Stoves and furnaces – Hot-air furnaces – Compressed air
Reissue Patent
1997-10-03
2001-04-10
Yeung, James C. (Department: 3743)
Stoves and furnaces
Hot-air furnaces
Compressed air
C126S09900D, C126S11600A
Reissue Patent
active
RE037128
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to furnaces, and, more particularly, to induced draft, fuel-fired furnaces having a standing pilot.
2. Description of the Related Art
High efficiency fuel-fired furnaces of the type herein concerned include a combustion chamber wherein fuel such as natural or liquified petroleum (LP) gas is burned creating hot gaseous products of combustion, i.e., exhaust gas. A burner having one or more exhaust ports formed therein is connected to a fuel source and burns the fuel which is ignited. The hot exhaust gas is circulated through a heat exchanger which is heated thereby. Air circulates past the heat exchanger and is heated thereby via convection heat transfer. The heated air is circulated through a living space by a circulating blower. In an induced draft furnace, an exhaust blower is located between the heat exchanger and the flue outlet of the furnace and draws the products of combustion through the heat exchanger and discharges them into an exhaust vent.
To ignite the fuel exhausted from the burner, it is known to use either an electronic ignition apparatus or a standing pilot. An electronic ignition apparatus is operably controlled when fuel is exhausted from the burner to ignite the fuel. An electronic ignition system is considerably more costly and complex than a standing pilot. A standing pilot maintains a continuously burning open flame regardless of whether fuel is exhausted from the burner. During periods of inactivity of the burner, therefore, it is necessary to vent the relatively small amount of combustion gas produced by the standing pilot to the flue and ambient environment. A furnace using a standing pilot is less expensive to manufacture than a furnace using an electronic ignition system and may therefore by preferred.
It is known to vent the combustion products produced by a standing pilot through the heat exchanger and into the flue. However, some high efficiency furnaces provide increased heat exchanger efficiency by increasing the pressure drop of the exhaust gas between the inlet and outlet of the heat exchanger. This may be accomplished by providing a longer flow path and/or appropriate sized conduits at various locations within the flow path. This higher pressure drop increases the efficiency of the heat exchanger when exhaust gas is circulated therethrough, thus requiring less heat transfer area for a given output; however, it also prohibits the venting of the standing pilot combustion products through the heat exchanger during periods of inactivity of the burner, i.e., idle flow conditions.
The higher pressure drop therefore further increases internal heat exchanger resistance prohibiting the safe venting of standing pilot combustion products. Thus, a standing pilot may be preferred to reduce manufacturing costs, but may not be safely vented into the heat exchanger and ultimately to the vent.
One method of obtaining the advantages of using a standing pilot while at the same time avoiding the problems of unsafe pilot gas venting mentioned above is to provide a vent tube disposed immediately above the standing pilot. The vent tube is connected to and in fluid communication with the outlet section of a draft inducing fan. Such an apparatus, however, requires relatively precise placement of the vent tube above the standing pilot flame and a specially manufactured or modified blower. Moreover, to prevent back flow of exhaust gas during operation of the blower, a special venturi section forming member must be rigidly fixed at a precise location within the blower adjacent the outlet of the vent tube, thereby further increasing manufacturing costs.
What is needed in the art is an apparatus and method which allows a standing pilot to be used with a high efficiency furnace by easily and inexpensively bypassing the combustion products of the standing pilot directly to the flue of the fuel-fired furnace.
SUMMARY OF THE INVENTION
The present invention provides an opening at the upper end of a vestibule section of a furnace using conventionally available components to allow venting of combustion products from a source of combustion products to the flue. Moreover, a drafthood is provided having openings formed therein for allowing the standing pilot combustion products to flow therethrough to the flue and may include a temperature sensor to detect a blocked flue condition.
The invention comprises, in one form thereof, an induced draft, fuel-fired furnace having a heat exchanger with an inlet and an outlet. A flue inlet defines a first cross-sectional area. A vented vestibule in fluid communication with the flue has disposed therein a burner in fluid communication with the heat exchanger inlet, a standing pilot adapted to ignite fuel operably discharged from the burner, a blower having an inlet in fluid communication with the heat exchanger outlet, and an outlet disposed at the inlet of said flue. The blower outlet defines a second cross-sectional area less than the first cross-sectional area. The portion of the first cross-sectional area not having the second cross-sectional area disposed immediately adjacent thereto defines a vent inlet opening allowing standing pilot combustion products to flow into the flue and ambient environment.
In another form of the invention, a drafthood is disposed in the vestibule and forms a plenum in fluid communication with the vent inlet opening. The drafthood includes an undersurface sealingly engaged with the blower outlet which extends immediately adjacent to a panel of the furnace. The undersurface is formed with an inlet adapted to receive combustion gases from the standing pilot, and a blocked flue detecting means adapted to detect a blocked exhaust gas flow condition in said flue.
An advantage of the present invention is that the combustion gas from the standing pilot is not circulated through the heat exchanger, thereby inhibiting potential associated corrosion of the heat exchanger and providing safe venting of the pilot.
Another advantage is that less expensive materials can be used to form the heat exchanger.
Yet another advantage is that the present invention can provide dual functionality of preventing heat exchanger corrosion and detecting a blocked vent.
Still another advantage is that the components within the vestibule need not be extensively and physically modified to vent the standing pilot to the vent.
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McKinney Steven W.
Tomlinson Ronald S.
Baker & Daniels
International Comfort Products Corporation (USA)
Yeung James C.
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