 Variable Speed Drives .............................................................................. 8-1

9.0 References ..................................................................................................... 9-1

Appendix : Value of Variable Speed Motors for Reducing Cycling Losses,

and Otherwise Improving R/F Efficiency ................................... A-1

iv

 EE-RM-93-801 COMMENT OR3

Table of Contents 

1.0 Introduction ................................................................................................. 1-1 

1.1 Stratospheric Ozone Depletion and the CFC Phase Out . ...... ........ ........... 1-1 

1.2 Global Warming ....................................................................................... 1-2 

1.3 DOE Appliance Energy Efficiency Standard Setting ............................... 1-2 

1.4 Other Regulatory and Policy Initiatives ................................................... 1-2 

2.0 Issues in Compressor and Motor Selection ............................................... 2-1 

2.1 Motor Technology Options ...................................................................... 2-3 

3.0 Single Speed Induction Motors - Current Practices in 

Refrigerator/Freezer Compressors ............................................................ 3-1 

4.0 Two Speed Motors ............................................................ ........................... 4-1 

5.0 Variable Speed Drives .. ............................................................................... 5-1 

5.1 Efficiency ................................................................................................. 5-4 

5.2 Variable Speed Motor/Drive Costs .......................................................... 5-5 

5.3 Variable Speed Drives - Life, Reliability ................................................. 5-7 

5.4 Description of Specific Variable Speed Motor/Drive Types ................... 5-8 

5.4.1 Electronically Commutated Permanent Magnet Rotor DC 

Motors .............................................................................................. 5-8 

5.4.2 Pulse Width Modulation Inverter/3 Phase Induction Motor ........... 5-9 

5.4.3 Six Step Inverter - 3 Phase Induction Motor Drives ....................... 5-11 

5.4.4 Switched Reluctance Motors .................... ....................................... 5-13 

6.0 Potential Value of Improvements ............................................................... 6-1 

7.0 Areas for R&D ........................................................................................... 7-1 

8.0 Conclusions ................................................................................................... 8-1 

8.1 One Speed Motors (Present Practice) ....................................................... 8-1 

8.2 Two Speed Motors ........ ................ ........................... ..................... ........... 8-1 

8.3 Variable Speed Drives .............................................................................. 8-1 

9.0 References ..................................................................................................... 9-1 

Appendix: Value of Variable Speed Motors for Reducing Cycling Losses, 

and Otherwise Improving RtF Efficiency ................................... A-I 

iv 
Table of Figures

Figure 2-1: Lorenz-Meutzner Refrigerator/Freezer Cycle ............................... 2-1

Figure 3-1: Typical Squirrel Cage Induction Motor Used in Domestic

Refrigerator Compressors (RSIR example) ................................... 3-2

Figure 3-2: OEM Cost of Single Speed Motors for Hermetic Refrigeration

Compressors, Versus Motor Efficiency and Compressor

Capacity ......................................................................................... 3-3

Figure 5-1: "Generic" Variable Speed Drive Block Diagram .......................... 5-2

Figure 5-2: Variable Speed Electronic Drive for a One-Quarter Horsepower

Electronically Commutated DC Motor .......................................... 5-3

Figure 5-3: PWM Operation for Varying Output Voltage to a DC Motor ....... 5-4

Figure 5-4: Comparison of Variable Speed Drive/Motor Efficiencies

(Fractional Horsepower) .................................................................. 5-6

Figure 5-5: Voltage and Current Output of a PWM Inverter (approximately

PWM frequency: 1.1 kHz) .............................................................. 5-10

Figure 5-6: Six Step Inverter Voltage and Current Wave Forms ....................... 5-12

Figure 5-7: Simplified Schematic of Switched Reluctance Motor

Configuration ................................................................................... 5-14

Table of Tables

Table 2-1: Alternative Refrigerants .................................................................. 2-3

Table 3-1: Refrigerator Compressor Motor Efficiency .................................... 3-4

Table 4-1: Potential Two Speed Motor Manufacturers .................................... 4-2

Table 5-1: Manufacturers of ECPM Controllers .............................................. 5-9

Table 5-2: Manufacturers of PWM Inverters .................................................... 5-11

Table 5-3: Manufacturers of Six Step Inverters ................................................ 5-13

Table 6-1: Summary of Calculated Energy Savings with Variable Speed

Compressor ...................................................................................... 6-2

Table 6-2: Present Value of Energy Savings of Variable to Speed

Compressor ...................................................................................... 6-2

Table 6-3: Present Value of Energy Savings of Variable to Speed

Compressor (Current Variable Speed Motor/Drive Technology .... 6-3

Table 6-4: Present Value of Energy Savings of Variable to Speed

Compressor (Efficient Low Speed -- Future Technology) .............. 6-3

V

 EE-RM-93-801 COMMENT OR3

Figure 2-1: 

Table of Figures 

Lorenz-Meutzner Refrigerator/Freezer Cycle 2-1 

Figure 3-1: Typical Squirrel Cage Induction Motor Used in Domestic 

Refrigerator Compressors (RSIR example) ................................... 3-2 

Figure 3-2: OEM Cost of Single Speed Motors for Hermetic Refrigeration 

Compressors, Versus Motor Efficiency and Compressor 

Capacity ....................................................................................... ,. 3-3 

Figure 5-1: "Generic" Variable Speed Drive Block Diagram .......................... 5-2 

Figure 5-2: Variable Speed Electronic Drive for a One-Quarter Horsepower 

Electronically Commutated DC Motor .......................................... 5-3 

Figure 5-3: PWM Operation for Varying Output Voltage to a DC Motor ....... 5-4 

Figure 5-4: Comparison of Variable Speed Drive/Motor Efficiencies 

(Fractional Horsepower) ................................ ............ .............. .... .... 5-6 

Figure 5-5: Voltage and Current Output of a PWM Inverter (approximately 

PWM frequency: 1.1 kHz) .............................................................. 5-10 

Figure 5-6: Six Step Inverter Voltage and Current Wave Forms ....................... 5-12 

Figure 5-7: Simplified Schematic of Switched Reluctance Motor 

Configuration ........................... ....................................... .......... ....... 5-14 

Table of Tables 

Table 2-1: Alternative Refrigerants .................................................................. 2-3 

Table 3-1: Refrigerator Compressor Motor Efficiency ................................. '" 3-4 

Table 4-1: Potential Two Speed Motor Manufacturers .................................... 4-2 

Table 5-1: Manufacturers of ECPM Controllers ..... .......................... ........ ....... 5-9 

Table 5-2: Manufacturers of PWM Inverters ........................ ...... ........ .... ...... .... 5-11 

Table 5-3: Manufacturers of Six Step Inverters ............. .............. ...... .......... ..... 5-13 

Table 6-1: Summary of Calculated Energy Savings with Variable Speed 

Compressor ...................................................................................... 6-2 

Table 6-2: Present Value of Energy Savings of Variable to Speed 

Compressor ...................................................................................... 6-2 

Table 6-3: Present Value of Energy Savings of Variable to Speed 

Compressor (Current Variable Speed Motor/Drive Technology .... 6-3 

Table 6-4: Present Value of Energy Savings of Variable to Speed 

Compressor (Efficient Low Speed -- Future Technology) .............. 6-3 

v 
Acknowledgements

During the course of this work , a number of compressor, motor, and variable speed

drive manufacturers were contacted, whose assistance and cooperation we acknowledge

and appreciate:

® Compressors: Tecumseh Products Co., Copeland, and Americold

® Motors: General Electric , A. 0. Smith, Emerson, and Baldor

® Variable speed drives: Toshiba, Emerson, Mitsubishi, Hitachi, Westinghouse,

Magnetek, Lenze, Vee Arc, Ranco, Inland, PMI, Minarik, EG&G, Fasco, Boston

Gear, and Graham

vi

 EE-RM-93-801 COMMENT OR3

Acknowledgements 

During the course of this work, a number of compressor, motor, and variable speed 

drive manufacturers were contacted, whose assistance and cooperation we acknowledge 

and appreciate: 

" Compressors: Tecumseh Products Co., Copeland, and Americold 

" Motors: General Electric, A. O. Smith, Emerson, and Baldor 

" Variable speed drives: Toshiba, Emerson, Mitsubishi, Hitachi, Westinghouse, 

Magnetek, Lenze, Vee Arc, Ranco, Inland, PMI, Minarik, EG&G, Pasco, Boston 

Gear, and Graham 

vi 
1. Introduction

The design of the domestic refrigerator -freezer will be undergoing a significant set of

changes over the next several years, driven by interrelated developments in a number of

national energy and environmental policy areas - the CFC phase out, growing concerns

about global warming, DOE appliance energy efficiency standard setting, and others.

These developments have created the need for a comprehensive examination of the

design options for domestic refrigerator/freezers. These interrelated options include

compressors, motors, refrigerants and lubricants, the refrigeration cycle, cabinet

insulation, and other aspects of cabinet thermal design.

This report covers the technology status of the motors that are used, or potentially could

be used, in the small hermetic compressors used in the refrigeration system of domestic

refrigerators, addressing the potential for and cost of improvements in the efficiency of

these motors. The status of applicable variable speed motor technology and potential

refrigerator energy savings is examined.

The environmental and energy policy background is discussed briefly below.

1.1 Stratospheric Ozone Depletion and the CFC Phase Out

Evidence accumulated over the past 15 years indicates that fully halogenated

chlorofluorocarbons (CFCs) have caused measurable deterioration of the atmosphere's

stratospheric ozone layer, which plays a significant role in attenuating solar ultraviolet

radiation. Increased levels of ultraviolet radiation would have a large number of

undesirable effects, including increased levels of skin cancers. Over the past few years,

this subject area has received renewed attention as the result of observations in the

mid-1980s of "gaps" in the ozone layer in the vicinity of the poles. As a result of this

attention, the Montreal CFC protocols were concluded in Fall, 1987. This international

agreement was signed and ratified by the major free world industrial nations requiring a

freeze, then phased production curtailments, of CFCs. By 1998, production of CFC-11,

CFC-12, CFC-113, CFC-114, and CFC-115, as well as certain "halons" were to be

reduced to 50% of 1986 levels. An additional provision provided for periodic review of

scientific evidence and adjustment of allowable levels of production accordingly. The

reassessment completed in 1990 resulted in a nearly total phase out of CFCs by the year

2000. The Clean Air Act of 1990 has codified this accelerated CFC phase out schedule

into U.S. environmental law. In April of 1991, NASA reported the results of

satellite-based measurements of stratospheric ozone levels indicating that ozone

depletion of 5% over the mid latitudes has already occurred. The likely result of this

development will be further acceleration of the timetable for CFC phase out. This has a

direct impact on R/F insulation and compressors which have been designed around the

characteristics of CFC- 11 and CFC- 12, respectively.

 EE-RM-93-801 COMMENT OR3

1.0 Introduction 

The design of the domestic refrigerator-freezer will be undergoing a significant set of 

changes over the next several years, driven by interrelated developments in a number of 

national energy and environmental policy areas - the CFC phase out, growing concerns 

about global warming, DOE appliance energy efficiency standard setting, and others. 

These developments have created the need for a comprehensive examination of the 

design options for domestic refrigerator/freezers. These interrelated options include 

compressors, motors, refrigerants and lubricants, the refrigeration cycle, cabinet 

insulation, and other aspects of cabinet thermal design. 

This report covers the technology status of the motors that are used, or potentially could 

be used, in the small hermetic compressors used in the refrigeration system of domestic 

refrigerators, addressing the potential for and cost of improvements in the efficiency of 

these motors. The status of applicable variable speed motor technology and potential 

refrigerator energy savings is examined. 

The environmental and energy policy background is discussed briefly below. 

1.1 Stratospheric Ozone Depletion and the CFC Phase Out 

Evidence accumulated over the past 15 years indicates that fully halogenated 

chlorofluorocarbons (CFCs) have caused measurable deterioration of the atmosphere's 

stratospheric ozone layer, which plays a significant role in attenuating solar ultraviolet 

radiation. Increased levels of ultraviolet radiation would have a large number of 

undesirable effects, including increased levels of skin cancers. Over the past few years, 

this subject area has received renewed attention as the result of observations in the 

mid-1980s of "gaps" in the ozone layer in the vicinity of the poles. As a result of this 

attention, the Montreal CFC protocols were concluded in Fall, 1987. This international 

agreement was signed and ratified by the major free world industrial nations requiring a 

freeze, then phased production curtailments, of CFCs. By 1998, production of CFC-ll, 

CFC-12, CFC-I13, CFC-1l4, and CFC-1l5, as well as certain "halons" were to be 

reduced to 50% of 1986 levels. An additional provision provided for periodic review of 

scientific evidence and adjustment of allowable levels of production accordingly. The 

reassessment completed in 1990 resulted in a nearly total phase out of CFCs by the year 

2000. The Clean Air Act of 1990 has codified this accelerated CFC phase out schedule 

into U.S. environmental law. In April of 1991, NASA reported the results of 

satellite-based measurements of stratospheric ozone levels indicating that ozone 

depletion of 5% over the mid latitudes has already occurred. The likely result of this 

development will be further acceleration of the timetable for CFC phase out. This has a 

direct impact on RlF insulation and compressors which have been designed around the 

characteristics of CFC-ll and CFC-12, respectively. 

1-1 
1.2 Global Warming

Concurrent with the accumulation of scientific evidence of stratospheric ozone

depletion, increasing concerns have been developing about global warming caused by

increasing atmospheric concentrations of carbon dioxide and the trace greenhouse gases.

The most significant of the trace greenhouse gases are the CFCs and methane.

The fact that the CFCs are powerful greenhouse gases has reinforced the pressures to

accelerate the CFC phase out time table. Measures to limit or reduce CO2 emissions

have been proposed. Because CO2 is one of the basic combustion products of all of the

fossil fuels used to produce energy for heating, transportation, and electric power

generation, measures to reduce CO2 emissions require the burning of less fossil fuels.

One regulatory measure to bring this about is increasing energy efficiency standards.

1.3 DOE Appliance Energy Efficiency Standard Setting

In February, 1989, DOE issued a final rulemaking under the Energy Policy and

Conservation Act, as amended, establishing minimum energy efficiency standards for

most categories of consumer appliances (Federal Register, 1989a). Depending on the

category, the standards take effect between 1990 and 1993. The standards for domestic

refrigerators and freezers went into effect on January 1, 1990, generally requiring

efficiency levels in line with the most efficient products available in the late 1980s,

whose efficiency was nearly double the levels prevailing only 10 to 15 years earlier.

Global warming (and national energy security issues) have resulted in the recent

adoption of significantly reduced levels of allowable electric energy consumption for all

categories of domestic refrigerators and freezers, effective on January 1, 1993 (the 1993

standards reduce allowable energy consumption by approximately 30% from the levels

under the current Federal regulations that took effect on January 1, 1990) (Federal

Register, 1989b).

1.4 Other Regulatory and Policy Initiatives

States are instituting reforms in planning and rate making that put demand reductions on

an equal playing field with building additional supply capacity. Integrated resource

planning, adopted by many states, requires utilities to evaluate every "resource"

(demand reduction or supply) in terms of total societal cost.

California, Oregon, Washington, most of the New England states, Wisconsin, and New

York have adopted ratemaking processes in which utility rates or return on investment is

adjusted so that utilities do not lose profits for forgone Kwh sales, but can profit from

demand reductions. In California and several other states, the non-pollution aspect of

demand reductions has led regulators to allow shared savings of customer bill reductions

to further increase utility profits. As a consequence of this change in utility regulation,

the demand for efficient refrigerators is rising.

 EE-RM-93-801 COMMENT OR3

1.2 Global Warming 

Concurrent with the accumulation of scientific evidence of stratospheric ozone 

depletion, increasing concerns have been developing about global warming caused by 

increasing atmospheric concentrations of carbon dioxide and the trace greenhouse gases. 

The most significant of the trace greenhouse gases are the CFCs and methane. 

The fact that the CFCs are powerful greenhouse gases has reinforced the pressures to 

accelerate the CFC phase out time table. Measures to limit or reduce CO2 emissions 

have been proposed. Because CO2 is one of the basic combustion products of all of the 

fossil fuels used to produce energy for heating, transportation, and electric power 

generation, measures to reduce CO2 emissions require the burning of less fossil fuels. 

One regulatory measure to bring this about is increasing energy efficiency standards. 

1.3 DOE Appliance Energy Efficiency Standard Setting 

In February, 1989, DOE issued a final rulemaking under the Energy Policy and 

Conservation Act, as amended, establishing minimum energy efficiency standards for 

most categories of consumer appliances (Federal Register, 1989a). Depending on the 

category, the standards take effect between 1990 and 1993. The standards for domestic 

refrigerators and freezers went into effect on January 1, 1990, generally requiring 

efficiency levels in line with the most efficient products available in the late 1980s, 

whose efficiency was nearly double the levels prevailing only 10 to 15 years earlier. 

Global warming (and national energy security issues) have resulted in the recent 

adoption of significantly reduced levels of allowable electric energy consumption for all 

categories of domestic refrigerators and freezers, effective on January 1, 1993 (the 1993 

standards reduce allowable energy consumption by approximately 30% from the levels 

under the current Federal regulations that took effect on January 1, 1990) (Federal 

Register, 1989b). 

1.4 Other Regulatory and Policy Initiatives 

States are instituting reforms in planning and rate making that put demand reductions on 

an equal playing field with building additional supply capacity. Integrated resource 

planning, adopted by many states, requires utilities to evaluate every "resource" 

(demand reduction or supply) in terms of total societal cost. 

California, Oregon, Washington, most of the New England states, Wisconsin, and New 

York have adopted ratemaking processes in which utility rates or return on investment is 

adjusted so that utilities do not lose profits for forgone Kwh sales, but can profit from 

demand reductions. In California and several other states, the non-pollution aspect of 

demand reductions has led regulators to allow shared savings of customer bill reductions 

to further increase utility profits. As a consequence of this change in utility regulation, 

the demand for efficient refrigerators is rising. 

1-2 
The Golden Carrot/early retirement program is one concrete manifestation of this trend.

Under the Golden Carrot, utilities are banding together to pool rebates to produce an

incentive for production of a R/F that is 30% better than DOE's 1993 standard in the 18

to 22 cubic foot range. With the impetus described earlier from CFCs, global warming,

and other state regulatory reforms, the Golden Carnot will provide a strong incentive for

vast improvements in energy efficiency.

 EE-RM-93-801 COMMENT OR3

The Golden Carrot/early retirement program is one concrete manifestation of this trend. 

Under the Golden Carrot, utilities are banding together to pool rebates to produce an 

incentive for production of a RlF that is 30% better than DOE's 1993 standard in the 18 

to 22 cubic foot range. With the impetus described earlier from CFCs, global warming, 

and other state regulatory reforms, the Golden Carnot will provide a strong incentive for 

vast improvements in energy efficiency. 

1-3 
2.0 Issues in Compressor and Motor Selection

To meet the dual challenge of designing for new blowing agents and refrigerants, while

meeting much higher efficiency standards, significant changes in the design of both the

cabinet and the refrigeration cycle are under consideration. There are many design

options, and it is important to evaluate the potential of each option to contribute

significant energy savings, without using CFCs and without increasing the cost of the

refrigerator beyond the value added by the change (with respect to energy costs or

utility) or decreasing the utility of the refrigerator to the consumer. Design options that

are being pursued in current R&D programs include:

® Low thermal loss cabinets ("super-insulated boxes") reduce energy consumption by

reducing the amount of cooling that is needed. To utilize heat exchangers effectively

and minimize cycling losses, the compressor capacity should be reduced in

proportion to the thermal load. However, sufficient compressor capacity may still be

required to provide a sufficiently fast pulldown for food preservation.

® Dual refrigeration loops (separate refrigeration systems for the refrigerator and

freezer compartment) take advantage of the increased COP at the higher evaporator

temperature that can provide the required cooling of the fresh food compartment.

® The Lorenz cycle, shown schematically in Figure 2-1 uses a non-azeotropic

refrigerant mixture with two evaporators and an interchanger to operate the fresh

food compartment and the freezer at separate evaporator temperatures for higher

efficiency. (Lorenz, 1975)

Figure 2-1: Lorenz-Meutzner Refrigerator/Freezer Cycle

® Variable speed compressor operation can save energy by allowing continuous

operation at low capacity, eliminating cycling losses and allowing more efficient

utilization of heat exchangers. Overspeed operation can provide additional capacity

for pulldown. The latter characteristic might be particularly advantageous with high

performance cabinets.

 EE-RM-93-801 COMMENT OR3

2.0 Issues in Compressor and Motor Selection 

To meet the dual challenge of designing for new blowing agents and refrigerants, while 

meeting much higher efficiency standards, significant changes in the design of both the 

cabinet and the refrigeration cycle are under consideration. There are many design 

options, and it is important to evaluate the potential of each option to contribute 

significant energy savings, without using CFCs and without increasing the cost of the 

refrigerator beyond the value added by the change (with respect to energy costs or 

utility) or decreasing the utility of the refrigerator to the consumer. Design options that 

are being pursued in current R&D programs include: 

.. Low thermal loss cabinets ("super-insulated boxes") reduce energy consumption by 

reducing the amount of cooling that is needed. To utilize heat exchangers effectively 

and minimize cycling losses, the compressor capacity should be reduced in 

proportion to the thermal load. However, sufficient compressor capacity may still be 

required to provide a sufficiently fast pulldown for food preservation. 

co Dual refrigeration loops (separate refrigeration systems for the refrigerator and 

freezer compartment) take advantage of the increased COP at the higher evaporator 

temperature that can provide the required cooling of the fresh food compartment. 

.. The Lorenz cycle, shown schematically in Figure 2-1 uses a non-azeotropic 

refrigerant mixture with two evaporators and an interchanger to operate the fresh 

food compartment and the freezer at separate evaporator temperatures for higher 

efficiency. (Lorenz, 1975) 

Figure 2-1: lorenz-Meutzner Refrigerator/Freezer Cycle 

2 Condenser 

HXl 

't----"'---;Fresh Food Evaporatort----, Temp 

HX2 

5 Freezer Evaporator Entropy 

.. Variable speed compressor operation can save energy by allowing continuous 

operation at low capacity, eliminating cycling losses and allowing more efficient 

utilization of heat exchangers. Overspeed operation can provide additional capacity 

for pulldown. The latter characteristic might be particularly advantageous with high 

performance cabinets. 

2-1 
One consequence of these design changes is a decrease in the compressor capacity

required to best match a given size refrigerator. Improved insulation and cabinet design

will reduce cooling loads, reducing required compressor capacity. Two compressor/two

evaporator systems meet the freezer and fresh food compartment heat loads with

separate refrigeration systems, obtaining, in theory, significant improvements in the

efficiency with which the load in the fresh food compartment is met (higher evaporating

temperatures, no defrost cycle). Even less compressor capacity is needed, especially in

the fresh food compartment where nominal compressor capacities of only 200 Btu/hr

may be needed. While the Lorenz cycle does not inherently result in a drastic

compressor capacity reduction, other compressor problems, such as high starting torque

requirements, have been observed. Variable speed compressors will tend to be smaller

displacement, with pulldown requirements met by overspeed operation.

Present commercially available low capacity compressors (<600 Btu/hr nominal

capacity) have very poor efficiencies, low enough in some cases to completely negate

the gains obtained from the design options described above. To realize the efficiency

benefits of reduced loads and dual evaporator systems will require improved efficiency,

lower capacity compressors.

Regardless of the R/F cabinet and refrigeration cycle design approach taken, increases in

the efficiency level that is available in refrigerant compressors will result in proportional

increases in the efficiency of the refrigerator using the compressor.

A major issue for compressor design is the change in refrigerant from CFC-12 to a low

ozone depletion, low global warming potential refrigerant. While CFC- 12 has been

shown to be a significant part of the cause of both stratospheric ozone depletion and

global warming, it is an excellent working fluid for domestic refrigerator/freezers. It has

a favorable pressure-temperature relationship, good thermodynamic efficiency, stability,

total miscibility with low cost mineral oil, and moderate temperature rise with

compression and is non-flammable, non-toxic, and low cost. Alternate refrigerants that

do not contain chlorine or have currently acceptable ozone depletion potentials do not

possess identical attributes of CFC- 12. Thus, compressor modifications or new designs

will be required to adapt to the characteristics of a selected alternative refrigerant. Table

2-1 lists some of the potential alternative refrigerants and their status, including

potential substitutes for CFC-11, CFC-114, and CFC-502, as well as for CFC-12.

The major working fluid options include the near drop in replacements for CFC-12 (i.e.,

those refrigerants having vapor pressure-temperature curves close to that of CFC- 12),

lower vapor pressure refrigerants such as HCFC-124, and non-azeotropic refrigeration

mixtures (NARMs). Lower vapor pressure refrigerants might be utilized in low

capacity systems (design options described above), if shown to result in higher

efficiency of low capacity compressors, by virtue of the larger displacement that would

be needed. The Lorenz cycle would utilize a NARM.

 EE-RM-93-801 COMMENT OR3

One consequence of these design changes is a decrease in the compressor capacity 

required to best match a given size refrigerator. Improved insulation and cabinet design 

will reduce cooling loads, reducing required compressor capacity. Two compressor/two 

evaporator systems meet the freezer and fresh food compartment heat loads with 

separate refrigeration systems, obtaining, in theory, significant improvements in the 

efficiency with which the load in the fresh food compartment is met (higher evaporating 

temperatures, no defrost cycle). Even less compressor capacity is needed, especially in 

the fresh food compartment where nominal compressor capacities of only 200 Btu/hr 

may be needed. While the Lorenz cycle does not inherently result in a drastic 

compressor capacity reduction, other compressor problems, such as high starting torque 

requirements, have been observed. Variable speed compressors will tend to be smaller 

displacement, with pulldown requirements met by overspeed operation. 

Present commercially available low capacity compressors «600 BtU/hr nominal 

capacity) have very poor efficiencies, low enough in some cases to completely negate 

the gains obtained from the design options described above. To realize the efficiency 

benefits of reduced loads and dual evaporator systems will require improved efficiency, 

lower capacity compressors. 

Regardless of the RtF cabinet and refrigeration cycle design approach taken, increases in 

the efficiency level that is available in refrigerant compressors will result in proportional 

increases in the efficiency of the refrigerator using the compressor. 

A major issue for compressor design is the change in refrigerant from CFC-12 to a low 

ozone depletion, low global warming potential refrigerant. While CFC-12 has been 

shown to be a significant part of the cause of both stratospheric ozone depletion and 

global warming, it is an excellent working fluid for domestic refrigerator/freezers. It has 

a favorable pressure-temperature relationship, good thermodynamic efficiency, stability, 

total miscibility with low cost mineral oil, and moderate temperature rise with 

compression and is non-flammable, non-toxic, and low cost. Alternate refrigerants that 

do not contain chlorine or have currently acceptable ozone depletion potentials do not 

possess identical attributes of CFC-12. Thus, compressor modifications or new designs 

will be required to adapt to the characteristics of a selected alternative refrigerant. Table 

2-1 lists some of the potential alternative refrigerants and their status, including 

potential substitutes for CFC-ll, CFC-114, and CFC-502, as well as for CFC-12. 

The major working fluid options include the near drop in replacements for CFC-12 (i.e., 

those refrigerants having vapor pressure-temperature curves close to that of CFC-12), 

lower vapor pressure refrigerants such as HCFC-124, and non-azeotropic refrigeration 

mixtures (NARMs). Lower vapor pressure refrigerants might be utilized in low 

capacity systems (design options described above), if shown to result in higher 

efficiency of low capacity compressors, by virtue of the larger displacement that would 

be needed. The Lorenz cycle would utilize a NARM. 

2-2 
Table 2-1 : Alternative Refrigerants

Substitute

Refrigerant

Displaced

Refrigerant _

Probable

L Availability

Description, Status, Comment

0

HCFC-22 CFC-12

CFC-502

Current Commercially available, widely used refrigerant.

Contains chlorine, will be phased out under I

Montreal Protocol Copenhagen Amendments

HFC-134a CFC-12 Current Commercially available, rapidly expanding

production

Ternary CFC-12 (w/HCFC-124)

1993

Available in limited amounts

HFC-152a CFC-12 Current Commercially produced and sold in fairly small

quantities, used primarily as a component in

CFC-500 (26%) and as a component in aerosol

propellant blends

HFC-123 CFC-11 1990-1991 Toxicity tests have shown sufficient toxicity to set

AEL at 10 ppm; commercially available

HFC-124 CFC-1 14 1993-95 Co-product of HCFC-1 23 production. Long term

toxicity testing started

HFC-125 CFC-502 Available in

limited amounts

Near-term availability in blends to replace CFC-502

HCFC-141 b CFC-11 Current Commercial production began in July 1988.

Toxicity testing underway. Possible use as a foam

blowing agent

HCFC-142b CFC-12, 114 Current Used in R22/R142b blends

NH3 CFC-11

CFC-12

CFC-502

Current Commercially available. Widely used in industrial

refrigeration sector. Toxic with low flammability

Source: Arthur D. Little, 1993

The major issues that need to be considered in adapting the compressor design to an

alternate refrigerant include the displacement required to obtain the intended capacity,

lubricant selection, and material compatibility, especially the motor winding insulation.

In summary, higher efficiency compressors are needed, especially in smaller capacities.

Motor technology is an important consideration, because increasing the efficiency of the

compressor motor is a straightforward way to improve compressor efficiency. For

variable speed compressors, the variable speed motor and electronic drive represent the

major technology component and the major cost driver.

2.1 Motor Technology Options

Motor efficiency impacts the overall energy consumption in a refrigerator/freezer in two

ways: 1) the compressor energy use is directly related to the motor efficiency for any

given compressor pump work; and 2) motor inefficiencies may result in additional

 EE-RM-93-801 COMMENT OR3

Table 2·1: Alternative Refrigerants 

ubstitute ulsplaced Probable Description, Status, Comment 

efrigerant Refrigerant Availability 

HCFC-22 CFC-12 Current Commercially available, widely used refrigerant. 

CFC-502 Contains chlorine, will be phased out under 

Montreal Protocol Copenhagen Amendments 

HFC-134a CFC-12 Current Commercially available, rapidly expanding 

production 

Ternary CFC-12 (w/HCFC-124) Available in limited amounts 

1993 

HFC-152a CFC-12 Current Commercially produced and sold in fairly small 

quantities, used primarily as a component in 

CFC-500 (26%) and as a component in aerosol 

propellant blends 

HFC-123 CFC-11 1990-1991 Toxicity tests have shown sufficient toxicity to set 

AEL at 10 ppm; commercially available 

HFC-124 CFC-114 1993-95 Co-product of HCFC-123 production. Long term 

toxicity testing started 

HFC-125 CFC-502 Available in Near-term availability in blends to replace CFC-502 

limited amounts 

HCFC-141b CFC-11 Current Commercial production began in July 1988. 

Toxicity testing underway. Possible use as a foam 

blowing agent 

HCFC-142b CFC-12,114 Current Used in R221R142b blends 

NH3 CFC-11 Current Commercially available. Widely used in industrial 

CFC-12 refrigeration sector. Toxic with low flammability 

CFC-502 

Source: Arthur D. Little, 1993 

The major issues that need to be considered in adapting the compressor design to an 

alternate refrigerant include the displacement required to obtain the intended capacity, 

lubricant selection, and material compatibility, especially the motor winding insulation. 

In summary, higher etIiciency compressors are needed, especially in smaller capacities. 

Motor technology is an important consideration, because increasing the efficiency of the 

compressor motor is a straightforward way to improve compressor efficiency. For 

variable speed compressors, the variable speed motor and electronic drive represent the 

major technology component and the major cost driver. 

2.1 Motor Technology Options 

Motor efficiency impacts the overall energy consumption in a refrigerator/freezer in two 

ways: 1) the compressor energy use is directly related to the motor efficiency for any 

given compressor pump work; and 2) motor inefficiencies may result in additional 

2-3 
compressor pump work requirements due to heating of the working fluid within the

compressor shell. Because of the combined effect of these two factors, a'10% increase

in motor efficiency could result in an overall compressor energy reduction of 13 to 16%.

The use of variable (either two-speed or continuously variable) speed compressor

operation, to reduce cyclic losses and improve heat exchanger utilization, has proven to

result in significant improvements (of approximately 25% to 30%) in seasonal

efficiency in air conditioning (Cann, 1989 ; Sulfstede, 1989) and commercial

refrigeration applications. These improvements accrue from reduced heat exchanger

loadings, which will result in thermodynamic performance advantages. In addition,

cycling losses are reduced by longer, or continuous , compressor operation. Potential

disadvantages are additional losses associated with electronics and increased fan

energies

Improvements might be achieved in domestic refrigerators, as well. Applications to

these smaller capacity ranges have been limited due to the costs of the electronics and

the current lack of a market demand. A major requirement for energy savings is the

reduction of fan and electronics energies during the lengthened cycle time. Again,

advanced motor technology will be required to realize the potential efficiency

improvements.

In view of the importance of motor technology to the potential efficiency improvements

of various design alternatives, this review of the motor technology applicable to small

hermetic refrigeration compressors was undertaken as part of a larger study to evaluate

the options for maximizing the efficiency of domestic refrigerators. The motor

characteristics documented in the report are being used in the overall study as part of the

input database for modeling and evaluating design options.

This report covers the technology status of electric motors to drive the small hermetic

compressors used in the refrigeration system of domestic refrigerators. Two general

areas are addressed:

® The potential for and cost of improvements in the efficiency of the motors currently

used in small hermetic refrigeration compressors , with particular emphasis on the

motors used in smaller (<800 Btu/hr nominal capacity) compressors.

® The status of variable speed (both two discrete speeds and continuously variable

speed) motors in terms of availability, efficiency , and cost.

This report is intended to serve three functions: 1) description of the state-of-the-art of

current motors and the potential for future improvements ; 2) summary of performance

and cost data as input to evaluations of refrigerator/freezer system design options; and

3) present preliminary results indicating the level of RIP energy consumption reductions

that can be obtained through the use of variable speed compressor operation.

 EE-RM-93-801 COMMENT OR3

compressor pump work requirements due to heating of the working fluid within the 

compressor shell. Because of the combined effect of these two factors, a to% increase 

in motor efficiency could result in an overall compressor energy reduction of 13 to 16%. 

The use of variable (either two-speed or continuously variable) speed compressor 

operation, to reduce cyclic losses and improve heat exchanger utilization, has proven to 

result in significant improvements (of approximately 25% to 30%) in seasonal 

efficiency in air conditioning (Cann, 1989; Sulfstede, 1989) and commercial 

refrigeration applications. These improvements accrue from reduced heat exchanger 

loadings, which will result in thennodynamic performance advantages. In addition, 

cycling losses are reduced by longer, or continuous, compressor operation. Potential 

disadvantages are additional losses associated with electronics and increased fan 

energies 

Improvements might be achieved in domestic refrigerators, as well. Applications to 

these smaller capacity ranges have been limited due to the costs of the electronics and 

the current lack of a market demand. A major requirement for energy savings is the 

reduction of fan and electronics energies during the lengthened cycle time. Again, 

advanced motor technology will be required to realize the potential efficiency 

improvements. 

In view of the importance of motor technology to the potential efficiency improvements 

of various design alternatives, this review of the motor technology applicable to small 

hermetic refrigeration compressors was undertaken as part of a larger study to evaluate 

the options for maximizing the efficiency of domestic refrigerators. The motor 

characteristics documented in the report are being used in the overall study as part of the 

input database for modeling and evaluating design options. 

This report covers the technology status of electric motors to drive the small hermetic 

compressors used in the refrigeration system of domestic refrigerators. Two general 

areas are addressed: 

.. The potential for and cost of improvements in the efficiency of the motors currently 

used in small hennetic refrigeration compressors, with particular emphasis on the 

motors used in smaller «800 BtU/hr nominal capacity) compressors. 

.. The status of variable speed (both two discrete speeds and continuously variable 

speed) motors in terms of availability, efficiency, and cost. 

This report is intended to serve three functions: 1) description of the state-of-the-art of 

current motors and the potential for future improvements; 2) summary of performance 

and cost data as input to evaluations of refrigerator/freezer system design options; and 

3) present preliminary results indicating the level of RfF energy consumption reductions 

that can be obtained through the use of variable speed compressor operation. 

2-4 
3. Single Speed Induction Motors - Current Practice in Refrigerator/Freezer

Compressors

The compressors used in all domestically produced and sold domestic refrigerators and

freezers in the U.S . are powered by 2 pole AC squirrel cage induction motors that

operate on normal household line power, i.e. 115 VAC, 60 HZ, 1 phase. The motors run

at a single speed, near 3500 RPM. In addition to running the compressor at the normal

range of loads, the motor must provide adequate starting torque, because small, single

cylinder compressors are difficult to start.

As shown in Figure 3-1, the basic arrangement of this type of motor consists of a rotor

and stator, each built up of a stack of electromagnetic grade steel laminations , as shown

in the cut-away rotor in Figure 3-1. The "squirrel cage" rotor has a series of lengthwise

aluminum bars cast into the rotor laminations. These bars are connected by rings at

each end of the stack. The stator laminations have a series of slots for the windings

which are aluminum or copper wire. Two sets of windings are provided , one being 90°

out of phase with the other . The main, or run, winding operates directly from line

current, and is always energized when the motor is running. The major design

categories of this type of motor involve the manner in which the secondary winding is

utilized for starting the motor and then running at normal speed. The basic categories of

induction motors are:

• RSIR or Resistance Start/Induction Run;

• CSIR or Capacitor Start/Induction Run; and

® PSC or Permanent Split Capacitor.

RSIR and CSIR motor use the secondary winding for starting only, the capacitor start

version providing higher starting torque. As shown in Figure 3-1 (a photograph of an

RSIR rotor and stator), the secondary winding uses much smaller diameter wire, which

can be energized for only a limited period of time without overheating. The RSIR

motor is very low cost, but is inherently limited to 8 - 10 percent less efficiency than

PSC motors. In PSC motors, the secondary winding also operates when the motor is

running. A capacitor in series with this winding shifts the phase of the input voltage

approximately 90°, so that both windings together create a rotating magnetic field. The

net effect is improved utilization of both the windings and the iron in the motor,

increasing the efficiency, but at the added cost associated with the capacitor.

Motor efficiencies may be improved by the following:

• Using additional material (increasing stack height and using larger diameter wire);

• Using low loss steel in the laminations; and

• Using thinner laminations

Figure 3-2 plots the estimated cost per motor (basis: the OEM price paid to the motor

supplier by the compressor manufacturer for production quantities of the motors) of

single speed induction motors vs. efficiency for motors sized for compressors having

nominal capacities between 200 and 800 Btu/hr. Note that for the smaller motors, the

maximum physically attainable efficiency is lower than for the larger motors, and as a

 EE-RM-93-801 COMMENT OR3

3.0 Single Speed Induction Motors - Current Practice in Refrigerator/Freezer 

Compressors 

The compressors used in all domestically produced and sold domestic refrigerators and 

freezers in the U.S. are powered by 2 pole AC squirrel cage induction motors that 

operate on normal household line power, i.e. 115 V AC, 60 HZ, 1 phase. The motors run 

at a single speed, near 3500 RPM. In addition to running the compressor at the normal 

range of loads, the motor must provide adequate starting torque, because small, single 

cylinder compressors are difficult to start. 

As shown in Figure 3-1, the basic arrangement of this type of motor consists of a rotor 

and stator, each built up of a stack of electromagnetic grade steel laminations, as shown 

in the cut -awa y rotor in Figure 3-1. The 11 squirrel cage 11 rotor has a series of lengthwise 

aluminum bars cast into the rotor laminations. These bars are connected by rings at 

each end of the stack. The stator laminations have a series of slots for the windings 

which are aluminum or copper wire. Two sets of windings are provided, one being 90° 

out of phase with the other. The main, or run, winding operates directly from line 

current, and is always energized when the motor is running. The major design 

categories of this type of motor involve the manner in which the secondary winding is 

utilized for starting the motor and then running at normal speed. The basic categories of 

induction motors are: 

.. RSIR or Resistance StartlInduction Run; 

" CSIR or Capacitor Start/Induction Run; and 

• PSC or Permanent Split Capacitor. 

RSIR and CSIR motor use the secondary winding for starting only, the capacitor start 

version providing higher starting torque. As shown in Figure 3-1 (a photograph of an 

RSIR rotor and stator), the secondary winding uses much smaller diameter wire, which 

can be energized for only a limited period of time without overheating. The RSIR 

motor is very low cost, but is inherently limited to 8 - 10 percent less efficiency than 

PSC motors. In PSC motors, the secondary winding also operates when the motor is 

running. A capacitor in series with this winding shifts the phase of the input voltage 

approximately 90°, so that both windings together create a rotating magnetic field. The 

net effect is improved utilization of both the windings and the iron in the motor, 

increasing the efficiency, but at the added cost associated with the capacitor. 

Motor efficiencies may be improved by the following: 

.. Using additional material (increasing stack height and using larger diameter wire); 

.. Using low loss steel in the laminations; and 

" Using thinner laminations 

Figure 3-2 plots the estimated cost per motor (basis: the OEM price paid to the motor 

supplier by the compressor manufacturer for production quantities of the motors) of 

single speed induction motors vs. etliciency for motors sized for compressors having 

nominal capacities between 200 and 800 Btu/hr. Note that for the smaller motors, the 

maximum physically attainable efficiency is lower than for the larger motors, and as a 

3-1 
Figure 3-1: Typical Squirrel Cage Induction Motor Used in Domestic Refrigerator Compressors (RSIR example)

Lamination

Stack

Cast in Place

Aluminum Conductor

Bars

Start Winding

(2 places)

Lead Wires and

Connector

 EE-RM-93-801 COMMENT OR3

Figure 3-1: Typical Squirrel Cage Induction Motor Used In Domestic Refrigerator Compressors (RSIR example) 

Run Winding --____ ..... 

(2 places) 

Lamination 

Stack 

Start Winding 

(2 places) 

~ 

Lead Wires and 

Connector 

111-______ Lamina t ion 

Cast in Place 

Aluminum Conductor 

Bars 

Stack 

4~~--____ ~Squirrel 

Cage Rotor 

3-2 
result, the cost-efficiency curves cross. Table 3-1 compares present practice in this

capacity range with estimated maximum efficiencies inherent in this motor type. From

Figure 3-2 and Table 3-1, it is apparent that:

Figure 3-2: OEM Cost of Single Speed Induction Motors for Hermetic Refrigeration Compressors,

Versus Motor Efficiency and Compressor Capacity

OEM Cost: Price each paid by compressor manufacturer to motor manufacturer for mass production

quantities. Includes cost of required relay , capacitor, etc.

Efficiency: Not accounting for any mechanical losses

Source : Table 3-1 and informal discussions on OEM cost levels with OEM suppliers of motors and

manufacturers of refrigeration compressors

® High motor efficiency (peak efficiency near 85%) is technically feasible in any

compressor capacity of interest, once all of the aforementioned measures to improve

efficiency have been applied.

® The cost of attaining the highest efficiency is significant, qualitatively. For the

smaller compressor capacities, the highest efficiency motors could cost up to 2 to 3

times more than the cost of the motors typically used currently.

 EE-RM-93-801 COMMENT OR3

result, the cost-efficiency curves cross. Table 3-1 compares present practice in this 

capacity range with estimated maximum efficiencies inherent in this motor type. From 

Figure 3-2 and Table 3-1, it is apparent that: 

Figure 3-2: OEM Cost of Single Speed Induction Motors for Hermetic Refrigeration Compressors, 

Versus Motor Efficiency and Compressor Capacity 

30 

I 

/ 

/ 

1/1 / ... Induction Run-oOllllill- / 1!! 

"0 20 "CI 

0 

Ol 

Ol 

.... 

..: '000 1/1 

0 600 0 

:iE AOO .I\s\ CS'ilSr 

W o~\ / ~ PSC 

0 10 e\ul'{\~ 1\ / 

~OO 

70 75 80 85 

Peak Motor Efficiency 

OEM Cost: Price each paid by compressor manufacturer to motor manufacturer for mass production 

quantities. Includes cost of required relay, capacitor, etc. 

Efficiency: Not accounting for any mechanical losses 

Source: Table 3-1 and informal discussions on OEM cost levels with OEM suppliers of motors and 

manufacturers of refrigeration compressors 

.. High motor efficiency (peak efficiency near 85%) is technically feasible in any 

compressor capacity of interest, once all of the aforementioned measures to improve 

efficiency have been applied. 

.. The cost of attaining the highest efficiency is significant, qualitatively. For the 

smaller compressor capacities, the highest efficiency motors could cost up to 2 to 3 

times more than the cost of the motors typically used currently. 

3-3 
Table 3-1: Refrigerator Compressor Induction Motor Efficiency

Today's Motor ] Possible

Compressor

Rating

200 Btu 1 1/16

400 Btu

600 Btu

800 Btu

1/8

1/6

1/4

Type Efficiency Type Efficiency

RSIR* 70-73% PSC** 84%

RSIR 73-76% PSC 86%

RSIR/PSC 78-82% PSC 86%

PSC 80-84% PSC 86%

* RSIR - "Resistance Start/Induction Run" Type Motor - requires relay.

°'PSC - "Permanent-Split Capacitor" Motor with PTCR start-assist device - requires capacitor.

Source: Data provided by GE Motors, 1/12/90

Only a few manufacturers produce compressor motors for R/F applications. Americold,

Matsushita, and Embraco make them for their own compressors; Americold supplies

compressors primarily to White Consolidated Industries. GE makes these motors for

sale to all compressor manufacturers. Tecumseh manufactures most of the motors for

their small compressors. A.O. Smith and Copeland make motors in the 1/2 and integral

horsepower sizes; Copeland provides them only for their compressors. Industrias

Copreci of Spain makes compressor motors, but they have not entered the U.S. market.

 EE-RM-93-801 COMMENT OR3

Table 3-1: Refrigerator Compressor Induction Motor Efficiency 

Today's Motor Possible 

Compressor Motor 

Rating HP Type Efficiency Type Efficiency 

200 Btu 1/16 RSIR* 70-73% PSC** 84% 

400 Btu 1/8 RSIR 73-76% PSC 86% 

600 Btu 1/6 RSIRIPSC 78-82% PSC 86% 

800 Btu 1/4 PSC 80-84% PSC 86% 

*RSIR - "Resistance Start/Induction Run" Type Motor - requires relay. 

**PSC - "Permanent-Split Capacitor" Motor with PTCR start-assist device - requires capacitor. 

Source: Data provided by GE Motors, 1/12/90 

Only a few manufacturers produce compressor motors for RfF applications. Americold, 

Matsushita, and Embraco make them for their own compressors; Americold supplies 

compressors primarily to White Consolidated Industries. GE makes these motors for 

sale to all compressor manufacturers. Tecumseh manufactures most of the motors for 

their small compressors. A.O. Smith and Copeland make motors in the 1/2 and integral 

horsepower sizes; Copeland provides them only for their compressors. Industrias 

Copreci of Spain makes compressor motors, but they have not entered the U.S. market 

3-4 
4. Two Speed Motors

Two speed motors provide a method for potentially improving system performance

because frequent on-off cycles can be largely replaced with long periods of half speed

operation, with reduced evaporator and condenser coil loading. There are two basic

arrangements of two speed motors, consequent pole and arrangements with separate sets

of two pole and four pole windings. The former arrangement is simpler, more compact,

and lower cost, but inherently lower in half speed efficiency in a fractional horsepower

motor.

Based on the limited information that is available relative to two speed motors for this

application, the performance and cost characteristics of a two speed motor for an 800

Btu/hr compressor, optimized for low speed efficiency, are (reference 5):

® 80% full speed efficiency

® 70% half speed efficiency

® Cost approximately that of a maximum efficiency single speed motor

(Figure 3-2, Table 3-1)

These efficiency numbers represent the estimated highest level of efficiency that might

be attained for this type of motor, in the output needed to operate an 800 Btu/hr

compressor. It should be emphasized that no 2 speed motors are actually in production

at this time for this application. Cost and efficiency estimates are the result of presales

preliminary design studies of a major supplier, and are subject to considerably more

uncertainty than the cost-efficiency curves in Figure 3-2 for single speed motors.

Table 4-1 shows some two speed motor manufacturers and the availability of two speed

motors. Two speed motors are not available from many U.S. motor manufacturers in

this size range. A.O. Smith and Copeland have made 1/2 and 1/3 horsepower

compressor motors but these are not in production. Baldor has made a 1/3 horsepower

compressor hermetic motor but it is three phase. Other manufacturers, including

Emerson, G.E., and potentially Americold are working on the development of two speed

motors at this time. The technology exists to make two speed motors, but there is not a

large enough market for them now. Two speed motors are most frequently used for fans

and pumps in integral horsepower sizes. Some residential central air conditioning

applications in the 1 1/2 to 5 horsepower range and larger use two speed compressors,

including Bristol (produces the 2 speed compressor), Copeland (produces the 2 speed

compressor), Lennox, Goodman (Janitrol), and Carrier.

 EE-RM-93-801 COMMENT OR3

4.0 Two Speed Motors 

Two speed motors provide a method for potentially improving system performance 

because frequent on-off cycles can be largely replaced with long periods of half speed 

operation, with reduced evaporator and condenser coil loading. There are two basic 

arrangements of two speed motors, consequent pole and arrangements with separate sets 

of two pole and four pole windings. The former arrangement is simpler, more compact, 

and lower cost, but inherently lower in half speed efficiency in a fractional horsepower 

motor. 

Based on the limited information that is available relative to two speed motors for this 

application, the performance and cost characteristics of a two speed motor for an 800 

Btulhr compressor, optimized for low speed efficiency, are (reference 5): 

" 80% full speed efficiency 

.. 70% half speed efficiency 

" Cost approximately that of a maximum efficiency single speed motor 

(Figure 3-2, Table 3-1) 

These efficiency numbers represent the estimated highest level of efficiency that might 

be attained for this type of motor, in the output needed to operate an 800 Btulhr 

compressor. It should be emphasized that no 2 speed motors are actually in production 

at this time for this application. Cost and efficiency estimates are the result of presales 

preliminary design studies of a major supplier, and are subject to considerably more 

uncertainty than the cost-efficiency curves in Figure 3-2 for single speed motors. 

Table 4-1 shows some two speed motor manufacturers and the availability of two speed 

motors. Two speed motors are not available from many U.S. motor manufacturers in 

this size range. A.O. Smith and Copeland have made 112 and 1/3 horsepower 

compressor motors but these are not in production. Baldor has made a 1/3 horsepower 

compressor hermetic motor but it is three phase. Other manufacturers, including 

Emerson, G.E., and potentially Americold are working on the development of two speed 

motors at this time. The technology exists to make two speed motors, but there is not a 

large enough market for them now. Two speed motors are most frequently used for fans 

and pumps in integral horsepower sizes. Some residential central air conditioning 

applications in the 1 1/2 to 5 horsepower range and larger use two speed compressors, 

including Bristol (produces the 2 speed compressor), Copeland (produces the 2 speed 

compressor), Lennox, Goodman (Janitrol), and Carrier. 

4-1 
Table 4-1: Potential Two Speed Motor Manufacturers

Manufacturer Smallest Size (hp) Status

A. 0. Smith 1/2 not in production

Copeland 1/3 not in production

Baldor 1/3

3 phase only

GE some development

Americold possible development

Emerson some development

Source: Americold, 1990; Baldor, 1990; Copeland, 1990; Emerson Electric, 1990; GE Motors, 1990; A.O.

Smith, 1990.

 EE-RM-93-801 COMMENT OR3

Table 4-1: Potential Two Speed Motor Manufacturers 

Manufacturer Smallest Size (hp) Status 

A. O. Smith 1/2 not in production 

Copeland 1/3 not in production 

Baldor 1/3 

3 phase only 

GE some development 

Americold possible development 

Emerson some development 

Source: Americold, 1990; Baldor, 1990; Copeland, 1990; Emerson Electric, 1990; G E Motors, 1990; A.O. 

Smith, 1990. 

4-2 
5.0 Variable Speed Drives

Variable speed drives allow motors to operate over a continuously variable speed range,

with the maximum speed not limited to the 3500 - 3600 RPM maximum speed of a 60

Hz induction motor. In domestic appliance applications , the variable speed drive is an

electronic device that converts input line electric power (115 VAC, 60 Hz, single phase)

to a multiple phase, adjustable output voltage and frequency , driving the motor at

variable speed. Potential benefits of variable speed drive of the compressor include:

® Follow refrigerator loads closely

® Allow for quick pull down

® Reduce evaporator loading

® Potential for better matching of individual evaporator loads in a cycled two

evaporator system

® Maximum speed can be greater than 3600 RPM, allowing reduced compressor

displacement, size, and cost

® Reduce cycling losses

® Reduce frosting

Variable speed drives are either commercially produced , or under development, to

operate three general categories of motors that are potentially applicable to domestic

refrigerator/freezers:

® Three phase induction motors

® Electronically commutated permanent magnet rotor DC motors (ECPM)

® Switched reluctance motors

The basic electronic hardware configurations of the variable speed drives used to

operate each of these motor types are very similar to each other. Figure 5-1 is a

simplified block diagram of a "generic" variable speed drive, highlighting the

similarities. After passing through an EMI filter (to minimize the transmission of

electronic noise back onto the AC line ), the input AC is rectified and filtered to DC.

Output transistors switch the DC to the individual motor windings , to suit the

characteristics of the motor being driven. Figure 5-2 is a photograph of a one quarter

horsepower variable speed drive containing these major subsystems, that has been

developed for a specific appliance application . In general , to drive any of the three

motor types over a wide speed range requires that the motor input voltage be varied,

and, for induction motors, that the DC supply be switched to synthesize an

approximately sinusoidal A/C output . Pulse width modulation (PWM) is the technique

most commonly used to effect this voltage variation . Figure 5-3 illustrates the operation

of PWM, to vary the input voltage to a DC motor. An output transistor is switched on

and off at a much higher frequency than the motor rotation frequency. The output

voltage is varied from 0 to the DC supply voltage by varying the length of the on time of

the output transistor from 0 to the full period of the square wave. The inductance of the

motor winding stores energy in excess of the average DC voltage during the pulse on

time, and releases the energy during the pulse off time to maintain current flow,

 EE-RM-93-801 COMMENT OR3

5.0 Variable Speed Drives 

Variable speed drives allow motors to operate over a continuously variable speed range, 

with the maximum speed not limited to the 3500 - 3600 RPM maximum speed of a 60 

Hz induction motor. In domestic appliance applications, the variable speed drive is an 

electronic device that converts input line electric power (115 VAC, 60 Hz, single phase) 

to a multiple phase, adjustable output voltage and frequency, driving the motor at 

variable speed. Potential benefits of variable speed drive of the compressor include: 

e Follow refrigerator loads closely 

" Allow for quick pull down 

" Reduce evaporator loading 

e Potential for better matching of individual evaporator loads in a cycled two 

evaporator system 

.. Maximum speed can be greater than 3600 RPM, allowing reduced compressor 

displacement, size, and cost 

" Reduce cycling losses 

.. Reduce frosting 

Variable speed drives are either commercially produced, or under development, to 

operate three general categories of motors that are potentially applicable to domestic 

refrigerator/freezers: 

• Three phase induction motors 

• Electronically commutated permanent magnet rotor DC motors (ECPM) 

.. Switched reluctance motors 

The basic electronic hardware configurations of the variable speed drives used to 

operate each of these motor types are very similar to each other. Figure 5-1 is a 

simplified block diagram of a "generic" variable speed drive, highlighting the 

similarities. After passing through an EMI filter (to minimize the transmission of 

electronic noise back onto the AC line), the input AC is rectified and filtered to DC. 

Output transistors switch the DC to the individual motor windings, to suit the 

characteristics of the motor being driven. Figure 5-2 is a photograph of a one quarter 

horsepower variable speed drive containing these major subsystems, that has been 

developed for a specific appliance application. In general, to drive any of the three 

motor types over a wide speed range requires that the motor input voltage be varied, 

and, for induction motors, that the DC supply be switched to synthesize an 

approximately sinusoidal NC output. Pulse width modulation (PWM) is the technique 

most commonly used to effect this voltage variation. Figure 5-3 illustrates the operation 

of PWM, to vary the input voltage to a DC motor. An output transistor is switched on 

and off at a much higher frequency than the motor rotation frequency. The output 

voltage is varied from 0 to the DC supply voltage by varying the length of the on time of 

the output transistor from 0 to the full period of the square wave. The inductance of the 

motor winding stores energy in excess of the average DC voltage during the pulse on 

time, and releases the energy during the pulse off time to maintain current flow, 

5-1 
smoothing the electric current to a nearly constant level (or, in an induction motor,

nearly sinusoidal wave form). During the off period of the pulse, current passes through

a diode "bypassing" the power transistor.

Figure 5-1 : "Generic " Variable Speed D rive Block Diagram

2% Loss) (Minimum 2% Loss)

115 VAC EMI Filter 115

VAC Rectifier DC

I Power

Transistor/

Diode

Bridge

I

Filter -

Capacitor

Control

Circuits

Source: GE Motors, 1990; Toshiba a,b; Lloyd, 1982

Motor

(1-2% Loss)

There are a variety of other techniques for varying motor speed electrically or

electronically, that are in use or under development. Those in use are generally used in

specialized industrial applications, usually at power levels in excess of 25 horsepower.

The three variable speed drive/motor combinations covered in this section represent

those technologies that have been developed, or are undergoing development for mass

market appliance applications and have the best potential for low cost production.

In addition to controlling the output transistors as required to control the speed of the

motor, the control section often performs other functions such as: fault detection,

protection, and reporting; status monitoring; driving panel displays; controlling

additional operation functions, such as reversing the rotation direction and dynamic

braking; overload protection; torque limiting; and others. Many general purpose

inverters include a large selection of these features, adding considerably to the cost. In a

cost driven appliance application, only those functions that are actually useful would be

included.

As the number of variable speed drives in service increases, regulations are likely to be

imposed requiring low frequency harmonic filtering (in addition to higher frequency

EMI filtering) on the input line. This type of regulation is already in place in Europe for

electronic motor drives drawing more than 200 watts from the AC line. This type of

filtering adds components and cost to the variable speed drive, with little effect on the

efficiency.

5-2

 EE-RM-93-801 COMMENT OR3

smoothing the electric current to a nearly constant level (or, in an induction motor, 

nearly sinusoidal wave form). During the off period of the pulse, current passes through 

a diode "bypassing" the power transistor. 

Figure 5-1: "Generic" Variable Speed Drive Block Diagram 

115 VAC 

GI---___iPi 

EMI Filter 

Filter----' 

Capacitor 

Source: GE Motors, 1990; Toshiba a,b; Lloyd, 1982 

(Minimum 2% Loss) 

Power 

Transistor! 

Diode 

Bridge 

Control 

Circuits (1-2% Loss) 

There are a variety of other techniques for varying motor speed electrically or 

electronically, that are in use or under development. Those in use are generally used in 

specialized industrial applications, usually at power levels in excess of 25 horsepower. 

The three variable speed drive/motor combinations covered in this section represent 

those technologies that have been developed, or are undergoing development for mass 

market appliance applications and have the best potential for low cost production. 

In addition to controlling the output transistors as required to control the speed of the 

motor, the control section often performs other functions such as: fault detection, 

protection, and reporting; status monitoring; driving panel displays; controlling 

additional operation functions, such as reversing the rotation direction and dynamic 

braking; overload protection; torque limiting; and others. Many general purpose 

inverters include a large selection of these features, adding considerably to the cost. In a 

cost driven appliance application, only those functions that are actually useful would be 

included. 

As the number of variable speed drives in service increases, regulations are likely to be 

imposed requiring low frequency harmonic filtering (in addition to higher frequency 

EMI filtering) on the input line. This type of regulation is already in place in Europe for 

electronic motor drives drawing more than 200 watts from the AC line. This type of 

filtering adds components and cost to the variable speed drive, with little effect on the 

efficiency. 

5-2 
Figure 5-2: Variable Speed Electronic Drive for a One-Quarter Horsepower Electronically Commutated DC Motor

5 inch

DC Power

Supply for

Control Circuits ---

Filter ---

Capacitors

Speed Control Input

and Output Connector

Source : Arthur D. Little photograph of ECM drive manufactured by GE Motors

Power

Transistors

5-3

 EE-RM-93-801 COMMENT OR3

Figure 5-2: Variable Speed Electronic Drive for a One-Quarter Horsepower Electronically Com mutated DC Motor 

DC P"wer 

Suppl.,' for 

Control Circuits 

Power Input and 

Output Lines 

[;,11 Filter 

.. ,-

Filter -----'/ 

Capacitors 

') inch ~I 

,------ Control 

Speed Control Input 

and Output Connector 

Source: Arthur D. Little photograph of ECM drive manufactured by GE Motors 

Power 

Transistors 

5-3 
Figure 5-3 : PWM Operation for Varying Output Voltage to a DC Motor

DC Supply

Voltage

Voltage

On Portion

(typical)

Current

-------- Average DC

Output

Off Portion

(Typical)

5.1 Efficiency

The overall efficiency of a variable speed motor and drive (shaft power output _ AC line

electric power input) is the product of the electronic drive efficiency and the motor

efficiency. Electronic drive efficiency for the three types of drive is nearly identical,

because the configuration of the power electronics (EMI filter - rectifier - filter - output

transistor/diode bridge) is essentially identical for each of the three drives. The

efficiency decreases with decreasing output voltage (and motor speed) and, to a lesser

extent, with decreased load (torque).

For small motors, the inherent efficiency of the three motor types are ofset from each

other by small increments:

® ECPM's have the highest efficiency , approaching 95% (motor only), because the

field is supplied by the permanent magnet rotor, with no electric resistance losses.

EOM's incur only minor ripple loss from PWM operation at intermediate input

voltages and speeds.

 EE-RM-93-801 COMMENT OR3

Figure 5-3: PWM Operation for Varying Output Voltage to a DC Motor 

- ,--- -

Voltage 1------- -

On Portion I 

(typical) ~ 

Current 

5.1 Efficiency 

- -

-

t--f---

,.--

----

,.-- DC Supply 

Voltage 

----------

Off Portion 

(Typical) 

~RIPPle 

Average DC 

Output 

Average 

DC Current 

The overall efficiency of a variable speed motor and drive (shaft power output + AC line 

electric power input) is the product of the electronic drive efficiency and the motor 

efficiency. Electronic drive efficiency for the three types of drive is nearly identical, 

because the configuration of the power electronics (EMI filter - rectifier - filter - output 

transistor/diode bridge) is essentially identical for each of the three drives. The 

efficiency decreases with decreasing output voltage (and motor speed) and, to a lesser 

extent, with decreased load (torque). 

For small motors, the inherent efficiency of the three motor types are of set from each 

other by small increments: 

.. ECPM's have the highest efficiency, approaching 95% (motor only), because the 

field is supplied by the permanent magnet rotor, with no electric resistance losses. 

ECM's incur only minor ripple loss from PWM operation at intermediate input 

voltages and speeds. 

5-4 
e Three phase induction motors are approximately 5 percentage points lower in

efficiency than ECPM's. The PWM waveform causes an additional 3-5% efficiency

degradation, at a reasonably high PWM frequency (10 KHz) and 5 - 10%

degradation at low PWM frequency (1 - 2 KHz), due to the content of higher

harmonics of the pulsed waveform.

Switched reluctance motor efficiencies are intermediate to the other two types, but

require very high quality iron in the laminations, and very precise timing of

energizing and deenergizing the stator poles, to attain the intermediate efficiency

level.

Figure 5-4 plots overall motor/drive efficiency vs. motor speed for each of the three

basic motor types (applicable to between 1/10 and 1/3 horsepower output).

5.2 Variable Speed Motor/Drive Costs

This subsection addresses prospective mass production costs of variable speed drives for

refrigerator compressor application. Sections 5.4.1 through 5.4.3 present current costs

for commercially available drives.

Estimates of eventual mass production costs of variable speed drives are subject to

considerable uncertainty, because there is no U.S. mass production (on the appliance

industry scale) and corresponding OEM sales upon which to base cost estimates. In

general OEM prices and manufacturing costs are commercially sensitive information

which manufacturers are reluctant to divulge to the public at large. General Electric is

marketing variable speed, electronically commutated motors, targeting mass market

applications - appliances, air conditioning, and automotive - and currently have total

motor/drive system sales for all applications approaching 50,000 units annually.

Applications range from 5 horsepower heat pump compressor drive motors to one half

horsepower indoor air blower motors for central air conditioning systems. The latter

(packaged one half horsepower, 1200 RPM motor and drive) are being sold to OEM

customers for approximately $125 each, with specific prices depending on volume and

other commercial arrangements (GE Motors, 1990). In Japan, PWM inverters are mass

produced for small "mini-split" heat pump applications, reportedly at a manufacturing

cost of the inverter of $25/horsepower (at average rated motor power output of about

1 1/2 horsepower) (Greenberg, 1988 p. 7). Others place the large volume purchase

direct material cost of the complete inverter in the Japanese mini-split heat pumps (the

major blocks shown in Figure 5-1 plus low frequency harmonic filtering on the input) at

approximately $70 per horsepower (GE Motors, 1990). With assembly costs, overhead,

and profit margin added in, full OEM pricing would be on the order of $100 to $125 per

horsepower.

It can be expected that the ultimate mass production OEM cost of a one quarter

horsepower motor and stator plus a drive on a printed circuit board (see Figure 5-2) will

be well under the $100 level. The cost of the motor will be similar to the cost of

premium efficiency single phase AC induction motors (Figure 3-2), on the order of $25,

 EE-RM-93-801 COMMENT OR3

.. Three phase induction motors are approximately 5 percentage points lower in 

efficiency than ECPM's. The PWM waveform causes an additiona13-5% efficiency 

degradation, at a reasonably high PWM frequency (10 KHz) and 5 - 10% 

degradation at low PWM frequency (1 - 2 KHz), due to the content of higher 

harmonics of the pulsed waveform. 

.. Switched reluctance motor efficiencies are intermediate to the other two types, but 

require very high quality iron in the laminations, and very precise timing of 

energizing and deenergizing the stator poles, to attain the intermediate efficiency 

level. 

Figure 5-4 plots overall motor/drive efficiency vs. motor speed for each of the three 

basic motor types (applicable to between 1110 and 113 horsepower output). 

5.2 Variable Speed Motor/Drive Costs 

This subsection addresses prospective mass production costs of variable speed drives for 

refrigerator compressor application. Sections 5.4.1 through 5.4.3 present current costs 

for commercially available drives. 

Estimates of eventual mass production costs of variable speed drives are subject to 

considerable uncertainty, because there is no U.S. mass production (on the appliance 

industry scale) and corresponding OEM sales upon which to base cost estimates. In 

general OEM prices and manufacturing costs are commercially sensitive information 

which manufacturers are reluctant to divulge to the public at large. General Electric is 

marketing variable speed, electronically commutated motors, targeting mass market 

applications - appliances, air conditioning, and automotive - and currently have total 

motor/drive system sales for all applications approaching 50,000 units annually. 

Applications range from 5 horsepower heat pump compressor drive motors to one half 

horsepower indoor air blower motors for central air conditioning systems. The latter 

(packaged one half horsepower, 1200 RPM motor and drive) are being sold to OEM 

customers for approximately $125 each, with specific prices depending on volume and 

other commercial arrangements (GE Motors, 1990). In Japan, PWM inverters are mass 

produced for small "mini-split" heat pump applications, reportedly at a manufacturing 

cost of the inverter of $25/horsepower (at average rated motor power output of about 

1 112 horsepower) (Greenberg, 1988 p. 7). Others place the large volume purchase 

direct material cost of the complete inverter in the Japanese mini-split heat pumps (the 

major blocks shown in Figure 5-1 plus low frequency harmonic filtering on the input) at 

approximately $70 per horsepower (GE Motors, 1990). With assembly costs, overhead, 

and profit margin added in, full OEM pricing would be on the order of $100 to $125 per 

horsepower. 

It can be expected that the ultimate mass production OEM cost of a one quarter 

horsepower motor and stator plus a drive on a printed circuit board (see Figure 5-2) will 

be well under the $100 level. The cost of the motor will be similar to the cost of 

premium efficiency single phase AC induction motors (Figure 3-2), on the order of $25, 

5-5 
Figure 5-4: Comparison of Variable Speed Drive/Motor Efficiencies (Fractional Horsepower)

100 1

90 1

U

60

25 50 75

Speed (Percent of Maximum)

Source: Arthur D. Little estimates based on data from references 5, 13-15.

100

varying with output in the same fashion as induction motors. The OEM cost of the

variable speed drive (either PWM inverter or ECPM drive with PWM speed control)

after several years of mass production can be expected to fall to between $25 and $40,

and be relatively insensitive to the power output level, as the control portion of the

circuit cost becomes a significant portion of the total. To reach this cost level requires a

very high level of integration of control circuitry.

The cost of the controller could be offset, to some extent, by operating the motor and

compressor at higher speeds, up to approximately 6000 - 7000 RPM, at nominal

capacity. Operating speeds of this magnitude are common practice for the variable

speed rotary compressors used in mini-split, room sized air conditioning systems, and

should be compatible with the smaller compressors used for R/Fs. This range of

operating speed has also been demonstrated in R/F capacity reciprocating compressors,

on a laboratory project basis (GE, 1990). In either case, the normal range of compressor

design optimization and durability issues would need to be addressed prior to

commercial production based on these higher speeds, but the higher speeds are clearly

feasible.

 EE-RM-93-801 COMMENT OR3

Figure 5-4: Comparison of Variable Speed Drive/Motor Efficiencies (Fractional Horsepower) 

100 

90 

~v<l~ ,., 

<> 

l: 

OJ 

(j 

;: 

w 80 OJ 

.:: 

~ 0 

'0 

:;; ... \O~ 

"C \~O>J.(j co 

l: ~V'r<'i>Se 70 :s 

E 

0 

u 

60 

25 50 75 

Speed (Percent of Maximum) 

Source: Arthur D. Little estimates based on data from references 5, 13-15. 

100 

varying with output in the same fashion as induction motors. The OEM cost of the 

variable speed drive (either PWM inverter or ECPM drive with PWM speed control) 

after several years of mass production can be expected to fall to between $25 and $40, 

and be relatively insensitive to the power output level, as the control portion of the 

circuit cost becomes a significant portion of the total. To reach this cost level requires a 

very high level of integration of control circuitry. 

The cost of the controller could be offset, to some extent, by operating the motor and 

compressor at higher speeds, up to approximately 6000 - 7000 RPM, at nominal 

capacity. Operating speeds of this magnitude are common practice for the variable 

speed rotary compressors used in mini-split, room sized air conditioning systems, and 

should be compatible with the smaller compressors used for RlFs. This range of 

operating speed has also been demonstrated in RlF capacity reciprocating compressors, 

on a laboratory project basis (GE, 1990). In either case, the normal range of compressor 

design optimization and durability issues would need to be addressed prior to 

commercial production based on these higher speeds, but the higher speeds are clearly 

feasible. 

5-6 
The resulting reduction in compressor displacement and motor size would allow some

reduction of the cost of these components, on the order of $5 to $10 at the OEM cost

level. The variable speed drive and motor replace the standard induction motor, whose

OEM cost is on the order of $15. The total of these offsetting cost reductions is on the

order of $20 - $25; the net increase in OEM component cost to the R/F manufacturer

associated with the VSD/motors, in mass production, can be expected to be on the order

of $25 - $30.

Total applied costs will include, in addition to motor and drive cost, the cost of the

refrigerator temperature controller, whose function is to determine the required

compressor speed and generate a speed control signal to the motor drive based on

cabinet interior temperatures and a control algorithm. These components replace the

mechanical thermostats used in current refrigerators. In production, the costs could be

expected to be comparable, with no net effect on the manufacturing cost or retail price

of an RIF.

5.3 Variable Speed Drives - Life, Reliability

Domestic refrigerators typically operate for periods on the order of 15 years, and do so

at a very high reliability level. Electronic variable speed drives have been available for

about two decades; drives technologically similar to todays state of the art drives have

been produced for well under 10 years. The latter time period is insufficient to establish

life and reliability relative to the 15 year expected lifetime of the refrigerator. In

general, however, electronic variable speed drives have established a good reliability

track record, consistent with solid state electronics in general. Key to achieving

longevity is provision of adequate cooling for the power electronics components and

control of environmental factors such as moisture condensation.

Simply by virtue of adding another component having a finite possibility of failure, the

addition of a variable speed drive might be expected to reduce the overall reliability of

the appliance. However, a number of factors related to the variable speed drive are

favorable to overall reliability:

® Electromechanical contactors, such as the relay used to switch the start windings in a

conventional induction motor are replaced with the more reliable solid state

electronics of the variable speed drive.

Control circuits will tend to be exclusively highly reliable solid state devices,

replacing the more failure prone electromechanical defrost timer, and thermostat.

® The already high level of compressor mechanical reliability will be improved by

reduced frequency of stop-start cycles.

Overall, given the high reliability of solid state electronics, it is reasonable to expect that

variable speed drives could be used in the domestic refrigerator without significantly

impacting the overall reliability of the appliance.

 EE-RM-93-801 COMMENT OR3

The resulting reduction in compressor displacement and motor size would allow some 

reduction of the cost of these components, on the order of $5 to $10 at the OEM cost 

level. The variable speed drive and motor replace the standard induction motor, whose 

OEM cost is on the order of $15. The total of these offsetting cost reductions is on the 

order of $20 - $25; the net increase in OEM component cost to the RiF manufacturer 

associated with the VSD/motors, in mass production, can be expected to be on the order 

of $25 - $30. 

Total applied costs will include, in addition to motor and drive cost, the cost of the 

refrigerator temperature controller, whose function is to determine the required 

compressor speed and generate a speed control signal to the motor drive based on 

cabinet interior temperatures and a control algorithm. These components replace the 

mechanical thermostats used in current refrigerators. In production, the costs could be 

expected to be comparable, with no net effect on the manufacturing cost or retail price 

of an RiF. 

5.3 Variable Speed Drives - Life, Reliability 

Domestic refrigerators typically operate for periods on the order of 15 years, and do so 

at a very high reliability level. Electronic variable speed drives have been available for 

about two decades; drives technologically similar to todays state of the art drives have 

been produced for well under 10 years. The latter time period is insufficient to establish 

life and reliability relative to the 15 year expected lifetime of the refrigerator. In 

general, however, electronic variable speed drives have established a good reliability 

track record, consistent with solid state electronics in general. Key to achieving 

longevity is provision of adequate cooling for the power electronics components and 

control of environmental factors such as moisture condensation. 

Simply by virtue of adding another component having a finite possibility of failure, the 

addition of a variable speed drive might be expected to reduce the overall reliability of 

the appliance. However, a number of factors related to the variable speed drive are 

favorable to overall reliability: 

• Electromechanical contactors, such as the relay used to switch the start windings in a 

conventional induction motor are replaced with the more reliable solid state 

electronics of the variable speed drive. 

.. Control circuits will tend to be exclusively highly reliable solid state devices, 

replacing the more failure prone electromechanical defrost timer, and thermostat. 

• The already high level of compressor mechanical reliability will be improved by 

reduced frequency of stop-start cycles. 

Overall, given the high reliability of solid state electronics, it is reasonable to expect that 

variable speed drives could be used in the domestic refrigerator without significantly 

impacting the overall reliability of the appliance. 

5-7 
5.4 Description of Specific Variable Speed Motor/Drive Types

The following subsections present brief descriptions of the operating principle of each

of these motor types with a variable speed drive, with a brief summary of the current

commercial status of each of the three VSD-motor technologies.

5.4.1 Electronically Commutated Permanent Magnet Rotor DC Motors

Electronically commutated permanent magnet rotor DC motors, also commonly referred

to as "brushless DC" motors, have a permanent magnet rotor and (usually ) three sets of

stator windings. As the rotor rotates, the stator windings are commutated , i.e. switched

in phase with the permanent magnet poles on the rotor. To control commutation timing,

rotor position is sensed and fed back to the ECPM controller and used as the basis for

timing the switching of the current to the motor windings by the power transistors in the

controller. In many brushless DC motor product offerings , rotor position is sensed by

Hall effect sensors in the motor . An additional set of lead wires is required to connect

the sensors to the controller . An alternate technique, developed and used by GE, senses

the back EMF in the off winding, and commutates on an initial rise of the EMF. The

advantages of this technique are the obvious cost savings of eliminated Hall effect

sensors and lead wires and, for hermetic compressors , the reduction of the number of

wires (to three) that must penetrate the hermetic shell of the compressor, reducing cost

and improving reliability.

The basic operational characteristic is identical to a conventional brush -type permanent

magnet DC motor (speed is proportional to DC supply voltage , torque is proportional to

current). To provide for variable speed operation , the ECPM controller must vary the

DC supply voltage to the motor, as well as providing for correctly timed commutation.

Pulse width modulation is a cost effective and efficient means of varying the DC voltage

supplied to the motor (Figure 5-3), because the high speed PRIM switching is done at

the same output transistors used for commutation . The effect of the high speed PWM

switching on the motor is a low level of ripple in the DC voltage and current to the

motor, which results in a modest increase in 12 R losses (decreasing the motor efficiency

by on the order of one percent) in the stator windings.

The high efficiency of electronically commutated DC motors is attributable to two basic

attributes of the motor:

® The permanent magnet rotor supplies the field, without requiring any input power, as

required with induction motors and wound field type DC motors.

® The placement of the windings on the stator allows room for more winding wire

cross section, allowing lower 12 R loss than in a typical brush type DC motor.

Permanent magnet materials that are used for ECPM rotors are:

® Ferrite;

® Rare earth - cobalt (samarium-cobalt); and

0 Neodymium - Iron - Boron (e.g. "Magnequench")

 EE-RM-93-801 COMMENT OR3

5.4 Description of Specific Variable Speed Motor/Drive Types 

The following subsections present brief descriptions of the operating principle of each 

of these motor types with a variable speed drive, with a brief summary of the current 

commercial status of each of the three VSD-motor technologies. 

5.4.1 Electronically Commutated Permanent Magnet Rotor DC Motors 

Electronically commutated permanent magnet rotor DC motors, also commonly referred 

to as "brushless DC" motors, have a permanent magnet rotor and (usually) three sets of 

stator windings. As the rotor rotates, the stator windings are commutated, i.e. switched 

in phase with the permanent magnet poles on the rotor. To control commutation timing, 

rotor position is sensed and fed back to the ECPM controller and used as the basis for 

timing the switching of the current to the motor windings by the power transistors in the 

controller. In many brushless DC motor product offerings, rotor position is sensed by 

Hall effect sensors in the motor. An additional set of lead wires is required to connect 

the sensors to the controller. An alternate technique, developed and used by GE, senses 

the back EMF in the off winding, and commutates on an initial rise of the EMF. The 

advantages of this technique are the obvious cost savings of eliminated Hall effect 

sensors and lead wires and, for hermetic compressors, the reduction of the number of 

wires (to three) that must penetrate the hermetic shell of the compressor, reducing cost 

and improving reliability. 

The basic operational characteristic is identical to a conventional brush-type permanent 

magnet DC motor (speed is proportional to DC supply voltage, torque is proportional to 

current). To provide for variable speed operation, the ECPM controller must vary the 

DC supply voltage to the motor, as well as providing for correctly timed commutation. 

Pulse width modulation is a cost effective and efficient means of varying the DC voltage 

supplied to the motor (Figure 5-3), because the high speed PWM switching is done at 

the same output transistors used for commutation. The effect of the high speed PWM 

switching on the motor is a low level of ripple in the DC voltage and current to the 

motor, which results in a modest increase in I2R losses (decreasing the motor efficiency 

by on the order of one percent) in the stator windings. 

The high efficiency of electronically commutated DC motors is attributable to two basic 

attributes of the motor: 

.. The permanent magnet rotor supplies the field, without requiring any input power, as 

required with induction motors and wound field type DC motors. 

It The placement of the windings on the stator allows room for more winding wire 

cross section, allowing lower eR loss than in a typical brush type DC motor. 

Permanent magnet materials that are used for ECPM rotors are: 

" Ferrite; 

.. Rare earth - cobalt (samarium-cobalt); and 

" Neodymium - Iron - Boron (e.g. "Magnequench") 

5-8 
Ferrite magnets are relatively low in magnetic field strength and cost. The latter two

materials have much stronger fields, resulting in more compact motors and more power

output from a given size stator. The cost, however, is considerably higher, so that

currently the least costly motor uses a ferrite rotor. There is a general expectation that

the Neodymium - Iron - Boron material will decrease in cost to the point where it is cost

effective. Table 5-1 lists suppliers of electronically commutated DC motors.

Table 5-1: Manufacturers of ECPM Controllers

Manufacturer

Available

Size

(hp)

Present Cost

(quantity 1) Comments

General Electric 1/5 - 8 1/2 250 - 300 in production

Emerson 1 starting production

Inland Motors 1/4 1,700 custom

Magnetek custom custom

PMI custom custom

Minarik custom custom

EG & G custom custom

Fasco custom custom

Source: Telephone conversations and/or product literature of the manufacturers listed.

5 .4.2 Pulse Width Modulation Inverter13 Phase Induction Motor

PWM inverters convert fixed frequency and voltage input electric power (e.g. 115 volt,

60 Hz, single phase residential electric power) into 3 phase variable frequency and

voltage output to an essentially conventional 3 phase induction motor. The PWM

inverter is a specific case of the "generic" variable speed drive of Figure 5-1, where the

PWM output of the output power transistors is switched to approximate the sinusoidal

voltage required to drive the induction motor efficiently. Figure 5-5 shows the voltage

and current waveforms that are typical of a PWM (with a relatively low PWM

frequency) inverter driving an induction motor.

In comparison with electronically commutated motors, PWM inverter driven, fractional

horsepower, induction motors are inherently limited to efficiencies roughly 10-15

percentage points lower. The major reasons for this are:

The induction motor maximum efficiency is a few percentage points lower than the

ECPM, for the reasons discussed in 5.4.1.

® The PWM sinewave approximation (Figure 5-5) results in some degradation of the

motor frequency, because of ripple and harmonics associated with the PWM square

waves. In addition, the PWM frequency is generally on a fixed carrier that is not

precisely synchronized with the timing of the output waveform. This results in some

asymmetry to the waveform, adding additional harmonic content to the waveform.

The net result is lower motor efficiency, by 3 to 5% for high PWM frequency, and

by 5 to 10% for low PWM frequency.

 EE-RM-93-801 COMMENT OR3

Ferrite magnets are relatively low in magnetic field strength and cost. The latter two 

materials have much stronger fields, resulting in more compact motors and more power 

output from a given size stator. The cost, however, is considerably higher, so that 

currently the least costly motor uses a ferrite rotor. There is a general expectation that 

the Neodymium - Iron - Boron material will decrease in cost to the point where it is cost 

effective. Table 5-1 lists suppliers of electronically commutated DC motors. 

Table 5-1: Manufacturers of ECPM Controllers 

Available 

Size Present Cost 

Manufacturer (hp) (quantity 1) Comments 

General Electric 1/5-81/2 250 - 300 in production 

Emerson 1 starting production 

Inland Motors 1/4 1,700 custom 

Magnetek custom custom 

PMI custom custom 

Minarik custom custom 

EG &G custom custom 

Fasco custom custom 

Source: Telephone conversations and/or product literature of the manufacturers listed. 

5.4.2 Pulse Width Modulation Inverterl3 Phase Induction Motor 

PWM inverters convert fixed frequency and voltage input electric power (e.g. 115 volt, 

60 Hz, single phase residential electric power) into 3 phase variable frequency and 

voltage output to an essentially conventional 3 phase induction motor. The PWM 

inverter is a specific case of the "genelic" variable speed drive of Figure 5-1, where the 

PWM output of the output power transistors is switched to approximate the sinusoidal 

voltage required to drive the induction motor efficiently. Figure 5-5 shows the voltage 

and current waveforms that are typical of a PWM (with a relatively low PWM 

frequency) inverter driving an induction motor. 

In comparison with electronically commutated motors, PWM inverter driven, fractional 

horsepower, induction motors are inherently limited to etIiciencies roughly 10-15 

percentage points lower. The major reasons for this are: 

.. The induction motor maximum efficiency is a few percentage points lower than the 

ECPM, for the reasons discussed in 5.4.1. 

.. The PWM sinewave approximation (Figure 5-5) results in some degradation of the 

motor frequency, because of ripple and hannonics associated with the PWM square 

waves. In addition, the PWM frequency is generally on a fixed carrier that is not 

precisely synchronized with the timing of the output waveform. This results in some 

asymmetry to the wavefonn, adding additional hannonic content to the wavefonn. 

The net result is lower motor etIiciency, by 3 to 5% for high PWM frequency, and 

by 5 to 10% for low PWM frequency. 

5-9 
Figure 5-5 : Voltage and Current Output of a PWM inverter (approximate PWM frequency : 1.1 kHz)

VOLTS

CURRENT

Source : Toshiba product literature

 EE-RM-93-801 COMMENT OR3

Figure 5-5: Voltage and Current Output of a PWM Inverter (approximate PWM frequency: 1.1 kHz) 

VOLTS 

CURRENT 

Source: Toshiba product literature 

5-10 
Partially offsetting the efficiency difference is a small advantage in induction motor cost

in comparison with permanent magnet rotor motor cost, attributable to the difference in

materials cost between a squirrel cage rotor and a permanent magnet rotor.

PWM inverters are widely used in the U.S. for 3 phase motor speed control in industrial

applications, primarily in integral horsepower and larger output. Table 5-2 is a partial

listing of sources of PWM inverters and current selling prices, which reflect low volume

production, small lot sales requiring significant application engineering assistance, and

the inclusion of various control, fault detection, and motor protection features beyond

those required to simply run the motor.

Table 5-2: Manufacturers of PWM Inverters

Manufacturer

Size

(hp) Model

Present Cost

(quantity 1) Comments

Toshiba 1/4 E Series 750

Emerson 1/2 Prism 600

Mitsubishi 1/2 Freqrol-F2, K

Hitachi 3/4 VWE 550

Westinghouse 1 AccuFlow JR 585

MagneTek 3/4 FHP 402 610

Lenze 1/4

Vee-Arc 3 PWM 7030 1575 AC applications

Ranco 3 500 AC applications,

starting production

Source: Telephone conversations and/or product literature of the manufacturers listed.

5.4.3 Six Step Inverter - 3 Phase Induction Motor Drives

Single phase voltage is first rectified and filtered, with SCR's in the rectifier to provide

a controlled, variable DC voltage. This voltage is then switched six times per cycle

(twice per phase times three phases) in order to emulate stepwise sine waves. The line

current will rise in an exponential manner and resemble a scalloped sound wave, since

motors are inductive devices. Typical voltage and current signals from a six step

inverter are shown in Figure 5-6.

Six step inverters are an essentially obsolete alternative to PWM inverters for driving

small, 3 phase induction motors at variable speeds. 10 to 15 years ago, when PWM

frequencies were limited to levels well under 1 KHz, the PWM approximation of a sine

wave was poor, and the higher harmonic content due to the fixed timing of the PWM

carrier was significant. At that time, the six-step technique, which is quite simple to

control and requires power transistor switching rates equal only to twice the motor

rotation frequency (times the number of motor pole pairs), were highly competitive with

PWM inverters with respect to performance and cost. As PWM frequencies have

increased and the control sophistication of PWM inverters has improved, the

competitive position of PWM has improved considerably.

5-11

 EE-RM-93-801 COMMENT OR3

Partially offsetting the efficiency difference is a small advantage in induction motor cost 

in comparison with permanent magnet rotor motor cost, attributable to the difference in 

materials cost between a squirrel cage rotor and a permanent magnet rotor. 

PWM inverters are widely used in the U.S. for 3 phase motor speed control in industrial 

applications, primarily in integral horsepower and larger output. Table 5-2 is a partial 

listing of sources of PWM inverters and current selling prices, which reflect low volume 

production, small lot sales requiring significant application engineering assistance, and 

the inclusion of various control, fault detection, and motor protection features beyond 

those required to simply run the motor. 

Table 5-2: Manufacturers of PWM Inverters 

Size Present Cost 

Manufacturer (hp) Model (quantity 1) Comments 

Toshiba 1/4 E Series 750 

Emerson 1/2 Prism 600 

Mitsubishi 1/2 Freqrol-F2, K 

Hitachi 3/4 VWE 550 

Westinghouse 1 AccuFlow JR 585 

MagneTek 3/4 FHP 402 610 

Lenze 1/4 

Vee-Arc 3 PWM 7030 1575 AC applications 

Ranco 3 500 AC applications, 

starting production 

Source: Telephone conversations and/or product literature of the manufacturers listed. 

5.4.3 Six Step Inverter - 3 Phase Induction Motor Drives 

Single phase voltage is first rectified and filtered, with SCR' s in the rectifier to provide 

a controlled, variable DC voltage. This voltage is then switched six times per cycle 

(twice per phase times three phases) in order to emulate stepwise sine waves. The line 

current will rise in an exponential manner and resemble a scalloped sound wave, since 

motors are inductive devices. Typical voltage and cun'ent signals from a six step 

inverter are shown in Figure 5-6. 

Six step inverters are an essentially obsolete alternative to PWM inverters for driving 

small,3 phase induction motors at variable speeds. 10 to 15 years ago, when PWM 

frequencies were limited to levels well under 1 KHz, the PWM approximation of a sine 

wave was poor, and the higher harmonic content due to the fixed timing of the PWM 

carrier was significant. At that time, the six-step technique, which is quite simple to 

control and requires power transistor switching rates equal only to twice the motor 

rotation frequency (times the number of motor pole pairs), were highly competitive with 

PWM inverters with respect to performance and cost. As PWM frequencies have 

increased and the control sophistication of PWM inverters has improved, the 

competitive position of PWM has improved considerably. 

5-11 
Figure 5-6: Six Step Inverter Voltage and Current Wave Forms

a) Voltage output of the three

Inverter phases

b) Motor connections

c) Voltage wave form acros d) Current wave form

each winding each winding

Source: Lloyd, 1982

Efficiencies for six step inverters are about the same as for PWM inverters, perhaps one

to two points lower. Efficiency of the drives decreases by one to two efficiency points

as the size of the drive decreases because the control signal losses remain about the

same. The output of these drives decreases the efficiency of the motor by about 10%

compared to across the line AC voltage because the output current is noisy, and the six

step waveform is only a crude approximation to a sinusoidal waveform and has

significant higher harmonic content.

Table 5-3 shows current manufacturers, sizes, efficiencies, and costs of six step

inverters. They are available from several sources, including Emerson, Lenze, and

Boston Gear. They are available in sizes as small as 1/4 horsepower. Most six step

inverters are marketed for fan, pump, and other industrial applications and provide

features that appeal to this market.

 EE-RM-93-801 COMMENT OR3

Figure 5-6: Six Step Inverter Voltage and Current Wave Forms 

a) Voltage output of the three 

Inverter phases 

c) Voltage wave form acros 

each winding 

Source: Lloyd, 1982 

b) Motor connections 

IA 

d) Current wave form 

each winding 

Efficiencies for six step inverters are about the same as for PWM inverters, perhaps one 

to two points lower. Efficiency of the drives decreases by one to two efficiency points 

as the size of the drive decreases because the control signal losses remain about the 

same. The output of these drives decreases the efficiency of the motor by about 10% 

compared to across the line AC voltage because the output current is noisy, and the six 

step waveform is only a crude approximation to a sinusoidal waveform and has 

significant higher harmonic content. 

Table 5-3 shows current manufacturers, sizes, efficiencies, and costs of six step 

inverters. They are available from several sources, including Emerson, Lenze, and 

Boston Gear. They are available in sizes as small as 114 horsepower. Most six step 

inverters are marketed for fan, pump, and other industrial applications and provide 

features that appeal to this market. 

5-12 
Table 5-3: Manufacturers of Six Step Inverters

Manufacturer

Size

(hp)

Model

(least power output)

Present Cost

(quantity 1)

Lenze 1 /2 611 470

Emerson 1/2 Horizon I 3400

Boston Gear 1/4 AFA 2100 C 1,000

Graham custom 1,000

Source: Telephone conversations and/or product literature of the manufacturers listed.

5.4.4 Switched Reluctance Motors

Switched reluctance motors are a relatively new technology, enabled by continuing

improvements in power and control electronics technology. As shown in Figure 5-7, the

motor consists of a rotor and stator, each having a different number of equally spaced

discrete poles. The rotor consists of a stack of iron laminations with individual poles

formed as shown in the Figure. There are no conductor bars and therefore no induced

current in the rotor. The stator is formed from a stack of iron laminations, with

individual, wound poles. The rotor position is sensed by an encoder in the motor

housing and pulses of current are applied to the stator poles to match the rotor angle.

The pulses are timed, as indicated in the Figure, so that each stator pole is energized as a

rotor pole approaches it, and deenergized when the rotor pole is aligned to it. The

"generic" drive of Figure 5-2 is applicable, with PWM used to match the input voltage

optimally to the speed and torque of the motor.

Switched reluctance motors have several unique attributes that are potentially

advantageous, depending on the application:

® Very high low speed torque;

® The rotor uses no conductor bars or permanent magnets, and the potential cost of the

motor is correspondingly lower;

® Overall motor/drive efficiency can approach ECPM motor/drive efficiency.

However, to realize high efficiency requires very precise timing of energizing and

deenergizing of the stator pole windings and very low loss (and high cost) lamination

materials, limiting the potential cost benefits.

These features are not the distinguishing advantages for a refrigerator compressor motor

that they are for vehicle traction drives or direct drives of washing machine agitators.

The technology was developed at Leeds and Nottingham Universities in England.

Switched Reluctance Drives, Ltd. in Leeds, England licenses the technology. No U.S.

manufacturer is in production of SRM's, but several development programs have been

initiated in the U.S. SRM's are being investigated for use in electric vehicles for

traction drives, where the characteristics high torque at low speed, (as needed for good

acceleration), and good efficiency at higher speed and low torque (cruising conditions)

 EE-RM-93-801 COMMENT OR3

Table 5-3: Manufacturers of Six Step Inverters 

Size Model Present Cost 

Manufacturer (hp) (least power output) (quantity 1) 

Lenze 1/2 611 470 

Emerson 1/2 Horizon I 3400 

Boston Gear 1/4 AFA 2100 C 1,000 

Graham custom 1,000 

Source: Telephone conversations and/or product literature of the manufacturers listed. 

5.4.4 Switched Reluctance Motors 

Switched reluctance motors are a relatively new technology, enabled by continuing 

improvements in power and control electronics technology. As shown in Figure 5-7, the 

motor consists of a rotor and stator, each having a different number of equally spaced 

discrete poles. The rotor consists of a stack of iron laminations with individual poles 

formed as shown in the Figure. There are no conductor bars and therefore no induced 

current in the rotor. The stator is formed from a stack of iron laminations, with 

individual, wound poles. The rotor position is sensed by an encoder in the motor 

housing and pulses of current are applied to the stator poles to match the rotor angle. 

The pulses are timed, as indicated in the Figure, so that each stator pole is energized as a 

rotor pole approaches it, and deenergized when the rotor pole is aligned to it. The 

"generic" drive of Figure 5-2 is applicable, with PWM used to match the input voltage 

optimally to the speed and torque of the motor. 

Switched reluctance motors have several unique attributes that are potentially 

advantageous, depending on the application: 

• Very high low speed torque; 

• The rotor uses no conductor bars or permanent magnets, and the potential cost of the 

motor is correspondingly lower; 

• Overall motor/dlive efficiency can approach ECPM motor/drive efficiency. 

However, to realize high efficiency requires very precise timing of energizing and 

deenergizing of the stator pole windings and very low loss (and high cost) lamination 

materials, limiting the potential cost benefits. 

These features are not the distinguishing advantages for a refrigerator compressor motor 

that they are for vehicle traction drives or direct drives of washing machine agitators. 

The technology was developed at Leeds and Nottingham Universities in England. 

Switched Reluctance Drives, Ltd. in Leeds, England licenses the technology. No U.S. 

manufacturer is in production of SRM's, but several development programs have been 

initiated in the U.S. SRM's are being investigated for use in electric vehicles for 

traction drives, where the characteristics high torque at low speed, (as needed for good 

acceleration), and good efficiency at higher speed and low torque (cruising conditions) 

5-13 
Figure 5-7 : Simplified Schematic of Switched Reluctance Motor Configuration

At rotor position and rotation direction shown:

® Winding A has just been switched off

® Winding B is off

Winding C was just switched on

of switched reluctance motors, as well as potentially lower motor costs, are key

advantages. The Japanese are currently developing this technology for use with "quiet"

washing machines. EPRI is also interested in this application; they are starting a project

with Whirlpool and Emerson. In general, this technology is at an earlier stage of

development and commercialization than the preceding three technologies.

 EE-RM-93-801 COMMENT OR3

Figure 5-7: Simplified Schematic of Switched Reluctance Motor Configuration 

At rotor position and rotation direction shown: 

• Winding A has just been switched off 

• Winding B is off 

Winding C was just switched on 

of switched reluctance motors, as well as potentially lower motor costs, are key 

advantages. The Japanese are currently developing this technology for use with "quiet" 

washing machines. EPRI is also interested in this application; they are starting a project 

with Whirlpool and Emerson. In general, this technology is at an earlier stage of 

development and commercialization than the preceding three technologies. 

5-14 
6.0 Potential Value of Improvements

This report has examined three areas of motor technology

® Constant speed induction motors and the potential for their efficiency improvement

® Two speed motor technology

® Variable speed motor technology

The value of the efficiency improvements obtainable for single speed induction motors

are considered in the compressor technology report (Dieckmann, 1991). The

combination of increased cost and degraded efficiency associated with two speed

induction motors in the fractional horsepower ranges leaves this a rather unattractive

option for this application.

The potential system performance advantages of a variable speed compressor were

examined parametrically, at the DOE closed door energy test condition, for the "typical"

18 cu ft. automatic frost free refrigerator/freezer with a top mounted freezer, as

described in the Appendix. The cases considered were:

® 1993 standards level cabinet thermal performance, as a baseline, and a high

performance cabinet (with 30% lower thermal loads).

® Current, fans and fan motors, and ECPM fans/motors.

For the high performance cabinets, the basis for the single speed compressor capacity

and maximum variable speed capacity was the capacity of the compressor in the

typical 1993 RIF, reduced by half the decrease in cabinet load from current thermal

performance, thereby maintaining puildown capability.

For each of the above cases, the performance with a single speed compressor was

compared with the performance with a current technology variable speed motor -

compressor and with a variable speed compressor having an efficient low speed

range. The efficiency vs. speed characteristic of current technology variable speed

drives was taken to be the upper, ECPM curve from Figure 5-4. The efficient low

speed range drive was assumed to have a system efficiency of 84% at the low speeds

where continuous steady state compressor operation would occur (30% of maximum

speed; an efficiency of 84% is comparable to the one half speed efficiency of current

technology drives).

Table 6-1 summarizes the energy savings for these cases that are attributable to

replacing the single speed compressor with a variable speed compressor (current

variable speed drive technology). The detailed underlying assumptions are presented in

the Appendix.

Table 6-2 summarizes the energy savings for these cases that are attributable to

replacing the single speed compressor with an efficient low speed variable speed

compressor, as described above. The detailed underlying assumptions are presented in

the Appendix.

 EE-RM-93-801 COMMENT OR3

6.0 Potential Value of Improvements 

This report has examined three areas of motor technology 

• Constant speed induction motors and the potential for their efficiency improvement 

• Two speed motor technology 

• Variable speed motor technology 

The value of the efficiency improvements obtainable for single speed induction motors 

are considered in the compressor technology report (Dieckmann, 1991). The 

combination of increased cost and degraded efficiency associated with two speed 

induction motors in the fractional horsepower ranges leaves this a rather unattractive 

option for this application. 

The potential system performance advantages of a variable speed compressor were 

examined parametrically, at the DOE closed door energy test condition, for the "typical" 

18 cu ft. automatic frost free refrigerator/freezer with a top mounted freezer, as 

described in the Appendix. The cases considered were: 

" 1993 standards level cabinet thermal performance, as a baseline, and a high 

performance cabinet (with 30% lower thermal loads). 

" Current, fans and fan motors, and ECPM fans/motors. 

.. For the high performance cabinets, the basis for the single speed compressor capacity 

and maximum variable speed capacity was the capacity of the compressor in the 

typical 1993 RlF, reduced by half the decrease in cabinet load from current thermal 

performance, thereby maintaining pulldown capability. 

.. For each of the above cases, the performance with a single speed compressor was 

compared with the performance with a current technology variable speed motor -

compressor and with a variable speed compressor having an efficient low speed 

range. The efficiency vs. speed characteristic of current technology variable speed 

drives was taken to be the upper, ECPM curve from Figure 5-4. The efficient low 

speed range drive was assumed to have a system efficiency of 84% at the low speeds 

where continuous steady state compressor operation would occur (30% of maximum 

speed; an efficiency of 84% is comparable to the one half speed efficiency of current 

technology dlives). 

Table 6-1 summarizes the energy savings for these cases that are attlibutable to 

replacing the single speed compressor with a valiable speed compressor (current 

variable speed drive technology). The detailed underlying assumptions are presented in 

the Appendix. 

Table 6-2 summarizes the energy savings for these cases that are attlibutable to 

replacing the single speed compressor with an efficient low speed variable speed 

compressor, as described above. The detailed underlying assumptions are presented in 

the Appendix. 

6-1 
Table 6-1 : Summary of Calculated Energy Savings with Variable Speed Compressor (Current

Variable Speed Motor/Drive Technology)

Cabinet Energy Fans

Consumption Single

Speed kWh/yr

Typical 1993 668 Fan A

604 Fan B

604 Fan C

Low Thermal 452 Fan A

Loss w/Constant 402 Fan B

Pulldown 402 Fan C

Energy Consumption kWh/yr

Variable Speed

I

Saving vs. Single

Speed

665 3

510 94

485 119

479 -27

351 51

329 73

Fan A Standard fans, 1 speed

Fan B ECPM fans, 1 speed

Fan C ECPM variable speed condenser and evaporator fans

Table 6-2: Summary of Calculated Energy Savings with Variable Speed Compressor (Efficient Low

Speed -- Future Technology)

Energy Consumption kWh/yr

Cabinet Energy Fans Variable Speed Saving vs. Single

Consumption Single Speed

Speed kWh/yr

Typical 1993 668 Fan A 638 30

604 Fan B 486 118

604 Fan C 464 140

Low Thermal 452 Fan A 460 -8

Loss w/Constant 402 Fan B 334 68

Pulldown 402 Fan C 313 89

Fan A Standard fans, 1 speed

Fan B ECPM fans, 1 speed

Fan C ECPM variable speed condenser and evaporator fans

The value of these energy savings is tabulated in Tables 6-3, and 6-4 assuming an

electric energy cost of 8¢ per kWh, for a range of real discount rates between 2 and 10

percent, over the projected 15 year life of the refrigerator. The discount rates cover a

range between real, after tax returns to savings accounts at the low end of the range, to

after inflation credit card interest rates at the high end of the range. For real discount

rates in the range that consumers would rationally choose for safe investments (at the

low end of the range), the present value of the saved energy is on the order of $75

greater than the incremental cost, at retail, of the variable speed drive. The efficient low

speed variable speed drive saves approximately 20 kWh/yr over current variable speed

drive technology; the present value of the savings is approximately $20.

 EE-RM-93-801 COMMENT OR3

Table 6-1: Summary of Calculated Energy Savings with Variable Speed Compressor (Current 

Variable Speed Motor/Drive Technology) 

Cabinet Energy 

Consumption Single 

Speed kWh/yr 

Typical 1993 668 

604 

604 

Low Thermal 452 

Loss w/Constant 402 

Pulldown 402 

Fan A Standard fans, 1 speed 

Fan B ECPM fans, 1 speed 

Fans 

Fan A 

Fan B 

Fan C 

Fan A 

Fan B 

Fan C 

Fan C ECPM variable speed condenser and evaporator fans 

Energy Consumption kWh/yr 

Variable Speed Saving vs. Single 

Speed 

665 3 

510 94 

485 119 

479 -27 

351 51 

329 73 

Table 6-2: Summary of Calculated Energy Savings with Variable Speed Compressor (Efficient low 

Speed -- Future Technology) 

Cabinet Energy 

Consumption Single 

Speed kWh/yr 

Typical 1993 668 

604 

604 

Low Thermal 452 

Loss w/Constant 402 

Pulldown 402 

Fan A Standard fans, 1 speed 

Fan B ECPM fans, 1 speed 

Fans 

Fan A 

Fan B 

Fan C 

Fan A 

Fan B 

Fan C 

Fan C ECPM variable speed condenser and evaporator fans 

Energy Consumption kWh/yr 

Variable Speed Saving vs. Single 

Speed 

638 30 

486 118 

464 140 

460 ·8 

334 68 

313 89 

The value of these energy savings is tabulated in Tables 6-3, and 6-4 assuming an 

electric energy cost of 8¢ per kWh, for a range of real discount rates between 2 and 10 

percent, over the projected 15 year life of the refrigerator. The discount rates cover a 

range between real, after tax returns to savings accounts at the low end of the range, to 

after inflation credit card interest rates at the high end of the range. For real discount 

rates in the range that consumers would rationally choose for safe investments (at the 

low end of the range), the present value of the saved energy is on the order of $75 

greater than the incremental cost, at retail, of the variable speed drive. The efficient low 

speed variable speed drive saves approximately 20 kWh/yr over current variable speed 

drive technology; the present value of the savings is approximately $20. 

6-2 
Table 6-3: Present Value of Energy Savings of Variable to Speed Compressor (Current Variable

Speed Motor/Drive Technology)

Present Value for Discount

Rates

Cabinet Fan Savings kWh/yr 1 2% 5% 10%

Typical 1993 A 3 3 3 2

B 94 98 81 60

C 119 124 102 76

Low Loss A -27

W/constant B 51 53 44 32

pulldown C 73 76 63 46

• Electric energy cost $.08/kWh

• Over 15 year life of appliance

• Fan configuration: Table 6-1 footnotes

Table 6-4: Present Value of Energy Savings of Variable to Speed Compressor (Efficient Low Speed

-- Future Technology)

Present Value for Discount

Rates

Cabinet Fan Savings kWh/yr 2% 5% 10%

Typical 1993 A 30 31 26 19

B 118 123 101 75

C 140 146 120 89

Low Loss A -8 -- --

W/constant B 68 71 58 43

pulldown C 89 93 76 57

• Electric energy cost $.08/kWh

• Over 15 year life of appliance

• Fan configuration: Table 6-1 footnotes

 EE-RM-93-801 COMMENT OR3

Table 6-3: Present Value of Energy Savings of Variable to Speed Compressor (Current Variable 

Speed Motor/Drive Technology) 

Present Value for Discount 

Rates 

Cabinet Fan Savings kWh/yr 2% 5% 10% 

Typical 1993 A 3 3 3 2 

B 94 98 81 60 

C 119 124 102 76 

Low Loss A -27 -- -- -- W/constant B 51 53 44 32 

pulldown C 73 76 63 46 

• Electric energy cost $.08/kWh 

• Over 15 year life of appliance 

• Fan configuration: Table 6-1 footnotes 

Table 6-4: Present Value of Energy Savings of Variable to Speed Compressor (Efficient low Speed 

-- Future Technology) 

Present Value for Discount 

Rates 

Cabinet Fan Savings kWh/yr 2% 5% 10% 

Typical 1993 A 30 31 26 19 

B 118 123 101 75 

C 140 146 120 89 

Low Loss A -8 -- -- -- W/constant B 68 71 58 43 

pulldown C 89 93 76 57 

• Electric energy cost $.08/kWh 

• Over 15 year life of appliance 

• Fan configuration: Table 6-1 footnotes 

6-3 
7.0 Areas for D

R & D resources could be applied usefully in two broad areas in motor technology: the

development of higher efficiency induction motors for use in compressors, especially

smaller compressors; and improvements in low speed performance of variable speed

motors and drives while reducing costs.

The techniques for designing higher efficiency induction motors are well known in the

hermetic motor industry. The major issues involved from the industry viewpoint are

product engineering and marketing issues of cost vs. market size, and integration with

the compressor. Because the motor is an integral part of the compressor package, high

efficiency motor development is best carried out in the context of high efficiency

compressor development. This subject, therefore, is discussed in greater length in the

compressor technology report (Dieckmann, 1991) that was prepared under this program.

Early development of small, high efficiency compressors would provide important

support to current programs to demonstrate the performance potential of R/F's with dual

loop systems and/or super insulated cabinets.

The results of the performance and payback analysis discussed in the Appendix and in

Section 6, respectively, clearly indicate that significant energy savings can be obtained

with variable speed compressors and fans. However, the savings are limited by the

rapid degradation in variable speed drive (VSD) - motor efficiency below 50% of

maximum speed. At current projected VSD - motor costs, the present value of the

energy savings, at $0.08/kWh over the 15 year life of the R/F is only marginally greater

than the likely increase in retail cost that would be needed to cover the incremental cost

of the motor and drive. R&D efforts, therefore, should be targeted to:

® Increase the low speed (1/4 to 1/3 of maximum) VSD - motor efficiency,

maximizing the savings that can be obtained with a variable speed compressor.

® Further efforts to reduce potential mass production costs, through increased

component integration and utilization of advances in component technology.

® Prototype development of a variable speed compressor based R/F could be pursued,

based on current technology, with detailed performance measurements providing a

basis for further assessment of the potential of this approach and for identifying areas

for improvement.

 EE-RM-93-801 COMMENT OR3

7.0 Areas for R&D 

R&D resources could be applied usefully in two broad areas in motor technology: the 

development of higher efficiency induction motors for use in compressors, especially 

smaller compressors; and improvements in low speed performance of variable speed 

motors and drives while reducing costs. 

The techniques for designing higher efficiency induction motors are well known in the 

hermetic motor industry. The major issues involved from the industry viewpoint are 

product engineering and marketing issues of cost vs. market size, and integration with 

the compressor. Because the motor is an integral part of the compressor package, high 

efficiency motor development is best carried out in the context of high efficiency 

compressor development. This subject, therefore, is discussed in greater length in the 

compressor technology report (Dieckmann, 1991) that was prepared under this program. 

Early development of small, high efficiency compressors would provide important 

support to current programs to demonstrate the performance potential of RIP's with dual 

loop systems and/or super insulated cabinets. 

The results of the performance and payback analysis discussed in the Appendix and in 

Section 6, respectively, clearly indicate that significant energy savings can be obtained 

with variable speed compressors and fans. However, the savings are limited by the 

rapid degradation in variable speed drive (VSD) - motor efficiency below 50% of 

maximum speed. At current projected VSD - motor costs, the present value of the 

energy savings, at $0.08lkWh over the 15 year life of the RlF is only marginally greater 

than the likely increase in retail cost that would be needed to cover the incremental cost 

of the motor and drive. R&D etlorts, therefore, should be targeted to: 

.. Increase the low speed (1/4 to 113 of maximum) VSD - motor efficiency, 

maximizing the savings that can be obtained with a variable speed compressor. 

III Further efforts to reduce potential mass production costs, through increased 

component integration and utilization of advances in component technology. 

III Prototype development of a variable speed compressor based RlF could be pursued, 

based on current technology, with detailed performance measurements providing a 

basis for further assessment of the potential of this approach and for identifying areas 

for improvement. 

7-1 
8.0 Conclusions

8.1 One Speed Motors (Present Practice)

2 pole AC squirrel cage induction motors running close to 3500 RPM and operating on

115 volts, 60 Hz, single phase AC are used universally in domestic refrigerator/freezers

and freezers. In the small capacity compressors (< 600 Btu/hr nominal capacity)

currently used in very small refrigerators, but potentially of interest for two

compressor/two evaporator system designs, low cost, low efficiency motors are

currently used.

Motors whose efficiency is very close (within 1 or 2 percentage points) to that of the

motors used in the best domestic refrigerator compressors, with outputs matching the

needs of smaller capacity compressors could be developed and manufactured fairly

readily. The costs would be considerably higher than that of presently used motors --

cost benefit analyses are needed to determine the optimum efficiency. The

cost-efficiency-power output data plotted in Figure 3-2 is reasonably accurate, and can

he used in these trade-offs.

8.2 Two Speed Motors

As with one speed motors, the technology to design and produce two speed motors is

well known. Two speed motors are inherently lower in efficiency than one speed

motors of comparable cost, on a comparable mass production basis -- by several

percentage points at maximum speed, and by close to 15 percentage points at half speed.

8.3 Variable Speed Drives

Inverter drives of induction motors and variable speed electronically commutated

motor/drives are both well developed and commercialized technologies for providing a

motor with continuously variable speed operation and control, although sales and

production in the U.S. have not yet reached mass production levels for any application

or class of applications. The latter is inherently higher in overall motor/drive efficiency

by close to 15 percentage points, for the reasons discussed in 5.4.1 and 5.4.2. In mass

produced configurations for domestic appliance applications, the costs of the electronic

drives can be expected to be equivalent, while the permanent magnet motor is slightly

higher in cost. The higher system efficiency of the electronically commuted motor and

drive is well worth the small differential in cost.

Currently there is no large scale mass production of either type drive in the U.S. GE is

marketing electronically commutated motors and drives targeted for mass market

applications - appliance and automotive. Total unit sales of GE ECPM motor/drive

systems are approaching 50,000 units annually, with rapid growth in unit sales coupled

with steady decreases in unit costs. Inverters are mass produced in Japan, for

applications such as small residential heat pumps. Manufacturing costs of these mass

produced inverters are on the order of $100 per horsepower (over a range of 1 to 3

horsepower). As U.S. production quantities increase, costs can be expected to fall

toward Japanese mass production cost levels.

 EE-RM-93-801 COMMENT OR3

8.0 Conclusions 

8.1 One Speed Motors (Present Practice) 

2 pole AC squirrel cage induction motors running close to 3500 RPM and operating on 

115 volts, 60 Hz, single phase AC are used universally in domestic refrigerator/freezers 

and freezers. In the small capacity compressors « 600 Btu/hr nominal capacity) 

currently used in very small refrigerators, but potentially of interest for two 

compressor/two evaporator system designs, low cost, low efficiency motors are 

currently used. 

Motors whose efficiency is very close (within 1 or 2 percentage points) to that of the 

motors used in the best domestic refrigerator compressors, with outputs matching the 

needs of smaller capacity compressors could be developed and manufactured fairly 

readily. The costs would be considerably higher than that of presently used motors --

cost benefit analyses are needed to determine the optimum efficiency. The 

cost-efficiency-power output data plotted in Figure 3-2 is reasonably accurate, and can 

be used in these trade-otIs. 

8.2 Two Speed Motors 

As with one speed motors, the technology to design and produce two speed motors is 

well known. Two speed motors are inherently lower in efficiency than one speed 

motors of comparable cost, on a comparable mass production basis -- by several 

percentage points at maximum speed, and by close to 15 percentage points at half speed. 

8.3 Variable Speed Drives 

Inverter drives of induction motors and variable speed electronically com mutated 

motor/drives are both well developed and commercialized technologies for providing a 

motor with continuously variable speed operation and control, although sales and 

production in the U.S. have not yet reached mass production levels for any application 

or class of applications. The latter is inherently higher in overall motor/drive efficiency 

by close to 15 percentage points, for the reasons discussed in 5.4.1 and 5.4.2. In mass 

produced configurations for domestic appliance applications, the costs of the electronic 

drives can be expected to be equivalent, while the permanent magnet motor is slightly 

higher in cost. The higher system efficiency of the electronically commuted motor and 

drive is well worth the small differential in cost. 

Currently there is no large scale mass production of either type drive in the U.S. GE is 

marketing electronically commutated motors and drives targeted for mass market 

applications - appliance and automotive. Total unit sales of GE ECPM motor/drive 

systems are approaching 50,000 units annually, with rapid growth in unit sales coupled 

with steady decreases in unit costs. Inverters are mass produced in Japan, for 

applications such as small residential heat pumps. Manufacturing costs of these mass 

produced invelters are on the order of $100 per horsepower (over a range of 1 to 3 

horsepower). As U.S. production quantities increase, costs can be expected to fall 

toward Japanese mass production cost levels. 

8-1 
The analyses in the Appendix and Section 6 indicate that at current real energy prices,

the energy savings resulting from variable speed compressor operation are sufficient to

payback the likely retail price differential that would result from the incremental

manufacturing costs of applying a variable speed compressor to a typical R/F. The

payback period is long, however; 5 to 10 years. One factor limiting the energy savings

is the degradation of motor and system efficiency at the reduced speeds (about 1/4 to 1/3

of maximum) that would be typical of steady state operation.

 EE-RM-93-801 COMMENT OR3

The analyses in the Appendix and Section 6 indicate that at current real energy prices, 

the energy savings resulting from variable speed compressor operation are sufficient to 

payback the likely retail price differential that would result from the incremental 

manufacturing costs of applying a variable speed compressor to a typical RIP. The 

payback period is long, however; 5 to 10 years. One factor limiting the energy savings 

is the degradation of motor and system efficiency at the reduced speeds (about 114 to 113 

of maximum) that would be typical of steady state operation. 

8-2 
9.0 References

Americold, 1990 (January), private communication.

Arthur D. Little, Inc., 1990 (August), " Impact of a CFC Ban on the Cost and

Performance of Household Refrigerators, Centrifugal Chillers, and

Commercial/Industrial Refrigertion Systems," Technical Memorandum to U.S. DOE.

Baldor, 1989 (November), private communication.

Cann, P., 1989 (November 28 - December 1), "Integrated Heat Pumps", Meeting

Customer Needs with Heat Pumps. Atlanta, GA., Sponsored by EPRI.

Copeland, 1990 (January), private communication.

Dieckmann, J.T., 1991, State of the Art SSurvev of Hermetic Compressor Technology

Applicable to Domestic Refrigerator/Freezers, report to EPA Global Change Division,

prepared by Arthur D. Little, Inc., Cambridge, MA.

Electric Power Research Institute, 1987, "ASD Directory," Second Edition, Palo Alto,

California.

Emerson Electric, 1990 (January), private communication.

Federal Register, 1989a (February 7), pp. 6077 - 8.

Federal Register, 1989b (November 17), pp. 47916 - 47938.

GE Motors, 1990a (January 12), Telefax summarizing induction motor efficiencies.

GE Motors, 1990b (January), private communication.

Greenberg, S., et al., 1988, Technology Assessment: Adjustable Speed Motors and

Motor Drives (Residential and Commercial Sectors), LBL-25080.

Lloyd, J. D., 1982, Variable - Speed Compressor Motors operated on Inverters,

AHSRAE Transactions V88, pt 1.

Lorenz, A., Meutzner, K., 1975, "On Application of Non-azeotropic Two-component

Refrigerants in Domestic Refrigerators and Home Freezers," IIR.

Lovins, A. B., et al., 1989 Edition (April), The State of the Art: Drivepower, Rocky

Mountain Institute, Snowmass, CO.

Smith, A.O., 1990 (January), private communication.

Sulfstede, L., 1989 (November 28 - December 1), "Residential Variable Speed

Technology." Meeting Customer Needs with Heat Pumps, Atlanta, GA., Sponsored by

EPRI.

 EE-RM-93-801 COMMENT OR3

9.0 References 

Americold, 1990 (January), private communication. 

Arthur D. Little, Inc., 1990 (August), "Impact of a CFC Ban on the Cost and 

Performance of Household Refrigerators, Centrifugal Chillers, and 

Commercial/Industrial Refrigertion Systems," Technical Memorandum to U.S. DOE. 

Baldor, 1989 (November), private communication. 

Cann, P., 1989 (November 28 - December 1), "Integrated Heat Pumps", Meeting 

Customer Needs with Heat Pumps. Atlanta, GA, Sponsored by EPR!. 

Copeland, 1990 (January), private communication. 

Dieckmann, J.T., 1991, State of the Art Survey of Hermetic Compressor Technology 

Applicable to Domestic Refrigerator/Freezers, report to EPA Global Change Djvision, 

prepared by Arthur D. Little, Inc., Cambridge, MA 

Electric Power Research Institute, 1987, "ASD Directory," Second Edition, Palo Alto, 

California. 

Emerson Electric, 1990 (January), private communication. 

Federal Register, 1989a (February 7), pp. 6077 - 8. 

Federal Register, 1989b (November 17), pp. 47916 - 47938. 

GE Motors, 1990a (January 12), Telefax summarizing induction motor efficiencies. 

GE Motors, 1990b (January), private communication. 

Greenberg, S., et aI., 1988, Technology Assessment: Adjustable Speed Motors and 

Motor Drives (Residential and Commercial Sectors), LBL-25080. 

Lloyd, J. D., 1982, Variable - Speed Compressor Motors operated on Inverters, 

AHSRAE Transactions V88, pt 1. 

Lorenz, A, Meutzner, K., 1975, "On Application of Non-azeotropic Two-component 

Refrigerants in Domestic Refrigerators and Home Freezers," IlR. 

Lovins, A B., et aI., 1989 Edition (April), The State of the Art: Drivepower, Rocky 

Mountain Institute, Snowmass, CO. 

Smith, AO., 1990 (JanuaIY), private communication. 

Sulfstede, L., 1989 (November 28 - December 1), "Residential Variable Speed 

Technology." Meeting Customer Needs with Heat Pumps, Atlanta, GA, Sponsored by 

EPR!. 

9-1 
Toshiba(a) International Corporation, Houston, Texas, Toshiba Instruction an

Maintenance Manual = Tosvert = 130E Transistor Inverter. Bulletin No. IMVT13OE230.

Toshiba(b) International Corporation, Houston, Texas, Toshiba Inverter Seminar (a 20

page brochure published by Toshiba).

 EE-RM-93-801 COMMENT OR3

Toshiba(a) International Corporation, Houston, Texas." Toshiba Instruction and 

Maintenance Manual.: Tosvert.: l30E Transistor Inverter. Bulletin No. IMVTl30E230. 

Toshiba(b) International Corporation, Houston, Texas, Toshiba Inverter Seminar (a 20 

page brochure published by Toshiba). 

9-2 
Appendix: Value of Variable Speed Motors for Reducing Cycling Losses, and

Otherwise Improving RIF Efficiency

One basic premise underlying the variable speed motor state of the art survey is that the

potential exists to obtain significant energy savings with an efficient variable speed

compressor. The primary sources of the savings are the elimination of losses associated

with on-off cycles, improved utilization of heat exchanger capacity, and, possibly,

savings in fan power if fans were operated at reduced speed (taking advantage of the

speed cubed fan power law) when the compressor speed is reduced. To examine this

basic premise, a series of comparative performance calculations were carried out, at the

standard DOE closed door energy test conditions, using the EPA refrigeration analysis

(ERA) model. As indicated in Table A-l, the main points of comparison are:

® Constant speed vs. continuously variable speed (e.g. cyclic operation vs. continuous),

® Effect of (importance of) fan efficiency,

® For a variable speed compressor, constant speed ECPM fans vs. variable speed

ECPM fans operated at reduced speed and substantially reduced power.

Table A-1: Matrix of Constant Speed vs. Variable Speed Cases

Cabinet Fans w/Single Speed Fans w/Variable Speed

Baseline Standard Efficiency Standard Efficiency

ECPM, 1 Speed ECPM, 1 Speed

ECPM, 1 speed ECPM, Variable Speed

High Performance Standard Eff iciency Standard Eff iciency

(Thermal load 2/3 of baseline) ECPM, 1 Speed ECPM, 1 Speed

ECPM, 1 Speed ECPM, Variable Speed

To obtain meaningful results on the comparative effects of variable speed and different

fan efficiency levels, the following assumptions were followed for all cases:

® The baseline R/F is an 18 cubic foot refrigerator freezer with automatic defrost and a

top mounted freezer, having freezer wall insulation 2 3/8 inch thick and fresh food

compartment insulation 1 7/8 inch thick (R value 8.0 'F/in per Btu/hr-ft2). The

annual DOE test energy use is approximately 20 kWh/yr over the 1993 standard

level (668 kWh/year vs. a 1993 standard level of 690 kWh/year). The freezer

volume is 4.6 cubic feet and the refrigerator volume is 13.4 cubic feet; the adjusted

volume is 20.9 cubic feet.

® The baseline compressor has a nominal EER of 5.3 and a nominal capacity of 865

Btu/hr.

® Losses associated with on-off cycling of the constant speed compressor are assumed

to add 2% to the compressor input power at a 50 percent duty cycle.

 EE-RM-93-801 COMMENT OR3

Appendix: Value of Variable Speed Motors for Reducing Cycling Losses, and 

Otherwise Improving RlF Efficiency 

One basic premise underlying the variable speed motor state of the art survey is that the 

potential exists to obtain significant energy savings with an efficient variable speed 

compressor. The primary sources of the savings are the elimination of losses associated 

with on-off cycles, improved utilization of heat exchanger capacity, and, possibly, 

savings in fan power if fans were operated at reduced speed (taking advantage of the 

speed cubed fan power law) when the compressor speed is reduced. To examine this 

basic premise, a series of comparative performance calculations were carried out, at the 

standard DOE closed door energy test conditions, using the EPA refrigeration analysis 

(ERA) model. As indicated in Table A-I, the main points of comparison are: 

.. Constant speed vs. continuously variable speed (e.g. cyclic operation vs. continuous), 

.. Effect of (importance of) fan efficiency, 

.. For a variable speed compressor, constant speed ECPM fans vs. variable speed 

ECPM fans operated at reduced speed and substantially reduced power. 

Table A-1: Matrix of Constant Speed vs. Variable Speed Cases 

Cabinet Fans w/Single Speed Fans wNariable Speed 

Baseline Standard Efficiency Standard Efficiency 

ECPM, 1 Speed ECPM,1 Speed 

ECPM, 1 speed ECPM, Variable Speed 

High Performance Standard Efficiency Standard Efficiency 

(Thermal load 2/3 of baseline) ECPM, 1 Speed ECPM, 1 Speed 

ECPM, 1 Speed ECPM, Variable Speed 

To obtain meaningful results on the comparative effects of variable speed and different 

fan efficiency levels, the following assumptions were followed for all cases: 

.. The baseline RlF is an 18 cubic foot refrigerator freezer with automatic defrost and a 

top mounted freezer, having freezer wall insulation 23/8 inch thick and fresh food 

compartment insulation 1 7/8 inch thick (R value 8.0 OF/in per Btu/hr-ft2

). The 

annual DOE test energy use is approximately 20 kWh/yr over the 1993 standard 

level (668 kWh/year vs. a 1993 standard level of 690 kWh/year). The freezer 

volume is 4.6 cubic feet and the refrigerator volume is 13.4 cubic feet; the adjusted 

volume is 20.9 cubic feet. 

.. The baseline compressor has a nominal EER of 5.3 and a nominal capacity of 865 

Btu/hr. 

" Losses associated with on-off cycling of the constant speed compressor are assumed 

to add 2% to the compressor input power at a 50 percent duty cycle. 

A-l 
® The ECPM compressor motor has about a 13% efficiency advantage over the

baseline unit, including electronics losses, at constant speed.

® The current technology variable speed motor and drive system efficiency-speed

relationship is assumed to be as shown in Figure 5-4 for electronically commutated

permanent magnet rotor (ECPM) motors. At maximum speed about 1/3 of the losses

(3% of the total input power) occur in the drive electronics, and the remainder (7%

of the total input power) occur in the motor. At lower speeds, a higher proportion of

the losses occur in the electronics.

® The "efficient low speed" variable speed drive is assumed to have an overall system

efficiency of 84% at 25% to 30% of maximum speed, comparable to the half speed

efficiency of current technology variable speed drives. 25% to 33% of maximum

speed is the steady state speed range that results when the compressor is sized to

provide pulldown performance comparable to current R/F. This level of low speed

variable speed drive performance is not currently available, but could potentially be

achieved through R&D.

® At 30% speed, assumed to be the lowest practical speed that will ensure proper

lubrication, the compressor motor drops efficiency 10% from the maximum speed

value, including electronics losses.

® The baseline steady state cabinet loads are 134 Btu/hr (fresh food compartment) and

135 Btu/hr (freezer), including the effect of mullion heaters and controls, but not the

power input to the evaporator fan, which varies with duty cycle and fan efficiency.

® The baseline condenser fan moves 90 ACFM through the condenser, and its motor

consumes 12 watts.

® The baseline evaporator fan moves 50 ACFM through the evaporator, and its motor

consumes 9.4 watts.

® ECPM constant speed fans are assumed to move the same air flow as the baseline,

with 3.6 watts power input to the motor.

® The effect of variable speed refrigerant mass flow and fan air flow on heat exchanger

performance is estimated using the heat exchanger routines within ERA.

® The "high performance" cabinet is assumed to have 70% of the steady state

conduction load as the baseline cabinet. This level of cabinet performance,

combined with refrigeration cycle improvements, would result in energy

consumption approaching the DOE "Level 5". The design measures to achieve this

reduction aren't specified for this study, but could include thicker walls, improved

door gaskets, carbon black insulation, and reduced anti-sweat heat. Pulldown

requirements are assumed to be identical. Therefore, the nominal compressor

capacity (maximum capacity for variable speed) is taken to be 85% of the baseline

cabinet compressor capacity.

A-2

 EE-RM-93-801 COMMENT OR3

.. The ECPM compressor motor has about a 13% efficiency advantage over the 

baseline unit, including electronics losses, at constant speed. 

.. The current technology variable speed motor and drive system efficiency-speed 

relationship is assumed to be as shown in Figure 5-4 for electronically commutated 

permanent magnet rotor (ECPM) motors. At maximum speed about 1/3 of the losses 

(3% of the total input power) occur in the drive electronics, and the remainder (7% 

of the total input power) occur in the motor. At lower speeds, a higher proportion of 

the losses occur in the electronics. 

.. The "efficient low speed" variable speed drive is assumed to have an overall system 

efficiency of 84% at 25% to 30% of maximum speed, comparable to the half speed 

efficiency of current technology variable speed drives. 25% to 33% of maximum 

speed is the steady state speed range that results when the compressor is sized to 

provide pulldown performance comparable to current RlF. This level of low speed 

variable speed drive performance is not currently available, but could potentially be 

achieved through R&D. 

.. At 30% speed, assumed to be the lowest practical speed that will ensure proper 

lubrication, the compressor motor drops efficiency 10% from the maximum speed 

value, including electronics losses. 

.. The baseline steady state cabinet loads are 134 Btulhr (fresh food compartment) and 

135 Btu/hr (freezer), including the effect of mullion heaters and controls, but not the 

power input to the evaporator fan, which varies with duty cycle and fan efficiency. 

.. The baseline condenser fan moves 90 ACFM through the condenser, and its motor 

consumes 12 watts. 

.. The baseline evaporator fan moves 50 ACFM through the evaporator, and its motor 

consumes 9.4 watts. 

.. ECPM constant speed fans are assumed to move the same air flow as the baseline, 

with 3.6 watts power input to the motor. 

.. The effect of variable speed refrigerant mass flow and fan air flow on heat exchanger 

performance is estimated using the heat exchanger routines within ERA. 

" The "high performance" cabinet is assumed to have 70% of the steady state 

conduction load as the baseline cabinet. This level of cabinet performance, 

combined with refrigeration cycle improvements, would result in energy 

consumption approaching the DOE "Level 5". The design measures to achieve this 

reduction aren't specified for this study, but could include thicker walls, improved 

door gaskets, carbon black insulation, and reduced anti-sweat heat. Pulldown 

requirements are assumed to be identical. Therefore, the nominal compressor 

capacity (maximum capacity for variable speed) is taken to be 85% of the baseline 

cabinet compressor capacity. 

A-2 
® Fan powers and air flow rates are unsealed, i.e., equal to the baseline cabinet case.

Tables A-2 and A-3 summarize the results of the efficiency comparison, for the baseline

cabinet and for the high performance cabinet. The major observations relative to these

results are:

® A substantial energy saving (10%) can be obtained by replacing the inefficient

fan/motor of typical current practice with a modest efficiency fan and motor.

® With the standard efficiency fan/motor, the variable speed drive operating at steady

state does not result in energy savings since the energy associated with 100% fan run

time more than offsets the compressor power savings.

a With ECPM fans, the VSD compressor results in a substantial net energy savings.

® A limitation on the compressor energy savings is the declining variable speed motor

system efficiency below half speed (using current technology). The last three cases

of Tables A-2 and A-3 are based on an assumed variable speed motor drive system

efficiency of 84% at 30% of nominal speed (vs. 90% at maximum speed and 84% at

one half speed, with current technology). For this improved level of low speed

motor performance, energy use is reduced by approximately 25 kWh/year over the

comparable, current variable speed technology case.

® The same general observations apply to the high performance cabinet, with increased

sensitivity of the variable speed options to the fan efficiency.

 EE-RM-93-801 COMMENT OR3

.. Fan powers and air flow rates are unscaled, i.e., equal to the baseline cabinet case. 

Tables A-2 and A-3 summarize the results of the efficiency comparison, for the baseline 

cabinet and for the high performance cabinet. The major observations relative to these 

results are: 

.. A substantial energy saving (10%) can be obtained by replacing the inefficient 

fanlmotor of typical current practice with a modest efficiency fan and motor. 

.. With the standard efficiency fanlmotor, the variable speed drive operating at steady 

state does not result in energy savings since the energy associated with 100% fan run 

time more than offsets the compressor power savings. 

.. With ECPM fans, the VSD compressor results in a substantial net energy savings. 

.. A limitation on the compressor energy savings is the declining variable speed motor 

system efficiency below half speed (using current technology). The last three cases 

of Tables A-2 and A-3 are based on an assumed variable speed motor drive system 

efficiency of 84% at 30% of nominal speed (vs. 90% at maximum speed and 84% at 

one half speed, with current technology). For this improved level of low speed 

motor performance, energy use is reduced by approximately 25 kWh/year over the 

comparable, current variable speed technology case. 

" The same general observations apply to the high performance cabinet, with increased 

sensitivity of the variable speed options to the fan efficiency. 

A-3 
Table A-2: Calculated Results - Standard Cabinets

Fan Watts Energy Inputs, kWh/day

Case Evap. Cond. Cabinet(') Duty Cycle Comp c2> Fans Aux?) Total Total

Load Inc.

Fan BtuH

% Speed Energy

kWh/yr

Baseline 9.4 12.0 280 .38 1.49 .20 .15 1.83 668

Constant Speed and

ECPM Fans

3.6 3.6 273 .37 1.44 .06 .15 1.66 604

ECPM at Full Speed,

Standard Fans

9.4 12.0 280 .37 1.28 .19 .15 1.62 591

ECPM at Full Speed, 1

ECPM Fans

3.6 3.6 273 .36 1.25 .06 .15 1.46 531

Variable Speed and 9.4 12.0 299 .98 1.17 .50 .15 1.82 665

Standard Fans 30%

Variable Speed 1

ECPM Fans

3.6 3.6 279 .90

30

1.09 .16 .15 1.40 510

Variable Speed 2.0 2.0 274 .91 1.09 .09 .15 1.33 485

Variable sp. Fans(4) 30%

Efficient Low Speed 9.4 12.0 299 .97 1.10 .50 .15 1.75 638

Variable Speed/Std

Fans

30%

Efficient Low Speed 3.6 3.6 279 .90 1.03 .16 .15 1.33 486

Variable Speed and

ECPM Fans

30%

Efficient Low Speed 2.0 2.0 274 .90 1.03 .09 .15 1.27 464

Variable Speed and

ECPM Fans

30%

(1) Base cabinet load except fans = 268 Btu/hr

(2) Incl. 2% for on-off cycling loss constant speed

(3) Aux: controls, defrost, anti-sweat heaters

(4) Fans at 83% speed, 83% air flow

 EE-RM-93-801 COMMENT OR3

Table A-2: Calculated Results - Standard Cabinets 

Fan Watts 

Case Evap. Condo Cabinet(l) 

Load Inc. 

Fan BtuH 

Baseline 9.4 12.0 280 

Constant Speed and 3.6 3.6 273 

ECPM Fans 

ECPM at Full Speed, 9.4 12.0 280 

Standard Fans 

ECPM at Full Speed, 3.6 3.6 273 

ECPM Fans 

Variable Speed and 9.4 12.0 299 

Standard Fans 

Variable Speed 3.6 3.6 279 

ECPM Fans 

Variable Speed 2.0 2.0 274 

Variable sp. Fans(4) 

Efficient Low Speed 9.4 12.0 299 

Variable SpeedlStd 

Fans 

Efficient Low Speed 3.6 3.6 279 

Variable Speed and 

ECPM Fans 

Efficient Low Speed 2.0 2.0 274 

Variable Speed and 

ECPM Fans 

(1) Base cabinet load except fans = 268 Btu/hr 

(2) Inc!. 2% for on-off cycling loss constant speed 

(3) Aux: controls, defrost, anti-sweat heaters 

(4) Fans at 83% speed, 83% air flow 

Duty Cycle 

% Speed 

.38 

.37 

.37 

.36 

.98 

-

30% 

.90 

-

30 

.91 

-

30% 

.97 

-

30% 

.90 

-

30% 

.90 

-

30% 

Energy Inputs, kWh/day 

Comp.(2) Fans AUX.(3) Total Total 

Energy 

kWh/yr 

1.49 .20 .15 1.83 668 

1.44 .06 .15 1.66 604 

1.28 .19 .15 1.62 591 

1.25 .06 .15 1.46 531 

1.17 .50 .15 1.82 665 

1.09 .16 .15 1.40 510 

1.09 .09 .15 1.33 485 

1.10 .50 .15 1.75 638 

1.03 .16 .15 1.33 486 

1.03 .09 .15 1.27 464 

A-4 
Table A-3: Calculated Results - High Performance Cabinet

Fan Watts Energy Inputs, kWh/day

Case Evap. Cond. Cabinet(') Duty Cycle Comp?) Fans AUx.(4) Total Total

Load Incl.

Fan, BtuH

% Speed(') Energy

kWh/yr

Baseline 9.4 12.0 200 .30 1.01 .16 .07 1.24 452

Constant Speed and

ECPM Fans

3.6 3.6 194 .29 0.98 .05 .07 1.10 402

ECPM at Full Speed,

Standard Fans

9.4 12.0 200 .30 .87 .15 .07 1.10 400

ECPM at Full Speed,

ECPM Fans

3.6 3.6 194 .29 .84 .05 .07 .97 353

Variable Speed and 9.4 12.0 216 .81 .82 .42 .07 1.31 479

Standard Fans 30%

Variable Speed 3.6 3.6 199 .74 .76 .13 .07 .96 351

ECPM Fans 30%

Variable Speed 2.0 2.0 195 .74 .76 .07 .07 .90 329

Variable sp. Fans(') 30%

Efficient Low Speed 9.4 12.0 216 .80 .78 .41 .07 1.26 460

Variable Speed and

Standard Fans

30%

Efficient Low Speed 3.6 3.6 199 .74 .72 .13 .07 .92 334

Variable Speed and

ECPM Fans

30%

Efficient Low Speed 2.0 2.0 195 .73 .71 .07 .07 .86 313

Variable Speed and

Variable Speed Fans

30%

(1) Base cabinet load less fans = 190 Btu/hr

(2) Baseline case compressor capacity 735 Btu/hr

(3) Intl 2% for on-off cycle losses of 1 speed compressor

(4) Auxiliary: controls, defrost, anti-sweat heaters

(5) Fans at 83% speed, 83% air flow

 EE-RM-93-801 COMMENT OR3

Table A-3: Calculated Results - High Performance Cabinet 

Fan Watts 

Case Evap. Condo Cabinet(1) Duty Cycle 

Load Inc!. % Speed(2) 

Fan, BtuH 

Baseline 9.4 12.0 200 .30 

Constant Speed and 3.6 3.6 194 .29 

ECPM Fans 

ECPM at Full Speed, 9.4 12.0 200 .30 

Standard Fans 

ECPM at Full Speed, 3.6 3.6 194 .29 

ECPM Fans 

Variable Speed and 9.4 12.0 216 .81 

Standard Fans -

30% 

Variable Speed 3.6 3.6 199 .74 

ECPM Fans -

30% 

Variable Speed 2.0 2.0 195 .74 

Variable sp. Fans(S) -

30% 

Efficient Low Speed 9.4 12.0 216 .80 

Variable Speed and -

30% 

Standard Fans 

Efficient Low Speed 3.6 3.6 199 .74 

Variable Speed and -

30% 

ECPM Fans 

Efficient Low Speed 2.0 2.0 195 .73 

Variable Speed and -

30% 

Variable Speed Fans 

(1) Base cabinet load less fans = 190 Btu/hr 

(2) Baseline case compressor capacity 735 Btu/hr 

(3) Incl 2% for on-off cycle losses of 1 speed compressor 

(4) Auxiliary: controls, defrost, anti-sweat heaters 

(5) Fans at 83% speed, 83% air flow 

Energy Inputs, kWh/day 

Comp.(3) Fans Aux.(4) Total 

1.01 .16 .07 1.24 

0.98 .05 .07 1.10 

.87 .15 .07 1.10 

.84 .05 .07 .97 

.82 .42 .07 1.31 

.76 .13 .07 .96 

.76 .07 .07 .90 

.78 .41 .07 1.26 

.72 .13 .07 .92 

.71 .07 .07 .86 

Total 

Energy 

kWh/yr 

452 

402 

400 

353 

479 

351 

329 

460 

334 

313 

A-5