The present invention relates to a positive input ventilation system, and in particular a positive ventilation system including an active carbon filter for reducing NOx levels within the habitable space of a building.

A significant proportion of UK households have been found to be poorly ventilated, which can result in condensation issues such as streaming windows, mould growth and poor indoor air quality. Older homes in particular are inadequately ventilated and air quality can be further worsened by factors such as occupant lifestyles, the installation of wall and loft insulation, and a reduction in the use of central heating due to increases in fuel costs.

It is known to provide Positive Input Ventilation (PIV) units in residential properties to improve air quality within the property, reduce or eliminate surface condensation and prevent mould growth. A PIV system typically comprises a fan unit, which is located within the loft or roof space of the property. The fan is arranged to draw external air into the property. An outlet diffuser vent is arranged to pump the external air drawn in by the fan from within the loft space into the habitable spaces of the building. The fan is configured such that the supply pressure of the air is greater than atmospheric pressure, which places the living space under a slight positive pressure. The application of a positive air pressure forces air within the space to flow out of the building through natural ventilation gaps such as window trickle vents, doors etc. Additional venting may be provide if required. In this way, the air within the living space is continuously replenished with fresh air. This reduces humidity and hence acts to remove or prevent condensation.

A standard natural ventilation system operates by extracting air from the property, and relies on air being drawn back into the property through multiple supply points such as window and door trickle vents. PIV units operate in reverse and actively supply air to the property. As such, the air supply is far more controllable. PIV units may include particulate filters to improve air quality by remove harmful particulates from the air. Indoor pollutants from cooking and cleaning, as well as pollen and Radon gas, and moisture generated through for example the drying of clothes and respiration of the occupants, are reduced as the air volume within the property is continuously replaced. It was also commonly understood that PIV systems acted to reduce harmful traffic emissions, such as NOx, from within the property in the same manner. However, the applicant has surprisingly found that the reverse is the case, and that PIV systems may actually increase the concentration of NOx within a property.

The applicant conducted air quality studies within residential properties in which PIV units are installed. During the study the levels of NOx within the property were measured with the PIV unit operating, and with the PIV unit not in operation. It was surprisingly found that the levels of NOx within the property increased rather than decreased while the PIV unit was operational. It was concluded that external air having higher levels of NOx due to traffic in the vicinity of the property was being drawn into the property, and was replacing the air within the property, which in a normal unventilated state would be lower in NOx than the external air. Therefore, while the improvements in air humidity, and

corresponding reduction in condensation and mould, were still achieved, there was conversely a decrease in air quality in terms of NOx levels.

It is therefore desirable to provide an improved positive input ventilation system which addresses the above described problems and/or which offers improvements generally.

According to the present invention there is provided a method of ventilating a habitable space as described in the accompanying claims.

In an embodiment of the invention there is provided a method of ventilating a habitable space within a building. The method comprises operating a fan to output air at a positive pressure exceeding atmospheric pressure. The air output by the fan is filtered using an active carbon filter to remove NOx therefrom. The active carbon filtered air is then supplied to the habitable space of the building. Conventional PIV systems do not include in-line filters, and PIV systems of the prior art are not know to include active carbon filters. Instead efforts are made to avoid restrictions in the supply airflow, such as would be created by an in-line active carbon filter. A PIV system must deliver airflow to the property at a predetermined positive supply pressure, and therefore restriction in the air supply flow path would need to be compensated for by increasing fan speed, and hence power, to ensure that the supply pressure is maintained. Therefore, any restriction in the flow path results in a reduction in efficiency. Furthermore, it was previously considered that positive input ventilation improved air quality within the property through forced air replacement. Hence, there was no perceived requirement for active carbon filtering. The present invention derives from the applicant's surprising discovery linking PIV systems to increased NOx levels within the property.

The fan is preferably arranged to draw air from outside the building. In a preferred embodiment the fan is located in the loft space of the building and draws airflow from within the loft space. External air is drawn into the loft space to replace the air transferred by the fan. The fan may alternatively or in addition include inlet ducting connected to the external atmosphere via an external inlet vent.

The air may exit the fan at outlet pressure PI and exit the active carbon filter at supply pressure P2 which is lower than outlet pressure PI due to pressure drop across the active carbon filter. Preferably the fan is operated such that the supply pressure P2 is a positive pressure exceeding atmospheric pressure.

Preferably the fan speed is boosted to overcome the pressure drop across the active carbon filter relative to the fan speed required without the carbon filter located within the supply flowpath.

The fan preferably includes at least one particulate filter arranged to remove particulate matter from the airflow output by the fan. The fan may include at least one air inlet and the at least one particulate filter is located at the at least one air inlet to filter air as it enters the fan.

The fan is preferably located within a loft space of the building.

The method may further comprise bypassing the active carbon filter based on external atmospheric conditions. The system includes a bypass channel and a bypass damper configured to bypass the active carbon filter by diverting airflow to the bypass channel. In normal operation, in which flow through the active carbon filter is desired, the bypass damper closes the bypass channel. The damper is also configured to close the main airflow channel when diverting airflow to the bypass channel.

The method may further comprise lowering fan speed when the active carbon filter is bypassed. Lowering fan speed advantageously reduces power and increase efficiency.

The method may comprise operating the bypass based on a schedule of operation which defines set times for operation of the active carbon filter.

The ventilation system preferably includes a controller configured to operate the bypass, and the active carbon filter is bypassed based on data indicative of the external NOx levels being below a predetermined level. The term "data indicative of the external NOx levels" includes any information relating to the external NOx levels. The data may for example by derived from historical government air quality data. By way of further example the data may be based on air quality forecast information. The data may alternatively include the output of a sensor providing real time monitoring of NOx levels. In a further alternative the data may be a schedule of operation which defines set times for operation of the active carbon filter.

The controller may comprise a timer and the timer may be programmed to operate the bypass during one or more pre-programmed periods of the day. The system may include at least one sensor arranged to generate said data indicative of external NOx levels.

The ventilation system may include a first air inlet arranged to draw air from within the loft space and a second air inlet arranged to draw external air from outside the property. The ventilation system may include a damper arranged to selectively close the second inlet and open the first inlet and vice versa. The system may comprise a first temperature sensor arranged to detect the temperature in the habitable space and a second temperature sensor arranged to detect the temperature in the loft space. The controller is configured to control the damper to close the second inlet and open the first inlet when the temperature within the loft space exceeds the desired temperature within the habitable space, to cause air at a lower temperature to be externally supplied. The controller is also configured to close the first inlet and open the second inlet when the loft temperature is equal to or less than the desired temperature within the habitable space, to take advantage of the thermal gain within the loft. Where the temperature within the loft is less than the desired temperature, the air may be heated by a heating element provided at the vent. The controller may monitor the measured temperatures, and the desired temperature, and operate the damper and/or heater accordingly.

In another aspect of the invention there is provided a positive input ventilation system comprising a fan configured to output a positive pressure airflow exceeding atmospheric pressure. A supply vent is provided for supplying airflow from the fan to a habitable space within a building. An active carbon filter is fluidly connected to the fan and the vent. The active carbon filter is arranged to filter airflow flowing from the fan to the vent. The term vent is used generally to mean any aperture arranged to permit the flow of air into a room, and includes diffusers, grills, open apertures or any other suitable air inlet. The active carbon filter may be an in-line filter located between the fan and the vent.

Alternatively the active carbon filter may be directly connected to the fan, or may be integrated in the vent. Preferably a supply duct defines the main airflow pathway and connects the fan and the vent, and the active carbon filter is an in-line filter located along said supply duct.

A bypass channel may be provided that is in fluid connection with the fan and the vent, meaning that air may be passed to the vent from the fan via the bypass channel. Flow control means, such as a bypass damper, is arranged to selectively divert flow from the active carbon filter to the bypass channel to bypass the active carbon filter. The damper is also configured to close the main airflow channel when diverting airflow to the bypass channel. A controller is configured to control operation of the flow control means. The bypass channel enables the carbon filter to be bypassed when not required. This advantageously removes the pressure drop across the carbon filter and allows the fan to be operated at a reduced speed, thereby improving efficiency. The controller may also be configured to decrease the speed of the fan when the active carbon filter is bypassed via the bypass channel to lower the power consumption of the fan and increase the efficiency of the system.

The controller is preferably configured to control the flow control means to the bypass channel to bypass the active carbon filter based on external atmospheric conditions. The external atmospheric conditions are preferably NOx levels, and more specifically may be N02 levels. The controller may be configured to operate the bypass based on historical measurement data relating to NOx levels. The data may be locally derived or may be based on national averages. The data will preferably indicate times periods when NOx levels exceed a minimum threshold. The data may be stored locally on the device, or may be provided to the device from a remote location. The remote provision of data, such as via a mobile network connection, or via an internet connection, enables the data to be updated periodically, or on a real time basis.

The positive input ventilation system may include one or more sensors located within the habitable space, within the loft space and/or externally. The one or more sensors may be configured to detect the level of NOx in the atmosphere. The controller may be configured to operate the bypass when one or more of the sensors indicates that the NOx levels exceed a predetermined threshold.

The controller is preferably configured to divert flow to the bypass channel to bypass the active carbon filter, and also to close the main flow channel, based on data indicative of the external NOx levels being below a predetermined level. The predetermined level may be a fixed value, or may vary depending on factors such as time of day, temperature, humidity or detected occupancy within the property.

The system preferably includes at least one sensor arranged to generate said data indicative of external NOx levels. The sensor may be local to the device and to the property, and may for example be mounted to an external surface of the property, or within the loft space. Alternatively the sensor may be located at a remote location and may supply data to numerous devices simultaneously.

The present invention will now be described by way of example only with reference to the following illustrative figure in which:

Figure 1 shows a ventilation system according to an embodiment of the invention;

Figure 2 shows a ventilation system according to an alternative embodiment of the invention; and

Figure 3 is a cross sectional view of the arrangement of Figure 2.

A residential building typically includes an apex roof having a loft or roof space. Referring to Figure 1, a loft space 1 sits atop the habitable space 2 of a building. The loft space 1 is separated from the habitable space by a ceiling 4. A ventilation unit 6 is provided, which is located within the loft space 1 of the building. The ventilation unit 6 includes a fan 8, which suspended from the roof joists within the loft space 1 by a cable 10 to minimise the transmission of vibration to the habitable space 2. Alternatively the fan 8 may be supported on the ceiling 12, or mounted in any suitable location within the loft space 1.

The fan 8 comprises air inlets 14 arranged to draw in air from within the loft space 1. Cylindrical particulate filters 15 are provided over the inlets 12 to remove particulate matter from the airflow entering the fan 8. The filters are preferably configured to filter particulate matter at the PM10 level. A supply duct 16 extends from the outlet 18 of the fan 8 and is connected to a vent 22 in the ceiling of the habitable space 2. Air flows from the fan 14 to the vent 22 via the supply duct 16, and into the habitable space 8 via the vent 22.

An active carbon filter 24 is provided as an in-line filter and is located along the supply duct 16 between the fan 14 and the vent 22. The active carbon filter 24 is connected to the supply duct 20 such that all air flowing to the vent 22 through the duct 16 passes through the active carbon filter 24. The duct 16 includes a first duct section 26 extending between the fan 14 and the active carbon filter 24, and a second duct section 28 extending between the active carbon filter 24 and the vent 22.

A heating element (not shown) may be provided at the vent 22 to heat air as it enters the habitable space. The heating element tempers the air and provides additional heating as it enters the property when the temperature of the supply airflow is less than the desired temperature within the property. The provision of a heating element at the vent 22 advantageously avoids heat loss along the supply duct that would occur if the air were to be heated at the ventilation unit.

The active carbon filter 24 is a cartridge filter, comprising a housing 30 containing one or more removable carbon filter cartridges containing an activated carbon material. The housing 30 includes an inlet 32 connected the first duct section 26 and an outlet 34 connected to the second duct section 28. The size of the housing 30 and number of cartridges may be varied depending on the required airflow and pressure drop. A bypass channel (not shown) is provided which is connected to the supply duct 16. The bypass channel is arranged to carry air between the fan 8 and the vent 22. A bypass damper is arranged to selectively divert airflow from the fan 8 between the carbon filter 24 and the bypass channel. In a first mode of operation the bypass damper blocks the bypass channel and directs flow through the carbon filter 24. In a second mode of operation the bypass damper blocks airflow to the carbon filter and directs flow through the bypass channel such that the airflow bypasses the carbon filter 24.

The ventilation system includes a controller configured to control operation of the bypass damper. The controller enables the system to automatically bypass the carbon filter 24 when flow through the filter is not desired. The controller may be programmed to operate the bypass damper on a timed basis, with the active carbon filter being bypassed in accordance with a pre-programmed schedule. The schedule may be selected to correspond to times of low atmospheric NOx levels, and may be calculated from historical measurement data relating to local and/or national NOx levels. Alternatively, the controller may be arranged to receive data from a remote source indicative of NOx. The remote course may provide real time data indicative of NOx levels, or may provide periodic updates to the operational schedule of the bypass.

Figure 2 shows an alternative embodiment in which an enclosure 100 comprises a fan section 101 and a filter section 102. The filter section 102 includes a first inlet 104 arranged to draw air from within the loft space within which the enclosure is located, and a second inlet 106 connected to an external vent to draw air from the external atmosphere via an external supply duct. Air is drawn through the first or second inlet 104,106 by a fan 108 housed within the fan section 101. A damper arrangement 110 is provided downstream of the first and second inlets 104,106 that is arranged to selectively close one of the first and second inlet 104,106 and open the other, such that when the first inlet 104 is open the second inlet 106 is closed and vice versa. As such, the unit may selectively draw air from within the loft or from externally. Temperature sensors may be provided to monitor the temperature with the loft and within the habitable space. When the temperature within the loft space exceeds the desired temperature within the habitable space, and ventilation is still required, the damper 110 is operated to cause air at a lower temperature to be externally supplied. Conversely, when the loft temperature is equal to or less than the desired temperature within the habitable space, the damper 110 may be controlled to cause air to be supplied from within the loft space to take advantage of the thermal gain within the loft. When the temperature within the loft is less than the desired temperature, the air may be heated by the heating element at the vent 22. A controller may monitor the measured temperatures, and the desired temperature, and operate the damper 110 and/or heater accordingly. A particulate filer 112 is provided downstream of the first and second inlet 104,106. The particulate filter 112 may be a PM2.5 or PM10 filter. An active carbon filter 124 is located downstream of the particulate filter 112. A bypass channel 126 is arranged parallel to the active carbon filter. A second damper 128 is arranged downstream of the active carbon filter 124 and bypass 126. The damper selectively closed the bypass 126 and opens flow through the active carbon filter 124 or blocks flow through the active carbon filter 124 and permits flow through the bypass 126. A secondary filter 130 is located downstream of the active carbon filter 124 to capture any particulates not filtered by the first filter 112. A controller controls operation of the damper. The controller may include a timer and may be programmed with an operational schedule to operate the damper at predetermined times to divert airflow through damper during predetermined periods of the day. The operational schedule may be configured to divert airflow through the bypass 126 and close the active carbon filter during periods of the day when NOx levels are expected to be low. Similarly the damper 126 is operated to divert flow through the active carbon filter 124 and close the bypass 126 during periods of the day when high NOx levels are expected. The controller may control the fan 108 to operate at a lower speed when flow is diverted through the bypass. Diverting the airflow through the bypass 126 when the active carbon filter 124 is not required advantageously reduces the airflow resistance and enables the fan to be operated at a slower speed. In addition, preventing flow through the active carbon filter 124 during these periods, rather than simply opening the bypass without closing the active carbon filter 124, significantly increases the life of the active carbon filter and the periods between filter changes. Figure 3 shows a cross sectional view of the enclosure 100. The active carbon filter 124 comprises a first active carbon filter section 136 and a second active carbon filter 138.

The first active carbon filter 136 and second active carbon filter 138 both have a filter body containing active carbon material, the body having a v-shaped cross section. The v- shaped cross section tapers outwardly in the downstream direction. A first void 140 is defined between an outer wall 142 of the first filter and the enclosure 100, and air flowing into the first void 140 is forced to flow through the outer wall 142 of the filter 136. A second void 144 is defined between the inner wall 146 of the first filter 136 and the inner wall 147 of the second filter 138. Air flowing into the second void 144 is forced to flow through the inner wall 146 of the first filter 136 and the inner wall 147 of the second filter 138. A third void 148 is defined between an outer wall 150 of the second filter 138 and the enclosure 100, and air flowing into the third void 148 is forced to flow through the outer wall 150 of the filter 138. The first filter 136 and second filter 138 are cartridge filters. The first filter 136 and second filter 138 are stacked on top of each other to form a substantially W-shaped configuration having an outer part 152 defined by the outer walls 142,150 which tapers inwardly in the upstream direction, and an inner part 154 defined by the inner walls 146,148 which is inverted in relation to the outer section 152 and tapers inwardly in the downstream direction. This configuration advantageously increases the surface area of the active carbon filter 124 exposed to the incoming airflow, which reduces the pressure drop across the filter 124 and hence reduces the required fan speed, making operation of the fan 108 more efficient. In addition, the increased surface area increases the efficacy of the active carbon filter 124.

For ease of installation, the fan section 101 and filter section 102 may be separable parts of the enclosure 100. The fan section 101 is detachably connected to the filter section 102, and a seal is provided therebetween. The two sections 101,102 are aligned and connected in-situ, which reduced the size and weight of the individual components handled by the installer.