GB2200978A - Electric water heating apparatus - Google Patents

Abstract

A water heating apparatus comprises a tank as a thermal store. The water in the tank is heated by two electric immersion heaters, a first 30 at the base of the tank which uses off-peak electricity and a second 32 at mid-tank height. Hot water for domestic consumption is obtained by passing cold mains water through a heat exchange coil in the tank. The coil is in two portions, one of which 36A is located between the first and second immersion heaters 30, 32 and the second of which 36B is located above the second heater 32 so that even if the first heater 30 is inoperative the second heater 32 can heat the water in the thermal store which is above the second heater and hot water can still be drawn off from the heat exchanger. <IMAGE>

Description

Improvements Relating to Electric Water Heating Apparatus Apparatus This invention relates to electric water heating apparatus, being apparatus including a tank for containing a body of water to be heated, and electric heating element means in the tank for the heating of the water.

The apparatus to which the invention relates is primarily, but not exclusively for use in connection with the heating of water for domestic purposes, and the tank may be of a size which is of the established volume to provide the hot water means of an average family, but it is to be appreciated that this is given only by way of example and is not intended to limit the invention. Typically, the tank may be of the order of 210 litres.

It is of course known to heat water in water tanks by means of an electric heating element means, which are usually referred to as electric immersion heaters as the elements are immersed in the water to be heated, but such immersion heaters have been used mainly in connection with the heating of water which is to be used domestically for consumption purposes. That is to say, water is drawn off the body of water as hot water is required for washing, bathing or showering.

There has however been little use of electric immersion heaters for the heating of water in a water tank, which water is to be used as. a thermal store. When water is used as a thermal store, it is heated by the electric immersion heaters, but is not consumed. Rather, the heat of the water in the store is transferred by heat exchange to secondary water which in turn is consumed. Recently, there has been considerable interest shown and considerable development has taken place in connection with the utilisation of thermal stores domestically, and the secondary water is supplied form the mains and passes through the heat exchange coil contained in the body of water forming the thermal store.Water from the mains therefore passes directly through the heat exchange coil in the thermal store, receives heat in the body of water, and emerges, heated, for consumption at taps, washing machines, shower roses and the like. This method of heating water for domestic consumption has a number of advantages, including that the heated water for consumption is mains pressure and therefore can be delivered readily to any location in the house.

The present invention is concerned with electric water heating apparatus which operates on the thermal store principle, and is constructed so as to provide for an economical use of the electricity which is utilised for the heating of the water constituting the thermal store.

When a body of water is heated to form a thermal store, it will be necessary that the heat exchanger for the secondary water will require to be of a certain length as related to the volume of the body of water forming a thermal store, as related tithe temperature to which the body of water has to be heated to enable normal demands of a domestic household to be satisfied, and so any particular system would be designed on this basis.

With these design considerations in mind, each system would require an optimal length of tubing for the heat exchange coil to achieve the desired result.

Additionally, it is also useful to provide the facility of heating water by means of off-peak electricity, as the cost of such electricity is much less expensive than the cost of the regular supply. The present invention takes these factors into account and provides in a general aspect that water heating apparatus comprises a tank for containing a body of water, a first electric immersion heater means towards the bottom end of the tank for heating the body of water using off-peak electricity, a second immersion heating means spaced above the off-peak heating means for heating the water above the second immersion heater means using regular electricity, and a heat exchange coil means having a first portion lying between the lower and upper immersion heating means, and a second portion lying above the second immersion heating means, said second portion suitably being of an optimum length for effective heat exchange.

By the arrangement described above, the off-peak hea-ting means can be used for beating the body of water during off-peak periods, whilst the second heating means can be used for heating the body of water above said second heating means on an as-required basis. By providing that the second portion of the heat exchange coil is of the optimum length, anciliary apparatus can be used to provide the normal requirements even when the off-peak heating means is switched off, and the portion of the body of water between the lower and upper heating means is relatively cool. On the other hand, when the body of water has been heated by the off-peak heating means, it will form a thermal store providing good heat output for the consumed water, which may supply the output requirements without the second heating means having to be switched on to any particular day.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawing of which the single figure shows in sectional elevation material part of an apparatus according to the present invention.

Referring to the drawing, a domestic water storage tank is indicated by reference numeral 10, and it will be seen to be surrounded by heat insulating material 12.

On top of the storage tank is mounted a primary cold water feed tank 14 which receives a supply of cold water from a mains pipe 16 and through a float controlled valve 18 controlled by a float 20 in conventional manner.

The tanks 10 and 14 may be constructed of any suitable material, but typically tank 10 will be of copper whilst tank 14 may suitably be of galvanised steel or the like.

Water from the tank iLl flows into the tank 10 through a feed pipe 22 which for the majority of its length is embedded in the insulation material 12 as shown and the pipe 22 enters the tank 10 through an outlet 24 at the base of tank 10.

There is an overflow pipe 26 leading from the top of tank 10 back into the tank 14. Both tanks 14 and 10 are open to atmospheric pressure.

In use, the tank 10 will be filled with water, for example to a level indicated by reference 28 and there may be appriopriate level controls and temperature controls in order to control the level and temperature of the body of water in the tank 10. For domestic uses, the tank 10 may have a capacity of the order of 210 litres, and the temperature of the water therein may be controlled so as to be of the order of 70-800C.

The water in the tank 10 is heated by means of two electric immersion heaters 30 and 32, the heater 30 being located inside the tank 10 at a position towards the base 34 thereof, and the heater 30 being connected to an off-peak electricity supply (now known in the United Kingdom as Economy 7) so as to receive cheap electricity for the heating of the water in the tank 10 during off-peak periods.

The immersion heating element 32 is located above the element 30 and is located approximately at mid height of the tank 10. This immersion heater is connected to the regular electricity s-upply. The rating of the two heaters may be the same or different as required and each may be coupled to an appropriate electrostatic control means for controlling the temperature to which the water is heated by the heating elements 30 and 32.

Contained within the tank 10 is a heat exchange coil means indicated generally by reference 36. Cold water is supplied to an inlet of the heat exchange coil means 36 from the mains through an inlet pipe 38 so that as the water passes through the coil means 36 it is heated and emerges as hot water through outlet pipe 40, and the water emerging from the heat exchange means 36 can be as hot as the temperature of the body of water in the tank 10 by virtue of the heat exchange, depending upon the mains pressure, the length and diameter of the heat exchange means 36 giving rise to a particular flow rate.

There is a branch pipe 42 coupling pipe 38 and 40, and pipe 40 has a mixing valve 44 so that hot water emerging from the heat exchange means is mixed with cold water passing through the branch pipe 42 so that the temperature of the water which is finally discharged from pipe 40 to a consumption point such as a tap or shower rose can be controlled by the appropriate setting of the valve 44. Valve Liil may be controlled automatically by a remote temperature setting device if required or it may simply be adjusted manually to give a required hot water output, The present invention concerns the arrangement of the heat exchange coil means 36, and it will be noticed that this coil means is in two sections, namely a first section 36A in the form of a single coil, and a second section 36B in the form of two series connected coils.

There is an expansion chamber break of the nature and for the purposes set forth in our co-pending patent Application No. 2153504, but the cold water still flows continuously through the two coil sections and the break 46 as though the assembly were a continuous pipe.

The length of the section 36 is chosen to provide sufficient hot water output when only the immersion heater 32 is in use, and therefore the apparatus will still be effective regardless of whether or not the immersion heater 30 has been operated.

Appropriate controls are provided for the monitoring and switching of the immersion heater units 30 and 32.

It is believed that operation of the apparatus will be understood from the foregoing, but by way of explanation, in the normal operation the immersion heater 30 will be operated during the off-peak period in order to heat the body of water to a thermostatically controlled temperature. Depending upon the initial temperature of the water, it may be unnecessary to have the immersion heater 30 switched on for the full period when off-peak electricity is available in that as soon as the body of water reaches the required temperature the immersion heater will switch off and will switch on again if necessary during the off-peak period.

As hot water is required, so it is drawn off from the pipe 40, this hot water being blended with cold from the branch pipe 42 so that it will be at a comfortable temperature. As the cold water flows through the heat exchange coil sections 36A and 36B it is heated by heat transfer and so extracts heat from the body of water in the tank 10. If at any time when hot water is required, the temperature of the thermal store is not sufficiently high, then the immersion heater 36A can be swit-ched on. This can be done automatically by thermostatic control, but in the embodiment which is envisaged, the switching on of the immersion heater 32 will be by manual operation or actuation of a time switch so that the heater 32 will run only for a maximum period of say one hour so that there will not be excessive use of more expensive electricity.The maximum period is set so as to heat that portion of the body of water in the tank 10 above the immersion heater 32 to a particular temperature whereby even if the lower portion if the water is cold, there will still be a full rated output from the apparatus. It can be seen therefore that the length of the heat exchange coil section 36B should be such as to give full output when only the upper portion of the water in the tank 10 has been heated by the immersion heater 32.

In a typical arrangement, where the tank is adapted to hold 210 litres of water, the length of section 36A may be 6 metres whilst section 36B may be 12 metres in length, the pipe used for the heat exchange coil section being finned copper tubing: Of the following specification Bore : 10.9 mm Wall thickness : 0.7 mm Fin height : 3 mm Fins/25 mm length : 11 The invention provides a novel and useful form of heating apparatus comprising the provision of a thermal store by which hot water for general consumption is heated. An advantage of this arrangement is that the body of water in the tank 10 is relatively constant, requiring only some make-up water from the primary tank 14, and therefore the amount of hard water scale deposit which can deposit on the immersion heating elements is limited to the total impurity in the body of water in the tank 10.This distinguishes the arrangement from known arrangements wherein the water in the tank 10 is drawn off for consumption purposes, because replacement of the water in the tank 10 means replacement of the hard water impurities which can deposit on the electrical heating elements.

In addition to being simply a thermal storage tank as illustrated in the drawing, the tank 10 may be connected to a closed heating circuit such a circuit comprising small bore piping and central heating radiators illustrated for example in dotted lines and by the reference numeral 48 in the figure. The hot water is in such case circulated from the interior of the tank through the small bore piping in the radiators and back to the tank. If the apparatus is to provide this space heating arrangement, it may be necessary to provide heaters 30 and 32 of a greater rating.

Claims (10)

1. Water heating apparatus comprising a tank for containing a body of water, a first electric immersion heater means towards the bottom end of the tank for heating the body of water using off-peak electricity, a second immersion heating means spaced above the off-peak heating means for heating the water above the second immersion heater means using regular electricity, and a heat exchange coil means having a first portion lying between the lower and upper immersion heating means, and a second portion lying above the second immersion heating means, said second portion suitably being of an optimum length for effective heat exchange.

2. Water heating apparatus according to Claim 1, including a -primary cold water feed tank connected to supply cold water to said tank for containing said body of water.

3. Water heating apparatus according to Claim 1 or 2, wherein said tank containing said body of water has a capacity in the order of 210 litres and temperature control means controlling the temperature of the water therein to the order of 70-800C.

4. Water heating apparatus according to any preceding claim wherein said second immersion heating means is located approximately at mid height of said tank.

5. Water heating apparatus according to any preceding claim, wherein said heat exchange coil is connected so as to have cold mains water supplied thereto, for heating therein and for delivery to domestic consumption points.

6. Water heating apparatus according to any preceding claim wherein said second portion of the heat exchange coil is in two series connected sections, of a total length sufficient to provide domestic hot water when only the second immersion heater is in use.

7. Water heating apparatus according to any preceding claim including controls controlling the apparatus so that the first immersion heater will be operative during off-peak periods, and the second immersion heater either switches on automatically during peak period due to thermostatic demand or by means of a timer.

8. Water heating apparatus according to any preceding claim, wherein the length of the first portion of the heat exchange coil is 6 metres and the length of the second portion is 12 metres.

9. Water heating apparatus according to any preceding claim, wherein the heat exchange coil is of finned tubing of the following specification: Bore :

10.9 mm Wall thickness : 0.7 mm Fin height : 3.0 mm Fins/per 11 mm length : 11 10. Water heating apparatus substantially as hereinbe fore described with reference to the accompanying drawings.