This invention relates to hot water heaters particularly but not exclusively to hot water heaters which can be used in domestic hot water systems.
US patent specification No. 2,404,860 discloses a hot water heater having a gas burner beneath a water vessel and passages which convey combustion products up one side of the vessel, across the top and down the other side so as to heat the water through the walls of the vessel. The combustion products are then discharged through a vertical pipe into a stack.
It is an object of the present invention to provide an efficient hot water heater in which a uniform water temperature distribution is possible.
According to the present invention, there is provided a hot water heater comprising a vessel for water, heating means for applying heat to one side of the vessel for heat transfer to water in the vessel adjacent to said one side to thereby establish a convection current in the water from said one side towards the top of the vessel, the heating means comprising a burner located below the vessel and which produces hot combustion products, the heating means further including a flue structure arranged to receive the hot combustion products from the burner the flue structure including a first exhaust duct at said one side and arranged so that combustion products from the burner pass upwardly through the first exhaust duct to heat water in the vessel at said one side, the flue structure further including secondary duct means spaced from said one side of the vessel, the secondary duct means being arranged to receive combustion products from the first exhaust duct and to pass combustion products from the burner in a downwards direction and to heat water in the vessel adjacent said secondary duct means. The heater is characterised by a balanced flue having an air intake through which air from atmosphere is drawn and supplied to said burner and having an exhaust in communication with said secondary duct means so that the combustion products from the secondary duct means enter the balanced flue and then escape to atmosphere through said exhaust, the air intake and exhaust being adjacent to each other, whereby combustion products from the burner pass upwardly through said first exhaust duct at said one side of the vessel and then pass downwardly through the secondary duct means, spaced from said one side of the vessel, and then pass to atmosphere through the exhaust of the balanced flue adjacent to the air intake of the balanced flue.
Preferably the first exhaust duct decreases in surface area in an upwards direction and/or the secondary duct means decreases in surface area in the downwards direction.
The secondary duct means preferably discharges combustion products away from the vessel at a bottom end of the secondary duct means to an exhaust arrangement of the balanced flue. The exhaust arrangement may include an exhaust chamber into the bottom of which combustion products from the secondary duct means enter, the exhaust chamber having a transfer opening at an upper portion thereof and through which combustion products pass into a flue outlet chamber having the exhaust for discharge of combustion products to atmosphere.
The secondary duct means preferably comprises second and third separate exhaust ducts which are disposed at respective opposite sides of the vessel relative the one side where the first exhaust duct is located. Preferably the opposite sides of the vessel where the second and third ducts are provided are not located diametrically opposite to the side of the vessel where the first duct is located. The opposite sides and the one side of the vessel where heating of water in the vessel by heat transfer through the vessel occurs preferably comprise a major proportion of the surface area of the vessel (4).
The first exhaust duct and the secondary duct means may be defined by a sheet metal member which includes formations which cooperate with the vessel to define the first exhaust duct and the secondary duct means. The sheet metal member may be located around the outside of the vessel, the sheet metal member having portions being spaced from the outside surface of the vessel to define the first exhaust duct and the secondary duct means, the sheet metal member being turned inwardly to define the formations which contact the outside surface of the vessel along substantially the entire height of the vessel and thereby define the boundaries of the first exhaust duct and the secondary duct means.
Preferred features of the invention will now be further described with refrence to the accompanying drawings, in which:
Figures 1 to 8 illustrate schematically a gas fired hot water heater 2. In these Figures, some parts have been omitted for clarity of illustration but such omitted parts will be either mentioned specifically or will be obvious and conventional components.
The heater 2 includes a cold water inlet 6 through the sidewall 29, near the bottom of the vessel 4, and a hot water outlet 8 located at the top of the vessel. Beneath the vessel 4 is a combustion chamber 11 the bottom of which is formed as a condensate tray 13 having an outlet 15. A burner 17 is located so as to project into the combustion chamber 11. More particularly, the combustion chamber includes an opening 19 through which the burner 17 passes. As best seen in Figures 7 and 8, the burner is generally wedge shaped and has a number of outlet orifices 25 on its narrow end.
The vessel 4 is surrounded by a partitioned flue structure 27 which serves to direct hot combustion products from the chamber 11 upwardly adjacent to one side 29 of the vessel and then downwardly adjacent to opposed sides 32 and 33 (see Figure 5) of the vessel and then to a balanced flue assembly 34, which is omitted in Figure 1 for clarity of illustration. The flue structure 27 is shaped so as to keep the hot exhaust products away from the side 36 which is opposite to the side 29 which first receives the combustion products from the chamber 11. The side 29 is therefore very hot whereas the opposite side 36 remains relatively cool. This establishes a convection current indicated by wavy arrows 38. The circulating convection current tends to promote a more uniform temperature distribution in the water throughout the vessel. This is in contrast to other hot water heaters which normally have a more or less static body of water within them with a significant temperature differential between the top and bottom. The circulating current tends to avoid overheating at the top of the tank which might otherwise occur and, in addition, leads to a greater volume of hot water being available to the user at a more or less uniform temperature.
The flue structure 27 is preferably formed from a sheet of stainless steel or aluminized steel and is shaped so as to generally surround the vessel 4 and to define three exhaust ducts 40, 42 and 35 adjacent to the sides 29, 32 and 33 respectively. The structure 27 includes grooves 46 and 48 the inner ends of which bear against the outer periphery of the vessel 4, as best seen in Figure 5. The grooves 46 and 48 define the boundary between the ducts 40 and the adjacent parts of the ducts 42 and 45. The outer ends of the ducts 42 and 35 are defined by inturned legs 50 and 52 of the structure 27. As best seen in Figure 4, the grooves 46 and 48 taper towards one another in the upward direction so that the duct 40 decreases in cross-sectional area in the upward direction. This tends to promote more uniform heat transfer to the vessel along its height because at the bottom where the exhaust gases are hottest, the area of the duct 40 is relatively wide. At the top, the exhaust gases have been cooled somewhat but are more concentrated owing to the smaller size of the duct 40. When the exhaust gases reach the top of the duct 40, they then pass adjacent to the top 21 of the vessel and then travel downwardly through the ducts 42 and 35 into the balanced flue structure 34. A heat shield 56 may be located near the centre of the top 21 of the vessel to prevent the exhaust gases from passing over that point. This avoids possible overheating or boiling of the water at the top centre of the vessel. The shield 56 preferably comprises a hollow cylindrical body which again may be made from stainless steel.
The vessel 4 and flue structure 27 are located within the housing 152 which is lined with insulating material 150, the housing 152 and insulating material 150 being shown in full in Figure 2 and indicated in part only in Figure 4. The flue structure 27 lies adjacent to the insulating material 150 and protects it from exposure to the exhaust gases. The insulation at the top of the vessel is protected by a plate 62. The housing 152 includes a base plate 64, a funnel 66 being provided to collect condensate from the outlet 15.
The heater includes a thermostatically controlled gas valve 68 which is located in the air inlet chamber of the balanced flue structure 34 and it functions in the usual way. A probe 69 extends into the vessel 4 for sensing the temperature of the water and controlling the valve 68 in the usual way. The valve 68 includes an outlet nozzle 72 which is located adjacent to the flared end 74 of an inlet pipe 76 to the burner 17. Primary combustion air is drawn into the flared inlet 74 in the usual way.
Figure 3 schematically illustrates the balanced flue structure 34. The structure 34 essentially comprises a box structure having sidewalls 75 and 76 and a top wall 77. The structure has an inner face 78 which is essentially open and lies adjacent to the flue structure 27. The box structure has an outer face which is open except for a flange 79 which extends inwardly from sidewalls 75, 76 and top wall 77 and across the bottom face 91 which is open at the inner part 93 and closed at the outer part 95. The outer face is closed by a removable cover (not shown) which permits access to the burner 17 and control valve 68. The box structure includes a partitioning plate 80 which is vertically disposed and forms an exhaust chamber 81 towards the inner face 78 of the structure and an inlet chamber 82 towards the outer face of the structure. It also includes a horizontally disposed plate 83 extending betwen the sidewalls 75 and 76 and the plate 80 and front face 79. The plate 83 defines a flue outlet chamber above it. The plate 80 includes a transfer opening 84 bounded by two baffle plates 85 to permit exhaust gases to pass from the chamber 81 into the outlet chamber and then through exhaust outlet grates 86 formed in the sidewalls 75 and 76. The sidewalls 75 and 76 also include air inlet grates 87 located beneath the grates 86 to permit air to be drawn into the inlet chamber 82. Because the grates 86 and 87 are located adjacent to one another, the arrangement acts as a balanced flue. Streams of exhaust gases, as indicated by arrows 88 from the exhaust ducts 42 and 35, enter the lower part of the chamber 81 from beneath the lower edges of the ducts 42 and 35 and then pass through the opening 84 and escape through the grates 86.
Inlet streams of air, as indicated by arrows 89 in Figure 3, pass through the grates 87 downwardly through the chamber 82 and exit through the open bottom part 93 so as to then be drawn into the combustion chamber 11 to provide secondary air for the burner 17. Since the probe 69 passes through the exhaust chamber 81 it may include heat shielding to prevent overheating.
Figures 7 and 8 illustrate the preferred arrangement for the burner 17. The burner is generally wedge shaped and is formed from upper and lower pressed steel portions 120 and 122. The front edges of the portions 120 and 122 are formed with accurate grooved portions which cooperation to form the row of outlet orifices 25 with cross lighting gaps.
The gas fuel inlet pipe 76 is connected near the rear part of the upper member 120 and an internal baffle 128 is provided so as to direct the gas air mixture towards the orifices 25. Mixing of the gases occurs in the body of the burner 17 as well as in the pipe 76. In use the burner 17 produces a row of flames which are located near the centre of the bottom of the vessel 4 and are directed generally towards the passage 40. Heat transfer will occur at the bottom of the vessel 4 as well as within the passages 40, 42 and 35.