Abstract:
Energy recovery devices, systems and methods, and energy recovery control systems and methods for efficient extraction and reuse of waste heat from exhaust fumes generated from cooking appliances.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the benefit of priority of U.S. provisional applications 61/332,176, filed May 6, 2010, and 61/359,212, filed Jun. 28, 2010, both of which are hereby incorporated by reference as if set forth in their entireties herein. 
     
    
     RELATED FIELD 
       [0002]    The present invention relates generally to energy recovery devices, systems and methods and more particularly to energy recovery devices and energy recovery control systems and methods for efficient extraction and use of waste heat. 
       BACKGROUND OF THE INVENTION 
       [0003]    Restaurants in general generate large amounts of heat and grease-laden exhaust from the frying and broiling of various food items which are prepared. This grease-laden hot exhaust is typically drawn up through a kitchen hood and exhaust duct combination to the atmosphere by a fan arrangement. However, the heat is generally lost up the exhaust duct. 
         [0004]    Any attempt to capture and reuse this waste heat runs into problems because energy recovery devices which use heat exchangers have either reduced heat-transfer properties due the grease that deposits on their surfaces, or because the heat extraction process employed to recover this heat is generally not very efficient. 
       SUMMARY OF THE INVENTION 
       [0005]    Systems and methods are disclosed to efficiently extract and reuse heat from heat sources such as cooking appliances and heat from exhaust ducts and other locations in commercial kitchens, for example. Devices, systems and method for recovering energy normally lost by radiant and convective emission are described. 
         [0006]    Energy recovery systems and method are disclosed to extract energy, in the form of heat, from various sources and employ the captured energy in various useful ways. Systems and methods are disclosed to efficiently control energy recovery from hot exhaust gases generated in exhaust systems. 
         [0007]    Heat energy is recovered from a variety of sources and transferred to one or more consuming processes and/or converted to another usable form, such as electricity. The present systems are adapted for use in commercial kitchens, but can be used in other locations. Commercial kitchens may provide opportunities for usefully consuming waste energy. For example, hot water, low temperature heat can be used for hot water heating or pre-heating, food warming, absorbent-based air conditioning, dehumidification (e.g., desiccant regeneration) and other purposes. In addition, existing and new thermoelectric technologies permit thermal energy to be converted directly to electrical energy with reasonable efficiency. 
         [0008]    The disclosed subject matter includes thermal energy recovery systems which may employ in various combinations, convective and radiant heat exchangers to recover heat from heat sources at respective temperatures; thermal storage, thermoelectric conversion devices, auxiliary heaters to boost fluid temperatures, valve final controllers, programmable controllers, and sensors. 
         [0009]    According to embodiments, the disclosed subject matter includes a system for recovering heat from exhaust air generated from a cooking appliance having a combustion fumes outlet and a cooking fume outlet. The has an exhaust hood configured for use over a cooking appliance to receive cooking fumes therefrom, the hood having filters opens to a filter plenum which is connected to an exhaust duct. The filter plenum supports the filters on one side thereof and having an opens opposite a side of the plenum on which the filters are supported which opens, via a bypass opens, to a bypass plenum. The bypass plenum is configured with an inlet to allow connection to a combustion fume outlet of the cooking appliance. The bypass opening is defined by an adjustable member to allow the size of the bypass opens to be selected. There is at least on tube heat exchanger in at least one of the duct and the filter plenum and it is connectable to a liquid cooling loop. A bypass heat exchanger is disposed in a flow path of the bypass plenum and configured to circulate a heat-exchange fluid therethrough. A circulating pump circulates heat-exchange fluid through the tube heat exchanger and then through the bypass heat exchanger and through a further loop to a load or thermal storage device. 
         [0010]    The tube heat exchanger may include a plurality of metal tubing portions in fluid communication with each other. The plurality of metal tubing portions may be position so that a majority thereof are spaced apart at least two tube diameters from each other to permit cleaning. 
         [0011]    The at least one tube heat exchanger may be two heat exchangers, one occupying a substantial fraction of the filter plenum and another in the exhaust duct. 
         [0012]    The system may include a panel type heat exchanger arranged to capture radiant and convective heat energy from the cooking appliance upstream of the filters. The panel type heat exchanger may be connected to receive heat transfer fluid from the at least one tube heat exchanger. 
         [0013]    The at least one tube heat exchanger may include a stack of parallel disk-shaped spiral metal tubing portions connected in series, the disks is spaced at least three tube diameters apart, on centers. 
         [0014]    The panel type heat exchanger may be movably coupled to the hood and have a selected position and orientation relative to the cooking appliance. The system may include a spraying device arranged within the filter plenum adapted to spray a contaminant-soluble cleaning solution onto the at least one tube heat exchanger. 
         [0015]    The system may include a catalytic converter positioned to receive hot fumes from the cooking appliance. The hood may have a shroud that descends from the hood on three sides and extends down to the cooking appliance. The cooking appliance may be a conveyor-type (chain) automated grill. The pump may be a variable speed pump. 
         [0016]    A controller may be connected to sensors or a communication channel to detect a state of the cooking appliance, wherein the state of the cooking appliance is one of an idle state and a cooking state. 
         [0017]    The controller device may be further configured to modify the speed of the variable speed pump based on the detected state of the cooking appliance such that a minimum temperature of the heat transfer fluid conveyed through the at least one heat exchanger is maintained. 
         [0018]    The controller device may be configured to continuously change a rate of heat recovery from the heat exchanger arrangement by modifying the speed of the variable speed pump based on a heat requirement of a load. 
         [0019]    The load may include a water storage and supply reservoir, and wherein the controller device continuously changes the speed of the pump based on a need for hot water in the water storage and supply reservoir. 
         [0020]    According to embodiments, the disclosed subject matter includes a heat recovery system for extracting and reusing heat from exhaust air generated from a plurality of cooking appliances, the heat recovery system. The system has a heat exchanger loop including a plurality of arrangements of metal tubing, each arrangement of metal tubing is disposed in a flow path of exhaust air generated from a corresponding cooking appliance, and each arrangement of metal tubing is configured to circulate a heat-exchange fluid therethrough. A circulating device is configured to circulate the heat-exchange fluid through the heat exchanger loop for heat transfer with said exhaust air, and configured to circulate the heat-exchange fluid between said heat exchanger loop and a location of heat utilization, wherein the plurality of arrangements of metal tubing are in fluid communication with each other. The cooking appliances may include at least one fryer. 
         [0021]    The heat-exchange fluid and the exhaust air may move substantially perpendicular to one another through the heat exchanger loop. The circulating device may include a pumping device to circulate the heat-exchange fluid from a fluid source to the heat exchanger loop and from the heat exchanger loop to the location of heat utilization. 
         [0022]    A controller device may control a rate at which heat is extracted from the heat exchanger loop. The controller device may control the heat recovery rate by controlling the flow rate of the heat-exchange fluid through the heat exchanger loop based on a heat requirement at the location of heat utilization. The pumping device may include a variable speed pump configured to change the speed and the flow rate of the heat-exchange fluid circulating through the heat exchanger loop, and wherein the controller device controls the flow rate of the heat-exchange fluid through the heat exchanger loop by changing the speed of the pump. The location of heat utilization may include a water storage and delivery system. The heat-exchange fluid may include water. 
         [0023]    The heat extracted from the heat exchanger loop may be in the form of heated water. The circulating device may circulate the heated water from the heat exchanger loop to the water storage and supply device. The heat requirement at the location of the heat utilization may include a minimum temperature requirement at which the water in the water storage and supply device needs to be maintained. The system may have a plurality of detectors, each detector being associated with a respective arrangement of metal tubing, the detectors being configured to detect a temperature of the heat-exchange fluid exiting the corresponding arrangement of metal tubing. The controller device may control the rate of heat recovery based on the detected temperature of the heat-exchange fluid exiting each of the arrangements of metal tubing. 
         [0024]    The controller device may control the rate of heat recovery by allowing the circulating device to only circulate the heat-exchange fluid having a predetermined temperature from the arrangements of metal tubing to the location of heat utilization. 
         [0025]    According to embodiments, the disclosed subject matter includes a method for controlling heat recovery from exhaust air generated from a plurality of cooking appliances by transfer of heat from the exhaust air to a heat-exchange fluid circulating through a plurality of heat exchanger arrangements, each arrangement associated with a corresponding cooking appliance, the plurality of heat exchanger arrangements is in fluid communication with each other and is disposed in the flow path of the exhaust air, the method comprising: circulating the heat-exchange fluid through the plurality of heat exchanger arrangements and between the heat exchanger arrangements and a source of heat utilization, the source of heat utilization including a water storage device; detecting the temperature of the heat-exchange fluid outputted from each of the heat exchanger arrangements; detecting a temperature of the water in the water storage device; and comparing the temperatures of the heat-exchange fluid outputted from each of the heat exchanger arrangements and the temperature of the water in the water storage device, wherein only the heat-exchange fluid having a temperature higher than the temperature of the water in the water storage device is circulated to the water storage device. 
         [0026]    Each of the heat exchanger arrangements may include a plurality of metal tubing arrangements disposed at different positions along the flow path of the exhaust air generated from a corresponding cooking appliance. 
         [0027]    According to embodiments, the disclosed subject matter include an exhaust hood, comprising: a hood portion with a recess and an exhaust vent opens to the recess, the vent having a holder for cartridge filters; the hood portion having an outlet adapted to be connected to an exhaust duct for discharge of waste fumes; a plate-type thermoelectric conversion device positioned in the hood recess and oriented such that a major surface thereof faces downwardly toward a location where a cooking device would be located for use of the hood portion. 
         [0028]    The plate-type thermoelectric conversion device may be incorporated in, positioned on, a movable sash that can be moved to a position that reduces the air flow aperture under the hood portion. 
         [0029]    A controller may be configured to receive data indicating an operating state of the appliance and to automatically position the sash and output a signal indicating to reduce a rate of exhaust by an exhaust fan. 
         [0030]    According to embodiments, the disclosed subject matter includes a system for recovering heat from exhaust air generated from a cooking appliance, comprising: an exhaust hood configured with at least one liquid cooled-heat exchanger arranged to capture heat from a cooker that emits fumes that are captured by the hood; at least one liquid cooled-heat exchanger is positioned and adapted for capturing heat by convection and/or radiation; an insulated tank selectively coupled to the at least one liquid cooled-heat exchanger by at least one control valve; a controller configured to determine an amount of thermal energy available from the at least one liquid cooled-heat exchanger and required by a heat-consuming load; the controller is further configured to flow a heat transfer fluid to one of a heat-consuming load and the insulated tank responsively to the amount of thermal energy available from the at least one liquid cooled-heat exchanger and required by a heat-consuming load and to add hot water from the thermal energy available from the at least one liquid cooled-heat exchanger and required by a heat-consuming load to the insulated tank when the heat available from the at least one liquid cooled-heat exchanger exceeds the amount required by the heat-consuming load. 
         [0031]    An insulated tank may be selectively coupled to the at least one liquid cooled-heat exchanger by at least one control valve; a controller configured to determine an amount of thermal energy available from at least one of the heat exchangers and required by a heat-consuming load; the controller is further configured to flow a heat transfer fluid to one of a heat-consuming load and the insulated tank responsively to the amount of thermal energy available from the at least one of the heat exchangers and required by a heat-consuming load and to add hot water from the thermal energy available from the at least one liquid cooled-heat exchanger and required by a heat-consuming load to the insulated tank when the heat available from the at least one of the heat exchangers exceeds the amount required by the heat-consuming load. 
         [0032]    According to embodiments, the disclosed subject matter includes an energy recovering system, comprising: an exhaust hood; a heat exchanger, of the type that receives and heats a heat transfer fluid, located in the hood to receive waste heat from exhaust products flowing through the exhaust hood; a thermal storage reservoir and filled with heat transfer fluid connected to the heat exchanger; a load supply outlet on the storage reservoir connected to a auxiliary heater, the heater is configured to raise the temperature of fluid drawn from the thermal storage reservoir to a level required by a heat-consuming load; a controller configured to operate the auxiliary heater and convey fluid to the load responsively to a load demand. The heat transfer fluid may be potable water. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  shows an automatic grill with portions removed to show heat exchanger components. 
           [0034]      FIG. 2  shows the embodiment of  FIG. 1  with exhaust parts in place. 
           [0035]      FIG. 3  shows the embodiment of  FIG. 2  with an exhaust guide in place. 
           [0036]      FIG. 4A  shows an automatic grill with a plate heat exchanger for recovering radiant heat positioned at different angles relative to a broiler. 
           [0037]      FIG. 4B  shows a detail of a duct heat exchanger. 
           [0038]      FIG. 5  shows a rear flue-bypass system with a crossflow heat exchanger. 
           [0039]      FIG. 6  shows a radiant heat recovery exchanger placed in a hood interior. 
           [0040]      FIG. 7  shows an energy recovery system with control system and sensors. 
           [0041]      FIG. 8  shows a rear flue-bypass system with a crossflow heat exchanger according to another embodiment of the disclosed subject matter. 
           [0042]      FIG. 9  shows a heat exchanger loop of an energy recovery device including three heat exchangers connected in series in a continuous fluid communication. 
           [0043]      FIG. 10  shows a heat exchanger loop of an energy recovery device including at least three heat exchangers connected in parallel in fluid communication with each other. 
           [0044]      FIG. 11  shows a heat exchanger loop of an energy recovery device for heat recovery in a system with multiple hoods. 
           [0045]      FIG. 12  shows a heat exchanger loop of an energy recovery device integrated with a water storage and supply reservoir. 
           [0046]      FIG. 13  shows a heat exchanger loop of an energy recovery device integrated with a water storage and supply reservoir including a controller device for controlling heat recovery. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]      FIGS. 1 to 3  show an energy or heat recovery device for a grill  116 . The chain broiler  116  receives food onto a grill configured as a conveyor belt  114  that passes food over a source of heat, such as a gas burner or wood fire. Radiant and convective heat and flue products emanate from an exhaust opening  118  at the top of the grill  116 . 
         [0048]    Fumes from the exhaust opening  118  are captured by an exhaust hood  120 . Fumes are drawn by an exhaust fan into a plenum  108  through grease filters  202  and removed through an exhaust duct  104  and a cooled product  126  ultimately discharged. 
         [0049]    A flat heat exchanger panel  112  is arranged to capture radiant energy and, under certain conditions (if the temperature is lower than the exhaust products) convective heat, emanating through the exhaust opening  118 . A bent tube heat exchanger  122  is located in the exhaust plenum  108  and captures heat convectively. The grease filters  202  serve to reduce the amount of fouling experienced by the heat exchanger  122 . An additional tube type heat exchanger  102  is provided in a rising exhaust duct stemming from an exhaust collar of the hood  120 . 
         [0050]    The flat heat exchanger  112  has the potential to operate at a higher temperature than the tube heat exchanger  122  and the duct heat exchanger  102  due to the radiant energy capture from the heat source and the primary convective transfer from exhaust outlet  118  with minimal dilution by bypass air from the surrounding space which is drawn in by the hood  120 . In an embodiment, the flat heat exchanger  112  supplies heat to a higher temperature load than the tube heat exchangers  102  and  122 . In an alternative embodiment, a heat transfer fluid is circulated in a counterflow arrangement through the tube heat exchangers  112  and  122  and then through the flat heat exchanger  112 . 
         [0051]    The tube heat exchangers may be of continuous tubing, for example copper tubing, and positioned within in the exhaust flow path. The duct heat exchanger  102  may be a stack of spiral heat tubing winds interconnected in series at their perimeters and centers as in  FIGS. 4A and 4B  or a toroidal winding or any other suitable arrangement. Preferably the bare tubing is arranged to allow easy cleaning by a spray wash. 
         [0052]    The flat heat exchanger panel  112  can be a single plate heat exchanger or a plate heat exchanger composed of multiple, thin, slightly separated plates, for example, that have large areas of fluid flow passage for heat transfer. The number and sizes of the plates can be varied. 
         [0053]    The flat exchanger panel  112  may receive radiant energy from a hot catalytic converter which may be provided in the exhaust outlet  118 . The catalytic converter achieves high temperatures for example in the area of 1200 F. As mentioned, the flat panel heat exchanger  112  also receives convective heat. In order to increase heat transfer and improve capture performance, the angle of inclination of the flat panel exchanger  112  relative to the cooking appliance (automatic grill, for example), as well as the vertical position of the plate relative of the grill can selected from a range of angles and position of the panel heat exchanger selected from a variety of locations, for example, as illustrated at  504 A through  504 D in the embodiment of  FIG. 4 . 
         [0054]    A three-sided box structure functions as a flow guide  302  and is open at the back facing the filter cartridges  122 . The flow guide  302  guides the exhaust air passing through the catalytic converter toward the plate heat exchanger  112  and from the plate heat exchanger toward the filter plenum  108 . The flow guide  302 , in an alternative embodiment, may be replaced with a wrap-around three-sided heat exchanger to scavenge further heat. Such a wrap-around heat exchanger may include a continuous spiraled metal tubing of copper, or each side can be a plate heat exchanger. 
         [0055]    In embodiments, fumes rising in the collar may draw fumes by natural convection which may be sufficient that no powered exhaust is required. Generally powered exhaust will be used to create a negative pressure in the duct  102  and plenum  108 . 
         [0056]    The heat exchangers are designed and are positioned within the exhaust system to maximize a surface area of a tubing wall between the exhaust air moving through the tubing portion and the heat-exchange fluid circulating therein. To increase the surface area fins or corrugations may be added to channel fluid flow or induce turbulence and therefore increase the heat exchanger efficiency. 
         [0057]    In embodiments all the heat exchangers may define a continuous flow path of a heat transfer or heat-exchange fluid. 
         [0058]    In embodiments, more air is drawn through the filters than passes out of exhaust opening  118  such that fumes are prevented from escaping. The escape is further inhibited by the flow guide. 
         [0059]    In embodiments where a water wash exhaust hood is positioned above the cooking appliance, the hood may include a spraying device arranged within the plenum of the exhaust hood and configured to spray a contaminant-soluble cleaning solution onto external surfaces of the heat exchanger “Crossflow HX” positioned within the plenum to remove the contaminant build-up therefrom. 
         [0060]    In an embodiment, the flat heat exchanger  112  may be movable allowing it to be positioned to serve to prevent water wash fluid from entering the exhaust opening  118 . 
         [0061]    The heat recovery system may employ a powered circulating device (not shown), such as a variable speed pump, to circulate the heat transfer fluid through all of the heat exchangers in fluid communication with each other and to move the heat transfer fluid between the heat exchanger arrangement and a heat utilization location which is external to the heat recovery device and external to the exhaust hood. This location is where the recovered energy or heat in the form of hot or heated water is reused. The circulating device may further include pipes, tubes, valves, etc. to carry out the transfer from the heat exchanger arrangement to the external heat utilization location. 
         [0062]      FIG. 4A  shows an embodiment that is similar to the embodiment of  FIGS. 1 to 3 . Referring to  FIG. 4 , an energy or heat recovery device  500  for a chain broiler  520  uses a cross flow tubing type heat exchanger assembly including a first part  508  in the plenum space  524  and a second part  511  in an exhaust duct section  510 . 
         [0063]    Various alternative embodiments of a panel heat exchanger are indicated at  504 A,  504 B,  504 C, and  504 D. Embodiment  504 B and  504 C positions and orientations may help to further guide exhaust flow to the filter  528  and into the plenum  524 . The panel exchanger may also be located more remotely such as at  504 A but positioned inside an exhaust guide  526 . 
         [0064]    The first part of the tube type heat exchanger  508 , in an embodiment and as illustrated, may consist of a series of lateral (going into the drawing page and perpendicular thereto) with 180 degree bends so the tubes traverse back and forth. The spacing between the tubes may be about twice their outer diameters (i.e., centers of adjacent tubes are three diameters apart) or more to allow for effective cleaning. 
         [0065]    As shown in  FIG. 4B  as well as  4 A, the tube heat exchanger second part  511  has a series of flat spiral disks  512  of tubing which are interconnected consecutively at their perimeters  514  and at their centers  516  to form a continuous heat transfer fluid flow path. The centerlines of the tubes may be spaced two or three diameters apart in the spiral winds. The tighter spacing in the spirals  512  may be compensated, for cleaning space purposes, by gaps between the parallel disks  512 . Preferably both tube type heat exchangers are formed close to the walls of the respective plenum or duct to prevent short-circuit flow of air, so a spacing of no more than two diameters is preferred. 
         [0066]    An exhaust collar  517  of the duct can be connected to an exhaust fan for extracting fumes from the hood. The plenum  524  has openings to accommodate filter cartridges  528 . The plate heat exchanger  504 A- 504 D receives radiant energy from a hot catalytic converter in the exhaust outlet  506 . 
         [0067]    In operation, exhaust air or exhaust fumes generated from the broiler flow through the catalytic converter and impinge the plate exchanger and are guided by the flow guide  526  toward the cartridge filters  528  (e.g. cleanable grease filters as used in restaurant hoods). The fumes flow through the filter cartridges  528  into the filter plenum  524  which houses the tube exchanger first part  508 . The fumes then flow through duct section  510  and across the first tube heat exchanger second part  511  and are finally exhausted. The tube heat exchanger first part  508  and second part  511  may be serially interconnected in parallel, or completely separate to feed heat to different loads. IN a preferred embodiment, heat transfer fluid flows from the second part to the first part ( 511  to  508 ). The plate exchanger  504 (A-D) may be connected to the second part to the first part ( 511 ,  508 ) or be connected to a separate load or thermal storage. 
         [0068]    Note in all of the embodiments, above and below, the heat exchangers themselves, or a load, may include a thermoelectric converter to convert heat directly into electricity. Examples of thermoelectric devices include thermopiles or new technologies employing nano surfaces and multilayer semiconductor. 
         [0069]      FIG. 5  shows a heat recovery device  400  for a cooking appliance  414  such as a griddle or fryer. A hood  410  has a rear-flue-bypass  408  which receives combustion fumes from a fuel fired heating device in the cooking appliance  414  and conveys the combustion products into a bypass plenum  416  and then through an adjustable opening  402  into the exhaust plenum  412 . Heat from the combustion fumes is recovered using a plate-fin cross flow tubing type heat exchanger  404  for convective heat transfer to a heat-exchange fluid circulating therethrough. The adjustable opening  402  is adjusted by a shutter plate  442  to allow ventilation of the fuel fired heater to be appropriate given the negative pressure in the plenum  412 . A duct tube type heat exchanger  440 —similar to exchanger  102  and  511  of embodiments 1-3 and 4A, 4B—may be used as well. Since combustion products may be hotter than fumes captured by the hood  410 , in an embodiment, heat transfer fluid flows from exchanger  440  to exchanger  404  to provide a higher temperature output. A lip  403  (running perpendicular to the plane of the page) may be provided to prevent grease from dripping into the bypass plenum  416 . 
         [0070]      FIG. 6  shows an exhaust hood  610  with a filter plenum  612  and filter  604 . An exhaust duct  618  is connected to an exhaust fan and draws fumes through the plenum  612  and the filters  604  from a cooker  614  with a hot surface  624  such as a griddle or fired grill. A flat panel heat exchanger  622  is fixedly supported as indicated at  622  to capture radiant heat from the hot surface  624 . 
         [0071]    In an alternative embodiment, a second flat panel exchanger  628  pivots from a home position  630  to a semi-shrouding position  634  to expand the area of radiant energy capture and to reduce the size of an aperture through which room air is drawn. A controller may position the heat exchanger  628  responsively to any of a variety of detected conditions such as occupancy (lack of occupancy) by a worker using an occupancy detector, time of day, operating condition of the cooker, video or infrared event recognition of a cooking phase. Techniques for such state or event detection are described elsewhere in the prior art so the details are not developed here. In the embodiment shown, the second flat panel exchanger  628  is closer to the hot surface  624  than the fixed one  622 , however, it may be located in a more remote position and only activated when in the fenestrating position shown at  634 . Any kind of mechanism may be used to make the panel  628  movable, including a pivot and arm as indicated at  648 . The movable panel may be a thermoelectric panel to allow for fast response and avoid the need to provide plumbing. 
         [0072]      FIG. 7  shows a control system  714 , multi-way valve interconnect  716 , tube heat exchangers  702 , radiant plate heat exchangers  704 , sensors for imaging  708 , flow Q, temperature and/or radiant flux  710 , production rate (which may be predicted or detected), quantitative load  713 , direct heat to electrical receiver/converter  704 , and auxiliary devices such as instantaneous fluid heater  728  to provide temperature boost, thermal storage  726 , and high  730  and low  724  temperature thermal loads all interconnected to define a combined energy recovery system. Note that in embodiments, any of the above elements may be omitted. Also, the selected multi-way valve interconnect may be replaced by fixed connections as appropriate where no selectable and controllable changes in connections are required. Omitted from the general drawing are one or more pumps because these may be positioned in any of the interconnections shown as appropriate. Pumps may be controlled by the controller  714 . Controller  714  is preferably a digital programmable controller with appropriate user interface and inputs and outputs for effecting commands and detecting conditions and events. The generalized system description applies to any and all embodiments disclosed herein modified accordingly. 
         [0073]    In the foregoing embodiments, the heat exchangers may be in a continuous fluid communication with each other and connected in series with each other, namely, in such a way as to allow the heat transfer fluid to enter the heat exchanger arrangement through the first heat exchanger through all of the heat exchangers before exiting the heat exchanger arrangement through the last heat exchanger. A pumping mechanism may be employed to pump the heat transfer fluid from a fluid source to the heat exchanger arrangement, and to circulate the transfer fluid through the heat exchanger arrangement. The heat transfer fluid may be water or water with an antifouling agent. In operation, fluid is transferred from a source to the energy recovery heat exchanger arrangement and circulated to a load responsively to an event or operating condition. For example, when temperature of an exchanger itself reaches a threshold, pumping may begin and the rate of pumping may be responsive to the exchanger or the return fluid temperature to the load. 
         [0074]    As fluid flows through the heat exchangers, it absorbs heat from the hot exhaust air, as a portion of the hot exhaust air is transferred to the copper tubing which in turn conducts its absorbed heat to the fluid circulating therein. Through this heat transfer, the fluid leaving the heat exchanger arrangement will be at a higher temperature than the fluid entering the heat exchanger arrangement, and at least a portion of the heat from the hot exhaust air is effectively recovered as hot fluid. The hot fluid leaving the heat exchanger arrangement can be used to supply hot fluid to different parts of the exhaust hood or different parts of the system, or it can be used to supply the restaurant with its hot fluid demand. 
         [0075]    The efficiency of the heat recovery device is dependent not only on how much heat is extracted from the exhaust air and how much of it is absorbed by the fluid, but also how much energy is saved in the process. 
         [0076]    In embodiments, the speed and flow rate of the fluid circulating through the heat exchanger arrangement so that the amount of fluid circulated is adjusted to fit a particular circumstance, need, or requirement. 
         [0077]    Adjusting the speed and flow rate of the fluid in the heat exchanger arrangement can be done using a variable speed pump to circulate the fluid through the heat exchanger arrangement. Changing the speed of the variable speed pump changes the speed and the flow rate of the fluid circulating through the heat exchanger arrangement. A controller device can automatically adjust the speed of the pump based on various factors, including, but not limited to, the demand for hot fluid, the status of the cooking appliance, the temperature of the fluid leaving the heat exchanger arrangement, etc. The controller device is configured to receive a signal from a sensor indicating a need for hot fluid at the location of heat utilization P, for example, and based on the received signal the controller device can adjust the pump speed to circulate the fluid in the heat exchanger arrangement having a corresponding flow rate and speed. The controller device is further configured to receive a signal from the cooking appliance (not shown), the signal indicating whether the cooking appliance is idle or is being used (working), and based on the received signal the controller device can adjust the pump speed to circulate the corresponding amount of fluid through the heat exchanger arrangement. 
         [0078]    The condition that there is abundance of heat that can be reclaimed which could significantly exceed demand may arise. Embodiments of any of the systems described herein may include an insulated storage tank sized for approximately the maximum predicted heat that can be reclaimed for a specified setpoint temperature. Such a tank may have a variable volume and may be filled to accommodate a corresponding amount of heat for consumption during times when heat demand exists but supply is not available or too low. For example, at an end of a work day and during off hours, the water level in the tank may be lowered by transferring heat from the tank and either storing in a cool source tank or draining. The cycle may be repeated for the next day or period, when the system is running. Such a structure provides a variable volume system with variable capacity. 
         [0079]    In any of the disclosed systems, the load can include a heat loop used for warming/holding well or tables and cabinets, for example, a dry or steam well table. 
         [0080]      FIG. 8  shows another embodiment of a heat recovery device  800  for a cooking appliance  824  such as a griddle, fryer, oven, or other cooker (fryer basket shown at  828  so this embodiment is a fryer). A hood  826  has a rear-flue-bypass  818  which receives combustion fumes from a fuel fired heating device in the cooking appliance  824  and conveys the combustion products into a bypass plenum  808  and then through an adjustable opening  814  into a filter  624  bearing filter plenum  844 . Heat from the combustion fumes is recovered using a plate-fin cross flow tubing type heat exchanger  806  for convective heat transfer to a heat-exchange fluid circulating therethrough. The adjustable opening  814  is adjusted by a shutter plate  846 . The shutter plate  846  and a fixed plate  848  which collectively define the opening  814  have angled flanges to cause grease to drip away from the heat exchanger  806  and also to minimize wash water getting into the bypass plenum  808  from the filter plenum  844 . The adjustable opening allows selection of the negative pressure in the bypass plenum to be regulated. A duct tube type heat exchanger—similar to exchanger  102  and  511  of embodiments 1-3 and 4A, 4B—may be provided as well. Couplings  810  may be provided for connecting the heat exchanger  806  to external fluid lines  812 . A wall standoff is shown at  804  and a combustion outlet standoff at  802 . The combustion outlet  818  supplies combustion gas to the bypass plenum  808 . An exhaust take-off is indicated at  845 . 
         [0081]      FIG. 9  illustrates another example of a heat transfer fluid flow in a heat exchanger loop of a heat recovery device. The heat recovery device can be any one of the heat recovery devices described in the embodiments. The heat exchangers are as shown at  906 ,  908 , and  910 . A circulation loop  901  circulates heat transfer fluid through the heat exchangers  906 ,  908 ,  901  in a series arrangement to recover thermal energy and convey heated heat transfer fluid to one or more loads  940 . The controller  902  can control the pump  912  which may be a variable speed pump, responsively to a temperature  904 . 
         [0082]      FIG. 10  illustrates another example of a heat transfer fluid flow in a heat exchanger loop of a heat recovery device. The heat recovery device can be any one of the heat recovery devices described in the embodiments. The heat exchangers are as shown at  906 ,  908 , and  910 . A circulation loop  905  circulates heat transfer fluid through the heat exchangers  906 ,  908 ,  901  in a parallel arrangement to recover thermal energy and convey heated heat transfer fluid to one or more loads  940 . The flows from the heat exchangers are combined at a junction for supply to one or more loads  940  or can be separately supplied to respective loads in an alternative embodiment. The controller  902  can control the pump  912  which may be a variable speed pump, responsively to a temperature  904 . A respective pump may also be provided to the flow loops respective to each exchanger. 
         [0083]      FIG. 11  shows the heat transfer fluid flow in a heat exchanger loop of a heat recovery device for a system that includes a plurality of exhaust hoods each with a corresponding cooking appliance  932 ,  934 ,  936 . Only three cooking appliances and associated hoods are shown but more or fewer may be provided. The heat exchanger loop includes a plurality of heat exchanger sets  906 ,  908 ,  910 , each set associated with a corresponding exhaust hood and/or cooking appliance. Each of the heat exchanger sets  906 ,  908 ,  910  may include one or plurality of heat exchangers, such as, but not limited to those described in the various embodiments such as embodiments of  FIGS. 1-3 . The plurality of heat exchanger sets  906 ,  908 ,  910  are in a fluid communication with each other so that a circulating device  928  can circulate heat transfer fluid simultaneously through all of the exchanger sets  906 ,  908 ,  910 , and so that the heat transfer fluid can exit simultaneously from each of the heat exchanger sets. In the present arrangement the heat transfer fluid can be affected simultaneously in all heat exchanger sets  906 ,  908 ,  910 . The circulating device may include a respective pump  928   a ,  928 B,  928 C, with each controlled responsively (e.g., negative feedback control) responsively to a respective sensor  922 ,  924 ,  926 . 
         [0084]    In operation, fluid is transferred from a heat transfer fluid source to the heat exchanger arrangement and circulated through each of the heat exchanger sets using the pumping mechanism. As the heat transfer fluid flows through the heat exchanger sets, it absorbs heat from the hot exhaust air through the metal tubing and it heats up. Through this heat transfer, the heat transfer fluid leaving the heat exchanger sets will be at a higher temperature than the heat transfer fluid entering the heat exchanger sets. Thus, at least a portion of the heat extracted from the hot exhaust air is effectively recovered as heated or hot heat transfer fluid. The hot heat transfer fluid leaving the heat exchanger arrangement can be used to supply hot heat transfer fluid to different parts of the exhaust hoods or different parts of the system or it can be used to supply the restaurant with its hot heat transfer fluid demand. 
         [0085]    The speed and flow rate of the heat transfer fluid circulating through each of the heat exchanger sets  906 ,  908 ,  910 , can be controlled so that the amount of heat transfer fluid circulated through each of heat exchanger set can be adjusted to fit a particular circumstance, need, or requirement. Adjusting the speed and flow rate of the heat transfer fluid in the heat exchanger sets can be done using variable speed pumps  928 A,  928 B,  928 C. Changing the speeds of the variable speed pumps changes the speed and the flow rate of the heat transfer fluid circulating through each of the heat exchanger sets. 
         [0086]    A controller device can automatically adjust the speed of each of the pumps  928 A,  928 B,  928 C individually, based on various factors, such as, but not limited to, the demand for hot heat transfer fluid, the status of the cooking appliances, the temperature of the heat transfer fluid leaving each of the heat exchanger sets, etc. The controller device  938  is configured to receive a signal from sensors  922 ,  924 ,  926  indicating a need for hot heat transfer fluid at the location of load  950 , for example, and based on that signal the controller can adjust each of the individual pump speeds to circulate the heat transfer fluid in the heat exchanger arrangement having a corresponding flow rate and speed. 
         [0087]    Note that although a junction  940  is shown which combines the separate flow streams, each stream could convey fluid to a respective load. In one embodiment, high temperature heat exchangers may be connected in parallel and flow together through a junction to a high temperature load, medium temperature heat exchangers may be connected in parallel and flow together through a junction to a medium temperature load, and low temperature heat exchangers may be connected in parallel and flow together through a junction to a low temperature load. For example, the radiant heat exchanger may be the high temperature heat exchanger, the bypass heat exchanger, the medium temperature heat exchanger, and the flue or filter plenum heat exchanger may be the low temperature heat exchanger. 
         [0088]    The controller device  938  may be further configured to receive signals from each of the cooking appliances  932 ,  934 ,  936 , each signal indicating whether the corresponding appliance is in a particular working state such as idle, low power, or full power, for example. Based on the signals received the controller  938  may adjust the speed of each pump to circulate a corresponding amount of heat transfer fluid through respective heat exchanger sets or to shut down circulation. 
         [0089]    The controller device is also configured to cut-off heat transfer fluid supply to any of the heat exchanger sets when the received signal indicates that the corresponding cooking appliance is in an idle state, thereby completely bypassing heat transfer fluid circulation through the heat exchanger set in the exhaust hood where the cooking appliance is not in use. 
         [0090]    The controller device is further configured to receive signals from a temperature detecting system (not shown), the signals indicating the temperature of each of the heat exchanger sets. The controller device can completely shut-off heat transfer fluid circulation through any of the heat exchanger sets that has a temperature below a predetermined minimum temperature. The predetermined minimum temperature is indicative of whether a cooking appliance is in a working or in idle state. The controller device is further configured to reverse the flow of heat transfer fluid through the heat exchanger arrangement so that heat transfer fluid flows from a heat exchanger set having a lower temperature to a heat exchanger set having a higher temperature between those heat exchanger sets that have a temperature above the predetermined minimum temperature. 
         [0091]      FIG. 12  shows the heat transfer fluid flow in a heat exchanger loop of any one of the energy recovery devices discussed in detail in the arrangements shown in the various disclosed embodiments integrated with a hot water storage and supply system  1200 . The heat exchanger loop  1214  can have one or more pumps  1204  and can include the heat exchanger  1216  arrangement of any of the embodiments in any combination where the system can include one or multiple exhaust hoods. 
         [0092]    In operation, external water from an external water supply source (City Water Supply, for example)  1212  enters a water storage reservoir  1206  to fill an interior volume of the storage reservoir  1206 . A valve (not shown) can be positioned between the entry point of the external water supply and the water storage reservoir. This valve can be closed at its entrance port to prevent more water being supplied to the water storage reservoir from the external water supply source and to prevent the interior volume being emptied in the direction of the external water supply source. Water from the water storage reservoir is transferred to the heat exchanger arrangement  1216  using a pump  1204 . The water is circulated through the heat exchanger arrangement  1216  and heat from the hot exhaust air is transferred to the heat transfer fluid circulating therethrough. Hot heat transfer fluid is transferred back to the water storage reservoir and used to heat the water therein by means of a heat exchanger (not shown) or the heat transfer fluid may itself be the same as the water in the tank. The tank water may be gray water or potable. Hot water from the storage reservoir is then further transferred to different distributing points to supply hot water where hot water is needed. Preferably the tank is insulated. The hot water may be selectively consumed at various stations  1210  such as a dishwasher. 
         [0093]      FIG. 10  shows the heat transfer fluid flow in a heat exchanger loop of any one of the energy recovery devices discussed in detail in the embodiment of  FIG. 8  integrated with a hot water storage and supply system. The heat exchanger loop represents the heat exchanger arrangement of the system. Only three cooking appliances and associated hoods are shown. However, the system can include any number of hoods/cooking appliances. The heat-exchanger arrangement includes a plurality of heat exchanger sets HX 1 , HX 2 , HX 3 , each set associated with a corresponding exhaust hood and/or cooking appliance. Each of the heat exchanger sets HX 1 , HX 2 , HX 3  includes a plurality of heat exchangers, such as, but not limited to, a “Panel HX”, a “Crossflow HX”, and a “Collar HX”, positioned within their respective hoods as shown in the heat recovery device of the embodiment illustrated in  FIGS. 1-3 . The plurality of heat exchanger sets HX 1 , HX 2 , HX 3 , are in a fluid flow communication with each other and are connected in parallel so that a circulating device can circulate heat transfer fluid simultaneously through all of the exchanger sets HX 1 , HX 2 , HX 3 , and so that the heat transfer fluid can exit simultaneously from each of the heat exchanger sets. 
         [0094]    The circulating device includes a pumping mechanism which moves water from a water source to the heat exchanger arrangement, and circulates the water through the heat exchanger sets. In operation, water is transferred from the water source to the heat exchanger arrangement and circulated through the heat exchanger sets using the pumping mechanism. As the water flows through the heat exchanger sets, it absorbs heat from the hot exhaust air and starts to heat up. Through this heat transfer, the water leaving the heat exchanger sets will be at a higher temperature than the water entering the heat exchanger arrangement, and at least a portion of the heat from the hot exhaust air is effectively recovered as hot water. The hot water leaving the heat exchanger arrangement can be used to supply hot water to different parts of the exhaust hoods or different parts of the system or it can be used to supply the restaurant with its hot water demand. 
         [0095]      FIG. 13  shows a system that combines features of the embodiments of  FIG. 11  and  FIG. 12 . Here, a controller device  1302  receives information from respective cooking appliances  932 ,  934 ,  936  (which may be fewer or more in number) indicating whether the corresponding appliance is in an idle or a working state, and based on the signals received, the controller device can cut-off water circulation through any heat exchanger set associated with a cooking appliance in an idle state and thereby completely bypass water circulation through the heat exchanger set in the exhaust hood where the cooking appliance is not in use. 
         [0096]    The controller device  1302  is further configured to receive signals from a temperature sensors  1302  (typ.), the signals indicating the temperature of the water leaving each of the heat exchanger sets  906 ,  908 ,  910 . The controller device  1302  can further receive a signal from a temperature sensor  1302  in the hot water storage reservoir indicating the temperature of the water in the reservoir to regulate the pumping. For example, the controller device may be configured to compare the temperature of the water exiting each of the heat exchanger sets with the temperature of the water in the storage reservoir, and allow the circulating device including flow diverters to transfer water only from those heat exchanger sets for which the exiting water has a higher temperature than the temperature of the hot water storage reservoir. Thus exiting water having a higher temperature than the temperature of the water in the storage reservoir will be allowed to flow through diverters D 1 , D 2 , and D 3  via pathways A to meet at a common point P from which the water is then circulated to the water storage reservoir. The water exiting the heat exchangers with temperatures below the temperature of the water in the storage reservoir will be diverted by the diverters D 1 , D 2 , and D 3 . 
         [0097]    It is therefore, apparent that there is provided, in accordance with the present disclosure, an energy recovery device and method for recovering and reusing heat from hot exhaust air generated from cooking appliances, and a controller device and method for controlling the rate of the heat recovery. Many alternatives, modifications, and variations are enabled by the present disclosure. Features of the disclosed embodiments can be combined, rearranged, omitted, etc. within the scope of the invention to produce additional embodiments. 
         [0098]    In particular, each of the described heat exchanger arrangements can further include additional heat exchangers present in the exhaust hood, such as, but not limited to, the three-sided wrap-around heat exchanger arrangement also used as the guiding device. 
         [0099]    Furthermore, certain features of the disclosed embodiments may sometimes be used to advantage without a corresponding use of other features. Accordingly, Applicant intends to embrace all such alternatives, modifications, equivalents, and variations that are within the spirit and scope of the present disclosure.