GB2042222A - Method and circuit for controlling switching on a heating or air- conditioning installation - Google Patents

Abstract

A control circuit for switching on heating or air-conditioning apparatus comprises a computer (10) which is supplied with a signal (U1) depending on the difference between a desired value Xk and actual room temperature tr a signal (U2) depending on measured outside temperature ta and possibly a supplementary signal (U3). The signal (U3) serves for an additional advance of the moment of switching on after a switched off period of more than 24 hours and is added to the signal (U1) in an addition network (12). Also supplied to the computer (10) are signal S+, S- from two control elements (14, 16). At these two control elements (14, 16), a heating-up gradient S (Figures 2 and 3) is set up and is adapted to characteristics of the heating apparatus and building. The resulting output signal U4 from the computer 10 is compared in a comparator 36 with a rising ramp voltage U5 derived by a D/A converter from timing pulses. As soon as U5 reaches U4 the heating apparatus is switched ON at maximum output precisely at moment 74 (Figure 3). <IMAGE>

Description

SPECIFICATION Method and circuit for controlling switching on a heating or air-conditioning installation This invention relates to a method of determining the optimum moment of switching on a heating or air-conditioning installation of the kind referred to in the preamble to Patent Claim 1 and a circuit arrangement for carrying out the method.

From U.S. Patent Specification No. 3,964,676 a circuit arrangement is known which is suitable for carrying out the above-mentioned method. The principle of such a method serves to achieve an optimum efficiency of a heating or air-conditioning plant in a building which is only used at certain times such as a business house or a school house. The efficiency is optimum when on the one hand a comfortable room temperature is only maintained during the period of occupation and on the other hand as much heating energy as possible is saved during the periods of non-occupation. The saving is greatest if the room temperature is allowed to drop to a permissible minimum during the periods of non-occupation and the latest possible moment is selected for the beginning of heating, then the rooms are heated up in the shortest time with the maximum heating power available.The moment of switching on is selected in the optimum manner so that the room temperature necessary for comfort is reached at the beginning of the period of occupation and not before.

The optimum moment of switching on is not a constant value, however, but depends on the cooling of the rooms to be heated and on the duration of heating up which is expressed hereinafter by the heating-up gradient. The heating-up gradient is given in K/h (0K/hour) and depends on the construction (insulation etc.) of the building to be heated, on the particular outside temperature prevailing and on the design temperature of the heating or air-conditioning plant. The design temperature corresponds to the lowest outside temperature for which the heating or air-conditioning plant is designed, that is to say is calculated and at which the heating or air-conditioning plant operated with the full heating power available can still just heat up the rooms.With the lowest outside temperature, the heating-up gradient is the lowest because the constant heat losses of the building are then at a maximum. The heating up by the same amount therefore takes longer with the lowest outside temperature than with a higher outside temperature at which the heating up gradient is greater.

Since the heating-up gradient is not a constant value either, as shown in the above part of the description, in order to achieve an optimum moment of switching on it is necessary to adapt the heating-up gradient to the heating or air-conditioning plant taking into consideration the design temperature and the construction of the building.

It is known to feed the given design temperature for a plant into a programmed control device to determine the optimum moment of switching on. In this case, however, there is no assurance that the moment of switching on can in fact be determined in the optimum manner by the control device because, as is known, many heating installations are over-dimensioned in their calculation as a result of safety additions.

The actual design temperature therefore lies at a lower value than that on which the calculation is based. The consequence when the calculated value is fed into the control device is a greater heating-up gradient than desired in such a case and hence a premature reaching of the room temperature necessary for comfort. The possibility of saving heating energy is not utilized in the optimum manner in such a case.

Another disadvantage of the said method of feeding in is that the heating-up gradient can only be adjusted by one point, namely to the design temperature which is only seldom reached. Such a method of adjustment does not permit, for example, that the coefficient of the heating-up gradients depending on values defined by a straight line of the outside temperature can be adjusted as desired for the optimum adaptation. For example, a deviation and an independent parallel displacement of the straight line is not possible.

Since the internal devices in the rooms to be heated cool down to a greater extent in a switching-off period lasting longer than one day, for example over a week-end, particularly with low outside temperatures, than only during a night, it is not sufficient to take into consideration the dropping room temperature which is defined in particular by the air temperature. Although the room temperature has reached the selected value at the beginning of the period of occupation, the required comfort is not present in such a case because the equipment objects and in particular also the walls of the room have cooled down to a greater extent than only during a night. In order to ensure comfort nevertheless at the beginning of the period of occupation, it is known, for example on Monday morning, to advance the moment of switching on additionally by a certain amount.Since the switching-off periods lasting longer than 24 hours may last from one day (individual holiday during the week) to several days (Christmas and New Year), however, the result is also a cooling to a different extent of the walls and equipment. No allowance is made for these differences in the methods or equipment belonging to the prior art.

The object of the invention is to give a method of determining the optimum moment of switching on which renders possible a complete adaptation to the given characteristics of the installation. Furthermore cooling to different extents as a result of switching-off periods of different lengths are additionally to be taken into consideration.

The present invention is a method of controlling the switching on of a heating or air-conditioning installation after a switching-off period wherein at a moment situated at a fixed time before the beginning of the period of occupation following on a switching-off period, a signal depending on room temperature, one depending on the outside temperature and one depending on time are evaluated to determine the moment of switching on, and in which the outside temperature is evaluated in the form of a heating-up gradient determined by two control values.

The present invention is also a circuit arrangement for carrying out the method of the preceding paragraph, in which a signal of the outside temperature and that of the difference between a desired value and the room temperature are connected to the inputs of a computer circuit, the output of which is connected to the first input of a first comparator, while the second input of the comparator is connected to the output of a timer, two control elements to adjust the heating-up gradients being associated with the computer circuit.

The method according to the invention is clear, can be easily explained and renders possible an adjustment of the heating-up gradient in the temperature range which occurs most frequently.

If the necessary control values are not known or only inaccurately, these can be determined in a relatively simple manner by a preferred method in which the control values are found by the rise values of the room temperature resulting during full heating power depending on the time with two different outside temperature values.

A method which renders possible an optimum adaptation even with switching-off periods of different lengths is provided in which the moment of switching on is advanced after a switching-off period lasting longer than 24 hours, and in which the moment of switching on is advanced by a further step after each further 24 hours.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which Figure lisa block circuit diagram of a circuit according to the present invention; Figure 2 is a nomograph to determine the heating-up gradients; Figure 3 is a function diagram of the circuit of Figure 1; and Figure 4 is a further function diagram to explain the additional early heating up.

The circuit arrangement shown in Figure 1 comprises a computer 10 to which signal voltages U1 and U3 are supplied through an addition network 12 and a signal voltage U2 and a reference voltage Uref are supplied directly. The output signal voltage of the computer 10 is designated by U4. Disposed between the addition network 12 and the computer 10 are two control elements disposed in parallel with one another in the form of potentiometers 14 and 16. The potentiometer 14 serves to adjust the heating-up gradient S+ and the potentiometer 16 serves to adjust the heating-up gradient S-. The voltage U3 supplied to the addition network 12 is adjustable at a control element in the form of a potentiometer 18. The voltage U1 supplied to the addition network 12 corresponds to the temperature difference between a desired value xk and the room temperature tr.The voltage U2 corresponds to the measured outside temperature te.

A temperatu re-responsive resistor 20, which is connected in series with a resistor 22 between the reference voltage Uref and earth, serves to measure the outside temperature te. The centre tap between these two resistors 20 and 22 is connected to the input of an amplifier 24, the output signal of which is the voltage U2 supplied to the computer 10.

A temperature-responsive resistor 26, which is connected in series with a resistor 28 between the reference voltage Uref and earth, serves to measure the room temperature. In order to adjust the desired value xk of the selected room temperature tr, a potentiometer 30 is provided which is connected in series with a resistor 32 between the reference voltage Uref and earth.

The connecting points between the temperature-responsive resistor 26 and the resistor 28 and between the potentiometer 30 and the resistor 32 are connected to the two inputs of a differential amplifier 34, the output signal of which is the voltage U1 supplied to the addition network 12. This voltage corresponds to the temperature difference Atr between the desired value xk and the room temperature tr.

The output signal voltage U4 of the computer 10 is supplied to the first input of a first comparator 36.

Supplied to the second input of the first comparator 36 is a voltage U5 which is a voltage rising proportionately depending on time. The output of the comparator 36 is connected to the set input S of a first and a second flip-flop circuit 38,40. The output Q of the first flip-flop circuit 38 is connected to the energizing winding of a relay A.

The reference voltage Uref is supplied to the first input of a second comparator 42. The voltage U5 depending on time is supplied to the second input of this comparator 42. The output of the comparator 42 is connected to the reset input R of the first flip-flop circuit 38.

The reset input R of the second flip-flop circuit 40 is connected to the output of a first counter 44.

The outputs of a switch contact 46 of a time switch not illustrated are connected to the set input S and to the reset input R of a third flip-flop circuit 48. in order to start the circuit arrangement for determining the optimum moment of switching on, the switch contact 46 points to the set input S of the third flip-flop circuit 48. In the position shown, the switch contact 46 is connected to the reset input R of the third flip-flop circuit 48, which position corresponds to the switching-off period of the heating or air-conditioning plant to be controlled.

The first counter 44, a second counter 50 and a third counter 52 are each connected through their first input to the output of an oscillator circuit 54. The output Q of the third flip-flop circuit 48 is connected to the second input of the second counter 50. The inverted output Q is connected to the second input of the first counter 44 and that of the third counter 52.

The output of the second counter 50 is connected to the input of a first digital-analogue converter 56, the output voltage of which is the voltage U5 rising proportionately depending on time.

The output of the third counter 52 is connected to the input of a second digital-analogue converter 58, the output voltage of which is the voltage U3.

The determination of the control values S- and S+ will now be explained with reference to the nomograph illustrated in Figure 2, which values are adjusted at the potentiometers 14 and 16 (Figure 1).

Plotted on the abscissae axis of this nomograph is a scale with the values of the outside temperature in degrees Celsius. At the outside temperature values of plus 20 degrees Celsius and minus 20 degrees Celsius an ordinate axis is illustrated in each case. The scales on these ordinate axes are related to a heating-up gradient which is here given in Vhour (K/h). The ordinate axis with an outside temperature ta of minus 20 degrees Celsius is designated by S-, while the ordinate axis with the outside temperature ta of plus 20 degrees Celsius is designated by S+. These values S- and S+ designate the values of the heating-up gradient to be adjusted at the potentiometers 14 and 16 in Figure 1. The outside temperature values of minus 20 degrees Celsius and plus 20 degrees Celsius are values selected arbitrarily and depend on the apparatus.

In order to determine the values S- and S+, the heating or the air-conditioning plant is switched on after a period of switching-off and the rise in the room temperature per hour is measured.

The measured value is plotted at the particular outside temperature prevailing, in the nomograph of Figure 2. In order to achieve an optimum adaptation it is an advantage to repeat the same process with a different outside temperature value. When two such measured points are available and have been plotted in the nomograph, a straight line 60 can be drawn through these two points and be extended to both sides. Then the corresponding control values can be read off on the ordinate scales S- and S+. In the example illustrated in Figure 2, this straight line extends over two K/h with the control value S- and over six K/h with the control value S+.

The downwardly extended straight line 60 ends at an outside temperature value of minus 40 Celsius. This is the theoretical value at which heating of the rooms to be heated or air-conditioned is no longer possible even with the maximum heating power available. At such an outside temperature value the existing room temperature could at most be maintained with the maximum heating power.

In the nomograph of Figure 2, above the abscissae, a second scale is plotted which is offset downwards by 5 degrees Celsius in relation to the outside temperature scale ta. This scale designated TAuslege jS related to the design temperature already mentioned in the introduction to the specification. In the example given in Figure 2, the straight line 60 ends at a design temperature of minus 35 degrees Celsius. This is therefore the lowest outside temperature value at which the plant can still just heat up the rooms connected up.

Since the finding of two measured values to determine the straight line 60 presupposes that these are picked up at two different outside temperature values t5, it is also possible, for the provisional determination, to draw the straight line 60 between a measured point and the design temperature tAuslege given for plant.

Such a determination admittedly only corresponds to the optimum if the given design temperature is in fact correct. Should the given design temperature not correspond to the actual design temperature, however, then such a determination is nevertheless more accurate than a control value which is based only on the design temperature, as is usual, for example, in the equipment belonging to the prior art.

The operation of the circuit arrangement of Figure 1 will be explained in more detail below with reference to the diagram of Figure 3. In order to avoid confusion, it is pointed out that the straight line 60 illustrated in Figure 2 does not represent the heating-up gradient but its coefficients can be read off from this straight line 60. In the diagram of Figure 3, on the other hand, the heating-up gradients S-, S+ and a heating-up gradient S assumed selectively and situated between the values S- and S+ are illustrated.

The abscissa designated by t corresponds to the time axis, which may be divided up into hours or days.

The ordinate corresponds to the room temperature tr in degrees Celsius. The value xk on the room temperature axis is the desired value of the room temperature set at the desired-value indicator 30 (Figure 1).

62 designates the period of occupation coming to an end which ends at the switching-off moment 64. A period of non-occupation 70 lies between the switching-off moment 64 and the beginning 66 of the following period 69 of occupation.

After the moment of switching off 64 the room temperature begins to drop in accordance with an e-function as shown by the curve 72. Atr designates the difference by which the room temperature 72 has dropped in relation to the desired value xk up to a moment of switching on 74.

The moment of switching on 74 is determined by the point of intersection between the sinking room temperature 72 and the outside temperature prevailing on which the heating-up gradient S is based. On the assumption that the heating-up gradient S has been selected in the optimum manner, then the rising room temperature 72' will correspond to the desired value xk precisely at the moment 66 when the following period of occupation 68 begins.

The heating-up gradients S-, S and S+ are represented by straight lines for the sake of simplicity in the diagram of Figure 3. The rising room temperature 72' will be slighly s-shaped in relation to such a straight line. Such a deviation is without significance, however, because all that matters is that the rising room temperature 72' reaches the desired value xk as accurately as possible at the moment 66.

The circuit arrangement of Figure 1 is intended to determine the optimum moment of switching on 74. In order to achieve this object, it is necessary that the determination should begin at a moment which is at an adequate distance before the beginning of occupation 66, so that heating up is still possible when the room temperature has sunk to the greatest extent and at the lowest outside temperature to be expected, so as to reach the selected room temperature at the beginning of occupation 66. For this purpose the time-switch contact 46 is switched over at the moment 76 to the set input S of the third flip-flop circuit 48 and so the determination of the optimum moment of switching on is initiated. The second counter 50, which receives pulses depending on time from the oscillator 54, is activated through the output Q of the third flip-flop circuit 48.The time pulses delivered by the second counter 50 are converted into the voltage U5 rising depending on time in the first digital-analogue converter 56.

The computer circuit consisting of the circuit elements 10, 12, 14, 16 delivers the signal voltage U4 in which the outside temperature ta, the room temperature difference Atr, the control values S- and S+ and possibly the signal voltage U3 to be explained more fully, are evaluated depending on the position of the potentiometer 18. The operatipn of this computer circuit is given in Claim 10 by a mathematical formula.

The voltage U4 now appears at the first input of the first comparator 36. As soon as the voltage U5, rising depending on time, at the second input of the first comparator 36 has reached the value of the voltage U4, the first comparator 36 gives an output signal to the set inputs S of the first and second flip-flop circuits 38,40.

Through these two flip-flop circuits, the two relays A and B are energized and through their contacts, the heating or air-conditioning plant, not illustrated, for heating up the rooms connected up is switched on at the maximum heating power available. This switching on is effected precisely at the moment of switching on 74.

The moment 76 for initiating the beginning of determination defined by the switching over of the time-switch contact 46 is advanced by a certain amount, for example by 9 hours, in relation to the beginning 66 of the period of occupation 68. In order to simplify the setting by the operator, the time switch actuating the switching contact 46 but not illustrated may be adapted so that this contact automatically operates 9 hours before the set time. In the diagram of Figure 3, the period of advance is designated by 78.

The electronic timer comprising the switching elements 50 and 56 is so dimensioned that its output voltage U5 reaches the reference voltage Uref precisely after the expiration of the period of time 78. As a result of equality of the two input voltages Uref and U5 at the second comparator 42, the first flip-flop circuit 38 receives a signal through its reset input R, as a result of which the output Q becomes without voltage and the first relay A drops. The last-mentioned function is effected at the moment 66, when the rapid heating up is terminated.

The second relay B remains energized until the second flip-flop circuit 40 receives a signal from the first counter 44 through its reset input R. The second relay B is intended to keep the normal regulating installation of the heating or air-conditioning plant switched on during the day. The first counter 44 serves to delay the switching off of the heating or air-conditioning plant by an amount which corresponds to the period of time 78. This delay serves for compensation because the time-switch contact 46 is switched back into its night position by such an amount before the end of occupation. The first counter 44 is activated through the inverted output Q of the third flip-flop circuit 48.

Figure 4 shows a diagram which extends over a period of several days. The function illustrated in this diagram differs from that of Figure 3 in particular in that the switching off period lasts longer than 24 hours.

Since, as already mentioned, the articles of equipment and the walls cool down to a greater extent in a room which is not heated for more than 24 hours than just during a night, it is advisable for the moment of switching on 74' to be additionally advanced in relation to the normal determination of the optimum moment of switching on. In the example illustrated, this advance is effected in that, during the determination of the optimum moment of switching on, a room temperature is used as a basis which is lower than the room temperature actually existing.

Since the said cooling down increases further depending on the number of days without occupation, it is provided within a period of non-occupation, to lower the value on which the determination of the optimum moment of switching on is based, by one step in each case. In the diagram of Figure 4, these reductions are effected at the moments 80 and 82. The moment 80 is displaced by 24 hours in relation to the moment of switching off 64'. The second moment 82 is displaced by a further 24 hours in relation to the first moment 80.

The broken line 84 gives the value on which the measurement is based. Instead of the room temperature difference Atr, after a switching-off period of more than two days, for example over a week-end, the value Atr' is used as a basis to determine the optimum moment of switching on 74'. Without this advance, the moment of switching on would have fallen on the moment of intersection 75 between the particular value of the sinking room temperature 72 and the gradient straight line S. From this diagram it can be seen that the period of the additional advance depends on the particular heating-up gradient and so on the outside temperature. With a lower outside temperature, corresponding to the gradient S-, a greater additional advance results than with the gradient S+, which is associated with a higher outside temperature.

The dependence of the additional advance on the heating-up gradient is an advantage through which the optimum determination of the moment of switching on 74' is ensured in every situation.

This additional advance is realized by the supplementary signal voltage U3 of which the component set at the potentiometer 18 is added to the voltage U1 dependent on the room temperature. The scale of the potentiometer 18 can be calibrated in "K.

The third counter 52 and the second digital-analogue converter 58 serve to produce the voltage U3. These two circuit elements 52 and 58 are so adapted that the output voltage U3 iS increased by a further step after each 24 hours. The third counter 52 is activated through the inverted output 0 of the third flip-flop circuit 48.

Claims (14)

1. A method of controlling the switching on of a heating or air-conditioning installation after a switching-off period wherein at a moment situated at a fixed time before the beginning of the period of occupation following on a switching-off period, a signal depending on room temperature, one depending on the outside temperature and one depending on time are evaluated to determine the moment of switching on, and in which the outside temperature is evaluated in the form of a heating-up gradient determined by two control values.

2. A method as claimed in claim 1, in which the control values are found by the rise values of the room temperature resulting during full heating power depending on the time with two different outside temperature values.

3. A method as claimed in claim 2, in which the first control value is determined with an outside temperature below 05C and the second with an outside temperature above 0DC.

4. A method as claimed in claim 2, in which the coefficient of the heating-up gradient is altered depending on the outside temperature linearly on a straight line situated between the two control values.

5. A method as claimed in claim 1, wherein the moment of switching on is advanced after a switching-off period lasting longer than 24 hours, and in which the moment of switching on is advanced by a further step after each further 24 hours.

6. A method as claimed in claim 5, in which in order to advance the moment of switching on, a supplementary signal is added to the signal depending on room temperature after each 24-hour step, as a result of which a greater drop in room temperature than is actually present is taken into consideration to determine the moment of switching on.

7. A circuit arrangement for carrying out the method of claim 1, in which a signal of the outside temperature and that of the difference between a desired value and the room temperature are connected to the inputs of a computer circuit, the output of which is connected to the first input of a first comparator, while the second input of the comparator is connected to the output of a timer, two control elements to adjust the heating-up gradients being associated with the computer circuit.

8. A circuit as claimed in claim 7, in which the supplementary signal is connected through a control element to the second input of an addition network, to the first input of which the signal of the room-temperature difference is applied and the output of which is connected to the computer.

9. A circuit as claimed in claim 8, in which the control elements for the control values of the heating-up gradient are disposed between the addition network and the computer.

10. A circuit as claimed in claim 9, in which the computer circuit is based on a function in accordance with the following formula:

in which: U1 signifies the signal voltage of the room temperature difference (xk - tr) U2 signifies the signal voltage of the outside temperature (ta) U3 signifies the signal voltage of the supplementary signal U4 signifies the output signal voltage of the computer circuit U5 signifies a voltage signal rising linearly in time Uref signifies a reference voltage ak signifies the angular position of the control element for the supplementary signal a5 signifies the angular position of the control element for the heating-up gradient with a lower control point aS+ signifies the angular position of the control element for the heating-up gradient with an upper control point.

11. A circuit as claimed in claim 7, in which, in order to produce the signal depending on time, a first timer is provided, the switching point of which is advanced by a fixed amount in relation to its time control value and that a second timer activated by the first timer is provided to deliver the signal depending on time.

12. A circuit as claimed in claim 11, in which the first timer is a time switch actuating a contact and the second timer is an electronic circuit delivering a voltage which is variable linearly depending on time.

13. A method of controlling the switching on of a heating or air-conditioning installation after a switching-off period, substantially as hereinbefore described with reference to the accompanying drawings.

14. A circuit for carrying out the method of claim 13 substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.