CA1311975C - Forced draft controlled mixture heating system using a closed combustionchamber - Google Patents
Forced draft controlled mixture heating system using a closed combustionchamberInfo
- Publication number
- CA1311975C CA1311975C CA000530541A CA530541A CA1311975C CA 1311975 C CA1311975 C CA 1311975C CA 000530541 A CA000530541 A CA 000530541A CA 530541 A CA530541 A CA 530541A CA 1311975 C CA1311975 C CA 1311975C
- Authority
- CA
- Canada
- Prior art keywords
- fuel
- air
- burner
- pressure
- combustion chamber
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N1/00—Regulating fuel supply
- F23N1/02—Regulating fuel supply conjointly with air supply
- F23N1/027—Regulating fuel supply conjointly with air supply using mechanical means
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2235/00—Valves, nozzles or pumps
- F23N2235/12—Fuel valves
- F23N2235/20—Membrane valves
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23N—REGULATING OR CONTROLLING COMBUSTION
- F23N2235/00—Valves, nozzles or pumps
- F23N2235/12—Fuel valves
- F23N2235/24—Valve details
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Regulation And Control Of Combustion (AREA)
Abstract
Abstract A high efficiency forced draft water and space heater maintains a desired air to fuel ratio and efficiency in combustion regardless of changes in air inlet pressure.
The heater uses a venturi type proportioner and associated fuel regulator to provide an air and fuel mixture of con-stant ratio which is drawn from the proportioner by a blower and introduced into a closed combustion chamber for efficient burning and heating of a surrounding body of water.
The heater uses a venturi type proportioner and associated fuel regulator to provide an air and fuel mixture of con-stant ratio which is drawn from the proportioner by a blower and introduced into a closed combustion chamber for efficient burning and heating of a surrounding body of water.
Description
1311~7~
FORCED DRAFT CONTROLLED MIXTURE HEATING
SYSTEM USING A CLOSED COMBUSTION CHAMBER
Field Of The Invention The present invention pertains generally to water and space heating systems and more particularly to a forced draft high efficiency combined heating system.
Background Of The Invention Water heating appliances and space heating appliances have undergone significant changes over the last several years. In the past, fuel was relatively inexpensive and water heaters and space heaters were designed for maximum reliability, simplicity and long life with only a small emphasis placed on fuel efficiency. This set of priorities has changed with the rising price of fuel. Over the last several years, water heaters and space heating furnaces have been designed with a much greater emphasis placed on fuel efficiency. These heaters are generally more complex than their less efficient ancestors.
An additional development has been the combining of water heating and space heating functions in a single appliance. This combination was developed to improve overall efficiency of the total water heating and space heating function within a given home, commercial building or vehicle. Moreover, savings on the space occupied by these appliances and installation expenses have been achieved by the combination of the two essential applia-nces into one high efficiency unit.
One such high efficiency combined water and space heating appliance is described in U.S. Patent 4,541,410 to Jatana. Jatana describes a heating apparatus in which air is mixed with fuel and introduced into a blower which moves the mixture under pressure into the burner of a closed . 30 combustion chamber. The combustion chamber is contained ,~ within a tank containing water. The products of combus-tion exit the combustion chamber and pass through a helical ~, tube of several turns within the body of water. The heat of combustion is extracted from the products of combustion ,, .
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- by conduction through the walls of the combusti~n chamber and the helical exhaust tube. A high efficiency water heater results. The heated water from the water heater i8 also used to heat the air of a home or building by piping the hot water to a heat exchanger contained within the ducts of the home ventilation system. While this apparatus provides a highly efficient water and air heater, certain problems remain.
In order to maximize efficiency, the Jatan~ heater traws combustion air from outside of the home or building being heated. This requires piping or ductq from outside the building to the heater. Such piping or ducts are unique to each building in which the appliance ~s installed.
Air to be mixed for combustion must be drawn through these ducts, and, due to variations in the length of the ducts, turns within the ducts and the like, the resistance of each individual installation to the flow of air will be different.
This often requires that valves governing the air supplied to the furnace and 8as supplied to the furnace be professionally ant individually ad~usted for each installation Any changes in the resistance of the ducts to the flow of air caused by the introduction of foreign ob~ects into the ducts, denting of the ducts or the like after adjust-ment m4y cause a change in the ratio of air to fuel ln the heater, negatively effecting efficiency.
The burner in the Jatana tevice is a cylindrically shaped screen contained within a cylindrical combustion chamber. It has been found that the introduction of the air and fuel mixture into this burner under pressure sometimes results in a swirling circumferential motion leading to noisy operatlon.
In the Jatana unit ant in many other high efficiency units several attitional problems ar$se. Thus, air in excess of what is required for proper combustion of the fuel i8 often mixed with the fuel to be certain that the burner is never supplied with too little air, resulting in incomplete combustion.
FORCED DRAFT CONTROLLED MIXTURE HEATING
SYSTEM USING A CLOSED COMBUSTION CHAMBER
Field Of The Invention The present invention pertains generally to water and space heating systems and more particularly to a forced draft high efficiency combined heating system.
Background Of The Invention Water heating appliances and space heating appliances have undergone significant changes over the last several years. In the past, fuel was relatively inexpensive and water heaters and space heaters were designed for maximum reliability, simplicity and long life with only a small emphasis placed on fuel efficiency. This set of priorities has changed with the rising price of fuel. Over the last several years, water heaters and space heating furnaces have been designed with a much greater emphasis placed on fuel efficiency. These heaters are generally more complex than their less efficient ancestors.
An additional development has been the combining of water heating and space heating functions in a single appliance. This combination was developed to improve overall efficiency of the total water heating and space heating function within a given home, commercial building or vehicle. Moreover, savings on the space occupied by these appliances and installation expenses have been achieved by the combination of the two essential applia-nces into one high efficiency unit.
One such high efficiency combined water and space heating appliance is described in U.S. Patent 4,541,410 to Jatana. Jatana describes a heating apparatus in which air is mixed with fuel and introduced into a blower which moves the mixture under pressure into the burner of a closed . 30 combustion chamber. The combustion chamber is contained ,~ within a tank containing water. The products of combus-tion exit the combustion chamber and pass through a helical ~, tube of several turns within the body of water. The heat of combustion is extracted from the products of combustion ,, .
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i 7 ~
- by conduction through the walls of the combusti~n chamber and the helical exhaust tube. A high efficiency water heater results. The heated water from the water heater i8 also used to heat the air of a home or building by piping the hot water to a heat exchanger contained within the ducts of the home ventilation system. While this apparatus provides a highly efficient water and air heater, certain problems remain.
In order to maximize efficiency, the Jatan~ heater traws combustion air from outside of the home or building being heated. This requires piping or ductq from outside the building to the heater. Such piping or ducts are unique to each building in which the appliance ~s installed.
Air to be mixed for combustion must be drawn through these ducts, and, due to variations in the length of the ducts, turns within the ducts and the like, the resistance of each individual installation to the flow of air will be different.
This often requires that valves governing the air supplied to the furnace and 8as supplied to the furnace be professionally ant individually ad~usted for each installation Any changes in the resistance of the ducts to the flow of air caused by the introduction of foreign ob~ects into the ducts, denting of the ducts or the like after adjust-ment m4y cause a change in the ratio of air to fuel ln the heater, negatively effecting efficiency.
The burner in the Jatana tevice is a cylindrically shaped screen contained within a cylindrical combustion chamber. It has been found that the introduction of the air and fuel mixture into this burner under pressure sometimes results in a swirling circumferential motion leading to noisy operatlon.
In the Jatana unit ant in many other high efficiency units several attitional problems ar$se. Thus, air in excess of what is required for proper combustion of the fuel i8 often mixed with the fuel to be certain that the burner is never supplied with too little air, resulting in incomplete combustion.
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131~975 Also, the burner of a high efficiency heater normally opera-tes most efficiently at a given gas pressure and a specific energy input level. Variations in gas pre6sure and variations in energy input level cause reductions in efficiency. Therefore, the capa-city, that i8 the input energy level, of a given furnace or heater cannot be easily adjusted while maintaining high efficiency.
Problems of stability sometlmes arise. Conditions in the combustion chamber change because of high outside wind, changes in gas pressure and the like and result in "fast cycllng" and other problems which negatively effect efflciency. "Fast cycling" is the rapid and repeated changing of the furnace from the on state to the off state.
It 1~ often noisy ant inefficient.
The present invention contemplates a new and improved apparatu~ and method which overcomes all of the above referred to problems and others and provide~ a water and space heating appliance of high efficiency, rellability, stability and quality.
Summary Of The Invention In accordance with the present invention, there is providet an appliance for proportioning fuel and air in a precise preselected ratio, pressurizing ant mixing such fuel and air and introducing such fuel and air into a closed combustion ch~mber. The proportioning of fuel ant air is accomplished in a venturi type proportioner in which fuel from a fuel regulator is introtuced into the '~ stre~m of air passing through the venturi at the venturi throat section. Pressurizing ant mixing of the fuel snd ` air i8 accompLished in a blower downstream fro~ the ven-; 30 turi proportioner.
Further in accordance with the invention, air pressure is sensed at the venturi air inlet section ad~acent to the venturl throat section and such pressure i~ used to regulate the amount of fuel deliveret to the fuel inlet at the venturi.
35~ Furth-r ln accordance with the invention, a fuel ; -3-~ : ~
-13~97~ MI-7251 regulator is provited which regulates fuel flow based on the difference between pressure at the venturi air inlet fiection and pressure at the venturi throat section, both such pres-sures being negative with respect to ambient pressure.
Yet further in accordance with the invention, the fuel regulator allows the passage of fuel only in response to a pressure difference indicative of proper air flow through the venturi.
Still further in accordance with the present invention, a combustion chamber is provided with a burner having a cyllndrical shape and vertically disposed interior dividers preventing swirling of fluid within the burner.
Still further in accordance with the present invention, th- combu~tlon chamber 18 provlded wlth an electrical igniter outside of the burner and the burner vertical divi-ders are provided with a deflector adapted to deflect a portion of the air and fuel mixture to the i~niter.
Still further in accordance with the invention, a method of proportloning, mixing and combusting fuel and air iB provided in which air and fuel are proportioned in a venturi type proportioner prior to being drawn into a blower where the fuel and air are pressurized and mixed and introduced lnto a combustion chamber.
The prlnclpal ob~ect of the present lnvention 18 the provision of a heater for heating water and air which iæ
highly efficient, precisely controlled and safe to operate.
It is a further ob~ect of the present invention to provide a heater having the amount of fuel introduced into the combustion chamber precisely con~rolled with respect to the amount of air introduced into the combustion chamber regardles~ of the reslstance of the air inlet path, varia-Jl tions in the feed pressure of fuel, variations in line voltage supplied to the furnace blower and other changes 1 in conditions.
~ 35 It is a further ob~ect of the present invention to , :
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13 1 1g7 ~ MI-7251 provide a heater having a homogenized air and fuel mixture of uniform proportions introduced into a combustion chamber for efficient combustion.
It is a further ob~ect of the present invention to provide an air and fuel proportioner and fuel flow regulator which will interrupt the flow of fuel to the appliance if appropriate air flow is not present.
Still ~nother ob~ect of the present invention i8 the provision of a heater which operates quietly.
Yet another ob~ect of the present invention is the provision of a heater which operates over a wide range of energy input levels while maintaining proper air and fuel proportions without the neet to read~ust the proportioning apparatus.
Yet another ob~ect of the present invention is the provision of a method of combusting fuel and air in which fuel wlll not be obtained from a fuel line unless proper air flow is sensed.
The lnvention may take physical form in certain parts and arrangements of parts, the preferred embodlment of which will be described in detail in the specification and illu-strated in the accompanying drawing~ which form a part hereof.
1~ Brief Description Of The Drawings FIGURE 1 is a slde elevation of a water and air heater, in accordance with the present invention, partially broken away, ehowlng the ma~or elements of the heater;
FIGURE 2 is an enlarged detail drawing of the venturi air and fuel proportioner, fuel regulator and blower portions of the devlce in FIGURE l;
; 30 FIGURE 3 is a side elevation of the combustion chamber and burner of the~device shown in FIGURE l; and, ~ FIGURE 4 is a cross sectional view of the burner taken 'J ,~ along line 4-4 in FIGURE 3.
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1311~7~
DeQcription Of The Preferred Embodiment Referring now to the drawings, wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, the figures show a heater A comprised of a stainle~s steel water containing tank lO supported upon a ba~e 12 and con-taining a combustion chamber 14 surrounded by a combustion chamber wall 16 and an exhaust gas exit tube 18. The water containlng tank lO is surrounded by a layer of insulation 19 and a protective ~acket 20 in the conventional manner.
The tank lO is filled with a stratified body of water 22 with the coldest water remaining in the bottom of the tank and the hottest water rising to the top. The water to be heated is introduced into the water containing tank lO
through inlet piping 24 leading through the bottom plate 25 of the tank and feedlng water to an inlet water diffuser 26. The diffuser 26 i8 a short, closet tube having aperture~
27 alon~ one of its side surfaces which introduces water into the tank lO near its bottom.
Hea~ed water is withdrawn from the tank lO through an outlet tube ~8 which is fixed to a fitting penetrating through the bottom plate 25 of the tank 10 and extends upwardly to the topmost region of the tank 10. The top of outlet tube 28 i8 open. Heated water passes through this opening into the tube, downwardly through the outlet tube, out of the ~ tank 10 and into the outlet hot water piping 32.
; Inlet piping 24 and outlet hot water piping 32 are connected to the domestic water piping of the building in i~ which the hea~er i8 tisposed thereby supplying hot water.
i 30 The inlet piping 24 ant outlet hot water piping 32 are also `~ connected through appropriate valves to a heat exchanger in the~space heating and ventilatinR system to provide heat for the buildihg in accortance with the teachings of Jatana 4,451,410.
~ ~ ~Heat Ls provided to the body of water 22 from the heat of ~ ~ , ~ 6-fuel combustion in combustion chamber 14. The equipment and method of supplying combustion gsses to the combustion chamber will be described below with reference to 8 system using natural gas as the input energy source.. Other fuels, such as bottled propane gas, can be used with only slight ad3ustments to the system easily accomplished by those skilled in the art. Use ; of bottled gas in 8 system such as thls is most appropriate in mobile home, csmper and marine applications. Both the hot water for domestic u8e and the interior space heating ln such a vehicle $8 provided by the single heater described herein.
When hot water 18 withdrawn from the water containing tank 10 through the outlet tube 28, additional cold water is drawn into the tank 10 through the inlet water diffuser 26.
When sufficient cold water is drawn into the tank 10, the ~drop ln w ter temperature i- sensed by a water temperature sensor 42. The~water temperature sensor 42 is connected to the~electric control clrcuitry contained in an electrical control box 44. Appropriate control circuitry is well known ln the art and wlll not be tescribed ln detail herein.
In response to the lowered wator temperature within the ;!i tank 10, sn lectrlc ignlter 46 ln combustion chamber 14 is turnet on. The igniter qulckly reaches a temperature suffi-ciently high to ignite a gas and fuel mixture. A blower 48 Is energlzet and a fuel reguIator 100 is turnet on. The blowor 48 traws~air from outs1te the building or vehicle ; through lr inlet tubing 52 lnto an air and fuel propor-tioner 54 where fuel i8 introduced to the airstream and ~7'`,'~ some mixing accurs. The air and fuel porportioner is 30~ ~ tescrlbed in~tetail hereafter. Thé air and fuel is drawn 1Dto the body of the blower 48 where it is pres-surizet and~mixet further. A homogeneous air and fuel mixture~result-~.
The blower 48 18 a blower in which the air and fuel 35~ ~ lntak- 1- near the center portion of the blower body and ,, ,~
1311~7~ MI-7251 the output is on the outer periphery of the blower. This is important as all bearings and other points at which leaks may develop between the interior of the blower and the exterior of the blower are maintained at less than atmos-pheric pressure during blower operation. If a leak should develop through the failure of a seal, ~uch a leak would result in 8 minor addition of air to the air and fuel mixture rather than fuel escaping from the blower.
The pressurizet and homogenized air and fuel mixture from the blower 48 18 directed through the output horn 56 of the blower 48 into the combustion chamber 14 through a combustion chamber inlet opening 58 in the tank bottom plste.
The Combustion Chamber As can be best seen in FIGURE 3, the blower output horn 56 is securely fastened to the tank bottom plate 25 by means of studs 57 passing through the flange of the output horn from the bottom plate 25. The blower output horn 56 is alignet wlth the combustion chamber inlet opening 58. The combustion chamber 14 i8 contalned within a cylindrical ¢ombu~tion chamber wall 16 which i8 welded around its ~ lower periphery to the bottom plate 25 of water containing ; tank 10. The top of the combustion chamber 14 is defined ; by a conical combustion chamber top 62 which i8 ,welded to the top of,the combustion chamber wall 16. The combustion chamber top 62 is provided with an exhaust aperture 64 whlch communicates with the exhaust gas exit tube 18, only a ~mall portion of which 18 shown in FIGURE 3. The exhaust ga~ exit tube 18 is welded to the topmo~t portion of the ,30, combuetion chamber top 62. The exhaust gas exit tube 18 is ~, comprised of a short vertical segment 18a leading upwardly from the combustion chamber and a helical segment 18b spiralling townwartly within the water containing tank 10. The lower ,, .
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end 18c of the exhaust gas exit tube exits the tank 10 through the tank bottom plate 25 and i8 connected to a duct removing exhaust gases from the structure being heated. Like water containing tank 10, the combustion chamber wall 16, the combustion chamber top 62 and the exhaust gas exit tube 18 are all fabricated from stainless steel.
The burner 70 is contained within the lower portion of the combustion chamber 14 and is comprised of a burner mounting plate 72 disposed below the tank bottom plate 25, a cylindrical burner ring 74 which is welded to the mounting plate and which passes through the combustion cham-~ ' ber lnlet opening 58, a cylindrical burner screen 76 which - is weldet to the top of the burner ring, and a burner end cap 78 which i8 welded to the top of the burner screen.
,' 15 The burner screen is a very fine mesh screen having .024 inch tiameter holes arrayet in a straight pattern resulting ' ln 517 holQs p-r square lnch. The mesh is 80 fine that only j~ 24% of the surface of the screen is actually open. The bur-''~ ner end C&p 78 is circular with a short cylintrical flange 80 'l 20 depenting from its periphery allowing welding of the cap to '~ ~ the scrQQn 76.
'1' Containet within the burner ring 74 ant burner screen 76 18 a burner divlder 82 comprised of three vertlcal plates , rsdlatlng from the center of the burner 70 to the surfaces of~the burner ring and the burner screen. The burner divider is as tall as~the burner ltself and divides the interior volume of the burner into three wetge shapet sectors. One ' of the burner divider plates is provided with a deflector 84 which teflQCt8 ~8 portion of the flow of combustion gases toward ,,th- l~nitQr 46. Al'l of the elements of burner 70 are '~ ~ fabricated from stainlQss steel.
,,~ A,burner tistrlbution plate 86 comprisQt of a thin sheet ' of'stainless~steQ} having a uniform pattern of small holes ,~ 87~ther-in is disposed ~ust below the burner mounting plate 72 at th-~,int-rfac-~between the burner 70 ant the blower i, .:: : : ,, , , ~ ~ ,, ::
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13~7~ MI-7251 output horn 56. Appropriste gasketing is, of course, inserted in this stack of elements such that the burner 70, burner distribution plate 86 and the blower output horn 56 are firmly and airtightly fixed to the bottom S plate 25 of the water containing tank 10.
In operation, the air and fuel mixture from blower 48 i8 forcet through the burner distribution plate 86 into the lnterlor volume of the burner 70. The burner distribution plate 86 assures an even distribution of combustion gases.
These gases flow upwartly through the sectors of the burner teflnet by the burner tlvlter 82. The burner tivider prevents the swirllng of these combustlon gases whlch mlght otherwise result ln nolsy operatlon.
The combustlon gases are forcet through the very small openings ln burner ~creen 76 where they are ignited by the existing flame front. Some gases are deflectet by the deflec-tor 84 to the lgniter 46 to establish this flame front at the ; beglnnlng of a heater cycle. The flne mesh of the burner screen prevents the mlgratlon of the flame front to the lnterior volume of the burner 70.
The heat of combustlon generatet outslte o the burner scre-n 76 heats the combustlon chamber wall 16 ant combus-tlon chamber top 62 and hence, the body of water 22 surround-ing the combustion chamber 14. The hot products of combustion exlt the coobustlon chamber 14 through the exhaust gas exit tube 18. As seen ln FIGURe 1, the exhaust gas exlt tube 18 convoy~ the exhaust gases on a hellcally townwartly spirall-ing path through the body of water 22 and hence outslte of the water cont~lnlng tsnk 10 ant outslde of the bulltlng or véhicle in whlch the heater A 18 locatet. It must be remem-bered that blower 48 has pressurlzet the combustlon gases, ,~ and hence the exhaust gases, allowlng the exhau~t gases to i~ follow the convoluted and lengthy heat exchange path de-scribet above. Forced traft 18 appllet: a natural draft 35~ l~ noe requlret.
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f . ~ ^t - , 131197~ MI-7251 The exhau6t gas exit tube 18 follows a counterclockwise downward spiral within the tank 10 The apertures 27 in the inlet water diffuser 26 are orientated such that cool water entering the tank 10 flows in a clockwise direc~ion The cold water is first brought into contact with the lowest ant coolest portion of the exhaust gas exit tube 18 and then spirals upwardly in a direction opposite to that of the exhaust gases in the exhaust gas exit tube This forced counterflow brings the coldest water into contsct with the coolest portion ,, 10 of the, exhaust gas exit tube 18 and brings progreQfsively warmer - water against wsrmer portions of the exhaust gas exit tube 18 N~gh efficiency hest exchange results The Air snt Fuel Proportioner ~' ` The proportioning of fuel to air in a heat-r is critical '~ 15 ~ to its fficiency In the heater A being described, propor-, ' tlonlng is accompllshed in the sir and fuel proportioner 54 ~;' ', (best seen in~FIGURE 23 which is positioned in the air stream ust~prlor to the blower 48 A gss pressure servo regulator lOO avallable from Robertshaw Controls Co and others operates '~ 20' ln concert wlth the alr and fuel proportioner 54 '~; ~ The posltlonlng of the alr and fuel proportloner 54 onthe lnlet ~ide of tho blower 48 18 lmportant In the past, it ha8 been 8uggested to use an alr snd fuel proportioner ,,~ to mix fuel with air sfter~the air ha~ been pressurized "',~,2S~ ln s~,blowor Such an arr-nge~ent csn result in incomplete mlxlng of the sir and fuel. There can be rich parts and lean parts ln the flow Whll- an elabor-te proportloner design could be made to mix~better, the present invention allows , the u~e o,f a less complex proportioner Moreov r, placing 30~ th~c,proportloner 54 on tbe inlet side of the blower 48 sllows'f'~ the proportloner 54 to operate correctly wlth almost any uel~ ~BUpply~ prefssure Th,e,~po-sIbllity of dangorous leaks of fuel to the atmos-,, "~ ; ; ph e`ls reduced~when the alr`and fuel proportloner performs It~ functi _ ~e;l~ ehAn'at o~pherlc pres~ur- With the 131~7~
air and fuel proportioner 54 on the inlet side of the blower 48, the pressure in the air and fuel proportioner 54 i8 maintained at less than atmospheric pressure by the suction of blower 48. A leak will result in a minor addition of air to the air and fuel mixture. If the air and fuel proportioner were locatet on the output side of the blower, pressures in the proportioner would be higher than atmospheric and leaks woult result in-fuel entering the atmosphere around the heater A.
The gas pressure servo regulator 100 i8 somewhat con-ventional but interacts with the air and fuel proportioner 54 ln a novel manner. The servo regulator 100 is comprised of B main valve diaphragm 102 which controls the flow of gas from the servo regulator gas lnput 104 through a main ; 15 valve sperture 106 to the eervo regulator output 108. A
pre~ure sensing regulator valve 110 regulates a small control flow from a main bleed line 112 connected to a main valve control chamber 114 below the main valve diaphragm 102. Gas flows into the main bleed line 118 and the main valve control chamber 114 from the gas input 104 through a bypass line 118 ant a small orifice 138. An electrically controlled two position operator valve 116 opens the main bleed line 112 in the "on" position and closes the main bleed line 112 and connects the main valve control chamber 114 to the bypass line 118 in the "off" position.
~ The air and fuel proportioner 54 i8 comprised of an ; air inlet section 122 having a fixed aiameter, a venturi throat section 124 of a diameter smaller than the diameter of the sir inlet section and an exit section 126 of a diameter larger than the venturi throat section diameter. The air inlet ~ection 122 ant the venturi throat section 124 are intercon-nected by a tapered section 128 providing a smooth transition between these two ~ections.
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' The i~ervo regulator 100 is shown in the "on" position in FIGURE 2 The flow of gas through the servo regulator is controlled such that gas pressure at the servo regulator gas output 108 is always maintsined at a constant level in compari-S son to a reference pressure sensed in a sèneing chamber 130 of the pressure sensing regulator valve 110 This is accom-plished by varying the pressure in the main valve control chsm-ber 114 If the output pressure drops below its desired pressure, this change is transmitted from the regulator output 108 to an output sensing chamber 132 in the pressure sensing regulator vslve llO through a passage 134 A dia-phragm 136 separating the reference sensing chamber 130 from - the output sensing chamber 132 responds to the changed pres~ure ~' tliference by openlng the sensing regulator valve 110 The pressure in the main v-lve control chamber 114;is controlled by tho flow of gas from the servo regulator gas input 104 ~; through~ the small oriflce~138 lnto the~ maln bl-ed llne 112 and through~the ensing valve llO When the senslng valve opened, a8 describet~above, the pressure ln the main ~ 20 Sl--t llne 112 and the main valve control chamber 114 "~ drop~ allowlng th- ~aln valve dlaphragm 102 to h ve down-'~ ' ' wardly ant lncreaslng the flow of ga~ through the main valve ap~rture 106 This incre~ases gas flow ant brings the servo r-gulator output pres~ure back'up to its te~ired value 2S ~ An lncrease ln pressure at the regulator output 108 closes the senslng regulator valve 110 and hence the main valve~aperture 106 by lncreaslng~the pressure in the maln ~ ' valve~controi chamber ll4 The servo regulator 100 thus p~ malntain~ an output pressure havlng a con~tant'difference , ~b, ' ~
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~. -1311~75 MI-7251 from a reference presQure. ThiQ output pressure is main-tained ~egardless o~ the flow rate through the main v~lve aperture 106 and regardless of fluctuations in input gas pressure as control is accomplished by meanQ of a small valve regulating a small flow in a bleed line which in turn regulates a main valve. This arrangement also pro-vide~ damping in response to quick small pressure changes - which also improves performance.
Several valve biasing sprin~s 142, 144 And 146 are selected ~nd adjusted in a convenLi~nal manner to seL the differen~e be-tween the reference pressure and the regulator output pressur~
selected. In the preferred embodiment this pressure differ-ence is set to be negligibly small when compared to other opera-ting pressures in the system.
Pressure regulators such as that just described usually compare the gas output preesure to atmospheric pressure. In the pre~ent inventlon, the reference sensing chamber 130 of the sensing regulator valve 110 is connected to the air inlet section 122 of the alr and fuel proportioner 54 by an air lnlet pressure line 148. Thus, output pressure of the servo regulator 100 is held constant with respect to the low air pressure at the air inlet section of the alr and fuel propor-tioner 54 which is the reference pressure referred to herein as sensed in chamber 130. The pressure difference const~nt selected in the preferret embodiment is 0.2 inches of water, whlch 18 negligibly small when compared to other system pressures and pressure differences when the blower 48 is in operation.
As is well known from the theory of venturi operation, when there is flow through the air and fuel proportioner 54, i the pressure ln the venturi throat section 124 is lower than the ~ pressure ln air lnlet section 122. The differential in the pres-!~ sures between the air inlet section 122 and the venturi throat section 124 is proportional to the square of the air flow ra~e.
j~ The gas output 108 of the servo regulator 100 i8 con-nected to an opening in the venturi throat section 124 by a ;, ::
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1 3 1 ~r~ MI-7251 low pressure fuel line 150. The flow rate of g88 through the low pressure fuel line 150, which acts as an orifice, into ven-turi throat section 124 is proportional to the ~quare root of the difference in pressure between servo regulator output 108 and the venturi throat section 124. As the servo regulator output pressure is substantially equal to the pressure in the air lnlet section 122, the flow of gas through the low pressure fuel line 148 and into the venturi throat section 124 is direct-ly proportional to the flow of air through the air and fuel pro-portioner 54 regardless of the volume of air flow or the inlet air pressure.
The ratio of fuel to air supplied by the air and fuel proportioner 54 is determined by the sizing of the air inlet section 122, the venturi throat section 124, and the resis-tance to flow of the low pressure fuel line 150. These sizes are selected in accordance with the well known theory of venturi action and known pressure regulator design parameters to select a desired air and fuel ratio. For natural gas fuel, the ratio uset is one part natural gas for sixteen parts air.
Z 20 In the preferred embodiment of the invention above described, that ratio is held within a reasonable tolerance when the heater A is operatlng at an input capacity of between 10,000 and 120,000 BTU's per hour.
System Operation When the water temperature sensor 42 informs the control circuitry ln the electrical control box 44 that water heating i8 required, the igniter 46 is energized. Forty-five seconds later, the blower 48 is turned on and servo regulator operator valve 112 i8 turned on enabling the servo regulator 100. The blower 48 traws a stream of air through the air inlet tubing 52 and the air and fuel proportioner 54. The passage of air through the air ant fuel mixer 54 causes a pressure differ-ential to develop between the air inlet section 122 and the venturi throat section 124. When this pressure differential 3S exceets a predetermined threshold, the gas servo regulator "~
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13~7~
100 allows the passage of ~as into the proportioner in an ~m~unL
proportional to the amount of air flowin~, through the proportioner 54. The currently preferred threshold pressure differential is 0.2 inches of water. A higher threshold of 0.8 or 1.0 inches of water has some advantages, but 0.2 inches of water appears to work be~t at present.
The air and fuel mixture from proportioner 54 is drawn at a pressure less than ambient pressure by the blower 48, pressurized, homogenized and introduced into the burner 70.
The mixture i8 forced through the burner screen 76 and ignlted by the igniter 46. A cylindrical flame front i8 established outside of the burner screen 76 within the combustlon chamber 14.
After 6 seconds of operation, ignition current to the igniter 46 Ls turned off. The igniter now functions a~ a combustion detector in a well known manner. If combustion is present, the blower continues to supply air and fuel to the burner until the water temperature sensor 42 indicates that no more heating is needet. If combustion is not detect-et, the blower i~ turned off and the system is reset.
The above tescribed heater is an extremely efficient ~ tevlce ant extremely safe. Proportioning of air ant fuel '; occurs at pressures less than atmospheric thereby assuring that no leaking of fuel from the regulator or proportioner will occur. Moreover, because the fuel is precisely metered into the air flow based upon the amount of air actually flowlng, obstructions inatvertantly or dellberately intro-duced into the air flow path cannot result in an overly rich mixture of air ant fuel leading to incomplete com-b w tion ln the combustlon chamber. Should the air flow ~ path be partially obstructed, fuel will be metered into i ~ the air and gas proportloner at a rate appropriate to the~amount of air available. The capacity of the system is reducet but its safety ant efficiency are maintalned at a much higher level than prior art devices. Moreover, ~s ~
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~ . . . .
131197~ MI-7251 should air flow be totally blocked, the pressure tifferential in the air and fuel proportioner 54 required for fuel flow will never develop and the servo regulator will not penmit the flow of gas.
Importantly, all of the alr and flow proportioning ad~ustment~ ln this heater can be performed at the factoryt Varistions in installstion such as variations ln air lntake and gas intake piping and exhaust gas piping do not effect proportioning significantly. There i~ no need for on-site fuel and air proportioner ad~ustment for such variations.
The mechanical gss pressure regulator 100 described above can be replacet by an electronic regulator which may be advantageous in certain applications. The pressure ~, tifferential between the air inlet section and the venturi throat section of the air and fuel mixer i8 read and digi-tizet in any of several well known manners. This signal 18 then used to control an electrically controlled valve or atomizlng fuel in3ector which introduces a precisely ~i .
measured amount of fuel into the airstream in the venturi throat ~ection 124 of the air and fuel proportioner. The proportioning of fuel and air and the threshold air flow reqùirement describet above are easily programmed into I an electronic controller.
,~ The invention has been described with reference to a preferret embodiment. Obviously, modifications and altera-tlons will occur to others upon the reading and understandinR
of this specification. It is our intention to include all such modifications ant alterations insofar as they come wlthin the 8cope of the appented claims or the equivalents thereof.
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131~975 Also, the burner of a high efficiency heater normally opera-tes most efficiently at a given gas pressure and a specific energy input level. Variations in gas pre6sure and variations in energy input level cause reductions in efficiency. Therefore, the capa-city, that i8 the input energy level, of a given furnace or heater cannot be easily adjusted while maintaining high efficiency.
Problems of stability sometlmes arise. Conditions in the combustion chamber change because of high outside wind, changes in gas pressure and the like and result in "fast cycllng" and other problems which negatively effect efflciency. "Fast cycling" is the rapid and repeated changing of the furnace from the on state to the off state.
It 1~ often noisy ant inefficient.
The present invention contemplates a new and improved apparatu~ and method which overcomes all of the above referred to problems and others and provide~ a water and space heating appliance of high efficiency, rellability, stability and quality.
Summary Of The Invention In accordance with the present invention, there is providet an appliance for proportioning fuel and air in a precise preselected ratio, pressurizing ant mixing such fuel and air and introducing such fuel and air into a closed combustion ch~mber. The proportioning of fuel ant air is accomplished in a venturi type proportioner in which fuel from a fuel regulator is introtuced into the '~ stre~m of air passing through the venturi at the venturi throat section. Pressurizing ant mixing of the fuel snd ` air i8 accompLished in a blower downstream fro~ the ven-; 30 turi proportioner.
Further in accordance with the invention, air pressure is sensed at the venturi air inlet section ad~acent to the venturl throat section and such pressure i~ used to regulate the amount of fuel deliveret to the fuel inlet at the venturi.
35~ Furth-r ln accordance with the invention, a fuel ; -3-~ : ~
-13~97~ MI-7251 regulator is provited which regulates fuel flow based on the difference between pressure at the venturi air inlet fiection and pressure at the venturi throat section, both such pres-sures being negative with respect to ambient pressure.
Yet further in accordance with the invention, the fuel regulator allows the passage of fuel only in response to a pressure difference indicative of proper air flow through the venturi.
Still further in accordance with the present invention, a combustion chamber is provided with a burner having a cyllndrical shape and vertically disposed interior dividers preventing swirling of fluid within the burner.
Still further in accordance with the present invention, th- combu~tlon chamber 18 provlded wlth an electrical igniter outside of the burner and the burner vertical divi-ders are provided with a deflector adapted to deflect a portion of the air and fuel mixture to the i~niter.
Still further in accordance with the invention, a method of proportloning, mixing and combusting fuel and air iB provided in which air and fuel are proportioned in a venturi type proportioner prior to being drawn into a blower where the fuel and air are pressurized and mixed and introduced lnto a combustion chamber.
The prlnclpal ob~ect of the present lnvention 18 the provision of a heater for heating water and air which iæ
highly efficient, precisely controlled and safe to operate.
It is a further ob~ect of the present invention to provide a heater having the amount of fuel introduced into the combustion chamber precisely con~rolled with respect to the amount of air introduced into the combustion chamber regardles~ of the reslstance of the air inlet path, varia-Jl tions in the feed pressure of fuel, variations in line voltage supplied to the furnace blower and other changes 1 in conditions.
~ 35 It is a further ob~ect of the present invention to , :
~ 4 ' , ~,, :~ :
13 1 1g7 ~ MI-7251 provide a heater having a homogenized air and fuel mixture of uniform proportions introduced into a combustion chamber for efficient combustion.
It is a further ob~ect of the present invention to provide an air and fuel proportioner and fuel flow regulator which will interrupt the flow of fuel to the appliance if appropriate air flow is not present.
Still ~nother ob~ect of the present invention i8 the provision of a heater which operates quietly.
Yet another ob~ect of the present invention is the provision of a heater which operates over a wide range of energy input levels while maintaining proper air and fuel proportions without the neet to read~ust the proportioning apparatus.
Yet another ob~ect of the present invention is the provision of a method of combusting fuel and air in which fuel wlll not be obtained from a fuel line unless proper air flow is sensed.
The lnvention may take physical form in certain parts and arrangements of parts, the preferred embodlment of which will be described in detail in the specification and illu-strated in the accompanying drawing~ which form a part hereof.
1~ Brief Description Of The Drawings FIGURE 1 is a slde elevation of a water and air heater, in accordance with the present invention, partially broken away, ehowlng the ma~or elements of the heater;
FIGURE 2 is an enlarged detail drawing of the venturi air and fuel proportioner, fuel regulator and blower portions of the devlce in FIGURE l;
; 30 FIGURE 3 is a side elevation of the combustion chamber and burner of the~device shown in FIGURE l; and, ~ FIGURE 4 is a cross sectional view of the burner taken 'J ,~ along line 4-4 in FIGURE 3.
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1311~7~
DeQcription Of The Preferred Embodiment Referring now to the drawings, wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, the figures show a heater A comprised of a stainle~s steel water containing tank lO supported upon a ba~e 12 and con-taining a combustion chamber 14 surrounded by a combustion chamber wall 16 and an exhaust gas exit tube 18. The water containlng tank lO is surrounded by a layer of insulation 19 and a protective ~acket 20 in the conventional manner.
The tank lO is filled with a stratified body of water 22 with the coldest water remaining in the bottom of the tank and the hottest water rising to the top. The water to be heated is introduced into the water containing tank lO
through inlet piping 24 leading through the bottom plate 25 of the tank and feedlng water to an inlet water diffuser 26. The diffuser 26 i8 a short, closet tube having aperture~
27 alon~ one of its side surfaces which introduces water into the tank lO near its bottom.
Hea~ed water is withdrawn from the tank lO through an outlet tube ~8 which is fixed to a fitting penetrating through the bottom plate 25 of the tank 10 and extends upwardly to the topmost region of the tank 10. The top of outlet tube 28 i8 open. Heated water passes through this opening into the tube, downwardly through the outlet tube, out of the ~ tank 10 and into the outlet hot water piping 32.
; Inlet piping 24 and outlet hot water piping 32 are connected to the domestic water piping of the building in i~ which the hea~er i8 tisposed thereby supplying hot water.
i 30 The inlet piping 24 ant outlet hot water piping 32 are also `~ connected through appropriate valves to a heat exchanger in the~space heating and ventilatinR system to provide heat for the buildihg in accortance with the teachings of Jatana 4,451,410.
~ ~ ~Heat Ls provided to the body of water 22 from the heat of ~ ~ , ~ 6-fuel combustion in combustion chamber 14. The equipment and method of supplying combustion gsses to the combustion chamber will be described below with reference to 8 system using natural gas as the input energy source.. Other fuels, such as bottled propane gas, can be used with only slight ad3ustments to the system easily accomplished by those skilled in the art. Use ; of bottled gas in 8 system such as thls is most appropriate in mobile home, csmper and marine applications. Both the hot water for domestic u8e and the interior space heating ln such a vehicle $8 provided by the single heater described herein.
When hot water 18 withdrawn from the water containing tank 10 through the outlet tube 28, additional cold water is drawn into the tank 10 through the inlet water diffuser 26.
When sufficient cold water is drawn into the tank 10, the ~drop ln w ter temperature i- sensed by a water temperature sensor 42. The~water temperature sensor 42 is connected to the~electric control clrcuitry contained in an electrical control box 44. Appropriate control circuitry is well known ln the art and wlll not be tescribed ln detail herein.
In response to the lowered wator temperature within the ;!i tank 10, sn lectrlc ignlter 46 ln combustion chamber 14 is turnet on. The igniter qulckly reaches a temperature suffi-ciently high to ignite a gas and fuel mixture. A blower 48 Is energlzet and a fuel reguIator 100 is turnet on. The blowor 48 traws~air from outs1te the building or vehicle ; through lr inlet tubing 52 lnto an air and fuel propor-tioner 54 where fuel i8 introduced to the airstream and ~7'`,'~ some mixing accurs. The air and fuel porportioner is 30~ ~ tescrlbed in~tetail hereafter. Thé air and fuel is drawn 1Dto the body of the blower 48 where it is pres-surizet and~mixet further. A homogeneous air and fuel mixture~result-~.
The blower 48 18 a blower in which the air and fuel 35~ ~ lntak- 1- near the center portion of the blower body and ,, ,~
1311~7~ MI-7251 the output is on the outer periphery of the blower. This is important as all bearings and other points at which leaks may develop between the interior of the blower and the exterior of the blower are maintained at less than atmos-pheric pressure during blower operation. If a leak should develop through the failure of a seal, ~uch a leak would result in 8 minor addition of air to the air and fuel mixture rather than fuel escaping from the blower.
The pressurizet and homogenized air and fuel mixture from the blower 48 18 directed through the output horn 56 of the blower 48 into the combustion chamber 14 through a combustion chamber inlet opening 58 in the tank bottom plste.
The Combustion Chamber As can be best seen in FIGURE 3, the blower output horn 56 is securely fastened to the tank bottom plate 25 by means of studs 57 passing through the flange of the output horn from the bottom plate 25. The blower output horn 56 is alignet wlth the combustion chamber inlet opening 58. The combustion chamber 14 i8 contalned within a cylindrical ¢ombu~tion chamber wall 16 which i8 welded around its ~ lower periphery to the bottom plate 25 of water containing ; tank 10. The top of the combustion chamber 14 is defined ; by a conical combustion chamber top 62 which i8 ,welded to the top of,the combustion chamber wall 16. The combustion chamber top 62 is provided with an exhaust aperture 64 whlch communicates with the exhaust gas exit tube 18, only a ~mall portion of which 18 shown in FIGURE 3. The exhaust ga~ exit tube 18 is welded to the topmo~t portion of the ,30, combuetion chamber top 62. The exhaust gas exit tube 18 is ~, comprised of a short vertical segment 18a leading upwardly from the combustion chamber and a helical segment 18b spiralling townwartly within the water containing tank 10. The lower ,, .
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end 18c of the exhaust gas exit tube exits the tank 10 through the tank bottom plate 25 and i8 connected to a duct removing exhaust gases from the structure being heated. Like water containing tank 10, the combustion chamber wall 16, the combustion chamber top 62 and the exhaust gas exit tube 18 are all fabricated from stainless steel.
The burner 70 is contained within the lower portion of the combustion chamber 14 and is comprised of a burner mounting plate 72 disposed below the tank bottom plate 25, a cylindrical burner ring 74 which is welded to the mounting plate and which passes through the combustion cham-~ ' ber lnlet opening 58, a cylindrical burner screen 76 which - is weldet to the top of the burner ring, and a burner end cap 78 which i8 welded to the top of the burner screen.
,' 15 The burner screen is a very fine mesh screen having .024 inch tiameter holes arrayet in a straight pattern resulting ' ln 517 holQs p-r square lnch. The mesh is 80 fine that only j~ 24% of the surface of the screen is actually open. The bur-''~ ner end C&p 78 is circular with a short cylintrical flange 80 'l 20 depenting from its periphery allowing welding of the cap to '~ ~ the scrQQn 76.
'1' Containet within the burner ring 74 ant burner screen 76 18 a burner divlder 82 comprised of three vertlcal plates , rsdlatlng from the center of the burner 70 to the surfaces of~the burner ring and the burner screen. The burner divider is as tall as~the burner ltself and divides the interior volume of the burner into three wetge shapet sectors. One ' of the burner divider plates is provided with a deflector 84 which teflQCt8 ~8 portion of the flow of combustion gases toward ,,th- l~nitQr 46. Al'l of the elements of burner 70 are '~ ~ fabricated from stainlQss steel.
,,~ A,burner tistrlbution plate 86 comprisQt of a thin sheet ' of'stainless~steQ} having a uniform pattern of small holes ,~ 87~ther-in is disposed ~ust below the burner mounting plate 72 at th-~,int-rfac-~between the burner 70 ant the blower i, .:: : : ,, , , ~ ~ ,, ::
:~:
13~7~ MI-7251 output horn 56. Appropriste gasketing is, of course, inserted in this stack of elements such that the burner 70, burner distribution plate 86 and the blower output horn 56 are firmly and airtightly fixed to the bottom S plate 25 of the water containing tank 10.
In operation, the air and fuel mixture from blower 48 i8 forcet through the burner distribution plate 86 into the lnterlor volume of the burner 70. The burner distribution plate 86 assures an even distribution of combustion gases.
These gases flow upwartly through the sectors of the burner teflnet by the burner tlvlter 82. The burner tivider prevents the swirllng of these combustlon gases whlch mlght otherwise result ln nolsy operatlon.
The combustlon gases are forcet through the very small openings ln burner ~creen 76 where they are ignited by the existing flame front. Some gases are deflectet by the deflec-tor 84 to the lgniter 46 to establish this flame front at the ; beglnnlng of a heater cycle. The flne mesh of the burner screen prevents the mlgratlon of the flame front to the lnterior volume of the burner 70.
The heat of combustlon generatet outslte o the burner scre-n 76 heats the combustlon chamber wall 16 ant combus-tlon chamber top 62 and hence, the body of water 22 surround-ing the combustion chamber 14. The hot products of combustion exlt the coobustlon chamber 14 through the exhaust gas exit tube 18. As seen ln FIGURe 1, the exhaust gas exlt tube 18 convoy~ the exhaust gases on a hellcally townwartly spirall-ing path through the body of water 22 and hence outslte of the water cont~lnlng tsnk 10 ant outslde of the bulltlng or véhicle in whlch the heater A 18 locatet. It must be remem-bered that blower 48 has pressurlzet the combustlon gases, ,~ and hence the exhaust gases, allowlng the exhau~t gases to i~ follow the convoluted and lengthy heat exchange path de-scribet above. Forced traft 18 appllet: a natural draft 35~ l~ noe requlret.
, ,, .
f . ~ ^t - , 131197~ MI-7251 The exhau6t gas exit tube 18 follows a counterclockwise downward spiral within the tank 10 The apertures 27 in the inlet water diffuser 26 are orientated such that cool water entering the tank 10 flows in a clockwise direc~ion The cold water is first brought into contact with the lowest ant coolest portion of the exhaust gas exit tube 18 and then spirals upwardly in a direction opposite to that of the exhaust gases in the exhaust gas exit tube This forced counterflow brings the coldest water into contsct with the coolest portion ,, 10 of the, exhaust gas exit tube 18 and brings progreQfsively warmer - water against wsrmer portions of the exhaust gas exit tube 18 N~gh efficiency hest exchange results The Air snt Fuel Proportioner ~' ` The proportioning of fuel to air in a heat-r is critical '~ 15 ~ to its fficiency In the heater A being described, propor-, ' tlonlng is accompllshed in the sir and fuel proportioner 54 ~;' ', (best seen in~FIGURE 23 which is positioned in the air stream ust~prlor to the blower 48 A gss pressure servo regulator lOO avallable from Robertshaw Controls Co and others operates '~ 20' ln concert wlth the alr and fuel proportioner 54 '~; ~ The posltlonlng of the alr and fuel proportloner 54 onthe lnlet ~ide of tho blower 48 18 lmportant In the past, it ha8 been 8uggested to use an alr snd fuel proportioner ,,~ to mix fuel with air sfter~the air ha~ been pressurized "',~,2S~ ln s~,blowor Such an arr-nge~ent csn result in incomplete mlxlng of the sir and fuel. There can be rich parts and lean parts ln the flow Whll- an elabor-te proportloner design could be made to mix~better, the present invention allows , the u~e o,f a less complex proportioner Moreov r, placing 30~ th~c,proportloner 54 on tbe inlet side of the blower 48 sllows'f'~ the proportloner 54 to operate correctly wlth almost any uel~ ~BUpply~ prefssure Th,e,~po-sIbllity of dangorous leaks of fuel to the atmos-,, "~ ; ; ph e`ls reduced~when the alr`and fuel proportloner performs It~ functi _ ~e;l~ ehAn'at o~pherlc pres~ur- With the 131~7~
air and fuel proportioner 54 on the inlet side of the blower 48, the pressure in the air and fuel proportioner 54 i8 maintained at less than atmospheric pressure by the suction of blower 48. A leak will result in a minor addition of air to the air and fuel mixture. If the air and fuel proportioner were locatet on the output side of the blower, pressures in the proportioner would be higher than atmospheric and leaks woult result in-fuel entering the atmosphere around the heater A.
The gas pressure servo regulator 100 i8 somewhat con-ventional but interacts with the air and fuel proportioner 54 ln a novel manner. The servo regulator 100 is comprised of B main valve diaphragm 102 which controls the flow of gas from the servo regulator gas lnput 104 through a main ; 15 valve sperture 106 to the eervo regulator output 108. A
pre~ure sensing regulator valve 110 regulates a small control flow from a main bleed line 112 connected to a main valve control chamber 114 below the main valve diaphragm 102. Gas flows into the main bleed line 118 and the main valve control chamber 114 from the gas input 104 through a bypass line 118 ant a small orifice 138. An electrically controlled two position operator valve 116 opens the main bleed line 112 in the "on" position and closes the main bleed line 112 and connects the main valve control chamber 114 to the bypass line 118 in the "off" position.
~ The air and fuel proportioner 54 i8 comprised of an ; air inlet section 122 having a fixed aiameter, a venturi throat section 124 of a diameter smaller than the diameter of the sir inlet section and an exit section 126 of a diameter larger than the venturi throat section diameter. The air inlet ~ection 122 ant the venturi throat section 124 are intercon-nected by a tapered section 128 providing a smooth transition between these two ~ections.
~ ~ ' ,, ~ -12-.j , . .
' The i~ervo regulator 100 is shown in the "on" position in FIGURE 2 The flow of gas through the servo regulator is controlled such that gas pressure at the servo regulator gas output 108 is always maintsined at a constant level in compari-S son to a reference pressure sensed in a sèneing chamber 130 of the pressure sensing regulator valve 110 This is accom-plished by varying the pressure in the main valve control chsm-ber 114 If the output pressure drops below its desired pressure, this change is transmitted from the regulator output 108 to an output sensing chamber 132 in the pressure sensing regulator vslve llO through a passage 134 A dia-phragm 136 separating the reference sensing chamber 130 from - the output sensing chamber 132 responds to the changed pres~ure ~' tliference by openlng the sensing regulator valve 110 The pressure in the main v-lve control chamber 114;is controlled by tho flow of gas from the servo regulator gas input 104 ~; through~ the small oriflce~138 lnto the~ maln bl-ed llne 112 and through~the ensing valve llO When the senslng valve opened, a8 describet~above, the pressure ln the main ~ 20 Sl--t llne 112 and the main valve control chamber 114 "~ drop~ allowlng th- ~aln valve dlaphragm 102 to h ve down-'~ ' ' wardly ant lncreaslng the flow of ga~ through the main valve ap~rture 106 This incre~ases gas flow ant brings the servo r-gulator output pres~ure back'up to its te~ired value 2S ~ An lncrease ln pressure at the regulator output 108 closes the senslng regulator valve 110 and hence the main valve~aperture 106 by lncreaslng~the pressure in the maln ~ ' valve~controi chamber ll4 The servo regulator 100 thus p~ malntain~ an output pressure havlng a con~tant'difference , ~b, ' ~
:
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~. -1311~75 MI-7251 from a reference presQure. ThiQ output pressure is main-tained ~egardless o~ the flow rate through the main v~lve aperture 106 and regardless of fluctuations in input gas pressure as control is accomplished by meanQ of a small valve regulating a small flow in a bleed line which in turn regulates a main valve. This arrangement also pro-vide~ damping in response to quick small pressure changes - which also improves performance.
Several valve biasing sprin~s 142, 144 And 146 are selected ~nd adjusted in a convenLi~nal manner to seL the differen~e be-tween the reference pressure and the regulator output pressur~
selected. In the preferred embodiment this pressure differ-ence is set to be negligibly small when compared to other opera-ting pressures in the system.
Pressure regulators such as that just described usually compare the gas output preesure to atmospheric pressure. In the pre~ent inventlon, the reference sensing chamber 130 of the sensing regulator valve 110 is connected to the air inlet section 122 of the alr and fuel proportioner 54 by an air lnlet pressure line 148. Thus, output pressure of the servo regulator 100 is held constant with respect to the low air pressure at the air inlet section of the alr and fuel propor-tioner 54 which is the reference pressure referred to herein as sensed in chamber 130. The pressure difference const~nt selected in the preferret embodiment is 0.2 inches of water, whlch 18 negligibly small when compared to other system pressures and pressure differences when the blower 48 is in operation.
As is well known from the theory of venturi operation, when there is flow through the air and fuel proportioner 54, i the pressure ln the venturi throat section 124 is lower than the ~ pressure ln air lnlet section 122. The differential in the pres-!~ sures between the air inlet section 122 and the venturi throat section 124 is proportional to the square of the air flow ra~e.
j~ The gas output 108 of the servo regulator 100 i8 con-nected to an opening in the venturi throat section 124 by a ;, ::
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1 3 1 ~r~ MI-7251 low pressure fuel line 150. The flow rate of g88 through the low pressure fuel line 150, which acts as an orifice, into ven-turi throat section 124 is proportional to the ~quare root of the difference in pressure between servo regulator output 108 and the venturi throat section 124. As the servo regulator output pressure is substantially equal to the pressure in the air lnlet section 122, the flow of gas through the low pressure fuel line 148 and into the venturi throat section 124 is direct-ly proportional to the flow of air through the air and fuel pro-portioner 54 regardless of the volume of air flow or the inlet air pressure.
The ratio of fuel to air supplied by the air and fuel proportioner 54 is determined by the sizing of the air inlet section 122, the venturi throat section 124, and the resis-tance to flow of the low pressure fuel line 150. These sizes are selected in accordance with the well known theory of venturi action and known pressure regulator design parameters to select a desired air and fuel ratio. For natural gas fuel, the ratio uset is one part natural gas for sixteen parts air.
Z 20 In the preferred embodiment of the invention above described, that ratio is held within a reasonable tolerance when the heater A is operatlng at an input capacity of between 10,000 and 120,000 BTU's per hour.
System Operation When the water temperature sensor 42 informs the control circuitry ln the electrical control box 44 that water heating i8 required, the igniter 46 is energized. Forty-five seconds later, the blower 48 is turned on and servo regulator operator valve 112 i8 turned on enabling the servo regulator 100. The blower 48 traws a stream of air through the air inlet tubing 52 and the air and fuel proportioner 54. The passage of air through the air ant fuel mixer 54 causes a pressure differ-ential to develop between the air inlet section 122 and the venturi throat section 124. When this pressure differential 3S exceets a predetermined threshold, the gas servo regulator "~
", , ~ -15-.~ , , , ' .^ ~ , .
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13~7~
100 allows the passage of ~as into the proportioner in an ~m~unL
proportional to the amount of air flowin~, through the proportioner 54. The currently preferred threshold pressure differential is 0.2 inches of water. A higher threshold of 0.8 or 1.0 inches of water has some advantages, but 0.2 inches of water appears to work be~t at present.
The air and fuel mixture from proportioner 54 is drawn at a pressure less than ambient pressure by the blower 48, pressurized, homogenized and introduced into the burner 70.
The mixture i8 forced through the burner screen 76 and ignlted by the igniter 46. A cylindrical flame front i8 established outside of the burner screen 76 within the combustlon chamber 14.
After 6 seconds of operation, ignition current to the igniter 46 Ls turned off. The igniter now functions a~ a combustion detector in a well known manner. If combustion is present, the blower continues to supply air and fuel to the burner until the water temperature sensor 42 indicates that no more heating is needet. If combustion is not detect-et, the blower i~ turned off and the system is reset.
The above tescribed heater is an extremely efficient ~ tevlce ant extremely safe. Proportioning of air ant fuel '; occurs at pressures less than atmospheric thereby assuring that no leaking of fuel from the regulator or proportioner will occur. Moreover, because the fuel is precisely metered into the air flow based upon the amount of air actually flowlng, obstructions inatvertantly or dellberately intro-duced into the air flow path cannot result in an overly rich mixture of air ant fuel leading to incomplete com-b w tion ln the combustlon chamber. Should the air flow ~ path be partially obstructed, fuel will be metered into i ~ the air and gas proportloner at a rate appropriate to the~amount of air available. The capacity of the system is reducet but its safety ant efficiency are maintalned at a much higher level than prior art devices. Moreover, ~s ~
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131197~ MI-7251 should air flow be totally blocked, the pressure tifferential in the air and fuel proportioner 54 required for fuel flow will never develop and the servo regulator will not penmit the flow of gas.
Importantly, all of the alr and flow proportioning ad~ustment~ ln this heater can be performed at the factoryt Varistions in installstion such as variations ln air lntake and gas intake piping and exhaust gas piping do not effect proportioning significantly. There i~ no need for on-site fuel and air proportioner ad~ustment for such variations.
The mechanical gss pressure regulator 100 described above can be replacet by an electronic regulator which may be advantageous in certain applications. The pressure ~, tifferential between the air inlet section and the venturi throat section of the air and fuel mixer i8 read and digi-tizet in any of several well known manners. This signal 18 then used to control an electrically controlled valve or atomizlng fuel in3ector which introduces a precisely ~i .
measured amount of fuel into the airstream in the venturi throat ~ection 124 of the air and fuel proportioner. The proportioning of fuel and air and the threshold air flow reqùirement describet above are easily programmed into I an electronic controller.
,~ The invention has been described with reference to a preferret embodiment. Obviously, modifications and altera-tlons will occur to others upon the reading and understandinR
of this specification. It is our intention to include all such modifications ant alterations insofar as they come wlthin the 8cope of the appented claims or the equivalents thereof.
,, , ., . ~
Claims (11)
1. A heating apparatus capable of maintaining a steady state efficiency of operation of approximately 95% over a wide range of input capacities of from about 10,000 to about 120,000 BTU's comprising:
a tank adapted to contain a body of fluid to be heated;
a sealed combustion chamber disposed within said tank having an inlet opening and an exhaust aperture;
an exhaust gas exit tube connected to said exhaust aperture and exiting said tank;
a burner disposed within said combustion chamber receiving fuel and air through said combustion chamber inlet opening;
an airtight fluid moving means having an output fixed to said combustion chamber inlet opening and having an inlet;
a venturi type air and fuel proportioner having an air inlet section of a first cross-sectional area in flow communication with a source of air, a venturi throat section of a second cross-sectional area smaller than said flow regulator output through a fuel aperture in said venturi throat section and having an outlet fixed to said fluid moving means inlet whereby a stream of air and a stream of fuel are drawn at less than standard atmospheric pressure through said air and fuel proportioner in response to operation of said fluid moving means;
said fuel regulator having an air inlet section pressure chamber connected by an air-tight tube to said air inlet section and valve means maintaining the pressure of fuel delivered to said fuel flow regulator output in fixed relationship to said air inlet section pressure; and said air-tight fluid moving means effective to mix said air and fuel into a combustible mixture away from said proportioner and direct said mixture at pressure above standard atmosphere into said burner.
a tank adapted to contain a body of fluid to be heated;
a sealed combustion chamber disposed within said tank having an inlet opening and an exhaust aperture;
an exhaust gas exit tube connected to said exhaust aperture and exiting said tank;
a burner disposed within said combustion chamber receiving fuel and air through said combustion chamber inlet opening;
an airtight fluid moving means having an output fixed to said combustion chamber inlet opening and having an inlet;
a venturi type air and fuel proportioner having an air inlet section of a first cross-sectional area in flow communication with a source of air, a venturi throat section of a second cross-sectional area smaller than said flow regulator output through a fuel aperture in said venturi throat section and having an outlet fixed to said fluid moving means inlet whereby a stream of air and a stream of fuel are drawn at less than standard atmospheric pressure through said air and fuel proportioner in response to operation of said fluid moving means;
said fuel regulator having an air inlet section pressure chamber connected by an air-tight tube to said air inlet section and valve means maintaining the pressure of fuel delivered to said fuel flow regulator output in fixed relationship to said air inlet section pressure; and said air-tight fluid moving means effective to mix said air and fuel into a combustible mixture away from said proportioner and direct said mixture at pressure above standard atmosphere into said burner.
2. The heating apparatus of claim 1 wherein said fuel flow regulator additionally comprises means maintaining said fuel flow regulator output pressure substantially equal to said air inlet section pressuring during steady state operation and allowing the passage of fuel only when a predetermined pressure differential exists between said air inlet section and said venturi throat section.
3. The heating apparatus of claim 2 wherein said predetermined pressure differential is between about 0.2 inches of water and about 1.0 inch of water.
4. The heating apparatus of claim 1 wherein said fuel regulator additionally comprises means sensing air flow through said air and fuel proportioner and allowing the passage of fuel to said air and fuel proportioner only when air flow is present.
5. The heating apparatus of claim 1 wherein said burner is a cylindrical burner comprising a mounting plate fixed to said tank, a lower ring fixed to said mounting plate, a cylindrical screen disposed above said lower ring and allowing the passage of fluid from the interior of said screen to the exterior of said screen, a circular top impervious to the flow of fluid closing the top of said screen and a vertical divider adapted to prevent the swirling of fluid within said burner.
6. The heating apparatus of claim 5 wherein said combustion chamber contains an igniter on the exterior of said burner and said burner divider has a deflector adapted to direct the flow of fluid toward said igniter.
7. The apparatus of claim 1 wherein said venturi throat section is formed by a wall and said fuel aperture is an opening through said wall.
8. A high efficiency method of heating water contained in a water containing tank comprising the steps of:
providing a venturi type air and fuel proportioner having an air inlet of a first cross-sectional area adapted to receive air from outside said tank, a venturi throat section of a second cross-sectional area smaller than said first cross-sectional area having a fuel aperture therein adapted to receive fuel, and an air and fuel outlet;
providing a gas regulator adapted to receive fuel from a gas line and provide fuel to said fuel aperture, said gas regulator having an air pressure chamber in pressure sensing communication with said proportioner air inlet;
providing an air-tight fluid mover having its air input tightly connected to said proportioner outlet and an output;
providing a closed combustion chamber within said water containing tank having a burner disposed therein, said burner adapted to receive air and fuel under pressure from said fluid mover, an igniter and exhaust gas outlet;
providing an exhaust gas exit tube within said water containing tank, said exit tube being connected to said combustion chamber exhaust gas outlet, following a long convoluted path within said water containing tank and exiting said water containing tank;
providing fuel from said gas regulator to said proportioner fuel aperture from said gas regulator at a pressure substantially equal to said proportioner air inlet pressure, thereby creating an air and fuel mixture in said proportioner of constant proportion over a broad range of input air flows;
energizing said fluid moving means to forcefully draw air and fuel at a negative pressure through said proportioner, and mix said air and fuel into a homogenized mixture at a positive pressure away from said proportioner and thereafter pass said air and fuel into said combustion chamber;
igniting said air and fuel mixture in said combustion chamber thereby creating combustion and products of combustion;
and forcing said products of combustion through said exhaust gas exit tube.
providing a venturi type air and fuel proportioner having an air inlet of a first cross-sectional area adapted to receive air from outside said tank, a venturi throat section of a second cross-sectional area smaller than said first cross-sectional area having a fuel aperture therein adapted to receive fuel, and an air and fuel outlet;
providing a gas regulator adapted to receive fuel from a gas line and provide fuel to said fuel aperture, said gas regulator having an air pressure chamber in pressure sensing communication with said proportioner air inlet;
providing an air-tight fluid mover having its air input tightly connected to said proportioner outlet and an output;
providing a closed combustion chamber within said water containing tank having a burner disposed therein, said burner adapted to receive air and fuel under pressure from said fluid mover, an igniter and exhaust gas outlet;
providing an exhaust gas exit tube within said water containing tank, said exit tube being connected to said combustion chamber exhaust gas outlet, following a long convoluted path within said water containing tank and exiting said water containing tank;
providing fuel from said gas regulator to said proportioner fuel aperture from said gas regulator at a pressure substantially equal to said proportioner air inlet pressure, thereby creating an air and fuel mixture in said proportioner of constant proportion over a broad range of input air flows;
energizing said fluid moving means to forcefully draw air and fuel at a negative pressure through said proportioner, and mix said air and fuel into a homogenized mixture at a positive pressure away from said proportioner and thereafter pass said air and fuel into said combustion chamber;
igniting said air and fuel mixture in said combustion chamber thereby creating combustion and products of combustion;
and forcing said products of combustion through said exhaust gas exit tube.
9. A heating apparatus comprising:
a tank adapted to contain a body of fluid to be heated;
a sealed combustion chamber disposed within said tank having an inlet opening and an exhaust aperture;
an exhaust gas exit tube connected to said exhaust aperture and exiting said tank;
a burner disposed within said combustion chamber receiving a combustible mixture of fuel and air from said combustion chamber inlet opening and means for igniting said combustible mixture within said combustible chamber;
proportioning means remote from said combustion chamber for drawing a metered amount of fuel and air therethrough, said proportioning means including regulator means and a venturi, said venturi having an air inlet section of a first cross-sectional area in communication with a source of air, a venturi throat section of a second cross-sectional area smaller than said first cross-sectional area and a transition section therebetween, said throat section having a fuel aperture in the wall thereof, said regulating means metering a precise amount of fuel through said fuel aperture into said throat section in fixed proportion to the amount of air flowing through said proportioning means and including an air inlet port connected by an airtight tube to said inlet section of said proportioning means, a fuel outlet port connected by a fuel-tight tube to said fuel aperture and valve means maintaining the pressure of fuel delivered to said throat section in fixed relationship to the air pressure at said air inlet port;
an airtight fluid moving means having an outlet sealed to said combustion chamber and a cylindrical inlet sealed and in fluid communication with said venturi throat section, said fluid moving means inlet having a diameter significantly larger than said venturi throat section and a distribution plate with small openings defining its outlet, said airtight fluid moving means operable to pull said fuel and air through said proportioning means at a pressure less than atmospheric and subsequently mix said fuel and air into a mixture which is combustible when said mixture impacts and is forced through said openings in said distribution plate and enters said combustion chamber, said airtight fluid moving means and said proportioning means effective to maintain a steady state efficiency of operation of approximately 95% over a range of said burner operation of anywhere between 10,000 and 120,000 BTU's per hour.
a tank adapted to contain a body of fluid to be heated;
a sealed combustion chamber disposed within said tank having an inlet opening and an exhaust aperture;
an exhaust gas exit tube connected to said exhaust aperture and exiting said tank;
a burner disposed within said combustion chamber receiving a combustible mixture of fuel and air from said combustion chamber inlet opening and means for igniting said combustible mixture within said combustible chamber;
proportioning means remote from said combustion chamber for drawing a metered amount of fuel and air therethrough, said proportioning means including regulator means and a venturi, said venturi having an air inlet section of a first cross-sectional area in communication with a source of air, a venturi throat section of a second cross-sectional area smaller than said first cross-sectional area and a transition section therebetween, said throat section having a fuel aperture in the wall thereof, said regulating means metering a precise amount of fuel through said fuel aperture into said throat section in fixed proportion to the amount of air flowing through said proportioning means and including an air inlet port connected by an airtight tube to said inlet section of said proportioning means, a fuel outlet port connected by a fuel-tight tube to said fuel aperture and valve means maintaining the pressure of fuel delivered to said throat section in fixed relationship to the air pressure at said air inlet port;
an airtight fluid moving means having an outlet sealed to said combustion chamber and a cylindrical inlet sealed and in fluid communication with said venturi throat section, said fluid moving means inlet having a diameter significantly larger than said venturi throat section and a distribution plate with small openings defining its outlet, said airtight fluid moving means operable to pull said fuel and air through said proportioning means at a pressure less than atmospheric and subsequently mix said fuel and air into a mixture which is combustible when said mixture impacts and is forced through said openings in said distribution plate and enters said combustion chamber, said airtight fluid moving means and said proportioning means effective to maintain a steady state efficiency of operation of approximately 95% over a range of said burner operation of anywhere between 10,000 and 120,000 BTU's per hour.
10. The burner of claim 9 wherein said valve means further includes first and second diaphragms, said first diaphragm controlling the flow of fuel to said fuel aperture said second diaphragm regulated by the pressure of said air tube on one side and a bleed passage from said fuel output on its opposite, the position of said second diaphragm controlling the position of said first diaphragm whereby gas supply pressures down to zero can be regulated by said valve means with minimum hunting of said valve means.
11. The burner of claim 10 wherein said burner includes a cylindrical burner ring having a bottom end secured to said distribution plate and a top end, a cylindrical burner screen of fine mesh welded to said top end of said cylindrical burner ring, an end cap welded to the top of said burner ring, three vertical plates extending from said distributor plate to said end cap and radiating from the center of said distribution plate to divide said burner into three compartments for reducing the noise of said combustible mixture of said fuel and air within said burner, an igniter adjacent said burner ring, and one of said vertical plates having a tab protruding therefrom to direct a portion of said combustible mixture of fuel and air through a portion of said burner screen adjacent said igniter.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US83299286A | 1986-02-26 | 1986-02-26 | |
| US832,992 | 1986-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1311975C true CA1311975C (en) | 1992-12-29 |
Family
ID=25263133
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000530541A Expired - Lifetime CA1311975C (en) | 1986-02-26 | 1987-02-25 | Forced draft controlled mixture heating system using a closed combustionchamber |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1311975C (en) |
| GB (1) | GB2186962B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ITTO20050818A1 (en) * | 2005-11-18 | 2007-05-19 | Cosmogas Srl | GAS HEATING SYSTEM WITH BURNER WITH PRE-LOADING PARTICULARLY A BOILER FOR HOUSEHOLD USE |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3741710A (en) * | 1971-12-20 | 1973-06-26 | L Nelson | Combustion control valve means and system |
| GB1537239A (en) * | 1976-03-12 | 1978-12-29 | British Gas Corp | Apparatus for flow-ratio control of gaseous fluids |
| GB1565310A (en) * | 1977-12-01 | 1980-04-16 | Battelle Development Corp | Method and apparatus for controlling fuel to oxidant ratioof a burner |
| US4588372A (en) * | 1982-09-23 | 1986-05-13 | Honeywell Inc. | Flame ionization control of a partially premixed gas burner with regulated secondary air |
| EP0110071B1 (en) * | 1982-10-19 | 1988-12-28 | Stordy Combustion Engineering Limited | Flow regulating device |
| US4645450A (en) * | 1984-08-29 | 1987-02-24 | Control Techtronics, Inc. | System and process for controlling the flow of air and fuel to a burner |
-
1987
- 1987-02-11 GB GB8703116A patent/GB2186962B/en not_active Expired - Fee Related
- 1987-02-25 CA CA000530541A patent/CA1311975C/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB2186962A (en) | 1987-08-26 |
| GB8703116D0 (en) | 1987-03-18 |
| GB2186962B (en) | 1990-03-21 |
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| MKEX | Expiry |