Abstract:
A warewash machine for washing wares includes a chamber for receiving wares, the chamber having at least one spray zone. A spray system is provided in the spray zone for spraying liquid onto wares for cleaning. A tank captures sprayed liquid that falls within the spray zone. The tank includes a primary recirculation path for delivering liquid from the tank to the spray system, and a secondary recirculation path for delivering water out of the tank and back into the tank, without spraying within the spray zone, in order promote mixing within the tank.

Description:
TECHNICAL FIELD 
       [0001]    This application relates generally to warewashers such as those used in commercial applications such as cafeterias and restaurants and, more particularly, to an idling system for such warewashers. 
       BACKGROUND 
       [0002]    Commercial warewashers commonly include a housing area which defines washing and rinsing zones for dishes, pots pans and other wares. In conveyor-type machines wares are moved through multiple different spray zones within the housing for cleaning (e.g., pre-wash, wash, post-wash (aka power rinse) and rinse zones). One or more of the zones include a tank in which liquid to be sprayed on wares is heated in order to achieve desired cleaning. Maintaining the water at the desired temperature is important for machine operation. Due to water movement within the tank, the temperature within the tank can be maintained relatively uniform when a spray recirculation pump is operating for spraying wares within the zone. However, when the machine is idling and/or the pump is not otherwise being used for spraying, the lack of water movement results in uneven water heating. 
         [0003]    Current warewash machines, especially flight type machines, use the major spray recirculation pumps to periodically stir and evenly distributes the heat in the tank(s) as well as warm the chamber(s)/zone(s) to position machine ready for a wash without dropping machine temperature to unacceptable levels. This approach results in substantial energy loss from the use of high numbers of high wattage pump(s) which generate steam to warm the chamber(s). This leads to energy loss through the exhaust as well as to the chamber/zone by cooling down quickly. 
         [0004]    It would be desirable to provide a warewasher idling system and method that reduces energy consumption while effectively maintaining desired water temperatures in the machine tanks. 
       SUMMARY 
       [0005]    In one aspect, a warewash machine includes a chamber for receiving wares, the chamber having at least one spray zone. Both a primary recirculation system for delivering liquid from a tank to a spray system, and a secondary recirculation system for stirring or mixing liquid within the tank without passage of the liquid through the spray system are provided. The secondary recirculation system may be operated during machine idling as needed to maintain desired tank temperatures, while flow through the primary recirculation system is maintained off. 
         [0006]    In another aspect, a warewash machine includes a chamber for receiving wares, the chamber having at least one spray zone, and a a spray system in the spray zone for spraying liquid onto wares for cleaning. A tank captures sprayed liquid that falls within the spray zone. The tank includes a primary recirculation path for delivering liquid from the tank to the spray system, and a secondary recirculation path for delivering water out of the tank and back into the tank, without spraying within the spray zone, in order promote mixing within the tank. 
         [0007]    In a further aspect, a warewash machine includes a chamber for receiving wares to be cleaned, the chamber having at least one spray zone and a liquid collection tank. A primary recirculation system delivers liquid from the collection tank to a spray system for spraying liquid in the spray zone. A secondary recirculation system is provided for mixing liquid within the tank without passage of the liquid through the spray system. 
         [0008]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic side elevation of one embodiment of a warewasher;
       and       
 
           [0011]      FIG. 2  is a schematic depiction of an exemplary secondary recirculation system for a wash zone; and 
           [0012]      FIG. 3  is a flow chart of an exemplary idling operating sequence. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIG. 1 , an exemplary conveyor-type warewash machine, generally designated  10 , is shown. Warewash machine  10  includes a housing  11  that can receive racks  12  of soiled wares  14  from an input side  16 . The wares are moved through tunnel-like chambers from the input side toward a blower dryer unit  18  at an opposite exit end  17  of the warewash system by a suitable conveyor mechanism  20 . Either continuously or intermittently moving conveyor mechanisms or combinations thereof may be used, depending, for example, on the style, model and size of the warewash system  10 . Flight-type conveyors in which racks are not used are also possible. In the illustrated example, the racks  12  of soiled wares  14  enter the warewash system  10  through a flexible curtain  22  into a pre-wash chamber or zone  24  where sprays of liquid from upper and lower pre-wash manifolds  26  and  28  above and below the racks, respectively, function to flush heavier soil from the wares. The liquid for this purpose comes from a tank  30  and is delivered to the manifolds via a pump  32  and supply conduit  34 . A drain structure  36  provides a single location where liquid is pumped from the tank  30  using the pump  32 . Via the same drain structure, liquid can also be drained from the tank and out of the machine via drain path  37 , for example, for a tank cleaning operation. 
         [0014]    The racks proceed to a next curtain  38  into a main wash chamber or zone  40 , where the wares are subject to sprays of cleansing wash liquid (e.g., typically water with detergent) from upper and lower wash manifolds  42  and  44  with spray nozzles  47  and  49 , respectively, these sprays being supplied through a supply conduit  46  by a pump  48 , which draws from a main tank  50 . A heater  58 , such as an electrical immersion heater provided with suitable thermostatic controls (not shown), maintains the temperature of the cleansing liquid in the tank  50  at a suitable level. Not shown, but which may be included, is a device for adding a cleansing detergent to the liquid in tank  50 . During normal operation, pumps  32  and  48  are continuously driven, usually by separate motors, once the warewash system  10  is started for a period of time. 
         [0015]    The warewash system  10  may optionally include a power rinse (also known as post-wash) chamber or zone (not shown) that is substantially identical to main wash chamber  40 . In such an instance, racks of wares proceed from the wash chamber  40  into the power rinse chamber, within which heated rinse water is sprayed onto the wares from upper and lower manifolds. 
         [0016]    The racks  12  of wares  14  exit the main wash chamber  40  through a curtain  52  into a final rinse chamber or zone  54 . The final rinse chamber  54  is provided with upper and lower spray heads  56 ,  57  that are supplied with a flow of fresh hot water via pipe  62  running from a hot water booster  70  under the control of a solenoid valve  60  (or alternatively any other suitable valve capable of automatic control). A rack detector  64  may be actuated when a rack  12  of wares  14  is positioned in the final rinse chamber  54  and through suitable electrical controls (e.g., the controller mentioned below), the detector causes actuation of the solenoid valve  60  to open and admit the hot rinse water to the spray heads  56 ,  57 . The water then drains from the wares and is directed into the tank  50  by gravity flow. The rinsed rack  12  of wares  14  then exits the final rinse chamber  54  through curtain  66 , moving into dryer unit  18 , before exiting the outlet end  17  of the machine. 
         [0017]    An exhaust system  80  for hot moist air may be provided. A cold water input 72 line may run through a waste heat recovery unit (not shown) to recover heat from the exhaust air. Other heat recovery components may also be employed. 
         [0018]    Referring now to  FIG. 2 , an exemplary schematic of a wash tank  50  with a small size, low wattage secondary recirculation pump  100  and recirculation path  90 , in addition to the larger size, high wattage major spray recirculation pump  48  is shown. Various temperature sensors T 1  and T 2  (e.g., thermocouples) are also provided, along with tank level sensors L 1  and L 2  (e.g., float switches or electrical impedance sensors). Although machine tank  50  is referenced, it is recognized that other tanks of a machine could include similar secondary recirculation arrangements. 
         [0019]    In normal practice, the heating element  58  switches ON when a lower temperature set point of liquid in the tank  50  is reached (as indicated by temperature sensor T 1 ) and switches OFF when an upper temperature set point is reached (as indicated by temperature sensor T 2 ). In addition, the heating element  58  only switches ON if the liquid is above a set lower level (as indicated by level sensor L 1 ) and remains OFF when the liquid is below the set lower level (as indicated by level sensor L 1 ). 
         [0020]    Operation of the secondary recirculation pump  100  may be tied to the heating element controls. Control of the secondary recirculation pump  100  may be according to the lower and upper temperature set points in the tank, as well as the low level setting to protect the pump. 
         [0021]    In this regard, the various temperatures corresponding to the lower and upper tank set temperature points, chamber temperature (as indicated by temperature sensor T 1 ) and the tank fluid temperature (per sensor T 2 ) may be used to control the secondary recirculation pump  100 . The lower and upper tank set points temperatures which control the heating element  58  may simultaneously control the secondary recirculation pump  100 . In normal operation the heating element  58  turns ON when the tank liquid temperature falls to lower temperature set point and switches OFF when the liquid temperature rises to the upper temperature set point. At the lower temperature set point the secondary recirculation pump  100  may turn ON simultaneous with the heating element  58  to ensure uniform mixing of the tank liquid until the upper temperature set point is reached, at which point both the heating element  58  and secondary recirculation pump  100  switch OFF simultaneously, consistent with satisfying Equation (1) below: 
         [0000]      Tank Fluid Temperature (per  T 2)−Chamber Temperature (per  T 1)&gt; Ta ( F )  (1)
 
         [0000]    Ta (F) may be a predetermined value. Equation (1) is a simple relation to show the use of temperature to control the secondary recirculation pump  100 . However, Equation (1) could represent other relationships. 
         [0022]    At any point in the idling process Equation (1) can activate both the secondary recirculation pump  100  and the heating element  58  to position the machine ready for washing. Also, Equation (1) can activate the secondary recirculation pump  100  without activating the heating source  58  until the tank liquid temperature drops to the lower set point and/or the chamber temperature activates the heating element  58 . Notably, in such idling operations the major spray pump  48  need not be operated at all. 
         [0023]    As shown in  FIG. 2 , a controller  200  may be provided for the above process a process as well as other machine functions. As used herein, the term controller is intended to broadly encompass any circuit (e.g., solid state, application specific integrated circuit (ASIC), an electronic circuit, a combinational logic circuit, a field programmable gate array (FPGA)), processor (e.g., shared, dedicated, or group—including hardware or software that executes code) or other component, or a combination of some or all of the above, that carries out the control functions of the machine or the control functions of any component thereof. The controller may include variable adjustment functionality that enables, for example, the upper and lower temperature set points to be varied and/or Equation (1) to be modified (e.g., via an operator/user interface associated with the controller  200  or via a restricted service/maintenance personnel interface). 
         [0024]      FIG. 3  shows an exemplary process algorithm based on Equation (1) and the tank temperature set points for activating the secondary recirculation pump  100  and heating element  58 . The chamber air temperature sensor T 1  and tank temperature sensor T 2  are checked at  300 . At  302 , if the tank temperature is at the upper temperature set point (e.g., UTSP stored in memory of the controller), then processing moves to  304  and if the tank temperature is at the lower temperature set point (e.g., LTSP stored in memory of the controller) then processing moves to  306 . At  304 , if the difference between the upper temperature set point and the chamber temperature is greater than specified temperature Ta or if the difference between the tank temperature and the chamber temperature is greater than specified temperature Ta, either condition being indicative of a lower than desired heat level in the chamber air, then processing moves to  308 , otherwise processing moves to  310 . 
         [0025]    At  308 , both the secondary recirculation pump  100  and heating element  58  are ON until either the difference between the upper temperature set point and the chamber temperature is less than specified temperature Ta or the difference between the tank temperature and the chamber temperature is less than specified temperature Ta (at which point the pump and heating element are turned OFF). This operations increases the chamber air temperature as is desired to add heat to wares in the chamber. At  310 , the pump  100  and the heating element  58  are OFF (because the chamber air temperature is sufficiently high). 
         [0026]    At  306 , the recirculation pump  100  and heating element  58  are both ON until the tank temperature reaches the upper temperature set point, at which point processing moves to  312 . At  312 , if the difference between the upper temperature set point and the chamber temperature is greater than specified temperature Ta or if the difference between the tank temperature and the chamber temperature is greater than specified temperature Ta, then processing moves to  314 , otherwise processing moves to  316 . 
         [0027]    At  314 , the recirculation pump  100  and heating element  58  are ON until either the difference between the upper temperature set point and the chamber temperature is less than specified temperature Ta or the difference between the tank temperature and the chamber temperature is less than specified temperature Ta (at which point the pump and heating element are turned OFF). At  316 , the pump and heating element are both turned OFF. 
         [0028]    The use of a small size low wattage secondary recirculation pump(s) to accomplish water mixing and heat/temperature distribution during idling reduces energy consumption while enabling maintaining of tank(s) temperature. The secondary pump could also be used to prep the machine from idle mode for operation. 
         [0029]    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, and that changes and modifications are possible. Accordingly, other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application. 
         [0030]    For example, each tank could include multiple secondary recirculation pumps and/or associated baffles within the tank for more effective stirring/mixing. Moreover, while a secondary recirculation pump  100  is primarily shown and described in  FIG. 2 , it is recognized that the primary pump  48  could alternatively be provided with dual flow paths (e.g., in addition to path  46 , a secondary recirculation system path  92  directly back to the tank  50  per  FIG. 2 ). The pump could have alternative outputs for each path and/or valves (shown as dotted line circles in  FIG. 2 ) along the paths  46  and  92  could be used to control the flow from the pump  48  to the desired location. In such an arrangement the secondary pump  100  could be eliminated and the primary pump  48  operated for recirculation during idling by controlling the flow to go directly back to the tank  50  and not through the spray system.