The invention relates to ventilation fans and an installation apparatus for installing the fan in a window. More particularly, the invention relates to domestic ventilation fans, e.g. extractor fans, most particularly axial ventilation fans.

In situations where it is not possible or not appropriate to install a ventilation fan (e.g. an extractor fan) directly in a wall or through a ceiling with ducting to the outside, it is often possible to install the fan in a window. A suitably sized hole is cut in the glass pane of the window and a mounting kit is used to clamp the window pane and to support the fan. This is often referred to as a "window kit".

As a window is much thinner than the wall of a building, a fan designed for window installation is usually designed to be of limited axial extent, i.e. it should not extend too far either side of the window. By contrast, the length of the fan is less of an issue in a wall or ceiling installation as there is more room to accommodate the fan.

To provide good and efficient control of the fan, e.g. incorporating sensors such as temperature and humidity sensors and controlling the fan based on those sensors to operate in an efficient manner, it is necessary to incorporate control PCBs (printed circuit boards). The fan unit therefore needs space to accommodate these PCBs and components. It is also desirable to incorporate voltage transformers and/or regulators within the fan so that a separate unit is not required for that. The components of those circuits are often large and bulky, e.g. transformers and capacitors.

Where a fan is to be installed in a wall, these components and circuit boards can be installed within the central spigot of the fan, along with the motor. This makes the spigot longer. However a longer spigot is usually undesirable in a window installation. In particular, a grille needs to be placed behind the spigot to prevent foreign objects from entering the fan from outside while allowing air to flow out of the rear of the fan. To minimise back draft into the fan when the fan is non-operational, the grilles for window kits have provided vents to the sides rather than directly rear facing vents. However this requires that the grille be spaced some way back from the rear end of the spigot in order to provide room for the air to change flow direction without creating too much resistance. Therefore in order to incorporate all of these features, without making the fan too long, the spigot had to be kept short and did not have room to house control circuits alongside the motor. Instead, control circuits could be mounted in the front mounting plate of the fan, but that then increases the size of the front of the fan, i.e. it presents a larger, more dominating frontage to the user in the room.

It is usually preferred to keep the size of the front of the fan to a minimum so as to provide a sleek, elegant, minimalist appearance from the inside. According to the invention there is provided a fan for installation in a window, the fan comprising a cylindrical main body having an inner spigot and a concentric outer sleeve such that air flows between the inner spigot and the outer sleeve; wherein the inner spigot houses a motor for driving an impeller and control electronics for controlling the motor; and wherein the fan further comprises a window attachment mechanism for attaching the fan in a window and a rear grille located behind the main body, the rear grille comprising a plurality of louvers that open when the fan is in operation.

Using a rear grille with louvers allows the grille to be placed much closer to the rear spigot and impeller than would be possible with other types of grille. Therefore the spigot can be made longer without impacting the overall length of the fan unit and thus impacting the appearance of the fan. Making the spigot longer provides extra space for the electronics to be housed inside the spigot, next to the motor and thus allows the front face of the fan unit to be kept to a small and attractive size. The louvers conveniently provide a back draught shutter as they are designed only to open in one direction. Therefore when the fan is inoperative, there is no (or minimal) back flow through the fan into the building. Although the louvers add some resistance to the air flow exhausting from the back of the fan, this is not excessive and does not impact significantly on the efficiency of the fan. Being able to incorporate more sophisticated controls into the smaller fan, improves the efficiency more than is lost through added air resistance.

In preferred embodiments the louvers are rotatably mounted so that they hang in a closed position when the fan is not in operation and swing open when air is driven through the fan. The louvers are preferably horizontally arranged. The louvers may be rotatably mounted about their upper edges so that they pivot around their upper edges when they swing open as the fan is operated, and hang closed under gravity when the fan is not in operation. If the louvers are mounted vertically, a spring or other biasing means will be required to shut them when the fan is not in operation. However this adds extra components and potentially extra air resistance and so is less preferred.

The number of louvers can be varied. Smaller louvers will require less energy to open, but a greater number are required to cover the necessary area. In particularly preferred embodiments 3 to 6, preferably 4 or 5 louvers are used for standard sized domestic ventilation fans with a diameter of 100 mm or 150 mm.

A low voltage electricity supply may sometimes be available, but normally it is preferred to wire the plug directly to the buildings mains supply or simply to plug the fan into a standard power socket connected to the buildings mains supply. In such cases, voltage transformation circuitry is required to convert the building mains supply (e.g. 240 Volt AC) to for example a 24 Volt DC supply for the motor. This needs to be housed within the fan unit and therefore preferably the spigot houses electronics for voltage transformation as well as electronics for controlling the fan motor. The PCBs for electronics and voltage control typically add around 30 mm to the length of the spigot.

The fan may have various features such as an overrun timer (connected to a light switch or a pull cord or both), humidity sensors and controls and speed control settings (e.g. to adapt the fan to different circumstances or to provide a temporary boost in speed when deemed necessary). These controls are also preferably housed within the spigot. Preferably the distance between the rear end of the impeller and the rear grille is between 5 mm and 50 mm, more preferably between 10 mm and 35 mm. The distance varies depending on the thickness of the window glass, e.g. single-glazed versus double-glazed windows.

Preferably the window attachment mechanism comprises an inside plate and an outside plate arranged to clamp the window pane in use. The fan main body is typically mounted to the inner plate and extends through the opening in the window, while the grille is typically mounted to the external plate.

Preferred embodiments of the invention will now be described, with reference to the accompanying drawings, in which:

Fig. 1 shows a rear isometric view of a fan with a window kit according to a first embodiment;

Fig. 2 shows a side view of the fan of the first embodiment;

Fig. 3 shows a rear isometric view of a second embodiment with louvers open;

Fig. 4 shows a cross-section through the first embodiment;

Fig. 5 shows an exploded view of a fan unit and window kit; and Fig. 6 shows a fan mounted on a window.

Fig. 1 shows a fan unit 100 with the various parts of a window kit according to the invention assembled together on a fan. The window is not shown in these drawings.

Fan unit 100 has a front mounting plate 120 which may be used to mount the fan unit 100 to a wall or ceiling if it is not being used with a window kit. Fan unit 100 also has a decorative front plate 130 which is separated from front mounting plate 120 so as to permit air flow into the fan unit 100 between the front plate 130 and the front mounting plate 120. The decorative front plate provides a more aesthetic appearance to the room in which the fan unit 100 is installed as it hides the grille and impeller from view from the room. The fan main body 1 10 comprises an outer sleeve and a concentric inner spigot 300. In use, air is driven axially by the impeller 330 between the spigot 300 and the outer sleeve. When the fan unit 100 is mounted in the window, the outer sleeve of the main body 110 extends through the aperture in the window.

The window kit comprises a separator 140 which spaces the front mounting plate 120 from the inside surface of the window to which the fan unit 100 is to be mounted. This separator 140 positions the fan unit 100 within the window opening in a balanced fashion. A rear mounting plate 150 is provided for contact with the outside surface of the window to which the fan unit 100 is to be mounted. The front mounting plate 130 and the rear mounting plate 150 are connected to each other in use by a number of screws (or similar fastening means) which extend through the opening in the window and squeeze front mounting plate 130 and rear mounting plate 150 together to clamp the window between the separator 140 and the rear mounting plate 150. The rear grille structure 160 is mounted to the outer side of the rear mounting plate 150 and covers the rear end of the fan unit 100. Reference numeral 200 indicates where the window would be if the assembly were mounted to a window.

Rear grille structure 160 comprises a number of louvers 170 (four in the

embodiment shown in Fig. 1 , but a different number of louvers may be used in other embodiments). The louvers are hinged around their top edge so that in the absence of any air flow through the fan unit 100, the louvers 170 hang under gravity as shown in Fig. 1. However, when the fan is activated and air is driven through the fan, the air pushes the louver 170 open, pivoting them around their upper edges and allowing air to pass and to be exhausted to the outside. Louvers 170 are openable only in the outer direction and cannot be blown inwards. The louvers 170 therefore act as a backflow shutter, preventing wind from causing a draught into the building when the fan is not in operation.

Fig. 2 shows the same fan unit 100 as Fig. 1 , but additionally shows a pull cord 180 and more clearly shows the gap 200 where the window is located when the fan unit 100 and window kit are mounted. Fig. 3 shows a rear isometric view of a fan unit 100, similar to Fig. 1 , but showing a second embodiment with five louvers 170 and with the louvers 170 open. Fig. 4 shows a cross-section through the fan unit 100 along the axis of the fan. A central spigot 300 is concentric with the fan main body 1 10 and houses the electronics for the fan as well as providing a mount point for decorative front plate 130. This cross-sectional view shows how two printed circuit boards 340, 350 are mounted within the central spigot 300 of the fan unit 100. PCB 340 contains voltage transformation circuitry while PCB 350 comprises control circuitry which drives motor 310 which is also mounted within the central spigot 300 and which has impeller 320 mounted on its motor shaft 330.

It can be seen that the rear face of the impeller is very close to the rear grille 165 which is part of the grille structure 160 together with louvers 170. The proximity of these elements is due to the length of the spigot 300 required to house the electronics. However, the proximity of the impeller and the grille structure 160 is not problematic due to the use of louvers 170 which open as soon as air is driven through the fan. The distance between the rear of the impeller 320 and the grille structure 160 varies between about 10 mm and 35 mm depending on the thickness of the glass in the window. Installation on a single glazed window will result in a distance of around 10 mm whereas installation on a double glazed window will result in a distance of around 35 mm. Housing the PCBs 340, 350 within the spigot 300 means that the fan can have a smaller overall size facing into the room. It can be seen from Fig. 4 that the front mounting plate 120 has minimal excess space around the air intake opening 400 so as to minimise the visual impact of the fan unit 100. At the same time, the overall length of the fan, including the window kit and rear grille structure 160 is not excessive as the distance between the impeller and the grille structure 160 is minimised, again reducing the visual impact of the fan unit 100 as a whole.

Fig. 6 shows the first embodiment mounted in a window 500. Rear mounting plate 150 and grille structure 160 are on the outside of the window 500, with the rear mounting plate 150 in contact with the window 500. Decorative panel 130, front mounting plate 120 and separator 140 are on the inside of the window 500 with the separator 140 in contact with the window 500.