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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to means for improving heating efficiency of
domestic space heating systems and, more specifically, to attachments for
furnace smoke pipes located in relatively unheated spaces.
Heating systems for many homes and other buildings include a furnace
located in a basement, utility room or other such location which is
relatively unheated compared to the rooms or other spaces to which heat is
supplied by the heating system. A smoke pipe of galvanized sheet metal, or
the like, extends from the combustion chamber of the furnace to a chimney
or outside vent opening. During periods of furnace operation the smoke
pipe exterior can become quite hot from the products of combustion passing
therethrough. Since the smoke pipe is generally located within the
relatively unheated space, the heat radiating therefrom is, for all
practical purposes, wasted.
It is a principal object of the present invention to provide a heat-saving
attachment which recovers a significant portion of the heat radiating from
a smoke pipe located in a relatively unheated space for delivery to a
relatively heated space.
It is a further object to provide a simple and inexpensive heat-saving
attachment which may be quickly and conveniently incorporated in existing
domestic heating systems.
Another object is to provide a heat-saving attachment for recovering
otherwise wasted heat from a furnace smoke pipe in an efficient manner by
providing electrical controls for forced air circulation means which are
timed to operate in predetermined relationship to operation of the furnace
burner.
Other objects will in part be obvious and will in part appear hereinafter.
SUMMARY OF THE INVENTION
In accordance with the foregoing objects, the invention comprises a jacket
which encloses the smoke pipe for a predetermined portion of the length
thereof which extends through a relatively unheated space between the
furnace and chimney. The jacket is preferably cylindrical, a few inches
larger in diameter than the smoke pipe, and is substantially sealed at its
opposite ends to the exterior of the smoke pipe, forming an annular space
or chamber between the smoke pipe and jacket. An intake opening is
provided near one end of the jacket to admit air from the relatively
unheated space or from a return duct connected to the heated space, into
the annular chamber wherein it is directed through baffle means to an
outlet opening near the opposite end of the jacket.
Preferably, an air intake fan is located in the intake opening and is
driven in conventional fashion by an electric motor, thereby forcing
circulation of air through the annular chamber. The switch contacts for
the motor are closed and opened automatically in response to like
operation of the switch contacts for the furnace burner, operation of
which is controlled in the usual manner by a thermostat located in some
desired remote location. For maximum efficiency of operation, timer means
provide a predetermined delay between turning on and off of the burner and
like operation of the fan motor.
The outlet opening of the annular chamber is connected to a duct through
which the air heated by the smoke pipe is conducted to a space to be
heated thereby. Further baffle means may optionally be provided within the
portion of the smoke pipe enclosed by the jacket to retard the flow of
combustion products therethrough, thus recovering a greater amount of the
available heat. The baffle means within the annular chamber are laterally
disposed to retard the flow of air therein as it absorbs heat from the
smoke pipe, such baffle means being disclosed in two embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevational view showing the attachment of the invention
incorporated with a conventional domestic heating system;
FIG. 2 is a fragmentary, elevational view in axial half section showing the
attachment and a portion of the smoke pipe of FIG. 1;
FIG. 3 is a plan view in section on the line 3--3 of FIG. 2;
FIG. 4 is a perspective view of further structure which may optionally be
incorporated in the smoke pipe of FIGS. 1 and 2;
FIG. 5 is a view similar to FIG. 1 showing certain variations in the
installation;
FIG. 6 is an elevational view, with portions broken away, showing a second
embodiment of the attachment; and
FIGS. 7A and 7B are full plan views in section on the lines 7A--7A and
7B--7B, respectively, of FIG. 6.
DETAILED DESCRIPTION
Referring now to the drawings, in FIG. 1 are shown portions of a typical
domestic heating system including furnace 10 wherein a suitable fuel is
burned within a combustion chamber to produce heated air for circulation
through ductwork, a portion of which is indicated by reference numeral 12,
to rooms or other spaces to be heated. Smoke and other products of
combustion are vented from the combustion chamber through flue or smoke
pipe 14 which in turn is connected to chimney 16 for exhaust to the
atmosphere. Furnace 10 and smoke pipe 14, or at least a portion thereof,
are located in a spaced generally indicated by reference numeral 18 such
as a basement, utility room, garage, or other such location which is
relatively unheated as compared to the space indicated by reference
numeral 20 which receives the heated air conveyed through ductwork 12.
That is, the temperature in space 18 will typically be significantly lower
than the temperature in space 20. Furthermore, the temperature in space 18
is not normally of any consequence in the overall operation of the heating
system which is primarily designed only to provide the required amount of
heat to space 20 and similar spaces to be heated. Thus, most or all of the
heat which is conducted through the walls of smoke pipe 14 and radiated
therefrom into space 18 is, in most typical situations, lost or wasted.
Although the heating system illustrated is of the hot-air type, the
invention may be employed with equal advantage in hot water, steam, or
other types of heating systems employing a furnace with combustion chamber
and smoke pipe located in a relatively unheated space.
The attachment of the present invention is constructed separately from the
heating system and may be conveniently installed concurrently with or at
any time after installation of the basic heating system. The attachment
includes jacket 22 which encloses a portion of smoke pipe 14 for a
predetermined portion of its length between ends 24 and 26 of jacket 22.
While the length of jacket 22 is not critical, it is preferred that it
extend approximately the full length of at least the straight run portion
of smoke pipe 14 which will, of course, vary from one installation to
another. Likewise, the diameter of jacket 22 is not critical, but should
be several inches larger than the diameter of smoke pipe 14. Although a
cylindrical configuration, concentric with smoke pipe 14, is preferred,
other cross-sectional configurations may be employed.
As best seen in FIG. 2, jacket 22 is supported upon smoke pipe 14 at ends
24 and 26, which form closures for the annular chamber, generally
indicated by reference numeral 28, formed between the outer walls of smoke
pipe 14 and inner walls of jacket 22. Intake opening 30 is provided in the
wall of jacket 22 adjacent end 24 and outlet opening 32 is similarly
provided adjacent end 26. Opening 30 is surrounded by short (e.g. 8 inch),
tubular section 34 within which are supported air intake fan 36 and
electric motor 38 which drives the fan blade. Opening 32 is surrounded by
duct 40 which extends from its connection with jacket 22 to an outlet end
shown in FIG. 1 and denoted by reference numeral 42.
Thus, annular chamber 28 communicates through opening 30 and tubular
section 34 with relatively unheated space 18, and through opening 32 and
duct 40 with relatively heated space 20. Preferably, end 24 and opening 30
are at a lower elevation than end 26 and opening 32. As air within chamber
28 is heated by radiation and convection due to the elevated temperature
of smoke pipe 14 during operation of furnace 10, it will rise and leave
chamber 28 through opening 30, being replaced by cooler air drawn in from
space 18 through opening 30. The rate of air flow through chamber 28 is
increased, of course, by operation of fan 36 and should be properly
balanced in accordance with the volume of chamber 28 and typical
temperatures of smoke pipe 14 in particular applications to achieve the
desired temperature rise in the air as it passes from opening 30 to
opening 32.
In order to increase the heat transfer efficiency, baffle means are
provided within chamber 28 to retard the flow of air therethrough. In the
embodiment illustrated in FIGS. 2 and 3, the baffle means comprises a
series of separate baffle plates 44 secured to the inner wall of jacket 22
and extending therefrom laterally across and spirally along chamber 28.
Preferably, baffle plates 44 extend only partially across chamber 28,
leaving a clearance between the inner edges of plates 44 and the outer
wall of smoke pipe 14. While it is possible to construct a single, spiral
plate extending substantially between positions adjacent openings 30 and
32, or completely from end 24 to end 26, it is preferred that a plurality
of separate plates be provided, as shown. Each of plates 44 extends
approximately 180.degree. around the circumference of jacket 22 in a
spiral path. Successive plates are spaced by several inches and are
preferably staggered by about 90.degree.. That is, successive baffle
plates are overlapped by about 90.degree. with respect to the
circumferential dimension of jacket 22.
Smoke pipe 14 reaches the elevated temperatures required for effective heat
transfer only during periods of operation of furnace 10, i.e., only while
fuel is being burned and products of combustion are passing through the
smoke pipe. In typical heating systems, operation of the furnace is
controlled automatically by means of one or more thermostats located in
the spaces to be heated. The temperature-responsive contacts of the
thermostat initiate electrical actuation of the furnace burner and
sometimes of other components such as blowers, pumps, etc. Referring again
to FIG. 1, a thermostat is indicated by reference numeral 46 in space 20
and is wired to control box 48 of furnace 10. Operation of one or more
portions of furnace 10 is initiated and terminated in conventional fashion
by electrical contacts in box 48 in response to signals controlled by
thermostat 46. Control box 48 is also connected, through timer 50, to fan
motor 38. Timer 50 establishes a predetermined time delay between
initiation of furnace operation and initiation of fan motor operation.
Likewise, a time delay may be established between termination of furnace
and fan motor operation. Although the delay is preferably adjustable, a
delay of about 50 seconds in a typical application will allow the smoke
pipe to reach an effectively elevated temperature prior to forced
circulation through jacket 22. Similarly, a delay in turning off fan motor
38 for a time after furnace operation is terminated will allow residual
heat in smoke pipe 14 to be absorbed by air passing through chamber 28.
In FIG. 4 is shown an optical additional baffle means which may be mounted
within smoke pipe 14 to retard the rate of flow of combustion products
therethrough. The baffle means of FIG. 4 does not replace, but rather
supplements the baffle means within chamber 28 formed by plates 44. The
baffle means within smoke pipe 14 is formed from a single, flat sheet of
metal 52, with semicircular cuts at intervals along its length bent
outwardly to form tabs 54. The width of sheet 52 is approximately equal to
the diameter of smoke pipe 14 and tabs 54 alternately extend in opposite
directions from sheet 52 to provide some degree of flow restriction. In
typical installations, baffle means such as that of FIG. 4 will be
desirable, if at all, only in smoke pipes of relatively large diameter or
where the pipe is essentially vertical in the area where it is surrounded
by the jacket of the heat saver attachment. It is also preferable that,
when baffle means are employed internally of smoke pipe 14, such as strip
52 having tabs 54 inhibiting flow therethrough, that the diameter of the
smoke pipe be somewhat larger (e.g., 1 or 2 inches) than required for
normal furnace operation.
In the usual installations, the smoke pipe is provided with a draft or
damper control. Although it is not critical, it is preferred that such
damper controls be located further from furnace 10 than is jacket 22, as
indicated at 56 in FIG. 1, since the products of combustion may be cooled
by the air enter ng at the damper. Again, the location of the damper
control above the heat saver attachment is especially desirable in
installations where the smoke pipe approaches a vertical orientation.
Although the smoke pipe may be of galvanized iron, or other conventional
materials, heat transfer efficiency of the present invention may be
enhanced by constructing at least that portion enclosed by jacket 22 of
copper, stainless steel, or a similar material to make maximum use of
retained heat. The preferred construction is to make all of the smoke pipe
section which is enclosed by the jacket, plus about one or two feet
additional on the downstream side of the jacket, of stainless steel to
protect against corrosion by moisture which may form due to the
temperature differential which results from removal of heat from this
portion of the pipe.
In FIG. 5 is shown an installation employing another embodiment of the
attachment, which is the preferred construction. Again, the illustrated
heating system is of the hot-air type with furnace 56 having a burner
providing heated air through ductwork 58 to spaces to be heated and having
smoke pipe 60 for venting the products of combustion to chimney 62 and
thence to the outside atmosphere. Jacket 64 surrounds smoke pipe 60 for a
portion of its length, in this case a vertically disposed section.
Although the length of jacket 64 is optional, a length of at last 30
inches is satisfactory for most typical installations.
Duct 66 connects the annular chamber between smoke pipe 60 and jacket 64,
at its outlet end, with space 68 to be heated. Although air may be drawn
into the annular chamber from relatively unheated space 70, as in the
installation of FIG. 1, duct 72 may be provided for return air from space
68. Fan 74 is provided, as in the previous construction, for drawing air
into the annular chamber at a desired rate during operation.
Jacket 64 is formed of outer and inner concentric, cylindrical walls of
sheet metal 76 and 78, respectively, with insulating material 80
therebetween. The use of insulating material is optional and will normally
be governed by the type and location of the installation. The portion of
smoke pipe 60 within jacket 64 is of larger diameter, preferably about one
inch, than the portion of the smoke pipe outside the jacket. The portion
outside the jacket has a diameter equal to that specified for use with the
particular furnace installation, the larger diameter portion within jacket
64 being denoted by reference numeral 60'. Transition sections 82 are
provided for connecting the different diameter portions 60 and 60' of the
smoke pipe at the upper and lower ends of jacket 64. The annular chamber
formed between inner wall 78 of jacket 64 and smoke pipe section 60' is
denoted by reference numeral 83. Conventional spacers (not shown) of heavy
gauge sheet metal may be provided at the top and bottom of jacket 64 to
keep the pipe perfectly round and each wall exactly spaced.
Baffle plates 84 and 86 extend laterally across annular chamber 83 at
alternating, spaced intervals of, for example, four or five inches,
depending on the width of chamber 83. As seen from a comparison of FIGS.
7A and 7B, baffle plates 84 and 86 are both annular, sheet metal plates
extending laterally across the full width and around the full periphery of
chamber 83. Each includes cut-out portions spaced equally about its
periphery, the plates differing in that cut-out areas 88 of plate 84
extend inwardly from the edge adjoining inner wall 78 of jacket 64, while
cut-out areas 90 of plate 86 extend inwardly from the edge adjoining smoke
pipe section 60'. Plates 84 and 86, and the succeeding plates which
alternate in the position of the cut-out areas, may be retained in place
within chamber 83 by frictional or press fit between wall 78 and smoke
pipe section 60'. Thus, as air travels upwardly within chamber 83 its flow
is impeded by plates 84 and 86, and it is caused to flow in an irregular
path through alternating cut-out areas 88 and 90, thereby maximizing heat
transfer from smoke pipe section 60'.
Also seen in FIGS. 7A and 7B is damper plate 92, mounted on shaft 94 for
rotating movement between blocking and unblocking positions with respect
to the interior of smoke pipe 60, either within or outside section 60'
thereof. Movement of damper plate 92 is controlled by a suitable solenoid
or similar means (not shown) electrically actuated in response to
operation of the furnace. That is, when the furnace burner is actuated
damper plate 92 is automatically moved to the open postion to allow free
flow of smoke and other combustion products through smoke pipe 60, and
when burner is not in operation, the damper plate is automatically moved
to a partially blocking position to impede flow of warm air out of the
chimney. Humidifiers and other such accessories may also be combined with
the attachment and associated warm air duct.
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