US20050037303A1

US20050037303A1 - Generation of electricity in a fireplace using thermoelectric module

Info

Publication number: US20050037303A1
Application number: US10/642,055
Authority: US
Inventors: Thomas Bachinski; David Oja
Original assignee: HNI Technologies Inc
Current assignee: HNI Technologies Inc
Priority date: 2003-08-15
Filing date: 2003-08-15
Publication date: 2005-02-17
Also published as: CA2470739A1

Abstract

The present invention generally relates to a use of a thermoelectric module in conjunction with a fireplace or stove to generate electricity to run certain features or peripheral devices related to the stove or fireplace. The thermoelectrical module may be positioned between interior and exterior walls of the stove or fireplace outside and protected from the fire generated in the combustion chamber of the stove or fireplace. Power generated by the thermoelectric module may be used for various purposes such as powering a blower, a control unit such as a microprocessor, lights, back-up systems, ignition systems, and flame control devices. Furthermore, the power generated by the thermoelectric module may be saved in a power storage device such as a rechargeable battery or capacitor for a later use by various devices associated with fireplace or stove.

Description

BACKGROUND OF THE INVENTION

1. Technical Field
The present invention generally relates to thermoelectric power and more specifically relates to generation of electric power for a fireplace using thermoelectric power.
2. Related Art
The popularity of gas burning stoves and fireplaces has increased significantly over the past several decades. Burning gas such as natural gas or propane is typically a much more efficient way of producing heat and far more clean and easy to control than burning wood, wood pellets, coal or oil. The efficiency and convenience of gas burning stoves and fireplaces is further enhanced by using such peripheral devices as a blower to circulate heated air through the room in which the stove or fireplace is placed, an ignition system to self-start the fire, back-up storage devices, and control systems that automatically or manually control various features of the stove or fireplace. Many of these devices require electrical power to operate and thus contribute to the cost of operating a gas stove or fireplace. Furthermore, in areas where electrical power is unavailable or expensive, many of these devices may not be an option for use with a gas stove or fireplace.
Many known stoves and fireplaces have reduced heat generating efficiency because much of the heat produced escapes through the combustion exhaust system or into the structure surrounding the stove or fireplace rather than heating the intended air space around the stove or fireplace. Improving the heat generating efficiency of stoves and fireplaces is an objective for many manufacturers of these products.
The use of thermoelectric modules to produce electricity using a heat source has been known for many years. FIG. 1 schematically illustrates a typical thermoelectric module 1 that includes a number of alternate negative (N) and positive (P) type semiconductor thermo elements connected in series by metal interconnectors 2, 4 that are sandwiched between two electrically insulated but thermally conducting plates H, C. A heat source connected to plate H and a heat sink connected to plate C provide a temperature differential across the thermo elements that in turn generate a current (I) that can be delivered to an external load (W).
Typically, increasing the temperature difference (ΔT) across a thermoelectric module will increase the power generated by the module within limits of the materials used and the configuration of the module. Those skilled in the art are aware that materials with a high figure-of-merit are preferred for use as thermo elements in a thermoelectric module. Heavily doped semi-conductors, such as tellurides of antimony and bismuth, are examples of materials with a high figure-of-merit value. Manufacturers of thermoelectric modules such as continue to make advances in the efficiency of thermoelectric modules by altering their designs or discovering new materials or combinations of materials that are most efficient.

SUMMARY OF THE INVENTION

The present invention generally relates to the use of a thermoelectric module in conjunction with a fireplace or stove to generate electricity to run certain features or peripheral devices related to the stove or fireplace. A thermoelectric module may be positioned adjacent to an exterior wall of the stove or fireplace or between interior and exterior walls of the stove or fireplace so long as the module is protected from the fire in the combustion chamber. Power generated by the thermoelectric module may be used for various purposes such as powering a blower, a control unit, lights, sensors, ignition systems, and flame igniting and control devices. Furthermore, the power generated by the thermoelectric module may be saved in a power storage device such as a rechargeable battery or capacitor for a later use by devices listed above.
One aspect of the invention relates to a thermoelectric fireplace that includes a combustion chamber enclosure having an outer surface and an inner surface defining a combustion chamber, an outer enclosure surrounding a portion of the combustion chamber enclosure, and a thermoelectric module positioned adjacent to the outer surface of the combustion chamber enclosure. In one embodiment, the thermoelectric also may be positioned between the combustion chamber enclosure and the outer enclosure. Heat generated in the combustion chamber in the combustion chamber enclosure is used by the thermoelectric module to generate power.
Another aspect of the invention relates to a thermoelectric system configured to generate power in a fireplace. The thermoelectric system includes a combustion chamber enclosure and an outer enclosure. The thermoelectric system includes a thermoelectric module positioned adjacent to the combustion chamber enclosure and positioned between the combustion chamber enclosure and the outer enclosure. The thermoelectric module generates power using heat provided in the combustion chamber enclosure.
A further aspect of the invention relates to a method of generating power in a fireplace using a thermoelectric system that includes a thermoelectric module. The fireplace includes a combustion chamber enclosure having inner and outer surfaces and an outer enclosure surrounding the combustion chamber enclosure. The method includes positioning the thermoelectric module adjacent to the outer surface of the combustion chamber enclosure between the combustion chamber enclosure and the outer enclosure, heating the combustion chamber enclosure, transferring heat from the combustion chamber enclosure to the thermoelectric module, and generating power in the thermoelectric module from the transferred heat.
A yet further aspect of the invention relates to a thermoelectric fireplace that includes a compression molded combustion chamber enclosure defining a combustion chamber, and a thermoelectric module positioned adjacent to the combustion chamber enclosure. The thermoelectric module is positioned relative to the combustion chamber enclosure so that heat generated in the combustion chamber is transferred to the thermoelectric module for the production of power.
The above summary of the present invention is not intended to describe each disclosed embodiment or every implementation of the present invention. Figures in the detailed description that follow more particularly exemplified embodiments of the invention. While certain embodiments will be illustrated and described, the invention is not limited to use in such embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of the following detailed description of various embodiments in the invention and in connection with accompanying drawings, in which;
FIG. 1 is a schematic representation of a known power generating thermoelectric module;
FIG. 2 is a perspective view of an example fireplace in which principles of the present invention may be applied;
FIG. 3 is a perspective side view of the fireplace shown in FIG. 2 with a portion of the fireplace outer enclosure removed to illustrate an example thermoelectric module and other aspects of the invention;
FIG. 4 is a cross-sectional view of one example embodiment of the invention taken along cross-sectional indicators 4-4 shown in FIG. 3;
FIG. 5 is a cross-sectional view of another example embodiment of the invention taken along cross-sectional indicators 5-5 shown in FIG. 3;
FIG. 6 is a top perspective view of an example thermoelectric module of the invention in use with a compression molded combustion chamber enclosure; and
FIG. 7 is a cross-sectional side view of another example embodiment of the invention with a heat source positioned in the fireplace plenum.
While the invention is amenable to various modifications and alternate forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is applicable to stoves and fireplaces that provide a heat source, and particularly to combustible gas fireplaces and stoves. The invention is directed to generating electrical power from heat provided by a stove or fireplace using a thermoelectric device. Power generated by the thermoelectric device may be used to power various features associated with the stove or fireplace. While the present invention is not so limited, appreciation of various aspects of the invention will be gained through a discussion of the examples provided below.
Embodiments of the present invention may be used in conjunction with gas, electric or other types of heat sources that generate heat to provide a temperature differential across a thermoelectric module thereby generating electric power. While the example embodiments of the present invention provided below are described in conjunction with example fireplaces, the present invention is equally applicable to other systems or apparatuses such as furnaces and stoves that generate heat for the purpose of heating an air space such as a home or commercial building. Some example fireplaces that may be used in accordance with the present invention include a direct vent, a universal vent, a B-vent, a horizontal/vertical-vent, a dual direct vent, and a multisided unit having two or three glass panels as combustion chamber side panels.
As used herein, the phrase “combustion chamber enclosure” may include any structure that at least partially encloses a space in which a flame is generated from combusting a material, solid or gas, or simulating a flame. The phrase “transferring heat” may include either convection or conduction heat transfer. A “thermoelectric module” as used herein will be more completely described below but generally relates to a device that generates electrical power in the presence of a temperature differential. A “heat source” may include, for example, an electric or gas heater.
Referring to FIGS. 2-5, respective front, side and cross-sectional views of an example embodiment of a fireplace 10 is shown. Fireplace 10 includes an outer enclosure 11, a combustion chamber enclosure 30, and a thermoelectric system 50. Outer enclosure 11 includes top, bottom, first and second side, and rear panels 12, 14, 16, 18, 20. Outer enclosure 11 may also include a front surface 22 into which first and second vents 23, 24 are formed. Vents 23, 24 are used to draw air into and exhausting air from the internal space of fireplace 10.
Combustion chamber enclosure 30 includes first and second side panels 31, 47, top and bottom panels 35, 39, and rear panel 43. As shown in FIGS. 3-5, first panel 31 includes outside and inside surfaces 32, 34, top panel 35 includes inside and outside surfaces 36, 38, bottom panel 39 includes inside and outside surfaces 40, 42, and rear panel 43 includes an outside surface 44.
Thermoelectric system 50 may include a thermoelectric module 52, heat sink 58 and leads 60, 62. Thermoelectric module 52 may include the basic configuration shown in FIG. 1, including a plurality of thermo elements P, N connected in series with connectors 2, 4 and positioned between heat conductive plates H, C. Other thermoelectric module configurations may be used so long as the thermoelectric module 52 is capable of using heat to generate electrical power. Heat sink 58 may be configured as a plurality of ribs as shown in FIG. 3, or other structures that enhances heat dissipation to increase the temperature differential between opposing sides of thermoelectric module 52.
In another thermoelectric system embodiment shown in FIG. 5, a portion of the system, such as a heat sink 158, may extend beyond the first side panel 16 and possibly even beyond an additional wall structure 80 positioned adjacent the fireplace 10. Heat sink 158 may then be exposed to a colder environment than that area between the combustion chamber enclosure 30 and the outer enclosure 11. For example, heat sink 158 may extend outside of a house where the fireplace resides so as to be exposed to cool/cold outdoor air. Such a configuration would create a much greater temperature differential across the thermoelectric module resulting in improved power output.
FIGS. 3-4 illustrate thermoelectric system 50 mounted to outside surface 32 of first side panel 31 of the combustion chamber enclosure 30. Thermoelectric system 50 is orientated with the thermoelectric module 52 secured to the combustion chamber enclosure 30 with the heat sink 158 positioned away from the combustion chamber enclosure. FIG. 4 illustrates the entire thermoelectric system 50 positioned between combustion chamber enclosure 30 and the first side panel 16 and a removable side panel 28 of outer enclosure 11. Similarly, FIG. 5 illustrates that at least a portion of the thermoelectric system 150 is positioned between combustion chamber enclosure 30 and outer enclosure 11. In other embodiments, the thermoelectric system may be mounted to the outside surfaces of the top, bottom, rear or second side panels 35, 39, 43, 47 of combustion chamber enclosure 30 for various reasons such as, for example, improving power generation efficiency or meeting the size and shape constraints of the fireplace.
Fireplace 10 may include auxiliary features that typically operate using electrical power. For example, fireplace 10 includes an energy storage device 70, a blower 72, a control unit 74, and an ignition system 26 (see FIG. 1). Energy storage device 70 may be, for example, a capacitor or rechargeable battery. Preferably, energy storage device 70 is capable of being charged with power from thermoelectric system 50 so that some of the fireplace features can operate when there fireplace is not generating heat sufficient for the thermoelectric system to produce power.
Blower 72 provides air circulation around the outside surface of combustion chamber 30 and within outer enclosure 11. Blower 72 typically draws cool air in through the lower first vent 23 and exhausts heated air through the higher second vent 24 on the front surface 22 of fireplace 10. In some embodiments, blower 72 may be configured solely for the purpose of cooling thermoelectric module 52 while a separate blower is used to circulate air into and out of the fireplace.
Control unit 74 may individually control or may represent any of a number of different control features that may be used with a fireplace. For example, control unit 74 may be an ignition system control such as the ignition system disclosed in U.S. Pat. No. 6,520,199 (which is incorporated herein by reference in its entirety), a main flame valve control, a heat sensor control, a blower control, or a power allocation control unit. Control unit 74 may include a microprocessor that is programmable to, for example, automatically charge or discharge energy storage device 70, turn on or off blower 72 at specified times during heating and cooling within combustion enclosure 30, automatically turning on or off the main flame of the fireplace, maintaining the ignition system 26, or manually igniting a pilot light of the fireplace (not shown).
FIG. 3 illustrates hard wires extending between control unit 74, blower 72 and energy storage device 70. However, in other embodiments, other communication technology such as infrared, remote control or other wireless communication may be used to send and receive control signals from the control unit 74 and various electronically controlled devices of fireplace 10.
The thermoelectric systems 50, 150 shown in FIGS. 3-5 may more efficiently generate power when blower 72 moves air across heat sink 58, 158 to increase the temperature differential across thermoelectric module 52, 152. In these examples, blower 72 draws cool air in the direction B across a bottom portion of the combustion chamber enclosure 30, moves the air in the vertical direction S across the thermoelectric system 50, 150, and exhausts the air out from the fireplace the intended air space in front of the fireplace. Typically, the exhausted air is heated relative to the intake air by the time the air is exhausted from the fireplace, thus providing heating of the intended air space while at the same time cooling the thermoelectric module. In other embodiments, different types of cooling devices may be used in place of or in addition to a blower to cool the thermoelectric system. One example alternative cooling device is a closed-loop liquid-state cooling system.
Power generation using thermoelectric system 50 may be started in several different ways. Heat is generated in the combustion chamber enclosure 30 using, for example, a gas fed flame, or may be generated by another heat source positioned between the combustion chamber enclosure 30 and the outer enclosure 28.
The flame may be started with the ignition system 26 that includes, for example, a standing pilot light or a pilot light that that is manually or automatically controlled by control unit 74 using power powered stored in energy storage device 70. As heat builds in or around the combustion chamber, the thermoelectric module 52 begins to draw heat from the heat source and converts that heat into electrical power. Control unit 74 may be used to power “on” the blower 72 either before or after the thermoelectric system 50 begins to generate electrical power by using energy stored in the storage device 70 or using energy produced by thermoelectric system 50. As noted above, blowing air across the heat sink 58 (for example, using blower 72) improves the power output from the thermoelectric system, and thus it may be advantageous to begin air movement across the heat sink at a very early stage. In some embodiments, energy storage device 70 may include a capacitor that provides a surge of power to meet the start up energy requirements for blower 72.
Power generated by the thermoelectric system 50 may be used for powering other features not shown in the Figures such as, for example, lights in and around the fireplace, moving devices in and around the fireplace such as an simulated flame element (see U.S. patent application Ser. No. 09/941,400), a simulated fuel bed (see U.S. patent application Ser. No. 09/851,803), an ember out of a log (see U.S. patent application Ser. No. 10/463,175), a touch switch (see U.S. patent application Ser. No. 10/199,983), a proximity sensor (see U.S. patent application Ser. Nos. 10/120,890 and 10/119,474), moving a lenticular screen (see U.S. patent application Ser. No. 09/859,719), a thermostat, and other alarms and sensors such as a carbon monoxide sensor and an associated alarm (all of the above listed patent applications are incorporated herein by reference in their entirety). Another sensor and alarm system may monitor the thermoelectric system and provide notification when the thermoelectric system is overheating or is in need of repairs so that the user or possibly the control unit can shut down the fireplace to conduct diagnostics and/or repairs.
Another example fireplace 200 that includes a thermoelectric system 250 is shown in FIG. 6. Fireplace 200 includes a combustion chamber enclosure 230 having an outer surface 232 and an inner surface 234 that defines a combustion chamber 229. Thermoelectric system 250 may be mounted to or otherwise positioned adjacent to outer surface 232 so that thermoelectric system 250 can use heat from combustion chamber 229 to generated power. Combustion chamber enclosure 230 may include inorganic fibers, binders and fillers, and may be made by a compression molding method to provide a compression molded article as disclosed in U.S. Patent Application Publication No. 2003/0049575 A1, which is incorporated herein by reference.
Thermoelectric system 250 may include the same or similar features as disclosed above, including a thermoelectric module 252, a heat sink 258, a control system (not shown), a power storage device (not shown), and a blower (not shown).
In a yet further example fireplace 300 shown in FIG. 7, a heat source 51 that generates a temperature differential in the thermoelectric system 50 may be positioned between the combustion chamber enclosure 30 and the outer enclosure 28 of the fireplace 300. For example, an electric heater and at least a portion of the thermoelectric module 52 of the thermoelectric system may be positioned between the combustion chamber enclosure and the outer enclosure.
One example thermoelectric system for a fireplace produces a DC voltage of about 5 to 15 V and is capable of providing current of about 250 to 1000 mA. The amount of voltage produced has a roughly inverse relationship to the amount of current that can be drawn from the system. In one particular example, the system provides a DC voltage of about 13 V and a current of about 500 mA. The current and voltage specifications for a thermoelectric module may also vary depending on whether the thermo elements are arranged in series or in parallel.
The thermoelectric system preferably includes two or more thermo elements or thermo plates connected in series or in parallel. One example thermoelectric system that provides sufficient power to run a blower and other basic electronic features for a standard residential gas fireplace includes five thermo plate connected in series, such as thermoelectric module Model No. TZ08119-02 made by Tellurex Corporation of Traverse City, Mich., U.S.A.
The present invention should not be considered limited to the particular examples or materials described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention may be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the instant specification.

Claims

1. A method of generating power in a fireplace using a thermoelectric system that includes a thermoelectric module, the fireplace including a combustion chamber enclosure having inner and outer surfaces and an outer enclosure surrounding the combustion chamber enclosure, the method comprising the steps of:

positioning the thermoelectric module adjacent to the outer surface of the combustion chamber enclosure between the combustion chamber enclosure and the outer enclosure;

heating the combustion chamber enclosure;

transferring heat from the combustion chamber enclosure to the thermoelectric module; and

generating power in the thermoelectric module from the transferred heat.

2. The method of claim 1, wherein the thermoelectric system further includes an energy storage device, and the method further comprises storing power from the generating step in the energy storage device.

3. The method of claim 1, wherein the thermoelectric system further includes a cooling device, and the method further comprises powering the cooling device with power from the generating step.

4. The method of claim 3, wherein the thermoelectric module includes a first side secured to the outer surface of the combustion chamber enclosure and a second side configured as a heat sink, and the method further comprises moving coolant across the heat sink with the cooling device.

5. The method of claim 1, wherein the positioning step includes positioning the thermoelectric module adjacent to a vertically extending wall of the combustion chamber enclosure.

6. The method of claim 5, further comprising drawing cool air from under a bottom side of the combustion chamber enclosure and moving the drawn air across the thermoelectric module.

7. The method of claim 1, further including positioning a portion of the thermoelectric module outside of the outer enclosure.

8. The method of claim 1, further comprising drawing air through a first fireplace vent, moving the drawn air across the thermoelectric module to cool a portion of the thermoelectric module, and exhausting the drawn air through a second fireplace vent.

9. The method of claim 1, wherein the thermoelectric system further includes a control unit, and the method further comprises controlling distribution of power in the thermoelectric system with the control unit.

10. The method of claim 9, wherein the controlling step includes powering a blower.

11. The method of claim 9, wherein the controlling step includes storing power in an energy storage device.

12. The method of claim 9, wherein the controlling step includes powering a pilot flame system.

13. The method of claim 9, wherein the controlling step includes opening and closing a main flame valve of the fireplace.

14. The method of claim 9, wherein the controlling step includes powering an electric light.

15. The method of claim 9, wherein the controlling step includes powering a filtration system.

16. The method of claim 9, wherein the controlling step includes powering a touch switch.

17. A thermoelectric system configured to generate power in a fireplace, the fireplace including a combustion chamber enclosure and an outer enclosure, the thermoelectric system comprising:

a thermoelectric module positioned adjacent to the combustion chamber enclosure and positioned between the combustion chamber enclosure and the outer enclosure;

whereby the thermoelectric module generates power from heat provided in the combustion chamber enclosure.

18. The system of claim 17, further comprising a cooling device configured to create a temperature gradient in the thermoelectric module.

19. The system of claim 17, wherein the cooling device is a blower.

20. The system of claim 17, further comprising a control system configure to control power distribution in the system.

21. The system of claim 17, further comprising a power storage device configured to store power generated by the thermoelectric module.

22. The system of claim 21, wherein the power storage device is a rechargeable battery.

23. The system of claim 21, wherein the power storage device include a capacitor and a battery.

24. The system of claim 17, wherein the thermoelectric module includes a heat sink.

25. The system of claim 17, wherein the thermoelectric module includes at least two thermoelectric plates.

26. A thermoelectric fireplace, comprising:

a combustion chamber enclosure having an inner surface defining a combustion chamber and an outer surface;

an outer enclosure surrounding a portion of the combustion chamber enclosure; and

a thermoelectric module positioned adjacent to the outer surface of the combustion chamber enclosure and positioned between the outer surface of the combustion chamber enclosure and the outer enclosure;

whereby heat generated in the combustion chamber is used by the thermoelectric module to generate power.

27. The fireplace of claim 26, wherein the combustion chamber enclosure includes top, bottom, rear, first side and second side panels, and the thermoelectric module is positioned adjacent to the outer surface of at least one of the panels of the combustion chamber enclosure.

28. The fireplace of claim 26, further comprising an ignition system operable using power at least partially provided by the thermoelectric module.

29. The fireplace of claim 26, wherein the thermoelectric module produces at least 5V DC voltage.

30. A thermoelectric fireplace, comprising:

a compression molded combustion chamber enclosure defining a combustion chamber; and

a thermoelectric module positioned adjacent to the combustion chamber enclosure, whereby heat generated in the combustion chamber is used by the thermoelectric module to generate power.

31. The fireplace of claim 30, wherein combustion chamber enclosure comprises an inorganic fiber and a binder.

32. The fireplace of claim 31, wherein the combustion chamber enclosure includes an inner surface defining the combustion chamber and an outer surface, and the thermoelectric module is positioned adjacent to the outer surface.

33. A thermoelectric fireplace, comprising:

a combustion chamber enclosure;

a thermoelectric module positioned between the combustion chamber enclosure and the outer enclosure; and

a heat source positioned between the combustion chamber enclosure and the outer enclosure;

whereby heat generated by the heat source is used by the thermoelectric module to generate power.