Patent Publication Number: US-6698385-B1

Title: Combustion chamber shield for hot water heaters

Description:
TECHNICAL FIELD 
     The present invention relates to a shield for a combustion chamber of a gas-fired hot water heater whereby to provide heat concentration in the combustion chamber and on a lower heat transfer wall of the inner casing and also to reduce heat loss through the skirt and the bottom end of the water heater. 
     BACKGROUND ART 
     With known gas-fired hot water heaters using combustion chambers, there is a substantial heat loss through the lower skirt of the housing which is disposed adjacent the combustion chamber of the water heater and through the lower end portion of the housing. With the new designs of sealed combustions, combustion air is supplied through a vertical duct which is in registry with a supply hole provided in the skirt and therefore the insulation in that area is reduced. Also, the insulation between the lower skirt and the outer casing is not sufficiently thick and this results in heat loss as sealed combustion chambers become very hot. Accordingly, there is excessive heat loss through the skirt and the lower region of the hot water heater housing and the performance or efficiency of the hot water heater is reduced. There is therefore a need to overcome this problem. 
     SUMMARY OF INVENTION 
     It is a feature of the present invention to provide a shield for the combustion chamber of a hot water heater which substantially overcomes the above-mentioned disadvantage of prior art water heaters of this type. 
     Another feature of the present invention is to provide a shield for the combustion chamber of a hot water heater and which shield reduces heat loss through the skirt and outer casing and the bottom end of the hot water heater housing by about 30 to 50 percent over previous designs. 
     According to a further broad aspect of the present invention there is provided a shield for the combustion chamber of a hot water heater wherein the heat in the sealed combustion chamber is concentrated on the lower transfer wall of the inner casing while at the same time reducing heat loss through the skirt and the bottom end wall of the housing. 
     According to above features, from a broad aspect, the present invention provides a shield for a combustion chamber of a hot water heater. The heater has an inner casing for the containment of water to be heated by a combustion chamber disposed under the inner casing. A burner and a pilot are provided in the combustion chamber. A flue pipe extends from the combustion chamber to evacuate combustion gases. An outer casing is secured spaced about the internal casing and insulated therefrom by a thermal insulating material. A support base is provided at a bottom end of the water heater. A skirt is provided about the combustion chamber and spaced internally from a lower end portion of the outer casing. Air passage means is provided to supply air to the combustion chamber. A heat shield, formed of metal, is secured in the combustion chamber and encircles and is spaced about the burner and pilot. The shield is spaced from the skirt. Air aperture means is provided in the shield to permit passage of combustion air supplied through the air passage means. The shield provides heat concentration in the combustion chamber and on a lower heat transfer wall of the internal casing and also reduces heat loss through the skirt and a bottom end of the combustion chamber. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a fragmented side view of a hot water heater having a sealed combustion chamber and illustrates a first example of the construction of the shield of the present invention; and 
     FIG. 2 is a view similar to FIG. 1 but showing a further example of the construction of the shield of the present invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, and more particularly to FIG. 1, there is shown generally at  10  a lower portion of a hot water heater and which illustrates the basic component parts thereof and more particularly its lower combustion chamber  11  which is provided with the heat shield  12  of the present invention. As hereinshown, the hot water heater has an inner casing  13  which is of elongated cylindrical shape and provided with a central flue  14  extending therethrough and exhausting at a top end in a manner well known in the art. Water  15  to be heated is contained within the inner casing  13  and dispensed therefrom, as is also well known in the art. 
     The hot water heater as herein illustrated is a gas-fired hot water heater and its sealed combustion chamber  11  is provided with a burner  16  and a pilot  17  which is provided with an igniter  18  to kick-start the burners  16 . A control  19  controls the burner and is provided with a water temperature sensor  20  to effectuate this control. This is also well known in the art. 
     An outer casing or shroud  21  is secured spaced about the inner casing  13  and an insulated material  22  such as identified by the trade mark Green Foam, registered trade mark of Giant Factories Inc., is injected in this space whereby to provide good insulation between the outer wall  13 ′ of the inner casing and the outer casing  21  which is usually a thin metal sheet cylinder. 
     The hot water heater is supported elevated from a support surface  23  by a support base  24  which is provided with vent holes  25  to provide air circulation under the bottom wall  26  of the housing which is in communication with the combustion chamber  11  which is hereinshown as a sealed combustion chamber, although not essential. Accordingly, it is desirable to have air circulation under this bottom wall. It is further pointed out that the entire hot water heater  10  may be supported elevated by other means such as a platform  23 ′ as shown in FIG. 2, depending on the location of the air intake ports which supplies air for combustion. If the air intake is low, then it is preferable that the combustion chamber be elevated as high as possible from the ground surface  23  in the event that ignitable gas fumes may circulate over the ground surface  23 , whereby to provide added security. The combustion chamber  11  may be a non-sealed combustion chamber wherein air is supplied thereto through the vent holes  25  in the support base  24 . Accordingly, the vertical duct  28 , as will be described later would not be required. As well, the bottom wall  26  would not be required or would have air openings therein. 
     A skirt  27  is disposed about the sealed combustion chamber  11  and spaced internally from a lower end portion  21 ′ of the outer casing  21 . Combustion air is supplied to the sealed combustion chamber by suitable means, and as herein shown by an elongated vertical duct  28 , which is secured at a lower end  29  to the combustion chamber  11 . The vertical duct  28  has a top inlet end  30  which is provided with aperture means, herein louvered openings  31  to admit air into the vertical duct to supply the combustion chamber. The inlet end  31  is elevated to reduce the risk of explosive gases entering the combustion chamber. 
     The present invention provides the heat shield  12  in the combustion chamber  11 . As shown in the embodiment of FIG. 1, this heat shield  12  is a cup-shaped cylinder shield having a circular flat bottom wall  36  and a cylindrical side wall  37  secured to the outer periphery of the bottom wall  36  and projecting thereabove. The cylinder shield has an open top end  38  facing the heat transfer wall  13 ″ of the inner casing  13 . This heat transfer wall  13 ″ is usually a concave dome-shaped wall with the flue  14  disposed centrally at the apex thereof. Spacing brackets  39  maintain the shield side wall  37  spaced from the skirt  27  and the bottom wall  36  spaced from the bottom wall  26  of the combustion chamber whereby to provide an air space  40  about the shield. The vertical duct  28  provides fresh combustion air in this space  40  to supply the burner. Air is drawn within the space  40  by the hot flame of the burner which creates a draft within the space about the shield  12  of the burner drawing air through the holes  41  and about the side walls  37  of the shield as well as over the top edge. This helps to cool the skirt  27  and the bottom wall  26 . For example, the skirt  27  without the shield attained temperatures of about 350° F. and with the shield this has been reduced to 150° F. 
     As can be seen, the shield  12  is provided with a plurality of apertures or holes  41  in at least a bottom wall  36 . Additional holes  41  may also be provided in the cylindrical side wall  37 . As an alternative, a single large through-bore  42  may be provided centrally in the shield bottom wall  36  in line with the burner  16  which is supported elevated at the center inside the heat shield  12 . This shield  12  provides heat concentration in the combustion chamber  11  and on the lower heat transfer wall  13 ′ of the inner casing and reduces heat loss through the skirt  27  and the bottom end wall  26  of the combustion chamber. 
     Referring now to FIG. 2, there is shown a further example of the construction of the heat shield, herein identified by reference numeral  12 ′. As can be seen, this shield  12 ′ is a bowl-like shield and therefore has the shape of an inverted dome which defines a concave inner surface  45  which faces the open top end  46  of the shield, and a convex outer surface  47  which is disposed spaced from the sealed bottom wall  26  of the combustion chamber and the skirt  27 . The open top end  46  faces the heat transfer wall  13 ″ of the inner casing and disposed concentrically below this heat transfer wall whereby heat radiation from the concave inner surface is concentrated on the heat transfer wall  13 ″ to achieve better heat exchange between the inner casing and the combustion chamber. 
     The heat shield  12 ′ is also provided with apertures  48  all around the inverted dome-shaped shield or alternatively a single large aperture  49  may be disposed at the apex of the dome and concentrically aligned with the burner  16 , similar to the aperture  42  in the previous embodiment of the shield as above-described. The dome shield  12 ′ is secured by the spacing brackets  39 ′ similar to the embodiment of FIG.  1 . As can be seen with this embodiment, the air space  50  surrounding the shield is much larger and this inverted dome-shape shield design enhances the heat concentration on the transfer wall and the reduction of heat loss through the skirt  27  and bottom end wall  26  of the sealed combustion housing. These shields are preferably, but not exclusively, formed of steel material capable of resisting the high temperature heat of the combustion chamber. 
     It is within the ambit of the present invention to cover any obvious modifications of the examples of the preferred embodiment described herein, provided such modifications fall within the scope of the appended claims.