GB2066521A - Control device for a heating apparatus with time-dependent lowering of heating characteristics - Google Patents

Abstract

In a control device for a heating apparatus with adjustable heating characteristic (set point) in which, with respect to a heating characteristic set for first periods, the heating characteristic is lowered during second, more particularly nightly, periods, the lowering of the heating characteristic is cancelled during said second periods if a room temperature comparator detects a lower temperature than a set minimally desired temperature in a room which is temperature controlled. Operation is also slightly influenced by the exterior temperature during each of the said periods. As shown, the outputs of a boiler water temperature sensor R2 and a room temperature sensor R4 are summoned and compared in OA with a reference value determined by resistors R5-R6 and R11-R13. In the daytime, R13 is short-circuited by relay contact S; but at night a clock KL de-energizes the relay so that the temperature set point is lowered. However, if room temperature comparator RTV detect a temperature below a desired minimum, the relay is again energized to restore the higher set point, to prevent freezing. <IMAGE>

Description

SPECIFICATION Control device for a heating appratus with room-temperature-dependent lowering of heating characteristics The invention relates to a control device for a heating apparatus with adjustable heating characteristics in which, with respect to a heating characteristic set for first periods, the heating characteristic is lowered during second, more particularly nightly, periods.

Devices of this type are known in practice. In a practical embodiment they substantially comprise a temperature sensor for the water temperature of the heating apparatus and a temperature sensor for the exterior temperature, in which the output signals of the sensors are amplified with independent amplifying factors and if desired, subsequently added, while the sum thus obtained is compared in comparator with an adjustable threshold value, in which furthermore the output signal of the comparator controls a gas valve or generally a device for the supply of fuel to the heating apparatus, and the threshold value is readjusted periodically, generally dependent on the so-called day or night-period.In such an embodiment the comparator may comprise a substractor to which the sum signal is conducted to a positive input thereof and a threshold value signal is conducted to a positive input thereof whilst the gas valve is opened if the output signal of the substractor is below zero and is closed if the output signal of the substractor is greater than zero. During the periods in which little heat is required for the room to be temperaturecontrolled, which periods are, in general, the nightly periods, the threshold value in such an embodiment is lowered, resulting in a lowering of the heating characteristics. The change of the threshold vaiue is often accomplished by means of a time switch.

Since the thresholds to be used for the night and day temperatures are set once only, such a control device has the disadvantage that the heating system may be put into operation without this being necessary. The installation may, for instance become operative at night while the room temperature corresponding to the lowered characteristics has either already been attained or is lower. This is caused, because the temperature of the water in the heating installation is dependent on the place where said apparatus is installed. If as a solution the heating characteristics would be lowered more, the risk exists that if the temperature for the room to be temperature-controlled becomes too low, due to atmospheric influence or otherwise, the water in that room might freeze.

If furthermore the water temperature has the value belonging to the set heating characteristics and the actual exterior temperature, while the room to be controlled is also heated by, for instance, any persons being present or incidental sun rays, the water temperature of the heating installation will get an unnecessarily high value as a result of the heating characteristics set in case a thermostat is incorporated in the gas-valve control device.

Furthermore, at the transition from night to day the heating installation will raise the temperature of the water to a higher value belonging to the new heating characteristics, and after this value has been reached while the water is cooled down by the room still being too cold, the heating installation will be switched on and off repeatedly so as to maintain the water temperature belonging to the heating characteristics. As a result thereof the room is heated up only slowly and the transistion from night to day should, in fact be set at an earlier moment.

It is the object of the present invention to alleviate these disadvantages and to provide a control device for a heating installation in which the lowering of the heating characteristics during the second periods is cancelled if a room temperature-comparator detects a temperature being lower than a set minimally desired temperature for a room to be temperaturecontrolled.

The control device according to the invention presents the advantage that the heating characteristics may be set sufficiently low and that, if the room temperature is too low during the night, the lowering of the heating characteristics is cancelled and freezing of the water in the heating system is provented with a minimum consumption of energy.

By making the setting of the heating characteristics dependent on the roomtemperature, thus causing the heating characteristics to be lowered if, for instance due to incidental sun rays the room temperature increases, a lower water temperature may suffice and particularly the losses resulting from a standstill will be reduced. The present embodiment moreover presents the advantage that at the transition from night to day a higher heating characteristic is so set, that the room is heated up sooner and that the day period may start less early, consequently accompanied by less consumption of energy.

The invention will be explained with reference to the drawing, wherein: Figure 1 is a simplified scheme of a known control device with heating characteristics and lowering of the heating characteristics, paritcularly during nightly periods.

Figure 2 is a simplified scheme of a control device according to the present invention.

In the control device according to Figure 1 the water temperature is defined by means of a series connection of the resistors Fli and R2 which, with their not-common connected leads are connected with the positive resp. with the negative terminals of a voltage source (not shown). The resistor R2 has a negative temperature coefficient and is, for instance electrically isolated, arranged in the water of the installation. The signal A at the interconnection of this series circuit is in inverse ratio with the water temperature. By a resistor R7 this signal is conducted to the negative input of an operational amplifier OA of which, by means of a resistor Rg, the output is fed back to the same negative input.For determining the room temperature, a circuit comprising the resistors R3, R4 and Ra identical with the first circuit comprising the resistors R1, R2 and R7, is connected with the negative input of the operation amplifier OA, so that the signals A resp. B corresponding to those temperatures are added to each other. A series connection of two resistors R5 and R6, which are connected with the positive resp. negative terminal of the voltage source, are connected with their interconnection, with the positive input of the operational amplifier OA.A resistor R1o may be connected in parallel with the resistor R6, particularly during the daytime, by means of a manually operated or clock controlled switch. The signal C to the positive input of the amplifier OA defines the heating characteristics of the installation, the heating characteristics being higher if the magnitude of this signal C is lower.

The device described hereinbefore operates such, that if the water temperature and the room temperature became lower or the signals A and B respectively become higher than in the state of equilibrium, i.e. being amplified together or separately getting higher than the threshold signal value C, the heating installation is put into operation. Since at night the threshold value C is higher than at the daytime, the water temperature and the room temperature should separately or together be more lower than in the daytime so as to put the installation into operation.

Figure 2 shows a preferred embodiment of a control device according to the present invention.

Arranged in the room and in parallel with the resistor R5 in Figure 1, there is connected a resistor R1l with negative temperature coefficient whilst in parallel with R6 there is connected at least one resistor R13. For setting the influence of the resistor R1l, an adjustable resistor R12 is arranged in one of the branches with the resistors R1l, R13 resp. If the room temperature is lower than desired during the nighttime and otherwise during the daytime the resistor R13 is short-circuited by means of a relay contact S of a relay REL and whether or not in series with a resistor as R1o in Figure 1.This relay is connected between the positive terminal of the voltage source and the collector of a NPN-transistor TR. The emitter of this transistor TR is connected with the negative terminal of the source, and its base is connected with the cathodes of two diodes D1 and D2 of which the anodes are connected with the outputs of a room temperature comparator RTV and of a clock unit KL resp. At an input the room temperature comparator RTV receives a comparison or reference signal from the interconnection of two resistors R15 and R16 which are switched in series and which are connected between the positive negative terminal resp. of the voltage source, of which at least one is preferably adjustable.Dependent on the logic used (positive or negative), the room temperature comparator may, for instance, be an integrated circuit such as known as LM39 11. The room temperature comparator RTV is mounted in the room of which the temperature is to be controlled and it compares the room temperature measured by itself with the reference value fed to the comparator, and with the output signal of the comparator having a lower value if the actual room temperature is higher than the minimally desired room temperature corresponding to the reference value. If, moreover, the clock device indicates by means of a low output signal that the night period -has been reached, the relay REL will be de-energised in other than aforementioned cases and thus the relay contact S will be opened.

As a result thereof the signal C which is fed to the positive input of the operational amplifier increases, which corresponds with a lowering of the heating characteristics.

If the clock device KI indicates by means of a high signal level at its output, that the day period has been reached, or if during the night the room temperature comparator detects a lower room temperature than that desired, the relay will be energised and the relay contact S is closed which corresponds to a raise of the heating characteristic.

In order to obtain a more effective and smooth operation of the heating installation, the control of the relay REL is delayed by means of a delay circuit. The delay circuit comprises a resistor R17 which is connected between the collector of the transistor TR, the input of room temperature comparator RTV, and a capacitor Co connected between said input and the negative terminal of the voltage source.

As compared with the devices to be used in practice, the devices shown in the drawings are simplified. So, the signals A and B which correspond to the water temperature and the room temperature resp. may first pass a voltage follower while, in view of the linearity of the resistors with a negative temperature coefficient and the desired magnitudes of the signals, the resistor circuits may further comprise resistors connected in parallel and/or in series with these NTC resistors. For obtaining a smoother control low pass filters comprising, for instance, capacitors with are connected in parallel with the NTC resistors may be additionally incorporated. Moreover, instead of the relay REL and its contact S, an electronic, i.e. a nonmechanical switch may be used.

Although the device described uses negative logics, i.e. with signals opposite or inverse to the corresponding temperature, the present embodiment can naturally also be applied in devices which use positive logics.

Claims (9)

1. A control device for a heating apparatus with adjustable heating characteristics in which, with respect to a heating characteristic set for first periods, the heating characteristic is lowered during second, more particularly nightly, periods, characterized in that the lowering of the heating characteristic is cancelled during said second periods if a room temperature comparator detects a lower temperature than a set minimally desired temperature for a room to be temperaturecontrolled.

2. A control device according to claim 1 which device measures the exterior temperature and the temperature of the water in the apparatus and then totalises signals, which are inversely proportional to those temperatures and which may be amplified with independent amplifying factors and compares the sum with a threshold value, whereby the installation if put into or out of operation if said sum becomes high or lower respectively, than the threshold value, whereby the threshold value signal is obtained from the interconnection of two, first and second, resistors connected in series with terminals of a voltage source while at night by increasing the first resistor connected with the negative terminal of the voltage source by means of a manually operated switch or of a switch controlled by an adjustable clock, the threshold value is raised, as a result of which occurs a lowering of the heating characteristics, characterized in that the first resistor or part thereof is shortcircuited by means of a relay contact of a control circuit dependent on the room temperature in case of at night said room temperature being lower than the set minimally desired room temperature or during the daytime, both resulting in a raise of the heating characteristics.

3. Apparatus according to claims 1-2, characterized in that the second resistor connected at the positive terminal of said voltage source is a resistor with a negative temperature coefficient which is arranged in said room and in that a third adjustable resistor is arranged in one of the branches from said interconnection to one of said terminals of said voltage source.

4. An apparatus according to claims 1-3, characterized in that said control circuit comprises a room temperature comparator arranged in said room, which comparator compares the room temperature measured by itself with a reference value, whereby an output signal of the comparator via a logic circuit does not energise said relay and opens its contact if said reference value is lower than the corresponding room temperature and if also the clock, of which an output is connected with another input of the logic circuit indicates on this connection that the period to lower the heating characteristic for, is not there.

5. An apparatus according to claim 4, characterized in that the signal corresponding to said reference value is derived from another interconnection of two resistors connected in series with said terminals of said voltage source.

6. An apparatus according to claim 5, characterized in that the logic circuit comprises two diodes of which the cathodes are connected with the basis of an NPN transistor of which the emitter is connected with the negative terminal of said positive terminal of the voltage source by said relay, while two respective anodes of the diodes are connected with an output terminal of said room temperature comparator and with an output terminal of said clock and said relay will not be energised then if both corresponding output signals fed to said respective diodes have a low voltage level.

7. An apparatus according to claim 6, characterized in that said relay, after termination of the initial energising, is maintained in the energised state for at least a predetermined period of time thereafter, by means of a delay circuit.

8. An apparatus according to claim 6, characterized in that said delay circuit comprises a reaction resistor which is connected between the collector of said transistor and the input terminal of said comparator for said reference signal, and a capacitor arranged between this input terminal and the emitter ot said transistor.

9. A control device for heating apparatus substantially as hereinbefore described with reference to Figure 2 of the accompanying drawings.

1 0. Any novel feature or combination of features herein disclosed.