AU2003202621A1

AU2003202621A1 - A water heater and a method of heating water in a tank

Info

Publication number: AU2003202621A1
Application number: AU2003202621A
Authority: AU
Inventors: Mark Keith Hammond
Original assignee: DUX Manufacturing Ltd
Current assignee: DUX Manufacturing Ltd
Priority date: 2002-03-13
Filing date: 2003-02-11
Publication date: 2003-09-22
Anticipated expiration: 2023-02-11
Also published as: AU2003202621B2

Description

WO 03/076852 PCT/AU03/00141 1 A Water Heater and a Method of Heating Water in a Tank Field of the Invention 5 The present invention relates to a water heater and a method of heating water in a tank. The invention has been primarily developed for use in a natural draft water heater that has a gas burner at the base of a water tank and a flue which passes through the water tank for heating water in the tank. 10 Background of the Invention Natural draft water heaters are well known and are used extensively in domestic water heating and other applications. The efficiency of such water heaters is considered 15 to be an important consideration by many owners or operators of such water heaters. Known natural draft, centrally flued, storage water heaters, as are common place in Australia and the United States of America, typically have a thermal efficiency of about 75 to 82%, when tested to recognised standards. Various methods have been 20 employed by manufacturers to improve the efficiency of natural draft water heaters. Australian patent applications no.'s 60889/96, 28685/97 and 82520/87 all disclose methods of heating the exterior of the water tank which take advantage of the greater surface area of the tank exterior compared to that of a central flue. Generally 25 speaking, these heaters direct the heated gasses from the burner to a space between the tank exterior and the interior of a cylindrical outer case surrounding the tank. The heated gasses pass up at least one side of the tank (between the tank and the outer case), travel across the top of the tank and then down the other side of the tank (again between the tank and outer case) before venting to atmosphere. This type of heater is up to 89% efficient. 30 International PCT patent application No. PCT/AU99/00818 (international publication No: WO 00/19153) discloses a natural draft water heater that has a housing surrounding the exterior of the water tank that is spaced away from the exterior of the water tank to define a generally annular cylindrical space between the radially outer 35 surface of the tank and the radially inner surface of the housing. The annular space is in WO 03/076852 PCT/AU03/00141 2 gas flow communication with the upper end of the tank flue such that, in use, heated gas pass up the central flue, over the top of the tank and down the annular space to thereby heat both the radially inner and the radially outer surfaces of the tank prior to exhausting from the heater. It is stated in the application that this arrangement offers improved 5 efficiency over earlier water heater arrangements in which heated gases that pass through the flue exit through an exhaust located near the top of the tank. Tests conducted by the Applicant on water heaters that correspond to that disclosed in the application indicated an efficiency of about 90%. 10 It is an object of the present invention to provide a water heater and a method of heating water in a tank with further improvements in efficiency. Summary of the Invention 15 Accordingly, in a first aspect, the present invention provides a water heater including: a tank with a substantially central flue having an outlet substantially adjacent the top of the tank, the tank being adapted for mounting with the flue substantially vertical; a burner located beneath the tank, the burner adapted to burn a fuel to discharge 20 heated gases up through the flue; a gas directing casing around at least some of the exterior of the tank and spaced away from said at least some of the exterior of the tank to define a space between the interior of the casing and said at least some of the exterior of the tank, said space having an inlet substantially at or adjacent the bottom of the tank and a relatively higher outlet; 25 and a gas directing duct remote from the tank exterior, the duct adapted to direct the heated gases from the flue outlet to the space inlet without substantial heat transfer from the heated gases in the duct to the tank exterior, wherein the heated gases sequentially flow from the burner, up the flue, down 30 the duct and through the space. The heated gases preferably flow in a generally upwards direction through the space.

WO 03/076852 PCT/AU03/00141 3 The exterior of the casing is preferably substantially covered by insulation and the duct is preferably disposed external to the insulation. The exterior of the duct is preferably also covered by insulation. 5 The casing preferably surrounds the entire exterior of the tank. The tank is preferably cylindrical and the space is preferably annular in cross section. The duct is preferably part toroidal in cross section. 10 The space inlet is preferably located at an elevation of about 0% to 15% the height of the tank. The space outlet is preferably located at an elevation of about 50% to 100% the height of the tank. The heater preferably includes an exhaust passage extending downwardly 15 between the space outlet to an exhaust passage outlet. The exhaust passage outlet is preferably located at an elevation higher than that of the space inlet, most preferably at an elevation of about 30% to 60% the height of the tank. In a second aspect, the present invention provides a method of heating water in a 20 tank having a substantially central flue, the method including the sequential steps of: passing heated gases up the central flue; directing the heated gases to substantially at or adjacent the bottom of the tank exterior without allowing substantial heat transfer between the gases and the tank exterior; and 25 directing the heated gases over at least some of the tank exterior towards an outlet higher than the bottom of the tank. The method preferably also includes the step of directing the heated gases to an exhaust passage extending downwardly between the space outlet to an exhaust passage 30 outlet. Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of 35 example only, in relation to the accompanying drawings in which: WO 03/076852 PCT/AU03/00141 4 Figure 1 is a cross-sectional side view of an embodiment of a water heater according to the invention; Figure 2 is a partial perspective view of the water heater shown in Fig. 1; and Figure 3 is a perspective view of the water heater shown in Fig. 1; 5 Detailed Description of the Preferred Embodiment Referring to the drawings, there is shown a natural draft water heater 10 10 according to an embodiment of the invention. The heater 10 includes a cylindrical steel water tank 12 with a central flue 14. The tank 12 has an outwardly concave (domed) bottom 16 and an outwardly convex (domed) top 18. The flue 14 has an inlet 20 adjacent the tank bottom 16 and an outlet 22 slightly above the tank top 18. 15 The tank 12 is shown almost completely filled with water 24. It will be well understood by those skilled in the art that cold water is introduced, via a cold water inlet 26 (see Figure 3), near the tank bottom 20. A burner 28, with an air inlet 29, is located beneath the tank bottom 20 and, again as is well understood by persons skilled in the art, the burner 28 is adapted to burn a fuel, preferably natural gas, and discharge heated gases 20 up through the flue 14. A cylindrical gas directing casing 30 surrounds, and is spaced apart from, the exterior of the tank 12 to define a single space 32, of annular cross section, between the entire exterior of the tank 12 and the interior of the casing 30. The space 32 has an inlet 25 34 which is located at an elevation of between about 2% to 10% of the height of the tank 12. The exterior of the casing 30 is surrounded by insulation 36. The water heater 10 also includes a gas directing duct 38 which, at its upper end, is in gas communication with the flue outlet 22 via a gas passage 40. At its lower end, the 30 duct 38 is in gas communication with the inlet 34 of the space 32. The duct 38 is thus able to direct gases leaving the flue outlet 22 to the inlet 34 of the space 32. The duct 38 is remotely positioned from the exterior of the tank 12 so that no heat transfer occurs between the gases travelling in the duct 38 and the exterior of the tank 12. In the preferred form shown, the duct 38 is disposed on the exterior of the insulation 36. In WO 03/076852 PCT/AU03/00141 5 another embodiment (not shown), the exterior of the duct 38 is also covered by insulation to reudce heat loss. The space 32 also has an outlet 42 in gas communication with an exhaust 5 passage outlet 44 via a downwardly extending exhaust passage 46. The outlet 42 is located at an elevation of between about 55% to 70% of the height of the tank 12 and the outlet 44 is located at an elevation of between about 35% to 50% of the height of the tank 12. 10 As best shown in Fig. 3, all of the previously described components of the water heater 10 are enclosed in a housing 48 with a lid 50. Figure 3 also shows a lower grill 52 over the burner inlet 29, an upper grill 54 over the exhaust outlet 44, a heated water outlet 56 and a fitting 57. The fitting 57 is for the fitment of a pressure and temperature relief valve, which are well known to persons skilled in the art. 15 The operation of the water heater 10 will now be described. In use, gas is burnt by the burner 28 which causes heated gases to travel up the flue 14 (see arrows 58) and heat the water 24 in the tank 12 by virtue of heat transfer from the heated gases to the water 24 through the common exterior wall of the flue 14 and interior wall of the tank 12 20 and through the tank bottom 16. The heated gases then pass out through the flue outlet 14, through the passage 40 (see arrows 60), and into the duct 38. The heated gases are then directed down through the duct 38 (see arrows 61) to the inlet 34 of the space 32. The heated gases then travel in a generally upward direction through the space 32 (see arrows 62) and further heat the water due to heat transfer from the heated gases to the water 24 25 through the exterior wall of the tank 12. The gases then flow through the exhaust passage 46 (see arrows 64) to the exhaust outlet 44, whereafter they vent to atmosphere (see arrow 65). The path of the heated gases through the space 32 is complicated but generally 30 involves the heated gases rising along and around the exterior of the tank 12 and, upon cooling, exiting through the space outlet 42. The water heater 10 according to the preferred embodiment of the invention provides improved efficiency over that disclosed in international PCT patent application 35 No. PCT/AU99/00818 as the heated gases are initially introduced into heat transfer with WO 03/076852 PCT/AU03/00141 6 the exterior of the tank near the bottom of the tank. This is because the water at the bottom of the tank is at its coolest, which results in the temperature differential, and thus the efficiency of the heat transfer, between the (colder) water and the (hotter) gases being maximised. This is in contrast to the prior art arrangement in which heated gases are 5 initially directed to the top of the tank where the adjacent water is at its hottest due to the hotter water rising in the tank. More particularly, tests conducted by the Applicant on prototype water heaters similar to that described with reference to the preferred embodiment water heater 10 10 indicated an efficiency of about 91.5%. Although the invention as been described with reference to a preferred embodiment, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

1. A water heater including: a tank with a substantially central flue having an outlet substantially adjacent the top of the tank, the tank being adapted for mounting with the flue substantially vertical; 5 a burner located beneath the tank, the burner adapted to burn a fuel to discharge heated gases up through the flue; a gas directing casing around at least some of the exterior of the tank and spaced away from said at least some of the exterior of the tank to define a space between the interior of the casing and said at least some of the exterior of the tank, said space having 10 an inlet substantially at or adjacent the bottom of the tank and a relatively higher outlet; and a gas directing duct remote from the tank exterior, the duct adapted to direct the heated gases from the flue outlet to the space inlet without substantial heat transfer from the heated gases in the duct to the tank exterior, 15 wherein the heated gases sequentially flow from the burner, up the flue, down the duct and through the space.

2. The water heater as claimed in claim 1, wherein the heated gases flow in a generally upwards direction through the space. 20

3. The water heater as claimed in claim 1 or 2, wherein the exterior of the casing is substantially covered by insulation.

4. The water heater as claimed in claim 3, wherein the duct is disposed 25 external to the insulation.

5. The water heater as claimed in claim 4, wherein the exterior of the duct is also covered by insulation. 30

6. The water heater as claimed in any one of the preceding claims, wherein the casing surrounds the entire exterior of the tank.

7. The water heater as claimed in any one of the preceding claims, wherein the tank is cylindrical. 35 WO 03/076852 PCT/AU03/00141 8

8. The water heater as claimed in claim 8, wherein the space is annular in cross section.

9. The water heater as claimed in claims 7 or 8, wherein the duct is part 5 toroidal in cross section.

10. The water heater as claimed in any one of the preceding claims, wherein the space inlet is located at an elevation of about 0% to 15% the height of the tank. 10

11. The water heater as claimed in claim 10, wherein the space inlet is located at an elevation of about 2% to 10% the height of the tank.

12. The water heater as claimed in any one of the preceding claims, wherein the space outlet is located at an elevation of about 50% to 100% the height of the tank. 15

13. The water heater as claimed in claim 12, wherein the space outlet is located at an elevation of about 55% to 70% the height of the tank.

14. The water heater as claimed in any one of the preceding claims, wherein 20 the heater includes an exhaust passage extending downwardly between the space outlet to an exhaust passage outlet.

15. The water heater as claimed in claim 14, wherein the exhaust passage outlet is located at an elevation higher than that of the space inlet. 25

16. The water heater as claimed in claim 15, wherein the exhaust passage outlet is located at an elevation of about 30% to 60% the height of the tank.

17. The water heater as claimed in claim 16, wherein the exhaust passage 30 outlet is located at an elevation of about 35% to 50% the height of the tank.

18. A method of heating water in a tank having a substantially central flue, the method including the sequential steps of: passing heated gases up the central flue; WO 03/076852 PCT/AU03/00141 9 directing the heated gases to substantially at or adjacent the bottom of the tank exterior without allowing substantial heat transfer between the gases and the tank exterior; and directing the heated gases over at least some of the tank exterior towards an 5 outlet higher than the bottom of the tank.

19. The water heater as claimed in claim 18, wherein further including the step of directing the heated gases to an exhaust passage extending downwardly between the space outlet to an exhaust passage outlet. 10

20. A water heater substantially as hereinbefore described with reference to the accompanying drawings.

21. A method of heating water in a tank, the method substantially as 15 hereinbefore described with reference to the accompanying drawings.