Push and Pull Premix Combustion System With Blocked Vent Safety Shutoff
A furnace with a push and pull combustion system is disclosed. The furnace may include a cabinet housing a burner box, a gas valve assembly, a premix chamber, a heat exchanger, a blower, an induced-draft blower, and a flue pipe. The gas valve assembly may meter gas into the premix chamber, while the blower may draw air into the premix chamber, wherein air and gas may mix to produce a lean gas/air mixture. The blower may also push the lean gas/air mixture into the burner box. The burner box may ignite the lean gas/air mixture to produce combustion products. A blocked vent safety shutoff switch may be mounted over an opening of the burner box to ensure negative pressure by detecting any leakage of combustion products. The induced-draft blower may pull the combustion products through the heat exchanger, the flue pipe, and out into the atmosphere.
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The present disclosure generally relates to furnaces and, in particular, relates to a push and pull premix combustion system with blocked vent safety shutoff in a furnace.
BACKGROUND OF THE DISCLOSUREGas furnaces are widely installed in homes for heating purposes. Furnaces contain a burner box wherein a mixture of gas and air are burned, creating hot gaseous products of combustion. One common type of furnace is an induced-draft gas furnace. In an induced-draft gas furnace, a gas valve typically establishes the flow of gas to the burners while a motor-controlled blower induces air for combustion by creating a negative pressure. Within the burner box, air and gas are mixed and ignited by an igniter, creating hot gaseous combustion products. Negative pressure is important for the furnace to operate safely. The negative pressure created by the induced-draft blower ensures that the gaseous combustion products are pulled through a heat exchanger and then pushed out of the home through a sealed vent system. In instances where the induced-draft blower may be operating ineffectively by not inducing enough air, an inappropriate air to gas mixture may occur reducing the designed in negative pressure and potentially allowing the furnace to emit combustion gases into the home. Combustion emission, also referred to as NO emission, is of increasing concern due to the health hazard and atmospheric pollution it creates. Moreover, regulations are mandating stricter emission limitations. A need for a lean gas/air mixture is thus in demand.
A known technique for achieving gas-lean operation is to premix the gas with air before burning it. Such premixing allows the gas and air mixture to burn cooler, reducing NOx production. A drawback to premixing the gas and air is that it increases the quantity of combustible mixture. Thus, increasing the potential for flame flash back, auto ignition, and detonation if positive pressures propagate into the burner box. Such hazards are unacceptable. Thus, a need for a gas-lean operating furnace that ensures negative pressure operation still remains.
SUMMARY OF THE DISCLOSUREIn accordance with one aspect of the disclosure, a push and pull combustion system for a furnace is disclosed. The push and pull combustion system may include a premix chamber, a gas valve assembly, a blower, a burner box, and an induced-draft blower. The premix chamber may mix gas and air to produce a lean gas/air mixture. The gas valve assembly, coupled to the premix chamber, may meter gas into the premix chamber. The burner box, downstream of the premix chamber, may have an igniter which may ignite the lean gas/air mixture to produce combustion products. The blower, coupled to the premix chamber, may draw air into the premix chamber. The blower may also push the lean gas/air mixture into the burner box. The induced-draft blower may pull the combustion products out of the burner box.
In accordance with another aspect of the disclosure, a furnace with a push and pull combustion system is disclosed. The furnace may include a cabinet housing therein a burner box, a gas valve assembly, a premix chamber, a heat exchanger, a blower, an induced-draft blower, and a flue pipe. The premix chamber may mix gas and air to produce a lean gas/air mixture. The gas valve assembly, coupled to the premix chamber, may meter gas into the premix chamber. The burner box, downstream of the premix chamber, may have an igniter which may ignite the lean gas/air mixture to produce combustion products. The blower, coupled to the premix chamber, may draw air into the premix chamber, wherein air and gas may mix to produce a lean gas/air mixture. The blower may also push the lean gas/air mixture into the burner box. The heat exchanger may be downstream of the burner box. The flue pipe may be downstream of the heat exchanger. The induced-draft blower, coupled in-between the flue pipe and the heat exchanger, may pull the combustion products through the heat exchanger, then push the combustion products through the flue pipe, and out into the atmosphere.
In accordance with yet another aspect of the disclosure, a method for controlling combustion emission for a furnace is disclosed. The method may include metering gas into a premix chamber, drawing air into the premix chamber, mixing gas and air within the premix chamber to produce a lean gas/air mixture, pushing the lean gas/air mixture into a burner box, igniting the lean gas/air mixture within the burner box to produce combustion products, and pulling the combustion products out of the burner box.
Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.
For a more complete understanding of the disclosed system and method, reference should be made to the embodiments illustrated in greater detail in the accompanying drawings, wherein:
It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and systems or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.
DETAILED DESCRIPTION OF THE DISCLOSUREIn
As stated above, premixing gas and air prior to combustion may ensure a leaner gas/air mixture and thus lower NO emission. However, in the event the induced-draft blower 110 may be operating ineffectively, i.e. inefficient air to gas mixture may occur, excessive NO emission may be produced and expelled into the atmosphere or even the home, in the event the flue pipe 132 may be clogged. In
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Another feature of the present disclosure may be reduced harmonics or acoustics, making the unit relatively quiet to operate. By way of background it is important to understand that as the positive pressure from upstream collides with the negative pressure from downstream, combustion resonance may occur in the burner box 204, 304. To reduce this combustion oscillation, openings 254, 354 in the burner box 204, 304 may allow the burner box 204, 304 to communicate with atmospheric pressure, thus decoupling the upstream and downstream acoustic paths. With the upstream and downstream paths decoupled, the two paths may no longer react to each other during combustion, thus eliminating combustion resonance and lowering sounds emitted by the furnace 200, 300. In one exemplary embodiment, the size of the opening 254, 354 relative to the volume of the burner box 204, 304 may determine the effectiveness of the decoupling.
Furthermore, in the event that positive pressure exceeds negative pressure in the burner box 204, 304, the gas valve assembly 206, 306 may be shutoff as a safety precaution. In one exemplary embodiment, positive pressure may exceed negative pressure if an imbalance in push versus pull occurs due to, but not limited to, the induced-draft blower 210, 310 operating ineffectively or malfunctioning, and/or the heat exchanger 208, 308 or the flue pipe 232, 332 being clogged. In
In one exemplary embodiment, the thermal switch 258, 358 may be an auto-resettable thermal switch with an algorithm as described in detail in U.S. Pat. No. 6,851,948, owned by the assignee of the present disclosure and the disclosure of which is incorporated herein by reference in its entirety. The auto-resettable thermal switch in disclosure '948 is capable of resetting itself, i.e. closing the bimetal element in the thermal switch, automatically. Furthermore, the algorithm in disclosure '948 ensures a self-recovery method without a significant increase in combustion product emissions into a given space.
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.
Claims
1) A push and pull combustion system for a furnace, comprising:
- a premix chamber capable of mixing gas and air to produce a lean gas/air mixture;
- a gas valve assembly coupled to the premix chamber and capable of metering gas into the premix chamber;
- a burner box downstream of the premix chamber;
- a blower coupled to the premix chamber and capable of drawing air into the premix chamber, and pushing the lean gas/air mixture into the burner box;
- an igniter associated with the burner box capable of igniting the lean gas/air mixture to produce combustion products; and
- an induced-draft blower capable of pulling the combustion products out of the burner box.
2) The push and pull combustion system of claim 1, wherein the burner box includes an opening and a blocked vent safety shutoff switch is mounted over the opening, the blocked vent safety shutoff switch adapted to make thermal contact with fluid flowing out of the opening, and sense leakage of combustion products out of the burner box.
3) The push and pull combustion system of claim 2, wherein the blocked vent safety shutoff switch is a thermal switch.
4) The push and pull combustion system of claim 1, wherein the blower creates an upstream path of positive pressure in the burner box, while the induced-draft blower creates a downstream path of negative pressure in the burner box, and wherein the burner box includes an opening for decoupling the upstream path from the downstream path by maintaining atmospheric pressure in the burner box.
5) The push and pull combustion system of claim 4, wherein the opening is sized relative to the volume of the burner box to determine the effectiveness of the decoupling.
6) The push and pull combustion system of claim 1, wherein the gas valve assembly meters gas into a premix blower and a premix motor draws air into the premix blower, the air and gas mixing in the premix blower to produce the lean gas/air mixture, the premix blower pushing the lean gas/air mixture into the burner box.
7) The push and pull combustion system of claim 1, wherein the gas valve assembly meters gas into a burner mixing tube and an air blower draws air into the burner mixing tube, the air and gas mixing in the burner mixing tube to produce the lean gas/air mixture, the air blower pushing the lean gas/air mixture into the burner box.
8) A furnace with a push and pull combustion system, comprising:
- a premix chamber capable of mixing gas and air to produce a lean gas/air mixture;
- a gas valve assembly coupled to the premix chamber and capable of metering gas into the premix chamber;
- a burner box downstream of the premix chamber;
- an igniter associated with the burner box and adapted to ignite the lean gas/air mixture to produce combustion products;
- a blower coupled to the premix chamber and adapted to draw air into the premix chamber, wherein air and gas mix to produce a lean gas/air mixture, the blower then pushing the lean gas/air mixture into the burner box;
- a heat exchanger downstream of the burner box;
- a flue pipe downstream of the heat exchanger;
- an induced-draft blower coupled in-between the flue pipe and the heat exchanger and adapted to pull the combustion products through the heat exchanger, the flue pipe, and out into the atmosphere; and
- a cabinet housing therein the burner box, the gas valve assembly, the premix chamber, the heat exchanger, the blower, the induced-draft blower, and the flue pipe.
9) The furnace of claim 8, wherein the burner box includes an opening and a blocked vent safety shutoff switch is mounted over the opening, the blocked vent safety shutoff switch adapted to make thermal contact with fluid flowing out of the opening and sense leakage of combustion products out of the burner box.
10) The furnace of claim 9, wherein the blocked vent safety shutoff switch is a thermal switch.
11) The furnace of claim 8, wherein the blower creates an upstream path of positive pressure in the burner box, while the induced-draft blower creates a downstream path of negative pressure in the burner box, and wherein the burner box includes an opening for decoupling the upstream path from the downstream path by maintaining atmospheric pressure in the burner box.
12) The furnace of claim 8, wherein the gas valve assembly meters gas into a premix blower and a premix motor draws air into the premix blower, the air and gas mixing to produce the lean gas/air mixture, and the premix blower pushing the lean gas/air mixture into the burner box.
13) The furnace of claim 8, wherein the gas valve assembly meters gas into a burner mixing tube and an air blower draws air into the burner mixing tube, the air and gas mixing to produce the lean gas/air mixture, and the air blower pushing the lean gas/air mixture into the burner box.
14) A method for controlling combustion emission for a furnace, comprising the steps of:
- metering gas into a premix chamber;
- drawing air into the premix chamber;
- mixing gas and air within the premix chamber to produce a lean gas/air mixture;
- pushing the lean gas/air mixture into a burner box;
- igniting the lean gas/air mixture within the burner box to produce combustion products; and
- pulling the combustion products out of the burner box.
15) The method of claim 14, wherein the air is drawn by a premix motor into a premix blower and gas is metered by a gas valve assembly into the premix blower, the air and gas mixing in the premix blower to produce the lean gas/air mixture, the lean gas/air mixture being pushed by the premix blower into the burner box.
16) The method of claim 14, wherein air is drawn by an air blower into a burner mixing tube and gas is metered by a gas valve assembly into the burner mixing tube, the air and gas mixing in the burner mixing tube to produce the lean gas/air mixture, the lean gas/air mixture being pushed by the air blower into the burner box.
17) The method of claim 14, wherein the combustion products are pulled out of the burner box by an induced-draft blower.
18) The method of claim 14, wherein the lean gas/air mixture is pushed into the burner box by a blower.
19) The method of claim 14, further comprising the step of ensuring negative pressure in the burner box by mounting a blocked vent safety shutoff switch relative to an opening of the burner box, the blocked vent safety shutoff switch detecting leakage of combustion products out of the burner box.
20) The method of claim 14, wherein pushing the lean gas/air mixture into the burner box creates an upstream path of positive pressure in the burner box and pulling the combustion productions out of the burner box creates a downstream path of negative pressure in the burner box, and wherein the burner box further includes an opening for maintaining atmospheric pressure in the burner box and decoupling the upstream path from the downstream path.
Type: Application
Filed: Dec 6, 2011
Publication Date: Jul 12, 2012
Applicant: Carrier Corporation (Farmington, CT)
Inventor: William J. Roy (Avon, IN)
Application Number: 13/311,886
International Classification: F24H 9/20 (20060101); F24H 9/02 (20060101); F23D 14/02 (20060101); F24H 3/06 (20060101);