[0001] The present invention relates to a ventilation system for ventilating a room, comprising: a lowered ceiling, defining a ceiling space which, when installed, is between the lowered ceiling and a ceiling of the room, the lowered ceiling having a ceiling surface area that is air permeable; a raised flooring, being supported by a support frame, defining a floor space which, when installed, is between the raised flooring and a floor of the room, the raised flooring being air permeable over a floor surface area that is opposite to the air permeable ceiling surface area; an air supply connected with an air supply inlet to the floor space for supplying air into the floor space; and an air outlet, connected to the ceiling space for exiting air from the ceiling space, wherein the air permeability of the raised flooring is such that air supplied via the air supply inlet enters the room via the raised flooring in a laminar, vertical air flow, displacing air in the room in the vertical direction and forcing air out through the ceiling surface area.

[0002] The invention further relates to a raised flooring and a lowered ceiling for such a ventilation system.

Background art

[0003] The current building standard of ventilation for rooms (Class A ventilation), such as classrooms, has at least one air inlet for supplying fresh air and at least one air outlet for removing air from the room. The ventilation system relies on the mixing of air inside the room to achieve a more homogeneous air quality throughout the room. When breathing, people and animals exhale small droplets, which form aerosols. Studies have shown that viruses, bacteria and other contamination bind to these aerosols. The lower the refreshing rate of the air inside a room, the higher the buildup of aerosols containing germs and viruses. Although the Class A ventilation systems provide some degree of refreshed air inside the room, these systems itself cause mixing of air inside the room and thereby cause the aerosols being spread throughout the room, allowing diseases spreading between occupants of the same room. Additionally, contaminated aerosols remain inside the room until the ventilation system has removed them, such that contaminants may even remain inside a room for a certain amount of time after a contagious person has left that room. As a result, persons with a lowered immune response or compromised immune system are facing an increased risk of becoming ill when using these spaces with other persons, as well as up to a certain amount of time after these other persons have left the room. This is especially problematic during, for example, flu season or pandemics such as COVID-19. A hypothesis being adopted by an increasing number of specialists around the world names the following four risk factors for a person contracting a disease indoor:

- the duration a person is within a room

- the type of pathogen

- the concentration of the pathogen, and - the amount of circulation within the room.

[0004] A ventilation system for providing a substantially vertical flow in a room has been developed by the applicant, and is described in NL2025707 and PCT/NL2021/050343. This ventilation system, seeks to reduce the risk of germs and viruses spreading between persons occupying the same room, compared to Class A ventilation systems. Furthermore, the system is easy and relatively cheap to install, even in existing buildings.

[0005] The system is continuously being further developed and improved upon by the applicant. In NL 2028139 a raised flooring structure has been presented, which could be implemented in the vertical ventilation system, replacing the flooring system with permeable floor tiles thereof. This raised flooring structure comprises panels with a closed surface, each panel being supported on a flooring member comprising a carrier profile with a top support surface and four side walls extending transversely to the top surface, which side walls comprise a number of apertures along their length. The panels have side edges that extend at a distance from the side walls, such that the side edges of the panels are spaced apart to form a ventilation gap there between, which gap is provided with a collection channel that extends below and/or along the side walls. In the raised flooring structure a flow path extends from a space between the side walls of a first carrier profile, via the openings to the collection channel to the ventilation gap between the adjacent panels.

[0006] The present invention seeks to provide further improvements to a vertical ventilation system.

Summary of the invention

[0007] Hereto, according to a first aspect of the invention a lowered ceiling for a ventilation system for ventilating a room in which air enters the room via a laminar, vertical air flow from a floor of the room is provided. This lowered ceiling comprises a ceiling surface, having a length and a width substantially matching a length and a width of a ceiling of the room, and a ceiling frame, which ceiling frame is arranged to hold the ceiling surface at a predefined distance from the ceiling of the room, wherein the ceiling surface comprises a plurality of ceiling plates, adapted for forming an air permeable ceiling surface area and at least one longitudinal element, having a V-shaped cross- section which protrudes from the ceiling surface into the room, said longitudinal element having a length extending along the width of the lowered ceiling, and being positioned at a predefined distance from an edge of the lowered ceiling, adjoined by ceiling plates on both sides.

[0008] The longitudinal element protrudes downwards from a height of the ceiling plates into the room, thereby locally reducing the distance between the raised floor and the lowered ceiling, resulting in associated local, substantially vertically upwards, airstreams reaching the lowered ceiling faster than air streams which are originating directly below a ceiling plate.Through having at least one longitudinal element extending along the width of the lowered ceiling, at least two compartmented ceiling areas are formed which are delimited on either side by either one of a longitudinal element or a wall of the room in which the system is placed. The slanted surfaces of the V-shaped cross-section of the longitudinal element guide the airflow towards one of the adjoining ceiling plates, thereby increasing air pressure towards the permeable surface area formed by the ceiling plates and increasing outflow through said permeable surface area. The increased outflow reduces air backup at a room-facing side of the air permeable ceiling plates, thereby reducing “backwash” from the ceiling which backwash might otherwise result in air containing aerosols flowing downwards back into the room. The reduction of backwash reduces turbulence occurring near the lowered ceiling, allowing the substantially vertical upward flow inside the room to remain laminar over a larger part of the height between raised floor and lowered ceiling. The guiding of the airflow along the slanted surfaces of the longitudinal elements substantially prevents any turbulence from returning back into the room, below the longitudinal elements.

[0009] In an embodiment, each of the plurality of ceiling plates is provided with a predetermined amount of through-openings, for making the ceiling plate air permeable.

[0010] In a further embodiment, a cross-section of each of the predetermined amount of through- openings is tapered along a direction perpendicular to the ceiling surface, having a width on a side of the plate facing the room that is larger than a width on a side of the plate which is facing away from the room. The tapered shape of the through-holes results in an increase in airflow there through, further improving the discharging of air from the room via the lower ceiling.

[0011] In an embodiment a width of the longitudinal element corresponds to a width of each one of the ceiling plates. This aids ease of installation, since all components used to make the lowered ceiling surface have equal dimensions. All components may be manufactured at standardized dimensions. A currently adopted standard dimension is 60cm for both the width and the length of each ceiling plate.

[0012] In an embodiment, the V-shaped cross-section of the at least one longitudinal element is symmetrical around a plane perpendicular to the ceiling surface and wherein the legs of the V- shaped cross-section are at an angle between 25° and 75°, preferably at an angle between 30° and 60°, most preferred at 45°. The symmetrical shape ensures an even distribution of the arriving airflow at both legs. The angle may be chosen such that a desired pressure increase is achieved at a roomfacing side of each permeable ceiling surface area and may depend on the available space and width of an adjoining permeable ceiling surface area.

[0013] In an embodiment, the at least one longitudinal element is a skylight. During use, the skylight produces heat, which heats the slanted surfaces of the V-shaped longitudinal element. This heat further increases the velocity of the air flowing along the slanted surfaces, such that the flow arrives at the air permeable ceiling plates faster, building up more pressure and as a result flowing through the air permeable ceiling plates faster, thereby exiting the room faster.

[0014] According to a second aspect of the invention, a lowered ceiling for a ventilation system for ventilating a room in which air enters the room via a laminar, vertical air flow from a floor of the room is provided, said lowered ceiling comprising a ceiling surface, having a length and a width substantially matching a length and a width of a ceiling of the room, and a ceiling frame, which ceiling frame is arranged to hold the ceiling surface at a predefined distance from the ceiling of the room, for forming a ceiling space between the ceiling of the room and the ceiling surface, wherein the ceiling frame is arranged to form at least two compartments, each compartment extending between the ceiling of the room and the ceiling surface and being closed off from one another, each of said compartments comprising an outlet which is directly connectable to an inside air inlet of an associated ventilation unit, and wherein the ventilation system further comprises a controller, connected to at least two sensors, each arranged in a respective one of the at least two compartments, and adapted to measure and/or control the air flow in each compartment independently. This allows the air quality being monitored for predefined areas of the room and/or the rate at which air is removed from the room being varied between the areas of the room below the corresponding at least two compartments.

[0015] In an embodiment, each of the at least two compartments have a width corresponding to a width of the ceiling surface and wherein the at least two compartments together have a length corresponding to a length of the ceiling surface.

[0016] Thus the at least two compartments are positioned in a row along the length of the ceiling. If the associated ventilation unit for the lowered ceiling is located at a longitudinal end of the room, a first of the at least two compartments will directly adjoin the longitudinal end, such that the second of the at least two compartments will extend with an outlet thereof through the first compartment, for being directly connectable to the ventilation unit. The same applies mutatis mutandis to any subsequent compartments, extending through the preceding compartments, including the first compartment, with their outlet, in orderto be directly connectable. This set-up enables the air exiting the room via the lowered ceiling being adjusted to compensate for any drop in pressure from air flowing into the room, which is let in as a vertical laminar flow via an air permeable floor and naturally occurs with an increasing distance from the ventilation unit.

[0017] In a further embodiment, the compartments are combined with a lowered floor comprising at least one longitudinal element according to the first aspect of the invention, wherein each of the at least two compartments extends between the ceiling of the room and a respective air permeable surface area of the lowered ceiling. Thus the compartments of the ceiling space correspond to the compartments formed in the ceiling area, by the presence of the V-shaped longitudinal elements. [0018] According to a third aspect of the invention, a ventilation system for ventilating a room is provided, comprising: a raised flooring, being supported by a support frame, defining a floor space which, when installed, is between the raised flooring and a floor of the room, the raised flooring being air permeable over a floor surface area; and a ventilation unit that is with an air supply inlet connected to the floor space for supplying air into the floor space; wherein the air permeability of the raised flooring is such that air supplied via the air supply inlet enters the room via the raised flooring in a laminar, vertical air flow, characterized in that the air supply outlet comprises an air distributor, extending along width of the raised flooring and having a plurality of ports, each of said ports being attached to an airsock which extends along a length of the raised flooring inside the floor space, such that a plurality of airsocks is located below the raised flooring, extending parallel to one another in a length direction of said raised flooring. The air distributor and airsocks ensure a substantially universal division of fresh air in the floor space, such that a substantially vertical laminar flow enters the room via the permeable raised floor at a substantially equal flow rate over the entire floor surface. Air socks are easy to place in the floorspace below the raised flooring as no tight tolerances are required to be adhered to during their installation. [0019] According to an embodiment, the air socks are F9 air socks or H14 air socks. F9 airsocks are fine filters, which filter the incoming air to achieve the best possible air quality. As a result, the F9 airsocks can replace the fine filters which are otherwise to be installed inside the ventilation unit. This makes for a more easy to manufacture and install ventilation system, since fine filter placement inside the ventilation unit itself requires tight tolerances in order to prevent leakages, which would pose a risk to the quality to be achieved. More importantly, a single airsock provides a filtering surface which is much larger than a filter which can be placed inside the ventilation unit, without requiring an increase in pressure at which air is lead through the filtering surface such that a desired vertical airflow of 1cm/min emitted from the raised flooring, over the permeable surface thereof, is achieved. As a result, the ventilation unit produces less noise, which is desirable for ventilation units located inside a room. For example, in a room having a length of 10m, a single air sock having a diameter of 15 cm already provides 47000 cm ² filter volume, while a maximum of two fine filters located inside a ventilation unit as described in PCT/NL2021/050343, each having a thickness of 5cm, can only provide 30000 cm ² of filter volume.

[0020] When, instead of F9 air socks using H13 or H14 air socks, the ventilation system can even be used in medical settings.

[0021] According to an embodiment, each air sock is provided with a roll-up system, arranged at a distal end of the airsock and adapted for rolling up the airsock. The roll-up system enables easier removal and installation, for example for installing new socks, as only a few floor tiles need to be removed to provide access to the attachment of the airsocks to the ports.

[0022] According to an embodiment, at least one of the plurality of air socks is provided with a drip hose at an upper position thereof, for adding liquid droplets to the air flowing through said air sock and wherein said at least one of the plurality of air socks is arranged in a gutter, which is adapted to collect and remove the liquid. The liquid droplets evaporate, thereby lowering the temperature of the air, such that the ventilation system can also provide an air conditioning function. Normal water is preferably used as liquid. Not all liquid may evaporate or return through condensation. In order to prevent water collecting in the floor space, the air sock is positioned in a gutter, which is arranged such that the liquid can be removed from the floorspace, e.g. through being connected to a drain. [0023] According to a fourth aspect of the invention, an air sock is provided for providing adiabatic cooling in a ventilation system, comprising a fabric hose, which is at a first position along the circumference provided with a drip hose, extending along a length of the fabric hose, and a draining shell, cupping a portion of the fabric hose which is opposite to the first position, and extending along the length of the fabric hose, such that moisture provided by the drip hose may collect in the draining shell during use. The draining shell may be a gutter-shaped element in which the air sock is positioned. Alternatively, a lower part of the air sock may be coated with a water impermeable material, such that the lower part of the air sock forms a draining shell which is integral with the air sock.

[0024] In an embodiment, the air sock further comprising a frame inside the air sock, which frame is formed such that the air sock is in a position which allows air flowing inside the air sock, said frame preferably comprising or being made from a metallic material, which metallic material preferably is aluminium. The incorporation of the frame allows the airsock also being used for removing air from a room, such as in the lowered ceiling of the vertical ventilation system described above. Warm air from the room enters into the reverse airsock where it is continuously moistened with liquid from the drip hose. This moisture evaporates and cools the warm air. The cool(er) air then flows through a MVHR in a ventilation unit, to which the air sock is connected via an air removal inlet. The cool air flowing through the MVHR turns the MVHR into a cold exchanger. The fresh outside air flowing towards the air supply outlet passes the MVHR, where heat is exchanged with the cool(er) air, effectively cooling the incoming fresh outside air prior to being let into the room. [0025] According to a fifth aspect of the invention, a ventilation system for ventilating a room, comprising: a lowered ceiling having a ceiling surface area that is air permeable; a raised flooring, being supported by a support frame, defining a floor space which, when installed, is between the raised flooring and a floor of the room, the raised flooring being air permeable over a floor surface area that is opposite to the air permeable ceiling surface area; and a ventilation unit which is with an air supply outlet connected to the floor space, for supplying air into the floor space, and with an air removal inlet connected to an outlet of the lowered ceiling for exiting air from the ceiling space, said ventilation unit comprising a MVHR system for exchanging heat between the exiting air and the air to be supplied; wherein the air permeability of the raised flooring is such that air supplied via the air supply inlet enters the room via the raised flooring in a laminar, vertical air flow, displacing air in the room in the vertical direction and forcing air out through the ceiling surface area, characterized in that the lowered ceiling comprises at least one air sock according to the fourth aspect of the invention, comprising a frame inside the air sock, which airsock forms part of the outlet of the lowered ceiling and is connected to the air removal inlet of the ventilation unit.

Brief description of the drawings

[0026] Embodiments of the present invention will be described by way of example, with reference to the attached drawings, in which:

[0027] Fig. 1 shows a perspective view of a classroom provided with a ventilation system as described in PCT/NL2021/050343;

[0028] Fig. 2 shows a side view of a ventilation system having a lowered ceiling according to an embodiment of the invention;

[0029] Fig. 3 shows a bottom view of the lowered ceiling of the ventilation system depicted in Fig. 2;

[0030] Fig. 4 shows a perspective view of a ventilation unit as described in PCT/NL2021/050343; [0031] Fig. 5A shows a perspective view of a raised flooring according to an embodiment of the invention;

[0032] Fig. 5B shows a planar view of a raised flooring according to an embodiment of the invention;

[0033] Fig. 5C shows a cross-sectional view of an air sock for use in the raised flooring as depicted in Fig. 5B; and

[0034] Fig. 5D shows a cross-sectional view of an alternative air sock, which is for use in lowered ceilings. Description of embodiments

[0035] Fig. 1 shows a perspective view of a classroom provided with a ventilation system 100 for providing substantially vertical ventilation, having a wall 9 extending between the floor and the ceiling of the room. The ventilation system in the room 100 is shown to have a raised flooring 10, a lowered ceiling 1 and an air supply inlet 3. The raised flooring 100 and lowered ceiling 1 are both air permeable over surface areas which are located opposite one another, covering a substantial surface area of the respective floor and ceiling of the room and being substantially parallel thereto. Due to the raised flooring and lowered ceiling, the room is vertically divided into three volumes: a floor space, between the floor of the room and the raised flooring 10, a user space for use of the room, extending between the raised flooring 10 and the lowered ceiling 1 , and a ceiling space, between the lowered ceiling 1 and the ceiling of the room. The air supply inlet 3 is connected to the floor space for supplying fresh air from the buildings air-conditioning system. The air permeability of the raised flooring 10 varies in dependence on distance from the air supply inlet 3 for forming a substantial vertical air flow entering the user space of the room through the raised flooring 10 having a substantially even flow rate over the permeable floor surface area. This causes the incoming fresh air to displace the air already present in the user space of the room vertically, forcing it towards the lowered ceiling 1 and through the lowered ceiling surface area for exiting the room. Through varying the air permeability of the raised flooring 10 in dependence on distance from the air supply inlet 3, the air entering the room through the raised flooring has substantially the same flow rate over the whole floor surface area substantially the same volume and flow speed, causing a vertical laminar flow of fresh air entering the room via the floor. The directly opposite permeable ceiling surface area allows the flow of fresh air being maintained substantially vertical and laminar over the entire height of the room between the raised flooring 10 and lowered ceiling 1 , preventing the mixing of air due to ventilation and minimizing transverse movement of aerosols inside the room, for example due to persons moving through the user space.

[0036] In the classroom, on the raised flooring 10, desks for pupils 91 and a teachers desk 90 are placed. In order to further prevent the chances of transverse spreading of aerosols between, for example, pupils and teacher, or to a specific pupil, the permeability of the raised flooring immediately under and around their desks 90, 91 may be increased with respect to the surrounding raised flooring, providing a protective zone. In this protective zone, the vertical laminar air flow is increased with respect to the vertical laminar air flow in the rest of the user space of the room, effectively creating a curtain-effect preventing substantially all air transfer from the rest of the user space of the room into the protective zone.

[0037] Although the example in Fig. 1 shows a classroom, the same ventilation system may be used in any room and protective zones can be set up where and as desired. The raised flooring may comprise permeable floor panels, as depicted, or have closed panels and be provided with a collecting channel below a ventilation gap between adjacent panels as known from NL 2028139, such that a flooring structure is obtained that combines good ventilating properties with the possibilities of cleaning the flooring panels with a liquid cleaning substance. The upward airstream that exits form the ventilation gaps between adjacent flooring panels results in a laminar flow of air that displaces large volumes of air of for instance 20m3-80m3 per m2 per hour, flowing upwards from the floor to an exit at the ceiling of the room, without any mixing or turbulence.

[0038] Physical performance tests have been performed in a classroom having a floorspace of approximately 50 m ² and volume of approximately 130 m ³ , fitted with both a ventilation system as described above, with closed floor panels, and with a Class A ventilation system according to current building regulations. During each test, either the Class A system or the above described system was used for ventilation. For the above described system, the edges of the closed floor panels were either semi-open or fully open. Furthermore, tests were performed with the central heating in the room off or on. Inside the classroom, 29 model persons were installed; 28 pupils and 1 teacher; as well as 6 particle counters, for measuring the aerosols in the classroom. In total, 18 tests were performed. During the performance tests, the classroom was ventilated at a rate of 1350 m ³ /hr. At the start of each test, aerosols were introduced into the room via 1 “sick” pupil for a period of 10 minutes, after which the concentration of aerosols was measured for 30 minutes. At the end of each test, the classroom was purged to recover the baseline (i.e. predetermined low amount of aerosols, approximately 99% lower than after the first 10 minutes of the test), prior to starting the next test. The results of the tests are shown in Table 1 , which provides the amount of aerosols counted by each particle counter during the 30 minutes.

Table 1: measuring results in a classroom of 50m ² and 130m ³ , ventilated at 1350 m ³ /hour.

[0039] As is clearly visible from the measuring results in Table 1 , a surprising difference in performance was found between the Class A system and the vertical ventilation system, wherein the vertical ventilation system outperforms the currently used Class A system. Depending on the particular set-up of the tested system, the vertical ventilation system was at least three times more effective, and up to 14 times more effective in removing aerosols from the room. Furthermore, the tests showed aerosols quickly spreading throughout the room, e.g. within minutes the amount of aerosols counted by each particle counter was in the same order of magnitude, when using the Class A system, while the vertical ventilation system largely prevents the spreading of aerosols throughout the room, both with open and with semi-open sides of the floor plates. Additionally, from the purging of the classroom in order to recover the baseline prior to the start of a new test, the applicant was surprised to find that the Class A system could not achieve the predetermined baseline within 20 minutes, while the vertical ventilation system required less than 20 minutes to do so.

[0040] A further observation during the tests was that the substantially vertical flow of the vertical ventilation system remained vertically laminar up to a height of approximately 120 cm, i.e. a height just above the seated pupils, above which height some turbulence started occurring in the vertical flow pattern. This turbulence was caused by some vertical airflows being sped up by a higher temperature thereof caused by the temperature from the pupils and/or the radiators, compared to to adjacent vertical flows, and thus arriving faster at the lowered ceiling, which is set to remove air from the room at an even rate over the surface of the ceiling. The incoming vertical flow was set at 1 cm/min, while (body) heat was found to speed up vertical flow to 20 cm/min. As a result, the faster vertical airflows would “bounce” against the ceiling and start mixing with the other vertical air flows as well as cause some aerosols to move downwards, away from the ceiling again. Based on these findings, a further improved ventilation system was sought, in which the mixing of air nearer to the ceiling is prevented.

[0041] Substantial improvements have been found by the implementation of one or more of the additional features depicted in Figs. 2 and 3.

[0042] Figs. 2 and 3 respectively show a cross-sectional side view of a room with a ventilation system having a lowered ceiling T according to an embodiment of the invention and a bottom view of the lowered ceiling T. The room has a vertical ventilation system built therein, with the lowered ceiling T mounted to the ceiling 9B of the room, opposite from the air permeable raised flooring 10’, which is mounted onto the floor 9A of the room. The lowered ceiling 1 ’ has a length L and a width W which substantially matches the length and the width of the ceiling of the room. The lowered ceiling 1 ’ is shown as having a ceiling surface, which consists of a plurality of air permeable ceiling surface areas 21 and longitudinal elements 25, and a frame comprising beam elements 28 which hold the ceiling surface at a predetermined distance from the ceiling 9B of the room. The longitudinal elements 25 each have V-shaped cross-sections that protrude into the room, away from the ceiling surface T and have a length substantially corresponding to the width W of the lowered ceiling T. The longitudinal elements 25 are oriented with their longitudinal direction parallel to the width W and are spaced apart from one another along the length L of the ceiling, each having an air permeable ceiling surface area 21 adjoining a respective leg end of the V-shaped cross-section, such that, when seen in the length direction of the room, air permeable ceiling surface areas 21 and longitudinal elements 25 are alternating one another. The permeable ceiling surface areas 21 each consist of a plurality of ceiling plates 23, which are provided with a predetermined amount of through-openings 22 for making the ceiling plates air permeable. A width of each one of the longitudinal elements, which corresponds to a distance between the ends of the legs of the V- shaped cross-section thereof, is the same as a width or length of each one of the ceiling plates 23. The longitudinal elements 25 are provided with lamps 26, such that the longitudinal elements 25 form sky lights, wherein the heat produced by the lamps 26 contributes to increasing the airflow along the slanted surfaces of the longitudinal elements 25. Further, the beam elements 28 are closed, such that compartments 29A, 29B, 29C, 29D are formed in the ceiling space.

[0043] Fig. 4 shows a perspective view of a ventilation unit 200 as described in PCT/NL2021/050343. The ventilation unit 200 as depicted consists of eight modules 201 , 202, 203, 204, 205, 206, 207, 208, together comprising air inlet piping Pi, air outlet piping Po, a course filter 216, an air supply fan 212, an air removal fan 214, a bypass 210 and a mechanical ventilation heat recovery (MVHR) system 217. Each module 201 , 202, 203, 204, 205, 206, 207, 208 is dedicated to a specific function within the ventilation unit 200, such that there is an outside air inlet module 201 comprising an outside air inlet Ai1 , an outside air outlet module 204 comprising an outside air outlet Ao2, an inside air inlet module 208 comprising the air supply inlet 3’, an inside air outlet module 205 comprising the air outlet 2’, an air supply fan module 207 comprising the air supply fan 212, an air removal fan module 203 comprising the air removal fan 214 and two MVHR system modules 202,206 comprising the MVHR system 217 and bypass 210. The modules 201 , 202, 203, 204, 205, 206, 207, 208 are stacked together in two columns of equal height.

[0044] The air inlet piping Pi extends between the outside air inlet Ai1 , which forms a first air inlet of the ventilation unit 200, and an air supply inlet 3’, which forms a second air outlet Ao2 of the ventilation unit 200, through the inside air inlet module 208 and the MVHR system modules 202, 206, via the air supply fan module 207 to the outside air outlet module 205. The air supply inlet 3’ as depicted in the figures extends along the bottom surface of both the outside air outlet module 205 and the inside air outlet module 204, such that incoming air is distributed along a width of the floor prior to entering the floor space. The course filter 216 is arranged in the air inlet piping Pi between the outside air inlet Ai and the MVHR system modules 202, 206, ensuring any dust, debris and other undesired contaminants are filtered from the incoming air prior to entering the MVHR system. An additional fine filter may be located just before the air supply inlet 3’ for further filtering of the air to achieve a higher quality air, said filter having a shape similar to the course filter 216, and being located at the top of modules 204 and 208, or at the bottom of modules 203 and 207. The fine filter may be an F9 filter, which results in allergens such as pollen being removed from the air. A downside of the use of such a filter, having sufficient volume for filtering to a high quality air, inside the ventilation unit, is that the ventilation unit produces noise due to the air supply fan having to work harder to produce sufficient pressure for the air being provided to the floorspace at a pressure which is high enough to achieve a laminar vertical air flow over the entire floor area at a substantially equal flow rate. Thus solutions have been sought to improve the provision of air with the ventilation unit, both in order to achieve a higher quality air and in order to reduce noise produced by the unit.

[0045] A solution has been found by turning the air supply inlet 3’ into a diffuser, which divides the supplied air equally over a plurality of evenly spaced outlets 31 , each of which outlets 31 having an air sock 116 connected thereto, as shown in the perspective and planar views of the raised flooring according to an embodiment of the invention depicted in Figs. 5A and 5B. The airsocks 116 each extending along the length L of the raised floor, inside the floor space under the floor tiles 11 . The combination of the diffuser 3’ and air socks 116 ensures that air is air is provided at a more uniform pressure over the entire floor area. Thus a more uniform vertical flow rate is achieved from the permeable raised floor, without requiring additional air pressure from the ventilation unit. In fact, the air supply fan may be run at a lower setting in order to achieve the same flow rate from the floor, thereby reducing noise and saving energy.

[0046] The airsocks 116 can be made from filter cloth, and thus F9 or H14 airsocks can be used, instead of the fine filter in the lower modules of the ventilation unit. The filtering volume achievable through the use of airsocks 116 is significantly larger than the filtering volume that can be fitted inside of the ventilation unit, thus a much higher air quality can be achieved.

[0047] In the setup depicted in Figs. 5A and 5B one air sock 116 is located below each row of floor tiles 11 . This is a preferred arrangement. However, alternative set-ups with more or less air socks can be used, depending on the length of the floor and the air quality requirements.

[0048] Fig. 5C shows a cross-sectional view of an embodiment of an air sock for use in the raised flooring as depicted in Figs. 5A and 5B. The air sock 116’ is shown as comprising a cloth 117 with a substantially circular cross-section, which is achieved during use, when the ventilation unit to which it is connected is supplying air. It will occur to the skilled person that air socks with other cross-sectional shapes may also be used. For example, non-circular air socks may be preferred in order to prevent air socks from rolling over. Further, the skilled person will understand that, in case the airsock is an F9 or H14 air sock, the cloth 117 is F9 or H14 cloth. At the top of the cross-section a drip hose 119 is shown to be attached to the air sock. Although the drip hose 119 is depicted as being inside the air sock, the drip hose 119 may also be positioned onto the outer surface of the air sock. The drip hose has a length substantially equal to the length of the cloth 117 and provides moisture to the air flowing through the air sock, during use. The cloth 117 is positioned in a gutter 118, having a shell-shaped surface covering a lower part of the cloth 117. The gutter 118 is adapted for collecting moisture which is provided by the drip hose and not taken up by the air, and provided with means (not shown) to remove the water from the floorspace, such as for example a drain. Through the provision of moisture to the air supplied via the air sock, adiabatic cooling takes place. Alternative shapes for the gutter will occur to the skilled person and fall within the scope of the invention. Alternatively, a lower side of the filter cloth 117 may be coated with a material which is non-permeable to moisture.

[0049] Fig. 5D shows a cross-sectional view of an alternative air sock 116’”, which is for use in lowered ceilings. In addition to the features already described in relation to Fig. 5C, the air sock 116’” further has a frame 120, which is adapted for holding the cloth 117 of the air sock in an open state, such that air from around the sock 116”’ can pass through the cloth 117 into the air sock. [0050] The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the added claims.