FR2506912A1 - Automatic controller for natural or forced convection electric heater - uses triacs supplying both heater and fan motor to control temperature of room - Google Patents

Abstract

The heater has an electric heating element and a fan, driven by an electric motor. A set temperature is chosen and the actual temperature is compared against the set temperature. The power supplied to the heater and to the fan motor is reduced if the measured temperature exceeds the set temperature. The controller comprises two triac switches (TR1,TR2), one supplying the heater and the other the motor (M). The triac gates are connected to temperature sensitive elements (A) and to ramp generator type comparators, to give variable power flow.

Description

 The object of the present invention is a method for controlling a convection radiator comprising an electric heating device and a turbine driven by an electric motor, and adapted to operate alternately according to heating regimes by natural convection or heating by forced convection , and a control system for the implementation of this method.

 Methods and systems for automatic control of radiators of this type are already known. However, they have numerous drawbacks, for example requiring a large number of control members, for example two thermostats associated respectively with the heating device and with the turbine, and a selector switch when the heating device consists of two elements which can both be put into service simultaneously or separately. On the other hand, it turned out that the coordination of the settings of the two thermostats and of the control which had hitherto been manual of the two heating elements, to obtain optimum operation of the radiator is difficult for a person unfamiliar with Another disadvantage lies in the fact that the heating device and the turbine are switched off from operation at full power, which causes annoying noises, in the case of the turbine and, in relatively small premises, temperature overruns beyond a desired level which are brief but still annoying.

 The object of the present invention is to overcome these drawbacks for a radiator of the type indicated above.

 To achieve this goal, the method of controlling a radiator of this type is characterized in that, as the temperature in the room to be heated approaches the previously selected setpoint temperature, the device is automatically lowered and gradually the heating power of the heating device and the speed of rotation of the turbine and provides for the automatic stopping of the latter when the temperature in the room, after having continued to increase, reaches a predetermined value and in that the the turbine is restarted when the temperature at ground level has dropped by a significant value.

 Leegsthne de conslande for implementing the method according to the invention is characterized in that the power circuit of the heating device comprises a device sensitive to the temperature prevailing in the room to be heated and capable of gradually reducing the current flowing through the heating device, as the temperature approaches a predetermined set temperature, the motor power circuit includes a variable resistor and a switch, and in that a device connection of the two power circuits is provided, which includes means sensitive to a variation of the current of the heating device and produce a control signal of said variable resistance, so as to bring about a progressive reduction of the current of the motor as a result of a reduction in the heater current, and a switch open control signal when a predetermined temperature is reached te and a switch closing control signal at a temperature below this predetermined temperature, the two temperatures corresponding to current values dJtectable by the connecting device.

 According to advantageous features of the invention, the temperature-sensitive device is formed by a triggering semiconductor element controlled by a thermostat circuit, the variable resistance is formed by a transistor connected in series with a rectifier bridge and the resistance of the collector-emitter path is adjustable by variation of a polarization resistance sensitive to temperature, the connection device is formed by a heating resistor mounted in parallel on the trip switch, the switch located in the power circuit of the motor is a thermal switch and the latter and the temperature-sensitive resistor are placed so as to be heated by the heating resistor.

The invention will be better understood, and other objects, characteristics, details and advantages thereof will appear more clearly during the explanatory description which follows, made with reference to the appended schematic drawing given solely by way of example illustrating a embodiment of the invention, and in which
- The single figure schematically shows a control device for implementing the method according to the invention.

 The invention is applicable to a convection radiator adapted to operate alternately according to heating regimes by natural convection or heating by forced convection. This radiator essentially comprises for this purpose an electrical resistance heating device and a turbine or fan rotated by an electric motor. In heating mode by natural convection, hot air exits through an upper opening, since the turbine is out of service. On the other hand, in forced convection heating mode, the turbine, now in service, expels hot air through a lower opening, for example at ground level of the room to be heated.

 In the single figure which represents an embodiment of the control device for a radiator of the type which has just been described, the electric motor is designated by the letter M. The electric resistance heating device consists of two heating elements S1, a which can be connected in parallel using a switch I1. A switch I2 is provided for connecting the motor M and the heating device to the AC power supply source, formed for example by the network.

As shown in the figure, the heating element S1 is mounted in a first power circuit in series with the tripping semiconductor element such as a TRI triac controlled by a control circuit
In such a way that the switching of the Triac always takes place during a passage par tio of the mains voltage.

The circuit d. command A decides the switching time according to the information it receives from a transmitter
E1 of a setpoint representative of the pre-selected setpoint temperature and of a generator or transmitter S2 giving signals to the control circuit representative of the actual temperature in the room to be heated. This temperature is preferably captured at ground level. In the control circuit A, a voltage in the form of a sawtooth is superposed on the setpoint voltage coming from the setpoint transmitter E1. This arrangement of the control circuit A * which is known per se and is commercially available, has the consequence that the Triac TR1, from a certain temperature threshold, for example relatively close to the signal temperature, prohibited the passage of entire alternation blocks, the number of which gradually increases as the actual temperature approaches the set temperature. This means that the durations during which the Triac TRI is blocked become progressively longer.

 Referring again to the figure, it can be seen that a heating resistor R8 is mounted in parallel on the Triac TRI.

The motor N is inserted into a second power circuit in series with a full-wave rectifier bridge P and a transistor T arranged to constitute a variable resistance The resistance of the collector-emitter path of the transistor is variable by variation of a thermal resistance RT interposed between the collector of the transistor and an amplifier circuit
B of the type known per se, for example of the Darlington type, acting on the base of the transistor. The motor power circuit further includes a thermal switch fT7 in series with the motor N.

 it appears from the figure that the power circuit of the heating element S1 and of the engine are electrically isolated from each other. But by arranging the thermal resistance RT and the thermal switch IT1 near the heating resistor R5, we obtain that a heating of the latter causes a heating of RT and of the thermal switch which is chosen to interrupt the power circuit at a predetermined temperature. The resistor RT and the switch IT1 are therefore connected to the heating resistor RS by thermal coupling.

 As mentioned above, the heating element S2 can be mounted in parallel with the heating element S1 by closing the switch I1.

However, the invention provides the possibility of operating the heating element S2 according to an individual mode. To this end, the system according to the invention comprises a third power circuit which comprises a second tripping semiconductor element constituted in the example represented by a Triac TR2.

The heating element a can be switched in this power circuit by closing a switch I3 and opening the switch I1. The Triac TR2 control signals are produced by a second thermal switch IT2 which applies, via an ignition capacitor C, an ignition signal to the Triac control terminal. A resistance
R is interposed between this control terminal and the corresponding input terminal of the system according to the invention.

To complete the description of the control system, it is noted that several lamps L1 to L4 are provided to allow signaling of the state respectively of the input switch 12, of the heating elements
S1 and S2 and the IT1 thermal switch.

The control system according to the invention, which has just been described, operates as follows
According to a first mode of operation, the heating elements S1etS2 are mounted in parallel.

Switch I1 is open and switch I3 is closed. After closing the switch 12, the heating elements S1, S2 each with a power for example of 1000 Watt operate at their maximum power since the Triac TRI is controlled accordingly by its control circuit A. The engine n is traversed by its maximum current because the thermal resistance RT does not yet influence the transistor T.

 This operating state of the radiator is maintained 3until the temperature in the room to be heated reaches a threshold value at a predetermined distance below the set temperature. From the moment the actual temperature exceeds this threshold, the sawtooth voltage which is superposed on the setpoint voltage, inside the control circuit A, begins to be effective. The control circuit then begins to block the Triac TR1. The blocking time of the Triac TR1 is short-term, but becomes longer as the actual temperature approaches the set temperature.

As the Triac blocking periods gradually increase, the heating power gradually decreases. Since during the blocking periods of the Triac a current flows through the heating resistor R8 mounted in parallel to the Triac
TR1, this resistance becomes increasingly hot and on the other hand heats the thermal resistance RTce which causes an increase in the resistance constituted by the transistor T. Consequently, the current of the motor n decreases which causes the reduction of its speed of rotation. This means that as the temperature in the room to be heated approaches the set value, the heating power gradually decreases and causes the engine to slow down gradually.

 If the temperature in the room continues to increase, despite the reduction in the heating power and the engine speed, the heating resistor R8 continues to heat up. Due to the thermal coupling between the heating resistor RS and the thermal switch 1T1 located in the power circuit of the motor N, the tripping temperature (for example to twist 650 C) will be reached. With the engine power circuit open, the engine stops.

Thanks to the thermal bond between the heating resistance
S, the thermal resistance RT and the thermal switch IT1, there is an adjustable relationship between the minimum speed of rotation of the motor and the instant of stopping of the latter.

 After stopping the engine and the turbine, the radiator switches from the forced convection heating regime to the natural convection heating regi3e.

The air circulation through the radiator is reversed and the real temperature sensor (E2) which is located close to the ground notices a decrease in temperature at this level of the room. This results in the Triac TRI blocking periods becoming shorter, the current through the heating resistor decreases and this resistance cools slightly. 'shutdown and restarts only after more significant cooling of the room. The hysteresis of the thermal switch also results in the instant when the engine is restarted the thermal resistance RT in the bias circuit of the transistor T is less hot than at the moment of the engine shutdown. The resistance of the transistor is therefore lower. This means that the current at the start of the motor is relatively high. The restart of the motor is therefore guaranteed.
The control system according to the invention is adapted to automatically ensure the optimal operation of a radiator which can operate at two different ratings, for example at 1 kW or at 2 kW, without the manual intervention of a user being necessary . For this purpose, the two heating elements are made electrically independent, thanks to the second Triac TR2 and to the switch S3, the switch S2 being open.

 In these conditions, the device firstly operates at full power, because the two heating elements S1 and S2 are each traversed by its maximum working current. As described above, the heating power of the heating element S1 gradually decreases, as the actual temperature approaches the set temperature, once the aforementioned temperature threshold is exceeded. On the other hand, the second heating element continues to operate at full power. Then, the system orders the engine to stop. If the temperature in the room to be heated continues to rise, the heating power of the first heating element S1 continues to decrease gradually to O. If during this time the temperature of the heating resistor R8 rises the second thermal switch 1T2 can reach its switch-on temperature. This results in the deactivation of the second heating element 82. Since there is no more heating, the temperature in the room decreases slightly and the first heating element S1 is restarted thanks to the increasing periods. long passage of the Triac TRI.

The hysteresis of the thermal switch 1T2 ensures that the second heating element RS2 does not resume its function until after the first element S1 has reached a relatively high level of heating power. The IT2 switch will open at approximately 80 C.

 It is obvious that the control system which has just been described, by way of example, can be modified at numerous points without leaving the scope of the invention.

Indeed, the gradual reduction of the heating power and the rotation speed of the engine as well as the stopping of the latter can be achieved in other ways than that which has been described and which is illustrated by the figure. Thus the heating resistance could be replaced by a normal resistance and the progressive variation of the current passing through this resistance could be detected and exploited to control the variable resistance constituted in the example represented by a transistor connected in series with the motor. This connection between the resistance associated with the circuit of the heating device and the variable resistance forming part of the motor circuit could be carried out in any known manner. One could for example consider using for this purpose a photo-coupler whose voltage output could be taken from the resistor and the output circuit of which could be part of a bias circuit of the transistor or of an additional stage associated with it. Instead of the thermal switches, other types of switches could then be used, controlled by the current passing through the aforementioned resistor associated with the heating element and mounted in parallel on the tripping semiconductor, a current which is representative of the temperature in the room to be heated.

The hysteresis in the behavior of the switch could be introduced for example by an electronic circuit. Such circuits are known in the art.

 In general, it should be noted that the invention is in no way limited to the embodiment described and shown which has been given only by way of example.

In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are executed according to the spirit and implemented in the context of protection as claimed.

Claims (14)

 1. A method of controlling a convection radiator, adapted to operate alternately according to natural convection heating or forced convection heating regimes and comprising an electric heating device and a turbine driven in rotation by an electric motor, according to which a set temperature is chosen for the room to be heated and it is heated by automatically operating the radiator according to one or the other heating regime comparison of the actual temperature in the room and the set temperature , characterized in that, as the local temperature approaches the set temperature, the heating power of the heating device and the speed of rotation of the turbine are automatically and gradually reduced and provides automatic shutdown of the latter when the temperature in the room> after continuing to increase, reaches the value d this instruction, and in that lbn provides for automatic and progressive restarting of the turbine when the temperature at ground level has decreased by a significant value.  2. Method according to claim 1, characterized in that provision is made for the gradual reduction on approaching the set temperature, of the speed of rotation of the turbine as a function of the reduction in the heating power.  3. Method according to one of the preceding claims, for a radiator comprising an additional heating element, characterized in that this additional heating element is inserted into a separate power circuit and provides for an automatic interruption of this circuit in function of the heating power of the aforementioned heating device during the phase of progressive reduction of the heating power of the latter.  4. Control system for implementing the method according to one of the preceding claims, characterized in that the power circuit of the heating device (S1, 82) comprises a device (TR1) sensitive to the temperature prevailing in the space for heating and capable of gradually reducing the current flowing through the heating device, as the temperature approaches a preset temperature chosen, as the engine power circuit (N) comprises a variable resistor T and a switch (IT1) and in that a connection device (Rs, *) of the two power circuits is provided, which comprises means (R8) sensitive to a variation in the current of the heating device (51,82) and producing a control signal of said variable resistance (T) so as to cause a progressive reduction of the motor current (M) following a reduction of the aforementioned current, and a control signal of opening of the switch (I T1) when the set temperature is reached and a signal to close this switch at a temperature close to the ground, which is lower than the set temperature.  5. System according to claim 4, characterized in that the temperature-sensitive device is formed by a tripping semiconductor element (TRI) controlled by a circuit (4 with which is associated a thermostats element  6. System according to reveniication 5, characterized in that the semiconductor element (TR1) is constituted by a Triac with commutation during the passage through zero of the supply voltage of the heating device, the control device (A ) of the Triac (TR1) comprising a setpoint generator E1 to which is superimposed a potential in the form of a sawtooth, this Triac (TR1) letting through whole blocks of alternations whose number decreases with the approach of the temperature setpoint.  7. System according to one of claims 4 to 6, characterized in that the variable resistor (arranged in the motor power circuit (M) is formed by a transistor connected in series with a rectifier bridge (PX the resistance of the path) collector-emitter of the transistor being variable by variation of a bias resistance.  8. System according to one of claims 5 to 7, characterized in that a resistor (R,) is mounted in parallel on the trigger element (TR1) mounted in the power circuit of the heating device.  9. System according to claim 8, characterized in that the resistor (Rp above is a heating resistor and the bias resistor of the transistor (T) is a resistor (RT) sensitive to temperature and is mounted close to the heating resistor for be influenced by its temperature.  10. System according to claim 9, characterized in that the switch Tl) mounted in the circuit of the motor M is a thermal switch opening at a predetermined temperature, this switch being located at a place at which its temperature is determined by the heating resistance (Rs).  11. Control system according to one of claims 4 to 10, characterized in that it comprises an additional heating element (S2) which is mounted in a separate power circuit comprising a thermal switch (IT2) whose temperature trigger is greater than that of the first  thermal switch (I1) and in that the temperature of the thermal switch (IT2) is determined by the temperature of the heating resistor (Rs).  12. System according to one of claims 4 to 7, characterized in that the connecting device between the engine power circuit and the heating power circuit is formed by a transformer member dlune voltage taken from the above-mentioned parallel resistance in a control voltage for the bias resistance of transistor T.  13. The system of claim 12, characterized in that the connecting device is formed by a photo-coupler, the bias resistance being that of the output circuit of the photo-coupler  14. Switch according to one of claims 4 to 9 and 71 to 13, characterized in that the switch IT1 mounted in the power circuit of the motor M is a switch with two thresholds, a closing threshold and an opening threshold , the closing threshold being lower than the opening threshold.