WO1989007740A1

WO1989007740A1 - Electric boiler control system

Info

Publication number: WO1989007740A1
Application number: PCT/GB1989/000129
Authority: WO
Inventors: George Hepburn
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-02-10
Filing date: 1989-02-10
Publication date: 1989-08-24
Anticipated expiration: 1990-08-10
Also published as: GB8803079D0; GB2215019A; AU3293289A; GB8822762D0

Abstract

A boiler control system is described for use with an electric boiler (10; 50) and heat supply network. The boiler control system has a plurality of separate heating elements (20 : 66a, b), each of which is arranged to be independently operable at a particular temperature in response to a signal from a temperature sensor (22 : 60). In one arrangement a signal probe (60) is used in combination with potentiometers (94) to control switching of relays to supply power to the respective heating elements (66a, b). In another arrangement each heating element (20) has an associated thermostat (22) which is presettable to control the switching of power to the element (20).

Description

ELECTRIC BOILER CONTROL SYSTEM

The present invention relates to a control system and particularly, but not exclusively, to a boiler control system for use with an electric boiler and heat supply network. A boiler control system should satisfy a number of desirable criteria in addition to being reliable and relatively inexpensive. The temperature of liquid in the tank should be finely controlled at a desirable level. This control should be exerted by using a minimal amount of power in the operation of the apparatus. The heat transfer from any heating element to the liquid should be efficient and the tank should reach a desired temperature level reasonably quickly after being switched on. The boiler control apparatus should also be modular to make all parts easily accessible thus minimising problems of maintenance or replacement. In addition, the boiler control system and boiler should be very compact and be able to be stored in a small space, for example, a kitchen cupboard, where electricity and water can be supplied, especially when the boiler is used in the domestic scene or in small business premises.

Existing electric boiler control systems include a large heating element with an associated thermostat which is immersed in a liquid, usually water, contained in a storage tank. When the boiler is switched on the heating element is actuated and the element is switched off when a thermostat detects the water temperature above a preset level. Such heating elements consume considerable amounts of power and cause steep gradients of temperature increases. In fact, the heating element uses substantially the same amount of power at all temperature levels of water in the tank. Because of the steep temperature gradients, the thermostatically controlled switching levels of the heating element may be fairly wide, and thus relatively fine control of water temperature, using low power is not obtained. Such fine control may be required, for instance, when the heat supply network is relatively small or requires minimal heating. In addition, a single heating element does not result in efficient heat dispersal when used in a tank because liquid in the parts of the tank furthest^' from the heating elements is heated last.

An object of the present invention is to provide a boiler control system which obviates or mitigates at least one of the aforementioned problems.

This is achieved by providing a boiler with a control system which has a plurality of separate heating elements, each element being independently operable under the control of a temperature sensor.

In one embodiment a plurality of heating elements are disposed in a tank, each element having an associated thermostat. Each of the thermostats are pre-settable at different temperatures to permit the heating element switch on and off when the liquid in the tank is at different temperatures. Thus minimal power is used to heat up the liquid in the tank and to maintain the liquid at a desired temperature.

According to one aspect of the present invention there is provided a boiler control system for use with an electric boiler having a container for storing a liquid to be heated and a pump for pumping said liquid around a heat supply network, said boiler control system comprising a plurality of separate heating elements, each of said heating elements being disposed inside said container and spaced from each adjacent heating element, temperature sensor means disposed inside said container for sensing the temperature of liquid in said container, temperature preset means associated with each heating element and each temperature preset means being independently pre-settable at a particular temperature value to control the operation of its respective heating element around said respective temperature, whereby the temperature of liquid in said tank, for supply to the heat dissipation network, is determined by the cumulative effect of the independent switching of each heating element by its associated temperature preset means.

Preferably each element has a respective temperature sensor means associated therewith which extends into said container in proximity to said associated heating element. Alternatively said temperature sensor means is a single probe and each temperature preset means is disposed outside the container and coupled to a respective relay which is actuable in response to the temperature of liquid in the tank and to the preset temperature to permit power to be supplied to each respective heating element.

Preferably also, an additional temperature sensor is disposed inside said container and is coupled to said control system, said additional thermostat causing the switching off of all the heating elements if the temperature of liquid in the container exceeds a pre-set value.

Preferably also, each heating element is coupled to visual indication means, said visual indication means indicating whether each heating element is in operation. Conveniently, said visual indication means are provided by neonlamps or light emitting diodes electrically coupled to each heating element, one indication means being coupled to each respective heating element such that, in use, when an individual heating element is actuated and draws current, its respective visual indication means is also actuated.

Preferably also, further visual indication means is electrically coupled to said boiler control system, said further visual indication means showing when said boiler control system is in operation. Preferably, continuous control of said boiler is provided by said boiler control system.

Alternatively, a timing clock is connected to the electrical power supply to said boiler control system, said timing clock providing timing signals which determine whether or not the boiler control system will be in operation at any given time.

According to a second aspect of the present invention there is provided A method of controlling the temperature of liquid in a container using a boiler control system having separate heating elements and a temperature sensor for sensing the temperature of liquid in the container and respective temperature preset means associated with each heating element, said method comprising the steps of:- switching on all of said heating elements; switching off each heating element, in turn, as the temperature of the liquid in the container rises above a pre-set level associated with each individual thermostat; and switching on respective heating elements if the temperature of liquid in the tank falls below pre-set levels associated with each individual heating element.

According to another aspect of the present invention there is provided an electric boiler having a container for storing a liquid to be heated and a pump for pumping said liquid round a heat supply means, said container having a plurality of separate heating elements disposed therein and spaced apart, temperature sensor means disposed inside said container for sensing the temperature of liquid in said container, temperature preset means associated with each heating element, each temperature preset means being independently presettable at a particular temperature value to control the operation of its respective heating element around said respective temperature, whereby the temperature of liquid in said tank, for supply to the heat dissipation network. is determined by the cumulative effect of the independent switching of each heating element by its associated temperature preset means.

Preferably each element has a respective temperature sensor means associated therewith which extends into said container in proximity to said associated heating element.

Alternatively said temperature sensor means is a single probe and each temperature preset means is disposed outside the container and coupled to a respective relay which is actuable in response to the temperature of liquid in the tank and to the preset temperature to permit power to be supplied to each respective heating element.

These and other aspects of the present invention will become apparent from the following description when taken in combination with the accompanying drawings in which:- Fig. 1 is a perspective and partially cut-away view of an embodiment of a boiler control apparatus in accordance with the present invention; Fig. la is a plan view of a thermostat control dial with a thermostat in the boiler control apparatus shown in Fig. 1, and

Fig. 2 is a circuit diagram for the boiler control apparatus shown in Fig. 1. Fig. 3 depicts a boiler control apparatus similar to that shown in Fig. 1 according to a second embodiment of the invention;

Fig. 4 depicts a detailed and enlarged front view of the control panel of Fig. 3; and Fig. 5 is an end view of the panel shown in Fig. 4 taken in the direction of arrow 5.

Reference is first made to Fig. 1 of the drawings which shows an embodiment of an electric boiler control system. An electric boiler and associated control apparatus, generally indicated by reference numeral 10, comprises a water tank 12 in the form of an elongate metal box, and a pump 14 mounted within a pressed metal housing 16, shown partially in broken outline. The boiler 10 is connected to a heat supply network (not shown) by an inlet pipe 17 which is connected to the bottom of tank 12 and an outlet pipe 18 connected to the top of tank 12. Pipe 18 is connected, via a T-piece 19, to a header tank (not shown) and to the feeder pipe 21 via pump 14. The header tank has a water level control system as well known in the art to ensure that the heating system is fully primed.

Disposed within the tank 12 are six 2.5kw heating elements 20 giving a maximum rating of 15kw, these elements are of a general *ϋ' shape and are spaced around the inside of the tank 12. The heating elements 20 are electrically connected to the boiler control system via terminals 23 and earth bar 25. Each heating element 20 has an associated thermostat 22 disposed within the tank 12 in close proximity to its associated heating element 20. Thermostats 22 have temperature control dials 24 mounted on the top of the tank 12. In addition a high level cut off (HLCO) thermostat 26 is disposed within the tank, this HLCO thermostat 26 has an associated HLCO temperature control dial 28 mounted on the side of the tank 12. Each thermostat 22 is connected to its associated heating element and will cause its heating element 20 to switch on and off as will be described.

Electrically connected to each heating element 20 is an indicator lamp 30. Each heating element 20 has its own respective lamp 30 which illuminates when its respective heating element 20 is switched on. The indicator lamps 30 are mounted on the exterior of housing 16 and indicate the level of energy being used by the control system. Also mounted on the housing 16 is power supply lamp 32. This illuminates when the boiler control system is energised.

When the boiler control system is energised the heating elements 20 are actuated and cause the temperature of the water in tank 12 to rise. Each thermostat 22 causes its associated heating element 20 to switch off when the temperature of water in the tank passes a pre-set value determined by each thermostat 22. The temperature cut-off value of each thermostat 22 is different and each can be set by the adjustment of control dials 24, of each respective thermostat 22. Control dial 24 is best seen in Fig. la which shows various temperature values at which the thermostat 22 may be set. The thermostat 22 can be set to switch off the heating element 20 at any temperature between 40° and 80°. When the boiler control system is energised the water temperature in the tank 12 is low and all the heating elements 20 are 'on'. As the temperature of the water rises over the pre-set cut off temperature value of each thermostat 22, the respective heating elements 20 each switch 'off* in turn. When the temperature of water in the tank 12 is above the highest pre-set temperature value of any thermostat 22, all the heating elements 20 are Off. As a safety feature the HLCO thermostat 26 causes all heating elements 20 to be switched "off* if the temperature of water in the tank rises above the pre-set value on HLCO control dial 28. This pre-set value can be any temperature up to 100° and is usually 90°. The temperature of water in the tank drops to 75° before any of the heating elements 20 are actuated again. In addition, any excess pressure in the tank 12 can be released by opening safety valve 29 mounted at the bottom of tank 12.

With the heating elements 20 'off' and with some water being circulated by pump 14 around the heat supply network, the water temperature in the tank 12 will fall. As the water temperature falls below a pre-set value of any thermostat 22 the associated heating element 20 for that thermostat 22 switches 'on' and heats the water.

The number of heating elements 20 which are actuated at any one time depends on the ambient temperature of water in the tank 12. Thus power drawn by the heating elements 20 is related to the temperature of water in the tank 12.

The tank 12 is made of steel and is 5 mil thick. The tank 12 has a steel top plate 13 mounted on a welded coller 15 of tank 12 with a rubber gasket 17 disposed therebetween. The top plate 13 is held to flange 15 by stainless steel screws (not shown in the interest of clarity) . In addition, bleed valve 33 mounted on the side of tank 12 allows air to exit tank 12 when the tank is being filled with water.

Reference is now made to Fig. 2 of the drawings, which is a circuit diagram for the boiler control system. Heating elements 20 are connected in parallel across terminals 23 and common earth bar 25. These terminals 23 are connected in parallel to a voltage supply 34 through thermostats 22, 4-pole contactors 36 square D type PC 310 EN and 10 amp fuses 38. In this embodiment two contactors rated at 20 Amps are used as the boilers rated at 14.7kw (50,000 BTU) although one contactor may be used with a smaller rated boiler, for example lOkw. When the boiler control system is energised the contactors 36 are energised, thus each thermostat 22 and associated heating element 20 are simultaneously energised. Each thermostat 22 senses the temperature of water in the tank and causes the heating element 20 to switch *on' or 'off'¹ as previously described.

Connected between each heating element 20 and its associated thermostat 22 is an indicator lamp 30. These lamps 30 give an indication of whether a particular heating element 20 is actuated or not. When the heating element 20 is 'on' the lamp 30 is illuminated.

Also connected to voltage supply 34 through 5 amp fuse 40 and connectors 42, each in parallel to the heating element circuits are HLCO thermostat 26 and pump 14. The pump 14 is energised when the boiler control system is energised and pumps water around the heat supply system as is well known in the art. The HLCO thermostat 26 is energised with relays 36 and causes all heating elements 20 to cut out if the temperature of water in tank 12 rises above a pre-set value which is preset for safety reasons. Pipe 18 provides an earth for the circuit to which earth bar 25 is connected and all other electrical components in the circuit are also earthed to the pipe. The boiler control system can be arranged to run continuously, or alternatively, it could be operated by a timing clock 44, best shown in Fig. 2. The timing clock 44 provides control signals which determine which periods of the day the boiler control system will be energised. The timing clock 44 send signals which completes the circuit for all the heating elements 20 and pump 14, thus energising the entire boiler control system.

A second embodiment of the present invention will now be described with reference to Figs 3 to 5 of the accompanying drawings in which like numerals refer to like parts. Referring firstly to Fig. 3 a boiler 50 consists of a water tank 52 and a pump 54 mounted within a housing 56 and which has a control panel 58 with control apparatus for controlling operation of the boiler 50 as will be described in detail. The boiler 50 is basically the same as boiler 10 except for the following changes.

In this case no thermostats are present, instead two temperature probes are used, a first thermistor probe 60 for sensing the temperature of the water within tank 54, and a second ther ister probe 62 for sensing when the temperature of water in the tank 54 is too hot and for sending a signal to switch off the boiler 50. Pump 54 is kept running after the boiler 50 is switched off so that excess heat is dissipated through the heating system. Probe 62 replaces the high temperature cut-out switch or thermostat 28 of Fig. 1.

The water tank 52 has a top plate 64 welded thereto which has 3 spaced elongate cut-outs for receiving the heating element pairs 66a,b which are then fastened by studs 70 to the plate 64. Each heating element pair 66a,b provides 2x2.4kw, that is 4.8kw/pair. Probes 62, 64 are also inserted into the tank 52 via apertures. A small ball-u-fix (trade mark) valve 72 is disposed in pupe 18 and is used with bleed valve 73 so that the water supply to the boiler 50 can be shut-off to allow elements 66a, b and/or probes 62, 64 to be replaced.

Reference is now made to Figs. 4 and 5 of the drawings which shows the control panel front plate 76 which is adapted to be bolted onto housings 56. Connected to the plate 76 via pillars 78 is a printed circuit board (PCB) assembly 80 for providing boiler control as will be described. The PCB assembly 80 consists of PCT's 82, 84 which are spaced by 5 mounting pillars and which are connected by a conductor harness 86 to provide electrical power and signal carrying facilities. PCB 82 carries a 240/24 volt transformer 88 and bridge rectifier (not shown) for supplying power to the electronics and the control electronics and PCB 84 carries the load assembly. In particular PCB 84 carries 6 heater load relays 90, each relay being connected to a respective heating element 66a, b via 6.3mm tag connections 92. Six internal pots 94, one of which is shown, are mounted on the solder side of PCB 82 for setting the temperature at which the respective heating element is switched on when the boiler is switched on all heating elements are switched on as before. In this embodiment the desired tank temperature is 80-85°C and the first heating element pot 94 is set so that the element carries on until the temperature comes within 12° C of the set point and then successive elements are set to drop out at 2°C intervals until the desired tank set point is obtained. All the potentio enters are coupled to the tank thermister probe 60. When the temperature exceeds a predetermined value the appropriate relays open and power is disconnected from the heating elements.

Conversely if the temperature falls the elements are switched on in accordance with their preset value. Thermistor probe 62 is connected via an internal pot, not shown, to a limit relay 96 so that the power supply to the whole boiler (except the pump 54) is interrupted when the water temperature in the tank gets too high, say 95°C. As in the first embodiment an LED indiσater 98 is connected to each relay to indicate whether the relay is closed and the respective heating element is being actuated; that is being supplied with current when each LED lights up its heating element is 'on'. The limit relay has an LED 100 coupled thereto to show when the boiler -is switch on. Each element is connected in series to a fuse 102 and all elements are connected in parallel in a manner similar to that shown in Fig. 2 of the drawings. The fuses 102 are disposed on front plate 76 for ease of access.

A temperature adjustment potentiometer 104 is also mounted on the front panel to allow the temperature set-point to be varied and this can be adjusted by the user or it can be factory set. Adjustment of the set-point does not affect the internal potentiometer settings. Also terminal blocks 106 are provided on PCB 82 to allow additional sensors to be connected to the control apparatus, for example an external first sensor, not shown, and/or a background heat sensor for detecting if the night temperature in a house fall beneath a particular preset value. This allows the system to have flexibility in that the temperature can be set for the boiler to operate around 80°C during the day and around 60°C during the night.

Several modifications can be made to the embodiments hereinbefore described without departing from the scope of the invention. Firstly, any suitable number of heating elements may be used. The ratings of the heating elements used can be changed to provide a larger or smaller power rating of the boiler. If each heating element is rated at lo5kw the boiler rating is 9kw which is approximately 30,000 BTϋ. If each heating element is rated at 2kw, the boiler rating is 12kw which is approximately 40,000 BTϋ, and accordingly if each heating element is rated at 2.41kw the boiler rating is 14.5kw, that is approximately 50,000 BTD. The tank 12 could be any shape such as cylindrical and could be made of a suitable temperature resistant material such as a high temperature plastic The housing could also be made of another material such as plastic. The heating elements could be of any shape suitable for efficient heat transfer.

In the first embodiment the indicator lamps could be replaced by another form of power consumption indicator such as an analogue meter or digital display. The contactors may be replaced by relays.

With regard to the second embodiment the fuses may be disposed inside the panel 76 to prevent tampering or access by an unauthorised user and the electronic sensing and switching could be carried out under solid state control using, for example, a microprocessor based circuit and this would facilitate interconnection to external sensors. Furthermore, although the boiler and the boiler control system disclosed herein is combinable with a single radiator which operates independently, with the elements and rating of the radiation being determined by the power requirements. The boiler and the radiater are combined within a single housing structure, which appears to be substantially the same as a typical radiater in appearance.

Advantages associated with the embodiments hereinbefore described are that the boiler control apparatus can provide fine control of the temperature level of a liquid in a tank using minimal power due to the use of several heating elements. As smaller elements are used the power required to operate them is correspondingly less. Heat transfer from the elements to the liquid is generally efficient, especially at the initial 'heating up' period as the heating elements are spaced around the container. Because of efficient heat transfer the boiler reaches a desired operating temperature reasonably quickly. When the liquid in the container is cool, several heating elements are in operation but when the liquid is relatively warm only one or two elements may be in operation to maintain the temperature of liquid in the container, thus less power is used to operate the boiler control system at high liquid temperatures. In addition, the boiler control system is modular and thus each part is easily removed for maintenance or replacement, thus facilitating any servicing necessary to maintain the system. The boiler control system is also very compact, with different ratings of boiler are all accommodated in relatively small housings with the same dimensions, that is, 21" high, 8¹/2" deep and 13" wide. This housing fits into most small cupboards and can be supplied with electricity and water. This makes the boiler control system especially attractive to the domestic user and to owners of small business premises.. The boiler control system is clean and quiet in operation and unlike gas, there is no requirement for an outside wall or flue. The anticipated running costs of the boiler control system are less than that of similar boiler systems. The boiler control system can also be fitted as a replacement boiler to an existing central heating system which uses solid fuel or oil. Also, the boiler system is readily connectable to external sensors to permit flexibility of operation.

Claims

1. A boiler control system for use with an electric boiler having a container for storing a liquid to be heated and a pump for pumping said liquid around a heat supply network, said boiler control system comprising a plurality of separate heating elements, each of said heating elements being disposed inside said container and spaced from each adjacent heating element, temperature sensor means disposed inside said container for sensing the temperature of liquid in said container, temperature preset means associated with each heating element and each temperature preset means being independently pre-settable at a particular temperature value to control the operation of its respective heating element around said respective temperature, whereby the temperature of liquid in said tank, for supply to the heat dissipation network, is determined by the cumulative effect of the independent switching of each heating element by its associated temperature preset means.

2. A boiler control system as claimed in claim 1 wherein, each element has a respective temperature sensor means associated therewith which extends into said container in proximity to said associated heating element.

3. A boiler control system as claimed in claim 1 wherein said temperature sensor means is a single probe and each temperature preset means is disposed outside the container and coupled to a respective relay which is actuable in response to the temperature of liquid in the tank and to the preset temperature to permit power to be supplied to each respective heating element.

4. A boiler control system as claimed in claim 1 or claim 2 wherein six heating elements are disposed inside said container.

5. A boiler control system as claimed in any preceding claim wherein an additional temperature sensor is disposed inside said container and is coupled to said control system, said additional thermostat causing the switching off all the heating elements if the temperature of liquid in the container exceeds a pre-set value.

6. A boiler control system as claimed in any preceding claims wherein each heating element is coupled to visual indication means, said visual indication means indicating whether said heating element is in operation.

7. A boiler control system as claimed in claim 6 wherein said visual indication means are provided by neon lamps or light emitting diodes electrically coupled to each heating element, one indication means being coupled to each respective heating element such that, in use, when an individual heating element is actuated and draws current, its respective visual indication means is also actuated.

8. A boiler control system as claimed in claim 6 or claim 7 wherein further visual indication means is electrically coupled to said boiler control system, said further visual indication means being arranged to illuminate to show when said boiler control system is in operation.

9. A boiler control system as claimed in any preceding claim wherein continuous control of said boiler is provided by said boiler control system.

10c A boiler control system as claimed in any of claims 1 to 8 wherein a timing clock is connected the electrical power supply to said boiler control system, said timing clock provided timing signals which determine whether ornot the boiler control system will be in operation at any given time.

10. A boiler control system as claimed in any preceding claim including temperature adjustment means for setting the desired container temperature, said temperature adjustment means being coupled to said temperature probe and to said temperature presetting menas for causing the system to operate about a different container temperature.

11. A method of controlling the temperature of liquid in a container using a boiler control system having separate heating elements and a temperature sensor for sensing the temperature of liquid in the container and respective temperature preset means associated with each heating element, said method comprising the steps of:- switching on all of said heating elements; switching off each heating element, in turn, as the temperature of the liquid in the container rises above a pre-set level associated with each individual thermostat; and switching on respective heating elements if the temperature of liquid in the tank falls below pre-set levels associated with each individual heating element.

12. An electric boiler having a container for storing a liquid to be heated and a pump for pumping said liquid round a heat supply means, said container having a plurality of separate heating elements disposed therein and spaced apart, temperature sensor means disposed inside said container for sensing the temperature of liquid in said container, temperature preset means associated with each heating element, each temperature preset menas being independently presettable at a particular temperature value to control the operation of its respective heating element around said respective temperature, whereby the temperature of liquid in said tank, for supply to the heat dissipation network, is determined by the cumulative effect of the independent switching of each heating element by its associated temperature preset means..

13. An electric boiler as claimed in claim 12 wherein each element has a respective temperature sensor means associated therewith which extends into said container in proximity to said associated heating element.

14. An electric boiler as claimed in claim 12 wherein said temperature sensor means is a single probe and each temperature preset means is disposed outside the container and coupled to a respective relay which is actuable in response to the temperature of liquid in the tank and to the preset temperature to permit power to be supplied to each respective heating element.

15. An electric boiler as claimed in any one of claims 12 to 14 wherein an additional temperature sensor is disposed inside said container and is coupled to said control system, said additional temperature sensor causing the switching off all the heating elements if the temperature of liquid in the container exceeds a pre-set value.

16. An electric boiler as claimed in any one of clais 12 to 15 wherein each heating element is coupled to visual indication means, said visual indication means indicating whether said heating element is in operation.

17. A boiler control system substantially as hereinbefore described with, reference to Figs. 1 and 2, or Figs. 3 to 5 of the accompanying drawings.

18. A method of controlling the temperature of liquid in a container substantially as hereinbefore desribed.

19. An electric boiler substantially as hereinbefore described with reference to Figs. 1 and 2, or to Figs. 2 to 5 of the accompanying drawings.