Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
  • F24H1/18—Water-storage heaters
  • F24H1/20—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes
  • F24H1/205—Water-storage heaters with immersed heating elements, e.g. electric elements or furnace tubes with furnace tubes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
  • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
  • F23L11/00—Arrangements of valves or dampers after the fire

Definitions

• the present invention relates to a water heater and a method of operating same.
• the invention has been primarily developed for use in a natural draft water heater that has a gas burner at the base of the water tank and a flue which passes through the water tank for heating water in the tank.
• Natural draft water heaters are well known and are used extensively in domestic water heating and other applications. The energy efficiency of such water heaters is considered to be an important consideration by many purchasers and owners of such water heaters.
• the Australian Gas Association conducts performance testing for water heaters and generates a Star (Trade Mark) rating indicating the heater's overall energy efficiency (e.g. 5 Star).
• Star Trade Mark
• the Star rating is, generally speaking, a combination of: Efficiency; and Maintenance.
• Efficiency is a measure of the energy transfer from fuel to heated water (i.e. heat exchanging efficiency).
• Maintenance is a measure of retaining stored energy in the water (i.e. insulation effectiveness).
• Natural draft water heaters operate in two modes: a 'heating' mode when the main burner is operating (i.e. alight); and an 'idle' mode when the main burner is not operating.
• a 'heating' mode when the main burner is operating (i.e. alight); and an 'idle' mode when the main burner is not operating.
• a constantly operating pilot flame only the burner's pilot flame is alight in idle mode.
• water heaters that have an electronically controlled gas valve that re-ignites the main burner electronically there is no pilot flame alight in idle mode.
• a water heater with a pilot flame and an open flue i.e. a flue vented directly to atmosphere without restriction
• a damper i.e. a flow control valve downstream of the flue which is controlled to block the flue opening to atmosphere when in idle mode.
• the damper adds to the cost and complexity of the water heater and can also create a safety hazard if it jams in the closed position when the heater is in the heating mode.
• 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 having an air inlet and a pilot flame and being adapted to a burn a fuel to discharge heated gases up through the flue; and a heated gas outlet duct of substantially unrestricted cross-section having an upper, first end in gas communication with the flue outlet and a second, lower end in gas communication with atmosphere, wherein, when only the pilot flame is burning, the heated gas outlet duct is adapted to restrict the air drawn into the flue via the air inlet to the minimum amount required to maintain the pilot flame alight.
• the length of the duct is preferably approximately 20% to 30%, most preferably 25%, of the length of the flue.
• the duct and the flue are preferably cylindrical and have approximately equal diameters.
• 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 having an air inlet and an electronically controlled ignitor and being adapted to a burn a fuel to discharge heated gases up through the flue; and a heated gas outlet duct of substantially unrestricted cross-section having an upper, first end in gas communication with the flue outlet and a second, lower end in gas communication with atmosphere, wherein, the duct has approximately the same cross sectional area of the flue and is approximately 25% of the length of the flue.
• the duct and the flue are preferably cylindrical.
• the present invention provides method of maintaining a pilot flame alight in a water heater having a tank with: a bottom; a top; and a substantially central flue, the method including the steps of: directing the heated gases from the pilot flame from the tank bottom to the tank top via the flue; and directing the heated gases from the tank top to atmosphere via a generally downwardly directed duct of substantially unrestricted cross-section, the duct being adapted to restrict the gas flow drawn into the flue to only the minimum amount required to maintain the pilot flame alight.
• the present invention provides a method of operating a water heater in idle mode, the water heater having a tank with: a bottom; a top; a burner with a pilot flame; and a substantially central flue, the method including the steps of: directing the heated gases from the pilot flame from the tank bottom to the tank top via the flue; and directing the heated gases from the tank top to atmosphere via a generally downwardly directed duct of substantially unrestricted cross-section, the duct being adapted to restrict the gas flow drawn into the flue to only the minimum amount required to maintain the pilot flame alight.
• Figure 1 is a cross-sectional schematic side view of an embodiment of a water heater according to a first embodiment of the invention.
• the water heater 10 includes a cylindrical steel water tank 12 with a central flue 14.
• the flue 14 has a length Ll and a spiral baffle 16 therein.
• the tank has an outwardly concave (domed) bottom 18 and an outwardly concave (domed) top 20.
• the flue 14 has an inlet 22 adjacent the tank bottom 18 and an outlet 24 slightly above the tank top 20. In use, the tank 12 is almost completely filled with water.
• cold water is introduced from mains water supply via a cold water inlet (not shown) near the tank bottom 16 of the tank 12 and hot water is drawn off for use via a hot water outlet (not shown) near the top 20 of the tank 12.
• a burner 26 is located beneath the tank bottom 18.
• the burner 28 has a pilot flame (not shown) and is adapted to burn fuel, preferably natural gas, and discharge heated gases up through the flue 14 for heat transfer to the water in the tank 12.
• the exterior of the tank 12 is surrounded by insulation 28.
• the tank 12 and the insulation 28 are contained within an outer casing 30, which includes an air inlet 32.
• the air inlet 32 is in gas communication with the burner 26 via passage 34.
• the burner 28 also has an associated gas control system 36.
• the water heater 10 also includes a heated gas outlet duct 40 having a first upper end 42 connected to the outlet 22 of the flue by an insulated U-shaped connector 44 and a lower second end 46 open to atmosphere.
• the duct 40 has a length L2 and has a substantially open or unrestricted cylindrical cross-section (i.e. free of valves or dampers and the like).
• the duct 40 is adapted to provide a resistance to the gas flow therethrough such that when the water heater is in idle mode (i.e. only the pilot flame is burning) the gas passing through the duct 40 is subjected to a balancing resistance, which limits the air drawn into the flue 14 to only the minimum that is required to achieve combustion and maintain the pilot flame alight.
• the energy that would ordinarily be lost, in idle mode, through an unrestricted outlet is minimised and the Star rating of the water heater is improved, particularly the Maintenance-based component of the Star rating.
• the resistance of the duct 40 is primarily adjusted by varying its diameter and length.
• the diameter of the duct 40 is approximately equal to that of the flue 16 to avoid choking the gas flow through the flue/duct.
• the duct length L2 is approximately 25% of the flue length L2. Further, it will be appreciated by those persons skilled in the art that other factors can influence the resistance provided by the duct 40 including material and internal surface finish.
• the relative length of the duct 40 is determined by the following iterative process. Firstly, the gas supply for the pilot flame is established as the minimum amount possible to meet environmental (e.g. wind) and legislative requirements.
• the water heat 10 is tested, without the duct 40 attached, and the restriction of the baffle 16 adjusted to meet emission requirements and maximise the Efficiency-based
• the duct 40 is then attached. As discussed above, this improves the Maintenance-based Star rating component. However, it also generally lead to a reduction in the Efficiency-based Star rating component.
• the baffle 16 is then adjusted, by making it less restrictive, to increase the Efficiency-based component until an acceptable level of emissions is reached.
• the length of the duct 40 is then adjusted to seek improvements in the Maintenance-based component. This process continues in an iterative manner until the overall Star rating is maximised.
• the water heater 10 provides improved efficiency as the duct 40 increases the transfer of heat from the pilot flame to the water when the heater 10 is in idle mode by reducing heat loss from the flue 14 to atmosphere. This improves the Maintenance-based Star rating component. More particularly, it is estimated that water heaters similar to that described with reference to the water heater 10 will, in idle mode, transfer approximately 80% of the pilot flame energy to the water and only lose approximately 20% through the flue. Further, such water heaters do not exhibit a loss in their Efficiency-based Star rating component sufficient to compromise their Star rating overall. Moreover, this is achieved in a relatively mechanically simple arrangement that is not susceptible to blocking or other mechanical failure.
• a water heater (not shown) according to a second embodiment of the invention is similar to the heater 10 except it has an electronically controlled gas valve that re-ignites the main burner electronically. This heater has no pilot flame alight in idle mode.
• the duct 40 also improves the Star rating of this heater as it provide a resistance to, and thus slows, the flow of the heated air (ie. air heated by transfer from the surrounding water) leaving the flue.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Heat-Pump Type And Storage Water Heaters (AREA)
• Details Of Fluid Heaters (AREA)
• Instantaneous Water Boilers, Portable Hot-Water Supply Apparatuses, And Control Of Portable Hot-Water Supply Apparatuses (AREA)

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• 2006
  • 2006-08-01 US US11/992,079 patent/US20090142720A1/en not_active Abandoned
  • 2006-08-01 CN CN2006800336139A patent/CN101263347B/zh not_active Expired - Fee Related
  • 2006-08-01 WO PCT/AU2006/001085 patent/WO2007030855A1/en active Application Filing
  • 2006-08-01 NZ NZ566630A patent/NZ566630A/en not_active IP Right Cessation

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