Gas water heater

A gas water heater includes a power burner, a flue tube, an exhaust plenum, and a draft hood. The flue tube includes a portion that describes at least a 360° loop. Products of combustion are forced through the flue tube under the influence of the power burner, and enter the exhaust plenum. In the exhaust plenum, the pressure of the products of combustion drops such that the products of combustion flow into the draft hood substantially entirely under the influence of natural convection. In one embodiment, the power burner fires down into the flue tube through a side wall of the water heater, the loop of the flue tube is near the bottom of the water heater, and the plenum is in the top of the water heater.

BACKGROUND

The present invention relates to a gas water heater, and more particularly to a gas water heater that utilizes a power burner and an exhaust plenum to permit natural convection exhaust of products of combustion, or a coiled flue tube, or a combination of power burner, coiled flue tube, and exhaust plenum.

SUMMARY

In one embodiment, the invention provides a water heater comprising a water storage tank having a side, top, and bottom, the tank having a first hole in the side of the tank and a second hole in one of the top and bottom of the tank, a heat exchanger having an inlet end and an outlet end, the inlet end secured in one of the first and second holes and the outlet end secured in the other of the first and second holes, the heat exchanger describing at least a 360° loop between the inlet and outlet ends, and a burner mounted in the inlet end of the heat exchanger to provide a flow products of combustion into the heat exchanger.

In some embodiments, the inlet end of the heat exchanger is secured in the first hole, and the outlet end of the heat exchanger is secured in the second hole, which is in the top of the water heater. In some embodiments, the water heater may also include a plenum in the top of the tank. In such embodiments, the outlet end of the heat exchanger communicates with the plenum such that the pressure of the products of combustion are reduced as they exit the heat exchanger, and the products of combustion exhaust from the water heater substantially entirely under the influence of natural convection.

In another embodiment the invention provides a method of manufacturing a water heater, the method comprising forming a water storage tank having a side, top and bottom, forming a first hole in the side of the tank, and a second hole in one of the top and bottom of the tank, forming a heat exchanger from a straight metal tube by bending the tube to form an at least 360° loop, the heat exchanger having an inlet end and an outlet end with the at least 360° loop in between, securing the inlet end of the heat exchanger in the first hole of the tank, and securing the outlet end of the heat exchanger in the second hole of the tank.

In yet another embodiment the invention provides a method of interfacing a natural convection vent construction with a water heater having a flue and a power burner providing products of combustion to the flue under positive pressure, the method comprising interposing an exhaust plenum between the flue and the natural convection vent construction, lowering the pressure of the products of combustion within the plenum, and permitting the products of combustion to rise out of the plenum and into the natural convection vent construction substantially entirely under the influence of natural convection.

In still another embodiment the invention provides a method for heating water in a water storage tank with a power burner, the method comprising forcing, under the influence of the power burner, products of combustion downwardly in the tank, then turning the products of combustion at least 360° within the tank, then forcing, under the influence of the power burner, products of combustion upwardly in the tank, then expanding the products of combustion to decouple the products of combustion from the influence of the power burner, and then exhausting the products of combustion substantially entirely under the influence of natural convection.

DETAILED DESCRIPTION

FIGS. 1 and 2illustrate a water heater10including a generally cylindrical tank15having a side20, a top25and a bottom30. The illustrated tank15has a longitudinal tank axis35which in the illustrated embodiment is vertical, but could be horizontal in alternative embodiments. In such embodiments with a horizontal longitudinal tank axis35, the tank15is tipped 90° such that what is illustrated as the top and bottom25,30inFIGS. 1 and 2become side walls of the tank15, and the portion of the side20of the cylindrical tank15facing upwardly becomes the top of the tank15. In other embodiments, the tank15may be provided in shapes other than cylindrical.

An insulating jacket40surrounds the tank15. A cold water inlet spud45and a hot water outlet spud50are affixed to the top25of the tank15. Cold and hot water pipes communicate with the inside of the tank15through the respective cold and hot water spuds45,50. A dip tube55extends into the tank15from the cold water inlet spud45to deliver cold water into the tank15. Although the illustrated inlet and outlet spuds45,50are on the top25of the tank15, in other embodiments the spuds may also (or instead) be provided on the side20of the tank15to provide alternative options for connecting the cold and hot water pipes. Having spuds in multiple locations on the water heater helps to accommodate the various cold and hot water pipe connections that may be encountered in various buildings.

Water in the tank15is heated by means of a power burner60, a heat exchanger or flue tube65, an exhaust plenum70, and a draft hood75. Mounted to the side20of the tank15or to the insulation jacket40is an enclosure80that surrounds the power burner60. The power burner60includes a premix burner83extending into the flue tube65, an electric motor85, and a blower90. The burner60creates products of combustion by burning a fuel/air mixture, and the motor85drives the blower90to force the products of combustion into the flue tube65under positive pressure.

The flue tube65includes a straight segment95terminating in an inlet end95aand a straight segment100terminating in an outlet end100a. The flue tube65is substantially fully submersed in the water tank15, with the inlet end95asecured in a hole in the side20of the tank15and the outlet end100asecured in a hole in the top25of the tank15and extending into the plenum70. In other embodiments the inlet end95amay be secured in a hole in the top25or bottom30of the tank15, and the outlet end100amay be secured in a hole in the side20or bottom30of the tank15.

In the illustrated embodiment, the straight segment95extends downwardly into the tank15at an angle Θ of between about 20° and 45° with respect to vertical. The flue tube65then describes a loop105of at least 360° (i.e., there may be multiple loops). Although in the illustrated embodiment, the loop105is about an axis that is substantially perpendicular to the tank longitudinal axis35(i.e., perpendicular to the plane ofFIG. 2), in other embodiments the loop105may be about a different axis, including an axis that is parallel and/or collinear with the tank longitudinal axis35. From the loop105, the straight segment100rises up to the exhaust plenum70within about 10° of vertical (i.e., within a 10° cone around the longitudinal axis35).

With reference toFIG. 3, the flue tube65terminates in the plenum70, which is part of the top25of the water tank15. To facilitate cost-effective manufacturing, the flue tube65extends into the plenum70to the extent necessary (e.g., on the order of ¾″) to weld the flue tube65to the plenum70. In other embodiments, the flue tube65may be made flush with the bottom of the plenum70through a flange or other structural interface between the flue tube65and plenum70. The same holds true for the connection of the inlet end95aof the flue tube65to the water tank15. The inlet end95amay extend out of the tank15to facilitate welding, or may be flush-mounted.

A baffle110is positioned in the straight segment100of the flue tube65to reduce the velocity and pressure of the products of combustion as they approach the outlet end100aof the flue tube65. The shape and length of the baffle110may vary from what is illustrated, provided the basic functionality is met. The baffle110may be designed to reduce velocity and pressure of the products of combustion such that the products of combustion creep over the outlet end100aof the flue tube65and “spill” into the plenum70. Alternatively, the baffle110may include an optional deflector115that directs products of combustion down into the plenum70should the products of combustion have more velocity and pressure, in which case the deflector115prevents the products of combustion from rising directly into the draft hood75. The baffle110may be supported by the outlet100aof the flue tube65and may extend the entire length of the straight segment100down to the top of the loop105. The flow of the products of combustion within the plenum70is represented by the arrows inFIG. 3. In the plenum70, the pressure of the products of combustion drops near or below atmospheric pressure, and the products of combustion are therefore able to rise out of the plenum70and into the draft hood75substantially entirely under the influence of natural convection. In the draft hood75, the products of combustion mix with ambient air (as represented by the additional arrows around the draft hood75).

In this regard, the plenum70and baffle110may be said to uncouple the flow of the products of combustion from the power burner60. In other words, the products of combustion enter the plenum70under the influence of the power burner60, but exhaust from the plenum70without the influence of the power burner60. Thus, the present water heater10can be retrofitted into a Category I venting system despite the fact that the water heater10utilizes a power burner60.

The flue tube65is formed from a single, seamless tube that is bent to include the straight segments95,100and the loop105. The term “seamless” is used herein to describe a tube that includes no circumferential welded joints joining segments of the tube together, and is not intended to exclude tubes that have longitudinal (whether welded or not) seams created by forming the flue tube into a cylinder from a flat or curved sheet of metal. The flue tube65may be formed from a metallic material, such as stainless steel, aluminum, or another suitable material. Because the flue tube65is formed of a single, seamless tube, there are no welding joints between the inlet and outlet ends95a,100a. Weld joints and the material around weld joints are often particularly vulnerable to failure under fatigue, which may arise from the periodic heating and cooling in the normal operation of a water heater. The present invention therefore reduces the likelihood of fatigue failure within the flue tube by using a single seamless tube.

The loop sections105illustrated in FIGS.2and4-7are but a few examples of how the flue tube65may be bent to meet the requirements of the present invention. With reference toFIG. 2, the loop105describes a smooth, unbroken arc of between about 270° and 360°. InFIG. 4, the loop105includes three substantially straight segments120. InFIG. 5, the loop105includes five substantially straight segments125. InFIG. 6, the loop105includes a U-shaped portion130and substantially straight segment135. InFIG. 7, the loop105includes four substantially straight segments140. In each of FIGS.2and4-7, the segments of the loop105and the straight segments95,100are joined with transitional radiused corners145for smooth flow. The radiused corners145on either side of the substantially straight segment140at the bottom of the loop105inFIG. 7describe arcs of about 90°, while the other radiused corners in the embodiments of FIGS.2and4-7describe smaller arcs.

The flue tube65provides the same efficiency as other heat exchangers but with less heat transfer area due to the turbulent flow of combustion gases through the flow pattern. The loop105of the flue tube65provides a longer flow path for combustion gases which leads to a higher level of heat transfer, and higher thermal efficiencies when compared to U-shaped or straight flues. Since this type of heat exchanger eliminates the need for a dry combustion chamber, scale and lime buildup is reduced, which extends the life of the tank15. Also, since there is only one flue tube65, there are fewer welds, which may result in lower cost of manufacturing and a longer life. The power burner60may be a low NOx burner that creates NOx emissions of less than 55 ppm, and in some cases less than 20 ppm.

A water heater according to the present invention provides greater tank capacity in a smaller tank and footprint than known water heaters. In one embodiment, for example, the water heater10has a height (measured from the bottom30of the tank15to the top of the draft hood75) of less than 67.5 inches, a tank footprint not greater than 1,020 square inches, and a tank capacity of at least 71 gallons. A water heater in accordance with the present invention may have, for example, an efficiency of at least about 82%.

Manufacturing a water heater according to the present invention includes the steps of forming the water storage tank15, providing a first hole in the side of the tank and a second hole in one of the top and bottom25,30of the tank. While in the illustrated embodiment, the second hole is formed in the top25of the tank15, in other embodiments it might be formed in the bottom30. The heat exchanger65is then formed from a straight seamless metal tube, including the loop105between the inlet and outlet ends95a,100a. The inlet end95ais secured (e.g., welded or fastened via a flange on the inlet end95a) in the first hole and the outlet end100ais secured in the second hole (e.g., is extended into the plenum70). The power burner60is then inserted into the inlet end95aof the flue tube65in order to force products of combustion into the flue tube65. The draft hood is installed on top of the water heater10and communicates with the plenum70. A water heater according to the present invention can replace an existing atmospheric water heater without the need to modify the exhaust structure. Because of the relatively high capacity-to-size ratio of a water heater according to the present invention, the present water heater should be able to retro-fit into the space occupied by most existing gas water heaters without reducing, and in most cases actually increasing, the hot water capacity for the user.