The present invention relates to the field of ventila¬ tion, more precisely the invention concerns a method according to the preamble of the accompanying claim 1 and assembly according to the preamble of the accompanying claim 2 to reduce noise and/or to control flow associated with a flow system of gaseous medium, such as a ventilation system and especially branch ducts of an air flow ductwork. The invention concerns also use of a module silencer.

In a common ventilation system main noise sources are a main air fan in a main duct and air flow turbulence phenomenoπs produced by curves and forks of the ductwork both flow regulators in the branch ducts of the skeleton ductwork.

It is a known fact, that any user is not satisfied with a noisy ventilation system in spite technical performance of the same would be otherwise acceptable. Further different regulations and instructions claim certain maxim decibel values which a ventilation system should not exceed.

Traditionally noise damping in a ventilation system is carried out so that in the main duct subsequent to the main fan comprises a primary silencer in order to reduce fan noise and further in order to achieve an adequate total damping the branch ducts are provided with secondary silencers placed immediately subsequent to a flow regulator to reduce noise produced by air flow turbulence.

The primary silencer is located usually inside the main duct and is constructed of modules into a form of a cell, depending on the size of the duct a sufficient number of the modules are placed therein with a distance from each other both one on the other and side by side. The elongate silencer modules, having a four-corned cross- section in respect to the flow direction, boarder into the intermediate spaces thereof and inside the inner surface of the duct wall thin flow defiles, wherein the damping occurs so that absorption mass of the modules absorbs part of the noise. As examples of silencer of this type can be mentioned the module silencer "SABINE" developed and sold by

Ilmacoπ Oy and the module silencer in accordance with the published specification SE-410217 or 428496.

A secondary silencer placed into a branch duct subse¬ quent to a flow regulator is usually elongate cartridge with a ring- shaped cross-section having a continuous outer mantel and perforated inner mantel and a layer of noise absorbing material sandwiched there between. In the silencer of this type the diameter of the hollow space inside the inner mantel corresponds usually the diameter of the branch duct, so the advantage of the secondary silencer is that it do not cause any flow resistance or any obstacle for sweeping. However, the disadvantage is that low voices which are harmful especially for a human ear, i.e. voices within the octave bands S3 and 125 Hz get through the silencer but as extremely little dampened, unless the length of the silencer is selected very long, which in practice is in most cases impossible and increases expenses disproportionaly high. The disadvantage of the silencer of this type is also that it demands space in the direction oh height. As an example of the secondary silencer of this type can be mentioned the silencer K&V-160-600 sold by Lapinleimu Oy, the damping performances thereof are presented in the table below.

_*

Damping (dEO

KAV-160-600 4 5 10 23 30 32 24 16 -

63 125 250 500 1000 2000 4000 8000 average frequencies of octave bands (Hz)

However, the secondary silencer described above suffers from the disadvantage, that in front thereof is used a regulator which is usually either an iris-regulator according to the FI patent 57742 (Halton Oy) or a cone-regulator according to the FI patent 58394 (Otson Ltd), which both are provided with mobile segments for adjusting a flow area in the cross direction. Further in the field plate and lamella solutions to be turned have been proposed among other things. In common the regulators of this type suffer from the disadvantage, that adjust¬ ing is difficult in case ventilation demands will change afterwards, and that to carry out sweeping of the duct efficiently they form an

obstacle which is extremely difficult to avoid. Further with the sweeping there exists continuously the potential risk, that the sweeping means may break the regulator or change the set ing thereof.

One object of the present invention is to eliminate the above mentioned disadvantages and weaknesses which relate to the previously known ventilation systems both to provide a new, efficient solution to reduce noise and control gas flow associated with a flow system of gaseous medium, especially in branch ducts which branch from the main ducts thereof. Second object of the invention is to provide an integrated solution to cover damping and regulation demands for gaseous medium flow system, such as a ventilation system. Third object of the invention is to reduce space in a height direction necessary for the silencer.

According to the invention these objects have been achieved by the assembly and method mentioned in the beginning and by the use of a module silencer, characterizing features thereof are disclosed in the accompanying claims.

Hence the present invention is based on that new and ingenious basic insight that a massive noise absorbing silencer module is placed inside a casing joined to a flow duct to form an obstacle for a rectilinear flow course, whereby in the casing the gas flow course is forced to turn and be guided through the free space between the outer surface of the silencer module and the inner surface of the casing, preferably past the silencer, whereby inside the casing the free flow area in the cross direction will determine at least mainly the rate of flow resistance, i.e. flow control. ^

As the main advantages of the invention can be men ion¬ ed, that the damping and control solution according to the invention is compact and uncomplicated and economically advisable, that the silencer according to the invention and the control system engaged thereto can be transferred rapidly and easily aside for the period of cleaning procedure, that the replacement of the absorption mass unit is simple to carry out, that the silencer according to the invention do not necessarily take space in a height direction more than the actual ductwork, and that in the solution according to the invention are combined reactive and absorbing damping, which results to an essential¬ ly improved damping performance than earlier was possible to achieve.

The invention is described in the following in greater detail by means of certain advantageous embodiments thereof relating to the ventilation with reference to the accompanying drawing, wherein figure 1 illustrates schematically in a simplified way a multiple duct ventilation system for conducting utility air into room spaces, figure 2 is a partial section view of a first advantageous embodiment according to the invention, which is useful e.g. in the ventilation system according to the figure 1, figure 3 is a partial longitudinal section view of a second advantage- ous embodiment of the invention, and figure 4 is a partial longitudinal section view of a third advantageous embodiment of the invention.

As can be seen from the figure 1 the ventilation system includes in the air flow direction: means 1 for closing and opening the ventilation system; means 2,3 for pretreating fresh air to be taken from outdoors, i.e. at least for filtering and warming the same; the main air fan 4, which sucks air from outdoors and blows it into the main duct 6, which includes a primary silencer 5 in the beginning thereof. As can be seen further from the figure 1 the main duct branches into at least one skeleton duct 7, which then branches into branch ducts 8 conducting air into room spaces 9 via distribution ducts provided usually with adjustable air distribution valves.

According to the present invention damping of the turbulence noise caused of forks of the ductwork 6,7,8 of such a ventilation system and the noise caused of the main duct, partially damped by means of a primary silencer 5, to a desired level as well as control of the air flow to be conducted into a branch duct 8 leading to a room space 9 is accomplished by an integrated damping and flow control arrangement 10 or 10' to be incorporated with the branch duct 8.

To reduce noise to a desired level and besides to control air flow the arrangement according to the invention illustrated in the figure 2 includes a casing element 11 of an angular form, which is joined to a flow connection with the branch duct 8 and is at least in the direction breadth thereof wider than the inner diameters of the duct opening 14 of the branch ducts connected to the opposite ends 12, 13 thereof. A noise absorbing damping module 15, having reduced

diameters at least in the direction of the breadth of the casing, preferably also angular in form, is fitted inside the casing 11 which module prevents a rectilinear flow path through the casing 11 and forces the air flow to bend and to be directed between the outer surface of the damping module 15 and the inner surface of the casing 11, preferably past the damping module 15 towards the opening 14 of the branch duct at the opposite end 13 of the casing 11, whereby the free transverse flow area between the damping module 15 and the casing 11 defines a flow resistance of the noise damping and control arrangement according to the invention.

By dimensioning and placing the noise damping module 15 inside the casing 11 so that the inner free transverse area of the casing 11 becomes smaller than the transverse flow area of the duct B the flow resistance will increase. Hence the arrangement according to the invention can be used directly as a flow controller.

In the particularly preferred embodiment of the inventi¬ on illustrated in the figure 2 the massive noise absorbing mass of the noise damping module is of porous material, preferably of fibre mass, which is wrapped up to prevent fibre loosening. In order to certify form permanence of the noise damping module 15 the fibre mass thereof in angular form is strengthened by means of longitudinal edge stiffen¬ ing 16. In order to guide the air flow and to increase efficiency of the noise damping, especially reactive noise damping, at least the face gable 17 of the noise damping module 15 towards the input air flow is covered by metal 18. In order to achieve an efficient deviation of the input air flow after the duct opening as efficiently as possible the area of the face gable 17 is dimensioned larger than the transverse flow area of the duct 8, especially the duct opening 14 open into the casing 11, further the face gable 17 is positioned in respect to the duct opening 14 so that it extends radially outside the circumference defined by the duct opening. Hence the air flow deviates as forced by the face gable of the noise damping module 15 first 90° and then by the influence of the inner wall of the casing 11 again 90° between the noise damping module and the inner wall of the casing 11. This flow defile is defined by on one hand the porous absorption mass and on the other casing mantel of metal, due to the different acoustic qualities thereof noise absorption into the absorption mass increases.

As even mentioned above flow control is materialized in this preferred embodiment simply by altering by means of the noise damping module 15 size of the transverse free flow area inside the casing 11. For this purpose according to this embodiment the face gable 17 of the noise absorbing module 15 include means 19,20 for adjusting, i.e. for decreasing or increasing and respectively for decreasing or increasing the free transverse flow area of the air defile, the intermediate space between the face gable 17 of the noise absorbing module 15 and the opposite inner surface of end wall 12 of the casing 11, in which intermediate space the air flow is deviated 90° in respect to the input air flow. It is not most essential to the present inventi¬ on what kind of means 19,20 are used to accomplish the adjusting. As an example of suitable means can be mentioned a pair screw pins 19 attached to the face gable 17 of the noise absorbing module 15, which pins penetrate the end wall 12 of the casing 11, and tightening, blade o corresponding nut means 20 adapted round the screw pins 19 outside the casing 11, by means of which the noise absorbing module 15 can be positioned inside the casing 11 with a suitable distance from the end wall 12 of the casing. By means of second nut means adapted round the nut pins 19 inside the casing 11 it is possible to certify permanence of the positioning, which second nut means are tightened after the adjusting against the inner end wall 12 of the casing 11.

In order that installation and replacement of the no-ise absorbing module would easy to perform in a most convenient way the casing is designed to be possible to reopen. In the preferred embodi¬ ment of the invention according to the figure 2, in which the casing 11 extends in the horizontal direction on both sides the outer dimensions of the duct 8 with 5-20 cm, preferably about 10 cm, and in the vertical direction at the most with about 5 cm, bottom of the casing can be reopened, in case the duct 8 is placed to run above an intermediate ceiling, whereby via the open casing is convenient to carry our besides the replacement of the noise absorbing module sweeping of the duct 8. In this embodiment for accomplishing a casing 11 to be opened, one edge section of the bottom body includes a hinge arrangement 22, which makes possible turning thereof, and one other edge section includes bar means 23 for locking the bottom body. Naturally there is a reason to arrange

sealing between turning part 21 of the casing and the steady part of the casing in order to eliminate air leakages.

In the following diagram damping performance of one assembly according to the preferred embodiment of the present invention is compared with the ring cartridge silencer (Lapinlei u Oy) mentioned above.

CdBD damping

63 125 250 500 1000 2000 4000 8000 average frequencies of octave bands CHzD

In figure 3 is illustrated the second advantageous embodiment of the invention. In accordance with this embodiment the casing 11 joined to the duct 8 is tubular. Respectively the noise damping module inside the casing is a revolution symmetrical noise damping cartridge 15. In accordance with this embodiment the damping cartridge 15 forces the input gas flow from the duct 8 to be directed • into the flow defile having a cross-section of ring-shaped form, whereby in this embodiment the noise damping takes place in the ring- shaped flow defile defined by the outer surface of the cartridge 15 and the inner surface of the casing 11. As can be seen from the figure in this embodiment the transverse area of the cartridge is larger than the transverse flow area in the duct - from the point of performance with the invention this is naturally not necessary but the cartridge can also be dimensioned larger than the duct dimensions. In order to control gas flow the noise damping cartridge 15 include a movable gable element 18 facing the input duct 8, by means of which the distance between the end of the duct 8 open into the casing 11 and the noise damping cartridge 15 is possible to select optionally, i.e. the regulatory air flow resistance. In this embodiment means for locking

the selected distance are composed of screw pins extending from the cartridge and of nut means attached to be rotating at the gable element, by means of which the total length of the noise damping cartridge 15 can be changed. Due to the fact that in this embodiment has been used a band tightening to fix the damping cartridge it is possible to use instead of the movable gable element a steady gable plate and to provide a desired adjusting by shifting the cartridge in respect to the bands.

In figure 4 is illustrated the third preferred embodi- ment of the invention. In accordance with this embodiment the casing 11 joined to the duct 8 is a rectangular prism. Correspondingly the noise damping element installed inside the casing into a steady position is a noise damping cartridge 15 having a form of a rectangular ^' prism. In accordance with this embodiment the noise damping cartridge 15 divides the input gas flow from the duct 8 into two sections, whereby the damping of the noise takes place in the flow defiles defined by the side walls of the cartridge 15 and the opposite sides of the casing 11. As can be seen from the figure in this embodiment the transverse area of the cartridge is larger than the transverse flow area in the duct - from the point of the performance of the invention this is naturally not necessary but the cartridge can also be dimensioned smaller than the duct dimensions. In order to control gas flow in this embodiment inside the input duct 8 is adapted movably in respect thereof tubular means or a corresponding, the free end of which includes radially extending flange means 27 corresponding the inner dimensions and form of the casing. By shifting the position of the tubular means 26 especially location of the flange means it is possible to optionally adjust the distance between the end of the duct 8 open into the casing and the noise damping cartridge 15, i.e. to change the inner flow resistance of the casing. In this embodiment means for locking the selected position of the tubular means 26 are composed of tightening screws adapted through the duct wal1.

From the point of noise damping there is concerning different embodiments described and illustrated with reference to the figures 1-4 above there is further reason to mention that there is provided at the very beginning of the flow defile an acoustic aperture having extremely good acoustic qualities, hence the damping performance

with the noise damping assembly according to the present invention is highly increased in respect the solutions according to the prior art. Further there is reason to emphasize that due to the different acoustic performances of the metallic inner surface of casing and the porous silencer cartridge there is provided an improved noise absorption into the porous fibre absorbent of the silencer cartridge, and hence an improved noise damping, especially concerning noise of low frequencies. The invention is described above only by means of certain preferred embodiments thereof relating to ventilation. Natural- ly this is not meant to limit the invention to concern purely ventila¬ tion or the illustrated solutions according to the embodiments. As it is evident to any skilled in the art in the spirit and scope of the accompanying claims the invention can be modified and varied within extremely wide limits. Especially there is a reason to emphasize that the casing and/or the noise damping module do not have to omit necessa¬ rily a rectangular form but instead they may have a cross-section profile of any continuous circumference in form as far as the transver¬ se section area of the noise damping module is smaller than the transverse section area of the casing to provide at least one flow defile between the noise damping module and the wall of the casing having a location deviated from the central line of the duct. Further there is a reason to mention that instead of a flat gable plate of the noise damping element it is possible also to use for guiding the flow a shaped front plate which in a form of a cone may extend inside the duct for accomplishing the flow control, whereby the ring-shaped flow defile between the conical surface and the inner surface of the duct form the "i flow controller. Separately there also reason to mention that material alternatives presented above are not essential from the point of the present invention nut any suitable materials having sufficient rigidity and noise absorbing performance can be used. Further there is a reason to mention that the control can be accomplished also by constructing the casing slidable in respect to the duct pipes, whereby the flow resistance is altered by shifting the length, by which the end of the duct extends inside the casing.