The invention relates to an indoor air purifier ac- cording to the preamble of claim 1.

BACKGROUND OF THE INVENTION

Recently people have become increasingly aware of the quality of air in different buildings and the neces- sary quality requirements. More and more people are showing symptoms in schools, kindergartens, offices and other public facilities, caused by impurities in air, such as mould, dust, pollen, even radon. The problems may be due to personal severe hypersensitivi- ties to certain substances or to general structural defects and damages in the facilities being used. In any case, finding out the causes and repairing the structures is not done quickly, but easily becomes a matter of years. As a result, temporary facilities must often be used.

Permanent or temporary solutions have been offered to these problems by various efficient air purifiers that are free-standing and detached from the structures and thus quickly deployable, i.e. just liftable onto the floor of the space in question and connectable to a socket. The air purifier is formed by a case-type structure housing one or more different types of fil ^¬ ters and a fan causing air to flow from the space be- ing cleaned through the filters, and back to the space after being purified. The purification degree depends on the type, quality and number of the filters used. At least some air purifiers provided with activated carbon filters work very well, removing for instance mould spores and radon almost completely from the air. In an attempt to make air purifiers more and more ef ^¬ ficient, i.e. to generate greater and faster airflows, the devices must be made larger and provided with big- ger fans. This increases both motor noise from the ro ^¬ tation of the fan, as well as the swishing sound of the airflow caused by flow resistances of the struc ^¬ tures. Thus, with increased efficiency the drawbacks are also increasing, as the constant and steady hum- ming and swishing of the air are in many cases rather disturbing in otherwise calm and quiet environments, such as classrooms and offices.

OBJECT OF THE INVENTION

The object of the invention is to remedy the defects of the prior art mentioned above. Specifically the ob ^¬ ject of the invention is to disclose a new indoor air purifier that is small and light, i.e. easily trans ^¬ portable and movable, yet efficient and quiet enough that it may operate in any facility almost unnoticed.

SUMMARY OF THE INVENTION

The indoor air purifier according to the invention comprises a frame case, for example made of a suitable wood board. The shape of the frame case is freely se ^¬ lectable to suit the decor in question; however, from the manufacture point of view a rectangular parallele ^¬ piped is in most cases most preferred. A fan and an electric motor for rotating the fan, and at least one filter are housed inside the frame case. Further, the frame case is provided with an air inlet and outlet, whereby the fan is arranged to generate an airflow travelling from the inlet via the filter to the out ^¬ let, i.e. to draw air from the inlet to the interior of the frame case and blow out the filtered air from the outlet. According to the invention, an active noise reduction arrangement is provided inside the frame case in the airflow between the inlet and the outlet. Preferably, two active noise reduction ar ^¬ rangements are provided in the airflow between the in- let and the outlet, one of them before and the other one after the fan, each one of the active noise reduc ^¬ tion arrangements comprising a microphone and a speak ^¬ er, and the microphone and the respective speaker are located on different sides of the filter before the fan and after the fan.

In one embodiment of the invention, two active noise reduction arrangements are provided inside the frame case, one before and the other one after the fan. Preferably the active noise reduction arrangement com ^¬ prises a microphone provided in the airflow for de ^¬ tecting prevailing noise, and a speaker for forming anti-noise to compensate for the noise detected. Thus the active noise reduction arrangement continuously modifies the anti-noise being generated based on the noise made by the air purifier.

Preferably the purifier comprises more than one fil ^¬ ter, such that before the fan there is at least one filter and after the fan there is at least one filter. In one embodiment of the invention the purifier comprises an activated carbon filter, for example before the fan, and additionally a HEPA filter, for example after the fan. Even more preferably, between the inlet and the activated carbon filter, a prefilter is arranged for removing larger impurities entrained with the airflow, such as debris, insects and pollen.

In one embodiment of the invention the microphone and the respective speaker are located on different sides of the filter in the airflow passing through the puri- fier. In another embodiment of the invention the microphone and the respective speaker are located sub ^¬ stantially side by side in proximity to each other in the airflow passing through the purifier. In this case the microphone and the speaker may for example be ar ^¬ ranged in immediate proximity to the fan before the fan and/or after the fan.

In one embodiment of the invention the control of the microphone and the respective speaker is provided with delay that is proportional to the distance between the microphone and the speaker. Thus, noise detected in a certain place is compensated for in another place at the moment the noise reaches that place.

ADVANTAGES ACHIEVED WITH THE INVENTION

The indoor air purifier according to the invention has significant advantages over the prior art. The indoor air purifier according to the invention enables air to be purified practically without noise. Further, as the purifier itself may be integrated to the furniture of the space being treated, the invention enables air to be purified completely unnoticeably and non- disturbingly . It will only be noticed from the clean and fresh air of the space.

SHORT DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to the accompanying drawing that schemati- cally illustrates one air purifier according to the invention .

DETAILED DESCRIPTION OF THE INVENTION

One air purifier according to the invention as illus- trated in the figure comprises a frame case 1 shaped as a rectangular parallelepiped that is placed upright on a floor 10. In the interior space delimited by the frame case there is, substantially halfway through in the vertical direction, a fan 2 rotated with an elec ^¬ tric motor. The fan 2 is disposed its own space be- tween a horizontal lower partition wall 11 and upper partition wall 12, whereby the fan is able to draw air through an opening 13 of the upper partition wall and blow it down below the lower partition wall. The upper edge of the frame case 1 is provided with an inlet 6 and its lower edge is provided with an outlet 7. Thus when the fan is operating the airflow circulates through the interior space of the frame case. Further, immediately after the inlet 6 there is a hor- izontally disposed first filter, i.e. a prefilter 5, followed by an activated carbon filter 3 with a cylindrical surface. In this embodiment, after the fan 2 there is also a HEPA filter. Thus the air drawn with the fan 2 from the inlet 6 into the frame case 1 pass- es through three different filters before returning through the outlet 7 to the air space outside the pu ^¬ rifier .

In the purifier, inside its frame case, there are two active noise reduction arrangements. The first one of them is arranged before the fan so that in proximity to the inlet 6 there is a microphone 8 by which pre ^¬ vailing noise in that area, which is mainly noise from the fan and its motor, is detected.

The microphone is then, via suitable control electron ^¬ ics, connected to a speaker 9 in the space before the fan but after the activated carbon filter, by which speaker anti-noise is directed to this space to compensate for the noise detected with the microphone. Correspondingly, immediately after the fan 2 there is another speaker 9, its corresponding microphone 8 being located below the HEPA filter in proximity to the outlet 7. Because the noise carried out from the puri ^¬ fier comes out from the frame case almost exclusively through the air inlet and outlet 6 and 7, this way, with two active noise reduction arrangements the sound waves coming out from both inlet and outlet can be compensated for, such that the purifier becomes prac ^¬ tically noiseless.

The invention has been described above by way of exam ^¬ ple with reference to the accompanying drawings; how ^¬ ever, different embodiments of the invention are pos ^¬ sible within the scope defined by the claims.