Pipe joints or couplings – With casing – lining or protector – Insulated
Reexamination Certificate
2001-03-01
2003-10-07
Browne, Lynne H. (Department: 3679)
Pipe joints or couplings
With casing, lining or protector
Insulated
C285S192000, C285S049000, C052S220800, C052S232000, C052S219000
Reexamination Certificate
active
06629706
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a ventilation duct construction, comprising a ventilation duct which is provided with insulation and through which air is allowed to flow, as well as a method of providing a ventilation duct. An increased fire-retardant capability of the ventilation duct is achieved by means of the invention.
Fire-retardant capability is here defined as the capability to resist such a temperature rise of the duct air as causes a temperature rise on the outside of the construction.
TECHNICAL BACKGROUND
To prevent fire from spreading in ventilation ducts, it is common to provide the ventilation ducts with some kind of insulating material, such as rock wool, which is resistant to high temperatures and thus prevents fire from spreading. Conventionally, insulation is arranged on the outside of the wall of the duct and is in most cases provided with an outer metal cover.
The ventilation ducts serve to convey air, but noise also propagates easily. By insulating, at least in some sections of the ducts, the inside of the ducts with sound-absorbing material, such as rock wool or glass wool, and lately also materials which are less fire-retardant, e.g. polyester insulation, it is possible to absorb noise efficiently. Hereinafter, sound-absorbing sections of ventilation ducts will also be referred to as sound absorbers.
In case of fire, it is very important to keep down the temperature of the outside of insulated ventilation ducts or sound absorbers as long as possible to increase the fire safety of the surroundings and close objects.
Since sound absorbers often are enlarged in cross-section compared with other ventilation duct sections and contain insulation with a limited fire-retardant capability, the problems of bulkiness and of obtaining a sufficient degree of fire-retardancy may be accentuated.
SUMMARY OF THE INVENTION
Therefore, one object of the present invention is to provide an insulated ventilation duct construction, in which the time during which the outside temperature can be kept down in case of fire is prolonged, while the construction remains compact.
It is also an object to provide a simple method which increases the fire-retardancy of an insulated ventilation duct or duct sound absorber.
According to the present invention, these and other objects which will become apparent in the following are achieved by means of a ventilation duct construction, a sound absorber construction and a method, which have the features stated in the appended claims.
The invention is thus based on the understanding that the fire-retardant capability can be increased by arranging, at least partially, a supplemental thin boundary layer outwardly of the insulated duct or the sound absorber, which boundary layer, on the one hand, provides a supplemental cover configuration having what might be considered as a heat-exchange function and, on the other, provides an additional air insulation effect.
According to one aspect of the invention, a protective or shielding sheet made of metal is thus arranged at least partially around and close to the duct and its associated insulation, not in direct contact with the insulated duct, but instead at a short distance from the same so that an air gap is formed therebetween.
Surprisingly, it has been found that this simple measure imparts a much improved fire-retardant capability to the construction. Preferably, the thermal bridge between the shielding sheet and the duct and its associated insulation is made very small, which can easily be achieved with the aid of suitably designed spacer means. Thus, the time of heating the shielding sheet is prolonged and in particular the time of heating its outside, i.e. the outside of the entire construction.
One advantage of said construction is that the shielding sheet, at least initially, has a cooling effect on the hot air in the gap which has been heated by fire. The thicker the selected shielding sheet, the better the cooling capability. The selection of the width of the air gap as well as the thickness of the shielding sheet must be adjusted to the demands on weight and space. It has been found that a satisfactory effect is obtained even when using a very thin shielding sheet and a very small air gap. The shielding sheet is made of metal, such as galvanised steel sheet or stainless steel sheet. A typical shielding sheet of galvanised steel shows a satisfactory effect even with a thickness of less than 10 mm. The shielding sheet preferably has a thickness of less than a few millimeters, more preferably about 1 mm. The size of the air gap, i.e. the distance between the shielding sheet and the insulated duct, is typically less than 50 mm, preferably less than 20 mm, more preferably less than a few millimeters, such as about 1 mm.
The shielding sheet also has another effect, namely that of distributing the heat over the shielding sheet in case it is locally exposed to a considerable temperature rise. This function is particularly pronounced if the shielding sheet is made of a material having good thermal conductivity.
According to one embodiment, the shielding sheet can be provided with through-holes to improve the circulation of air and heat exchange. This is because cold ambient air is to be drawn into the gap through openings at the ends of the shielding sheet, when the hot air leaks out of the gap through the holes of the shielding sheet. As a result, a circulation of air is provided which contributes to the cooling of the air gap and the shielding sheet. The number, shape and size of the holes can be selected depending on the desired qualities of the shielding sheet. However, the size and the number of the holes have to be chosen, since too big or too many holes could counteract the purpose of the shielding sheet. It has, however, been found that good effects are achieved also when the total area of the holes equals half the area of the shielding sheet.
Depending on the circumstances and the security aspects that must be taken into consideration, the position of the shielding sheet may vary. It is possible to surround an entire ventilation duct of about one hundred meters with a shielding sheet in accordance with the invention, preferably in separate sections so as to provide openings for the intake of air. But it is also possible to provide a ventilation duct with shielding sheet only locally along one or more specially selected sections, such as a sound absorber section. Irrespective of the above-mentioned alternatives, it is not necessary to arrange shielding sheet along the entire circumference of the ventilation duct. It is quite possible that extra protection is needed only along a part of the circumference of the duct.
If the ventilation duct is being passed through a through hole in a wall, a shielding sheet according to the invention may be provided at the location of such a section of the ventilation duct.
Thus, according to another aspect of the invention a protecting or shielding sheet is arranged at least partially around and close to a section of the duct near a wall having a through hole, through which the duct is passed. The shielding sheet comprises a first portion extending essentially in parallel with the ventilation duct, and a second portion extending essentially in parallel with the penetrated wall and being located at an end of said first portion nearest to the penetrated wall. The shielding sheet is thus arranged at such a distance that an air gap is formed between the shielding sheet and both the duct and the penetrated wall.
This second aspect of the invention is particularly advantageous in case of fire on one side of the wall through which the ventilation duct is penetrated. Such a fire may increase the temperature in the ventilation duct on said one side, the rising temperature effect propagating through the duct and thus reaching the other side of the wall. A shielding sheet on the other side will provide the inventive fire-retardant effect.
The first portion of the shielding sheet has primarily a cooling effect on the air in the gap between the ven
Browne Lynne H.
Burns Doane Swecker & Mathis L.L.P.
Hewitt James M.
Saint-Gobain Isover AB
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