Note: Descriptions are shown in the official language in which they were submitted.
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REFRIGERATED DISPLAY MERCHANDISER
WITH IMPROVED AIR CURTAIN
BACKGROUND OF THE IN17EI PI'I N
[002] The present invention relates generally to refrigerated display
merchandisers of
the type used in supermarkets, mini-marts, convenience stores and other
commercial
establishments for displaying and merchandising refrigerated or frozen
products for
sale. More particularly, the present invention relates to open-front
refrigerated display
merchandisers of the type wherein a curtain of cold refrigerated air is passed
downwardly across the open front product display region of the merchandiser.
[003] Refrigerated display merchandisers, also commonly referred to as display
cases,
having open front display regions are commonly used in supermarkets, mini-
marts,
convenience stores and other commercial establishments for displaying and
merchandising refrigerated or frozen products for sale. The open front nature
of such
display cases permits the consumer to simply reach into the product display
region to
select and remove a product for purchase without the inconvenience of needing
to open
a door to access the product. Customarily, a curtain of cold refrigerated air
is passed
downwardly at a relatively high velocity across the open front of the display
case to
form an invisible boundary between the product display region and the region
of the
store in front of the display case. This air curtain not only helps retain
cool refrigerated
air within the product display region of the display case, thereby cooling the
display
product on the shelves of the display case, but also functions to isolate, to
a certain
extent, the product display region from the ambient air within the store.
Ambient air
that does enter into open product display region undesirably causes increased
energy
consumption by increasing the cooling demand on the refrigeration system
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with the display case. Further, such ambient air may also cause a local
temperature rise
within the product display region sufficient to result in an undesirable rise
in product
temperature that could adversely impact upon product quality.
[Gp4] A problem encountered with vshen passing a curtain of refrigerated air
downwardly across the open front of the product display region of the display
case lies
in the entrainment of ambient air into the stream of refrigerated air forming
the air
curtain. Turbulence exists at the boundary between the relatively high
velocity c n
air and the generally quiescent ambient air lying in front of the display
case. As a result
of such turbulence, some ambient air is undesirably entrained into the air
curtain.
Multiple air curtain display cases have been developed in the prior art to
address this
entrainment problem. For example, display cases having two adjacent, parallel,
but
independently generated, air curtains of refrigerated air are common in the
art.
Typically, such as disclosed by Maehara in U.S. Patent 4,633,677, the
outermost air
curtain has a slightly higher temperature than the innermost air curtain, so
as to protect
the colder innermost air curtain from the impact of ambient air entrainment.
[005] Also, it is well known in the art to establish a third air curtain of
relatively high
temperature ambient air outwardly of one or two refrigerated air curtains as a
means of
reducing entrainment of ambient air from the store into the refrigerated air
curtains.
Abraham, in U.S. Patent 4,267,706, discloses establishing an ambient air
curtain
outwardly of an innermost refrigerated air curtain, with the outer ambient air
curtain
being directed downwardly parallel to and adjacent to the inner refrigerated
air curtain.
Beckwith et al, in U.S. Patents 3,648,482 and 3,850,003, MacMaster et al, in
U.S.
Patent 3,827,254 and Roberts, in U.S. Patents 5,345,778 and 5,357,767, each
disclose
establishing an ambient air curtain outwardly of a pair of refrigerated air
curtains. The
curtain closest the product display region of the display case is coolest,
while the center
curtain is at a temperature slightly warmer than the innermost curtain, but
substantially
cooler than the outermost ambient air curtain. The center curtain of warmer
refrigerated
air serves to buffer the innermost colder refrigerated air curtain from warrn
air intrusion
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from the outermost ambient air curtain. The outermost curtain of ambient air
is directed
substantially vertically downwardly, either parallel to and adjacent the
center air curtain
or slightly inwardly toward the center air curtain, so as to preclude
refrigerated air from
the center and innermost refrigerated air curtains from spilling out of the
prcduct
display region of the display case. The outerrnost ambient air curtain itself
ideally spills
into the store near the base of the display case so as to not be drawn into
the air return
inlets through which the refrigerated air curtains return to the evaporator
compartment.
[096] Although generally effective to substantially reduce the amount of
entrainment
of ambient air into the recycled refrigerated air as compared to a single air
curtain
design, significant entrainment still occurs in the case of refrigerated
merchandisers
having two or three air curtains. It is generally recognized that entrainment
is reduced
when adjacent air curtains in such multiple air curtain designs have
relatively the same
velocity so that shear instabilities at the interface between air curtains is
minimized.
Therefore, in typical prior art merchandisers, the respective discharge
velocities of the
separate air curtains, that is the discharge velocities of the respective air
streams as they
pass out of their respective nozzles at the top of the display case, are
designed to be
substantially equal, be there two or three air curtains present. However, as
the air
curtains flow downwardly, the outer air curtain tends to spread and spill into
the store
thereby reducing in velocity, while the inner air curtain tends to increase in
velocity due
to buoyancy effects and the addition of air from within the refrigerated
display case. As
a result, as the air curtains pass downwardly, the shear instabilities at the
interface of
adjacent air curtains increase, resulting in increased entrainment of higher
temperature,
moister air into the inner air curtain of refrigerated. Consequently, a need
exists for an
improved air curtain system that addresses the problem of entrainment into the
inner air
curtain of refrigerated air without significant expense.
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SUMMARY OF THE INVENTION
[007] The refrigerated merchandiser of the present invention includes a
display case
defining a product display region having an open-front isolated from the
ambient air of
the store by means of a downwairdly directed inner air curtain of relatively
cold
refrigerated air and a downwardly directed outer air curtain, most
advantageously of
relatively warmer air. In accordance with the present invention, the discharge
velocity
of the outer air curtain is maintained at a velocity at least 1.4 times the
discharge
velocity of the inner air curtain, and most advantageously in the range of
about 1.4 to
about 2.4 times greater than the discharge velocity of the inner air stream.
In a preferred
embodiment, the outer air curtain comprises ambient air.
BRIEF DESCRIPTION OF THE DRAWINGS
[008] Figure 1 illustrates a side elevatiorr profile of a preferred embodiment
of a
refrigerated merchandiser having an open-front display case with a dual stream
air
curtain separating a first environment within the display case from a second
environment external of the display case; and
[009] Figure 2 is a graphical presentation showing the variation of load
demand on the
cooling system associated with the refrigeration merchandiser as the air
curtain velocity
ratio changes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[010] Referring now to Figure 1, the refrigerated merchandiser 10 includes an
outer
cabinet 12 and an inner cabinet liner 20 that defines within its bounds an
open-front
product display region 30. The outer cabinet has a base 13, a rear wall 14
extending
upwardly from the back of the base 13, a top wall 15 extending forwardly from
the rear
wall and a pair of side walls 16 extending vertically from the base 13 to the
top wall 15
and forwardly f-rom the rear wall 14. The inner cabinet liner 20 has a top
panel2g, a
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back pane126, a bottom panel 24 and opposed side panels 23 which together
bound the
open-front product display region 30. Each of the cabinet base 13, rear wall
14, top
wall 15 and side walls 16 is insulated, as in conventional practice, to
thermally isolate
the interior of the cabinet 12, including the product display region 30, from
e~~ces'sive
heat transfer therethrough.
[011] Perishable product 80 being merchandized may be displayed on shelves lg
disposed within the product display region 30 and upon the upper surface of
the bottom
panel 24. The product display region 30 has an open front 25 so as to permit
consumers
to not only view, but also reach into the product display region 30 to select
and remove
items of product 80 that they desire to purchase. Product display region 30 is
cooled in
a conventional manner to a desired product temperature, typically to a
temperature
between -10 F to less than about 40 F, depending upon what product is being
merchandised therein and whether the product is frozen or non-frozen.
[012] The refrigerated merchandiser 10 further includes a refrigeration
compartment
40, typically disposed in the portion of the display cabinet 12 between the
base 13 and
the bottom panel 24, as depicted in Figure 1, wherein components of the
refrigerant
system, typically a tube coil evaporator 50 and a air mover 60, such as for
example one
or more fans, are housed. However, it is to be understood that the specific
type of air
mover employed is not relevant to or limiting of the present invention. As in
conventional practice, refrigerant passing through the tubes of the evaporator
40 cools
air passing over the surface of the evaporator tubes. The refrigerant is
typically supplied
from a remote refrigeration unit located elsewhere within the store. However,
it is to be
understood that the present invention may also be employed on stand-alone
refrigerated
merchandisers that include their own refrigeration unit for providing the cold
refrigerant.
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[013] An air circulation duct 32 is formed between the rear wall 14 and the
top wall 15
of the outer cabinet 12 and the back panel 26 and top panel 28, respectively,
of the inner
cabinet liner 20. Air mover 60 serves to direct air from air inlet 4.2 through
the
compartanent 40 so as to traverse evaporator 50, and thence through duct 32 to
a fara air
oeatlet 34. As noted before, this circulating air ha: been cooled to a desired
teraaperatum
as it traverses the evaporator 50. From the first air outlet 34, the cool
refrigeration air is
directed via vanes provided within the first air outlet 34 downwardly along
first path
across the open front 25 of the product display region back to air inlet 42.
Thus, the
refrigerating air is recycled and repeatedly recirculated through the
compartment 40 and
duct 32 to converse energy expended in cooling the refrigeration air. Further,
through
the afore-described cooling arrangement, a cool air curtain 45 is formed
across the
open-front product display region 30 from top to bottom thereof. To provide
further
cooling air directly to the product display region 30, a plurality of openings
24 may be
provided in the back panel 26 through which a portion of cold refrigerating
air
circulating through duct 32 may pass directly into the product display region
30. This
refrigerating air will also be drawn by the air mover back through the air
inlet 42 into
the compartment 40 to be recirculated.
[014] A second air outlet 70 is provided outwardly of the first air outlet 34
at the top
front of the cabinet 12. In contrast to existing refrigerated merchandisers,
second air
outlet 70 serves to direct relatively warm air generally downwardly along a
second path
lying outwardly of the first path followed by the cool refrigerating air. In
this manner, a
relatively warm outer air curtain 65 is formed outside, i.e. further away from
the product
display region 30, of the relatively cool inner air curtain 45. The relatively
warm outer
air curtain 65 serves as a buffer between the relatively cool inner air
curtain 45 and the
ambient environment of the store. Further, when the outer air curtain 65
reaches the
base region of the display cabinet 12, it spills outwardly into the store
rather than into
the air inlet 42 in the forward end of the base portion of the cabinet.
Consequently, the
entrainment of warm air into the relatively cool inner air curtain and
subsequent passage
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through inlet 42 into the compartment 40 is minimized, thereby reducing energy
consumption in cooling the recirculating refrigeration air.
[015] The first air outlet 34 and second air outlet 70 are located at top and
forward
region of display case 12, with the second air outlet 70 being located
outwardly of the
first air outlet 34, that is, closer to the front of the display cabinet 12.
As noted
previously, first air outlet 34 is in communication with duct 32 and directs
relatively
cool air driven by air mover 60 downwardly across open front of the product
display
region 30 to form the inner air curtain 45. The second air outlet 70 is in
fluid
communication with a source of relatively warm air, for example ambient air
from the
store, and directs relatively warm air driven by a second air mover 72
associated
therewith downwardly to form an outer air curtain 65.
[016] The outer air curtain 65 is directed downwardly at a discharge velocity
that is at
least 1.4 times greater than the discharge velocity of the inner air curtain
45. The term
discharge velocity refers to the velocity of the air stream discharging from
its respective
air outlet at the top of the display case 30. Ergo, the discharge velocity of
the inner air
curtain 45 is the velocity of the air stream discharging from air outlet 34
and the
discharge velocity of the outer air curtain 65 is the velocity of the air
stream discharging
from air outlet 70. Most advantageously, the discharge velocity of the outer
air curtain
65 is maintained at a level of about 1.4to about 2.4 times faster than the
discharge
velocity of the inner air stream 45.
[017] Referring now to Figure 2, the vertical axis thereof represents the load
reduction
factor, which is the refrigeration load of the dual air curtain compared to
the load for an
inner air curtain only, and the horizontal axis represents the ratio of the
velocity of the
outer air curtain in that of the inner air curtain. Accordingly, the lower the
load
reduction factor, the more effective is the dual air curtain. As illustrated
in Figure 2, the
effectiveness of dual parallel air curtains as a barrier in reducing passage
of flow across
the air curtain is maximized by maintaining the ratio of the discharge
velocity of the
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outer curtain to the discharge velocity of the inner curtain within the range
of from
about 1.4 to about I.S. Maintaining the air curtain velocity ratio within this
range
minimizes the velocity gradient, and therefore shear instabilities, between
the adjacent
air curtains along the length of the interface between the adjacent air
ctart,ains, thereby
resulting in less entrainment of air from the higher velocity air curtain into
the lw'ver
velocity air curtain. Therefore, an very effective separation barrier may be
maintained
between two enviromxaents through use of the present invention through a dual
air
curtain of parallel streams of a first and a second fluid by maintaining the
discharge
velocity of the outer air stream a level of about 1.4 to about 1.8 times
faster than the
discharge velocity of the inner air stream.
[018] The aforementioned description is exemplary rather than limiting. Many
modifications and variations of the present invention may be recognized by
those
skilled in the art in light of the above teachings that will fall within the
spirit and scope
of the present invention. The preferred embodiments of this invention have
been
disclosed. Accordingly, within the scope of the appended claims, the invention
may be
practiced otherwise than as specifically described. For this reason the
following claims
should be studied to determine the true scope and content of this invention.
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