Patent Application
20250067464
Cooking appliances typically generate substantial heat that is either transferred to the ambient space, burdening native air conditioning (AC) systems, or vented outside for removal of cooking gases along with the heated airflow. Commercial kitchens are often required to employ air exhaust systems, typically a vent hood, with a prescribed performance for air volume movement of heated air vented for a stove or flattop. Thermal energy expelled from the cooktop is also vented to the atmosphere in the exiting airflow.
A waste heat extraction and capture device located in a stream of waste heat from a cooking appliance extracts heat energy from heated air destined for venting to an ambient exterior. Exhaust fans and hoods are positioned for receiving and exhausting hot air venting off a cooking surface, and typically direct the heated cooking gases to ambient atmosphere for avoiding a buildup of hot air, cooking grease and other vapors emitted as a byproduct of food preparation. A heat transfer element disposed above the cooking surface recovers heat for recapturing thermal energy that would otherwise be simply expelled. A fluid traveling through the heat transfer element is heated by the passing exhaust stream of waste heat, and can be stored for subsequent use, such as for potable hot water, interior space heating, or other cooking processes. An attachment strap, bracket or mechanism secures the heat transfer element in the vent hood that is typically tapered for effective heat gathering, and is positioned downstream of filters or traps for grease so as to avoid clogging the heat transfer element.
In a particular configuration, a method and apparatus for extracting the waste heat from the cooking burners and using that heat to heat cold water to hot water from a water storage tank. Unheated water from a water storage tank is pumped into a heat extracting device. A heat exchanger, car radiator, metallic coils and or recuperators are considered to be a waste heat extracting device. It is placed above the burners inside the range hood. Once the cooking starts, and the exhaust fan is on, the exhaust fan draws an updraft of the heat from the burners, and the heat extracting device below the exhaust fan becomes heated. During the process, when the heat extracting device reaches a steady state temperature, cooler water is pumped to the heat extracting device inlet and hot water is generated by extracting the waste heat from the burners and flows into the water storage tank. A thermostat controls the water flow to the heat extracting device. Recirculating the water from a water storage tank to the waste heat extracting device helps to save the utility bills for saving energy usage.
Configurations herein are based, in part on the observation that conventional commercial cooking appliances generate large amounts of heat that are lost to outside ventilation due to building codes, cooking grease retention and control, and mitigation of cooking odors in a retail establishment. Unfortunately, thermal energy in the heated air is also vented and lost along with airborne particulate matter and odors. Accordingly, configurations herein substantially overcome the shortcomings of conventional cooking appliance heat loss by disposing the hear transfer element in the waste stream of thermal energy for recapturing thermal energy from a fluid pumped through the heat transfer element to receive at least a portion of the waste heat from thermal exchange.
In an example configuration, a waste heat extraction device includes a heat transfer element having a fluid vessel disposed in a stream of waste heat, and a vertical attachment securing the heat transfer element in the stream of waste heat, such as inside a vent hood of a cooking appliance. A pump in fluidic communication with the fluid vessel circulates a heated fluid through the fluid vessel, and a pump controller is responsive to a temperature of the heated fluid in the fluid vessel in response to the stream of waste heat, such that the pump controller is adapted to circulate the heated fluid based on predetermined waste heat recapture conditions. A recapture tank completes a fluid loop connected to the fluid vessel for receiving and storing the heated fluid.
The foregoing and other features will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.
The present disclosure relates to a method and apparatus for extracting the waste heat generated from a kitchen burner, and more particularly to a method and apparatus for extracting the waste heat and utilization of that heat to heat cold water to hot water for saving utility bills. Waste heat generated by the cooking burners becomes energy that is unused as it is exhausted to the open atmosphere. Recovering part of that waste heat can be used to heat cold water to hot water and saves utility bills. An apparatus and a method of utilizing the waste heat generated from the kitchen burners is described to heat cold water to hot water as the water circulated from a water storage tank. This approach for recovering the waste heat and utilizing that heat to heat cold water to hot water can save the planet from global warming and will help consumers or businesses save their energy bill by reducing the energy consumption. A device and method for utilizing exhaust heat that is generated by the cooking burners when they are turned on and utilizing that exhaust heat to generate hot water in a water storage tank is described herein.
It is estimated that 25 to 50% of industrial energy input is lost as waste exhaust heat from hot equipment surfaces or heated products. Recovering that waste heat will generate energy savings and it will also reduce the environmental impact.
Conventional approaches include the following. In U.S. Pat. No. 8,051,637B2, there is a disclosed heat energy recapturing and recycling a used heat absorbing radiator and a gas turbine engine for recapturing and reconverting waste heat to electric power and applied to make a diamond.
In U.S. Pat. No. 9,318,682B2, Lorimer et. Al. showed an apparatus to extract heat for converting thermal energy to electric energy by using thermoelectric units.
In U.S. Pat. No. 8,938,964B2, Kanou and Kasuya showed a waste heat utilization apparatus for an internal combustion unit.
The above refenced conventional approaches use the waste heat for producing electric power and for internal combustion whereas the present disclosure teaches using the waste heat generated form cooking burners in restaurant and residential kitchens for heating cold water or other heated liquid into hot water in a water storage tank. Using this exhaust heat from the kitchen burners in turn saves the energy consumption that would otherwise be needed to supply the recaptured heat.
In a basic configuration, the waste heat extraction device disclosed herein includes a heat transfer element including a fluid vessel disposed in a stream of waste heat, and a vertical attachment securing the heat transfer element in the stream of waste heat, typically in a vent hood above the cooking surface. A pump is in fluidic communication with the fluid vessel for circulating a heated fluid through the fluid vessel, and a pump controller is responsive to a temperature of the heated fluid in the fluid vessel in response to the stream of waste heat. The pump controller is adapted to circulate the heated fluid based on predetermined waste heat recapture conditions, and a recapture tank connected to the fluid vessel receives and stores the heated fluid.
In operation, the described method and apparatus extracts the waste heat from the cooking burner and uses that heat to heat cold water to hot water from a water storage tank. The cold water is pumped to the heat extracting device. Any suitable heat exchanger, car radiator, metallic coils, recuperators and the like may be employed for the waste exhaust heat extracting device. The waste heat extraction device is placed above the burner or cooking surface and below the exhaust fan inside a cooking range hood. Copper, aluminum, or stainless-steel coils can also be used for extracting the waste heat. Once the burners are turned on, and the exhaust fan activated, the exhaust fan draws the heat generated from the cooking burners for venting to the open atmosphere. During this process, when a heat extracting device is exposed to the heat generated by the cooking burners and reaches a steady state temperature of 400° to 500° F., cold water is pumped into the inlet of the heat extracting device from a water storage tank. Cold water provides a temperature differential that will extract the waste heat from the heat extracting device which has a large surface area for extracting the waste heat. Cold water is heated by absorbing the heat from the heat extracting device and the heated water or other liquid then flows into the water storage tank through an open valve. A thermostat is used in the hot water pipe to the water storage tank, or elsewhere in the recirculation loop between the heat exchanger and storage tank. A typical hot water storage temperature is maintained between 120° to 130° F. When the hot water temperature exceeds a predetermined water temperature, the thermostat will automatically shut off the valve and the water flow will stop. As the water temperature in the storage tank drops below the required temperature, the inlet pump will turn on and the water will flow from the storage tank to the heat extracting device for extracting the exhaust heat, and the cycle iterates.
A heat transfer element is defined by suitable heat extracting device 11, such as a heat exchanger, car radiator, metallic coils and recuperator can be used to extract the waste heat 14 efficiently. This heat extracting device 11 is placed 12 inches above the burners and below the exhaust fan and exhaust filter 7 as shown in
Looking further in
The cold water 6 and hot water 2 pipes or conduits may form a closed system with the heat transfer element and storage tank 1, and therefore only a single pump is needed on either the supply to the heat transfer element or the hot water 2 return. A thermostatic control ensures that the pump 5 operates only when heating the water, meaning that the waste heat 14 is flowing at a temperature greater than ambient and above a setpoint or temperate of the storage tank 1. Generally, waste heat recapture conditions are based on an activation of a source of waste heat and a demand for recaptured thermal energy in the heated fluid. The waste heat recapture conditions are indicative of a temperature of the heated fluid above a threshold defined for useable recycled heat. A typical setting is 200° F., however any suitable temperature may suffice. Typical domestic hot water for dishes and bathing is usually capped at 140° F.
The pump 6 provides for passing the cooler water 6 source through the heated fluid (vent gases) for receiving potable hot water. An additional connection to the storage tank 1 may be used for directing the heated fluid to a hot water recycling application, i.e. simply a potable hot water usage such as dish washing.
Since the vent hood 12 is disposed above the cooking appliance, the heat transfer element 11 is suspended immediately above the stove or burner emitting the heat via attachment within the vent hood. Vertical attachment may include one or more brackets 20-1 . . . 20-2 (20 generally) attaching the heat transfer element to an interior void 18 of an exhaust conduit to an exterior ambient environment. It is preferable that the vertical attachment engages an interior of a circumference of the exhaust conduit. The brackets 20 may be “L” shaped disposed on opposed sides of the vent hood 12 within the void 18. A tapering of the vent hood 12 tends to draw and accelerate flow of the waste heat approaching the fan 11.
The venting conduit may include a tapered vent hood, with a varying cross section. In such an arrangement, the transverse member 32 may be disposed based on a length corresponding to the cross section. It is preferable, but not required, to secure the heat transfer element between a filtering element and a propulsion source for the waste heat flow, such that the filtering element is adapted for grease capture to avoid excess airborne grease droplets from falling on and possibly impeding airflow through the heat exchanger 11.
Particular examples and use cases of waste heat recapture using a vertically suspended or attached heat exchanger above a cooking heat source follow.
A car radiator in open air was placed in front of two portable heaters in open air. Radiator inlet and outlet lines were placed in two buckets. From a first bucket, a cold-water inlet tube was connected to the radiator inlet. A hot-water outlet tube from the radiator was placed inside a second bucket. Heaters were turned on and measured the radiator surface temperature by using an infrared thermometer (ETEKCITY® LASERGRIP 800). Average temperature after 15 minutes reached 100° F. Cold waters at 45° F. was then pumped from bucket 1 to the radiator inlet and collected the extracted hot water from the radiator outlet into bucket 2. After 15 minutes, water temperature reached to 65° F. in bucket 2 and noticed the average temperature of the heated radiator surface dropped to 70° F. due to cold water flowing through the radiator. The experiment taught us that the cold water when passed through a heated radiator surface, it can extract the heat from the high surface area of the radiator fins and the 45° F. cold water was heated to 70° F.
A significant feature of the disclosed approach is to recapture the waste heat from the kitchen burners and utilizing that heat to heat cold water to hot water for reducing the energy bill of the restaurant or home for generating potable hot water. In restaurants, gas or electric energy is used to heat the hot water which is in great demand and usage for cooking and cleaning. Recapturing the waste heat also reduces the carbon emission into the open atmosphere. Other configurations may also employ a filter underneath the high surface area radiator to protect the radiator from grease and soot particles. Conventional approaches require wide spacing between louvers, fins and/or the fluid vessel for allowing grease and cooking particles to pass, reducing efficiency of the heat transfer. The filter can be replaced periodically as needed.
The disclosed approach is adapted to connect to a building/residence potable hot water supply. In a restaurant context, this allows the captured heat to source hot water for use in restaurant operations, such as washing dishes and cookware. In contrast to conventional approaches, the recapture tank 1 is engaged with a potable hot water source 52 for sourcing a potable hot water source 52 and hot water tap 51. The potable hot water source may include a native hot water facility 50 such as a tank or tankless arrangement. The native hot water source 50 may be engaged with a municipal water source 54, so that the captured heat supplements the native hot water facility 50, in the event that a blend of captured hot water 2 needs addition heating.
In the present approach, a heat extracting device is placed on top of the range inside a kitchen exhaust hood and it will be exposed to waste heat generated from the burners at a finite distance from the burners. Extracted heating surface can reach in excess of 500° F. depending on number of burners running at one time and the distance between the burners and the heat extracting device placement. If the heat extracting device is placed closer to burners, it will be heated more and the device is placed at a higher distance from the burners, it will be heated less.
Measurement results of kitchen exhaust temperature in a Restaurant Cooking Range. Distance from the burners to exhaust filter (exhaust fan is located above the filter)=24 inches. A K-type thermocouple was used to measure the temperatures (using a Kamtop Digital Thermometer).
When the burners were turned on:
If a heat extracting device is placed 12 in. above the burner, the device will reach a temperature more than 300° F. when only one burner is turned on. When multiple burners (typically 4 burners in a residential kitchen) are turned on for cooking food, the heat extracting device temperature expected to be well above 400° F. When a steady state temperature is reached at the heat extracting device surface, a cold-water can be pumped into the inlet o the heat extracting device from the water storage tank. Cold water will extract heat and will produce hot water which will then flow into a water storage tank through an open valve.
Measurement results of kitchen exhaust temperature in a Restaurant Cooking Range. Distance from the burners to exhaust filter (exhaust fan is located above the filter)=30 inches. A K-type thermocouple was used to measure the temperatures (using a Kamtop Digital Thermometer).
When the burners were turned on:
If a heat extracting device is placed 12 in. above the burner, the device will reach a temperature more than 300° F. when only one burner is turned on. When multiple burners in the restaurant kitchen will be turned on for cooking or grilling the food, the heat extracting device temperature is expected to be well above 400° F. When a steady state temperature is reached at the heat extracting device surface and the water storage tank temperature drops below the set temperature of 120° to 130° F., cold-water can be pumped into the inlet of the heat extracting device from the water storage tank. Cold water will extract heat and will produce hot water which will then flow to the water storage tank through an open valve.
While the system and methods defined herein have been particularly shown and described with references to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.
