Abstract:
In one aspect, a food thawing cabinet includes at least one thawing chamber and one or more wall blowers and a heater for producing a controlled high volume of air flow over food product, with the heater controlled in a cyclic manner. In another aspect, various advanced control techniques for controlling heat input are provided in an effort to lower the time required to thaw frozen food products in a safe manner.

Description:
CROSS-REFERENCE  
       [0001]    This application claims the benefit of provisional application Serial No. 60/438,954, filed Jan. 9, 2003, the entirety of which is incorporated herein by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present application relates generally to cabinets utilized for thawing frozen foods, and more particularly to a food thawing cabinet with an improved air flow system and heat control system for rapidly thawing frozen foods in a controlled, safe manner.  
         BACKGROUND  
         [0003]    It is known to provide thawing cabinets for thawing frozen food products in commercial environments such as restaurants and cafeterias. Achieving high speed thawing while maintaining food safety is an important consideration.  
         SUMMARY  
         [0004]    In one aspect, a food thawing cabinet includes at least one thawing chamber and one or more blowers and a heater for producing a controlled high volume of air flow over food products, with the heater controlled in a cyclic manner. High volume air flow and controlled heat input can effectively expedite the thawing process. In another aspect, various advanced control techniques for controlling heat input are provided in an effort to lower the time required to thaw frozen food products in a safe manner. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is front, upper perspective of one embodiment of a thawing cabinet;  
         [0006]    [0006]FIG. 2 is a front, lower perspective of the cabinet of FIG. 1;  
         [0007]    [0007]FIG. 3 is a perspective of a mullion part of the cabinet of FIG. 1;  
         [0008]    [0008]FIG. 4 is an enlarged view of a comer part of FIG. 3;  
         [0009]    [0009]FIG. 5 is another perspective view of the mullion part;  
         [0010]    [0010]FIGS. 6A and 6B are control drawings;  
         [0011]    [0011]FIG. 7A is a flow chart of one embodiment of a thawing operation;  
         [0012]    [0012]FIG. 7B is a flow chart of a standard refrigeration cycle;  
         [0013]    [0013]FIG. 8 is a flow chart of another embodiment of a thawing operation; and  
         [0014]    [0014]FIG. 9 is a flow chart of another embodiment of a thawing operation. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Referring to FIGS.  1 - 5 , a thawing apparatus  10  includes a cabinet structure  12  including a thawing chamber  14  and a thawing chamber  16 , with a mullion/center wall  18  separating the chambers. Two doors (not shown) may be provided on respective sides of the mullion  18  for providing access to the chambers  14  and  16 . The mullion  18  includes a side  20  facing the thawing chamber  14 , the side  20  having a plurality of air flow openings therein, including a set of air intake openings  22  for passing air from the thawing chamber  14  into an interior  24  of the mullion  18  and a set of air outlet openings  26  for passing air from the interior  24  of the mullion  18  to the chamber  14 . An opposite side  28  of the mullion faces the thawing chamber  16 , the side  28  also having a plurality of air flow openings therein, including a set of air intake openings  30  for passing air from the thawing chamber  16  into the interior  24  of the mullion and a set of air outlet openings  32  for passing air from the interior  24  of the mullion to the thawing chamber  16 . In the illustrated embodiment the air intake openings  22  and  30  on respective sides of the mullion  18  are positioned toward the rear part of the mullion  18  and are vertically distributed slots, and the air outlet openings  26  and  32  on respective sides of the mullion are smaller openings that are distributed both vertically and laterally over a remaining part of the respective mullion side.  
         [0016]    A plurality of blowers  34  are associated with the mullion  18  for causing air flow into and out of the interior  24  of the mullion when operated. In the illustrated embodiment the blowers take the form of three vertically spaced dual squirrel cage blowers arrange in the interior  24  of the mullion, just inside of the inlet openings  22  and  30 . The spaced apart squirrel cages of each blower  34  are driven by dual output shaft motors positioned between the cages. As best seen in FIG. 5, the illustrated blowers  34  include outlets  36  positioned to blow air through the remainder of the mullion interior  24 . Although not shown, a vertical panel will be provided in the interior of the mullion to separate the input and output sides of the blowers to prevent a back draw from the downstream side of the blowers, with the panel having openings aligned with the outlets  36  of the blowers  34  to allow air to exit the blowers.  
         [0017]    A heating element  38  is also associated with the mullion  18  for heating air prior to passing it from the interior  24  of the mullion into either of the thawing chambers  14  and  16 . In the illustrated embodiment the heating element is a single, elongated and U-shaped resistive heating element that is positioned within the interior  24  of the mullion and proximate the outlets  36  of the blowers  34  to have the air from the blowers pass thereover.  
         [0018]    The cabinet  10  also includes a top-mounted refrigeration system  40 , including a compressor  42 , a condenser coil  43 , and an evaporator  44  with associated blower (not shown). The refrigeration system blower may be a squirrel cage blower. The evaporator section of the system is in flow communication with the chamber  14  via inlet openings (not shown ) in the top wall  46  of the chamber  14  beneath the evaporator  44  and outlet/return openings  48 . An evaporator coil temperature sensor  51  (FIG. 6A) may also be provided as part of the refrigeration system.  
         [0019]    A temperature sensor  50  may be provided in association with the mullion  18  for sensing a temperature of air delivered from the interior  24  of the mullion  18  to the thawing chambers  14  and  16 . In the illustrated embodiment the sensor  50  is positioned within the interior  24  of the mullion  18  and is spaced apart from the heating element  38  so as to sense the overall temperature of the air within the mullion interior  24  as opposed to sensing the air temperature immediately coming off of the heating element  38 .  
         [0020]    When the blowers  34  are operated, they draw air in from the chambers  14  and  16  and deliver it past the heating element  38  to create a pressurized condition at the downstream side of the blowers  34 . The pressurized condition causes substantially uniform air flow through the outlet openings  26  and  32  into respective chambers  14  and  16 .  
         [0021]    An exemplary control system is shown in FIG. 6A. A controller  60  is connected to receive inputs from both temperature sensors  50  and  51  and is also connected to control the operation of the mullion blowers  34 , the heating element  38  and the refrigeration system  40 , including its blower. The controller  60  may receive input from any suitable user input device or devices  64 , such as switches, input keys or input knobs. The controller  60  may also effect display of information to an operator via one or more displays  62 . A more detailed schematic of one embodiment of a controller  60  in association with various cabinet components is shown in FIG. 6B, the controller  60  being comprised of a logic/processing unit  70  in combination with the various relays, contacts and switches shown. The evaporator blower  72  is also shown.  
         [0022]    One embodiment of high-level system operation is described with reference to the flow charts shown in FIGS. 7A and 7B. When the unit is turned ON as indicated at  100 , the controller turns on the blowers at  102 . Typically this step would involve operation of both the mullion blowers  34  and the refrigeration system blower, but variations are possible, such as operation of only the mullion blowers  34  or operation of only certain (e.g., less than all) of the mullion blowers  34 . At step  104 , if the temperature sensed by the mullion temperature sensor  50  is less than a thawing set point TT1, a thawing operation is initiated at step  106 . Otherwise at step  108  the temperature is checked to see if it is above a set point TR1 for initiating a refrigeration operation as per the flow chart of FIG. 7B. In one embodiment, step  108  may be carried out using the evaporator coil temperature sensor  51 . However, it is also recognized that the mullion temperature sensor  50  could be used. Steps  104  and  106  are repeated until one of a thawing operation or a refrigeration operation is initiated.  
         [0023]    The thawing operation begins with energization of the heating element  38  at step  106 . Next, the mullion temperature sensor  50  is monitored at step  110  until the temperature rises above the thawing set point TT1, at which point the heater is de-energized at step  112 . At step  114  the mullion temperature sensor  50  is checked to determine if the temperature is below a thawing set point TT2, which is less than TT1. If so, operation returns to step  106 . If not, at step  116  the temperature is checked against refrigeration set point TR1 to determine whether to initiate a refrigeration operation. Thus, during a thaw cycle the blowers are typically maintained ON and the heating element is cyclically turned ON (e.g., energized and OFF (e.g., de-energized) according to the sensed temperature set points TT1 and TT2. In one embodiment, TT1 is between 35° F. and 39° F. and TT2 is about 1° F. to 3° F. less than TT1. In a more specific example TT1 is about 37° F. and TT2 is about 36° F.  
         [0024]    Subsequent to an affirmative determination at step  108  of FIG. 7A, the refrigeration system is turned on at step  200 , per FIG. 7B, and at step  202  the temperature is monitored to see when it falls below a refrigeration set point TR2, which is lower than set point TR1. When the temperature falls below the set point TR2, the refrigeration system is turned OFF at step  204  and processing returns to step  104  in FIG. 7A. In one embodiment, mullion temperature sensor  50  is monitored for the purpose of step  202 . In one implementation, the temperature set point TR2 is about 38° F. and the temperature set point TR1 is about 40° F., but variations are possible.  
         [0025]    In one embodiment it is contemplated that all mullion blowers  34 , as well as the refrigeration system blower, will be operated during all steps of both refrigeration operations as well as thawing operations, as well as during transition from one operation to another. However, it is recognized that the operation of the blower motors themselves also contributes to the heat input of the cabinet. Accordingly, in certain embodiments it may be advantageous to only energize a limited number of the blowers (e.g., turn OFF one or more mullion blowers and/or turn OFF the refrigeration system blower). For example, as the food product approaches a thawed state during repeated thawing cycles, one or more of the mullion blowers  34  and/or the refrigeration system blower could be turned OFF at the same time the heating element is de-energized at step  112  (FIG. 7A) in order to further reduce the heat input to the system. Such a partial shut down of blower operation could be activated by tracking the change in time period between an affirmative (YES) answer at step  110  and an affirmative answer at step  114 , which represents a temperature change rate within the system. As the food product thaws, this time period will get longer and longer. The controller may be set to initiate the partial blower shut down when the time period exceeds a certain set time period. This operation results in a method for thawing frozen food product using a cabinet with at least one thawing chamber holding the food product, the cabinet including a heating element, a plurality of blowers and a temperature sensor, where the method involves: during initial cycles of the thawing operation operating all blowers; subsequent to the initial cycles, and as a cold load produced by the food product decreases, turning at least one blower OFF to reduce heat input from operation of blower motors, while maintaining at least one blower ON. In another example, it may be desirable to operate less than all mullion blowers  34  during refrigeration cycles in order to reduce heat input, increasing the ability of the thawing apparatus to reduce the temperature of warm or hot food products added to one of the chambers  14  or  16  and also decreasing the energy consumption of the unit.  
         [0026]    In another embodiment of a thawing operation described with reference to the flow chart of FIG. 7A, steps  120 ,  122 ,  124  and  128  correspond to steps  100 ,  102 ,  104  and  108  respectively of FIG. 8. However, given an affirmative decision at step  124 , a variation in the manner in which the heating element  38  is energized is provided. In particular, at step  126  the temperature is examined to determine if it is below set point TT2, which is lower than set point TT1. If so, the heating element is energized at a first power level at step  130 . On the other hand, a negative decision at step  126  results in energization of the heating element at a second power level at step  132 , with the second power level being less than the first power level. In the illustrated embodiment the first power level is a full (100%) power level and the second power level is a 50% power level. In one embodiment, such energization control of the heating element can achieved by varying the duty cycle of a PWM (pulse width modulated) signal used to control current delivered to the heating element. Subsequent to step  130 , at step  134  the temperature is monitored to determine if it rises above set point TT2. If so, the energization of the heating element is reduced at step  132 . Subsequent to step  132 , at step  136  the temperature is monitored to determine if falls back below temperature set point TT2. If so, the heater is again energized at the higher power level per step  130 . If not, the temperature is checked at step  138  to determine if the temperature increases above the set point TT1, at which point the heater is de-energized at step  140 . Steps  142  and  144  correspond to steps  114  and  116  respectively of FIG. 7A.  
         [0027]    The thawing operation of FIG. 8 results in a method for controlling heat input to a thawing cabinet during a thawing operation using a cabinet with at least one thawing chamber holding food product, the cabinet including a heating element, at least one blower and a temperature sensor, the method involving the steps of: selectively energizing and de-energizing the heating element in accordance with a first temperature set point (e.g., TT1); wherein current is delivered to the heating element to produce a first power level when the temperature is below a second temperature set point (e.g., TT2) that is below the first temperature set point; wherein current is delivered to the heating element to produce a second power level when the temperature is above the second temperature set point, where the second power level is less than the first power level; wherein the heating element is de-energized when the temperature exceeds the first temperature set point. This operation advantageously reduces the heat input to the system as the temperature during the thawing cycle approaches the set point TT1.  
         [0028]    In the illustrated embodiment of FIG. 8, two possible power levels for the heating element are utilized. However, it is recognized that more than two such power levels could be used, each initiated at its own temperature set point. Further, in another example the staged energy reduction of the heating element as the temperature approaches the set point TT1 could be achieved utilizing the proportional part of a PID controller. Specifically, where the set point TT1 is 37° F. and the proportional band is set at 1° F., the 50% power reduction is achieved when the temperature reaches 36° F. Where the set point TT1 is 37° F. and the proportional band is set at 2° F., a 33% power reduction, relative to full power, would be implemented when the temperature reaches 35° F. and a 66% power reduction, relative to full power, would be implemented when the temperature reaches 36° F.  
         [0029]    In still another embodiment of a thawing operation described with reference to FIG. 9, steps  150 ,  152 ,  154  and  158  correspond to steps  100 ,  102 ,  104  and  108  respectively of FIG. 7A. It is assumed that at step  154  temperature set point TT1 is at a first level, for example, 37° F., and it is assumed that at step  158  temperature set point TR1 is set at a first level, such as 40° F. Given an affirmative decision at step  154 , and a decision at step  156  that a thaw cycle has just started, a variation in the initial temperature set point TT1 is made. In particular, at step  160  temperature set point TT1 is set to a higher level, in this example 45° F., and temperature set point TR1 is set to a higher level, in this example 48° F. The heating element is energized at step  162  until the temperature exceeds set point TT1. At step  166  a count NT of thaw cycles is incremented and at step  168 , if the thaw cycle count has reached a certain count, NTMAX, at step  170  the set point TT1 is set back to the lower level (e.g., 37° F.) and the temperature set point TR1 is set back to its lower level (e.g., 40° F.). Steps  172 ,  174  and  176  correspond to steps  112 ,  114  and  116  respectively of FIG. 7A. An additional step  178  is provided before entering a refrigeration cycle to be sure that the temperature set point TR1 is set back to an appropriate level for normal refrigeration. During initial thawing cycles (e.g., up to NTMAX) refrigeration is initiated if the temperature exceeds the higher set point TR1 as defined step  160 , and during subsequent thawing cycles refrigeration is initiated if the temperature exceeds the lower set point TR1 as defined at step  170 .  
         [0030]    The thawing operation of FIG. 9 provides a thawing method in which, during one or more initial cycles the heating element is (i) energized when the temperature indicated by the temperature sensor is below a first set point, (ii) de-energized when the temperature indicated by the temperature sensor reaches the first set point and (iii) energized when the temperature indicated by the temperature sensor fall back below the first set point by a certain amount; and subsequent to the one or more initial cycles the heating element is (i) energized when the temperature indicated by the temperature sensor is below a second set point, (ii) de-energized when the temperature indicated by the temperature sensor reaches the second set point and (iii) energized when the temperature indicated by the temperature sensor falls back below the second set point by a certain amount; wherein the first set point is a higher temperature than the second set point. This type of operation facilitates a faster thawing time by adding more heat to the system during initial thaw cycles, when the cold load of the frozen food product is greatest and can more quickly bring the air temperature within the thawing chamber back down below a normally accepted level, such as 40° F. In the illustrated embodiment the higher TR1 temperature set point is used for a specified number of cycles as set by NTMAX, but it is recognized that other techniques to transition from the higher TR1 set point back to the lower TR1 set point could be used, such as monitoring a change in the time period taken between an affirmative decision at step  164  and an affirmative decision at step  174 , which represents a temperature change rate taking place in the system.  
         [0031]    It is also contemplated that various combinations of the above-described embodiments of thawing operations could be provided. For example, in the embodiment of FIG. 8 a step could be added to also shut down one or more blowers at desired times to reduce heat input from the blower motors. In another example, the embodiments of FIGS. 8 and 9 could be combined to provide for both a staged energization reduction of the heating element and a higher TR1 set point for one or more initial thawing cycles.  
         [0032]    In one embodiment, the a full power level of the heating element  38  is about 1300 watts, each mullion blower  34  can move air at a rate of 125 ft 3 /min and adds heat to the system at a rate of about 35 watts when running, the evaporator blower can move air through the evaporator at a rate of about 325 ft 3 /min and adds heat to the system at a rate of about 125 watts when running, and a total thawing chamber volume is between about 40 ft 3  and 50 ft 3 . Of course, these specifications are exemplary only and variations are possible, such as a higher power heating element and/or more or less fans with higher or lesser air flow. However, as a general rule a high volume of air flow is desirable for better thawing, and in one embodiment the mullion blowers are sized and operated to move a volume of air corresponding to a total thawing chamber volume every 5 to 10 seconds. In another embodiment, the combined operation of the mullion blowers and the refrigeration system blower moves a volume of air corresponding to a total thawing chamber volume every 2 to 6 seconds.  
         [0033]    It is to be clearly understood that the above description is intended by way of illustration and example only and is not intended to be taken by way of limitation. For example, while a two chamber unit is primarily described, single chamber thawing units are possible and thawing units with more than two chambers are also possible. Other changes and modifications could be made, including both narrowing and broadening variations and modifications of the appended claims.