Abstract:
A water heater including a water container, a combustion chamber adjacent the water heater, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, a flue having an upper portion and a lower portion operatively connected to the combustion chamber and extending through at least a portion of the water container, and a catalytic converter located in the upper portion of the flue. The water heater may also reduce NO x  and CO emissions generated by a water heater having a radiant burner including activating the burner in response to the temperature of water in the water heater as needed, and substantially removing accumulated foreign matter on the burner by periodically activating the burner irrespective of the water temperature for a selected amount of time.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to water heaters, in particular, water heaters that produce low levels of carbon monoxide.  
       BACKGROUND  
       [0002]     The increasing utilization of burners that achieve lower and lower levels of NOx emissions oftentimes does not promote complete combustion of the fuel. This can result in production of higher levels of CO, which is undesirable. Also, new high efficiency or low emission burners utilize small ports and oftentimes act as filters. Over time, such burners may become covered with or subjected to the presence of lint, dirt, oils and the like that are normally found in residential and commercial environments. As the small ports fill with such extraneous material, the levels of CO may increase.  
         [0003]     Economic and effective solutions to the presence of CO generated by water heaters have not been entirely successful.  
         [0004]     Also, the HVAC, water heater and small appliance industries are continuously updating product designs to meet more stringent combustion emission, energy efficiency, and safety (flammable vapor and lint, dirt and oil resistant) requirements. To achieve these requirements, new burner technologies are being utilized that replace older burner technologies.  
         [0005]     The new burner technologies typically utilize significantly reduced port size to achieve desired performance improvements. Unfortunately, these smaller ports may collect foreign materials (such as lint, dirt or oil aerosols) present in the air drawn into the combustion system. As these materials collect on or in the burner ports over time, the performance of the burner may degrade, resulting in higher emissions of carbon monoxide, nitrogen oxides, and overall lower efficiency.  
         [0006]     One way of reducing this problem is to utilize a filter on the incoming combustion air. However, such filters add extra cost and often add significant pressure drops that either cannot be overcome or necessitate use of fans or blowers.  
         [0007]     Some of the new burner technologies unload a portion of the foreign materials that collect in the ports during burner ignition. The unloading process is due to the large, short duration local pressure and velocity gradients achieved during initial ignition of the combustion gas (typically natural gas or propane). The local pressure and velocity gradients create pressure and friction forces that dislodge some portion of the foreign materials from the burner ports, allowing the burner to return to, or approach, the original “as new” condition.  
         [0008]     Additionally, in some of the new burner designs, the flame holder material containing the small ports operates at a high temperature while the burner is operating. When the burner is shut off, the flame holder temperature rapidly drops, approaching ambient temperature. The rapid rise and fall of the flame holder temperature creates thermal movement and stresses in the flame holder, causing the foreign materials to loosen or fall off.  
       SUMMARY OF THE INVENTION  
       [0009]     This invention is in one aspect directed to a water heater that includes a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, a flue having an upper portion and a lower portion operatively connected to the combustion chamber and extending through at least a portion of the water container, and a catalytic converter located in the upper portion of the flue.  
         [0010]     In another aspect, the invention is directed to a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, a substantially vertically oriented flue extending through the water container and having an upper portion opening at the top of the water container and a lower portion opening into the combustion chamber, a baffle positioned in the flue, and a catalytic converter connected to the baffle and located in the upper portion of the flue and adapted to convert at least a portion of CO flue gases generated in the combustion chamber to CO 2 .  
         [0011]     In still another aspect, the invention is directed to a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, a substantially vertically oriented flue extending through the water container and having an upper portion opening at the top of the water container and a lower portion opening into the combustion chamber, a baffle positioned in the flue, and a catalytic converter formed on at least a portion of the baffle and located in the upper portion of the flue and adapted to convert at least a portion of CO flue gases generated in the combustion chamber to CO 2 .  
         [0012]     In yet another aspect, the invention is directed to a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber and arranged to combust fuel to heat water in the water container, a substantially vertically oriented flue extending through the water container and having an upper portion opening at the top of the water container and a lower portion opening into the combustion chamber, a baffle positioned in the flue, and a catalytic converter connected to a removable and elongated baffle comprising a plurality of flow turbulating fins positioned in the flue, wherein the catalytic converter is formed from wound corrugated stainless steel foil coated with a metal catalyst connected to the baffle and located in an upper quartile of the flue such that the metal catalyst facilitates conversion of at least a portion of flue gases generated in the combustion chamber to CO 2 .  
         [0013]     This invention further relates to a water heater including a water container, a combustion chamber adjacent the water container, a burner associated with the combustion chamber, a temperature sensor associated with the water container, a controller that actuates the burner in response to water temperature detected by the temperature sensor and periodically actuates the burner irrespective of water temperature to decrease possible accumulation of foreign materials on the burner.  
         [0014]     This invention still further relates to a method of reducing NO x  and CO emissions generated by a water heater having a radiant burner including activating the burner in response to the temperature of water in the water heater as needed, and substantially removing accumulated foreign matter on the burner by periodically activating the burner irrespective of the water temperature for a selected amount of time. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood that this invention is not limited to the precise arrangements and instrumentalities shown.  
         [0016]      FIG. 1  is a schematic front elevation view of a water heater, taken partially in section, for ease of understanding in accordance with aspects of the invention.  
         [0017]      FIG. 2  is a top plan view of a catalytic converter utilized in accordance with aspects of the invention.  
         [0018]      FIG. 3  is a front elevational view of a portion of a baffle and catalytic converter in accordance with aspects of the invention.  
         [0019]      FIG. 4  is an inverted perspective view of a draft hood and debris catcher in accordance with aspects of the invention.  
         [0020]      FIG. 5  is a top plan view of the draft hood and debris catcher shown in  FIG. 4 .  
         [0021]      FIG. 6  is a schematic partial sectional view of a water heater in accordance with other aspects of the invention and having a radiant burner. 
     
    
     DETAILED DESCRIPTION  
       [0022]     It will be appreciated that the following description is intended to refer to specific embodiments of the invention selected for illustration in the drawings and is not intended to define or limit the invention, other than in the appended claims.  
         [0023]     Turning now to the drawings generally and  FIG. 1  in particular, one aspect of the invention is disclosed. A water heater  10  includes a water tank/container  12  having a water inlet  14  and water outlet  16 . A substantially vertically oriented flue  18  extends upwardly through the tank and outwardly of the top of the water heater  10  at opening  20 . The top of water heater  10  is covered with a top pan  22  and has a draft hood  24  resting on top of it. Draft hood  24  also is aligned with opening  20 . Flue  18  contains an elongated baffle  26  having a multiplicity of flow turbulating fins  28 . Baffle  26  extends substantially from the upper end of tank  12  to the lower end of tank  12  although other lengths of baffle  26  may be employed. The lower end of tank  12  has an opening  30  formed from tank bottom  32 . A catalytic converter  34  is also located within flue  18  and resides in an upper portion of flue  18 . Catalytic converter  34  connects to baffle  26  and is sized and shaped to slide into flue  18  and have a substantially similar yet slightly smaller diameter as flue  18 . Baffle  26  may be made from any number of materials such as carbon steel, stainless steel, aluminized steel and the like.  
         [0024]     Water heater  10  has an outer jacket  36  that surrounds a layer of insulation  38 . Insulation  38  is preferably made from any number of foam type of insulations well known in the art and/or fiberglass insulation such as around the lower portion of water heater  10 .  
         [0025]     A combustion chamber  40  is located below tank  12  and is formed by tank bottom  32 , skirt  42  and bottom pan  44 . Legs  46  connect to top pan  44  and support water heater  10 .  
         [0026]     A burner  48  is positioned within combustion chamber  40  and above at least one opening (not shown) in bottom pan  44 . The opening may be covered with an air inlet/flame trap such as an air inlet/flame type trap of the type disclosed in any of U.S. Pat. Nos. 5,797,355; 6,142,106 and 6,085,699, for example. Similarly, burner  48  can be of any type well known in the art including standard stamped sheet metal steel burners, low NOx burners, radiant heat burners or the like.  
         [0027]     Of course, water heater  10  includes other components not described or shown herein that assist in its operation. Those components are well known in the art and need not be discussed herein.  
         [0028]      FIG. 2  shows one preferred catalytic converter  34  in accordance with aspects of the invention. Catalytic converter  34  is preferably a substantially round disc formed from wound corrugated stainless steel foil. The corrugations preferably form “cells” in a range of between about 10 cells and about 100 cells per square inch. Preferably, the number of cells is at a density of about 40 cells per square inch. Also, the disc is preferably between about ⅛ inches and 4 inches in thickness, most preferably about 1 inches in thickness. It is advantageous to have the catalytic converter facilitate substantially laminar flow of flue gases through flue  18 .  
         [0029]     The stainless steel of catalytic converter  34  is preferably wash coated with one or more coatings of the oxide type such as aluminum oxide, zirconium oxide and titanium oxide, or the like. A catalyst metal is applied to the wash coating, the catalyst preferably being platinum metal, although other catalyst metals may be employed. Alternately, the catalyst converter can be made of a stainless steel that has a high aluminum content such as aluminum content of between about 4.3 percent and about 6.0 percent. The stainless steel having the high aluminum content is then also coated with a catalyst metal such as platinum or the like.  
         [0030]     Catalytic converter  34  preferably converts carbon monoxide (CO) into carbon dioxide (CO 2 ). Catalytic converter  34  preferably converts about 20 percent to about 100 percent of CO in flue gases generated in the combustion chamber to CO 2 . This results in a very low quantity of CO flowing out of water heater  10  even when high quantities of CO are generated in combustion chamber  40  under the least desirable conditions.  
         [0031]     As shown in all of  FIGS. 1, 2  and  3 , catalytic converter  34  is positioned in flue  18  and connects to baffle  26 . Catalytic converter  34  may also be connected to flue  18  or suspended in flue  18  by means other than baffle  26  if desired. Catalytic converter  34  is positioned in an upper portion of flue  18 , that upper portion meaning the upper half of flue  18 , as opposed to the lower half of flue  18 . Baffle  26  has a lower portion with a plurality of fins  28  and an upper leader portion  50  as particularly shown in  FIG. 3 . Leader  50  has a pair of arms  52  that support baffle  26  in flue  18 . Arms  52  hang on the edge of opening  20  of flue  18 . This allows baffle  26  and catalytic converter  34  to be readily removed from flue  18  if desired.  
         [0032]      FIGS. 4 and 5  show draft hood  24  removed from water heater  10 . Draft hood  24  has a plurality of legs  54  that preferably connect to top pan  22  and are used to center draft hood  24  over opening  20 . Draft hood  24  connects to an exhaust line (not shown) in a conventional manner to exhaust flue gases from water heater  10  into a chimney, a wall opening or the like to the outer atmosphere. Draft hood  24  also contains a debris catcher  56  which has a “bowl” or “umbrella” shape such that debris falling downwardly toward flue  18  can be caught and then collect in a lower most portion of debris catcher  56 . Debris catcher  56  has a diameter that is preferably substantially the same as the diameter of flue  18  or slightly larger to prevent debris from falling into flue  18  and fouling catalytic  34  or falling down toward and onto burner  48  which, depending on the type of burner, could decrease the performance/efficiency of burner  48 . Debris catcher  56  connects to draft hood  24  by a plurality of legs  58 . Debris catcher  58  is preferably made from a material that is non-corrosive to both moisture and elevated temperatures.  
         [0033]     We discovered that it is advantageous to locate catalytic converter  34  in an upper portion of flue  18 , preferably in the upper quartile, more preferably in the upper quintile of flue  18 . The construction of catalytic converter  34  should be such that the pressure drop through converter  34  is low enough not to impede the flow of flue gases through flue  18 , especially for natural draft water heaters. As previously noted, metallic structures such as stainless steel structures for catalytic converter  34  are more desirable due to the inner wall thicknesses that provide for more open flow areas.  
         [0034]     The structure of catalytic converter  34  should have enough active surface area to be able to convert sufficient amounts of CO to CO 2 . The surface area of the honeycomb structure is determined by the cell count (cells per inch) and cell length and accordingly should be about 40 cells per inch and have a cell length (of thickness of the catalytic converter disc  34 ) of about ½-1 inches. This structure also facilitates laminar flow of the flue gases flowing through flue  18  to maximize water heater performance.  
         [0035]     We also discovered that it is advantageous to have catalytic converter  34  function at an appropriate temperature which is from about 600° F. to about 1100° F. This temperature range was discovered to be in the above-mentioned upper portion of the water heater, preferably the upper quartile.  
         [0036]     We also discovered that the catalytic converter can be in the form of a coating applied to baffle  26  and have high effectiveness. Application of a coating of platinum to baffle  26  is especially advantageous. The platinum coating is better adhered to baffle  26  by first wash coating with aluminum oxide, zirconium oxide, titanium oxide, some combination of those elements or the like. The coating provides the additional advantage that standard baffle dies used to fabricate baffle  26  may continue to be used instead of specialized dies.  
         [0037]     The catalytic converter coating should have enough active surface area to be able to convert sufficient amounts of CO to CO 2 . Coverage of baffle  26  depends on the size and shape of baffle  26 . This approach has the further advantage that it does not disturb the natural flow of flue gases flowing through flue  18 , thereby maximizing water heater efficiency.  
         [0038]     One aspect of this invention artificially creates extra burner cycles (more than those created by the load on the appliance) to reduce accumulation of foreign materials in the burner ports and increase burner performance. The manner of creating the extra burner cycles includes, but is not limited to, solid state times in electronic controlled applications and mechanical timers in mechanical thermostat type controllers triggered by: pressure, bi-metal thermostats or time delay relays. The exact time of extra burner cycles depends upon the application and burner technology utilized.  
         [0039]     We have discovered a water heater that utilizes a wire mesh radiant pre-mix burner that consistently achieves low NOx emissions. Water heaters with inputs less than 75 kbtu must pass stringent test requirements, including a lint, dirt and oil (LDO) test that simulates the accumulation of LDO in the burner over a twenty year period during a nominal 20 hour test. Testing has shown that these burners, if cycled often during the test (every 10-15 minutes), continue to operate close to the “as new” performance levels. If the burner is not cycled regularly, burner performance drops significantly, resulting in high concentrations of carbon monoxide and nitrogen oxides in the flue gas. Gas valve controls can be equipped with electronic controls, powered either by the residential electric supply, or by thermopiles producing mV electrical power from the pilot burner. Such electronic control technologies can be adapted to cycle the burner more often than the ON-OFF cycles created by the actual demand for hot water. Additionally, convenience mechanical thermostat controls can be adapted with timing devices that add the additional burner cycles.  
         [0040]     For example, the average burner ON period for a residential water heater is 20 minutes. When equipped with a timing device in the control, the burner can be cycled one or more times within the 20 minute period to ensure the burner ports remain clear of foreign materials. The duration of the burner OFF period can be very short, such that the consumer does not notice a drop in the delivered hot water.  
         [0041]      FIG. 6  shows a water heater that in some aspects is similar to the water heater shown in  FIG. 1 . Like elements in  FIG. 6  have the same reference number as  FIG. 1 .  
         [0042]     The water heater  10  in  FIG. 6  includes a radiant screen gas burner  126 . Although  FIG. 6  depicts a particular type of radiant screen burner, other radiant burners of this type, including various pre-mix radiant burners, may be used. Burner  126  connects to a venturi  44  that receives fuel from fuel supply line  28  as well as combustion air. Fuel and combustion air mix as they pass through venturi  44 , enter burner  126  and ignite on the upper surface of the screen  125  at the top of burner  126 .  
         [0043]     As shown in  FIG. 6 , gas control valve  30  contains a controller and the controller actuates burner  126  in response to water temperature detected by a sensor on an as-needed basis. Of course, the controller can be programmed or pre-programmed to actuate the burner at various selected temperatures.  
         [0044]     The controller also periodically actuates burner  126 , irrespective of the water temperature. This periodic actuation decreases the possible accumulation of foreign materials on the radiant screen of the burner  126 . The controller may periodically actuate burner  126  at a selected time interval such as, for example, about every one hour or three hours or four hours, as desired. The actuation period for such periodic actuation can be very short, such as about a minute or two or the like. Also, it is possible that, in the event the burner is activated for longer than the selected time period, the controller deactivates the burner for another selected period of time, followed by reactivating the burner. The selected period of time may be about 10 sec or thereabout, while the another selected time period may be about 30 sec or thereabout.  
         [0045]     Alternatively, the controller can actuate burner  126  at a selected time when burner  126  has not been actuated in response to water temperature for a selected period of time. In other words, if burner  126  has not operated for a period of time, such as about one or two or three hours, the controller can actuate burner  126  after the passage of a selected period of time.  
         [0046]     Operation of the periodic burner cycles assists in decreasing the potential accumulation of foreign materials on the surface of the burner, thereby keeping the surface of the burner in as close to “as new” condition as possible by avoiding the collection of lints, dirt, oil and the like within the pores or openings in the screen surface. This keeps generation of NO x  and CO as low as possible.  
         [0047]     For example, water tank  16  may be made of a number of sizes and may be made from a wide variety of materials such as metals and/or plastics. Foam insulation  14  may similarly be made from any number of high energy efficient foam insulations well known in the art.  
         [0048]     The bottom of the water tank  16  may have various shapes, either with lower flanges as shown or as a flat construction. Other modifications may be made, including use of foam insulation between the bottom of tank  16  and bottom pan  20 . Also, outer jacket  12  may be made from any number of materials such as rolled metals, preferably steel, or extruded vinyl materials and the like. Also, top pan  18  and bottom pan  20  may be deep-drawn, stamped or the like, or be made from metal, plastic or other suitable materials. Various types of heating elements may be utilized.  
         [0049]     The adjustment temperatures for the set point and the conditions necessary for set point adjustment are fully variable and the values used herein are examples for illustration purposes only. One skilled in the art will note that many set point usage combinations are possible without varying from the spirit and scope of the invention.  
         [0050]     Although this invention has been described in connection with specific forms thereof, it will be appreciated that a wide variety of equivalents may be substituted for the specified elements described herein without departing from the spirit and scope of this invention as described in the appended claims.