GB2151815A - An electronic switching device fitted to boilers to save fuel - Google Patents

Abstract

When a boiler is cycling between the thermostat on/off temperatures a high proportion of the energy is wasted. The device provides a longer OFF period without a deterioration in space temperature. This results in a saving of fuel. When the thermostat calls for heat, capacitor C2 begins to charge and at a certain level of charge causes operation of relay RL1 to operate the heating device. The delay can be adjusted by means of VR1. <IMAGE>

Description

SPECIFICATION Electronic switching device for boilers This invention relates to an electronic switching device to be fitted to gas fired and oil fired boilers to increase thermal efficiency of boilers and save fuel.

The water temperature in a boiler is controlled by a thermostat to switch the burner on when the water temperature drops below the selcted set point. It will switch the burner off when the temperature reaches the set point. On light and moderate loads this results in frequent cycling of the burner resulting in a waste of energy and fuel.

The present invention consists of an electronic circuit incorporating a variable time delay, all fitted in a heat resisting box with two sets of connecting leads external to the box.

The device is electrically connected between the boiler thermostat and burner control valve. The boiler firing is delayed by the amount of time selected by the variable timing knob.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying circuit drawings.

While the boiler thermostat is open, no input is provided so that the solenoid cannot operate, there is no supply to 02 and C2 is discharged. When the boiler thermostat closes, a supply of 17.5 V to Q2 is established. Resistors R2 and R3 divide this voltage so that 15V is provided to pin 3 of Q2. This is 86% of 17.5 V and equal to the voltage across C2 charged through VR11R4 after two time constants.

Initially, the voltage at pin 2 of 02 is less than that at pin 3 and the output (pin 7) is 17.5 V and RL1 cannot operate. The solenoid is therefor held closed. After a time, t, the voltage at pin 2 has risen to a value just greater than 15V (pin 3) and the comparator switches with pin 7 going to OV.

RL1 is activated and the solenoid valve opens. During the time, td, pin 7 is at 17.5 V and D4 and D5 are reversed biassed. When pin 7 goes to O V, D4 and D5 conduct through R2/VR1/R4. Thus pin 3 is dropped to 0.6 V and pin 2 to 1.2 V. This has two effects. (a) The voltage at pin 2 is now always greater than at pin 3 and the relay is held in as long as the supply is present and (b) the voltage across C2 is reduced to < 7 1V maintaining timing integrity if the supply is removed and re-established within seconds. R4 is incuded to limit the current through D4 and D5 when VR1 is minimum (O V). Its value is a compromise between current limitation and the inherent time delay it introduces when VR1 is minimum.

1. An electronic switching device comprising of a printed circuit, variable timing delay and other electronic componants fitted in a heat resisting case. This is then electrically connected between the boiler thermostat and burner solenoid valve.

2. An electronic switching device as claimed in Claim 1 wherein a digital read out of hours and minutes run is incorporated.

3. An electronic switching device as claimed in Claim 1 wherein a probe is connected to the boiler or flow pipe adjacent to the boiler. This would provide an electronic signal to bypass the timed outlet if the water temperature is below a selected set point.

4. An electronic switching device as in Claim 3 wherein an additional probe is connected to the return pipe. A mean temperature of flow and return provides a signal to bypass the timed outlet if that temperature is below a selected set point.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Electronic switching device for boilers This invention relates to an electronic switching device to be fitted to gas fired and oil fired boilers to increase thermal efficiency of boilers and save fuel. The water temperature in a boiler is controlled by a thermostat to switch the burner on when the water temperature drops below the selcted set point. It will switch the burner off when the temperature reaches the set point. On light and moderate loads this results in frequent cycling of the burner resulting in a waste of energy and fuel. The present invention consists of an electronic circuit incorporating a variable time delay, all fitted in a heat resisting box with two sets of connecting leads external to the box. The device is electrically connected between the boiler thermostat and burner control valve. The boiler firing is delayed by the amount of time selected by the variable timing knob. A specific embodiment of the invention will now be described by way of example with reference to the accompanying circuit drawings. While the boiler thermostat is open, no input is provided so that the solenoid cannot operate, there is no supply to 02 and C2 is discharged. When the boiler thermostat closes, a supply of 17.5 V to Q2 is established. Resistors R2 and R3 divide this voltage so that 15V is provided to pin 3 of Q2. This is 86% of 17.5 V and equal to the voltage across C2 charged through VR11R4 after two time constants. Initially, the voltage at pin 2 of 02 is less than that at pin 3 and the output (pin 7) is 17.5 V and RL1 cannot operate. The solenoid is therefor held closed. After a time, t, the voltage at pin 2 has risen to a value just greater than 15V (pin 3) and the comparator switches with pin 7 going to OV. RL1 is activated and the solenoid valve opens. During the time, td, pin 7 is at 17.5 V and D4 and D5 are reversed biassed. When pin 7 goes to O V, D4 and D5 conduct through R2/VR1/R4. Thus pin 3 is dropped to 0.6 V and pin 2 to 1.2 V. This has two effects. (a) The voltage at pin 2 is now always greater than at pin 3 and the relay is held in as long as the supply is present and (b) the voltage across C2 is reduced to < 7 1V maintaining timing integrity if the supply is removed and re-established within seconds. R4 is incuded to limit the current through D4 and D5 when VR1 is minimum (O V). Its value is a compromise between current limitation and the inherent time delay it introduces when VR1 is minimum. CLAIMS

1. An electronic switching device comprising of a printed circuit, variable timing delay and other electronic componants fitted in a heat resisting case. This is then electrically connected between the boiler thermostat and burner solenoid valve.

2. An electronic switching device as claimed in Claim 1 wherein a digital read out of hours and minutes run is incorporated.

3. An electronic switching device as claimed in Claim 1 wherein a probe is connected to the boiler or flow pipe adjacent to the boiler. This would provide an electronic signal to bypass the timed outlet if the water temperature is below a selected set point.

4. An electronic switching device as in Claim 3 wherein an additional probe is connected to the return pipe. A mean temperature of flow and return provides a signal to bypass the timed outlet if that temperature is below a selected set point.