Patent Publication Number: US-6662757-B2

Title: Explosion proof gas-fired water heater

Description:
TECHNICAL FIELD 
     The present invention relates to an explosion proof gas-fired water heater whereby to shut off the gas burner and pilot upon the detection of abnormal life-threatening conditions in the vicinity of the gas-fired water heater. 
     BACKGROUND ART 
     Gas-fired water heaters can be hazardous if these are utilized in areas where there is a risk that combustible vapors may propagate in the area of such burners. Usually combustible vapors will accumulate on a floor surface and slowly build up and rise thus creating a large area of ignitable gas vapors. If such a cloud of vapors propagates into the combustion chamber of a gas-fired water heater they will ignite and cause a very serious explosion and usually destroying the gas-fired water heater and fragmenting the gas line to add further fuel to the fire. Needless to say, such explosion would be disastrous to any person in the immediate vicinity of the gas-fired water heater. 
     Another disadvantage of gas-fired water heaters is that they are usually installed in garages where fumes are released by automobiles due to gas leakage or paint, glues and other such combustible vapor generating products that we find in workshops where such items are usually stored. The basement is another hazardous location where we find these products. Various attempts have been made to deal with this problem but none have proven satisfactory. 
     A still further problem with gas-fired water heaters is that the air intake for the combustion chamber can become obstructed diminishing the supply of oxygen thus causing carbon monoxide which can seep into the air through the draft hood causing death to the residents. 
     SUMMARY OF INVENTION 
     It is a feature of the present invention to provide an explosion proof gas-tired water heater and wherein the supply of fresh air to the combustion chamber is made through at least one supply channel with the combustion chamber being sealed. One or more vapor detectors are associated with the channel to detect the presence of combustible vapors and the detectors operate switches to shut off the gas burner and pilot before the combustible vapors reach the gas burner and pilot through the air supply channel. 
     Another feature of the present invention is also to delay the propagation of the combustible vapors to the gas burner and pilot by disposing the intake port of the air supply channel at a predetermined distance elevated from the floor surface so that the combustion chamber has sufficient time to cool before the vapors can propagate into the combustion chamber through the supply channel. 
     Another feature of the present invention is to provide a gas-fired water heater wherein the fresh air intake port is provided in a support base of the water heater and wherein baffle walls are spaced from the intake port and the combustion chamber to delay the propagation of combustible vapors to the combustion chamber and further wherein the vapor detectors are disposed adjacent the fresh air intake port. 
     Another feature is to additionally provide a baffle and air dispenser perforated wall about the combustion chamber to optimize gas combustion. 
     A still further feature is to position the intake port of the supply channel substantially elevated from a floor surface such that explosive vapor clouds do not rise to the intake port to cause an explosion in the sealed combustion chamber. 
     A further feature is to provide a flame arrestor at the intake of the supply channel where it is easy to service and clean to ensure good supply of oxygen for the combustion. 
     Another feature is to provide a pressure detector in the supply channel to shut off the gas supply to the burner and pilot in the sealed combustion chamber should the supply channel intake become blocked or partly blocked to supply sufficient oxygen. 
     According to the above features, from a broad aspect, the present invention provides an explosion proof gas-fired water heater having a housing provided with a water reservoir and a sealed combustion chamber thereunder. A flue pipe is disposed above the combustion chamber and extends through the reservoir. A gas burner and pilot are provided in the combustion chamber. A gas supply line having a gas having gas supply shut-off valve is secured to the burner and pilot. A sealed combustible air channel lies fresh air to the combustion chamber and has an air supply intake disposed elevated from a floor surface of the water heater a distance of at least 40 inches whereby combustible vapors will not propagate to the air supply intake to enter the combustion chamber and reach the gas burner and pilot through the air supply channel. One or more vapor detectors are associated with the channel to detect the presence of combustible vapors. The vapor detectors are connected to a switching means to shut-off the gas burner and pilot before the combustible vapors reach the gas burner and pilot through the air supply channel. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The preferred embodiments of the present invention will now be described with reference to the accompanying drawings in which 
     FIG. 1 is a partly fragmented aide view showing the construction of a gas-fired water heater incorporating the present invention and wherein the fresh air supply channel is constituted by one or more vertical conduits; 
     FIG. 2 is a view similar to FIG. 1 but with the conduit differently shaped and the vapor detectors disposed slightly differently; 
     FIG. 3 is a fragmented side view showing a gas-fired water heater provided with two vertical fresh air conduits; 
     FIG. 4A is a fragmented side view showing a still further embodiment of the present invention and wherein the support base of the gas-fired water heater is provided with air intake ports and baffle plates to delay the propagation of combustible vapors and wherein one or more vapor detectors are secured adjacent the air intake ports; 
     FIG. 4B is a section view of the base showing the disposition of a baffle plate; 
     FIG. 5 is a schematic side view of a gas valve showing the connection of the vapor sensors to the relay coil of a gas valve; 
     FIG. 6 is a schematic diagram showing the connection of the vapor sensor to the electromagnet of a gas valve; 
     FIG. 7 is a schematic diagram showing the vapor detector system connected to the gas valve and the hot surface igniter of the burner; 
     FIG. 8 is a view similar to FIG.  1  and wherein a baffle and air dispenser perforated wall is disposed about the combustion chamber to optimize gas combustion, and 
     FIG. 9 is a schematic side view of a gas-fired water heater having a sealed combustion chamber and a vertical supply channel equipped with a pressure sensor safety system to shut-off the gas supply. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to FIG. 1, there is shown generally at  10  an explosion proof gas-fired water heater constructed in accordance with the present invention. The gas-fired water heater comprises a housing  11  having an inner tank  12  and an outer wall  13  which is spaced from the inner tank and insulated by an insulating material disposed between the outer wall and inner tank. A combustion chamber  14  is disposed under the bottom wall  15  of the inner tank. A flue  16  extends through the inner tank for the discharge of combustible product and to heat the water in the inner tank, as is well known in the art. 
     The combustion chamber  14  is provided with a gas burner  17  and a pilot  18 . The pilot  18  and the burner  17  are supplied gas through the supply gas line  19  through a gas valve  20 . A spark ignition system  21  or equivalent is provided to ignite the pilot  18 . 
     With the present invention the combustion chamber is provided with a sealed bottom wall  22  in one of its embodiments. The fresh air necessary to provide combustion is supplied through one or more supply channels  23 . As herein shown, the supply channel  23  is a vertical housing provided with sealed surrounding walls  24  and connected to the outer wall  13  of the water heater. The fresh air intake louvers  25  are disposed in an upper section of the supply channel  23 . A flammable vapor detector  26  is hereinshown as secured to a bottom wall  27  of the supply channel  23  whereby to detect combustible vapors adjacent the floor surface  28  on which the hot water heater  10  is mounted. Accordingly, if dangerous combustible vapors accumulate they will be detected early before they rise to the fresh air intake louvers  25 . As soon as the vapor detector  26  detects such vapors it will shut off the supply of gas by actuating the gas valve  20  as will be described later. As a safety feature a further flammable vapor detector  29  is located close to the fresh air intake. 
     The length of the supply channel  23  may vary dependent on the type of burners being used whereby upon detection of gas adjacent the floor area sufficient time will elapse before the combustible vapors reach the combustion chamber as they have to rise to the fresh air intake louvers and then down through the supply channel to the combustion chamber and this can take sometimes an hour or more. After the burner and pilot are extinguished by the actuation of the gas valve to place it in a closed condition the heat within the combustion chamber and flue will cause a draft through the flue bringing in fresh air to cool the combustion chamber whereby to prevent any hot surfaces to become in contact with the combustible vapors if they eventually propagate into the combustion chamber. 
     FIG. 2 is a view similar to FIG.  1  and as can be seen the fresh air intake louvers  25 ′ are disposed on the side wall  30  of the supply channel  23 ′. Also the flammable vapor detectors  26  and  29  are disposed at different locations simply to illustrate that various constructions of such fresh air supply channels are possible. As can be seen in both FIG.  1  and FIG. 2 the top walls  31  and  31 ′ are sloped whereby to prevent the placement of foreign articles onto these stop walls which could obstruct the fresh air intake louvers or prevent someone placing a piece of cloth or rag which may be soaked with a flammable liquid such as turpentine or kerosene as we usually find in workshops or garages to cause a fire. 
     Referring now to FIG. 3 it illustrates that the hot water heater may be provided with two or more supply channels  23  about the gas-fired water heater. As hereinshown the flow of fresh air enters the louvers  25  and propagates into the supply channel  23  between the outer casing or wall  13  and down into the support base  32  of the gas-fired water heater. The support base is a sealed base and it is provided with air intake ports  33  which directly feed the combustion chamber. The intake ports are provided all about the support base  32 . 
     As shown if FIGS. 4A and 4B the support base  32  is in contact with outside air. Such a support base may be used with gas burners of low capacity wherein the combustion chamber cools very quickly. However, in order to detect combustible vapors and to retard their propagation to the combustion chamber, vapor detectors  34  are disposed immediately adjacent the air intake ports  35  of the base  32 . Furthermore, baffle walls  35 ′ in the form of concentric rings are secured spaced apart from one another and extend from a top wall  36  and a bottom wall  37  of the base. Accordingly, the air entering the air intake port must propagate about these walls before reaching the combustion chamber, as is shown by the dotted line  38 . As soon as the sensor  34  detects the presence of combustible vapors it will shut off the gas burner  17  and pilot  18 . This embodiment is disclosed to show a further version of the present invention but the preferred version is the one as illustrated in FIGS. 1-3. 
     Referring now to FIG. 5 there is shown a schematic illustration of the construction of the gas valve  20 . This gas valve is associated with a heat detector probe  40  (ECO) which extends into the water reservoir  41  of the inner tank  12  whereby to actuate the relay coil  42  of the gas shut off valve  43  when the temperature in the water reaches a preset value. It also protects the water heater in the event of malfunction where the water temperature could reach a cut-off point, which is usually 190° F. When the hot water in the tank reaches the preset value as set by the sensor  44 A in the ECO probe  40 , the valve  20  shuts off the gas supply. The heat detector probe switch  44  moves to an open state causing the gas shut off valve  43  to close only in emergency situations. The thermo couple  45  is left on as it controls the valve to supply gas. It is located next to the burner. The thermo couple  45  is utilized to maintain the flame on. 
     As hereinshown the vapor sensors are normally open switches  26  and  29  and these are operated by a 9-volt battery or thermopile much like the fire detectors which are in common household use. When the battery or thermopile goes to a low charge an alarm is sound indicating that the battery needs to be replaced. These sensors, herein sensors  26  and  29  are connected through the high heat detector probe  40 , as hereinshown, to the relay coil  42  and as soon as they are closed they energize the relay coil  42  to move the gas shut off valve  43  to a closed position whereby to cut-off the supply of gas to the pilot  18  and the burner  17 . 
     FIG. 6 illustrates the connection of a vapor sensor such as vapor sensor  26  to the electromagnet or relay coils  42 . The supply of the coil is by the ECO, as is obvious to a person skilled in the art. 
     FIG. 7 the use of a hot surface igniter  47  instead of a gas pilot and wherein the vapor sensor generally indicated at reference numeral  50  controls the gas valve  20  and hence the hot surface igniter  47  of the gas burner as the igniter is only provided a current when the electromagnetic valve is opened. A flame sensor  48  detects the presence of the flame. When the valve  20  is closed the igniter is off. 
     FIG. 8 shows a cylindrical flame arrestor and air dispenser plate  60  is disposed all around the combustion chamber  14  to optimize gas combustion whereby to achieve higher gas input. The holes  61  in the flame arrestor plate can be between ¼ of an inch to one inch in diameter. This plate provides a baffle to retard the flow of combustible fumes and at the same time provides improved air distribution and flow within the combustion chamber. It also acts as a baffle to prevent flames from exiting through the bottom and of the water heater if there is an explosion in the combustion chamber. 
     It is pointed out that all embodiments of the fresh air supply channels and baffles all meet the LINT tests and CSA tests and regulations. 
     Referring now to FIG. 9 there is shown a further embodiment of the present invention wherein the air supply channel  23 ′ is substantially elevated from the floor surface  62  to position its intake  64  a distance of at least 40 inches from the floor surface. The air supply intake  64  is hereinshown by the slope wall  65  having louvers  66  therein and further louvers  66 ′ provided in the opposed side walls in the upper part of the channel  23 ′. The air intake  64  may also be constituted by a removable air filter  67 , hereinshown in phantom lines, mounted at the top end of the air supply channel  23 ′ or simply an opening provided with removable filters to permit ease of cleaning. The upper part of the channel may also be removable by removing screws  68  whereby the upper portion of the channel is also removable for cleaning, particularly if a fine mesh screen is provided inside the upper portion of the channel behind the louvers. Accordingly, it can be appreciated that the intake of this supply channel can be maintained substantially clean of lint at all times whereby to ensure for a proper oxygen supply to the burner chamber  14 ′. It is pointed out that if lint obstructs the air intake ports then the supply of oxygen is greatly diminished and the burner emits carbon monoxide which is released in the flue  16 , and decreases the speed of evacuation of the combustible product with the risk of causing spillage of carbon monoxide through the draft hood  69  provided about the exit end of the flue pipe  70 . This spilling in a residential household could cause death to its residents. 
     In order to avoid the inadequate supply of combustion air there is provided a pressure sensing means in the form of a mechanical or electronic pressure sensor  63  which is mounted in the supply pipe  23 ′ whereby to monitor the pressure inside the pipe and compare it to outside ambient pressure. Should the air supply not be adequate, a auction will be created inside the supply pipe  23 ′ by the up draft in the flue pipe causing a pressure differential between the air inside the air supply channel and ambient air. If these conditions continue for a predetermined time the pressure sensor will actuate the gas supply shut off valve to extinguish the burner and pilot. An audible and/or visual alarm can then be triggered to inform the occupants that the filter or the air louvers are blocked and require cleaning. It can be appreciate that the cleaning is made very accessible due to its convenient location as compared with the flame arrestor circumferential plate  60  as shown in FIG.  8 . It is also pointed out that the present method of detecting the differential pressure is much more reliable than trying to detect the CO (carbon monoxide) emission content in the flue pipe which is not a very reliable method. 
     It is within the ambit of the present invention to cover any obvious modifications of the embodiments described herein, provided such modifications fall within the scope of the appended claims.