AIR FILTRATION DEVICE AND METHOD

The invention relates to an air filtration device for filtering contaminated air in a room that is accessible to persons, which device comprises a housing provided with an air inlet and an air outlet, as well as air moving means for moving air from the air inlet to the air outlet in a direction through a filter element. The invention further relates to an air filtration method for filtering contaminated air in a room that is accessible to persons, wherein contaminated air is moved from an air inlet, through a filter element, to an air outlet. The invention is in particular aimed at filtering air contaminated by cigarette and/or cigar smoke in catering establishments such as cafes, restaurants, discotheques and the like, in short, places where smoking is allowed.

Such an air filtration device and method are generally known. In many countries it is legally prohibited for health reasons to smoke cigarettes and cigars in public places, although in some countries such a smoking ban does not apply in particular to catering establishments, such as cafes and restaurants. However, breathing cigarette and cigar smoke for prolonged periods of time during working hours constitutes a health hazard for people who work in the catering industry. Consequently, some countries are preparing legislation to prohibit the smoking of cigarettes and cigars in catering establishments as well.

The object of the invention is to provide an air filtration device and method for filtering in particular air contaminated by cigarette and/or cigar smoke in catering

establishments, so that the extent to which catering personnel breathe such smoke is reduced to an acceptable minimum.

In order to accomplish that object, an air filtration device of the kind mentioned in the introduction is characterised in that the air filtration device operates according to the displacement principle, wherein the capacity of the air filtration device has been selected so that contaminated air present in the room is circulated X times through the filter element, said value X ranging between 25 and 88, in particular between 40 and 65, more in particular at least substantially equalling 60. Although the principle of displacement as such is well-known in the field of air ventilation, within the framework of the invention the following is furthermore noted with regard to this principle. The present air filtration device supplies filtered air to the room via the air outlet thereof in a manner which minimises the extent to which filtered air being supplied and contaminated air present in the room are mixed. This is realised by supplying filtered air to the room at a low velocity via the air outlet (preferably in a lower part of the room) whilst simultaneously exhausting contaminated air via the air inlet (preferably in a higher part of the room) . In principle the aforesaid low velocity varies from 0.075 m/s to 0.35 m/s. Said velocity will vary from 0.15 m/s to 0.35 m/s in case of a horizontal direction of flow of the filtered air and from 0.075 m/s to 0.2 m/s in case of a vertical direction of flow thereof. The density of the filtered air in the aforesaid lower part will in that case be higher than the density of the contaminated air in the aforesaid higher part, so that contaminated air is forced upwards by convection. This displacement effect is further enhanced by the

difference in air pressure caused by the high recirculation ratio effected by the displacement means. Tests have surprisingly shown that the above-indicated circulation rate (viz. X times per hour, said value X ranging between 25 and 88, in particular between 40 and 65, more in particular at least substantially equalling 60) on the one hand results in a high air quality as regards the absence of smoke particles and on the other hand does not lead to air flows (draught) that are objectionable to persons present in the room.

In a preferred embodiment of an air filtration device according to the invention, the air inlet is mounted near a ceiling of the room and the air outlet is mounted near a floor of the room. As already explained above, an optimum air displacement is realised in this way, with the boundary between filtered air being supplied and contaminated air present in the room preferably being present at a height of 1.80 from the floor of the room. As a result, guests of the catering establishment and catering personnel (for example attendant staff, such as waiters) will breathe relatively clean air. Important is that the circulation of air in the room in principle takes place without air from outside the room being mixed therewith, so that the present air filtration device consumes comparatively little energy. If the air outlet is mounted near the floor of the room, a horizontal or a vertical flow of the filtered air is effected. In another preferred variant, an air outlet is mounted near the ceiling of the room, so that a vertical air flow is effected.

In another preferred variant of an air filtration device according to the invention, the air filtration device supplies filtered air to the room via the air outlet, which

air has a temperature at least substantially equal to a temperature of the contaminated air in the room. No cooling of filtered air takes place, therefore.

In another preferred embodiment of an air filtration device according to the invention, the filter element comprises an active carbon filter. Preferably, the filter element comprises an active carbon filter in combination with one or more other filters, all of which are in particular configured as plate filters.

As already said before, the invention also relates to a method for filtering contaminated air in a room that is accessible to persons, wherein contaminated air is moved from an air inlet, through a filter element, to an air outlet, characterised in that contaminated air present in the room is circulated X times through the filter element, said value X ranging between 25 and 88, in particular between 40 and 65, more in particular at least substantially equalling 60, and wherein filtered air is supplied to the room on the basis of the displacement principle. Preferably, contaminated air is supplied to the air inlet near a ceiling of the room and filtered air is supplied to the room via the air outlet near the floor of the room.

In a preferred embodiment of an air filtration method according to the invention, filtered air having a temperature at least substantially equal to a temperature of the contaminated air in the room is supplied to the room. More in particular, contaminated air present in the room is circulated X times through the filter element at least substantially without being mixed with air from outside the room.

The invention will now be explained in more detail with reference to figures illustrated in the drawing, in which

Figure 1 schematically shows the constructional components of a preferred variant of an air filtration device according to the invention; and

Figure 2 schematically shows the air flows in a cafe in which the contaminated air is filtered by two air filtration devices shown in figure 1.

Figure 1 shows a compact air filtration device 1 according to the invention, which is mounted at a decentral location in, for example, a cafe. Said device successively comprises (from top to bottom) an air inlet 2 mounted near a ceiling of the cafe, a prefilter 3, a first sound absorber 4, a fan 5, an optional second sound absorber 6, a high efficiency dust filter 7, an active carbon filter 8 and an air outlet 9 mounted near a floor of the cafe. These constructional components of the air filtration device 1 form separate units and are interconnected by means of an air line 10.

Near the ceiling of the cafe, air contaminated by cigarette and cigar smoke is drawn in by the fan 5 via the air inlet 2. The fan 5 first passes said contaminated air through the prefilter 3, which is configured as a plate filter, i.e. a frame provided with a synthetic fibre mat- The prefilter 3 functions to collect coarse dust and the like and thus protect other components of the air filtration device 1. The efficiency of the prefilter 3 ranges between G3 and G4 according to the CEN EN 779 standard. The contaminated air then passes the high efficiency dust filter 7 (filter class HlO according to the EN 1822 standard) and subsequently the

active carbon filter 8. The two filters 7,8 are likewise configured as plate filters. Finally, the air thus filtered is blown into the cafe in horizontal direction via the air outlet 9.

The capacity of the fan 5, the effective diameters of the air inlet 2, the air outlet 9 and the air line 10, the capacities of the filters 3,7,8 and the sound absorbers 4,6 have been preselected separately and in conjunction with each other such that contaminated air present in the cafe is filtered 60 times per hour in this specific case.

Figure 2 schematically shows a cafe in which two air filtration devices 1,1' of the type as shown in figure 1 are disposed. Each air filtration device 1,1' supplies filtered air in horizontal direction to the cafe at a low velocity via their respective air outlets 9,9' near the floor. As figure 2 shows, contaminated air is simultaneously exhausted from the cafe via the respective air inlets 2,2' near the ceiling. The density of the filtered air in the area near the floor is higher than the density of the contaminated air near the ceiling, so that contaminated air is forced upwards by convection. This displacement effect is further enhanced by the difference in air pressure caused by the high circulation ratio effected by the fan 5. The above-indicated circulation rate (viz. 60 times per hour) on the one hand results in a high air quality as regards the absence of small particles, whilst on the other hand it does not lead to air flows that are objectionable to persons present in the room.

The invention is not limited to the embodiment as shown herein, but it also extends to other preferred variants that fall within the scope of the appended claims.