Note: Descriptions are shown in the official language in which they were submitted.
r . C
RHEE B7557CIP 2 0 2 9 5 4 7
JRK/dlb
d6/28/go
COMPACT, HIGH EFFICIEI~CY HEAT EXCHANGER
FOR A FUEL-FIRED ~ORCED AIR HEATING FURNACE
BACKGRO~ND ~F THE INVENTION
The present invention relates generally to heat
exchangers for fuel-~ired, forced air heating furnaces, and
more particularly relates to compact, hiBh efficiency heat
exchangerq for such furnaces, and associated fabrication
techniques for constructing the heat exchangers.
The National Appliance Energy Conservation Act of
1987 require~ that all forced air furnaces manufactured
after January 1, 1992, and having heating capacities between
45,000 ~tuh and 400,000 Btuh, must have a minimum heating
efficiency of 78~ based upon Department of Energy test
procedures. For two primary reaqonq, each relating to
conventional heat exchanger de~ign, the majority of furnace~
currently being manufactured do not meet this 78% minimum
efficiency requirement.
First, until recently, mo~ furnace efficiencies
~5 were rated based upon "indoor ratings", meaning that the
heat loQses through the furnace hou~ing wall~ to the
surroundin~ space were ignored, the impllcit a~sumption
being that the furnace was installed in an area within the
conditioned space (such as a furnace clo3et or the like) qo
that the heat transferred outwardly through the furnace
hou~ing ultimately functioned to heat the conditioned qpace.
Under the new efficiency rating scheme, however, furnace
efficiencies will be penalized for heat tran~ferred
B ` ~
'~
~ ~ 2 9 5 ~
. ~
RHEE B7557CIP
JRK/dlb
06~28/90
outwardly through the furnace housing to the surrounding
space on the asqumption that the furnace will be installed
in an unheated area, such a3 an attic, even if the furnace
will ultimately be installed within the conditioned space.
Gas-fired residential furnaces are typically
provided with "clamshell" type heat exchangers through which
the burner combustion products are flowed, and exteriorly
across which the furnace qupply air is forced on its way to
the conditioned space served by the furnace. The
conventional clamshell heat exchanger is positioned within
the furnace housing and is normally constructed from two
relatively large metal stampings edge-welded together to
form the heat exchanger body through which the burner
combustion products are flowed. In the typical upflow
furnace, the clamshell heat exchanger body has a large
e~panse of vertically disposed side surface area which
extend3 parallel to adjacent vertical qide wall portions of
the furnace housing. In a similar fashion, in hsrizontal
; flow furnaces the clamshell heat exchanger body has a large
expanqe of horizontally dispo~ed side surface area which
extend3 parallel to the adjacent horizontally extending side
wall portion of the furnace housing.
Due to the large surface area of clamshell heat
exchangers, and its orientation within the furnace housing,
there is a correspondingly large (and unde~irable) outward
heat transfer from the heat exchanger through the furnace
housing which represents a los~ of available heat when the
furnace i9 install0d in an unheated space. This potential
heat transfer from the heat exchanger through the furnace
30I housing side wall3 to the adjacent 3pace correspondingly
diminishes the efficiency rating of the particular furnace,
2029~7
~ a
RHEE B7557CIP
JRK/dlb
06/28/go
under the new efficiency rating formula, even when the
furnace is not installed in an unheated space.
The second heat exchanger-related factor which
undesirably reduces the overall heating efficiency rating of
a furnace of this general type arises from the fact the the
typical clamshell heat exchanger has a relatively low
internal pressure drop. ~ccordingly, during an ?loff cycle"
of the furnace, this ~1009e~ heat exchanger design permits
residual heat in the heat exchanger to rather rapidly escape
through the exhaust vent system (due to the natural buoyancy
of the hot combustion gas within the heat exchanger) instead
of being more efficiently transferred to the heating supply
air which continues to be forced across the heat exchanger
for shor~ periods after burner shutoff. Stated in another
manner, in the typical clam hell type heat exchanger the
retention time therein for combust-ion products after burner
shut off is quite low, thereby significantly reducing the
combustion product heat which could be usefully transferred
to the continuing supply air flow being forced externally
across the heat exchanger.
In addition to these heating efficiency problem3,
conventional clamshell type heat exchangers have a long
"dwell period~l (upon cold start ' up) during which
condensation i~ formed on their interior surfaces and
remains until the hot burner combustion products flowed
; internally through the heat exchanger e~aporates such ',
, condensation. This dwell period, of cour~e, i9 repeated
each time the furnace is cycled. 8ecause of these lengthy
dwell periods (resulting from the large metal ma~s of the
clamshell heat exchanger which must be re-heated each time
the burners are energized), inte'rnal corrosion in clamshell
20295~7
RHEE B7557CIP
JRK/dlb
06/2s/go
heat exchangers tends to be undesirably accelerated.
Theqe and other problem~, limitations and
di~advantages oommonly as~ociated with clam~hell heat
exchangers have been substantially lessened by the compact,
high efficiency configurational design incorporated in the
heat exchanger illuqtrated and deqcribed in my copending
Canadian application serial no. 2,003,802 ~iled November 24,
1989. Briefly, that heat exchanger comprises horizontally
spaced apart inlet and outlet manifolds interconnected by
horizontally spaced apart, vertically serpentined, relatively
small diameter flow transfer tubes. A plurality of larger
diameter primary inlet tubes extend horizontally beneath the
manifolds and have upturned discharge end portions connected to
the underside of the inlet manifold.
With the heat exchanger operatively installed in an
upflow furnace, the inlet oY a draft inducer fan is
connected to the outlet manifold and burner flames are
flowed into the open inlet end~ of the primary inlet tubes.
Operation of the draft inducer fan drawq hot burner
combuqtion productq sequentially through the primary inlet
tubes, the inlet manifold, the ~erpentined flow transfer
tube3, and the outlet ~anifold for discharge by the fan to a
suitable vent stack.
A3 originally envisioned, the compact heat
l exchanger illustrated and described in U.S. Patent
4,974,579 was to be fabricated utilizing a
generally conventional welding proce~ to join the sections
of each of its manifoldq, and to secure the primary inlet
tube~ and the flow tranQfer tubes to the manifolds. In
subqequent further development of the heat exchanger,
however, it ha~ become de~irable to even further reduce it~
2029~7
~3
RHEE B7557CIP
JRK/dlb
06/28/go
overall construction cost by essentially eliminating the
need to form weld joints therein. It is accordingly an
object of the present invention to provide a compact furnace
heat exchanger which is similar in configuration and
operation to the heat exchanger just described, but which is
assembled essentially without using a welding process to
join or form its components.
SUMMARY OF THE INV~NTION
The present invention provides a compact, high
efficiency heat exchanger which may be operatively
positioned in the supply plenum housing portion of an
induced draft, fuel-fired forced air heating furnace and is
operative to reduce heat outflow from the heat exchanger
through the housing side walls 9 and thereby increase the
overall heating efficiency rating of the furnace. When
operatively disposed within the supply air plenum of the
furnace, the heat exchanger has a first total peripheral
surface area facing parallel to the direction of
blower-produced air flow through the supply air plenum and
externally across the heat exchanger, and a second total
peripheral surface area which outwardly faces a side wall
section of the housing in a direction transverse to the air
flow acros~ the heat exchanger.
Importantly, the first peripheral ~urface area of
the heat exchanger is sub~tantially greater than its second
peripheral surface area. Accordingly, the radiant heat
emanating from the heat exchanger toward the hou inB ~ide
wall section is substantially les than its radiant heat
directed parallel to the air flow. In this manner, the
available heat from the heat exchanger is more efficiently
apportioned to the supply air J thereby reducing outward heat
RHEE B7557CIP 2 0 2 ~ 5 4 7
JRK/dlb
06/28/go
loss through the furnace housing.
In a preferred embodiment thereof, the heat
exchanger of the present invention is generally similar in
configuration to the compact heat exohanger illustrated and
described in my copending Canadian application serial no.
2,003,802 ~iled Novemb~r 24, 1989, and includes: an inlet
manifold, an outlet manifold spaced apart from the inlet
manifold in a direction transverse to the supply air flow; a
plurality of relatively large diameter, generally L-shaped inlet
tubes positioned upstream of the inlet and outlet manifolds and
having discharge portions connected to th~ inlet manifold; and
a series of relatively small diameter flow transfer tubes each
connected at its opposite endq to the inlet and outlet
manifolds, the small diameter flow transfer tubes being
serpentined in the direction of supply air flow externally
acro~s the heat exchanger~
During operation of the furnace in which the heat
exchanger of the present invention is operatively installed,
a draft inducer fan operatively connected to the heat
exchanger outlet manifold draws burner flame~ sequentially
through the larger diameter inlet tubes, the inlet manifold,
the serpentined flow tran fer tubes, and the outlet
manifold, and then di~oharges the combustion products into a
suitable vent stack.
The serpentined, small diameter flow transfer tubes
of the heat exchanger function to create a ~ubstantial
resistance to burner combu~tion product flow through the
heat exchanger, and impart turbulence to the combustion
product throughflow r to thereby improve the thermal
efficiency of the heat exchanger.
According to an important feature o~ the present
., . ~
2029547 c
RHEE B7557CIP
JRK/dlb
06/28/so
invention, the compact heat exchanger is assembled using an
essentially weldless fabrication process in which the
combustion tubes are swedged to the manifolds.
Ad~itionally, each of the manifolds is defined by two
sections, each of which has a peripheral edge portion. At
each manifold, one of these two peripheral edge sections is
folded around the other peripheral edge section and crimped
therewith to form a weldless, essentially air tight joint
extending around the manifold. Additionally7 in a preferred
embodiment of the compact heat exchanger, the outlet
manifold is provided with a diqcharge conduit portion which
is Qwedged to a support plate portion of the heat exchanger.
The inlet end of each of the primary inlet tube i~ also
swedged to the support plate.
BRIEF DESCRIP?ION OF THE DRAWINGS
FIG. 1 is a perspective view of a compact heat
exchanger, for a fuel-fired air heating furnace, which
embodieq principles of the present invention and is
assembled using a weldles~ fabrication technique;
FIG. 2 is an enlarged qcale right side elevational
view ot` the heat exchanger;
FIG. 3 is an enlarged scale partial cross-~ectional
view of the dashed circle area ~'A~ in Fig. 2; and
FIG. 4 is an enlarged scale partial crosq sectional
view of the dashed circle area "B" in ~ig. 2.
D~TAILED DESCRIPTION
Illustrated in Figq. 1 and 2 i~ a compaot, high
efficiency heat exchanger lO which embodies principles of
the present invention and is ~imilar in configurat$on and
operation to the heat exchanger illu~trated and de~cribed in
my U.s. Patent 4,974,579-
B
G
202q5~7
RHEE B7557CIP
JRK/dlb
06/28/go
Like its counterpart in that patent, the heat ex¢hanger
10 may be operatively installed in the ~upply plenum housing
portion of an upflow, fuel-fired forced air heating furnace
to heat the supply air 12 flowing upwardly through the
supply plenum, exteriorly traverqing the heat exchanger 10,
and being delivered to a conditioned space. As ~ubsequently
described in greater detail herein, the heat exchanger 10 is
assembled using an essentially weldless fabrication
technique which materially reduces the overall construction
costs associated with the heat exchanger.
Heat exchanger 10 include~ a center or support
plate structure 14, an outlet manifold 16 positioned
rightwardly adjacent the support plate 14, an inlat manifold
18 spaced rightwardly and horizontally apart from the outlet
manifold, a plurality of relatively large diameter,
generally L-shaped primary inlet tubes 20 poqitioned beneath
the manifolds 16 and 18 and interconnected at their opposite
ends to the support plate 14 and the underside of the
manifold 18, and a horizontally spaced qerie~ of vertically
serpentined, relatively small diameter flow transfer tubeq
22 connected at their opposite endq to the outlet manifold
16 and the inlet manifold 18.
The outlet manifold 16 has a leftwardly projecting
discharge conduit 24 which is secured to the ~upport plate
structure 14 and may be connected to a draft inducer fan
(not 3hown) a~sociated with the furnace in wh~ch the heat
exchanger 10 is operatively installed. During operation of
the furnace and its associated draft inducer fan, hot burner
combustion products 26 are sequentially flowed in~o the open
inlet ends 20a of tubeq 20, through the tubeQ 20 into the
....
B 8
202q547
RHEE B7557CIP
JRK/dlb
o~/2s/so
inlet manifold 18, through the qmaller diameter tube~ 22
into the outlet manifold 16, and into the draft inducer fan,
through the discharge conduit 24, f'or delivery to an
external exhaust stack.
In a manner similar to that described in my
copending Canadian application serial no. 2,003,802 filed
November 24, 1989, the heat exchanger lO has a vertically facing
total peripheral surface area, and a horizontally facing total
peripheral surface area which is substantially less than the
vertically facing total peripheral surface area. Accordingly,
the radiant heat emanating from the heat exchanger lO toward the
vertical sids wall section of the furnace in which it iq
installed is ~ubqtantially les~ than its radiant heat
directed parallel to the flow of the supply air 12. In thi~
manner, the available heat from the heat exchanger 10 is
more efficiently apportioned to the supply air 1Z, thereby
materially reducing outward heat loss through the furnace
hou~ing. The serpentined, small diameter flow transfer
tubes 22 of the heat exchanger 10 function to create a
substantial resiYtance to burner combustion product flow
through the heat exchanger, and impart turbulence to the
combustion product throughflow, to thereby improve the
thermal efficiency of the heat exchanger.
A~ mentioned above, the heat exchanger 10
assembled using a weldle~ fabrication process which will
now be described with initial reference to Figs. 2 and 3.
The outlet housing 16 has a hollow fir~t qection 28 with a
rear wall 30 and an open left or front end bordered by a
peripheral flange 32, and a second section defined by a
plate member 34 to which the di~charge conduit 24 is ~ecured
in a manner subsequently de~cribed. In constructing the
$,,~
RHEE B7557CIP
JRK/dlb
06/28/go
outlet housing 16, a peripheral edge portion 34a Of the
plate member 34 is folded rearwardly over the flange 32, and
a crimp 36 (Fig. 3) is formed around the periphery of the
housing section peripheral portions 32 and 34 to form a
weldless, essentially air tight joint between the two
sections of the housing 16.
The inlet housing 18 is formed fro~ hollow front
and rear sections 38 and 40 (Fig. 2) having facing
peripheral edge port~ons that, as viewed in Fig. 2,
diagonally slope downwardly and rightwardly. In a manner
similar to the folding and crimping of the peripheral edge
portions 32 and 34a Of the outlet manifold 16, one of these
peripheral edge portions 38a~ 40a is folded over the other
one, and a peripheral crimp is then formed in the
interlocked edge portions to form a weldless, essentially
air tight diagonal joint around the manifold 18.
Referring now to Fig. 4, each of the outlet ends
22a Of the small diameter flow transfer tubes 22 is
operatively secured to a lower end portion of the rear wall
30 of outlet manifold 16 by a weldless swedge joint 42. In
forming each of the swedge joints 42, the tube outlet end
22a is inserted inwardly through a circular opening 44
formed through the rearwall 30 and circumscribed by an
inturned circular flange 46. A generally conventional
cylindrical swedging tool 48, having radially expandable
portions 50 and 52, is inserted into the inlet end 22a f
the tube 22. A tapered pin member 54 i~ then driven
rightwardly into the hollow center of the tool 48 to
radially expand its portions 50 and 52 as indicated by the
arrows 54. The radially outward movement of the swedging
tool portions 50, 52 correspondingly forms annular radial
RHEE B7557CIP 2029547
JRK/dlb
06/28/go
bulges 56 and 58 in the outlet end of tube 22, the bulge 56
being positioned inwardly of the flange 46, and the bulge 58
being ~`ormed at She outer ~ide surface of the rear wall 30
of the outlet manifold 16. These bulgeq 56, 58 axially lock
the tube 22 to the housing 16 and form a weldless,
e~entially air tight seal at the juncture between tube 22
and the manifold 16. After the swedge joint 42 is formed,
the pin 54 may be removed from the 3wedging tool 48 to
permit retraction of its portions 50, 52 and removal of the
tool 4a from the tube 22.
Similar swedge joints 42a-42e are respectively
formed between the di~charge conduit 24 and the support
plate structure 14; the di3charge conduit 24 and the outlet
hou~ing plate member 34; the inlet ends of the tubes 22 and
a top portion of the front side wall o~ inlet housing
section 38; the tubes 20 and the bottom wall of the inlet
hou~ing section 38; and ~he inlet end~ o~ the tubes 20 and
the ~upport plate ~tructure 14. It will be appreciated
that, at each of the manifolds 16 and 18, the tubing swedge
joints are formed prior to the folding and crimping together
of the manifold section~.
It should also be noted that the diagonal
orientation of the folded and crimped ~oint line on inlet
manifold 18 faeilitate3 acceq~ to the interior of manifold
se4tion 38 for the swedging tool 48.
From the foregoing it can readily be ~een that the
heat exchanger 10 provide~ the configurational and
operational adYantage~ of the compact heat exchanger
illustrated and described in my copending Canadian application
serial no. 2,003,802, while the weldless assembly technique of
the present invention facilitates a substantial reduction in
~ 11
202~
RHEE B7557CIP
JRK/dlb
06/28/go
its overall construction costO
The Yoregoing detailed description is to be elearly
understood as being given by way of illustration and example
only, the ~pirit and scope of the present invention being
limited solely by the appended claims.
What is claimed is:
