Note: Descriptions are shown in the official language in which they were submitted.
CA 02859511 2014-08-18
DOMESTIC GAS-FIRED WATER HEATER CONDENSING FLUE SYSTEM
TECHNICAL FIELD
(0001) The present invention relates to domestic gas-fired water heaters and
more
particularly to a condensing flue system of such water heaters to increase the
thermal
efficiency of the flue gases.
BACKGROUND OF THE INVENTION
(0002) Various flue pipe heat exchange arrangements and designs are known to
extract heat from the hot flue gases leaving the combustion chamber and
convected
through the flue pipe extending in the water tank to transfer the heat from
the flue gases
to the water within the tank which surrounds the flue pipe. Baffles are
commonly
installed in the flue pipe to increase the heat transfer by slowing the speed
of the flue
gases while increasing turbulence thereof for longer contact of the hot gases
with the
flue pipe wall and the baffle plates mounted therein. Various baffle designs
have been
developed to achieve this improved heat transfer. However, condensation
develops in
the flue pipe and this is undesirable. An ideal design is to prevent or
substantially
minimize the formation of condensation in the vertical flue pipe section
directly above
the combustion chamber while extracting maximum heat from the flue gas to heat
the
water in the tank. Condensation is known to cause corrosion of the steel and
the baffle
plates.
(0003) Several know designs have been patented to increase the efficiency of
the
water heater by the extraction of heat from the flue pipe as it exits the
water heater tank.
The extracted heat may be used to heat water circulated from the bottom of the
water
tank to the top of the tank. However, those known system designs have their
limitations
and usually the flue gases are exhausted to atmosphere at higher than
desirable
temperatures. Ideally, the flue gases should be exhausted at about 100 degrees
F, to
provide for an efficient heat transfer system. It is also known to extract
heat from the
hot flue gases for other purposes than for heating the water in the tank of
the water
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heater. For example, the extracted heat may be used for local heating of the
air or
heating another liquid in a heat exchanger.
(0004) More recently, different approaches have been suggested wherein the
flue
pipe is configured to have two or more sections extending through the water in
the
water tank. These are commonly referred to as multi-pass condensing type flue
designs. However, these designs have resulted in other problems such as
occupying
extra space in the water tank and therefore reducing the tank capacity for
water or
increasing the size of the tank to accommodate the extra flue length and
therefore
adding to increase costs. They have also resulted in condensation evacuation
problems. The extra costs of the flue pipe and its installation cost is not
recoverable
after the life of the water heater.
SUMMARY OF THE INVENTION
(0005) It is a feature of the present invention to provide a domestic gas-
fired water
heater condensing flue system which substantially overcomes some of the above
mentioned deficiencies of the prior art.
(0006) It is another feature of the present invention to provide a domestic
gas-fired
water heater condensing flue system having an external high efficiency heat
exchange
flue conduit having a narrow flue gas internal passage surrounded by water
circulated
from the bottom of the tank to the top of the tank and fitted to the outside
of the water
tank whereby it is recyclable after the life of the water tank.
(0007) Another feature of the present invention is to provide a domestic gas-
fired
water heater condensing flue system comprised by an inverted U-shaped flue
disposed
substantially vertically in the water tank and having a conduit, from the
domestic water
line, disposed in a downward section of the flue pipe to extract heat from the
flue gas to
feed heated water to the bottom section of the tank while acting as a baffle
to improve
heat transfer to the water in the tank.
(0008) According to the above features, from a broad aspect, the present
invention
provides a domestic gas-fired water heater condensing flue system comprising a
water
tank having a domestic water line inlet and a hot water outlet. A combustion
chamber is
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provided under the bottom wall of the water tank. A flue pipe is sealing
secured in the
water tank and extends from a bottom opening in the bottom wall, through the
water
tank and out of a sealed top opening in the top wall of the water tank. A
blower is
secured to the flue pipe above the top wall for directing hot flue gases from
the
combustion chamber to an external heat exchange flue conduit section. The
external
heat exchange flue conduit section has an internal passage through which the
flue
gases are convected by the blower. A sealed water channel surrounds at least a
major
length of the external heat exchange flue conduit section. The water channel
has an
inlet connection at a lower end thereof and an outlet connection at an upper
end
thereof. The inlet connection receives water from a lower section of the water
tank and
the outlet connection delivers heated water from the water channel to an upper
section
of the water tank. Water convection means convects water from the inlet
connection to
the outlet connection with the water being displaced about the internal
passage to
extract heat therefrom to heat the convected water for release in the upper
section of
the water tank and to cool the flue gases in the internal passage. An exhaust
flue pipe
section is secured at an exit end of the external heat exchange flue conduit
section.
(0009) According to another broad aspect of the present invention there is
provided a
domestic gas-fired water heater condensing flue system comprised of a water
tank
having a water inlet and a hot water outlet. A combustion chamber is provided
under a
bottom wall of the water tank. The water tank has a sealed top wall. An
inverted U-
shaped flue pipe which defines an integrally formed upward section and a
downward
section is retained vertically in the water tank. The upward section is
sealingly secured
at an inlet end thereof to an opening is the bottom wall of the water tank to
receive hot
flue gases from the combustion chamber. The downward section is sealingly
secured
at an outlet end thereof to an exit opening in a side wall of a bottom section
of the water
tank spaced above the bottom wall. A blower is connected to the exit opening
for
convecting flue gases therefrom to an external exhaust flue pipe. A heat
exchange
water conduit extends inside the downward section. The heat exchange water
conduit
has a sealed inlet connection through a top end section of the downward
section for
coupling with a pipe connected to the domestic water line. The heat exchange
conduit
has a sealed outlet connection through a lower end section of the downward
section to
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provide the water inlet of the water tank for releasing domestic water pre-
heated by the
hot flue gases displaced in the downward section of the flue pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
(0010) A preferred embodiment of the present invention will now be described
with
reference to the examples thereof as illustrated in the accompanying drawings
in which:
(0011) Figure 1A is a simplified cross-sectional view of a water heater
illustrating
some basic components thereof and to which is secured the external heat
exchange
flue conduit of the present invention to extract heat from the exit end of the
flue pipe
above the water heater and to heat water recirculated from the bottom of the
water tank
to the top of the tank;
(0012) Figure 1B is a simplified perspective view of a water heater having the
external
heat exchange flue conduit secured to the outside wall of the water heater;
(0013) Figure 2 is a fragmented perspective view showing the construction of
the
external heat exchange flue conduit;
(0014) Figure 3 is a transverse section view illustrating the operation of the
external
heat exchange flue conduit;
(0015) Figure 4 is a perspective view, partly fragmented, of the top end of
the external
heat exchange flue conduit;
(0016) Figure 5 is a transverse section view through the external heat
exchange flue
conduit;
(0017) Figure 6 is a fragmented side view illustrating the flue coupling at
the top end
of the external heat exchange flue conduit;
(0018) Figure 7 is a simplified cross-section view illustrating a modification
of the
internal flue gas passage in the external heat exchange flue conduit;
(0019) Figure 8 is a perspective view, partly fragmented, illustrating a
further
modification wherein the water channel is a water pipe coiled about the
external heat
exchange flue conduit section;
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(0020) Figure 9 is a transverse section view illustrating a further modified
construction
of the external heat exchange flue conduit;
(0021) Figure 10 is a simplified cross-section view illustrating a further
modified
embodiment wherein an inverted U-shaped flue pipe is supported vertically in
the water
tank to extract heat from the hot flue gases;
(0022) Figure 11 is a fragment cross-section view illustrating a modification
of the heat
exchange water conduit formed as a spiral heat exchange water conduit, and
(0023) Figure 12 is a fragmented cross-sectional view illustrating a further
modification wherein a spiral baffle is secured about the heat exchange water
conduit
disposed with the downward section of the flue pipe.
DETAILED DESCRIPTION
(0024) Referring now to the drawings and more particularly to Figure 1 there
is
illustrated generally at 10 a domestic gas-fired water heater incorporating
therewith a
first example of the external condensing flue system 11 of the present
invention. Herein
shown, are some basic parts of a domestic gas-fired water heater 10 and
comprising a
water tank 12 having a combustion chamber 13 equipped with a gas burner 13'
disposed under a bottom wall 14 of the tank to heat the water 16 in the tank
12. A flue
pipe 15 extends vertically in the tank and is surrounded by the water 16 to be
further
heated by the hot flue gases 17 convected through the flue pipe which is in
heat
exchange with the water 16 through the walls 18 of the flue pipe. A blower 19
is
mounted on the top wall 20 of the tank to draw the hot flue gas from the
combustion
chamber 13. The flue pipe 15 is sealingly secured between holes formed in the
bottom
and top walls of the water tank 12. An outer casing 21 surrounds the tank 15
and
insulation 22 is injected or otherwise disposed in the gap 23 between the tank
15 and
the outer casing 21, as is conventional in the construction of water heaters.
(0025) With further reference to Figures 2 to 6, there will now be described
the
construction and operation of the condensing flue system 11 of the present
invention.
As herein illustrated, the system comprises an external heat exchange flue
conduit
section 24 forming a narrow internal passage 25 through which the flue gases
17 are
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forced by the blower 19. The blower could also be secured downstream of the
flue
conduit section 24 to draw the hot gasses there through. A sealed water
channel 26
surrounds the internal passage 25 in at least a major length of the flue
conduit section
24. The water channel 26 has an inlet connection 27 at a lower end thereof and
an
outlet connection 28 at an upper end thereof. These connections 27 and 28 are
adapted
to receive quick-connect couplings of a flexible hose (not shown). The inlet
connection
27 receives water from a lower section 29 of the water tank via a small pump
30
coupled thereto. The outlet connection 28 delivers heated water 30 from the
top end of
the water channel 26 into the upper part 31 of the tank containing hot water.
It is noted
that the water from the bottom of the water tank 12 may be convected through
the water
channel 26 by natural convection of water due to the differential in water
temperature
between the cooler water in the tank lower section 29 and the hot water in the
tank
upper section 31. Figure 3 illustrates the downward flow direction of the flue
gases, see
arrow 25", and the upward flow direction of the circulated tank water, see
arrow 36'.
(0026) As can be seen from Figures 2 to 5, the internal passage 25 is a narrow
rectangular passage formed by a narrow conduit 25' having opposed elongated
side
walls 32 and short end walls 33 to define an extended or large heat exchange
surface
area all about the internal passage containing hot flue gas. The water channel
26 is
defined by the space between an outer casing 34 of the external condensing
flue
system 11 which is herein shaped like the internal passage and defining
opposed
parallel side walls 35 and opposed parallel end walls 36. The narrow inner
conduit 25' is
constructed of stainless steel material and the outer casing 34 of copper
material or
stainless steel. As can be seen from Figure 5, brackets 37 interconnect the
inner
conduit 25' to the outer casing 34 and oriented not to obstruct the flow of
water to the
outlet connection 28.
(0027) Referring to Figures 4 and 5, it can be seen that the blower 19 is
coupled to
the top of the external condensing flue system 11 by an external flue pipe
section 45
and a flue coupling 46. The flue coupling 46 is designed to fit over a top end
coupling
extension 47 of the external condensing flue system 11 whereby the flue gases
are
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directed into the internal passage 25 thereof under pressure from the blower.
Other
suitable coupling arrangements are also possible.
(0028) As shown in Figure 1A, the bottom end of the internal passage 25 opens
in a
u-shape pipe coupling 38 equipped with a condensate trap 39 which is connected
to a
drain (not shown) to evacuate condensate water from the bottom of the internal
passage and the exhaust flue pipe 40 exhausting the cooled flue gases to
atmosphere.
The entire external condensing flue system 11 is a reusable system which can
be easily
disconnected from the water heater 10 by disconnecting the conduits 27 and 28
from
the water tank 12 which supports the system 11 and the connection to the
blower 14
and the exhaust flue pipe 40. The system can be easily re-connected to a
replacement
water heater. As shown in Figure 1 B, the system 11 is neatly packaged against
the
water heater outer casing 21 and concealed by a removable panel 41.
(0029) Figure 7 illustrates a possible modification to the internal passage
conduit 25
'which is herein shown as being manufactured from a heat conductive and
formable
material, such as malleable copper, to define an undulating internal passage
50 to
increase the heat exchange surface area of the narrow conduit 25' to improve
heat
exchange with the surrounding water.
(0030) Figure 8 illustrates another modification of the external condensing
flue system
11 wherein, instead of a channel being formed about the narrow flue conduit
25', the
water from the tank12 is recirculated about the conduit 25' by a water pipe 51
coiled
about the narrow flue conduit 25'. An insulating material is preferably
applied over the
coiled water pipe 51 and the conduit 25'. This arrangement however would not
be as
compact as the preferred design of Figures 1 to 5. Another possible design is
to secure
concentric conduits together as shown in Figure 9, wherein an inner conduit 52
formed
of heat conductive material is used as the exhaust gas conduit and the outer
spaced
conduit 53 forms the water channel about the inner conduit. Such an
arrangement is
more compact, but the heat exchange surface area is greatly reduced and
therefore not
achieving the same efficiency as the embodiment of Figure 1 to 5.
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(0031) Referring again to Fig. 1A the system of the embodiment of Figures 1 to
9 is
controlled by a programmable controller 54 which receives signals from a
thermostat
(not shown), and water temperatures sensors 55 and controls the gas valve 56,
the
blower 19 and the pump 30 to operate the water heater to heat water when water
is
drawn from the tank through the hot water conduit 57 at the top of the tank.
As hot water
is drawn out from the top of the tank, domestic water is introduced at the
bottom of the
tank through conduit 58 or a dip tube as obvious to a person skilled in the
art
(0032) Referring now to Figures 10 to 12 there is shown another embodiment
wherein
an inverted U-shaped flue pipe 60 is supported substantially vertically in an
inverted
manner entirely inside the water tank 12. The inverted U-shaped flue pipe 60
defines
an upward flue section 61 and a downward flue section 62 integrally formed and
interconnected by a curved neck section 63 to permit smooth convection of the
flue
gases between the sections. The U-shaped flue pipe is retained in the tank by
its
welded connections, at an inlet end thereof, about an opening 64 formed in the
bottom
wall 65 of the tank above the combustion chamber 66, and its welded
connection, at an
outlet end thereof, to the tank sidewall 67 above and closely spaced from the
tank
bottom wall 65.
(0033) A blower 68 is connected to an exit coupling 69 for drawing flue gases
therefrom to an external exhaust flue pipe 70. As herein shown, the inlet
water supply
for the tank 12 is provided by a heat exchange conduit 71 connected to the
domestic
supply line 72 and extending through the downward section 62 of the inverted U-
shaped
flue pipe 60 from a sealed coupling 73 at the top end of the downward section
to a
further sealed coupling 74 at a bottom end thereof. The open end 75 of the
heat
exchange conduit 71 releases pre-heated domestic water into the bottom end of
the
tank 12. The domestic water supply through the heat exchange conduit is heated
by the
hot flue gases drawn down in the downward section 62 of the flue pipe and the
turbulence it cause by obstructing the flue gases. This obstruction also acts
as a baffle
and adds to the retention time of the flue gases and improves the heat
transfer to the
downward section 62 of the flue pipe for heat exchange with the water 16 in
the tank 12.
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(0034) The retention time of the flue gases can also be achieved by securing
baffle fin
plates 76 or other obstructing formations in the downward section 62 of the
flue pipe.
Such baffles plates 76 are shown in Figure 1A and are well known in the art.
The plates
76 may be formed in a metal strip secured in the flue pipe with the plates
spaced-apart
from one another and angularly disposed in an outward direction to retard the
flow of
the flue gases. As shown in Figure 12, the heat exchange conduit 71 may have a
spiral
vane 77 secured thereabout to impart a spiral motion to the hot flue gases to
extend to
flow path of the hot gases by creating a spiral movement of the gas against
the inner
surface of the downward section 62 of the flue pipe 60 to improve heat
transfer to the
surrounding water in the tank.
(0035) Figure 11 shows a further modification of the heat exchange conduit 71
wherein the conduit is shaped as a spiral heat exchange water conduit 78
welded to the
outer side wall of the heat exchange water pipe to provide heat exchange
contact. It
has an outer diameter smaller than the inner diameter of the downward section
62 of
the flue pipe whereby to create a space 79 between the outer diameter of the
spiral
water conduit 78 and the internal side wall 80 of the flue pipe downward
section 62.
Accordingly, the spiral water conduit 78 constitutes a flue gas dampening
means or
baffle to cause turbulence of the flue gases drawn in the downward section of
the flue
pipe by the blower 68 sucking the flue gases from the combustion chamber 66.
As
shown by arrow 81 some of the hot gases pass straight down inside the spiral
conduit
while other of the gases impinge on the coil and cause turbulence along the
internal
side wall 80 as indicated by arrows 82. Typically, the spiral conduit 78 and
the flue pipe
60 are constructed of stainless steel.
(0036) As shown in Figure 10 a controller 83 receives temperature signals from
the
sensors 84 and 85 in the water tank 12 and controls the operation of the gas
burner 86
in the combustion chamber 66 through a gas valve 89 and a valve 87 secured to
the
domestic water line 72 and the heat exchange conduit 71. The controller 83
also
controls the operation of the blower 68 and the water supply valve 87. The
controller is
also programmed to work with the thermostat, not shown, to perform other
functions as
known in the art.
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(0037) A condensate trap 88 is secured under the blower at the lower end
juncture of
the downward section 62 of the flue pipe and the external exhaust flue pipe 70
to
channel condensation water from these pipes to a suitable drain as is well
known in the
art.
(0038) It is within the ambit of the present invention to cover any
modifications of the
examples of the preferred embodiments described herein, provided such
modifications
fall with the scope of the appended claims.
