US20120178031A1

US20120178031A1 - Push and Pull Premix Combustion System With Blocked Vent Safety Shutoff

Info

Publication number: US20120178031A1
Application number: US13/311,886
Authority: US
Inventors: William J. Roy
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2011-01-11
Filing date: 2011-12-06
Publication date: 2012-07-12

Abstract

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.

Description

FIELD OF THE DISCLOSURE

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 DISCLOSURE

Gas 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 NO_xproduction. 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 DISCLOSURE

In 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.

BRIEF DESCRIPTION OF THE 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:

FIG. 1 is a block diagram of an embodiment of a furnace with a pull combustion system constructed in accordance with the teachings of the prior art;

FIG. 2 is a front perspective view of an embodiment of a furnace with a pull combustion system constructed in accordance with the teachings of the prior art;

FIG. 3 is a block diagram of an embodiment of a furnace with a push and pull premix combustion system constructed in accordance with the teachings of the present disclosure;

FIG. 4 is a front perspective view of an embodiment of a furnace with a push and pull premix combustion system constructed in accordance with the teachings of the present disclosure;

FIG. 5 is a perspective view of an embodiment of a furnace with an exploded view of a push and pull premix combustion system constructed in accordance with the teachings of the present disclosure;

FIG. 6 is a block diagram of a second embodiment of a furnace with a push and pull premix combustion system constructed in accordance with the teachings of the present disclosure;

FIG. 7 is a partial perspective view of a furnace with a blocked vent safety shutoff coupled to a push and pull premix combustion system constructed in accordance with the teachings of the present disclosure.

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 DISCLOSURE

In FIGS. 1 and 2, a furnace 100 with a pull combustion system which may be operated according to the principles of the prior art is illustrated. Pull combustion systems operate with negative pressure throughout the combustion system, wherein air and gas are pulled into a burner box for combustion, and then upon ignition, combustion products may be pulled out of the burner box. Induced-draft furnaces commonly utilize a pull combustion system. The induced-draft furnace 100 may include a cabinet 102, housing therein a burner box 104, a gas valve assembly 106, a heat exchanger 108, an induced-draft blower 110, and a circulating air blower 112. In operation, gas valve assembly 106 may meter the flow of gas 114 through a gas manifold 116, through a burner tube 118, and into the burner box 104. Simultaneously, the induced-draft blower 110 may pull atmospheric air 120 from an air inlet 122 of the burner tube 118 into the burner box 104, wherein air 120 and gas 114 may be mixed and then ignited by an igniter 124. A flame sensor 126 housed in the burner box 104 may ensure that combustion successfully occurs and a flame 128 may be present. Hot gaseous combustion products 130 may then be drawn through the heat exchanger 108 by the induced-draft blower 110 and expelled through a flue pipe 132, out of the home, and into the atmosphere. As the hot gaseous combustion products 130 flow through the heat exchanger 108, air 134 may be heated as it blows across the heat exchanger 108, circulated through the air ducts (not shown), and directed back into home by the circulating air blower 112.
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 FIGS. 3-5, the present disclosure therefore provides a furnace 200 with a push and pull premix combustion system. The following description may be made with reference to a furnace 200, but it should be understood that the present disclosure contemplates incorporating a push and pull premix combustion system with a water heater, boiler, or any other type of unit capable of combustion.
Referring now to FIGS. 3 and 4, a furnace 200 may include a cabinet 202, housing therein a burner box 204, a gas valve assembly 206, a heat exchanger 208, an induced-draft blower 210, a circulating air blower 212, and a premix chamber 235 housing within it, a premix blower 236 with a premix blower motor 238. In operation, gas valve assembly 206 may meter the flow of gas 214 into the premix chamber 235, while atmospheric air 220 may be drawn into the premix chamber 235 by the premix blower motor 238. The premix blower 236 may mix gas 214 and air 220 and may push a lean gas/air mixture 240 through a gas manifold 216, past a flow tuning screen 242 and a burner mixing tube 244, and into the burner box 204. Within the burner box 204, the lean gas/air mixture 240 may be ignited by an igniter 224. A flame sensor 226 housed in the burner box 204 may ensure that a combustion successfully occurred and a flame 228 may be present. Hot gaseous combustion products 230 may then be pulled through the heat exchanger 208 by the induced-draft blower 210 and expelled through a flue pipe 232, out of the home, and into the atmosphere. As the hot gaseous combustion products 230 flow through the heat exchanger 208, air 234 may be heated as it blows across the heat exchanger 108, circulated through the air ducts (not shown), and directed back into home by the circulating air blower 212.
Referring now to FIG. 5, an exploded view of the push and pull premix combustion system in furnace 200 is illustrated. The gas valve assembly 206 may be coupled to the premix chamber 235, housing within it, the premix blower 236 and the premix blower motor 238. The premix blower motor 238 may be coupled to the premix blower 236. The premix chamber 235 may be coupled to the gas manifold 216. The gas manifold 216 may be coupled to the burner mixing tubes 244 with at least one flow tuning screen 242 in between each burner mixing tube 244 and gas manifold outlet 216 a. Mixing tube adapters 246 may mount the burner mixing tubes 244 to the burner box 204. The flame sensors 226 and igniters 224 may be accommodated by the burner box 204. The burner box 204 also may house premix burners 248, which may be mounted onto the burner box 204. A cell panel adaptor bracket 250 may mount the burner box 204 to the furnace 200.
In FIG. 6, another exemplary embodiment of a furnace 300, similar to furnace 200 is disclosed. The furnace 300 may operate similarly to furnace 200 with at least one exception. Instead of gas 214 and air 220 being premixed in the premix chamber 235, as depicted with furnace 200, gas 314 and air 320 may be premixed within a burner mixing tube 344 in furnace 300. In operation, gas valve assembly 306 may meter the flow of gas 314 through a gas manifold 316 and into the burner mixing tube 344. Simultaneously, an air blower 352 may draw atmospheric air 320 into the burner mixing tube 344, wherein air 320 and gas 314 may be mixed. Within burner mixing tube 344, a lean gas/air mixture 340 may then be pushed by the air blower 352 into the burner box 304, wherein it may be ignited by an igniter 324. A flame sensor 326 housed in the burner box 304 may ensure that a combustion successfully occurred and a flame 328 may be present. Hot gaseous combustion products 330 may then be pulled through the heat exchanger 308 by the induced-draft blower 310 and expelled through a flue pipe 332, out of the home, and into the atmosphere. As the hot gaseous combustion products 330 flow through the heat exchanger 308, air 334 may be heated as it blows across the heat exchanger 308, circulated through the air ducts (not shown), and directed back into home by the circulating air blower 312.
In FIGS. 3-6, as the lean gas/ air mixture 240, 340 is pushed into the burner box 204, 304, a positive pressure may start to accumulate in the burner box 204, 304, and may leak into the heat exchanger 208, 308. If a positive pressure is formed in the heat exchanger 208, 308, any breach in the heat exchanger 208, 308 may result in combustion products leaking out of the heat exchanger 208, 308 and into the home air 234, 334. To avoid this, the positive pressure may be negated by the greater negative pressure created in the burner box 204, 304 by the pulling-effect of the induced- draft blower 210, 310. The negative pressure may ensure that any breach in the heat exchanger 208, 308 would not result in combustion products leaking out of the heat exchanger 208, 308, and into the home air 234, 334.
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 FIGS. 3, 6, and 7, a blocked vent safety shutoff (BVSS) housing 256, 356 may be mounted over the opening 254, 354 of the burner box 204, 304 in such a manner so as not to block the opening 254, 354. The BVSS housing 256, 356 includes an opening 256 a, 356 a which may be aligned with the opening 254, 354 on the burner box 204, 304. A thermal switch 258, 358 may be coupled to the BVSS housing 256, 356. It is to be understood that any other type of a temperature sensor, besides the thermal switch 258, 358, may be incorporated herein. As positive pressure exceeds negative pressure in the burner box 204, 304, hot gaseous combustion products 230, 330 may seep out of the opening 254, 354, making thermal contact with the thermal switch 258, 358. Once the temperature of the outwardly flowing hot gaseous combustion products 230, 330 reaches a specific level, a bimetal element (not shown) in the thermal switch 258, 358 may open and shutoff the gas valve assembly 206, 306.
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 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.