GB2186724A

GB2186724A - Heating control system

Info

Publication number: GB2186724A
Application number: GB08703530A
Authority: GB
Inventors: Walter Maggs Sweetenham
Original assignee: Horstmann Gear Group Ltd
Current assignee: Horstmann Gear Group Ltd
Priority date: 1986-02-19
Filing date: 1987-02-16
Publication date: 1987-08-19
Anticipated expiration: 2007-02-16
Also published as: IE870408L; GB8703530D0; GB8604128D0; IE59542B1; GB2186724B

Abstract

In an off-peak water heating system 10, comprising a main heater timeswitch 42 and a booster heater switch 43, a neon lamp 100 is connected between the power input to the circuit and a thermostat switch (25, Fig. 2 not shown) associated with the booster heater (24), the neon lamp lighting up when the water temperature falls below an unacceptable value. The neon lamp may be omitted and the booster heating switch is then supplemented or replaced by a switch which is automatically activated by closure of the thermostat (25) during the on-peak period to switch on the booster heater (24). <IMAGE>

Description

SPECIFICATION Heating control system The present invention relates to a heating control system and more particularly to a system for controlling the supply of heat to the hot water tank of a domestic hot water system. It is typically applied to an electric water heating system of Economy 7 type in which most or all of the water heating occurs substantially between the hours of midnight and 7 am at a cheap rate, but is also applicable to white meter installations or any other hot water systems based on time-of-day tariffs.

A common feature of Economy 7 systems is the provision of a boost facility. If the consumer has used a lot of water during a particular day, the water in the hot water tank or cylinder becomes cold. To overcome this problem a manually-operated boost timeswitch may be provided which operates typically for a period of one hour. Whereas the night time off-peak electricity is supplied to a lower heating element within the hot water cylinder, the boost timeswitch actuates an upper heating element. It is usually arranged that the amount of hot water (typically 50 litres) in the portion (typically one third) of the cylinder above the upper heating element can be heated up thereby to the desired temperature in the one hour period. If this temperature is reached before the end of the period, the electricity supply circuit is opened by a thermostat.

A problem with such boost arrangements is that the consumer does not always know that the heating boost is necessary until the water from the hot taps begins to run luke warm and then cool. Thus if it is desired to run a bath, there must be a wait of up to an hour before the water is hot enough; this interruption in the supply of hot water is inconvenient.

Accordingly there has long been a desire to provide an automatic device to indicate to the consumer that the hot water remaining in the cylinder is limited. One proposed solution is to provide a temperature sensor connected to the outside of the cylinder element. This, however, has two main disadvantages. Firstly, many Economy 7 hot water cylinders are prelagged so that either access holes would need to be made in the surrounding insulation or a new design of insulating jacket would be necessary.

Secondly extra wiring would be necessary between the cylinder and the controller or a separate, indicating panel. This would be inconvenient since it would involve one or more extra steps during installation. Also it would require a modified wiring run between the controller and the cylinder (usually these wires are specially thermally insulated). In addition, a further power supply might be required.

The present invention seeks to overcome or reduce one or more of the above disadvantages.

According to a first aspect of the present invention there is provided an electrical heating circuit comprising a timeswitch for actuating an electrical heating element, the circuit also comprising means which, whenever said timeswitch is open, or said timeswitch and a further switch in the circuit are open, detects and/or indicates whether a thermally-actuated switch in series with said timeswitch, or with said further switch and a second electrical heating element, is closed.

According to a second aspect of the present invention there is provided a hot water heating control circuit comprising first, second, third, fourth and fifth electrical terminals, the first and second terminals being supply terminals arranged to be connected via a first timeswitch and the fifth and third terminals to a first electrical heating element, and via a second timeswitch and the fourth and third terminals to a series connection of a second electrical heating element and a thermal switch actuated by the second heating element, wherein means are connected between the first and fourth terminals for detecting and/or indicating closure of the thermally-actuated switch when the second timeswitch is open.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig. 1 is a circuit diagram of a heating control system in accordance with the present invention; Fig.2 shows the connections between the heating elements and the circuit of Fig.1; and Fig.3 is a front view of a controller containing the circuitry of Fig. 1.

Referring now to the drawings, there is shown an Economy 7 type heating system 10, Fig.1 mounted within a controller box 30, Fig.3. Electrical terminals 1 to 5 are provided, of which 1 (live in) and 2 (neutral in) are connected to mains supply 20, Fig.2, and 3 (neutral out), 4 (first live out) and 5 (second live out), are connected to upper (boost) and lower (off peak) heating elements 24, 26.

Inside the controller 30, terminals 1 and 2 are connected to an isolating switch 11. Only the clock motor M of the off peak timeswitch 12 is connected upstream of switch 11. As shown, switch 42 of timeswitch 12 is in its "off" condition with its movable contact, which is connected to the live terminal of switch 11, engaging the "normally closed" fixed contact NC. This normally closed fixed contact is in turn connected by line 54 to the movable contact of the switch 43 of a boost timeswitch 13, which is also shown in its off condition i.e. with the movable contact engaging the normally closed contact NC. The NC contact of switch 43 is connected via a line 53 to the neutral terminal of isolating switch 11.

The neutral terminal of the isolating switch 11 is connected to output terminal 3 which constitutes a common neutral for the heating elements 24, 26.

When timeswitch 12 turns "on" at a time set on the timeswitch, the contact of switch 42 moves to engage the "normally open" fixed contact NO, which is directly connected to output terminal 5, which is the live supply for the off peak heating element 26. Simultaneously a circuit is formed via the neutral terminal of switch 11, line 53, the movable contact of switch 43, fixed contact NC of switch 42, an "off-peak" neon indicator lamp 14, and the live terminal of switch 11. Accordingly lamp 14 lights up.

The supply of electricity to heating element 26 is interrupted by thermostat 27 opening when the desired temperature has been reached at the level of element 26. The timeswitch 12 turns "off" at a time set on the timeswitch, typically 7 am or thereabouts.

If during the day a heating boost is reguired the consumer turns on timeswitch 13, which is a manually initiated timer (e.g. a run-on timer) automatically switching off after a time period which may be adjustable. This time period is typically one hour but could be 2 hours or more. The contact of switch 43 moves to engage the "normally open" contact NO, which is directly connected by a line 55 to output terminal 4, which is the live supply for the boost heating element 24. Simultaneously a circuit is formed via the neutral terminal of isolating switch 11, line 53, fixed contact NC of switch 43, a "boost" neon indicator lamp 15, line 54, the movable contact of switch 42 and the live terminal of isolating switch 11. Accordingly lamp 15 lights up.

The supply of electricity to heating element 24 is interrupted by thermostat 25 opening when the desired temperature has been reached by the water at the level of element 24.

As described so far, the heating control system is known. In the present embodiment a "calling" neon indicating lamp 100 is provided connected between the live terminal of isolating switch 11 and the live output terminal 4. Of course the connection to the isolating switch can be made at any electrically equivalent position such as the corresponding end of indicator 14 or any point therebetween. Similarly the connection to the output terminal 4 can be made at any electrically equivalent position such as fixed contact NO of switch 43 or any point therebetween.

Lamp 100 is automatically actuated by the thermostat 25 for the boost heating element as follows. At 7 am say, the cylinder is full of hot water after the automatic nightime operation of heating element 26. Both thermostats 25 and 27 are open. As hot water is used up, cold water enters the cylinder at the bottom and thermostat 27 closes. If a substantial amount of hot water is used during the day, the cold water level reaches the upper thermostat 25 so that this also closes. This completes a circuit via the live terminal of isolating switch 1.1, neon lamp 100, the lower part of line 55, terminal 4, thermostat 25, the resistive heat element 24, terminal 3 and the neutral terminal of isolating switch 11.Thus lamp 100 lights up to indicate to the consumer that the hotwater supply is running low and that, if a substantial further amount of hot water is required that day, boost timeswitch 13 should be operated.

Subsequent closure of the switch 43 of timeswitch 13 lights up lamp 14 (as described above). It also causes lamp 100 to be extinguished since both terminals of the lamp are now connected to the live terminal of isolating switch 11; the lower terminal of lamp 100 is connected thereto as before and the upper terminal via the upper part of line 55 the movable contact of switch 43 (which is of course now closed), line 54 and the movable contact of switch 42. At the end of the boost operation the thermostat 25 will normally have opened again so that the lamp 100 is not lit up. The thermostat operates with a "differential" so that a substantial fall in water temperature occurs before the contact closes.

The advantage of the above-described arrangement is that it permits a warning to be given to the consumer that the hot water supply is running low without any additional detection devices, power supplies or external wiring being necessary. Only a minor modification of the internal circuit of controller box 30, and the provision of an additional lamp 100 are required, so that the arrangement can be employed in existing heating systems simply by replacing controller 30. This fulfils a need of the user of which the supply authorities have been aware for a long time.

With the circuit as described so far, it has been found that the neon lamp 100 glows dimly all the time. This has been attributed to a low insulation resistance either in the cables leading to the immersion heater or in the immersion heater itself. This problem is solved by inserting a shunt resistor 105 of approximately 300k ohms.

Various other modifications may be made to the above described arrangement. For example, although an arrangement having two separate heating elements 24, 26 has been described, the elements could be the short (boost) and long (off peak) heating elements of a dual immersion heater. Alternatively only a single heating element can be provided which is actuated either by timeswitch 12 or timeswitch 13; in this case terminals 4 and 5 are directly linked.

The boost timeswitch 13 can act for a fixed period of greater than or less than one hour or its period of operation may be variable. It can be a run-back timer or may be set digitally. It can be a mechanical, an electromechanical or an electronic device.

Any convenient type of indicator may be used instead of the neon lamp 100. Boost timeswitch 13 may be supplemented or replaced by a switch which is automatically actuated by closure of thermostat 25 during the day to switch on the boost heating element 24; in this case lamp 100 may be omitted if desired.

The invention may be employed in a wide range of control systems and is not limited to those of the Economy 7 type. One circuit may comprise a series connection of a first switch, an electrical heating element, a thermal switch operated by the heating element, and a source of electrical power, the neon lamp or other indicator being connected in parallel with the first switch.

Claims

1. An electrical heating circuit comprising a timeswitch for actuating an electrical heating element, the circuit also comprising means which, whenever said timeswitch is open, or said timeswitch and a further switch in the circuit are open, detects and/or indicates whether a thermally-actuated switch in series with said timeswitch, or with said further switch and a second electrical heating element, is closed.

2. A circuit according to Claim 1, wherein the timeswitch is operated by a clock motor on a daily time schedule.

3. A circuit according to Claim 1 or 2, wherein a said further switch is connected to the timeswitch, the further switch being a manually-operable run-back timer switch.

4. A circuit according to any preceding claim, wherein the detecting/indicating means comprise a lamp connected between a power input to the circuit and the thermally-actuated switch.

5. A circuit according to Claim 4, wherein the lamp has a shunt resistor connected thereacross.

6. A circuit according to any preceding claim, wherein the detecting/indicating means comprises a switch which is automatically actuated by closure of the thermally-actuated switch to switch on the heating circuit.

7. A circuit according to any preceding claim, wherein the thermally-actuated switch is a thermostat operated by the respective heating element.

8. A hot water heating control circuit comprising first, second, third, fourth and fifth electrical terminals, the first and second terminals being supply terminals arranged to be connected via a first timeswitch and the fifth and third terminals to a first electrical heating element, and via a second timeswitch and the fourth and third terminals to a series connections of a second electrical heating element and a thermal switch actuated by the second heating element, wherein means are connected between the first and fourth terminals for detecting and/or indicating closure of the thermally-actuated switch when the second timeswitch is open.

9. A circuit according to Claim 8, wherein the first timeswitch is driven by an electrical clock motor connected between said first and second terminals and the second timeswitch is a manually operable run-back timer.

10. A circuit according to Claim 8 or 9, wherein the detecting/indicating means comprises a neon lamp with a shunt resistor connected thereacross.

11. A circuit substantially as herein described with reference to the accompanying drawings.