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(11) | EP 1 672 287 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A method for controlling the temperature in a feed pipe |
| (57) The present invention relates to a method and control system (2) for controlling
at least the temperature in a feed pipe (6, 8) of an enclosed pressurised water heating
system (1) comprising heat exchangers (9) connected to a boiler (3). The boiler (3)
has a water outlet (4) connected to the feed pipe (6, 8), at least some of which feed
pipe (6, 8) is provided by a pipe (8) of thermoplastic material. Essentially, the
method comprises measuring the temperature of the feed water adjacent the boiler feed
outlet (4) and comparing this measured temperature with a base temperature. When the
measured temperature exceeds the base temperature, that measured temperature is recorded
as a critical temperature and can be used to carry out various actions, such as cutting
off the boiler (3) immediately or possibly cutting off the operation of the boiler
(3) after a preset time. In one embodiment, it is carried out by using a thermistor
(15) mounted on the exterior of the feed water pipe (6). There may also be provided
means for sensing the pressure in the feed water and stopping the operation of the
boiler when the pressure in the feed water is outside preset limits.
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[0001] The present invention relates to a method for controlling at least the temperature in a feed pipe of an enclosed pressurised water heating system of the type comprising heat exchangers connected to a boiler having a feed water outlet connected to a feed pipe, at least some of which feed pipe is provided by a pipe of a thermoplastics material and a return inlet for cooled system water from a return pipe. Further, the invention relates to a computer program for carrying out such a method and further relates to a control system for carrying out such a method.
[0002] Originally, such central heating systems always had pipes of metal, whether it be cast iron, mild steel or, more often, copper. However, there are considerable advantages in using a thermoplastics material for such pipe, not alone on the basis of cost, but also because of its general flexibility and the ability to bend the pipe easily without the necessity of complex bending equipment, as is required, for example, with metal pipes. Such thermoplastics pipe is additionally much less expensive than, for example, copper piping. It is also easier to fit and generally is much more attractive to installers.
[0003] Various standards govern the use of such thermoplastic pipes in heating systems, such as, for example, British Standard Specification No. BS 7291.
[0004] There are, however, certain problems with such pipes. Because they are of a thermoplastics material, they can fail if the temperature in the pipe exceeds a critical temperature. Not alone can they fail if this critical temperature is exceeded but they can fail if a lower critical temperature is maintained in the thermoplastics pipe over an extended period. While most boilers are fitted with thermostats that ensure the temperature will not exceed a preset amount, unfortunately during start-up and indeed during operation of the boiler when the boiler is cut off and then started again, the water temperature can be momentarily exceeded. In other words, the actual temperature of the water leaving the boiler might exceed a critical temperature, but for a very short period of time and as such, would not cause difficulties. However, when the temperature of the feed water exceeds some critical temperature for an extended period, then failure of the thermoplastics pipe can occur, particularly where the thermoplastics pipe is connected to a metal fitting such as, for example, feeding a radiator or other heat exchanger.
[0005] The effect of failure can, in some case, be catastrophic because the system may be operating at a pressure of the order of 3 bar or, in some cases, more, and then the escaping water can often flash off as steam and can cause considerable injury, let alone damage to the surrounding structure.
[0006] Indeed, there have been so many accidents and difficulties in relation to such thermoplastic pipes. In some instances, certain companies and organisations have refused to maintain domestic central heating systems using thermoplastics pipes as serious accidents and failures have occurred as the pipes have deteriorated over time. The problem is that heretofore no efficient control system has been developed to allow the boilers to operate satisfactorily and at the same time to protect the thermoplastic piping. As stated above, there are always surges in temperature that do not matter which add to the difficulty in protecting the pipes. For example, when a boiler is in start-up mode, very often the first water delivered out the boiler outlet is at a very high temperature which immediately drops and this transient increase in temperature does not cause any problems to the thermoplastic pipe. Thus, if a thermostat is set such as to avoid the delivery of water out of the boiler at this temperature, the boiler can then only operate at much reduced temperatures which again is not satisfactory. As the boiler is stopped and started throughout its normal running, often for relatively small time intervals, there are these surges in temperature which are relatively harmless. However, if such a surge in temperature is exceeded for more than a relatively short period of time, then problems can arise.
[0007] The present invention is directed towards overcoming the problems in the use of thermoplastic piping in such heating systems.
Statements of Invention
[0008] According to the invention, there is provided a method for controlling at least the temperature in a feed pipe of an enclosed pressurised water heating system comprising heat exchangers connected to a boiler having a feed water outlet connected to a feed pipe, at least some of which feed pipe is provided by a pipe of a thermoplastics material and a return inlet for cooled system water from a return pipe, the method comprising, on the system operating:
measuring the temperature of the feed water adjacent the boiler feed outlet;
comparing the measured temperature with a base temperature;
on the measured temperature exceeding the base temperature, recording that measured temperature as a critical temperature;
deciding on the action to be taken having regard to the specific critical temperature and the elapsed time during which it occurred; and
taking the appropriate action having regard to the decision.
[0009] The advantage of this is that the boiler will not necessarily be shut down when there is an immediate surge in temperature. It will only occur when this critical temperature, which could be quite a low temperature, has been exceeded for a preset time. This ensures that the boiler can operate in normal operating mode without continuously being shut down and thus the incidence of false alarms will be nullified.
[0010] In one method according to the invention, an action database of critical temperatures exceeding the base temperature and corresponding instructions for action to be taken is prepared and the decision for action on a specific critical temperature being measured is taken having regard to the corresponding instruction for action in the database. It is very useful to have such a database because many different actions can be taken.
[0011] Ideally, in many instances, the action taken is to shut down the boiler for a predetermined time.
[0012] In one method of carrying out the invention, the time when the shut-down of the boiler occurred is recorded and on subsequent shut-downs being recorded of the frequency of shut downs within an extended predetermined time period exceeds a preset number, the boiler is permanently shutdown requiring manual intervention to restart.
[0013] In the method according to the invention, in one embodiment the action comprises one or more of:
an audible alert;
a visual alert;
an immediate shutdown of the boiler;
an instruction to continue monitoring and to shutdown, unless the measured temperature falls below the critical temperature before a preset elapsed time; and
an instruction to record and store the frequency of critical temperature occurrences not individually requiring shutdown.
[0014] In one embodiment of the invention, the temperature of the exterior of the feed pipe is measured.
[0015] In this latter method, in one embodiment the temperature of the exterior of the feed pipe is measured adjacent the feed pipe of thermoplastics material nearest the feed water outlet.
[0016] In a method of carrying out the invention, the initial step is performed of preparing an action database of critical temperatures exceeding a base temperature and corresponding instructions for action to be taken having regard to the critical temperature and the elapsed time during which the critical temperature was maintained, then on the measured temperature exceeding the critical temperature:
the action database is accessed;
the appropriate instruction extracted; and
the appropriate action is carried out having regard to the instruction.
[0017] In another method according to the invention, the length of time each occurrence when a critical temperature occurred in the water heating system over an extended period is aggregated and if this exceeds a preset aggregate time, appropriate action is taken.
[0018] In another method according to the invention, the pressure of the feed water is measured and when it falls outside a preset range, the boiler is shut down.
[0019] The method may be carried out using a computer program comprising computer instructions for carrying out the method, which computer program may be embodied on a record medium, a computer memory, a read only memory or an electrical signal carrier.
[0020] In another aspect of the invention, the control system comprises:
a thermistor for mounting on the exterior of the feed water pipe;
a controller connected to the thermistor having control means for carrying out the method; and
a switch for operating the boiler in response to the control means.
[0021] In another embodiment of the invention, the controller comprises an analog to digital converter (ADC) connected to the thermistor and an arithmetic logic unit (ALU) and associated timer.
Detailed Description of the Invention
[0023] The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawing of a diagrammatic layout of a water heating system in accordance with the invention.
[0024] The basic premise of the present invention is based on the observation that it is not so much the incident of a critical temperature being exceeded in a thermoplastic pipe that causes the problem but that critical temperature being exceeded over a period of time. Most thermoplastic pipes are able to withstand quite high temperatures over relatively small periods of time but will rapidly deteriorate at much lower temperatures if that lower temperature is maintained over a long period of time.
[0025] Referring to the drawing, there is illustrated a water heating system, in this case part of a domestic central heating system, indicated generally by the reference numeral 1, to which is connected a control system, namely a controller, indicated generally by the reference numeral 2, and surrounded by the interrupted lines. The water heating system 1 comprises a boiler 3 having a water outlet 4 and a water inlet 5. The water outlet 4 feeds a feed pipe comprising a feed pipe 6 of metal connected by a pipe connector 7 to a further feed pipe 8 of thermoplastics material. The feed pipe 8 in turn feeds in conventional manner, for example, a heat exchanger, in this embodiment, a radiator 9. The return inlet is in turn fed from a return pipe 10. All of this is conventional.
[0026] Mounted on the feed pipe 6 adjacent to the pipe connector 7 is a thermistor 15 forming part of the controller 2. The controller 2 comprises a conditioner 16 connected to the thermistor 15 and then to an analog to digital converter (ADC) 17 and from thence to an arithmetic logic unit (ALU) 18. Connected also in the system is a timer 19. The ALU 18 is connected to a relay 19 in a power feed line 20 to the boiler 3. Any other type of controller could be used.
[0027] In practice, a database is prepared of critical temperatures and times which will cause an action to be taken, usually to cause the relay 19 to operate and cut off the boiler.
[0028] It will be appreciated that many forms of controller and control logic may be used. For example, the boiler may be cut off permanently, it may be simply cut off for a short period of time, but if the boiler were to exceed the critical temperature again within an extended period, then the boiler might be shut off. There are many ways in which the boiler could be controlled. It is envisaged, for instance, that what effectively is done is that the thermistor, which is mounted on the outside of the feed pipe 6, will measure the temperature of the feed water, which temperature will then be fed to the ALU 18 which will take the appropriate action. Generally, there will probably be a database of temperatures and times. Thus, for example, if a particular temperature was exceeded for five minutes in the pipe, the boiler might be shut off. Similarly, if a higher temperature was sensed, the boiler might be shut off after one minute. Indeed, if a higher critical temperature was exceeded, the boiler might be shut off immediately.
[0029] It is also envisaged that various recording means may be provided such that when the critical temperature is exceeded in a water heating system over a number of short intervals of time, these short intervals of time could be aggregated and if the aggregate of these times exceeded a critical aggregate time in that period, the boiler could also be shut off or some other action could be taken.
[0030] The thermistor obviously measures the temperature on the outside of the pipe and the temperature and indeed the control system used, will depend entirely on the actual thermoplastics material being used and indeed on the water heating system itself. Indeed, one could envisage a system where the first portion of the heating system might consist of metal piping and the thermoplastic piping might not be connected for the first part of the system. In this way, the water heat would be sufficiently dissipated as not to provide surges in temperature and indeed critical temperatures within the thermoplastics piping which might cause inadvertent operation of the control system. Indeed, the manner in which the system will be controlled will be dependent almost entirely on the type of system.
[0031] It is envisaged that a database would be used, for example, giving numerous instructions, actions and so on. The following are simply given as examples only and it must not be presumed that these would be the temperatures and instructions used in practice. In the following table, some of the actions and controls are mutually exclusive.
TABLE
| Thermistor Temperature °C | Duration Minutes | Instruction/Action |
| 90 | 20 | Shut off permanently |
| 95 | 3 | Shut off for 30 minutes. Restart. If occurs over next 24 hours for more than 3 minutes, shut off permanently. |
| 95 | 5 | Shut off |
| 100 | 0.25 | Shut off |
[0032] It will be appreciated that any other temperature sensing device could be used, other than a thermistor, however, a thermistor is particularly advantageous in that it can be easily fitted to the exterior of a pipe.
[0033] It is envisaged that additionally the pressure of the feed water may be measured and when it falls outside a preset range, the boiler is shut down. One of the major causes of serious conditions and failures in such water heating systems occurs when the amount of water in the system falls to a dangerously low level. What then happens is that the boiler has relatively little water and then generates an amount of steam which is then delivered out of the boiler and in certain instances, if the boiler runs dry and subsequently water is added to the boiler, a serious explosion or mishap can occur. It will be appreciated that it is of vital importance to ensure than when the level of the water falls low in the system, then system shuts down. It is thus envisaged that some form of pressure sensor may be mounted in the feed water pipe adjacent the exit to the boiler and indeed, in conjunction with a temperature probe or temperature measuring device, to measure both the pressure of the feed water and also the temperature. Then, when the feed water falls outside a preset range, the boiler can be shut down. In many instances, it may be a drop in pressure that is more important than an increase in pressure.
[0034] It will also be appreciated that when the pressure is also being sensed, it may be more advantageous to have both the pressure and temperature sensors within the pipe.
[0035] It will be readily appreciated that the method of the invention may be carried out by any program device and may use, for example, computers or may be embodied in a computer program, either on a record medium, in a computer memory, in a read only memory or on an electrical signal carrier.
[0036] As well as the arrangement of controller described above, many programmable devices utilising a computer program may be used. Such a computer program can have program instructions to carry out the methods of the present invention. The computer can be embodied in a record medium, stored in a computer memory, embodied in a read only memory and/or carried on an electrical signal carrier.
[0037] In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms "include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.
1. A method for controlling at least the temperature in a feed pipe of an enclosed pressurised
water heating system comprising heat exchangers connected to a boiler having a feed
water outlet connected to a feed pipe, at least some of which feed pipe is provided
by a pipe of a thermoplastics material and a return inlet for cooled system water
from a return pipe, the method comprising, on the system operating:
measuring the temperature of the feed water adjacent the boiler feed outlet;
comparing the measured temperature with a base temperature;
on the measured temperature exceeding the base temperature, recording that measured temperature as a critical temperature;
deciding on the action to be taken having regard to the specific critical temperature and the elapsed time during which it occurred; and
taking the appropriate action having regard to the decision.
2. A method as claimed in claim 1, in which an action database of critical temperatures
exceeding the base temperature and corresponding instructions for action to be taken
is prepared and the decision for action on a specific critical temperature being measured
is taken having regard to the corresponding instruction for action in the database.
3. A method as claimed in claim 1 or 2, in which the action taken is to shut down the
boiler for a predetermined time.
4. A method as claimed in claim 3, in which the time when the shut-down of the boiler
occurred is recorded and on subsequent shut-downs being recorded of the frequency
of shut downs within an extended predetermined time period exceeds a preset number,
the boiler is permanently shutdown requiring manual intervention to restart.
5. A method as claimed in any preceding claim, in which the action comprises one or more
of:
an audible alert;
a visual alert;
an immediate shutdown of the boiler;
an instruction to continue monitoring and to shutdown, unless the measured temperature falls below the critical temperature before a preset elapsed time; and
an instruction to record and store the frequency of critical temperature occurrences not individually requiring shutdown.
6. A method as claimed in any preceding claim, in which the temperature of the exterior
of the feed pipe is measured.
7. A method as claimed in claim 6, in which the temperature of the exterior of the feed
pipe is measured adjacent the feed pipe of thermoplastics material nearest the feed
water outlet.
8. A method as claimed in any preceding claim, in which the initial step is performed
of preparing an action database of critical temperatures exceeding a base temperature
and corresponding instructions for action to be taken having regard to the critical
temperature and the elapsed time during which the critical temperature was maintained,
then on the measured temperature exceeding the critical temperature:
the action database is accessed;
the appropriate instruction extracted; and
the appropriate action is carried out having regard to the instruction.
9. A method as claimed in any preceding claim, in which the length of time each occurrence
when a critical temperature occurred in the water heating system over an extended
period is aggregated and if this exceeds a preset aggregate time, appropriate action
is taken.
10. A method as claimed in any preceding claim, in which the pressure of the feed water
is measured and when it falls outside a preset range, the boiler is shut down.
11. A computer program comprising program instructions for carrying out the method of
any preceding claim.
12. A computer program as claimed in claim 11 embodied on a record medium.
13. A computer program as claimed in claim 11 stored in a computer memory.
14. A computer program as claimed in claim 11 embodied in a read only memory.
15. A computer program as claimed in claim 11 carried on an electrical signal carrier.
16. A control system (2) for carrying out the method as claimed in any preceding claim
comprising:
a thermistor (15) for mounting on the exterior of the feed water pipe (6);
a controller (2) connected to the thermistor (15) having control means for carrying out the method; and
a switch (19) for operating the boiler in response to the control means.
17. A control system (2) as claimed in claim 16, in which the controller (2) comprises
an analog to digital converter (ADC) (17) connected to the thermistor (15) and an
arithmetic logic unit (ALU) (18) and associated timer (19).
18. A control system as claimed in claim 16 or 17, in which the switch (19) is a relay
connected to the power input (20) of the boiler (3).