Abstract:
A warewasher for washing wares includes a housing defining an internal space with at least one spray zone for washing wares. A liquid delivery system provides a spray of liquid within the spray zone. A tank includes an inlet that is connected to a hot water source for filling the tank with hot water. The liquid delivery system receives water from the tank. An exhaust vents heated air from the housing. A final rinse system is connected to a cold water source. A heat recovery system is located between the final rinse system and the cold water source. The heat recovery system transfers heat from the exhaust air to the cold water provided from the cold water source. A valve associated with the hot water source selectively supplements the water exiting the heat recovery system with hot water from the hot water source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application Ser. No. 61/043,589, filed Apr. 9, 2008, the details of which are hereby incorporated by reference as if fully set forth herein. 
    
    
     TECHNICAL FIELD 
     This application relates generally to warewasher systems which are used in commercial applications such as cafeterias and restaurants and, more particularly, to such a warewasher system including a heat recovery system with hot water supplement. 
     BACKGROUND 
     Commercial warewashers may include a heat recovery system that is installed in an outlet exhaust system of the warewasher to recover heat. The heat is usually transferred to the fresh water supply in the rinse cycle thus reducing the energy required to heat the water supply. However, upon system start up the exhaust system temperature is not sufficiently high to reach desired operating temperatures and the amount of time needed to wait for the source water to reach temperature can be objectionable. 
     SUMMARY 
     In an aspect, a warewasher for washing wares includes a housing defining an internal space with at least one spray zone for washing wares. A liquid delivery system provides a spray of liquid within the spray zone. A tank includes an inlet that is connected to a hot water source for filling the tank with hot water. The liquid delivery system receives water from the tank. An exhaust vents heated air from the housing. A final rinse system is connected to a cold water source. A heat recovery system is located between the final rinse system and the cold water source. The heat recovery system transfers heat from the exhaust air to the cold water provided from the cold water source. A valve associated with the hot water source selectively supplements the water exiting the heat recovery system with hot water from the hot water source. 
     In another aspect, a method of washing and rinsing wares by providing heated rinse water to a rinse station of a warewasher is provided. The method includes providing a spray of liquid to a spray zone within a housing using a liquid delivery system. A tank is filled with hot water from a hot water source and the liquid delivery system receiving water from the tank. Heated air is vented from the housing through an exhaust. A final rinse system is connected to a cold water source. Heat is transferred from the exhaust air to cold water provided from the cold water source using a heat recovery system located between the final rinse system and the cold water source. Water exiting the heat recovery system is selectively supplemented with hot water from the hot water source using a valve associated with the hot water source. 
     In another aspect, a warewasher for washing wares including a housing defining an internal space with at least one spray zone for washing wares. An exhaust path is provided for venting air from the housing. A liquid delivery system provides a spray of cleaning liquid within the spray zone. A final rinse system delivers a spray of rinse liquid for rinsing wares within the housing. A hot water booster feeds the final rinse system. A hot water booster filling arrangement includes a heat recovery system associated with the exhaust path. The heat recovery system is connected with a cold water input and arranged to transfer heat from exhaust air to cold water from the cold water input. An output of the heat recovery system is operatively connected to fill the hot water booster. A flow path delivers water from a hot water source to the hot water booster. A valve is located along the flow path. The valve is controlled to selectively deliver water from the hot water source to the hot water booster in dependence upon at least one monitored condition of the hot water booster filling arrangement. 
     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 
         FIG. 1  is a diagrammatic, section view of an embodiment of a warewash system; 
         FIG. 2  is a diagrammatic illustration of an embodiment of a heat recovery system with hot water supplement for use in the warewash system of  FIG. 1 ; 
         FIG. 3  is a diagrammatic illustration of another embodiment of a heat recovery system with hot water supplement for use in the warewash system of  FIG. 1 ; and 
         FIGS. 4 and 5  illustrate another embodiment of a heat recovery system with hot water supplement. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , an exemplary conveyor-type warewash system, generally designated  10 , is shown. Warewash system  10  can receive racks  12  of soiled wares  14  from an input side  16  which are moved through tunnel-like chambers from the input side toward a dryer unit  18  at an opposite end 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 . 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  via a pump  32  and supply conduit  34 . A drain system  35  provides a location where liquid is pumped from the tank  30  using the pump  32  and where liquid can be drained from the tank, for example, for a tank cleaning operation. 
     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 liquid 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. 
     The warewash system  10  may optionally include a power rinse 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. 
     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 ,  58  that are supplied with a flow of fresh hot water via pipe  60  under the control of fill valve  62 . A rack detector  64  is actuated when rack  12  of wares  14  is positioned in the final rinse chamber  54  and through suitable electrical controls, the detector causes actuation of the solenoid valve  62  to open and admit the hot rinse water to the spray heads  56 ,  58 . The water then drains from the wares into tank  50 . The rinsed rack  12  of wares  14  then exit the final rinse chamber  54  through curtain  66 , moving into dryer unit  18 . 
     Referring now to  FIG. 2 , the warewash system  10  is provided with a heat recovery system  70  that utilizes warm, humid air from within the system (e.g., typically at about 105° F. to 120° F., such as 114° F.) flowing through an exhaust  72  to heat cold water (e.g., typically at about 45° F. to 60° F., such as 50° F. or 55° F.) flowing from a cold water source  74 . The illustrated heat recovery system  70  includes a heat recovery coil  76  located within an exhaust conduit (represented by dashed lines  78 ) of the exhaust  72 . The heat recovery coil  76  is in a heat exchange relationship with the warm air flowing through the exhaust conduit  78 . In some embodiments, the heat exchange relationship between the heat recovery coil  76  and the heated air can provide a temperature increase in the water of about 40 to 45° F. or more. A booster heater  80  (e.g., an electric or steam booster heater) is in communication with the heat recovery coil  76  to receive water from the heat recovery coil. The booster heater  80  can provide a temperature increase to the water of about 40 to 80° F. The booster heater  80  then delivers the heated water to the final rinse station  54 , e.g., at a temperature of at least about 180° F. 
     As can be appreciated, during start-up or reactivation of the warewash system  10 , it takes time for the warm, humid air exiting the exhaust to reach temperature (e.g., about 114° F.). During this time, the water exiting the heat recovery coil  76  may not be sufficiently heated to reach the desired rinse temperature after leaving the booster heater  80  or the time period required for the booster heater to raise the water temperature to the desired rinse temperature may be deemed excessive. 
     A control valve  82  is provided to selectively and controllably mix hot water with water exiting the heat recovery coil  76 . A temperature sensor  86  is located downstream, but near the heat recovery coil  76  to monitor the temperature of water exiting the heat recovery coil. A controller  85  receives an indication from the temperature sensor  86  and responsively opens and closes the control valve  82  based on whether the water temperature is below a predetermined temperature (e.g., about 100 to 140° F., such as about 105° F. depending on the type of booster heater  80 ). In one embodiment, the control valve  82  is a fully open or fully closed type valve. In this embodiment, it may be desirable to size the control valve  82  to allow in enough hot water to assure water flowing into the booster heater  80  will be at or above the predetermined temperature, even in a no heat recovery case from the heat recovery coil. If the temperature of the water exiting the heat recovery coil  76  is below the predetermined temperature, the controller  85  opens the control valve  82  thereby allowing an amount of hot water from a hot water source  84  (e.g., boiler) to supplement the cooler water flowing from the heat recovery coil in order to raise the water temperature to at least the desired temperature. If the temperature of the water exiting the heat recovery coil  76  is at or above the predetermined temperature, the controller  85  closes the control valve  82  thereby preventing hot water from the hot water source from supplementing the water flowing from the heat recovery coil. The controller  85  can continuously monitor the water temperature of water exiting the heat recovery coil  76  to open and close the control valve  82  as needed. The hot water source  84  also provides hot water (e.g., at about 120° F.) to fill the tank  30 ,  48  ( FIG. 1 ) for a washing operation. In an alternative embodiment, the control valve  82  may be a modulating control valve that continuously monitors temperature of water exiting the heat recovery coil  76  using a thermostat control  86  and responsively varies an amount of hot water allowed to mix with water exiting the heat recovery coil. 
     Referring now to  FIG. 3 , an alternative warewash system  10   a  includes a modulating control valve  82   a . The modulating control valve includes a thermostat control  86   a  located downstream of mixing node N and upstream of the booster heater  80 . The modulating control valve  82   a  varies the amount of hot water allowed to mix with the water exiting the heat recovery coil  76  based on the temperature detected by the thermostat control  86   a . If the water entering the booster heater  80  is less than the predetermined temperature, the rate of hot water allowed to supplement the water may be increased in order to reach the desired temperature. Because the temperature of the air flow through the exhaust  72  increases as the warewash system  10  warms up, the temperature of the water entering the booster heater  80  will rise. This rise in temperature of water entering the booster heater  80  is detected by the thermostat control  86   a , which will, in response, cause the control valve  82  to reduce the amount of hot water flowing therethrough as higher hot water flow rates will no longer be needed to reach the desired water temperature. The amount of hot water allowed to supplement the water exiting the heat recovery coil  76  may be continuously adjusted based on temperature of the water entering the booster heater  80 . In an alternative embodiment, the control valve  82   a  may be a fully open and close type control valve. 
       FIG. 3  shows another alternative embodiment that includes a thermostat control  86   b  (represented by dashed lines) located downstream of the booster heater  80 . Control valve  82   b  is opened or closed (or continuously modulated) based on whether the final rinse water is above or below the predetermined temperature (e.g., of at least about 180° F.). The embodiment of  FIG. 2  could likewise be modified to place the sensor  86  downstream of the booster heater  80 . 
     Referring now to  FIGS. 4 and 5 , another warewash system embodiment  10   b  is illustrated. In this embodiment, three valves  90 ,  92  and  94  are used to control flow of water into the booster heater  80 . Valve  90  is associated with a low flow path  96  that receives water from the heat recovery coil  76  of the heat recovery system  70 , valve  92  is associated with a high flow path  98  that also receives water from the heat recovery coil of the heat recovery system and valve  94  is associated with a hot water path  100  that receives hot water from the hot water source  84 . Although not shown here, the hot water source  84  also fills the tank, as described above. A flow restrictor  102  is provided along the low flow path  96  for restricting flow of water therethrough when the valve  90  is open. A temperature sensor  104  is provided to monitor temperature of water flowing from the heat recovery coil  76 . Check valves  106  and  108  prevent back flow of water into the paths  96 ,  98  and  100 . 
     When temperature of the water flowing from the heat recovery coil  76  is at or below a predetermined temperature (e.g., between 100° F. and 140° F., such as about 105° F.), the valve  90  associated with the low flow path  96  and the valve  94  associated with the hot water path  100  are opened (or allowed to remain open) and the valve  92  associated with the high flow path  98  is closed (or remains closed) such that only a small portion of the water entering the booster heater  80  comes from the heat recovery coil  76  and a majority of the water entering the booster heater  80  comes from the hot water source  84 . When the air in to the heat recovery system  70  (see arrow  110 ) heats the cold water flowing into the heat recovery coil  76  to or above the predetermined temperature, the valves  90  and  94  are closed and the valve  92  is opened such that all the water entering the booster heater  80  is provided from the heat recovery coil  76 . 
     As described above, the valves  90 ,  92  and  94  are fully open or fully closed type valves. However, the valves  90 ,  92  and  94  may be modulated valves. The valves  90 ,  92  and  94  may be controlled by a controller  112 , for example, that receives a signal from the temperature sensor indicative of temperature. Or, for example, the valves  90 ,  92  and  94  may be switched open or closed directly by a signal from the temperature sensor. 
     The above-described heat recovery systems with hot water supplement can be advantageous in a number of ways including during an initial start-up operation to reduce the amount of time needed for the final rinse water to reach the desired temperature of 180° F. For example, hot water may be used to supplement the water exiting the heat recovery coil  76  when the warewash system  10  is activated, but has been idle for some time. In certain embodiments, the thermostat control  86  may monitor water temperature only during an initial start up period, or the thermostat control may be used to continuously monitor water temperature throughout operation of the warewash system  10 . Hot water may be mixed with the water exiting the heat recovery coil  76  in situations where the heat recovery coil&#39;s efficiency has decreased, for example, due to clogging. In some embodiments, the hot water supplement may be used continuously to bring the water exiting the heat recovery coil  76  up to temperature. For example, in some buildings, the cold water source  74  may provide cold water at a temperature less than 50 degrees such that the temperature increase provided by the heated air in the exhaust  72  cannot bring the temperature of the water exiting the heat recovery coil to the desired temperature. In these instances, the water exiting the heat recovery coil  76  may be continuously supplemented with the hot water from the hot water source  84 . The above-described heat recovery system  70  may be used with a number of commercial warewashers such as the FT900 Flight Type warewasher or the C-Line warewasher, both commercially available from Hobart Corp., Troy Ohio. Significant energy savings can be realized without sacrificing high temperature rinse performance. 
     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. For example, other configurations of heat recovery systems could be provided for transferring heat from the machine exhaust air to the incoming cold water (e.g., a heat pump arrangement). Further, while the downstream side of the hot water supplement control valve is shown and described as joining with the flow path of water exiting the heat recovery system, embodiments are contemplated in which the hot water flow path leads directly into the booster without pre-mixing with the water exiting the heat recovery system. Accordingly, other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application.