GB2061566A - Control apparatus - Google Patents

Abstract

A control system for a boiler (1) in a domestic hot water and/or central heating system and having a thermostat and an electrically operable valve (both not shown) controlling fuel supply to the boiler comprises a parallel connection of a switch (40c or 50c) and a high impedance (31) provided in the valve supply circuit so that when the switch is open, the valve will not operate even if the boiler thermostat closes to turn the boiler on. Thus unnecessary cycling of the boiler is eliminated and the boiler can be made to fire only in dependence on a thermostat in the water tank and/or a room thermostat. The switch (50c) is operated by a relay (50) controlled by a room thermostat (10), while the switch (40c) is similarly controlled by one of two water tank thermostats (8, 9) at different heights in the tank. The high impedance (31) is a lamp which, when lit, indicates that the boiler would be ON if it were not for the present system. <IMAGE>

Description

SPECIFICATION Control apparatus The present invention relates to apparatus for and a method of controlling a central heating system.

Conventional central heating systems generally comprise a boiler supplying heat to a heat transfer medium which is then circulated by a pump to a number of radiators suitably positioned throughout the building to be heated and a control system to control the action of the boiler and pump. The boiler is usually gas, oil or solid fuel fired, the heat transfer medium water, possibly with an anti-corrosive additive, and the pump electrically driven. A hot water storage tank is also provided heated by a heater located in the tank through which the heat transfer medium is circulated. This circulation may either be forced, that is provided by the pump, or simply the result of convection. The control system is fairly simple.

In the vast majority of installations, the system comprises a thermostat to regulate boiler temperature and a room thermostat to control the central heating pump (which circulates hot water around the radiators). Once the room temperature is at the desired level the pump is automatically switched off and water circulation ceases until the house begins to cool. However, during those periods when hot water is not actually required by the system, the -boiler continues to go through its firing cycle whenever the boiler temperature drops fractionaily below its pre-set maximum. When energy was cheap such a simple control was adequate, but with the ever mounting cost of energy a more economic system is desirable.

According to one aspect of the present invention, there is provided control apparatus for controlling the operation of a boiler having a thermostat controlling an electrically energisable valve controlling supply of fuel to the boiler comprising a parallel connection of a high impedance and a switch in the electrical supply to the boiler valve whereby, when the switch is closed, the impedance is shorted out and when the switch is open should the thermostat contacts close the valve will not be energised because of the limiting effect of the high impedance.

By the invention, therefore, unnecessary firing of the boiler is reduced or even eliminated and considerable economies effected. It is possibie to make the control apparatus of the invention itself dependent on a temperature dependent control located in a water tank and/or in a room.

In one embodiment of the invention the control apparatus is itself controlled by one of at least two temperature dependent controls located at different heights in a water tank, means being provided for selecting the temperature dependent control that is to govern the control apparatus.

The control apparatus of the invention may include a timing means which incorporates a switch means constituting a further control of boiler firing.

The invention also comprises a central heating system having a control or control apparatus as defined above.

In order that the invention may be more clearly understood, one emboidment thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a simplified diagram of a central heating system, Figure 2 shows a circuit diagram of one form of domestic central heating control system for the central heating system of Figure 1, Figure 3 shows the front panel of a box housing part of the control system of Figure 2, Figure 4 is a circuit diagram of a modified domestic central heating control system for the system of Figure 1, Figure 5 is a circuit diagram of a further embodiment of a domestic central heating control system, and Figure 6 shows the front panel of a box housing part of the control system of Figure 5.

In the drawings, like parts of the different embodiments have been given the same reference numerals.

Referring to Figure 1, a boiler 1 heats a heat transfer medium which is circulated by means of a pump 2 round a plurality of radiators 3 to 5. The medium is also circulated through a heater 6 disposed in a hot water storage tank 7 by means of convection (this is commonly referred to as gravity circulation).

Two thermostats 8 and 9 are clamped to the outer surface of the tank 7. Thermostat 8, known as the normal thermostat, is clamped to the tank about one third the height of the tank from the top of the tank and thermostat 9, known as the bath thermostat is clamped to the tank about one third the height of the tank from the bottom of the tank.

A room thermostat 10 is provided, for example, located in the living room where, for example, radiator 3 is located. This thermostat controls the operation of the heating pump 2 so that when the room temperature falls below a preset minimum the thermostat contacts close to supply the pump which then pumps more medium round the circuit and therefore to the radiators.

The boiler 1 has its own internal thermostat so that when the temperature of the boiler falls below a preset minimum the boiler fires to raise the temperature of the heat exchange medium in the boiler again. The boiler temperature will of course fall when the pump 2 is operating as heat is effectively being extracted from the medium by the radiators 3 to 5, but it will also fall due to heat loss from the boiler 1 itself irrespective of whether the pump is operating. Hot water removed from the hot water tank will also depress the boiler temperature since this lowers the temperature of the medium circulated from the boiler 1 to the heater 6.

The control system comprises three neon indicator lamps for each of the three thermostats and for the boiler. Lamps 20 to 22 are provided for thermostat 8, lamps 23 to 25 for thermostat 9, lamps 26 to 28 for thermostat 10 and lamps 29 to 31 for the boiler 1. Lamps 20, 23, 26, 29 and 31 are green and the remainder are red. Two relays, the water relay and heating relay are provided. The coils 40 of the water relay may be connected in parallel with either the lamp-22 of the lamp 25 by a two pole two position changeover switch 41.

The live terminal 42 of this switch 41 is connected to the live terminal of the conventional central heating control. This water relay controls three sets of contacts 40A, 40B, 40C which are in turn associated with the lamps 29 to 31 respectively. If desired a water pump 43 to pump water to the heater 6 may be provided connected across the terminal of the relay coil so that when the relay is energised so also is the pump.

The heating relay has a coil 50 connected in parallel with the lamp 28 and across the terminals of the pump 2. This relay coil controls the operation of three sets of contacts 50A, 50B and 50C respectively associated with the contacts 40A,40B and 40C. The live terminal 51 of the heating selector is connected to the live terminal 51 of the heating part of the circuit. For convenience the hot water, space heating and boiler control parts of the overall control circuit have been respectively referenced 1 5, 1 6 and 1 7.

The operation of the circuit is as follows. All relay contacts are shown in the de-energised state. As with a conventional system, the householder can select hot water only or hot water and space heating together. In the former case only parts 1 5 and 17 of the circuit are active and in the latter case all of the circuit is active. In the latter case if terminal 51 is live lamp 27 is on showing that heating has been selected. The pump 2 is energised (assuming the room is not up to temperature and) as the thermostat contacts will be closed. The lamp 26 is shorted out and therefor off, the lamp 28 is on and the coil relay 50 is energised moving contacts 50A, B and C to their energised positions.The boiler is therefore energised through contact 50C the lamp 31 is shorted out and off, the lamp 30 supplied from the permanently live terminal 52 through contact 50B and therefore on showing the boiler has been selected on the lamp 29 is off, its supply being broken by contact 50A.

When the room gets up to temperature, the thermostat 10 contacts open, the pump is switched off, the lamp 26 is turned on as it is no longer shorted by the thermostat and the lamp 28 turns off. The contacts 50A to C return to their deenergised condition. Should the boiler temperature fall its own thermostat contacts will close and the boiler would under normal circumstances fire even though there is no heat required of it. This firing is prevented because the valve controlling fuel supply can only now be energised through lamp 31 (50C is open) and the impedance is too high to allow sufficient current to pass. The lamp 31 therefor lights showing that an economy is being made, but the boiler does not fire. However, the boiler might still be energised through the hot water part 1 5 of the circuit.

The design of the hot water part of the circuit is based upon the fact that there are two general but distinct hot water requirements in a normal domestic household. They are a relatively low hot water requirement which might exist for a large part of the day and a relatively high bath requirement which only exists perhaps once or twice a day. The former requirement is satisfied if the hot water tank is only one third full of hot water and the latter when the hot water tank is more than two thirds full of hot water.

To select the first, normal, requirement the switch 41 is switched to the position shown.

Lamp 21 lights showing normal hot water has been selected. Lamp 22 lights being supplied through closed contacts of thermostat 8 showing the water is warming up (lamp 20 is shorted out and therefor off) and the water relay 40 is energised to energise contacts 40A, B and C. Thus lamp 29 is off, lamp 30 on through contact 40B showing the boiler selected and lamp 31 off as it is shorted out by contact 40C. The boiler is directly energised through contact 40C. When the water reaches temperature (approximately one third of the tank full) the contact of thermostat 8 opens. Relay coil 40 is de-energised, contacts 40A, B and C switch back to the position shown, lamp 20 light showing the water is ready and lamp 22 is extinguished. Lamp 21 remains lit. If pump 43 is fitted it will be operated when coil 40 is energised.When the contacts 40A to C return to their original positions the boiler is still connected through the lamp 31 to the live terminal 42. As mentioned previously the impedance of the lamp 31 is so high, however, that were the boiler thermostat to close insufficient current would pass through the contacts to energise the solenoid valve to fire the boiler. When these thermostat contacts do close, the lamp is nevertheless lit showing that with a conventional system the boiler would be firing even though there is no heat requirement. The fact that lamp 31 lights up shows that an economy is being made and the time that this lamp is lit is an indication of the extent of the economy.

If a bath is required the switch 41 is simply switched to its other position. Relay coil 40 is energised but this time through the thermostat 9 which is one third of the height of the tank 7 from the bottom of the tank 7. Lamps 24 and 25 light up, lamp 23 remains off and contacts 40A to 40C switch to their energised positions. Boiler 1 is therefore once again directly energised through contact 40C. When the tank is up to temperature, the thermostat 9 contacts open, lamp 23 lights up and lamp 25 is extinguished, relay coil 40 is deenergised and contacts 40A to C return to their de-energised position. The lamps 31 then fulfills the same function as previously.

The above described arrangement introduces new levels of controlability and efficiency to conventional oil and gas central heating systems.

It saves fuel by eliminating wasteful boiler cycling after rooms have reached the preset temperature and also by allowing the householder to vary the volume of hot water stored in the domestic hot water cylinder.

With the great majority of central heating installations, the usual way of finding out what the system is doing at a given time is to check the boiler and hot water cylinder, feel the radiators and test the room thermostat.

With the system described above, not only can key operating phases be monitored at a glance, an indicator light shows when the economy control facility has automatically switched itself in and the boiler is prevented from wasteful intermittent firing.

It will be appreciated that the above described embodiment is only one way of putting the invention into effect and that many modifications can be made. Some modifications can be seen in the circuit of Figure 4 which will now be described.

The circuit of Figure 4 differs from that of Figure 2 in that a suppressor, for reducing radio and television interference, consisting of a series connected resistor 60 and capacitor 62 is provided in the hot water circuit 1 7 across either the normal thermostat 8 or the bath thermostat 9, whichever happens to be switched into the circuit.

A suppressor 6OA, 62A is also provided in the space heating circuit 1 6 across the room thermostat 1 0. A further suppressor 60B, 62B is connected in the boiler control circuit 1 7 across the contacts 40C and 5OC. Yet a further suppressor 60C,62C is provided in the boiler circuit. The suppressor 60C, 62C is intended to suppress radio or television interference which may arise from a common pump which can optionally be connected to relay contacts 40B and 50B at 63.

It will be noted that in the embodiment of Figure 4 the lamp 29 is omitted and contacts 40A and 50A can be used for some other purpose or even eliminated altogether. A further difference is apparent at contact 40B and 50B in that a green lamp 64 is connected across the contacts lo provide the same indication as provided by lamp 29 in the embodiment of Figure 1.

Referring now to the embodiment of Figure 5 the circuit can be further controlled by a time switch 70 across the mains supply. The time switch may be of the kind known per se which includes a clock and adjustable means which cause the switch to open or close et selected times. A three position switch 72 is provided for the hot water circuit and a second three position switch 74 is provided for the space heating circuit.

These switches enable the circuits 14 and 16 independently to be off, on continuously or subject to control by the time switch 70.

In this embodiment only one thermostat is provided in the water tank. While this leads to a slight diminutum in economy of boiler operation that is balanced by a considerably simplification of the hot water circuit 15. Further simplification of the circuit is achieved by omission of lamps 24, 27 and all the lamps in the boiler circuit 1 7 hence removing the requirement for relay contacts 40B and 50B. In this embodiment therefore there are lamps 25 and 28 which, when lit, indicate the the water circuit 1 5 and space heating circuit 1 6 respectively are heating up. Lamps 23, when lit, indicates that the water in the tank is up to temperature and when lamps 26 is lit it is an indication that the room is upto temperature.

The lamps 25, 28, 23 and 26 together with the switches 72 and 74 and time switch 70 may conveniently be placed on the front panel of a housing for the circuit, such as is illustrated in Figure 6.

Claims (8)

1. Control apparatus for controlling the operation of a boiler having a thermostat controlling an electrically energisable valve controlling supply of fuel to the boiler comprising a parallel connection of a high impedance and a switch in the electrical supply to the boiler valve whereby, when the switch is closed, the impedance is shorted out and when the switch is open should the thermostat contacts close the valve will not be energised because of the limiting effect of the high impedance.

2. Control apparatus as claimed in Claim 1, further comprising a temperature dependent control located in a water tank and/or in a room adapated to control the control apparatus.

3. Control apparatus as claimed in Claim 2, wherein the said apparatus is controlled by one of at least two temperature dependent controls located at different heights in a water tank, means being provided for selecting the temperature dependent control that is to govern the control apparatus.

4. Control apparatus as claimed in any preceding claim, further comprising timing means incorporating switch means that additionally controls boiler firing.

5. Control apparatus as claimed in any preceding claim wherein visual signalling means are provided for indicating when the switch is open and the boiler thermostat contacts closed.

6. Control apparatus as claimed in Claim 2 or any claim dependent thereon, wherein visual signalling means are provided for indicating that the control apparatus is governed by a temperature dependent control.

7. Control apparatus as claimed in Claim 2 or any claim dependent thereon wherein visual indication means are provided for indicating that the boiler is operating to raise the temperature to that set by a temperature dependent control and/or that the temperature has been raised by the boiler to that set by a temperature dependent control.

8. Control apparatus for controlling the operation of a boiler substantially as described herein with reference to Figures 1 to 3, Figure 4 or Figures 5 and 6 of the accompanying drawings.