Although it is possible to provide apertures in walls or windows of buildings of a non-circular shape, such as a square apertures, it is often found to be easier and more convenient to produce a circular aperture, particularly where the aperture is of a relatively small diameter such as a five or six inch diameter aperture.

It is already known to provide heat exchange ventilators for fitting into apertures in walls or windows of buildings but often such known heat exchange ventilators are not of a design which is suitable for fitting into a circular aperture of relatively small diameter and is capable of providing adequate volumes of air flow and efficiency of heat exchange between the outgoing and incoming air.

The object of this invention is to provide a heat exchange ventilator in which the above problems are al leviated.

According to this invention, a heat exchange ventilator for mounting in a circular aperture in a wall or window of a building comprises a heat exchange unit of

circular cross-sec ion, the unit having at least two concentric annular passages extending for a major portion of the length of the unit through which outgoing and incoming air flows, wherein the air flow in adjacent passages are in opposite directions relative to the length of the unit.

Preferably, the unit has a plurality of concentric annular passages.

Preferably, also, each annular passage has an inlet at one end of the unit and an outlet at the opposite end of the unit which are angularly spaced-apart.

Each annular passage, preferably, has two angularly spaced-apart inlets and two angularly spaced-apart out lets. Preferably, the two inlets are diametrically opposite one another and the two outlets are diametr cally opposite one another.

Preferably, also, the two diametrically opposed inlets and the two diametrically opposed outlets are angularly spaced-apart by ninety degrees.

The air in each passage, preferably, flows in a he1 ical path.

Preferably, each passage is provided with air flow direction control means for producing air flow in a helical path over the length of the passage.

Preferably, also, the air flow direction control

means comprises an air flow guide in the form of a helix extending along the length of the passage.

The air flow guide is, preferably, an insert located in the passage between the inner and the outer wall thereof.

Alternatively, the air flow guide may be a helical projection formed on the inner and/or the outer wall of the passage.

Preferably, the walls of the passages are formed by winding strips of sheet material in a helical path to produce a cylinder and the helical projection forming the air flow guide is formed by interengaging formations on the overlapping or interconnecting edges of the strip.

Manifold means is, preferably, provided at each end of the unit to collect and separate the incoming and outgoing air from the inlets and outlets of each of the passages.

Preferably, fan means is provided for drawing incoming air and expelling outgoing air through the associated passages in the unit.

Preferably, also, the fan means comprise two fans disposed at opposite ends of the unit.

Each fan is, preferably connected to the manifold at the associated end of the unit. Preferably, a single driving means is provided for driving each fan and the two fans may be connected

together by a drive shaft extending through the centre of the unit.

A preferred embodiment of this invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings of which:-

Figure 1 is a partly sectioned side view of a heat exchange ventilator with parts omitted for the sake of clarity;

Figure 2 is a partly sectioned diagrammatic side view of a heat exchange unit of the heat exchange ventilator; Figure 3 is an end view of one end of the heat exchange unit;

Figure 4 is an end view of the opposite end of the heat exchange unit; Figure 5 is a perspective view of one end of the heat exchange unit; and

Figure 6 is a perspective view of a partly dismantled section of the heat exchange unit.

Referring now to the drawings, a heat exchange ventilator indicated generally at 10 for mounting in a circular aperture (not shown) of for example, five or six inches diameter, in a wall or window of a building (not shown) to provide ventilation and extract heat from the outgoing air to raises the temperature of the incoming air comprises a heat exchange unit 12 located in and extending through the aperture. The heat exchange unit 12 comprises

a series of concentric tubes 14 formed of thin sheet metal or foil which when assembled together form a plurality of concentric annular passages 16 through which incoming or outgoing air passes along the length of the unit 12. The outgoing air flows along alternate passages 16 to the incoming air to optimise heat transfer therebetween.

Each passage 16 is provided at one end with two inlet openings 18 each extending through a ninety degree sector and the two ninety degree sector openings are diametrically opposed. The remaining diametrically opposed ninety degree sectors at said one end of the passage 16 are closed by sealing means such as inserts or blanking plates 20. The passage 16 is provided at the opposite end with two similar outlet openings 22 which again extend over diametrically opposed ninety degree sectors, the remaining ninety degree sectors again being closed by inserts or blanking plates 20 but the two inlet openings 18 and the two outlet openings 22 are angularly spaced-apart by ninety degrees so that air can not flow straight through the passage 16 but must have a helical form whose angle of rotation is at least ninety degrees. This thus increases the length of the flow path of the air through the passage 16 and produces a corresponding increase in the efficiency of the heat transfer from the outgoing air flow to the incoming air flow in the adjacent passage 16.

Each passage 16 is provided with an air flow guide 24 in the form of a helical insert which increases the effective length of the flow path of the air through the passage 16 by causing the air flow to complete several rotations during the flow from the inlet 18 to the outlet 22. Where the tubes 14 are formed by winding strips of sheet metal or foil in a helical path on a mandrel or former the air flow guide 24 is conveniently formed by the interengaging formations on the overlapping or interconnecting edges of the strips.

A manifold 26 is provided at each end of the heat exchange unit 12. The manifold 26 at said one end of the unit 12 provides connections between the inlets 18 in the two diametrically opposed ninety degree sectors indicated generally at 28 for the outgoing air, and connections between the outlets 22 in the two diametrically opposed ninety degree sectors indicated generally at 30 for the incoming air shown in Figure 3 of the drawings.

The manifold 26 at said opposite end of the unit 12 provides connections between the inlets 18 in the two diametrically opposed ninety degree sectors indicated generally at 32 for the incoming air, and connections between the outlets 22 in the two diametrically opposed ninety degree sectors indicated generally at 34 for the outgoing air shown in Figure 4 of the drawings.

A fan 36 is provided at each end of the unit 12 and

is connected to the associated manifold 26, the fan 36 at the inner end of the heat exchange ventilator 10 drawing incoming air through the unit 12 and the fan 36 at the outer end of the heat exchange ventilator 10 drawing outgoing air through the unit 12. The fans 36 are drivably connected together by a drive shaft 38 extending through the centre of the unit 12 of the heat exchange ventilator 10 which is driven by a single electric motor 40.

The formation of the heat exchange unit 12 as a cylinder with a plurality of annular concentric passages 16 makes the heat exchange ventilator 10 particularly suitable for mounting in a small diameter circular aperture in the wall or window of a building whilst providing adequate volumes of air flow and efficient heat exchange between the outgoing and incoming air.

In a modification, an alternative method of driving the interconnected fans in the heat exchange ventilator 10 to either replace or supplement the action of the electric motor 40 consists of providing an axial flow fan at the interior end, a centrifugal fan at the exterior end and spacing the outlet from the centrifugal fan a distance of, say, 100 mm. from the external surface of the wall of the building. Wind blowing onto the wall produces rotation of the axial flow fan which acts as a windmill and produces corresponding rotation of the centrifugal fan to draw air from the building through the heat exchange ventilator.

This alternative method of driving the fans operates due to the different characteristics of axial and centrifugal fans and the phenomenon of there being higher pitot pressure created at the surface of the wall than at a point spaced, say, 100mm. away from said surface when a wind is blowing onto the wall.