GB2081471A - Method and arrangement for controlling room heating - Google Patents

Abstract

Room heating control is effective to monitor the cooling curve during a period of non-utilisation of the room and, in response thereto, to commence room heating again at an instant appropriate for ensuring that the room will reach the required temperature again substantially at the commencement of the next utilisation period. The actual temperature theta of the room during cooling is subtracted from the utilisation temperature theta N and the difference is integrated and the integral used to determine, from integral values and corresponding heating- up times which are stored in a memory, the time required to heat the room to temperature theta N, the room heater being switched on when the expected heating-up time corresponds with the time remaining before commencement of the next utilisation period. The system is designed to improve its performance with repeated use. <IMAGE>

Description

SPECIFICATION Method and arrangement for controlling a room heating The invention relates to a method for controlling a room heating for heating a room which during predetermined utilisation times is held by regulation within predetermined tolerance limits at a desired temperature and the room heating is switched off at the end of each utilisation time, a signal indicating the actual temperature of the room being continuously or cyclically furnished, and an arrangement for carrying out the method.

In many buildings, such as schools, administration buildings, offices, etc., it is necessary to keep a large number of rooms at a defined desired temperature for predetermined utilisation periods whereas outside the utilisation periods the room heating is to be switched off to save energy, except for maintaining a predetermined minimum temperature, for example to prevent freezing. It is known and usual to provide a temperature control for maintaining the desired temperature during the utilisation times, said temperature control switching the room heating on and off on the basis of an actual value signal furnished by a room temperature sensor and a desired value signal set at a desired value generator in such a manner that on the average the desired value temperature is maintained.The temperature control may be common to several or all rooms and accordingly made multi-channel or for cyclic operation. The utilisation times are set at a time switch and in accordance with the requirements this may be set with a daily, weekly or annual programme. If the utilisation times for several rooms or room groups are different a plurality of time switches is provided or a multi-channel time switch.

In heating systems of this type it is necessary for the room heatings to be switched on before the start of a utilisation period so that at the start of the utilisation time in each room the desired temperature has substantially been reached. The heating-up times necessary from this purpose are of course different from room to room and also vary in dependence upon the ambient conditions, in particular the outer temperature. A simple method frequently employed is to switch the room heatings of all rooms on simultaneously at a defined time soon enough for the room with the longest heating-up time to reach the desired temperature before the start of the utilisation time even under the most unfavourable conditions.

This method obviously results in a considerable wasting of energy.

The problem underlying the invention is to provide a method with which the room heating of each room can be individually controlled in such a manner that the desired temperature is achieved just at the start of each utilising time even under fluctuating conditions, and an arrangement for carrying out said method.

In accordance with the invention, there is provided method of room heating control for a room which during predetermined utilisation times is held by regulation within predetermined tolerance limits at a desired temperature and the room heating is switched off at the end of each utilisation time, a signal indicating the actual temperature of the room being continuously or cyclically furnished, wherein during the cooling of the room with the heating system switched off after the end of each utilisation time the cooling curve defined by the variation of the actual temperature as a function of the time is determined, a preheating time in which after switching on the room heating the desired temperature is achieved being associated with each cooling curve, and wherein the room heating is switched on as soon as the preheating time associated with the cooling curve reaches or exceeds the time interval remaining before the start of the next utilisation time.

In the method according to the invention the switch-on instant of the room heating before the start of each utilisation period is determined on the basis of the cooling behaviour in the preceding non-utilisation period. All necessary information for determining the switch-on instant is thus obtained solely from the time variation of the room temperature which is detected by the room temperature sensor present in any case for the temperature control during the utilisation times. The dooling curve depends on parameters which are also decisive for the necessary heating-up time; these are firstly the specific parameters of the room, e.g. thermal capacity and thermal insulation, and secondly the variable parameters, in particular the outer temperature.

As long as the other parameters determining the heating-up, such as the heating power, may be considered constant, there may thus be associated with each cooling curve of a room a pre-heating time ending at the start of the next utilisation time in which the desired temperature is just reached.

The method referred to above requires only that the parameters of the heating-up can be reproduced for each cooling curve; they may however be different from cooling curve to cooling curve. The method is therefore also applicable to heating systems in which the heating power (e.g. the preliminary temperature of a hot-water heating) is varied in dependence upon the outer temperature. Since each cooling curve is associated with a predetermined outer temperature, in this case as well as for a certain cooling curve the same heating power and thus the same heating-up time is obtained.

A particularly advantageous embodiment of the method according to the invention is that during the cooling of the room with the heating system switched off after the end of each utilisation time the difference between the desired temperature and the actual temperature is formed cyclically and by integration of the difference values the cooling area reached up to each integration instant determined, that with each value of the cooling area a preheating time is associated in which after switching on of the room heating the desired temperature is reached, and that the room heating is switched on as soon as the preheating time associated with the last value of the cooling area determined reaches or exceeds the time interval remaining before the start of the next utilisation time.

The use of the cooling area obtained by integration of the temperature difference as parameter for the cooling behaviour has several advantages. Firstly, the cooling area represents a magnitude particularly suitable for determination of the switch-on instant because it is proportional to the loss energy during cooling. Furthermore, the switch-on instant can be determined on the basis of a single time-dependent quantity which in turn depends in clear manner on the quantities characteristic of the cooling behaviour, i.e. time and temperature. Finally, the integration compensates brief disturbing influences and fluc tuations.

For example, the relationship between the cooling behaviour and the necessary heatingup times could be determined for each room experimentally. This procedure would however be rather troublesome and tedious. A particular advantage of the method according to the invention resides however in that it permits an independent determination of the preheating times associated with the cooling curves of a room, a continuous optimisation of the values determined and an adaptation to slowly changing conditions.This is done according to an advantageous further development of the invention in that for each value of the cooling area an associated heating-up time is determined experimentally by measuring the time for the switching on of the room heating until reaching the desired temperature, and that the measured heating-up time is stored as the preheating time associated with the value of the cooling area.

Admittedly, with this embodiment of the method in an initial stage some deviations from optimum operation arise so that the desired temperature is achieved slightly before or after the start of the utilisation time. These deviations are however far smaller than with the known methods operating with fixed maximum heating-up times and they rapidly become smaller with increasing number of the measured values. With constant cooling and heating-up conditions an optimised state is reached after a relatively short time. With long-time trend shifts a gradual adaptation takes place.

An arrangement for carrying out the preferred embodiment of the method comprising a room sensor which furnishes an actual value signal indicating the actual temperature, a desired value generator which furnishes a desired value signal indicating the desired temperature, timing means at which the utilisation times may be set, and a temperature control which receives the actual value signal and the desired value signal and during the utilisation times furnishes an adjustment signal controlling the switching on and off of the room heating, is characterised according to the invention by a subtraction circuit which receives the desired value signal and the actual value signal and furnishes a difference signal representing the difference between the desired value and actual value, an integrator which receives the difference signal and furnishes an integration signal representing the integral of the difference signal, a memory in which for various values of the integration signal associated values of preheating times are stored, and by a circuit arrangement which for each value of the integration signal takes the associated value of the preheating time from the memory, compares said value with the time interval remaining before the start of the next utilisation time and initiates the switching on of the room heating if said value is equal to or more than said time interval.

For automatic determination and optimising of the stored values the arrangement preferably contains a timer which is set in operation when the room heating is switched on, a comparator which compares the desired value signal and the actual value signal and on determination of identity initiates the transfer of the time value determined in the timer to the memory, and a control means which effects storing of the time value in the memory at an address which is associated with the value of the integration signal furnished by the integrator at the instant of switching on of the room heating.

Further features and advantages of the invention will be apparent from the following description of an example of embodiment which is illustrated in the drawings, wherein: Figure 1 is a time diagram of the temperature behaviour of a room for explaining the principle on which the invention is based, Figure 2 is a block diagram of an arranged ment for carrying out the method according to the invention and Figure 3 are diagrams explaining the mode of operation of to 8 the arrangement of Fig.

2.

The principle underlying the invention will first be explained with the aid of the diagram of Fig. 1. This diagram shows the variation of the temperature of a room during the cooling phase and the subsequent heating-up phase in a non-utilisation period.

To avoid errors, in the drawings and in the following description all instants are designated with the letter "t" and all time intervals with the letter "T".

In Fig. 1 the utilisation interval preceding the non-utilisation period ends at the instant to. The next utilisation interval starts at the instant tN. During the utilisation intervals a conventional temperature control means ensures that the room temperature is held at a constant utilisation desired value aN- The non-utilisation period starts at the instant to and ends at the instant tN. At the instant to the room heating is switched off by a time switch means. The temperature of the room then drops substantially in accordance with an exponential function which depends mainly on the thermal capacity of the room, the heat transfer resistance and the outer temperature. If it is assumed that the thermal capacity and the heat transfer resistance remain substantially constant, the rate of cooling depends primarily on the outer temperature.Fig. 1 shows as example a cooling curve K, corresponding to an average outer temperature, a cooling curve K2 for a higher outer temperature and a cooling curve K3 for a very low outer temperature.

In all cases the room heating is to be switched on during the non-utilisation period at such an instant that at the instant tN of the start of the next utilisation interval the desired temperature aN is reached. Early switching on is undesirable because heating energy would be wasted and later switching on is undesirable because the room would be too cold at the start of the utilisation interval.

The switch-on instant must be made different in dependence upon the conditions obtaining. As example it is assumed in Fig. 1 that with a cooling according to the curve K, the switching on of the room heating must take place at an instant tsi which lies at an interval Tv, before the instant tN. After the switching on of the room heating the temperature increases in accordance with a curve H, which depends on various parameters, in particular the power of the room heating, but also on parameters decisive for the cooling as well, such as thermal capacity, heat transfer resistance and outer temperature, since the room heating must cover the heat losses to the outside during the heating up as well. For simplification, it is assumed that the heatingup curve H, is linear, which is however not the case in reality.

Since the cooling curve K, already expresses all the parameters which are equally decisive for the cooling and the heating up, such as thermal capacity, heat transfer resistance and outer temperature, with a constant heating power it may be assumed that the desired temperature 0N with relatively high accuracy is always achieved precisely at the instant tN if the switching on always takes place at an instant tsi corresponding to the same point S, of the curve K,.At the point S, the room temperature has dropped during the cooling time TK1 from the desired value 19N by the amount AS, to the amount fl,. The point S, of the curve K, is thus clearly characterised by the cooling duration TK1 and the temperature difference i\S,. At the switch-on instant tsi the preheating time Tv, begins and ends at the instant tN.

If the cooling takes place in accordance with the curve K2 the switching on must take place at an instant ts2 which is substantially later than the instant tsi and thus corresponds to a substantially shorter preheating time Tv2.

For the heating up according to the curve H2 takes place more rapidly for two reasons: firstly, the temperature difference A 2 is smaller and secondly the temperature rise is steeper because the outer temperature is higher and accordingly the heat losses are lower. The switch-on instant ts2 corresponds to a point S2 on the curve K2 which is clearly defined by the cooling time TK2 and the temperature difference reached A192 Correspondingly, for the cooling according to the curve K3 the switching on must take place at an instant ts3 so that during the heating up according to the curve H3 the desired temperature 19N is reached precisely at the instant tN.The necessary preheating time Tv3 is substantially greater than the preheating time Tv, associated with the curve K, becuase firstly the temperature difference A03 is greater and secondly the heating up takes place more slowly because of the lower outer temperature. The corresponding point S3 on the curve K3 is again clearly defined by the temperature difference i\83 and the associated cooling time TK3.

After from the cooling curves K1, K2, K3 illustrated in Fig. 1, of course, an infinite number of other cooling curves is of course possible. However, as long as constant conditions can be assumed a preheating time Tvi, TV2, ..... . at the end of which the desired temperature is again just reached is clearly associated with each cooling curve. The curve points S" S2, S3 of all the cooling curves associated with the corresponding switch-on instants tsi, tis2, ts3. . . lie on a switching time curve S. To ensure that the room temperature reaches the desired value 0N precisely at the instant tN the room heating must be switched on just at the instant at which the respective cooling curve K1, K2... intersects the switching time curve S.

However, the practical realisation of this principle involves considerable difficulties.

Firstly, for each room a large number of cooling curves K1, K2... and the associated switching time curve S must be plotted. Furthermore, for each cooling operation it must be determined which cooling curve the cooling follows and the intersection of the respec tive cooling curve with the switching time curve S must then be determined.

In Fig. 2 of the application an arrangement is illustrated which by constant adaptation for each room automatically determines the preheating time associated with the various cooling curves and initiates the switching on of the room heating at the respective optimum instant.

Before the construction and mode of operation of the arrangement of Fig. 2 is described in detail the principle on which the mode of operation of this arrangement is based will be explained with the aid of Figs. 3, 4 and 5. As criterion for the cooling behaviour of the room the area obtained by integration of the temperature difference AO over the cooling time is used. Fig. 3 shows in the same manner as Fig. 1 again the three cooling curves K1, K2, K3, the preheating times Tv,, TV2, Tv3 associated with said cooling curves and the corresponding heating-up curves H1, H2, H3, as a result of which the desired temperature 0N is reached in each case at the instant tN.

Furthermore, the cooling areas A,, A2, A3 associated with the three cooling curves K,, K2, K3 are represented by different hatchings.

The cooling area A, corresponding to the curve K, is obtained by continuously or cyclically measuring the room temperature, calculating the temperature difference AO with respect to the desired temperature 0N and integrating this temperature difference from the instant to to the switching instant tsi.

Correspondingly, for the curve K2 the cooling area A2 is obtained by integration of the temperature difference AO between the instants to and ts2 and for the curve K3 the cooling area A3 by integration of AS between the instants to and tis3. Each of these areas is proportional to the energy which has been lost during the cooling phase.

Fig. 4 shows to the same time scale as Fig.

3 the increase of the areas corresponding to the curves K1, K2, K3 as a function of the time by the curves AKi, AK2, AK3. Furthermore the switching time curve SA is shown which in the A/t plane of the switching time curve S corresponds to the O/t plane. The curves AKi, AK2, AK3 intersect the switching time curve SA at the points SA1, SA2, SA3 which correspond to the area values A1, A2 and A3 and the switching instants tsi, ts2 and ts3 respectively.

As apparent from the diagram of Fig. 4 by the switching time curve SA a preheating time Tv is clearly associated with each area value A. This association is illustrated in the diagram of Fig. 5 which shows the preheating time Tv as a function of the area A. The curve SA passes through the origin of the coordinate system because the area zero corresponds to the preheating time zero; for the area zero means that the room has not cooled during the non-utilisation period. In this case, no preheating is necessary to reach the desired temperature.

If it is first assumed that the association illustrated in Fig. 5 between the preheating time Tv and the area A is already known, the arrangement of Fig. 2 operates in the following manner: It determines continuously the temperature difference AS and calculates by time integration of said temperature difference the area A reached up to the integration instant. It compares the preheating time Tv associated with the area A calculated, and resulting from the durve SA of Fig. 5, with the time interval remaining up to the instant tN.

As soon as the associated preheating time Tv reaches or exceeds the remaining time interval the arrangement initiates the switching on of the room heating.

The arrangement of Fig. 2 is designed for the control of room heating and temperature regulation of any desired number of rooms. It employs the means generally provided for temperature control for holding the room temperature at the desired value 8N during the utilisation times. These parts are represented above the dot-dash line. Provided in each room is a temperature sensor 1 a, 1 b. .1 n which furnishes an electrical signal expressing the room temperature. The temperature sensors 1 a, ... 1 n are connected to a cyclically operating measured value pickup means 2 which is controlled by a clock means 3.The measured value pickup means 2 samples cyclically at predetermined intervals the temperature signals furnished by the temperature sensors 1 a, 1b... 1 n. The sampling cycle may be relatively long because the temperatures change only slowly. For example, a cycle time of ten minutes is sufficient so that even with a large number of rooms adequate time is available for detecting and evaluating each temperature signal.

The utilisation times are set at a time switch 4 which furnishes signals indicating the instants to and tN (Fig. 1) of the start and end of the utilisation times.

Finally, a temperature regulator 5 is provided which during the utilisation times furnishes at outputs 5a, 5b...5n to the various rooms adjustment signals which control the switching on and off of the room heating means so that the room temperature is held on the average at the desired temperature 19N The desired value is set at a desired value generator 6. The temperature control 5 may also operate cyclically and is then also controlled by the clock means 3.

If different utilisation times and/or desired values are provided for various rooms a plumP ity of time switches 4 and desired value generators 6 may be provided, or the time switch 4 and the desired value generator 6 may be multi-channel.

The circuit components illustrated beneath the dot-dash line of Fig. 2 effect the switching on of each room heating corresponding to the method described above in each non-utilisation interval in such a manner that the desired temperature 0N is reached just at the instant tN of the start of the next utilisation time. For simplification, the mode of operation of the circuit will be described only for one room; for the remaining rooms the method proceeds in the same manner in the associated cycle times. The cyclic time-sharing operation of the circuits is also controlled by the clock means 3 as indicated by the output 3a.

The measured value pickup means 2 furnishes for the room number i an electrical signal which represents the instantaneous temperature at of the room detected by the temperature sensor 1 i and for simplicity is also denoted by Op Connected to the output of the measured value pickup means 2 is a subtraction circuit 7 which at the second input receives the signal furnished by the desired value generator 6 and representing the utilisation desired value SN. The subtraction circuit 7 thus furnishes at the output the signal 0N0i = hOj which represents the temperature drop shown in Fig. 1 after the switching off of the room heating during the non-utilisation period.

Connected to the output of the subtraction circuit 7 is the input of an integrator 8 which integrates the signal A0j with respect to the time and thus furnishes at the output a signal which represents the cooling area A, reached up to this integration instant. This signal is supplied to the input of an arithmetic unit 9.

Connected to the arithmetic unit 9 are two memories 10 and 11 which are driven by a common address circuit 1 2. It will first be assumed that the relationship represented in Fig. 5 by the curve SA between the preheating time Tv and the cooling area A has already been determined for each room. Stored in the memory 10 are the values occurring in practise of the cooling area A for each room with the desired fineness of the subdivision at predetermined addresses and in the memory 11 at the same addresses the associated values of the preheating time Tv are stored. The memories 10 and 11 thus contain at the same addresses value pairs of A and Tv corresponding to the curve SA of Fig. 5.The circuit components described hitherto of Fig. 2 operate in the following manner: At the instant to at the end of the utilisation time the time switch 4 furnishes a signal which effects that the control 5 furnishes at the output 5i associated with the respective room an adjustment signal by which the room heating of the respective room is disconnected. The room thus cools along one of the curves K (Fig. 3). The subtraction circuit 7 furnishes cyclically the temperature difference AOj and the integrator 8 furnishes cyclically the signal Ai which at the respective instant represents the value so far reached of the cooling area corresponding to the respective curve of Fig. 4.The arithmetic unit 9 compares the instantaneous value of the signal A with the values stored in the memory 10 and determines the address of the stored area value coming closest to the instantaneous value. Via the address circuit 1 2 it takes from the memory 11 the value of the preheating time Tv stored at the same address. The value of Tv taken from the memory 11 is compared in the arithmetic unit 9 with the residual time TR remaining until the instant tN of the start of the utilisation time; this residual time is calculated by the arithmetic unit 9 from the actual time and the instant tN set in the time switch 4. The residual time TR becomes of course continuously smaller whilst the preheating time Tv increases corresponding to the curve SA of Fig. 5 with increasing area A.

As long as the value of the preheating time Tv taken from the memory 11 is smaller than the residual time TR the operation repeats itself in the manner outlined. As soon as the arithmetic unit 9 establishes that the preheating time Tv taken from the memory 11 is equal to the residual time TR or exceeds said residual time TR it furnishes at the output 9a for the control 5 a signal which switches on the temperature control for the respective room number i. Since the temperature of this room is beneath the desired value 0N the switching on of the control means that the room heating is switched on and remains switched on until the desired value 0N is reached. Because of the relationships explained with the aid of Figs. 3, 4 and 5 the desired value 0N is reached just at the instant tN.

As already mentioned the mode of operation outlined above assumes that the value pairs of A and Tv corresponding to the switching time curve SA of Fig. 5 are already stored in the memories 10 and 11 for each room.

Admittedly, this switching time curve SA could be determined and stored for each room but this would involve considerable expenditure.

The arrangement of Fig. 2 is therefore additionally provided with means which for each room automatically determine the value pairs of A and Tv to be stored and continuously improve them by adaptation until all the final value pairs are stored in the memories 10 and 11.

For this purpose the arrargement of Fig. 2 comprises a comparator 1 3 and a timer 14.

The timer 14 has a control input 1 4a which is connected to the arithmetic unit 9 so that the timer 14 can be set in operation and stopped by the arithmetic unit. The output of the timer 14 is connected to the write-in input memory 11 via a gate circuit 1 5 controlled by the output of the comparator 1 3. The opening of the gate circuit 1 5 by the comparator 13 can be permitted or blocked by the arithmetic unit 9 at an additional control input 15a. Furthermore, the output of the integrator 8 is con nected via a gate circuit 1 6 controlled by the arithmetic unit 9 to the write-in input of the memory 10.

The comparator 1 3 receives at its input the signal flj representing the actual temperature from the output of the measured value pickup means 2 and at the other input the signal 0N representing the desired value from the desired value generator 6; it furnishes at the output a signal which opens the gate circuit 1 5 as soon as the actual value signal 8, is reached or exceeds the desired value signal 6 N ( N)- The mode of operation of this amplified arrangement will be explained with the aid of the diagrams of Figs. 6, 7 and 8.

It will be assumed that the system is newly installed and no values are available for the cooling behaviour of the rooms. The memories 10 and 11 are empty.

The diagram A of Fig. 6 shows the temperature curve of a room for the first operation of the arrangement. It is however assumed that during the preceding utilisation time a temperature control to the utilisation desired value ON has already been carried out.

At the instant to the time switch 4 switches the temperature control off. The room cools in accordance with a cooling curve K8. The integrator 8 determines continuously the increase of the cooling area A.

Since no comparison values for the preheating time Tv are available the arithmetic unit 9 initiates the switching on of the room heating via the control 5 at an instant tM which is so chosen that even under the most unfavourable conditions it is certain that the desired temperature diN is reached before the instant tN of the start of the next utilisation time. This corresponds to the procedure usual with known heating systems.

Furthermore, at the instant tM the arithmetic unit 9 opens the gate circuit 1 6 so that the value of the area A reached at the instant tM is stored at a predetermined address in the memory 10. Finally, at the instant tM the arithmetic unit 9 sets the timer 14 in operation.

The room is now heated up in accordance with the heating-up curve H8 of the diagram A. Since the instant tM corresponds to a maximum heating-up time under the most unfavourable conditions in a normal case the desired temperature an will be reached after a heating-up time THa at an instant t8 which lies a considerable error time tFa before the instant tN. At this instant the normal temperature regulation by the control 5 then starts.

Since at the instant t8 the actual temperature 8; reaches the desired temperature 0N the comparator 1 3 emits a signal which opens the gate circuit 1 5. The time value reached by the timer 14, representing exactly the heating-up time THa, is therefore entered into the memory 11 at the same address at which the associated area Aa is stored in the memory 10. The time value in the memory 11 thus represents the preheating time Tva which is associated with the area value A8 in the memory 10.

Corresponding to the previously outlined mode of operation of the arrangement of Fig.

2, for all future switching operations each stored preheating time Tv is calculated backwards from the instant tN. The diagram D of Fig. 6, which represents the area A as a function of the time t in the same manner as in the diagram of Fig. 4, shows that the point SAa corresponding to the value pair Aa Tva does not lie on the area curve A, corresponding to the cooling curve K8 but on a different area curve AKb. The stored value pair thus cannot be achieved when the cooling again takes place according to the same cooling curve Ka. The point S, also does not lie exactly on the switching time curve SA.

The diagram B of Fig. 6 shows what happens when the cooling of the room takes place according to the curve Kb on the area curve AKb of which the previously stored value pair A8, Tva lies. In accordance with the previously outlined normal mode of operation the arithmethic unit 9 establishes at the instant tsb that the integrated area has just reached the stored value Aa for which the associated pre heating time Tva stored in the memory 11 is equal to the residual time TR still remaining until the instant tN. It therefore initiates the switching on of the room heating at the instant tsb. Simultaneously, the arithmetic unit 9 again sets the timer 14 in operation.An opening of the gate circuit 16 can be dispensed with because the area value at the output of the integrator 8 is equal to the area value already in the memory 10.

The heating up of the room is now according to the curve Hb of the diagram B so that the desired temperature 0N is reached at an instant tb which once again is a certain error time TFb before the instant tN. For the heating up time THb is, for two reasons, shorter than the preheating time TVa: firstly, the temperature difference AOb at the switch-on instant t is smaller than the temperature difference 91.

at the instant tM of the diagram A and secondly the heating-up curve Hb is steeper than the heating-up curve H8 because the cooling curve Kb corresponds to a higher outer temperature. It is however apparent that the error time TFb is already considerably smaller than the error time TFa.

The error time TFb shows however that the previously stored preheating time Tva was not correct. The arithmetic unit 9 therefore permits the opening of the gate circuit 1 5 by the output signal of the comparator 13 when at the instant tb the signal Aj is equal to the desired value signal aN. Thus, at the instant t8 the time value THt, indicated by the timer 14 is introduced into the memory 11 at the same address at which previously the preheating time THa was stored whilst the previously stored value is erased. Thus, the preheating time TVb is now associated with the area Aa.

The diagram D shows that the point SAb corresponding to the new value pair A8, TVb no longer lies on the area curve AKb but on a new area curve AKe. The point SAb is already substantially closer to the switching time curve SA than the point SAa.

The diagram C of Fig. 6 shows the case where the cooling of the room follows the curve Kc on whose area curve AKC the last value pair A8, TVb is stored lies. The cooling area integrated by the integrator 8 thus reaches the value A8 at the instant tsc which lies at the time interval TVb before the instant tN. The arithmetic unit 9 initiates the switching on of the room heating at the instant ts, and sets the timer 14 in operation.The heating up takes place according to the curve Hc so that the desired temperature aN is reached at the instant to which once again lies before the instant tN, the remaining error time TFC being however now very small. At the instant to the comparator 1 3 furnishes a signal which opens the gate circuit 1 5 so that the measured heating-up time THO is stored as new preheating time Tvo in the memory 11 at the address associated with the area A8 whilst the previously stored value TVb is erased.

It is thus apparent that a continuous optimisation of the stored value pairs takes place until finally the preheating time Tv associated with a certain area A is so accurate that the remaining error is negligible. From this instant on by blocking the gate circuit 1 5 the arithmetic unit 9 prevents further change of the stored values unless greater deviations over longer periods indicate that the room parameters have permanently changed.

With the aid of the diagrams of Fig. 6 it has been explained how the value of the preheating time associated with a predetermined area value is optimised by continuous adaptation.

The spacial case was considered where the already stored value pairs were again reached exactly on new curves. However, this will be relatively rarely the case in practise. For example, as long as the value pair corresponding to the switching time curve SA has not been stored the last value pair stored cannot be achieved if successive coolings take place along the same curve as is the case when the outer temperature remains unchanged. Nevertheless, in this case as well the system can conduct a continuous optimisation of the stored value pairs by interpolation or extrapolation. This will be explained with the aid of the diagrams of Fig. 7.

For comparison, the diagram A of Fig. 6 is again considered which shows the cooling according to the curve K8, the switching on of the room heating taking place at an instant tM so that the preheating time TVa corresponding to the heating-up time THa is associated with the area Aa. This happens when the system is first set in operation in the manner described above. Thus, the value pair A8, Tva is stored in the memories 10 and 11. The diagram F of Fig. 7 again shows the curve point SAa which corresponds to this value pair and which does not lie on the area curve AKa.

It is assumed in the diagram E of Fig. 7 that the next cooling operation takes place according to the same curve Ka. The area A8 is again reached at the instant tM; however, at the instant tM the arithmetic unit 9 detects that the residual time remaining up to the instant tH is greater than the stored preheating time TVa. Thus, at this instant the room heating is not yet switched on.

The correct switch-on instant lies of course at the inter-section of the area curve AKa with the switching-time curve SA (diagram F); however, this intersection is not known.

It would be possible not to initiate the switching on of the room heating until the instant at which the remaining residual time is exactly equal to the stored preheating time TVa. However, the resulting error would be relatively high. Moreover, in this case the desired temperature 0N would not be reached until after the instant tN, which is undesirable.

Therefore, a more accurate approximation value is determined by interpolation in that the switching curve SA is substituted in approximation by a straight line which passes through the two already known points, i.e.

firstly through the exact curve point tH corresponding to the preheating time zero and secondly through the point SAa corresponding to the stored value pair A8, TVa. The intersection of this straight line with the area curve AKa gives an area A8. The arithmetic unit 9 switches the room heating on at the instant tS.

at which the integated area reaches the value A8. Simultaneously, the arithmetic unit 9 opens the gate circuit 1 6 to store the area value A8 in the memory 10 but at an address different to the previously stored area Aa.

Finally, at the instant tsa the arithmetic unit 9 sets the timer 14 in operation.

The heating up now takes place according to the curve H8, the desired temperature 0N not being reached exactly at the instant tM because the switching instant tsa is only an approximation. The remaining error time TF8 is however relatively small. As soon as the comparator 1 3 determines that the desired temperature has been reached the measured heating-up time THe is stored in the memory 11 as the pre-heating time TVe associated with the area value A8.

The curve point 5A8 (diagram F) represented by the stored value pair A8, TVe lies slightly beside the switching time curve SA but the error is very small. By a few further interpola- tions of the type outlined the accurate value pair associated with the curve K8 can be rapidly determined.

Finally, with reference to Fig. 8 it will be explained how the interpolation or extrapolation takes place in the case where the cooling follows new curves which however do not correspond to the stored value pairs.

In Fig. 8 as well the diagram A is shown again for comparison and indicates how the first stored value pair Ah, Tva is obtained on the basis of the cooling curve Ka. The curve point SAa corresponding to said value pair is again shown in the area diagram I of Fig. 8.

The diagram G shows the case where the next cooling is along a curve Kg which corresponds to a very much lower outer temperature. The area integrated over this curve reaches the value A8 before the instant tM.

Switching on with the stored preheating time TVa would result in a very great error time and in particular the desired temperature 0N would not be reached until a considerable time after the start of the utilisation time.

A linear extrapolation is therefore again made with the aid of the straight line through the abscissa point tN and the point S, as indicated in diagram I of Fig. 8. The intersection of this straight line with the area curve AK9 belonging to the curve Kg gives the area value Ag. The room heating is thus switched on at the instant tsg at which the area integrated by the integrator 8 has reached the value Ag. At the same time the corresponding area value is stored in the memory 10 at a predetermined address and the timer 14 set in operation.

The heating up then takes place according to the curve Hg so that the desired temperature 0N is reached at the instant tg Admittedly, this instant is after the instant tN of the start of the utilisation time but the error time TF9 is small. At the instant when the desired value is reached the comparator 1 3 initiates introduction of the heating-up time TH9 measured by the timer 14 into the memory 11 where it is stored at the same address at which the area Ag is stored in the memory 10.A value pair A,, To is thus obtained which represents the point SA9 which is already relatively close to the switching-time curve SA In contrast, the diagram H shows the case where after the storing of the first value pair Aat Tva the cooling takes place according to a curve Kh which corresponds to a relatively high outer temperature so that the area integrated over this curve has not yet reached the stored value A8 when the residual time remaining until the instant tN is equal to the stored preheating time TVa. In this case an interpolation takes place in that the arithmetic unit initiates the switching on of the room heating at the instant tsh at which the area curve AKh (diagram I) associated with the curve Kh intersects the straight line which passes through the abscissa point tN and the point SAa. The area value Ah which is stored at the same instant tsh in the memory 10 corresponds to this intersection. Furthermore, at the instant tsh the timer 14 is again set in operation. The heating up follows the curve Hh, the desired value AN being reached at the instant th which is slightly before the instant tN. On reaching the desired value the comparator 1 3 initiates the introduction of the measured heating-up time THh into the memory 11 so that in the memories 10 and 11 at the corresponding addresses the value pair Ah, TVh + is now stored.The corresponding curve point SAh (diagram I) is already very close to the switching-time curve 5A When in subsequent heating cycles the cooling takes place according to curves corresponding to the value pairs which have been stored according to the diagrams of Figs. 7 and 8 the stored value pairs are corrected in the same manner as explained previously with the aid of Fig. 6. In this manner a continuous optimisation of the stored value pairs is conducted until finally the error times found are below predetermined tolerance limits.

If however the cooling is along curves for which no value pairs have been determined and stored further linear interpolations are made in the manner explained with the aid of Figs. 7 and 8, the interpolation straight lines being drawn however through the two nearest points for which value pairs are already stored.

The optimisation method described automatically takes account of all the parameters which influence the cooling and heating up, each optimised value pair remaining valid as long as the parameters associated with said value pair remain unchanged. On the other hand, it is of no consequence if certain parameters (e.g. the heating power) have different values for different value pairs. The method described is therefore suitable also for heating systems in which the heating power of the room heating means is changed in dependence upon the outer temperature.

By suitable plausibility checks the stored value pairs may be prevented from changing when due to irregularities temporary deviations occur. For example, provision may be made for carrying out no correction when the error detected is greater than in the preceding case. For normally the error time TF becomes progressively smaller. For this method it is merely necessary in an additional memory to keep also the last error time for each value pair. On the other hand, to detect permanent changes in the room parameters provision may be made for making a correction when increasing errors are repeated several times.

A parameter which can be subjected to sudden changes is the duration of the nonutilisation period. The use of the cooling area as characteristic for the cooling behaviour proves particularly advantageous in this respect because changes of the duration of the non-utilisation period are thereby already taken into account to a great extent. For the magnitude of the cooling area is proportional to the energy lost during cooling which must be supplied again during the heating up; the relationship given by the stored value pairs between the cooling duration and heating-up time is thus substantially maintained when the duration of the non-utilisation period (which is equal to the sum of the cooling time and the preheating time) is changed. The already stored value pairs thus give on a change of the utilisation times very useful approximations which required only slight corrections.

The construction of the circuits described (subtraction circuit, integrator, memories, comparator, clock means, arithmetic unit) will not be described in detail because these are circuits with which the expert is familar and which can be made indifferent manners depending on the technology used. The processing of the signals may be analog or digital, inserting as required at various points the necessary digital-analog converters and analog-digital converters. These steps are also known to the expert and will therefore not be described in detail.

It is also possible to replace the circuits described by a suitably programmed microcomputer.

Claims (14)

1. Method of room heating control for a room which during predetermined utilisation times is held by regulation within predetermined tolerance limits at a desired temperature and the room heating is switched off at the end of each utilisation time, a signal indicating the actual temperature of the room being continuously or cyclically furnished, wherein during the cooling of the room with the heating system switched off after the end of each utilisation time the cooling curve defined by the variation of the actual temperature as a function of the time is determined, a pre-heating time in which after switching on the room heating the desired temperature is achieved being associated with each cooling curve, and wherein the room heating is switched on as soon as the preheating time associated with the cooling curve reaches or exceeds the time intervalremaining before the start of the next utilisation time.

2. Method according to claim 1, wherein during the cooling of the room with the heating system switched off after the end of each utilisation time the difference between the desired temperature and the actual temperature is formed cyclically and by integration of the difference values the cooling area reached up to each integration instant determined, wherein with each value of the cooling area a preheating time is associated in which after switching on the room heating the desired temperature is reached, and wherein the room heating is switched on as soon as the preheating time associated with the last value of the cooling area determined reaches or exceeds the time interval remaining before the start of the next utilisation time.

3. Method according to claim 2, wherein for each value of the cooling area an associated heating-up time is determined experimentally by measuring the time from the switching on of the room heating until reaching the desired temperature, and wherein the measured heating-up time is stored as the preheating time associated with the value of the cooling area.

4. Method according to claim 3, wherein the value of the preheating time associated with a given value of the cooling area is replaced by storing the last measured value of the heating-up time with erasure of the previously stored value and wherein by this adaptive procedure in time the final value pairs are determined.

5. Method according to claim 3 or 4, wherein for values of the cooling area for which no associated values of the preheating time have yet been determined a value is interpolated or extrapolated on the basis of the values already found.

6. Method according to claim 3, wherein for the first heating-up operation for which no values of the preheating time have yet been determined a maximum preheating time is fixedly defined.

7. Arrangement for carrying out the method according to any one of claims 2 to 6, comprising a room temperature sensor which furnishes an actual value signal indicating the actual temperature, a desired value generator which furnishes a desired value signal indicating the desired temperature, timing means at which the utilisation times may be set, a temperature control which receives the actual value signal and the desired value signal and during the utilisation times furnishes an adjustment signal controlling the switching on and off of the room heating, a subtraction circuit which receives the desired value signal and the actual value signal and furnishes a difference signal representing the difference between the desired value and actual value, an integrator which receives the difference signal and furnishes an integration signal representing the integral of the difference signal, a memory in which for various values of the integration signal associated values of preheating times are stored, an a circuit arrangement which for each value of the integration signal takes the associated value of the preheating time from the memory, compares this value with the time interval remaining before the start of the next utilisation time and initiates the switching on of the room heating if said value is equal to or more than said time interval.

8. Arrangement according to claim 7, further comprising a timer which is set in opera tion when the room heating is switched on, a comparator which compares the desired value signal and the actual value signal and on determination of identity initiates the transfer of the time value determined in the timer to the memory, and a control means which effects storing of the time value in the memory at an address which is associated with the value of the integration signal furnished by the integrator at the instant of switching on of the room heating.

9. Arrangement according to claim 7, further comprising a second memory, a circuit arrangement which at the instant of the switching on of the room heating effects the transfer of the value of the integration signal furnished by the integrator to the second memory, and a control means which effects the storing of the value of the integration signal in the second memory at an address associated with said value.

10. Arrangement according to any one of claims 7 to 9, wherein the circuit arrangement controlling the initiation of the room heating and the storing is an arithmetic circuit.

11. Arrangement according to claim 10, wherein the arithmetic circuit is so formed that for values of the integration signal for which no associated value of the preheating time has yet been stored it determines an approximation by interpolation or extrapolation.

1 2. Arrangement according to any one of claims 7 to 11, associated with a plurality of rooms with separately controllable room heatings, wherein a cyclically operating measured value pickup means is provided which cyclically samples and supplies to the arranged the actual value signals furnished by the room temperature sensors, the arrangement being arranged for the cyclic processing of the sample value.

13. A method of room heating control as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

14. Arrangement for room heating control substantially as herein described with reference to the accompanying drawings.