WO1999001702A1

WO1999001702A1 - Humidifier

Info

Publication number: WO1999001702A1
Application number: PCT/GB1998/001906
Authority: WO
Inventors: Stephen Palmer Verney; Anthony Fleming
Original assignee: Js Humidifiers Plc
Priority date: 1997-06-30
Filing date: 1998-06-30
Publication date: 1999-01-14
Also published as: GB9713785D0; GB2326938A; EP0922185A1

Abstract

The invention relates to a humidifier adapted to be mounted in or on a ceiling; the humidifier comprising a housing (2); mounting means for mounting the housing (2) on or in the ceiling; a fan (26) for drawing air through the humidifier from an air inlet (12) to an air outlet (18); an evaporative matrix (6) disposed between the air inlet (12) and air outlet (18), and water supply means (42) for supplying water to the evaporative matrix (6) such that air passing from the air inlet (12) to the air outlet (18) is humidified by evaporation from the matrix (6).

Description

HUMIDIFIER

This invention relates to a humidifier of the type in which an air stream is passed over a humidifying evaporative matrix. More particularly, the invention relates to humidifiers adapted to be mounted on or in ceilings.

Evaporative humidifiers are well known. Such humidifiers consist of a water-retaining matrix constructed so as to provide a large surface area from which water can evaporate. Water is supplied to the matrix from a suitable source and a current of air is caused to pass over the matrix such that water evaporates from the matrix into the air stream thereby humidifying the air. However, a problem with current humidifiers is that they tend to be relatively bulky and this can create problems in environments such as offices where there may be little or no floor or wall space available in which to mount humidifiers.

The present invention makes use of the fact that in many buildings, false ceilings are provided such that there is a ceiling void or plenum space between the false ceiling and the actual ceiling. Such plenum spaces typically are relatively shallow and typically are only 20 to 30 centimetres in depth.

Accordingly, one object of the present invention is to provide a humidifier which is sufficiently compact to be mounted in the plenum spaces found above the false ceilings in many industrial buildings and offices.

Another object of the invention is to provide a means for modifying air conditioning units of the "Fan Coil" type so as to incorporate an evaporative humidifier assembly. Fan coil air conditioning units, which are often mounted in the plenum spaces of buildings, comprise an air inlet, an air outlet, a fan for drawing air through the unit, and either a heating element or a cooling element or both. The present invention sets out to provide a modular unit or cassette which can be used in an air conditioning unit of the "fan coil" type in place of the heating or cooling element.

In a first aspect, the invention provides a humidifier adapted to be mounted in or on a ceiling; the humidifier comprising a housing; mounting means for mounting the housing on or in the ceiling; a fan for drawing air through the humidifier from an air inlet to an air outlet; an evaporative matrix disposed between the air inlet and air outlet, and water supply means for supplying water to the evaporative matrix such that air passing from the air inlet to the air outlet is humidified by evaporation from the matrix.

The housing is preferably adapted to be mounted in a plenum space so as to be substantially flush with the underside of a false ceiling defining the lower limit of the plenum space.

The mounting means can take the form of brackets for suspending the housing in a large ceiling void or plenum space so as to be flush with the lower surface of the false ceiling; or the mounting means can be adapted to allow the housing to be connected directly to the underside of a floor, ceiling or roof above the plenum space.

The housing, when mounted in or on the ceiling, preferably has a maximum horizontal length greater than its maximum height. For example, the housing may have a horizontal length at least three times the height of the housing, preferably at least four times the length of the housing.

The housing may have, in horizontal sequence, an air inlet; an air inlet chamber; a filter housing; an evaporative matrix; a fan chamber; an outlet chamber; and at least one air outlet. The housing preferably has a plurality of air outlets. In one embodiment, for example, the housing has two air outlets. In another embodiment the housing has four or more such air outlets. The humidifier may be provided with trunking connectable to the or each air outlet so as to distribute humidified air to different parts of a room or different rooms in a building.

The air inlets and/or the air outlets may each be mounted on respective removable mounting members so that mounting members having differing numbers of inlets and outlets may be interchanged. The mounting members may simply take the form of housing end plates which can be, for example, removably secured to a main body of the housing by means of fastening elements such as bolts.

The humidifier may comprise, or have associated therewith, heating means for heating humidified air from the humidifier. Such heating means can take the form of an in-line heater disposed within the housing or in ducting or pipe-work associated with the housing, for example upstream of the air inlet or downstream of the air outlet.

The humidifier is most preferably adapted to be serviceable from the underside thereof while mounted in or on the ceiling. Thus, for example, the underside of the housing can have at least one access hatch or door to permit access to the interior of the housing for servicing purposes.

Preferably, the evaporative matrix is mounted in a supporting structure (hereinafter referred to as the "evaporative matrix assembly") which is removable from the housing. The evaporative matrix assembly can comprise a supporting framework having an evaporative matrix removably mounted in the upper part thereof, and a water reservoir or drip tray defined by the lower part of the supporting framework. The evaporative matrix may be presented in the form of a "cassette" which simply slots into the upper part of the housing, and enables the evaporative matrix to be removed as a whole and replaced by a fresh matrix. Removal of the evaporative matrix has the additional advantage of making servicing or reconditioning of the drip tray/water reservoir easier.

Water is supplied to the matrix from water dispensing means arranged above the matrix, surface water passing out from the lower surface of the matrix into the water reservoir. The water reservoir is typically in the form of a tray having an inclined surface such that water can collect at a lower surface of the tray, thereby reducing the amount of water stored in the tray.

The reservoir is typically provided with a water inlet, a water outlet and an overflow. Water level-detecting means such as a float valve may be provided for controlling flow of water into the reservoir.

Water dispensing means are arranged above the matrix, and connected to the housing, for directing water downwardly onto the matrix. The water dispensing means can take the form of a spray head, or for example a spray bar in the form of a length of tubing, closed at one end and having a plurality of openings along its length through which water may pass.

The evaporative matrix may comprise an inert support material coated with a water-insoluble substance having high water retention capacity. For example, the matrix can be formed from fibre glass matting, paper or sheets coated with a water-absorbing ceramic substance.

The evaporative matrix preferably takes the form of a plurality of corrugated sheets of the water absorbing material, each sheet lying in an upstanding plane, preferably a substantially vertical plane. The term vertical as used herein refers to the orientation of the plane when the humidifier is mounted in place in or on the ceiling. The sheets are preferably substantially parallel. The ribs of the corrugated sheet are preferably inclined with respect to the horizontal such that excess water can flow out of the channels formed between the sheets and down the edges of the sheets into the reservoir. It is preferred that the ribs of adjacent sheets are inclined in opposed directions.

The sheets of corrugated material typically have a corrugation height up to about 5mm, for example in the range of 3.5 to 4.5, e.g. 3.9 to 4.2mm, and a pitch of approximately 100 to 140 (e.g. 120) corrugations per metre. The corrugated sheets can be glued together, for example by means of a porous glue such as an emulsion of kaolin in a suitable binder such as an organic binder. It is preferred however that the sheets are not glued together but instead are loosely packed within the framework.

In order to ensure a more even flow of air through the humidifier, a perforated baffle may be positioned downstream of the evaporative matrix, but between the evaporative matrix and the fan. The perforated baffle can take the form of a perforated plate, for example a plate in which the area of the perforations represents at least 30%, for example 30% to 70%, more preferably at least 40%, and in particular at least 50% of the area of the plate. The perforations will usually be uniformly distributed over the plate and typically are of substantially uniform size. The perforations can be, for example of a size in the range 3 to 5mm, for example 3.6 to 3.8mm.

The presence of the perforated baffle is particularly preferred when the fan used to draw the air through the humidifier is of a type which creates an airflow through the evaporative matrix in which there is a significant variation in flow rate across the width of the matrix. For example, when a centrifugal fan is used, air is drawn into the fan through air inlets at either side of the fan and a consequence of this, in the absence of the baffle, is that air is drawn more rapidly through the peripheral regions of the matrix than through the centre thereby leading to uneven evaporation from the matrix across its width. By using a baffle as defined above, the airflow rate through the matrix, and hence the rate of evaporation, is evened out across the width of the matrix.

The spray head above the matrix is usually supplied by a water line which is fed from the reservoir beneath the evaporative matrix. Water can be recirculated between the reservoir at the spray head by means of a suitable recirculation pump. The recirculation pump is preferably of a type which is capable of delivering a relatively low flow rate, for example from 10 to 100 litres per hour. The recirculation pump can be, for example, a solenoid pump, a peristaltic pump or a sump pump but preferably it is a solenoid pump.

A valve means (for example a solenoid valve) can be interposed between the reservoir and the spray head for controlling flow of water to the spray head. The valve means may have an inlet and two or more outlets such that it can direct water either to the spray head or to another destination, for example to waste. The valve means preferably has two outlets, one connected to the spray head and the other connected to a drain outlet. The drain outlet may be connected to a second pump means and thence to waste.

By virtue of this arrangement, the valve means may be actuated to allow a proportion of the water (e.g. 5%) to be bled off from the recirculating water flow. The resulting drop in water level within the reservoir activates the level sensing means which in turn allows water to pass in through the water inlet to top up the level in the reservoir. In this way, as a result of the controlled bleed and replenishment, the water in the humidifier is prevented from becoming stagnant. In circumstances where very hard water is used, the bleed rate can be higher than 5%, for example 30 or 40% per cycle or more. The valve means can be linked to a control means incorporating a timer such that at regular intervals, for example at least once daily, the reservoir can be emptied completely and a completely fresh volume of water introduced into the humidifier.

As a further means of ensuring that the water does not become stagnant, and contaminated with, for example, microorganisms, a solid phase disinfecting or sterilising medium can be mounted within the reservoir. One such disinfecting or sterilising medium consists of a support matrix coated with a microbicidal silver material. For example, a disposable fabric coated with a sparingly soluble silver salt can be mounted within the reservoir. Alternatively, an ultraviolet radiation source may be used for disinfecting the water.

The first pump, which circulates water between the reservoir and the spray head, is preferably linked to means for measuring the humidity of the air passing in through the air inlet. Such means, which can be, for example a humidistat, can be mounted externally of the humidifier, for example in a room. Alternatively, the humidistat can be mounted within the housing in the region of the air inlet. The humidistat is operatively connected to the first pump such that if the humidity of the air exceeds a certain value, the pump can be shut down, subsequently to be restarted when the humidity falls below the desired value.

In a second aspect, the invention provides an evaporative matrix assembly for use in an evaporative humidifier as hereinbefore defined, the evaporative matrix assembly comprising a supporting framework having an evaporative matrix material disposed in the upper part thereof, and a water reservoir or drip tray disposed in the lower part thereof. The evaporative matrix can be in the form of a cassette which is removably attached to the supporting framework. It is envisaged that the evaporative matrix assembly could be used in combination with a fan coil air conditioning unit, in place of or together with the heating and/or cooling elements of the fan coil unit, so as to provide an evaporative humidifier in accordance with the invention. The evaporative matrix assembly can be fitted to the fan coil unit together with all the necessary controls ab initio, for example by the original manufacturer, or as a retro-fit by replacing the heating/cooling element in an installed unit.

The water supply to the humidifier can be treated to reduce the mineral content and/or remove particulate matter and/or disinfect or sterilise the water. For example, the water supply can be connected in-line with a water treatment module comprising one or more elements selected from a sediment filter, a granular activated carbon filter, a reverse osmosis membrane, and an ultraviolet radiation source. The water treatment module is typically connected upstream of the water inlet.

The humidifier typically is provided with appropriate control circuitry controlling the duration of the humidifying action of the humidifier and, for example the water recycling and replenishment functions. The control circuitry can comprise a microprocessor-based controller which enables the humidifier to be controlled locally or via a building management system (BMS) . Alternatively, some functions, such as the water recycling/ replenishment function can be fixed in the factory such that such that subsequent adjustment in situ must be carried out by service engineers.

In a further aspect, the invention provides a method of humidifying air in a room, which method comprises mounting an evaporative humidifier as hereinbefore defined in or on a ceiling of the room, passing air into an inlet of the humidifier, humidifying the air and directing the humidified air into the room.

In a still further aspect, the invention provides a ceiling having fitted therein or thereon a humidifier as hereinbefore defined.

In another aspect, the invention provides a method of converting a fan coil air conditioning unit to an evaporative humidifier, which method comprises removing a heating and/or cooling element from the air conditioning unit and inserting therein an evaporative matrix assembly as hereinbefore defined.

The invention will now be illustrated, but not limited, by reference to a specific embodiment as shown in the accompanying drawings of which;

Figure 1 is a plan view from beneath of a humidifier according to one embodiment of the invention;

Figure 2 is a side view of the humidifier shown in Figure 1 ;

Figure 3 is an end view from direction D of the humidifier shown in Figures 1 and 2;

Figure 4 is a side sectional elevation showing schematically the interior of the embodiment of Figures 1 to 3;

Figure 5 is an isometric view of an evaporative matrix assembly;

Figure 5a is an isometric view of an evaporative matrix cassette forming part of the evaporative matrix assembly of Figure 5;

Figure 6 is a longitudinal sectional elevation through the evaporative matrix assembly of Figure 5;

Figure 6a is an isometric view of a supporting framework forming the lower part of the evaporative matrix assembly of Figure 5; Figure 7 is a schematic illustration illustrating the layout of the hydraulic components of the humidifiers; and

Figure 8 is a partial isometric view of the upper end of the evaporative matrix assembly of Figure 5 showing the mounting of a spray bar in the assembly.

Referring now to the figures, a humidifier according to one embodiment of the invention comprises a housing 2 fabricated from galvanised steel plate. The housing interior is divided into a number of compartments and thus comprises an air inlet chamber 4, an evaporative matrix assembly 6, a fan chamber 8 and an air outlet chamber 10. Air inlet chamber 2 is provided with an opening 1 2 defined by a spigot-like formation 1 6 which can be connected to air inlet trunking (not shown) leading to a ceiling grille. The spigot 1 6 defining the air inlet opening 1 2 forms part of a removable end plate 14 which can be secured by means of bolts (not shown) to the main body of the housing.

At the other end of the humidifier, there are provided two spigot formations 1 8 defining air outlets. Spigot formations 1 8 are formed on a removable end plate 20 which, as with removable end plate 14, can be secured to the main body of the housing by means of bolts (not shown) or other suitable removable fastening means. Spigot formations 16 and 1 8 can be connected to trunking for directing humidified air to different parts of a room or building. Instead of two spigot formations, the removable end plate 20 could be provided with more than two, for example, three, four, five, six, seven or eight such spigot formations. Thus air can be directed from the humidifier to one of a plurality of locations within the building. Since the end plate 20 is removable, the humidifier can readily be adapted to provide more, or fewer, air outlets as required.

At the downstream end of the air inlet chamber, immediately preceding the evaporative matrix assembly 6 is an air filter 22. Air filter 22, as the name suggests, removes particulate matter from the air stream passing through the humidifier, thereby preventing the various components of the humidifier from clogging up after prolonged use.

Immediately downstream of the evaporative matrix assembly 6, is a perforated baffle plate 24 which can be formed, for example, from galvanised steel. The perforated baffle plate 24 has an array of regularly spaced holes across its surface. The area of the holes in total corresponds to approximately 50% of the total area of the plate. The purpose of the perforated baffle plate 24 is to even out the air flow across the width of the evaporative matrix to ensure that the rate of evaporation of water from the matrix is as uniform as possible across the matrix. The baffle plate 24 also helps to ensure that the correct volume of air is drawn through the fan.

Mounted within the fan chamber 8 is a centrifugal fan 26 having air intakes on either side thereof and an air outlet 28 communicating with the air outlet chamber 10. The fan can be, for example, a Torrin DDL146-1 80 model having an optimum flow rate of 0.1 8m³/s.

On the underside 30 of the housing 2 are provided service hatches 32 and 34. Service hatch 32 allows entry to the fan chamber so that the fan can be accessed or removed for servicing. Service hatch 34 can be opened to allow removal of the evaporative matrix assembly 6 and/or the air filter 22.

Mounted on a side of the main housing body 2 is a pump housing 36 within which is concealed an in-line recirculation pump 38 and solenoid valve 40. In this embodiment, the recirculation pump has a maximum flow rate of 1 .1 litres per minute. The solenoid valve is a two way valve which can be, for example, an Asco 1060035 N/C % model operating at 24 volts and 5 watts. The recirculating pump 38 is connected via solenoid valve 40 to a spray bar 42 which is constituted by a length of 9.5mm (3/8 inch) diameter stainless steel tubing closed at one end, and having an array of thirteen 2mm diameter openings along its length.

As shown in Figure 8, the spray bar 42 is mounted in the upper end of the evaporative matrix assembly 6 such that water can be sprinkled downwardly onto the evaporative matrix.

The evaporative matrix assembly 6 is illustrated in Figures 5, 5a, 6, 6a and 8 and comprises a stainless steel support framework 44 formed from end panels 46 and 48 connected by inclined base 50 and side walls 51. Side walls 51 have inwardly facing ledges or flanges 52 to support the lower edges of an evaporative matrix cassette 53. The evaporative matrix cassette has a framework defined by a pair of end walls 54 connected by top and bottom rails 55, 56, the bottom rails 56 being of an L-shape in cross-section, and within the framework of the cassette is an evaporative matrix pad 57. As can be seen from Figures 5a and 6a, the evaporative matrix cassette 53 can simply slot into the support framework 44 where it is held in place by the spray bar 42 as described below.

Thus, end panels 46 and 48 of the support framework 44, and end walls 54 of the evaporative matrix cassette, have openings 46a, 48a, 54a and 54b respectively for receiving the two ends 42a, 42b of the spray bar 42. Openings 48a and 54b are of rectangular shape to accommodate the correspondingly rectangularly shaped end 42b of the spray bar, the purpose of the rectangular shape being to prevent rotation of the spray bar. Openings 46a and 54a are of circular shape for receiving the threaded end 42a of the spray bar. The spray bar 42 is attached to the evaporative matrix assembly by inserting it through openings 46a and 54a such that the rectangular end passes through rectangular opening 54b in side wall 54 and engages opening 48a; nut 72 then being tightened on the threaded end 42a to hold the spray bar and evaporative matrix cassette 53 in place.

Evaporative matrix pad 57 consists of strips of a corrugated fibreglass sheet material formed from chopped 9 micron glass fibre coated with a water-insoluble absorbent ceramic material. One such material is a chopped glass fibre material available from JS Humidifiers PLC under the name "Hematrix". The strips 58 are stacked in upright fashion such that they extend between and are supported by the in-turned ledges 52 of the side walls 51 of the support framework 44. The individual strips 58 are arranged such that with each adjacent pair, the angles of inclination of the ribs or corrugations are opposed. For example, the ribs of two adjacent sheets may be arranged at approximately 90 degrees with respect to each other.

The height of the corrugations of a typical sheet material is approximately 4mm and the material has approximately 120 corrugations per metre.

As can be seen from Figure 6, the base 50 of the support framework 44 is inclined downwardly from end panel 48 to end panel 46 such that water gathers in the end nearest to end panel 46 and forms a reservoir 60. The angle of inclination is such as to provide at least a 1 :20 slope, and the reservoir has a capacity of at least 1 .5 litres.

End panel 46 has three openings each surrounded by a spigot formation for connection to an external hose or line. Opening 62 is connected by means of tubing or piping (not shown) to recirculation pump 38. Opening 64 is connected via a supply line (not shown) to a water supply. Overflow opening 66 is connected via a length of tubing (not shown) to waste. By way of example, the overflow is at least 10mm in diameter.

Mounted inside the base 50 on an upstanding wall 50a thereof is a water level detector 68 comprising a float operatively linked to a switch (not shown). Water level detector is operatively connected by means of appropriate wiring (not shown) to a water inlet controller (not shown) for controlling flow of water to the water inlet 64. Alternatively, inlet 64 can be connected to a float valve which automatically allows water into the reservoir 60 once the water level has fallen below a certain level.

The arrangement of the various hydraulic components of the humidifier is shown in Figure 7.

In use, water is supplied through the water inlet opening 64 to the reservoir 60 and is then pumped by the recirculation pump 38 via solenoid valve 40 to the spray bar 42. A proportion, usually about 5%, of the water is bled off from the system along the drainage line 70 at the solenoid valve 40. Water is ejected from the spray bar such that it falls on to the strips 58 making up the evaporative matrix pad 57. Some of the water is absorbed by the absorbent coating, and excess water runs along the channels defined by the corrugations to the edges of the pad 57, and down the edges into the reservoir 60.

An air stream through the humidifier passing from the air inlet chamber 4 through the evaporative matrix assembly 6, fan chamber 8 and air outlet chamber 10 is created by centrifugal fan 26. The air is initially filtered by the filter 22 and then passes through the evaporative matrix pad 57 where it picks up moisture from the surface of the pad and is thereby humidified. The air then passes through perforated baffle plate 24, into the fan 8 and out through the air outlet chamber 10 and air outlets 18.

The air outlets may simply be vented into the plenum space above the ceiling and other means employed for circulating the humidified air into the room below, or the air outlets 18 may be connected via trunking or conduit (not shown) to direct the humidified air into a desired room, for example via ceiling grilles.

As water is evaporated from the evaporative matrix pad 57, and water is bled off to drainage line 70, the level of water in the reservoir 60 falls. The falling water level is detected by the water level detector 68 and fresh water is introduced through water inlet opening 64.

As a further means of preventing microbial contamination of the water in the reservoir, a strip of fabric coated with a sparingly soluble microbicide such as a silver salt can be mounted within the reservoir. The microbicidal fabric typically is provided as a disposable element which can be replaced as and when required.

At regular intervals, determined by a timer within a controller 76 located within the pump housing 36, the water within the humidifier is completely replaced. Thus the solenoid valve 40 is switched so as to direct all water to drainage line 70, and water is sucked out of the reservoir via the solenoid by means of a sump pump 74. Fresh water is then introduced through the float valve controlled water inlet.

The operation of the humidifier can be controlled locally by means of a humidistat or by manually operable controls mounted near to the humidifier. For example, the manually operable controls can comprise a temperature sensor for controlling an in-line heater, or a manually operable humidistat, or the speed of the fan. he local controls can also include an on- off button. Alternatively the humidifier can be controlled remotely by means of a building management system (BMS). Thus, the humidifier can be provided with a microprocessor-based controller (not shown) which can be linked in to the BMS or can be programmed locally. The controller can control a single humidifier, or multiple humidifiers to operate as a single zone, or example in open-plan offices. Alternatively, control of the humidifier can be simplified by fixing certain parameters, such as the duration of the drainage/flushing cycle, in the factory such that subsequent adjustment would need to be carried out by service engineers.

The advantages of the humidifier of the present invention arise from its ability to be incorporated into a plenum space of ceiling void thereby remaining hidden, and not taking up valuable floor or wall space in the room. It will readily be apparent that numerous modifications and alterations can be made to the humidifier shown in the accompanying drawings without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.

Claims

1 . A humidifier adapted to be mounted in or on a ceiling; the humidifier comprising a housing; mounting means for mounting the housing on or in the ceiling; a fan for drawing air through the humidifier from an air inlet to an air outlet; an evaporative matrix disposed between the air inlet and air outlet, and water supply means for supplying water to the evaporative matrix such that air passing from the air inlet to the air outlet is humidified by evaporation from the matrix.

2. A humidifier according to claim 1 wherein the housing is adapted to be mounted in a plenum space so as to be substantially flush with the underside of a false ceiling defining the lower limit of the plenum space.

3. A humidifier according to claim 1 or claim 2 wherein the mounting means takes the form of brackets for suspending the housing in a large ceiling void or plenum space so as to be flush with the lower surface of the false ceiling.

4. A humidifier according to any one of the preceding claims wherein the mounting means is adapted to allow the housing to be connected directly to the underside of a floor, ceiling or roof above the plenum space.

5. A humidifier according to any one of the preceding claims wherein the housing, when mounted in or on the ceiling, has a maximum horizontal length greater than its maximum height.

6. A humidifier according to any one of the preceding claims wherein the housing has, in horizontal sequence, an air inlet; an air inlet chamber; a filter housing; an evaporative matrix; a fan chamber; an outlet chamber; and at least one air outlet.

7. ^~ A humidifier according to any one of the preceding claims wherein the housing has a plurality of air outlets.

8. A humidifier according to any one of the preceding claims wherein the housing is provided with trunking connectable to the or each air outlet so as to distribute humidified air to different parts of a room or different rooms in a building.

9. A humidifier according to any one of the preceding claims wherein the air inlets and/or the air outlets are each mounted on respective removable mounting members.

10. A humidifier according to claim 9 wherein the mounting members take the form of housing end plates.

1 1 . A humidifier according to claim 10 wherein the housing end plates are removably secured to a main body of the housing by means of fastening elements.

12. A humidifier according to any one of the preceding claims further comprising heating means for heating humidified air from the humidifier.

13. A humidifier according to claim 12 wherein the heating means takes the form of an in-line heater disposed within the housing.

14. A humidifier according to any one of the preceding claims which is serviceable from the underside thereof while mounted in or on the ceiling.

5. A humidifier according to claim 1 4 wherein the underside of the housing has at least one access hatch or door to permit access to the interior of the housing for servicing purposes.

6. A humidifier according to any one of the preceding claims wherein the evaporative matrix is mounted in a supporting structure which is removable from the housing.

7. A humidifier according to claim 1 6 wherein the supporting structure comprises a supporting framework, the evaporative matrix being removably mounted in the upper part thereof, and a water reservoir or drip tray being defined by the lower part of the supporting framework.

1 8. A humidifier according to any one of the preceding claims wherein water is supplied to the matrix from water dispensing means arranged above the matrix.

19. A humidifier according to claim 1 8 wherein the water dispensing means takes the form a spray bar in the form of a length of tubing, closed at one end and having a plurality of openings along its length through which water may pass.

20. A humidifier according to any one of the preceding claims wherein the evaporative matrix comprises an inert support material coated with a water-insoluble substance having high water retention capacity.

21 . A humidifier according to any one of the preceding claims wherein the evaporative matrix takes the form of a plurality of corrugated sheets of the water absorbing material, each sheet lying in an upstanding plane.

22. A humidifier according to claim 21 wherein the corrugated sheets have ribs which are inclined with respect to the horizontal.

23. A humidifier according to claim 22 wherein the ribs of adjacent sheets are inclined in opposed directions.

24. A humidifier according to any one of claims 21 to 23 wherein the sheets are loosely packed within the framework.

25. A humidifier according to any one of the preceding claims wherein a perforated baffle is positioned downstream of the evaporative matrix, but between the evaporative matrix and the fan.

26. A humidifier according to any one of the preceding claims wherein a spray bar or spray head above the evaporative matrix is supplied by a water line which is fed from a reservoir beneath the evaporative matrix.

27. A humidifier according to claim 26 wherein a recirculation pump is provided for recirculating water between the reservoir and the spray bar or spray head.

28. A humidifier according to claim 26 or claim 27 wherein a valve means is interposed between the reservoir and the spray head for controlling flow of water to the spray head.

29. A humidifier according to claim 28 wherein the valve means has an inlet and two or more outlets such that it can direct water either to the spray head or spray bar, or to waste.

30. A humidifier according to claim 28 or claim 29 wherein the valve means is linked to a control means incorporating a timer such that at regular intervals the reservoir can be emptied completely and a fresh volume of water introduced into the humidifier.

31 . A humidifier according to any one of the preceding claims wherein a solid phase disinfecting or sterilising medium is mounted within the reservoir.

32. An evaporative matrix assembly for use in an evaporative humidifier as defined in any one of the preceding claims, the evaporative matrix assembly comprising a supporting framework having an evaporative matrix material disposed in the upper part thereof, and a water reservoir or drip tray disposed in the lower part thereof.

33. A method of humidifying air in a room, which method comprises mounting an evaporative humidifier as defined in any one of the preceding ciaims in or on a ceiling of the room, passing air into an inlet of the humidifier, humidifying the air and directing the humidified air into the room.

34. A ceiling having fitted therein or thereon a humidifier as defined in any one of the preceding claims.

35. A humidifier substantially as described herein with reference to the accompanying drawings.