US2722372A - Draft control apparatus - Google Patents

Description

Nov. 1, 1955 H. c. EDWARDS DRAFT CONTROL APPARATUS Filed April 2, 1952 INVENTOR HOWARD C. EDWARDS m g I Z 00% W2 ATTORNEYS United States Patent 0.

DRAFT CGNTROL APPARATUS Howard C. Edwards, Canton, Ohio, assignor, by mesne assignments, to John 'E. Miller, Canton, Ohio, as trustee Application April 2, 1952, Serial No. 280,053

6 Claims. (Cl. 230-95) This invention relates to draft control, and more particularly relates to the draft control of household heating such as furnaces, space heaters, hot water heaters, and overhead unit heaters, although the control may be used in other environments.

In the common heating installation the smoke pipe which carries the products of combustion from the furnace to the chimney is ordinarily provided with a check damper Which when closed prevents exterior air from entering the pipe and when open allows air to be drawn in from the outside to reduce the draft at the furnace, the reduction being in accordance with the amount ofdraft and the extent to which the damper has been opened. Should the chimney be cold when the fire in the furnace is started or a demand for heat is made, the opening of the damper would hinder the initial establishment of a draft in the chimney due to the fact that any air that is sucked in through the damper would be relatively cool and thus delay an increase in the temperature and draft in the chimney. With such constructions, even with the damper closed, when the chimney is cold and the fire in the furnace is started, or a demand for heat is made, the lack of draft in the chimney impedes the flow of the products of combustion through the smoke pipe and up the chimney. As a result, the impeded products of combustion build up back pressure in the furnace and this in turn impedes the inflow of combustion supporting air and results in imperfect combustion and the creation of smoke and soot which frequently finds its way into the room through cracks in the furnace and damper.

To ameliorate these objectionable conditions it has been proposed heretofore to force outside air into the smoke pipe in a stream directed toward the chimney with the view of inducing the products of combustion to flow into the stack faster and thereby stop the tendency for back pressure in the furnace to build up and to heat the chimney quicker. An example of an arrangement designed to that end may be found in Patent No. 2,164,880 of G. A. Merkt issued July 4, 1939.

My present invention has for an object an improvement over said prior constructions in many respects not only in functioning and operation but also in structure whereby said improvements in operation and results are accomplished.

It is also well known that it is objectionable to have too strong a draft in the chimney, as frequently occurs after the fire has been going in the furnace for some time, and the damper in the smoke pipe is not properly adjusted. It is an object of this invention to provide a construction which not only operates to increase the draft when the chimney is relatively cool but also to reduce or dampen the draft when the chimney becomes so hot as to have objectionably strong draft. The optimum draft in chimneys of household furnaces is in about the range of 0.05 to 0.07 inch of water; and a more specific object of this invention is to provide a draft controlling device or apparatus which will quickly build up chimney pressure within that range when thefurnace is first lighted or when- 2 ever there is a demand for heat and will maintain the draft pressure within that range during the entire time the furnace fire is burning.

I have discovered that cold turbulent gases in the chimney where the gases enter the chimney from the smoke pipe interferes with the flow from the smoke pipe and thus interferes with the establishment of a proper draft in the chimney. Such turbulence and back pressure is particularly noticeable in furnaces having gun type oil burners where it causes severe pulsating. Accordingly another object of my invention is to provide a draft controlling device of the character stated above and which is so constructed that it will not cause turbulence of the gases in the chimney where they are received from the smoke pipe.

During recent years there has been an increasing use of overhead unit heaters, ordinarily gas fired, in the remodeling of old buildings without central heating facilities, or in which it is not desirable to install new central heating equipment. The unit heaters ordinarily exhaust through a pipe extending through a wall or window and are not provided with a chimney. An important object of this invention is to provide draft control apparatus for such unit heaters which will insure proper discharge of the products of combustion from the room in which the heater is used.

Another object of this invention is to provide a draft controlling device of the character stated above and which is of simple, durable and inexpensive construction, is simple and easy to install and is quiet, reliable and efiicient in operation.

A further object of this invention is to provide a draft controlling construction of the character described and which construction permits the adaptation of the invention to smoke pipes of any one of a number of different diameters.

The smoke pipes of household furnaces are usually only from 30 to 60 inches in length; and a still further object of this invention is to provide a draft controlling device of the character stated and which can be used with and installed on such household furnace smoke pipes without detracting from the efliciency and functioning of the heating device.

Other objects of this invention will be in part obvious and in part pointed out hereinafter.

In accordance with this invention there is an apparatus or device which may be installed conveniently in a smoke pipe which leads from a furnace to a chimney for the furnace and which device has parts outside of the smoke pipe and parts inside of the smoke pipe. The device in combination with the smoke pipe provides means for causing an annular stream of air to flow from an intermediate point in the smoke pipe toward the chimney in such a way that the annular stream of air converges to an apex before reaching the chimney, thus constituting means for accelerating the flow of the products of combustion in the smoke pipe to the chimney and at the same time providing a space of suflicient length between said apex and the chimney to cause turbulence occasioned by the air stream to subside and to avoid turbulence in the chimney where the smoke pipe discharges into the chimney. The parts of the draft control device are so shaped, dimensioned and relatively positioned as to accomplish the above and to provide means for quickly elevating the draft pressure when the chimney is cool and the furnace fire first lighted or whenever there is a demand for heat and to provide means for maintaining the stack draft pressure at about the range of 0.05 to 0.07 inch of water while there is a demand for heat from the furnace, as will be pointed out more in detail hereinafter.

My invention takes advantage of the law of aerodynamics whereunder the rate of flow of a stream of air can be accelerated by introducing into said air stream another air stream flowing in the same direction at a' greater velocity. In short in accordance with my invention I provide an apparatus or device associated and combined with a smoke pipe of a furnace and which includes means for introducing a stream of air into the smoke pipe, means for establishing the size of the air stream where it is discharged into the stream of combustion products flowing through the smoke pipe, means for establishing the velocity of the air stream at said point, and means for causing the air stream to flow in a certain directional formation or shape in the smoke pipe, all so constructed, arranged and coordinated that when the stack draft is undesirably low the introduced air stream will act on the combustion products in the smoke pipe in such a way as to accelerate their rate of flow from the furnace to the chimney and when the draft in the chimney is undesirably high the introduced air stream will dampen or decelerate the velocity of the flow of the combustion products passing through the smoke pipe from the furnace to the chimney.

This invention accordingly consists in the features of construction, arrangement of parts, combinations of elements and dimensional relationship of parts which will be more clearly described hereinafter and the scope of the application of which will be set forth in the claims that follow.

In order that a clearer understanding of this invention may be had attention is hereby directed to the accompanying drawings, forming a part of this application and illustrating certain possible embodiments of this invention and in which:

Figure l is a longitudinal sectional view of a section of smoke pipe equipped with a draft control embodying this invention, the blower assembly being shown in elevation and the furnace, an adjacent length of smoke pipe and chimney being indicated by dot and dash lines;

Figure 2 is a transverse sectional view thereof and is taken on the line 2-2 of Figure 1;

Figure 3 is a transverse sectional view thereof and is taken on the line 33 of Figure l; and

Figure 4 is a diagrammatic view of certain parts with certain measurements indicated thereon.

Similar reference characters refer to similar parts throughout the several views of the drawings.

My invention is applicable to smoke pipes of different diameters, but for the purpose of illustrating one possible embodiment of this invention we will assume that the drawings accompanying this application show my invention applied to a smoke pipe having a diameter of 6 inches.

Referring to the drawings there is shown or indicated therein a furnace F, a chimney S, a smoke pipe section 10 with which my draft control device is associated and combined, and a smoke pipe section P bridging the space between the furnace end of the smoke pipe section 10 and the furnace. Obviously, two lengths of smoke pipe are not necessarily required since the draft control device may be associated and combined with a smoke pipe which extends all the way from the furnace to the chimney. The reason a two-section smoke pipe is indicated in the drawings is to illustrate that a unit comprising a smoke pipe section, such as 10, with my draft control device asso ciated and combined therewith may be made and installed in heating installations in which the distance between the furnace and the chimney are not the same. In household furnace installations the distance between the furnace and the chimney is usually between 30 to 60 inches. Because of this short distance, certain dimensions must be controlled within narrow limits if an acceptable efliciency of operation is to be obtained. In some the distance is more and in some less. Therefore by installing the draft control mechanism on a relatively short section of smoke pipe, for instance one 27 inches or so long, the draft control unit may be installed by adding, if required, a second section of smoke pipe of the proper length to connect the furnace end of the control unit to the furnace.

Within the smoke pipe section 10 are two circular pipelike members 11 and 12, the member 11 being toward the furnace end of pipe section 10 and forming with the adjacent wall of the pipe section 10 one section or part A of a plenum chamber therebetween; and the other member 12 being positioned to extend from the discharge end of member 11 toward the chimney. The member 11 is formed at its end toward the chimney with a flat annular portion 13 which seats against and about the inside of the smoke pipe 10 and is secured thereto and the opposite end of member 11 is formed to have a narrow axially extending annular lip 14. The Wall 15 of member 11 has slight convex curvature from the portion 13 of member 11 to the lip portion 14. For a smoke pipe of 6 inch diameter a curvature having a radius of approximately 33 /2 inches is preferred. The center of curvature is toward the stack slightly from the lip 14 in order that the member 11 converges throughout its length. In the 6" size shown, the center of curvature will be about /2 inch toward the stack from the lip 14. The purpose and functioning of this curvature will be pointed out more fully hereinafter. The furnace end of section 11 is shown to be about 2 inches within the end of smoke pipe 10.

The end of the member 12 nearest the member 11 is formed with an annular short nozzle 16 which tapers outwardly toward the member 11, overlaps the lip 14 and has its extremity seated against and about the inside of the smoke pipe 10. The opposite end 17 of member 12, that is the end toward the chimney, also seats about and against the inside of the smoke pipe 10. The wall portion 18 of the member 12 tapers outwardly from the nozzle 16 to the outer end of member 12. From the hump 19 where the wall 18 joins the chimney end of nozzle 16, the wall 18 has a slight convex curvature, for instance a radius of about 33 /2 inches, and this curved portion of the wall 18 extends for about 2 /2 inches from the hump 19 toward the stack and then the wall 18 tapers straight to its end 17. The center of curvature is spaced so the member 12 expands continually from its minimum diameter at hump 19.

A hole is cut through the side of the smoke pipe 10 at the plenum chamber A and a hood 20 is fastened, as by welding to the smoke pipe and covers this hole. The interior of the hood opens into the plenum chamber A and provides another part or section A of the plenum chamber which is composed of both plenum chamber sections A and A. The hood 20 has an inlet opening 21 and an assembly of blower 22, driving motor 23 and air discharge duct 24 is mounted on the hood with the discharge duct at the hood inlet opening 21 so that the blower forces air under pressure into the plenum chamber AA. The securing of the blower-motor assembly to the hood may be accomplished by fastening, as by welding, one web of an annular angle iron 25 about the end of the duct and securing the other web of the angle iron 25 to the hood about its opening, as by bolts 26.

In operation the blower 22 forces air under pressure into the plenum chamber AA. The curved wall 15 and lip 14 of section 11 cause all the flue gases from the furnace to be moving in a direction substantially parallel with the axis of the smoke pipe at the time it first intermingles with the air from the nozzle 16. The nozzle 16 will deflect the air striking it in a definite and closely confined direction. The angular relation of the annular nozzle 16 to the axis of the smoke pipe 10 is such that the annular stream of air flowing from the nozzle converges to an apex, indicated at X, at which point the air projected from the different points about the annular nozzle intermingles with the products of combustion in the smoke pipe and any turbulence that may be present dies out. The angle of the nozzle 16 is such that when combined with the convexly curved members 11 and 12, said apex X of the air stream is a sufficient distance in advance of the chimney opening as to insure the absence of substantially any turbulence where the smoke pipe discharges into the chimney.

In order to obtain satisfactory efliciencies when installed in the average heating unit, itis essential that certain dimensions be controlled within critical limits. Both the sections 11 and 12 should be curved about a radius ranging from about 20 to 40 inches at their ends adjacent one another. The distance from lip 14 to the outer Wall smoke pipe 10 should range from about Zia" for a 6" smoke pipe to about /8" for a smoke pipe. The distance from the hump 19 to the wall of the smoke pipe should be about $1 less. The angle between the nozzle 16 and the wall of the smoke pipe should be between 20 and 40 and preferably is approximately 27. The combination of the convex surfaces of the two sections and the annular nozzle at the minimum cross section of the apparatus within the limitations described eliminates the turbulence which would be caused by the apex X being within the chimney.

For optimum performance, the area of the annual opening should be substantially the same as the discharge area of the blower. In the usual domestic installation, that will mean a range from about 3 /2 to 7 /2 square inches. Since the capacity of the blower will be varied from about 50 to 300 cubic feet per minute, depending on the size of the furnace and chimney, there will be a range within which the annular area may vary. Ordinarily, the air supplied by the blower will be about 30% of the volume of the flue gases entering the smoke pipe 10, but may vary from about 25% to as much as 60%.

A rough chart showing suggested data to be followed for smoke pipes of several different diameters issubmitted as follows:

Diameter of smoke pipe 6 7" 8" 9 10 Length of smoke pipe sec 1 tion "inches" 17% 18% 21 22 24 Length of Section 11. do 5 m; 5% 6% 6% 6% Length of Section 12.. do 6 16 8% 1034s 11 11 Spacing 11,? see Fig. 4

do is a Ms %2 Spacing b, see Fig. 4 A w n 9 0--.- B 6 6 Spacing 0, see Fig. 4 A A do %6 Me 364 %2 952 Discharge area at nozzle in square inches: 1

The discharge area at the nozzle can be varied in accordance with the capacity of the blower, L" indicating the lower limits and H the upper limits.

In operation, when the usual thermostat turns on the heating unit, if the heating units is the ordinary gas or oil unit suitable connections, not shown, will close the circuit to the motor 23 of the blower 22 and starts the blower. In a coal furnace, the motor 23 may be electrically connected with the stoker motor, or in a hand-fired unit mechanically connected with the usual draft controls. The air from the blower is discharged into the plenum chamber AA and thence flows outwardly through the nozzle 16 into the space defined by member 12. The rapid flow of air from nozzle 16 immediately provides a draft in member 11 and tends to draw products of combustion from the furnace F through the smoke pipe P. Thus even though the chimney S has not been heated, suflicicnt draft is provided to prevent back pressure in the furnace with the resultant blowing of soot throughout the house.

After the burner has been in operation for some time the chimney S will be hot and tend to increase the natural draft above the desired range. The air discharged from the blower counteracts this tendency in two respects. It will decrease the temperature of the gases in the stack and thereby decrease the natural draft. In addition, the added air introduced into the chimney by the blower causes increased pressure drop in the chimney with a resultant diminishing of the draft. Hence, the apparatus of this invention provides a stabilizing influence increasing the draft to the desired range when the natural draft is low and decreasing the draft to the proper value after the furnace has reached its normal operating temperature.

By following the directions and instructions given above, a draft control may be constructed and installed in a smoke pipe leading between a furnace and a chimney and which will result in the stack draft being built up quickly to at least 0.05 inch of water when the furnace is first lighted or a demand for heat is made and will result in the stack draft remaining at between 0.05 and 0.07 inch of water during all of the time the heating unit is on. A device constructed and installed in accordance with the above disclosure accomplishes all of the objects of the invention stated hereinbefore.

It will be appreciated that the device herein described results in a minimum obstruction to flow of flue gases, the cross sectional area at lip 14 being only slightly less than the area of the smoke pipe, and the surfaces being smooth and unobstructed. With this structure a maximum efliciency, as measured by the ratio of cubic feet of gases entering the smoke pipe 10 to the cubic feet of air supplied by the blower, is obtained. Since the air supplied by the blower usually will be slightly warm air from the basement, and is in addition to the combustion air, a high efliciency is essential.

However, as many different embodiments of this invention could be made and many changes could be made in the above construction without departing from the scope of this invention, it is understood that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A draft inducing unit for heating apparatus, comprising a pipe section adapted to be interposed between the exhaust of a heating device and a flue, a venturi assembly in said section, including a compression member constricted at its outlet end, and a separate, coaxial expansion member, constricted at its inlet end, the adjacent constricted ends of said members being separated longitudinally to define a restricted peripheral slot, opening to the interior of said venturi assembly, the inlet and exhaust ends respectively, of said members being oppositely directed and flaring into sealed contact with said pipe section, an axially converging lip formed on the inlet end of said expansion member which terminates at its outer edge, in sealed contact with said pipe section and completely overlies said slot and the constricted end of said compression member, said pipe section being concentric with and spaced radially outwardly from said compression member to form with the latter, the annular boundary walls of a plenum chamber in said pipe section, surrounding said compression member substantially from end to end and having an annular discharge mouth directed toward said lip and communicating therethrough, with said restricted slot, and a blower operatively connected to the intake end of said chamber.

2. A unit as claimed in claim 1, wherein the walls of said compression member and expansion member are concave in cross-sectional profile.

3. A draft inducing unit for heating apparatus, comprising an annular pipe section adapted to be interposed between the exhaust of a heating device and a flue, and forming the outer boundary of a plenum chamber coaxial with said pipe section, a coaxial compression tube, secured at its inlet end to the pipe section and forming the inner peripheral boundary of said plenum chamber, its discharge end having converging walls which form a restricted passageway, concentric with the pipe section, said plenum chamber having an annular outlet surrounding the discharge end of said compression tube, a funnelshaped flange, the flaring outer edge of which overlies the discharge end of said compression tube in spaced relation thereto and is sealed to said pipe section, to form a converging throat, an expansion tube coaxial with said compression tube and spaced longitudinally therefrom, said expansion tube being connected at its inlet end to the throat of said flange and flaring towards its opposite end into sealed engagement with said pipe section, the spaced adjacent ends of said tubes forming a restricted annular slot lying within the confines of the funnel-shaped flange and placing the plenum chamber outlet in communication with the interior of said compression and expansion tubes, and a blower operatively connected to the inlet end of said chamber.

4. A draft inducing unit for heating apparatus, including a cylindrical pipe section adapted to be interposed between the exhaust of a heating device and a flue, a venturi assembly in said pipe section, comprising a gradually restricted, flue gas compression nozzle, and a coaxial, truncated, flue gas expansion cone, said pipe section being concentric and co-extensive with said nozzle, and spaced radially outwardly from the latter to form therewith the defining annular walls of a plenum chamber surrounding and co-extensive with said compression nozzle, the restricted discharge extremity of said nozzle being directed toward said cone in a line substantially parallel with the axis of said nozzle and cone and spaced immediately in advance of the restricted inlet extremity of said cone, to form a restricted annular slot leading to the interior of said venturi assembly, a funnel-shaped flange contiguous with said inlet extremity of said cone, with its diverging wall overlying said slot and terminating in sealed engagement with said pipe section to form a converging boundary wall for the adjacent exhaust end of said plenum chamber, and a blower operatively connected to the intake end of said plenum chamber.

5. A draft inducing unit for heating apparatus, including a cylindrical pipe section adapted to be interposed between the exhaust of a heating device and a flue, a venturi assembly in said pipe section, comprising a gradually restricted, flue gas compression nozzle, and a coaxial, truncated, flue gas expansion cone, said pipe section being concentric and co-extensive with said nozzle, and spaced radially outwardly from the latter to form therewith the defining annular walls of a plenum chamber surrounding and co-extensive with said compression nozzle, the restricted discharge extremity of said nozzle being directed toward said cone in a line substantially parallel with the axis of said nozzle and cone and spaced immediately in advance of the restricted inlet extremity of said cone, to form a restricted annular slot leading to the interior of said venturi assembly, a funnel-shaped flange contiguous with said inlet portion of said cone, with its diverging wall surrounding said slot and overlying the restricted extremity of said nozzle, terminating in sealed engagement with said pipe section, said flange forming with the discharge extremity of said nozzle, respectively converging walls of an annular mouth opening from the plenum chamber into said expansion cone, immediately in advance of the restricted inlet extremity thereof, and a blower operatively connected to the intake end of said chamber.

6. A draft inducing unit for heating apparatus, comprising a cylindrical pipe section adapted to be interposed between the exhaust of a heating device and a flue, a venturi assembly in said pipe section, comprising a gradually restricted flue gas compression nozzle, and a coaxial, truncated, flue gas expansion cone, said pipe section being concentric and coextensive with said nozzle, and spaced radially from the latter to form therewith the defining walls of a plenum chamber having its maximum annular cross-sectional area adjacent the restricted end of said nozzle, the restricted discharge extremity of said nozzle being directed toward and substantially parallel with the axis of said nozzle and cone, and spaced immediately in advance of the restricted inlet extremity of said cone, to form a restricted annular slot leading to the interior of said venturi assembly, a funnel-shaped flange contiguous with said inlet extremity of said cone, with its diverging wall overlying said slot and terminating in sealed engagement with said pipe section to form a converging boundary wall for the adjacent exhaust end of said plenum chamber, and a blower operatively connected to the intake end of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 542,864 Thomas July 16, 1895 1,604,271 Friedman Oct. 26, 1926 1,612,838 Schultz Ian. 4, 1927 1,942,048 Clark Jan. 2, 1934 2,111,266 Hopkins Mar. 15, 1938 2,361,861 Masowich Oct. 31, 1944 2,584,326 Campbell Feb. 5, 1952 FOREIGN PATENTS 7,127 Germany Jan. 21, 1880

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