US20090308332A1

US20090308332A1 - Water heater with forced draft air inlet

Info

Publication number: US20090308332A1
Application number: US12/545,582
Authority: US
Inventors: Emadeddin Y. Tanbour
Original assignee: AO Smith Corp
Current assignee: AO Smith Corp
Priority date: 2007-10-01
Filing date: 2009-08-21
Publication date: 2009-12-17

Abstract

A water heater includes an air intake assembly that includes a blower for providing primary and secondary air to a combustion chamber at pressures above atmospheric pressure. The primary air is mixed with gaseous fuel and the mixture is combusted at a burner in a partially premixed but substantially diffusion flame having an envelope. Combustion of the mixture is completed within the envelope in the presence of secondary air at elevated pressure. A 24 V controller provides power to a user interface and a powered anode in the tank. The controller receives input from a pressure sensor in the air intake assembly, a flame sensor in the combustion chamber, and a flammable vapor sensor outside the water heater. The controller controls operation of the blower and a gas valve. A flue and baffle arrangement in the tank causes products of combustion from the burner to lose pressure and vent at near atmospheric pressure at the top of the flue. An air distributor plate creates a substantially uniform distribution of pressurized secondary air within the combustion chamber.

Description

This application claims priority under 35 U.S.C. 120 to U.S. patent application Ser. No. 11/865,378 filed Oct. 1, 2007, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present invention relates to a water heater having a forced draft air inlet.

SUMMARY

In one embodiment, the invention provides a water heater comprising: a tank for water to be heated; a powered anode extending into the tank and creating an electrical current to reduce corrosion of the tank; a combustion chamber; an exhaust structure; a flue in the tank communicating between the combustion chamber and the exhaust structure; a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank; a centrifugal blower forcing primary and secondary air into the combustion chamber at pressure above atmospheric; a gas valve for controlling a supply of gaseous fuel to the burner; a user interface for programming operating parameters of the water heater; and a 24 V controller that provides power to the user interface and powered anode, and that controls operation of the blower and gas valve.
In some embodiments, the water heater may include a pressure sensor operatively interconnected with the 24 V controller; wherein the pressure sensor generates a signal in response to sensing that the pressure of air downstream of the blower is below a minimum threshold; and wherein the 24 V controller closes the gas valve in response to receiving the signal from the pressure sensor. In some embodiments, the water heater may include a flammable vapor sensor operatively interconnected with the 24 V controller; wherein the flammable vapor sensor generates a signal in response to sensing the presence of flammable vapors outside of the water heater in concentrations above a maximum threshold; and wherein the 24 V controller closes the gas valve in response to receiving the signal from the flammable vapor sensor. In some embodiments, the water heater may include a pressure sensor sensing the pressure of air downstream of the blower; and a flammable vapor sensor sensing the presence of flammable vapors outside of the water heater; wherein the 24 V controller closes the gas valve upon the occurrence of any of the following: (a) conditions dictated by the user interface, (b) the pressure sensor sensing air pressure below a minimum threshold, and (c) the flammable vapor sensor sensing flammable vapors external to the water heater in concentrations above a maximum threshold.
In another embodiment, the invention provides a water heater comprising: a tank for water to be heated; a combustion chamber; an exhaust structure; a flue in the tank communicating between the combustion chamber and the exhaust structure; a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank; an air intake assembly including an air inlet above the combustion chamber and a conduit communicating between the air inlet and the combustion chamber; a centrifugal blower within the air intake assembly operable to suck air into the air intake assembly through the air inlet and force primary and secondary air into the combustion chamber through the conduit at pressure above atmospheric; a gas valve for controlling a supply of gaseous fuel to the burner; a controller that controls operation of the blower and gas valve; and a flammable vapor sensor external of the combustion chamber and lower than the air inlet, the flammable vapor sensor being operatively interconnected with the controller and operable to generate a signal in response to sensing the presence of flammable vapors outside of the water heater in concentrations above a maximum threshold; wherein all primary and secondary combustion air supplied to the combustion chamber flows through the air inlet and conduit; and wherein the controller closes the gas valve in response to receiving the signal from the flammable vapor sensor. In some embodiments, the flammable vapor sensor is lower than at least one of the combustion chamber and burner.
In another embodiment, the invention provides a water heater comprising: a tank for water to be heated; a combustion chamber; an exhaust structure; a flue in the tank communicating between the combustion chamber and the exhaust structure; a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank; an air intake assembly including an air inlet above the combustion chamber and a conduit communicating between the air inlet and the combustion chamber; a centrifugal blower within the air intake assembly operable to suck air into the air intake assembly through the air inlet and force primary and secondary air into the combustion chamber through the conduit at pressure above atmospheric; a gas valve for controlling a supply of gaseous fuel to the burner; a controller that controls operation of the blower and gas valve; and a baffle in the flue that restricts flow sufficiently to reduce the pressure of the products of combustion to near atmospheric upon flowing out of the flue into the exhaust structure. In some embodiments, the blower is an axial-intake, centrifugal blower. In some embodiments, the exhaust structure is a category I vent structure.
In another embodiment, the invention provides a water heater comprising: a tank for water to be heated; a combustion chamber; an exhaust structure; a flue in the tank communicating between the combustion chamber and the exhaust structure; a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank; an air intake assembly including an air inlet above the combustion chamber and a conduit communicating between the air inlet and the combustion chamber; a centrifugal blower within the air intake assembly operable to suck air into the air intake assembly through the air inlet and force primary and secondary air into the combustion chamber through the conduit at pressure above atmospheric; a gas valve for controlling a supply of gaseous fuel to the burner; and a controller that controls operation of the blower and gas valve; wherein the air intake assembly includes an interior space, all primary and secondary air being provided to the combustion chamber flowing through the interior space; and wherein the blower is mounted within the interior space of the air intake assembly.
In some embodiments, the blower is an axial-intake, centrifugal blower. In some embodiments, the air intake assembly includes a longitudinal extent; and the air intake assembly includes a two-piece construction divided along the longitudinal extent of the air intake assembly. In some embodiments, the interior space of the air intake assembly is non-cylindrical and has an equivalent hydraulic diameter of a four inch inner diameter tube. In some embodiments, at least a portion of the interior space of the air intake assembly is non-cylindrical to accommodate mounting the blower in the interior space; and the non-cylindrical portion of the interior space defines a minor dimension and a major dimension that is perpendicular to the minor dimension and at least twice the minor dimension. In some embodiments, the air intake assembly includes a partition that divides the interior space into an inlet side communicating with ambient air and an outlet side communicating with the combustion chamber, the partition including a window; and the blower is within the inlet side of the interior space and forces primary and secondary air into the outlet side of the interior space through the window in the partition. In some embodiments, the air intake assembly includes a louvered opening communicating between the inlet side and ambient air; and all air sucked into the inlet side of the interior space by the blower flows through the louvered opening. In some embodiments, the water heater further comprises a pressure sensor communicating with the interior space, the pressure sensor operable to disable the gas valve to cut off the supply of gaseous fuel to the burner when pressure within the interior space drops below a minimum threshold. In some embodiments, the air intake assembly includes an exterior surface, a sensor mounting cavity in the exterior surface and a wire routing channel in the exterior surface; the air intake assembly further includes a hole communicating between the sensor mounting cavity and the interior space; the pressure sensor is mounted within the sensor mounting cavity and communicates with the interior space through the hole; and the blower includes a power cord that is received in the wire routing channel.
In another embodiment, the invention provides a water heater comprising: a tank for water to be heated; a combustion chamber; an exhaust structure; a flue in the tank communicating between the combustion chamber and the exhaust structure; a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank; an air intake assembly including an air inlet above the combustion chamber and a conduit communicating between the air inlet and the combustion chamber; a centrifugal blower within the air intake assembly operable to suck air into the air intake assembly through the air inlet and force primary and secondary air into the combustion chamber through the conduit at pressure above atmospheric; a gas valve for controlling a supply of gaseous fuel to the burner; a controller that controls operation of the blower and gas valve; an air distributor plate having a generally horizontal top surface defining a plurality of edges, and a bottom surface at least partially defining a secondary air distribution space and a primary air plenum; wherein all primary and secondary air flows into the respective primary air plenum and secondary air distribution space; wherein the air distributor plate defines a primary air opening for the provision of primary air from the primary air plenum to the burner; and wherein the air distributor plate includes a plurality of secondary air openings for substantially axisymmetric distribution of secondary air around the air distributor plate.
In some embodiments, the air distributor plate has first, second, third, fourth, fifth, and sixth edges; wherein the air distributor plate has generally vertical surfaces extending from the first, second, third, fourth, and fifth edges to at least partially define the secondary air distribution space; wherein the generally vertical surfaces define the secondary air openings; and wherein the substantially axisymmetric distribution includes secondary air flow rates through the plurality secondary air openings with standard deviation less than 0.88 from average secondary air flow rate. In some embodiments, the standard deviation is less than 0.10. In some embodiments, the standard deviation is about 0.08. In some embodiments, the water heater further comprises an air diverter secured to an edge of the air distributor plate to direct all primary and secondary combustion air from an air intake to the respective primary air plenum and secondary air distribution space. In some embodiments, the water heater further comprises a plenum pan mounted to a bottom surface of air distributor plate to at least partially define the primary air plenum. In some embodiments, the plenum pan includes a plurality of tabs; the distributor plate includes a plurality of slots through which tabs extend; and the tabs are bent against the top surface of distributor plate to secure the plenum pan to the bottom surface of the distributor plate. In some embodiments, the distributor plate includes an integral first locating member, an integral burner locating member, an integral manifold pocket, and an integral manifold clearance indentation; wherein a portion of the burner mates with the burner locating member; the water heater further comprising a gas manifold for the provision of gaseous fuel from the gas valve to the burner, the manifold extending into the manifold clearance indentation during installation, and the manifold extending into the manifold pocket when installed; and a condensation tray including a first mating portion that mates with the first locating member, and a second mating portion that extends around the manifold pocket. In some embodiments, the distributor plate includes first and second locating members; the water heater further comprising a condensation tray having first and second clocking points that mate with the respective first and second locating members; wherein the condensation tray is secured to the distributor plate with a single threaded fastener in combination with mating of the first and second clocking points with the first and second locating members. In some embodiments, the water heater further comprises a condensation tray mounted in the combustion chamber; wherein the burner includes a condensate drain that directs condensation to the condensation tray. In some embodiments, the condensation tray has a containment capacity at least equal to the volume of condensate predicted during heavy condensation cold start of the water heater. In some embodiments, the condensation tray is dimensioned to cause a sufficient surface area of condensate in the condensation tray to be exposed to heat in the combustion chamber to result in total evaporation of the condensate upon the water heater reaching steady-state combustion and normal operation.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a water heater embodying the present invention.

FIG. 2 is an exploded view of the water heater.

FIG. 3 is a cross-section view of the water heater taken along line 3-3 in FIG. 1.

FIG. 4 is an illustration of the control system and wiring of the water heater.

FIG. 5 an exploded view of an air intake assembly of the water heater from a first perspective.

FIG. 6 is an exploded view of the air intake assembly from a second perspective.

FIG. 7 is a cross-section view of the air intake assembly.

FIG. 8 is an exploded view of the combustion chamber assembly of the water heater.

FIG. 9 is an exploded view of the combustion chamber assembly from a second perspective.

FIG. 10 is a perspective view of a partially assembled combustion chamber assembly with arrows indicating the flow of primary and secondary air.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.
FIGS. 1-3 illustrate a water heater 10 that includes a tank 15 in which water is heated and stored, a combustion chamber assembly 20 supporting the tank 15, an air intake assembly 25 through which combustion air is provided to the combustion chamber assembly 20, high temperature insulation 30 surrounding the combustion chamber assembly 20, a foam dam 32 above the high temperature insulation 30, and a jacket 35 surrounding the tank 15, high temperature insulation 30, and foam dam 32. Foamed-in-place insulation is introduced into an annual space defined between the jacket 35 and tank 15, above the foam dam 32.
The tank 15 includes a flue 40, a baffle 45 in the flue 40, an inlet spud 50, an outlet spud 55, an anode spud 60 or anode hole, a temperature probe hole 65, a drain valve 70, and a T&P valve 75 (i.e., temperature and pressure valve 75). Hot products of combustion created in the combustion chamber assembly 20 flow up from the combustion assembly through the flue 40. As the products of combustion flow through the flue 40, heat is transferred from the products of combustion to the flue 40 wall and then to the water surrounding the flue 40. The baffle 45 restricts the flow of products of combustion through the flue 40, which increases the time during which the products of combustion dwell within the flue 40. Generally speaking, an increase in the dwell time also increases the amount of heat transferred from the products of combustion to the water in the tank 15 through the flue 40 wall. Also, the pressure of the products of combustion drops as the products of combustion flow through the restricted flow path of the flue 40 and baffle 45 assembly.
There are many types, styles and designs for baffles, and the baffle 45 may be removable from the flue 40 or permanently fixed within the flue 40 (as with metallurgical bonding such as brazing or welding, or with mechanical fasteners). In other embodiments, the baffle 45 may be integrally formed with the flue 40 wall. As will be discussed in more detail below, the baffle 45 restricts the flow of products of combustion such that the products of combustion are at atmospheric pressure or near atmospheric pressure when they flow out of the flue 40. As used in this disclosure, “near atmospheric” means a pressure of exhaust that is within a range for which a natural draft (e.g., Category I) vent structure or exhaust structure (as illustrated at 77) is suitable, even if such pressure of exhaust is above atmospheric pressure.
A cold water pipe 80 is threadedly interconnected to the inlet spud 50 and a hot water pipe 85 is threadedly interconnected to the outlet spud 55. A dip tube 90 is threaded or otherwise fit within the inlet spud 50. As hot water is drawn from the tank 15 through the hot water pipe 85, cold water flows into the bottom of the tank 15 through the cold water pipe 80 and dip tube 90. A powered anode 95 (FIG. 4) is threaded or otherwise secured into the anode spud 60. The powered anode 95 generates current which reduces the rate of tank 15 corrosion or eliminates tank 15 corrosion altogether. The drain valve 70 permits draining of water from the tank 15 during servicing, and the T&P valve 75 permits pressure to be released from the tank 15 in the event of high pressure within the tank 15 resulting from overheating of the water.
With additional reference to FIG. 4, the water heater 10 also has a control system 100, which includes a controller 105, a gas valve 115, a user interface 120, a pressure sensor 125 having a pressure tap 126 (FIG. 5), a FV sensor 130 (i.e., a flammable vapor sensor), a hot surface igniter 135, and a flame sensor 140. The controller 105 in the illustrated embodiment is a 24V controller 105 (i.e., 24 Volt controller) which is powered by a 24 Volt power supply which may be provided, for example, by a transformer 150 that is plugged into a standard voltage outlet. The controller 105 includes a processor for receiving inputs from the sensors 125, 130, 140 and user interface 120, and monitoring and controlling operation of the water heater 10.
A powered anode wire 160 interconnects the controller 105 and the powered anode 95 for the provision of power to the powered anode 95. Power and/or communications (as necessary for functionality) between the controller 105 and the other control system 100 components are provided by way of a user interface wire 165, a pressure sensor wire 170, a FV sensor wire 175, an igniter wire 180, and a flame sensor wire 185. Wireless communication between the controller 105 and one or more of these components is possible for other embodiments.
In the illustrated embodiment, the gas valve 115 and controller 105 are integrated into a single unit, but in other embodiments the gas valve 115 and controller 105 may be separate units with a suitable wired and/or wireless connection. The gas valve 115 includes a temperature probe 190 that extends into the water in the tank 15 through the probe hole 65. The gas valve 115 receives a supply of gaseous fuel (e.g., natural gas) from a source of gaseous fuel, through a hook-up line 200. A supply line 205 delivers the gaseous fuel from the gas valve 115 to the combustion chamber assembly 20 to create the products of combustion discussed above. The user interface 120 permits the operator or user of the water heater 10 to program operating parameters, such as target water temperature and vacation settings.
The air intake assembly 25 is illustrated in FIGS. 5-7. The air intake assembly 25 includes a shell 220 having a first piece 225, a second piece 230, a partition 235, and a blower 240. The first piece 225 includes a pressure sensor cavity 250 formed in its exterior surface (which faces the water heater 10). A central hole 251 in the pressure sensor cavity 250 communicates between the sensor mounting cavity and the interior space of the air intake assembly 25. The pressure tap 126 of the pressure sensor 125 extends through the central hole 251. The first piece 225 also includes a power cord channel 255 or wire routing channel in its exterior surface. The first piece 225 also defines an elbow 260 which interconnects to the combustion chamber assembly 20. The first piece 225 also includes mounting flanges 265 to accommodate fasteners 270 that secure the air intake assembly 25 to the jacket 35. Mounted to the second piece 230 is air inlet 280, which in the illustrated embodiment is a plate with a louvered window. In other embodiments, the air inlet 280 may be formed integrally with the second piece 230. All combustion air for the water heater 10 flows into the water heater 10 through the air inlet 280.
To achieve a high quality, attractive shell 220, it is preferable to form the first piece 225 and second piece 230 by injection molding, but the shell 220 may be alternatively constructed as a single, integrally-formed part through blow molding. The first piece 225 and second piece 230 are interconnected with adhesive or another suitable joining process along a joining line or interface extending generally along a longitudinal extent of the air intake assembly 25 (i.e., a vertical interface). A gasket 285 is captured between the edges of the first piece 225 and second piece 230 at the interface to create a substantially air tight seal. The surfaces of the first piece 225 and second piece 230 that face each other are referred to as their internal surfaces.
The internal surfaces define an interior space 290 of the air intake assembly 25. Although the interior space 290 (or the shell 220 generally) is non-cylindrical, the geometry of the internal surfaces is designed to give the overall air intake assembly 25 a hydraulic functionality equivalent to a cylindrical conduit or tube of standard size (e.g., the air intake assembly 25, although non-cylindrical in shape, functions equivalently to a standard 4 inch inner diameter PVC conduit). Thus, the air intake assembly 25 achieves the same hydraulic performance as a standard cylindrical conduit, but with a more aesthetically pleasing non-cylindrical shape. The interior space 290 defines a minor dimension and a major dimension (both perpendicular to the longitudinal extent and each perpendicular to the other). The major dimension may be, for example, at least twice the minor dimension. It is possible to construct the intake assembly 25 such that only a portion of the interior space 290 is non-cylindrical.
The partition 235 is generally flat and includes a partition window 295. The partition 235 is mounted to one or both of the internal surfaces of the first piece 225 and second piece 230. The partition 235 divides the interior space 290 of the air intake assembly 25 into an inlet side 297 and an outlet side 298. The inlet side 297 is above the partition 235 and communicates with ambient air (i.e., air surrounding the water heater 10) through the air inlet 280. The outlet side 298 is below the partition 235 and communicates with the combustion chamber assembly 20 through the elbow 260. The partition 235 reduces or eliminates recycling of air from the outlet side 298 back into the blower 240. The blower 240 is mounted within the inlet side 297 of the interior space 290. The non-cylindrical shape of the inlet side 297 accommodates the shape and size of the blower 240. In the illustrated embodiment, the blower 240 is an axial inflow, centrifugal blower. In the illustrated embodiment, the blower 240 is of relatively small size, producing less than about 15 CFM (“cubic feet per minute”) of airflow with a maximum static pressure head or pressure rating of less than 2 inches water column or in some embodiments a fraction of 1 inch of water column. This is in comparison to blowers for known power burners which are multiple times larger than blower 240. For example, in a known residential 120,000 Btu/hr power burner application, the associated blower has a mid-range operating airflow rate of about 80 CFM to 140 CFM. Known power burner models of above 120,000 Btu/hr employ a blower that operates at 160 CFM and above. Static pressure head of such power burners (i.e., the above-mentioned 120,000 Btu/hr power burner and those above 120,000 Btu/hr) is on the order of 11 inches water column. Commercial water heater power burners have even higher airflow rates and static pressure ratings than the models described above.
In other embodiments, the blower 240 could be an axial fan or other air moving device that achieves the basic functionality of sucking ambient air into the inlet side 297 through the air inlet 280 and forcing the air into the outlet side 298 and combustion chamber assembly 20 at pressures above atmospheric pressure. The term “pressurized,” as used throughout this disclosure means at a pressure higher than atmospheric pressure. The blades of the blower 240 are of a known design referred to as a “squirrel cage,” and the blower 240 includes a volute casing 300. The pressure of the air rises as it is forced through the volute casing 300. The blower inlet communicates with the air inlet 280 and the blower outlet communicates with the partition window 295. A blower wire 305 or power cord communicates between the pressure sensor 125 and the blower 240 and is received in the power cord channel 255.
With reference to FIGS. 3 and 7, the blower 240 sucks ambient air through the air inlet 280 into the inlet side 297 at atmospheric pressure, raises the pressure of the air above atmospheric, and forces the pressurized air into the outlet side 298 through the partition window 295. In this regard, the inlet side 297 may be referred to as the low pressure side of the interior space 290 and the outlet side 298 may be referred to as the high pressure side. Also, the illustrated water heater 10 may be termed a forced draft water heater because combustion air is pressurized in the combustion chamber, and products of combustion are forced up the flue 40 under the influence of positive pressure at the air inlet assembly. This is contrasted with an induced draft water heater 10 in which a blower at the top of the flue 40 draws the products of combustion up the flue 40 by creating a low pressure region at the top of the flue 40 (i.e., at the inlet to the blower) and a high pressure region at the outlet of the blower.
Turning now to FIGS. 8-10, the combustion chamber assembly 20 includes a stand 310, a bottom plate 315, a skirt 320, a burner-door assembly 325, an air diverter 330, an air distributor plate 335, a primary air pan 340, and a condensation tray or condensation pan 345. The bottom plate 315 rests on the stand 310 and is joined to the skirt 320 by a folding or other metal joining method. The skirt 320 extends upwardly from the bottom plate 315, and supports the bottom of the water tank 15. A combustion chamber 347 (FIG. 10) is defined by the bottom plate 315, skirt 320, and bottom of the tank 15. In the illustrated embodiment, the combustion chamber 347 is below the water in the water tank 15, and is not a submerged combustion chamber which is surrounded by water. The stand 310 elevates the combustion chamber assembly 20 from the floor or surface on which the water heater 10 stands, to reduce temperatures to which the floor is exposed during operation of the water heater 10.
The skirt 320 includes an opening 350 and an inlet fitting 352. An inlet gasket 353 fits snuggly over the inlet fitting 352, and also fits snuggly within the elbow 260 of the air intake assembly 25. The inlet gasket 353 creates a substantially airtight seal between the air intake assembly 25 and the combustion chamber assembly 20 so that substantially all high pressure air flowing from the air intake assembly 25 is delivered to the combustion chamber assembly 20 and does not leak to the surrounding environment. The air inlet 280 is above the combustion chamber 347. The air intake assembly 25 functions as a conduit between the air inlet 280 and the combustion chamber 347.
The burner-door assembly 325 includes a door 355 that fits over the opening 350 in the skirt 320. In the final assembly, a shield 357 (FIG. 1) is mounted to the jacket 35 and covers the portions of the burner-door assembly 325 that are exterior of the skirt 320. The burner-door assembly 325 also includes a gas manifold 360 (FIG. 9) attached to the door 355 and communicating with the gas supply line 205 through the door 355. The igniter wire 180 and flame sensor wire 185 pass through the door 355 and are surrounded by a grommet 363 or the like for a substantially air-tight seal between the wires and the door 355. In other embodiments, the burner-door assembly 325 may be of the type described and illustrated in U.S. patent application Ser. No. 12/431,525 filed Apr. 28, 2009, the entire contents of which is incorporated into this disclosure by reference.
The burner-door assembly 325 also includes an air duct 365 supported by the gas manifold 360, a burner 370 supported by the air duct 365, and a mounting bracket 375 on the gas manifold 360. Gaseous fuel from the gas manifold 360 is mixed with primary air in the air duct 365 to form a partially premixed combustible mixture, and the combustible mixture is burned by the burner 370, as will be discussed in more detail below. The mounting bracket 375 supports the hot surface igniter 135 and flame sensor 140 near the burner 370 so that the combustible mixture can be ignited and monitored.
The burner 370 includes a condensation drain hole 380. Condensate that pools on the burner 370 drains through the condensate drain hole 380 to the condensation pan 345. This can occur, for example, during a cold start of the water heater 10. Condensation that collects in the condensation pan 345 evaporates and is exhausted through the flue 40 with products of combustion when the water heater 10 is operating at steady state. More specifically, the condensation pan 345 is dimensioned to cause a sufficient surface area of condensate in the condensation pan 345 to be exposed to heat in the combustion chamber 347 to result in total evaporation of the condensate upon the water heater reaching steady-steate combustion and normal operation. The condensation pan 345 should be of a size sufficient to pass heavy condensation tests.
The air distributor plate 335 is designed to evenly distribute secondary air in the combustion chamber 347 to promote even combustion at the burner 370. The air distributor plate 335 includes a top surface 410 and a bottom surface 415 that are generally planar and horizontal. In the illustrated embodiment, the air distributor plate 335 includes a first edge 421, a second edge 422, a third edge 423, a fourth edge 424, a fifth edge 425, and a sixth edge 426, all of equal length and at equal angles, and in this regard may be termed a “hex plate” due to its hexagonal shape. Depending from the first edge 421, second edge 422, third edge 423, fourth edge 424, fifth edge 425, and sixth edge 426 is a respective first side wall 431, second side wall 432, third side wall 433, fourth side wall 434, fifth side wall 435, and sixth side wall 436. These side walls 431-436 define generally vertical surfaces. Formed in these respective side walls are a first opening 441, second opening 442, third opening 443, fourth opening 444, fifth opening 445, and sixth opening 446. The first-fifth openings 441-445 may collectively be referred to as “secondary air openings” and are at least partially defined by the generally vertical surfaces.
The first side wall 431 includes a portion that extends from the first edge 421 to the bottom plate 315, and another portion that extends only partially (e.g., halfway) from the first edge 421 toward the bottom plate 315. The first side wall 431 does not extend the entire length of the first edge 421. Consequently, the first opening 441 includes a portion that extends fully between the first edge 421 to the bottom plate 315, and another portion that extends only partially from the bottom plate 315 toward the first edge 421 (i.e., the space between the bottom plate 315 and the short portion of the first side wall 431).
The third side wall 433 is actually divided into roughly equal portions on either side of the third opening 443, such that the third opening 443 is roughly centered with respect to the third edge 423. The fifth opening 445 is defined at opposite ends of the fifth side wall 435. The sixth side wall 436 is actually two relatively small wall portions or tabs at opposite ends of the sixth edge 426, such that the sixth opening 446 is relatively large and centered with respect to the sixth edge 426.
The air diverter 330 includes a lip 450 and feet 455. The feet 455 sit on and are mounted with fasteners to the bottom plate 315, and the lip 450 extends along the top surface 410 of the air distributor plate 335 along the sixth edge 426 over the sixth opening 446. Side walls of the air diverter 330 extending from opposite ends of the lip 450 down to the feet 455 are positioned along the sixth side wall 436 portions at opposite ends of the sixth opening 446. Consequently, the air diverter 330 surrounds the sixth opening 446, and places the inlet fitting 352 and sixth opening 446 in communication. Substantially all combustion air flowing at elevated pressure from the air intake assembly 25 is diverted downwardly by the air diverter 330, through the sixth opening 446 and under the air distributor plate 335.
Formed in the air distributor plate 335 are a three slots 460 that accept three tabs 465 of the primary air pan 340. The tabs 465 are extended up through the slots 460 and bent over to secure the primary air pan 340 to the bottom surface 415 of the air distributor plate 335. The air distributor plate 335 is mounted to the bottom plate 315 with three fasteners 470. A primary air plenum is defined between the primary air pan 340 and the bottom surface 415 of the air distributor plate 335, and a secondary air plenum or secondary air distribution space is defined by the space that surrounds the primary air pan 340 between the bottom surface 415 of the air distributor plate 335 and the bottom plate 315.
The air distributor plate 335 also includes an integral first locating member 485, an integral burner locating member 490, an integral manifold pocket 495, and an integral manifold clearance indentation 500. The first locating member 485 is in the form of a concave bump or boss in the top surface 410 of the air distributor plate 335. The first locating member 485 and integral manifold pocket 495 define two clocking points for mounting the condensation pan 345 to the air distributor plate 335. More specifically, the condensation pan 345 includes a first mating portion and a second mating portion that receive the respective first locating member 485 and the integral manifold pocket 495. This ensures that the condensation pan 345 is positioned properly to receive condensation that drains from the burner 370. With the first locating member and integral manifold pocket 495 received in indentations in the condensation pan 345, a single threaded fastener 510 may be used to secure the condensation pan 345 to the air distributor plate 335.
The burner locating member 490 is in the form of a raised trapezoidal base in the top surface 410 and a primary air hole 515. The a primary air opening or primary air hole 515 communicates with the primary air plenum. The air duct 365 of the burner-door assembly 325 fits snuggly around the raised trapezoidal base of the burner 370 locating member, such that substantially all primary air flowing through the primary air hole 515 from the primary air plenum flows into the air duct 365 for eventual delivery to the burner 370. In other embodiments, the base of the burner locating member 490 can be other shapes, but it preferably will snuggly receive the bottom edge of the air duct 365 to ensure that the air duct 365 receives substantially all primary air flowing out of the primary air plenum and primary air hole 515.
The manifold pocket 495 is a convex (with respect to the top surface 410) deformation with an opening 520 at one end. The manifold pocket 495 receives a distal end of the gas manifold 360 to secure the manifold with respect to the combustion chamber 347. The manifold clearance indentation 500 is a concave (with respect to the top surface 410) deformation that permits the burner-door assembly 325 to be inserted into the opening 350 in the skirt 320 at an angle and then tilted into the operable position without the gas manifold 360 bumping into the top surface 410 of the air distributor plate 335.
In operation, the controller 105 monitors water temperature with the temperature probe 190 and controls the temperature of water within the tank 15 based on the settings input by an operator through the user interface 120. When water temperature drops below a low-end set point (e.g., due to standby heat loss or during a draw of hot water from the tank 15 and the resultant introduction of cold water into the tank 15 through the dip tube 90), the controller 105 engages the blower 240. When operating properly, the blower 240 creates high pressure in the outlet side 298 of the air intake assembly 25. The high pressure is sensed by the pressure sensor 125 through the pressure tap 126, and a signal is sent to the controller 105 confirming that the blower 240 is operating properly.
The high pressure air from the air intake assembly 25 is forced into the combustion assembly through the inlet fitting 3352 on the skirt 320. The air diverter 330 directs the high pressure air into the primary air plenum and secondary air plenum under the air distributor plate 335. The flow of high pressure air into the primary air plenum is subsonic, which results in feedback waves through the air particles to the air diverter 330. The feedback waves result in a balance of high pressure air flowing into the primary air plenum and secondary air plenum, and avoid an undesirable amount of high pressure air flowing into the primary air plenum at the expense of air supply to the secondary air plenum. The pressurized primary air flows from the primary air plenum up through the primary air hole 515, and into the air duct 365 of the burner-door assembly 325.
Once the controller 105 has confirmed that the blower 240 is operating properly, the controller 105 provides power (i.e., electrical current) to the hot surface igniter 135, to cause the hot surface igniter 135 to achieve a temperature sufficient to ignite a fuel-air mixture. The controller 105 determines that the hot surface igniter 135 has achieved such temperature by known means, or assumes that the hot surface igniter 135 has achieved such temperature after the passage of sufficient time.
Once the controller 105 has confirmed that the blower 240 is operating properly and the hot surface igniter 135 is at an appropriate temperature to ignite a fuel-air mixture, the controller 105 opens the gas valve 115 to permit gaseous fuel to flow from the gas hook-up line 200, through the gas valve 115, to the gas supply line 205, and to the gas manifold 360. The gaseous fuel flows out of the gas manifold 360 into the air duct 365, where it mixes with pressurized primary air to create a pressurized (above atmospheric pressure) partially premixed fuel-air mixture. The fuel-air mixture flows from the air duct 365 into the burner 370.
The illustrated burner 370 is a pancake style burner 370 having burner orifices around its perimeter. The illustrated burner 370 is in the combustion chamber 347 and is below the water tank 15, and may be termed an “upwardly firing” burner because products of combustion rise upwardly from the burner 370. The fuel-air mixture flows out of the burner orifices and is ignited by the hot surface igniter 135 to create a ring of flame around the burner 370. The flame sensor 140 confirms to the controller 105 that the flame is present on the burner 370. The flame created by the burner 370 combusting the primary air and fuel mixture is a partially premixed but substantially diffusion flame having an envelope. Combustion of the diffusion flame is completed within the diffusion flame envelope in the presence of secondary air.
The partially premixed, diffusion flame produced by the burner 370 in the present invention includes a fuel-rich core that is surrounded by a flame envelope into which secondary air is diffused to complete combustion and lower NOx emissions. The core region includes insufficient air to complete combustion of the fuel, which is why the diffusion flame is referred to as “partially” premixed. The diffusion flame front consequently propagates from the flame envelope inward to complete the combustion of the core region with the help of the secondary air. The majority of air required for complete combustion and reduced NOx is added at the flame envelope in the form of secondary air.
The partially premixed diffusion flame of the present invention is distinguished from the flame created by fully premixed power burners. Fully premixed power burners include sufficient air in the air/fuel premixture to support full combustion of the fuel and low NOx emissions. Indeed, in most power burner applications, the blower that is part of the power burner is pushing more air than is required for complete combustion because the blower is also required to force the products of combustion out the flue at elevated pressure for the purpose of direct venting or utilization of the products of combustion for another purpose (e.g., space heating) downstream of the water heater. The blower in a power burner is typically much larger than the blower contemplated by the present invention, in terms of airflow (measured in CFM) and static pressure head (measured in inches of water column) as discussed above.
Secondary air collects in the secondary air plenum under the air distributor plate 335. The secondary air is pressurized (i.e., above atmospheric pressure) and flows out of the secondary air plenum through the first opening 441, second opening 442, third opening 443, fourth opening 444, and fifth opening 445. The openings 441-445 are sized and spaced to create substantially axisymmetric distribution of secondary air flowing out of the secondary air plenum and into the combustion chamber 347 around the burner 370. The air distributor plate 335 and openings 441-445 create a substantially uniform supply of secondary air to the combustion chamber 347. Uniform airflow out of the secondary air plenum reduces potential surface/floor temperature issues and also gives rise to improved combustion. A design that minimizes standard deviation of air flow rates from the average secondary air flow rate for the openings 441-445 is desirable for improving combustion. The combined size and geometry of the primary plenum and air distributor plate 335 can achieve standard deviations of less than 1.35, with standard deviations reaching 0.88 and as low as 0.08 in some embodiments.
To summarize the air flow and combustion process, pressurized combustion air flows under the air distributor plate 335 from the air diverter 330 through the sixth opening 446 at one side of the air distributor plate 335. The pressurized combustion air is divided into primary air, which flows into the primary air plenum, and secondary air, which flows into the secondary air plenum. Both the primary air and secondary air are pressurized due to the blower 240 forcing the air into the combustion chamber 347. The primary air is mixed with gaseous fuel and is ignited at the perimeter of the burner 370 to create a diffusion flame. The secondary air, despite entering the secondary air plenum from the sixth side of the air distributor plate 335, is substantially evenly distributed through the first through fifth openings 441-445 due to the size, shape, and position of the openings 441-445. The high pressure secondary air flows around the sides of the air distributor plate 335 and completes combustion of the fuel-air mixture within the envelope of the diffusion flame.
Combustion of the fuel-air mixture at the diffusion flame creates products of combustion. The blower 240 pressurizes the entire combustion chamber 347 to a pressure higher than atmospheric, and the products of combustion also have natural buoyancy owing to their high temperature. As a result, the products of combustion rise and are forced into the flue 40. The products of combustion transfer heat to the baffle 45 and flue 40, which in turn transfer heat to the water. The burner 370 continues to generate products of combustion as discussed above, until the temperature probe 190 senses that the water temperature has reached the desired set point or high-end set point (as programmed at the user interface 120).
The flow of the products of combustion is restricted as they flow up through the flue 40 by the restricted flow path caused by the baffle 45. The products of combustion lose pressure as they flow from the flue inlet end (lower end of the flue 40 communicating with the combustion chamber 347) to the flue outlet end (upper end of the flue 40 communicating with the venting structure 77). The blower 240 is sized to create a known pressure (also called head pressure or head) in the combustion chamber 347. Given the known pressure in the combustion chamber 347, the flue 40 and baffle 45 are designed to reduce pressure in the products of combustion to near atmospheric at the flue outlet to permit the water heater 10 to benefit from a pressurized diffusion flame in the combustion chamber 347, a restricted flow flue 40 and baffle 45 assembly to increase dwell time of the products of combustion, and a Category I atmospheric venting configuration.
The FV sensor 130 is positioned external of the combustion chamber assembly 20, relatively low or close to ground level because flammable vapors tend to be heavier than air and would typically collect close to ground level. The FV sensor 130 is lower than the air inlet 280, and in the illustrated embodiment is lower than the burner 370 and combustion chamber 347. If during the operation of the water heater 10, the FV sensor 130 senses the presence of flammable vapors outside of the water heater 10 in concentrations above a maximum threshold, the FV sensor 130 generates a signal to the controller 105 and the controller 105 can shut down operation of the water heater 10 by closing the gas valve 115. Elevating the air inlet with respect to the FV sensor 130 increases the likelihood that the FV sensor 130 will sense the presence of the flammable vapors and the controller 105 will shut down the gas valve 115 prior to the flammable vapors being entrained in the incoming combustion air and reaching the burner 370. In view of the FV sensor 130 and the functionality described above, the water heater 10 of the present invention is deemed a flammable vapor ignition resistant (“FVIR”) water heater.
Similarly, if the pressure sensor 125 senses that the pressure of air downstream of the blower 240 (i.e., in the outlet side 298) is below a minimum threshold, the pressure sensor 125 generates a signal to the controller 105 and the controller 105 can shut down operation of the water heater 10 by closing the gas valve 115. Likewise, if the flame sensor 140 fails to sense the presence of a flame at the burner 370, the flame sensor 140 generates a signal to the controller 105 to shut down operation of the water heater 10. In all cases, the generation of a signal can include the cessation of a signal or the changing of a signal.
Thus, the invention provides, among other things, a water heater including a 24 volt controller to control various powered aspects of the water heater, a water heater, a sealed combustion chamber water heater with a FV sensor lower than the air inlet for the combustion chamber; a forced-draft water heater having a blower in the air inlet and a baffle in the flue such that combustion occurs at elevated pressure but pressure of products of combustion drop to near atmospheric at the outlet end of the flue; a water heater having an air intake assembly having an internally-mounted blower mounted inside; and a water heater having an air distributor plate for substantially axisymmetric distribution of secondary air in the combustion chamber. Various features and advantages of the invention are set forth in the following claims.

Claims

1. A water heater comprising:

a tank for water to be heated;

a powered anode extending into the tank and creating an electrical current to reduce corrosion of the tank;

a combustion chamber;

an exhaust structure;

a flue in the tank communicating between the combustion chamber and the exhaust structure;

a burner in the combustion chamber operable to burn a mixture of primary combustion air with gaseous fuel in a partially premixed but substantially diffusion flame having an envelope, such that combustion of the mixture is completed at the diffusion flame envelope in the presence of secondary air to produce products of combustion, the products of combustion flowing through the flue to the exhaust structure to heat the water in the tank;

a centrifugal blower forcing primary and secondary air into the combustion chamber at pressure above atmospheric;

a gas valve for controlling a supply of gaseous fuel to the burner;

a user interface for programming operating parameters of the water heater; and

a 24 V controller that provides power to the user interface and powered anode, and that controls operation of the blower and gas valve.

2. The water heater of claim 1, further comprising a pressure sensor operatively interconnected with the 24 V controller; wherein the pressure sensor generates a signal in response to sensing that the pressure of air downstream of the blower is below a minimum threshold; and wherein the 24 V controller closes the gas valve in response to receiving the signal from the pressure sensor.

3. The water heater of claim 1, further comprising a flammable vapor sensor operatively interconnected with the 24 V controller; wherein the flammable vapor sensor generates a signal in response to sensing the presence of flammable vapors outside of the water heater in concentrations above a maximum threshold; and wherein the 24 V controller closes the gas valve in response to receiving the signal from the flammable vapor sensor.

4. The water heater of claim 1, further comprising a pressure sensor sensing the pressure of air downstream of the blower; and a flammable vapor sensor sensing the presence of flammable vapors outside of the water heater; wherein the 24 V controller closes the gas valve upon the occurrence of any of the following: (a) conditions dictated by the user interface, (b) the pressure sensor sensing air pressure below a minimum threshold, and (c) the flammable vapor sensor sensing flammable vapors external to the water heater in concentrations above a maximum threshold.

5. A water heater comprising:

a tank for water to be heated;

a combustion chamber;

an exhaust structure;

an air intake assembly including an air inlet above the combustion chamber and a conduit communicating between the air inlet and the combustion chamber;

a centrifugal blower within the air intake assembly operable to suck air into the air intake assembly through the air inlet and force primary and secondary air into the combustion chamber through the conduit at pressure above atmospheric;

a gas valve for controlling a supply of gaseous fuel to the burner;

a controller that controls operation of the blower and gas valve; and

a flammable vapor sensor external of the combustion chamber and lower than the air inlet, the flammable vapor sensor being operatively interconnected with the controller and operable to generate a signal in response to sensing the presence of flammable vapors outside of the water heater in concentrations above a maximum threshold;

wherein all primary and secondary combustion air supplied to the combustion chamber flows through the air inlet and conduit; and

wherein the controller closes the gas valve in response to receiving the signal from the flammable vapor sensor.

6. The water heater of claim 5, wherein the flammable vapor sensor is lower than at least one of the combustion chamber and burner.

7. A water heater comprising:

a tank for water to be heated;

a combustion chamber;

an exhaust structure;

a gas valve for controlling a supply of gaseous fuel to the burner;

a controller that controls operation of the blower and gas valve; and

a baffle in the flue that restricts flow sufficiently to reduce the pressure of the products of combustion to near atmospheric upon flowing out of the flue into the exhaust structure.

8. The water heater of claim 7, wherein the blower is an axial-intake, centrifugal blower.

9. The water heater of claim 7, wherein the exhaust structure is a category I vent structure.

10. A water heater comprising:

a tank for water to be heated;

a combustion chamber;

an exhaust structure;

a gas valve for controlling a supply of gaseous fuel to the burner; and

a controller that controls operation of the blower and gas valve;

wherein the air intake assembly includes an interior space, all primary and secondary air being provided to the combustion chamber flowing through the interior space; and

wherein the blower is mounted within the interior space of the air intake assembly.

11. The water heater of claim 10, wherein the blower is an axial-intake, centrifugal blower.

12. The water heater of claim 10, wherein the air intake assembly includes a longitudinal extent; and wherein the air intake assembly includes a two-piece construction divided along the longitudinal extent of the air intake assembly.

13. The water heater of claim 10, wherein the interior space of the air intake assembly is non-cylindrical and has an equivalent hydraulic diameter of a four inch inner diameter tube.

14. The water heater of claim 10, wherein at least a portion of the interior space of the air intake assembly is non-cylindrical to accommodate mounting the blower in the interior space; and wherein the non-cylindrical portion of the interior space defines a minor dimension and a major dimension that is perpendicular to the minor dimension and at least twice the minor dimension.

15. The water heater of claim 10, wherein the air intake assembly includes a partition that divides the interior space into an inlet side communicating with ambient air and an outlet side communicating with the combustion chamber, the partition including a window; and wherein the blower is within the inlet side of the interior space and forces primary and secondary air into the outlet side of the interior space through the window in the partition.

16. The water heater of claim 15, wherein the air intake assembly includes a louvered opening communicating between the inlet side and ambient air; and wherein all air sucked into the inlet side of the interior space by the blower flows through the louvered opening.

17. The water heater of claim 10, further comprising a pressure sensor communicating with the interior space, the pressure sensor operable to disable the gas valve to cut off the supply of gaseous fuel to the burner when pressure within the interior space drops below a minimum threshold.

18. The water heater of claim 17, wherein the air intake assembly includes an exterior surface, a sensor mounting cavity in the exterior surface and a wire routing channel in the exterior surface; wherein the air intake assembly further includes a hole communicating between the sensor mounting cavity and the interior space; wherein the pressure sensor is mounted within the sensor mounting cavity and communicates with the interior space through the hole; and wherein the blower includes a power cord that is received in the wire routing channel.

19. A water heater comprising:

a tank for water to be heated;

a combustion chamber;

an exhaust structure;

a gas valve for controlling a supply of gaseous fuel to the burner;

a controller that controls operation of the blower and gas valve;

an air distributor plate having a generally horizontal top surface defining a plurality of edges, and a bottom surface at least partially defining a secondary air distribution space and a primary air plenum;

wherein all primary and secondary air flows into the respective primary air plenum and secondary air distribution space;

wherein the air distributor plate defines a primary air opening for the provision of primary air from the primary air plenum to the burner; and

wherein the air distributor plate includes a plurality of secondary air openings for substantially axisymmetric distribution of secondary air around the air distributor plate.

20. The water heater of claim 19, wherein the air distributor plate has first, second, third, fourth, fifth, and sixth edges; wherein the air distributor plate has generally vertical surfaces extending from the first, second, third, fourth, and fifth edges to at least partially define the secondary air distribution space; wherein the generally vertical surfaces define the secondary air openings; and wherein the substantially axisymmetric distribution includes secondary air flow rates through the plurality secondary air openings with standard deviation less than 0.88 from average secondary air flow rate.

21. The water heater of claim 20, wherein the standard deviation is less than 0.10.

22. The water heater of claim 20, wherein the standard deviation is about 0.08.

23. The water heater of claim 19, further comprising an air diverter secured to an edge of the air distributor plate to direct all primary and secondary combustion air from an air intake to the respective primary air plenum and secondary air distribution space.

24. The water heater of claim 19, further comprising a plenum pan mounted to a bottom surface of air distributor plate to at least partially define the primary air plenum.

25. The water heater of claim 24, wherein the plenum pan includes a plurality of tabs; wherein the distributor plate includes a plurality of slots through which tabs extend; and wherein the tabs are bent against the top surface of distributor plate to secure the plenum pan to the bottom surface of the distributor plate.

26. The water heater of claim 19, wherein the distributor plate includes an integral first locating member, an integral burner locating member, an integral manifold pocket, and an integral manifold clearance indentation; wherein a portion of the burner mates with the burner locating member; the water heater further comprising a gas manifold for the provision of gaseous fuel from the gas valve to the burner, the manifold extending into the manifold clearance indentation during installation, and the manifold extending into the manifold pocket when installed; and a condensation tray including a first mating portion that mates with the first locating member, and a second mating portion that extends around the manifold pocket.

27. The water heater of claim 19, wherein the distributor plate includes first and second locating members; the water heater further comprising a condensation tray having first and second clocking points that mate with the respective first and second locating members; wherein the condensation tray is secured to the distributor plate with a single threaded fastener in combination with mating of the first and second clocking points with the first and second locating members.

28. The water heater of claim 19, further comprising a condensation tray mounted in the combustion chamber; wherein the burner includes a condensate drain that directs condensation to the condensation tray.

29. The water heater of claim 28, wherein the condensation tray has a containment capacity at least equal to the volume of condensate predicted during heavy condensation cold start of the water heater.

30. The water heater of claim 28, wherein the condensation tray is dimensioned to cause a sufficient surface area of condensate in the condensation tray to be exposed to heat in the combustion chamber to result in total evaporation of the condensate upon the water heater reaching steady-state combustion and normal operation.