AU2007237334B2 - A Forced Draft Water Heater - Google Patents

Abstract

A forced draft water heater The present invention provides a forced draft gas water heater including a tank having a minus end, wherein a forced draft burner is located so as to apply heat to a substantial portion of the minus end. I'102 A I'A B1 1Q 202 B

Description

A forced draft water heater Field of the invention [001] This invention relates to gas heated water heating systems, and particularly to forced draft gas water heating systems. Background of the invention [002] One type of gas water heater system uses a vertical cylindrical tank with a minus end which is a part spherical concavity at the base. This tank is usually used in conjunction with a central flue running up the centre of the cylinder to provide an additional heat exchange surface and to vent the combustion products. [003] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application. [004] It is desirable to improve the efficiency of such systems when they are used with forced draft heating. Summary of the invention [005] The present invention provides a forced draft gas water heater includes a tank having a minus end, wherein a forced draft burner is located so that flames radially directed from said burner under fan force impinge on and apply heat to a substantial portion of the minus end. [006] The tank can be tubular. [007] The tank can have a circular cylindrical section, but it can alternatively be formed in other shapes such as square section, rectangular section, oval section, etc., as required. [008] The tank can be supported on a base which provides a cavity in which a fan is located. [009] The fan can be located to the side of the tank. [010] A combustible mixture of air and gas can be fed to the input of the fan. [011] The fan motor can be a squirrel cage (brushless) motor. [012] The tank can include a flue. [013] Ducting can be provided to direct the combustion products from the flue to at least a portion of the external wall of the tank.

2 [014] The ducting can provide a jacket surrounding the top of the tank and extending at least part way down the side walls of the tank. [015] The ducting can include an outer skirt which redirects the combustion products at least part way up the outer wall of the jacket. [016] The jacket can be at least partially thermally insulated from the atmosphere. [017] A diffuser can be located above the top of the flue. [018] A combustion chamber can be formed with a lower wall, the rim of which is effectively sealed to the minus end. [019] Effective sealing can take place at or near to a lowermost rim of the minus end. [020] The lower wall of the combustion chamber can be substantially flat. [021] The lower wall of the combustion chamber can be dished. [022] The forced draft burner can be located so as to apply flame and or combustible product to a substantial portion of the minus end. [023] The fan can be located upstream of the burner. Brief description of the drawings [024] An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [025] Figure 1 is a schematic view of a forced draft heater arrangement according to a first embodiment of the invention; [026] Figure 2 is a schematic view of an alternative arrangement including an external ducting jacket; [027] Figure 3 is a schematic view of another arrangement according to an embodiment of the invention, in which the burner is lowered in relation to the burner of Figures 1 & 2; [028] Figure 4 is a schematic view of an embodiment of the invention having a fan external to the footprint of the tank. [029] Figure 5 is a schematic view of a further embodiment of the invention in which the flue outlet is ducted to a skirt surrounding the tank. [0301 Figure 6 is a schematic view of a further embodiment of the invention applied to a tank without a flue.

3 [031] Figure 7 is a partial view of detail of the sealing of the combustion chamber according to an embodiment of the invention. [032] Figure 8 is a part sectional view of a water heater embodying the invention. [033] For the sake of clarity, the water inlet and outlet connections are not shown in the drawings. The insulation normally applied to the exterior of the water heater is also not shown. Detailed description of the embodiments [034] Figure 1 shows a forced draft gas water heater in which the tank 102 has a minus end 104, and a central flue 106. Plate 204 together with the minus end 104 forms a sealed combustion cavity into which the burner 110 projects. The flames and/or the resultant forced draft combustion products can extend laterally for a significant distance in the sealed chamber. The arrows are included as illustrative of a directional pattern for the flame and/or combustion products but may not represent the actual flame and combustion product flows under all operating conditions. The flames are forced radially from the burner under the fan force to impinge on the minus end 104 to heat the water in tank 102 under the force of the fan 112. The flue provides the main path to the external atmosphere from the chamber formed by the minus end 104 and the plate 204. The combustion products escape up the flue 106 under the forced draft from the fan 112. [035] The plate 204, which, in one embodiment, includes a metal plate 804 and an insulation member 802 (see Figure 7), also serves to insulate fan 112 from the heat. [036] In the drawings, elements common to the arrangement of Figure 1 are given the same nomenclature. [037] In Figure 1, the forced draft burner 110 is located within the minus end cavity. [038] The forced draft flame and/or combustion products shown illustratively by the solid arrows impinge on at least part of the minus end wall 104, thus heating at least part of the water below the line A-A. The combustion products then travel up the full length of the flue 106 and continue to transfer heat to the water while in the flue 106. [039] The burner 110 is separated from the fan 112 by thermal insulator member 802. Metal plate 804 can also be sealed with the minus end to exclude or reduce the entry of air to the chamber defined by plate 204 and minus wall 104 other than via the burner 110 as described in more detail with reference to Figure 7 below. [040] The burner 110 in the arrangement of Figure 1 can be of smaller height than those previously used. The larger surface area being heated requires less overall heat input to achieve 4 the same heating effect. The height "H" from the top of the burner 110 to the circular inner rim 113 of the base of the flue can be selected to provide a sufficient flow path, while at the same time ensuring that radially directed flames will impinge on and heat the minus end wall 104. In one embodiment the height H is not less than 30 mm for a 75 mm diameter flue to ensure a flow path of sufficient cross-sectional area is achieved. [041] Flow constriction means, such as the baffle shown in Figure 8 can also be incorporated in the flue to slow the speed of the combustion products up the flue. [042] The fuel gas, and/or a mixture of the gas and air are fed to the fan. A feed line is shown illustratively as pipe 116. In practice, where the feed line 116 can carry both air and gas, and the feed line must be dimensioned to carry sufficient air and gas to support the forced draft combustion. [043] While the fan is illustrated as an axial fan, other fans can also be used. In particular, a tangential blower can be used. [044] Preferably the fan motor is a non-sparking motor, such as a squirrel cage induction motor. [045] In the embodiment shown in Figure 2, an external jacket 302 surrounds the tank. This jacket defines an external duct which maintains the combustion products in contact with the external wall of the tank. At the base of the jacket, the combustion products can be vented to atmosphere at 304 or directed through an external flue (not shown) to a desired discharge location. The jacket 302 can extend the full length of the tank or can extend only part way down the external wall of the tank. The jacket thus enables the use of at least part of the external wall of the tank as a heat exchanger so that additional heat can be extracted from the combustion products and transferred to the water in the tank via the external wall. [046] The use of a forced draft burner means that the cavity between the jacket 302 and the external wall of the tank can be narrower than would be the case if natural convection were relied on to drive the combustion products through the jacket cavity. This narrowness allows a thicker amount of insulation to be use while maintaining a pre-existing outside diameter of housing. Such a housing is shown at 902 in Figure 8. [047] Figure 3 shows a further embodiment of the invention, in which the external jacket is partly enclosed by a skirt 402 which ducts the exhaust gasses up at least part of the external wall of the jacket. Again the combustion products can be vented to atmosphere at 404 or can be discharged via an external flue (not shown).

5 [048] Also shown in Figure 3 is an alternative arrangement for the location of the burner 110. The burner 110 is lowered in relation to the minus end 104 to ensure an even greater area of the minus end is exposed to the flame/combustion products. This is achieved by having at least part of the burner below the lower rim of the minus end 104. Preferably, the whole of the burner is located below the lower rim of the minus end. [049] In Figure 4, a further embodiment includes an insulated chamber 508 into which the burner 502 projects through a side wall. The burner is fed with a gas and air mixture from fan 504 via feed line 506. [050] The combustion products are forced through the flue 106 by fan pressure and thermal convection, passing across the wall of minus end 104 on the way. [051] Also shown in Figure 4 is a cap 510 closing part of the skirt exit, which forces the combustion products to exit through vent 512. The vent 512 can have a relatively small opening to atmosphere so that the combustion products are directed to a particular location. [052] Preferably there are two exit vents such as 512 located on opposite sides of the tank so that wind pressure on one side will not block flow on the other side. [053] Figure 5 illustrates an alternative embodiment of the invention including an external duct 602 which directs the flue discharge down at least part of the length of the side of the tank. Duct 602 has an outlet 608 which opens into a skirt 604 surrounding at least part of the tank. Skirt 604 is closed by an annular lid 606 and has an outlet 610 through which the combustion products are discharged. The duct 602 can be insulated from the tank 102, or it can be in contact with the tank. [054] The lower wall or floor 610 of the combustion chamber is dished, having a "V" shaped section. [055] Figure 6 shows a water heater in which the tank does not include a flue. In this embodiment of the invention, the minus end does not have a path at the top for the combustion products to escape through. Instead, vent apertures 706 are provided in a support member 704 at the base of the minus end, and the combustion products are forced through these apertures. An external jacket 702 surrounds at least the base of the tank and ducts the hot gasses up the exterior wall of the tank. This configuration produces a flow pattern which is different from the flow pattern of the flued tank embodiments described above, as the combustion products need to exit the minus end at the bottom thereof.

6 [056] As shown in Figure 6, the lower wall or floor 710 of the combustion chamber is dish shaped with curved walls. [057] Figure 7 shows details of the sealing of plate 204 to the minus end 104 to form the combustion chamber. The plate 204 is composed of a metal support plate 804 supporting an insulating member 802. The metal plate 804 includes an annular projection 818 which terminates in an inner rim 820. Burner 110 can be connected to the rim 820 by any suitable means. In this case, burner 110 is connected to rim 820 by screws such as 822. [058] Preferably, the insulator member 802, which has a cylindrical wall around its periphery, sits in the cavity formed by support plate 804. The outside surface of rim 808 is held by a slight interference fit in the minus end 104. A sealed combustion chamber is achieved by using a seal or gasket 810 which is deformable and preferably made of a polymeric material or silicone. The seal 810 will be radially deformed by the weight of the tank 102 which exerts a compressive downward force on seal 810. The deformation will cause a seal to be formed with that portion of the outside surface of the rim 808 not inside minus end 104, simultaneously with sealing the lowermost rim of minus end 104. The seal 810 is prevented from moving radially out of contact with these sealing surfaces by the circlet 816. A sealing compound can be used between the proximate faces of the insulation member 802 and the extended skirt 830 of the minus end 104. [059] The insulating member 802 is formed from a fibrous ceramic in the shape of an annulus. A hole 805 through the insulating member accommodates a window 824 in support plate 804, to allow vision of the flame of the burner. A reflecting surface, such as a polished metal mirror, can be provided at an angle so that the reflection of the flame can be observed from outside the housing. [060] The tank 102 is supported on a support 828, which, in the present example is a steel pedestal having the flared rim 808 at the top. An access cut out 806 is provided in pedestal 828 to provide access to the fan 112, and to permit observation of the flame through window 824 and an angled mirror, not shown. [061] The metal support plate 804 can be attached to the pedestal 828 by any suitable means, such as by welding, riveting, bolting, etc., to the upper edge of rim 808. In one embodiment, the metal support plate 804 has an upright extension along at least part of the edge of insulator plate 802, and the base 828 includes an upright extension from the inner edge of rim 808 within which the upright extension of metal support plate 804 is a press fit. Additional sealing compound can be provided to seal this press fit joint.

7 [062] A condensation trap in the form of an annular trough 812 collects any condensation run-off from the outside of tank 102. The trough 812 can be part of a plastic first circlet having a snap-fit connections such as 814, which engage with appropriate detents in a second circlet 816. [063] The base of circlet 816 is an inward rim which forms a seat for seal 810, so as to contain the seal 810 when deformed by the weight of the tank 102. [064] Figure 8 shows a cut away view of a water heater embodying the invention showing the flue baffle. [065] The tank 102 includes a flue 106 and minus plate 104. Inside flue 106 is a flue baffle 910 which serves to reduce the flow speed of the combustion products by continually redirecting the flow, providing a greater period for the heat to transfer to the walls of the flue. The baffle 910 ensures a turbulent flow of combustion products through the flue 106. [066] The duct jacket 302 and the outer wall of the tank 102 define a cylindrical flow path 312 around tank 102 for the combustion products. The flow path 312 is vented through vent 906. In one embodiment, the duct 302 is approximately 8 mm in width. [067] An outer housing 902 encases the jacket 302 and defines a space 904 which can be filled with a suitable insulating material (not shown). A recess can be provided in the housing cavity for a thermostat. [068] Hot water outlet pipe 926 near the top of the tank passes from the tank through the jacket 302 and housing 902. A cold water inlet 928 is similarly provided near the bottom of the tank. [069] Where ever it is used, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise", "comprised" and "comprises" where they appear. [070] It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention. [071] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention can be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all 8 modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims (17)

1. A forced draft gas water heater including a tank having a minus end, wherein a forced draft burner is located so that flames radially directed from said burner under fan force impinge on and apply heat to a substantial portion of the minus end.

2. A forced draft gas water heater as claimed in claim 1, wherein the tank is tubular.

3. A forced draft gas water heater as claimed in claim I or claim 2, wherein the tank has a circular cylindrical section.

4. A forced draft gas water heater as claimed in any one of the preceding claims, wherein the tank is supported on a base which provides a cavity in which a fan is located.

5. A forced draft gas water heater as claimed in any one of claims I or 2, wherein the fan is located to the side of the tank.

6. A forced draft gas water heater as claimed in any one of the preceding claims, wherein a combustible mixture of air and gas is fed to the input of the fan.

7. A forced draft gas water heater as claimed in any one of the preceding claims, wherein the forced draft gas water heater includes one of the following: a fan motor; a non-sparking fan motor; a motor including a squirrel cage; and a brushless motor.

8. A forced draft gas water heater as claimed in any one of the preceding claims, wherein the tank includes a flue.

9. A forced draft gas water heater as claimed in any one of the preceding claims, wherein ducting is provided to direct the combustion products from the flue to at least a portion of the external wall of the tank. 10

10. A forced draft gas water heater as claimed in claim 9, wherein the ducting provides a jacket surrounding the top of the tank and extending at least part way down the side walls of the tank.

11. A forced draft gas water heater as claimed in claim 9 or claim 10, wherein the ducting includes an outer skirt which redirects the combustion products at least part way up the outer wall of the jacket.

12. A forced draft gas water heater as claimed in any one of claims 9 to 11, wherein the jacket is at least partially thermally insulated from the atmosphere.

13. A forced draft gas water heater as claimed in any one of the preceding claims, wherein a diffuser is located above the top of the flue.

14. A forced draft gas water heater as claimed in any one of the preceding claims, wherein a combustion chamber is formed with a lower wall, the rim of which is effectively sealed to the minus end.

15. A forced draft gas water heater as claimed in claim 14, wherein effective sealing takes place at or near to a lowermost rim of the minus end.

16. A forced draft gas water heater as claimed in claim 14 or claim 15, wherein the lower wall of the combustion chamber is substantially flat.

17. A forced draft gas water heater as claimed in claim 14 or claim 15, wherein the lower wall of the combustion chamber is dished.