GB2210966A - Ventilating fan control arrangement - Google Patents

Abstract

An extractor fan is responsive to a rate of increase of temperature in excess of a predetermined rate. The temperature is sensed by two sensors, one of which is associated with a mass of significant thermal capacity, the outputs of the two sensors being compared to generate a control signal when the outputs differ by a predetermined amount. The fan is located in a kitchen where a rapid rise in temperature indicates cooking is taking place and water vapour is likely to be generated. A humidity sensor and timer may also be associated with the fan. <IMAGE>

Description

Description of Invention Improvements in or relating to a ventilating fan control arrangement THE PRESENT INVENTION relates to a control arrangement for a ventilating fan and more particularly relates to a control arrangement for a fan known as a extractor fan, although it is to be appreciated that such fans may operate not only to extract air from a space being ventilated, but also to inject fresh air into that space.

At the present point in time it is common to use extractor fans in many domestic situations where it is designed to ventilate the space to maintain predetermined conditions. It has been proposed previously to provide an extractor fan which is controlled in response to signals from a relative humidity sensor, so that the extractor fan is actuated whenever the relative humidity exceeds a predetermined level. The sensor may be associated with a timer so that whenever a relative humidity in excess of a predetermined level has been sensed, the timer will subsequently operate the fan for a minimum predetermined period of time, as dictated by the timer.

Fans of this type may be utilised in a satisfactory manner in bathrooms, where the relative humidity tends to rise when the bathroom is in use.

However, if a fan of this type is utilised in a kitchen situation, the fan may not operate in a satisfactory manner. The reason for this is that when a cooking operation is commenced, usually the temperature within the kitchen rises, and thus the relative humidity level tends to drop, since at an increased temperature air may hold an increased amount of moisture. It is possible that an entire cooking operation may be accomplished without the relative humidity exceeding the level necessary to trigger operation of the fan but, at the end of the cooking operation, the air within the kitchen will be warm, and will be carrying a significant amount of moisture. As the air then cools down, the relative humidity level will rise, and the fan will be actuated when the relative humidity level reaches the threshold of the sensor.However, by that time, moisture will be beginning to condense on exposed surfaces within the kitchen, and although the fan will then be actuated, nevertheless considerable condensation may occur before the fan is able to extract all the saturated air from the space to be ventilated.

It might be thought that an extractor fan, in such a situation, may be actuated in response to the temperature within the kitchen. However, such an arrangement would not prove to be satisfactory, since the temperature within a kitchen may reach the threshold value on a hot day, or if the central heating is turned up for any reason.

The present invention seeks to provide an improved control arrangement for an extractor fan.

According to this invention there is provided a control arrangement for a ventilating fan, said control arrangement comprising a sensor arrangement comprising sensor means adapted to sense the temperature within a space to be ventilated by the fan and to respond to a rate of increase of temperature in excess of a predetermined rate to activate the fan.

Preferably the sensor arrangement additionally comprises means to sense the relative humidity within the space to be ventilated b the fan, and to respond to a relative humidity in excess of a threshold rate to activate the fan.

Conveniently the fan is activated by the sensor arrangement by means of a timer adapted to cause the fan to be actuated for a predetermined period of time after the sensor arrangement has sensed conditions in excess of the predetermined limits to actuate the fan.

Preferably the sensor arrangement comprises two temperature sensing elements, means to pass signals derived from said two temperature sensing elements to a comparator and means to delay the signal in response to a rise in temperature from one sensing element.

Conveniently said comparator comprises a differential amplifier.

said delay means may comprise electronic delay means in the form of a delay circuit to delay a signal from said sensing element, such as an RC network, but preferably said delay means comprises an element having a relatively high thermal capacity in direct contact with one said sensing element.

Conveniently said sensing elements comprise heat sensitive diodes connected in parallel, in parallel resistive lines with a predetermined potential applied thereacross, said signals being potentials derived from said resistive lines at points adjacent said diodes.

The invention also relates to a ventilating fan provided with such a control arrangement.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIGURE 1 is a block diagram of one embodiment of a control arrangement in accordance with this invention, showing a possible modification; and FIGURE 2 is a circuit diagram of a rate of temperature change sensor which forms part of the arrangement as illustrated in Figure 1.

Referring to the drawings, a control arrangement for an extractor fan comprises a sensor 1 which is adapted to sense, and respond to, a rate of increase of temperature which exceeds a predetermined rate of increase of temperature. This sensor is connected to a timer, so that whenever a rate of increase of temperature in excess of the predetermined rate is sensed the timer is triggered, and the timer will then cause a fan to run for at least a predetermined period as set by the timer. The timer is connected directly to the extractor fan 3 to activate the extractor fan. Optionally a humidity sensor 4 may be provided, also connected to trigger the timer when a humidity in excess of a predetermined humidity is sensed.

It will be understood, from the block diagram, that the fan will be activated for a predetermined period of time whenever the temperature rises at a rate in excess of the predetermined rate, or whenever a humidity in excess of the predetermined humidity is sensed.

The rate of temperature change sensor 1 and the humidity sensor 4 may be located at any convenient place within a space to be ventilated. Thus the sensors 1 and 4 may be mounted on or adjacent the fan 3, or may be mounted at any other convenient position.

If the described arrangement is mounted in a kitchen, and a meal is to be cooked, when the actual cooking starts, and the cooker is turned on to heat saucepans, or frying pans, the temperature in the room rises rapidly. This rapid rise in temperature will be sensed by the temperature change sensor 1 and will trigger the fan via the timer circuit. As the temperature keeps rising at a rate above the predetermined rate the timer remains set. The temperature eventually levels off, when an equilibrium position is reached.

At this time the temperature change sensor sends no more signals to the timer 2, but the timer continues to be activated for a predetermined time delay, for example twenty minutes. After this period of time the fan stops. However, if the humidity sensor 4 is provided and if, during the period of twenty minutes, the humidity rises to the threshold level of the humidity sensor, the timer is again set and thus the fan will continue to run until after the humidity has been reduced below the threshold level, and even then the timer will ensure that the fan runs for the preset period of twenty minutes after the humidity has passed below the threshold level.

It has been found, in experimentation, that during the cooking of a meal, the temperature fluctuates repeatedly as cooking elements are turned on and off, and as the oven door is opened, and thus it has been found that a fan provided with a rate of temperature change sensor operates substantially continuously during any cooking operation. This helps ensure that any moisture present in the air during the cooking operation, and also any smells, are rapidly extracted from the space being ventilated.

It is to be understood that it will be possible to utilise any appropriate sensor responsive to a predetermined rate of increase of temperature-, but a preferred rate of temperature change sensor is illustrated in Figure 2 of the accompanying drawings.

The sensor illustrated in Figure 2 comprises various electrical components connected between a positive power rail 5, and an earth rail 6. The earth rail is connected, to the tap 7 on a rheostat 8, one terminal of which is connected to a series connection comprising a resistor 9 and a heat sensitive diode 10 and the other terminal of which is connected to a series connection comprising a corresponding resistor 9' and a corresponding heat diode 10'. The series connections of resistors and diodes 9, 10, 9', 10' are connected in parallel, and the terminals of the diodes 10, 10' are connected through a further resistor 11 to the earth rail 6. The rheostat 8 may be adjusted so that in an initial condition the current flow through both arms of the parallel connection of the resistors and diodes is the same.

Leads 12 and 13, connected to the junctions between the resistor 9 and diode 10, and the resistor 9' and the diode 10' respectively are connected to the differential inputs of a differential amplifier which thus acts as a comparator. A suppresion capacitor 14 is associated with the differential amplifier. The output of the differential amplifier is fed, by means of biassing resistors 15, 16 to the base of an amplifying transistor 16, the output of which 17 is fed to the timer 2.

In the described embodiment the diode 10 is in contact with a body 18 having a significant thermal capacity such as, for example, an aluminium washer, whereas the diode 10' is not provided with any such body.

It will be appreciated that the diodes 10,10' will be located at a position where they are exposed directly to the temperature within the space to be ventilated by the fan 3. If the temperature rises gradually, the temperature of the diode 10' will always be slightly greater than the temperature of the diode 10, since the diode 10' will tend to follow the fluctuations in temperature more rapidly than the diode 10 because of the presence of the body 18 associated with the diode 10. However, if the temperature within the space rises very rapidly, the diode 10' will have a significantly greater temperature than the diode 10, since it will take some noticeable period of time for the body 18 providing the thermal capacity to absorb sufficient heat for the temperature of the diode 10 to be equivalent to the temperature of the diode 10'.

It will be appreciated that the potential present on the lead 12 or on the lead 13 depends upon the temperature of the respective diode 10 or 10'. The effective resistance provided by the diode 10 or 10' is inversely proportional to the temperature, and thus the potential sensed is indicative of the temperature of the diode. When the arrangement is initially set up by adjusting the rheostat 8 the voltages on the leads 12, 13 will be the.same.

It will be understood that the differential amplifier may be pre-set to act as a comparator, with the amplifier providing no output when the two input signals are virtually the same, and providing an output only when the potentials present on the leads 12 and 13 differ to a predetermined extent. When the temperature rises rapidly, the potentials will differ by this predetermined extent (due to the fact that there is a delay in the temperature of the diode 10 rising and thus there is a delay in the potential present on the lead 12 being equivalent to the potential present on the lead 13) and the differential amplifier will provide an output signal.

The output of the differential amplifier is further amplified by the amplyfing transistor 16, thus triggering the timer 2.

Whilst reference has been made to an arrangement in which two sensing diodes are utilised, and in which specific means are provided to delay a signal originating from one diode subsequent to a rise in temperature by providing that diode with a large associated thermal mass, it is to be appreciated that other expedients may be adopted, and thus one diode may be associated with an electric delay circuit, such as an appropriate RC network.

Whilst the invention has been described with reference to one preferred embodiment many modifications may be effected without departing from the invention.

Claims (12)

1. A control arrangement for a ventilating fan, said control arrangement comprising a sensor arrangement comprising sensor means adapted to sense the temperature within a space to be ventilated by the fan and to respond to a rate of increase of temperature in excess of a predetermined rate to activate the fan.

2. An arrangement according to claim 1, wherein the sensor arrangement additionally comprises means to sense the relative humidity within the space to be ventilated by the fan, and to respond to a relative humidity in excess of a predetermined threshold to activate the fan.

3. An arrangement according to claim 1 or claim 2 wherein the fan is activated by the sensor arrangement by means of a timer adapted to cause the fan to be actuated for a predetermined period of time after the sensor arrangement has sensed conditions in excess of the predetermined limits to actuate the fan.

14. An arrangement according to any one of the preceding claims wherein the sensor arrangement comprises two temperature sensing elements, means to pass signals derived from said two temperature sensing elements to a comparator and means to delay the signal in response to a rise in temperature from one sensing element.

5. An arrangement according to claim 4, wherein said comparator comprises a differential amplifier.

6. An arrangement according to claim 4 or 5, wherein said delay means comprises electronic delay means in the form of a delay circuit to delay a signal from said sensing element.

7. An arrangement according to claim 6 when said delay means comprises an RC network.

8. An arrangement according to claim 4 or 5, wherein said delay means comprises an element having a relatively high thermal capacity in direct contact with one said sensing element.

9. An arrangement according to any one of claims 4 to 8, wherein said sensing elements comprise heat sensitive diodes connected in parallel, in parallel resistive lines with a predetermined potential applied thereacross, said signals being potentials derived from said resistive lines at points adjacent said diodes.

10. An arrangement for controlling a ventilating fan substantially as herein described with reference to, and as shown in, the accompanying drawings.

11. A ventilating fan provided with a control arrangement according to any one of claims 1 to 10.

12. A ventilating fan provided with a control arrangement according to any one of claims 1 to 10.

12. Any novel feature or combination of features disclosed herein.

Amendments to the claims have been filed as follows 1. According to this invention there is provided a control arrangement in combination with a ventilating fan, said control arrangement comprising a sensor arrangement comprising sensor means adapted to sense the temperature within a space to be ventilated by the fan and to respond to a rate of increase of temperature in excess of a predetermined rate to activate the fan.

2. An arrangement according to claim 1, wherein the sensor arrangement additionally comprises means to sense the relative humidity within the space to be ventilated by the fan, and to respond to a relative humidity in excess of a predetermined threshold to activate the fan.

3. According to another aspect of this invention there is provided a control arrangement for a ventilting fan, said control arrangement comprising a sensor arrangement comprising sensor means adapted to sense the temperature within a space to be ventilated by the fan and to respond to a rate of increase of temperature in excess of a predetermined rate to activate the fan, the sensor arrangement additionally comprising means to sense the relative humidity within the space to be ventilated by the fan, and to respond to a relative humidity in excess of a predetermined threashold to activate the fan.

4. An arrangement according to any one of the preceding claims wherein the fan is activated by the sensor arrangement by means of a timer adapted to cause the fan to be actuated for a predetermined period of time after the sensor arrangement has sensed conditions in excess of the predetermined limits to actuate the fan.

5. An arrangement according to any one of the preceding claims wherein the sensor arrangement comprises two temperature sensing elements, means to pass signals derived from said two temperature sensing elements to a comparator and means to delay the signal in response to a rise in temperature from one sensing element.

6. An arrangement according to claim 5, -wherein said comparator comprises a differential amplifier.

7. An arrangement according to claim 5 or 6, wherein said delay means comprises electronic delay means in the form of a delay circuit to delay a signal from said sensing element.

8. An arrangement according to claim 7 when said delay means comprises an RC network.

9. An arrangement according to claim 5 or 6, wherein said delay means comprises an element having a relatively high thermal capacity in direct contact with one said sensing element.

10. An arrangement according to any one of claims 5 to 9, wherein said sensing elements comprise heat sensitive diodes connected in parallel, in parallel resistive lines with a predetermined potential applied thereacross, said signals being potentials derived from said resistive lines at points adjacent said diodes.

11. An arrangement for controlling a ventilating fan substantially as herein described with reference to, and as shown in, the accompanying drawings.