Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF TEIE INV~NTION
The present invention relates to single air condult
refrigerated display cases having an ambient air defrost sytem.
Of primary concern are display cases having access openings in
their front walls. Both within the specification and the claims
of the present application, all references to refrigeration
apparatus or refrigeration operations are intended to include
cooling both at a temperature below 32F, such as associated with
frozen food display cases, and in excess of 32F, such as
typically associated with dair~ food and fresh meat display
cases.
Refrigerated display cases having only a single air
conduit with both front and top access openings have been used
for many years. Such open front cases are conventionally
utilized for displaying dairy and meat productsO
In the operation of all types of refrigerated display
cases, it is desirable to include a system capable of
automatically defrosting the display case. The defrost
cycle can be actuated either at set periodic times or when
the frost buildup within the system has reached a certain
predetermined level. Such systems are typically thermostat-
ically controlled so as to switch from a refrigeration cycle
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to a defrost cycle of operation. By this manner of operation,
it is possible to avoid any significant frost buildup within
the display case.
Typically within the prior art, there have been
three different approaches employed for defrosting refriger-
ated display cases. The Eirst approach involves the use of
electric resistance heaters that are arranged adjacent to the
refrigeration coils of the refrigeration mechanism. During
a defrost cycle, these heaters supply heat in an effort to
` 10 melt the frost buildup on the coils but also adds warmer air
to the air conduit for circulation within the case. The
particular technique is relatively simple both in its construc-
tion and operation. However, since the electrical heaters
are high voltage heaters that utilize significant electricity
during operation, with the rapidly increasing cost of electric-
ity it has become extremely uneconomical to employ such systems.
Furthermore, the warm air circulated in the case can raise
the temperature of the case too high. Thus, attempts have
been made to find other alternatives to such a system.
A second type of system circulates hot compressed
- gaseous refrigerant through the refrigeration coils during
the defrost cycle. During the defrost ~cycle, a valve control
mechanism shuts off the supply of refrigerant to the refrigera-
: tion coils and alternatively feeds superheated compressed
gaseous refrigerant through the coils. This hot gas serves
~; to melt any frost buildup that has occurred on the refrigera-
: tion coils but simultaneously provides heat within the air
conduit which can be circulated through the display case,
which again is disadvantageous. While this type of system
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does not suffer from the high cos-t of opera-tion of the
electrical heater defrost system, the heated gas sys-tem
involves a relatively high construction cost. Due to the
requirement that the system be able to selec-tively switch
between the supply of heated gas and refrigerant to the
refrigeration coils, a complicated valving structure must
- be provided. Such a mechanism significantly increases the
cost of construction of the display case. In addition,
the provision of such a complicated system only increases
- 10 the number of complex parts capable of breaking down and
necessitating costly repairs.
The third type of system employed for defrosting
display cases relles upon ambient air. It is this general
category with which the invention of the present application
is concerned. One type of system that employs ambient air
during the defrost cyle is exemplified by those embodiments
illustrated in U.S. Patent Nos. 3,403,525, 3,850,003 and
3,937,033, all to Beckwith et al. Each of these systems
uses fans separate from the main air circulating fans. These
extra fans are turned on during the defrost cycle for pulling
- ambient air from outside of the display case into the air
conduits. A second type of system is illustrated in U.S.
Patent No. 3,082,612 to Beckwith, which system draws ambient
air into the main circulation path through ports located in
the lower front panel of the refrigerated display case. Such
ports are normally closed during the refrigeration cycle and
are opened during the defrosting-cycle. The Beckwith et al.
'003 patent indicates that the concepts described in patents
Nos. 3,082,612 and 3,403,525 did not prove to be practical
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and hence were not commercially feasible.
Finally, a third type of ambient air defros~ing
system is shown in U.S. Pat~nt No. 4,144,720 to Subera et al.,
which is assigned to the same assignee as the present applica-
tion. In the foregoing patent application, an open frontrefrigerated display case having primary and secondary air
conduits is disclosed. In this system, reversible fans are
employed for reversing the direction of flow of air within
the conduits and simulataneously drawing in air from outside
of the display case.
Another system employing reversible fans for ambient
air defrost is shown in U.S. Patent No. 4,026,121. This
patent, however, refers to short-circulating the air flow
between the primary and secondary air bands for the purpose
of supplying warmer air to the primary band.
It has been recognized that an ambient air defrost
operation can be incorporated into an open top refrigerated
display case as disclosed in U.S. Patent No. 4,120,174 to
- Johnston. The Johnston patent illustrates an open top case
having a single air conduit extending around the c;ase.
During the refrigeration cycle, the air flows in a first
direction and during the defrost cycle the direction of the
air flow is reverse with ambient air being drawn into the
conduit. The quantity of air flow during the defrost cycle
~ ~is greater than during refrigeration. The defrost air,
after passing through the conduit, is expelled in a direction
up and over the refrigerated case. It has been found during
the development of the present inventlon, that with a defrost
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air flow pa-ttern such as disclosed in the Johnston paten-t a
significant portion of the expelled air will fall back towards
the access opening in the refrigerated case and reenter the
air conduit at the other side of the access opening.
Similar to the open top display case of the above-
identified patent to Johnston, there also are open front
single air conduit cases which employ the same air defrost
techniques as disclosed by the Johnston patent. During
the defrost operation of such air defrost cases, the volume
of the reverse air flow is relatively high and significantly
greater than the air flow flow during the refrigeration cycle.
Such a greater air flow is utilized so as to minimize the
time needed for the defrost operation. As shown in Figure 1,
which illustrates this type of prior art display case, the
higher air volume flow causes the warmer defrost air to
re-enter the display case which potentially can damage the
products in the case. In addition the greater air flow
causing the cold air to flow upwardly can result in hitting
the customer in the face with such cold air.
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SU~M~RY OF T~E INVENTION
An object of the present invention is to provide
an improved ambient air defrost system within a single air
conduit open front refrigerated display case.
Another object of the present invention is to
provide an energy efficient open front refrigerated display
case employing an improved ambient air defrost system in
which the ambient air is drawn into the air conduit by re-
versing the direction of flow of air through the conduit.
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A further object of the present invention is to
provide an open front refrigerated display case having a
single air conduit and a reversible fan arranged within the
conduit for propelling air in a forward direction through
the refrigeration coils during a refrigeration cycle and
circulating air in a reverse direction so as to draw in
ambient air from outside of the case during a defrost cycle
and to prevent the defrost air when expelled from the conduit
from being drawn back into the refrigerated case.
A still further object of the present invention
is to provide an improved procedure for defrosting an open
front refrigerated display case by the use of ambient air.
These objectives are achieved by the utilization
of a refrigerated display case with a front access opening
that is constructed in accordance with the present invention.
The display case is providedwith an approximatel~ U-shaped
air conduit that extends around the display case and has
openings at its opposite ends at opposite sides of the access
opening of the display case. Arranged within the air conduit
are the refrigeration coils and at least one reversible fan.
- In larger display cases, it is often necessary to use either
two or three fans spaced along the longitudinal axis of the
_ case in order to generate a sufficient force for circulating
the air; in such a system, however, each fan preferable
would be a reversible fan and operate in the same manner
as disclosed herein in accordance wi-th the present invention.
The reversible fan arranged within the U-shaped
air conduit is capable of either circulating in a first
direction towards the refrigeration coils during a refrigeration
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cycle or when the case is switched into a defrost cycle
circulating the air in a second, opposite, direction. For
the sa~e of convenience herein, the first direction shall
be referred to as the forward direction and the second,
opposite, direction as the reverse direction. The openings
in the ends of the air conduit are aligned so that during
the refrigeration cycle, refrigerated air leaves a first
of the openings in a path towards the second opening so as
to form an alr curtain across the access opening in the display
case. This air travelling across ~he access opening in the
display enters the second opening in the air conduit and is
drawn along the conduit back towards the fan thereby establish-
ing a continuous refrigerated air band. When the display
case is switched into a defrost cycle, th~ refrigeration
coils are deactivated and the direction of air flow is re-
versed. The volume of the air flow during defrost is lower
than the volume during refrigeration. During such reverse
air flow, the air leaves the air conduit through the second
opening. The air leaving the conduit is cooler than the
ambient air since it has passed over the refrigeration coils
for defrosting them; this expelIed defrost air being some-
what cooled, therefore, is denser than the ambient air.
The dense defrost air being propelled at a lower volume and
hence slower speed will fall to the floor as it leaves the
air conduit. Hence the defrost air falls away from the display
case; i.e., towards the outside of the display case, thereby
preventing portions of the defrost air from reentering the
case and travelling across the access opening in the case
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and being drawn back into the air condui-t. With such an
air flow pattern, the defrost air also will not hit the
customer in the face with cold air. The area of the second
opening can be constructed to help direct the defrost air
flow away from the display case. Consequently, during the
reverse flow of air no air curtain is established and hence
ambient air from outside of the case is drawn in through
the first opening in the air conduit. Such ambient air
being warmer than the refrigerated air serves to defrost the
refrigeration coils.
It is advantageous to avoid having the defrost
air flow reenter the display case and also reenter the air
conduit. While the ambient air as it passes over the evapora-
tor coils expels heat to the coils and the air drops in
temperature, the temperature of such air is still warmer
than the temperature to which the products are refrigerated.
If the defrost air reenters the conduit then this will
significantly slow down the defrost operation. In addition,
if the defrost air contacts the products it will raise the
temperature of the products. By causing the defrost air
to fall away from the refrigerated case, the products are
protected without detrimentally increasing the defrost time
perlod .
As frost accumulates-on the evaporator coils during
the refrigeration cycle, the conduit becomes blocked. Hence
when the defrost cycle is initiated the ~uantity of air flow
will be substantially less than the air flow during the
refrigeFation cycle. As the defrost cycle continues and the
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frost is eliminated, the defrost air flow will rise back
toward the level of the re~rigeration air flow, although
not surpassing it.
In order to eliminate the buildup of condensation
and frost on the grill structures mounted at the openings
at the ends of the air conduit, it may be desirable to pro-
vide some type of mechanism for generating heat in these
areas. For this purpose, within each of the areas, tubes
containing the liquid refrigerant used in the system can
be provided. These tubes are connected to the line that
carries the liquid refrigerant for the refrigeration coils.
Since the liquid refrigerant is warmer than the refrigerated
air, the tubes provide a limited quantity of heat within
each of the openings. The quantity of heat, however, is
sufficient to help eliminate the condensation and the re-
sulting buildup of frost.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional side elevational view of
- an open front refrigerated display case in accordance with
the prior art, when the display case is operated during a
; defrost cycle with the air flow being relatively high.
Figures 2 and 3 are sectional side elevational
views of one embodiment of an open front refrigerated display
case in accordance with the present invention, with Figure 2
showing the air flow pattern during refrigeration and
Figure 3 showing the pattern during defrost.
Figures 4 and 5 are views similar to Figures 2 and
3 respectively of another embodiment of the present invention.
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DESCRIPTION OF THE PREFERRED EMBODIMENTS
An open front refrigeratecl display case 2 construc-t-
ed in accordance with the present invention is illustrated in
Figure 2. The display case has top, bottom, rear and side
walls along with a partial front ~all. All of these walls
are appropriately insulated. Front wall 4 has an access
opening 6. Positioned above bottom wall 8 are a plurality
of shelves 10, 12 and 14. The spacing between shelf 10 and
bottom wall 8 is large enough to enable the fans and if
desired the refrigeration coils, which are described later
herein, to be arranged within that location. Extending along
the top wall, rear wall and bottom wall is an air conduit
16. Arranged within air conduit 16 is at least one fan 18.
While only one fan is illustrated, typically for refrigerated
cases that are eight feet long, two fans are employed and
for cases twelve feet long there are three fans. The number
of fans merely depends on the length of the case and the
sige of the fans but have no bearing upon the scope of the
present lnvention. All the fans arranged within air conduit
16 are reversible fans capable of being driven for propelling
air in either direction.
ir conduit 16 has openings 20 and 22 at both of
its ends at the top of the refrigerated display case. A
directional control grill 24 is mounted across opening 20.
Grill 24 is preferable constructed so as to assist in direct-
ing air leaving a:ir conduit 16 through opening 20 towards
opening 22 on the opposite side of access opening 6 of the
display case. At the opposite side of the display case
across opening 22 there is only positioned a cover plate
having a plurali-ty of openings. The cover plate arxanged
across opening 22 helpsto diffuse the air emitted during
defrost. Such air directing grill structure and cover plate
are generally known ln the prior art. In addition to help-
ing in controlling the direction of Elow of the air enteringand leaving openings 20 and 22, the grill and cover plate
also protect the openings from various debrls, such as trash,
keys and coins.
Refrigeration coils 26 are positioned within air
conduit 16 at a location either adjacent to or above fan
18, such as shown in the figures. In a conven~ional manner,
when the display case is operated in a refrigeration cycle,
the air passing through refrigeration coil 26 is cooled,
or refrigera-ted. The extent to which air is cooled depends
on the use to which the display case is to be put. If the
display case is to serve for holding frozen food, then the
air must be sufficiently cooled so as to maintain the
interior of the case below 32F. If, however, the display
case is used for storage of non-frozen products, such as
20~ dairy products, then a termperature slightly in excess of
- 32F can be maintained. The term refrigeration, however,
as used herein is intended to cover both types of system.
- Turning now to the structural arrangement in the
area of opening 22, as shown in Figures 2 and 3, the inner
surface 28 of the top part of the lower portion of front
wall 4 is sloped in a direction towards the outside of dis-
play case 2. This sloped construction of surface 28 helps
to direct air leaving conduit 16 through opening 22 during
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a defrost operation in a direction away from the display
case as shown by the arrows in Figure 3.
During the refrigeration cycle of operation of
the display case, air is circulated through air conduit
16 by fan 18 in a forward direction towards and through
refrigeration coils 26, which are activated for cooling.
The volume of air flow during refrigeration is between 1000
and 1400 cfm. The air is cooled wllen passing through refrig-
eration coils 26. The cooled air then travels through tlle
remaining portion of conduit 16. As the air reaches opening
20 in conduit 16, it is forced out through grill 24 in a
direction towards opening 22. In this manner, a curtain of
cooled air is established across access opening 6 of the
display case. The cooled air serves to refrigerate the
lS products in the display case and also separate the warmer
ambient air outside of the display case from the cooler
air inside of the display case.
The air emitted through grill structure 24 and
traveling across the access opening is received into open-
ing 22 in the air conduit. This air is then drawn back intoair conduit 16 by a suction force established by fan 18.
Thus, during the refrigeration cycle a continuous band of
cooled air is circulated by fan 18 through the display case.
The direction of travel of such air along the air band is
illustrated in Figure 2.
Turning now to the defrost cycle, the air flow
during this cycle of operation is illùstrated in Figure 3O
In any one of different conventional manners, the display
case can be thermostatically or otherwise controlled so as
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-to switch between the refrigeration cycle and the defrost
cycle. By one such technique, the switching can occur when
a cer-tain degree of frost bui.ldup is detected on the refrig-
eration coils. Another possible alternative is at set time
intervals to switch the operation of the display case from
a refrigeration cycle to a def.rost cycle.
During the defrost cycle, the operation of fan
18 is reversèd so as to propel air in a reverse direction
away from refrigeration coils 26. When the fan is operated
in this mode, air passes along conduit 16 out through open-
ing 22. The air upon exiting from opening 22 is diffused
and falls to the floor outside of the.case. In addition,
the lower portion of wall 4 at its upper end has sloped
inner surface 28. As the air leaving conduit 16 during the
defrost cycle passes along sloped wall 25, the path of air
curves into an arc directed up and away from display case 2.
Thus, in this mode of operation, there is no air curtain
established across the access opening of display case 2 and
also no continuous air band established through the display
case. The volume of air flow during the.defrost operation
is between 800 and 1100 cfm and should be less than the
air flow during refrigeration. If the air flow during defrost
is increased to above 1600 cfm then a curtain of air will
be es-tablished across access opening 6 during the defrost
25: operation.
As air is propelled out of conduit 16 through
opening 22, a partial vacuum is estabiished within the air
conduit so as to cause air to be sucked into the conduit
through opening 20. Since there is no air curtain in
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existence across the top of the display case during the de-
frost cycle, the air sucked into the conduit through open-
ing 20 is drawn from the ambient air surrounding the display
case. Since such ambient air is of a higher temperature
than the refrigerated air during the refrigeration cycle,
such ambient air serves to defrost any frost buildup within
the system, lncluding, in particular, on the refrigeration
coils. The direction of air flow during the defrost cycle
is shown by the arrows in Figure 3.
Another embodiment of the invention is sho~n in
Figures 4 and 5. Display case 30 has an access opening 32
and an air conduit 36. The major difference between display
case 30 and display case 2 is the absence of sloped inner
wall 28. Otherwise both display cases operate in substantially
the same manner.
The present invention may be embodied in other
specific forms without departing from the spirit or essential
characteristics thereof. The present embodiments are pre-
sented merely as illustrative and not restrictive, with
the scope of the invention being indicated by the attached
claims rather thanthe foregoing description. All changes
which come within the meaning and range of equivalency of
the claims are therefore intended to be embraced therein.
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