WO2011002711A1

WO2011002711A1 - Flat tube heat exchanger for boilers and water heaters

Info

Publication number: WO2011002711A1
Application number: PCT/US2010/040194
Authority: WO
Inventors: Scott Rowe; Ozzie Missoum
Original assignee: Laars Heating Systems Company
Priority date: 2009-06-29
Filing date: 2010-06-28
Publication date: 2011-01-06

Abstract

A boiler or water heating system (10) includes a coiled heat exchange tube (18) having a major diameter and a minor diameter and a gap defined between adjacent turns of the tube (18), the tube (18) also having a non-circular cross-section with a dimension along a major axis (J) that is larger than a dimension along a minor axis (N), the major axis (J) of the non-circular cross-section of the heat exchange tube (18) being non-perpendicular to a coil axis (22) of the heat exchange tube (18) thereby providing a surface of the tube (18) extending between the major and minor diameters of the heat exchange tube ( 18) that promotes the gravitational migration of condensate along the surface of the heat exchange tube (18) and through the gap defined between adjacent turns of the heat exchange tube (18) in a direction toward or away from the coil axis (22).

Description

FLAT TUBE HEAT EXCHANGER FOR BOILERS AND WATER HEATERS

FIELD OF THE INVENTION

This invention relates to heat exchangers for boilers.

BACKGROUND OF THE INVENTION

Hydronic boilers operate by way of heating water (or any other fluid) to a preset temperature and circulating the water throughout a building or a home typically by way of radiators, baseboard heaters, and so forth. Hydronic boilers typically include a burner for introducing hot combustion gases into a housing of the boiler, and a heat exchanger including hollow tube members fitted within the boiler housing. Water is circulated through the hollow tube members of the heat exchanger for heat exchange with the hot combustion gases introduced into the boiler housing.

Hydronic boilers may also be referred to as condensing boilers when they are configured to condense the water vapor in the combustion gases to capture the latent heat of vaporization of the combustion gases produced during the combustion process. When the water vapor condenses to a liquid phase onto a surface of the tube members of the boiler, latent energy is released as sensible heat onto the surface of the tube members. The latent energy is absorbed by the water within the tube members.

Condensing boilers recover energy normally discharged to the atmosphere through the use of a secondary heat exchanger which absorbs residual heat in the flue gas to heat the water stream.

Condensate that forms on the hollow tube members fitted within the boiler housing may be highly acidic and has the potential to damage or impair those hollow tube members. It would be advantageous to provide a condensing boiler that is configured to limit the build-up of condensate on those hollow tube members to prolong the product life, performance and reliability of the condensing boiler.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed description when read in connection with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures:

FIG. 1 depicts a front, top and right side perspective view of a first exemplary embodiment of a condensing boiler.

FIG. 2 depicts a cross-sectional perspective view of the condensing boiler of FIG. 1 taken along the lines 2-2. FIG. 3 depicts a cross-sectional perspective view of the condensing boiler of FIG. 1 taken along the lines 3-3.

FIG. 4 depicts an exploded view of the condensing boiler of FIG. 1.

FIG. 5 depicts a perspective view of the primary heat exchanger of the condensing boiler of FIG. 1.

FIG. 6 depicts an exploded view of the primary heat exchanger of FIG. 5.

FIG. 7 depicts a cross-sectional elevation view of the primary heat exchanger of FIG. 5 taken along the lines 7-7.

FIG. 8 depicts a cross-sectional elevation view of a second exemplary

embodiment of a condensing boiler.

FIG. 9 depicts a cross-sectional elevation view of the heat exchanger of the condensing boiler of FIG. 8.

FIG. 10 depicts a schematic cross-sectional elevation view of a third exemplary embodiment of a condensing boiler.

FIG. 11 depicts an exemplary embodiment of a heat exchanger for a condensing boiler.

FIG. 12 depicts a cross-sectional view of the heat exchange assembly of FIG. 11 taken along the lines 12-12.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.

FIGS. 1-4 depict a fluid heating system 10 according to a first exemplary embodiment of the invention. The fluid heating system 10 may also be referred to herein as a water heating system, a boiler, a hydronic boiler, a water heater, a pool heater, or a condensing boiler. The fluid heating system 10 generally comprises a flue chamber 12, a burner 30 that is oriented to deliver combustion gases into the interior region defined by the flue chamber 12, a primary heat exchange tube assembly 14 mounted within the interior of the flue chamber 12 and a secondary heat exchange tube assembly 16 that is fluidly coupled to the primary heat exchange tube assembly 14 and mounted within the interior of the flue chamber 12. The combustion gases produced by the burner 30 heat fluid that is delivered through the heat exchange tube assemblies 14 and 16. Although the fluid heating system 10 is described hereinafter for heating water, it should be understood that the fluid heating system 10 is configured to heat any type of fluid, including steam. The primary heat exchange tube assembly 14 includes one or more (three shown) heat exchange tubes 18(1), 18(2) and 18(3) (referred to collectively as tubes 18) that are each coiled helically about a central coil axis 22. Similarly, heat exchange tube assembly 16 includes one or more (three shown) heat exchange tubes 20(1), 20(2) and 20(3) (referred to collectively as tubes 20) that are each coiled helically about a central coil axis 22. The central coil axis 22 of the primary heat exchange assembly 14 is spaced apart from and is oriented substantially parallel to the central coil axis 24 of the secondary heat exchange tube assembly 16. As best shown in FIG. 4, each tube 18 and 20 is a hollow member defining a fluid passageway and includes an inlet end 49 and 32 for receiving fluid and an outlet end 43 and 47 for expelling fluid, respectively. Each tube end extends substantially parallel to its respective coil axis so that the tube ends can be directly connected to a common header or a common manifold. The tubes 18 and 20 are optionally formed from a material that is non- corroding and acid resistant, such as stainless steel. Alternatively, the material may be coated with a material that is non-corroding and acid resistant.

The flue chamber 12 includes a first semi-cylindrical section 31 for

accommodating the heat exchange tubes 18 of the primary heat exchange tube assembly 14, a second semi-cylindrical section 33 for accommodating the heat exchange tubes 20 of the secondary heat exchange tube assembly 16, and a third semi-cylindrical section 35 for accommodating an air inlet vent 34. The flue chamber 12 is formed from a material that is substantially impervious to gas flow to retain combustion products produced by the burner 30 within the interior of the flue chamber 12.

A manifold 17 is coupled to the top end of the first semi-cylindrical section 31 of the flue chamber 12. The manifold 17 includes an inlet port 15 through which water is delivered, a hollow annular interior 37 for receiving water delivered through the i nlet port 15, and three apertures (two shown in FIG. 2) defined on a lower surface of the interior 37 that are each fluidly connected to an inlet end 32 of a heat exchange tube 20 of the secondary heat exchange tube assembly 16. In operation, water that is delivered through the inlet port 15 passes into the hollow annular interior 37 of the manifold 17 and is distributed through the heat exchange tubes 20 of the secondary heat exchange tube assembly 16.

A header 26 is coupled to the bottom end of the flue chamber 12. The header 26 is configured to fluidly connect the primary heat exchange tube assembly 14 with the secondary heat exchange tube assembly 16. Specifically, the header 26 includes a hollow annular interior 38 (FIG. 2) defining a fluid passageway, three apertures (not shown) defined on a top surface 41 of the interior 38 that are each fluidly connected to an outlet end 47 (FIG. 4) of a heat exchange tube 20 of the secondary heat exchange tube assembly 16, and three apertures (not shown) defined on a top surface 41 of the interior 38 that are each fluidly connected to an inlet end 49 (two shown in FIG. 4) of a heat exchange tube 18 of the primary heat exchange tube assembly 14. In operation, water within the heat exchange tubes 20 of the secondary heat exchange tube assembly 16 is delivered into the hollow annular interior 38 of the header 26 and is distributed into the heat exchange tubes 18 of the primary heat exchange tube assembly 14.

Another manifold 19, that is structurally similar to manifold 17, is coupled to the top end of the second semi-cylindrical section 31 of the flue chamber 12. The manifold 19 includes a hollow annular interior 39 defining a fluid passageway, three apertures (two shown in FIG. 2) defined on a lower surface of the interior 39 that are each fluidly connected to an outlet end 43 of a heat exchange tube 18 of the primary heat exchange tube assembly 14, and an outlet port 21 through which water is expelled from the manifold 19. In operation, water within the heat exchange tubes 18 of the primary heat exchange tube assembly 14 is distributed into the hollow annular interior 39 of the manifold 19 and expelled through the outlet port 21. The heated water is ultimately delivered to the end-user.

A refractory board and/or blanket 28 is positioned beneath each heat exchange tube assembly 14 and 16 for supporting and sealing the heat exchange tube assemblies 14 and 16. Another refractory board and/or blanket 29 is positioned above each heat exchange tube assembly 14 and 16. The refractory boards and/or blankets 28 and 29 may be replaced by other means of sealing the heat exchange tube assemblies 14 and 16 to the manifolds 17 and 19 and the header 26.

The burner 30 is mounted to the manifold 19 and is positioned to extend within the interior of the flue chamber 12 along the coil axis 22 of the primary heat exchange tube assembly 14. The burner 30 is configured to deliver combustion gases into the interior of the flue chamber 12. As best shown in FIG. 3, the flue chamber 12 defines a passage 13 for the flow of combustion gases from the burner 30 to a flue vent outlet 23. The flue vent outlet 23 is mounted to the header 26 to provide a passage through which the combustion gases are expelled from the interior of the flue chamber 12.

Although not shown, the inlet air passage 34 is fluidly connected to the burner 30 for delivering air to the burner 30. Air delivered to the burner 30 is mixed with fuel and the mixture is combusted by the burner 30. The inlet air passage 34 is positioned through the third semi-cylindrical section 35 of the flue chamber 12 between the primary heat exchange tube assembly 14 and the secondary heat exchange tube assembly 16 such that the air inlet passage 34 is capable of being heated by the combustion products. It should be understood that the section 35 may be any other shape to facilitate heat exchange between the flue products and the combustion air.

Referring now to the operation of the water heating system 10, the path of the products of combustion produced by the burner 30 is depicted by arrows in FIGS. 2 and 3. Air within the inlet air passage 34 is delivered to the burner 30 and is combined with fuel to produce a fuel-air mixture. The burner 30 is configured to combust the fuel-air mixture and emit products of combustion in a radial direction, as shown, toward the minor diameter of the heat exchange tubes 18. The combustion products are directed through gaps defined between adjacent convolutions of the heat exchange tubes 18. As the hot combustion products pass over the exterior surfaces of the tubes 18, thermal energy is exchanged with water within the tubes 18, thereby heating the water within the tubes 18.

As best shown in FIG. 3, the combustion products then travel through the passage 13 provided in the flue chamber 12. The passage 13 extends from the major diameter of the heat exchange tube 18 of the primary heat exchange tube assembly 14 to the major diameter of the heat exchange tube 20 of the secondary heat exchange tube assembly 16. As the hot combustion products pass over the exterior surface of the inlet air passage 34, thermal energy is exchanged with the air within the inlet air passage 34, thereby heating the air within the inlet air passage 34. The combustion products then travel through gaps defined between adjacent convolutions of the heat exchange tubes 20. As the hot combustion products pass over the exterior surfaces of the tubes 20, thermal energy is exchanged with water within the tubes 20, thereby heating the water within the tubes 20. The combustion products are ultimately expelled through the flue vent outlet 23.

Referring now to the path of the water flow through the boiler 10, cold water (or other fluid) is introduced through the inlet port 15 of the manifold 17. The water enters the interior 37 of the manifold 17 and travels through the secondary heat exchange tube assembly 16. As the water passes through the secondary heat exchange tube assembly 16 it absorbs heat from the combustion products, as previously described. The heated water is then delivered into the header 26 and through the primary heat exchange tube assembly 14 where it is again exposed to heat from the combustion products of the burner 30. The twice-heated water is then distributed into the interior 39 of the manifold 19 that is fluidly coupled to the primary heat exchange tube assembly 14. The twice-heated water is expelled through the outlet port 21 provided in the manifold 19 and delivered to an end-user.

As the products of combustion are directed over the exterior surfaces of the heat exchange tube assemblies 14 and 16, condensate forms on those exterior surfaces. As described in greater detail with reference to FIGS. 5-7, the geometry of the heat exchange tube assemblies 14 and 16 is tailored to promote the migration of condensate along the surfaces of the heat exchange tube assemblies 14 and 16, to limit or prevent condensate from settling along those surfaces.

FIGS. 5-7 depict the primary heat exchange tube assembly 14 of the water heating system 10. The general description of the primary heat exchange tube assembly 14 provided hereinafter with reference to FIGS. 5-7 also applies to the secondary heat exchange tube assembly 16, with the exception that the angle of the convolutions of the tubes 20 of the secondary heat exchange tube assembly 16 differs from that of tubes 18 of the primary heat exchange tube assembly 14 (see FIG. 2) with respect to their coil axes. The primary heat exchange tube assembly 14 includes one or more separate coiled heat exchange tubes 18 (three shown), each having an inlet end 49 and an outlet end 43. Each tube 18 includes a plurality of convolutions. In assembled form of tube assembly 14, a gap is defined between adjacent convolutions, i.e., turns, of the heat exchange tubes 18. Each gap provides a passageway through which combustion products produced by the burner 30 and condensate formed on the exterior surfaces of the tubes 18 are delivered.

The gap defined between adjacent turns of the heat exchange tubes 18 may vary in size in a radial direction, i.e., from one end of the gap toward the minor diameter of the heat exchange tube 18 to an opposite end of the gap toward the major diameter of the heat exchange tube 18. More particularly, the size of the gap at the end of the gap toward the minor diameter of the heat exchange tube 18 is larger than the size of the gap at the opposite end of the gap toward the major diameter of the heat exchange tube 18. Alternatively, the size of the gap at the end of the gap toward the minor diameter of the heat exchange tube may be smaller than the size of the gap at the opposite end of the gap toward the major diameter of the heat exchange tube.

Although not shown, a spacer may be positioned between adjacent convolutions of the tubes 18 to create gaps between those adjacent convolutions. Alternatively, the exterior surfaces of the tubes 18 may be dimpled to form the gaps between the adjacent convolutions of the tubes 18. As another alternative, a rod may be attached (e.g., welded) to each convolution of the tubes 18 to maintain the gap between the adjacent convolutions.

As shown in FIG. 7, the cross-section of each heat exchange tube 18 is substantially ovular. Alternatively, the cross-section of each heat exchange tube 18 may be rectangular. More generally, each heat exchange tube 18 has a non-circular cross-section defining a major diameter and a minor diameter. For each convolution of tube 18, a dimension along a major axis ^VJ' is larger than a dimension along a minor axis ^λN.' The cross-sectional shape of each convolution of tube 18 may vary from that shown and described herein. According to one aspect of the invention, the major axis 'J' of each convolution of the heat exchange tubes 18 is both non-perpendicular and non-parallel to the coil axis 22 of the heat exchange tube 18.

According to another aspect of the invention, an acute angle 'K' is defined between the major axis T of each convolution of the tubes 18 and a horizontal plane Η' that is perpendicular to the coil axis 22 of the heat exchange tube 18. The acute angle may also be referred to herein as a draining angle. According to still another aspect of the invention, the angle ^λK' defined between the major axis 'J' of each convolution of the tubes 18 and the horizontal plane Η' is between about 2 degrees and about 88 degrees. According to yet another aspect of the invention, the angle 'K' is about 20 degrees. The angle ^VK' may vary from that shown and described herein.

Like the heat exchange tubes 18 of the primary heat exchange tube assembly 14, the tubes 20 of the secondary heat exchange tube assembly 16 shown in FIG. 2 have a non-circular cross-section defining a major diameter and a minor diameter. For each convolution of tube 20, a dimension along a major axis is larger than a dimension along a minor axis. According to one aspect of the invention, the major axis of the non-circular cross-section of each heat exchange tube 20 is both non-perpendicular and non-parallel to the coil axis 24 of the heat exchange tubes 20.

According to another aspect of the invention, an acute angle is defined between the major axis of each convolution of the tubes 20 and a horizontal plane that is perpendicular to the coil axis 24 of the heat exchange tube 20. According to still another aspect of the invention, the acute angle that is defined between the major axis of each convolution of the tubes 20 and the horizontal plane is between about 2 degrees and about 88 degrees. According to yet another aspect of the invention, the acute angle is about 20 degrees.

The acute angle of the secondary heat exchange tube assembly 16 is a negative angle measured in a counter-clockwise direction starting from the horizontal plane, whereas angle "K" of the primary heat exchange tube assembly 14 is a positive angle measured in a clockwise direction starting from the horizontal plane Η.' In other words, the slopes of the tubes 18 and 20 are offset by about 90 degrees.

The angled geometry of the tubes 18 and 20 promotes the gravitational migration of condensate along the angled surfaces of the heat exchange tubes 18 and 20 from a higher elevation to a lower elevation. The condensate travels within the gaps defined between adjacent convolutions of the heat exchange tubes 18 and 20. The angled exterior surface of the tubes 18 promotes the gravitational migration of condensate in a direction away from coil axis 22, whereas, the angled exterior surface of the tubes 20 promotes the gravitational migration of condensate in a direction toward the coil axis 24. The condensate pools, i.e., collects, on the surfaces of the header 26. Although not shown, drain ports are provided in the header 26 for expelling the acidic condensate from the water heating system 10.

The flow of the combustion products assists in urging the condensate along the angled surfaces of the heat exchange tubes 18 and 20. More particularly, the path of the combustion products (depicted by the arrows in FIGS. 2 and 3) follows substantially the same path as the gravitational migration path of condensate along the angled surfaces of the heat exchange tubes 18 and 20. In other words, as the combustion products travel across the surfaces of the tubes 18 and 20, those combustion products move the condensate that has collected on the surfaces of the tubes 18 and 20 in the same direction as the gravitational migration path (i.e. from a higher elevation to a lower elevation. In sum, both gravitational forces and the flow of combustion products move the condensate along the angled surfaces of the heat exchange tubes 18 and 20 from a higher elevation to a lower elevation). Limiting settlement of acidic condensate on the surfaces of the tubes 18 and 20 prolongs the product life of the heat exchange tubes 18 and 20, and, consequently, the entire water heating system 10.

FIG. 8 depicts a cross-sectional elevation view of a second exemplary

embodiment of a boiler 100. The boiler 100 generally includes a flue chamber 160, a burner 140 positioned within the interior of the flue chamber 160 for producing products of combustion, and a heat exchanger 120 that is configured for containing water (or other fluid) to be heated by the products of combustion. The flue chamber 160 is embodied as a cylindrical sleeve. The heat exchanger 120 is positioned within the interior of the flue chamber 160. An annular passage 162 is defined between the interior revolved surface of the flue chamber 160 and the major diameter of the heat exchanger 120.

The heat exchanger 120 is embodied as a single coiled tube including a primary heat exchange portion 114 positioned at an elevation above a secondary heat exchange portion 116. The primary heat exchange portion 114 is fluidly coupled and integral with the secondary heat exchange portion 116, i.e., both portions 114 and 116 comprise the single coiled tube. Although not explicitly shown, gaps are provided between adjacent convolutions of the heat exchanger 120 for channeling combustion products and condensate.

A circular baffle plate 130 is positioned within the minor diameter of the heat exchanger 120 at an elevation between the primary heat exchange portion 114 and the secondary heat exchange portion 116 of the heat exchanger 120. The circular baffle plate 130 is positioned to direct the combustion products across the heat exchange surfaces of both the primary heat exchange portion 114 and the secondary heat exchange portion 116 to maximize heat transfer between the products of combustion and water that is within the heat exchanger 120.

A manifold 122 is coupled to the bottom end of the flue chamber 160. The manifold 122 includes an inlet port 123 through which water is delivered into the boiler 100, a hollow annular interior 137 defining a fluid passageway, and at least one aperture (not shown) defined on a lower surface of the interior 137 that is fluidly connected to an inlet end 132 of the heat exchanger 120. A flue vent outlet 129 is mounted to the manifold 122 to provide a passage through which combustion products are exhausted from the boiler 100.

Another manifold 124 is coupled to the top end of the flue chamber 160. The burner 140 is mounted to the manifold 124 to extend downward into the interior of the boiler 100. The manifold 124 includes a hollow annular interior 139 defining a fl uid passageway, one aperture (not shown) defined on a lower surface of the interior 139 that is fluidly coupled to the outlet ends 143 of the heat exchanger 120, and an outlet port 126 through which water is expelled from the manifold 124.

Referring now to the operation of the water heating system 100, the path of the products of combustion produced by the burner 140 is depicted by arrows in FIG. 8. The burner 140 combusts a fuel-air mixture and emits products of combustion in a radial direction, as shown, toward the minor diameter of the primary heat exchange portion 114 of the heat exchanger 120. The combustion products flow from the minor diameter to the major diameter of the heat exchange portion 114 through the gaps defined between adjacent convolutions of the primary heat exchange portion 114.

The baffle plate 130 forces the combustion products to flow over the heat exchange surfaces of the primary heat exchange portion 114 before the combustion products flow over the heat exchange surfaces of the secondary heat exchange portion 116. In other words, by virtue of the baffle plate 130, the combustion products are prevented from flowing toward the secondary heat exchange portion 116 of the heat exchanger 120 without first flowing over the heat exchange surfaces of the primary heat exchange portion 114.

As the hot combustion products pass over the exterior surfaces of the primary heat exchange portion 114, thermal energy is exchanged with water within the primary heat exchange portion 114, thereby heating the water within the primary heat exchange portion 114. The combustion products then travel downwardly through the passage 162 provided in the flue chamber 12. The combustion products then travel through the gaps between the convolutions of the secondary heat exchange portion 116 from the major diameter of the secondary heat exchange portion 116 to the minor diameter of the secondary heat exchange portion 116. As the hot combustion products pass over the exterior surfaces of the secondary heat exchange portion 116, thermal energy is exchanged with water within the secondary heat exchange portion 116, thereby heating the water within the secondary heat exchange portion 116. The combustion products are ultimately expelled through the flue vent outlet 129.

Referring now to the path of the water flow through the boiler 100, cold water is introduced into the hollow annular interior 137 of the manifold 122 through the inlet port 123. The water is then directed into the secondary heat exchange portion 116 of the heat exchanger 120. As the water passes through the secondary heat exchange portion 116 it absorbs heat from the combustion products of the burner 140, as previously described. The heated water is then delivered into the primary heat exchange portion 114 of the heat exchanger 120 where it is again exposed to heat of the combustion products of the burner 140. The twice-heated water is then distributed into the manifold 124 that is fluidly coupled to the primary heat exchange tube assembly 120. The twice-heated water is expelled through the outlet port 126 provided in the manifold 124 for use by an end-user.

As the products of combustion are directed over the heat exchange surfaces of the heat exchange tube portions 114 and 116, condensate forms on the exterior surfaces of those surfaces. As described in greater detail with reference to FIG. 9, the geometry of the heat exchanger 120 is tailored to promote the migration of condensate in order to limit or prevent settling of condensate along those heat exchange surfaces.

FIG. 9 depicts a cross-sectional elevation view of the heat exchanger 120 of the boiler 100 of FIG. 8. The heat exchanger 120 is embodied as one or more coiled tubes (three shown). The primary heat exchange portion 114 is fluidly coupled and integral with the secondary heat exchange portion 116, i.e., both portions 114 and 116 comprise the coiled tubes. The primary heat exchange portion 114 transitions to the secondary heat exchange portion 116 by a twist 119 formed in the heat exchanger 120. The baffle plate 130 is positioned at an elevation corresponding to the twist 119 of the heat exchanger 120.

The geometry of the primary heat exchange portion 114 is similar to that of the primary heat exchange tube 18 of FIG. 7, and the geometry of the secondary heat exchange portion 116 is similar to that of the secondary heat exchange tube 20 of FIG. 1. More particularly, according to one aspect of the invention, the major axes ^λB' and ^λD' of the heat exchanger tube 120 are both non-perpendicular and non-parallel to the coil axis ^λA.' An acute angle is defined between the major axes ^ΛB' and ^λD' and their respective horizontal planes. The range of acute angles described with reference to the tubes 18 and 20 of FIGS. 1-7 also apply to the primary heat exchange portion 114 and the secondary heat exchange portion 116, respectively, of the heat exchanger 120.

The angled geometry of the convolutions of the heat exchanger 120 promotes the gravitational migration of condensate along the angled surfaces of the heat exchanger 120 from a higher elevation to a lower elevation. The angled exterior surfaces of the primary heat exchange portion 114 promotes the gravitational migration of condensate in a direction away from the coil axis ^λA/ whereas, the angled exterior surfaces of the secondary heat exchange portion 116 promotes the gravitational migration of condensate in a direction toward the coil axis ^λA.' The condensate pools, i.e., collects, on the surfaces of the header 122. Although not shown, drain ports are provided in the header 122 for expelling the acidic condensate from the boiler 100.

The flow of the combustion products assists in moving the condensate along the angled surfaces of the heat exchanger 120. More particularly, the path of the combustion products (depicted by the arrows in FIG. 8) follows substantially the same path as the gravitational migration path of condensate along the angled surfaces of the heat exchanger 120. As the combustion products travel across the surfaces of the heat exchanger tube 120, those combustion products move the condensate that has collected on the surfaces of the heat exchanger tube 120 in the same direction as the gravitational migration path. In sum, both gravitational forces and the flow of combustion products move the condensate along the angled surfaces of the heat exchanger tubes 120 from a higher elevation to a lower elevation.

FIG. 10 depicts a schematic cross-sectional elevation view of a third exemplary embodiment of a condensing boiler 200. The condensing boiler 200 is structurally and functionally similar to the boiler 100 of FIG. 8, with the exception that the primary heat exchanger 214 and the secondary heat exchanger 216 of the boiler 200 are embodied as separate tubes that are fluidly coupled together by a manifold 240. The heat exchangers 214 and 216 are structurally identical and are inverted with respect to each other within the interior of the flue chamber 212. Each heat exchanger 214 and 216 may comprise one or more coiled tubes (three shown).

Although not shown, the manifold 240 includes a hollow interior for containing water, and apertures defined on its exterior surface for fluidly coupling with the ends of the heat exchangers 214 and 216. In addition to transferring water between the primary heat exchanger 214 and the secondary heat exchanger 216, the manifold 240 serves as a baffle, like the baffle 130 of FIG. 8, to urge the products of combustion along the heat exchange surfaces of the primary heat exchanger 214 before the combustion products flow over the heat exchange surfaces of the secondary heat exchanger 216. FIG. 11 depicts an exemplary embodiment of a heat exchange assembly 320 of a condensing boiler and FIG. 12 depicts a cross-sectional view of the heat exchange assembly 320 of FIG. 11 taken along the lines 12-12. The heat exchange assembly 320 includes a first heat exchange portion 330 and a second heat exchange portion 340 positioned about the circumference of the first heat exchange portion 330. Both of the heat exchange portions 330 and 340 are functionally equivalent to the primary heat exchange tube assembly 14 of FIGS. 5 and 6. The ends 332 and 342 of the heat exchange portions 330 and 340, respectively, are coupled to a manifold or a header (not shown). The opposing ends 334 and 344 of the heat exchange portions 330 and 340, respectively, are also coupled to a manifold, or a header (not shown). The heat exchange portions 330 and 340 are arranged such that, in use, product of combustion generated by a burner (not shown) are first directed through the gaps defined between the adjacent convolutions of the first heat exchange portion 330 and then through the gaps defined between the adjacent convolutions of the second heat exchange portion 340.

Although this invention has been described with reference to exemplary embodiments and variations thereof, it will be appreciated that additional variations and modifications can be made within the spirit and scope of this invention. Although this invention may be of particular benefit in the field of condensing boilers, it will be appreciated that this invention can be beneficially applied in connection with water heaters and other heating systems as well.

Claims

What is Claimed:

1. A boiler or water heating system comprising :

a flue chamber substantially impervious to gas flow from an interior defined by the flue chamber;

at least one heat exchange tube assembly mounted within the interior of the flue chamber, the heat exchange tube assembly having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the heat exchange tube also having a non-circular cross-section with a dimension along a major axis that is larger than a dimension along a minor axis, the major axis of the non-circular cross-section of the heat exchange tube being non-perpendicular to the coil axis of the heat exchange tube thereby providing a surface of the heat exchange tube extending between the major and minor diameters of the heat exchange tube that promotes the gravitational migration of condensate along the surface of the heat exchange tube and through the gap defined between adjacent turns of the heat exchange tube in a direction toward or away from the coil axis; and

a burner oriented to deliver combustion gases into the interior of the flue chamber for flow through the gap defined between adjacent turns of the heat exchange tube.

2. The boiler or water heating system of claim 1, wherein the major axis of the non-circular cross-section of the heat exchange tube is oriented at an acute angle with respect to a horizontal plane that intersects the coil axis of the heat exchange tube.

3. A boiler or water heating system comprising:

a primary heat exchange tube assembly and a secondary heat exchange tube assembly, each having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the central coil axis of the primary heat exchange assembly being spaced apart from and substantially parallel to the central coil axis of the secondary heat exchange tube assembly;

a burner oriented to deliver combustion gases into contact with the primary heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the primary heat exchange tube assembly from the minor diameter of the heat exchange tube to the major diameter of the heat exchange tube; and

a flue chamber enclosing the primary heat exchange tube assembly and the secondary heat exchange tube assembly, the flue chamber being substantially impervious to gas flow from an interior defined by the flue chamber, and the flue chamber defining a passage for the flow of combustion gases from the major diameter of the heat exchange tube of the primary heat exchange tube assembly to the major diameter of the heat exchange tube of the secondary heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the secondary heat exchange tube assembly from the major diameter of the secondary heat exchange tube to the minor diameter of the secondary heat exchange tube.

4. A boiler or water heating system comprising :

a plurality of heat exchange tube assemblies mounted within the interior of the flue chamber, each heat exchange tube assembly having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the heat exchange tube also having a non-circular cross-section with a dimension along a major axis that is larger than a dimension along a minor axis, the major axis of the non-circular cross-section of the heat exchange tube being non-perpendicular to the coil axis of the heat exchange tube, thereby providing a surface of the heat exchange tube extending between the major and minor diameters of the heat exchange tube that promotes the gravitational migration of condensate along the surface of the heat exchange tube and through the gap defined between adjacent turns of the heat exchange tube, one of the heat exchange tube assemblies being oriented such that the gravitational migration of condensate is promoted along the surface of the heat exchange tube in a direction away from the coil axis and another of the heat exchange tube assemblies being oriented such that the gravitational migration of condensate is promoted along the surface of the heat exchange tube in a direction toward from the coil axis; and

a burner oriented to deliver combustion gases into the interior of the flue chamber for flow through the gap defined between adjacent turns of the heat exchange tubes of the heat exchange tube assemblies such that the direction of flow of combustion gases is the same as the direction of gravitational migration of condensate in each of the heat exchange tube assemblies.

5. A boiler or fluid heating system comprising :

a primary heat exchange tube assembly and a secondary heat exchange tube assembly, each having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or fluid heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the central coil axis of the primary heat exchange assembly being spaced apart from and substantially parallel to the central coil axis of the secondary heat exchange tube assembly;

a burner oriented to deliver combustion gases into contact with the primary heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the primary heat exchange tube assembly from the minor diameter of the heat exchange tube to the major diameter of the heat exchange tube; a flue chamber enclosing the primary heat exchange tube assembly and the secondary heat exchange tube assembly, the flue chamber being substantially impervious to gas flow from an interior defined by the flue chamber; and

an inlet air passage connected to deliver air to be mixed with fuel for combustio n in the burner, the inlet air passage extending through the interior of the flue chamber at a location between the primary heat exchange tube assembly and the secondary heat exchange tube assembly, thereby pre-heating inlet air.

6. A boiler or water heating system comprising :

a primary heat exchange tube assembly and a secondary heat exchange tube assembly, each having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the primary heat exchange tube assembly being positioned over the secondary heat exchange tube assembly;

a burner oriented to deliver combustion gases into contact with the primary heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the primary heat exchange tube assembly from the minor diameter of the heat exchange tube to the major diameter of the heat exchange tube; a flue chamber enclosing the primary heat exchange tube assembly and the secondary heat exchange tube assembly, the flue chamber being substantially impervious to gas flow from an interior defined by the flue chamber, and the flue chamber defining a passage for the flow of combustion gases from the major diameter of the heat exchange tube of the primary heat exchange tube assembly to the major diameter of the heat exchange tube of the secondary heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the secondary heat exchange tube assembly from the major diameter of the heat exchange tube to the minor diameter of the heat exchange tube; and

5 a header coupled to the primary heat exchange tube assembly and secondary heat exchange tube assembly, the header being configured to direct fluid from the heat exchange tube of the primary heat exchange tube assembly to the heat exchange tube of the secondary heat exchange tube assembly.

7. A boiler or water heating system comprising:

o a heat exchange tube assembly having at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the heat exchange tube assembly having a primarys heat exchange portion positioned over a secondary heat exchange portion;

a burner oriented to deliver combustion gases into contact with the primary heat exchange portion of the heat exchange tube assembly for flow through the gap defined between adjacent turns of the heat exchange tube of the primary heat exchange portion of the heat exchange tube assembly from the minor diameter of the heat0 exchange tube to the major diameter of the heat exchange tube;

a flue chamber enclosing the primary and secondary heat exchange portions of the heat exchange tube assembly, the flue chamber being substantially impervious to gas flow from an interior defined by the flue chamber, and the flue chamber defining a passage for the flow of combustion gases from the major diameter of the heat

5 exchange tube in the primary heat exchange portion to the major diameter of the heat exchange tube in the secondary heat exchange portion for flow through the gap defined between adjacent turns of the heat exchange tube in the secondary heat exchange portion from the major diameter of the heat exchange tube to the minor diameter of the heat exchange tube; and

o a barrier traversing the central coil axis at a location between the primary heat exchange portion and the secondary heat exchange portion of the heat exchange tube assembly, thereby directing combustion gases from the minor diameter of the heat exchange tube in the primary heat exchange portion to the major diameter of the heat exchange tube in the primary heat exchange portion and into the passage defined by₅ the flue chamber for flow of combustion gases from the major diameter of the heat exchange tube in the primary heat exchange portion to the major diameter of the heat exchange tube in the secondary heat exchange portion, thus promoting flow of the combustion gases from the major diameter of the heat exchange tube in the secondary heat exchange portion to the minor diameter of the heat exchange tube in the secondary heat exchange portion.

8. A heat exchange tube assembly for a boiler or water heating system, the heat exchange tube comprising at least one heat exchange tube coiled helically about a central coil axis oriented to extend vertically or horizontally when the boiler or water heating system is installed for operation, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the heat exchange tube also having a non-circular cross-section with a dimension along a major axis that is larger than a dimension along a minor axis, the major axis of the non-circular cross-section of the heat exchange tube being non- perpendicular to the coil axis of the heat exchange tube, thereby providing a surface of the heat exchange tube extending between the major and minor diameters of the heat exchange tube that promotes the gravitational migration of condensate along the surface of the heat exchange tube and through the gap defined between adjacent turns of the heat exchange tube in a direction toward or away from the coil axis.

9. The heat exchange tube assembly of claim 8, further comprising spacers positioned between the adjacent coils, the spacers being sized to establish the gap through which combustion gases flow.

10. The heat exchange tube assembly of claim 8, wherein ends of the heat exchange tube are oriented to extend substantially parallel to the central coil axis.

11. The heat exchange tube assembly of claim 8, the heat exchange tube having first and second portions, wherein an angle defined between the major axis of the non-circular cross-section of the first portion of the heat exchange tube and the coil axis of the heat exchange tube differs from an angle defined between the major axis of the non-circular cross-section of the second portion of the heat exchange tube and the coil axis of the heat exchange tube.

12. The heat exchange tube assembly of claim 8, wherein the gap defined between adjacent turns of the heat exchange tube varies in size from one end of the gap toward the minor diameter of the heat exchange tube to an opposite end of the gap toward the major diameter of the heat exchange tube.

13. The heat exchange tube assembly of claim 12, wherein the size of the gap at the end of the gap toward the minor diameter of the heat exchange tube is substantially equal to or larger than the size of the gap at the opposite end of the gap toward the major diameter of the heat exchange tube.

14. The heat exchange tube assembly of claim 12, wherein the size of the gap at the end of the gap toward the minor diameter of the heat exchange tube is substantially equal to or smaller than the size of the gap at the opposite end of the gap toward the major diameter of the heat exchange tube.

15. A method of manufacturing a boiler or water heating system comprising the step of:

positioning a heat exchange tube assembly having at least one heat exchange tube coiled helically about a central coil axis within an interior of a flue chamber, the coiled heat exchange tube having a major diameter and a minor diameter and a gap defined between adjacent turns of the heat exchange tube, the heat exchange tube also having a non-circular cross-section with a dimension along a major axis that is larger than a dimension along a minor axis, the major axis of the non-circular cross-section of the heat exchange tube being non-perpendicular to the coil axis of the heat exchange tube thereby providing a surface of the heat exchange tube extending between the major and minor diameters of the heat exchange tube that promotes the gravitational migration of condensate along the surface of the heat exchange tube and through the gap defined between adjacent turns of the heat exchange tube in a direction toward or away from the coil axis.

16. The method of claim 15 further comprising the step of positioning a burner oriented to deliver combustion gases in the interior of the flue chamber for flow through the gap defined between adjacent turns of the heat exchange tube.

17. The method of claim 15 further comprising the step of positioning another heat exchange tube within the flue chamber, wherein an angle defined between the major axis and the coil axis of the another heat exchange tube differs from an angle defined between the major axis and the coil axis of the heat exchange tube.

18. The method of claim 17 further comprising the step of fluidly coupling the heat exchange tubes together.

19. The method of claim 17 further comprising the step of positioning a baffle between the heat exchange tube and the another heat exchange tube.

20. A method of forming a heat exchange tube assembly for a boiler or water heating system comprising the step of:

forming a heat exchange tube having a body coiled body helically about a central coil axis, the heat exchange tube having a non-circular cross-section with a dimension along a major axis that is larger than a dimension along a minor axis, the major axis of the non-circular cross-section of the heat exchange tube being non- perpendicular to the coil axis of the heat exchange tube thereby providing a surface of the heat exchange tube extending between the major and minor diameters of the heat exchange tube that promotes the gravitational migration of condensate along the surface of the heat exchange tube and through the gap defined between adjacent turns of the heat exchange tube in a direction toward or away from the coil axis.

21. The method of claim 20 further comprising the step of forming two distinct portions of the tube sharing the same coil axis, wherein an angle defined between a major axis of a first portion of the tube and the coil axis differs from an angle defined between a major axis of a second portion of the tube and the coil axis, thereby providing a surface of the first portion that promotes gravitational migration of condensate in a direction away from the coil axis and providing a surface of the second portion that promotes gravitational migration of condensate in a direction toward the coil axis.

22. The fluid heating system of claim 5, wherein the gap defined between adjacent turns of the heat exchange tube varies in size from one end of the gap toward the minor diameter of the heat exchange tube to an opposite end of the gap toward the major diameter of the heat exchange tube.

23. The fluid heating system of claim 5, wherein the fluid to be heated comprises steam.