TECHNICAU FIEUD

[001] Embodiments of the present invention relate to modules and systems for filtering air, in particular outside air such as street air, more particular cleaning the air from fine dust but also from other pollutants, aerosols and/or odours, in particular from air pollutants caused by vehicles due to tyre abrasion and residues of combustion engines such as nitrogen oxides.

BACKGROUND

[002] Air pollution is a global phenomenon, is hard to escape and may pose severe risks both for human health and the environment. According to the World health organization (WHO), about 91% of the world’s population live in places where air quality levels exceed WHO limits. Further, exposure to ambient (outdoor) air pollution currently causes an estimated number of 4.2 million death every year due to stroke, heart disease, lung cancer and chronic respiratory diseases.

[003] Even in regions like Europe, where there are strict environmental regulations and air quality has (on average) improved over recent decades, the concentration of important air pollutants such as fine dust and nitrogen oxide may at least temporarily be too high, in particular in cities and/or close to highways, motorways, airports and ship ports. Despite the wide use of filter systems in industrial plants, ongoing improvements in vehicle technology, driving bans and speed reductions on particularly affected roads, emission limits for air pollution are not always met. The European Environment Agency (EEA) considers air pollution even as the biggest environmental health risk in Europe.

[004] Accordingly, there is a need to further improve air quality.

SUMMARY

[005] According to an embodiment of an air filter module, the air filter module includes a first sub-module including an activated carbon filter for filtering air, an inlet in fluidic connection with the activated carbon filter for supplying the activated carbon filter with an aqueous medium, and an outlet in fluidic connection with the activated carbon filter, and a second sub- module. The second sub-module is connected with the first sub-module, and includes a further filter for filtering the air. The further filter includes a particulate filter material different from activated carbon.

[006] The air filter module allows for a surprisingly high filtering effect of air with respect to air pollutants, in particular fine dust and nitrogen oxides (NOx), with comparatively low resource and/or energy consumption, is relatively easy to adapt to external conditions, and/or is well scalable and may be used in parallel, respectively. Furthermore, the filtered air may be humidified, cooled and/or enriched with air-quality improving substances if desired.

[007] Accordingly, air, in particular ambient air but also indoor air may be very efficiently cleaned. This even makes it possible to improve air quality in particularly exposed areas such as on or near busy roads.

[008] The above-mentioned effects can be achieved in particular when the air is filtered successively by the further filter and the activated carbon filter. For this purpose, a flow of the air through the filter module may be generated and a pressure drop across the filter module may be applied, respectively.

[009] The particulate filter material of the further filter is typically configured to at least reduce a concentration of nitrogen oxides (NOx), in particular mono-nitrogen oxides (NO) in the air.

[0010] The particulate filter material may in particular include or even be made of a wool and/or a zeolite, in particular a heat-treated zeolite.

[0011] For example, the particulate filter material of the further filter may at least substantially consist of a natural zeolite, in particular a clinoptilolite and/or a heat-treated zeolite, in particular a heat-treated natural zeolite.

[0012] A (minimum or mean) grain size of the typically heat-treated zeolite particulate filter material of the further filter is typically larger than about 0.3 mm, more typically larger than about 1 mm.

[0013] The term “grain size” of a particle or particulate material (PM) as used herein refers to an equivalent diameter of the particle and the particulate material, in particular an equivalent diameter as it can be determined by sieving.

[0014] Further, the grain size of the zeolite, in particular a maximum grain size of the zeolite (particles) is typically smaller than about 35 mm, more typically smaller than about 30 mm. [0015] Even further, the grain size of the zeolite is typically in a range from about 1.5 mm to about 28 mm.

[0016] Likewise, a porosity of the zeolite is typically in a range from about 20 % to about 35 %, more typically in a range from about 22 % to about 32 %.

[0017] The above-mentioned parameter values and ranges for the zeolite have been shown to be particularly favourable for the filtering of air over longer times (at least some days), especially for filtering NOx and dioxin out of the air.

[0018] The parameter values and ranges of the zeolite for highest cleaning effect may, however, depend on the expected environmental conditions, in particular on air temperature (range), air humidity (range) and the oil content of the air.

[0019] Note that, again typically depending on the expected environmental conditions, a lower grain size of the zeolite than 0.3 mm may result in clogging while the filter efficiency for zeolite with a grain size of more than 35 mm or even 30 mm may be too low.

[0020] The activated carbon filter typically uses particulate activated carbon, in particular carbon fibres, granular activated carbon and/or carbon particles.

[0021] For reasons of high long-time filter efficiency of the (pre-filtered) air with respect to remaining air pollutants, in particular fine dust, a porosity of the filter material of the activated carbon filter is typically in a range from about 20 % to about 35 %, more typically in a range from about 22 % to about 32 %.

[0022] Furthermore, air quality may be further improved and/or the activated carbon filter may be cleaned by supplying the aqueous medium to the activated carbon filter.

[0023] More particular, the activated carbon filter maybe flowed through with the aqueous solution permanently, at regular intervals or depending on the degree of pollution and/or ambient air humidity.

[0024] In so doing, the activated carbon filter may be cleaned and/or the air quality further improved, i.e. further cleaned, cooled and/or moistened if desired.

[0025] Fine dust and other pollutants from the (prefiltered ambient) air flowing through the activated carbon filter, may be bound by the medium trickling down the activated carbon filter and finally discharged via the outlet of the first sub-module, for example discharged into a storage tank for the aqueous medium. In the following, the storage tank for the aqueous medium is also referred to as main tank.

[0026] Due to the evaporation of water, both a pleasant temperature and humidity of the filtered air may be achieved. This can significantly improve the microclimate.

[0027] In other word, further improving the air quality by means of the activated carbon filter may be carried out in a typically well controllable manner similar as in a graduation tower, in analogy to the saline principle and similar to nasal inhalation, respectively.

[0028] The aqueous medium may be water, especially salty water.

[0029] Furthermore, the aqueous medium may (further) include suitable additives such as an antifreeze and/or one or more air-quality improving substances designed to bind or render air pollutants, e.g. caused by motor vehicles, harmless like urea-based substances, germ-reducing substances and/or substances with a (further) positive biological effect, in particular when inhaled, for example a plant-based active substance such as a terpene.

[0030] Depending on the expected air flow rate during operation, a volume of the filter material of the activated carbon filter and/or a volume of the particulate filter material is typically larger than about 5 1, more typically larger than 101 or even 25 1.

[0031] Furthermore, the volume of the filter material of the second sub-module may at least substantially corresponds to the volume of the particulate filter material.

[0032] Typically, a fluid distribution device is arranged between the inlet and the activated carbon filter.

[0033] Further, a fluid collecting device may be arranged between the activated carbon filter and the outlet.

[0034] The fluid distribution device and the fluid collecting device may be parts of an irrigation system and/or flushing system for the activated carbon filter.

[0035] The first sub-module and/or the second sub-module, typically both may be respective filter cartridges.

[0036] Furthermore, the filter module may include a frame or flow-through housing configured to be stacked on top of another frame or flow-through housing of the same type.

[0037] Accordingly, mounting of an array of air filter modules (to a larger air filter system) may be facilitated. [0038] Further, a sealing may be attached to the frame or the flow-through housing for at least substantially preventing bypassing the further filter and/or the activated carbon filter.

[0039] Accordingly, a particular high quality of the filtered air may be guaranteed.

[0040] The filter module may further include a third sub-module which typically includes a substrate for growing plants.

[0041] In addition, the third sub-module may include an inlet in fluidic connection with the substrate for watering the substrate with another aqueous medium, for example water or even a culture medium, and optionally an outlet in fluidic connection with the substrate for discharging excess medium and/or rain water, preferably in a storage tank for the other aqueous medium. In the following, the storage tank for the other aqueous medium is also referred to as further tank.

[0042] The third sub-module is typically arranged upstream (with respect to air flow) the first and second sub-modules.

[0043] Accordingly, plants growing on the substrate of the third sub-module may contribute to air filtering and be operated as a first filter for the air to be filtered, respectively.

[0044] This allows further positive effects to be achieved in terms of both insect protection, e.g. by providing a bee pasture, and air cleaning.

[0045] In this context, it should also be mentioned that the air to be filtered can be enriched with secondary plant substances such as terpenes by growing suitable plants, which can lead to a positive synergistic effect on air quality.

[0046] Furthermore, the plants may also contribute to a pleasant appearance of the air filter module and/or provide protection or at least inhibition against vandalism.

[0047] The plants may be protected by a mesh which is arranged above the substrate and through which plants can grow.

[0048] The second sub-module is typically arranged between the third sub-module and the first sub-module.

[0049] Further, the third sub-module may be mechanically connected with the second sub- module. This may facilitate combining air filter modules.

[0050] Even further, the third sub-module may be spaced apart from the second sub-module as the particulate filter material is typically to be kept dry (protected from being watered). [0051] According to an embodiment, an air filter system includes a filter module as explained herein, typically several respective filter modules, even more typically several substantially equal filter modules, for example, at least three, at least four or an integer multiple thereof.

[0052] The filter modules which are arranged over each other may be mechanically and/or fluidically connected with each other.

[0053] Alternatively or in addition, the filter modules may be attached to a frame of the air filter system, for example a metal frame. In the following, the frame of the air filter system is also referred to as main frame.

[0054] The filter modules may form a filter column, in particular a filter column with filter modules arranged at and/or on a lateral surface of a virtual cylinder and/or around a main vertical axis of the air filter system and/or the virtual cylinder.

[0055] For example, the air filter system may have several layers which are arranged over each other, wherein each layer has three or more (in particular at least substantially identical) filter modules which are typically arranged symmetrically with respect to the main vertical axis.

[0056] In this embodiment, ambient air may flow (typically be pumped) from the outside, through the filter modules and as cleaned air towards the main vertical axis (and typically vertically upwards for discharging).

[0057] In other words, the filter modules may be are arranged in and/or form an array, in particular a two-dimensional array.

[0058] The main frame may be attached to and/or carried by a base of the air filter system.

[0059] Within the base the following additional (fluidic) components of the the air filter system may be arranged:

- a main tank for the aqueous medium in fluidic connection with at least one of the inlet of the first sub-module of the filter module and the outlet of the first sub-module of the filter module,

- a main pump for pumping the aqueous medium from the main tank to the inlet of the first sub-module of the filter module(s), in particular to one or more respective uppermost one(s) of the filter module(s),

- a filter in fluidic connection with and arranged between the main tank and the outlet of the first sub-module of the filter module(s), in particular to one or more respective lowermost one of the filter module(s), the filter typically having a waste container for the filter residues such as fine dust deposit,

- a further tank for the other aqueous medium in fluidic connection with the inlet of the third sub-module of the filter module(s), and/or

- an irrigation pump for pumping the other aqueous medium from the further tank to the inlet of the third sub-module of the filter module(s), in particular to one or more respective uppermost one(s) of the filter module(s).

[0060] Typically, the main tank has a storage capacity of at least 200 1, more typically of at least 4001 or even 5001 or 7501.

[0061] The air filter system typically further includes a fan for generating a flow of the air through the filter module.

[0062] Typically, the fan is arranged above the filter module(s), the main frame and/or the base.

[0063] The fan may be a radial fan or an axial fan. However, it has been found out that an axial fan is more efficient for generating the flow through the filter module(s) and/or more silent during operation, in particular when the filter modules form a filter column as explained above, and the fan is arranged at least substantially coaxial with respect to a main vertical axis of the virtual cylinder.

[0064] In particular for outside applications of the air filter system, the rated power of the fan is at most about 1000 W or even 750 W.

[0065] The (air) filter capacity of air filter system may be at least 2000 m ³ /h, typically at least 4000 m ³ /h or even more typically at least 8000 m ³ /h, at least 16000 m ³ /h or even at least 24000 m ³ /h.

[0066] Typically, the energy consumption per filtered air is less than 0.1 Wh/m ³ or even .08 Wh/m ³ .

[0067] Furthermore, the air filter system may include one or more or even all of the following aerodynamic elements (for improving airflow and/or reducing energy consumption at given airflow through the filter system):

- a baffle plate arranged between the filter module and the fan for diverting the air flow; - an aerodynamic resistance structure arranged between the filter module(s) and the fan, and comprising an air resistance which increases step-wise or continuously with decreasing distance to the fan;

- a funnel for cross section adjustment between an air inlet of the fan and an internal space surrounded by the filter modules; and

- an air deflector for facilitating and/or maintaining a swirl of the airflow within the internal space of the air filter system (in the following also referred to as internal space), the air deflector being typically arranged in the funnel.

[0068] For example, due to the aerodynamic resistance structure the pressure drop along the main vertical axis may be compensated such that a substantially equal flow through the filter modules in different vertical heights may be achieved despite the pressure drop.

[0069] The aerodynamic resistance structure may include throttle plates and/or one or more sheets with holes or slits having a respective area which decreases with increasing vertical height.

[0070] For example, a cylindrical (metal) sheet with holes or slits decreasing in size with increasing vertical height may be used as aerodynamic resistance structure.

[0071] Further, the funnel and air deflector in combination with the fan, in particular the axial fan, have been found to allow for reducing the power of the fan after initially generating the swirl at a higher power of the fan. This is due to the fact the swirl is facilitated by the deflector.

[0072] Furthermore, the air filter system typically includes a sensor system. Accordingly, controlling and/or maintenance of the air filter system may be facilitated.

[0073] The sensor system may include one or more of even all of the following sensors:

- a temperature sensor for measuring a temperature of the air to be filtered;

- a humidity sensor for measuring a humidity of the air to be filtered;

- a further humidity sensor for measuring a humidity of the substrate;

- a status sensor for monitoring the aqueous medium, typically including a turbidity sensor and/or a level sensor for determining a level of the aqueous medium in the main tank;

- a level sensor for determining a level of the further aqueous medium in the further tank; - a flow detector for determining a pressure, a pressure difference, a flow rate and/or a flow velocity of the air within the air filter system;

- a chemical sensor for detecting a concentration of a chemical compound in the air to be filtered and/or for determining a concentration of the chemical compound, for example a respective NOx-sensor; and

- a particle detector for detecting the fine dust in the air to be filtered and/or for determining a concentration of the fine dust and/or a size distribution of the fine dust.

[0074] Typically, the air filter system further includes a control unit connected with the sensor system for receiving respective measuring values.

[0075] The control unit is typically configured to use the received measuring values to control at least one of the main pump, the irrigation pump, and the fan.

[0076] Accordingly, the air filter system may be operated autonomously (at least for several hours) and/or operated energy efficiently by considering external and/or as internal conditions into account.

[0077] For example, the flow rate through the air filter system may be chosen in accordance with the determined concentration of the fine dust and/or the determined concentration of the chemical compound(s).

[0078] Furthermore, the control unit may be connected via a network with an external computer system supervising the air filter system,

[0079] Typically, the external computer system is connected with several air filter systems.

[0080] For example, data of the status sensor may be transferred to the external computer system and used for scheduling maintenance of the air filter system(s).

[0081] Furthermore, the control unit is typically configured to perform the methods explained herein.

[0082] According to an embodiment of a method for filtering air, the method includes generating an airflow through one or more filter modules as explained herein.

[0083] The airflow is typically generated such that the first sub-module(s) filters air which is pre-filtered by a respective second sub-module. [0084] Furthermore, the airflow may be generated such that the second sub-module filters air which is pre-filtered by a respective third sub-module.

[0085] The air filter module and air filter systems as explained herein may be used for filtering and/or cleaning the air, in particular ambient air but also indoor air.

[0086] Those skilled in the art will recognize additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] The components in the figures are not necessarily to scale, instead emphasis being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts. In the drawings:

[0088] Fig. 1A illustrates a side view of filter module for filtering air according to an embodiment;

[0089] Fig. IB illustrates another side view of the filter module shown in Fig. 1A according to an embodiment;

[0090] Fig. 1C illustrates a cross-section of an air filter system according to an embodiment;

[0091] Fig. 2A illustrates a side view of an air filter system according to an embodiment;

[0092] Fig. 2B illustrates a cross-section of the air filter system shown in Fig. 2A according to an embodiment;

[0093] Fig. 2C illustrates a cross-section of a filter module according to an embodiment;

[0094] Fig. 2D illustrates a side view of the filter module shown in Fig. 2C according to an embodiment;

[0095] Fig. 3 A illustrates a perspective view of an air filter system according to an embodiment;

[0096] Fig. 3B illustrates a perspective view of a part of the air filter system shown in Fig. 3A according to an embodiment;

[0097] Fig. 3C illustrates a cross-section of the air filter system shown in Fig. 3A according to an embodiment;

[0098] Fig. 4A illustrates another perspective view the air filter system shown in Fig. 3A according to an embodiment; [0099] Fig. 4B illustrates a perspective view of a base of the air filter system shown in Fig. 3A according to an embodiment;

[00100] Fig. 5A illustrates another perspective view the air filter system shown in Fig. 3A according to an embodiment; and

[00101] Fig. 5B illustrates measurement results on filter performance of an air filter system as shown in Fig. 5A.

[00102] For better orientation, some of the figures also show a Cartesian coordinate system (x, y, z), wherein x and y typically represent horizontal coordinates and z a vertical coordinate.

DETAILED DESCRIPTION

[00103] In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as "top," "bottom," "front," "back," "leading," "trailing," etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[00104] The drawings may not be scaled and are for illustrative purposes only. For clarity, the same elements or manufacturing steps have been designated by the same reference numerals (or reference numerals that differ only in the first digit) in the different drawings if not stated otherwise.

[00105] With reference to Fig. 1A and Fig. IB showing respective side views, a filter module 100 for filtering air is explained.

[00106] In the exemplary embodiment, air filter module 100 includes a first sub-module 110 having an activated carbon filter 111 for filtering the air, an inlet 115 in fluidic connection with the activated carbon filter 111 for supplying the activated carbon filter 111 with an aqueous medium, and an outlet 116 in fluidic connection with the activated carbon filter 111 for discharging the aqueous medium typically including dispersed and/or dissolved filter residues such as fine dust removed from the air and the activated carbon filter 111, respectively.

[00107] This not only enables air humidification and cooling as desired, but also enables the carbon filter 111 to self-clean.

[00108] Typically, (self-)cleaning of carbon filter 111 requires a higher flow rate of the aqueous medium compared to air humidification and air cooling.

[00109] However, this may depend on external conditions.

[00110] A second sub-module 120 mechanically connected with the first sub-module is typically arranged upstream with respect to an air flow 1 of air to be filtered. The second sub- module 120 has a further filter 121 for filtering the air.

[00111] The further filter 121 is typically a dry air filter and includes a particulate filter material which is different from activated carbon, in particular wool or zeolite.

[00112] The first and second sub-modules 110, 120 are typically implemented as filter cartridges.

[00113] Furthermore, the respective extensions d _y , d _z of the sub-modules 110, 120 in directions y, z which are perpendicular to the (intended) airflow direction (positive x-direction in Fig. 1A and Fig. IB), i.e. the vertical extensions d _z of the sub-modules 110, 120 and the horizontal extensions d _y of the sub-modules 110, 120, may be at least substantially equal to each other.

[00114] For example, d _y may be in a range from about 40 cm to about 1.50 m, and d _z may be in a range from about 30 cm to about 1.50 m.

[00115] The extension d _xi , d _X 2 of the sub-modules 110, 120 may also be equal, but may also differ from each other.

[00116] For example, d _xi may be in a range from about 20 cm to about 75 cm, and d _X 2 may be in a range from about 20 cm to about 75 cm.

[00117] Fig. 1C shows a horizontal cross-section through an exemplary air filter system 500 having four air filter modules 100 as explained above this regard to Fig. 1A and Fig. IB.

[00118] As illustrated in Fig. 1C, the air filter modules 100 may be arranged in the circumferential manner so that the first sub-modules 110 surround an inner space 503 for the filtered air. [00119] As illustrated in figure Fig. 2A showing a view on an air filter system 500’, air filter modules 100 may also be arranged vertically over each other.

[00120] The two (hidden) first sub-modules of modules 100 may be directly mechanically connected to each other, especially detachably.

[00121] Further, the inlet 115 of the first sub-module of the lower air filter module 100 may be fluidically connected (detachably connectable) with the outlet 116 of first sub-module of the upper air filter module 100.

[00122] Fig. 2B illustrates a vertical cross-section through the air filter system 500’ . Note that Fig. 1C may even correspond to a horizontal cross-section through the air filter system 500’.

[00123] As illustrated in figure Fig. 2B, an air pumping system including a fan 550 may be provided on top of the filter modules 100 so that ambient air is sucked through the filter modules 100 (see dashed-dotted arrows 1), pumped as cleaned air through the internal space 503 of the air filter system 500’ (see dashed-dotted arrows G), and finally discharged to the outside (see dashed-dotted arrows 1”).

[00124] The fan 550 is typically arranged coaxial with respect to the main vertical axis 5.

[00125] In addition to the fan 550, the air pumping system may include a typically frusto- conical funnel 551 for cross section adjustment between an air inlet of the fan 550 and the inter space 503 of the air filter system defined by the first sub-modules and activated carbon filters 111, respectively, and/or an aerodynamic resistance structure for vertical pressure drop compensation (not shown) which may be surrounded by the filter module 100.

[00126] As indicated by the small dashed arrow in Fig. 2B, forming and maintaining of an air swirl in the air flow 1 ’ may be facilitated by an air deflector (not shown) arranged in the funnel 551.

[00127] For example, the air deflector may have several inclined wings arranged around the main axis 5.

[00128] With reference to Fig. 2C and Fig. 2D, a further filter module 200 for filtering air is explained. [00129] Filter module 200 also includes a first sub-module 210 with an activated carbon filter 211 and a second sub-module 220 with a further filter 221 as explained a above with respect to figures 1A, IB.

[00130] However, a third sub-module 230 having a substrate 231 for growing plants, an inlet 235 for supplying the substrate 231 with another aqueous medium, and an outlet 236 for discharging excess medium is arranged upstream the first and second sub-modules 210, 220 with respect to the intended airflow direction 1 through the filter module 200.

[00131] The third sub-module 230 may also be implemented as a cartridge.

[00132] As illustrated in figure 2D, the horizontal extension d _y 3 of the sub-module 230 in y-direction may be smaller than the horizontal extensions d _yi , d _yi of the sub-modules 210, 220.

[00133] Accordingly, a respective part of the ambient air may not be filtered by the plants growing on substrate 231. This may be desired to reduce the overall aerodynamic resistance of filter module 200 and an air filter system with filter modules 200, respectively.

[00134] Likewise, the vertical extension of the sub-module 230 may be smaller and the vertical extension of the sub-modules 210, 220.

[00135] For example, when seen in airflow direction (x-direction), an area of the third sub-module 230 may be in a range from about 25% to about 100%, more typically in a range from about 50% to about 75%.

[00136] Fig. 3A illustrates a perspective view of an air filter system 600. Filter system 600 is similar to the air filter systems 500, 500’ explained above with regard to figures 1C, 2B.

[00137] However, the exemplary air filter system 600 has 9 substantially identical filter modules 300 each of which includes a respective first sub-module 310, a respective second sub- module 320 and a respective third sub-module 330 (see also figure 3C illustrating a cross- section through horizontal plane E also showing the inner space 603 between the filter modules 300, and their first sub-modules 310, respectively).

[00138] The filter modules 300 are attached to an (inner) main frame 631 of an inner housing 630 of the air filter system 600, typically using a respective click system (not shown).

[00139] The inner housing 630 may be rack-like and/or formed by the frame 631 and (metal) plates (see also Fig. 4A). [00140] Further, the filter modules 300 are arranged in three groups around a main vertical axis 5. Each group has three modules 300 on top of each other.

[00141] One of the three groups shown in Fig. 3A, namely the group with the three denoted third modules 320, is shown in Fig. 3B when seen from the internal space.

[00142] As illustrated in figure 3B, the first sub-modules 310 may be connected to a watering system, in particular an integrated irrigation tray 615 arranged on top and fluidically connected with the inlet of the uppermost first sub-module 310, and an integrated drip tray 616 fluidically connected with the inlet of the lowermost first sub-module 310, and having a drain (not shown) at the bottom.

[00143] Likewise, air filter system 600 may have a similar watering system for the third sub-modules 330.

[00144] However, for safety reasons, the third sub-modules 330 may be spaced apart from the respective second sub-modules 320 by the spacer 225 as illustrated in figure 4C.

[00145] As illustrated in Fig. 4A, the frame 631, for example a respective aluminium frame 631 is typically mounted on a base 610 which is illustrates in more detail in figure 4B.

[00146] Within the base 610 a main tank for an aqueous medium, a main pump for pumping the aqueous medium from the main tank to the integrated irrigation tray(s) 615, a filter in fluidic connection with and arranged between the integrated drip tray(s) 616 and the main tank, a further tank for the other aqueous medium used for watering the substrates of the third sub-modules 330, and an irrigation pump for pumping the other aqueous medium from the further tank to the third sub-modules 330 may be arranged (all not shown).

[00147] Further, the base 610 may be provided with the shown external ports 611 - 614 for the main tank and the further tank.

[00148] As schematically illustrated in Fig. 5A, air filter system 600 is typically provided with a fan 650 for generating an air flow through the filter modules 300.

[00149] Furthermore, a typically ring-shaped planter 660 for growing further plants may be arranged above the filter modules 300.

[00150] The cleaned air is typically discharged from air filter system 600 at a height of at least about 1.8 m, at least about 2 m or even 3 m. In this way, high air currents in the head area of passers-by can at least be substantially avoided. [00151] The (vertical) height of air filter system 600 may be in a range from about 2 m to about 15 m, more typically in a range from about 2 m to about 4 m, or even more typically in a range from about 2.50 m to about 3.50 m.

[00152] The (horizontal) extension (diameter) of air filter system 600 may be in a range from about 1 m to about 6 m, more typically in a range from about 1 m to about 2.50 m, or even more typically in a range from about 1.25 m to about 1.75 m.

[00153] However, these values may depend on the planned place of use. For example, the dimensions given may be significantly smaller for residential applications.

[00154] In addition, an external cladding may be provided which at least partially covers the technical components otherwise visible from the outside, such as the frame 631, e.g. an appropriate wood panelling.

[00155] With the external cladding and suitable planting of the filter module 300 and/or the planter 660, the external appearance of air filter system 600 may even be reminiscent of a tree.

[00156] Fig. 5B illustrates measurement results on the filter performance of the air filter system 600 with zeolite as particulate filter material of the further filter of the second sub- module and even unplanted third sub-modules. Curves a and b show the concentration CPMIO of particulate matter with a size of at least 10 pm (i.e. fine dust) in the ambient air to filtered (upper curve a) and the filtered air (lower curve b) as function of time t over about eleven days.

[00157] The shown long-term measurements impressively prove the excellent filter effect of the filter modules and systems described herein.

[00158] Measurements at TLTV Sud have confirmed a filter efficiency of up to 85% (percentage of fine dust, NOx removed) and above with a controllable filter capacity of 14000 m ³ /h and a comparatively low energy requirement of only 0.75 kWh at the highest pump rate of the used air filter system.

[00159] Furthermore, additional measurements with an air filter system which is similar to air filter system 600, but additionally provided with a UV-illumination unit for irradiating the air filtered by the filter modules and an inner space surrounded by the filter modules, respectively, reveal that germs like viruses and bacteria can be efficiently killed or at least inactivated. [00160] For example, the UV-illumination unit may include one or more UV-light sources, in particular one or more UV lamps or UV LEDs that may be arranged between the filter modules and the fan. In particular, the UV-illumination may include a substantially ring- shaped arrangement (array) of several UV-light sources typically arranged in an upper portion of the inner space.

[00161] Apart from space, only an electrical power connection is currently desirable for operating the air filter systems described herein.

[00162] Due to the at least partially existing self-cleaning ability of the used filters, only low follow-up costs are to be expected.

[00163] Furthermore, the operating costs may also be comparatively low due to the possible easy emptying of any waste container and easy filling of the tanks.

[00164] Even further, the typically available sensors enable demand-oriented control and remote maintenance.

[00165] All this makes the use of the filter modules and filter systems described herein very promising for improving air quality, improving the micro climate and/or increasing the biodiversity in cities (in particular busy streets, "hot spots", pedestrian zones, shopping arcades), in public transport (airport, train station, subway, etc.), in farms / livestock farming, but also in office buildings, production buildings and the like.

[00166] Although various exemplary embodiments of the invention have been disclosed, it will be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the spirit and scope of the invention. It will be obvious to those reasonably skilled in the art that other components performing the same functions may be suitably substituted. It should be mentioned that features explained with reference to a specific figure may be combined with features of other figures, even in those cases in which this has not explicitly been mentioned. Such modifications to the inventive concept are intended to be covered by the appended claims.

[00167] While processes may be depicted in the figures in a particular order, this should not be understood as requiring, if not stated otherwise, that such operations have to be performed in the particular order shown or in sequential order to achieve the desirable results. In certain circumstances, multitasking and/or parallel processing may be advantageous. [00168] Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper” and the like are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc. and are also not intended to be limiting. Like terms refer to like elements throughout the description.

[00169] As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise.

[00170] With the above range of variations and applications in mind, it should be understood that the present invention is not limited by the foregoing description, nor is it limited by the accompanying drawings. Instead, the present invention is limited only by the following claims and their legal equivalents.

Reference numbers

1 1 air flow

5 main axis

100, 200, 300 filter module

110.210. 310 first sub-module

111.211. 311 activated carbon filter

115 inlet

116 outlet

120, 220, 320 second sub-module

121 further filter / prefilter

231 substrate for growing plants

235 inlet

236 outlet

500, 500’, 600, 600’ air filter system

503, 603 inner space

550, 650 fan, air unit

551 funnel

610 base

630 (inner) housing

631 (inner) main frame