Method and device for de-icing an intake aperture

Disclosed is an apparatus and a method for de-icing an intake opening (2) in an intake duct (1) of a fire alarm system, through which ambient or equipment air is drawn in and supplied to a detector for sensing a fire parameter. To effectively remove an ice deposit on the intake opening (2) there is provided, in or on the intake opening (2), an elastic element having a through-hole (3) coaxial with the intake opening (2) which is adapted to be subjected to a compressed air blast in order to de-ice the intake opening (2) (FIGS. 4a to 4c).

The present invention relates to apparatus and method for de-icing an 
intake opening in an intake duct of a fire alarm system through which 
ambient or equipment air is drawn in and fed to a detector for sensing a 
fire parameter. 
Fire detection devices are also known, for example, under the technical 
term "equipment protection devices". Typical applications for fire 
detection devices are EDP equipment and especially individual components 
thereof, as well as similar electronic equipment such as, for example, 
measuring, control and regulating equipment, communication devices and 
related apparatus, and the like. The term "fire parameter" denotes 
physical values which undergo measurable changes in the vicinity of an 
incipient fire, e.g. the ambient temperature, the solid, liquid, or 
gaseous content of the ambient air (formation of smoke particles or 
aerosols, or steam) or the ambient radiation. 
A fire detection device to which the present invention relates splits off a 
representative fraction of the equipment cooling air by means of a piping 
or ducting system, or actively draws in ambient or equipment air at 
predetermined locations and then feeds this representative fraction to the 
above-mentioned detector. For drawing-in the ambient or equipment air the 
intake pipes or ducts are provided with intake openings. Of course such a 
fire detection system is also needed in a refrigerated warehouse or 
refrigerated store room, if it is desired to detect a fire with high 
reliability even in the earliest stage of its development. An important 
prerequisite for this is that the fire detection device can continuously 
pull in a sufficient representative quantity of air and feed it to the 
detector. In refrigerated store rooms and refrigerated warehouses this 
needed continuity of air supply is imperiled through icing-up of the 
intake openings, and in other spaces or equipments through dirt 
accumulation. 
From each of DE (German patent document) 21 36 968 B2 and DE (German patent 
document) 33 48 107 C2, there is known an air intake system for a fire 
detection device having plural intake pipes through which ambient or 
equipment air is drawn in via intake openings. In the system of DE 21 36 
968 B2, cleansing of the intake openings takes place solely through 
compressed air. In the system of DE 33 48 107 C2 these are electrically 
heated in response to lessening through-flow of air in order to prevent 
icing-up of the intake openings. The disadvantage of this air intake 
system is that electrical leads need to be located in or at least on the 
intake pipes in order to supply the heating resistors. The electrical 
leads have the disadvantage that they are difficult to service, that if 
positioned in the intake pipes they can readily lead to fouling of the 
pipes through deposit of dust particles on the leads, and finally they are 
apt to interfere with sensitive electronic equipment through the 
relatively high heating currents and their accompanying electrical and 
electromagnetic fields. 
In view of these disadvantages, it is an object of the present invention to 
provide an alternative solution for preventing the icing-up of intake 
openings of a fire detection device. 
This object is achieved in accordance with the invention by the apparatus 
having the characteristics of claims 1 and 8 as well as by the method 
having the characteristics of claim 9. 
The special advantages of the device according to the invention are that 
the elastic or flexible element can provide a de-icing apparatus which is 
easy to implement for the intake openings in an intake duct of a fire 
alarm system. To that end, the elastic element is attached to the intake 
duct in such a manner that it covers the intake opening which takes the 
form of a through-hole in the intake duct, so that the through-hole is 
positioned coaxially with that intake opening, whereby the diameter of the 
intake opening is reduced to the diameter of the through-hole in the 
elastic element. If an ice rim forms on the intake opening, an appropriate 
compressed air device delivers a compressed air blast through the intake 
duct, whereupon the elastic element is reversibly extended and deformed 
and breaks off the ice deposit. Furthermore, the flexible element is 
attached to the intake duct in such a manner that it covers the intake 
opening, except for a remaining through-hole which can, for example, also 
take the form of an annular slot. If a rim of ice forms on the intake 
opening, there again occurs the compressed air blast through the intake 
duct, whereupon the flexible element lifts up from the intake opening and 
delivers a mechanical impact to the edge of the intake opening during 
resilient return and thereby detaches the ice deposit. For the time being, 
the manner in which the flexible element delivers the mechanical impact to 
the intake opening or its edge shall remain undetermined. What is 
essential is only that a possible ice accumulation on the rim of the 
intake opening can be removed through the mechanical action of a flexible 
impact delivering element. 
Finally, the method according to the invention provides an advantageous 
process for using a compressed air blast through the intake duct to 
stretch, or lift up from the intake opening an appropriately designed 
de-icing element, which subsequently, during subsidence of the compressed 
air blast and operation of a restoring force, suddenly contracts or 
springs back and, in so doing, detaches the ice accumulation from the 
intake opening. Here too, for the time being, the specific form of the 
de-icing element shall remain completely indeterminate. For example, a 
membrane of rubber or rubber-like material can be the previously described 
elastic element, or else a resilient tongue can be the previously 
described flexible element. 
The need for delivering the compressed air blast is determined in all three 
embodiments by an airflow sensor of known kind, which is set to a 
predetermined desired value of the mass flow of the intake air. If the 
open cross-section of the intake opening is reduced through icing, the air 
through-flow lessens and the airflow sensor detects a system fault, as 
soon as the air mass flow falls below the threshold. 
Advantageous specifics of the invention are defined in the dependent 
claims. 
For construction and attachment of the elastic element to the intake duct 
three possibilities are contemplated: according to a first alternative the 
elastic element forms part of the intake duct itself. According to a 
second alternative, the elastic element forms part of a flexible collar 
which is clamped at least partway around the intake duct and, according to 
a third alternative, the elastic element consists of an elastic collar of 
rubber or rubber-like material which encircles the intake duct. The two 
latter alternatives have the advantage that retrofitting of the de-icing 
device is possible without difficulty by later attaching the collar to the 
intake duct. 
Whereas the elastic element according to the second alternative is attached 
to the intake duct by a clamp latch, to attach the elastic collar 
according to the third alternative there is preferably provided a hole at 
one end and a nipple, or tab at the opposite end, the nipple being adapted 
to be pushed through the hole to fasten the elastic collar and to be held 
in place there. This is readily possible because the elastic collar takes 
the elongated form of a strap which can be stretched in its lengthwise 
direction by virtue of its elastic material when the nipple is pushed 
through the hole. 
To enhance the durability of the elastic element it is contemplated that 
its through-hole has a reinforced edge which partially extends into the 
intake opening of the intake duct. 
From the foregoing explanations it is apparent that, after application of 
the elastic or flexible collar, the intake opening consists essentially of 
the through-hole in the elastic element. Since the intake openings in an 
intake duct system can have different diameters depending on the 
applicable requirements, it is contemplated that the elastic elements are 
inventoried with different sizes of through-holes. This makes it possible 
to use intake ducts in the form of yard ware pipes with standardized 
intake openings, the desired diameter of the intake opening being provided 
by the de-icing collar. The different de-icing collars can also be made 
inexpensively because a single injection molding machine with different 
nozzles can be used.

FIG. 1a is a perspective illustration of a segment of an intake duct 1 in 
the form of a cylindrical pipe. This pipe segment is part of a piping or 
duct system by means of which a representative fraction of the cooling air 
for equipment to be guarded, or the ambient air in a space to be guarded, 
is drawn in and supplied to a detector. For drawing in the ambient or 
equipment air the intake pipes or ducts are provided with intake openings 
2, of which only one is shown here. 
FIG. 1b shows the same perspective illustration of the pipe segment, but 
here surrounded by an elastic de-icing collar 5 at the location of intake 
opening 2. This de-icing collar 5 has a through-hole 3 (see FIG. 2), 
which, when the de-icing collar 5 is correctly positioned, is coaxial with 
the intake opening 2 and thus constitutes the intake opening 2. 
FIG. 1c shows the reverse side of pipe segment 1 of FIG. 1b and illustrates 
how the elastic de-icing collar 5 is attached to the pipe segment 1. This 
is further described below with reference to FIGS. 3 to 4c. 
FIG. 2 is a top view of the elastic de-icing collar 5 which has an 
elongated shape similar to a strap. It is made of rubber or rubber-like 
material or, for example, also of elastic plastic. In the middle there is 
provided the through-hole 3 which has previously been mentioned in 
relation to FIG. 1b, which is located coaxially with intake opening 2 when 
the elastic collar 5 is correctly positioned. At one end 6, the de-icing 
collar 5 has a slot 7 and on its opposite end 9 a tab 10 which, however, 
is better seen in FIG. 3. 
FIG. 3 shows a vertical cross-section along line A--A through the elastic 
de-icing collar 5 of FIG. 2. In this illustration there can be seen the 
tab 10 attached to the top of de-icing collar 5 and made of the same 
material as the de-icing collar 5. It can further be seen from FIG. 3 that 
the through-hole 3 has a reinforced edge 11, which enhances the load 
bearing capacity and thereby also the durability of the de-icing collar 5. 
FIGS. 4a to 4c show the manner of attaching the elastic de-icing collar 5 
to the intake duct segment 1. Initially this has only the intake opening 2 
in the form of a standard hole in pipe 1 (FIG. 4a). To apply the elastic 
de-icing collar 5 it is placed around the intake duct segment 1 so that 
the through-hole 3 of collar 5 engages the intake opening with its 
reinforced edge 11. The de-icing collar 5 is then wrapped around the pipe 
segment 1 so that the end 9 bearing tab 10 rests with its underside 12 
directly on the outer surface of pipe segment 1, while the end 6 with slot 
7 is pulled over tab 10 by stretching the de-icing collar 5 and is hooked 
onto the tab. This final state is illustrated in FIG. 4c. Of course, 
closing of the elastic de-icing collar around the reverse side from intake 
opening 2 can also be accomplished by Velcro.RTM., or the like. 
FIG. 5 shows a cross-section of an intake duct segment 1 having an intake 
opening 2 which is covered by a different embodiment of a collar. In this 
case, the elastic element 4, which contains the through-hole 3 and covers 
the intake opening 2 and thereby reduces it in practice to the 
through-hole 3, is part of a flexible collar 8 which is clamped almost 
completely around intake duct segment 1. In this case, the elastic element 
4 also consists of elastic material so that it can respond in the desired 
manner to a compressed air blast. 
The operation of the de-icing device is now described once again with 
reference to FIG. 4c. During operation of the fire alarm system, ambient 
or equipment air is continuously drawn into intake duct 1 through intake 
opening 2, or rather through-hole 3, in the direction of arrow 3a. If an 
ice deposit forms on the edge of through-hole 3, a compressed air blast is 
applied to intake duct 1, whereupon the elastic de-icing collar is 
reversibly stretched and deformed in the vicinity of the intake opening 
and the ice deposit is broken off. 
FIG. 6 again shows a perspective illustration of a segment of an intake 
duct 1 corresponding to FIGS. 1a to 1c. In this embodiment, the collar 8 
also consists of flexible material, as in the embodiment according to FIG. 
5. To remove an ice deposit on the intake opening, there is provided here 
a flexible element 13 which is configured as a leaf spring and attached at 
its fixed end 15 to collar 8, while its free end 14 is pivotably 
positioned above intake opening 2. To prevent excessive deflection of 
flexible element 13, a stop 18 is provided. The collar 8, made of flexible 
material, is clamped around intake duct 1 and is made as a single unit 
with flexible element 13 and stop 18. Again, a through-hole 3 coaxial with 
intake opening 2 in intake pipe 1 is provided in flexible element 13, 
through which the ambient, or equipment air is drawn in, either 
exclusively or additionally. 
FIG. 7 shows a cross-section through the intake duct 1 according to FIG. 6. 
From this illustration it can be seen that the freely pivotable end 14 of 
flexible element 13 has a plug 17, which is integral with flexible element 
13 and narrows toward intake opening 2 in the form of a conic section. The 
position of the plug inside intake opening 2 represents the normal 
operating state of the fire alarm system, in which air is continuously 
drawn in through intake opening 2, or rather through a through-hole in 
plug 17, and fed to a detector (not shown). In this operating state the 
plug 17 partially engages the intake opening 2 and rests with its conical 
outer surface 16 against edge 11a of intake opening 2. As a result the air 
is drawn in exclusively through through-hole 3. However it is also 
possible to construct flexible element 13 with plug 17 in such a manner 
that, in operation, there still remains an annular slot between the conic 
outer surface 16 of plug 17 and the edge 11a of intake opening 2, through 
which ambient or equipment air can be drawn in, either in addition, or 
exclusively. 
FIG. 8 shows a cross-section along line A--A of FIG. 7. From this 
illustration it is apparent that flexible collar 8 does not encircle 
intake duct segment 1 completely, but only partially, so that collar 8 can 
be readily applied to intake duct segment 1 transversely to its lengthwise 
direction. Thus, intake duct segment 1 and collar 8 form a clamp 
connection. 
In what follows, the operation of this embodiment of the de-icing device is 
described once again, with reference to FIG. 7. During operation of the 
fire alarm system, ambient or equipment air is continuously drawn into 
intake duct 1 through intake opening 2, or rather through-hole 3. If an 
ice deposit forms on the edge 11 of through-hole 3, a compressed air blast 
is again applied to the intake duct 1, whereupon the plug 17 located at 
the free end 14 of flexible element 13 is deflected in the direction of 
arrow 19 and thereafter resiliently returned under the influence of the 
restoring force of flexible element 13, thereby applying a mechanical 
impact with its conical outer surface 16 against edge 11a of intake 
opening 2. Through this mechanical action, an ice deposit is reliably 
removed. 
Of course, alternative embodiments of the de-icing element are possible. 
Their configuration is mainly determined by their reliability of operation 
and ease of attachment and not least by their manufacturing cost. It is 
important that the de-icing element be so constructed that it creates a 
response to the compressed air blast by which the ice deposit on the 
intake opening is detached.