GB2177858A

GB2177858A - Control system for a domestic heating appliance

Info

Publication number: GB2177858A
Application number: GB08517471A
Authority: GB
Inventors: Kulwant Mandir
Original assignee: Valor Heating Ltd
Current assignee: Valor Heating Ltd
Priority date: 1985-07-10
Filing date: 1985-07-10
Publication date: 1987-01-28
Also published as: GB8517471D0

Abstract

A domestic heating appliance includes a load 14 and a triac 16 connected in series across a mains supply 12. The load 14 may be one or more electrical heating elements, flame effect lighting, a solenoid winding of a fuel valve, or a fan. The triac may be triggered by a phase control circuit including a manually adjustable resistor 19. A thermostat switch may be connected across capacitor, 20 or resistor 18 may be a thermistor. An alternative control circuit includes a zero voltage switch (31), (Figure 2), which increases the number of whole half-cycles for which triac 16 is fired in a given period with increase in level of a control signal. The appliance may be an electric convector or radiant heater, a gas fire, or a gas, liquid fuel or electrically- powered cooker. <IMAGE>

Description

SPECIFICATION Control system for a domestic heating appliance This invention relates to a control system for a domestic heating appliance.

In presently known domestic heating appliances which consume electrical energy, electrical heating elements are controlled by one or more mechanical switches. In presently known heating appliances which consume liquid or gaseous fuel, the flow of fuel is controlled either by a mechanically operated valve or by a solenoid operated valve, the winding of which is connected in series with a mechanical switch. These conventional methods of controlling domestic heating appliances suffer from the disadvantage that only limited control is possible.

It is an object of this invention to provide a new or improved control system for a domestic heating appliance in which the abovementioned disadvantage is overcome or reduced.

According to this invention there is provided a control system in a domestic heating appliance, said control system comprising switch means formed from at least one semi-conductor and arranged to control the consumption of fuel energy by the heating appliance, and a control circuit for said switch means.

The term "fuel energy" as used herein is intended to include within its meaning energy provided as liquid or gaseous chemical fuel and electrical energy.

Where the heating appliance consumes electrical energy, the switch means may be connected in series with a heating device comprising at least one electrical heating element.

Where the heating appliance consumes liquid or gaseous fuel, the switch means may be connected in series with a solenoid winding of a solenoid valve arranged to control the flow of liquid or gaseous fuel.

The system may be arranged to control flame effect lighting used in the heating appliance.

In the preferred embodiment, the switch means comprises a triac. The control circuit may include a manual setting device, said setting device being adjustable to a set of preset ievels or, alternatively, continuously adjustable. The control circuit may also include one or more sensors.

This invention will now be described in more detail, by way of example, with reference to the drawings in which: Fig. 1 is a circuit diagram of a control system embodying this invention; Fig. 2 is a circuit diagram of another control system embodying this invention.

Referring now to Fig. 1,the control system shown there has a pair of mains supply terminals 10 and 11 connected to a source 12 of mains electricity. The terminal 10 is connected through a rail 13, an electrical load 14, a rail 15, a switch means in the form of triac 16, and a rail 17 to terminal 1 liThe triac 16 is operated by a control circuit which includes a resistor 18, a variable resistor 19 and a capacitor 20 connected between rails 15 and 17. The junction of resistor 19 and capacitor 20 is connected through a resistor 21 and a capacitor 22 to rail 17 and the junction of resistor 21 and capacitor 22 is connected through a dial to the control terminal of triac 16.

For a reason which will be explained below, resistor18 is provided with a pair of terminals 23 and 24 and a terminal 25 is connected between resistor 19 and capacitor 20.

The variable resistor 19 may be operated by a manual control device which is either of the type which is adjustable to a number of preset positions or of the continuously variable type.

In operation, during each half cycle of the mains supply, capacitor 20 is charged through resistors 18 and 19 and consequently capacitor 22 is charged through resistor 21. When the voltage across capacitor 22 reaches the threshold voltage of diac 23, triac 16 is fired thereby energising the load 14 for the remainder of the half cycle. By adjusting variable resistor 19, the phase angle in each half cycle at which triac 16 is fired can be adjusted thereby adjusting the duty cycle of load 14.

The circuit shown in Fig. 1 may include one or more sensors which influence operation of the appliance. For example, the electrical switch of a thermostat may be connected between terminal 25 and rail 17. With such a thermostat, the load 14will be energised with the duty cycle set by variable resistor 19 but this will be overridden by the thermostat. As another possibility, the resistor 18 may be replaced by a thermistor connected between terminals 23 and 24.

Turning now to Fig. 2, this control system includes the mains supply terminal 10,11, mains supply 12, load 14, and triac 16 shown in Fig 1. However, in this circuit, the control circuit comprises a resistor 30 and an integrated circuit 31 connected between rails 13 and 17. The integrated circuit 31 comprises a Plessey type SL433A zero voltage switch and the output of this switch is connected through a rail 32 to the control terminal of triac 16. The zero voltage switch 31 has an input terminal 33.

In operation, the zero voltage switch 31 fires triac 16 at the beginning of selected half cycles of the mains supply in accordance with the voltage level at terminal 33. Thus, when the voltage at terminals 33 is at a minimum level, zero voltage switch 31 maintains triac 16 in a fully off condition. Then, as this voltage level is increased, zero voltage switch 31 increases the number of half cycles for which triac 16 is fired during a given time period. With the voltage at terminal 13 at a maximum level, triac 16 is fired for each half cycle.

The voltage at terminals 33 may be controlled simply by a manually operated potentiometer which can be set either to a number of discrete setting positions or which is continuously variable.

Alternatively, the voltage at terminals 33 may be controlled by a further circuit which in turn is responsive to various inputs which may include manual inputs and inputs provided by sensors as thermistors. These sensors may include attenuation or amplification circuits.

Where the source of heating energy is electrical energy, the load 14 shown in Figs. 1 and 2 may be one or more electrical heating elements. Where the source of heating energy is gaseous or liquid chemical fuel the load 14 may be the solenoid winding of a solenoid operated valve which controls the flow of such fuel. The load 14 may also be a fan forming part of a heating appliance.

The domestic heating appliance may be a space heater such as an electric convector heater, an electric radiant heater, or a gas fire or the domestic appliance may be a cookerfuelled by gas, liquid fuel, or electricity.

The present invention may be used also to control fuel effect lighting forming part of a domestic heating appliance. With such fuel effect lighting, the lighting mayform the load for 14 shown in Figs. 1 and 2. In the case of Fig. 2, there may be provided control circuitry which is arranged to cause the fuel effect lighting to flash or vary in brightness in a desired manner. The load 14 may also comprise fuel effect lighting connected in parallel with electric heating elements or a solenoid winding of a solenoid operating valve.

Aithough in both Figs. 1 and 2, the switch means takes the form of a triac it is within the scope of the present invention to use other semi-conductor devices. For example, a pair of silicon controlled rectifiers may be used in place of the triac.

Claims

1. A control system in a domestic heating appliance, said control system comprising switch means formed from at least one semi-conductor and arranged to control the consumption of fuel energy by the heating appliance, and a control circuit for said switch means.

2. A control system as claimed in claim 1 in which the heating appliance consumes electrical energy, and said switch means is connected in series with a heating device comprising at least one electrical heating element.

3. A control system as claimed in claim 1 in which the heating appliance consumes liquid or gaseous fuel, and said switch means is connected in series with a solenoid winding of a solenoid valve arranged to control the flow of liquid or gaseous fuel.

4. A system as claimed in claim 1 in which the heating appliance includes flame effect lighting, and the switch means is arranged to control the flame effect lighting.

5. A control system as claimed in any one of the preceding claims in which the switch means comprises a triac.

6. A control system as claimed in any one of the preceding claims in which the control circuit includes a manual setting device, said setting device being adjustable to a set of preset levels.

7. A control system as claimed in any one of claims 1 to 5 in which the control circuit includes a manual setting device, said setting device being continuously adjustable.

8. A control system as claimed in any one of the preceding claims in which the control circuit includes at least one sensor.

9. A control system in a domestic heating appliance substantially as hereinbefore described with reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.