FI129388B

FI129388B - An air purifier module, an air purification system, an air handling unit, and use of an air purifier module

Info

Publication number: FI129388B
Application number: FI20195485A
Authority: FI
Inventors: Pekka Rantanen; Ismo Lippojoki
Original assignee: Aavi Tech Ltd
Priority date: 2019-06-07
Filing date: 2019-06-07
Publication date: 2022-01-31
Also published as: WO2020245508A1; FI20195485A1

Abstract

According to an example aspect of the present invention, there is provided an air purifier module, comprising: at least one air cleaning unit, comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow; wherein all creepage distances in the module are at least 2 mm/kV, preferably at least 3 mm/kV, more preferably in the range 2 to 5 mm/kV.

Description

TITLE An air purifier module, an air purification system, an air handling unit, and use of an air purifier module

FIELD

[0001] The present invention concerns an air purification system that can be affixed to an air handling unit (AHU) in order to replace conventional mechanical filters. Particularly, the present invention relates to an air purifier module comprising an electrostatic precipitator.

BACKGROUND

[0002] An air purifier is a device that is used in order to clean the air in a room from dust and other contaminants. Air purifiers can be based on various kinds of collection principles of contamination, such as mechanical filtration, precipitation, activated carbon, gravitation, and centrifugation. Commercial air purifiers can operate either as small stand- alone units, especially in individual rooms and households, or as larger units that can be affixed, as one of the major components, to an air handling unit (AHU). An air handling unit is usually a large compartment containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers. Large air purifiers are used especially on an industrial scale, but also in AHU?s serving whole buildings. O [0003] Air that is supplied to buildings is processed in an air handling unit (AHU) to LÖ meet the requirements set for intake air. Fresh air from the outside is filtered, and at least

O © most of the particles and aerosols are removed from the air. In some cases even small

N I particles, odours, and toxic gases are removed. Filtration targets are defined in local a = 25 — standards or building codes. Fresh air might be mixed with recirculating air, which must be

LO 2 cleaned as well. Air can be heated or cooled to have a desired temperature. In most cases

LO @ filtering is performed by mechanical filters made from a fibre fabric or a similar material.

O N Such filters are a simple and inexpensive solution for removing small amounts of dust or particles from air.

[0004] When the quality of outdoor air is very low and the particle load to the filters is high, the maintenance interval, i.e. the time between changing of filters, is very short. This means high annual and lifetime costs for a user. If regular maintenance is neglected, air flow will drop. If the output flow is not regulated, negative pressure is created in the — building and dirty air will come through the construction.

[0005] In electrostatic purification some ozone is produced. Ozone is harmful to humans even in very small concentrations and therefore it is necessary to minimize ozone production in air purifiers. The amount of ozone produced is a function of the voltages and currents used in electrostatic purification and the construction of the purifier.

— [0006] An electrostatic precipitator (ESP), or an electrostatic air purifier, is a device that removes fine particles, like dust and smoke, from a flowing gas by electrostatic attraction. However, it does not work on odours. An ESP includes an ionizer which ionizes, or electrically charges, particles of the incoming air. The charged particles are then attracted to and trapped by collector plates that are oppositely charged. The trapped — particles stick to the plates until they are removed. Collector plates are usually formed as an assembly of parallel conductive plates or nested cylinders.

[0007] Particles accumulated on a collector must be regularly removed in order to maintain good purification efficiency. Depending on the method by which particles are removed from the collector plates, ESPs may be divided into two categories: dry and wet.

— The dry variant is the most abundantly used, basic form of an ESP. In industrial-scale dry ESPs the removal of accumulated dust can be accomplished by using rappers: the dirt and dust is shaken loose by vibration.

N [0008] In wet precipitators, a continuous supply of water is used for forming a wet 3 layer on the surfaces of the collector to remove the dirt therefrom.

N 25 — [0009] It is known to use washing devices for removing accumulated dust from E collector surfaces.

2 [0010] JP 2002035641 A discloses a washing device for an electrostatic dust o collector in which a plurality of dust-collecting plates is arranged parallel to each other. N The washing device consists of a multistage cylinder in which cylinders having smaller — diameters are housed and to which a pressure is applied by compressed air. Water washing nozzles are fitted to the front end of the multistage cylinder so as to be rotatable clockwise and counterclockwise and used for jetting high-pressure water. A wire-drum type winch is used for controlling the extension speed of the multistage cylinder.

[0011] US 4240809 discloses an electrostatic air cleaner intended for commercial and industrial air cleaning applications. The air cleaner includes a number of precipitator cells having spaced parallel plates for collecting dirt particles, and a vertically disposed traversing pipe-like spray header containing a number of spray nozzles for directing a spray of wash or rinse fluid onto the collecting plates in order to remove collected particles. The header is traversed horizontally across the precipitator cells by means of a trolley.

[0012] KR 101436381 discloses an electrostatic precipitator which can automatically clean hazardous materials collected on a surface of a dust collecting electrode during the operation of the electrostatic precipitator by periodically and alternately driving two dust collecting parts. The hazardous materials are continuously collected by using one dust collecting part when the other collecting part is subject to the cleaning operation.

— [0013] US 3156547 discloses an electronic air cleaner containing a wash manifold. During the washing operation, the manifold is moved from one side of the electronic air cleaner to the opposite side. During the movement of the wash manifold, one of various liguids is applied to the cells from manifold. The liguids are supplied to manifold as it moves back and forth through a hose.

— [0014] US 6620224 BI discloses an air purification device including: a first electrode in the shape of a hollow cylinder having both ends open; a second electrode in the shape of a solid needle having a tip end portion of a predetermined length including a N pointed tip; a dielectric member covering the second electrode except the tip end portion; > and a power supply for applying a high voltage across the two electrodes in order to create e 25 acorona discharge, for generating ozone and ion wind.

E [0015] There is a need for an improved air purifier that can be affixed to an air 2 handling unit in demanding environments with high levels of airborne particles. Examples D of such demanding environments include construction sites, factories, and industrial > facilities. Air impurities originating from construction or renovation work are particularly difficult to handle as they tend to form stubborn calcium deposits on the collection surfaces.

[0016] Manual maintenance and cleaning of the collector plates of an electrostatic air purifier is not always possible due to lack of know-how, personnel or facilities. Thus, there is a further need for developing an air purifier that better tolerates accumulation of dust on its surfaces without any substantive deterioration of purification efficiency.

[0017] There is a need to make the cleaning and washing of an electrostatic precipitator easier and to increase the maintenance intervals.

[0018] At least some embodiments of the present invention are intended to overcome at least some of the above discussed disadvantages and restrictions of the known air purifiers.

SUMMARY OF THE INVENTION

[0019] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0020] According to a first aspect of the present invention, there is provided an air purifier module, comprising: at least one air cleaning unit, comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow; wherein all creepage distances in the module are at least 2 mm/kV, preferably at least 3 mm/kV, more preferably in the range 2 to S mm/kV.

[0021] According to a second aspect of the present invention, there is provided an air = purification system, comprising several air purifier modules according to the first aspect O . . .

N arranged in parallel and/or in series.

8 0 [0022] According to a third aspect of the present invention, there is provided an air

N I handling unit, comprising: the air purification system according to the second aspect; a a = 25 — blower configured to blow air through the air handling unit; and a heating element and/or a

LO LS cooling element configured to heat and/or cool the air.

O o [0023] According to a fourth aspect of the present invention, there is provided use of the air purifier module according to the first aspect for purifying air originating from a building site or a construction site.

[0024] At least some embodiments of the present invention provide significant advantages. The present air purifier module can replace mechanical filters in an air handling unit. In some embodiments, size of the present module is comparable to the size of a mechanical filter with the same air flow capacity. High purification efficiency can be 5 reached even on days when air quality is at a low level and particle mass concentrations are high.

[0025] At least some embodiments of the present invention provide advantages on markets where the quality of outdoor air is poor and the use of mechanical fibre filters is challenging. In developing countries the operation and maintenance culture is not as — developed as in western countries, and there is a demand for purifiers not requiring frequent manual maintenance.

[0026] At least some embodiments of the present invention provide lower lifetime costs, continuous high purification efficiency and ease of use.

[0027] At least some embodiments of the present invention provide better tolerance with regard to accumulation of dust on the collector plates and other parts of the system.

[0028] In at least some embodiments of the present invention, ozone production is reduced.

DESCRIPTION OF THE DRAWINGS

[0029] FIGURE 1 illustrates an air cleaning unit comprising an ionizer and a = collector according to an embodiment of the present invention. & > [0030] FIGURE 2 illustrates in more detail an air cleaning unit comprising an

O 0 ionizer, a collector and electrical insulation of support rods.

N E [0031] FIGURE 3 illustrates in more detail an air cleaning unit comprising an 10 25 ionizer and a collector. The head (tip) of each ionization electrode is non-isolated. The D sidewalls of the ionization electrodes have been coated by an electrical insulator material. > The electrodes are located inside ionization pipes.

[0032] FIGURE 4 illustrates in more detail a high voltage connector according to an embodiment of the present invention.

[0033] FIGURE 5 illustrates air cleaning units connected to each other (in series) with high voltage connections.

[0034] FIGURE 6 illustrates air cleaning units connected to each other (in series) with high voltage connections in more detail.

[0035] FIGURE 7 shows two embodiments of an ionization net comprising ionization electrodes, and an ionization cell structure of an ionizer according to an embodiment of the present invention. The ionization electrode net is inserted into the cells in order to form the ionizer.

[0036] FIGURE 8 illustrates a collector in which the distance between adjacent collector cells is 5.5 mm.

[0037] FIGURE 9 illustrates an air purification system capable of holding six air cleaning units. Four units are shown.

[0038] FIGURE 10 illustrates a partly assembled air handling unit comprising two air cleaning units and a filter. — [0039] FIGURE 11 is the air handling unit of FIGURE 10 with a washing system assembled between the two air cleaning units.

[0040] FIGURE 12 illustrates a large air purification system capable of holding four air purifier modules. Each air purifier module comprises two air cleaning units and a washing system. — [0041] FIGURE 13 illustrates as a side view two air purifier modules with two air S cleaning units in each module. 3 [0042] FIGURE 14 illustrates four air purifier modules with two air cleaning units in N each module and a washing system on both sides of the air cleaning units.

I a + [0043] FIGURE 15 illustrates four air cleaning units and a washing system. 0 5 25

O O N EMBODIMENTS

[0044] DEFINITIONS

[0045] In the present context, the term “air cleaning unit” refers to a unit comprising an ionizer and a collector. The term “collector” refers to one or more collector surfaces, for example a set of parallel collector plates.

[0046] In the present context, the term “air purifier module” refers to a module comprising two air cleaning units and, optionally, a washing system between the two units.

[0047] In the present context, the term “air purification system” refers to an assembly of several air purifier modules. In such an assembly, individual modules are arranged in parallel to form a matrix with a larger face area and/or in series. In a serial configuration, outlet air coming from the frontmost air purifier module is lead to an inlet of — the subsequent air purifier module for further purification.

[0048] In the present context, the term “air handling unit” refers to a unit comprising an air purification system, which system comprises at least one air purifier module, and further functionalities for transferring and treating air. Examples of such additional functionalities include blowers, heating or cooling elements, filter racks or chambers, — sound attenuators, and dampers.

[0049] In the present context, the term “creepage distance” means the shortest distance along the surface of a solid insulating material between two conductive parts.

[0050] The invention provides a modular air purification system with an improved structure and versatility.

[0051] The air purification system of the present invention is based on electrostatic precipitators. N [0052] The air purification system of the present invention comprises one or more 3 air purifier modules. In one embodiment, the module comprises two air cleaning units, N each having an ionizer and subseguently a plurality of collector plates having walls and E 25 forming channels between them for receiving an air flow. Air flow can be horizontal or LO vertical as well. 3 2 [0053] In one embodiment, there is a washing system in between said two air N cleaning units, the washing system comprising a nozzle that is configured to jet a cleansing solution towards one or both of the air cleaning units. Preferably, there is a washing system integrated into each air purifier module. In one embodiment, the nozzle that is configured to jet a cleansing solution towards the air cleaning (or each air cleaning unit) is capable of achieving a pressure that is larger than 50 bars, in particular larger than 80 bars.

[0054] The air purifier module preferably comprises means for parallel and/or serial assembly with further similar air purifier modules.

[0055] In one embodiment, in an air purifier module the ionizer comprises a net of electrodes having a general shape of a cylinder or a cone; at least 90 % of the lateral surface of said electrodes, preferably substantially the entire lateral surface of said electrodes, is coated with an electrical insulator material; and the tips of the electrodes are not coated with an electrical insulator material.

— [0056] In one embodiment, rails are used for sliding air purifier modules sideways to place inside an air purification system. High voltage is supplied to the modules by connecting the modules to each other by connecting rods. When the modules are slid to place, the respective rods are slid into the connection points in the modules. The connection of the outermost modules (the first module and the last module in a row of modules) to high voltage is realized by means of connecting rods located outside the casing.

[0057] In one embodiment, air cleaning units slide on rails from side. High voltage is connected between units by means of connecting rods which slide into the connectors in the air cleaning units preferably to form a water tight connection when the units are slid — together. High voltage to the last units is connected by rods located outside the casing. The connecting rods comprise an insulated metal tube. The connectors in the air cleaning units comprise a banana plug.

O N [0058] One embodiment comprises connecting rods having an insulated metal tube 3 and connectors in purifier units which have a banana plug.

N I 25 — [0059] If the system comprises several modules, they can be assembled in series, i.e. > consecutively, to achieve higher purification efficiency. The modules can also be o assembled in parallel (to a matrix) to form an air purification system with a face area that is > larger than a face area of a single air purifier module. They can even be assembled by N using both serial and parallel configurations.

[0060] Preferably, each air purifier module comprises a washing system and one or more air cleaning units on one or both sides of the washing system. In one embodiment, there is one air cleaning unit on each side of a washing system. In another embodiment, there is a matrix of air cleaning units, e.g. a 2 x 2 matrix or a 1 x 2 matrix, on each side of a washing system.

[0061] An air cleaning unit of the present invention comprises an ionizer and a collector. The ionizer is located in front of the collector in order to charge the particles and to enable the collector to trap those particles. The ionizer comprises charged electronic surfaces or electrodes, which generate electrically charged air or gas ions which attach to airborne particles. The collector includes electrostatic collector plates.

[0062] In one embodiment, the ionizer comprises a honeycomb made of 66 mm hexagonal tubes. There is one ionization electrode in the middle of each tube. Thus, the distance or gap from the tube wall to the electrode is 32 mm. Preferably, the nominal voltage is 14 kV and the maximum voltage is 16 kV.

[0063] In one embodiment, the ionization current is in the range 4 to 9 mA.

[0064] In one embodiment, the ionization voltage is in the range 12 to 16 kV.

[0065] In one embodiment, electrodes of the ionizer are insulated except their tips to minimize ozone production.

[0066] In one embodiment, the collector plate package is designed to have a separation of 5.5 mm, a voltage of 6 kV and thus a collection efficiency of 95 %. = [0067] The separation of the collector plates is preferably 4 mm to 6 mm, more N preferably 5 mm to 6 mm, even more preferably at least 5.5 mm. The advantage of having 3 a separation of at least 5.5 mm is that water droplets are not trapped between the plates N during washing, and liguid bridges are not formed.

I a - 25 — [0068] The voltage between the collector plates is preferably less than 60 kV, more

LO X preferably less than 50 kV, for example 5 to 10 kV. 3 o [0069] In one embodiment, all creepage distances in the air purifier module, or at least in a collector of the air purifier module, are at least 2 mm/kV, preferably at least 3 mm/kV, more preferably 4 to 10 mm/kV.

[0070] In one embodiment, the voltage between the collector plates is less than 50 kV, and creepage distances are at least 2 mm/kV.

[0071] In one embodiment, the voltage between the collector plates is less than 60 kV, preferably it is in the range from 10 to 20 kV. Preferably all creepage distances in the module are in the range from about 20 to about 60 mm.

[0072] Collector and ionizer parts must be washable and regularly washed, because coal-based dust and impurities conduct electricity.

[0073] The ratio between effective channel length and distance between the collector plates shall be preferably at least 10, more preferably at least 15.

[0074] The material of the collector plates may be any suitable conducting material, for example a metal or an electrically conductive plastic or an electrically conductive polymer. Suitable electrically conductive polymers include polyfluorenes, polyphenylenes, polypyrenes, polyazulenes, polynaphthalenes, polypyrroles, polycarbazoles, polyindoles, polyazepines, polyanilines, polythiophenes, poly(3,4-ethylenedioxythiophene), poly(p- — phenylene sulphide), polyacetylenes, poly(p-phenylene vinylene). Suitable metals include stainless steel and aluminium in any suitable form, such as a plate or a grid.

[0075] Preferably, the material of the collector plates is stainless steel, preferably stainless steel EN 1.4307 or better. This material enables the use of a high pressure, e.g. larger than 50 bars, for spraying a cleansing liquid onto the collector plates and ionizer — surfaces. It also makes it possible to use strong detergents, e.g. acidic detergents that are capable of removing calcium deposits, or alkaline detergents.

S [0076] In an air cleaning unit, preferably all such metal parts and metal surfaces of LÖ the collector and the ionizer which are exposed to the air to be purified are made of

O 0 stainless steel. The advantage is that strong detergents can be used for cleaning said

N I 25 — surfaces of the air cleaning unit.

a a o [0077] In an air handling unit, preferably all inner metal parts inside a casing of the D air handling unit are made of a same material, most preferably of stainless steel.

O N [0078] In some embodiments, dispensing of the cleansing solution is performed by applying high pressure. Preferably, the pressure is larger than 50 bars, for example 60 to 90 — bars, more preferably larger than 80 bars, for example from 85 to 100 bars.

[0079] According to one embodiment, the air handling unit does not contain any active carbon filter so that the pressure drop across the air purification system remains small, preferably below 40 Pa, more preferably below 30 Pa, for example 10 to 25 Pa.

[0080] In some embodiments, the air handling unit receives circulated air.

[0081] In the embodiments in which air circulation is used, ozone removal is preferably applied. Ozone can be removed by using an active carbon filter or a catalyst.

[0082] In some embodiments, the present air purification system is a modular part of an air handling unit. An air handling unit according to the present invention may be further equipped with a mixing chamber, means for recirculating air, and means for reducing — ozone concentration.

[0083] In one embodiment, the air purifier module comprising means for parallel and/or serial assembly with further air purifier modules.

[0084] One embodiment provides an air purification system, comprising several air purifier modules as discussed above. They can be arranged in parallel and/or in serial arrangement. Further, in an air purification system, a high voltage source can be connected to the ionizer and the collector by means of insulated metal tubes. Such insulated metal tubes can be slid inside insulated connector parts of the air cleaning unit. To secure the connection, there can be one or more spring loaded connectors.

[0085] One embodiment provides an air handling unit, which comprises an air purification system for example as discussed above with a blower configured to blow air through the air handling unit; and a heating element and/or a cooling element configured N to heat and/or cool the air.

N 3 [0086] In an air handling unit, the volumetric air flow is preferably in the range 0.5 N to 20 m/s, for example 0.7 to 14 m/s. Air velocity is preferably in the range 1.0 to 3.0 E 25 — m/s, for example 2.0 to 2.5 m/s. LO . . . . . . LS [0087] If the volumetric air flow is in the range 0.7 to 14 m/s, it is preferable to use

LO @ at least 12, more preferably 16 air purifier modules. 16 air purifier modules (each for

O N example 600 mm x 600 mm) can be arranged so that 4 modules are laid to a 2x2 matrix, and 4 such matrices are then laid in series. In such an arrangement, the face area is 2400 mm x 2400 mm.

[0088] According to an embodiment, the flow rate of air is in the range 1200 to 3200 m’/h.

[0089] The dimensions of the face area of an air purifier module can be for example: 600 mm (length) x 600 mm (width), or 300 mm x 600 mm, or 600 mm x 300 mm. The depth of an air purifier module can vary in the range 300 mm to 750 mm.

[0090] Preferably, the length of an air purifier module is equal to or less than 600 mm.

[0091] Preferably, the width of an air purifier module is equal to or less than 300 mm.

[0092] The mechanical parts of the ionizer and the collector plates should preferably have no sharp edges to minimize ozone production and thus to avoid the use of an active carbon filter.

[0093] The present invention is applicable for purifying indoor air or outside air both in new buildings and in existing buildings. In the latter case, mechanical fibre filters can be replaced by the present technology. Preferably, mechanical fibre filters are not used in an air handling unit according to the present invention.

[0094] The present invention is also applicable for purifying air and process gases at construction sites and manufacturing sites.

[0095] According to an embodiment, the air to be purified contains impurity — particles or droplets with a diameter smaller than 1 um.

N [0096] Example

N 3 [0097] In this example we used an air purification system comprising two air purifier N modules in series. Each module contained an ionizer and a collector. The air to be purified E originated from an aerosol generator and contained oil droplets with a diameter smaller 10 25 than 1 um as impurities. The ionization voltage was in the range 12 to 16 kV. The D ionization current was in the range 4.2 to 8.4 mA. The flow rate of air was in the range > 1271 to 3167 m*/h. The results are shown in Table 1 below. The purification efficiency was very good: more than 90 % of the impurities were removed. The ozone yields stayed on low levels, below 40 ppb.

Table 1. Results Ionization Current | Flow rate | Purification | Os yield voltage (kV) | (mA) (m*/h) (%) (ppb) S -

O

N 00 Tr a

LO 00 + S [0098] It is to be understood that the embodiments of the invention disclosed are not N limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0099] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[00100] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, — these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along — with alternatives for the various components thereof It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[00101] Furthermore, the described features, structures, or characteristics may be — combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One SN skilled in the relevant art will recognize, however, that the invention can be practiced N without one or more of the specific details, or with other methods, components, materials, 3 25 — etc. In other instances, well-known structures, materials, or operations are not shown or N described in detail to avoid obscuring aspects of the invention. i

[00102] While the forgoing examples are illustrative of the principles of the present 3 invention in one or more particular applications, it will be apparent to those of ordinary 2 skill in the art that numerous modifications in form, usage and details of implementation N 30 can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[00103] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a — singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[00104] The present invention can be industrially applied in the field of air purification in centralized ventilation systems, industrial buildings, construction and — building sites, commercial buildings and office buildings.

ACRONYMS LIST AHU air handling unit ESP electrostatic precipitator

CITATION LIST Patent Literature JP 2002035641 A N US 4240809

N 3 20 KR 101436381 co

N US 3156547 x a

LO 00 +

LO O O N

Claims

CLAIMS:

1. An air purifier module, comprising: — at least one air cleaning unit, comprising as a cascade an ionizer and subsequently a plurality of collector plates, wherein adjacent collector plates form channels that are configured to receive an air flow; wherein all creepage distances in the module are at least 2 mm/kV, preferably at least 3 mm/kV, more preferably in the range 2 to 5 mm/kV; wherein: — the ionizer comprises a net of electrodes having a general shape of a cylinder or a cone; — at least 90 % of the lateral surface of said electrodes is coated with an electrical insulator material; — the tips of the electrodes are not coated with an electrical insulator material; and — the material of the metal parts of the ionizer and the collector plates is stainless steel.

2. The air purifier module according to claim 1, wherein the voltage between the collector plates is less than 60 kV, preferably in the range from 10 to 20 kV.

3. The air purifier module according to claim 1, wherein the voltage between the collector plates is in the range from 10 to 20 kV, and all creepage distances in the module are in the range from 20 to 60 mm. O 25

4 The air purifier module according to any of the preceding claims, wherein: 3 — substantially the entire lateral surface of said electrodes is coated with an electrical S insulator material. x a O

5. The air purifier module according to any of the preceding claims, further comprising a D 30 washing system integrated into each air purifier module and comprising at least one nozzle > that is configured to jet a cleansing solution towards said at least one air cleaning unit with a pressure that is larger than 50 bars, preferably larger than 80 bars.

6. The air purifier module according to any of the preceding claims, further comprising means for parallel and/or serial assembly with further air purifier modules.

7 An air purification system, comprising several air purifier modules according to any of the claims 1 to 6 arranged in parallel and/or in series.

8. The air purification system according to claim 7, wherein a high voltage source has been connected to the ionizer and the collector by means of insulated tubes, such as metal tubes, wherein the insulated tubes, or insulated metal tubes, have been slid inside insulated connector parts of the air cleaning unit in particular so as to form a water tight connection, and wherein spring loaded connectors secure the connection.

9. An air handling unit, comprising: — an air purification system according to claim 7 or 8; = ablower configured to blow air through the air handling unit; and — a heating element and/or a cooling element configured to heat and/or cool the air.

10. Use of the air purifier module according to any of claims 1 to 6 for purifying air originating from a building site or a construction site.

11. The use according to claim 10, wherein said air comprises oil droplets as impurities.

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