The present invention relates to an improvement in air purifying systems.

US 2006/0191415 (Johnson) discloses a device for trapping particulate matter suspended in exhaust from diesel engines and for separating gases from particles. The device comprises a spiral exhaust channel which directs particles entrained in the flow to be captured by a mesh whereas the gases are not affected by the spiral and are captured separately.

CN 205372827 (Yiming) discloses a duct-type plasma air disinfection purifier. The duct-type plasma air disinfection purifier comprises a box body, fans, a plasma generator and an anion generator, wherein the two fans are separately arranged on the side wall and the top end of the box body; the outer side of each fan is provided with a fan housing; a flow guiding sheet is connected between the two fan housings; a flow guiding channel is formed by the flow guiding sheet; the plasma generator and the anion generator are separately and fixedly arranged on the bottom end in the box body; and the electrodes of the plasma generator and the anion generator penetrate through the flow guiding sheet and are arranged in the flow guiding channel.

Despite the prior art there remains a need for further improvements to air purifying systems, in particular to stand alone air purification systems which are intended for use in the domestic environment.

Accordingly, and in a first aspect, there is provided a domestic air purifier system comprising a removable particulate filter, a fan or impeller and which is powered by a motor, an air duct through which air passes in an air flow direction and is purified, and said air duct comprising a duct wall and wherein a portion of said duct wall comprises a gas filter.

We have surprisingly found that effective removal of harmful gases can be achieved by using a gas filter disposed in an airflow direction. This is in contrast to air purifiers in the literature and on the market where the same gas filters are purposefully disposed to cross the air flow direction and so force air through them. Such designs result in an undesirable pressure drop as the airflows through the device. Pressure drops lead to increased fan speeds and increased noise, both of which are undesirable performance characteristic in the minds of the consumer. This is particularly the case when the device is to be used in a bedroom and at night where quiet yet effective performance is highly desirable.

Preferably, the gas filter comprises a resilient, or bendable material. This permits the filter to be located according to the design of the air purifying system and not to be engineered accordingly.

Preferably, the gas filter is a carbon filter such is known in the art. Preferably, it is an activated carbon filter.

Preferably, the gas filter comprises a duct surface and which is flush with the duct wall. This arrangement of gas filter in the air duct improves the flow of air through the device and yet still maintains a level of acceptable performance. Preferably, the gas filter comprises means for attachment to the duct wall. The duct wall accordingly preferably comprises means to receive the gas filter.

Suitably preferred means for attachment include lugs, slots, friction fits and snap-fit arrangements. Preferably, the gas filter comprises a substantially rigid frame for providing improved fitting means. Such a frame may constitute metal or plastic and may form a perimeter frame or a mesh type frame arrangement. More preferably, the means for attaching gas filter to the duct wall is disposed on the substantially rigid frame. In a more preferred embodiment, the gas filter is removable from said frame such that replacement of the gas filtration media can be done while maintaining use of the frame.

Preferably, the air duct is configured such that the airflow direction changes at least once during passage through the device. Where the airflow changes direction is referred to as a bend, or, where the change in direction is 45 or 90 degrees, an elbow. Changes in direction can also be created by casing and flow guides such as bends, junctions, constructions, meshes, etc. In such an embodiment, the air will be filtered while its direction is changed with low pressure drop and energy input. The device is thus more energy efficient in the context of gaseous filtration.

Systems according to the invention typically involved drawing air into the system in one direction and expelling it in another. In between, the airflow might change direction one or more times depending on the design of the system. In other words, there might be one or more bends in the air flow from the air displacement means to the particulate filter, or where the air flow exits the system.

Where there is a change in airflow direction this is usually between the fan and the particulate filter. Preferably, the gas filter is disposed where the airflow direction is changed and more preferably, the gas filter is disposed at the far wall in a bend.

Preferably, the system additionally comprises a removable particulate filter. Particulate filters are tasked with capturing particulate matter as it passes through the filter in the airflow. Preferably, the removable particulate filter is a High Efficiency Particulate Air (HEPA) filter. It is to be understood that while the filter part of an air purifier is a vital part of its function, air purifiers are not commonly manufactured with a filter in place. They are practically always manufactured separately and most importantly often by a different commercial enterprise than of the manufacturer of the air purifier itself. It is also typical for a manufacturer of filters to manufacture filters for different air purifier models made by different manufacturers. The particulate filter is to be contrasted with the pre-filter or any dust filter which is present. Pre-filters and dust filters are not considered HEPA filters as they do not have the particulate capturing capability exhibited by HEPA filters.

Preferably, the particulate filter is disposed such that air passing along the airflow direction passes through the particulate filter.

The system comprises an air displacement means. Typical air displacement means include fans and impellers. The air displacement means may be disposed at the beginning or at the end of the airflow such that the air is either pushed through the system or pulled through it. Typical fans include radial fans and axial fans. It is preferred that the device according to the invention comprises a radial fan. Radial fans are far more energy efficient than axial fans and also create an airflow which is less likely to result in turbulence when passing over the gas filters disposed along the duct walls of the system.

In such a system the air is cleaned of unwanted gases by passing over the gas filter and not necessarily through it. The surprising benefit is not just that the air can be cleansed of gases merely by passing over such a filter, rather than passing through it, but also that there is no loss in gas cleansing capability with such a system. Accordingly, the same amount of gas can be cleansed for the same energy consumption. The fan speed can be lowered and therefore less energy used to drive the airflow through the system.

Preferably, the gas filter has a porous member and is preferably comprises a foamy filter.

A preferred gas filter comprises activated carbon which is a commercially available form of carbon that has been processed to make it more porous.

Preferably, the gas filters are replaceable. However, in view of their being internally located, it is preferred that the system also comprises means for permitting appropriate access to the gas filters. Preferably, the system comprises a door or other suitable access which can be opened permitting removal and replacement of gas filters.

The system may also preferably comprise a pre-filter or dust filter at the air inlet and/or outlet. Such a filter is not a HEPA filter as it lacks the physical density to act as a filter for small particles such as PM10 and PM2.5’s but they will stop dust from entering the system and also act as a poke guard preventing injury or damage to the user or the system.

Preferably, the system also comprises a sensor for sensing the concentration of particular gases in the ambient air. More preferably, the operational parameters of the system may be determined by the results obtained from the sensor. For example, if more formaldehyde is detected, the fan speed may be increased. Alternatively, an indication may be made either through a user interface or via smart phone to the consumer that the gas levels are such that modification of the operation might be beneficial. For example, the fan speed might be modified, the filters might need changing or the placement of the system in a domestic environment might be changed.

In a second aspect there is provided a method of removing unwanted gases from ambient air by passing over a gas filter in a system as described in any of claims 1 to 5. Unwanted gases include formaldehyde, nitrous oxide and volatile organic carbon moieties.

Embodiments of the invention are now described with reference to the following non-limiting drawings in which:

Figure 1 is a typical construction found in many commercial products. The air duct (1 ) defines the air flow (A) as created by the fan (2). The air passes through a particulate filter (4) and an activated carbon filter (3). Figure 2 is an embodiment according to the invention and where the activated carbon filters (3) are disposed at the sides of the air duct (1 ) such that the air flow passes by them and not through them. The particulate filter (4) is in the same position as in Figure 1. Figure 3 is a further embodiment and where the duct is bent (at 5) to form an elbow. The activated carbon filter (3) in this instance is only disposed on the far surface of the air duct (1 ) at the bend. The particulate filter (4) in this embodiment is disposed before the carbon filter (3).