GB2472182A

GB2472182A - Air Vent

Info

Publication number: GB2472182A
Application number: GB0909558A
Authority: GB
Inventors: Jose Paulo Barnfather Dos Sautos Nunes
Original assignee: MACH ACOUSTICS Ltd
Current assignee: MACH ACOUSTICS Ltd
Priority date: 2009-06-04
Filing date: 2009-06-04
Publication date: 2011-02-02
Also published as: WO2010139951A1; GB0909558D0

Abstract

Attenuators to be used in the control of the spread of noise/speech through ventilation systems for low energy buildings (figs 5.0 to 8.0). The low air speeds (<1m/s) common to low energy ventilation systems, allows for rigid or semi rigid materials to form a range of attenuators 10.0. Rigid and semi rigid materials are processed into building blocks to generate self supporting or tessellating structures to create the building blocks to form splatters (figs. 2.1 or 3.0) or the entire attenuator. The slow air speed used to ventilate low energy buildings allows for the gap between the blocks forming splitters to be reduced, allowing the performance of the attenuator to be increased and tuned to a specific requirement. It is proposed to shape the building blocks forming splitters, such to maximize the acoustic performance of the attenuator.

Description

Title: Nat Vent

Description

ATTENUTOR TO BE USED IN COMBINATION WITH LOW ENERGY BUILDINGS

This invention relates to improving the acoustic design and manufacture of attenuators, specifically designed for buildings ventilated with low air speeds. These low air speeds through vents and attenuators are common to low energy and naturally ventilated buildings. /

The drawings isted and described below wdl be referred to in the rest of the descriptton to aid explanation.

Figure 1.0 Conventional Attenuator Figure 2.0 NAT Vent Attenuator -Example 1 and 2 Figure 3.0 Splitter Building Block Figure 4.0 Dimensions of the NAT Vent Attenuator Figure 5.0 Example of cross ventilation. Nat vent shown installed within the partition to circulation spaces. The Nat Vent is used to maintain the sound insulation of this partition, whilst allowing cross flow through the classroom and other cellular spaces.

Figure 6.A The steel above this partition restrains the use of a cross talk attenuator. Here the NAT Vent has been designed in combination with the steel, where the air passes thought the steel.

Figure 6.B This second design option proposes that the NAT Vent bends around the steel.

Figure 7.0 Example of cross ventilation. Here, the NAT Vent is used to maintain the sound insulation of the partition between two cellular spaces or between a cellular spaces and circulation spaces.

The NAT Vent is also used to enhance the acoustic performance of the facades.

Figure 8.0 Illustration of the NAT Vent installed into partition between a cellular space and a circulation space/zone. The shown flap is not required in all cases.

Figure 9.0 Example of material section such that the product can be made fire resistant, from recycled materials or to a budget.

Figure 10.0 Example of construction. 10.1 Block of material is cut.10.2 Waste material is removed 10.3 Wings for each of the splitters are bent down. 10.4 Splitters are stacked on top of each other. 10.5 The product is installed into a building or into a super structure.

Figure 11.0. Example of construction 11.1 Block of raw material is cut. 11.2 The waste material is removed. 11.3 Slitters are separated. 11.4 Every other splitter is rotated 11.5 The splitters are stacked to form the NAT Vent. The splitters are installed into a building or housed in a super structure.

Figure 12.0 Example of extruded material. 12.1 Raw material is extruded through a die. 12.2 The extruded material is cut into sections. 12.3 The material is stacked, the NAT Vent is installed into a building or super structure.

Figure 13.0 Example of tessellated shape by cutting 13.1 Block of raw material is cut. 13.2 Splitters are separated. 13.3 The tessellated shape creates the flow path. 13.4 Denser material can be mixed with less dense material to optimize performance 13.5. The splitters can be combined with solid elements.

Figure 14.0 Reactive Components. 14.1 and 14.3 act as a mass as a result of sound waves forcing the air to move between the splitters. The air mass 14.1 is different to 14.3, due to the configuration of the splitters, which depends on the tuning optimization needed. 14.2 acts as a spring since the air is compressed within this zone.

The Natural Vent Attenuator is therefore a product specifically designed for low energy buildings and aims to overcome the clashes between natural ventilation and acoustics. The Natural Vent Attenuator can be incorporated into the façade of a building to reduce noise ingress 7.0, as well as being incorporated above a partition to control noise transfer between partitioned spaces, 5.0, 6.A, 6.B, 7.0, 8.0, whilst allowing the passage of air through the building. The innovative concepts within this product, enables the performance of the attenuator to be specifically designed to the acoustic requirements of a given building, a buildings applications needs and the building construction process.

The low air speed through attenuators means that pressure drops across these units do not increase dramatically when changes are made to the standard rectilinear or chevrons design, thus still allowing a required volumetric rate of air to ventilate a space with said requirement by forces associated with natural ventilation. As such, there is considerably more design flexibility in terms of the air path through the attenuator, which in turn results in considerable benefits to the acoustic performance of the attenuator.

The low air speeds through these attenuator means that alternative forms of construction can be used.

The low air speed considerably reduces wind load on the splitters. It is therefore possible to used rigid and semi rigid materials to form single component splitters. The use of rigid and semi rigid materials enables splitters to be formed as the building blocks 2.4, 2.5, 3.0, 9.0, 10.4, 11.3, 12.2 which are pre shaped 10.1, 11.1, 12.1, 13.1 prior to the construction of the attenuators by cutting, extrusion, heating, etc. These building blocks can then be fixed, interlocked, sandwiched, layered, tessellated together to form a structure, seff supporting structure or part of a super structure 1.1, 2.6, resulting in an attenuator.

CONVENTIONAL ATTENUATORS

Mechanical ventilation systems within conventional buildings use large fans, ducts, etc. to provide ventilation and extraction to cellular and other forms of accommodation. The accepted method of reducing fan and other noises within these systems is to insert a purposely manufactured attenuator, 1.0, in the duct work between the fan and the accommodation to be served. The nature of the manufacture of these attenuators means that they are produced in standard sizes and shapes. Due to the high air speeds within these systems, there is a need to design attenuators to mitigate a gain in pressure drop across attenuators. This is performed partly by restricting the minimum gap between the splitters 1.3, which in turn controls and limits the acoustic performance of these attenuators.

The high air speed within mechanical ventilation systems means that the physical construction of the attenuator is required to be robust 1.5. It is vital that the shape of the splitters are not deformed with wind loads, the rigidity of the splitters ensures that the air gap 1.3 between each splitter is maintained constant.

The splitters are also required to be manufactured such that small pieces and parts of the attenuators do not break off and blow downstream of the attenuator.

Conventionally, splitters are formed from mineral wool or other acoustically absorbent materials 1.4, held within a metal or rigid enclosure/housing 1.2 or attach to a framing system. These enclosures/frames are then fixed screw, bonded, welded, crimped etc. into a large secondary super structure 1.1. The result is a robust product constructed from many parts, where each of these parts undergoes a range of processes during the manufacture of the product.

Conventional attenuators are therefore not directly suited to the application of low energy buildings, based upon the following reasons: * Their design intent is to control noise from fans and other industrial noise sources, rather than prevent noise ingress into buildings and the control of speech through ventilation vents in partitions.

a The manufacturing of conventional attenuators limits their form to round or rectilinear shapes.

The sizes of conventional attenuators are seen to have fixed dimension, ranging by fixed increments. This therefore limits the application of conventional attenuators to be integrated to a specific buildings requirement.

* The design of conventional attenuators is limited by a compromise between pressure drop and the acoustic performance of the attenuator.

* As a result, these products do not achieve particularly high levels of acoustic attenuation at a comparable length to the NAT Vent.

* The high air speeds requires the splitters to be robust such not to deform under wind loads.

* This robustness increases the range of manufacturing processes and materials used, which increases cost and limits the shape and size of the attenuators as well as the acoustic performance.

LOW ENERGY BUILDINGS

The Natural Vent Attenuator (NAT Vent) is a product specifically designed for low energy buildings and aims to overcome the clashes between natural ventilation and acoustics. The NAT Vent can be incorporated into the façade of a building to reduce noise ingress, as well as being incorporated into partitions to control noise transfer, whilst allowing the passage of air through the building.

In low energy buildings, air is conventionally brought into the building via open vents in the building facade. The movement of air is driven through the building as a result of wind and very small pressure changes, often caused by buoyant air movements. As a result, low energy buildings typically use large open vents >0.25m2 in the building's façade as well as large vents >0.25m2 in partition to allow the flow of air through the building.

This type of ventilation is extremely energy efficient but allows for the passage of environmental noise (road, rail and aircraft) into buildings. As such, these types of buildings can only be built on quiet sites away from roads, trains lines and other noise sources. This seriously limits the number of sites available to low energy buildings. The Nat Vent is therefore proposed to be incorporated into the façade 7.0, 7.2, 7.3 of a building such to increase the acoustic resistance of the façade and increase the number of sites available to natural ventilation.

Low energy buildings work most effectively when "cross ventilation" is employed. In this case, air is brought in through the building façade and then passes across a given space and out through a partition into another part of the building e.g. corridor, atrium, etc. In the case of cross ventilation, the spread of noise through a partition is a second major limiting factor. The spread of noise across a partition through a ventilation system is known as cross talk 5.0, 6.A, 6.B, 7.0, 8.0. The NAT Vent is used to maintain the acoustic performance of the partition.

Buildings only require a minimal level of fresh air to replenish oxygen and other vital requirements. It is therefore often the case for the air within a building to re-circulate. Air recirculation is undertaken such to make use of the existing hot/temper air held in a building. Within some low energy buildings, air is collected at given points, top of an atrium, end of a circulation zone, etc. and then pushed back through the building into occupied cellular spaces. To reduce energy consumption, it is vital that ventilation passes with low flow resistance are provided between the air collection point, the vented accommodation and vice versa. The drawback of these air paths is that they are large and have the potential to allow the passage of sound. The low pressure drop, bespoke shape and high acoustic performance of the NAT Vent, makes it ideal for these applications.

Within a naturally ventilated building, the acoustic requirements needed from attenuators can be much higher, since the attenuators are required to match the performance of the partition. The size of these vents are also typically very large >0.25m2, meaning that the vents can seriously compromise the performance of the partition. Conventional attenuators will need to be impractically long to match the performance of the partition between two spaces. Additionally, one or more attenuators are needed per cellular space, hence cost is a primary limiting factor of conventional attenuators. The size of conventional attenuators is also fundamental as they cannot be too big and intrusive as they will be visible from within the room, which is not desirable to architects.

SPECIFICATION

The NAT Vent is specifically aimed at improving the acoustics of naturally ventilated, low energy buildings, outside of the residential sector. The ventilation rates to these buildings are very much dependent on the heat gain and ventilation requirements.

The NAT Vent is designed to ventilate spaces which require ventilation openings with a free area of at least 0.5% of the ventilated spaces floor area.

The NAT Vent is seen to have a minimum face area of <0.25m2, the free area of at least 0.125m2.

The air speed through the NAT Vent will be less than I ms1.

The acoustic performance of the NAT vent depends upon the required level of separation required across this device. 545 dB Dnew The size of the unit is dependent upon the ventilation rate and free area requirements of specific buildings. The overall dimension of the NAT Vent is also proportional to where the installation of the NAT Vent occurs within the building. Figure 4.0 provides the dimension range for the NAT Vent.

INNOVATIVE STEPS

Manufacturing -Splitter Shape -Eliminating the housing or super structure 1.1, 2.6 as well as supporting elements to a splitter 1.1, 1.2, 1.5, enables the manufacturing process used to form an attenuator to be adapted. Processing semi rigid and rigid acoustically absorbent materials enables splitters to be formed as a single part 2.4, 2.5, 3.0, 10.3, 11.2, 12.3, 13.1. The principle innovative step is therefore to form an absorbent, standalone structure, to be used as the repeated building blocks used to form the attenuators for low energy buildings 9.0 -13.0.

The shape, form and properties of these building blocks can be designed such to facilitate in the construction of the attenuators. It is proposed to design and shape these single component buildings such that each building block interlocks, rests against, stacks, layers, fits against the multiple blocks forming the attenuator 9.0 -13.0.

This process means it is possible to generate the entire attenuator from splitter building blocks. Building blocks will be shaped and sized such that air ways and splitter within the attenuators will be self supporting. This eliminates the requirements for shelves, brakes, housing and other structural supports when forming attenuators. The shape of the building blocks will be selected such to minimize waste.

The attenuator building blocks will be cut from a block of material 10.1, 12.2, formed by raw materials; granulated, liquid or semi rigid by pressing, heating, extruding, or chemical means 10.1, 11.1, 12.2, is proposed to form the attenuator building blocks 3.0. Working with the raw materials means greater flexibility in terms of size. Raw materials can easily be cut, shaped or extruded into non standardized sizes (any size) 3.0.

Since it is possible to form the entire attenuator from building blocks, an attenuator super structure 1.1, 2.6 is no longer required in all instances.

In some instances, the building blocks will be combined with solid elements 13.5 such to boost the acoustic performance of the splitters and attenuator.

The shapes of these building blocks can be selected such to increase and tune the acoustic performance of the attenuator, as well as reduce manufacturing times and aid with air flow through the attenuator Splitter and Lining Material -Density -The density of the materials used within the design of the attenuator and splitters is important. A low density material offers a higher level of acoustic absorption, which in turn provides high levels of acoustic attenuation through the air path of the attenuator. In contrast, the passage of sound directly through a light material is greater than that of a denser material.

Therefore, the selection of light weight materials can compromise the performance of the attenuators by allowing the passage of sound through the solid section of the attenuator, noting that the levels of acoustic attenuation through the attenuators air path and the propagation of sound through solid components making up the splitters is frequency dependant.

Where dense materials are used to form the splitters, the low frequency performance of the attenuator is increased. On the other hand, the overall performance of the attenuator is compromised as a result of reduced levels of acoustic absorption.

Such to overcome this issue, it is proposed to use materials with different densities within the construction of the NAT Vent 13.4. These denser materials could be used to form splitters in their own right or combined within or around splitters such to increase the density of the splitter.

The density of the materials is therefore a known factor in the performance of these products. It is also known that combining materials of different densitys can affect the performance and frequency performance of the product.

Splitter and Lining Material -Absorbent Properties -The level of attenuation provided by an attenuator has a strong correlation with the level of acoustic absorption provided by the materials used to form the attenuator. Levels of acoustic absorption will have an effect on both the magnitude and frequency characteristics of the attenuator -the higher the level of absorption, the better the performance of the attenuator. There is therefore a desire to increase the performance of the attenuator as much as possible by means of material selection.

Splitter and Lining Material -Rigidity and Robustness -The rigidity of the materials selected will be such that splitters and other elements will be self supporting and do not deform or sag over time or under wind loads.

Splitter and Lining Material -Partial -These attenuators will be used within ventilation systems. Partial size and partial migration of these partials will therefore be considered.

Splitter and Lining Material -Fire Properties -In the case where fire resistance is required, material selection when forming the attenuator will be considered 9.0.

Splitter and Lining Material -Recycled Properties -In the case where recycled materials are required, material selection when forming the attenuator will be considered 9.0.

Splitter and Lining Material Cost Properties -In the case where costs of materials is required to be reduced, material selection when forming the attenuator will be considered 9.0.

Splitter and Lining Material -Surface Finish -The surface finish and shape of the materials used to form the splitters will be selected such to mitigate against pressure drops as a result of roughness, consequential boundary layer effects and the recirculation of air.

Splitter and Lining Designs -Reduced gap between splitters -As the gap between splitters is reduced, the acoustic performance of the attenuator tends to rise. Likewise, the pressure drop across the attenuator increases. As noted, this is often a restraining factor when designing and selecting attenuators.

The low air speeds within low energy buildings allows for a significantly greater variation in gap size 2.2, due to the reduced air speeds and subsequent reduced pressure drop across the attenuator. This allows the acoustic performance of the attenuator to be increased. The frequency response of the attenuator is also known to be a function of the gap size. It is therefore intended to vary the gap size such to tune the frequency response and magnitude performance of the attenuator. This lends the NAT Vent to be * designed such to specifically mitigate against road noise, air craft noise, train noise, speech and any other noise type within a defined or semi defined characteristic.

Splitter and Lining Designs -Increasing the surface area of splitters -The acoustic performance of an attenuator is a function of the surface area of the splitters. The shape, cross section and layout of the splitters within the attenuator has a significant impact upon its acoustic performance. Due to high air speeds, it is conventional to use straight, rectangular splitters, with or without shaped bull noses to reduce the pressure drop through conventional attenuators.

The low air speed enables alternative splitter shapes. The surface area of these new splitters can increase the effective area of the splitter by 5% percent or more, comparing 10.5 and 11.5. This is achieved by moving away from the standard rectilinear of the chevron shape.

Removing elements required for structure and robustness 1.2, 1.5 of the splitter can also be used to increase in the surface area of the splitters significantly.

Splitter and Lining Designs -Reducing the line of sight through the attenuator -Making the air and sound pass through bends, chevrons and other torturous elements forming the attenuator will increase the performance of the attenuatàr. These techniques will therefore be used to enhance the acoustic performance of the attenuator and are only seen to be practical when air speeds are low.

Splitter and Lining Designs -Baffles -Reducing the line of sight through attenuators is known to increase the acoustic performance of the attenuator. One method of reducing the line of sight through the attenuator is to use baffles. Again, baffles are not conventionally used due to the pressure drop through attenuators.

Splitter and Lining Designs -Reactive components -Reactive components 13.0 are regularly used to reduce noise levels within ducts containing gas flow. The pressure drop through these systems is typically high and therefore this type of noise attenuation is conventionally used to control noise from combustion engines. The key advantage of reactive components is their high level of attenuation and the capacity to frequency tune the performance of the attenuator.

There are two types of reactive components; the first a mass element 14.1, 14.3, here the centre of gravity of a slug of gas/air is moved/oscillates as a result of the partial movement of sound. This slug of gas has an effective mass and therefore has a reluctance to oscillate movement, which in turn results in a reactive component. The second potential reactive component is a spring/capacitive element 14.2.

Here, the partial movement of sound compresses a volume of gas 14.2, the centre of gravity of this volume remains constant. As a result of the air being compressed and expanded, a reactive component is formed.

In the case of attenuators for low energy buildings, the air flow rate through the attenuator is low and therefore the addition of reactive components on pressure drops is seen to be acceptable. Such to tune and enhance the performance of these attenuators, reactive components are proposed. The use of reactive components will be to increase the acoustic resistance of the attenuator, as well as to reduce the required levels of material within the attenuator to provide a given level of acoustic performance.

Splitter and Lining Designs -Air Flow -The shape, angle, edge details and other factors within the design of the splitters and attenuators, all affect the air resistance of the attenuator. It is therefore proposed to shape splitters by means of sweep and round air paths, such to mitigate against turbulent flow and increased levels of pressure drop through the attenuator. These sweeps are formed by cutting, pressing, extruding heating materials.

Jntegration-Depending upon the function and location of the NAT Vent within a building, the NAT Vent will require to be combined with other elements such as fire dampers, air flow dampers, thermal air flow dampers and other elements 9.0.

Claims

CLAIMS1. An acoustic splitter in which its form, from a rigid or semi-rigid material allows for air paths to be present and is so, a building block, in which combinations of multiple splitters will create an attenuator requiring no additional fixing to form the air paths due to its structure, this is possible due to the low air speeds in which it would be subject to in low energy buildings.
2. As a result of 1, it is possible to use flow restrictive and torturous paths between acoustically absorbent elements, without having a prohibitive restraint on the attenuator pressure drop
3. As a result of I & 2, it is possible to reduce the gap between splitters.
4. As a result of I & 2, it is possible to arrange the splitters into baffles within the attenuator
5. As a result of I & 2, it is possible to insert dense baffle into the air flow path of the attenuator.
6. As a result of I & 2, it is possible to arrange the splitter and other elements to form reactive acoustic components within the attenuator.
7. As a result of 1 -6, it is possible to frequency tune the acoustic performance of the NAT Vent.
8. As a result of 6, it is possible to adjust the attenuation provided by the attenuator.
9. As a result of 1 & 2, it is possible to design and manufacture splitter shape such to maximize the effective surface area of the splitter without a negative effect on pressure across the unit.
10. As a result of 6, it is possible to reduce material levels/quantities within attenuators as a result of the benefits of using reactive components.
11. As a result of 1, the robustness and rigidity of splitters and attenuators can be reduced or removed.
12. As a result of 11, it is possible to form splitters from a single material with rigid or semi rigid properties, providing acoustic absorption.
13. As a result of 12, it is possible to shape splitters to form building blocks.
14. As a result of 13, the entire attenuator can be formed from splitter building blocks.
15. Splitter building blocks are to be formed by cutting, extruding, heating, pressing, etc.
16. As a result of 15, it is possible to build the attenuator to any size.
17. As a result of 15, it is possible to shape the attenuator into any shape.
18. As a result of 15, the shape of the splitter can be selected such to increase the surface area of the attenuator.
19. As a result of 15, the assembly of the attenuator can take place on site.
20. As a result of 1, 11, 12, 13, 14, 15, it is possible to remove bull noses and other structures around splitters to maximize the acoustic performances.
21. As a result of 1, 11, 12, 13, 14, 15, it is possible to remove bull nose and other structures around splitters such to reduce the cost of the attenuator.
22. As a result of 1, 11, 12, 13, 14, 15, it is possible to remove all structures supporting splitters and other acoustically absorbent materials within the attenuator.
23. As a result of 1, 11, 12, 13, 14, 15, it is possible to shape splitter building blocks such that self supporting structures are created.
24. As a result of II, 12, 13, 14, 15, it is possible to pre shape the splitters prior to the attenuators assembly.
25. As a result of 11, 12, 13, 14, 15, it is possible to shape the splitters such to add sweeps and other shapes such to minimize the pressure drop across the attenuator.
26. As a result of 11, 12, 13, 14, 15, it is possible to shape the attenuator to suit the buildings needs, rather than have a building fit around an attenuator.