Patent Abstract:
A fuel fired appliance exhaust gas parameter sensor for continually detecting gas parameter emissions, such as CO, NOx and O 2 , may be located above the appliance near the appliance exhaust outlet. The sensor may be located near or under a draft hood located near the exhaust outlet. The sensor remains relatively cool by draft air moving from outside the draft hood and into a chimney, the draft being hastened by the heated, rising chimney gases. A sensor bracket may be attached to the appliance and the sensor to appropriately position the sensor under the draft hood. Alternatively, the sensor may be located on a tube that continually samples combustion exhaust. The tube may be located outside of the draft hood perimeter to maintain a low sensor temperature, while multiple tube coils around the exhaust outlet may be used to further cool the sampled gas.

Full Description:
FIELD 
     The present disclosure relates generally to a flue gas sensor for a gas-fired appliance and, more specifically, to an apparatus that measures exhaust gas parameter concentrations while maintaining a low ambient apparatus temperature during regular appliance operation. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. Monitoring of flue gas parameters, such as carbon monoxide (“CO”), Nitrogen Oxides (“NOx”), and Oxygen (“O 2 ”) in a fuel fired appliance, such as a gas fired water heater, is desirable to alert surrounding inhabitants of specific levels of such exhaust gas parameters. Traditionally, such gas parameter monitoring was accomplished with a device located some distance away from the actual flow of hot, combusted flue gases. Such known devices, however, may not satisfactorily measure such gas parameters because they must be located away from the actual flow of the hot, post-combustion flue gases. This is because locating such a detection device in the actual flow of the combustion gases may subject the device to temperatures above 200 degrees Celsius, which may potentially damage the sensing instrument or its exterior casing. Locating a sensor away from the actual flow of combusted gases may delay detection, and locating a device in such a flow within a flue, may cause a sensor to become damaged and inoperable. 
     Additionally, when an exhaust gas parameter measuring device, such as a CO sensor, is located outside of the exhaust flow, in a reduced temperature zone, the device may only detect emission parameters when the combustion exhaust is blocked downstream of the detecting device, that is, blocked above the detecting device in a chimney. In such an instance, the exhaust flue gases are normally caused to “back up” and overflow outside of a draft hood until the combustion gases reach the detecting device located outside of the proximity of the exhaust flow. This may delay detection. 
     In the alternative, if the air intake, that is, the air upstream of a CO detecting device is restricted or blocked, but the exhaust flue downstream of a CO detecting device is not blocked, a CO gas detecting device located outside of the combustion exhaust flow is not capable of detecting exhaust gas CO levels that may result from improper combustion. This is because the exhaust flue is free from blockage and the flue gas parameter detecting device is located outside of the exhaust flow. The exhaust gas will not “back up” and alternatively flow toward such a device when only the airflow upstream of the sensor is compromised. 
     What is needed then is a device that does not suffer from the above limitations. This will result in an exhaust gas parameter detection device that detects gas parameters under all operating conditions, even when an exhaust flue is restricted downstream or upstream of the device. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, an exhaust gas parameter sensor for a flue of a fuel fired appliance is disclosed. More specifically, an apparatus for detecting specific combustion gas parameter emissions, such as CO, NOx, and O 2 , from a gas fired appliance exhaust is disclosed. The combustion gas parameter sensor may be positioned under a draft hood, just below a chimney for the combustion exhaust gas of the fuel fired appliance, making the sensor susceptible to specific gas parameters in the exhaust gas. 
     Just above the top surface of the appliance of which a combustion gas parameter sensor is associated, an exhaust outlet is located, above which, a draft hood is located. The draft hood permits fresh air to be drawn into the exhaust stream within the draft hood and subsequently, the exhaust chimney. The combustion gas parameter sensor may be located under the draft hood where the sensor is subject to cooling by fresh air drawn into the draft hood, before the fresh air, mixed with combustion gas, passes into the chimney. 
     A bracket may be utilized to position the combustion gas parameter sensor under the draft hood. By using a bracket, the sensor may be positioned within the geometric confines of the draft hood, to make the sensor more susceptible to exhaust gas parameters. Furthermore, the bracket may position the sensor such that air is permitted to flow over all sides of the sensor, between the draft hood and the sensor, and between the sensor and the appliance top surface, so that cooling of the sensor is possible in its location proximate the exhaust stream. 
     Alternatively, the combustion gas parameter sensor may be located on an exhaust sampling tube, through a wall of which exhaust gas parameters may be sensed by the sensor. One end of the sampling tube may be positioned in the exhaust port, where exhaust gases are drawn in, while the other end may be positioned in the exhaust chimney, where sample exhaust gases are expelled. Sampled exhaust gases are cooled as they pass through the tube, which may coil around the top surface of the appliance. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a partial cross-sectional side view of a water heater; 
         FIG. 2  is a side view of a water heater depicting a draft hood and example position of a combustion gas parameter sensor; 
         FIG. 3  is a perspective view of a water heater depicting a draft hood, flue pipe, exhaust chimney, and example location of a combustion gas parameter sensor; and 
         FIG. 4  is a perspective view of another embodiment depicting placement of a draft hood, exhaust flue, chimney and example placement of a combustion gas parameter sensor. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring now to  FIGS. 1-4  and more specifically to  FIG. 1 , the operative workings of the present disclosure will be depicted and explained.  FIG. 1  depicts a conventional fuel fired water heater  10 , such as a gas fired water heater. Water heater  10  includes an outer housing  12  within which resides a water storage tank  14 , around which is a layer of insulation  16 . A gas fired burner assembly  18  resides at the bottom area of the water heater  10  that, when ignited, heats the water within water area  20 . The water storage tank  14  has a generally elongated cylindrical shape, the majority of which is positioned above burner assembly  18 . A generally conically shaped hood portion  22  is sealingly secured to a lower portion of tank  14  and lies around and generally above the burner assembly  18 . A lower end of an axially elongated flue pipe  24  is sealingly secured to hood portion  22 . The flue pipe  24  projects outwardly through outer housing  12  at the outer housing upper end  26 . Such projecting end of the flue pipe  24  serves as an exhaust outlet  24 . The flue pipe  24  directs smoke and combustion gases into a chimney  60  via a draft hood  27 . 
     In operation, combustion gases generated by the firing of burner assembly  18  are directed upwardly through flue pipe  24  via hood  22  and serve to transfer heat to the water contained in water area  20  within storage tank  14 . In many cases, a spirally shaped or zig zag baffle member  28  is supported within flue pipe  24  and serves to create a mixing of the combustion gases as they flow upwardly through flue pipe  24 . The baffle member  28 , by contributing to the mixing of combustion gases, improves heat transfer to the water by reducing any thermal boundary layer that may form along the internal surface  30  of flue pipe  24 . 
     The water heater  10  also includes suitable fittings  32  and  34  for facilitating the flow of water into and out of the water heater  10 . Specifically, fitting  32  is for connection of a cold water supply pipe to supply cold, unheated water to the tank  14 . Fitting  34  is for connection of a pipe to supply heated water to a home or facility after being heated in the water heater  10 . The water inlet  32  is provided with a dip tube  36  that directs the inflow of cold water to the bottom of the storage tank  14 . 
     Additionally, water heater  10  includes a control assembly  38  for controlling the supply of gas to burner assembly  18  in response to the sensed temperature of the water within storage tank  14 . A drain spigot and valve assembly  40  is also provided for enabling the user of the water heater  10  to periodically flush debris from the bottom of tank  14  as well as to drain the tank  14  in the event of any necessary maintenance. To actually heat water in the storage tank  14 , the burner assembly  18  is utilized in conjunction with control assembly  38 . 
     The burner assembly  18  heats the water in the storage tank  14  by utilizing a pilot light  42 , which produces a flame  44 , an igniter  46 , which is used to light the pilot light  42 , a gas line  48  that directs the flow of gas to the burner assembly  18 , and a flame sensor  50 . The flame sensor  50  is normally a device that sends a signal to the control assembly  38  upon sensing the presence of a flame  44 . The control assembly  38  is used by a user to govern the temperature of the water within the storage tank  14  and thus the amount and duration of natural gas supplied to the burner assembly  18 . Upon utilization of the burner assembly and the subsequent heating of water within water area  20  of the storage tank  14 , combustion gases from the flame  44  pass upward through the flue pipe  24  to the upper end  26  of the water heater  10 . 
     Once at the upper end  26  of the water heater  10 , the combustion gases exit the upper end  26  via the exhaust outlet  24  and pass into and through the draft hood  27 . The draft hood  27  is secured in place by a number of hood legs  52 . Each hood leg  52  has a hood foot  54  and a hood riser  56  that together serve to create an air gap  58 . The air gap  58  permits air to pass into the draft hood  27  to facilitate and hasten the passage of combustion gases into the chimney  60 . The warmed combustion gases exiting through the chimney  60  facilitate the drawing of air through the air gap  58  due to convection currents caused by the phenomenon of heat rising. As thus far described, water heater  10  is of a construction typical for gas water heaters currently in use.  FIGS. 2-4  will now be more specifically referred to, in conjunction with  FIG. 1 , to better depict the operative workings of the present invention. 
       FIGS. 2 and 3  depict an upper end  26  of a water heater  10  depicting a location of a combustion gas sensor  62 . As depicted, the combustion gas sensor  62  is located under the draft hood  27 , and more specifically, in  FIG. 2 , the combustion gas sensor  62  is located under the slanted or angular portion of the draft hood  27 , relative to the upper end  26 , which is horizontal, of the water heater  10 . The combustion gas sensor  62  is positioned under the draft hood  27  by using a sensor bracket  63 . The sensor bracket  63  has a sensor bracket foot  64  and a sensor bracket riser  66 . The sensor bracket foot  64  is secured to the upper end  26  by using a suitable fastener, such as a screw, rivet or bolt. By utilizing a sensor bracket  63 , the combustion gas sensor  62  can be manipulated under the draft hood  27  for easy installation. Additionally, by making the combustion gas sensor  62  a separately positioned piece, advantages of the sensor  62  relative to the combustion gases are realized. 
     An advantage of the combustion gas sensor  62  and the sensor bracket  63  is that it can be added to any existing gas fired appliance where monitoring of specific gas parameters such as, but not limited to, CO, NOx and O 2  are desired to be monitored. Another advantage of the combustion gas sensor  62  is that its placement permits ambient air to be drawn over its entire surface to cool the sensor  62 , due to its placement in a position of elevated temperatures. More specifically, generally horizontal currents  68  are drawn around the combustion gas sensor  62  when the gas fired burner assembly  18  is fired and supplying heat to the water in the storage tank  14 . The generally horizontal air currents  68  are generated by the combustion gas vertical currents  70 , which result from the general burning of gas by the gas fired burner assembly  18 . When the heated combustion gasses rise through the flue pipe  24  and exit the flue pipe  24 , the gases continue upward, past the upper end  26 , into the draft hood  27 , and into the chimney  60 . The heated combustion gases are represented by the vertical currents  70 . The heat of the vertical currents causes generation of convection currents which results in the horizontal currents  68  being drawn from outside the draft hood  27 , into the draft hood  27  and subsequently up the chimney  60  to join and mix with the vertical currents  70 . 
     Because gas fired appliance combustion gases typically can reach 300 degrees C., placement of a combustion gas sensor near the combustion gases, or directly in the flow of the combustion gases, may result in malfunctioning of a combustion gas sensor or a shortened life span of such a sensor. However, with the arrangement depicted in  FIGS. 2 and 3 , because the combustion gas sensor  62  is located away from the vertical currents  70  of the combustion gases but in the flow of horizontal currents  68 , the sensor  62  does not suffer from the disadvantages of being proximate to, or in, 300 degree C. combustion gases. By placing the combustion gas sensor  62  under the draft hood  27  as depicted in  FIGS. 2 and 3 , horizontal currents are permitted to flow around all sides of the combustion gas sensor  62 . The currents can flow between the wall of the draft hood  27  and the sensor  62 , and between the sensor  62  and the upper end  26 . In this fashion, the life of the combustion gas sensor  62  can be prolonged, and combustion gases can be detected long before such gas might “back up” and spill out of the draft hood  27 . 
     Another advantage of the placement of the combustion gas sensor  62  as depicted in  FIGS. 2 and 3  is that it can detect combustion gases at all times, that is, continually. More specifically, combustion gases are detectible when the gas fired appliance is normally operating or combusting, when the flue pipe is blocked downstream of the sensor  62 , and when there is blockage upstream of the sensor  62 . 
     Contrary to that depicted in  FIGS. 1-4 , if a gas sensor, such as a CO detector, is located away from the draft hood, then CO is typically not detected until such CO gases “back up” and spill outside of the draft hood and reach a remote CO detector. This scenario normally would occur when, for instance, the appliance chimney is blocked. In another scenario, when there is blockage of the intake air around the burner assembly at the bottom of a water heater, then CO may not be detected at all since there is simply a blockage of air intake, even though combustion is not proper, which may result in combustion gas imbalances. In such a scenario, the combusted gases would pass through the appliance undetected, or back up at the bottom of the appliance, causing a delayed detection of elevated CO in the exiting combustion gases. 
     By placing the combustion gas sensor  62  as depicted in  FIGS. 2 and 3  the forgoing scenarios are avoided, and flue gases can be detected before they spill out of the draft hood  27  or other possible appliance outlet. Although not shown, a wire or control cord connects the combustion gas sensor  62  to the control assembly  38 . In the event of unfavorable combustion flue gas detection, the combustion gas sensor  62  causes the control assembly  38  to shut off the gas fired appliance so that combustion is halted.  FIG. 4  is another arrangement of a flue gas sensor that also permits flue gas detection, and will now be explained. 
       FIG. 4  depicts another arrangement of a flue gas sensor  72 . In such an arrangement, the flue gas sensor  72  fluidly communicates through a wall of a flue gas sampling tube  76  that is secured to the upper end  26  by a bracket  80 . A communication wire  74  effectively communicates the gas sampling findings to the control assembly  38 . In the event the gas sampling findings warrant shutting off of the appliance  10 , such as in the detection of an unsafe level of CO, the control assembly  38  will communicate with the burner assembly  18  to do such. The sensor  72  is located on the sampling tube  76  to permit the sensor  72  to be located away from the elevated temperatures of combusted flue gas, which may contribute to a shortened sensor life. A shortened sensor life is avoided, and in fact, sensor life is optimized by locating the sensor  72  on the gas sampling tube  76 . Not only is the sensor  72  located away from the heated combustion gas flow  82  of the combustion gases  82  exiting from the flue pipe  24 , but the sample gas  78 , or gas within the sampling tube  76 , is permitted to cool as the gas progresses through the sampling tube  76 . Heat is transferred from the sample gas  78  to the tube  76  and then into the air surrounding the tube  76 . To facilitate heat transfer, a material such as copper or aluminum may be used for the tube  76 , although other materials may be used. Furthermore, longer tube  76  lengths can be used when increased heat transfer is desired. 
     An advantage of the sampling tube  76  is that as the gas is permitted to pass through the sampling tube  76 , which coils around the upper end  26  of the heater  10 , the gas cools, which prolongs sensor  72  life. In the event of the necessity of a sampling tube  76  longer than that depicted in  FIG. 4 , the sampling tube  76  may be coiled around the flue pipe  24 , outside the perimeter of the draft hood  27 , in multiple coils. By causing the sample gas  78  to travel farther through the sampling tube  76 , the heat transfer out of the sample gas  78  will continue before the gas reaches the sensor  72 . 
     In order for the combustion gas sensor  72  to be supplied with a steady flow of combustion gas, a first sample tube end  84  is inserted down into the flue pipe  24  while a second sample tube end  86  is inserted up into the chimney  60 . By arranging the tube in such a manner, the heated combustion gas  82  rising into the chimney  60 , draws sampling gas  78  through the sampling tube  76 , that is, in the first end  84  and out the second end  86 . The sampling gas  78  is forced into the sampling tube by the heated, rising gas  82  and further fostered by the drawing action at the second end  86 , which is caused by convection currents of the heated gas passing the second end  86 . 
     Another advantage of using the sampling tube  76  is that the combustion gas sensor  72  and sampling tube  76  may be installed as an add-on option to existing water heaters or other gas fired appliances not so equipped. The flue gas sensor depicted in the figures and described above may be any kind of combustion gas sensor. For instance, the sensors may sense CO, NOx, or O 2  parameters; however, other gas components may be sensed as such need becomes evident. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

Technology Classification (CPC): 5