SOUND-ABSORBING EXTERIOR COMPONENT OF A BUILDING FACADE

Description

Technical field

[0001] The application concerns a sound-absorbing external component of a building façade for sound absorption of sound waves arriving at the component from the urban area (external noise). State of the art

[0002] Omnipresent noise from various sources represents a significant burden in urban areas. It can cause health damage, impede communication, and generally reduce the quality of life. In addition to noise reduction measures at the sound sources, considerations must be given to how sound waves propagate through urban areas, with all their sound-reflecting surfaces. Special noise protection structures such as noise barriers are only partially applicable or remain almost ineffective in the sometimes confined spaces, e.g., in streets in built-up areas. Horizontal surfaces such as roads and sidewalks are subject to high mechanical and weather stress, so that other functions, including acoustic ones, can only be integrated to a limited extent. However, a very large "urban area" with previously neglected acoustic potential represents, for example,Building facades and other vertical surfaces of transport and infrastructure structures represent a major challenge. However, the design of the acoustic functionality of building facades has so far mostly been considered with a single acoustic purpose and in a single direction: the sound insulation effect from the outside to the inside. Sometimes the inside of the facade surface is used and designed to improve interior acoustics by using sound absorbers to reduce the reverberation time in the room. Numerous solutions and sound absorbers have been proposed for this purpose, ranging from transparent micro-perforated surface elements to absorb sound from the room side even in front of glass surfaces.

[0003] The reverse perspective, i.e., the functionalization and impact of facades on urban space, is still unfamiliar, although parallels and synergistic effects with interior acoustics clearly exist due to the harmony of their features. In an urban context, most facades, despite a wide variety of designs, are characterized by their sound-reflecting behavior. Not only in pronounced urban canyons, these hard surfaces amplify all sound events in the immediate vicinity of the sources and simultaneously carry them far into the urban environment. Reducing sound energy enables the absorption or dissipation of sound waves when they hit corresponding surfaces. This effect on the urban environment can be calculated and evaluated.Although current calculation options are not yet fully equipped for this purpose, they nevertheless provide initial indications of the positive acoustic effect of sound-absorbing building facades and comparable surfaces.

[0004] Materials, layers, and structures, such as those used in sound-absorbing noise barriers, offer well-known possibilities for achieving extremely high levels of sound absorption. This is feasible with approximately 50 mm thick layers of optimized, open-pore materials, even with various coatings and coverings for protective or decorative purposes. Sound absorbers based on resonance systems are rarely used alone, as they do not meet the usually specified broadband absorption spectrum. However, in combination with porous materials, resonance-type absorbers can improve broadband absorption.

[0005] Against this backdrop, the possibilities for equipping building facades with sound-absorbing properties must be considered. Theoretically, additional sound-absorbing layers could be placed on numerous facade systems. However, this is counteracted by costs, often unresolved fastening issues, architectural and aesthetic requirements, and building physics risks, e.g., with regard to thermal insulation or long-term resistance to hygrothermal stresses, vegetation, and soiling. In practice, some building facades contain materials that, if selected correctly from an acoustic perspective, could absorb sound without compromising their other hygrothermal functions. A related challenge is enabling sound penetration into the facade with additional sound-absorbing components. A further challenge from an acoustic perspective lies in the need for adaptation or optimization.The sound absorption spectrum must correspond as closely as possible to the noise spectrum, and the highest possible sound absorption effect is achieved for the range of sound incidence angles applicable in urban areas. In this case, it is important to consider, for example, where and in what spatial context sound propagates and how its spectral composition changes in the process. The noise directly adjacent to a main road is broadband, caused by various traffic noise sources. In a connected side street, the spectrum changes, for example, due to diffraction effects at the edges of buildings and the like. Depending on the location and configuration, the task therefore arises of a simple, effective and at the same time structurally and economically adapted design of the sound absorbing effectiveness, for example without having to significantly change the external appearance.

[0006] DE 295 12 787 U1 discloses a noise protection device, particularly for roadsides and tunnels. A variety of components containing resonators can be combined to form a noise-absorbing arrangement. Various resonators are present that respond to different frequency ranges, thus enabling broadband attenuation.

[0007] DE 1 712 145 U discloses a panel-shaped component for cladding walls and ceilings. Its exterior features a perforated cover that has little or no influence on the flow of sound. A sealed or perforated membrane is arranged with a gap behind the perforated cover. Behind the membrane is an air space divided by ribs or a continuous air space, which is closed off at the rear of the panel by the panel's rear wall.

[0008] From DB NETZE, release TM: 4-2015-10115 I.NPF 2, dated February 4, 2015, a noise protection device is known which has an aluminum expanded metal with a perforated area of ​​approximately 60% or a perforated aluminum sheet with a perforated area of ​​approximately 40% on the side facing the sound source, which is the rail side in the application described.

[0009] EP 1 391 570 A2 discloses a facade wall designed as a soundproof wall. The facade wall consists of facade panels suspended in a substructure that is attached to a stationary building wall. The facade panels are designed as soundproof facades by having horizontal ribs on their front side and vertical grooves on their back side. The ribs and grooves form openings in an overlapping area that are arranged in a hole pattern in the facade panel. However, they are not visible from the front side because they are covered by the horizontal ribs that slope downwards on the front side of the facade panel. A soundproof mat can be arranged on the side facing away from the front side of the facade panel.

[0010] From JP 2017 044 796 A an arrangement for sound absorption in the interior is known, whereby a combination of a micro-perforated surface and a porous layer is taught, cf. Fig. 2 and paragraph

[0021] of this document.

[0011] Further prior art is known from DE 1 695 391 U, from DE 10 2011 055 009 A1 and from JP H03-25108 A.

[0012] The object of this invention is therefore to provide a sound-absorbing exterior component with structurally and architecturally integrated sound absorption capacity that can be spectrally adapted to the respective noise situation. Solution

[0013] To solve the aforementioned problem, a sound-absorbing exterior component is proposed, which serves to absorb external noise. The sound-absorbing exterior component is designed in such a way that all protective functions (e.g., wind and rain, heat and moisture, etc.) as well as the architectural design options are permanently maintained.

[0014] First, the general solution and various designs will be presented.

[0015] A sound-absorbing external component of a building façade is proposed, which has the following features: on the side facing away from the building there is a perforated sheet material (4), e.g. made of metal, glass, wood, plastics and other composite materials, a chamber (5) serving for rear ventilation on the side of the perforated sheet material (4) facing the building, usually so that the perforated sheet material (4) and the chamber (5) form a cavity resonance system, on the side of the chamber (5) facing away from the perforated sheet material (4) there is a further sheet material (6), e.g. made of textile, film or membrane-like materials or corresponding composites thereof, with a specific flow resistance of less than 4,000 Pa s / m, adjoining the further sheet material (6) is a porous layer (7), e.g. made of open-pore fibrous, foamed, fleece-like or porous materials, with a length-related flow resistance between 5,000 and 50,000 Pa s / m 2<.

[0016] The sound-absorbing exterior component comprises two acoustically independent but coordinated systems located between an interior space (1) or its outer wall (2) and the exterior space (3). The system facing the exterior, i.e. usually the urban space, represents a cavity resonance system containing a perforated sheet structure (4) on the outer side facing the exterior space (3) and a chamber (5) behind it in the manner of an air layer or air spring. Viewed in this form alone, e.g. with an assumed reverberant rear wall, the system already exhibits sound absorption which depends on the design parameters of the perforated sheet structure (4), i.e. its shape, geometry (including the holes) and the resulting flow resistance, as well as the chamber (5), in particular the chamber depth.However, the sound absorption coefficient of this resonance system cannot achieve the high and broadband characteristics required for a significant noise reduction effect, e.g., on the order of magnitude of highly absorbent noise barriers (e.g., according to the Additional Technical Contract Conditions and Guidelines for the Construction of Noise Barriers on Roads, ZTV-Lsw06). In order to achieve this target sound absorption value, an additional sheet structure (6) with precisely matching characteristics is required on the side of the chamber (5) facing away from the perforated sheet structure (4), to which a porous layer (7) is attached. The desired broadband sound absorption is achieved through the interaction of the perforated and additional sheet structure, the porous layer, and the chamber. However, this requires specific, acoustically relevant parameters of the components involved.In order to determine and adjust these parameters, an impedance model must be taken into account. The acoustic impedance on the surface of the ventilated curtain wall component determines the reflection factor, which in turn leads to the sound absorption coefficient. The appropriate acoustic setting and adjustment of the parameters of the individual components of the ventilated curtain wall facade is carried out using impedance model calculations, whereby the sound spectrum and angle of incidence of the sound must also be taken into account. The parameters resulting from this optimization must, however, also fulfill other functions not related to acoustics. The perforated surface structure (4) acts as protection against the weather and mechanical stress from the outside. It must therefore be made of durable and stable materials. The chamber (5) serves as the through- or through-flow of sound.Rear ventilation to ensure that the porous layer (7) dries out, which in turn serves to insulate the building. To achieve this, the additional surface structure (6) must be permeable to diffusion and exhibit high resistance to water and air ingress. These functions must be fulfilled in such a way that they meet standardized requirements. This means that the optimization task in terms of sound absorption takes on further dimensions in the form of other building physics parameters. This complexity makes it difficult to consistently determine suitable acoustic parameters for the components of the ventilated curtain wall component. In order to provide architectural and structural design freedom, value ranges or adjustment options for the acoustic parameters are desirable in order to be able to optimize the acoustic effect of the ventilated curtain wall component with little effort and with hardly any externally noticeable changes under different operating conditions.

[0017] In this sense, the perforated area ratio of the perforated sheet (4) offers design flexibility. The perforated area ratio is the quotient of the perforated area and the total area and can theoretically lie between 0 (closed) and almost 1 (almost completely open). In practice, a perforated area ratio of perforated sheet structures for sound absorbers is possible from around 0.01, as is the case with micro-perforated sound absorbers, but it can also reach high values, e.g. with wire mesh or expanded metal. The thickness of the perforated sheet (4) is such that the perforated area ratio must also increase with increasing thickness. The depth of the chamber (5) for typical ventilated components, e.g. in facades, is approximately 10 to 40 mm and must be taken into account acoustically but not determined. The specific flow resistance rS of the remaining sheet (6) is, however, crucial.In addition to parameters such as open porosity and structure factor, specific flow resistance has a significant influence on sound absorption. It describes the ratio of the pressure difference Δp [Pa] in front of and behind a material layer to the velocity of the air flowing through it u [m / s]: . rS = Δp / u Pa s / m

[0018] The specific flow resistance of an insulating material increases with increasing layer thickness. Therefore, the linear flow resistance is also used as a material characteristic by referring to this layer thickness d [m] in the flow direction: r = rS / d Pa s / m 2

[0019] For the additional sheet material (6), numerous tests have shown that its specific flow resistance must be less than 4,000 Pa s / m. This characteristic is unusual for two reasons. Firstly, sheet materials in ventilated curtain walls have not yet been considered at all with regard to the flow resistance of their components. In view of the associated standard DIN EN ISO 13859, this value is neither determined nor applied. Secondly, only a few materials allow a combination of this flow resistance with the other requirements, such as a resistance to water penetration of class W1 to W2 and a water vapor diffusion resistance (sd value) in the typical order of 0.02 m.In terms of water penetration, class W1 is met if a material can withstand a water column of 200 mm for two hours, while class W2 is sufficient if the amount of water passing through at such a water column of 200 mm is less than 100 ml / m 2<.

[0020] In addition, it should be noted that the specific flow resistance should normally be at least 100 Pa s / m.

[0021] Somewhat more common is the material definition of the porous layer (7) using the length-related flow resistance, in this case. As already stated, this is also an important acoustic parameter for sound absorption. Since this layer is usually significantly thicker than acoustically necessary due to the required high level of thermal insulation, the specific flow resistance is not suitable in this case. It is important that the length-related flow resistance of the porous layer (7) is between 5,000 and 50,000 Pa s / m 2<. This value range, in close coordination with the specific flow resistance of the other surface structure (6), allows the use of different insulation materials, e.g. for weight or cost reasons. With the features described so far, a sound-absorbing exterior building component can be designed that absorbs sound waves arriving at the component from urban areas, i.e. external noise, across a wide bandwidth and at a high level.

[0022] The arrangements described at the beginning in DE 295 12 787 U1, DE 1 712 145 U and DB NETZE, release TM: 4-2015-10115 I.NPF 2, dated February 4, 2015, are not suitable for use on facades. The state of the art described is optimized to achieve sound absorption, but the requirements for a facade are not met. The chamber (5) provided here, which serves for rear ventilation, is a challenge from an acoustic point of view. Although the perforated sheet structure (4) serves as protection against the weather, the perforation in particular allows moisture to penetrate. With a facade, it is important that the moisture is removed again. This is achieved through the rear ventilation in the chamber. Therefore, the chamber serving for rear ventilation is essential for a facade, but not required for a noise barrier or a sound-absorbing device attached to a tunnel wall.

[0023] The chamber (5) serving as rear ventilation should preferably be vertically flow-through with as little obstruction as possible. No lateral limitations are required. Essentially, only fastening elements for the mechanical attachment of the perforated surface structure (4) to the rest of the facade are required, which should be designed in such a way that the rear ventilation function is not disrupted.

[0024] In one embodiment, the perforated sheet material (4) contains, on its side facing the chamber (5), a layer (8) which is at most a few millimeters thin, e.g. made of textile, film-like, or membrane-like materials or corresponding composites thereof, the specific flow resistance of which, divided by the perforated area proportion of the perforated sheet material (4), has a value between 300 and 500 Pa s / m. The thin layer (8) is generally no more than 5 mm thick. A person skilled in the art can determine a suitable value based on the information described here.

[0025] A number of acoustic design options apply to the perforated sheet (4). For example, sound absorption can be controlled by applying a layer (8) that is a maximum of a few millimeters thick on the side of the perforated sheet (4) facing the chamber (5). The thin layer can be applied, for example, by coating, adhesive, or cladding. The specific flow resistance of the thin layer, divided by the perforated area of ​​the perforated sheet (4), should be between 300 and 500 Pa s / m.

[0026] In a further embodiment, an additional perforated surface structure is located on the side of the thin layer (8) facing the chamber (5). This protects the thin layer from mechanical stress.

[0027] In one embodiment, the openings of the perforated sheet (4) are filled flush with porous material (9). It should be noted here that perforated elements always have a plurality of openings, since the perforations are also considered openings. If the openings are filled flush with porous material, as in the present embodiment, the external appearance is that of a flat, closed surface. The acoustic effect is comparable to that of the thin layer (8).

[0028] In one embodiment, the perforated sheet (4) is inclined outward relative to the vertical. Even a slight inclination is sufficient. Thus, the perforated sheet can be inclined outward from below, i.e., away from the building. At the upper end of the perforated sheet, a non-perforated sheet can lead back toward the building.

[0029] Due to the outward inclination, rain coming diagonally from above cannot reach the openings directly, while sound coming diagonally from below can penetrate the openings almost unhindered.

[0030] In one embodiment, the openings of the perforated sheet (4) are oriented obliquely downwards. Thus, the above statements regarding the inclination of the perforated sheet (4) apply to rain and sound.

[0031] In one embodiment, the chamber (5) has vertical sound-absorbing strips (10) to dampen the cavity. These should generally be arranged in such a way that rear ventilation is not obstructed or is obstructed as little as possible.

[0032] In one embodiment, air purification devices (11) comprising fans and filters are located in the chamber (5). Such devices can improve rear ventilation. Furthermore, under certain circumstances, air can be drawn in and purified from the outside, usually a polluted urban area.

[0033] In one embodiment, the porous layer (7) is divided into at least two layers with different properties by at least one water vapor permeable separating layer (12), e.g. made of textile, film or membrane-like materials or corresponding composites thereof. The two layers can be made of different materials. This can make it easier to meet all acoustic and other building physics requirements. The separating layer (12) generally has a high resistance to air penetration and water penetration, thus fulfilling the above-mentioned classes W1 and W2. A high resistance to air penetration can be considered to be met if the air permeability at a pressure difference of 50 Pa is less than 0.1 cubic meters of air per square meter and hour. Description of the characters

[0034] Further details are explained using the figures. Fig. 1Exemplary embodiment of the ventilated curtain wall component according to the invention Fig. 2Exemplary embodiment of the component according to the invention with a layer 8 that is at most a few millimeters thick on the side of the perforated sheet structure 4 facing the chamber 5 Fig. 3Exemplary embodiment of the component according to the invention with double-sided protection of the layer 8 against mechanical stress by positioning it between two perforated sheet structures 4 Fig. 4Exemplary embodiment of the component according to the invention with flush filling of the openings in the perforated sheet structure 4 with porous material 9 Fig. 5Exemplary embodiment of the component according to the invention with a perforated sheet structure 4 that is slightly inclined outwards compared to the vertical Fig. 6Exemplary embodiment of the component according to the invention with openings in the perforated sheet structure 4 that are oriented obliquely downwards Fig.7Exemplary embodiment of the component according to the invention with vertical sound-absorbing strips 10 in the chamber 5 for damping the cavity without obstructing the rear ventilation Fig. 8Exemplary embodiment of the component according to the invention with devices for air purification 11, consisting of fans and filters, in the chamber 5 Fig. 9Exemplary embodiment of the component according to the invention with a water vapor diffusion-open separating layer 12 with high resistance to air and water passage in the porous layer 7 .

[0035] The figures are briefly explained below. To avoid repetition, reference is made to the above explanations of the general solution approach, particularly regarding the functional relationships.

[0036] In Figure 1An interior space 1 of a building can be seen, which is separated from the exterior space 3 by a wall 2. The perforated sheet structure 4 borders the exterior space 3. On the side of the perforated sheet structure 4 facing away from the exterior space 3 and towards the building, there is a chamber 5 serving for rear ventilation, to which another perforated layer 6 is connected. This is followed by a porous layer 7, which borders the wall 2 of the building.

[0037] To the Figures 2 to 9 only the differences to Figure 1 mentioned.

[0038] Figure 2 differs from Figure 1 in that a thin layer 8 is attached to the perforated layer 4 on the side facing the chamber 5.

[0039] According to Figure 3 the thin layer 8 is also protected by a perforated layer on the side facing the chamber.

[0040] According to Figure 4the openings of the perforated sheet 4 are filled flush with porous material 9.

[0041] Figure 5 shows a design in which the perforated surface structure 4 is inclined outwards from the vertical, i.e. from below away from the building.

[0042] Figure 6 shows a design in which the openings of the perforated surface structure lead diagonally downwards.

[0043] In Figure 7 vertical sound-absorbing strips 10 are shown in the chamber 5.

[0044] In Figure 8 In the chamber 5, a device 11 for air purification is shown, which has fans and filters.

[0045] In Figure 9 Finally, an embodiment is shown in which the porous layer 7 is divided into two layers with different properties by a water vapor diffusion-open separating layer 12 with high resistance to air and water penetration.

Claims

1. A sound-absorbing exterior component of a façade of a building, that has the following features: - a perforated sheet-like structure (4) on the side facing away from the building, - a chamber (5) on the side of the perforated sheet-like structure (4) facing the building, wherein rear ventilation is provided for removing moisture from the chamber (5), - on the side of the chamber (5) facing away from the perforated sheet-like structure (4) there is a further sheet-like structure (6) with a specific flow resistance of less than 4,000 Pa s / m, - a porous layer (7) with a length-related flow resistance of between 5,000 and 50,000 Pa s / m2 is adjacent to the further sheet-like structure (6).

2. The sound-absorbing exterior component according to claim 1, characterised in that the perforated sheet-like structure (4) includes, on its side facing the chamber (5), a layer (8), which is at most several millimetres thin, the specific flow resistance of which, divided by the proportion of the perforated surface area of the perforated sheet-like structure (4), has a value of between 300 and 500 Pa s / m.

3. The sound-absorbing exterior component according to claim 2, characterised in that an additional perforated sheet-like structure is located on the side of the thin layer (8) facing the chamber (5).

4. The sound-absorbing exterior component according to any one of the preceding claims, characterised in that the openings of the perforated sheet-like structure (4) have a filling of porous material (9) flush with the surface.

5. The sound-absorbing exterior component according to any one of the preceding claims, characterised in that the perforated sheet-like structure (4) is inclined outwards from the vertical.

6. The sound-absorbing exterior component according to any one of the preceding claims, characterised in that the chamber (5) has vertical sound-absorbing strips (10) for damping the cavity.

7. The sound-absorbing exterior component according to any one of the preceding claims, characterised in that air purification devices (11), comprising fans and filters, are located in the chamber (5).

8. The sound-absorbing exterior component according to any one of the preceding claims, characterised in that the porous layer (7) is divided into at least two layers with different properties by means of at least one separating layer (12) which is open to the diffusion of water vapour.