U.S. patent application number 11/957896 was filed with the patent office on 2009-06-18 for fireplace with exhaust heat exchanger.
This patent application is currently assigned to HNI Technologies Inc.. Invention is credited to Richard E. Burkey, Jack J. Wells.
Application Number | 20090151711 11/957896 |
Document ID | / |
Family ID | 40533466 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090151711 |
Kind Code |
A1 |
Wells; Jack J. ; et
al. |
June 18, 2009 |
FIREPLACE WITH EXHAUST HEAT EXCHANGER
Abstract
A heat exchanger system and method for transferring heat from
exhaust air from a fireplace to air to be delivered to a living
space is described. Heated exhaust air is passed through a heat
exchanger before exhaustion from the structure. The heat exchanger
couples the exhaust duct and the intake duct and transfers
otherwise unused heat from the waste products to the outside air to
increase the overall efficiency of the heated product source.
Inventors: |
Wells; Jack J.; (Rice,
WA) ; Burkey; Richard E.; (Chewelah, WA) |
Correspondence
Address: |
FAEGRE & BENSON LLP;PATENT DOCKETING - INTELLECTUAL PROPERTY (77012)
2200 WELLS FARGO CENTER, 90 SOUTH SEVENTH STREET
MINNEAPOLIS
MN
55402-3901
US
|
Assignee: |
HNI Technologies Inc.
Muscatine
IA
|
Family ID: |
40533466 |
Appl. No.: |
11/957896 |
Filed: |
December 17, 2007 |
Current U.S.
Class: |
126/523 |
Current CPC
Class: |
F24B 7/025 20130101 |
Class at
Publication: |
126/523 |
International
Class: |
F24B 1/185 20060101
F24B001/185 |
Claims
1. A fireplace heat exchange system comprising: a firebox including
a plurality of panels combining to define a combustion chamber
having a combustion inlet port in fluid communication with a source
of combustion air and an exhaust outlet port; a combustion element
adapted to generate heat and exhaust products in the combustion
chamber via combustion of a fuel source with combustion air
received through the combustion inlet port; a plenum defining an
air intake end and an air output end, the plenum including a
plurality of walls combining to define an air pathway between the
air intake and air output ends; and a first heat exchanger
including: a housing having an outer surface disposed within the
plenum, the housing defining a first end in fluid communication
with the exhaust outlet port and a second end; and a plurality of
baffle plates within the housing, the plurality of baffle plates
defining at least a first internal pathway within the outer
housing, the first internal pathway extending through a plurality
of 180 degree turns from the first end of the heat exchanger to the
second end of the heat exchanger.
2. The system of claim 1, further comprising a first air assist
device adapted to promote a flow of the exhaust products out of the
combustion chamber through the exhaust outlet port, through the
first internal pathway of the heat exchanger, and out of the distal
end of the heat exchanger.
3. The system of claim 1, wherein the air output end is in fluid
communication with a living space, the system further comprising a
second air assist device adapted to draw air through the air
pathway over the outer surface of the heat exchanger and into the
living space.
4. The system of claim 1, wherein the first internal pathway of the
heat exchanger defines a counter flow component relative to the air
pathway between the air intake and air output ends of the
plenum.
5. The system of claim 1, wherein the first internal pathway of the
heat exchanger further defines a cross-flow component relative to
the air pathway between the air intake and air output ends of the
plenum.
6. The system of claim 1, further comprising a second internal
pathway within the housing separate from the first internal
pathway, the second internal pathway extending through a plurality
of 180 degree turns from the proximal end of the heat exchanger to
the distal end of the heat exchanger.
7. The system of claim 1, wherein the outer surface of the heat
exchanger housing includes a plurality of heat transfer assist
structures.
8. The system of claim 1, further comprising a second heat
exchanger in fluid communication with the first heat exchanger, the
second heat exchanger including: a housing having an outer surface
disposed within the plenum, the housing defining a first end in
fluid in communication with the second end of the first heat
exchanger and a second end; and a plurality of baffle plates, the
plurality of baffle plates defining at least a first internal
pathway within the housing, the first internal pathway extending
through a plurality of 180 degree turns from the first end of the
second heat exchanger to the second end of the second heat
exchanger.
9. The system of claim 8, wherein the second heat exchanger is
fluidly coupled to the first heat exchanger in a generally stacked
relationship such that the second heat exchanger is spaced a
distance from the first heat exchanger, wherein air flows between
the outer surfaces of the second heat exchanger and the first heat
exchanger.
10. A fireplace heat exchange system located within a building
structure having a plurality of walls defining at least one living
space, the system comprising: a plenum defining an air intake end
and an air output end, the plenum including a plurality of walls
defining an air pathway between the air intake and air output ends;
a firebox located within the plenum, the firebox including a
plurality of panels defining a combustion chamber having at least
one combustion 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 in the combustion
chamber via combustion of a fuel source with combustion air
received through the combustion inlet port; and a first heat
exchanger mounted to the firebox located within the plenum, the
first heat exchanger including: a housing having an outer surface
disposed within the plenum, the housing defining a first end in
fluid communication with the exhaust outlet port and a second end;
and a plurality of baffle plates within the housing, the plurality
of baffle plates defining at least a first internal pathway within
the outer housing, the first internal pathway extending through a
plurality of 180 degree turns from the first end of the heat
exchanger to the second end of the heat exchanger.
11. The system of claim 10, further comprising a first air assist
device adapted to promote a flow of the exhaust products out of the
combustion chamber through the exhaust outlet port, through the
first internal pathway of the heat exchanger, and out of the distal
end of the heat exchanger.
12. The system of claim 10, wherein the air output end is in fluid
communication with a living space, the system further comprising a
second air assist device adapted to draw air through the air
pathway over the outer surface of the heat exchanger and into the
living space.
13. The system of claim 10, the first heat exchanger further
comprising a first portion in fluid communication with a second
portion, wherein the first portion is angularly offset from the
second portion by at least ninety degrees.
14. The system of claim 10, wherein the housing of the first heat
exchanger shares a common panel with the firebox to which the first
heat exchanger is mounted, wherein no space exists between an outer
surface of the firebox and the outer surface of the heat exchanger
housing.
15. The system of claim 10, wherein the first heat exchanger is
mounted to the firebox such that it is spaced a distance from an
outer surface of the firebox, wherein air is permitted to flow
between the outer surface of the first heat exchanger housing and
the outer surface of the firebox.
16. The system of claim 10, wherein the outer surface of the heat
exchanger housing includes a plurality of heat transfer assist
structures.
17. The system of claim 10, further comprising a second heat
exchanger in fluid communication with the first heat exchanger, the
second heat exchanger including: a housing having an outer surface
disposed within the plenum, the housing defining a first end in
fluid communication with the second end of the first heat exchanger
and a second end; and a plurality of baffle plates, the plurality
of baffle plates defining at least a first internal pathway within
the housing, the first internal pathway extending through a
plurality of 180 degree turns from the first end of the second heat
exchanger to the second end of the second heat exchanger.
18. The system of claim 17, wherein the second heat exchanger is
fluidly coupled to the first heat exchanger in a generally stacked
relationship such that the second heat exchanger is spaced a
distance from the first heat exchanger, wherein air flows between
the outer surfaces of the second heat exchanger and the first heat
exchanger.
19. A method of transferring heat from a combustion chamber to air
to be delivered to a living space, the method comprising: passing
hot exhaust air from a combustion chamber into a first heat
exchanger located within a plenum having a plurality of walls
defining an air pathway between an air intake end and an air output
end, the heat exchanger including a housing defining an exhaust air
inlet and an exhaust air outlet, the housing having an outer
surface and a plurality of baffle plates within the housing
defining an internal pathway from the exhaust air inlet to the
exhaust air outlet, causing the exhaust air to flow along the first
internal pathway through a plurality of 180 degree turns from the
exhaust air inlet of the heat exchanger to the exhaust air outlet
of the heat exchanger; and passing air through the plenum along the
air pathway between the air intake and air output end and over the
outer surface of the heat exchanger housing such that heat is
transferred from the combustion chamber to the air passing through
the plenum and from the relatively hot exhaust air passing through
the heat exchanger to the air passing through the plenum.
20. The method according to claim 19, further comprising creating
positive pressure within the combustion chamber to assist passing
exhaust air from the combustion chamber to the heat exchanger, and
along the internal pathway located within the heat exchanger
housing.
21. The method according to claim 19, further comprising assisting
passage of the air through the plenum from the input end to the
output end and into the living space.
22. The method according to claim 19, further comprising passing
the relatively hot exhaust air from the first heat exchanger to a
second heat exchanger located within the plenum, the second heat
exchanger in fluid communication with the exhaust air outlet of the
first heat exchanger, the second heat exchanger including a housing
defining an exhaust air inlet and an exhaust air outlet, the
housing having an outer surface and a plurality of baffle plates
within the housing, the plurality of baffle plates defining at
least a first internal pathway within the housing, the first
internal pathway extending through a plurality of 180 degree turns
from the exhaust air inlet of the heat exchanger to the exhaust air
outlet of the heat exchanger.
23. The method according to claim 19, wherein transferring heat
from the combustion chamber to the air passing through the plenum
and from the relatively hot exhaust air passing through the heat
exchanger to the air passing through the plenum achieves an overall
efficiency greater than about 90%.
Description
BACKGROUND
[0001] 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.
[0002] 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.
SUMMARY
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a side schematic view of a heat exchange system
according to some embodiments.
[0009] FIG. 2 is a side schematic view of a heat exchange system
according to some embodiments.
[0010] FIG. 3A is a side schematic view of a heat exchange system
according to some embodiments.
[0011] FIG. 3B is another side schematic view of a heat exchange
system according to some embodiments.
[0012] FIG. 4 is a front schematic view of a heat exchange system
according to some embodiments.
[0013] FIG. 5 is a cross-sectional view of a heat exchanger for use
in a heat exchange system provided according to some
embodiments.
[0014] FIG. 6 is a cross-sectional view of a heat exchanger for use
in a heat exchange system provided according to some
embodiments.
[0015] FIG. 7 is a cross-sectional view of a heat exchanger for use
in a heat exchange system according to some embodiments.
[0016] 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.
DETAILED DESCRIPTION
[0017] FIGS. 1-3B are side schematic views of a fireplace heat
exchange system 10 according to various embodiments of the present
invention. FIG. 4 is a front schematic view of a fireplace heat
exchange system 10 according to another embodiment of the present
invention. The fireplace heat exchange system 10 can be used to
extract heat from heated exhaust air produced by the combustion of
a variety of fuel sources with air including gas, wood, pellets,
corn, biomass, and the like. The heat exchange system 10 is located
within a structure, for example within a wall space of a
residential, commercial, or industrial building.
[0018] Referring to FIGS. 1-4, the heat exchange system 10 includes
a firebox 14, a burner system 26, and a heat exchanger 40. The
firebox 14 has a plurality of panels 18 combined to define a
combustion chamber 22. In some embodiments, the panels 18 of the
firebox 14 include two opposing side panels (not shown), top and
bottom panels, and a rear panel. As shown in FIGS. 1-3B, the
firebox 14 also includes at least one panel 20 that allows a user
to access the combustion chamber 22. The front of the firebox 14
optionally includes glass doors or a sealed glass panel. In some
embodiments, the firebox 14 is of a type employed with one or more
of the following heat generating devices: a wood burning fireplace;
a gas fireplace (including fireplaces that include a gas-start
mechanism); a wood burning stove; a corn burning stove; a pellet
stove; a wood furnace; or other heat generating devices.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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, FIG. 3A schematically shows
heat transfer assist structures 46 including a plurality of
undulations or ridges whereas FIG. 3B shows heat transfer assist
structures 46 including a plurality of pins or fins.
[0025] 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.
[0026] 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.degree. F. to about 850.degree. F. In contrast, the
temperature of the exhaust air leaving the heat exchanger 40 via
the second end 52 ranges from about 120.degree. F. to about
180.degree. 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.degree. F. to about
180.degree. 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.
[0027] As shown in FIGS. 1-2, the first end 48 of the heat
exchanger housing 44 is optionally coupled to the exhaust air
outlet port 36 of the combustion chamber 22 such that the heat
exchanger is spaced a distance from the outer surface 53 of the
firebox 14. Air flow is permitted between the outer surface 53 of
the firebox 14 and the outer surface 50 of the heat exchanger
housing 44.
[0028] As shown in FIGS. 3A and 3B, the first end of the heat
exchanger 40 is optionally coupled to the exhaust air outlet port
36 of the combustion chamber 22 such that the heat exchanger 40 is
mounted flush with the outer surface 53 of the firebox 14 such that
no space exists between the outer surface 53 of the firebox 14 and
the outer surface 50 of the heat exchanger housing 44. In some
embodiments, the heat exchanger housing 44 shares a common panel
with the firebox 14.
[0029] As shown in FIGS. 2-3B, the heat exchanger 40 optionally
includes a first portion 54 in fluid communication with a second
portion 56. Exhaust air generally flows freely between the first
and second portions 54 and 56 of the generally L-shaped heat
exchanger 40. The first portion 54 is angularly offset from the
second portion 56 such that the heat exchanger 40 is adapted to fit
over the top and rear panels 18 of the firebox 14. In some
embodiments, the first portion 54 is substantially orthogonal to
the second portion 56 such that the overall shape of the heat
exchanger 40 approaches and L-shape, although a variety of angular
offsets are contemplated, including 45 degree angular offsets, for
example. In some embodiments, the first portion 54 is angularly
offset from the second portion 56 by at least 90 degrees.
[0030] In some embodiments, the heat exchanger system 10 includes a
plurality of heat exchangers. For example, as shown in FIG. 2, heat
exchanger system 10 includes heat exchangers 40a and 40b which are
coupled to one another in a generally stacked configuration. The
first end 48a of heat exchanger 40a is coupled to and in fluid
communication with the exhaust air outlet port 36 of the combustion
chamber 22. Exhaust air flows from the combustion chamber 22 and
into the first heat exchanger 40a via the exhaust air outlet port
36. The exhaust air flows from the first end 48a to the second end
52a of the first heat exchanger 40a. Rather than being exhausted to
the outside, the exhaust air from the combustion chamber 22 flows
out of the second end 52a of the first heat exchanger 40a and into
the second heat exchanger 40b coupled thereto. The exhaust air then
flows along the internal pathway defined within the second heat
exchanger 40b from the first end 48b of the second heat exchanger
40b to the second end 52b, where it is then vented to the
outside.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] As shown in FIGS. 1-3B, the heat exchanger 40 and combustion
chamber 22 are optionally disposed within a plenum 62. The plenum
62 generally includes a plurality of walls defining an air pathway
66 extending between an air intake end 70 and an air output end 74.
In some embodiments, the air intake end 70 is in fluid
communication with a source of room air. In some embodiments, the
air intake end 70 is in fluid communication with a source of
outside air. If desired, the air flowing through the plenum 62 from
the air intake end 70 to the air output end 74 is a combination of
room air and outside air.
[0036] 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.
[0037] As shown in FIG. 4, in some embodiments heat exchanger 40 is
disposed within a plenum 62 provided separately and at a distance
from the firebox 14. This configuration facilitates remote location
of the heat exchanger 40 and plenum 62 from the heat generating
device that includes the combustion chamber 22. In some
embodiments, the combustion chamber 22 of the heat generating
device is fluidly connected to the heat exchanger 40 via one or
more air ducts. Additionally, one or more blowers, fans, dampers,
deflectors, plenums, and the like may be added to the heat exchange
system 10 to assist in the flow of heated exhaust air from the
combustion chamber 22 to the heat exchanger 40 located within the
plenum 62. In some embodiments, retrofitting the heat exchanger 40
and plenum 62 to a pre-existing heat generating device to form heat
exchange system 10 is simplified by providing heat exchanger 40 in
a plenum 62 that is separate and remote from the firebox 14. The
heat exchanger 40 disposed within the plenum 62 can also be adapted
to work with an existing heat generating device including an
existing heat exchanger.
[0038] 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.
[0039] FIGS. 5-7 are cross-sectional views of various embodiments
of the heat exchanger 40 including one or more internal pathways 84
for exhaust air flow. As briefly described above, the heat
exchanger 40 optionally includes a plurality of baffle plates 80
that define one or more internal pathways 84 for exhaust air flow
through the heat exchanger 40 to the outside via the second end 52.
In general, the overall effective length of the internal pathway 84
defined by the baffle plates 80 is longer than the length, width,
or height of the heat exchanger housing 44.
[0040] 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 FIGS. 3A and 3B, the outer
surface 50 of the heat exchanger 40 may include a plurality of heat
transfer assist structures 46 configured to maximize the surface
area over which the heat exchange process occurs.
[0041] 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.
[0042] 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.
[0043] As shown in FIG. 5, in some embodiments the baffle plates 80
define at least one internal pathway 84 extending from the first
end 48 to the second end 52 of the heat exchanger 40. The internal
pathway 84 can define a serpentine or tortuous path for the exhaust
air such that exhaust air flows in a single general direction from
the first end 48 to the second end 52 of the heat exchanger 40
along an internal pathway 84 extending through a plurality of 180
degree turns. As shown in FIG. 5, the heat exchanger 40 facilitates
the use of cross-flow (perpendicular to F) and parallel flow (in
the same direction as F) modes of heat exchange. In other
embodiments, the general direction of air flow is opposite to that
of the exhaust air flow through the plenum such that the heat
exchanger 40 exchanges heat via cross-flow and counter flow (flow
in an opposite direction to F) modes of heat exchange.
[0044] FIG. 6 shows another configuration for heat exchanger 40
according to some embodiments where the heat exchanger 40 defines a
first side 82a and a second side 82b and has a first end 83a and a
second end 83b. The heat exchanger 40 has an internal pathway 84
defined by the baffle plates 80. As shown in FIG. 6, the internal
pathway 84 is divided into a first segment 86a corresponding to the
first side 82a and a second segment 86b corresponding to the second
side 82b. The first segment 86a carries the air from the first end
83a to the second end 83b while the second segment 86b carries the
air back from the second end 83b to the first end 83a. Each segment
86 and 88 extends through a plurality of 180 degree turns. As
previously referenced, the first segment 86a directs the air flow
in a generally first direction. The second segment 86b directs the
flow of air in a generally second, opposite direction. This
configuration allows air flow traveling along a single internal
pathway as defined by the baffle plates 80 to have parallel flow,
counter flow, and cross-flow components relative to the air flow F
through the plenum 62 over the outer surface 50 of the heat
exchanger housing 44. In particular, the first segment 86a is
adapted for both parallel and cross-flow modes of heat exchange
while the second segment 86b is adapted for both counter flow and
cross-flow modes of heat exchange.
[0045] As shown in FIG. 7, some embodiments of the heat exchanger
40 include baffle plates 80 defining two internal pathways 90 and
92. Exhaust air flows from the combustion chamber 22 (see FIGS.
1-4) into the first end 48 of the heat exchanger 40 where it is
split and travels along internal pathways 90 and 92. Each internal
pathway 90 and 92 extends through a plurality of 180 degree turns.
In some embodiments, the directions of air flow along a substantial
portion of the first and second pathways 90, 92 are in generally
parallel, though opposite direction. The air flowing through each
pathway 90 and 92 converges back together at the second end 52 of
the heat exchanger 40 before being exhausted.
[0046] 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.
[0047] 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.
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