Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02552454 2006-07-17
FROST MANAGEMENT SYSTEM FOR A REFRIGERATED CABINET
FIELD OF THE INVENTION
This invention relates to refrigerated cabinets such as chest freezers and, in
particular,
to frost management systems for such devices.
BACKGROUND OF THE INVENTION
In refrigeration cabinets such as cold-wall freezers, a principal concern is
the
accumulation of frost on the inside liner walls. The formation of frost within
the
freezer may cause refrigeration system degradation, loss of cooling
efficiency,
cleanability and aesthetic issues. Freezer accessories such as baskets may be
"locked"
into position by frost accumulation. Freezers with frost accumulation may
provide
the impression that the last cleaning was prior to the frost accumulation.
Conventional defrost systems may create a dry humidity environment which may
adversely effect food products, such as ice cream.
A principal concern with frost is that it may form an insulating cushion
between the
cooling evaporator tubing coils and an interior portion of the cabinet. This
insulating
cushion reduces heat transfer efficiency in the evaporator tubing coils
through the
inner walls of the cabinet and impedes proper air circulation of refrigerated
air above
the freezer contents, which frequently is food.
The cabinets of cold-wall type freezers may for example be of the vertical
closed type
construction with insulated hinged solid or glass doors. The cabinets may also
for
example be of the horizontal open or closed type with solid insulated hinged,
glass
hinged or sliding glass lids. In vertical type freezers with hinged doors the
warm
ambient air is drawn into the freezer cabinet with every door opening. Higher
density
cooler air escapes with each door opening by dropping down to ground level. As
the
cool air flows down and out of the freezer, warmer moist air is drawn into the
cabinet
to make up the difference in air pressure within the freezer. In horizontal
chest
freezers the warmer low pressure ambient air is drawn into the freezer cabinet
with
each lid opening due to pressure differences between the cold low pressure air
inside
the freezer and the warmer higher pressure ambient air surrounding the freezer
cabinet. The moisture from the ambient air drawn into the cabinet will
condense
along the inside liner walls in the form of frost. The frost accumulates
preferentially
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along the liner walls in the open volume area between the upper level of the
freezer
contents and top of the freezer chest liner.
Conventional freezer defrosting requires a user to remove frozen food or other
products contained within the freezer cabinet, followed by turning off the
compressor.
Frost is removed by melting with placement of a fan directed into the cabinet,
spraying warm water on the cabinet walls, or simply letting the cabinet sit
for a
number of hours with the lid open to the ambient air.
Another defrosting method is to scrape frost off the cabinet walls without
increasing
the ambient temperature. A difficulty with this method is that it must be
frequently
done, and even so scraping may be physically demanding or cumbersome for the
user.
There is also a risk of damaging the freezer liner.
Yet another defrosting method is to use hot gas installed within the cabinet
walls. In a
defrost cycle of this method, there is a sudden release of hot high-pressure
refrigerant
gas into the extremely cold evaporator tubing for melting of the frost. Hot
gas
defrosting may require integration with refrigeration circuits, thus failure
of one
circuit may lead to mass failure of the apparatus. Hot gas defrosting may be
costly to
manufacture and install. There may be compressor failure if the defrost cycle
is too
long or if the hot gas solenoid valve is left on due to malfunction thereby
resulting in
compressor winding overheating and eventual burn out.
SUMMARY OF THE INVENTION
The present invention provides to a frost management system for use in a
refrigerated
cabinet such as a cold-wall freezer which addresses the shortcomings of prior
devices.
In a first aspect, the invention provides a frost management system for use in
a
refrigeration cabinet having a base and sidewalls defining an opening to
provide
access into the refrigeration cabinet, the sidewalls being conductive for heat
transfer
through the sidewalls. There is a first heating member positioned proximate to
the
opening exterior of the sidewalls which may be activated to melt frost
accumulated on
an interior of the sidewalls. A first activator is provided for the first
heating member,
the first heating member being activated for a time to cause the frost to be
melted,
thereby permitting the resulting liquid to flow down the sidewalls toward the
base and
be refrozen. In another aspect, the invention provides a second heating member
positioned proximate to the base of the refrigeration cabinet and exterior of
the
sidewalls for heating of ice accumulated on the sidewalls. There is provided a
second
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activator for the second heating member. The second heating member is
activated for
a time to melt a portion of the ice adjacent the sidewalls to enable its
removal.
In yet another aspect, the invention provides a method for managing frost in a
refrigeration cabinet having a base and sidewalls defining an opening to
provide
access into the refrigeration cabinet, including the step of heating a region
on the
sidewalls proximate to the opening for melting frost accumulated on an
interior of the
sidewalls into a liquid, thereby permitting the resulting liquid to flow down
the
sidewalls toward the base and be refrozen. In another aspect, a full defrost
may be
initiated by heating a lower portion and/or an upper portion of the sidewalls
for
melting a surface of the ice, and mechanically removing the ice from the
refrigeration
cabinet.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments will now be described by way of example with reference to the
accompanying drawings, through which like reference numerals are used to
indicate
similar features.
Figure 1 shows a perspective sectional view of a horizontal cold-wall type
freezer in
accordance with an embodiment of the present invention;
Figure 2 shows a perspective partial sectional view of a cabinet wall of
Figure 1;
Figure 3 shows a perspective view of a foil heater of the freezer of Figure 1
and a
block diagram of an example of controller circuitry;
Figure 4 shows a sectional side view of the freezer of Figure 1;
Figure 5 shows the same view as Figure 4 in a first mode of operation;
Figure 6 shows the same view as Figure 4 in a second or full defrost mode of
operation; and
Figure 7 shows a perspective sectional view of a vertical cold-wall type
freezer in
accordance with another embodiment of the present invention.
DETAILED DESCRIPTION
For clarity, "frost" may mean any deposition of vapors in saturated air,
including
water vapors, and may include ice-like or other crystalline formations.
Usually, frost
includes air or gas-filled interstices. A "refrigeration device" may mean any
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appliance that uses heat exchanging for cooling of an interior of such a
device.
Examples are cold-wall type freezers, which may for example be vertical or
horizontal freezers.
Reference is now made to Figures 1 and 2. Figure 1 shows a perspective view of
a
horizontal freezer 10 in accordance with an aspect of the present invention
with
portions cut away to reveal interior detail. Figure 2 shows a perspective
partially
sectional view of a cabinet wall 22 of the freezer of Figure 1.
Figure 1 shows the freezer 10 having four cabinet walls 22 and a base 14. In
the
example shown, there are four inner walls 12, a spiral coil of evaporator
tubing 16
outwardly from the out sides of inner walls 12, a heater foil. 18 adhered on
the
evaporator tubing 16 and inner wall 12, a thermal insulation 28 disposed on an
outer
side of the heater foil 18, a condenser tubing 30 on an outer side of the
thermal
insulation 28, and an outer wall 32 externally of the condenser tubing 30. The
four
inner walls 12 may be upstanding to form a rectangular box, and thereby define
an
interior 20 of the freezer 10 and an opening 21 for access to the interior 20.
The inner
walls 12 may be formed of any suitable heat conductive material, for example
metallic or plastic material. Accordingly, the inner walls 12 may be used to
conductively exchange heat for cooling of the interior 20. The opening 21 may
be
open to the ambient or a door may be constructed thereon as a lid (60 as shown
on
Figures 4 to 6) on top of the cabinet walls 22.
The evaporator tubing 16 is connected to a compressor (96 in Figure 3), as is
known
in the art. The evaporator tubing 16 acts as a cooling member, so that the
interior 20
of the freezer 10 becomes cooled by heat transfer through the inner walls 12.
As will
be apparent to the skilled person, the evaporator tubing 16 may be a
serpentine coil or
a spiral coil connected to an exterior of at least one of the inner walls 12.
In Figure 1, for illustrative purposes, heater foil 18 is shown cutaway so
that the
evaporator tubing 16 may be seen. A heating of the heater foil 18 will melt
frost
accumulation on the inner walls 12 as will be described in greater detail
below.
Thermal insulation 28 is exterior of the heater foil 18 and provides
insulation between
the evaporator tubing 16 and condenser tubing 30. The thermal insulation 28
may be
foam injected between the inner walls 12 and the outer walls 32. In the
example
shown, the condenser tubing 30 is spirally attached to an inside surface of
the outer
wall 32. At an end of the condenser tubing 30 is an expansion valve 97 (Figure
3), as
is known in the art. Four of the outer walls 32 define an exterior of the
freezer 10.
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The outer walls 32 may be formed of metal or other conductive material and may
be
utilized as a heat transfer surface for the condenser tubing 30. Accordingly,
heat from
the condenser tubing 30 is released to an exterior of the freezer via the
outer walls 32,
as is known in the art. Alternatively, condenser tubing 30 may be a serpentine
coil
rather than a spiral coil for heat exchanging to an exterior of the freezer
10.
Reference is now made to Figure 2, which shows a cabinet wall 22 of the
freezer 10.
It shows an upper portion 24 and a lower portion 26 of the cabinet wal122.
The components of the heater foil 18 are shown in Figure 3. In the example
shown,
heater foil 18 has two heat conductive sheets 44, 46 having heater wires 33,
34
disposed therebetween. Each conductive sheet 44, 46 may be formed of
conductive,
for example metal, foil and may have a peel off adhesive on one side and a non-
adhesive side. In one embodiment, heater wires 33, 34 are adhered to the
adhesive
side of conductive sheet 44. The other conductive sheet 46 then has its non-
adhesive
side adhered to the adhesive side of conductive sheet 44. The adhesive side of
conductive sheet 46 may then be adhered to an exterior of the inner walls 12,
as
shown in Figure 2. Heater wire 33 defines an upper region in the heater foil
18
corresponding to upper portion 24 of the cabinet wall 22 as shown in Figure 2.
Similarly, heater wire 34 defines a lower region in the heater foil 18
corresponding to
lower portion 26 of the cabinet wal122 as shown in Figure 2. The heater wires
33, 34
(Figure 3) are shown in a serpentine configuration for heating of the upper
and/or
lower portions of heater foil 18. Lead wires 36, 38 extend from heater wire 33
and
may be connected to a controller 98. When a current is applied to lead wires
36, 38,
heat is generated in heater wire 33. Accordingly, activation or energizing of
either
heating wire 33, 34 will heat a corresponding region in the conductive sheets
44, 46
by way of heat conduction, and will thereby heat the upper portion 24 and
lower
portion 26 of the cabinet wall 22. Lead wires 40, 42 extend from heater wire
33 and
may be connected to the controller 98. Lead wires 40, 42 operate in a similar
manner
to lead wires 36, 38. The controller 98 may also be used for setting
appropriate
heating times as will be described further.
Figures 4 to 6 show the operation of the freezer 10. As shown, the upper
heater wire
33 is located to heat the upper portion 24 of the cabinet wa1122, and lower
heater wire
34 is located to heat the lower portion 26 of the cabinet wall 22. Frost 50 is
shown in
Figure 4 as formed on the upper portion 24 of the cabinet wall 22. Figure 5
shows a
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first mode of operation, wherein the frost 50 is melted and reformed as ice 52
on the
lower portion 26 of the cabinet wa1122. Figure 6 shows a second mode or full
defrost
mode of operation, wherein a portion of the ice 52 and any additional frost is
melted
for removal by a user. The operation is controlled by the controller 98
(Figure 3) for
automatically effecting a predetermined cycle of operation of the compressor
96 and
the heater wires 33, 34 at predetermined, preferably regular, intervals.
The first mode of operation is preferably performed on the freezer 10 at
regular
intervals, for example, a 12-hour compressor 96 run time interval. In the
first mode of
operation, a first step in the cycle is that the compressor 96 may be
temporarily turned
off by the controller 98. The next step is the upper heater wire 33 is then
energized by
the controller 98 to melt the frost 50, the melted water being reformed as ice
52 on the
lower portion 26 of the cabinet wall 22. Since the compressor 96 is only
recently
turned off, the lower portion 26 remains sufficiently cold for refreezing of
the melted
frost. Frost 50 is undesirable as it may act as an insulator that reduces heat
transfer
efficiency in the evaporator tubing 16 through the inner walls 12 of the
cabinet and
impedes proper air circulation. On the other hand, ice 52 has a higher density
than
frost 50, and is substantially free from gas or air filled interstices.
Accordingly, ice 52
has less insulating properties than frost 50, and heat transfer between the
evaporator
tubing 16 and the interior 20 of the freezer 10 may be improved when frost 50
is
melted into ice 52. The upper heater wire 33 is thus activated by the
controller 98 for
a time to melt the frost 50. As can be appreciated, the upper heater wire 33
is
preferably heated for a selected time, dependent on the wattage, sufficient to
melt the
frost 50, but not so as to substantially increase the temperature of the
interior 20 of the
freezer 10. The last step in the cycle is that the controller 98 de-energizes
the upper
heater wire 33 and turns the compressor 96 back on for normal operation of the
freezer 10. After the next predetermined interval, for example after 12 hours
of
compressor 96 run time, the above described cycle is repeated, by melting the
frost 50
and refreezing the melted water into ice 52. The desired time of operation and
the
wattage of the heater wires 33, 34 may vary depending on the freezer 10 and
may be
determined by experimentation.
The following configuration may be used in one preferred form of the first
mode of
operation. The upper heater wire 33 and lower heater wire 34 may for example
be
rated at 2.5 watts per linear foot. This value is in compliance with the
Underwriters
Laboratories Inc. (TM) Commercial Freezers standard 471, which requires that
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resistance-type heater wires employed to prevent condensation are considered
in
compliance if the insulation is rated 176 F (80 C) or higher, the input is
less than 2.5
watts per foot (8.3 W/m), and adjacent heater wires are maintained not less
the 3/4
inch (19.1 mm) apart. Each heater wire 33, 34 will generate approximately 150
watts
of heat. It is suitable for the inner walls 12 to reach a maximum of about 50
F (10 C).
This configuration has been found to be suitable for melting of the frost 50,
without
significantly increasing the temperature of the interior 20 of the freezer 10.
The
thermal mass of the food product may also assist in compensating against the
slight
increase in temperature within the interior 20 of the freezer 10.
In another embodiment, the ice 52 acts as a "holdover cooling" feature, as
best
illustrated in Figure 5. In the interior 20 of the freezer 10, the ice 52 may
be frozen to
temperatures of around -25 F (-32 C) and lower. When the compressor 96 is
turned
off (either for the first mode of operation or other reasons, such as blackout
or circuit
malfunction), the ice 52 assists in maintaining the low temperature of the
interior 20
of the freezer 10.
The second mode or full defrost mode of operation is preferably performed on
the
freezer 10 when necessary, such as once every few months. A manual or
automatic
timer may be used to perform the cycle of operation constituting the second
mode. In
a first step of the cycle, the compressor 96 may be temporarily turned off by
the
controller 98. As shown in Figure 6, the lower heater wire 34 is then
energized by the
controller 98 to melt a portion of the ice 52. The ice 52 may then be removed
by a
user by gently prying the ice 52 from the inner walls 12 using a plastic
object such as
a spatula (not shown). The ice 52 may also fall to the base 14 of the freezer
10 for
removal by a user, as shown in Figure 6. The controller 98 then de-energizes
the
upper heater wire 33 and turns the compressor 96 back on for normal operation
of the
freezer 10.
In another embodiment, as best illustrated in Figure 6, instead of solely the
bottom
heater wire 34 being energized by the controller 98, both the top heater wire
33 and
bottom heater wire 34 are activated to melt a portion of any ice 52 or frost.
This
facilitates removal of any ice 52 or frost accumulated anywhere on the inner
walls 12,
by gently prying or removing by a user.
Figure 7 shows a perspective sectional view of a vertical cold-wall type
freezer 70 in
accordance with another embodiment of the present invention. The freezer 70
has
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three side cabinet walls 82, an upper cabinet wall 83, and a base 74. The side
cabinet
walls 82, upper cabinet wall 83, and base 74 form a rectangular box, and
thereby
define an interior 84 of the freezer 10 and an opening 81 for access to the
interior 84.
In the example shown, there are three inner side walls 72, a serpentine coil
of
evaporator tubing 76, a heater foil 78 adhered thereon, a thermal insulation
88, a
condenser tubing 80, and an outer wall 92. There is also a shelf 90 for
support of
products in the freezer 70. The opening 81 usually has a door (not, shown)
constructed thereon.
The inner side walls 72 may be used to conductively exchange heat for cooling
of the
interior 84. The evaporator tubing 76 surrounds an exterior of the inner side
walls 72
for cooling of the interior 84 of the freezer 70. The evaporator tubing 76 is
connected
to a compressor (e.g., 96 in Figure 3), as is known in the art. The evaporator
tubing
76 acts as a cooling member, so that the interior 84 of the freezer 70 becomes
cooled
by heat transfer through the inner side walls 72.
Heater foi178 is adhered exterior to the three inner side walls 72 and also
covers a
region of the inner side walls 72 proximate to the opening 81. For
illustrative
purposes, heater foil 78 is shown cutaway so that the evaporator tubing 76 may
be
shown. A heating of the heater foil 78 will melt frost accumulation on the
inner side
walls 72.
Thermal insulation 88 is exterior of the heater foil 78 and provides
insulation between
the evaporator tubing 76 and condenser tubing 80. In the example shown, the
condenser tubing 80 is in a serpentine configuration and attached to an inside
surface
of the outer wal192. At an end of the condenser tubing 80 is an expansion
valve (e.g.
97 in Figure 3), as in known in the art. The outer walls 82 may be formed of
metal or
other conductive material and may be utilized as a heat transfer surface for
the
condenser tubing 80. Accordingly, heat from the condenser tubing 80 is
released to
an exterior of the freezer via the outer walls 82, as is known in the art.
The heater foil 78 is similar to the heater foil 18 as shown in Figure 3, as
explained
above. Thus, similar to heater foil 18, there is a heater wire (not shown)
defining an
upper region and a heater wire (not shown) defining a lower region.
The operation of the vertical freezer 70 is similar to the operation of the
horizontal
freezer 10, as illustrated in Figures 4 to 6, explained above. Thus, the
freezer 70 is
operable in a first mode of operation and in a second or full defrost mode of
operation. For illustrative purposes, the heater foil 18 will be used, as
shown in
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Figure 3. In the first mode of operation, the first step is the compressor 96
may be
temporarily turned off by the controller 98. The next step is the upper heater
wire 33
is then energized by the controller 98 to melt the frost 50, the melted water
being
reformed as ice 52 on the side cabinet wall 82. The upper heater wire 33 is
thus
activated by the controller 98 for a time to melt the frost 50. The controller
98 then
de-energizes the upper heater wire 33 and turns the compressor 96 back on for
normal
operation of the freezer 70.
In the second mode of operation, the compressor 96 may be temporarily turned
off by
the controller 98. As shown in Figure 6, the lower heater wire 34 is then
energized by
the controller 98 to melt a portion of the ice 52. The ice 52 may then be
removed by a
user by gently prying the ice 52 from the inner side walls 72 using a plastic
object
such as a spatula (not shown). The ice 52 may also fall to the base 74 of the
freezer
70 for removal by a user. The controller 98 then de-energizes the upper heater
wire
33 and turns the compressor 96 back on for normal operation of the freezer 70.
In
another embodiment, as best illustrated in Figure 6, instead of solely the
bottom
heater wire 34 being energized by the controller 98, both the top heater wire
33 and
bottom heater wire 34 are activated to melt a portion of any ice 52 or frost.
This
facilitates removal of any ice 52 or frost accumulated anywhere on the inner
side
walls 72, by gently prying or removing by a user.
While the invention has been described in detail in the foregoing
specification, it will
be understood by those skilled in the art that variations may be made without
departing from the scope of the invention, being limited only by the appended
claims.
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