COMBUSTION AIR VENT CONTROL FOR FURNACES
Various apparatus are disclosed for controlling the combustion air vent of fuel-fired furnaces. For a first embodiment of the invention, a furnace-controlled air valve is placed in the combustion air duct. When the furnace begins a heating cycle, the valve is opened. When the heating cycle ends, the valve is closed and remains closed until the beginning of the next heating cycle. For a second embodiment of the invention, a positive-displacement air pump is placed in the combustion air duct. The air pump pumps air from the exterior into the mechanical room at a controlled rate during each heating cycle of the furnace. The air valve or the air pump is controlled directly or indirectly by the furnace thermostat.
This application has a priority date based on the filing of Provisional Patent Application No. 60/765,821, titled COMBUSTION AIR VENT CONTROL FOR FURNACES, on Feb. 7, 2006.
BACKGROUND OF THE INVENTION1. Field of the Invention
This invention relates to combustion furnaces and, more particularly, to the control of combustion air intakes for combustion furnaces having a combustion chamber that is not directly connected to the combustion air intake.
2. Description of the Prior Art
High-efficiency gas furnaces (those having efficiency ratings greater than 90 percent) typically have both a combustion air intake and a low-temperature exhaust vent, both of which are coupled directly to the combustion chamber of the furnace. As the combustion chamber is sealed from the room in which the furnace is installed, there can be little leakage of cold outside air into the room. Unfortunately, high-efficiency furnaces are not installed in the majority of new homes. Typically, they are installed in either new, high-end, custom homes or in existing homes by owners who are replacing an older furnace, and who intend to remain in those homes for a period sufficient to recover the additional cost required to purchase and install such furnaces. Most new homes constructed in this country are equipped with furnaces having efficiency ratings of around 80 percent. As homes have become increasingly airtight in an effort to minimize heat loss, building codes in effect in most states have evolved to require that a combustion air vent be provided between the exterior of the building and the mechanical room where the furnace is installed. In an airtight structure, a furnace will deplete the available oxygen and begin to produce carbon monoxide as combustion becomes increasingly incomplete. If the furnace exhaust vent is the only available conduit to the exterior, it is conceivable that the carbon monoxide would be drawn into the house as the furnace attempts to sustain the ongoing combustion of fuel. Because mechanical rooms are rarely well sealed from the rest of the house, combustion air vents can be a significant source of heat loss. This is particularly true when strong winds are blowing against the vent's exterior intake opening. In order to compensate for this heat loss, the furnace will use considerably more fuel than necessary to maintain a set temperature within the home. The effective efficiency of a furnace rated as being 80 percent efficient will be far less than 80 percent if it must compensate for an ongoing condition of significant heat loss. Another problem related to cold air entering the combustion air vent is that the dwelling's hot water heater is usually located in the same utility room or closet as the furnace. Even worse, the main water line may enter the dwelling in the utility room or closet. When outside temperatures drop significantly below freezing, the inlet water line of the water heater, the main water line, or both lines may freeze. This is not only annoying to the occupants, but likely to cause damage to the pipes—particularly if they are made of copper or brass.
What is needed is an inexpensive, safe, and reliable control for combustion air vents used with all types of combustion furnaces, which include gas-fired, oil-fired, corn-fired, wood-pellet-fired and coal-fired types which do not have the combustion air vent coupled directly to the furnace combustion chamber. The provision of such a control will greatly improve the effective efficiency of such furnaces by preventing leakage of cold air into the house through the combustion air vent.
SUMMARY OF THE INVENTIONThe present invention provides an apparatus for controlling the vent used to supply combustion air to combustion furnaces. For a first embodiment of the invention, a furnace-controlled air valve is placed in the combustion air duct. Many types of valves can be used, including flapper valves, poppet valves, butterfly valves, ball valves, and inflatable balloon valves. When the furnace begins a heating cycle, the valve is opened. When the heating cycle ends, the valve is closed and remains closed until the beginning of the next heating cycle. A solenoid or electric motor may be used to control a flapper valve, a butterfly valve and a ball valve. When an electric motor is used, position sensors or timed pulses can be used to ensure that the valve is in the proper position at the beginning of each cycle. An inflatable balloon valve can be controlled with an air pump that inflates the balloon through a one-way valve so that leakage through the pump will not deflate the balloon. Air pump operation can be timed or it can be shut off with a pressure sensor. Deflation of the balloon during heating cycles can be accomplished by sending a pulse of sufficient length to a solenoid-controlled valve which will permit the pressured air within the balloon to escape.
A second embodiment of the invention employs a positive-displacement air pump, which is placed in the combustion air duct and prevents most back-flow leakage of air. Many types of positive-displacement pumps are known in the art, including plunger or piston pumps, circumferential-piston pumps (characterized by the use of a pair of counterrotating rotors driven by external timing gears), diaphragm and bellows pumps, external gear pumps, internal gear pumps, lobed pumps, sliding vane pumps, flexible-vane pumps, nutating pumps, and twin screw pumps. When a heating cycle begins, the air pump begins to pump air into the mechanical room at a controlled rate that provides oxygen in an amount equal to or slightly less than the rate at which oxygen is being consumed by the ongoing combustion process. When the heating ends, the air pump stops pumping air, and does not begin pumping air again until the next heating cycle. As a safety feature, a bypass valve is opened if the air pump does not function. The air valve or air pump can be controlled by a voltage generated by either the thermostat or by the furnace. As a safety feature, the air valve may be a normally open valve that is held in a closed position between heating cycles by an electromagnet operated by the control voltage generated either by the thermostat or gas furnace. Alternatively, a warning signal can be broadcast indicating an air valve or air pump malfunction so that corrective action may be taken. Regardless of the type of positive-displacement air pump used, it should, ideally, be manufacturable at low cost, reliable over a long period of usage, and capable of relatively quiet operation. Leaf shutter valve, disc valve
The invention will now be described in detail with reference to the attached drawing figures.
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For any of the pumps 800, 900, 1000, 1100 or 1200, the pump is operated at a speed that pumps the amount of air required by the furnace 102 for complete combustion of fuel consumed. If a constant speed pump motor is used, impeller rotational speed can be adjusted by adjustable belt or gear drives. Alternatively, a variable speed motor can be used to set the desired rotational speed.
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Although only several embodiments of the invention have been disclosed herein, it will be obvious to those having ordinary skill in the art that changes and modifications may be made thereto without departing from the spirit and scope of the invention as hereinafter claimed. For example, poppet valves, leaf valves (e.g., a durable version of a camera shutter), and disc valves should be considered within the scope of the present invention. In addition, any type of positive-displacement, including single and double-screw type pumps, should also be considered to be within the scope of the present invention.
Claims
1. In combination with a fuel-burning furnace controlled by a thermostat, said furnace being installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control device comprising:
- an apparatus having a first state which blocks the flow of combustion air through the duct and a second state which allows the flow of combustion air through the duct; and
- a control apparatus which establishes and maintains said first state during periods between furnace heating cycles and establishes and maintains said second state during furnace heating cycles.
2. The combination of claim 1, wherein said apparatus is a valve having a movable control element which either closes the duct when in a first position corresponding to said first state or opens the duct when in a second position corresponding to said second state, said movable control element operating under the control of said thermostat.
3. The combination of claim 2, wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves.
4. The combination of claim 2, wherein said movable control element is moved between said first and second positions by mechanical actuators selected from the group consisting of an electromagnet in combination with a spring, an electromagnet in combination with gravitational force, DC electric motors and AC electric motors.
5. The combination of claim 1, wherein said apparatus is a positive-displacement pump which prevents combustion air from flowing through the duct when in said first state and pumps combustion air through the duct when in said second state.
6. The combination of claim 5, wherein said positive-displacement pump is selected from the group consisting of sliding vane pumps, flexible vane pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps.
7. The combination of claim 5, wherein said positive-displacement pump is powered by electrical current that is controlled by a switch that, in turn, is controlled by said thermostat.
8. The combination of claim 7, which further comprises a transistor to which is applied a control voltage corresponding to an output voltage from said furnace thermostat, and wherein a high level control voltage causes said transistor to transmit power to said switch, thereby turning it ON, and a low level control voltage causes said transistor to cut power to said switch, thereby turning it OFF.
9. The combination of claim 5, wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors.
10. In combination with a fuel burning heating device controlled by a thermostat, said heating device installed in an enclosure located within a habitable structure and requiring a duct for admitting combustion air from outside the structure into the enclosure, a duct control apparatus comprising:
- means for blocking the flow of combustion air through said duct during periods between furnace heating cycles; and
- means for allowing the flow of combustion air through said duct during furnace heating cycles.
11. The combination of claim 10, wherein said means for blocking and said means for allowing is a valve having a movable control element which either closes the duct when in a first position or opens the duct when in a second position, said movable control element operating under the control of said thermostat.
12. The combination of claim 11, wherein said valve is selected from the group consisting of balloon valves, flapper valves, ball valves, and butterfly valves.
13. The combination of claim 11, wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and a spring.
14. The combination of claim 11, wherein said movable control element is moved between said first and second positions by the combination of an electromagnet and gravity.
15. The combination of claim 11, wherein said movable control element is moved between said first and second positions by an electric motor selected from the group consisting of DC motors and AC motors.
16. The combination of claim 10, wherein said means for blocking and said means for allowing is a positive-displacement pump which operates under the control of said thermostat.
17. The combination of claim 13, wherein said positive-displacement pump is selected from the group consisting of vane pumps, flexible member pumps, external gear pumps, internal gear pumps, Roots-type pumps, and rotary lobe pumps.
18. The combination of claim 13, wherein said positive-displacement pump is powered by an electric motor selected from the group consisting of DC and AC motors.
19. The combination of claim 10, wherein said means for blocking and said means for allowing are directly controlled by electrical power passing through a switch that is controlled by a signal generated by said thermostat.
20. The combination of claim 10, wherein said switch is selected from the group consisting of solenoids, bipolar junction transistors, junction field-effect transistors, and insulated-gate field effect transistors.
Type: Application
Filed: Feb 7, 2007
Publication Date: Sep 6, 2007
Inventor: Scott David Cowan (Lehi, UT)
Application Number: 11/672,412
International Classification: F24C 15/00 (20060101); F24C 3/00 (20060101);