US20130333868A1

US20130333868A1 - Secondary heat exchanger for a furnace heat exchanger

Info

Publication number: US20130333868A1
Application number: US13/495,897
Authority: US
Inventors: Shiblee S. M. Noman; Ian Burmania
Original assignee: Lennox Industries Inc
Current assignee: Lennox Industries Inc
Priority date: 2012-06-13
Filing date: 2012-06-13
Publication date: 2013-12-19
Also published as: CA2818686A1

Abstract

Secondary heat exchanger assembly for a heat exchanger unit comprising a hot header box configured to receive combustion gases from a primary heat exchanger assembly of the heat exchanger unit, a cold header box configured to transfer combustion gases to an induction assembly of a furnace unit the heat exchanger unit is part of and heat transfer zone located between the hot and cold boxes. The zone includes secondary heat conduction tubes coupled to the hot box to receive the combustion gases passing through the hot box, and, coupled to the cold box to deliver the combustion gases to the colder box. Air, when blown from a blower unit of the furnace unit through the zone, has a non-uniform velocity profile across a width of the zone, and, a heat transfer mass of the zone across the width is configured to have a substantially similar-shaped non-uniform heat transfer mass profile.

Description

TECHNICAL FIELD

This application is directed, in general, to heating, ventilation and air conditioning (HVAC) systems and, more specifically, to a secondary heat exchange assembly the system and method of manufacturing the secondary heat exchange assembly.

BACKGROUND

To increase the efficiency of heat transfer, furnace heat exchangers often have a secondary heat exchange assembly located adjacent to the primary heat exchange assembly. It is desirable to maximize the heat transfer from the combusted gases passing through the secondary heat conduction tubes to the air blown over the exterior surfaces of these tubes.

SUMMARY

One embodiment of the present disclosure is secondary heat exchanger assembly for a heat exchanger unit. The secondary heat exchanger assembly comprises a hot header box and a cold header box. The hot header box is configured to receive combustion gases from a primary heat exchanger assembly of the heat exchanger unit. The cold header box is configured to transfer the combustion gases to an induction assembly of a furnace unit that the heat exchanger unit is part of. The secondary heat exchanger assembly also comprises a heat transfer zone located between the hot header box and the cold header box. The heat transfer zone includes secondary heat conduction tubes coupled to the hot header box to receive the combustion gases passing through the hot header box, and, coupled to the cold header box to deliver the combustion gases to the colder header box. Air, when blown from a blower unit of the furnace unit through the heat transfer zone, has a non-uniform velocity profile across a width of the heat transfer zone, and, a heat transfer mass of the heat transfer zone across the width is configured to have a substantially similar-shaped non-uniform heat transfer mass profile.
Another embodiment of the present disclosure is a method of manufacturing a secondary heat exchanger assembly for a heat exchanger unit. The method comprises providing a hot header box configured to receive combustion gases from a primary heat exchanger assembly of the heat exchanger unit, providing a cold header box configured to transfer the combustion gases to an induction assembly of a furnace unit that the heat exchanger unit is part of and forming a heat transfer zone between the hot header box and the cold header box including the heat transfer zone. Forming the heat transfer zone includes coupling secondary heat conduction tubes to the hot header box so as to receive the combustion gases passing through the hot header box, and, coupling the secondary heat conduction tubes to the cold header box so as to deliver the combustion gases to the colder header box. Air, when blown from a blower unit of the furnace unit through the heat transfer zone, has a non-uniform velocity profile across a width of the heat transfer zone, and, a heat transfer mass of the heat transfer zone across the width is configured to have a substantially similar-shaped non-uniform heat transfer mass profile.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates exploded isometric view of an example heating furnace that includes an example secondary heat exchanger assembly of the disclosure;

FIG. 2 presents an example air velocity profile of air directed from a blower of a furnace unit to the example secondary heat exchanger assembly depicted in FIG. 1;

FIG. 3 presents a detailed isometric view of an example secondary heat exchanger assembly of the disclosure, similar to the example assembly depicted in FIG. 1;

FIG. 4 presents another detailed isometric view of another example secondary heat exchanger assembly of the disclosure, similar to the example assembly depicted in FIG. 1;

FIG. 5 presents a detailed plan view, corresponding to view line 5 in FIG. 4, of another example secondary heat exchanger assembly of the disclosure, similar to the example assemblies depicted in FIGS. 1 and 3-4; and

FIG. 6 presents a flow diagram of an example manufacturing a secondary heat exchanger assembly for a heat exchanger unit, such as any of the secondary heat exchanger assemblies depicted in FIGS. 1, 3-5.

DETAILED DESCRIPTION

The term, “or,” as used herein, refers to a non-exclusive or, unless otherwise indicated. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
As part of the present disclosure, it was discovered that the air, passing from a blower of the furnace unit through the secondary heat exchanger assembly, has non-uniform velocity profile. In particular, it was discovered that the velocity of air passing through the center of the secondary heat exchanger assembly is greater than the velocity of air passing through the sides of the secondary heat exchanger assembly. Additionally, it was discovered that heat exchange efficiency can be improved by adjusting the heat transfer mass of the secondary heat conduction tubes and associated structures coupled to the tubes (e.g., heat exchange fins and collars) to match the air velocity profile.
One embodiment of the disclosure is a secondary heat exchanger assembly for a heat exchanger unit. FIG. 1 illustrates an exploded isometric view of an example secondary heat exchanger assembly 100 of the disclosure. The secondary heat exchanger assembly 100 can be part of a heat exchanger unit 102. In some embodiments, the secondary heat exchanger assembly 100 and the heat exchanger unit 102 can be part of a heating furnace 105. In some embodiments the heating furnace 105 can be a component of a HVAC system (not depicted).
As further depicted in FIG. 1, embodiments of the furnace 105 can include a cabinet 110, and the heat exchanger unit 102 can located within the cabinet 110. The furnace 105 can also include a blower unit 115 located in the cabinet 110 and positioned to force air flow in a direction 120 towards the heat exchange unit 102 (e.g., through an opening 125 in a exchange deck 127 if the unit 102 to the secondary heat exchanger assembly 100).
One of ordinary skill would appreciate that embodiments of the furnace unit 105 could include other components to facilitate the furnace's operation. For instance, the furnace 100 can also include a burner unit 130 coupled to primary heat conduction tubes 132 of a primary heat exchange assembly 134 of the heat exchanger unit 102. For instance, the furnace 100 can also include a induction fan assembly 136 configured to burn a heating fuel and a control unit 138 configured to coordinate the functions of the various units of the furnace 104 such as depicted in FIG. 1. One of ordinary skill would also appreciate, based on the present disclosure, how the secondary heat exchanger assembly 100 could be used in other types heating furnace units.
As also illustrated in FIG. 1, the secondary heat exchanger assembly 100 comprises a hot header box 140 configured to receive combustion gases from a primary heat exchanger assembly 134 of the heat exchanger unit 102, and, a cold header box 145 configured to transfer the combustion gases to an induction assembly 136 of the furnace unit 105 that the heat exchanger unit 102 is part of. The secondary heat exchanger assembly 100 also comprises a heat transfer zone 150 located between the hot header box 140 and the cold header box 145, the heat transfer zone 150 including secondary heat conduction tubes 155 coupled to the hot header box 140, to receive the combustion gases passing through the hot header box 140, and, is also coupled to the cold header box 145, to deliver the combustion gases to the colder header box 145.
As further illustrated in FIG. 1, in some embodiments of the assembly 100, the heat transfer zone 150 further includes perimeter side walls 157 located on either side of the secondary heat conduction tubes 155 and each connected to the hot header box 140 and the cold header box 145. The perimeter side walls 157 are configured to direct air from the blower unit 130 of the furnace unit 105 into the heat transfer zone 150.
With continuing reference to FIG. 1, FIG. 2 presents an example air velocity profile 210 of air blown from a blower unit 130 (e.g., a centrifugal blower) of a furnace unit 105 to the example secondary heat exchanger assembly 100. The profile 210 is across a width 160 within the heat transfer zone 150, and corresponds to a distance that is perpendicular to a central axis 162 through the zone 150 and running from the hot header box to the cold header box and also perpendicular to the direction 120 of air flow from the blower unit 130 through the zone 150. The heat transfer zone 150 is defined as the region of space between the outer edges 164 of the hot header box 140 and outer edges 166 of the cold header box 145.
As illustrated, air, when blown from the blower unit 130 of the furnace unit 105 through the heat transfer zone 150, has a non-uniform velocity profile across the width 160 of the heat transfer zone 150. For the disclosed secondary heat exchanger assembly 100, a heat transfer mass of the heat transfer zone 150 across the width 160, is configured to have a substantially similar-shaped non-uniform heat transfer mass profile 220.
Consider, for example, an embodiment as illustrated in FIG. 2, where the velocity profile 210 has a non-uniform parabolic shape, with higher velocities of air in the center than at the edges of the width 160 of the heat transfer zone 150. In such an embodiment, as illustrated in FIG. 2, the heat transfer mass profile 220 of the heat transfer zone 150 has a substantially similar-shaped parabolic profile, with a higher heat transfer mass in the center than at the edges of the width 160.
The term heat transfer mass, as used herein refers to the mass of the solid structures present in the heat transfer zone 150 that are configured to transfer heat from the combustion gases to these solid structures. The solid structure comprising the heat transfer mass can include, for example, the secondary heat conduction tubes 155 coupled to the hot and cold header boxes. The solid structure comprising the heat transfer mass also includes optional structures to facilitate heat transfer or the mechanical integrity of the heat transfer zone. Such structures include heat transfer fins in thermal contact with the secondary heat conduction tubes, or, collar structures configured to connect the secondary heat conduction tubes to the openings of both of the hot and cold header boxes.
In some embodiments, having air velocity profiles similar to that depicted in FIG. 2, adding additional heat transfer mass structures to the center of the heat transfer zone 150 can increase the overall efficiency of heat exchange. In other such embodiments, heat transfer mass can be removed from the edges of the heat transfer zone 150 with no substantial diminution in the efficiency of heat exchange as compared to, e.g., a secondary heat exchanger assembly having a uniformly distributed heat transfer mass across the width 160. Removing heat transfer mass structures from the sides, in turn, can provides a savings in material and manufacturing costs by reducing the number of component parts in the secondary heat exchanger assembly 100.
To further illustrate various aspects of such embodiments, FIGS. 3 and 4 presents detailed isometric views of different example secondary heat exchanger assembly of the disclosure, similar to the assembly 100 depicted in FIG. 1. FIG. 5 presents a detailed plan view, corresponding to view line 5 in FIG. 4, of another example secondary heat exchanger assembly of the disclosure, similar to the example assemblies 100 depicted in FIGS. 1 and 3-4.
For example embodiments presented in FIG. 3-5, the secondary heat conduction tubes 155 are depicted as having the same heat transfer mass as each other. For example, the secondary heat conduction tubes 155 are assumed to all be made of the same material, have a same inner diameter and wall thickness. However, in other embodiments any one or all of these features can be adjusted as part of providing the heat transfer mass profile 220 to mirror the air velocity profile 210.
As illustrated in FIGS. 3 and 4, it in some cases, the heat transfer zone 150 can be defined as to include a central subzone 310 that is parallel and proximate to the central axis 162 of the zone 150, running from the hot header box 140 to the cold header box 145, and two peripheral subzones 315, 320 adjacent to the central subzone 310 and parallel to and distal from the central axis 162. The heat transfer mass in the central subzone 310 is greater than the heat transfer mass in any one of the peripheral subzones 315, 320.
In some cases, for example, the central subzone 310, has an amount of the heat transfer mass of the secondary heat conduction tubes 155 that is greater than an amount of the heat transfer mass of the secondary heat conduction tubes 155 in either one of the peripheral subzones 315, 320.
Consider, for example, an embodiment where the central subzone 310, occupies about one-third of a total volume of the heat transfer zone 150 and the peripheral subzones 315, 320 each occupy about one-third of the total volume of the heat transfer zone 150. In some such embodiments, the amount of the heat transfer mass in the central zone 310 is about 10 percent or greater the heat transfer mass in any one of the peripheral subzones 315, 320. In some such embodiments, such as illustrated in FIG. 3, the central zone 135 has at least one more of the secondary heat conduction tubes 155 than the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 230. For example, as illustrated in FIG. 3, the heat transfer zone 150 can include two centrally located and staggered (e.g., not aligned in the air flow direction 120) 340, 345 of the secondary heat conduction tubes 155, a first one of the rows 340 having nine of the tubes 155, and a second one of the rows 345 having seven of the tubes 155.
In other such embodiments, the amount of the heat transfer mass in the central zone 310 is about 20 percent or greater than the heat transfer mass in any one of the peripheral subzones 315, 320. In some such embodiments, such as illustrated in FIG. 4, the central zone 135 has at least two more of the secondary heat conduction tubes 155 than the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 230. For example, as illustrated in FIG. 4, the heat transfer zone 150 can include three centrally located and staggered rows 410, 420, 430 of the secondary heat conduction tubes 155, first and second ones of the rows 410, 420 having nine of the tubes 155, and a third one of the rows 430 having five of the tubes 155.
The example embodiments presented in FIGS. 3 and 4 show heat transfer zones 150 with two rows 340, or three rows 410, 420, 430 and up the nine secondary heat conduction tubes 155 per row. In view of the present disclosure, however, one skilled in the art would understand that other embodiments could have different numbers of rows (e.g., from one to twenty rows, in some cases) and tubes per row (e.g., from one to up to twenty tubes 155 per row, in some cases), and still be within the scope of the disclosure.
In other embodiment, alternatively or additionally to having a greater different number of secondary heat conduction tubes 155 in central zone 310 as compared to the peripheral zones 315, 320, the heat transfer mass of other supporting structures, such as fins or collars, could be adjusted to provide the greater heat transfer mass in the central zone 310.
For instance, as illustrated in FIG. 5, in some embodiments the central subzone 310 has fins 510 and collars 520 coupled to the secondary heat conduction tubes 155 in the that provide an amount of the heat transfer mass that is greater than an amount of the heat transfer mass from the fins 510 and the collars 520 coupled to the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 320.
For instance, in some embodiments the central subzone 310 has a same number of the secondary heat conduction tubes 155 as in either one of the peripheral subzones 315, 320, and, fins 510 coupled to the secondary heat conduction tubes 155 in the central zone 310 provide an amount of the heat transfer mass that is greater than the heat transfer mass from the fins 510 coupled to the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 320.
Another embodiment of the present disclosure is a method of manufacturing a secondary heat exchanger assembly for a heat exchanger unit. FIG. 6 presents a flow diagram of an example method of manufacturing a secondary heat exchanger assembly 100 for a heat exchanger unit 102, such as any of the secondary heat exchanger assemblies 100 depicted in FIGS. 1, 3-5.
With continuing reference to FIGS. 1-5 throughout, the method 600 comprises a step 610 of providing a hot header box 140 configured to receive combustion gases from a primary heat exchanger assembly 134 of the heat exchanger unit 102.
The method 600 further comprising a step 615 providing a cold header box 145 configured to transfer the combustion gases to an induction assembly 136 of a furnace unit 105 that the heat exchanger unit 102 is part of.
The method 600 also comprises a step 620 of forming a heat transfer zone 150 between the hot header box 140 and the cold header box 145 including the heat transfer zone 150. Forming the heat transfer zone 150, in step 620, includes a step 630 of coupling secondary heat conduction tubes 155 to the hot header box 140 so as to receive the combustion gases passing through the hot header box 140. Forming the heat transfer zone 150, in step 620, also includes a step 635 of coupling the secondary heat conduction tubes 155 to the cold header box 145 so as to deliver the combustion gases to the colder header box 145.
As discussed in the context of FIG. 2, air, when blown from a blower unit 115 of the furnace unit 105 through the heat transfer zone 150, has a non-uniform velocity profile 210 across a width 160 of the zone 150, and, a heat transfer mass of the zone 155 across the width 160 is configured to have a substantially similar-shaped non-uniform heat transfer mass profile 220.
Some embodiments of the method 600 further include a step 640 connecting perimeter side walls to the hot header box and the cold header box such that the perimeter side walls 157 are located on either side of the secondary heat conduction tubes 155, the perimeter side walls 157 configured to direct air from a blower unit 130 into the heat transfer zone 150.
In some embodiments, the heat transfer zone 150 includes a central subzone 310 that is parallel and proximate to a central axis 162 running from the hot header box 140 to the cold header box 145 and two peripheral subzones 315, 320 adjacent to the central subzone 310 and running parallel to and distal from the central axis 162. In some such embodiments, forming the heat transfer zone 150, in step 620, includes a step 650 of providing a greater amount of the heat transfer mass in a central subzone 310 than an amount the heat transfer mass provided in any one of peripheral subzones 310, 320.
In some embodiments, providing the greater amount of the heat transfer mass in the central subzone, in step 650, includes a step 660 of providing the central subzone 310 with a greater amount of the heat transfer mass from the secondary heat conduction tubes 155 than the amount of the heat transfer mass provided from the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 320.
In some embodiments, forming a heat transfer zone 150, in step 620, includes a step 670 of connecting fins 510 to the secondary heat conduction tubes 155 such that the central zone 310 has a greater amount of the heat transfer mass from the fins 510 than an amount of the heat transfer mass from the fins 510 coupled to the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 320.
In some embodiments, forming a heat transfer zone 150, in step 620, includes a step 680 of connecting collars 520 to the secondary heat conduction tubes 155 such that the central zone 310 has a greater amount of the heat transfer mass from the collars 520 than an amount of the heat transfer mass from the collars 520 coupled to the secondary heat conduction tubes 155 in any one of the peripheral subzones 315, 320.
Those skilled in the art to which this application relates will appreciate that other and further additions, deletions, substitutions and modifications may be made to the described embodiments.

Claims

What is claimed is:

1. A secondary heat exchanger assembly for a heat exchanger unit, comprising:

a hot header box configured to receive combustion gases from a primary heat exchanger assembly of the heat exchanger unit;

a cold header box configured to transfer the combustion gases to an induction assembly of a furnace unit that the heat exchanger unit is part of;

a heat transfer zone located between the hot header box and the cold header box, the heat transfer zone including secondary heat conduction tubes coupled to the hot header box to receive the combustion gases passing through the hot header box, and, coupled to the cold header box to deliver the combustion gases to the colder header box, wherein,

air, when blown from a blower unit of the furnace unit through the heat transfer zone, has a non-uniform velocity profile across a width of the heat transfer zone, and, a heat transfer mass of the heat transfer zone across the width is configured to have a substantially similar-shaped non-uniform heat transfer mass profile.

2. The assembly of claim 1, wherein the heat transfer zone further includes perimeter side walls located on either side of the secondary heat conduction tubes and each connected to the hot header box and the cold header box, the perimeter side walls configured to direct air from the blower unit of the furnace unit into the heat transfer zone.

3. The assembly of claim 1, wherein the heat transfer zone includes a central subzone that is parallel and proximate to a central axis of the heat transfer zone, running from the hot header box to the cold header box and two peripheral subzones adjacent to the central subzone and parallel to and distal from the central axis, and wherein the heat transfer mass in the central subzone is greater than the heat transfer mass in any one of the peripheral subzones.

4. The assembly of claim 3, wherein the central subzone, has an amount of the heat transfer mass of the secondary heat conduction tubes that is greater than an amount of the heat transfer mass of the secondary heat conduction tubes in either one of the peripheral subzones.

5. The assembly of claim 3, wherein the central subzone, occupying about one-third of a total volume of the heat transfer zone, the amount of the heat transfer mass is about 10 percent or greater than the of the heat transfer mass in any one of the peripheral subzones, that each occupy about one-third of the total volume of the heat transfer zone.

6. The assembly of claim 3, wherein the central subzone, occupying about one-third of a total volume of the heat transfer zone, has about 20 percent or greater of the heat transfer mass than the heat transfer mass in any one of the peripheral subzones that each occupy about one-third of the total volume of the heat transfer zone.

7. The assembly of claim 3, wherein the central subzone, occupying about one-third of a total volume of the heat transfer zone has at least one more of the secondary heat conduction tubes than the secondary heat conduction tubes in any one of the peripheral subzones that each occupy about one-third of the total volume of the heat transfer zone.

8. The assembly of claim 7, wherein the heat transfer zone including two centrally located and staggered rows of the secondary heat conduction tubes, a first one of the rows having nine of the tubes, and a second one of the rows having seven of the tubes.

9. The assembly of claim 3, wherein the central subzone, occupying about one-third of a total volume of the heat transfer zone has at least two more of the secondary heat conduction tubes than either one of the peripheral subzones that each occupy about one-third of the total volume of the heat transfer zone.

10. The assembly of claim 9, wherein the heat transfer zone including three centrally located and staggered rows of the secondary heat conduction tubes, first and second ones of the rows having nine of the tubes, and a third one of the rows having five of the tubes.

11. The assembly of claim 3, wherein the central subzone, has fins and collars coupled to the secondary heat conduction tubes that provide an amount of the heat transfer mass that is greater than an amount of the heat transfer mass from the fins and the collars coupled to the secondary heat conduction tubes in any one of the peripheral subzones.

12. The assembly of claim 3, wherein the central subzone, occupying about one-third of a total volume of the heat transfer zone has a same number of the secondary heat conduction tubes as in either one of the peripheral subzones, and, fins coupled to the secondary heat conduction tubes in the central zone provide an amount of the heat transfer mass that is greater than the heat transfer mass from the fins coupled to the secondary heat conduction tubes in any one of the peripheral subzones.

13. The assembly of claim 1, wherein the assembly is part of the heat exchanger unit in the heating furnace.

14. The assembly of claim 14, wherein the heating furnace is a component of a HVAC system.

15. A method of manufacturing a secondary heat exchanger assembly for a heat exchanger unit, comprising:

providing a hot header box configured to receive combustion gases from a primary heat exchanger assembly of the heat exchanger unit;

providing a cold header box configured to transfer the combustion gases to an induction assembly of a furnace unit that the heat exchanger unit is part of;

forming a heat transfer zone between the hot header box and the cold header box including the heat transfer zone including:

coupling secondary heat conduction tubes to the hot header box so as to receive the combustion gases passing through the hot header box, and,

coupling the secondary heat conduction tubes to the cold header box so as to deliver the combustion gases to the colder header box,

wherein air, when blown from a blower unit of the furnace unit through the heat transfer zone, has a non-uniform velocity profile across a width of the heat transfer zone, and, a heat transfer mass of the heat transfer zone across the width is configured to have a substantially similar-shaped non-uniform heat transfer mass profile.

16. The method of claim 15, wherein the heat transfer zone further includes connecting perimeter side walls to the hot header box and the cold header box such that the perimeter side walls are located on either side of the secondary heat conduction tubes, the perimeter side walls configured to direct air from the blower unit into the heat transfer zone.

17. The method of claim 15, wherein the heat transfer zone includes a central subzone that is parallel and proximate to a central axis running from the hot header box to the cold header box and two peripheral subzones adjacent to the central subzone and parallel to and distal from the central axis, and forming the heat transfer zone includes providing an greater amount of the heat transfer mass in the central subzone than an amount of the heat transfer mass provided in any one of the peripheral subzones.

18. The method of claim 17, wherein providing the greater amount of the heat transfer mass in the central subzone includes providing the central subzone with a greater amount of the heat transfer mass from the secondary heat conduction tubes than the amount of the heat transfer mass provided from the secondary heat conduction tubes in any one of the peripheral subzones.

19. The method of claim 17, wherein forming the heat transfer zone further including connecting fins to the secondary heat conduction tubes such that the central zone has a greater amount of the heat transfer mass from the fins than an amount of the heat transfer mass from the fins coupled to the secondary heat conduction tubes in any one of the peripheral subzones.

20. The method of claim 17, further including connecting collars to the secondary heat conduction tubes such that the central zone has a greater amount of the heat transfer mass from the collars than an amount of the heat transfer mass from the collars coupled to the secondary heat conduction tubes in any one of the peripheral subzones.