GB2251681A - Controlling a ventilator fan speed and heater output - Google Patents

Abstract

A roof void ventilation unit has a motor-driven fan (26a) for drawing air from the roof void and delivering it to an outlet duct (15) adapted for fitting to the ceiling aperture, a heater (40) located in the flow path of the air from the roof void to the outlet duct (15), means (36) for detecting the temperature of the airflow in the outlet duct (15), and means (34, 35, 36, 37) for controlling the operation of the fan motor (26b) and of the heater (40) whereby to adjust the air flow rate and the heat supplied respectively, in dependence on the temperature of 34 the air. If the temperature of the delivered air falls below 20 DEG C the flow rate reduces (to 50% at 15 DEG C). Any further fall activates the heater, which is fully on at 8 DEG C. If the temperature falls still further the flow rate reduces further (to 10% at 0 DEG C). <IMAGE>

Description

A VENTILATOR UNIT The present invention relates to a ventilation unit, particularly a heater-ventilator unit for a building such as a house.

The problems that reduced ventilation cause in current, well-insulated houses due to increased condensation are well known and will not, therefore, be discussed. A problem which has only recently come to public prominence is the accumulation of radon gas in houses in certain localities, with the consequent enhanced risk of cancer for the inhabitants.

The provision of adequate ventilation therefore assumes greater importance but the main reason for good insulation, that is, the restriction of heat loss in order to minimise heating costs, remains. An object of the present invention is, therefore, to provide an improved ventilating system particularly, but not exclusively, for housing, the use of which does not impinge too greatly on the overall energy costs of the household.

Various systems are known for improving ventilation in housing. Some, for example, make use of extractor fans but the present invention is concerned with a system which uses a fan unit located in the loft and arranged to blow air into, rather than extract air from, the house itself.

In use of such a system, air is delivered into the house at a pressure slightly higher than atmospheric and causes the existing air to be forced out through gaps, cracks and apertures in the external wall structure. The warm, moist air within the house is thus gradually replaced by less moisture laden air while the increased pressure derived from the fan's operation also provides a barrier to the ingress of radon gas from the building structure or underlying rock. Any radon which does penetrate will, of course, be entrained in the ventilating air flow so as to minimise any build-up of gas within the house.

A difficulty found in use of known systems of this type, which the current invention seeks to overcome, is that the air drawn in from the roof void is often cold and, on mixing with the warmer moisture-laden air in the house, can in some circumstances cause condensation.

According to the present invention, there is provided a ventilator unit for installation in the roof void of a building to deliver air into the building through a ceiling aperture, the unit including a motor-driven fan for drawing air from the roof void and delivering it to an outlet duct adapted for fitting to the ceiling aperture, a heater located in the flow path of the air from the roof void to the outlet duct, means for detecting the temperature of the air flow in the outlet duct, and means for controlling the operation of the fan motor and of the heater whereby to adjust the air flow rate and the heat supplied respectively in dependence on the temperature of the air flow.

The unit of the invention thus provides for control of the flow rate and heating of the ventilating air flow introduced into a house so as to reduce the problems mentioned above with regard to the injection of cold air.

The adoption of a system in which both the fan motor and the heater are controlled, moreover, minimises the energy requirements of the unit since an increase in the air temperature in the outlet duct is achieved by a combination of increasing the thermal output of the heater and reducing the air flow rate by reducing the fan speed. Most conveniently the fan motor and heater will be electrically operated.

Although the heater could be located between the fan and the outlet from the unit, it is preferred for it to be located upstream of the fan.

The inlet to the fan unit is preferably protected by a filter which, in practice, is located at the inlet to the unit as a whole. The preferred filter is of activated carbon while additional protection may be provided by an electrostatically charged layer.

It is preferred to draw air into the unit over a relatively large area in order to prolong the working life of the filter and minimise the frequency with which it must be changed. For compactness of the unit and to facilitate the flow of air into it, this is achieved by the provision of a generally domed or pyramidal filter structure; a structure which utilises flat panels is preferred for cheapness and convenience of manufacture.

A further problem inherent in any ventilation system which employs a motor-driven fan is that of noise. The present invention also seeks to mitigate this problem and preferred embodiments provide a resilient suspension system for supporting the unit in the roof void to reduce the transmission of vibration from the unit to the roof structure. This system may include resilient mounts for supporting the unit on the ceiling joists but a resilient cord for suspending it from a structural member of the roof itself is preferred.

The noise problem is preferably also reduced by appropriate shaping of the motor-fan unit casing so as to deflect the noise from it, in operation, away from the outlet duct. For this purpose the casing preferably tapers towards the outlet duct so that its inner surface acts as a reflector to reflect the noise back towards the motor-fan unit.

In another aspect of the invention there is provided a method of ventilating a building comprising installing a heater-ventilator unit as described above in the roof void of the building with one outlet duct fitted to a ceiling aperture so that, in operation of the unit, air drawn from the roof void is directed into the building through the outlet duct and ceiling aperture, and regulating the temperature of the air leaving the outlet duct by controlling the operation of the fan motor and of the heater.

Embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a ventilator unit of the invention; Figure 2 is a perspective view of a variant of the unit of Figure 1; Figure 3 is a perspective view of a variant of the unit of Figure 1 showing parts of the unit separated; Figure 4 is a schematic diagram illustrating a further embodiment of the invention; Figure 5 is a block schematic diagram illustrating the main elements of the control system for the ventilator unit of the present invention; Figure 6 is a more detailed diagram illustrating the control system; Figure 6a is a diagram illustrating a detail of Figure 6; Figure 7 is a plot showing the variation of fan motor speed with temperature of a basic embodiment of the invention;; Figure 8 is a plot showing the variation of fan motor speed with temperature in an embodiment of the invention having a refrigeration unit or chiller; and Figure 9 is a plot showing the variation of fan motor speed with temperature in the embodiment of Figure 4 having an inlet duct for drawing in air from outside the roof void.

The inlet section 12 is formed by four identical triangular filter panels 16 arranged to form a hollow pyramid. Each panel 16 is of porous activated carbon 17 enclosed in a triangular supporting frame 18 and incorporating an electrostatically-charged layer.

The lower edges of the panels 16 are supported by a frame 19 of the underlying heater section 13. To this end, the heater frame 19 is square in plan and has an upper wall formed with a V-section channel 20 for receiving the lower edges of the panel frames 18. The variant of Figure 3 differs from the embodiment of Figures 1 and 2 in that the heater frame 19 has a projecting, box-shaped frame portion 21 surrounding the wall defining the channel 20.

The heater section frame 19 supports within it a heater, generally indicated 22, shown only in Figure 3. The heater 22 is constituted by a serpentine, 800-watt heater element; terminals for connection of the element 22 to a mains supply are shown at 23 in Figure 3.

The heater section 13 is in turn supported by a hollow casing 24 of the fan section 14. The casing 24 has a peripheral wall 25 in the form of an upwardly-flared frustum of a pyramid and houses an axially-arranged motor-driven fan unit 26.

As shown in Figure 1, the heater-section frame 19 has a peripheral wall which matches the tapered shape of the casing wall 25 and seats within it. In the variant of Figure 3, the casing 24 has a V-section channel 27, similar to the channel 20, around its upper end in which a mating wall (not shown) of the frame 19 is seated to support the heater section 13.

The motor/fan unit 26 of the fan section 14 is supported within the casing 24 by means of brackets 28 mounted on an annular base 29 of the casing 24. The upper end of the casing 24 is closed, apart from a central, circular aperture 30, by an annular wall 31 comprising a base wall of the heater-section frame 19 in the embodiment of Figure 2: in the embodiment of Figure 3, this closure is constituted, on the other hand, by an upper annular wall 32 of the casing 24.

The annular base 29 of the casing 24 defines a circular, axial outlet opening in which is sealed the upper end of the generally cylindrical outlet duct 15 which projects downwardly from the base 29. Junctions between the inlet section 12, heater-section 13 and fan section 14 are also sealed.

The ventilator unit described above defines an air flow path, in use, which is indicated by the arrows F in Figure 2. The fan/motor unit 26 is driven so as to draw air into the inlet section 12 through the filter panels 16. From here the air passes between the coils of the heater 22 to the axial inlet 30 to the fan/motor unit 26 where it is centrifuged into the surrounding chamber within the casing 24. The downward tapering of the chamber wall 25 then encourages the air to flow downwardly and radially inwardly, between the arms of the bracket 28, to the outlet duct 15.

In use, the unit 11 is installed in a loft, such as a house loft, with the lower end of the outlet duct 15 sealed in an aperture in the ceiling of the underlying room, preferably a landing area of the house. The unit 11 is supported by means of a resilient cord attached at its upper end to a roof member and at its lower end to the apex of the pyramidal inlet section 12. The resilient support, together with a resilient seal (if required) between the outlet duct and the ceiling, isolates the unit from the house structure so as to minimise any vibrations transmitted from the fan unit to the structure, in use, and hence the noise transmitted into the house when the unit 11 is operating. The noise transmission is also reduced by the choice of motor, which is commented on below, and the shaping of the fansection casing 24 which reflects noise from the motor away from the outlet duct 15.

In its installed position, the unit 11 causes air to be drawn from the roof void through the filter panels 16, where it is cleansed of dust, pollen, traffic fumes, etc, and through the heater 22 where it is heated. It is then discharged into the house itself so as to promote ventilation of the building by forcing air to circulate through the various rooms and out through the many gaps, cracks, etc, which exist around doors and windows and in the external structure.

The improved ventilation in itself reduces condensation problems within the house; heating of the air maintains this effect when the ambient air temperature is low. It is preferred for the temperature of the air leaving the outlet duct 16 to be substantially constant. This is achieved by means of the control system which will be described in relation to Figures 5 and 6 below. The system includes a temperature sensor which detects the air temperature in the outlet duct and generates a signal in response to which the operation both of the heater 22 and of the motor/fan unit 26 are controlled: as the temperature falls the speed of the fan motor 26 is progressively reduced down to a predetermined lower value and once this has been reached the heater is energised to heat the air flow to the desired temperature.The power supplied to the heater is increased at lower temperatures but the power to the fan motor is maintained at the lower value so as to reduce the air flow itself, thus minimising the additional heat required from the heater.

The energy required to operate the system as a whole is thus minimised, as are the running costs.

Running costs, or at least maintenance costs, are also reduced by the use of a fan motor which has an operating capacity considerably higher than that required in practice by the fan. The motor therefore runs at a far lower speed than that of which it is capable, with consequent reduction in noise and wear. It should, therefore, be maintenance free for many years and, apart from energy costs, the only other periodic cost is that for replacement of the filters.

The control system schematically illustrated in Figures 5 and 6 provides an adjustable programme for controlling the electric motor and the heater in the machine. Such adjustability is of particular value in enabling the machine to be used in a wide range of houses including those having no existing condensation problems or suspect radon gas. By supplying a controlled and adjustable volume of air to the house, it is possible to produce a predetermined rate of air change. This can be of importance since the modern practice of insulating and double glazing has given rise to a situation where the rate of change of air throughout a building is frequently too low for comfort and furthermore can, it is believed, lead to health problems.

The machine of the present invention operates to deliver a supply of air into the house which will be cleaned by flowing through the described multiple layer carbon filter elements which act to remove pollen and other airborne pollutants.

As illustrated in figure 5 the fan/motor unit 26 comprises of fan 26a and a motor 26b. The speed of rotation of the fan 26a is detected by a speed sensor 33 which generates an electrical signal which is passed to an operation control unit 37 which receives two inputs, one determining the motor speed and the other determining the heater control. These inputs arrive from a cental control unit 34 having two inputs, one form a temperature sensor 36 and one formed as a rotary switch on the casing, which can be adjusted manually by the operator to determine the maximum speed of the fan motor 26.

The output from the operation controller 37 is delivered on three output lines the first of which leads to a field effect transistor 38 which is connected in the power supply to the fan motor 26b. The second output is connected to a triac 39 connected in the circuit of the heating element 40, and the third output from the operation controller 37 is connected to a chiller or refrigeration unit drive 41.

The control system is shown in more detail in figures 6 and 6a. In figure 6 the operation controller 37 is shown in more detail whilst in figure 6a the central control unit 34 is shown in more detail. The central control unit 34 can be considered to comprise a profile generator operable to generate output electrical signals for controlling the speed of the fan motor 26b and the energization of the heater 40 in dependence on predetermined patterns of control stored in a memory.

This will be described in more detail in relation to figure 6a. The outputs from the central control unit 34 are supplied on two lines 41, 42 the latter of which leads to an operational amplifier 43 which receives, on it other input, a signal from a frequency-to-voltage converter 44 the other input to which is a signal from the speed sensor 33 the frequency of which is dependent on the speed of rotation of the fan 26a.

The output from the operational amplifier 43 is supplied to a driver circuit 44 for a metal- oxide silicon field effect transistor 45 in the circuit of the motor 26b, which operates to control the motor speed to that determined by the signal on the line 42.

The output from the cental control unit 34 on line 41 leads to a heater power regulator 46 the output to which is supplied to the gate electrode of the triac 47 in series with the heater element 40.

The central control unit 34 is illustrated in more detail in figure 6a. The temperature sensor 36 is connected to the gated temperature control oscillator 48 which receives a 10 millisecond gate pulse and generates a digital signal at its output which is supplied to a counter 49 the output signal of which is fed by a latch 50 to a read only memory (ROM) 51 which also receives an input from the power selector switch 35 which determines the maximum motor speed. The output from the ROM 51 is supplied via a latch 52 to two digital-to-analogue convertors 53, 54 respectively the former of which leads to output line 42 as a motor speed control voltage whilst the latter is applied to line 41 as the heater power control voltage.The ROM 51 stores the correlation between temperature and energization of the motor and the heater in accordance with patterns of control which are described hereinbelow in relation to figures 7, 8 and 9.

As illustrated in figure 7, the control pattern comprises a central maximum 55 between 200C and 300C over which range the fan motor 26b is controlled to run at the maximum speed determined by the setting of the control switch 35. As can be seen in figure 7 the switch 35 has 10 positions which can set the maximum motor speed at a value of between 100% of the motors rated operating speed and 50% of this rated speed.

If the temperature falls below 200C the motor speed is progressively reduced down to a value of 50% of its maximum set value. Between 150C and 70C the motor speed is controlled to be constant at this 50% value. However, if the temperature falls below 130C the heater is progressively energized, via the heater power regulator 46 and the triac 47 in such a way that a minimum energization is effected at 1300 whilst, if the temperature continues to fall, it reaches a maximum energization at 80C.

Slightly below this temperature, say at 70C, if the air temperature continues to fall, the heater, now being fully on, the fan motor is progressively reduced down to a minimum value in the region of 10% of the maximum value (regardless of the maximum setting) at which value it remains to provide a residual air flow below OOC.

In this way the progressive reduction in the air flow and progressive increase in the energization of the heater makes it possible to maintain the output air which is delivered into the house at a substantially constant temperature with a minimum of energy consumption. It will be understood that at lower temperatures relatively less fresh air is required to maintain comfort.

Of course, there is a possibility that the temperature conditions may reach the opposite end of the comfort range from the low temperature conditions described above, and again with reference to figure 7, once the temperature reaches 300C the fan motor is energized at a progressively lower rate, again down to a value set at a 50% of the maximum selected value, this being reached at about 350C above which the air flow rate remains constant this time, of course, without any energization of the heater.

In order to increase the degree of control which can be exercised at higher temperatures, a chiller or refrigeration unit, (not shown in the drawings) may be provided. Figure 8 illustrates the energization curves in a system provided with such a chiller. At the lower end of the range, that is below 200C, the operation of the system is the same as described in relation to figure 7.

At the upper end, however, the motor energization starts to be reduced at 240C namely 60C lower than in the embodiment of figure 7 so as to reach its minimum value at 300C. In the embodiment illustrated in figure 8 the chiller is energized at 230C as illustrated by the broken outline 57. In this embodiment the chiller is energized to its single (maximum) value at and above 230C.

Finally, figure 9 illustrates the control curve in an embodiment such as that illustrated in figure 4 having a secondary inlet. In the embodiment illustrated in figure 4 the unit is provided with an upper outer casing 58 having a first port 59 controlled by a closable shutter 60 and a second port 61 closable by a shutter 62. The casing 58 entirely surrounds the pyramid of filter units and the shutters 60 and 62 are controlled by a shutter drive motor 63. The port 59 is simply an opening in the casing which allows air from within the loft space to enter the apparatus, whilst the port 61 is connected to a flexible duct 64 leading to a secondary inlet 65.

Again, with reference to figure 9, the control pattern below 200C remains the same as in the embodiment described in relation the figures 7 and 8, with the port 59 open and the port 61 closed. If the temperature reaches 250C the motor 63 is energized to close the shutter 60 and open the shutter 62 thereby allowing air to be drawn from the secondary inlet 65 through the duct 64. Opening and closing of the shutters 60, 62 takes place progressively over a temperature band from 250C to 200C as illustrated by the chain line 66. Above this temperature the shutter 60 is entirely closed and the shutter 62 is fully open.

The secondary inlet 65 is preferably positioned on a north facing wall so that the temperature of air drawn in through the flexible duct in 64 is at a lower temperature than that in the loft space itself so that the effect is to maintain the temperature at the outlet from the unit.

Claims (18)

1. A ventilator unit for installation in the roof void of a building to deliver air into the building through a ceiling aperture, the unit including a motor-driven fan for drawing air from the roof void and delivering it to an outlet duct adapted for fitting to the ceiling aperture, a heater located in the flow path of the air from the roof void to the outlet duct, means for detecting the temperature of the air flow in the outlet duct, and means for controlling the operation of the fan motor and of the heater whereby to adjust the air flow rate and the heat supplied respectively in dependence on the temperature of the air flow.

2. A ventilator unit as claimed in Claim 1, in which the heater is located upstream of the fan relative to the air flow.

3. A ventilator unit as claimed in Claim 1 or Claim 2, in which the fan motor is housed in a casing shaped to deflect noise from the fan motor unit, in use, away from the outlet duct.

4. A ventilator unit as claimed in Claim 3, in which the casing tapers from an outlet end towards an outlet end connected to the outlet duct, the fan motor unit being located adjacent the inlet end.

5. A ventilator unit as claimed in Claim 4, in which the casing is in the form of a frustum of a pyramid.

6. A ventilator unit as claimed in any one of the preceding claims, further including an activated carbon filter located in the path of the air flow from the roof void to the fan.

7. A ventilator as claimed in any one of the preceding claims, further including resilient suspension means for suspending the unit within the roof void.

8. A ventilator unit as claimed in any preceding claim, in which the said control means includes means for selecting a working speed of the fan motor.

9. A ventilator unit as claimed in any preceding claim in which the said control means is operative to reduce the fan motor speed below its working speed when the detected temperature falls below a lower threshold.

10. A ventilator unit as claimed in Claim 9, in which the control means progressively reduces the fan motor speed with a fall in detected temperature, down to a predetermined lower valve.

11. A ventilator unit as claimed in Claim 10, in which the said control means energises the said heater when the fan motor is controlled to run at its said predetermined lower valve.

12. A ventilator unit as claimed in Claim 11, in which the said control means progressively increases the energization of the heater means with a reduction in temperature below the said lower threshold.

13. A ventilator unit as claimed in Claim 12, in which the control means is operative to reduce the fan motor speed below the said predetermined lower value at detected temperatures below the said lower threshold when the heater is fully energised.

14. A ventilator unit as claimed in any preceding claim, in which the control means is operative to reduce the fan motor speed at temperatures above a predetermined upper threshold.

15. A ventilator unit as claimed in any preceding claim, in which the casing includes a port communicating with a duct leading to an inlet positionable, in use of the unit, outside the loft void.

16. A ventilator unit as claimed in claim 15, in which are further provided means for opening and closing the said port in dependence on the detected temperatures, whereby to draw in air from outside the roof void when the temperature is above the said upper threshold level.

17. A ventilator unit as claimed in any of Claims 14 to 16, in which there are further provided refrigeration or chiller means and the said control means is operative to energise the said refrigerator or chiller means when the detected temperature rises above a given value.

18. A ventilator unit substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.