GB2216242A - Water heaters - Google Patents

Abstract

A water calorifier comprises a hot water storage vessel (1), a multi-element electric immersion heater means (4, 4', 4'') located in an upper part only of the vessel, an electric pump (6) for recirculating the heated water between upper and lower regions of the vessel and control means (5) for selectively energising the pump and one or more of the heating elements (4', 4'') during off-peak and peak electricity tariff periods. The calorifier is efficient and gives rise to savings in manufacturing costs because it is not necessary to provide respective flange-mounted heater units in both the upper and lower parts of the calorifier vessel. <IMAGE>

Description

Calorifiers This invention relates to water calorifiers for use in hot water supply installations, especially but not exclusively industrial or commercial installations, in which the water is heated directly by electric immersion heaters.

Most direct, electrically heated calorifiers used to store large quantities of hot water (say, for example between 700 and 1500 litres) for sanitary purposes in commercial or industrial premises, comprise upper and lower immersion heaters mounted in the side wall of the calorifier vessel and extending generally horizontally into the vessel. The upper heater usually has a significantly higher heat output than the lower heater (say, for example, 45 kW as against 15 kW) and is usually used only to provide day-time "boost" heating of the water, whereas the lower heater is used for overnight heating, preferably taking advantage of off-peak tariff electricity, the heating of much of the water taking place by natural convection. Typically, the output of the lower heater will be sized to heat the vessel contents steadily over a time period specified as part of the off-peak tariff.

One disadvantage of the dual heater calorifiers is, of course, the need to provide two heaters which adds to their cost and requires the provision of an additional, relatively large flanged opening in the vessel wall thus giving rise to a further potential point of weakness in the wall.

It is an object of the present invention to overcome that disadvantage and generally to improve the efficiency of electrically heated calorifiers.

According to the present invention there is provided a water calorifier including a vessel for storing hot water therein, heating means located only in an upper part of the vessel and comprising a plurality of electric immersion heater elements, an electric pump for recirculating the water between upper and lower regions of the vessel, and control means, comprising a time switch, adapted selectively to energise the pump and one or more of said elements, in response to thermostat means, thereby to heat said water.

In a preferred embodiment, the control means is adapted to energise one or more (but usually not all) of the heater elements during an off-peak tariff period, and to energise the pump during at least part of that period, the control means being further adapted to energise one or more (and usually all) of the elements during a peak tariff ("boost") period.

The electric pump may be of the submersible type but is preferably of the type commonly used in pumped hot water/heating systems, being located externally of the vessel and connected to the interior thereof by suitable pipe-work. The pump serves to circulate water within the vessel and render the temperature thereof substantially uniform during operation of the pump and is preferably arranged to pump water from an upper region of the vessel and to re-introduce it into the vessel in a lower region thereof.The pump may be arranged to operate so as to render the temperature substantially uniform at all times, although this is not essential; thus, it may be desirable for the pump to be inoperative in certain circumstances, for example where it is necessary to heat fairly quickly only a relatively small quantity of water in the upper part of the vessel during a peak-tariff (boost") period. Further, it may be desirable for the pump to operate only when the water is actually being heated during an off-peak electricity tariff period. In any event, however, at least continual operation is desirable to ensure that undue stagnation of water within certain parts, particularly the lower parts, of the vessel does not occur whereby micro-organisms such as Legionella will be prevented or dissuaded from breeding.

Indeed, the pump operation/thermostat may be arranged so as to achieve Pasteurisation of the whole water content of the vessel, for example by ensuring that the water becomes homogeneously heated to and at a pre-determined minimum temperature for about an hour.

In a preferred embodiment of the invention, the heat source consists of a single electric immersion heater unit located in an upper region of the vessel and having multiple heater elements. The relatively low electrical input usually required during off-peak tariff periods may be realised by arranging to switch on only one or some of the elements, whereas at other times (ie "boost" times), during which a higher input will usually be required, further, or alternative, heater elements may be switched on either manually or by the control means.

Thus, efficient off peak heating can be obtained from a single, multiple element immersion heater when used in conjunction with the pump. When such a single unit is employed (which, by way of example, may have a total input rating of, say, 45 kW), it would, as is conventional, be mounted on the vessel by bolts secured to a flange that is brazed or welded to the vessel. In that case, only one such flange mounting would be required in contrast with prior high capacity "commercial" calorifiers arranged to take advantage of the off-peak-tariff electricity, which require two such mountings. However, it is within the scope of the invention for the heat source to comprise two or more discrete immersion heater units, each comprising one or more elements, located in an upper region of the vessel.

Each unit will then preferably be mounted on a conventional boss which is significantly less expensive to provide than a flanged mounting.

A calorifier of the invention may be of the vented, low pressure type or of the unvented, high pressure type.

Other advantages that accrue from use of the invention are that the entire vessel capacity can be utilised during off-peak-tariff heating because of the provision of a pump, that a conventional and inexpensive two channel timer can be used to control off-peak and boost period heating and that sedimentation within the calorifier vessel is discouraged, again because of the provision of a pump.

An embodiment of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which is a diagrammatic view of an industrial calorifier of the invention. In the drawing, electrical connections are denoted by dashed lines.

Referring to the drawing, the calorifier includes a lagged vented cylinder 1, made for example of copper, having a hot water outlet 2 at its upper end and a low-pressure cold water inlet 3 at its lower end. An electric immersion heater unit 4 is located in an upper region (ie in the upper half) of the cylinder 1, being flange-mounted thereon, and is fitted with a thermostatic switch (not shown).The heater 4 comprises two banks 4', 4" each of three heating elements connected to different phases of a 3-phase AC mains supply via a control means, including a time switch 5 which may be programmed to energise one of the banks 4~, 4" during an off peak (eg ECONOMY 7) tariff period and both banks 4', 4" for one or more pre-set "boost" periods during the day time, subject of course to the thermostatic switch being in its "on" position. By way of example, each bank 4', 4" of heaters may have an input of 15 kW, ie a total available input of 30 kW.

The calorifier further includes an electric pump 6 connected to the AC mains source via the time clock 5, the pump 6 preferably operating only during off-peak heating, ie. when only one of the banks 4', 4" of elements is energised. The pump 6 is connected to the cylinder by suitable external pipework so as, in operation, to withdraw water from the upper regions of the cylinder 1 and deliver it into the lower regions thereof via pipe 7 and inlet 8. The pipe 7 may be replaced by an internal pipe 7' shown by the dashed and dotted line in the drawing.Substantially the whole of the water content of cylinder 1 is thus continuously mixed at least during an off-peak heating cycle so ensuring that it is maintained at a substantially uniform temperature which gradually rises until its desired, pre-determined temperature is reached whereupon the thermostatic switch cuts out.

If desired, there may be provided means to override the water heating programme, either manually or otherwise, for example by remote control.

The cylinder 1 may be completely drained down via drain valve 9 as and when necessary.

Although the calorifier specifically described above with reference to the drawing relates to a 3-phase AC powered calorifier for industrial use (in which context the invention is particularly useful), it will be appreciated that the invention is equally useful in a domestic environment especially where large quantities of water need to be heated.

Claims (10)

CLAIMS:

1. A water calorifier including a vessel for storing hot water therein, heating means located only in the upper part of the vessel and comprising a plurality of immersion heater elements, an electric pump for recirculating the water between upper and lower regions of the vessel, and control means, comprising a time switch, adapted selectively to energise the pump and one or more of said elements, in response to thermostat means, thereby to heat said water.

2. A calorifier according to claim 1 wherein said control means is adapted to energise one or more of said heater elements during an off peak electricity tariff period, and to energise the pump during at least part of said period, said control means being further adapted to energise at least one or more of said elements for the purpose of providing "boost" heating during a peak-tariff period.

3. A calorifier according to claim 2 wherein during said off-peak-tariff period, the control means is adapted to energise one or more, but not all, of said heater elements and, during a peak period, to energise all of said elements.

4. A calorifier according to claim 2 or claim 3 wherein the pump is normally inoperative during "boost" heating.

5. A calorifier according to any one of claims 1 to 4 wherein the heater elements are comprised in a single unit, and comprise two or more sets each of one or more heater elements, each of which sets is selectively energisable, as a whole, as aforesaid.

6. A calorifier according to claim 5 wherein each set comprises three heating elements connected to the respective phases of a 3-phase AC power supply.

7. A calorifier according to any one of claims 1 to 6 wherein said control means is arranged to control heating of the water in the vessel in accordance with a pre-determined time programme.

8. A calorifier according to claim 7 wherein said control means is associated with means to override, manually or otherwise, said programme.

9. A calorifier according to any one of claims 1 to 8 wherein the pump is arranged to pump water from an upper region of the vessel to a lower region of the vessel.

10. A water calorifier substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.