WO2004044499A1

WO2004044499A1 - Water heater with an external electric winding

Info

Publication number: WO2004044499A1
Application number: PCT/IT2002/000769
Authority: WO
Inventors: Aldo Stabile
Original assignee: Cadif Srl
Priority date: 2002-11-13
Filing date: 2002-12-09
Publication date: 2004-05-27
Also published as: AU2002368356A1; TWI235226B; TW200407522A; ITMI20022396A1; EP1563230A1

Abstract

Electric storage water heater wherein heat is generated by transformation of electric energy supplied to a helical electric winding (25) of a high conductivity electric conductor (26) substantially extending over the entire external surface of the tank (11).

Description

WATER HEATER WITH AN EXTERNAL ELECTRIC WINDING

Water heater, with generation of heat by an external high- conductivity electric winding, and the process for producing it

The invention concerns electric water heaters, especially those for bathrooms.

In electric water heaters, so widely used, especially in those for bathrooms that store hot water, the cold water is fed into a metal tank fitted with armoured electric heating elements which, by the

Joule effect, generate concentrated heat at a high temperature that spreads upwards from the heating elements to the top of the tank,

A thermostat turns off the heating elements when the desired temperature has been reached, automatically turning them on again when hot water is drawn off and replaced by cold water.

The space between the tank and its outer casing, also metal, is filled with insulating material, such as fiberglass, to prevent heat dispersal.

Tank capacity generally varies between 15 and 200 litres but to fill a bath the bigger size must be used, though this is obviously too large when only a small quantity, such as for shaving, is needed.

These water heaters therefore present considerable drawbacks.

A short life, both for the metal structure on account of stray current created between it and the armoured electric elements situated centrally and low down in the tank, making holes and cracks, and for the heating elements themselves due to the very high temperatures produced. Great loss of heat occurs in transferring it from the elements to the water due to the enormous thermal delta (300°C÷5000°C in the elements to tens of degrees in the water).

Very high thermal inertia because of the difficulty of transferring heat to the whole volume of water.

High manufacturing and running costs due to the need for insulation able to withstand the very high temperatures in the heating elements.

These disadvantages are aggravated by the fact of having to keep the water hot all the time, even when it is not needed. The present invention not only drastically lessens the above drawbacks, but also adds considerable advantages as will now be explained.

Subject of the invention is an electric storage water heater having a tank in which heat is generated by transformation of the electric energy supplied to the helical electric winding of a conductor of high electrical conductivity extended substantially over the entire outer surface of the tank.

The cross section of the conductor is the minimum compatible with mechanical strength for determing maximum diffusion of heat, at substantially the same moment as that in which it is generated, to the volumes of water at various levels.

In one execution the electric conductor is made of copper.

In one execution the tank is made from a die-cast aluminium tube.

In another execution the tank is made of plastic material, shaped like an overturned bottle with a rounded top and truncated cone-shaped bottom with helical grooving round the outer cylindrical wall.

The electric winding is laid inside this helical grooving.

The tank is lodged in a casing the internal dimensions of which are greater than the external dimensions of the tank thus creating a cavity into which a mass of heat insulating material is inserted.

The heat-insulating material is preferably foam polyurethane. In one type of execution the helical electric winding of the conductor presents electrical connections to an electronic regulation circuit.

Said electrical connections, placed at the ends of the winding and at intermediate points, separate the winding into a number of sections A, B, C, at successive levels one below another starting from the top.

When heating is begun the regulating circuit transfers the entire electric power available to the first section A of the winding starting, as stated, from the top one.

When the volume of water present in said first section A has been heated to the set temperature, this circuit transfers the available electric power to the water in the second section B, and so on to the volumes of water in the sections of winding below, once the previous section has been heated.

The water contained in the first section A of the winding, starting from the top, can be drawn off through a tube provided for the purpose.

The invention offers evident advantages.

Practically unlimited life both for the structure, freed from the destructive ef ects of stray current, and for the means that transform electric energy into heat. Since the heat when generated is already diffused, maximum temperature levels in the heating elements are in fact very much lower than in the means at present used so avoiding the very high stresses associated thereto.

The normally required heat-resisting insulation for the heating elements, not only costly but also^' shortlived, is no longer needed.

Running costs are greatly reduced because of lower thermal inertia since the heat-generating means substantially extend all the way up the tank.

Transfer of heat from heat generator to water is facilitated by conduction between the large matching surfaces of the generator and the thin wall of the tank. The possibility of concentrating both generation of heat as well as transferring it the water, automatically, volume by volume, from the uppermost section to the lowest, not only speeds up heating but also makes immediately available for use the volume of water that is ready first.

Reduced manufacturing costs, especially of the tank, made by blow- extrusion, due to the constructional simplicity of the heat generator require no special, and very costly, means of insulation, since temperatures are kept low. Characteristics and purposes of the disclosure will be made still clearer by the following examples of its execution illustrated by diagramatically drawn figures.

Fig. 1 Water heater with tank made from an extruded aluminium tube, a longitudinal section and detail of the wall. Fig. 2 Alternative version of the tank made of plastic material with a helical groove on the outside of the cylindrical wall, longitudinal section and detail of the wall. Fig, 3 Alternative version of electrical eonneetions. The installed water heater 10, is formed of an extruded alumiuinm tank 11 , with cylindrical wall 12, top 13 and bottom 14.

Cold water flows from the tube 17 connected to the duct 20, with fawcet 18 and safety valve 19, while hot water is carried to the takeoff point 23 through a fawcet 22 and inner tube 21 that extends to the top of the tank. A helical winding 25, of copper wire 26 with cladding 27 of insulating material, passes round the cylindrical wall 12. A casing 30 is disposed round the tank 11 , said casing having in it an aperture 31 at the bottom, internal dimensions of the casing being greater than the external dimensions of the tank 11 , so forming a cavity between casing and tank to be filled with heat-insulating foam material 35. Electrodes 40, 41 at the ends of the winding 25 can be seen inside said foam material, said electrodes coming from the connector block 45 for connection to the electricity mains by wire 46 and plug 47. Figure 2 shows an alternative execution in which the tank 50 is of plastic material shaped like an overturned bottle with tubular extensions 53, 54 through the truncated-hole shaped aperture 52 to receive the incoming cold water pipe and the outgoing hot water pipe respectively. The cylindrical wall 51 presents helical grooving 55 inserted into which is the unclad electric wire 57 of the winding 56 to be joined to the connector box by terminal electrodes 58, 59. Figure 3 shows a further alternative execution 60 of the water heater in Figure 1 , in which the helical winding 25 presents connections both for the terminal electrodes 61 , 64 and for two more intermediate electrodes 62, 63, thus separating the winding into successive sections A, B, C, starting from the top.

These electrodes .61-64 connect up with the regulating device 70 containing an electric circuit, not- shown for- simplicity, whieh circuit, when heating is started, automatically transfers all available electric power to the first section A of the winding comprised between the connections to electrodes 61 and 62.

As soon as temperature of the volume of water in said section A has reached the set level, available electric power is automatically switched to the next section B of the winding, and so on until all the volumes of water in successive sections of the winding, from the top downwards, have been heated.

Claims

1. Electric storage water heater (10), with tank (11 , 50), characterized by the generation of heat by transformation of electric energy supplied to a helical electric wiring (25, 26) of a conductor (26, 27) of high electric conductivity extended substantially over the whole external surface of the tank (11 , 50).

2. Water heater (10) as in claim 1 , characterized in that the electric conductor (26, 57) presents the minimum thickness compatible with mechanical strength and maximum width for determining maximum diffusion of heat, substantially at the moment of its generation, to the volumes of water at various levels.

3. Water heater (10) as in claim 1 , characterized in that the tank (11 ) is made from a die-cast aluminium tube.

4. Water heater (10) as in claim 1 , characterized in that the electric conductor (26, 57) is of copper.

5. Water heater (10.) as in claim 1 , characterized in that the electric conductor (26) is clad with insulating material (27).

6. Water heater (10) as in claim 1 , characterized in that the tank (50) is of plastic material.

7. Water heater (10) as in claim 6, characterized in that the shape of the tank (50) is substantially that of an overturned bottle with rounded top and truncated cone-shaped bottom (52).

8. Water heater (10) as in claim 6, characterized in that the winding (56) with electric conductor (57) is inserted into helical grooving (55) on the external wall of the tank (50).

9. Water heater (10) as in claims 1 to 8, characterized in that the tank (11 , 50) is disposed inside a casing (30) whose internal dimensions are greater than the external dimensions of the tank (11 , 50) so forming a cavity in which a mass (35) of heat-insulating material is inserted.

10. Water heater (10) as in claim 9, characterized in that the heat-insulating material (35) is polyurethane foam.

11. Water heater (10; 60) as in claim 1 , characterized in that the helical electric winding (25, 56) of the electric conductor (26, 57) presents electric connections to an electronic regulation circuit (70), said electric connections being disposed at the ends of said winding and at intermediate points, separating said winding into a number of sections A, B, C at successive levels starting from the top, said electronic regulating circuit (70) transferring, when heating is started, all available electric power to the first section A, of the winding then, when the volume of water present i said first section A has been heated to the set temperature, switching available electric power to the volume of wafer present in the next section B, and so on until all the volumes of water present in successive sections of the electric winding have been heated, from the top downwards.

12. Water heater (10, 60) as in claim 11 , characterized in that the volume of water corresponding to the first section A, starting from the top, of the electric winding (25, 56), can be drawn off through a pipe provided for the purpose.

13. Process for the production of a water heater as described in claims 1-12.