Food preparation table with air blast chiller

A food preparation table comprises a storage compartment; a food preparation surface above the storage compartment; a cold wall tank adjacent the food preparation surface and above the storage compartment, the tank having a liner forming the inside walls and floor of the tank, refrigerant cooling passageways in heat transfer relationship on the outside of the liner; and support rails; a plurality of food storage pans each having flanges for supporting the pans on the support rails and side and bottom walls forming the food storage portion of the pan and extending from the flanges downwardly into the tank; a refrigeration system comprising a source of compressed refrigerant, an evaporator and interconnecting refrigerant lines that supply refrigerant to the evaporator and the tank refrigerant cooling passageways; and an air distribution system which circulates air past the evaporator to cool the storage compartment and inside the tank where it impinges on the inside walls of the liner and from there onto the walls of the food pans.

FIELD OF THE INVENTION 
The present invention relates to a food preparation table with a 
refrigerated compartment or tank into which open top pans for storing food 
products are placed. The present invention is particularly directed to an 
improved pizza preparation table. 
BACKGROUND OF THE INVENTION 
In the food service industry, there is a need for refrigerated food storage 
in which different food items are readily available for preparation of 
foods such as sandwiches and pizza. In the "fast food" industry it has 
become a common practice to utilize preparation tables, which make the 
foodstuffs conveniently available to preparation personnel while 
maintaining the foodstuffs properly refrigerated. 
Preparation tables, such as those used in fast food service, are typically 
constructed as a table in an arrangement, which provides refrigerated food 
storage and a work surface for food preparation. In a typical arrangement, 
the preparation table is provided with refrigerator cabinets under the 
table top for overnight food storage, a flat working surface at the front 
of the table top and a so-called "rail" which is part of the work area 
near the back of the table. The rail is an open-top refrigerated 
compartment usually extending the width of the table, with the open-top 
elevated several inches above the flat work surface at the front. The rail 
arrangement is used for ergonomic reasons and the refrigerated compartment 
thereof is provided with a plurality of open top food pans that are 
disposed side-by-side across the width of the rail. With the open top food 
pans supported near the upper surface of the rail, the food is easily 
reachable by the food preparation person standing at the front of the 
table. The refrigerated compartment in the rail is typically known as a 
"cold wall" pan or tank comprising a sheet metal open top pan or tank with 
refrigerant tubing bonded to the exterior surface of the pan liner. The 
tank constitutes the side walls and bottom wall of a refrigerated 
compartment and the food pans are supported therein by a rim or flange on 
the front and back of the pans which rest on ledge, or rails, inside the 
tank. 
One of the difficulties with this arrangement is that the food in the upper 
portion of the open food pans is subjected to the ambient room 
temperature, which may be high enough to cause degradation of the food 
quality. With the food pans supported so that they extend downwardly into 
the refrigerated compartment, the food in the bottom of the pans is 
adequately refrigerated, but the food in the top of the pans may not be. 
Several possible solutions to this problem have been suggested. One is to 
lower the temperature of the cold wall tank. However, in the case of a 
high ambient temperature, when the temperature of the air below the pans 
is reduced adequately to maintain the food in the upper portion of the 
pans sufficiently cooled, freezing of food in the lower portion is likely 
to occur. It is desirable, in general, for proper food preservation to 
maintain the food at a temperature no higher than 40.degree. F., but 
higher than the freezing temperature. 
Recently the National Sanitation Foundation (NSF) has promulgated a 
standard that requires all the food in the pans to be maintained at a 
temperature in the range of 33.degree. F. to 41.degree. F. Some food 
preparation tables have been promoted as meeting this standard. However, 
prior art food preparation tables have a number of drawbacks. 
For example, the food preparation table disclosed in U.S. Pat. No. 
5,363,672 has additional heat sink walls built on top of the typical cold 
wall pan, which are designed to provide an upper cooling zone above the 
product pans. One problem with this design is that the food preparation 
worker has to reach deeper to pick up food items in the pan. Worse yet, 
the heat sink walls are cold enough that moisture in the air can condense 
on them and run down into the product pans. 
Other food preparation table designs have relied on a curtain of cold air 
being blown across the top of the food pans. U.S. Pat. Nos. 5,168,719 and 
5,282,367 disclose food preparation tables with such a design feature. One 
drawback to this design is that the air that blows across the tops of the 
pans tends to dry out the food stored in the pans. Also, there is a high 
level of cold air lost to the room and warm air infiltration into the 
system. 
Another food preparation table design is disclosed in U.S. Pat. No. 
5,355,687. This design utilizes a plurality of cooling elements running 
perpendicular to the length of the tank. In this way each food product pan 
is surrounded on all sides by either the cold wall of the tank or an 
auxiliary cooling element. One of the problems encountered with this 
design is that the cooling area is thus divided up into "pigeon holes," 
and only product pans of the same dimension as the "pigeon holes" can be 
used. That is, a particular user cannot decide to interchange wider pans 
than those designed into the table. Since each food preparation table may 
be put to different uses, where different amounts of one product or 
another are preferably stored in an accessible location, and wherein the 
pan dimensions most desirable for use may change over the life of the food 
preparation table, if not quite frequently, this lack of flexibility is a 
distinct disadvantage, compared to most food preparation tables, where any 
combination of pan sizes can be utilized so long as they all fit within 
the length of the rail. Further, the amount of pan space is reduced by the 
space taken up by the auxiliary cooling elements. 
Other designs have removed the bottom of the tank so that the cold air in 
the storage cabinets comes into contact with the bottom of the pans. One 
drawback to this design is that anything that spills or condenses in the 
tank can fall down into and contaminate food stored in the lower cabinets. 
Another problem that has to be dealt with is that the food preparation 
table should be able to accommodate pans of the different standard depths, 
such as 4-inch and 6-inch deep pans. When 6-inch deep pans are to be used, 
there is very little room between the bottom of the pans and the 
conventionally designed cold wall tanks. If the tank were made taller, it 
would be more difficult to reach up into the pans to remove the food, and 
may not fit into the space available, which was designed for an earlier, 
shorter model food preparation table. Alternatively, if the tank were made 
deeper, it would encroach into the storage compartment space. 
Thus, there is a need for a food preparation table that can meet the NSF 
standard without the drawbacks noted above. In particular, it would be 
advantageous if a food preparation table could be constructed with little 
modification to conventional designs so that existing manufacturing 
fixtures and designs can be utilized as much as possible, and the 
resulting food preparation table will fit within the space designed for 
prior tables. 
SUMMARY OF THE INVENTION 
A food preparation table has been invented which can meet the NSF standard 
without the drawbacks noted above. In a first aspect, the invention is a 
food preparation table comprising a) a storage compartment; b) a food 
preparation surface above the storage compartment; c) a cold wall tank 
adjacent the food preparation surface and above the storage compartment, 
the tank comprising i) a liner forming the inside walls and floor of the 
tank; ii) refrigerant cooling passageways in heat transfer relationship on 
the outside of the liner; and iii) support rails; d) a plurality of food 
storage pans each having flanges for supporting the pans on the support 
rails and side and bottom walls forming the food storage portion of the 
pan and extending from the flanges downwardly into the tank; e) a 
refrigeration system comprising a source of compressed refrigerant, an 
evaporator and interconnecting refrigerant lines that supply refrigerant 
to the evaporator and the tank refrigerant cooling passageways; and f) an 
air distribution system which circulates air past the evaporator to cool 
the storage compartment and inside the tank where it impinges on the 
inside walls of the liner and from there onto the walls of the food pans. 
By using an air circulation system that causes air to impinge on the cold 
wall of the liner and then to contact the product pans, the pans can be 
adequately cooled without freezing the content of pans. The air 
circulation system can be built into existing pizza preparation table 
designs with fairly little modification. Preferably the temperature of the 
walls of the tank is set by an evaporator pressure regulating (EPR) valve 
such that there is no chance that the impinging air will be cold enough to 
freeze food in the product pans, even if the lids on the pizza table are 
closed over the tops of the pans, such as at night when the table is not 
in use. 
These and other advantages of the invention will be best understood in view 
of the attached drawings.

DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS OF THE 
INVENTION 
The preferred food preparation table of the present invention is a pizza 
preparation table 1 as shown in FIGS. 1-8. The pizza table 1 is very 
similar to a two-section pizza preparation table Model PTA-20 from McCall 
Refrigeration, Parsons, Tennessee. Because of that similarity, many 
details of the pizza table 1 will not be described herein. Instead, those 
features by which the Model PTA-20 was modified to create the present 
invention will be focused on. 
The pizza table 1 is conventional in that it has a cabinet 5 that encloses 
two bottom storage compartments 17 (FIG. 2), closed by cabinet doors 6, 
and a machine compartment 10, housing a compressor and condenser (shown 
schematically in FIG. 12). On top of the cabinet are a tabletop 4 and a 
cold wall tank 3. Tank lids 16 may be closed when the table 1 is not in 
use. Inside the tank 3 are multiple food product pans 2, only two of 
clarity. In use, the entire tank 3 would be filled with pans 2, which can 
have different widths depending on the preference of the user. 
The pizza table 1 is also conventional in that an evaporator coil 9 is 
located between compartments 17 in a wall structure with fans 8. The fans 
draw air up from the bottom of the compartments 17, past the evaporator 
coil 9 and circulate the refrigerated air throughout the compartment 17. A 
drip tray 7 is located under the evaporator coil to collect any moisture 
that may condense on the evaporator coil 9. 
The cold wall tank 3 is also conventional in some respects. It is made with 
of two pieces of sheet metal formed into respectively an inner liner 19 
and an outer housing 18 with foam insulation 12 in between, best seen in 
FIG. 5. Refrigerant passageways are connected in a heat transfer 
relationship with the liner 19. Preferably, refrigerant tubing 25 is taped 
with metal tape to the outside of the liner 19 and covered with foam 
insulation 12. 
The cold wall tank 3 and cabinet 5 have been modified in the first 
embodiment of the invention to include a blower 13 (FIGS. 2 and 4), a tank 
supply duct 15 and an air return duct 14, best seen in FIGS. 4-5. A 
channel 22 acts as a supply air inlet between the blower 13 and the supply 
duct 15. In FIG. 4 the supply air duct 15 is shown in full lines up above 
the tank 3, and in phantom lines within the tank 3 on the bottom of the 
liner 19 where it is properly positioned for use. A return air duct cover 
28 covers the opening of the air return duct 14 in the bottom of the tank 
3. Preferably the cover 28 is held on by nylon screws 29. 
It should be noted that the liner 19 is made with a sloped bottom, as is 
conventional, so that any condensate in the tank 3 will run to one end and 
out a drainpipe 21. As a result, the tank duct 15 in this first embodiment 
has a different height over its length, so that it will fit under the 
deepest product pans 2 to be used in the tank 3. The location of the 
blower 13 and hence the supply air inlet 22 into the duct 15 is generally 
going to coincide with the location of the evaporator coil 9, so that 
cooled air coming directly off of the evaporator coil will be forced 
through the blower 13 into the duct 15. On the other hand, the location of 
the return air inlet 14 is positioned so as to return air from the tank 3 
into one of the compartments and to best regulate airflow within the tank. 
For example, the evaporator coil is generally located off center of the 
table 1, since it is between the compartments 17 and the compartments 17 
are of equal size but the machine compartment 10 fills up one end of the 
cabinet 5. Since the tank 3 is usually as long as the entire cabinet 5, 
the supply air inlet 22 will typically be located (at least in a two 
compartment pizza table) closer to one end of the duct 15 than the other. 
Also, because the duct has different cross sectional heights to 
accommodate the slop of the bottom of the liner 19, airflow out the ends 
of the duct 15 will not be uniform. Placement of the air return can then 
be designed to assure proper airflow within the tank 3. 
The most significant aspect of the duct design is that it causes air to 
impinge on the end walls of the tank 3, which are fitted with refrigerant 
cooling as explained below. The air is preferably forced by the blower 13 
at high flow rates, such as 50 cfm at 0.2 inches of water static pressure. 
The air thus exits the ends of the duct 15 at a high velocity so that it 
has good convection heat transfer with the chilled end of the tank 3. In 
one embodiment, the duct 15 is only 1/8 inch shorter than the inside of 
the liner 19. As a result the duct end is only 1/16 of an inch from each 
end of the liner. The preferred duct 15 has an opening of about 3/4 inch 
high at one end and 3/16 inch high at the other end. 
In the embodiment depicted in FIG. 4, extra supply air outlets 23 are 
formed in the top of the duct. However, at present it is believed that 
these outlets are not very effective because the air that flows through 
them, while being cooled by evaporator coil 9, does not impinge on the 
cold walls of the tank, and hence is not cold enough to adequately cool 
the food product pans 2. Therefore preferably only two outlets 23 are 
provided. 
As noted above, the end walls of tank 3 need to be cooled for the duct 
embodiment of FIG. 4. This is accomplished by adding additional 
refrigerant tubing 24 in heat transfer connection with the ends of the 
tank liner 19. The refrigerant tubing in place on the outside of the liner 
19 is shown in FIG. 6. The shape of the additional refrigerant tubing 24 
prior to being folded on its ends to fit against the end walls of the 
liner is shown in FIG. 7. FIG. 8 shows the conventional refrigerant tubing 
25 that is used on the bottom and side walls of the liner 19 before it is 
bent. In the preferred embodiment of the invention the additional section 
of refrigerant tubing 24 is connected at one end with the regular section 
25. The second ends of the extra tubing 24 and regular tubing 25 are 
connected to the remainder of the refrigeration system in a conventional 
fashion. 
FIG. 12 shows the refrigeration system used in the preferred embodiment of 
the invention. It is conventional in that the refrigeration system circuit 
includes a compressor 31, a condenser 32 (housed in machine compartment 
10) as well as a conventional receiver tank 33 and filter/drier 34. From 
the filter/drier 34 refrigerant can flow to either evaporator 9 in the 
storage bin or to the cold wall evaporator 35, made up of tubing sections 
24 and 25 in cold wall tank 3. Conventional thermal expansion valves 36 
and 37 precede the evaporator on both parts of the system. An evaporator 
pressure regulating (EPR) valve 38 is included on the cold wall tank 
portion of the refrigeration circuit. However, both portions of the 
circuit are rejoined at a common suction line back into the compressor. 
When a thermostat (not shown) in the storage compartment 17 indicates a 
need for more refrigeration, the compressor starts up. The thermal 
expansion valves 36 and 37 meter refrigerant into the evaporators 9 and 
35, depending on the outlet temperature of the evaporators. 
During the compressor on time, the EPR valve 38, with a pressure setting of 
62 PSIG, keeps the tank wall temperature from falling below 25.degree. F. 
During the compressor off time, the refrigerant (preferably 404A) that 
remains in the cold wall tubing sustains the tank temperature until the 
compressor restarts. 
The temperature of the air stream coming off the ends of the tank liner 
from duct 15 stays between 33.degree. to 35.degree. F., about 8 to 
10.degree. F. above the tank wall temperature. This circulating air 
provides the dominant cooling mechanism for the product in the pans 2. 
Even though the tank walls are below freezing, the pans 2 are kept from 
freezing because they are suspended in the well of the tank and do not 
contact the side or end walls of the liner 19. 
FIGS. 9, 10 and 11 show second, third and fourth embodiments of the cold 
wall tank. In the second embodiment shown in FIG. 9, the duct 115 is 
slotted on its sides, and preferably still open on its ends. As a result, 
air is forced out of the slots 118 on the sides of the duct and impinges 
at a high rate of speed on the side walls of the liner 19. The refrigerant 
tubing for this embodiment may be modified so that the side walls are 
provided with adequate heat transfer. 
In the third embodiment, shown in FIG. 10, slots 218 are provided in the 
ends as well as on the sides of the duct 215. Hence air impinges not only 
on the side walls, but also on the end walls of the liner 19, which are 
appropriately cooled. The sides and ends of the duct can be beveled, such 
as at a 45.degree. angle as shown, so that the air is blasted upward and 
outward toward the walls of the tank. 
In the fourth embodiment, shown in FIG. 11, the duct is in the form of a 
closed loop pipe 316. The pipe includes slots 318 on the sides and the 
ends of the rectangular loop. The slots are preferably positioned on the 
outside of the pipe so as to direct the air partially upward as well as 
outwards toward the walls of the liner. The pipes can have round cross 
sections as shown, or could be oval, triangular, square or some other 
cross section. 
Preferably the duct, regardless of its construction, will be configured so 
that the air exits the duct in close proximity to the walls of the tank, 
to maximize the connective heat transfer. 
The preferred pizza tables have several advantages. Full or half size metal 
pans or their combination may be used. The pizza tables do not employ an 
air curtain. Accordingly, the air movement in the surrounding environment 
does not affect the on-going cooling process in the tank. Pans are blast 
chilled from the sides and bottoms. Food products stored in the pans will 
not be dehydrated or adversely affected by the blasting air under the 
pans. Access to the food product pans is full and unrestricted by 
confining barriers. No hutch, skirt or other confining walls are used 
around the products. On the other hand, the bottom of the tank is not open 
to the food storage cabinets below. A cover over the return air duct 
prevents food dropped inside the tank from falling through the return air 
inlet. Cabinet internal spacing is not occupied or restricted by auxiliary 
components such as blowers or ductwork. The blower used is in the wall 
between the compartments 17. Storage capacity in the compartments 17 is 
not reduced by a deepened tank that would occupy part of the compartment 
17 storage space. The tables can be built using many of the same parts and 
manufacturing fixtures used to build other food preparation tables. 
It should be appreciated that the apparatus of the present invention is 
capable of being incorporated in the form of a variety of embodiments, 
only a few of which have been illustrated and described above. For 
example, in a larger pizza preparation table, having three compartments 17 
and two evaporators 9, two blowers 13 could be used to supply air to a 
common duct 15. Two separate refrigeration systems could be used, with 
their own compressors, condenser and thermostat, one for the cold wall 
tank and one for the food storage compartment. The invention may be 
embodied in other forms without departing from its spirit or essential 
characteristics. The described embodiments are to be considered in all 
respects only as illustrative and not restrictive, and the scope of the 
invention is, therefore, indicated by the appended claims rather than by 
the foregoing description. All changes that come within the meaning and 
range of equivalency of the claims are to be embraced within their scope.