Patent Application
20090151711
The present invention generally relates to fireplaces, and more specifically fireplaces equipped with one or more heat exchangers for transferring heat from the fireplace exhaust air to air to be delivered to a living space.
In combustion fireplaces, such as gas or biomass burning fireplaces, hot exhaust air produced during combustion exits the fireplace at a relatively higher temperature than its surroundings, carrying with it some potentially useful thermal energy. This results in less than optimal fireplace efficiency.
Some embodiments relate to a heat exchange system including a firebox, a combustion element, a plenum, and at least one heat exchanger. The firebox includes a plurality of panels combining to define a combustion chamber. The combustion chamber includes a combustion air inlet port in fluid communication with a source of combustion air and an exhaust air outlet port. The combustion element is disposed within the combustion chamber. The plenum defines an air intake end and an air output end and includes a plurality of walls defining an air pathway between the air intake and air output ends. The heat exchanger includes a housing having an outer surface disposed within the plenum. The housing includes a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the heat exchanger. Additionally, an outer surface of the heat exchanger may include a plurality of heat transfer assist structures such as air foils, pins, ridges, fins, and the like.
In some embodiment, the heat exchange system includes a second heat exchanger coupled to and in fluid communication with the first heat exchanger. Like the first heat exchanger, the second heat exchanger also includes a housing having an outer surface disposed within the plenum. The housing includes a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the second heat exchanger.
Other embodiments relate to a fireplace heat exchange system located within a building structure defining a living space. The fireplace heat exchange system includes a plenum, a firebox, a combustion element, and at least one heat exchanger. The plenum defines an air intake end and an air output end and includes a plurality of walls defining an air pathway between the air intake and air output ends. The firebox is located within the plenum. The firebox includes a plurality of panels that define a combustion chamber. The combustion chamber includes at least one combustion air inlet port in fluid communication with a combustion air source and an exhaust air outlet port. A combustion element adapted to generate heat and exhaust products via combustion of a fuel source with combustion air received through the combustion air inlet port is disposed within the combustion chamber. Additionally, a heat exchanger is mounted to the firebox located within the plenum. The heat exchanger includes a housing having a first end coupled to the exhaust air outlet port of the combustion chamber and a second end. Additionally, the heat exchanger includes a plurality of baffle plates within the housing. The baffle plates define at least one internal pathway within the housing. The internal pathway extends through a plurality of 180 degree turns from the first end to the second end of the heat exchanger.
Still other embodiments relate to a method of transferring heat from heated exhaust air to air to be delivered to a living space. The method includes passing relative hot exhaust air from a combustion chamber into a first heat exchanger located within a plenum. The plenum includes a plurality of walls defining an air pathway between an air intake end and an air output end. The heat exchanger includes a housing, an exhaust air inlet and an exhaust air outlet. The housing has an outer surface and a plurality of baffle plates. The plurality of baffle plates defines at least a first internal pathway within the housing. The first internal pathway extends through a plurality of 180 degree turns from the exhaust air inlet to the exhaust air outlet of the heat changer. The method also optionally includes passing air through the plenum along the air pathway defined between the air intake and air output ends and contacting the air with the outer surface of the heat exchanger housing. Additionally, the method includes transferring heat from the relatively hot exhaust air passing through the heat exchanger to the air passing through the plenum.
While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive.
While the invention is amenable to various modifications and alternative forms, various embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims.
Referring to
The firebox 14 can be made from a variety of suitable materials capable of withstanding the high temperatures. In some embodiments, the firebox 14 is formed of a compression molded material including an inorganic fiber and a binder, such as the compression molded materials described in U.S. Pat. No. 7,098,269, entitled “Compression Molded Inorganic Fiber Articles, and Methods and Compositions Used in Molding Same,” which is incorporated herein by reference in its entirety, although a variety of firebox materials are contemplated.
The burner system 26 is located in the combustion chamber 22 and is adapted to generate heat and exhaust products via combustion of a fuel source with combustion air. The burner system 26 is adapted for use with one or more of a variety of fuel sources, such as wood, gas, pellets, corn, and biomass, among others, although in some embodiments the burner system 26 is used to combust natural gas. Depending on the type of fuel, the burner system 26 includes regulator valves, fuel feed lines, igniter mechanisms, nozzles, and/or other elements, for example, generally associated with a burner system. An exemplary gas burner system is shown and described in U.S. Pat. No. 6,048,195, entitled “Hollow Ceramic Fiber Burner-log Element,” which is incorporated herein by reference in its entirety.
In some embodiments, the combustion chamber 22 includes at least one combustion air inlet port in fluid communication with a source of combustion air and an exhaust air outlet port 36. Combustion air is optionally drawn from the living space, such air being referred to as room air. Combustion air can also be drawn into the combustion chamber 22 from outside of the structure in which the heat exchange system 10 is located, also described as outside air. In some embodiments, the combustion chamber 22 includes more than one combustion air inlet port with combustion air including a combination of room air and outside air. In some embodiments, faux logs, embers, or other accessories are placed in the combustion chamber 22 to help simulate a wood fire.
The heat exchanger 40 is coupled to and in fluid communication with the exhaust air outlet port 36 provided in the combustion chamber 22. The heat exchanger 40 includes a housing 44 defining a first end 48 and a second end 52 and includes a plurality of baffle plates 80 defining at least one internal pathway within the housing 44 (described in further detail below). The heat exchanger 40 defines a substantially closed pathway through which exhaust air travels from the combustion chamber 22 to the outside.
The heat exchanger 40 is optionally adapted to work with any of a variety of heat generating devices, such as a gas fireplace or pellet stove, for example. According to some embodiments, the heat exchanger 40 maintains a low profile when coupled to the firebox 14, for example by substantially tracking or otherwise complementing the profile of the firebox 14, in order to minimize an overall height and/or head space of the heat exchange system 10. In some embodiments, the heat exchanger 40 is adapted to work with a heat generating device having an energy output ranging from about 15,000 to about 60,000 BTU, from about 30,000 to about 40,000 BTU, for example, as well as other energy outputs.
The heat exchanger 40 is made from a high heat conductivity, corrosion-resistant material, according to some embodiments. Exemplary materials include: sheet metal, stainless steel, coated stainless steel, aluminum, aluminum alloys, and ceramics, for example, as well as other suitable materials. In some embodiments, the outer surface 50 of the heat exchanger housing 44 may be smooth. In other embodiments, the outer surface 50 of the heat exchanger housing 44 includes a plurality of heat transfer assist structures 46 such as air foils, pins, ridges, fins configured to increase heat transfer, for example by increasing the surface area of the outer surface 50. For example,
The first end 48 of the heat exchanger housing 44 is coupled to and in fluid communication with the exhaust air outlet port 36 located in the combustion chamber 22. The second end 52 is in fluid communication with the outside of the structure or other appropriate exhaust location to serve as an exhaust port. Heated exhaust air, including any waste products produced during the combustion process, flows from the combustion chamber 22 via the exhaust air outlet port 36 and into the heat exchanger 40. The heated exhaust air flows through the heat exchanger 40 along the internal pathway defined by the baffle plates 80, and is ultimately vented outside via the exhaust port.
The exhaust air entering the first end 48 of the heat exchanger 40 has a higher temperature than the exhaust air exiting the heat exchanger 40 via the second end 52 which serves as the exhaust port. Typically, the temperature of the heated exhaust air entering the first end 48 of the heat exchanger 40 ranges from about 650° F. to about 850° F. In contrast, the temperature of the exhaust air leaving the heat exchanger 40 via the second end 52 ranges from about 120° F. to about 180° F. According to one embodiment, the heat exchanger 40 is configured such that at least a portion of the exhaust air condenses before being disposed to the outside such that the exhaust air temperature is lowered to a level permitting the use of PVC piping or other ducting material at the exhaust port. For example, the temperature of the air exiting the heat exchanger 40 has a temperature ranging from about 120° F. to about 180° F. The condensate from the exhaust air is optionally collected in a condensate trap located at the lowest point of the heat exchanger 40. In some embodiments, the condensate trap includes a drain and a seal for draining the condensate from the heat exchanger 40. Alternately, a pan such as a drip pan, or a reservoir, is used for collecting the condensate.
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In some embodiments, the heat exchanger system 10 includes a plurality of heat exchangers. For example, as shown in
In some embodiments, the first heat exchanger 40a is coupled to the second heat exchanger 40b in a generally stacked configuration such that space exists between the outer surface 50a of the first heat exchanger 40a and the outer surface 50b of the second heat exchanger 40b such that air flow between the outer surfaces 50a, 50b of the two heat exchangers 40a, 40b is permitted. The coupled heat exchangers 40a, 40b are optionally mounted to the firebox 14 such that a space exists between the outer surface 50a of the first heat exchanger 40a and the outer surface 53 of the firebox 14, for example to allow airflow therebetween.
The coupled heat exchangers 40a, 40b may be mounted flush to the outer surface 53 of the firebox 14, such that no space exists between the outer surface 50a of the first heat exchanger 40a and the firebox 14, for example to enhance heat transfer between the firebox 14 and the heat exchanger(s) 40a, 40b. In still other embodiments, the first heat exchanger 40a is mounted to the firebox 14 such that the heat exchanger housing 44 of the first heat exchanger 40a and the firebox 14 share a common panel. Similarly, the second heat exchanger 40b may be coupled to the first heat exchanger 40a such that the outer surface 50a of the first heat exchanger 40a is flush with the outer surface 50b of the second heat exchanger 40b and/or the second heat exchanger 40b may be coupled to the first heat exchanger 40a such that the first and second heat exchanger housings 44 share a common wall.
According to some embodiments, the first heat exchanger 40a is coupled to the second heat exchanger 40b in a side by side configuration where exhaust air flows from the first heat exchanger 40a to the second heat exchanger 40b via an air duct or other fluid communication means extending between them.
The flow of heated exhaust air out of the combustion chamber 22, through the heat exchanger 40, and to the outside may be assisted by an air assist device 58 located within the combustion chamber 22. The air assist device 58 creates a positive pressure environment within the combustion chamber 22 pushing the heated exhaust air from the chamber 22 into and through the heat exchanger 40 until the exhaust air is vented to the outside. Exemplary air assist devices include, but are not limited to, fans, blowers, and others.
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Air travels through the plenum 62 from the air intake end 70 to the air output end 74 and flows over an outer surface 50 of the heat exchanger housing 44. As a result, the air traveling along the pathway 66 defined by the plenum 62 becomes heated via a heat exchange process with the heated exhaust air flowing through the heat exchanger 40. In some embodiments, relatively cool outside air is used as the source of air to be heated, where the outside air becomes superheated and a portion of the exhaust air condenses, increasing the overall efficiency of the heat exchange process. Once the air is heated, it is returned to the living space and the relatively cooler exhaust air is exhausted outside via the second end 52.
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According to some embodiments, the flow of air to be heated through the plenum 62 is assisted by one or more air assist devices 64 located within the plenum 62. The air assist device 64 can be used to push or draw the air from the air intake end to the air output end 74 over the heat exchanger 40 and then to return the heated air to the room or structure. Exemplary air assist devices include, but are not limited to, fans, blowers, and the like.
The baffle plates 80 generally slow the flow of heated exhaust air through the heat exchanger 40, increasing the residence time of the heated exhaust air within the heat exchanger 40. In general terms, the longer the heated exhaust air resides within the heat exchanger 40, the more efficient the heat exchange process will be with the air flowing over its outer surface 50. As described above with reference to
The various embodiments heat exchangers 40 are each optionally disposed within the plenum 62 such that the air flowing through the heat exchanger 40 is generally parallel or counter to the air flowing from the air intake end 70 to the air output end 74 of the plenum 62. The 180 degree turns created by the baffle plates 80 result in the addition of a cross flow component between the exhaust air flowing through the internal pathways 90, 92 within the heat exchanger 40 and the air to be heated flowing over the outer surface 50 of the heat exchanger housing 44.
If more than one heat exchanger 40 is used, the heat exchangers need not have the same internal pathway configuration defined by the baffle plates 80. Additionally, one heat exchanger 40 may be oriented within the plenum 62 such that the exhaust air flowing through the heat exchanger 40 is generally parallel to the air to be heated flowing through the plenum 62. An additional heat exchanger 40b may be coupled to a first heat exchanger 40a such that the exhaust air flow through the second heat exchanger 40b is counter to the air flow through the plenum 62 and the first heat exchanger 40a. In some embodiments, the opposite configuration is used in which the exhaust air flows through the first heat exchanger 40a is counter to the air flowing through the plenum 62 and the exhaust air flow through the second heat exchanger 40b is generally parallel to or in the same direction as the air flowing through the plenum 62.
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Various embodiments of a heat exchanger according to the present invention increase the overall efficiency otherwise achieved using heat generating devices such as gas fireplaces. For reference, overall energy efficiency or Annual Fuel Utilization Efficiency (AFUE) is calculated according to the Department of Energy Testing procedure (10 CFR Part 430). Where the fuel being consumed within the heat generating device, for example natural gas, has a moisture content of about 6% to about 7% energy efficiency of about 93% is an approximate upper limit for the system 10. Thus, in some embodiments, the system 10 includes a natural gas fireplace heat generating device and is adapted to achieve an energy efficiency of about 93%. According to further embodiments, the system 10 is adapted to have an energy efficient ranging from about 75% to about 93%. According to still further embodiments, the system 10 is adapted to have an energy efficient ranging from about 90% to about 93%, for example.
Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.
