Ventilation systems

Abstract: A control for a fan 1 has a temperature sensor 10 and a humidity sensor 11 the outputs of which are supplied to a processor 8. The processor 8 switches on the fan when certain temperature and humidity conditions are met. The processor 8 turns on the fan 1 in response to an increase in temperature and humidity, a larger increase in humidity being required for a smaller increase in temperature. The fan 1 is also turned on when humidity rises above a certain threshold value, which is lower for higher temperatures.

Description: This invention relates to ventilation systems including a ventilation device, a humidity sensor, a temperature sensor and a processor that receives outputs from the humidity and temperature sensors and provides ventilation output control signals to activate the ventilation device. Fan controllers that respond to a rise in humidity in a room, are known, such as, for example, from GB2133588. One problem with such controllers is that they may cause nuisance switching of the fan, or they may switch the fan on later than is desirable. Nuisance switching can be caused when the room temperature drops, such as at night, since this will lead to a rise in humidity that can be sufficient to trip the fan on. Furthermore, the fan may not be switched on quickly enough when the room temperature rises, such as during cooking or bathing. GB 2209070A describes a ventilation system in which a fan is turned on when a trigger level is exceeded, which is dependent primarily on relative humidity and has a slight inverse dependence on temperature. It is an object of the present invention to provide improved ventilation systems. According to the present invention there is provided a ventilation system of the above-specified kind, characterised in that the processor provides the ventilation output control signals to the ventilation device in response to a first predetermined change in sensed humidity with respect to a reference level of humidity accompanied by a first predetermined change in temperature with respect to a reference level of temperature, and in response to a second predetermined change in sensed humidity different from the first change accompanied by a second predetermined change in temperature different from the first change. The processor is preferably produces the output control signals when the first and second changes in temperature are increases in temperature, the first increase being greater than the second, and when the first change in sensed humidity is less than the second. The processor preferably produces the output control signals when the first and second changes in temperature are falls in temperature, the first fall being greater than the second and when the first change in sensed humidity is greater than the second. The processor may also provide a ventilation output control signal when humidity rises above a certain threshold value, which may be different at different temperatures, preferably the humidity threshold being lower at higher temperatures than at lower temperatures. A fan ventilation system including a ventilation fan and a control unit in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows the system schematically; and Figure 2 illustrates variations in humidity with temperature. The fan ventilation system comprises a conventional electric fan 1 mounted in an opening 2 in a wall 3 so as to ventilate a room 4. The fan has an electric motor 5 connected by a wire 6 to a control unit 7, which may be a separate unit or be incorporated into the fan unit. The control unit 7 includes a microprocessor 8 and a memory 9, and is connected to receive inputs from a temperature sensor 10 and a humidity sensor 11 of conventional kind. The control unit 7 also has a manual control 12. The control unit 7 monitors the temperature and humidity from the sensors 10 and 11 to establish a normal reference level, which is updated at intervals and stored in the memory 9. The microprocessor 8 then compares real time values of temperature and humidity with this reference level to determine whether or not an output signal should be supplied to the fan motor 5 to turn on the fan 1. More particularly, the control unit 7 is arranged to turn the fan 1 on after a predetermined rise in humidity from the reference level. The control unit 7 trips on the fan 1 after a low rise in humidity, if this is accompanied by a large rise in temperature, or after a higher rise in humidity, if this is only accompanied by a relatively small increase in temperature. Also, if there were a fall in temperature from ambient, the control unit 7 would only turn on the fan 1 after a greater increase in humidity than would be necessary to trip at the ambient temperature. The table below is an example of humidity changes necessary to cause the fan 1 to be tripped on for different changes in temperature. The table could be stored as a look-up table in the memory 9 or it could be implemented as an algorithm. Temperature Rise °C Humidity % change for trip 10 20 8 22 6 24 4 26 2 28 0 30 -2 32 -4 34 -6 36 -8 38 Figure 2 shows the variation in moisture content with temperature at four different saturations: 70%, 80%, 90% and 100%. Thus, if there were a high level of moisture-causing activity in the room 4, such as cooking, the temperature would rise fairly rapidly, so the fan 1 would be turned on relatively quickly. A low level of activity, however, such as respiration, would only cause a slower temperature rise so it would take longer before the trip value of temperature and humidity was reached. A fall in room temperature, such as at night, would usually lead to a rise in sensed humidity levels but, because this is accompanied by a drop in ambient temperature, this rise in humidity would have to be high before the fan was turned on. In addition to, or instead of, responding to the above changes in humidity, the system responds when humidity rises above certain threshold values, even if the difference between ambient humidity and these threshold values is less than the values above. This ensures that the fan is operational in situations where there are prolonged high levels of ambient humidity and also improves the response of the controller at night. Different threshold values are set for different temperatures, as illustrated below. This table could be stored as a look-up table or it could be implemented as an algorithm. Temperature °C Threshold Humidity % 20 70 18 75 16 80 14 85 12 90 10 95 Once tripped on, the controller checks whether the humidity and temperature have fallen below the trip level. When these values fall below the trip-off level, the controller turns the fan off. The trip-off value could be equal to the trip-on value but would normally be some predetermined value below the trip-on value, or below the ambient value. Alternatively, the fan could simply remain on for a predetermined time and then be turned off. By contrast, in a conventional, humidity-controlled fan system, the fan would be turned on at the same humidity level, whatever the temperature. Thus, it would either be turned on later than is desirable, when there is a high level of activity, or be turned on too soon, when there is a low level of activity. Also, the increase in humidity caused by a drop in room temperature can be sufficient to trigger a conventional fan to come on, even though there is no need for ventilation. The present invention avoids these disadvantages. It will be appreciated that the present invention is not restricted to use with fans but could be used with other ventilation devices such as automatic vents. Also, the invention is not confined to ventilation of rooms but could be used in other applications where it is necessary to ventilate a space subject to humidity and temperature changes. The system could be arranged to drive the fan continuously at a low level and then at a higher level when the humidity/temperature rises above the trip level. The control unit need not have a microprocessor but could have a dedicated electrical circuit that performs the necessary monitoring.

Claims: A ventilation system including a ventilation device (1), a humidity sensor (11), a temperature sensor (10) and a processor (8) that receives outputs from the humidity and temperature sensors and provides ventilation output control signals to activate the ventilation device, characterised in that the processor (8) provides the ventilation output control signals to the ventilation device (1) in response to a first predetermined change in sensed humidity with respect to a reference level of humidity accompanied by a first predetermined change in temperature with respect to a reference level of temperature, and in response to a second predetermined change in sensed humidity different from the first change accompanied by a second predetermined change in temperature different from the first change. A ventilation system according to Claim 1, characterised in that the processor (8) produces the output control signals when the first and second changes in temperature are increases in temperature, the first increase being greater than the second, and when the first change in sensed humidity is less than the second. A ventilation system according to Claim 1 or 2, characterised in that the processor (8) produces the output control signal when the first and second changes in temperature are falls in temperature, the first fall being greater than the second, and when the first change in sensed humidity is greater than the second. A ventilation system according to any one of the preceding claims, characterised in that the processor (8) also provide a ventilation output control signal when humidity rises above a certain threshold value. A ventilation system according to Claim 4, characterised in that the humidity threshold value is different at different temperatures. A ventilation system according to Claim 5, characterised in that the humidity threshold is lower at higher temperatures than at lower temperatures.

Inventors: NGAI KWOK M, NGAI, KWOK M.
Applicants: SMITHS GROUP PLC
Application year: 1995
Main classification: G05D22
IPC codes: F24F11, F24F7