AU2002302185A1

AU2002302185A1 - A storage water heater with reduced heat maintenance rate

Info

Publication number: AU2002302185A1
Application number: AU2002302185A
Authority: AU
Inventors: Jim Jensen
Original assignee: Rheem Australia Pty Ltd
Current assignee: Rheem Australia Pty Ltd
Priority date: 2001-06-12
Filing date: 2002-06-04
Publication date: 2003-05-15
Anticipated expiration: 2022-06-04

Description

A storage water heater with reduced heat maintenance rate

Field of the Invention

This invention relates to gas or fuel heated water heaters. It concerns the commonplace types having an upright cylindrical storage tank for storing heated water with a combustion space below the tank, housing both a main and pilot burner; the most common option includes also a single tubular heat exchanger flue passing axially through the tank. It more specifically concerns attempts to reduce heat loss from water heaters while the main burner is in stand-by mode.

Background of the Invention

Gas fuelled water heaters conventionally have the flue terminating closely above the top of the tank but extended by a connection to a duct which conveys waste products of combustion upwardly above the heater to discharge to atmosphere outdoors. Also conventionally, such heaters have, in the combustion chamber beneath the tank, a main burner of large output that heats water in the tank rapidly and a very low output pilot burner, the sole purpose of which is to remain alight when the main burner is not alight, to be available to reignite the main burner on demand. This ensures automatic unattended operation without the need for any auxiliary power source such as electricity mains connection or equivalent means to reignite the main burner electrically.

Pilot burners need to be of sufficiently stable burning characteristics not to be extinguished due to spurious causes such as stray draughts or a pressure wave which accompanies each ignition of the main burner. To meet that requirement pilot burners are generally not satisfactory unless they are of a size that converts gas to heat energy at the rate of 0.3 to 0.4 Mega Joules per hour.

The above described type of heater wastes a substantial amount of energy over time as "standby losses". Stand-by losses are those arising because the heat of the pilot flame passes directly upward through the flue, driven by the natural buoyancy of the heated gases in the flue. Also included in this class of loss is the buoyancy-driven draught caused by heat transfer from the hot water stored in the tank, through the flue wall to the gases in the flue, adding to the updraught and hence the wasteful heat loss. This type of loss is continuous, regardless of whether the main burner is alight to raise the water temperature to the required level that is reflected by the setting of a conventional thermostatically controlled gas valve.

Summary of the invention The present invention provides a storage water heater having a cylindrical storage tank that stores heated water and which has a tubular heat exchanger flue passing axially through the tank; the flue terminating above the top of the tank; a combustion chamber beneath the tank housing a main burner that heats water in the tank and a pilot burner which remains alight when the main burner is not alight; a duct communicating with the top of the flue which includes: an upper radially extending portion; and a downwardly and axially extending portion, a radial surface of which is in direct contact with an external surface of an upper portion of a vertical wall of the tank, said upper radially extending portion extending to one side of said tank, the axially extending portion having a width which is less than the diameter or width of the tank.

The heater can further include a lower radially extending terminal portion communicating with the axially extending portion and extending away from the vertical wall of the tank. Preferably tank and duct are enclosed by heat insulation.

The lower radially extending terminal portion can terminate beyond said heat insulation layer that encapsulates the tank and duct.

The radial surface of said axially extending portion of the duct can be curved to match an outside radius of the vertical wall of the tank to maximise heat exchange to the hot water in the tank from the gases in the axially extending portion.

The lower terminal portion can join the axially extending portion of the duct at a height that satisfies the condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct.

The axially extending portion can have a width in the range of 30% to 95 % of the width or diameter of the tank.

The axially extending portion is preferably located within, on, or along one half or one side of said tank. The upper radially extending portion can extend from said flue to one side or half of said tank.

The upper radially extending duct can extend in three directions away from said flue, said three directions being generally in the same plane and approximately 90 degrees apart.

The invention also provides a storage water heater including: a cylindrical storage tank that stores heated water and which has a tubular heat exchanger flue passing axially through the tank; the flue terminating above the top of the tank; a combustion chamber beneath the tank housing a main burner that heats water in the tank and a pilot burner which remains alight when the main burner is not alight; a duct communicating with the top of the flue; including: an upper radially extending portion; an axially extending portion the radially inward surface of which is in direct contact with an external surface of an upper portion of a vertical wall of the tank; and wherein the tank, flue and duct are enclosed by heat insulation; a lower radially extending terminal portion communicating with a lower part of the axially extending portion and extending away from the vertical wall of the tank beyond the heat insulation; wherein the radially inward surface of the axially extending portion of the duct is curved to extend its area of contact with an outside radius of the vertical wall of the tank; and wherein the lower terminal portion joins the axially extending portion of the duct at a height that satisfies the condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct, the axially extending portion having a width which is less than the diameter or width of the tank.

The axially extending portion can have a width in the range of 30% to 95 % of the width or diameter of the tank. The axially extending portion is preferably located within, on, or along one half or one side of said tank.

The upper radially extending portion can extend from said flue to one side or half of said tank.

The present invention further provides a duct communicating with the top of the flue which comprises: an upper radially extending portion; and a downwardly and axially extending portion, the radially inward surface of which is in direct contact with an external surface of an upper portion of a vertical wall of the tank. In addition, there is provided a lower radially extending terminal portion communicating with the axially extending portion and extending away from the vertical wall of the tank beyond a heat insulation layer that encapsulates the tank and duct. A radially inward surface of the downwardly axially extending portion of the duct is curved to match an outside radius of the vertical wall of the tank to maximise heat exchange to the hot water in the tank from the gases in the axially extending portion. Importantly, the lower terminal portion joins the axially extending portion of the duct at a height that satisfies the condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct.

Brief description of the drawings

The invention is described further with the aid of reference to a presently preferred example as illustrated in the accompanying drawings in which:

Fig 1 is a front elevation of a water heater tank as used in a water heater embodying to the invention; Fig 2 is a plan view of the water heater tank of fig 1.

Fig 3 is a side elevation of the tank in Fig 1;

Fig 4 is a cross-section at the line JJI-III in Fig 1 showing in addition other structure comprising the water heater; Fig 5 is a cross-section at the line rV-IV in Fig 2.

Fig 6 is a graph of thermal efficiency of a given type of water heater.

Detailed Description of the Embodiments

Figs 1 and 2 show a cylindrical gas-fuelled water heater tank 10, having a cylindrical axis 12. The tank 10 comprises a vertical cylindrical wall 14, a lower end wall 16, an upper end wall 18. The vertical wall conventionally comprises an inlet connection 20 for cold water entry, an opening 22 in which to insert a thermostat sensor, a hot water outlet connection 24 and a temperature and pressure relief valve connection 26. To improve the thermal efficiency of the water heater, as will be further described below, this invention provides a duct 28 communicating with the top of the flue 44 The duct 28 comprises: an upper radially extending portion 30 and a vertical portion 32. The vertical portion 32 is curved, with an inside radius matching the outside radius of the vertical wall 14 of the tank 10 so that the duct 28 makes direct contact with the external surface of an upper portion of a vertical wall 14 of the tank 10. In addition, there is an opening 34 towards or substantially at the lower end of the vertical portion of the duct 28.

Fig 3 shows the duct 28 in elevation view, correspondingly numbered to Figs 1 and 2. The component radial portion 30 and its joinder to the vertical portion 32 is more evident than can be seen

Fig 4 shows a gas-fuelled water heater 40, including the cylindrical tank 10, , having a cylindrical axis 12. As with Figs 1 to 3, the tank 10 comprises the vertical cylindrical wall 14, the lower end wall 16, the upper end wall 18 and a second vertical cylindrical wall 42 defining a vertical flue passage 44 passing through the centre of gravity of the tank. The two cylindrical walls 14 and 42 and two end walls 16 and 18 enclose a storage space 46 for storage of heated water. The flue passage 44 conventionally houses a baffle 48 to enhance to some extent heat transfer from the flue passage 44 to the water storage space 46. The outer vertical wall conventionally includes an inlet connection 43 for cold water entry, the opening in which to insert a thermostat bulb 47, a connection 49 for hot water outlet and a connection 51 for a temperature and pressure relief valve.

The thermal efficiency of the water heater can be impressed by providing the duct 28 communicating with the top of the flue passage 44. The duct 28 includes an upper, horizontal portion 30 which radially extends to join to a vertical portion 32. The radially inward surface of the vertical portion 32 is curved to an arc of a circle with an inside radius which matches the outside radius of the tank so that a radially inner wall of the vertical portion is in direct contact with the external surface of an upper portion of a vertical wall 14 of the tank 10. In addition, there is an opening 34 at the lower end of the vertical portion 32. The opening 34 connects to a second horizontal portion 50 of the duct 28 which extends away from the vertical wall 14 of the tank 10 to clear the outside surface of a heat insulation layer 52 that encapsulates the tank and duct. The second horizontal portion 50 may connect to a flue terminal or may further extend from the heater if required, such as to discharge outside of a room housing the heater. The lower horizontal portion 50 of the duct effectively terminates the vertical leg of the duct at a height that satisfies the significant condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct. The actual height of the second horizontal portion 50 of the duct 28 is not necessarily related to a particular datum height with respect to the other items in the heater. In this embodiment it is at a height that is approximately at the midpoint between the position of the heat-source, namely the main burner, and the outlet of hot gases from the heater. Different design variables applicable to particular models of heater will result in different actual heights of outlet to yield the optimal flue "locking" behaviour of the heater as a whole when in use. Fig 5 shows the vertical leg 32 of the duct 28 being curved to an arc of a circle with an inside radius which matches the outside radius of the tank 10 so that a radially inner wall of the vertical portion is in direct contact with the external surface of the vertical wall 14 of the tank 10. The cross- sectional area of the vertical leg of the duct is substantially uniform throughout its length.

As can be seen from the figs 1 to 5, the vertical portion 32 has a width which is less than the diameter or width of the tank. This width can be in the range of 30% to 95 % of the width or diameter of the tank. Such a width means that the vertical portion 32 is located within, on, or along one half or one side of the tank 10.

Also, it can be seen that the radial portion 30 extends from said flue 42 to one side or half of tank 10. another feature of the radial portion 30 is that it extends in three directions away from the flue 42. By this it is meant that the portion 30, as can be seen in figure 2, extends away from the flue in directions to the left of the page, to the right of the page and to the bottom of the page, that is, three directions being generally in the same plane and approximately 90 degrees apart. Fig 6 shows diagrammatically how the embodiment above can reduce gas consumption in a water heater of a given specification. The graph relates the thermal efficiency of a given type of water heater and its maintenance rate against a simplified numeric rating developed by the Australian Gas Association, referred to as the "Star Rating." The rating concept is aimed at assisting consumers in purchasing decisions related to gas burning appliances in general, whereby the higher the star rating, is an indication of how economical the appliance is with its consumption of fuel. A star rating for a water heater is determined by testing and, as shown on the graph, many commercial models yield results in the 2 to 3 star category. When the present invention was applied to a conventional model of water heater having a star rating of approximately 2.5, the star rating of the improved heater was about 4.3. This improvement was as a result of a substantial reduction in maintenance rate, without significant change in thermal efficiency.

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 or drawings. AH of these different combinations constitute various alternative aspects of the invention. The foregoing describes embodiments of the present invention and modifications, obvious to those skilled in the art can be made thereto, without departing from the scope of the present invention.

Claims

1. A storage water heater having a cylindrical storage tank that stores heated water and which has a tubular heat exchanger flue passing axially through the tank; the flue terminating above the top of the tank; a combustion chamber beneath the tank housing a main burner that heats water in the tank and a pilot burner which remains alight when the main burner is not alight; a duct communicating with the top of the flue which includes: an upper radially extending portion; and a downwardly and axially extending portion, a radial surface of which is in direct contact with an external surface of an upper portion of a vertical wall of the tank, said upper radially extending portion extending to one side of said tank, said axially extending portion having a width which is less than the diameter or width of the tank.

2. A storage heater as claimed in claim 1, further including a lower radially extending terminal portion communicating with the axially extending portion and extending away from the vertical wall of the tank.

3. A storage heater as claimed in claim 1 or 2, wherein said tank and duct are enclosed by heat insulation.

4. A storage heater as claimed in claim 3, wherein said lower radially extending terminal portion terminate beyond said heat insulation layer that encapsulates the tank and duct.

5. A storage heater as claimed in any one of claims 1 to 4, wherein said radial surface of said axially extending portion of the duct is curved to match an outside radius of the vertical wall of the tank to maximise heat exchange to the hot water in the tank from the gases in the axially extending portion.

6. A storage heater as claimed in any one of claims 2 to 5, wherein said lower terminal portion joins the axially extending portion of the duct at a height that satisfies the condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct.

7. A storage heater as claimed in any one of claims 1 to 6, wherein said axially extending portion has a width in the range of 30% to 95% of the width or diameter of the tank.

8. A storage heater as claimed in any one of claims 1 to 7, wherein axially extending portion is preferably located within, on, or along one half or one side of said tank.

9. A storage heater as claimed in any one of claims 1 to 8, wherein said upper radially extending portion extends from said flue to one side or half of said tank.

10. A storage heater as claimed in any one of claims 1 to 9, wherein said upper radially extending duct extends in three directions away from said flue, said three directions being generally in the same plane and approximately 90 degrees apart.

11. A storage water heater including: a cylindrical storage tank that stores heated water and which has a tubular heat exchanger flue passing axially through the tank; the flue terminating above the top of the tank; a combustion chamber beneath the tank housing a main burner that heats water in the tank and a pilot burner which remains alight when the main burner is not alight; a duct communicating with the top of the flue; including: an upper radially extending portion; an axially extending portion the radially inward surface of which is in direct contact with an external surface of an upper portion of a vertical wall of the tank; and wherein the tank, flue and duct are enclosed by heat insulation; a lower radially extending terminal portion communicating with a lower part of the axially extending portion and extending away from the vertical wall of the tank beyond the heat insulation; wherein the radially inward surface of the axially extending portion of the duct is curved to extend its area of contact with an outside radius of the vertical wall of the tank; and wherein the lower terminal portion joins the axially extending portion of the duct at a height that satisfies the condition that, when the pilot flame alone is alight, an average buoyancy force exerted on gases in the flue substantially balances an average opposing buoyancy force exerted on gases in the axially extending portion of the duct; said axially extending portion having a width which is less than the diameter or width of the tank.

12. A storage heater as claimed in claim 11, wherein said axially extending has a width in the range of 30% to 95 % of the width or diameter of the tank.

13. A storage heater as claimed in any one of claims 11 or 12, wherein said axially extending portion is located within, on, or along one half or one side of said tank.

14. A storage heater as claimed in any one of claims 11 to 13, wherein said upper radially extending portion extends from said flue to one side or half of said tank.

15. A storage heater as claimed in any one of claims 11 to 15, wherein said upper radially extending duct extends in three directions away from said flue, said three directions being generally in the same plane and approximately 90 degrees apart.