Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02818686 2013-06-12
A SECONDARY HEAT EXCHANGER FOR A FURNACE HEAT EXCHANGER
TECHNICAL FIELD
[0001]
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
[0002] 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
[0003]
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
-1-
CA 02818686 2013-06-12
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.
[0004]
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.
-2-
CA 02818686 2013-06-12
BRIEF DESCRIPTION
[0005]
Reference is now made to the following descriptions taken
in conjunction with the accompanying drawings, in which:
[0006]
FIG. 1 illustrates exploded isometric view of an example
heating furnace that includes an example secondary heat exchanger
assembly of the disclosure;
[0007]
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;
[0008]
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;
[0009]
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;
[0010]
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
[0011] 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
[0012]
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.
[0013] As
part of the present disclosure, it was discovered that
the air, passing from a blower of the furnace unit through the
-3-
CA 02818686 2013-06-12
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.
[0014]
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).
[0015]
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).
[0016]
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
-4-
CA 02818686 2013-06-12
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.
[0017] 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 ex140changer 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.
[0018] 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.
[0019]
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
-5-
CA 02818686 2013-06-12
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.
[0020] 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.
[0021]
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.
[0022]
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.
[0023] In
some embodiments, having air velocity profiles similar
to that depicted in FIG. 2, adding additional heat transfer mass
-6-
CA 02818686 2013-06-12
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.
[0024] 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.
[0025]
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.
[0026] 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
-7-
CA 02818686 2013-06-12
greater than the heat transfer mass in any one of the peripheral
subzones 315, 320.
[0027] 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.
[0028] 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.
[0029] 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
-8-
4
CA 02818686 2013-06-12
_
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.
[0030] 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.
[0031] 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.
[0032] 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.
[0033] 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.
[0034] Another embodiment of the present disclosure is a method
of manufacturing a secondary heat exchanger assembly for a heat
-9-
,
1
. CA 02818686 2013-06-12
_
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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
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
-10-
,
i
. CA 02818686 2013-06-12
perimeter side walls 157 configured to direct air from a blower
- unit 130 into the heat transfer zone 150.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
-11-
,
CA 02818686 2013-06-12
[0044]
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.
-12-
