Transcript No Slide Title

Application of a Variable Speed Compressor to a
Residential No-Frost Freezer
John Dieckmann, Member, TIAX LLC, Detlef Westphalen, Member, TIAX LLC,
William Murphy, TIAX LLC, Paul Sikir, Member, Sub-Zero Freezer Company,
Christopher Rieger, Sub-Zero Freezer Company
Seminar 41 January 27, 2004
Continuously Variable Capacity Modulation
General Discussion
Continuously variable capacity modulation has significant advantages over
on-off capacity control in many refrigeration and air conditioning
applications.
 Energy
efficiency
 Maximize HX utilization, minimize temperature lift
 Flow rate cubed fan power law
 Temperature
 Humidity
control
control
 Noise
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Continuously Variable Capacity Modulation
General Discussion
Maximum capacity vs. design load and part load.
 Refrigeration
and air conditioning systems need to have enough capacity to
maintain the desired temperature at a worst-case, design load operating
condition
 For
example, residential air conditioning systems face a worst-case load
when the outdoor temperature and humidity and insolation are high and
indoor heat generation levels (from people, lights, appliances, etc.) are high.
Often conditions are much more moderate and less capacity is required
 Home
refrigerators face maximum loads when door openings are frequent,
warm items have been placed in the interior, and when the indoor
temperature is high. When the refrigerator is left undisturbed for an extended
period of time, the cooling load is much less
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Continuously Variable Capacity Modulation
General Discussion
The energy efficiency benefits of continuously variable capacity
modulation are attributable to three main factors.
Reduced Temperature Lift
On
Off
Reduced Air Moving Power
On
Variable
Ambient - DOE energy test procedure
Freezer temperature - DOE energy test procedure
5 oF
Percent of Maximum Power
90oF
100%
Air moving power into
a fixed system = flow
rate cubed
80%
60%
40%
20%
0%
0%
Time
20%
40%
60%
80%
100%
Percent of Maximum Air Flow
In addition, continuous capacity modulation eliminates losses associated
with on-off cycling.
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Continuously Variable Capacity Modulation
General Discussion
Energy efficient caveats – home refrigeration scale.
 The
method used to continuously modulate capacity must be efficient
 Throttle valves, like a suction pressure regulator are very inefficient
 Hot gas bypass is very inefficient
 Variable speed compressor operation can be a highly efficient means of
capacity modulation
 Variable
speed compressor - energy pluses and minuses:
 Losses in electronic drive
 ECM motor efficiency > induction motor efficiency for fractional horsepower
motors
 Compressor speed range
 Refrigerant
 Fan
flow control
efficiency and speed modulation efficiency
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Continuously Variable Capacity Modulation
General Discussion
High compressor efficiency must be maintained at part load.
7
Compressor EER
6
5
4
3
2
1
0
0
1000
2000
3000
4000
5000
Compressor Speed (RPM)
The turndown range should be wide enough to allow steady state operation
at DOE test conditions.
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Continuously Variable Capacity Modulation
General Discussion
Cost-effectiveness of variable speed drive in home refrigerators and
freezers.

There are many options for reducing the energy consumption of a home
refrigerator
 Thicker foam insulated walls
 Increased thermal resistance of door perimeter thermal break and door gasket
 More efficient evaporator fan
 More efficient condenser fan
 Vacuum panel insulation
 Variable speed compressor

A basic market issue remains - if the efficiency advantage and energy cost
savings are not recognized by the buyer, no market pull
 With home refrigerators, annual electric energy cost savings ~$10 - 20/year
 Appliance stores display many brands, sizes, colors, features no room for
premium efficiency
 Energy savings are significant on a national basis, hence standards
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Continuously Variable Capacity Modulation
General Discussion
More energy efficiency caveats - component availability.
 GRAPH
Global
Production of Variable
speed Refrigerant
Compressors for Home
Refrigerators
 ECM
fans
 2-speed
ECM fans
 Variable
speed ECM fans
 Small
thermostatic
expansion valves
Data?? Source???
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Continuously Variable Capacity Modulation
Application to 700 TF
NAECA - Energy efficiency standards and the energy test procedure (10
CFR 430 etc).

Many (18) product classes (top mount, side by side, with through the door ice
dispenser, manual defrost, automatic defrost, freezers, etc.)
 Efficiency requirement for each product class is expressed in terms of
maximum allowable annual energy consumption (as determined by the DOE
energy test procedure 10 CFR 430 subpt B, App A1 and B1) vs. interior
volume: Emax = a(AV) + b

The current requirements (in effect since July, 2001) for the “upright freezer with
automatic defrost” product class (Class 9) are particularly stringent
 Emax = 12.43 AV + 326.1 (AV in cubic feet)
 For freezer, AV = 1.73 x actual interior volume
 For the 700 TF, AV = 1.73 x 15.31 = 26.49 cubic feet
 For the 700 TF, maximum annual energy under the current standard is 655
kWh/year (1.795 kWh/day), 17% less than under the previous standard (in
effect from 1/1/93 through 6/30/01
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Continuously Variable Capacity Modulation
Application to 700 TF
The efficiency standard for Class 9, upright freezer with automatic defrost
is plotted here.
Maximum Annual Energy
Consumption, kWh
900
800
700
600
500
400
700 TF
300
200
100
0
0
5
10
15
20
25
30
Adjusted Volume
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Continuously Variable Capacity Modulation
General Discussion
The 700 TF (“tall freezer”) is a “Euro-styled” upright freezer designed to be
built into kitchen cabinets.
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Continuously Variable Capacity Modulation
700 TF Product Description
The 700 TF (“tall freezer”) is a “Euro-styled” upright freezer designed to be
built into kitchen cabinets.
 Thin
walls to maximize
internal volume
 Upper
half accessible by
opening door
 Lower
half has two pullout drawers
 Significant
door/drawer
perimeter requiring
gaskets and thermal
breaks
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Continuously Variable Capacity Modulation
700 TF
The basic factors influencing refrigerator/freezer energy consumption.
Input to Defrost
Heater
Evaporator
Fan
Heat Leak
into Cabinet
Electric Energy
Input
Input to Fan
Input to Antisweat
Heaters
Heat Leak
into Cabinet
90oF
0oF
Refrigeration System COP
Total Thermal Load
to Refrigeration
System

Compressor COP

Condenser Fan Energy

Evaporator + condenser D T’s
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Continuously Variable Capacity Modulation
700 TF
Cabinet Heat Leak
The cabinet heat load was measured by the “reverse heat leak” method.
Watts to Defrost
Vari ac
Watts to Fan
90oF
0oF

Set up in a 0oF chamber

Electric energy input is easily measured

Wattage is adjusted until cabinet steady-state interior
temperature is 90oF

Average temperature of the insulation is approximately the
same as it would be at DOE test conditions
The measured cabinet heat leak of the 700 TF was ~420 Btu/hr.
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Continuously Variable Capacity Modulation
700 TF
Energy Design Option
There are a range of options for reducing energy use.
Option for Reducing Energy Use
Thicker walls, conventional foam insulation
700 TF Pre-July 2001
Not compatible with overall design goals
Good evaporator fan motor (PSC)
Best evaporator fan motor (ECM or equivalent)
Good condenser fan motor
Best condenser fan motor
Large evaporator (low DT)
Large condenser (low DT)
High EER compressor
Demand defrost/adaptive defrost
Improved door/drawer thermal break
Refrigerant waste heat for antisweat heaters
Vacuum panel insulation
Variable speed compressor
Relatively few options that haven’t already been used were available to
reduce energy use by 17% to meet July, 2001 standards level.
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Continuously Variable Capacity Modulation
Implementation in 700 TF
Compressor
The key component is the variable speed compressors.
 Variable
speed compressors were nominally available from approximately
five compressor manufacturers
 Full capacity EER’s varied from ~6 Btu/watt-hr to low 5’s
 Speed turndown ranges varied from 2 to 1 to 2 1/2 to 1
 Final
selection for production was strongly influenced by strength of
manufacturer’s commitment to supply compressors reliably
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Continuously Variable Capacity Modulation
Implementation in 700 TF
Other important components needed to implement variable speed.
 Speed
control for temperature control
 700 TF was already electronically controlled (microprocessor based), with
thermistors used for temperature sensing, display, and control
 The existing microprocessor had ample under used capacity to implement
a set of speed control algorithms, new software was needed
 Control board hardware modifications were needed to provide the speed
control signal to the compressor drive electronics
 Evaporator
fan - ideally variable speed, but only commercially realistic
alternatives were single speed
 Expansion
device - capillary was found to be adequate
 Evaporator
and condenser sizes were maintained at previous sizes (might be
some potential to cost-optimize by down-sizing)
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Continuously Variable Capacity Modulation
General Discussion
Performance Test Data
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Continuously Variable Capacity Modulation
General Discussion
Conclusions/Observations/Acknowledgements
 Capacity
modulation in a home refrigerator or freezer can reduce the annual
energy consumption by 15% to 25% (as measured by the DOE Test
Procedure)
 The
costs of variable speed compressors and the electronic, microprocessorbased control system needed to control the speed have been decreasing,
increasing the potential for cost effective applications.
 Beyond
energy savings, advantages include quiet part load operation, better,
steadier temperature control and better food preservation
 Acknowledgement:
Subzero and the Technology and Innovation Group of
Arthur D. Little (since spun off as TIAX LLC) collaborated on this project
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