The present invention relates to thermoelectric generators. More specifically, the present invention relates to a stove having a thermoelectric generator.
Use of wood and coal stoves is surprisingly common. These stoves are used by many people around the world, including remote locations throughout North America. Many of the people who rely on wood/coal stoves do so because they do not have ready access to electricity.
Thermo-electric generators for wood and coal stoves are known. The generators use heat from the stove and convert it to electric power which can be used to power external loads. Heat passes through a hot side plate of the generator to a cold side plate and a thermoelectric module uses the temperature difference between the hot side plate and cold side plate to convert the heat to electric power. Therefore, the higher the temperature difference between the hot side plate and cold side plate, the more electric power is generated
However, the heat from a wood or coal stove varies substantially. Further, the generators are typically located either on top of the stove or in the stovepipe, which does not provide the most efficient use of the heat from the stove. One common embodiment attaches the generator to the chimney of the wood stove (see http://www.hi-z.com/websit13.htm). In another embodiment, the generator is free-standing, and is placed on the wood stove (see http//hi-z.com/websit10.htm).
Each of these approaches has drawbacks. In the first case, a modification to the chimney is required, specifically to draw heat from the flue gases. The chimney of a modem wood stove is carefully designed to optimize the combustion of flue cases, and to maintain the heat of the flue gases so that the stove draws properly, and to prevent buildup of combustion byproducts (creosote) on the inside of the chimney. Any modification to the chimney will reduce the efficiency of the stove, create more pollution, and create a safety hazard with the buildup of creosote.
In the second case, the generator is placed on the surface of the stove. The placement of the generator directly over the fire causes risk of failure of the generator if the hottest part of the combustion is directly below the generator. Another drawback is that the stove top insulates the generator from the fire, so that this arrangement may also result in the heat being too low. In some stoves, there is an internal insulating plate or baffle that is designed to prevent the full heat from reaching the top surface.
In both cases, the ambient air used for cooling is drawn from near the stove top, where the air is warmed by the stove, and is not the coldest air in the room because of normal stratification where the warm air in a room rises and the cool air falls.
In Canadian Patent Application 2,470,739, the thermoelectric module is used with a fireplace and must be incorporated right within the original structure of the fireplace.
A thermo-electric generator for a wood or coal stove is disclosed. According to teachings of this invention, the hot side plate of the generator is in a direct path of the heat from the stove. In this way, heat from the stove is more efficiently harnessed by the generator, resulting in more efficient electricity conversion. Preferably, the cold side plate is situated to be exposed to the ambient air close to the ground, which is typically cooler thus providing for a larger temperature gradient.
In one embodiment, the generator is incorporated within the door of the wood stove. The door comprising the generator can be installed on any typical wood/coal stove. The installed door then positions the hot side plate of the generator in a direct path of the heat. The door may be interchangeable with the standard door, where the standard door has a heatproof transparent window to observe the fire, and the generator door has no window or a smaller window.
The generator may also comprise cooling fins on the cold side plate, optional cooling fans, and electric controls combined with the appropriate fasteners and wiring. An optional guard can be placed on the exterior of the hot side plate on the side exposed to the heat. This may serve to protect the hot side plate from the direct heat. Preferably, the guard is a steel wire log guard.
In another embodiment, a bimetal operated mechanism can be used to protect the module from excess heat. When the stove surface is too hot, the bimetal strip forms a curve that lifts the assembly away from the stove surface, pressing against the force of the compression springs. When the stove surface is cooler, the bimetal strip returns to its normal, flat profile, lying within a slot provided in the lower surface of the pad.
The modules can be used in a side by side arrangement for multiple module use in a generator. Alternatively, a ‘floating’ arrangement where each module is attached to its own hot side pad and cold side pad, forming a module assembly can be used. The floating pad approach allows the module to more closely and evenly absorb heat from the uneven stove surface.
Alternatively, the floating pad has also been found to be useful in the construction of a stove top generator. In either embodiment, (door mounted generator or stove-top generator) use of the floating pad adds an additional benefit with respect to field service, since separate pads for each module provide for much easier replacement of failed modules, as the failed assembly can be easily removed without affecting the other modules.
Electric devices may be run directly from the generator, for example lights, circulating fans, radios, or computers; devices may be charged by the generator, for example cameras, cell phones, GPS or computers, or the energy may be stored in a battery.
Embodiments of the invention in accordance with these teachings have some of the following features:
Other aspects and advantages of embodiments of the invention will be readily apparent to those ordinarily skilled in the art upon a review of the following description.
Embodiments of the invention will now be described in conjunction with the accompanying drawings, wherein:
This invention will now be described in detail with respect to certain specific representative embodiments thereof, the materials, apparatus and process steps being understood as examples that are intended to be illustrative only. In particular, the invention is not intended to be limited to the methods, materials, conditions, process parameters, apparatus and the like specifically recited herein.
Referring to
Thermoelectric modules are widely available. Most are designed to create a temperature differential for cooling purposes, for refrigerators. TE modules for power generation use the same basic principles, but are designed to withstand higher temperatures on the hot side so that higher temperature difference can be achieved. The higher the temperature a module can withstand, the more useful it is in this application. One skilled in the art will understand the operation of a TE generator.
Embodiments of the invention will be described with reference to a wood stove, but one skilled in the art will appreciate that the teachings can be equally useful for other types of stoves such as coal stoves.
Referring to
As seen in
The cold side plate 16 is positioned to be exposed to the ambient room temperature. Preferably the generator 10 is mounted to the stove 20 such that the cold side plate 16 is relative low to the ground, where the ambient air is coolest thus generating a higher temperature gradient. The cold side plate 16 includes cooling fins 33. Vertical fins will enhance the airflow through natural convection.
Thermo-electric modules 14 are sandwiched between the hot 12 and cold 16 side plates to convert the thermal energy from the temperature gradient into electrical energy. Such thermo-electric modules 14 are known in the art. Preferably, the module used is a 35 mm module. Larger, more powerful modules are available, however such modules are harder to manufacture, meaning that for a given power output the cost to manufacture would be higher. For example, four 35 mm modules can be used to create a generating surface of 70 mm×70 mm with a cost four times the cost of one module. The manufacturing cost of a single module 70 mm×70 mm would be ten times the cost of a single module. Choosing the right size module will optimize the cost. However, the invention in accordance with these teachings will work with any size module, as one skilled in the art will appreciate.
Referring to
The cooling fans 18 are preferably mounted such that the fan intake is exposed to the cooler ambient air closer to the floor.
The wiring is standard wiring for a thermoelectric generator that one skilled in the art will be familiar with.
A mechanism to protect the generator 10 from overheating may be included. Overheating may come from an overly hot fire, or from firewood resting on the internal hot-side plate. One form of protection would be a grillwork guard 40 to prevent burning wood from resting directly on the generator mechanism.
Another form of protection may be a lifter that forces the generator assembly away from the heat to interrupt the transfer of heat by conduction and convection.
The modules within the generator can be oriented in any suitable manner.
Accordingly, in a preferred embodiment, the modules are arranged in a floating arrangement.
Alternatively, referring to
In either embodiment, (door mounted generator or stove-top generator) use of the floating pad adds an additional benefit with respect to field service. Separate pads for each module provide for much easier replacement of failed modules, as the failed assembly can be easily removed without affecting the other modules. Assembly of modules between the hot and cold plates requires special equipment and techniques not available to the general public so replacing a failed module is not possible. Replacing the failed assembly requires simple tools.
In the embodiment of
Electric devices may be run directly from the generator, for example lights, circulating fans, radios, or computers; devices may be charged by the generator, for example cameras, cell phones, GPS or computers, or the energy may be stored in a battery.
Although embodiments of the invention have been described with respect to wood or coal stoves, the invention can also be used in other types of stoves, such as stoves that burn a very steady temperature of fuel such as an oil drip stove.
Numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/894,719 filed Mar. 14, 2007, incorporated by reference herein.
Number | Date | Country | |
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60894719 | Mar 2007 | US |