Underfloor air supply unit

Abstract

The invention relates to an underfloor air supply unit (100) for use in a raised access flooring system having a raised floor, a void space below the floor and a room space above the floor. The unit has a housing (101) having a top surface (102) configured to be generally parallel to the raised floor, a first inlet (120) below the top surface of the housing and configured to receive void air VA from the void space, a second inlet (130) in the top surface configured to receive air from the room space, and an outlet (140) in the top surface configured to supply air to the room space. The unit also has a fan (150) to draw air from the first and / or second inlet and to supply air to the outlet. The unit defines an air flow path from the second inlet to the outlet in which the direction of air flow is reversed such that the second inlet and the outlet are located on the same side of the fan in the top surface. In one embodiment, the second inlet (130) and outlet (140) are aligned in the X direction and are adjacent in the Y direction and the second inlet comprises two second inlets (131, 132) separated in the Y direction by a single outlet (140).

Description

[0001] Underfloor Air Supply Unit

[0002] Technical Field

[0003] The present invention relates to an underfloor air supply unit suitable for installation in a raised access flooring system.

[0004] Background

[0005] A raised access flooring system typically comprises an array of flooring sections, usually square, which are mounted on raised supports above the structural floor of the building below. The void created allows services to be supplied to where they are needed, such as electricity, water, network cabling, etc.

[0006] Underfloor air supply units are known and these are generally configured to have the same footprint as a square floor section to enable them to fit conveniently into a standard floor array. One industry standard size for a floor section is 600mm x 600mm. Underfloor air supply units can take a supply of air from the void under the raised floor. This void air may be supplied from elsewhere inside the building or from outside the building, and the void air may ambient air or may have been treated or conditioned in some way, for example by being heated or cooled, filtered, humidified or dehumidified. The air supply unit may receive the void air through ducting, however ducting may not be required where the void as a whole is supplied with the air for the one or more units in the system. The units can also take a supply of room air from above the raised floor. This room air will usually be ambient air taken directly from the room which has not be preconditioned in any way. The unit is therefore capable of supplying void air, room air and a mixture of the two.

[0007] A standard underfloor air supply unit therefore has two inlets, one from the void under the raised floor for void air and one from the space above for room air, and an outlet to the space above the raised floor. Therefore, an inlet aperture and an outlet aperture, which are typically covered by grilles, are required in the top surface of the unit from and to the room space above. The apertures in a standard unit are located at each end of the square unit (which may be considered the length in the X direction) and may span the full width of the unit in the orthogonal direction (which may be considered the Y direction). The fan will be located in the middle of the unit, between the two apertures. This arrangement means that effectively an entire standard floor section typically of 600mm x 600mm area must be open and uncovered for a standard two aperture unit to be installed correctly.

[0008] This requirement may affect where a standard two aperture underfloor unit can be placed in a cellular flooring system where open floor area may be at a premium, and where entire open 600mm x 600mm sections may be unavailable or few in number within a given cellular configuration. As an example, the positioning of furniture or partitioning may restrict the available open floor area such that a standard two aperture unit cannot be installed.

[0009] Given these limitations, standard two aperture underfloor units may have to be placed in unsuitable positions which may impact system functionality and occupant comfort, such as underneath desks or other furniture which will impact airflows and therefore system functionality, or directly underneath chairs which will cause occupant discomfort. In these cases, the office layout design may have to be changed to accommodate the standard units, which ultimately undermines the flexibility of the system, being one of the major reasons for usage.

[0010] The present invention, at least in preferred embodiments, aims to address problems associated with prior art underfloor air supply units, including one or more of the problems discussed above.

[0011] Summary of the Invention

[0012] The present invention provides an underfloor air supply unit for use in a raised access flooring system, the system comprising a raised floor, a void space below the floor and a room space above the floor, the unit comprising: a housing having a top surface configured to be generally parallel to the raised floor in use, a first inlet below the top surface of the housing and configured to receive void air from the void space in use, a second inlet in the top surface configured to receive air from the room space in use, an outlet in the top surface configured to supply air to the room space in use, and a fan to draw air from the first and / or second inlet and to supply air to the outlet in use, wherein the unit defines an air flow path from the second inlet to the outlet in which the direction of air flow is reversed such that the second inlet and the outlet are located on the same side of the fan in the top surface.

[0013] The void air may be supplied from elsewhere inside the building or from outside the building. The void air may ambient air or may have been treated or conditioned in some way, for example by being heated or cooled, filtered, humidified or dehumidified. The void air may be supplied through ducting, however ducting may not be required where the void as a whole is supplied with the air for the one or more units in the system. The room air will typically be ambient air taken directly from the room which has not be preconditioned in any way. The unit is therefore capable of supplying void air, room air and a mixture of the two.

[0014] The fan may selectively draw all of the air from the first inlet or from the second inlet, or a proportion from both inlets. In some embodiments, as discussed below, the unit has a "fully open" position in which the first inlet is open and the second inlet is closed, so that all of the air is drawn from the first inlet (void air). In the "fully closed" position, the second inlet is open and air is drawn from the second inlet (room air). In the fully closed position, the first inlet may be closed so that all of the air is drawn from the second inlet (room air), or the first inlet may be partially closed so that at least some air is still drawn from the first inlet (void air), e.g. for ventilation purposes. Positions between fully open and fully closed may also be possible. The unit may include means such as a damper, discussed below, to selectively control the supply of air from the first inlet and second inlet to the fan. The unit, housing and top surface may be considered to have a length in the X direction, a width in the Y direction and a height in the Z direction. The unit may be designed to fit within or provide a module of the flooring system, such as a 600 x 600 mm module.

[0015] As mentioned above, the unit reverses the direction of air flow from the second inlet to the outlet such that the second inlet and the outlet are located on the same side of the fan in the top surface. In prior art units, air flow through the unit is generally (when considering the length or X direction) only in one direction, i.e. straight, from one end to the other, with the fan being between the inlet and the outlet. By reversing the direction in the air flow path, a more compact path is achievable, i.e. a shorter "footprint" in the X direction. The fan does not then have to be located between the inlet and outlet, which allows the inlet and the outlet to be located on the same side of the fan. The fan may be located at one end of the unit. The direction reversal may also occur within the fan itself. With the top surface inlet and outlet on the same side of the fan, a more compact arrangement is possible allowing a single grille and a smaller footprint. The inlet and the outlet no longer need to be separated by a gap for the fan, and could for example be adjacent to one another, as discussed below.

[0016] The direction of air flow is reversed when considering the length or X direction of the unit. The component of the direction of air flow in the X direction may be reversed at a point or section in the air flow path so that the second inlet and the outlet can be located on the same side of the fan.

[0017] The air flow path preferably turns through an angle of greater than 90, 100, 110, 120, 130, 140, 150, 160, 170 or 180 degrees, preferably about 180 degrees, or substantially 180 degrees, to reverse the air flow direction. The air flow path preferably turns through an angle of greater than 90 degrees in the X direction so that there is a component in the X direction which is back towards the original direction.

[0018] The air flow path will also deviate in at least one of the other directions (Y, Z or both) to provide a path to the outlet. Preferably therefore, the air flow path reverses in the X- direction and also deviates in at least one of the width (Y) direction and the height (Z) direction.

[0019] The point or section of the air flow path at which the direction is reversed may be provided in ducting (e.g. a bend, curve, elbow, etc.) or may be provided by or within the fan.

[0020] In a preferred embodiment therefore, the air flow path is configured to reverse direction within the fan. The fan may be configured to turn the air path substantially through 180 degrees.

[0021] The fan inlet and outlet may be on the same side of the fan (in the length or X direction). The fan typically has an axis of rotation. In a preferred embodiment, the axis is aligned in the Y direction, and the second inlet and outlet are located to the same side of the axis in the X direction.

[0022] As mentioned above, the fan can be located at or provide the point of reversal to conveniently change direction of the air flow back towards the outlet, and therefore the fan does not have to be located between the inlet and outlet.

[0023] In a preferred embodiment, the air flow path is configured to supply air at a first level in the unit before the direction of air flow is reversed and wherein the air flow path is at a second level in the unit after the direction of air flow is reversed. The first level may be below or above the second level (in the height or Z direction).

[0024] In a preferred embodiment, the unit further defines a second air flow path from the first inlet to the outlet in which the direction of air flow is also reversed. The air flow path from the second inlet to the outlet and the second air flow path from the first inlet to the outlet may merge together prior to the reversal of direction. In this embodiment, the first and second inlets may be on the same side of the fan in the X direction. The second air flow path may not be reversed in direction if the first and second inlets are on the opposite sides of the fan. In a preferred embodiment, the second inlet and the outlet are substantially adjacent to one another in the top surface of the unit. The second inlet and outlet do not have to be immediately or directly adjacent, although they can be. There may be a separating wall at least, or possibly a relatively narrow dividing / sepa rating section forming part of the top surface, but adjacent is to be distinguished from prior art where the inlet and outlet are at opposite ends of the unit (in the Y direction), spaced by the distance required by the fan, so these are not adjacent. Adjacent is when considered in plan view, and this may be in the X or Y direction.

[0025] As discussed above, locating the second inlet and outlet adjacent to one another (and preferably in a central position) frees up one or both ends of the unit for the siting of furniture, partitions, etc. The second inlet and outlet can share a single grille, which may be a similar design to one of the grilles of the current two-grille unit.

[0026] In a preferred embodiment, the areas of the adjacent second inlet and outlet combine to define a total second inlet / outlet area in the top surface of the housing. The area preferably extends less than the length of the top surface in the X direction, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length. The area may extend across less than, substantially all or all of the width of the top surface in the Y direction, and / or may be located substantially centrally or towards or at one side in the Y direction. The area may be located substantially centrally in the top surface in the X direction, or off- centre, such as towards or at one end of the top surface in the X direction.

[0027] In a preferred embodiment, the second inlet and the outlet are aligned in one of the X and Y directions and are adjacent in the other of the X and Y directions. Aligned means that the inlet and outlet are generally in alignment in the relevant direction. This may be in relation to the centreline of the inlet and outlet, or in relation to an edge for example. With the second inlet and outlet aligned in one direction, the second inlet and outlet may or may not be coextensive in the other direction. In one embodiment, the second inlet and outlet are aligned in the X direction. The second inlet and outlet may be adjacent in the Y direction. The combined width of the second inlet and outlet may extend substantially across the width of the top surface in the Y direction. The length of the second inlet and / or outlet in the X direction preferably extends less than the length of the top surface, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length. The second inlet and outlet may be coextensive in the X direction. The second inlet and / or outlet may comprise a single or more than one inlet / outlet respectively. In a preferred arrangement, the second inlet comprises two second inlets separated in the Y direction by a single outlet.

[0028] In another embodiment, the second inlet and outlet are aligned in the Y direction. The second inlet and outlet may be adjacent in the X direction. The width of the second inlet and / or outlet may extend substantially across the width of the top surface in the Y direction. The combined length of the second inlet and outlet in the X direction preferably extends less than the length of the top surface, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length. The second inlet and outlet may be coextensive in the Y direction. The second inlet and / or outlet may comprise a single or more than one inlet / outlet respectively. The second inlet and outlet may have substantially the same length in the X direction.

[0029] The unit preferably further comprises a damper to selectively control the supply of air from the first inlet and / or second inlet to the fan. The damper may supply all of the air to the fan from the first inlet or from the second inlet, or may supply a proportion from both inlets. The damper is preferably a plate or flap, whose position may be controlled by a motor. In some embodiments, the damper extends across substantially the width of the unit in the Y direction. The damper may direct air to the first level discussed above.

[0030] The unit preferably further comprises a heater to heat the air supplied to the outlet. At least in preferred embodiments, the invention addresses the requirement for an underfloor air conditioning unit (that is a single part of a larger underfloor air conditioning system), that can be installed into the infrastructure of a raised access flooring system utilising 600mm x 600mm interlocking floor panels, that does not require the total effective open area of a 600mm x 600mm floor panel to function correctly. In addition to this, the portion of the open area required by the underfloor unit to function correctly, of the total 600mm x 600mm area lent by the raised access flooring system infrastructure, can be adjusted along either the X axis or the Y axis depending on underfloor unit orientation.

[0031] The invention is advantageous where open floor area is restricted such that the entire open area of a 600mm x 600mm floor panel (where an industry standard 2 grille underfloor unit could be installed) is either unavailable or seldom available. This situation is common in cellular spaces where furniture and partition walls restrict open floor area such that a standard 2 grille unit cannot be installed.

[0032] A unit that fulfils the above requirements can make use of the partial open area of a 600mm x 600mm section of the raised access flooring system, where an industry standard 2 grille unit could not.

[0033] The invention, specifically an underfloor air conditioning unit that achieves the complete function of a standard 2 grille unit, whilst using 1 grille of a type identical to a standard 2 grille unit that is adjustable in position along 1 axis of a 600mm x 600mm section of a raised access floor system, allows installation in a space where open floor area is restricted where a standard 2 grille unit may be impossible to install, or is installed in such a way that is detrimental to the function of an underfloor air conditioning system as a whole, or is installed in such a way that is unfavourable to the comfort of the occupants. The single grille underfloor unit can be installed in 600mm x 600mm section of floor with only a partial open area whereby the same 600mm x 600mm may be partially covered by a piece of furniture or a partition wall. Some further features and advantages of the invention, at least in preferred embodiments, are provided below:

[0034] • recirculates and supplies air to an above raised access floor space via a single exposed grille of the same dimensions as a single grille on an industry standard unit which requires two grilles.

[0035] • smaller visual footprint above floor (single grille).

[0036] • smaller under floor footprint due to the way the internals have been laid out. This reduces material used and increases flexibility of placement (under partition walls where it would be impossible to place a standard 2 grilled unit without impairing function).

[0037] • Grille placement within a 600 x 600 floor tile can be adjusted (impossible with standard 2 grille units).

[0038] • Units can be placed directly adjacent to each other without impairing function.

[0039] • Chassis is constructed so that the unit is separated into two distinct lower and upper sections with the separating wall parallel to the top and bottom of the unit. A fan chamber is present at one end of the unit that is separate and open to the upper and lower sections of the unit. The chassis encloses the internal volume of the unit so that is airtight except for specified areas used for inlet and outlet.

[0040] • Room inlet and fan outlet areas are adjacent to each other along the area covered by a single air grille. The inlet and outlet areas are open and are situated on the top surface of the upper section of the unit.

[0041] • Two room inlet sections are situated either side of a single fan outlet section separated by a non-permeable wall perpendicular to the top of the unit that is an integral part of the construction of the unit chassis.

[0042] • An underfloor inlet area is situated on the lower half of one of the side elevations that is parallel with the longitudinal direction of the single air grille which allows a direct path from the lower unit section into the floor void for air to travel through.

[0043] • A centrifugal fan assembly is fixed internally on the opposite side of the unit to the underfloor air inlet within the fan chamber. • The fan is orientated such that air is drawn from inside the bottom section of the unit and is discharged into the top section of the unit by way of turning the air 180 degrees from its original direction of travel.

[0044] • Internally, the bottom section of the unit is open so that air is drawn directly from the underfloor inlet into the centrifugal fan assembly, where it is then discharged into the top section of the unit.

[0045] • The aforementioned fan outlet area covered by the single air grille is situated in the top section of the unit and has a direct air path to the centrifugal fan assembly.

[0046] • The room inlet areas that are adjacent to the fan outlet area are open to the lower section of the unit so that air can move directly from above the unit (recirculation air) to the lower section of the unit.

[0047] • Across the entire open width of the lower section of the unit a damper is installed parallel to the orientation of the underfloor inlet.

[0048] • The damper is actuated by an electrical motor and has two final positions: fully "open" and fully "closed".

[0049] • The damper is rectangular in shape and is attached to the unit shell by two opposed and concentric, rotational joints situated closely to the ends of the short sides of the rectangular damper. These joints are placed closely to the top surface of the lower section of the unit so that under tension from the electrical motor, or by the force of gravity the damper rotates around the rotational joints to block or open the internal area of the unit lower section.

[0050] • In the fully "open" position the motor is engaged rotating the damper in the clockwise direction under tension from the electrical motor. The damper rotates until it comes into contact with the top surface of the lower section of the unit. The damper is parallel and directly adjacent with the top surface of the lower section at this point.

[0051] • In this open position, the damper forms a seal with top surface of the lower section of the unit so that the two room air inlet areas are now separated from the lower section of the unit, and air cannot move from above the unit into the lower section. In this open position, the path from the underfloor inlet through the lower section of the unit to the centrifugal fan assembly is completely open to the traversal of conditioned air.

[0052] • In the fully "closed" position the motor is disengaged and the damper rotates anticlockwise by force of gravity until it comes into contact with mechanical minimum opening stop of the unit. The damper spans between the top and bottom surface of the lower section of the unit at this point.

[0053] • In this closed position, the room inlet areas in the upper section of the unit are open to the lower section of the unit so recirculation air from above the unit can pass freely to the lower section of the unit.

[0054] • In this closed position, the path from the underfloor inlet through the lower section of the unit to the centrifugal fan assembly is partially blocked to the traversal of conditioned air.

[0055] • The "open" damper position corresponds to the unit being in "supply mode", and the "closed" damper position corresponds to the unit being in "recirculation mode". These two modes are the basis of how the unit regulates room conditions.

[0056] • As sections for room inlet and fan outlet are directly adjacent to each other, "supply" and "recirculation" modes are achieved with a single grille.

[0057] Brief Description of the Drawings

[0058] Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0059] Fig. 1 shows a schematic side view of a conventional underfloor air supply unit in supply mode, supplying air to the room space above;

[0060] Fig. 2 shows the conventional underfloor air supply unit of Fig. 1 in recirculation mode, supplying recirculated air to the room space above;

[0061] Fig. 3 shows a schematic plan view of a conventional underfloor air supply unit and an example floor plan;

[0062] Fig. 4 shows a plan schematic view of an underfloor air supply unit in accordance with the invention; Fig. 5A shows a sectional view of the underfloor air supply unit of Fig. 4 from line A-A; Fig. 5B shows a sectional view of the underfloor air supply unit of Fig. 4 from line B-B; Fig. 5C shows a sectional view of the underfloor air supply unit of Fig. 4 from line C-C;

[0063] Fig. 6A shows a plan schematic view of the underfloor air supply unit of Fig. 4 in recirculation mode;

[0064] Fig. 6B shows a sectional view of the underfloor air supply unit of Fig. 6A from line A-A; Fig. 7A shows a plan schematic view of the underfloor air supply unit of Fig. 4 in supply mode;

[0065] Fig. 7B shows a sectional view of the underfloor air supply unit of Fig. 7A from line A-A;

[0066] Fig. 8 shows a schematic plan view of an underfloor air supply unit in accordance with the invention and example floor plans; and

[0067] Figs. 9A to 9D shows examples of different second inlet and outlet configurations in accordance with the invention.

[0068] Detailed Description of a Preferred Embodiment

[0069] Figs. 1 and 2 show a schematic view of a conventional underfloor air supply unit 10 situated in a raised access flooring system. The flooring system comprises a raised floor R mounted on raised supports (not shown) above the structural floor S of the building. A void V is created between the two floors.

[0070] The underfloor air supply unit 10 is located in the void V and has a top surface 11 parallel with and generally co-planar with the raised floor R. The unit comprises a first inlet 12 below the top surface which receives void air VA from the void space, a second inlet 13 in the top surface to receive room air RA (Fig. 2) from the room space, and an outlet 14 in the top surface which supplies supply air SA to the room space. The unit 10 also includes a fan 15 to drive air to the outlet 14 and an optional heater 16 between the fan and the outlet for heating the air.

[0071] The second inlet 13 and the outlet 14 are fitted with grilles to prevent access to the interior of the unit and to provide a safe surface in the raised floor in the event that the unit is stood on or walked on. The second inlet 13, outlet 14 and grilles are at opposite ends of the unit (i.e. along the length of the unit in the X direction) as seen in Figs. 1 and

[0072] 2, with the fan in between. The second inlet 13, outlet 14 and grilles will generally extend the full width of the unit in the Y direction.

[0073] A damper 17 is used to control the source of air to the fan. In Fig. 1, the unit is in supply mode with the damper 17 in a raised position so that void air VA from the void space, received through inlet 12, is supplied to the room space above as supply air SA. In Fig. 2, the unit is in recirculation mode with the damper 17 in a lowered position so that room air RA from the room space above is recirculated, optionally via heater 16, back to the room space as supply air SA. In recirculation mode, the damper may be configured to allow a small amount of void air VA to bleed through to ensure a quantity of fresh air is included in the supply air SA.

[0074] Fig. 3 shows a schematic plan view of a conventional underfloor air supply unit and an example floor plan. A standard floor module is 600mm x 600mm. The grilles for the second inlet and outlet are located at opposite ends of the unit (i.e. along the length of the unit in the X direction). They extend across substantially the full width of the unit in the Y direction. The example floor plan shows some of the floor modules being obstructed by a partition wall and furniture, and therefore a conventional underfloor unit could not be sited in these locations.

[0075] An underfloor air supply unit in accordance with an embodiment of the invention will now be described, with reference to Figs. 4, 5A, 5B and 5C. Figs. 5A, 5B and 5C show sectional views of the unit of Fig. 4 from lines A-A, B-B and C-C respectively.

[0076] The underfloor air supply unit 100 has a housing 101 including a top surface 102 which, when located in the void V in use, will be parallel with and generally co-planar with the raised floor R.

[0077] First inlet 120 is located below the top surface 102 and receives void air from the void space, second inlet 130 is located in the top surface to receive room air and outlet 14 is located in the top surface to supply air to the room space. The unit 10 also includes a fan 150 to drive air to the outlet 140, having a motor 151 and two impellers 152. A heater 160 is provided between the fan 150 and the outlet 140 for heating the air as required. A damper 170 controls the source of air to the fan and its position is controlled by means of motor 171 which can shorten or lengthen ribbon 172 to move the damper between supply mode and recirculation mode, with positions between also being possible.

[0078] In the embodiment shown, second inlet 130 comprises two inlets 131 and 132 which are separated in the Y direction by the outlet 140. Room air is received by inlets 131 and 132 at an upper level of the unit and this air is directed by damper 170 to a lower level of the unit where it is supplied to the fan impellers 152. Inlets 131 and 132 are trapezoidal in plan due to the presence of angled baffles 103 in the upper level, which channel the supply air from the impellers to the outlet 140. Control electronics may be located in a compartment 104.

[0079] Figs. 6A and 6B show plan and sectional schematic views of the underfloor air supply unit of Fig. 4 in recirculation mode. Damper 170 is in the lowered position and therefore void air VA is prevented from entering the unit via first inlet 120, or is at least restricted to an extent. The damper 170 directs room air RA from second inlets 130 via the upper level 105 to lower level 106, where the air enters impellers 152. Within the impellers, the air flow path is turned through 180 degrees in the X direction and is also transferred from the lower level 106 back to the upper level 105. Angled baffles 103 in the upper level channel the air from the impellers to the outlet 140, via heater 160.

[0080] Figs. 7A and 7B show plan and sectional schematic views of the underfloor air supply unit of Fig. 4 in supply mode. Damper 170 is in the raised position and therefore room air RA is prevented from entering the unit via second inlet 130. The damper 170 allows void air VA from the first inlet 120, which is in the lower level 106 of the unit, to pass to the impellers 152. Within the impellers, the air flow path is again turned through 180 degrees in the X direction and is also transferred from the lower level 106 to the upper level 105. Angled baffles 103 in the upper level channel the air from the impellers to the outlet 140, via heater 160. Fig. 8 shows a schematic plan view of an underfloor air supply unit in accordance with the invention and example floor plans. Compared to the conventional air supply unit shown in Fig. 3, it can be seen that it is possible to employ a unit of the present invention with a single grille G located inwardly from each end in the X direction, even where the floor module is obstructed in part by a partition wall or furniture.

[0081] Figs. 9A to 9D show examples of different second inlet and outlet configurations in accordance with the invention. In Figs. 9A and 9B, the second inlet 130 and outlet 140 are aligned in the Y direction and are adjacent in the X direction. In Fig. 9B, there is a dividing section (in hatched lines) between the second inlet and outlet. In Figs. 9C and 9D, the second inlet 130 and outlet 140 are aligned in the X direction and are adjacent in the Y direction. In Fig. 9D, there are two outlets 140 separated by one second inlet 130.

Claims

Claims1. An underfloor air supply unit for use in a raised access flooring system, the system comprising a raised floor, a void space below the floor and a room space above the floor, the unit comprising: a housing having a top surface configured to be generally parallel to the raised floor in use, a first inlet below the top surface of the housing and configured to receive void air from the void space in use, a second inlet in the top surface configured to receive air from the room space in use, an outlet in the top surface configured to supply air to the room space in use, and a fan to selectively draw air from the first and second inlets and to supply air to the outlet in use, wherein the unit defines an air flow path from the second inlet to the outlet in which the direction of air flow is reversed such that the second inlet and the outlet are located on the same side of the fan in the top surface.

2. The air supply unit of claim 1, wherein the air flow path turns through an angle of greater than 90, 100, 110, 120, 130, 140, 150, 160, 170 or 180 degrees, preferably about 180 degrees, or substantially 180 degrees in the length (X) direction of the unit, to reverse the air flow direction.

3. The air supply unit of claim 2, wherein the air flow path deviates in at least one of the width (Y) direction and the height (Z) direction.

4. The air supply unit of any preceding claim, wherein the air flow path is configured to reverse direction within the fan.

5. The air supply unit of claim 4, wherein the fan inlet and outlet are on the same side of the fan (in the length or X direction).

6. The air supply unit of any preceding claim, wherein the air flow path is configured to supply air at a first level in the unit before the direction of air flow is reversed and wherein the air flow path is at a second level in the unit after the direction of air flow is reversed.

7. The air supply unit of claim 6, wherein the first level is below the second level (in the height or Z direction), or wherein the first level is above the second level (in the height or Z direction).

8. The air supply unit of any preceding claim, wherein the unit further defines a second air flow path from the first inlet to the outlet in which the direction of air flow is reversed.

9. The air supply unit of claim 8, wherein the air flow path from the second inlet to the outlet and the second air flow path from the first inlet to the outlet merge together prior to the reversal of direction.

10. The air supply unit of any preceding claim, wherein the second inlet and the outlet are substantially adjacent to one another in the top surface of the unit.

11. The air supply unit of claim 10, wherein the areas of the adjacent second inlet and outlet combine to define a total second inlet / outlet area in the top surface of the housing, and wherein the area extends less than the length of the top surface in the X direction, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length.

12. The air supply unit of claim 11, wherein the area extends across substantially all of the width of the top surface in the Y direction.

13. The air supply unit of claim 11 or 12, wherein the area is located substantially centrally in the top surface in the X direction, or is located at one end of the top surface in the X direction.

14. The air supply unit of any preceding claim, wherein the second inlet and the outlet are aligned in one of the X and Y directions and are adjacent in the other of the X and Y directions.

15. The air supply unit of claim 14, wherein the second inlet and the outlet are aligned in the X direction and are adjacent in the Y direction.

16. The air supply unit of claim 15, wherein the combined width of the second inlet and the outlet extends substantially across the width of the top surface in the Y direction.

17. The air supply unit of claim 15 or 16, wherein the length of the second inlet and the outlet in the X direction extends less than the length of the top surface in the X direction, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length.

18. The air supply unit of any of claims 15 to 17, wherein the second inlet comprises two second inlets separated in the Y direction by a single outlet.

18. The air supply unit of claim 14, wherein the second inlet and the outlet are aligned in the Y direction and are adjacent in the X direction.

19. The air supply unit of claim 18, wherein the second inlet and the outlet extend substantially across the width of the top surface in the Y direction.

20. The air supply unit of claim 18 or 19, wherein the combined length of the second inlet and the outlet in the X direction extends less than the length of the top surface in the X direction, and preferably less than half the length, and further preferably between a third and a half of the length, and still preferably about a third of the length.

21. The air supply unit of any preceding claim, further comprising a damper to selectively control the supply of air from the first inlet and / or second inlet to the fan.

22. The air supply unit of any preceding claim, further comprising a heater to heat the air supplied to the outlet.

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