Ventilation systems

Details Ventilation systems Ventilation systems

1999-11-22

2001-01-16

Yeung, James C. (Department: 3743)

Stoves and furnaces

Stove hoods

C126S29900R

Reexamination Certificate

active

06173710

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to ventilation systems and particularly but not exclusively to ventilation systems for commercial kitchens.
2. Related Art
Ventilation systems are usually required in commercial kitchens to remove smoke, smells and other unwanted airborne or gaseous substances. Typical systems comprise an extractor fan, the inlet to which is located as close as possible to the source of the smoke etc. in an attempt to prevent it from coming into contact with staff working in the kitchen, and an air supply to replace the extracted air with fresh air. A large canopy is provided above the appliance or appliances which are a potential source of smoke etc. Air and smoke etc. is removed from the canopy via an outlet provided at an upper region of the canopy. Such canopies should ideally be as large as possible in order to maximise the capture of the smoke etc. which may drift not only upwards, but also sideways. The canopy therefore takes up a large space, which is particularly inconvenient in smaller kitchens. Furthermore restrictions are placed on the minimum height of the lower edge of the canopy above the floor, in order to provide adequate headroom for staff and this means that, particularly where a kitchen has a low ceiling, the canopy is restricted as to how deep it may be and therefore how effectively it may capture the smoke.
With the known ventilation systems, in order to obtain adequate smoke extraction it is generally necessary to employ large and noisy extractor fans. These consume a lot of power and require correspondingly large ducting which is bulky and can be difficult to accommodate where space is restricted. Even with large canopies and high air extraction rates, known ventilation systems are not completely effective in removing smoke etc. from the kitchen.
SUMMARY OF THE DISCLOSURE
According to the present invention there is provided a ventilation system for a kitchen, comprising air extraction means to be arranged generally above a kitchen appliance and air distribution means arranged to form a downwardly flowing air curtain outwardly of the air extraction means.
With such a ventilation system, the rate at which air is extracted may be significantly reduced since the air curtain actively re-directs the air towards the air extraction means rather than simply containing it. Any smoke that does not enter the extraction means and is moving outwardly away from the extraction means, will impinge upon the air curtain. The outer edge of a body of such smoke, which is moving towards the air curtain, will thus be given a downward component of movement with respect to its inner edge, causing it to curl so that it starts to move inwardly towards the extraction means. Thus, less air needs to be extracted to achieve the desired removal of smoke. Such a reduction in air extraction confers significant benefits by requiring smaller fans, which therefore make less noise, consume less power and require less bulky ducting which makes them easier and cheaper to install.
For example, in a particular kitchen, which would have required an extraction rate of approximately 142-170 m
3
/min (5000-6000 cu.ft/min) with a conventional system, it was found that when using a preferred embodiment of the present invention, an extraction rate of only approximately 74 m
3
/min (2600 cu.ft/min) was needed to achieve acceptable smoke removal.
The advantages of providing a ventilation system with an air curtain may be realised if a canopy is also provided to contain smoke etc. Preferably however, no canopy is used since it is no longer necessary in order to produce satisfactory results. Without a canopy, much less space in the kitchen is taken up by the ventilation system.
Whilst the air distribution means could be arranged level with or below the air extraction means, preferably the air distribution means is arranged at a level above the level of the air extraction means. Therefore the air extraction means may be located at a relatively low level, close to the source of smoke etc., for example substantially vertically adjacent a kitchen appliance e.g. an oven. The proximity of the air extraction means to the kitchen appliance makes the air extraction means even more effective, further enabling the extraction rate to be reduced. The air distribution means can be at a higher level, providing sufficient headroom for staff, whilst still being effective to form the air curtain. This is to be contrasted with known systems in which a canopy extends downwardly to the same level as, or below, the air extraction means. In such a known system, therefore, the headroom requirement for the canopy determines the lowest position for the air extraction means and thus limits the effectiveness of smoke removal.
It may be possible for the air distribution means to direct air horizontally outwardly in such a way that a downwardly flowing air curtain is subsequently formed. Preferably, the air distribution means is arranged to direct air at least partially downwardly and most preferably it directs air both downwardly and outwardly, for example at approximately 45° to the vertical. Such arrangements have been found to be highly effective in re-directing air to the air extraction means when it is drifting away from it.
The air extraction means could be arranged as a plurality of discrete inlets. Preferably, the air extraction means comprises air inlet means following a defined path, as viewed in plan, and the air distribution means comprises air outlet means also following a defined path, as viewed in plan, the path of the air outlet means being substantially similar in shape to the path of the air inlet means. With this arrangement, an air curtain may be provided which corresponds in shape to-the air extraction means. For example, the air curtain in combination with physical barriers such as kitchen walls or partitions can effectively surround the air inlet means of the air extraction means. Such an arrangement is the most effective way of ensuring that any smoke moving away from the air extraction means is re-directed towards it.
The air inlet means and air outlet means could follow any suitable paths, depending upon the application to which the system is put e.g. linear paths is for use with a line of cooking appliances along one wall of a kitchen, or even circular paths respectively above and around an appliance in the middle of a kitchen. Preferably though, the air inlet path and the air outlet path are substantially U-shaped. This is a particularly convenient arrangement for example for use above a commercial free-standing oven such as a pizza oven, since respective opposite portions (the limbs of the “U”) of the air inlet means may be associated with the entry and exit points to the oven and a further portion (the base of the “U”) may be associated with the outer facing side of the oven. The fourth side can be blocked e.g. by a wall or backplate.
The air distribution means may be configured in any suitable arrangement to distribute the air, but preferably comprises a plenum chamber which is divided into sub-chambers by vertically extending walls in order to maintain a substantially equal air flow along the length of the air curtain. In arrangements where the air outlet means has discrete portions (e.g. the two limbs and the base of a “U” shape), then a sub-chamber may be associated with each such air outlet portion, with the plenum chamber being divided according to the lengh of the air outlet portions to maintain a desired distribution of air flow to the respective portions. This is advantageous in ensuring that whatever lateral direction smoke emanates from a kitchen appliance, then it will inevitably encounter an effective air curtain to re-direct it towards the air extraction means.
The air curtain provided by the present invention may also have a beneficial cooling effect for those working in its vicinity in the kitchen. However, in a preferred embodiment, the ventilation system further comprises at least one controllable air outlet arranged to delive

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