Atmospheric gas burner and control system

A gas and solid fuel burning chamber is provided with a control system for the safe and efficient operation of a gas burner. The simple control system uses multiple thermocouples in series to permit the safe operation of the gas burner in a vented device without the need for a draft hood. A combination of gas and solid fuel is demonstrated where gas can be used to start the solid or as an independent source of heat. The control system comprises generally of thermocouples for measuring the flame temperature, the combusted gas temperature and the overall chamber internal temperature and producing signals to regulate the flow of fuel to the gas burner in response thereto.

TECHNICAL FIELD 
The invention relates generally to the field of atmospheric heating devices 
such as fireplaces and more particularly to the manufacture of a gas 
burner in such a heating device and a control system therefore. 
BACKGROUND OF THE INVENTION 
Gas burners have been used in fireplaces and similar heating devices both 
as a primary heat source, often with ceramic logs, and as a wood starter. 
Gas burners burn cleaner than wood and provide a simple, clean way to 
start wood fires. 
While gas burners have advantages, they can impose the serious threat of 
gas leakage from a non-burning gas source. When gas is allowed to escape 
under the atmospheric pressure conditions, it can form a highly explosive 
and generally toxic mixture with the ambient air. 
Prior art gas burners for wood fire starting also require manual shutoff. 
Thus, if a casual user forgets to turn off the gas supply, the gas will 
remain burning wasting fuel. 
Various safety systems have been designed to protect against gas leakage 
when the burner fails to light or when there exists a temporary 
interruption in the gas supply. Such systems include the traditional draft 
hood, measuring pilot burner temperature as in U.S. Pat. No. 3,111,161 and 
measuring the temperature in a blast tube of a power gas burner as in U.S. 
Pat. No. 4,655,705. However, these systems do not provide automatic 
controls for a solid fuel starter. Furthermore, the draft hood is 
inefficient as a safety device because it draws unnecessary air out of the 
home, and when combined with spillage detection, it becomes expensive to 
operate. Powered burners are also costly and have not gained wide 
acceptance in dual fuel appliances. 
Having the ability to burn either gas or solid fuel in the same combustion 
chamber gives the user the option of what fuel to use and makes starting a 
wood fire easier and cleaner. While gas fire starters for fireplaces have 
been used for many years, they generally do not have optimum safety 
controls and are generally not approved for use with liquid propane gas 
which is heavier than air. 
SUMMARY OF THE INVENTION 
An object of the current invention is to provide a gas burning heating 
device that uses a thermocouple control system that eliminates the need of 
a draft hood. Another object of the present invention is to provide a 
heating device that operates alternatively as a gas burning device or as 
solid fuel burning device that incorporates an automatic gas starter. 
Still another object of the present invention is to provide a gas burner 
for a heating device that can utilize at least liquid propane or natural 
gas as fuel. 
An improved gas assisted atmospheric burning chamber and control system has 
been developed according to the present invention which substantially 
overcomes the drawbacks of the prior art gas burners discussed above. 
The present invention provides a gas burner for use as a primary source of 
heat or as a solid fuel fire starter. The present invention also provides 
a gas burner that can be operated from both natural gas or liquid propane 
gas. 
In addition, the present invention provides a control system for a gas 
burner that provides safe and efficient operation of the gas burner. The 
control system allows for the automatic shutoff of the gas burner in the 
event of loss of flame or once the solid fuel fire is sufficiently 
burning. This prevents gas leakage when no flame exists and eliminates 
wasted gas flow when the wood fire is burning sufficiently. Moreover, the 
gas burner and control system according to the present invention is a 
simple system that is low cost. 
The present invention thus involves providing a gas burner for a 
atmospheric heating chamber and control system for the safe and efficient 
operation of the gas burner. 
The present invention also includes a variable flow valve. The valve is 
preferably operated by a manual valve knob and a solenoid, actuated in 
response to signals generated by temperature sensors. Temperature sensors 
such as thermocouples are placed according to the invention to measure gas 
flame temperature, flue flow temperature and solid fuel fire temperature. 
In a preferred embodiment, the temperature sensors provide control signals 
such that the signal from the solid fuel fire temperature is opposed to 
the signals from the gas flame temperature and flue flow temperature. 
The solenoid operates the valve such that the valve remains open when the 
gas burner is utilized as the primary heat source. The solenoid will also 
close the valve in the event of a flame out or backdraft in the flue as 
determined by the corresponding temperature sensor. When the gas burner is 
used as a solid fuel fire starter, the solenoid automatically closes the 
valve after the solid fuel has sustained ignition. In this mode, the 
solenoid automatically shuts the valve when the solid fuel fire is 
generating enough heat to be self sufficient. 
Additional advantages of the present invention include the gas burner being 
located in the upper rear of the heating chamber at the base of a 
refractory baffle which reflects the gas heat toward the solid fuel and 
the glass front of the appliance, which is preferably an efficient, 
semi-airtight EPA approved wood heater. A flue damper can be used to 
regulate the air supply to provide for better heating efficiency. 
Another advantage of the present invention is that the primary air for the 
gas source is supplied by a shutterless intake combined with a shrouded 
orifice construction. This provides good gas/air mixing with both natural 
and liquid propane gas without the necessity of having access for the 
purpose of adjustment. 
Other details, features, objects, uses and advantages of this invention 
will become apparent from the embodiments thereof presented in the 
following specification and claims, as well as in the enclosed drawing.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a heating chamber 10 is provided to be used for solid 
fuel burning or gas burning. Gas is supplied to a gas controlling system 
20 at an inlet 11 from a source not shown. For domestic use, the present 
invention preferably uses 11" WC LP gas (normal house pressure liquid 
propane) or 7" WC NAT gas (normal house pressure natural gas) or 
equivalents thereof. 
A valve 12 regulates the gas flow to the heating chamber 10. The variable 
flow valve 12 is sized so that it gives reasonable adjustment of gas flow 
according to the gas and amount of heating desired. In an exemplary 
embodiment for a domestic use, valve 12 may be sized to provide 
approximately 20,0000 BTU/HR for the appropriate gas flow when using 
either of the above-mentioned gasses. 
Valve 12 includes two operating mechanisms. Valve knob 12b is provided to 
operate the valve manually. An actuator 12a, which is preferably a 
solenoid 12a, is provided to automatically operate the valve 12 according 
to control signals. For simplicity, valve 12 may be a push/pull valve so 
that the valve knob 12b and solenoid 12a can adjust the flow rate through 
valve 12 through simple translational movement. In this manner the valve 
knob 12b can be depressed to open valve 12 against the closure force of 
the solenoid 12a. Once the solenoid 12a receives open signals, the valve 
12 will remain open without pressure on the valve knob 12b. 
The gas that passes through valve 12 is supplied to gas burner 19 via a 
fuel flow path comprising piping 24. Shutterless intake 14 and orifice 13 
can be inserted in piping 24 to mix the gas with primary air and create a 
gas/air mixture for combustion. FIG. 2 shows orifice 13 recessed in shroud 
14b which expands the gas before it is mixed with air which is inducted 
through the intake holes 14a. The shroud 14b also gives the mixing air 
proper flow direction for a preferred mixing. The orifice 13 can be 
properly sized according to the gas type desired. For instance, a No. 53 
drill can be used for liquid propane and a No. 47 drill can be used for 
natural gas. 
The gas or gas/air mixture is supplied to the gas burner 19 where it is 
combusted. The burner 19 is located within the heating chamber 10 to 
direct the combustion heat toward a solid fuel such as wood, not shown. 
This allows the heating chamber 10 to be used as a dual mode heater. In a 
first mode, no solid fuel is supplied and the gas burner 19 is used as the 
primary heat source. In a second mode, solid fuel is provided and the gas 
burner 19 is used for igniting the solid fuel and automatically shuts off 
thereafter. 
Preferably, gas burner 19 is located in heating chamber 10 at the base of a 
refractory baffle 26 at the upper back of the heating chamber. In the 
preferred embodiment shown in FIGS. 1, 6 and 7, air 22 is introduced into 
the chamber 10 through a slot 27 in the refactory baffle 26 and is mixed 
and combusted with the gas to form combusted gas 21. The combusted gas 21 
flows from the gas burner 19 toward the center of the heating chamber 10 
where a solid fuel source can be located. The combusted gas flows, as 
indicated by arrow 21a, from the heating chamber 10 over and behind the 
refractory baffle 26. The combusted gas then flows (arrow 216) across a 
temperature sensor 17. Finally, the combusted gas flows in the direction 
of arrow 21c into a flue 28 where it is directed to outside, ambient 
conditions. 
A traditional flue damper 23 can be used to regulate the air flow and 
provide for further heating efficiency of the heating chamber 10. Air flow 
indicated by arrow 22 is inducted from ambient conditions and then 
introduced into the heating chamber part way up the baffle 26 through the 
slot 27. This provides an air flow from the back of the heating chamber 10 
so that the top front of the heating chamber 10 receives the greatest 
amount of heat. 
In a preferred embodiment, four temperature sensors 15a, 15b, 16 and 17 
communicate with solenoid 12a to control the gas flow. Preferably the 
temperature sensors are coupled to solenoid 12a. The temperature sensors 
according to a preferred embodiment are connected in a series relationship 
to control the solenoid 12a so that the signal received from the 
thermocouples 15a, 15b, 16 and 17 is based on the additive effect of the 
temperatures sensed. As one skilled in the art can appreciate, temperature 
sensors 15a, 15b, 16 and 17 could provide separate signals to a 
microprocessor or other logic center for controlling solenoid 12a as shown 
in FIG. 4. Other inputs 17', such as room temperature could be provided, 
and valve controller 12b can provide flow control for valve 12 so as to 
provide temperature control as well as the safety features discussed 
herein. 
Again, according to a preferred embodiment, a first thermocouple 16 is 
located on top of the burner 19 to sense the gas flame temperature and 
serves to hold the valve 12 open for gas flow after ignition of the gas 
burner 19. A second thermocouple 17 is located approximate the base of the 
flue 28 to sense the flue flow temperature as shown in FIGS. 6 and 7. The 
thermocouple 17 is insulated from the combustion chamber by the refractory 
baffle 26. Thermocouple 17 provides a signal that supports the signal of 
thermocouple 16 as the flame and combustion gas temperatures increase to 
hold the valve 12 open after ignition of the gas burner 19. Two 
thermocouples 15a and 15b are located under the gas burner 19 to sense the 
temperature of heating chamber 10. In particular, the thermocouples 15a 
and 15b are located to primarily sense heat from the solid fuel source not 
shown, but they also sense the temperature of the heating chamber 10 as a 
whole. Heat sensors 15a and 15b thus may be differently positioned 
depending on factors such as size, shape or capacity of the combustion 
chamber. The exact position for these heat sensors will be easily 
determined by persons of ordinary skill in the art based on the teachings 
herein. 
FIG. 3 shows the preferred electrical circuit consisting of the four heat 
sensors/thermocouples 15a, 15b, 16 and 17, electrical grounds 25 and valve 
solenoid 12a. The polarity shown at 12a is that which opens valve 12. As 
shown in FIG. 3, the thermocouples 16 and 17 support the open circuit 
while thermocouples 15a and 15b oppose the open circuit. 
In the preferred embodiment, shown in FIG. 5, the thermocouples 15a, 15b, 
16 and 17 are preferably constructed of Alumel and Chromel, 0.102 inch 
diameter wires. Chromel wire 42 is used to form both thermocouple 17 and 
15b, alumel wire 43 is used to form thermocouples 15b and 16 and chromel 
wire 44 is used to form thermocouples 16 and 15a. Alumel wire 41 is 
connected to negative side of solenoid 12a and the alumel wire 45 is 
connected to the positive side of solenoid 12a. By using this 
construction, the wires 42, 43 and 44 are used both as an interconnection 
between thermocouples and as one half of each junction of the 
thermocouples as shown in FIG. 5. In this manner, the system provides a 
system control system based on the additive effect of the thermocouples 16 
and 17 minus the additive effect of the thermocouples 15a and 15b. These 
thermocouples provide approximately 30 mv at 1800 degrees Fahrenheit. 
A first function of the control system is to shut off the gas when there is 
no gas flame so that gas does not flow from the burner when it is unlit. A 
second function is to shut off the gas if the flue is blocked or there is 
negative pressure in the dwelling so as to cause flue reversal. A third 
function is to shut off the gas when the two thermocouples 15a and 15b are 
heated by the solid fuel source so that the gas burner 19 operates as a 
fire starter that automatically shuts off. This will save fuel and avoid 
flash back (combustion inside the gas burner 19). 
To operate the gas burner 19 as the primary heat source, no solid fuel is 
supplied to the heating chamber 10. To light the gas burner 19, a door 27 
to the heating chamber 10 is opened, which insures no explosive gas build 
up. The valve knob 12b is depressed or turned to open valve 12 while 
holding a match or a hand held piezoelectric igniter to the gas burner. 
Once gas burner 19 is lit, the gas flame temperature and flue flow 
temperature will increase and thermocouple 16 and 17 will send open 
signals to the solenoid 12a. The valve knob 12b must be held against the 
solenoid for approximately fifteen to thirty seconds for the thermocouples 
to hold the valve 12 open. Thereafter, the valve 12 will remain open 
automatically by the solenoid 12a as long as the gas flame temperature and 
flue flow temperature remain high. Thermocouples 15a and 15b will sense 
the rise in temperature of heating chamber 10 and bring the electrical 
system output closer to the solenoid shut off value. In this manner, the 
sensitivity of the system in general is increased to provide a safe 
system. 
In the event of a gas flame loss, the thermocouple 16 will sense the 
decrease in gas flame temperature and send a close signal to the solenoid 
12a and shut off the valve 12. In the event of flue reversal or negative 
pressure in the dwelling, the thermocouple 17 will sense the decrease in 
temperature of the combusted gas flow and close the valve 12. Once the 
valve 12 is closed the thermocouple 16 senses the decrease in temperature 
from the loss of gas flame and the valve 12 will not automatically reopen. 
To operate the gas burner 19 as a solid fuel starter, solid fuel such as 
wood logs are placed in the heating chamber 10 in front of the gas burner 
19. The gas burner 19 is ignited in the same manner described above. In 
this mode the thermocouples 16 and 17 will initially send signals to the 
solenoid 12a to hold the valve 12 open. However, as the solid fuel catches 
fire and rises in temperature, thermocouples 15a and 15b will override 
thermocouples 16 and 17 and send signals to the solenoid 12a to close the 
valve 12. Again, once the valve 12 is closed and the gas burner 19 goes 
out, the thermocouple 16 will sense the drop in temperature and prohibit 
any automatic reopening of the valve 12. 
As is evident from the discussion above, two thermocouples 15a and 15b are 
used to offset the signals of the thermocouple 16 and 17. Based on the 
teachings of the present invention contained herein, one skilled in the 
art may add or subtract heat sensors in various locations and provide for 
the proper signals through other means such as a control logic device for 
receiving signals and manipulating them according to predetermined 
instructions. Further, the addition of remote ignition and thermostatic 
control also will be evident to anyone experienced in the field. 
It is noted that the above description is merely illustrative of the 
invention, and that numerous modifications and embodiments may be devised 
by those skilled in the art without departing from the inventive concept 
herein. Accordingly, the true spirit and scope of the present invention is 
only to be determined by the claims appended hereto.