Note: Descriptions are shown in the official language in which they were submitted.
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DSM DEFROST DURING HIGH DEMAND
BACKGROUND OF THE INVENTION
The present disclosure relates generally to refrigerators, and more
particularly to a defrost
heater system for a refrigerator.
Most refrigerators, such as that as disclosed in U.S. Pat. No. 5,711,159,
include an
evaporator that normally operates at sub-freezing temperatures in a
compartment
positioned behind the freezer compartment. A layer of frost typically builds
up on the
surface or coils of the evaporator. Defrost cycles are needed in order to melt
any frost or
ice that forms or builds upon on the refrigeration coils of the evaporator in
a refrigeration
system. Typical defrost systems utilize defrost heaters to melt the ice build
up. The
defrost heater may be similar to the heating elements on an electric stove and
can be
generally located near or beneath the cooling coils, which are concealed
behind a panel in
the refrigeration or freezer compartment. During the defrost cycle, the
defrost heater gets
hot. As a result of its proximity to the cooling coils, any ice or frost build-
up on the coils
melts. As disclosed in U.S. Pat. No. 5,042,267, filed on Oct. 5, 1990, and
assigned to
General Electric Company, assignee of the present invention, a radiant heater
is often
positioned inside a housing and below the evaporator to warm the evaporator by
both
convection and radiant heating in order to quickly defrost the evaporator.
However, existing radiant defrost heaters consume a significant amount of
energy.
Demand Side Management (DSM) is growing in importance as it has become
recognized
that much of the cost of generating electrical power is determined by the peak
electrical
power demand. The utility industry as well as the government and companies are
developing strategies to limit peak electrical power demand by shifting some
of the loads
from high electrical power demand periods to low electrical power demand
periods.
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The peak energy use of an appliance such as a refrigerator typically occurs
during the
defrost cycle. The amount of energy that can be consumed by a refrigerator
during a
defrost cycle is about 500 watts. The rules agreed to by industry for DSM
enabled
refrigerators is that during a high electrical power demand period, the energy
draw of the
refrigerator should be controlled so that it is at most one-half (50%) of the
peak
refrigerator energy usage.
A DSM enabled refrigerator can be controlled such that a defrost cycle
requested or
scheduled during a high demand period is delayed. However, there are
situations where a
defrost cycle is initiated or started during a low demand period and is still
in process
when a high demand period occurs.
Once a defrost cycle is initiated, it is important to not terminate the
defrost cycle until all
of the frost or ice buildup has melted. If the defrost cycle is prematurely
stopped while
there is still a mixture of frost and water on the evaporator, this mixture
will have a
tendency to refreeze into solid ice. It is much more difficult to remove solid
ice from an
evaporator than frost. Frost tends to be more evenly distributed than solid
ice and is less
likely to eventually completely insulate the evaporator and reduce or block
airflow.
Blocked airflow will result in a service call due to lack of cooling. Thus, an
incomplete
or skipped defrost cycle can result in an ice-clogged evaporator. It would be
advantageous to be able to safely reduce power usage in a refrigerator during
a defrost
cycle without risking the formation of an ice-clogged evaporator.
Accordingly, it would be desirable to provide a system that addresses at least
some of the
problems identified above.
BRIEF DESCRIPTION OF THE INVENTION
As described herein, the exemplary embodiments overcome one or more of the
above or
other disadvantages known in the art.
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One aspect of the exemplary embodiments relates to a method. In one
embodiment, the
method includes providing a standard supply of electrical power to a defrost
heater during
a standard defrost cycle for a refrigeration system of an appliance, detecting
a high
energy demand period during the standard defrost cycle, and enabling a reduced
consumption of electrical power by the defrost heater in a low power defrost
cycle.
In another aspect, the present disclosure is directed to a control system for
a defrost
heater in a refrigeration system. In one embodiment the control system
includes a power
supply connection, a controller configured to determine a demand side
management state
signal, and a power switching unit coupled between the power supply connection
and the
defrost heater, the power switching unit configured to switch a power
consumption state
of the defrost heater in a defrost cycle from a standard power consumption
mode to a
reduced power consumption mode when the demand side management state signal is
detected during the standard consumption mode.
In a further aspect, the present disclosure is directed to a refrigerator. In
one
embodiment, the refrigerator includes a compartment, an evaporator in heat
transfer
association with the compartment, a defrost heater associated with the
evaporator, and a
controller configured to switch an energy consumption state of the defrost
heater from a
standard energy consumption state to a reduced energy consumption state when a
peak
power demand state is detected.
These and other aspects and advantages of the exemplary embodiments will
become
apparent from the following detailed description considered in conjunction
with the
accompanying drawings. It is to be understood, however, that the drawings are
designed
solely for purposes of illustration and not as a definition of the limits of
the invention, for
which reference should be made to the appended claims. Moreover, the drawings
are not
necessarily drawn to scale and unless otherwise indicated, they are merely
intended to
conceptually illustrate the structures and procedures described herein. In
addition, any
suitable size, shape or type of elements or materials could be used.
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BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
Fig. 1 is a perspective view of one embodiment of an exemplary appliance
incorporating
aspects of the present disclosure;
Fig. 2 is a schematic view of one embodiment of an exemplary appliance
incorporating
aspects of the present disclosure;
Fig. 3 is a schematic illustration of an embodiment of a defrost heater
control system
incorporating aspects of the present disclosure;
Fig. 4 is schematic illustration of an embodiment of a defrost heater control
system
incorporating aspects of the present disclosure;
Fig. 5 is a schematic view of one embodiment of a defrost heater sheath that
can be used
in a system incorporating aspects of the present disclosure;
Fig. 6 is a schematic illustration of an embodiment of a defrost heater
control system
incorporating aspects of the present disclosure;
Fig. 7 is a schematic illustration of an embodiment of a defrost heater
control system
incorporating aspects of the present disclosure; and
Fig. 8 is a flow chart illustrating an exemplary embodiment of a process
incorporating
aspects of the present disclosure.
DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
Referring to Fig. 1, an exemplary appliance such as a refrigerator,
incorporating aspects
of the disclosed embodiments is generally designated by reference numeral 100.
In this
example the appliance 100 is shown as a refrigerator, but in alternate
embodiments the
appliance may be any suitable cooling or refrigeration appliance that utilizes
a radiant
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heater for a defrost cycle, such as for example an air conditioning unit. The
aspects of the
disclosed embodiments are generally directed to providing a reduced power
consumption
state or mode for a defrost heater in a refrigeration and cooling appliance
such as a
refrigerator. In order to comply with DSM requirements, power consumption of
an
appliance such as a refrigerator must be able to be reduced by approximately
one-half
during periods of peak energy usage or demand. The aspects of the disclosed
embodiments can detect a need to enter such a reduced power consumption state,
generally referred to herein as a "DSM state", and reduce the power
consumption of the
evaporator heater while still maintaining a suitable length of the defrost
cycle to ensure
that the defrost cycle is not prematurely terminated, which would result in
ice and frost
buildup
The refrigerator 100 shown in Fig. 1 is a top mount household refrigerator 100
having a
body or cabinet 110, which includes a top 112, a bottom 114, and opposed sides
116. As
shown in Fig. 1, the top 112, bottom 114 and opposed sides 116 generally
define an
opening 120. Within the opening 120 is defined an upper compartment 122 and a
lower
compartment 124, the upper and lower compartments 122, 124 being separated by
a
mullion 126. In the example of Fig. 1, the upper compartment 122 defines a
freezer
compartment, while the lower compartment 124 defines a fresh food storage
compartment. In alternate embodiments the refrigerator 100 can include any
suitable
number of compartments, in any suitable configuration or orientation.
As is shown in Fig. 1, each of the compartments 122, 124 may have an access
opening,
which is normally closed by a door, in this embodiment shown as freezer door
132 and
fresh food storage door 134. In alternate embodiments, the freezer and fresh
food storage
compartments can be arranged in any suitable manner. The aspects of the
disclosed
embodiments are not limited to a top mount household refrigerator and other
refrigerator
compartment configurations may include, for example, the fresh food storage
compartment mounted above the freezer storage compartment, the fresh food
storage
compartment and freezer storage compartment mounted side by side, a
combination of
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stacked compartments and side by side compartments, or a single door
refrigerator. It is
contemplated that the disclosed embodiments are applicable to other types of
refrigeration and cooling appliances, such as air conditioners, for example,
and are not
intended to be limited to any particular type or configuration of the
exemplary
refrigerator shown in Fig. 1.
Referring to Fig. 2, in one embodiment, the exemplary components for a
refrigeration
system 200 for the refrigerator 100 generally includes a compressor 202, a
condenser 204
and an evaporator 206. The components of the refrigeration system 200
typically
communicate with each other through the refrigeration conduit 208 in a manner
that is
generally known in the art. As shown in Fig. 2, a condenser fan 210 is used to
cool the
condenser 204. Evaporator fan 212 directs an airflow stream across the coils
of the
evaporator 206 and into the compartments 122, 124 in a manner that is
generally known.
The particular arrangement, location and configuration of the refrigeration
system 200 is
merely exemplary, and in alternate embodiments the compressor 202, condenser
204 and
evaporator 206 could be configured at any suitable location of the
refrigerator 100 for
providing the required heat transfer and cooling.
Operation of the compressor 202 is typically thermostatically controlled to
maintain the
temperature within the freezer and fresh food compartments 122, 124 within a
controlled
range. The evaporator 206 is generally configured to operate at temperatures
below
freezing. As is generally understood, there is a tendency for frost or ice to
build up on the
surfaces of the evaporator 206. In one embodiment, for the purpose of
periodically
removing accumulated frost from the surfaces of the evaporator 206, an
electrical defrost
heater 216 is provided. The electrical defrost heater 216 can be any suitable
heater for
warming the surfaces of the evaporator 206, such as for example a radiant
heater. The
defrost heater 216 can be periodically energized by operation of a control or
controller
218.
Fig. 3 illustrates one embodiment of a system 300 for controlling a defrost
heater 216 in
accordance with the aspects of the present disclosure. As shown in Fig. 3, a
power
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supply or source 302, such as the local power grid, for example, is coupled to
a DSM
control 304, which in turn provides or enables a suitable supply of electrical
power to the
defrost heater 216. During normal operation, the power supply 302 provides
power, such
as household alternating current ("AC") power to the various components of the
appliance 100, including the defrost heater 216. The DSM control 304 is
configured to
regulate whether the defrost heater 216 receives full power or one-half power
to enable a
full power defrost cycle or a one-half power defrost cycle of the defrost
heater 216,
depending upon the level of electrical power demand, which can generally be
indicated
by a DSM state signal 310. For example, during a period of relatively low
electrical
power demand, or when a DSM mode is not enabled, the defrost heater 216 will
be
energized by a full power electrical signal 306. During a period of relatively
high
electrical power demand, or when a DSM mode or state is enabled, the defrost
heater 216
will be energized or powered by a one-half power electrical signal 308. A
state of the
DSM control 304 determines whether the defrost heater 216 receives the full
power input
signal 306 or the one-half power input signal 308.
In one embodiment, the state of the DSM control 304 is determined by the DSM
State
signal 310. The DSM State signal 310 will generally indicate a DSM state when
a period
of high electrical power demand exists, and the power consumption of the
appliance 100
must be reduced. The DSM state signal 310 is typically generated or
transmitted by the
local power or utility company, or other suitable entity that determines power
grid and
load conditions. Generally, the DSM state signal 310 is transmitted over the
power lines
or via a wireless connection and is detected by, for example, the DSM control
304 in the
appliance 100. Alternatively, the DSM state signal 310 can be sent over a side
band via
FM radio. In alternate embodiments, any suitable method of transmitting and
receiving
the DSM State Signal 310 can be used.
Fig. 4 illustrates one embodiment of the DSM control 304 of Fig. 3. In this
example, the
power supply 302 is coupled to a switch or relay 402. The switch 402 is
configured to
couple the power supply 302 to one of two branches of the power supply
circuit,
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generally referenced as 406. The first branch 306 provides the full power,
regular defrost
cycle. The second branch 308 provides the reduced or half power DSM defrost
cycle. In
one embodiment, the half power DSM defrost branch 308 includes a power
reduction
device 404 in series between the power supply 302 and the defrost heater 216.
When the
power supply 302 is connected to the half power branch 308, the power
reduction device
404 will reduce the electrical power supplied to, or able to be consumed by,
the defrost
heater 216 by approximately one-half to comply with DSM requirements. While
the
aspects of the disclosed embodiments generally refer to the power supply 302
as an AC
power supply, in alternate embodiments the power supply 302 can comprise a
direct
current (DC) power supply. In such embodiments, the power reduction device 404
will
be configured to reduce a DC power supply input by approximately one-half.
In one embodiment, the power reduction device 404 comprises one or more diodes
or
other suitable electronic components that are configured or arranged to
conduct electrical
current in only one direction. In one embodiment, the power reduction device
404
comprises a standard rectifier diode.
When the power reduction device 404 is a diode and the AC power supply 302 is
coupled
to the half power branch 308, the diode will block one-half of the cycle of
the AC power
signal.
As another example, in one embodiment, the power reduction device 404
comprises a
triode for alternating current (TRIAC). As is generally understood, a TRIAC is
an
electronic component or solid state switch that can modify the shape of the
alternating
current wave being supplied by the power supply 302.
In one embodiment, referring to Fig. 5, the defrost heater 216 can comprise a
two wire
defrost heater sheath 506 having a high power input 502 and a low power input
504.
Power from the power supply 302 is sent to the high power input 502 for a
conventional
defrost during low electrical power demand periods, and to the low power input
504
during high or peak electrical power demand periods. In alternate embodiments,
the
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power reduction device 404 can comprise any suitable device for reducing a
power
supply input by approximately one-half.
Referring to Fig. 6, in one embodiment, a system 600 for controlling a reduced
power
defrost state or cycle is shown, where the defrost heater 216 of Fig. 1
comprises two
separate defrost heaters, a primary defrost heater 602 and a secondary defrost
heater 604.
In one embodiment, the secondary defrost heater 604 can be configured to use
approximately one-half of the power used by the primary defrost heater 602. In
this
example, the DSM control 304 can comprise a suitable switch or relay that
switches the
power supply 302 between the primary defrost heater 602 and the secondary
defrost
heater 604. The DSM state signal 310 will be used to determine which of the
defrost
heaters 602, 604 is energized. During peak electrical power demand periods,
the DSM
control 304 will turn off the high power primary defrost heater 602 and
energize the low
power heater 604.
In another embodiment, both the primary defrost heater 602 and the secondary
defrost
heater 604 can comprise low power defrost heaters. In this embodiment, when
the DSM
state signal 310 indicates a state of low power demand so that a normal
defrost cycle can
be initiated, the DSM control 304 will enable both the primary defrost heater
602 and the
secondary defrost heater 604 to be energized. If the state of the DSM signal
310 changes
or indicates a high power demand state, the DSM control 304 is configured to
disable one
of primary or secondary defrost heaters 602, 604 so that the power consumption
is
reduced by the required amount.
It can generally be anticipated that when the defrost heater 216 is powered
with, or only
using, one-half of the power using during a conventional defrost cycle, that
the time to
complete the defrost cycle will take longer than normal. As noted, it is
important not to
terminate a defrost cycle until all of the frost or ice has melted in order to
avoid creating
an ice-blocked evaporator. Any negative effects of having a longer defrost
cycle are
generally outweighed by the disadvantages of terminating the defrost cycle too
early. In
one embodiment, referring to Fig. 7, the controller 218 includes a clock/timer
702. The
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clock/timer 702 is generally configured to monitor, determine and set the time
period of
the defrost cycle. In one embodiment, when a conventional or high power
defrost cycle
is initiated, the timer 702 is activated. The timer 702 will control the
length of the
conventional defrost cycle according to a pre-determined time period or
standard. When
the pre-determined time period has expired, the conventional defrost cycle can
be
terminated. This pre-determined time period for a conventional defrost cycle
will
generally be understood to be established according to acceptable standards or
the defrost
history of the appliance 100.
When a low power defrost state or cycle is initiated during a high power
defrost cycle, in
one embodiment, a determination is made as to the time remaining in the
defrost cycle.
In one embodiment, a time determination module or calculator 704 can be used
to
calculate the time remaining in the defrost cycle, which can be stored or
retrieved from
the clock/timer 702. Based on the determination of the remaining time, a new
time
period for the low power defrost cycle can be calculated and set, the
calculation of which
can generally be a factor of the heating capability of the defroster heater
216 in a one-
half power mode and the time remaining from the conventional defrost cycle. In
one
embodiment, the calculations can be pre-determined, stored, and retrieved from
a look-up
table 706 or other suitable database or memory 710. Alternatively, the time
calculator
708 can incorporate a suitable low power time calculation algorithm that
utilizes the
remaining time from the conventional defrost cycle, the power level for the
low power
cycle, and/or historical time values for low power defrost cycles, to
calculate a new time
period for the low power defrost cycle.
In one embodiment, referring again to Fig. 7, the controller 218 can be
configured to
detect the DSM state signal 310 and control the switching of the power supply
input to
the defrost heater 216 between the standard, high power setting and the DSM
state, low
or half-power setting. In one embodiment, the controller 218 includes or is
coupled to a
Defrost Heater Power Control 712 that regulates and switches the power
supplied to the
defrost heater 216. For example, when the DSM state signal 310 indicates a
period of
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low power demand, the controller 218 can cause the Defrost Heater Power
Control 712 to
enable a standard supply of electrical power to be delivered to the defrost
heater 216.
When the DSM state signal 310 indicates a period of peak or high power level
demand, a
DSM state, the controller 218 can cause the Defrost Heater Power Control 712
to enable
a reduced supply of power, or half-power, to be delivered to the defrost
heater 216.
Fig. 8 illustrates an exemplary process incorporating aspects of the disclosed
embodiments. A conventional defrost cycle is initiated 802 during a period of
low energy
demand or usage. During this conventional defrost cycle, a DSM signal to
reduce power
is received 804. In accordance with the aspects of the disclosed embodiments,
the
electrical power supplied to, or consumed by the defrost heater 216 is reduced
806 by
approximately one-half (50%), or such other suitable value. In one embodiment,
a new
time period for the low power defrost cycle is determined and set 808. This
allows the
low power defrost cycle to substantially completely melt any frost or ice
accumulation
even though the power consumption of the defrost heater 216 is reduced.
The aspects of the disclosed embodiments generally provide a reduced power
consumption state or mode for a defrost heater in a refrigeration and cooling
appliance
such as a refrigerator. In order to comply with DSM requirements, power
consumption
of an appliance such as a refrigerator must be able to be reduced by
approximately one-
half during periods of peak energy usage or demand. The aspects of the
disclosed
embodiments can detect a need to enter a reduced power consumption state and
reduce
the power consumption of the evaporator heater while ensuring that the defrost
cycle is
not prematurely terminated, which would result in ice and frost buildup.
Thus, while there have been shown, described and pointed out, fundamental
novel
features of the invention as applied to the exemplary embodiments thereof, it
will be
understood that various omissions and substitutions and changes in the form
and details
of devices illustrated, and in their operation, may be made by those skilled
in the art
without departing from the invention. Moreover, it is expressly intended that
all
combinations of those elements and/or method steps, which perform
substantially the
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same function in substantially the same way to achieve the same results, are
within the
scope of the invention. Moreover, it should be recognized that structures
and/or elements
and/or method steps shown and/or described in connection with any disclosed
form or
embodiment of the invention may be incorporated in any other disclosed or
described or
suggested form or embodiment as a general matter of design choice.
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