AU2010239124B2

AU2010239124B2 - Improvements in water heaters

Info

Publication number: AU2010239124B2
Application number: AU2010239124A
Authority: AU
Inventors: Dragan Music
Original assignee: Rheem Australia Pty Ltd
Current assignee: Rheem Australia Pty Ltd
Priority date: 2009-04-21
Filing date: 2010-02-26
Publication date: 2014-03-27
Anticipated expiration: 2030-02-26
Also published as: NZ596020A; WO2010121287A1; AU2010239124A1

Abstract

A gas fired water heater (2.002) including a tank (2.010), a gas burner (2.014) at the base of the tank, a flue (2.018) in fluid communication with combustion products from the burner and extending upwards from the burner through the tank, and an external jacket (2.020) closed at the top (2.024) and spaced from the exterior of the tank and extending at least part way down the exterior of the tank, and an exhaust outlet (2.028) located at a predetermined distance above the base of the flue.

Description

1 Improvements in Water Heaters Field of the invention [001] This invention relates to improvements in gas water heaters. [002] The invention is particularly suited for centrally flued gas heaters. Background of the invention [003] Australian patent AU2002302185 describes a gas fired water heater with a central flue having a pilot burner and an external duct adapted to direct the combustion gases downward after they have exited the central flue. The length of the external duct is selected to balance the buoyancy of the heated gas in the flue when the burner is in the stand-by mode, ie, when only the pilot burner is alight and heat is transferred through the wall of the flue from the water to the gas in the flue. [004] Australian patent AU768568 describes a gas fired water heater with a central flue inside the water tank to direct the combustion gases upward to the top of the tank from the burner located at the base of the flue, and an external jacket spaced from the exterior of the water tank to conduct the combustion gases down the outside of the tank to the bottom of the tank. The external jacket has a further annular cavity around the lower portion of the external jacket, the annular cavity having an opening to atmosphere to permit the escape of the flue gases at a selected distance above the base of the jacket while preventing perturbation from ambient conditions such as wind. The central flue, the external jacket, and the annular cavity form a path for the flue gases. This configuration is intended to optimize the amount of heat extracted from the flue gases through the walls of the flue and the external jacket for the purpose of heating the water in the tank. [005] The annular cavity is intended to provide a flue lock to prevent the gas in the flue gas path from removing heat from the water tank by convection when the gas burner is turned off. In addition, the annular cavity assists in preventing wind drafts from interfering with the operation of the water heater. [006] For any particular configuration of water heater, a corresponding minimum amount of gas needs to be burnt in order to ensure that there is sufficient heat to drive the flue gases through the flue gas path.

2 [007] 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. Summary of the invention [008] The present invention provides a gas fired water heater including a tank, a gas burner at the base of the tank, a flue in fluid communication with combustion products from the burner and extending upwards from the burner through the tank, and an external jacket closed at the top and spaced from the exterior of the tank which with the flue forms a combustion products flow path, said flow path after said flue terminating adjacent the exterior of said tank and at the base of said tank, and an exhaust outlet located at a predetermined distance above the base of the flue, the combustion products flow path providing flow resistance. [009] The flue and the space between the exterior of the tank and the jacket form a combustion gas flow path. [010] The flow path provides a flow resistance. [011] The flow path can include a flue baffle. [012] The heater can include a vented housing enclosing the exhaust outlet. [013] The housing can include a pair of cross-flow vents located to permit ambient wind to flow transversely to the flow of combustion gases from the exhaust outlet. [014] The vents can include vanes oriented to direct wind entering the vents away from the exhaust outlet. [015] The heater can include an exhaust duct connected to the exhaust outlet, the duct being adapted to direct combustion gases away from the outside of the external jacket. [016] The exhaust duct can include a cowling at its outlet adapted to direct the combustion gases transversely in relation to the flow of combustion gases in the exhaust duct. [017] The exhaust outlet can be located at a distance above the base of the flue such that, in the stand-by state, the buoyancy of the flue gases are approximately in equilibrium. Brief description of the drawings [018] 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: 3 [019] Figure 1 is a schematic illustration of a water heater implementing an embodiment of the invention. [020] Figure 2 is an illustration of the construction of the water heater of Figure 1. [021] Figures 3 to 7 show views of the exhaust duct suitable for use in an embodiment of the invention. [022] Figure 8 is an illustration of the features of a vent used in an embodiment of the invention. [023] Figure 9 illustrates an alternative embodiment of the outlet of the exhaust duct. [024] The numbering convention used in the drawings is that the digits in front of the full stop indicate the drawing number, and the digits after the full stop are the element reference numbers. Where possible, the same element reference number is used in different drawings to indicate corresponding elements. Detailed description of the embodiment or embodiments [025] Figure 1 illustrates a water heater having an external shell 1.004 and an exhaust access 1.006 having a pair of cross-flow vents 1.008, only one of which is visible in Figure 1. [026] Figure 2 illustrates internal and flow details of a water heater such as that shown in Figure 1. [027] As seen in Figure 2, the water heater includes a cylindrical water tank 2.010 having a concave base or minus end 2.009 and a convex top or plus end 2.011. A gas burner 2.014 is located below the concave end 2.009 of the tank 2.010. The burner 2.014 directly heats the concave end 2.009 of the tank and the combustion gases can flow through a centrally located flue 2.018 passing through the tank. A continuously burning pilot flame can be used to light the burner when a burner control valve is opened thermo statically or by a controller in response to a temperature sensor. [028] The central flue 2.018 extends through the centre of the tank and conducts combustion gases from gas burner 2.014 through the centre of the water tank 2.010, the walls of the flue providing an internal heat exchanger to deliver heat from the combustion gases to the water in the tank. Additional flow impedance in the form of a flue baffle 2.019 can be included in the flue to provide adjustment for the flow impedance. The impedance can provide a meander path through the flue or it can increase turbulence or flow resistance of the flow of combustion gases. The flow impedance can include baffles or vanes.

4 [029] The tank is surrounded by an external heat exchanger having a cylindrical body 2.020 and topped by a domed roof 2.024, there being a cylindrical gap between the tank 2.010 and the external heat exchanger jacket 2.020 and between the top of the tank and the domed roof of the external heat exchanger. The insulation on the outside of the external heat exchanger jacket 2.020 ensures that the heat from the combustion gases is delivered to the exterior surface of the cylindrical wall 2.010 and the top of the water tank 2.011. The external heat exchanger is in fluid communication with the internal flue 2.018. It will be noted from Figure 2 that external heat exchanger jacket 2.020 extends to the base of the tank 2.010 and thus the combustion products flow path extends in one direction with respect to the tank 2.010. [030] The outer shell 2.004 of the water heater system surrounds the outer heat exchanger jacket 2.020, 2.024, with the cavity 2.005, between the system's outer shell and the outer heat exchanger jacket 2.020, being filled with thermal insulation, such as polyurethane or fibreglass. The outer heat exchanger jacket 2.020 encloses at least the upper portion of the sides of the water tank 2.010 and extends down to an exhaust outlet duct 2.028 via which the combustion gases are discharged. [031] The exhaust outlet duct 2.028 can be located at a selected height above the base of the water tank. If the outlet is too low, the exhaust gases will not be discharged efficiently, and if the outlet is too high, the efficiency of the system will be degraded as the flow rate of the hot gases will be too fast. The location of the exhaust duct 2.028 can be selected to maintain the buoyancy balance described in earlier patent application W002101302. The optimal height will depend on such factors as the heat energy input, the gas flow resistance from the burner to the outlet, and the heat absorption into the water in the tank. In one embodiment, these factors are controlled so the outlet or exhaust duct 2.028 can be located in the middle third of the height between the burner and the top of the tank. [032] The end of the exhaust outlet duct 2.028 can be provided with a cowling 2.030. A housing, which can have an access door for providing access to the controls of the water heater can also include a cross-flow ventilation arrangement in the form of a pair of apertures such as 2.008. Vanes such as 2.032, some of which are not illustrated for clarity, can be provided to assist in angling the direction of any external wind away from directly impinging on the end of the exhaust outlet duct 2.028. The cowling 2.030 also assists in preventing cross-winds from directly impinging on the end of the exhaust outlet duct 2.028.

5 [033] Details of an embodiment of the exhaust duct 2.028 and cowling 2.030 are shown in Figures 3 to 7. Figure 3, being an end view of the exhaust duct, shows the circular cross section of the duct 3.028, and the cowling 3.030. Figure 4 being a side view of the exhaust duct shows general shape of the duct 4.028 and the cowling 4.030. Figure 5, being a second end view, from the end opposite to that of Figure 3, showing the general shape of the cowling 5.030. Figure 6, being an underside view, shows the duct 6.028 and a view of the inner portions of the cowling 6.030. Figure 7 illustrates the duct in an isometric view showing the duct 7.028 and the cowling 7.030. [034] The external shell 2.004 of the water tank 2.010 can be constructed from sheet steel panels secured together with "lock seams", top and bottom end caps and a front cover to form a weather resistant outer casing. [035] The cylinder 2.010 can be made from fully welded mild steel, with a convex top and concave bottom, and lined with vitreous enamel and supported on a circular sheet steel cylinder support. The cylinder is surrounded by sheet steel external heat exchanger 2.020 that is insulated by rigid polyurethane foam. [036] The burner assembly 2.014 can comprise a continuous pilot and main burner centrally located under the internal flue tube 2.018. [037] The gas control can incorporate a thermostat, over-temperature cutout, gas regulator, pilot gas control and safety shut off features. [038] Central flue tube 2.018 discharges into a plenum between the top of the cylinder 2.011 and the dome 2.024 of the external heat exchanger. Flue gases are diverted through about 1800 at the top of the flue and are then diverted downwards at the junction of the plenum and the cylindrical walls 2.010 of the tank and the external heat exchanger wall 2.020. The flue gases then flow down the sides of the water tank 2.010 and flow towards the outlet duct 2.028. [039] Figure 8 is illustrative of the orientation of the vanes 2.032 of the cross-flow vents 2.008 of the housing 2.006. The vent 8.008 includes a frame having a top 8.040, sides 8.042, 8.044, and a base 8.046. For the purposes of illustration only, slots 8.048, 8.050 for receiving vanes, such as 8.052 (shown by way of example in dashed outline), are shown in the top and base of the vent. In practice, the vent and its vanes can be moulded as a single piece, but the slots are used to illustrate the orientation of the vanes. As shown by the angle 0, the slots are inclined to the normal to the major dimension of the base 8.046 and top 8.040 of the frame of the vent 8.008. Alternatively, the angle 0 can be zero, so that the vanes 2.032 will be at right angles to the 6 edge of the vent. In the vent illustrated in figure 8, the side 8.042 is located towards the front of the housing, the exhaust duct entering the housing at the rear of the housing. Thus the vanes will divert any ambient wind towards the front of the housing. It will be understood that the opposite vent will also have vanes directing the wind towards the front of the housing. Thus the other vent will be a mirror of the vent shown in Figure 8. In one embodiment, the pitch of the vanes is such that there is no line-of sight through the housing. Thus the spacing of the vanes along the major dimension will be less than the distance between the front of a vent and its rear, measured along the major dimension. [040] Inner and outer flue liners can be made of zinc or zinc/aluminium coated steel, located coaxially around the cylinder. Spacing between flue liners and cylinder can be maintained by dimples pressed into the inner and outer flue liners. [041] A condensate tray can be fitted around bottom edge of cylinder for collection of condensate formed between flue liners and cylinder. Such a condensate tray a two-piece design made from 30% glass filled polypropylene and 33% glass filled nylon. Condensate can be drained via a condensate outlet attached to the tray. [042] The dome 2.024 can be zinc or zinc/aluminium coated steel, formed into dome shape, and attached to top of inner flue liner to produce sealed flueway over the outer surface of cylinder. [043] The housing or flue terminal 2.006 can be made from UV stabilised thermoplastic polymer, located at the front of the shell. The vertical box section includes air inlet and flue products outlet, and can be open to atmosphere at both sides. [044] Rigid polyurethane can be injected between the flue liner side walls and shell, and a 50 mm thick fibreglass disc can cover the top of the flue liner. [045] Heat exchange takes place through all surfaces of the storage cylinder or water tank 2.010. The outside surface of cylinder shell or storage tank 2.010 is enamelled for corrosion protection against the condensate. [046] The balance type flue terminal provides air inlet and flue products outlet at the front of the heater to give stable operation under adverse wind conditions. [047] Figure 9 illustrates an alternative exhaust outlet arrangement, in which the cowling 7.030 (Figure 7) is replaced by a pair of baffles 9.062, 9.064 projecting from the sides of the vent 9.060. The vent can be a rectangular section duct projecting through the insulation to the 7 outside of the shell 9.004. The housing 9.006 can have a pair of cross-flow vents, and the baffles assist in reducing the effect of cross-wind on the vent. [048] We have found that a centrally flued water heater having an internal flue and an external jacket which extends only part way down the outside of the tank can achieve similar efficiencies to the previously discussed system while using less gas. For example, a system according to the present invention and using 30 MJ/hr can produce efficiency similar to that of a system as described in AU768568 which uses 42 MJ/hr. [049] In this specification, reference to a document, disclosure, or other publication or use is not an admission that the document, disclosure, publication or use forms part of the common general knowledge of the skilled worker in the field of this invention at the priority date of this specification, unless otherwise stated. [050] In this specification, terms indicating orientation or direction, such as "up", "down", "vertical", "horizontal", "left", "right" "upright", "transverse" etc. are not intended to be absolute terms unless the context requires or indicates otherwise. These terms will normally refer to orientations shown in the drawings. [051] 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. [052] 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. [053] 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. [054] While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may 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 modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein.

Claims

1. A gas fired water heater including a tank, a gas burner at the base of the tank, a flue in fluid communication with combustion products from the burner and extending upwards from the burner through the tank, and an external jacket closed at the top and spaced from the exterior of the tank which with the flue forms a combustion products flow path, said flow path after said flue terminating adjacent the exterior of said tank and at the base of said tank, and an exhaust outlet located at a predetermined distance above the base of the flue, the combustion products flow path providing flow resistance.

2. A heater as claimed in claim 1, including a vented housing enclosing the exhaust outlet.

3. A gas fired water heater as claimed in claim 3, wherein the housing includes a pair of cross-flow vents located to permit ambient wind to flow transversely to the flow of combustion gases from the exhaust outlet.

4. A gas fired water heater as claimed in claim 4, wherein the vents include vanes oriented to direct wind entering the vents away from the exhaust outlet. .

5. A gas fired water heater as claimed in any one of the preceding claims, including an exhaust duct connected to the exhaust outlet, the duct being adapted to direct combustion gases away from the outside of the external jacket.

6. A gas fired water heater as claimed in claim 6, wherein the exhaust duct includes a cowling at its outlet adapted to direct the combustion gases transversely in relation to the flow of combustion gases in the exhaust duct.

7. A gas fired water heater as claimed in any one of the preceding claims, wherein the gas fired water heater is a natural draft heater.

8. A gas fired water heater as claimed in any one of the preceding claims, wherein the exhaust outlet is located at a distance above the base of the flue such that, in the stand-by state, the gases in the flue are in a state of equilibrium.

9. A gas fired water heater substantially as herein described with reference to the accompanying figures of the drawings.