CA2130963A1 - Controlled heat input combustion-type water heater - Google Patents

Abstract

A forced draft gas-burning water and/or space heater is provided in which overheating and vaporization are reduced or prevented by a blower adjustment to deliver fuel at a variable and controlled rate to a combustion chamber to allow the burner to produce a preselected heat output. The burner heat output is regulated by control circuitry in response to the rate at which hot water is withdrawn from the tank and cooler incoming water creates a demand for heat.

Description

xpress Mail Label TB577482884US
21 ~0963 -CON~ROLLED ÆAT INPUT COMBUSllON-lYPE WATER ~IEATER
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The present invention relates generally to water heaters and more particularly to - a water heater using a forced draft combustion system which reduces loc~li7e-1 S overh~tin~.
Background of the I~ lion Highly fuel efficien~ gas burning water heaters are often provided with powered or forced draft combustion systems. Such combustion ~y~le~s employ a blower for forcing the gas/air combustion mi~cture to the burner and into the combustion chamber of 10 the heating appliance.
High efficiency power assisted water heating appliances are disclosed in U.S. Pat.
No. 4,766.883 to Cameron et al and in U.S. Pat. No. 5,085,579 to Moore, Jr. et al, which patents are assigned to the same assignee as that of the present application. The disclosure of Patent Nos. 4,766,883 and 5,085,579 is incorporated herein by reference.
lSMoore 5,085,579 discloses a water heating apparatus in which a combustible gas/air mixmre is introduced into a blower which moves the mixture under pressure into a vertically extending tubular burner within a closed combustion chamber contained within a tank cont~ining water. The products of combustion exit the combustion chamber - and pass through a helical tube of several turns within the body of water. The heat of 20 combustion is extracted from the products of combustion by conduction through the walls of the combustion chamber and the helical exhaust tube. A high efficiency water heater thereby results.
The heated water from the water heater may also be 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 25 home ventilation or heating system.
Large amounts of energy can be generated by burning a pressunzed mixture of fuel i 3 0 ~
and air. Furthermore, as the burner and exhaust tubes are almost entirely ~ ounded by water to be h~ted, most of the ~ generated by the burner is quic,kly L~.r~l~ to the ~ o~ n~ water. While this configuratdon results in a highly efficient water heater, it can also create problems which decrease the theoredcal efficiency of the system.
Heat flows so rapidly from the burner and e~haust tubing to the ~urloullding water that some regions within the tank may be heated locally to a higher temperature than is called for before a thermostat can deactivate the burner. In some cases, the overhe~tin~
may be sufficient to vaporize portions of the water re~l-lting in the generation of ste~m.
Overhe~tin~ the water is inefficient because extra fuel is consumed to heat the water to an excessive temperature. It can also cause noise as small bubbles of vapor form and collapse. Moreover, when steam is produced, it must be vented to prevent pressure from building up within the tank. This releases energy to the surrol-n~lin~s which could have been used to heat the water. The overheating and vaporization of water both prevent a forced draft combustion system from operating at its maximum efficiency.
lS The rate at which hot water is drawn from the tank determines the rate at which cool, replacement water in the tank must be heated and, hence the rate of production of energy. If the water in the tank is heated too quickly, regions of water in the tank may overheat or vaporize. If the water is heated too slowly, hot water will not be available to replace the water being withdrawn from the tank. Thus, a water heater used to supply large quantities of hot water must heat water more rapidly than a water heater which is required to produce a lesser quantity of hot water. A purchaser of a water heater must select a model adequate to supply maximum normal hot water requirements. Water heaters are generally available in a limite~ number of different sizes. This often means obt~ining an overcapacity model that heats water at a faster rate than needs require. Use of a water heater which heats water more quickly than necess~ry to replace hot water - being used can contribute to the ove.l.c~ and v~po~ on problem~ mentioned above.
It is not pr~c~ic~l, however, to stoclc ~o7~n.C of dirre,ent mo le!c each suited to a narrow range of supply rates; th~refore, the ineffici~r~ries associated with using a system which heats at too high a rate have been impractical to avoid.
S Objectc of the IL.~lion It is an object of the invention to provide an efficient water heater capable ofregulating variable energy input in response to the need.
It is another object of the present invention to provide a water heater which pre-vents portions of water within a tank from being overhe~te~l or vaporized even when water is withdrawn, replaced and heated at a high rate.
It is another object of the present invention to provide an efficient water heater which avoids overheating or vaporizing water within a tank and consumes less energy than other water heaters.
It is yet another object of the present invention to provide a water heater which heats water at a variable rate which varies in response to changes of the rate at which water is withdrawn from the tank.
It is a further object of the present invention to provide a water heater which is capable of generating heat at a predeterrmined precise rate.
These and other objects and advantages of the invention will become apparent from the following detailed descripdon when read in conjunction with the drawings.
S-lmm~-y of the Invention The invention is directed to a new and improved apparatus which overcomes the problems associated with existing water heaters and provides a gas-burning water heater with variable heat input and which minimi7es the overheating and/or vaporization of water in the tank.

21~0963 - - In accordance with the ~ t invention,- a h-o~tin~ apparatus is provided which generates a variable amount of e~r~ based on variadons of hot water re~ ents of the user. The amount of energy generated by the burner is controlled by reguladng the rate of supply of gas-air mi~cture into the burner. This is achieved by a variable speed S blower, a pre~lete~ ,.,ill~1 ~rate being obtainable by accurately setdng the blower speed at the factory. Very precise setting~ can be achieved by using a strobe light, for e~ample, to time the blower speed. Accordingly a burner is provided which efficiently heats water at a controlled rate commensurate with the rate at which hot water is, at any moment, being withdrawn from the tank. If desired, the blower speed adjustment mech~ni.~m can 10 be disabled after being set at the factory so that the blower m~int~in.c the preset speed and heat is supplied to the water at a constant rate.
In another embodiment, the blower speed may be adjusted during operation by control circuitry in response to changes of the rate at which hot water is withdrawn from the tank. The burner thereby heats the water more rapidly when hot water is being lS withdrawn at a high rate, and heats more slowly along with slow withdrawal.
Brief Description of the Dr~wings FIGURE 1 is a side elevational view, partially in vertical section, of a water heater embodying features of the invention; and FIGURE 2 is a schematic perspective view of a blower apparatus operative in 20 combination with the water heater shown in FIGURE l.
Det~i1e~1 Descl iylion of the Invention Referring now to the drawings wherein the structures and steps shown are for thepurpose of illustrating preferred embodiments of the invention only and not for the purposes of limitin~ same, the Figures show a water heater A including the usual tank 25 lO supported in an upright position upon a cylindrical base 12. A closed combustion ~1 30963 -~ ~ ch~ml~er- 14 is located at the bottom of tank 10 and defined in part by an upst~n~lin~
cylindrical wall 16, yfefelably st~inl~cs steel, having a stainless steel e~h~lst gas e~it tube 18 at its top. Tank 10 is ~ullou~ded by a layer of in.clll~tion 20 and a protective jacket 22 in the coll~ell~ional manrler.
S When water heater A is in use, tank 10 is filled with a stratified body of water 24 with the coldest water r~m~ining in the bottom portion of the tank and the hottest water rising to the top portion. The water to be heated is introduced into water tank 10 through inlet piping 26 leading through bottom plate 17 of tank 10, preferably of st~inless steel, - and feeding water to an inlet water diffuser 30. Diffuser 30 is a short, closed stainless steel tube secured within tank 10 to bottom plate 17 thereof in a vertical orientation and having apertures 32 along one of its side surfaces through which water is introduced into the tank near its bottom.
Heated water is withdrawn from tank 10 through an outlet tube 34 which is fixed to a fitting 36 penetrating through bottom plate 17 of tank 10, and extends upwardly to an upper region of tank 10. The top of outlet tube 34 is open. Heated water passes through this top end opening into tube 34 and downwardly out of tank 10 and through a hot water outlet 38.
Cold water inlet piping 26 and hot water outlet piping 38 are connected to the water piping of the b~ n~ in which the water heater A is disposed, thereby supplying 20 hot water. They may also be connecte-l through a~proyriate valves to a heat exchanger in a space heatin~ and ventil~ting system to provide heat for the building in accordance with the teachings of the aforementioned Cameron et al U.S. Pat. No. 4,766,883 and Jantana U.S. Pat. No. 4,451,410.
Heat is provided to the body of water 24 from the heat of fuel combustion in 2S combustion chamber 14. The equipment and method of supplying combustion gases to ~ ~ 2130963 - ~ combusdon chamber 14 is described hereinafter with r~f~ ce to a system using natural gas as the input energy source. Other fossil fuels, such as bot~ed yro~ gas and the like can be used with only slight adjustments easily accomplished by those skilled in the art.
S When hot water is withdrawn from tank 10 through outlet tube 34, additional cold water is ~lmitterl into the tank through inlet water diffuser 30. When sufficient cold - water is drawn into tank 10, the temperature drop of the water body 24 is sensed by a water temperature sensor 40. The sensor 40 is conn~cte~l to the electric control circuitry contained in an electrical control box 42. A~pro~-iate control circuitry is well known in the art and will not be described in detail herein.
In response to the re~ ce~ water temperature within tank 10, an electric igniter 44 located within bottom region of combustion chamber 14 is energized. The igniter quickly reaches a temperature sufficiently high to ignite a gas and fuel mixture introduced into combustion chamber 14 from a burner 50 located therein. A blower 52 is automatically energized in a manner further described in detail and a fuel regulator 54 is automatically turned on. Blower 52 draws air from outside the water heater or the vehicle through air inlet tubing 56 into an air and fuel proportioner 58, as described in the above-mentioned Cameron et al U.S. patent, where fuel is introduced to the air stream and mixed with the air. The rnixture is drawn into the body of blower 52 where it is pressurized and mixed further. A homogeneous air and fuel mixture results. This mixture is burned in burner 50 to heat the water in tank 10. The combustion product is vented through exhaust tubing 18, which, as shown, winds through the water in tank 10 so that further heat from the exhaust gases can be transferred to the water.
To subst~nti~lly prevent loc~li7e~1 regions within tank 10 from being overheatedwhen burner 50 is activated, water heater A further includes the ability to provide precise -- capacity selecdon. Blower 52 is one in which the air and fuel intake is near~the center portion of the blower body and its output is on the outer ~,i~h~l~ of the blower. The presauli~ed and homogenized air and fuel mi~cture from blower 52 is directed through output horn 60 of the blower and into the bottom end of burner 50 within combustdon S chamber 14 through a sealed burner inlet opening 62 centrally located in bottom plate 17 of tank 10.
Blower 52 is powered by a variable speed motor 53, which includes a speed control 101 comprising a variable resistor in series with power supply line 105. The resistance of speed control 101 is varied by means of an adjusting screw 107, as shown 10 in FIGURE 2. Varying the resistance in power line 105 varies the voltage supplied to motor 53 (which may be a DC brushless motor) which in turn affects the speed of blower 52 and the amount of fuel supplied to burner 50. The speed of motor 53 can be accurately pre-set at the factory, if desired, by turning screw 107 while mor~itoring the motor speed through an opening 103 in the motor cover using a standard strobe timing 15 light, for e~ample. Screw 107 may be fixed in the desired position with a drop of adhesive or solder (not shown). In this manner, the heat generation rate of burner S0 can be accurately controlled so that the overheating and vaporization problems men~ioned above are minimi7e~1 or prevented entirely.
In aCcor-iance with this invention the rate at which burner 50 heats the water can 20 be controlled in response to the demand to reduce overheating. It will, therefore, be appreciated that by employing a precisely controlled burner, the problems of overheating and vaporization are greatly re~ ce~l without significantly altering the energy used by the water heater.
In an alternative embodiment, the rate at which burner 50 heats the water 24 may25 be adjusted automatically to correspond to the rate at which hot water is drawn &om tank 10 through outlet tube 34 and hot wateF outlet 38. When the hot water wi~ l rateis increased the blower speed is coll~spo~ gly increased to provide ~ itional fuel and air to burner 50. This causes the illCo~iL~g cold water to be heated rapidly. Bec~lse of the large flow rate of cold water entering tank 10 when hot water is being drawn off S rapidly, overh~7n~ is not a signific~nt problem. When little or no hot water is being withdrawn, the blower speed is decreased autom~*c~lly so that burner 50 heats the ~urrounding water more slowly.
An ~l.r~pliate blower speed is deterrnined by monitoring either the volume of water passing through hot water outlet 38 or the temperature of the water. A sensor 37 in hot water outlet 38 provides information on temperature or flow rate to control box 42 through a cable 39. When the volumetric flow rate of hot water being withdrawn is large, control box 42 signals speed control 101 through a cable 104 to increase the blower speed. When hot water is being withdrawn at a lower rate the blower speed is decreased to avoid overheating the water. In a similar manner, sensor 37 may be connected to sense the temperature of the water in outlet 38. ~hen the temperature sensed by sensor 37 falls below the water temperature which tank 10 is supposed to provide, control box 42 signals speed control 101 to increase the blower speed and heat the water more rapidly. When the water in the hot water piping rises above a preset temperature, the blower speed is decreased to prevent overhP~*ng. In conjunction with temperature sensor 40, which signals control box 42 to turn burner 50 on and off based on the temperature of the water in tank 10, sensor 37 facilitates the production of hot water having a consistent temperature.
From the above description, it will be evident that this invention provides an improved water heater which minimi7es loc~li7e~1 overhe~tin~ and vapori_ation of water within the tank and thereby increases the efficiency of the water heater. While the 2i3D96~
~_ a~ alus has bee~ described herem for y~L~iular use in a water heater, it sholild be unde~ hat It may be employed as well in other devices m w~ch the loc~li7e~
ov~l.P~ P of water is a problem. Further, bIower 52 rnay be loc~ in a number of alte~tive loc~tion~ and co~L~-lcted in a variety of configurations. Similarly, a wide - S variety of flues or combinations of flues known in the art may be used. Alternatively, burners, water tanks, outer jackets, foam inc~ tion, thermostats, and the like may be sub~LiLu~d for those shown and described.

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Claims (14)

1. A water heater comprising means for containing a body of water to be heated, a burner connected to burn a mixture of fuel and air to generate heat output means for conducting heat from said burner to heat said body of water, and a heat output adjuster connected to said burner for controlling the heat output rate of said burner to said body of hot water.

2. The apparatus of claim 1, wherein said heat output adjuster includes a variable speed blower for regulating the amount of said mixture supplied to said burner.

3. The apparatus of claim 1 including a speed adjuster for setting the speed of said variable speed blower.

4. The apparatus of claim 1 wherein said blower is electrically driven, and including means for supplying a voltage to said blower.

5. The apparatus of claim 3 wherein said speed adjuster comprises means for varying said voltage.

6. The apparatus of claim 4, wherein said means for varying said voltage comprises a variable resistor.

7. The apparatus of claim 3, wherein means are provided wherein said speed ad-juster is disabled after said blower reaches a preselected rate of heat generation in said burner.

8. The apparatus of claim 7 adjusting means are provided for said burner whereinsaid heat output adjuster is responsive to changes in the rate at which hot water is drawn from said tank.

9. A water heater including a water tank, a water inlet, a water outlet, a burner adapted to burn a mixture of gas and air to heat the water within said tank and having a heat output, and means for adjusting the heat output of said burner responsive to changes of the rate at which hot water is drawn from said tank.

10. An apparatus according to claim 9, wherein said means for adjusting the heatoutput of said burner comprises a variable speed blower for providing said mixture to said burner.

11. An apparatus according to claim 10, wherein said variable speed blower includes a speed adjuster for adjusting the speed of said blower.

12. An apparatus according to claim 11 including means for supplying a voltage to said blower and wherein said speed adjuster comprises means for varying said voltage.

13. An apparatus according to claim 12, wherein said means for varying said voltage comprises a variable resistor.

14. A water heater comprising a water tank, a water inlet, a water outlet, a burner having a heat output and comprising a combustion chamber adapted to burn a mixture of gas and air to heat said water within said tank, a variable speed blower having means for supplying a voltage thereto and adapted to supply a mixture of fuel and air to said burner, wherein said variable speed blower includes speed adjustment means for varying the speed of said blower.