GB2190517A - Method of regulating room temperature and means for performing this method - Google Patents

Abstract

The setting of a thermostat 13 is higher by a predetermined amount than the normal day-time desired value. The normal day-time desired value is obtained by heater 20 acting on thermostat sensor 17. A microprocessor 1 delivers a series of output data D each comprising the address of a zone I, II, III and a command specifying the electric power to be supplied to the heating resistors 20 in that zone. The power may be varied to give variable modification of the thermostat setting. The power variation may be applied so as to produce a gradual change in the desired room temperature. <IMAGE>

Description

SPECIFICATION Method of regulating room temperature and means for performing this method This invention relates to a method and means of re gulating room temperature.

The invention relates to a method of regulating room temperature, wherein the room is supplied with heat under the influence of a thermostat, particularly a thermostatic valve of a hot water heating installation, and the actual desired value is reducible from a day-time desired value setforthe habitation of a person by supplying electric powerto a heating resistor associated with a thermostat sensor to a desired value which is lower than the inherent desired value ofthe thermostat, and to means fdr performing this method.

DE-OS 2253511 discloses a method ofthis kind in which the sensors ofthermostatic valves of a hot water heating installation can be heated by heating resistors in order to achieve a so-called night reduc tion whereby the room temperature at night is reduced to a lower value than the day-time desired value.

The day-time desired value of each room corresponds to the inherent desired value of the thermostatic valve and can be selected by setting a knob. The heating resistors are controlled by switches which can be operated by a synchronous clock. Several voltages are available at the secondary side of a transformer having a plurality oftappings.

Consequently, each heating resistor can be supplied with an electric power which differs from that ofthe other heating resistors. This results in different sizes of reductions in the desired value during the night.

The invention is based on the problem of developing a method of the aforementioned kind so that novel regulating possibilities are provided.

This problem is solved according to the invention in that the inherent desired value ofthe thermostat is higherthan the daytime desired value by a predetermined amount and the heating resistor is also supplied with electric power during the day so that the day-time desired value results from the setting at the thermostat and the heating ofthe thermostat sensor and that, to achieve a regulated characteristic with higher desired value, the supplied electric power is reduced.

The present invention provides a method of regulating room temperature in which a room is supplied with heat underthe control of a thermostat and the desired temperature setting is effectively reduced by supplying electrical powerto a heating resistor associated with a sensor ofthe thermostat, characterized in thatthethermostat is set to a temperature value higher than the desired day-time temperature in the room and the heating resistor is supplied with electrical power during the day so that the desired day-time temperature of the room corresponds to the thermostat setting as effectively re duced by the electrical heating ofthe thermostat sensor, and i n that to provide a hig her regulated temperature in the room the electrical power supplied to the heating resistor is reduced.

The invention also provides means for regulating the temperature of a room comprising a thermostat to control the supply of heat to the room and means to effectively reduce the desired temperature setting comprising means to supply electrical power to a heating resistor associated with a sensor ofthe thermostat, characterized in that control means are provided and arranged to supply the heating resistor with electrical power during the day so that, when the thermostat is set to a temperature value higher than the desired day-time temperature in the room, the desired day-time temperature of the room corresponds to the thermostat setting as effectively reduced by the electrical heating ofthethermostat sensor, and characterized by means to provide a higher regulated temperature in the room by reducing the electrical power supplied to the heating resistor.

The invention also provides a central heating controllerforcontrolling a plurality ofthermostats, each adjustabletoasetvalueand having a respective sensor associated with a respective heating resistor, the central heating controller comprising a microprocessor provided with a digital store for storing a desired heating program, wherein the microprocessor is arranged to transmit output data signals each comprising the address of a zone at which a thermostat, or plurality of thermostats to be controlled similarly are located, and a command representing the electric power to be fed to the heating resistors, the arrangement being such that the heat command is on the basis that the thermostat in question is set to a temperature higherthan the desired day-time temperature in the room and the heating resistor in question is to be supplied with electrical power during the day so that the desired day-time temperature of the room corresponds to thethermo stat setting as effectively reduced by the electrical heating ofthethermostatsensor, and such asto provide a higher regulated temperature in the room by reducing the electrical power supplied to the heating resistor in question.

Sincetheday-timedesiredvalue,thatistosaythe value desired bythe user ofthe room during the normal hours ofthe day, lies below the inherentdesired value of the thermostat resulting from its constructional parameters (for example by reason of the prestressing of a desired value spring), thethermo stat sensor has to be heated by the heating resistor not only during night reduction but also to achieve the normal day4ime desired value. This gives the prerequisite that the actual desired value can not only be lowered but also raised. This occurs by reducing the electric power. This results in a numberof new regulating possibilities as will hereinafter be described in more detail.

Preferably, the electric power during day-time operation is such that the day-time desired value is from 1 to 3"C, preferably about 2"C, below the in herent desired value ofthe thermostat. This range is then also available for increasing the actual desired value.

It is favourable if, when changing the actual desired value from a first to a second value, the electric power is smoothly altered along a ramp function.

The smooth change can take place continuously or in small steps. This will avoid the user experiencing uncomfortable surges in the temperature. Also, one obtains a good current distribution.

Particularly during the heating-up phase ofthe room, the actual desired value should be raised smoothly. The inclination of the ramp is selected with reference to the inertia prnparties of the room to be heated and the associated radiator. If in the case of a plurality of thermostatic valves the actual des iredvalueisto besmoothlyincreasedsimu- ltaneously,thereis no dangerofthevalvesim- mediately opening completely, which would impair the proper distribution ofthe hot water. This is part icularly important in the case of remote central heating where charging is according to the number of cubic meters.

Preferably, the actual desired value is increased at a time-spacing before the time when use of the room is to be expected and is gradually returned to the day-time desired value at a time-spacing afterthis time. Such temporary increase in the desired value pre-heats the room and makes sufficient heat energy available so thatthe coldness from the cold walls that cooled off during the nightwill not have an unpleasant effect. The gradual reduction of the actual desired value is practically unnoticeable bythe users.

Particularly comfortable regulation is achieved if the actual desired value is smoothly increased during the hours of the evening up to an increased desired value which remains constant. When the user of the room is no longer working in the evening but is sitting quietly and relaxed, this increase in temperature is found to be particularly pleasant.

Avery important regulating possibility is that, to correct the proportional band error ofthe thermostat, the desired value is changed in relation to the external temperature. The lower the external temperature and the higherthe quantity offiow, the largerwill also be the regulating departure of a proportional valve. This error can now for the first time be corrected automatically.

A particularly simple change in the electric power is obtained in that the heating resistor is inter mittently fed with current and, forthe purpose of changing the actual desired value, the pulse-pause ratio of the current is altered. One can use comparatively long cycle and pause periods because the inertia of the thermostatsensor ensures the form- ation of a good mean value.

in some cases, it is advisable that during current supplythe voltage drop is measured at a resistor through which this currentflows and an error signal is delivered if the voltage drop falls below a lower limiting value or rises above an upper limiting value.

In this way, one can in good time detect a short cir cuitoraninterruption in the region of the heating resistor.

Means four performing this method, comprising thermostats, particularly thermostatic valves, of which the sensors are each associated with a heating resistor and have an adjustable inherent desired value and comprising control elements which control the supply of electric powerto the heating resistors and can be influenced depending on a desired value programme stored in a central location, are characterized according to the invention in that the central location contains a main microprocessor which is provided with a digital desired value program store and which, depending on the desired value program and possibly additional input values, delivers a series of output data which each comprise the address of a zone with a thermostat or a plurality of thermostats which are to be influenced similarly and a command which characterises the electric power to be supplied to the heating resistors ofthe thermostats there located, and that each zone is associated with a control apparatus which stores a command corresponding to its own address and, depending thereon, so actuates at least one control el ement that the electric power supplied to the associated heating resistor corresponds to the command.

Since the output data, which may contain other information in addition to the address and the command, is continuously computed and delivered by the main microprocessor, the actual desired value of each thermostat can be changed at anytime, namely in jumps as well as continuously. The main microprocessor primarily takes into account the desired value programme stored for each zone. Sincethis program is superimposed on the inherent desired value of the thermostat, the user can change the baselineofthisprogramatwill byadjusting this inherent desired value. The additional expenditure in each zone is comparatively low because the control apparatus and the associated control element may be of simple construction.

It is particularly favourable if an external temperature sensor is connected to the main micro processor byway of a signal channel. The respective external temperature can then also be taken into accountwhen calculating the actual desired value. This can particularly be employed for correcting the Pband error in thermostatic valves.

Advantageously, the control element is a switching element which can be intermittently switched to the conductive state by the control apparatus. It may, for example, be a simple switching transistor.

In particular, the control apparatus may operate the switching element at a predetermined switching frequency but for variable switching-on periods. The control apparatus need then only control the variable switching off instant.

It is of particular advantage if the feed lines supplying the electric power also connect the main microprocessor to the control apparatuses and at the same time form data conduits. The cost of conduits and laying them will then be extremely low. In the simplest case, it is sufficient for a two conductor system to interconnect the control apparatuses and to conneck the latter to the main microprocessor.

In a preferred embodiment, the control apparat usesareformed bysubsidiarymicroprocessors.

These can readily convert simple command data to the corresponding switching times orthe like.

Further, it isfavourable for auxiliary control appar atusesforoperating units each having an on-offfunction to be connected to the main microprocessor by way ofthe two conductor system and likewise to be operable by its output data comprising an address and a command.The main microprocessorcanthen also switch pumps, fans and otherworking equip ment on and off at the propertimes, operation taking place with a similar data structure asforthethermo- stats.

A particularly recommended apparatus is characterised by a full-wave rectifier, a coding apparatus which impresses the output data ofthe main microprocessor bit by bit of the rectified alternating voltage in the region of its zero positions as voltage gaps with two different widths, and decoding apparatus associated with each control apparatus for detecting the voltage gaps and their widths and deriving the respective bit therefrom. The voltage gaps can be readily produced, for example by a switching element, and can be readily detected. Since they are disposed in the region of the zero positions, they do not affect the supplied electric power.

Methods and means of regulating roomtem- peratu re will now be described, with reference to the accompanying drawings, in which: Figure lisa schematic block diagram of equipment according to the invention; Figure2shows the thermostat attachment of a valve and associated control apparatus; Figure 3 is a diagram illustrating the intermittent supply of electric power; Figure 4 is a time diagram showing the change in the actual desired value against day-time desired valueTS upon rapid heating; Figure5is a time diagram showing the change in the actual desired value against day-time desired value during comfort heating in the evening;; Figure 6shows plotted against the external temperature Tithe change in actual desired value relat ive to the day-time desired valueTS for correcting proportionality error; Figure 7is a day-time diagram of a curve for a desired value program showing the departure ofthe actual desired value from the inherent desired value ES of the thermostat; Figure 8 is a time diagram showing an electricvol- tage U1 with added voltage gaps; and Figure 9 is a modification of the Figure 1 equipment.

Referring to the drawings, Figure 1 shows a main microprocessor 1 which is arranged at a central location Z and provided with a desired value program store 2. With the aid ofthe setting knobs 3, programs can be stored forthe zones l, ll and Ill of a hot water heating installation, particularly times, magnitudes and rate of change of the alterations. Further, the main microprocessor 1 is connected to an external temperature sensor 4. The inputs 5 are for the supply ofothervalues, for exa m ple, i nte rna I tem peratu res, wind speed, position of the sun and such like. The main microprocessor 1 has a plurality of outputs 6 through which different parts of the installation can be operated, for example, circulating pumps, a priority switch for hot water, rapid heating of the boiler, night-time illumination and such like.

For the regulation of interest here, it is the output 7 that is important. Through it, output data D is delivered to a coding apparatus 8. The output data comprises at least one address for the individual zones I, II and Ill and a command which represents an electrical power magnitude. Generally, however, the output data will comprise additional information,for example synchronisation signals, temperature information and such like. We are here concerned with digital output data which is superimposed in the coding apparatus 8 on a current I flowing in the two cables 9 and 10 of a two conductor system 11.Afull- wave rectifier 12 is connected to a source of alternating voltage U so that a rectified alternating current corresponding to Figure 8 flows in the two conductor system 11.The coding apparatus 8 comprises a switching element which (a) has no influence at all on the zero regions of the half voltage waves or (b) provides the zero regions with a broad gap in the current/voltage or (c) provides them with a narrow gap in the current/voltage. The broad current/voltage gap can for example correspond to the value logic 1 and the narrow current/voltage gap to the value logic 0.

The hotwater heating installation comprises a plurality ofthermostatic valves 13 which are is posed in a plurality of zones l, ll and III of a houseto be heated. Generally,therewould be more than the illustrated number of zones, for example eight. In the illustrated example, each zone corresponds to one room and therefore contains only one thermostatic valve. It is also possible, however, to take a plurality of rooms in which the actual desired value is to be controlledsimilarlyandtocombinethem into one zone with a plurality of thermostatic valves. The thermostatic valve 13 comprises a housing 14 and a thermostat attachment 15.The operating element located within this attachment is connected byway of a capillarytube 16to atemperature sensor 17 disposed in a housing 18. If,forexample,thesensor17 comprises a liquid-vapourfilling,thetemperature- dependent vapour pressure is effective in the operating element of the attachment and the valve assumes a position of equilibrium because a desired value spring acts oppositely to the operating element. The attachment has a knob 19 with the aid of which the inherent desired value ES of the thermostatic valve can be changed by, for example, adjusting the desks ired value spring. If the sensor 17 has a liquid filling, the knob 19 can be used to changethe position ofthe operating element in the attachment.

Applied to the sensor 17 there is an electric heating resistor 20 which can be fed by way of the two conductor system 11 with a current derived from the half-wave voltage U1 of Figure 8 when a control element in the form of a switching element 21 ,forex- ample, a switching transistor, has been broughtto the conductive state. Operation is by way of a control apparatus in the form of a subsidiary microprocessor 22 associated with a decoding apparatus 23 which may also form part of this microprocessor 22. The decoding apparatus 23 scans the zero regions of the half-wave voltage Ur, determines the logical bits coded therein and stores those values which appertain tothe address ofthezone in question. By reason of information received appertaining to this section, the switching element21 is broughtto the conduct- ive state. The switching-off time is controlled depending on time on the basis of the stored command data, as is shown in Figure 3. The individual blocks correspond to a plurality of half-waves. The switching-on pointisfixed bythecycleperiod offifteensec onds. It will be seen that the duration ofthe switched- on period decreases in the order ofthe blocks d, e, f and g so that in this way heating ofthe sensor 17 is variable bythe heating resistor 20.

The housing 18 accommodates the stated com ponents 17, 2G, 21, 22 and 23.

The inherent desired value ES of the thermostatic valve that would obtain if the heating resistor were not effective has a highervaluethan desired by the user in the course of a normal day. Figure 7 shows thatthe inherent desired value mayfor example be 23"C whereas the day-lirne desired value is only supposed to amount to 21C. This reduction by 2'C is achieved with the aid of the heating resistor 20. The day-time desired value TS therefore results from two components, the inherent desired value SE and the electric power supplied to the heating resistor 20. If the electric power is changed, the reduction in relation to the inherent desired value is altered.If one changes the inherent desired value, the entire desired value program is displaced.

Since heating power is already required to achieve the day-time desired value, the actual desired value can not only be decreased in relation to the day-time desired value but also increased. For example, if heating powercorresponding to the blocke in Figure 3 is required to reach the day-time desired value, the actual desired value can be raised by reducing the heating power according to the blocks f and g.

A regulating characteristioworking with such an increase is evident from Figure 4. Starting from the day-time desired value TS, this shows that the actual desired value is suddenly increased by 1 .5 C and later returns gradually to the day-time desired value byway of a ramp function. The increase in desired value takes place half an hour before use is expected to commence (0 hour) and remainsunchangedfora further hour after commencement of use. The desired value is then returned linearly for a further hour. The users who arrive find the room to be comfortable. The coldness potential ofthe walls that have cooled off during the night is eliminated as rapidly as possible. The gradual return ofthe temperature is practically unnoticed by the user.

The time diagram of Figure 5 illustrates a regulation for comfort. In the evening, the actual desired value is gradually raised by 1 .5"C above the day-time desired value TS over a course of three hours, in this case between 7 p.m. and 10 p.m.

Subsequently,this increased desired value remains unchanged until, say, midnight The rise takes into accountthat a person sitting quietly finds a somewhat higher temperature to be comfortable than a person who is working and moving about.

Thistemperature increase is eliminated when the user retires to go to sleep.

Figure 6 shows how the desired value temperature TS can be varied by 1"C in relation to the external temperature T0 for correction purposes. Below an external temperature of -9 C,there is zero correction. Above + 90C, the correction is 1 "C.

Between these two external temperatures, the correcting temperature rises steadily. In this way, one compensates for the P-band error of the thermostatic valves.

Figure 7 shows a curve P representing the course ofthe program from Oto 24 hours. The day-time desired value is about 2"C below the inherent desired value ofthe thermostat. This takes into account a basic reduction of 1.5 C and a P-band error correction of 0.5 C. At night, a night-time reduction of 9"C in relation to the inherent desired value takes place between midnight and 4 a.m. to reach, say, 15"C. This is achieved by strongly heating the sensor 17. At 4a.m., an increase takes place to the day-time desired value and at 6.30 a.m. there is a further rise by 1.5 C because the first users of the room are to be expected by 7 a.m. The section h of curve Ptherefore corresponds to Figure 4.The normal day-time desired value TS is setforfrom 9 a.m. to 7 p.m.There is then a gradual r-ise by 1.5"C to increasethefeeling of comfort. The portion g of curve P therefore corresponds to Figure 5. There is therefore a cold phase Al, a heating phase A2, a warm phase A3 and a cooling phase A4. The length of the heating-up phase A2 depends on the extent two which the room had previously cooled off and what heat-storing properties the room and radiators have.

Figure 7 shows, by means of chain-dotted lines forming a branch P1 ofthe graph, how the desired value may be constantly increased over a ramp function during the heating-up phase A2.

Although all ramp functions are illustrated as straight lines, they may be composed of small steps.

The entire system is preferably operated at mains frequency and with a reduced voltage of, say, 24V. In one embodiment, the main microprocessor 1 operated so that it transmitted new output data to the individual subsidiary microprocessors 22 every three seconds. These data are stored and cancelled upon the arrival of new data. Accordingly, onlythose data are employed that had last been transmitted before expiry of the 15 second cycle.

The main microprocessor may also detect the mains voltage and, in relation to any fluctuations in the mains voltage, alter the length ofthecurrent blocks (Figure 3). For example, the mean value of voltage U is measured and fed to the main microprocessor 1 by way of an input 5.

Figure 1 also diagrammatically indicates howa monitoring device 24 measures the voltage drop during current supply at a resistor 25 in series with the heating resistor 20 and, upon a departure ofthe measured value from a predetermined range, delivers an error or alarm signal to operate a light signal generator 26. The user ofthe room can therefore notice the error if the heating resistor happens two be short-circuited or there is an interruption in the current.

Figure 9 shows that, in addition to the control apparatuses 22 for the thermostatic valves 15 of radiators 27, the two conductor system 11 could be connected to auxiliary control apparatuses 28to 34 for additional operating units which each have an on-offfunction. Merely by way of example, these auxiliary control apparatuses have the following function: The auxiliary control apparatus 28 operates a frost safety device. The auxiliary control apparatus 29 switches on the fuel and/orairsupply for a heating boiler 35. The auxiliary control apparatus 30 switches on a circulating pump 36 for heating a hotwater supply heater 37. The auxiliary control apparatuses 31 so operate the mixing valve 39 byway of a control device 38 that the boiler temperature increases rapidly.The auxiliary control apparatus 32 operates a circulating pump40 in the forward direction. The auxiliary control apparatus 33 may serve to switch illumination on. The auxiliary apparatus 34 serves to switch on a safety device. The auxiliary control apparatuses are likewise each operated by an address in the output data D and switched by a command likewise contained in the output data. In a practical example of heating installation, only the auxiliary control apparatuses required for the purposes in question need be provided. The main microprocessor 1 at the central location Z is able to operate all auxiliary control apparatuses in addition to the control apparatuses 22 for the thermostatic valves 15 butthese possibilities do not have to be fully utilised.

It need not be apparent from external appearances thatthe thermostat is set to a higher inherent desired value than the day-time desired value. It is only necessary to adjustthe setting scale at the thermostat by the nominal 2"C reduction brought about by the heating.

Claims (32)

1. A method of regulating room temperature in which a room is supplied with heat under the control of a thermostat and the desired temperature setting is effectively reduced by supplying electrical power to a heating resistor associated with a sensor ofthe thermostat, characterized in that the thermostat is settoatemperaturevalue higherthan the desired day-time temperature in the room and the heating resistor is supplied with electrical power during the day so that the desired day-time temperature ofthe room corresponds to the thermostat setting as effectively reduced by the electrical heating of the thermostat sensor, and in that to provide a higher regulated temperature in the room the electrical power supplied to the heating resistor is reduced.

2. A method as claimed in claim 1, wherein the thermostat comprises a thermostatic valve in a hot water heating installation.

3. A method as claimed in claim 1 or claim 2, whereinthethermostatis set to a value in the range from 1 to 3"C inclusive higherthan the desired day-time temperature.

4. A method as claimed in claim 3, wherein the thermostat is setto a temperature approximately 2 C higherthan the desired day-timetemperature.

5. A method as claimed in any preceding claim, including changing the electrical power supplied to the heating resistor gradually when changing from one desired room temperature value to another.

6. A method as claimed in any preceding claim, including raising the desired room temperature gradually during a heating-up phase.

7. A method as claimed in any preceding claim, including raising the desired room temperature sometime in advance ofthetimeatwhich use of the room is expected and, some time afterthattime at which use ofthe room was expected, gradually returning to the day-time value.

8. A method according to any preceding claim, including gradually increasing the desired room temperature during the hours ofthe evening up to a highervaluewhich is then held constant.

9. A method as claimed in any preceding claim, including modifying the desired room temperature in relation to external temperature in order to correct proportionality error in the thermostat.

10. A method of claimed in any preceding claim, wherein the current supply to the heating resistor is intermittent and the desired room temperature is changed by changing the mark-space ratio ofthe current.

11. A method as claimed in any preceding claim, wherein while current is being fed, the voltage drop at a resistortraversed by the current is monitored and an error signal generated if the voltage drop falls below a lower limiting value or rises above an upper limiting value.

12. Amethodofregulating room temperature substantially as herein described with reference to, and as illustrated by, Figures 1 to 8 of the accompanying drawings.

13. A method as claimed in claim 12 but modified substantially as herein described with reference to, and as illustrated by, Figure 9 ofthe accompanying drawings.

14. Meansfor regulating the temperature ofa room comprising a thermostat to control the supply of heat to the room and means to effectively reduce the desired temperature setting comprising means to supply electrical power to a heating resistor associated with a sensor of the thermostat, characterized in that control means are provided and arranged to supply the heating resistorwith electrical power during the day so that, when the thermostat is set to a temperature value higherthan the desired day-time temperature in the room,the desired day4imetemperature of the room corresponds to the thermostat setting as effectively reduced by the electrical heating of the thermostat sensor, and characterized by means to provide a higher regulated temperature in the room by reducing the electrical power supplied to the heating resistor.

15. Means as claimed in claim 14, wherein the control means comprises a microprocessor having a digital programstorefordesiredvalues.

16. Means as claimed in claim 15, wherein the microprocessor is arranged to control a plurality of thermostats in different location zones, each thermostat having a respective heating resistor, and the microprocessor is arranged to generate data signals representing the zone in which a thermostat lies and the electrical power to be supplied to the associated heating resistor.

17. Acentral heating controllerforcontrolling a plurality of thermostats, each adjustable to a set value and having a respective sensor associated with a respective heating resistor, the central heating controller comprising a microprocessor provided with a digital store for storing a desired heating prog ram, wherein the microprocessor is arranged to transmit output data signals each comprising the address of a zone at which a thermostat, or plurality of thermostats to be controlled similarly are located, and a command representing the electric powerto be fed to the heating resistors, the arrangement being such thatthe heat command is on the basis that the thermostat in question is setto a temperature higher than the desired day-time temperature in the room and the heating resistor in question isto be supplied with electrical power during the day so thatthe desired day-time temperature of the room corresponds to the thermostat setting as effectively reduced by the electrical heating of the thermostat sensor, and such as to provide a higher regulated temperature in the room by reducing the electrical power supplied to the heating resistor in question.

18. Acontrolleras claimed in claim 17,wherein the microprocessor is provided with a signal channel for receiving signals from an external temperature sensor.

19. Acontrolleras claimed in claim 17 orclaim 18, including a data signal coding apparatus to code the zone address and command signals on a rectified alternating voltage by creating first and second gap lengths inthezero region ofthe rectified alternating voltage to represent logic 1 and logic 0 signals respectively.

20. A heating control system comprising a controller as claimed in any one of claims 17 to 19, and a plurality of control units each to control a thermostat or group of thermostats in a respective zone, wherein each control unit is arranged to recognize its own zone address in the data from the microprocessor and to control electrical heating power to the heating resistor(s) in question in accordance with the command associated with that zone address.

21. A heating control system as claimed in claim 20, wherein each control unit comprises a respective switching element to provide an ON/OFF control of electrical heating power to the heating resistor(s) in question.

22. A heating control system as claimed in claim 21 ,wherein the switching element is arranged to be operated on the basis of a predetermined switching frequency butforvariable ON durations.

23. A heating control system as claimed in any one of claims 20 to 22, wherein power supply lines for providing power to the heating resistors also serve as a data channel connecting the microprocessorto the control units.

24. A heating control system as claimed in claim 23, wherein the power supply lines are constituted buy a conductor-pairwiring system.

25. A heating control system as claimed in any one of claims 20 to 24, wherein each control unit comprises a respective microprocessor.

26. A heating control system as claimed in any one of claims 20 to 25, wherein one or more auxiliary control means are provided and are arranged to respond to zone address and command signals from the microprocessor for controlling one or more respective ON/OFF devices to be used in the system.

27. A controller or heating control system as claimed in any one of claims 17 to 26, wherein the arrangement is such as to carry out a method claimed in any one of claims 5,6,7 and 8.

28. A heating control system substantially as herein described with reference to, and as illustrated by, Figure 1 of the accompanying drawings.

29. A heating control system as claimed in claim 28, wherein the coding of data and supply of power is substantially as herein described with reference to, and as illustrated by, Figures 3 and 8 ofthe accompanying drawings.

30. A heating control system as claimed in claim 28 or claim 29, wherein the system is arranged to operate substantially as herein described with reference to, and as illustrated by, any one or more of Figures 4,5,6 and 7 ofthe accompanying drawings.

31. A heating control system as claimed in any one of claims 28 to 30 but modified substantially as herein described with reference to, and as illustrated by, Figure 9 ofthe accompanying drawings.

32. Acentral heating system comprising a plurality of hot-water radiators, a heating control system as claimed in any one of claims 20 to 31,and a plurality ofthermostatic hot-water radiator valves controlled by the control system.