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.