CONSTRUCTION METHOD FOR THE BUILDING OF A SWIMMING POOL

The present invention relates to a swimming pool, swimming pool modules and the construction method for the building of a swimming pool.

Especially, this invention relates to a swimming pool with large dimensions, for example a public swimming pool. A public swimming pool has relatively large dimensions compared to a private pool; the length of a competitive swimming pool can easily exceed 25 m.

Public swimming pools need to be easily accessible, typically they are recessed in the floor, in other words, the upper edge of the swimming pool coincides with the floor from which the swimmers can approach, enter or leave the swimming pool. Public swimming pools are embedded, for example arranged in, and for example firmly fixed with the structure of a building. This is a large distinction compared to a typical private pool.

Furthermore, public swimming pools have to meet legal standards and certain regulations. For example a certain concentration of chlorine needs to be in the water at all times, the water must be adequately purified and refreshed, given the high intensity of use and the large amount of people entering the swimming pool.

Public swimming pools have to be more wear-resistant then private swimming pools. Besides, available budgets for public swimming pools are relatively small, therefore the cost of materials and building processes must be limited. Also the cost for the maintenance of the swimming pool needs to be as limited as possible. For example, the cost of energy required for changing and refreshing water, water purification and water circulation, but also the cost for the cleaning of the walls of the swimming pool are preferably kept as low as possible.

In particular, the present invention relates to a public indoor swimming pool, which is characterized by a relatively low exposure to nature and weather elements in comparison with outdoor swimming pools. For example, the temperature difference to which a public indoor swimming pool is exposed is relatively small.

Different types of public swimming pools and construction methods are known in the state of the art of construction. Typically swimming pools are built with a concrete bottom and sidewalls, on which tiles are applied. This has both an esthetic purpose as a waterproofing function, it is also easier to maintain because of its smooth surface, compared to any rough surface, on which dirt and other deposits are more easily attached (for example, uncoated concrete).

Working with concrete and tiles is very labor intensive and therefore very expensive. Tiles often detach from the concrete surface due to a variation in water pressure, temperature and other factors. This must be repaired to prevent further permanent damage to the pool. Simple, fast and reliable reparation is not easy in public pools. Filtering, buffering and pump systems require specially equipped spaces and occupy a significant volume in the building.

Private pools are often simpler in construction and maintenance but are not suited as a public pool, especially as a public indoor pool. In particular, typical private swimming- pool constructions are not suited for application of relatively large (25 m in length and more) and deep pools (maximum depth greater than 1 ,75m). For private pool, there are solutions available 'in one piece', made of plastic. However, these plastic walls can retain only limited pressure without deformation. These pools are therefore often embedded in the ground, so that the adjacent ground can provide a counter-pressure. This is not an option for public, indoor swimming pools.

Therefore there is a need in the building industry for new public swimming pools that can be built up quickly, with relatively inexpensive materials, and which are relatively simple and inexpensive to maintain. A first aspect of the present invention relates to a swimming pool, comprising a sidewall which exists of a plastic inner pane and a plastic outer pane, connected to each other with a connecting device, hereby forming an enhanced sidewall. The sidewall consists mainly of plastic, a material which, among other things has a relatively large bendability.

The double-walled sidewall has the advantage that plastic can be used for the construction of relatively large and deep swimming pools, such as a public swimming pool. A number of plastic materials are very durable when used in swimming pool conditions. In addition, the structure can be realized at low cost.

Another advantage of plastic walls is that they have a very smooth surface and are very hygienic. Neither tiles nor any other protective process needs to be applied on the plastic walls before they can be used as a swimming pool wall. Moreover, they are visually and aesthetically similar to a tiled pool, while they are able to form shapes which are difficult or impossible to achieve by a tiled wall.

In preferred embodiments, the side wall is constructed modular. The plastic modules preferably comprise an inner and outer plastic pane, connected to each other by connecting devices. Preferably, the modules which form the side wall are connected to each other by means of gluing or welding, forming hereby a very strong side wall which is waterproof. Hereby are for example the inner panes (walls), and preferably both inner and outer panes (walls), of adjacent modules connected to each other by means of gluing or welding. Preferably, the modules constituting a sidewall are also connected by means of gluing or welding to a plastic floor to realize a watertight pool.

In preferred embodiments, the maximum diagonal dimension (typically corresponding to the diagonal of a competition pool) of the pool area is greater than 25 m.

In preferred embodiments, the side wall has a height that is greater than 1 ,75 m.

In pools with these dimensions, typically used as public swimming pools, the forces exercised by the water are considerably larger than in pools with smaller dimensions, typically used as private pools.

In preferred embodiments, the connecting device comprises a number of connecting ribs. These connecting ribs are preferably arranged at regular distances between the inner pane and the outer pane. The connecting ribs can be arranged, for example, at distances between 10 cm and 100 cm, more preferably at distances between 20 cm and 80 cm, for example, at distances of 60 cm, from each other.

The connecting ribs can also comprise, for example, plastic or are fully made of plastic. The connecting ribs are preferably on their first end connected to the inner wall / the first side pane for use as the inner wall, and at their second end connected to the outer wall / a second pane for use as an external wall, this preferably by gluing or welding.

In preferred embodiments, the connecting ribs define at least one vertical stiffening of the side wall. The connecting ribs can define, for example, at least one vertical column in the side wall. Hereby two vertical ribs, which continuously extend over a large part or the entire height of the side wall, together, and respective connecting parts of the inner wall and outer wall, can define an upstanding shaft. This upstanding shaft is preferably only open at the top, optionally also at the bottom.

In preferred embodiments, the distance between the inner pane and outer pane exceeds 20 cm, or 25 cm. More preferably, this distance exceeds 40 cm. The distance is preferably in the range of 20 to 100 cm. More preferably, this distance is in the range of 40 cm to 300 cm, or in the range of 70, 80, 90 or 100 cm to 250 or 275 or 300 cm. The larger this distance, the greater the stability that can be reached by the double wall, meaning the side wall of the swimming pool. The greater the distance, the more space is created between the inner and outer panes; the more room there is released which can also be usefully used, as will be described further.

The inner pane and outer pane preferably have a constant thickness between 0.5 and 5 cm, more preferably a thickness between 1 and 2.5 cm. These walls can use commercially available plastic panes.

In preferred embodiments, the inner pane and outer pane are arranged in such a way that the area of the region, defined between the inner pane and outer pane, over the entire perimeter of the swimming pool, equals at least 3% of the floor area of the pool, more preferably at least 8%, or at least 15%. The area of the region defined between the inner pane and outer pane, over the entire perimeter of the swimming pool, for example, can be more than 15 m2. In preferred embodiments, the pool comprises an open filter system arranged in the side wall. An open filter system may be provided, for example, in one or more vertical shafts.

A sufficiently large area allows for sufficient filter area to be available when designing an open filter in the side wall of the pool. Legal regulations differ from country to country, but in general, the filter capacity is provided by a function of the size of the pool, or/and especially the number of swimmers. This number is relatively large for public pools in comparison with private pools.

In preferred embodiments, there is in the vertical shaft, during use, a space of at least 10, 20 or 30 cm above the upper surface of the open-system filter, for example a space with a height between 30 cm and 80 cm. In this way, there is a sufficient height available, when backwashing the filter, to allow the filter to expand and to be able to wash away the collected dirt. In this space, for example, a drain may be arranged. In preferred embodiments, the filter pack from the open filter system has a height of at least 1 meter, including support layers. The filter pack is preferably, including support layers, at least 125 cm high. Such heights are usually not encountered in private pools. The greater the heights of the filter pack, the more efficient the filtering can be done.

In preferred embodiments, at least one vertical shaft is open at the top, and is adapted to be able to receive unfiltered water from the swimming pool. The vertical shafts are preferably near their lower end provided with an outlet for filtered water. Further, the pool preferably includes means to direct the water from the outlet back to the pool, such as a system of pipes and pumps. Further, the swimming pool preferably comprises means for washing the filters. This can be done, for example, by pumping pool water from the swimming pool or a basement buffer backwards through the filter pack, subsequently diverting the water to the sewerage or a buffer basement. In preferred embodiments, the inner pane, outer pane and the connecting rib of the double-walled sidewall are made of a similar plastic material. The plastic material for inner and / or outer pane and / or connecting ribs may, for example, differ from a fiber- reinforced composite.

In alternative embodiments, outer and inner pane, and optionally also the connecting ribs, are made of different materials. Preferably, the materials of the inner pane, outer pane, and connecting ribs have a coefficient of thermal expansion of the same order of magnitude (for example, CTEinnerpane / CTEouterpane within the range of 0.2-1 , or within the range 0.4-1). The coefficient of thermal expansion of the inner wall is preferably smaller than that of the outer wall. The inner wall is preferably stiffer than the outer wall. In alternative embodiments, the inner wall and connecting ribs are made of the same plastic material, or consist of the same plastic material, while the outer wall comprises a different plastic material or is composed of this different plastic material.

In preferred embodiments, the inner wall consists of a lower part and an upper part, e.g. a part adjacent to the water surface in the pool in use, which is made of different materials. The upper part, the wall part in line with the water surface, is superior

(smoother, harder and of a lower coefficient of thermal expansion so that it is easier to clean, it is less easily damaged and bends less under load e.g. of swimmers, divers, etc.). The outer wall and ribs are (mostly) made of low-grade material. For example, the upper part can be made of composite aluminum-acrylate and the lower part (and also, for example, the ribs and the outer wall) of polypropylene or polyethylene. For the connection of the lower part and the upper part, wherein the lower part and the top part consist of a different material and, for example, have a different coefficient of thermal expansion, is preferably a (sliding) dovetail connection used.

In preferred embodiments, the bending of the plastic modules is less than 1 /250th of the smallest dimension of the pool area (e.g. depth of the pool). The inner wall and outer wall preferably have each self an E-modulus of up to 10.000 MPa.

Plastic materials typically have a large coefficient of thermal expansion. The materials of the inner and outer walls, for example, can have a coefficient of thermal expansion which exceeds 0,1 is E-4 m / (mC°). In preferred embodiments, the plastic material of the inner wall and outer wall is independently selected from the collection of polypropylene, polyethylene, PVC, acryl or acrylic composites.

In preferred embodiments, the inner wall comprises composite aluminum-acrylate.

In preferred embodiments, the plastic material comprises composite aluminum-acrylate for the inner wall adjacent to the water, and polypropylene for the other parts. In certain embodiments, the side walls can be additionally supported by concrete or metal reinforcements.

In preferred embodiments, the concrete or steel reinforcements are disposed at least partly between the inner wall and the outer wall. In preferred embodiments, at least a part of the double-walled sidewall is arranged as a buffer or buffer basement in which water can be collected. This may for example be combined with another part of the double-walled sidewall which is arranged as an open filter.

In preferred embodiments, the swimming pool has an overflow system, which is during use completely filled with water up to the top of the upstanding side wall, and where the water flows over the inside pane of the double-walled side wall and therefore is collected / buffered in the space between inner and outer pane.

The use of the double-walled side wall as a filter and / or buffer brings the additional advantage that this side wall itself is more weighted and, therefore, increasingly exercising counter-pressure against the pressure of the water in the swimming pool during use. A greater distance also provides greater stability of the sidewall.

In preferred embodiments, the floor is made from the same material as the inner or / and outer wall, wherein the bottom and the side wall form a whole, and where the whole is placed on the ground which allows the construction to slide in its direction of expansion. This offers the advantage that dilatation of the plastic materials may take place without a significant increase of stress.

In preferred embodiments, the floor comprises a plastic material (for example made of the same material as the inner wall or the lower part of the internal walls / or the part of the inner wall near the water surface and / or the outer wall), in which the bottom and the side wall are a whole, and where the whole is anchored to a part of the building by anchors, in which there are no thermal stresses induced at a predetermined temperature of the swimming pool.

In preferred embodiments, the side wall is anchored to a part of a building by anchors, in which there are no thermal stresses induced at a predetermined temperature of the swimming pool. The above two embodiments have the advantage that there can't be buckling due to thermal stresses and that the build-up of these stresses is minimal at the intended operating temperature.

A second aspect of the present invention concerns the use of the swimming pool modules as building blocks of a swimming pool, where the pool modules comprise a plastic inner and a plastic outer pane, which are connected to each other by a connecting device.

A third aspect of the present invention relates to a modular method of building a swimming pool, comprising the anchoring of swimming pool modules to a part of the building structure at a predetermined operating temperature.

It is further to note that the features present in the description of various aspects of the invention, also are applicable to the other aspects, such as this will be understood by a professional.

The above and other advantageous features and objects of the invention will become more apparent and the invention will be better understood by reference to the following detailed description when read in conjunction with the respective drawings.

The description of the aspects of the present invention is done by means of specific embodiments and with reference to, but not limited to, certain drawings. The illustrated figures are only schematic and should not be regarded as limiting. For example, certain elements or features may be presented out of proportion or scale relative to other elements.

In the description of certain embodiments according to the present invention, different properties are sometimes grouped together in a single embodiment, figure, or description for the purpose to contribute to the understanding of one or more of the various inventive steps. This should not be interpreted as afford all properties of the group are necessarily present to solve a specific problem. Figures 1 (a), 1 (b), 1 (c), 1 (d) and 1 (e) illustrate preferred embodiments of the present invention. A section of a swimming pool wall 1 , or a swimming pool module 1 used for the swimming pool wall, is made up of an internal plastic pane 2 (inner wall of the swimming pool 11) and an external plastic pane 3 (outside of the swimming pool 11 ). These panes are, preferably fixedly, connected to each other by means of a number of ribs (41 , 42). These ribs are at a first end connected to the first pane 2 (for example, for use as the inner wall), and at a second end with a second pane 3 (for example, for use as an external wall). They may also be connected to the bottom or the top of the module (not shown). The ribs serve as spacers between the two panes and provide an enhanced pool wall structure. The distance d between the two panes, for example, is chosen so that there is sufficient internal volume created in the pool wall. The ribs may be for example, perpendicularly arranged with respect to the main surfaces of the plastic panes. The ribs 4 are preferably arranged homogeneously distributed in the space between the two plastic panes 2 and 3. Thus, the ribs 41 may, for example be arranged according to a vertical direction when the panes are mounted as a swimming pool wall. The ribs 42, or other ribs 42, can also be arranged horizontally. An embodiment that includes both horizontal ribs 41 and vertical ribs 42 is shown in Fig. 1(b). Fig. 1 (c) shows a further embodiment of a double-wall sidewall, wherein the inner wall 2 has a longitudinal recess 20, forming a standing edge on which swimmers can rest. This recess may be applied, for example at a depth of about 1.3 m, with a depth of at least 10 cm. The presence of a longitudinal recess may constitute a weakening of the inner wall. The presence of the double wall, thus also of the outer wall, however, ensures sufficient strength of the side wall. In preferred embodiments, at least for the end sides of the pool, the vertical ribs are provided at positions corresponding to positions where the forces by the swimming lines 16 are exercised, so that these forces can be optimally absorbed by the wall. In a practical embodiment, the vertical ribs can be arranged parallel, 50 cm from each other.

Figures 1 (d) and 1 (e) show a double wall in which the material of the upper part of the inner wall is of a superior quality as the lower part of the inner wall. Outer wall and ribs are made out of a lower-grade material. At the top an overflow drain is drawn. The drain joints the platform by a connecting piece, also fabricated in the higher quality material. The plastic wall may expand freely with respect to the structural platform and the concrete slab on which the pool rests. Figure 8 illustrates a (preferably sliding) dovetail connection which can be used in preferred embodiments between the lower parts (e.g. the vertical ribs 41) and the upper part 44 of the inner wall, wherein the lower part is of a lower grade material and the upper part of a higher grade material. This situation can for example occur at the edge of the pool where the easily visible and more easily damageable upper part, which for example, forms the rim, for example, can be carried out in aluminum-acrylate. The upper edges 4 1 of the ribs 41 may be connected to the upper part 44 of the swimming pool. The upper part of the wall 44 (arranged horizontally, and thicker depicted in Figure 1 (d)), for example, can slide over the dovetails of the ribs by means of notches 441. The upper part of the wall 44, for example, 2,5 m in length and may not be glued to each other to form the complete rim. As a result of temperature differences, small joints may arise between the separate upper inner wall parts

(edgeparts).

In preferred embodiments, the ribs extend over the entire height or width of a swimming pool module. Parallel, along with respective sections of inner wall 2 and outer wall 3, K shafts defining vertical ribs 4 are preferably placed at a distance of between 20 cm and 100 cm, for example at a distance of 50 cm. As will be described later, these vertical shafts K can be advantageously used to house an open filter (corresponding to a volume V1). In these embodiments, it is not excluded that there are also horizontal or otherwise oriented ribs present, such as, for example, shown in Fig. 1 (b); the latter can then be perforated and comprise suitable openings. In certain embodiments, for example, form the differently oriented ribs a downwardly oriented narrowing of the funnel-type. Both the vertical ribs and horizontal ribs may each be mounted on a, possibly different, regular distance from each other.

The ribs may, for example also be embodied by connecting rods which are, for example, rectangular or circular in cross-section (e.g. with a diameter of between 1 cm and 10 cm), and are arranged at positions in accordance with a regular grid. For example, the grid spacing can be between 20 cm and 100 cm, for example 50 cm.

The ribs 4 can be placed between the plastic panes, for example, by means of gluing or welding.

In alternative embodiments, the density (number of ribs per m ² wall surface) of ribs at a first end (e.g. lower end when set) of the swimming pool modules are higher than at the second end (e.g. top end when set). Indeed, the forces exerted on the pool wall are greater at greater depths. A stepped or continuously increasing density of ribs 4 from top to bottom along the pool module can be designated for this purpose.

In embodiments, the pool 11 consists of substantially identical modules 1.

In embodiments, the pool consists primarily of 1 1 identical modules 1.

In alternative embodiments of the present invention, differently shaped modules can be connected to each other.

For example, flat plastic panes, panes 2,3 are used as described in relation to Figures 1 (a) and / or 1 (b), but, for example, the ribs can be different in number, density or arrangement, for a variety of modules of the same pool . The number of ribs may be a function of the predetermined function that will exercise the modules in the construction of the pool 11. Moreover, it is an advantage of plastic panes that they can be simple and inexpensive shaped. They can be shaped, for example by curved or other complex surfaces such as bulges, recesses, curves etc, preferably to the inner wall 2. This not only allows to easily form rectangular pools, but also to construct more complex shapes. In embodiments, the inner wall and the outer wall are substantially parallel arranged so that the distance between them remains constant. In alternative embodiments, for example, the inner wall 2 may be provided with protuberances, while the outer wall is flat, or in accordance with a generally flat or curved surface. The part, different from the protrusions, may, for example, remain substantially parallel with the outer wall. In one example, protrusions may, for example, form a structure that can serve as a ladder, or for example form a sitting surface. The internal volume V of the side wall (or pool module) preferably performs a buffer function for the swimming pool 11 (see Fig. 6). This buffer function can be used as one or more, or all, of the following types of water buffer;

- Displacement water (V4) of the pool, the water level is kept constant in an infinity pool. The displacement of water which is produced by the submerged body of the swimmers must then be stored;

Backwash water for the filters (V3), filters are periodically cleaned by washing water through the filter in counter-current. Therefore water from the swimming pool 12 is used. This is the most economical choice because changing of the pool water is needed because typically not all 'contamination' of the swimming pool is captured by the filters. The backwash water is preferably not sucked in from the pool itself, but rather from a significant buffer volume, since for example, this would have the following drawbacks:

• The water level drops so that the skimming of the water stops. This

skimming is necessary in order to discharge all the floating pollution;

• Sucking can cause major suppression in the pool allowing swimmers to be sucked onto the grills.

- Additional water (V6) because it is not economical to install a filter that purifies all dirt from the pool water. Moreover, a part of the water vaporizes. Both

phenomena require refilling of the swimming pool with fresh water. For different reasons (for example, heat recovery, simplicity of control, ...), a buffer volume is provided which can be filled up with water;

- Intake protection pumps (V7): Usually, the water must be pumped out of the

buffer. In order to avoid that the pump would run dry, a minimum residual volume of water in the buffer is needed.

- Sewage (V2): when backwash ing the filter, it is often not possible to dispose the large flow of water directly to the sewerage system because of the limited capacity of the sewerage connection. Moreover, one often wants to draw the heat from the backwashing water; but to do this economically, a longer time i necessary. Therefore, the backwashing water is typically buffered;

- Empty water (V8): Some pools are left empty outside the opening hours in order to avoid evaporation and thus save energy.

The created volume V can also be used / adapted for the storage of, for example, swimming material such as swimming boards, swimming lines etc. (V5). For example, there may be at one end of the pool, in this space along the width of the pool, a rollable swimming line system be arranged at regular intervals, without that this would interfere with the swimmer to enter the swimming pool.

The created volume can also house a part of the infrastructure for the pool, such as for example, pumps and other systems, which should normally be installed in a different, additional space. Also, the technical corridor 9 which is typically present for public pools, can thus be reduced in dimension.

A wall, e.g. the outer wall 111 of a building G, for example, may be arranged adjacent to at least a part of the platform 10 of the pool 11.

In preferred embodiments, the side wall is connected to the bottom 7 / a floor pane 71 of the pool 1 1 (see Fig. 4 and Fig. 5(a, b)). The side walls may be glued, for example, with a concrete floor 7 of a building structure (Fig. 5(a, b)), or the side walls may be glued, for example, with a floor pane 71 which, in turn, is glued to a concrete floor 7 of a building structure .

In an alternative, the side walls can, for example, be connected to a plastic floor pane 71 (for example by means of gluing or welding; Fig. 4), and the whole of the side wall and floor pane (or panes - that are also connected to each other by for example gluing / welding) are slidably mounted relative to a building structure G.

In preferred embodiments, the pool 11 , in particular, the side wall is also provided with further support structures 5, 6, for example, as illustrated in Fig. 2(a), 2(b) and Fig. 3.

In preferred embodiments, illustrated in Fig. 2(a), the side wall is / the pool modules are near their upper end, when mounted, supported by one or a number of support structures (5). For example, a metal or concrete beam may be arranged around the pool for this purpose. For example, this beam can be part of a building structure.

In preferred embodiments, illustrated in Fig. 2(b) the side wall is supported by one or more profiles (51 , 52), which run through the vertical ribs and are fitted in the horizontal direction. To this end, the ribs may include corresponding apertures, which are adapted to receive the profiles, and thus the shape of which preferably corresponds to the cross section of the profiles. The profiles may preferably be of metal or a material with similar support properties, such as, for example, fiber-reinforced plastic profiles, for example, of the type of epoxy / carbon, vinyl ester / carbon, poly ester / glass, etc. In preferred embodiments, which may be combined with embodiments described in relation with Fig. 2(a) and Fig. 2(b), one or several concrete columns can be arranged through the plastic panes, i.e. in between the inner wall 2 and the outer wall 3. These concrete columns preferably extend in the vertical direction, when the pool modules 1 are mounted. The concrete columns may be set, for example, in a vertical shaft K defined between two vertically oriented ribs 4. In the alternative, or in combination with it, metal profiles can also be placed in this direction and position.

Figures 5(a) and 5(b) illustrate how the additional support structures may perform other functions. Indeed, the swimming pool profiles / the double-walled side wall is at the top supported by a concrete structure 10, which actually forms the platform 10 around the pool 1 1. This platform 10 is in turn carried by concrete support structures 56, which further define a technical corridor 9, adjacent the double-walled side wall. The upper surface of the platform 10 preferably lies at about the same level as the upper end of the side wall (typically slightly below that level, or draining away from the pool, in order to avoid, for example, cleaning water entering the pool). At the top of the side wall, at the level of the platform 10, preferably an overflow drain is arranged. During use, the pool is completely filled and water runs through the overflow drain, in the double-walled side wall. For example, the double-walled side wall can be used as a buffer volume (buffer basement) or comprise an open filter system 8.

The double-wall may comprise vertical ribs (41) (Fig. 5 (a)), or a combination of vertical and horizontal ribs (42) (Fig. 5 (b)). The presence of horizontal ribs allows the forces to be diverted to a vertical support. Fig. 7 illustrates a cross-sectional view of a swimming pool or swimming pool module 1 in use, of an embodiment in which an open filter system 8 is arranged in the double wall of the pool 11 , in accordance with aspects of the present invention. The double wall separates the technical corridor 9 and the pool 12. A pool module 1 comprises vertical ribs extending over the height of the side wall, and thus defines vertical shafts K between the inner wall 2 and outer wall 3. To achieve a horizontal distribution / movement of the water, apertures 410 can be provided, preferably in the vertical ribs (shown for example in Figures 1 (d) (e)). This is preferably in the higher part of the wall (upper 50%, 60%, or upper, or upper 70%, or 80% of the upper wall) where the force exercised by the swimming pool water is lower. Also, lower apertures can be made, provided that additional ribs are provided which compensate for the attenuation. In such a shaft K, support layers 81 and filter layers 80 are arranged such as this is known by a professional in open filter systems, which together form the filter pack 88. In preferred embodiments, there is a water column of at least 30 cm above the upper surface of the open filter system, the top of this water column is at the same time the fluidization height. There can thus be the built up of a pre-pressure of at least 30 cm water, which can improve the filtering process or speed it up. In addition to the height of the filter pack 88 and the height of the water column 82 is preferably an additional space 83 available. In the spaces 82 and / or 83 may, for example, a draining gutter 17 be arranged, which can discharge filth water, for example to the sewer R, for example during the backwashing of the filter during a cleaning process.

Preferably, the vertical shaft is open at the top, and is adapted to be able to receive unfiltered water from the swimming pool 12. For this purpose, there can be at the top of the side wall / column, an overflow drain 13. At least some / the vertical columns are preferably near their lower end provided with an outlet 15 for filtered water (which can also be an input during the backwashing of the filters). Further, the pool area preferably comprises means to direct the water from the output back to the pool, such as a system of pipes and pumps P. As stated previously, the pool preferably includes means for washing the filter pack 88. This may for instance be effected by pumping pool water from the pool and let it flow through the filter pack in the reverse way, subsequently the water can be diverted, for example, to the sewerage R.

While the principles of the invention have been described above in connection with specific embodiments, it is to be clearly understood that this description is made only by way of example, and is not limiting the scope of protection which is defined by the appended claims. While some herein described embodiments, some but no other features include, comprised in other embodiments, are combinations or features of different embodiments, intended to be within the scope of the invention, and form different embodiments, as would be understood by a professional.