High capacity fuel-fired liquid heating apparatus

A fuel-fired high capacity liquid heating appliance, representatively a boiler or a water heater, has a fluid heat exchanger extending around a combustion chamber into which first and second fuel burners extend, the first and second burners respectively having associated blowers for supplying combustion air thereto. Illustratively, the combustion chamber is oval-shaped, with the burners extending into opposite ends the combustion chamber If one of the burners is not firing while the other burner is firing, a control system starts the non-firing burner's blower, to protect it from overheating by the firing burner, if the control system senses an excess temperature in the non-firing burner. The heat exchanger comprises a series of fluid receiving tubes extending between baffle-free header structures iteratively sized to equalize fluid flow rates through the heat exchanger tubes over a wide flow rate range.

BACKGROUND OF THE INVENTION

The present invention generally relates to liquid heating apparatus and, in a representatively illustrated embodiment thereof, more particularly provides a specially designed high capacity gas-fired commercial heating appliance illustratively in the form of a water heater or boiler

As conventionally manufactured, multiple burner high capacity fuel-fired liquid heating appliances, such as water heaters or boilers, may have associated therewith various design challenges such as protecting non-firing burners from overheating by adjacent firing burners, and equalizing fluid flow through heat exchanger tubing sections over wide flow rate ranges. Accordingly, it would be desirable to provide a high capacity fuel-fired liquid heating appliance which effectively addresses these design challenges. It is to these design challenges that the present invention is primarily directed.

DETAILED DESCRIPTION

The fuel-fired liquid heating apparatus10depicted inFIGS. 1-3is representatively a high capacity gas-fired commercial water heater or boiler illustratively having, depending on the model provided, a maximum firing rate in the range of from about 2,000,000 Btuh to about 5,000,000 Btuh, but alternatively could utilize a different type of fuel, have a different firing rate capacity, or could be utilized to heat a liquid other than water without departing from principles of the present invention. In the illustrated representative embodiment thereof, the apparatus10has a vertically elongated outer metal jacket12having a generally rectangular configuration, top and bottom ends14and16, front and rear sides18and20, left and right sides22and24, and an interior space26.

Operatively disposed within the interior26of the jacket12is a specially designed heat exchanger assembly28that embodies principles of the present invention. The heat exchanger assembly28, as best illustrated inFIG. 3, has a hollow outer body or baffle30with a vertically elongated configuration and, along its vertical length, an elongated, generally oval cross-sectional shape. The interior of the body30defines for the apparatus10a combustion chamber32and, for purposes later described herein, a series of side wall openings34are formed through the vertical side wall of the body30. Extending vertically along an interior side periphery of the combustion chamber32are a series of fin/tube type heat exchanger tubes36which are coupled, by subsequently described bottom and top header groups38and39, to water inlet and outlet connections40and42extending outwardly through the rear side20of the outer jacket12.

A pair of combustion air blowers44and46are positioned as shown within the jacket12above the rounded side portions48of the heat exchanger outer body30, with the outlets of the blowers44,46being respectively coupled to the inlets of a pair of tubular fuel burners50,52that extend downwardly into the combustion chamber32as later described herein. Gaseous fuel is supplied to the burners50,52via a fuel supply line54extending inwardly through the rear side20of the jacket12. Fuel control valves56,58disposed in the line54are respectively associated with the burners50,52. As can be seen inFIG. 3, the burners50,52are positioned in the combustion chamber32, within the generally oval array of heat exchanger tubes36, at the opposite ends of a central portion of the combustion chamber32that extends between the burners50,52and is substantially devoid of structure intervening between the burners50,52.

Other controls operatively associated with the high capacity liquid heating apparatus10include a temperature controller60, a dual safety device/ignition system62, and an LCD display64on the front side18of the jacket12, and an electrical/power supply66positioned on the rear side20of the jacket12.

During firing of the liquid heating apparatus10, combustion air68is drawn into the interior of the jacket by one or both of the blowers44,46via a filtered air intake70on the rear side20of the jacket. Combustion air68drawn into one or both of the blowers44,46is forced into one or both of the burners50,52wherein the air mixes with fuel supplied to the burners and is combusted with the fuel to form hot combustion products72that are downwardly discharged into the combustion chamber32. Combustion products72entering the combustion chamber32are forced across the finned heat exchanger tubes36to transfer combustion heat to water74being flowed therethrough via the inlet and outlet connections40and42. Reduced temperature combustion products72are then discharged to the interior jacket space26, via the side wall openings34in the heat exchanger body30and flow outwardly from the jacket interior26via a combustion product outlet connection76on the rear side20of the jacket12.

A suitably supported vertical baffle panel83(seeFIG. 3) is disposed within the jacket12, forwardly of the combustion product outlet connection76, and functions in a generally conventional manner to prevent short circuiting of the hot combustion products72from the heat exchanger assembly28to the combustion product outlet connection76.

Turning now toFIG. 4, a schematically depicted control system80is operative to receive a water temperature signal82transmitted, for example, from a temperature sensor (not shown) that detects the temperature of water exiting the water outlet line42, and responsively energize and modulate either or both of the blower/burner sets44,50and46,52, including modulating their associated fuel valves56and58, as necessitated by operating conditions and the particular water temperature set point.

In addition to providing the control flexibility of utilizing dual burners operatively positioned in a horizontally spaced apart relationship within a single combustion chamber, the present invention provides the additional advantageous aspect of protecting the burners50,52from thermal damage in the event that either of them is in a non-firing state while the other burner is being fired under the control of the system80.

This unique feature is achieved in the present invention by operatively associating with each of the burners50,52a temperature sensing device such as the illustrated thermistors84and86, to provide to the control system80burner temperature signals88,90respectively indicative of the temperatures of the air inside the burners50and52. If one of the burners50,52is in a non-firing state during the firing of the other burner and the non-firing burner's thermistor temperature signal is above a predetermined magnitude, the control system80is automatically operative to start the blower associated with the non-firing burner and initiate a flow of cooling air through the non-firing burner to protect it (and its associated controls) from overheating due to the heat being generated within the combustion chamber32by the firing burner.

Further overheating protection for the non-firing burner is afforded by the elongated, preferably generally oval cross-sectional shape of the vertical heat exchanger body30within which the two burners50,52extend downwardly through the top sides of the rounded horizontally opposite end portions of the body30inwardly of the interior array of heat exchange tubes36. This places the burners50,52at substantially a maximum horizontal operational distance away from one another within the combustion chamber32, thereby lessening the firing heat transferred to the non-firing burner from the firing burner.

FIGS. 5-7illustrate a heat exchange tube and header portion92of the heat exchanger assembly28removed from the overall liquid heating apparatus10. The tube and header portion92includes the previously mentioned vertically extending finned heat exchange tubes36and the bottom and top water heater groups38,39between which they extend. The bottom header group38is operatively mounted on the bottom side of a bottom closure plate94which forms the bottom end of the combustion chamber32. The top header group39is mounted on the top side of a top closure plate96which forms the top end of the combustion chamber32and through which the aforementioned burners50,52downwardly extend into the combustion chamber32.

As best illustrated inFIGS. 6 and 7, the bottom water flow header group38representatively comprises a generally oval array of three separate arcuate headers38a,38band38c, and the top water flow header group39representatively comprises a generally oval array of two separate arcuate headers39aand39b. By way of non-limiting example, there are forty eight vertical finned heat exchange tubes36in the heat exchanger assembly28. A first group of twelve tubes36interconnects the headers38aand39a; a second group of twelve tubes36interconnects the headers39aand38b; a third group of twelve tubes36interconnects the headers38band39b; and a fourth group of twelve tubes36interconnects the headers39band38c. As illustrated, an inlet connection98(connectable to the exterior inlet connection40) is coupled to the bottom header38a, and an outlet connection100(connectable to the exterior outlet connection42) is coupled to the bottom header38c.

During operation of the liquid heating apparatus10, water74flows sequentially (1) into the bottom header38athrough the inlet connection98; (2) upwardly from the bottom header38ainto the top header39athrough the first group of tubes36; (3) downwardly from the top header39ainto the bottom header38bthrough the second group of tubes36; (4) upwardly from the bottom header38binto the top header39bthrough the third group of tubes36; (5) downwardly from the top header39binto the bottom header38cthrough the fourth group of tubes36; and then (6) outwardly through the outlet connection100.

According to a further aspect of the present invention, the interiors of the headers in the bottom and top header groups38and39are devoid of baffles which are customarily utilized in liquid heat exchanger headers in an attempt to equalize flow through their associated heat exchanger tubes. Instead of utilizing these baffles, which tend to undesirably increase the liquid pressure drop through their associated heat exchanger structures, in the present invention the interiors of the headers in the bottom and top header groups38and39are iteratively configured to provide a substantially equal water flow through each of the finned heat exchange tubes36(within about a ±10% range) over a wide variation in total water flow rate through the heat exchanger assembly28. By way of non-limiting example, such flow rate range is between about 60 gpm to about 270 gpm. After the iterative design of the interior configurations of the baffle-free headers is completed, the accuracy of the designed-for balancing of the water flow through the tubes36over the desired water flow rate range may be verified using a conventional computational flow dynamics (CFD) analysis program well known to those skilled in this particular art.

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.