A WATER HEATING TANK

Abstract: A hot water cylinder (10) having upper and lower horizontally extending immersion heaters (13, 12) is provided with a pair of spaced parallel upright baffle plates (14) positioned one on each side of the lower heating element (12) to cause a column of heated water to rise centrally within the cylinder (10) and to circulate downwardly outside the baffles thus to create substantially complete circulation by convection of heated water within at least the lower part of the cylinder to ensure a substantially uniform water temperature therein. In an alternative arrangement of a helical upright heating coil (23) the baffle plate is formed as a cylindrical sleeve (24) within the coil such that heated water rises outside the sleeve (24) and circulates downwardly inside the latter. The provision of the baffle avoids the creation of pockets of cooler water in the base of the cylinder (10) in which bacteria may breed.

Description: A WATER HEATING TANK THIS INVENTION concerns a water heating tank and preferably, though not exclusively, a hot water cylinder having an input for unheated water, and outlet for heated water, and at least one internal heat source such as an immersion heater or indirect heating coil. A typical domestic hot water cylinder includes a horizontal immersion element which passes across the internal space near the bottom of the cylinder and produces substantially uniform temperature in the water above the element. This is by natural convection. The zone below the level of the element however becomes stratified and is heated only by conduction through the water or, minimally, by conduction through the copper wall. Also, since the cold water input is usually close to the bottom of the cylinder and beneath the heating element, this lower region of the cylinder usually contains water at a temperature of no greater than 30 to 35°C, a temperature which provides an ideal condition for the development of, for example, legionella bacteria. For indirectly heated cylinders, a heating coil supplied with hot water from a boiler may replace the immersion element, but the temperature at the bottom of the cylinder will again be in the region of 20 to 40°C. An object of the present invention is to provide a water heating tank of the kind described but wherein substantially uniform heating of the water throughout the vessel is ensured such that when the heat source is active the temperature of the water throughout the vessel is above the ideal temperature for breeding of bacteria. According to the present invention there is provided a water heating tank comprising a vessel having an input for unheated water, an outlet for heated water, and at least one internal heat source; characterised by an upright baffle arranged adjacent to said heat source and extending downwardly at least to the lower extremity of the heat source, the lowermost extremity of the baffle being located close to the bottom of the vessel, thus to create substantially complete circulation, by convection, of heated water within the vessel and to ensure a substantially uniform water temperature throughout the vessel. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a vertical cross-section through a typical domestic hot water cylinder and incorporating two immersion heaters and a pair of baffles in accordance with the invention; Fig. 2 is a vertical cross-section taken on line II— II of Fig. 1; Fig. 3 is a vertical cross-section similar to Fig. 1 of a commercial hot water cylinder incorporating a pair of baffles in accordance with the invention; and Fig. 4 is a vertical cross-section similar to Fig. 1 of a domestic hot water cylinder but incorporating an indirect heating coil instead of immersion heaters. Referring initially to Figs 1 and 2, a typical domestic hot water cylinder comprises a cylindrical copper vessel 10 having an external insulation jacket 11 extending around all but that part of the cylinder wall which rests on the floor. Unheated water is fed to the cylinder via an inlet pipe A near the bottom, and heated water may be released via an outlet pipe B at the top. In this example, the cylinder is equipped with two horizontally extending electrical immersion heater elements 12 and 13 disposed in vertically spaced relationship one close to the bottom and the other to the top of the vessel. It is common practice for the lower heating element 12 to be operative during the night using reduced price electricity. If the volume of water heated is insufficient for use during the following day, then the upper element 13 may be used on a normal tariff. In accordance with the invention and as best illustrated in Fig. 1 , there is provided a pair of upright parallel baffle plates 14 which extend generally diametrically across the cylinder, one on each side of a vertical line between the heating elements 12 and 13. As can be seen from Fig. 1, the baffles extend above and below the lower heating element 12, with their lower extremities very close to the bottom of the cylinder, and the upper extremities located below the upper heating element 13. The baffles are soldered or otherwise sealingly attached along their upright edges to the internal wall surfaces of the cylinder and may in fact rest upon the domed bottom surface of the cylinder as can be seen in Fig. 1. The presence of the baffles causes a column of heated water to rise between the baffles and this creates a continuous circulation of the heated water within the vessel as illustrated by the arrows 15 in Fig. 1, thus to ensure a substantially uniform temperature throughout the body of water. If the flow area created beneath each baffle Is no greater than one half of the flow area between the baffles, then the circulation rate will ensure that all of the water at the bottom of the cylinder is maintained in circulation thus to prevent stagnant pockets. By ensuring that the baffles terminate below the upper heating element 13 the additional heat created by the upper element is generally not circulated to the entire body of water but is retained within the upper region of the cylinder where a small volume of water heated to a higher temperature, may be required. In a typical hot water cylinder the baffles 14 will extend right across from wall to wall and be placed approximately 75mm apart, extending upwards to a level which may be between 50mm above the top of the lower element 12, and 40mm below the bottom of the upper element 13. If required, the baffles 14 may form two walls of a box-like duct open at the top and bottom and into which the heating elements extend with a sealed connection thereto. Experimentally, the assembly illustrated in Figs. 1 and 2 was found to create a temperature on the underside of the copper at the lowest point of the cylinder, of 57°C when the bulk water temperature was measured at 60°C. Thus, it may be assumed that a substantially uniform temperature throughout the vessel is created. Referring now to Fig. 3, in a typical commercial cylinder, where the bottom is dome shaped at 20 similar to the top, the baffles 21 extend across the vessel and terminate at the bottom close to the wall. Referring now to Fig. 4, where an indirect heating coil 23 is provided, an open-ended cylindrical baffle 24 may be inserted which, for optimum performance, extends above and below the heating coil 23 , which thus operates similarly to the baf fle assembly illustrated in Figs. 1 to 3. A cylindrical column of heated water will circulate upwardly outside the baffle 24 and downwardly inside the latter. By locating the bottom of the baffle 24 close to the bottom of the cylinder as illustrated in Fig. 4, the circulation is such that a substantially uniform temperature within the body of water will, again, be created. Alternatively a cylindrical baffle may surround a centrally located heating coil so that the heated water will rise within the baffle and recirculate downwardly outside the latter. By ensuring a substantially uniform temperature throughout the body of water, this not only eliminates tepid zones where legionella bacteria may multiply but it also increases the effective volume of heated water contained at any one time within the cylinder thus avoiding the need for larger cylinders where increased volumes of water may be required over a short period.

Claims: CLAIMS 1. A water heating tank comprising a vessel having an input for unheated water, an outlet for heated water, and at least one internal heat source; characterised by an upright baffle arranged adjacent to said heat source and extending downwardly at least to the lower extremity of the heat source, the lowermost extremity of the baffle being located close to the bottom of the vessel, thus to create substantially complete circulation, by convection, of heated water within the vessel and to ensure a substantially uniform water temperature throughout the vessel. 2. A water heating tank according to Claim 1 , wherein the heat source extends generally horizontally across the vessel and said baffle comprises a pair of upright plates arranged in spaced parallel relationship one on each side of the heat source above and below the latter. 3. A water heating tank according to Claim 2, wherein the baffle plates are attached along their respective upright edges to the internal wall surfaces of the vessel. 4. A water heating tank according to Claim 2 or Claim 3, wherein the vessel is cylindrical and the baffle plates extend generally diametrically across the vessel, the lower extremities of the baffle plates resting upon a domed central region of the base to the vessel. 5. A water heating tank according to Claim 4, comprising a pair of vertically spaced heating elements each extending generally diametrically across the vessel, one close to the bottom and the other close to the top of the vessel, the baffle plates extending upwardly from a level beneath the lower element to a level beneath the upper element and spaced apart one on each side of a vertical line between the heating elements such that, in use, a column of heated water is caused to rise between the baffles and to circulate downwardly outside of the latter thus to create a continuous circulation of heated water vertically around the baffles. 6. A water heating tank according to any one of Claims 2 to 5, wherein the flow area created beneath, each baffle is no greater than one half of the flow area between the baffles. 7. A water heating tank according to Claim 4, wherein the baffle plates are placed at or in the region of 75mm apart and extend upwardly to a level which may be between 50mm above the top of the lower element and 40mm below the bottom of the upper element. 8. A water heating tank according to any one of Claims 2 to 7, in which the baffles form two walls of a box-like duct open at the top and bottom and into which heating elements extend with a sealed connection thereto. 9. A water heating tank according to Claim 1, wherein said internal heat source comprises an indirect heating coil located with its centric axis upright in the vessel, and the baffle comprises an open-ended cylinder fixed and located within the diametrical bounds of the heating coil such that in use a cylindrical column of heated water will circulate upwardly outside the baffle and downwardly inside the latter. 10. A water heating tank according to Claim 9, wherein said cylindrical baffle extends to positions above and below the top and bottom of the heating coil respectively. 11. A water heating tank according to Claim 1, in which said upright baffle comprises an open-ended cylinder positioned to surround the heat source such that in use a column of heated water will circulate upwardly within the cylinder and downwardly outside the latter.

Inventors: AXCELL BRIAN P, AXCELL, BRIAN, P.
Applicants: AXCELL BRIAN P, UNIV MANCHESTER, THE VICTORIA UNIVERSITY OF MANCHESTER
Application year: 1993
Main classification: F24H1
IPC codes: F24D17, F24H1