GB2210156A - Heat-exchanging ventilation apparatus - Google Patents

Abstract

Heat-exchanger ventilation apparatus for a room or like building interior, comprising a multiple glazed window arrangement and/or a window frame arrangement and/or a duct member locatable in a window pane with two separate air-flow passages between the panes 11 to 15 Fig 4 of the window or two separate air spaces within the window frame 55 fig 14 and/or duct member with said separate passages being in heat exchanging relationship and being such as to permit outflow of interior air and inflow of exterior air with air displacement means being provided to effect said air flows. <IMAGE>

Description

HEAT-EXCHANGING VENTILATION APPARATUS The present invention relates to heat-exchanging ventilation apparatus for location in a window space and which will preferably also function as a window permitting passage of light and is primarily concerned with the domestic market.

The apparatus according to the invention is intended to permit the removal of stale, warm air from a room - which will normally be a centrally heated room - and the replacement with fresh air which is warmed or heated air using energy from the warm air of the toom.

With most central heating systems, air in a room is heated by radiators and, for reason of economy, any gaps in window frames or doors are preferably minimized to reduce the disadvantageous effect of cold draughts. Such virtual sealing of a room often leads to a build-up of carbon dioxide, methanes, cooking smells, bacteria and smoke and this is clearly undesirable.

Hitherto ventilation systems for providing fresh air in a room involved either the opening of a window or a door, the SW5tChtilg~víì of ar. extractor fan which leads directly through a wall or window pane to the exterior atmosphere. All such ventilation means simply result in the warm or heated air of the room passing directly to atmosphere and are very uneconomical.

It is an object of the present invention to. provide apparatus which permits the reclamation of heat from air extracted from a room by preheating the incoming fresh air, and the apparatus is intended to be particularly acceptable: since it is provided in the form of a window and locatable in a window space without provision of a bulky separate heat exchanger which would require additional provision of additional wall passages and involve further space to be occupied.

In its broadest and general aspect, the present invention comprises a multiple glazed window arrangement with two separate air-passages therethrough in heat-exchanging relationship to permit outflow of interior air and inflow of exterior air with air displacement means being provided to effect said air flows.

According to the present invention heat-exchanging ventilation apparatus is provided in the form of a window and comprises a plurality of adjacent transparent or translucent sheets, spaced apart to define air-flow passages therebetween, a first air inlet on one first side of the apparatus for cooler air and a first air outlet on the opposite, second side of the apparatus with both said first inlet and first outlet being in communication via at least one first air-flow passage, a second air inlet on said second side of the apparatus for hot or heated air and a second air outlet on said first side of the apparatus with both said second inlet and said second outlet being in communication via at least one second air-flow passage with at least said first and second air-flow passages being in heatexchanging interrelationship, and air displacing means for causing the flow of air through said air-flow passages.

Whilst an arrangement with two sheets or panes is possible, it is preferred that three, five or seven panes be used so as to achieve a one, two or three pass heat exchanger with five sheets of panes being the likely preferred.

As mentioned, the apparatus is intended to function as a window permitting the passage of light and is intended to be located in a normal or standard window space as provided in domestic or other premises. Thus, the sheet material is referred to as being transparent or translucent or may be any other glazing material should, for any reason, non-transparent or opaque material be envisaged - such as mirrored glass and such is intended to be also within the scope of the present invention.Normally the sheets will be of glass, such as float glass or sheets of polycarbonate or other translucent or transparent plastics material or the like or a combination thereof e.g. the inner and outer sheets of a three, five or seven sheet arrangement may be of glass whilst the sheets located therebetween may be of plastics material such as polycarbonate with appropriate spacing members between the sheets, if required to reduce, any bowing effect. Desirably, the use of glazing sheets which have improved heat transference characteristics is to be selected. For applications where clarity of vision through the window is not important, a "twin-wall" ribbed polycarbonate might be considered for improved strength.

The sheets will be spaced apart so as to achieve optimum performance having regard to pressure drop and heat exchanger efficiency. In one embodiment it is envisaged the sheets be of 4 mm float glass and 3 mm polycarbonate sheets might be used with a possible spacing of 3 to 6 mum., although any desired spacing can be used.

The sheets will preferably be mounted in a frame which should be of material to fit in with modern window systems and may be moulded such as extruded frame of, for example, wood, aluminium or UPVC - the rigidity of aluminium indicating that it might be a preferred choice.

Suitable inlet and outlet means will be provided.

Manifold or ducting means will be provided with a multi path heat exchanger arrangement so as to ensure that flow of the heated or- unheated air is achieved with minimum pressure drop and without mixture of the inlet and outlet air flows.

The ducting means may be provided by passages or recesses in the actual frame which holds the sheets or may be inserted therein or thereover or the sheets may be formed such as by 0 having corner portions cut at an angle such as 45 with suitable passage closure members being provided to separate the airflow.

In a preferred embodiment, where plurality of vertically disposed sheets are proposed, in a rectangular frame, manifold means are provided as the vertical sides of the frame to ensure the requisite alternate flow of incoming and outgoing air.

The ducting means may be formed in the frame by the vertical sides each being of generally U-section with flat bottom and when viewed from above and one end. The passage defined by each U-section is divided by a horizontal partition wall which separates incoming air from outgoing air. The panes sealingly abut the partitions and passage closure means are provided at the the ends of alternate passages extending from the partition to a horizontal cross-piece i.e. along half of the side of alternate passages, to keep the incoming and outgoing flow passages separate from each other. The opposite manifolds are alternate handed to achieve the requisite ducting effect of flow generally diagonally of the panes.

The air displacing means will preferably be two fans which may have a single drive motor - or other devices such as air movers which operate as a result of compression of air although such may prove too noisy. The fans will preferably be adjusted to effect required air changes, for example, two to three air changes per hour in rooms such as kitchens or bathrooms in the range of 10 - 15 cubic meters.

As might be expected, effectiveness increases as the number of passages increases and there may be an efficiency dependence on mass flow rate and overall temperature difference.

In tests, a five pane arrangement was 1.8 times effective from heat exchange point of view as that of a three pane arrangement whereas the effectiveness of a seven pane arrangement was only 1.2 times that of a five pane unit.

It is considered preferable that equal inlet and outlet air-flow rates be provided.

Suitable filters on the inlet and/or outlet ducts or regions may be provided to remove contaminants from the air and means for removing moisture may be provided on one or both air flow passages, as desired. Additionally, suitable passages may be provided in the lower frame or elsewhere so as to permit the drainage of any condensation which might actually occur.

Condensation drain means might especially be provided in the exhaust passage where condensation is more likely to occur.

In a preferred embodiment a filter such as activated charcoal may be used and electric central means for the fans be provided to periodically reverse the fan driver to effect cleaning and/or drying or removal of moisture from tbe filters.

It is desirable to design the apparatus to achieve minimal pressure drop and the edge details of the entry and exit for the outlet passages and the flow ducting means require particular design attention in this connection.

The sheets will preferably be parallelly arranged extending in vertical planes and spaced apart, e.g.in the order of perhaps 3 to 6 mm or dimensions approximately equivalent to the width of the sheet being used although appropriate changes can be effected to achieve desired air flow etc as regards in the dimension of the spacing. The edges around the sheets will be sealed by suitable means such as high density selfadhesive tapes or foam strips or preferably a seal of a foamfilled tubular neoprene type. Preferably the seal is of a foam-filled tubular neoprene type.

Any drainage ducts must be kept as small as possible to reduced air flow escaping by such by-pass route.

In a domestic environment or in hospitals, schools or other public buildings, it is to be expected that occasional cleaning will be required to permit the removal of dust, smoke, fat, bacteriological growth etc. and it will be desirable for the sheets to be so mounted: as to be readily dismounted or dismountable to permit such cleaning. Suitable clamping means or the like will be preferably provided and operable to ensure an even pressure when in the clamp position and hence a good seal around the edge of the sheets and, preferably, a "toggle" type of action device is preferred to a simple screw down clamp.

As mentioned, if the apparatus is used in a kitchen or bathroom it is to be expected that large amounts of condensation will occur in the cooling airstream and suitable gaps in the foam strip along the frame or at the bottom edge of the sheets would allow water to escape although should not permit the escape of too much air therethrough.

In one arrangement with three or more sheets, each air-flow passage comprises a plurality of passages inters connected in series with the different flow-passages being alternately arranged.

It is considered highly desirable, however, for the arrangement of one air flow to be split amongst separate passages to achieve a parallel flow arrangement and, similarly, the other air flow will be split amongst the separate passages between the sheets to achieve parallel air flow.

The inlet flow and outlet flow may be in the same direction or in opposite directions.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which : Fig. 1 is a schematic illustration of an embodiment of the invention showing the overall outline of a complete heat-exchanging and ventilation apparatus; Fig. 2 is a schematic vertical section through one fan housing section of the apparatus of Fig. 1 which draws air from the room to outlet to the exterior; Fig. 3 is a schematic elevational view from inside of a room looking out with the fan housings removed and showing the horizontal partitions in the vertical, hollow side frames forming the ducting manifolds; Fig. 4 is a section on the line X-X of Fig. 3, showing vertical panes, the horizontal partition and end closures for some of the flow passages in one ducting means;; Fig. 5 is a section on the line Y-Y of Fig. 3 showing similar details as Fig. 4 but of the other, oppositely arranged ducting means; Fig. 6 is a schematic horizontal section through a ventilation apparatus as that of Figs. 3 to 5 illustrating the air-flow paths required with appropriate ducting means.

Fig. 7 is a schematic elevation of the air-flow passages between the sheets viewed end-on and illustrating the air-flow paths therethrough; Fig. 8 is an elevation of a heat exchanging ventilation apparatus; Fig. 9 is an exploded schematic perspective view showing the passages through a five sheet ventilation apparatus with suitable manifold means; Fig. 10 is a schematic plan view illustrating the heat exchange principle and wherein heated and unheated air flows, driven by fans (A and B) are separated by a single glass sheet C which is the heat exchange material - additional sheets not being illustrated; Fig. 11 is a cross-sectional detail of one prototype arrangement; Fig. 12 is a cross sectional detail of an embodiment with drainage areas; and Fig. 13 are schematic illustrations of alternative possible air-flow paths.

Fig. 14 is a schemative elevation illustrating a different and simpler embodiment wherein two separate air passages are provided in a rectangular window frame and are in heat exchanging relationship because of a thermally conductive separating wall; Fig. 15 is a plan view of the frame of Fig. 14 illustrating two motors for moving air in opposite directions in the passages and indicating the respective inlets and outlets; Fig. 16;is a section on the line X-X of Fig. 14.

A transparent air heat exchange or heat-exchanging ventilation apparatus 1 is illustrated in Figs. 1 and 2 and; comprises a frame 2 (of wood or extruded aluminium or plastics material) suitably shaped and dimensioned as to be locatable in a window opening. The frame has a plurality, preferably five, of spaced apart glazing sheets referenced generally by reference number 3, which are sealed at their edges with the frame 2 by suitable sealing means. The glazing sheets 3 may be of glass or polycarbonate or different arrangements or -combinations thereof. Apart from transparent or translucent glazing sheets mirrored glass or possibly one-way mirrored glass might be used, as desired.

The vertical side frame members 2' and 2" are of hollow channel section and have suitable ducting means therein to ensure the outgoing room air and the incoming fresh air-flows do not mix but rather pass through the flow passages defined between the glass sheets 3 in heat exchanging relationship, i.e. preferably in alternate disposition.

Whilst five sheet arrangements are preferred the apparatus of Fig. 1 is merely a schematic illustation of the general disposition of the various parts.

Fig. 2 is a vertical section through a left-hand end portion of the apparatus of Fig. lwherein a fan 5 is illustrated driven by motor 6 and energizable by on/off switch 7 with the electric circuitry not shown. A filter medium of known kind e.g. activated charcoal is disposed beneath the motor 6 in the air flow passage leading thereto so that air from the room R maybe drawn through the inlet duct at the bottom through the filter 8 and displaced through the air flow passages between sheets 3.

A similar fan, drive motor and operating switch arrangement is provided on the other vertical side for-the intake passage for drawing air from the outside 0 of the room through the passage between sheets 3 to the inside and suitable filter means anchor moisture removing means (nbt shown) may also be provided in the intake or inlet region for such. Whilst not illustrated, other means for removing moisture from the air might also be provided in the region of filter or the filter itself may also function to remove moisture. A suitable housing 9 encloses the filter and motor etc. and has an inlet opening 10 with possibly grills thereon in the lower region.

In the embodiments of Figs. 3 - 7, the air displacement means and filters etc. are not shown for the sake of clarity and five glazing sheets 11 - 15 are illustrated in Fig. 3 and are arranged parallel and in vertical planes in a schematically illustrated frame 2, 2', 2" and suitable sealing means will be provided at:the edges of the sheets as required. The frame will preferably be extruded metal or plastics xith appropriate channels for location of the sheets 11 - 15.

The vertically extending frame sides 2', 2" are formed of channel section with suitable ribs and spacers so as to support the sheets 11 - 15. Each side section 2', 2" forms a manifold means 16, 17 for ducting the air flows to the appropriate passages between the sheets 11 - 15 and thence to room or exterior atmosphere as appropriate. The manifold means 16, 17 are oppositely arranged as will be apparent from the drawings. Half-way up each'charnel section of sides 2' ,2" a horizontal dividing wall or partition 18, 19 respectively, is provided sealed to the channel walls to divide the charnels into upper and lower halves.

In each side 2', 2", passage closure portions or members are provided to close-off access to the upper or lower manifolds from the;pflssages between the sheets 11 - 15. More specifically, manifold 16 has passage closure members 20 and 21 closing the end of the first and third air flow passages, counted from the left, from the upper manifold duct 22.

Manifold 16 has closure members 23, 24 closing the end of the second and fourth air flow passages counted from the left-hand, from the lower manifold duct 25.

Manifold 17 is an almost identical arrangement except that upper passage closure members 26, 27 are located to close the first and third air flow passages counted from the left of Fig. 5, from the upper manifold duct 28 and lower closure members DO, 30' are located to close the first and third air flow passages from lower manifold duct 29. In Fig. 3 only closure members 20 and 30' are illustrated for the sake of clarity.

Additional, vertical baffle plates (not shown) are provided in the upper and lower ducting passages extending parallel to the sheets 11 - 15 on each side to ensure the air flows between the sheets as required and does not by-pass such heat exchanging region. Furthermore said additional baffle plates avoid unnecessary cavities and, depending on design features separate the inlet and outlet ducts in the fan housings 10, 10' from the main air ducting means 16, 17.

(Two vertical baffles or dividing walls 39 are illustrated in Fig. 7).

For each ducting means 16 and 17, the inlet and outlet passages thereto (not shown) are on opposite sides thereof and in an upper region thereof. Of course, because of opposite inflow and outflow the inlets and outlets of the two ducting means 16, 17 are oppositely identified. The fan housings 10, 10' lead air either to the inlet to ducting means 16 or from the outlet from ducting means 17 respectively, and which are both located on the room side R of the apparatus.

Suitable housings or covers (not shown) are provided on the exterior side of the apparatus frame to duct incoming, fresh air from a lower part or a frame, upwardly to the inlet of ducting means 17 or to duct outgoing stale air from the outlet of ducting means 16 in an upper region of the frame downwardly to a lower region of the frame in a protected manner to avoid the ingress of rain or any disadvantageous effect of strong winds.

In explanation of the air flows through ducting means 16, 17, one air flow (stale air) enters an upper region of ducting means 17 from room R and the fan and enters through opening 31 to the passage between sheets 11 or 12 and traverse such and exits therefrom through opening 32 in ducting means 16 and is then ducted to opening 33 leading to the passage between sheets 13, 14 and flows generally diagonally upwardly to opening 34 in ducting means 17 and thence to outside.

The other air flow (intake fresh air) enters from outside 0, into upper region of ducting means 16 and enters the passage between sheets 14, 15 via opening 35, traverses this heat exchange passage and exits via opening 36 in ducting means 17, and is ducted to opening 37 to the passage between sheets 12, 13 and flows upwardly to opening 38 and thence to outlet to room R.

Various modifications and changes may be made to the arrangements specifically described, such as suggested in the introduction of the specification, whithout departing from thescope of the present invention.

In Figs. 11 and 12, part of a prototype construction is illustrated comprising five glazing sheets 40 provided mounted in frame 41 and secured in position by clamping frame 42 against backing plate 43. Sealing and spring strips 44 of foam material are located between sheets 40. Fig. 12 iS modified by omission of two strips and provision of drainage ducts 45 into two spaces between the sheets 40.

An alternative test prototype is schematically illustrated in Fig. 13 having hot air inlet and outlet ducts 46,47 and cold air inlet and outlets 48,49. In the manifold means (not shown) the air flows 50,51 are split and flow in parallel in opposite directions between sheets 52.

In the embodiment schematically illustrated in figs. 14-16, instead of providing air-flow passages between window panes as in the previous embodiments, the air flow passages are provided in tubular frame members which are preferably arranged as a rectangular frame to the window pane W which may be a single sheet.

A rectangular and tubular window frame 55 is illustrated and is formed from four hollow rectangular tube sections 56 preferably of extruded plastics material and joined together in the corner regions by mitre joint connections (not shown). The hollow interior of tube sections 56 is provided with two channels or retaining projections 57,57., 58,58 into which there may be slid, to be retained therein, sheets 59 of thermally conductive material such as copper or aluminium which is preferably corrugated to improve the heat transfer characteristics. The sheets. are provided along the length of all sides of the frame 55 so as to divide the frame into an inner flow passage 60 and an outer flow passage 61 separated from each other by sheets 59.Inlet and outlet openings 62, 63 are provided in opposite sides of tube section 56 adjacent each other for inner passage 60 whilst inlet and outlet openings 64, 65 are provided in opposite sides of outer flow passage 61 and a partition wall 66,67 provided extending to separate the inlet and outlets and permit air to be pumped through.

Two electric motors with fans 68, 69 are provided respectively for drawing air through passage 61 and blowing air through passage 60. Suitable dividing walls are provided in the plastics housings to ensure separation between the motor passages to ensure two separate air flows. The housings will preferably be shaped to protect the motors from rain. In a preferred embodiment, both the motors are located on the normally outside of the frame 55 to reduce the noise in the room.

One air passage will have warm air flowing from the interior of the room with which the frame is associated whilst the other passage will have fresh air from the exterior passing therethrough and into the room. The fresh air inlet will preferably be adjacent the room air outlet and the air flows be in opposite directions to ensure optimum heat transfer.

Instead of a rectangular frame as illustrated, other shapes are possible. It is even envisaged within the scope of the invention for the heat-exchanging ventilation apparatus to comprise an elongate member locatable as-a hollow side, top our middle dividing portion of a window or window frame with a dividing wall forming two separate air passages being of thermally conductive material to facilitate heat transfer.

Suitable inlet and outlet passages may be provided at opposite ends of the elongate member for each passage with motors and fans to enable air to be drawn from the room and air to be drawn from the outside. Whilst a single motor might be possible, two motors are preferred.

Fig. 17 illustrates such an elongate member 70 as a dividing frame between two window panes W1, W2 located thereagainst by means (not shown) and having inlet and outlet passages and electric fan motors (not shown) as will be apparent opposite direction of flow is preferred.

Claims (25)

1. Heat-excnanger ventilation apparatus for a room or like building interior, comprising a multiple glazed window arrangement and/or a window frame arrangement and/or a duct member locatable in a window pane with two separate air-flow passages between the panes of the window or two separate air spaces within the window frame and/or duct member with said separate passages being in heat exchanging relationship and being such as to permit outflow of interior air and inflow of exterior air with air displacement means being provided to effect said air flows.

2. Heat-exchanging ventilation apparatus in the form of a window and comprising a plurality of adjacent transparent or translucent sheets spaced apart to define air-flow passages therebetween, a first air inlet on one first side of the apparatus for cooler air and a first air outlet on the opposite, second side of the apparatus with both said first inlet and first outlet being in communication via at least one first air-flow passage, a second air inlet on said second side of the apparatus for hot or heated air and a second air outlet on said first side.iof the apparatus with both said second inlet and said second outlet being in communication via at least one second air-flow passage with at least said first and second airflow passages being in heat-exchanging interrelationship, and air displacing means for causing the flow of air through said air-flow passages.

3. Apparatus as claimed in claim 2, in which the glazing sheets are mounted in a rectangular frame and the normally vertically extending side frame members have ducting means therein to duct the separate air flows to and from the air flow passages between the glazing sheets and the inlets and outlets.

4. Apparatus as claimed in claim 3 in which each side frame member is a hollow member of substantially U-shaped section when viewed from above with the shanks of the U extending towards the sheets and wherein the sheets extend parallely into the space between the ends of the shanks and the upper and lower edges are sealed relative to the upper and lower frame members; dividing wall means and passage closure means being provided in said frame member to effect the required ducting.

5. Apparatus as claimed in any of claims 2 to 4, in which five sheets are provided.

6. Apparatus as claimed in claims 4 and 5 in which each frame member has an inlet and outlet for its associated airflow and located,for example, in an upper region of said member, in which a horizontal dividing wall separates the interior of the frame member into upper and lower chambers with said inlet and outlet leading into said upper chamber and with at least one vertical separator baffle extending from the region of one sheet to the web of the U section to prevent the associated air flow from by-passing the two air flow passages between the sheets which it should traverse in opposite directions, the reversal and return of each: 'air flow being effected by the ducting means in the lower half of the opposite frame member; and in which passage sealing or closure means are located at the ends of pairs of sheets to close one or the other half thereof from the ducting means such that the air flows alternate between the sheets to achieve optimum heat exchange effect,

7.Apparatus as claimed in claim 6, in which the passage closure means in each upper and lower halves of each frame member are alternately disposed so as not to be contiguous and so as to have a through flow passage adjacent at least one side in staggered arrangement relative to the closure means of the upper and lower halves, and in which the closure means of the two frame members are oppositely arranged so that each air flow enters its associated frame member, flows downwardly through an air flow passage between two glazing sheets enters the lower chamber of the opposite frame member acting as ducting means and is ducted past the closed lower half of the adjacent air flow passage to enter and flow from the lower half of the next-but-one air flow passage between two further sheets and to flow upwardly to the exit opening leading to the ducting means in the first mentioned frame member and thence to the outlet therefrom or other means.

8. Apparatus as claimed in any of claims 2 to 7, in which two fans and drive motors are provided to effect displacement of said two air-flows.

9. Apparatus as claimed in at. least claims 3 and 8, in which' one of said fan and motor and control means therefor is mounted on the normally interior side of each said vertical side frame member and further ducting means are provided to communicate with the associated ducting means of the respective said frame member.

10. Apparatus as claimed in at least claim 8, in which said fans are operable in opposite directions to effect, in use, inflow and outflow of air from a room (R) and control means are provided to periodically reverse the flows to clean any filters or moisture removal means which may be provided.

11. Apparatus as claimed in at least claim 5, wherein four air-flow passages are provided between the sheets and the ducting means are provided to cause each air-flow to split into divided flows which pass in the same direction through alternately located air flow passages between the sheets and, preferably the intake and outlet flows are in opposite directions through the air flow passages between the sheets.

12. Apparatus as claimed in any of claims 2 to 11, in which drain ducts are provided at the bottom of at least one air flow passage, preferably the exhaust air streams for the discharge of any condensation which may accummulate.

13. Apparatus as claimed in any of claims 2 to 12, in which air filter and/or moisture removal means are provided in the inlet regions.

14. Apparatus as claimed in claim 13, in which activated charcoal is provided as the moisture removal means.

15. Heat exchanging ventilation apparatus substantially as herein described with references to the accompanying drawings.

16. Apparatus as claimed in any of claims 1 to 15, in which at least three sheets are provided and the two outermost sheets are of glass and the inner sheet or sheets are of polycarbonate or other plastics material to act as the heat exchange means.

17. Heat-exchanging ventilation apparatus for a room or other interior space of a building, comprising a duct means or member locatable in a window space and having two separate air-flow passages extending therealong,each passage having an inlet and outlet opening on opposite sides of the duct member, a partition or dividing wall of thermally conductive material being provided between and separating said two air flow passages, and air displacement means being provided to effect said air flows.

18. Apparatus as claimed in claim 17, in which said duct means comprise a hollow window frame for receiving window panes and/or a hollow window surround for receiving a window frame, and/or an elongate side frame or window dividing frame which is preferably rectilinear.

19. Apparatus as claimed in claim 17 or 18, in which said dividing wall or walls is or are made of copper, aluminium or the like conductive material which is preferably corrugated, finned or the like to improve heat transfer.

20. Apparatus as claimed in any of claims 17 to 19, in which the dividing wall is received in channels or between parallel projections on opposite sides of each duct member which is preferably of plastics material.

21. Apparatus as claimed in any of claims 17 to 20, in which the air displacement means is an electrically driven fan or fans - preferably one for each air-flow passage.

22. Apparatus as claimed in any of claims 17 - 21, in which the fans are such as to displace the air flows in opposite directions with the fresh air inlet being adjacent the room air outlet to the exterior.

23. Apparatus as claimed in claim 20, in which a channel or projections are provided on at least one surface of the duct member for receiving the edge of a window pane for retention therein.

24. Apparatus as claimed in any of claims 17-23 in which the duct means is a rectangular hollow frame and the corners are preferably mitred.

25. Apparatus substantially as herein described with reference to the accompanying drawings.