Patent Application
20070207420
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.
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 (“O2”) 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.
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 O2, 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.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
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
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.
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 O2 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
Another advantage of the placement of the combustion gas sensor 62 as depicted in
Contrary to that depicted in
By placing the combustion gas sensor 62 as depicted in
An advantage of the sampling tube 76 is that as the gas is permitted to passes through the sampling tube 76, which coils around the upper end 26 of the hater 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
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 O2 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.
