Water heater with reduced localized overheating

A water and/or space heater is provided in which water is circulated to prevent the localized overheating or vaporization thereof.

The present invention relates generally to water heaters and more 
particularly to a water heater which reduces localized overheating of 
water during heating. 
BACKGROUND OF THE INVENTION 
Highly fuel efficient gas burning water heaters are often provided with 
powered or forced draft combustion systems. Such combustion systems 
typically employ a blower for forcing the gas/air combustion mixture to 
the burner and into the combustion chamber of 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 disclosures of U.S. Pat. Nos. 4.766,883 
and 5,085,579 are incorporated herein by reference. 
Moore 5,085,579 discloses a water heating apparatus in which a combustible 
gas/air mixture 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 containing 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 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 alternatively 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 home ventilation or heating system. 
Large amounts of energy can be generated by burning a pressurized mixture 
of fuel and air. Furthermore, as the burner and exhaust tubes are almost 
entirely surrounded by water to be heated, most of the energy generated by 
the burner is quickly transferred to the surrounding water. While this 
configuration results in a highly efficient water heater, it can also 
create problems which decrease the theoretical efficiency of the system. 
Heat flows so rapidly from the burner and exhaust tubing to the surrounding 
water that some regions within the tank may be heated to a higher 
temperature than is called for before a thermostat can deactivate the 
burner. In some cases, the heat may be sufficient to vaporize portions of 
the water resulting in the generation of steam. Overheating 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 surroundings which could have been used to heat water. The overheating 
and vaporization of water both prevent a forced draft combustion system 
from operating at its maximum efficiency. 
These problems are aggravated by the fact that the hottest water in a water 
tank is located near the top of the tank and lower temperature water forms 
a layer near the tank bottom due to the difference of densities of hot and 
cold water. This is normally a desirable occurrence for it allows hot 
water to be drawn from the top of the tank without being mixed with colder 
water from the supply line. 
A high capacity burner of the type contemplated herein can heat cold water 
rapidly enough to overheat or even vaporize a portion of the water in the 
tank. 
The rate at which hot water is drawn from the tank determines the rate at 
which cool water in the tank must be heated and, hence the amount of 
energy that the burner must produce. 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 should, accordingly, select a model adequate 
to supply maximum normal hot water requirements. 
Water heaters are generally available in a limited number of different 
sizes. This often means obtaining an overcapacity model that heats water 
at a faster rate than needs require. Use of a water heater which heats 
water more quickly than necessary to replace hot water being used can 
contribute to the overheating and vaporization problems mentioned above. 
It is not practical, however, to stock dozens of different models each 
suited to a narrow range of supply rates; therefore, the inefficiencies 
associated with using a system which heats at too high a rate have been 
impractical to avoid. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a water heater of the 
power assisted type which prevents portions of water within a tank from 
being overheated or vaporized. 
It is another object of the present invention to provide a water heater 
which reduces the negative effects of temperature layering within a tank. 
It is another object of the present invention to provide an efficient water 
heater which avoids overheating or vaporizing water within a tank without 
requiring substantially more energy to operate than other water heating 
apparatuses. 
These and other objects and advantages of the invention will become 
apparent from the following detailed description when read in conjunction 
with the drawing. 
SUMMARY 
The invention is directed to a new and improved apparatus which overcomes 
these problems and provides a gas-burning water heater which minimizes 
overheating and/or vaporization of water in the tank. 
A water heating apparatus is provided including a small pump which 
circulates water within the tank when the burner is activated so that any 
water separated into layers of different temperature will be mixed. The 
circulating pump operates only when the burner is in operation to take 
advantage of the benefits of mixing of hotter and colder layers. Thus, 
when heat flows into the water from the burner and combustion gas exhaust 
tube, the water circulates in response to activation of the burner to 
prevent uneven heating. The burner can then generate more heat without 
vaporizing the water. 
When the burner is not in operation, the circulating pump is disengaged and 
the hottest water tends to rise toward the top of the tank where it can be 
drawn off in the usual manner. There is less danger of overheating than in 
prior water heaters because substantially less heat flows from the burner 
and exhaust tube to the water when the burner is off. Moreover, because 
the circulating pump only moves water from place to place in the tank, it 
need not be very powerful and does not contribute significantly to the 
amount of energy used by the water heater.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to FIG. 1 wherein the structures and steps shown are for the 
purpose of illustrating preferred embodiments of the invention only and 
not for the purposes of limiting same, FIG. 1 shows a water heater A 
including a water tank 10 supported in an upright position upon a 
cylindrical base 12. A combustion chamber 14 is located at the bottom of 
tank 10 and defined in part by an upstanding steel cylindrical wall 16 
having a steel exhaust gas exit tube 18 at its top. The water tank 10 is 
surrounded by a layer of insulation 20 and a protective jacket 22 in the 
conventional manner. 
When water heater A is in use, with the burner inactivated, tank 10 
normally contains stratified body of water 24 with the coldest water 
remaining in the bottom portion of the tank and the hottest water having 
risen to the top portion. The water to be heated is introduced into water 
tank 10 through inlet piping 26 leading through bottom steel plate 17 of 
tank 10 and feeding water to an inlet water diffuser 30. Diffuser 30 is a 
short, closed 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 the topmost 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 therethrough and out of tank 10 and into a hot water outlet 
38. 
Inlet piping 26 and hot water outlet 38 may be connected to the domestic 
water piping of the building in which the water heater A is disposed, 
thereby supplying hot water. Inlet piping 26 and hot water outlet 38 may 
also be connected through appropriate valves to a heat exchanger in a 
space heating and ventilating 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 combustion chamber 14. The equipment and method of supplying combustion 
gases to combustion chamber 14 is described hereinafter with reference to 
a system using natural gas as the input energy source. Other fuels, such 
as bottled propane gas and the like can be used with only slight 
adjustments to the system easily accomplished by those skilled in the art. 
Both hot water for domestic use and interior space heating may be provided 
by a single heater such as described herein and in the above mentioned 
U.S. Patents to Cameron et al and Jantana. 
When hot water is withdrawn from tank 10 through outlet tube 34, additional 
cold water is admitted into the tank through inlet water diffuser 30. When 
sufficient cold water is drawn into tank 10, the temperature drop of the 
water 24 is sensed by a sensor 40 connected to electric control circuitry 
contained in an electrical control box 42. Appropriate control circuitry 
is well known in the art and will not be described in detail herein. 
In response to the sensor 40, an electric igniter 44 located within bottom 
region of combustion chamber 14 is energized. The igniter quickly ignites 
a gas and fuel mixture introduced into combustion chamber 14 from a burner 
50 located therein. A blower 52 is energized and a fuel regulator 54 is 
turned on. Blower 52, shown in FIG. 2 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 some mixing occurs. 
The air and fuel mixture 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 products are vented through exhaust tubing 18 and out of water 
heater A. Exhaust tubing 18 winds through the water in tank 10 so that 
heat from the exhaust gases is transferred to the water. 
To substantially prevent regions within tank 10 from being overheated when 
burner 50 is activated, water heater A further includes a pump 21 adapted 
to circulate water 24 within tank 10. Pump 21 is activated through a cable 
31 extending from control box 42 which is responsive to a sensor 37 
located in hot water outlet 38, which controls the activation of pump 21 
in response to temperature or flow rate of the outgoing hot water. 
Pump 21 is shown attached to jacket 22. However, it is often preferred to 
mount pump 21 below tank 10. With pump 21 mounted on the side of the tank 
10, a lower tube 23 passes through a lower opening 25 and connects pump 21 
to the body of water 24 inside tank 10. An upper tube 27 connects to pump 
21, runs alongside jacket 22, passes through an upper opening 29 
connecting pump 21 to the body of water 24 within tank 10. Upper tube 27 
may also be positioned between tank 10 and jacket 22 or elsewhere. 
When the pump 21 is located below the tank 10, lower tube 23 and upper tube 
27 may both be arranged to penetrate through the bottom of tank 10. Lower 
tube 23 terminates near the bottom of tank 10 and upper tube 27 terminates 
near the top of tank 10. The tubes and pump are thereby protected within 
the water heater structure. 
Pump 21 is, as stated, connected to electrical control box 42 by line 31 
and is activated whenever blower 52 is energized. This causes the water 
from tubes 23, 27 and 29 to remove and re-introduce water from and into 
tank 10 to circulate the tank water and minimize the likelihood that 
portions of the body of water 24 will be overheated. It is also possible 
for pump 21 to be activated in other ways such as when burner 50 is 
activated, when sensor 40 transmits a desired signal, when fuel regulator 
54 is turned on, and the like. It will be appreciated that moving water 
from one point to another within a tank of water requires little energy 
and that only a small pump is needed. 
Blower 52 is one in which the air and fuel intake is near the center 
portion of the blower body and the output is on the outer periphery of the 
blower. The pressurized and homogenized air and fuel mixture from blower 
52 is directed through output horn 60 of the blower and into the open 
bottom end of burner 50 within combustion chamber 14 through a circular 
burner inlet opening 62 centrally located in bottom plate 17 of tank 10. 
Blower 52 is powered by a motor 53. Motor 53 includes a speed control 101 
in series with power supply line 105. Preferably, blower 52 is a variable 
speed blower wherein the resistance is varied by an adjusting screw 107. 
Varying the resistance in power line 105 varies the voltage supplied to 
motor 53 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 set at 
the factory during assembly of water heater A as shown in FIG. 3 while 
monitoring the motor speed through an opening in the motor cover using a 
standard strobe timing light. In this manner, the heat generated by burner 
50 can be accurately controlled so that the overheating and vaporization 
problems mentioned above are minimized. 
A high capacity pump could be used instead of pump 21 to rapidly circulate 
the water in tank 10 and partially compensate for the use of an 
unnecessarily large burner. Rapidly moving water spends less time in 
contact with the extreme heat of burner 50 and is, therefore, less likely 
to be overheated or vaporized. A pump sufficiently powerful to circulate 
water in this manner, however, has increased energy requirements that 
decrease the efficiency of the system. Conversely, the rate at which 
burner 50 heats the water can be reduced to reduce overheating. This, 
however, results in a lower output of hot water. 
It will, therefore, be appreciated that by utilizing a small circulating 
pump, the problems of overheating and vaporization are greatly reduced 
without significantly altering the energy requirements of the water 
heater. The small pump 21 preferred herein may be of any number of types 
and designs so long as it performs the task of adequately circulating 
water from and into tank 10 in the vicinity of the hot metal surfaces of 
combustion chamber 14 and exhaust tubing 18. 
In another embodiment, the rate at which burner 50 heats water 24 may be 
varied to correspond to the rate at which hot water is drawn from tank 10 
through outlet tube 34 and hot water outlet 38. When large amounts of hot 
water are being drawn from tank 10, the blower speed may be increased to 
provide more fuel and air to burner 50. This causes the incoming cold 
water to be heated rapidly. Because of the large amount of cold water 
entering tank 10 when hot water is being drawn off rapidly, overheating 
may not be a significant problem. When little or no hot water is being 
withdrawn, the blower speed may be decreased so that burner 50 heats the 
surrounding water more slowly. 
The proper blower speed is determined by monitoring either the flow rate of 
water passing through hot water outlet 38 or the temperature of the water, 
or both. 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 
withdrawal rate of hot water is high, control box 42 signals speed control 
101 through a cable 104 to increase the blower speed. When less hot water 
is being withdrawn, the blower speed is decreased to avoid overheating the 
water. In a similar manner, sensor 37 may be adapted to sense the 
temperature of the water in outlet 38. When the temperature sensed by 
sensor 37 falls below the water temperature which tank 10 is intended 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 overheating. 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 we have provided an 
improved water heater which minimizes or prevents localized overheating 
and vaporization of water within the tank and thereby increases the 
efficiency of the water heater. 
While the apparatus has been described herein for particular use in a water 
heater, it should be understood that it may be employed as well in other 
devices in which localized overheating of water is a problem. Further, 
water inlets and outlets may be relocated to various positions on tank 10; 
a single vertically oriented flue extending through the length of tank 10 
may be used; various forms of blowers and locations of blowers may be 
employed, as well. Equivalent elements may be substituted for those 
selected for illustration in the drawings, and parts and directions of 
water flow may be reversed, and certain features of the invention may be 
used independently of other features, all without departing from the 
spirit and scope of the invention, which is defined in the appended 
claims.