GB2209070A - Humidity and ventilation control - Google Patents

Abstract

To prevent dam and mould in a well-insulated modern house, humidity control is often necessary, but causes customer concern. In the invention, humidity control is provided by using a fan 14 in a cooker hood 10, venting to an outside wall 13. The fan is turned on when the general house humidity rises too high, as sensed by a humidity sensor 20, which is preferably of a self-cleaning type. It is also controlled by a conventional manual 4-position (off plus 3 speeds) control switch 15, and by a cooking temperature sensor 22. The humidity trigger level may be varied in dependence on the ambient temperature (sensed by a temperature sensor 21). A second humidity sensor (40, Fig. 2) may be located e.g. in or near a bathroom. This preferably has low sensitivity, but sets the fan to high speed; the sensor 20 will then sense the damp air being drawn from the bathroom and continue extraction (at low speed). Any suitable type of heat exchanger can be used in place of the simple wall vent 12. <IMAGE>

Description

The present invention relates to humidity and ventilation control.

Ventilation control for a domestic house, by means of a fan mounted in a wall or window, is well known. In a simple installation, the fan is provided with a direct on-off switch (usually with a pull cord).

Modern houses are currently built with particular regard to energy conservat ion. Heat losses can occur by heat conduction. Hence walls and windows are constructed to give low heat conduction, e.g. by filling cavity walls and by double glazing windows. Heat losses can also occur by direct heat transport, by the influx of cold air from outside and the efflux of warm air from inside.

Hence houses are designed and constructed so that the natural ventilation is kept to the minimum consistent with the need to maintain the air fresh for breathing. In particular, such houses often contain few or no chimneys.

While the natural ventilation of such houses is adequate for breathing, problems often occur with dampness. The normal breathing and perspiration of an occupant generates an appreciable quantity of water vapour, and domestic activities such as washing, bathing, showering, and cooking usually generate considerably more. In cool or cold weather this can result in substantial condensation on walls and windows; although the insulation of these results in them not being so cold as in older style houses, this is more than outweighed by the reduced ventilation compared to older style houses. Condensation, with the attendant problems such as growth of mould, can thus occur in rooms which are relatively cool (such as bedrooms) or particularly damp (such as kitchens and bathrooms).

To overcome this problem, it is necessary to provide some form of forced ventilation and a control system which operates the ventilation means properly.

As noted above, it is well known to provide ventilation fans. These alone are however insufficient, because the house occupier is unlikely to use them in such a way as to avoid problems with condensation. It has therefore become known to provide humidity sensing means which automatically control the fan. Manual control of the fan is also normally retained -so that the user can turn the fan on regardless of the humidity control, though if the humidity control turns the fan on, the manual control cannot normally over-ride this to turn the fan off.

However, while this arrangement is reasonably effective technically, it suffers from the disadvantage that it is embarrassing for a house builder to have to explain to the house purchaser that the house is liable to suffer from problems of dampness.

There is therefore a need for a humidity and ventilation control system which achieves technical effectiveness while minimizing consumer concern.

Accordingly the present invention provides a humidity and ventilation system comprising a cooker hood including a fan connected to an external vent and a control switch for the fan, and a humidity sensor controlling the cooker hood fan in logical OR combination with the control switch.

This arrangement has various advantages. Thus it utilizes a single ventilation means for two different purposes - kitchen atmosphere control and general house humidity level control. Also, it 'goes a long way towards overcoming consumer concern, since a house purchaser is not likely to be concerned by the provision of a cooker hood in the kitchen; in fact, many new houses are often provided with fitted kitchens automatically by the builder.

The external vent may comprise a heat exchanger.

Preferably, the humidity sensor is of the self-cleaning type and has associated with it a temperature sensor and a circuit providing temperature set-back.

The humidity sensor and associated temperature sensor are preferably located on the cooker hood in a position to sense the humidity of the ambient air in the kitchen in which the cooker hood is located.

The cooker hood preferably also has a further temperature sensor incorporated therein responsive to the temperature of the air rising from the cooker below to control the fan in logical OR combination with other fan control signals.

Preferably the system also includes one or more further humidity sensors located elsewhere in the house.

The system preferably also includes an indicator, which is preferably located on the cooker hood, for indicating the state of the system.

The system may utilize a microprocessor for processing the signals from the various sensors and controlling the fan.

Further significant features of the system will become apparent from the following description of a humidity and ventilation system embodying the invention, and a modification thereof, given by way of example and with reference to the drawings, in which: Fig. 1 shows a cooker hood and associated elements forming part of the system; Fig. 2 is a block diagram of the circuitry of the system; and Fig. 3 is a block diagram of the circuitry of the modified system Fig. 1 shows a cooker hood 1(! containing a fan 14 which, when operated, draws air through the lower surface of the hood 10 and expels it via a duct 11 leading to a wall vent 12 in an outside wall 13. The hood has a conventional manual control switch 15 on its front for controlling the fan 14.The switch may conveniently have four positions; off, low speed, medium speed, and high speed. Any suitable type of heat exchanger can be used in place of the simple wall vent 12.

Some cooker hoods can optionally be set to recirculate the air inside the kitchen, so that the air is merely passed through a filter to remove grease and smells. It will be realized that such a mode of operation is incompatible with the present invention, for which it is necessary for the air to be vented to the outside of the house. This is because, with the present invention, moisture must effectively be removed from inside the house, and in practice this can only be achieved by expelling moist air to the outside. While it is theoretically possible to remove moisture in a recirculating system, to achieve that in practice would require an air conditioning system.

The cooker hood also contains a humidity sensor 20, two temperature sensors 21 and 22, a display unit 23, and a circuit board 24 which are utilized by the present system. The two sensors 20 and 21 are located side by side on the cooker hood in a position.where they sense the humidity and temperature of the ambient air in the kitchen, while the sensor 22 is located so as to sense the temperature of the air coming directly from the cooker (not shown) below the hood. A suitable location for the sensors 20 and 21 is on the vertical front panel of the cooker hood, for example where shown.The sensor 22 may be mounted on the underneath of the cooker hood, as shown; another suitable location is in the interior of the cooker hood, mounted on the circuit board 24. (This assumes, of course, that the circuit board 24 is not thermally insulated, and is capable of withstanding the temperatures encountered in the cooker hood as a result of cooking.) Fig. 2 is a block diagram of the circuitry of the present system. Since the humidity sensor 20 is located in a cooker hood in a kitchen, it will be exposed to cooking effluvia even if it is mounted on the side or top of the hood 10, and must therefore be of a type which is tolerant of such effluvia. It is preferred to use a self-cleaning sensor, of the semiconductive ceramic type (e.g.

made from MgCr20.TiO). Associated with this is a humidity sensor cleaning circuit unit 30, which operates at suitable intervals (e.g. every 30 min) to heat the humidity sensor 20 to a high enough temperature to drive off (by evaporation and/or oxidation) any oily deposits which may have been formed on the sensor 20 and which would, if allowed to build up, "poison" it.

The sensor 20 feeds a set-back circuit unit 31 which is also fed by the temperature sensor 21. The circuit 31 combines the two sensor signals into a resultant signal which reaches a trigger level dependent primarily on the relative humidity (RH) but also having a slight inverse dependence on temperature.

A suitable characteristic is one which reaches the trigger level at an RH of 0.80 for a temperature of 15 CC or below, at an RH of 0.65 for a temperature of 21 CC or above, and is approximately linear between those values. This circuit 31 feeds a trigger and logic circuit 32 which generates a high output signal when the signal from circuit 31 exceeds the trigger level. Circuit 32 is also fed from the cleaning circuit 30, to disable it when the humidity sensor 20 is being cleaned or has just been cleaned but is still hot, and from an RH control circuit 33 which provides for adjustment of the trigger level. The circuit 32 also includes a hysteresis timer which maintains the output signal high for a suitable predetermined time, e.g. 1 min, once it has gone high, to prevent unduly rapid cycling of the system.

The circuit 32 feeds a logic circuit 34 which is also fed from the manual cooker hood control switch 15 and controls the fan 14. The switch 15 has three positions (apart from the off position), and produces an ON signal on one of three lines corresponding to the three fan speeds (low, medium, and high). The signal from circuit 32 is logically OR'ed onto the low speed line to the fan 14, so that the fan is driven at the low speed if it is set to that speed by the switch 15 or if the humidity as sensed by the sensor 20 is too high. The low speed line includes an inhibit gate (not shown) controlled by the medium and high speed lines so as .to inhibit any signal on the low speed line if either the medium or the high speed line is energized, and the medium speed line contains a similar inhibit gate (not shown) controlled by the high speed line.

The logic circuit 34 also feeds the display unit 23, which may be or include a digital display, and which displays the state of the system. Specifi- cally, the display unit is preferably arranged to give a reminder signal if the fan has been switched to low speed by the switch 15. Without this, there is a danger that the user may forget that the fan has been switched on by the switch 15 and will assume instead that the fan is running under the control of the humidity sensor 20.If this happens, then the fan may be left to continue running continuously under the control of the switch 15 when it would otherwise be switched off in due course when the humidity fell below the level required by the sensor 20. (The same effect can be produced by the temperature sensor 21.) The display 23 may also indicate generally which signals (i.e. from the humidity sensor 20, the temperature sensor 21, and the manual control unit 15) are active, i.e. causing the fan to run.

The display 23 may also be used to display other information, e.g. the temperature sensed by the sensor 21 or the relative humidity sensed by the humidity sensor 20. For this, of course, control means for changing the displayed information and connections from the sensors would be needed. A clock circuit (not shown) may be included, and the display may be arranged to show the temperature when that is causing the fan to run, the relative humidity when that is causing the fan to run, and the time otherwise. Obviously, means may be provided for causing the display to display temporarily any other desired one of these quantities (relative humidity, temperature, and time) in preference to the quantity it would normally be displaying.

The temperature sensor 22 is connected to a trigger circuit 35 (generally similar to the trigger circuit 32) which in turn feeds the logic circuit 34, which OR1s the signal from the circuit 34 onto the low speed fan drive line, along with the signals from the switch 15 and the circuit 32. Hence if the temperature of the air underneath the cooking hood 10 reaches a predetermined level (a suitable value is 30 OC), the fan 14 will again be switched to low speed regardless of the state of the switch 15.

The system also includes a remote humidity sensor unit 40, comprising a humidity sensor 41, a temperature sensor 42, a humidity sensor cleaning circuit 43, a set-back circuit 44, an adjustment control circuit 45, and a trigger circuit 46, analogous to units 20, 21, 30, 31, 32, 33, and 34 respectively. This remote unit 40 is located at a suitable location in the house where the sensing of high humidity is valuable, e.g. in or near a bathroom or shower room. (A generally suitable height for the remote sensors 41 and 42 is about 1.5 m above floor level.) > Circuit 46 feeds the logic circuit 34, which OR's the signal from it with the other signals which control the low fan speed. It is obvious that further remote humidity sensing units (and remote temperature sensing units) may similarly be connected into the system.

It is clear that the system operates to sense a high humidity level in the kitchen or at the location of the remote unit 40, and causes the fan 14 in the cooker hood 10 to run at low speed for as long as the humidity is above a defined level. The cooker hood can also be operated normally by the switch 15 on the cooker hood; if the various elements controlling the fan call for different fan speeds, the fan will run at the highest of the various speeds called for.

It will be realized that the trigger circuit 31 (and the corresponding circuit 46) can be modified to sense an additional level (or two such levels) of humidity, with the logic circuit 34 being correspondingly modified to OR the higher humidity signals appropriately onto the medium speed control line (or the medium and high speed control lines) to the fan 14, so that the fan can be controlled at two (or three) speeds by the humidity sensing.

Alternatively or additionally, a remote sensor located say in or near a bathroom may be arranged to cause the fan to run at say the high speed if it senses a humidity above a defined level. In this case, fast extraction would be desirable since there would be a large amount of very damp and hot air, while its extraction by means of the cooker hood would be of relatively low efficiency because it would become mixed with air from elsewhere in the house on its way to the cooker. However, the sensor near the bathroom could be set with low sensitivity, i.e. to detect only a very high humidity level, since once the extraction process has been initiated, the sensor 20 on the cooker hood would respond. to the humidity level of the air being drawn from the rest of the house generally into the kitchen, and this would include the humid air from the bathroom.

Fig. 3 shows a modification of the circuitry of Fig. 2, in which a microprocessor 50 is used. The sensing elements remain unchanged, and are given the same references. The humidity sensor cleaning circuit 51 corresponds to circuit 30 but in a modified form, since it no longer needs to include a timing element or to control a trigger circuit, but is controlled from the microprocessor 59 (which is assumed to contain a clock circuit, not shown). The microprocessor 50 also controls the fan 14 via a fan driver circuit 52. The remote sensor unit 53 contains a relative humidity sensor, a temperature sensor, and a humidity sensor cleaning circuit corresponding to elements 20, 21, and 51. The various sensors are connected to a multiplexer 54, which is controlled by the microprocessor 50 and which feeds an analog-to-digital converter 55 which in turn feeds the microprocessor, so that the microprocessor samples the values of all the various quantities being sensed at a suitable rate. A manual control device 56 is also connected to the microprocessor; this serves as the manual control switch 15, and may also be used to change a variety of settings of the program stored in the microprocessor. The microprocessor will of course perform the functions of the set-back circuit 31, the trigger circuit 32, etc.

Claims (11)

C la ims

1 A humidity and ventilation system comprising a cooker hood including a fan connected to an external vent and a control switch for the fan, and a humidity sensor -controlling the cooker hood fan in logical OR combination with the control switch.

2 A humidity and ventilation system according to claim 1 wherein the external vent comprises d heat exchanger.

3 A humidity and ventilation system according to either previous claim wherein the humidity sensor is of the self-cleaning type.

4 A humidity and ventilation system according to any previous claim wherein the humidity sensor has associated with it a temperature sensor and a circuit providing temperature setrback.

5 A humidity and ventilation system according to any previous claim wherein the humidity sensor and associated temperature sensor (if any) are located on the cooker hood in a position to sense the humidity of the ambient air in the kitchen in which the cooker hood is located.

6 A humidity and ventilation system according to any previous claim wherein the cooker hood also has a further temperature sensor incorporated therein responsive to the temperature of the air rising from the cooker below to control the fan in logical OR combination with other fan control signals.

7 A humidity and ventilation system according to any previous claim wherein the system also includes one or more further humidity sensors located elsewhere in the house.

8 A humidity and ventilation system according to any previous claim wherein the system also includes an indicator for indicating the state of the system.

9 A humidity and ventilation system according to claim 8 wherein the indicator is located on the cooker hood.

10 A humidity and ventilation system according to any previous claim wherein the system includes a microprocessor for processing the signals from the various sensors and controlling the fan.

11 A humidity and ventilation system substantially as herein described and illustrated.