Patent Application
20090255487
The present invention generally relates to fuel-fired heating appliances and, in a representatively illustrated embodiment thereof, more particularly relates to a fuel-fired direct vent water heater having a specially designed sealed combustion chamber assembly incorporated therein.
Modern fuel-fired direct vent water heaters are commonly provided with a “sealed” combustion chamber. In this context, the term “sealed” means that the water heater combustion chamber does not exceed the internal pressure-created leakage test flow rates set forth in section 2.33.3 of the American National Standard/CSA Standard for Storage Water Heaters With Input Ratings of 75,000 Btu Per Hour or Less.
While this sealed combustion chamber design provides the direct vent water heater with a variety of operational advantages, including facilitating a flammable vapor ignition resistant design of the water heater, it also tends to introduce a variety of undesirable operational characteristics including diminished ignition performance leading to sooting in the combustion chamber, decreases in burner flame stability, increased NOx emissions and a lessening in combustion performance. It would thus be desirable to provide a combustion chamber assembly for a fuel-fired heating appliance, such as a water heater, in which these potential design problems are eliminated or at least substantially diminished.
In carrying out principles of the present invention, in accordance with an illustrated embodiment thereof, a fuel-fired heating appliance is provided with a specially designed combustion chamber assembly. Representatively, but not by way of limitation, the appliance is a direct vent water heater, and the combustion chamber assembly incorporated therein is of a sealed configuration.
The combustion chamber assembly, which forms a bottom portion of the water heater disposed beneath the storage tank portion of the water heater through which a flue upwardly extends, comprises a hollow body having an interior circumscribed by a side wall, a plate member extending generally transversely to the side wall and dividing the interior into a combustion chamber, from which a flue upwardly extends through the tank, and an air intake plenum disposed beneath the combustion chamber. A fuel burner is centrally disposed in the combustion chamber in a spaced relationship with the plate member, and in a facing relationship with a central portion thereof. An air transfer opening extends through the central portion of the plate member.
According to one aspect of the invention, a first wall structure is disposed in the air intake plenum and extends inwardly from the combustion air intake opening. The first wall structure forms a first passage for receiving air drawn inwardly through the combustion air intake opening and flowing a portion of the received air to the air transfer opening for transfer therethrough into the combustion chamber, the first passage having a volume substantially less that that of the air intake plenum. Illustratively, the first passage has a progressively narrowing configuration operative to funnel the portion of the received air to the air transfer opening, and the first wall structure includes two elongated, opposite sloped support leg structures underlying the plate member. Additional combustion air entering the air intake plenum may bypass the air transfer opening and flow into the combustion chamber via openings in the support legs and a peripheral gap circumscribing an outer edge portion of the plate member and disposed between such outer edge portion and a facing portion of the interior surface of the hollow body.
According to another aspect of the invention, a second wall structure is disposed in the combustion chamber and extends from the central portion of the plate member to adjacent the fuel burner, the second wall structure forming a second passage for receiving combustion air exiting the air transfer opening and flowing the received combustion air to the fuel burner. Illustratively, the second passage has a progressively narrowing configuration and is operative to funnel the received combustion air to the fuel burner. Preferably, the second wall structure includes an air transfer member having a hollow, generally frustroconical configuration with an open inlet end portion positioned against the plate member and circumscribing the air transfer opening therein, and a smaller area open outlet end portion positioned adjacent the fuel burner and separated therefrom by a gap through which combustion air may outwardly pass.
Illustratively, the fuel burner has a fuel/air mixture-receiving inlet structure generally aligned with the open outlet end portion of the air transfer member, and the water heater further comprises a fuel discharge nozzle disposed in the inlet end portion of the air transfer member and being operative to discharge received fuel for mixture with combustion air entering the air transfer member via the air transfer opening in the plate member.
This invention provides a fuel-fired heating appliance which is representatively a direct vent water heater 10, a lower portion of which is somewhat schematically depicted in
Water heater 10 is illustratively a gas-fired direct vent water heater and has a combustion chamber 12 underlying the bottom wall 13 a vertically oriented, generally circularly cross-sectioned water storage tank 14 through the interior of which a flue 16, communicating with the combustion chamber 12, upwardly extends. A gas burner 18 is disposed within the combustion chamber 12 and is supplied with fuel through a gas supply line 20 connected to the usual thermostatic gas valve 21 mounted on a side portion of the tank 14. Combustion air 22 is also supplied to the burner 18, in a unique manner subsequently described herein, via an air delivery passage 24 extending downwardly through an insulation space 26 disposed between the tank 14 and a metal jacket structure 28 outwardly surrounding the tank 14 in a manner similar to that shown in
Combustion chamber 12 forms a portion of a specially designed sealed combustion chamber assembly A that houses the burner 18 and embodies principles of the present invention. Combustion chamber 12 is bounded on its top side by the bottom wall 13 of the tank 14, and on its side by a downward side wall extension 14a of the tank 14. The bottom wall of the combustion chamber 12 is defined by a circular air transfer plate structure 30 which also forms the top wall of an air inlet plenum 32 that underlies the combustion chamber 12 and communicates with the air passage 24 via a side wall opening 34 of the plenum 32. Air inlet plenum 32 has a bottom wall 35. Air transfer openings 36 (see
With reference now to
As illustrated in
As may be best seen in
With reference now to
At the same time, combustion air 22 is drawn downwardly through the passage 24 and into the air transfer plenum 32 through its side wall opening 34. Combustion air 22 drawn into the air transfer plenum 32 in this manner travels leftwardly therethrough (as viewed in
A first portion of the combustion air 22 entering the air transfer plenum 32 passes upwardly through the plate openings 36 (see
A second portion of the combustion air 22 entering the air transfer plenum 32 passes upwardly through the plate openings 36 (see
A third portion of the combustion air 22 entering the air transfer plenum 32 bypasses the transfer plate openings 36 and flows upwardly into the combustion chamber 12 via the gap 38 (see
As can be readily seen from the foregoing, despite the introduction of combustion air 22 to the plenum 32 via only a limited circumferential side wall portion thereof, the sealed combustion chamber assembly A of the present invention functions to provide accurate positional control of the delivered combustion air by routing primary combustion air 22a to a location directly beneath the centrally located burner 18, for mixture with the discharged fuel 64), and by routing secondary air flows 22b,22c uniformly to the periphery of the burner 18 for supporting the flame 58 which it creates. Because of this positional control of incoming combustion air, the sealed combustion chamber assembly A provides the water heater 10 with enhanced ignition performance, decreased NOx emissions, and increased combustion performance.
As previously mentioned herein, the present invention is not limited to water heaters, but may also be utilized to advantage in a variety of other types of fuel-fired heating appliances such as, for example but not by way of limitation, boilers and furnaces. A variety of modifications may be made to the representatively disclosed heating appliance structure without departing from principles of the present invention. For example, the combustion air may be delivered to the water heater through a path external to the outer jacket portion of the water heater. Additionally, while the representatively depicted water is a direct vent water heater, it could be an alternative type of water heater.
The foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.
