Showing posts with label 2. Acoustics and Facades. Show all posts
Showing posts with label 2. Acoustics and Facades. Show all posts
2.1 Attenuation Incorporated into a Facade
One of the main difficulties in designing low energy buildings can be the prevention of noise break-in via vented facades. This chapter looks at a range of options and details which can be used to prevent environmental noise break-in from motorways, dual carriageways, trains, aeroplanes, inner city noise and other noise sources.
To overcome this issue an attenuator is selected and incorporated into the facade. This attenuator is typically combined with a damper such to control the flow of air into the building with a weather louvre being used externally to provide the weather protection. MACH Acoustics describes this combination of units as the ‘NAT Vent Box’. The outline schematic of this system is shown below. The damper can take the form of a thermal volume control damper, open-able vents within the facade, thermal insulated doors etc.
To overcome this issue an attenuator is selected and incorporated into the facade. This attenuator is typically combined with a damper such to control the flow of air into the building with a weather louvre being used externally to provide the weather protection. MACH Acoustics describes this combination of units as the ‘NAT Vent Box’. The outline schematic of this system is shown below. The damper can take the form of a thermal volume control damper, open-able vents within the facade, thermal insulated doors etc.
2.2 NAT Vent Box
The key elements making up the Nat Vent Box are shown in the illustration to the left. Air is brought in through the external weather louvre 11, then through a volume control damper 10. The volume control damper can either be used to seal the building or manage/control the fl ow of air into the building. This damper can be manually operated by means of a handle or Teleflex cable. Motorised thermal dampers can be used in combination with a BMS system. A second important function of the thermal damper is to maintain the thermal line/thermal performance of the building envelope when shut.
The noise reduction across this unit is achieved through the attenuator 9. The attenuator is incorporated between the thermal damper and an internal louvre 8. The attenuator is formed by stacking W-shaped tiles which creates a honeycomb structure, restricting the passage of sound. Air however, is still allowed to fl ow through the central paths of the honeycomb body. The difference between the external noise levels and the required internal noise levels, governs the depth of the attenuator 9, the greater the difference the deeper the attenuator.
Finally, the internal louvre can be manufactured from wooden slats, perforated metal, or a conventional internal louvre can be used.
The noise reduction across this unit is achieved through the attenuator 9. The attenuator is incorporated between the thermal damper and an internal louvre 8. The attenuator is formed by stacking W-shaped tiles which creates a honeycomb structure, restricting the passage of sound. Air however, is still allowed to fl ow through the central paths of the honeycomb body. The difference between the external noise levels and the required internal noise levels, governs the depth of the attenuator 9, the greater the difference the deeper the attenuator.
Finally, the internal louvre can be manufactured from wooden slats, perforated metal, or a conventional internal louvre can be used.
2.3 Locating Inlet Vents and Cross Vents as a Noise Control Measure
Locating Air Inlet Vents
The orientation of a building has a significant impact upon noise levels at the different facades of the building. It is often the case that facades on the opposite side of a building to a significant noise source will be considerably lower than those on the noisy side of the building.
By orientating the building and by placing non-critical spaces on the noisy side of a building, it is possible to form a good acoustic buffer. In these instances, cross vent can be used where the air intake is placed on the quiet side of the building. Cross ventilation to an atrium or circulation zone is then used to provide the air extract. Alternatively, single sided ventilation could be used for sensitive spaces on the quiet side of a building.
1 shows sound levels around a building in the form of a noise map. The classroom on the far side of building to the A40 are vented using openable windows.
Cross Vent to Assist with the Prevention of Noise Break-in
In instances where a building is located on an exceptionally noisy site, cross ventilation can improve the feasibility of natural ventilation. Cross ventilation has an important advantage over single sided ventilation, in that air inlet vents can be between 25% to 75% smaller than those required for single sided ventilation. This significant reduction in vent size helps considerably in preventing noise break-in, as smaller vents restrict the passage of sound into a building.
The orientation of a building has a significant impact upon noise levels at the different facades of the building. It is often the case that facades on the opposite side of a building to a significant noise source will be considerably lower than those on the noisy side of the building.
By orientating the building and by placing non-critical spaces on the noisy side of a building, it is possible to form a good acoustic buffer. In these instances, cross vent can be used where the air intake is placed on the quiet side of the building. Cross ventilation to an atrium or circulation zone is then used to provide the air extract. Alternatively, single sided ventilation could be used for sensitive spaces on the quiet side of a building.
1 shows sound levels around a building in the form of a noise map. The classroom on the far side of building to the A40 are vented using openable windows.
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In instances where a building is located on an exceptionally noisy site, cross ventilation can improve the feasibility of natural ventilation. Cross ventilation has an important advantage over single sided ventilation, in that air inlet vents can be between 25% to 75% smaller than those required for single sided ventilation. This significant reduction in vent size helps considerably in preventing noise break-in, as smaller vents restrict the passage of sound into a building.
2.4 Bench Seating
Adding attenuation to the vented facade of a single storey building is comparatively easier than a multistory building, since it is often possible to extend the building envelope, accommodating the additional depth of the NAT Vent Boxes.
In the case of single storey buildings, it is common to maintain a simple vertical thermal line, by placing the thermal damper into the line of the facade 4. The acoustic attenuation in this instance is placed on the external side of the building. This design approach has been implemented by MACH Acoustics on several projects.
The NAT Vent Box has been installed under bench seating, flower boxes, play boxes, small steps in the facade and other elements. These units have all been used to hide and accommodate the additional facade depth often required when naturally ventilating a building on a particularly noisy site.
A second advantage of single storey buildings is the potential to incorporate the NAT Vent Box above or within roof lines, above corridors, over storage rooms and other areas.
In the case of single storey buildings, it is common to maintain a simple vertical thermal line, by placing the thermal damper into the line of the facade 4. The acoustic attenuation in this instance is placed on the external side of the building. This design approach has been implemented by MACH Acoustics on several projects.
The NAT Vent Box has been installed under bench seating, flower boxes, play boxes, small steps in the facade and other elements. These units have all been used to hide and accommodate the additional facade depth often required when naturally ventilating a building on a particularly noisy site.
A second advantage of single storey buildings is the potential to incorporate the NAT Vent Box above or within roof lines, above corridors, over storage rooms and other areas.
2.5 Window Details
The details used to incorporate the attenuation box into a seat or play box are very similar to those used when incorporating the NAT Vent Box into the facades of buildings. As noted, it is often easier to extend out the facade line of single storey buildings such to accommodate deep attenuators. This in turn means that it is seen as possible to provide natural ventilation irrespective of noise levels. The illustration below 1 was used to control noise break-in to a sensitive office space in close proximity to a major motorway.
Installation of the Attenuator
Forming the NAT Vent Attenuator by tessellated, W-shaped foam blocks, means that this product can easily be dropped into a timber enclosure or metal duct work. The W-shaped tiles compress and can be cut to any size; hence these units are extremely easy to accommodate into the facade of a building 2
Installation of the Attenuator
Forming the NAT Vent Attenuator by tessellated, W-shaped foam blocks, means that this product can easily be dropped into a timber enclosure or metal duct work. The W-shaped tiles compress and can be cut to any size; hence these units are extremely easy to accommodate into the facade of a building 2
2.6 Window Systems and Curtain Walling
The thermal damper is one of the main factors affecting the cost and depth of the NAT Vent Box. Replacing the damper with an openable or motorised vent/window, eliminates both the thermal damper and weather louvre from the box make up. This typically reduces costs by ≈50% and can reduce its depth by ≈225mm.
Facade and window manufacturers can easily accommodate openable vents in curtain walling or window frames. Placing the NAT Vent Attenuator directly behind an open vent, provides a simple, cost effective design solution for preventing noise break-in.
High level air inlet
In the case where noise levels are exceptionally high, for example due to motorway noise, flight paths or inner city noise, the depth of the attenuator is required to be increased. The additional depth of the NAT Vent Box can be accommodated by using a high level bulkhead 11.
Facade and window manufacturers can easily accommodate openable vents in curtain walling or window frames. Placing the NAT Vent Attenuator directly behind an open vent, provides a simple, cost effective design solution for preventing noise break-in.
High level air inlet
In the case where noise levels are exceptionally high, for example due to motorway noise, flight paths or inner city noise, the depth of the attenuator is required to be increased. The additional depth of the NAT Vent Box can be accommodated by using a high level bulkhead 11.
2.7 Louvred Facade
As shown, the NAT Vent Box can be used to provide a vertical air inlet. This arrangement provides a design opportunity to provide colour and depth to a building’s façade.
A second advantage is that it is often possible to place NAT Vent Boxes within the corner of a room. Here, it may be easier to incorporate a deeper Vent Box 1 - 4. Alternatively, it may be possible to pull the facades out in certain areas such to accommodate a deeper NAT Vent Box. Both of these designs are recommended when external noise levels are particularly high.
A further benefit of using a vertical louvre is the potential to incorporate acoustic attenuation into the blades. For free area reasons, this design can only be adopted if the louvres run vertically.
A second advantage is that it is often possible to place NAT Vent Boxes within the corner of a room. Here, it may be easier to incorporate a deeper Vent Box 1 - 4. Alternatively, it may be possible to pull the facades out in certain areas such to accommodate a deeper NAT Vent Box. Both of these designs are recommended when external noise levels are particularly high.
A further benefit of using a vertical louvre is the potential to incorporate acoustic attenuation into the blades. For free area reasons, this design can only be adopted if the louvres run vertically.
2.8 Internal Sliding Doors and Windows
The presented illustrations show alternative arrangements 9 – 13. In this case, the NAT Vent Attenuator is placed on the outside of a thermally insulated door or sliding window. The key advantage of this scheme is that it again eliminates the need for a thermal damper. Additionally, it can often be easier to accommodate the NAT Vent Box outside of the thermal line.
2.9 Double Facade
Double facades can be used to control environmental noise break-in without the need for acoustic attenuation. When using a double facade, air enters the building through conventional open windows. The acoustic protection is achieved by acoustically screening these windows by means of a secondary facade. Air enters the void between the two facades via a gap at the bottom of the outer, secondary facade. The edges of the secondary facade are typically taken back to the primary building envelope. Attenuation may be required at the air inlet between the two facades. The advantage of this type of facade is the fact that simple openable windows can be used. It is also possible to form buildings with an interesting and unique appearance.
The drawbacks are clearly cost and space and for these reasons this type of noise control measure is somewhat uncommon.
It is also important to note that the acoustic separation between two rooms can be compromised when windows are open. Acoustic splitters or absorption may be required.
The drawbacks are clearly cost and space and for these reasons this type of noise control measure is somewhat uncommon.
It is also important to note that the acoustic separation between two rooms can be compromised when windows are open. Acoustic splitters or absorption may be required.
2.10 Secondary Facades - External Ventilation Shafts
An alternative to secondary facades is to use external chimneys. This scheme uses very similar principles to that of a double facade; the difference being that the external chimneys are only used over the ventilation openings. This arrangement clearly has cost and space saving advantages over that of double façades.
A second architectural advantage is that it is possible to provide an animated facade. Forming the chimneys from glass or other translucent materials, allows interesting designs in the form of graphics to be incorporated within the chimneys, adding further interest to the facade of the building.
One of the drawbacks of this design is that acoustic treatment may be required within the chimneys to prevent the spread of sound along its length. This may be required to maintain the acoustic separation across floors. If this is the case, acoustic art work could be used to give the architectural design and also to provide the acoustic absorption within the chimneys.
A second architectural advantage is that it is possible to provide an animated facade. Forming the chimneys from glass or other translucent materials, allows interesting designs in the form of graphics to be incorporated within the chimneys, adding further interest to the facade of the building.
One of the drawbacks of this design is that acoustic treatment may be required within the chimneys to prevent the spread of sound along its length. This may be required to maintain the acoustic separation across floors. If this is the case, acoustic art work could be used to give the architectural design and also to provide the acoustic absorption within the chimneys.
2.11 External Spaces as Secondary Facades
Secondary Façade as a Functional Space
Often there is a need for spaces such as cloakrooms, changing areas, walkways, balconies and other non-acoustically sensitive spaces to be located adjacent to a building. By making these spaces external and unheated, i.e. open covered spaces, it is possible to use these areas as a secondary facade . If required, additional acoustic protection can be added by means of placing an attenuator within the secondary facade 1. This attenuator could be located under benches, cupboards, shelving areas, raised areas etc. This would be an ideal way of preventing noise break-in from low flying aircraft, nearby rail lines, or a large main road such as a motorway.
Acoustic screening and ventilating from under a building
Acoustic screening is an effective method of controlling noise break-in to a building.
Illustration 2 shows how a large, suspended, raised (play) area was used to accommodate the fall in the land across a school site. This play area provided a highly effective screen to aircraft noise and potentially other major noise sources. The acoustic attenuation is provided as the vents under the deck have little or no visibility to the noise sources affecting the development. In simple terms, providing an air inlet under the building prevented noise ingress into the building.
Often there is a need for spaces such as cloakrooms, changing areas, walkways, balconies and other non-acoustically sensitive spaces to be located adjacent to a building. By making these spaces external and unheated, i.e. open covered spaces, it is possible to use these areas as a secondary facade . If required, additional acoustic protection can be added by means of placing an attenuator within the secondary facade 1. This attenuator could be located under benches, cupboards, shelving areas, raised areas etc. This would be an ideal way of preventing noise break-in from low flying aircraft, nearby rail lines, or a large main road such as a motorway.
Acoustic screening and ventilating from under a building
Acoustic screening is an effective method of controlling noise break-in to a building.
Illustration 2 shows how a large, suspended, raised (play) area was used to accommodate the fall in the land across a school site. This play area provided a highly effective screen to aircraft noise and potentially other major noise sources. The acoustic attenuation is provided as the vents under the deck have little or no visibility to the noise sources affecting the development. In simple terms, providing an air inlet under the building prevented noise ingress into the building.
2.12 Solar Shading and Acoustic Screening to Open Windows
‘Acoustic Scaled Models of Vented Facades’ is a technology which has been developed by MACH Acoustics. This technology enables the effects of acoustic screens attached directly to the facade of a building to be assessed. Scaled models are typically used to assess the acoustics of auditoriums during the design stages. For major concert halls, a scaled model of the auditorium is built such to assess its acoustic performance and characteristics. Scaled models are used due to their practical, accurate and cost effective nature. The same principles apply to the design of screened acoustic facades. MACH Acoustics has developed a method of assessing the acoustic resistance of screens attached directly to the facade of a building by means of scaled models.
The illustration below shows two design options where screened facades were proposed in order to add acoustic attenuation to a vented facade within an inner city office block. This method of noise control is simple, cost effective and provides the additional acoustic resistance such to prevent inner city noise being a nuisance within the office accommodation. Screened facades are also a good method of meeting the requirements set out by BREEAM. The drawback of this system is that these screens can only enhance the performance of an open-able window by around 5 to 7 dB, meaning that these facades can only be used when external noise levels are moderately high.
The illustration below shows two design options where screened facades were proposed in order to add acoustic attenuation to a vented facade within an inner city office block. This method of noise control is simple, cost effective and provides the additional acoustic resistance such to prevent inner city noise being a nuisance within the office accommodation. Screened facades are also a good method of meeting the requirements set out by BREEAM. The drawback of this system is that these screens can only enhance the performance of an open-able window by around 5 to 7 dB, meaning that these facades can only be used when external noise levels are moderately high.
2.13 Screening under overhangs and above roof
The scheme below provides three design options incorporating acoustic screens into the facade of a development. In these instances, the air inlet vents are acoustically screened by baffles which break the line of sight to a given noise source. The acoustic screens are, in this instance, created by extending parts of the facade or adding panels to the facade such to cover the air inlet vents.
Option 1 - Overlapping Façades
With a perpendicular air inlet to the facade, this design provides an ideal screen to a noise source propagating from the left-hand side of the building.
Option 2 - Solar Shading and Acoustic Screening
Here a solid transparent screen incorporated into the solar shading, provides acoustic screening to a noise source directly in front of the building.
Option 3 - Photovoltaics used as Acoustic Screens
Photovoltaics provide acoustic screens in this instance. The photovoltaics are used to provide solar shading, power and acoustic attenuation, all within the building’s facade. Off-setting the photovoltaics and placing the air vents directly behind these panels provide high levels of acoustic resistance.
Option 1 - Overlapping Façades
With a perpendicular air inlet to the facade, this design provides an ideal screen to a noise source propagating from the left-hand side of the building.
Option 2 - Solar Shading and Acoustic Screening
Here a solid transparent screen incorporated into the solar shading, provides acoustic screening to a noise source directly in front of the building.
Option 3 - Photovoltaics used as Acoustic Screens
Photovoltaics provide acoustic screens in this instance. The photovoltaics are used to provide solar shading, power and acoustic attenuation, all within the building’s facade. Off-setting the photovoltaics and placing the air vents directly behind these panels provide high levels of acoustic resistance.
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