GB2234059A - Solid fuel-effect electric fire - Google Patents

Abstract

An electric heater simulating the appearance of a solid fuel fire comprises a plurality of heating elements (R1 - R5) connected in parallel to an A.C. mains supply. In use, the elements would be located in a housing simulating a solid fuel fire and covered with a bank of artificial coals 30. Each element has a triac connected in series therewith, the triacs being controlled by a microprocessor, which thus controls the energy supplied to each of the elements. By controlling the energy supply, individual elements can be selectively driven beyond their rated capacity so as to produce a visible glow through the bank of coals, the supply to the elements being time-multiplexed between the elements in a pseudo-random manner such that individual elements are not run at high temperatures for excessive periods and such that a continuously varying glow is visible through the coals. The fire is also well suited to remote control by means of a hand-held unit. <IMAGE>

Description

"SOLID-FUEL-EFFECT ELECTRIC FIRE" The present invention relates to a domestic electric room heater, hereinafter referred to as an electric fire, adapted to simulate the visual appearance of an open, solid-fuel fire.

Numerous attempts have been made in the past to provide electric fires simulating solid-fuel fires, however these have generally been visually unrealistic. A more recent proposal involved the use of artificial coals, of the ceramic fibre type utilised in gas fires simulating solid-fuel fires, placed in contact with an open resistance-wire element which was driven at a very high temperature to create the effect of glowing coals. In this case, however, the life of the element was extremely short (approximately six weeks in normal use), and the glow effect was static.

It is an object of the present invention to provide a solid fuel effect electric fire which is visually more realistic, and obviates or mitigates the operating problems or limitations of existing fires.

Accordingly, the invention provides an electric fire comprising a plurality of heating elements arranged beneath a bank of artificial coals, the elements being electrically connected in parallel with one another for connection to an A.C. mains supply, means for varying the current supplied to each of the elements, and control means for controlling the operation of said current varying means, the arrangement being such that when the supply energy is not divided equally among all of the elements at least one of the elements heats up sufficiently to produce a visible glow, and the control means being adapted to continuously vary the supply of energy to each of the elements.

The control means preferably varies the supply of energy in a pseudo-random manner to simulate the visual effect of the glow from live coals. It is particularly preferred that the supply current is time-multiplexed between the various elements such that only one element is supplied with current at any one time.

Preferably also, the current varying means comprises a plurality of semiconductor switching devices, such as triacs, connected in series with the individual heating elements, and the control means comprises a microprocessor connected to said semiconductor switching means.

The elements are preferably mineral coated resistance elements, and the artificial coals are preferably formed from thermally insulating ceramic fibre material.

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 schematic circuit diagram of an electric fire embodying the invention; Figs. 2(a) and 2(b) are, respectively, schematic top and front views illustrating the arrangement of the heating elements in a first embodiment of the invention; and Fig. 3 is a schematic perspective view illustrating the arrangement of heating elements in a second embodiment of the invention.

Referring now to the drawings, an electric fire embodying the invention comprises a plurality of electric heating elements R1, R2 .... Rn, which in use are connected in parallel across the A.C. mains supply 10. Each branch of the circuit further includes a triac TR1, TR2 ... TRn, or other suitable switching or current control device, connected in series with the respective heating element R1, R2 ... Rn, and each triac TR1, TR2 ... TRn is in turn connected to a microprocessor 20 which controls their operation and hence the current flowing in each element R1, R2 ... Rn. The elements R1, R2 ... Rn are preferably of the mineral insulated resistance type.

Figs. 2(a) and 2(b) illustrate one possible physical arrangement of heating elements R1 to R5. In this embodiment the elements R1 to R5 are of an elongate generally planar shape, and are arranged horizontally in a spaced, parallel series across the width of the fire. A seen in Fig. 2(b), alternate elements R1 to R5 are preferably staggered vertically, and a bank of artificial, thermally insulating, ceramic fibre coals 30 is arranged on and around them.

Fig. 3 shows an alternative embodiment wherein the elements R1 to R5 are disposed on the horizontal and vertical faces of stepped support structure 40. A bank of artificial coals (not shown) would, again, be arranged on and around the elements R1 to R5.

In practice, the elements and coals would be located in a housing simulating the appearance of a solid-fuel fire.

In order to simulate the appearance of live, glowing coals, the heating elements are heated to a temperature where they glow relatively brightly, such that the glow is visible through the bank of artificial coals. In order to achieve the required visual effect, the elements must be driven beyond their rated power, which normally would considerably reduce their operating life. In order to avoid this, and at the same time to produce a more realistic visual effect, the microprocessor 20 controls the triacs TR1, TR2 ... TRn such that the application of current to the elements R1, R2 ... Rn is time multiplexed.The multiplexing is performed between the various elements R1, R2 ... Rn in a pseudo-random manner, and the programming of the microprocessor 20 ensures that the individual elements are not run at high temperatures for excessive periods of time, either continuously or in aggregate. In this way the required glow is obtained without compromising the operational life of the elements, and the glow varies continuously in an apparently random manner, thus giving the impression of live, glowing coals.

In the case of an A.C. mains supply of 240 volts and 13 amps, eight heating elements each having a continuous power rating of 390 Watts and a resistance of 18.5 ohms might be utilised. Thus, if all but one of the elements are switched out of the circuit, the remaining element draws 13 amps from the mains supply and is required to dissipate 3120 Watts of power. The element rapidly heats up to a high temperature (approximately 8500C) giving the required glow, whereafter it is switched out of the circuit and another element is switched in.

The elements are switched in and out of the circuit in a pseudo-random manner, but the switching pattern is controlled such that each element is run at full power for one eighth of the total time. It is preferred that the switching takes place at the zero-crossover of the A.C. supply, so that with a 50Hz supply the timing of the switching pattern is in 20 millisecond increments.

Depending upon the design of the fire (ie the numbers and parameters of the elements) and the effect required, the programming might be such that only one element is switched "on" at any one time, or else they might be switched in pseudo-random numbers and combinations. A manual control (not shown) might also be provided for selecting different microprocessor programs which allow the total output of heat and the visual effect from the fire to be varied.

The manner in which the elements are switched in and out of the circuit will depend upon a number of factors, including the desired visual effect. The periods for which individual elements are switched on, in particular, is at least partly dependent upon their thermal inertia, which affects the rate at which they heat up and cool down (and hence the rate at which the glow appears and fades), and the programming of the switching pattern might provide for longer periods of connection while the elements are heating up from "cold", and shorter periods once the fire has been operating for a certain time. It will be appreciated that programming means other than a microprocessor might be used, such as logic suquencers etc.

It should be noted that in the present example, using ceramic fibre coals, the perceived glow comes from the hot elements, and not as a result of the coals being heated to the point where they themselves glow.

A further advantage of the fire is that the use of solid state components for controlling the energy supplied to the heating elements makes it ideally suited to remote control from a hand-held unit of the type commonly used with television sets, video tape recorders etc. The remote unit could be used to switch the fire on and off and to control the overall heat output by varying the energy supplied to the elements, and possibly also to control the visual effect produced by the fire as previously discussed. The details of the design and programming of such remote control units are well understood and will be readily apparent to those skilled in the art. It will be appreciated that the numbers and programming, and physical configuration of the elements may be varied widely, as may the cosmetic design of the complete fire. Heating elements of types other than mineral-insulated resistance elements might also be used, possibly including induction-heating arrangements.

Claims (14)

1. An electric fire comprising a plurality of heating elements arranged beneath a bank of artificial coals, the elements being electrically connected in parallel with one another for connection to an A.C. mains supply, means for varying the current supplied to each of the elements, and control means for controlling the operation of said current varying means, the arrangement being such that when the supply energy is not divided equally among all of the.elements at least one of the elements heats up sufficiently to produce a visible glow, and the control means being adapted to continuously vary the supply of energy to each of the elements.

2. The fire of claim 1, wherein the control means varies the supply of energy in a pseudo-random manner to simulate the visual effect of the glow from live coals.

3. The fire of claim 2, wherein the supply current is timemultiplexed between the various elements such that only one element is supplied with current at any one time.

4. The fire of claim 1, claim 2, or claim 3, wherein the current varying means comprises a plurality of semiconductor switching devices, connected in series with the individual heating elements.

5. The fire of claim 4, wherein the control means comprises a microprocessor connected to said semiconductor switching means.

6. The fire of any preceding claim, wherein the elements are of the mineral coated resistance type.

7. The fire of any preceding claim wherein the artificial coals are formed from thermally insulating ceramic fibre material.

8. The fire of any preceding claim, wherein the elements are generally elongate and are arranged horizontally in a spaced parallel series across the width of the fire.

9. The fire of claim 9, wherein alternate elements are staggered vertically.

10. The fire of any of claims 1 to 7, wherein the elements are disposed on horizontal and vertical faces of a stepped supporting structure.

11. The fire of any preceding claim, wherein there are n elements and the energy supplied to the elements is controlled such that each element is run at full power for an aggregate period of 1/n of the total running time of the fire.

12. The fire of any preceding claim, wherein the switching of elements in and out of the circuit is performed at the zerocrossover of the A.C. supply.

13. The fire of any preceding claim, wherein the periods during which individual elements are run continuously are relatively longer when the fire is first switched on and relatively shorter once it has been operating for a predetermined time.

14. The fire of any preceding claim, including semiconductor switching devices and microprocessor means for controllably varying the energy supplied to the elements, and further including a programmed remote control unit and means responsive to signals received from said remote control unit for remotely controlling the operation of the fire.