NAT Vent Attenuator · intercity train between Swansea and London. Such a site is acoustically challenging before even considering natural ventilation. By performing an environmental

NAT Vent Attenuator

Sustainable Acousticsphone 0117 944 1388 email [email protected]

www.machproducts.com

Bristol Trelawney House, Surrey Street, Bristol, BS2 8PS

London 11 Sandycombe Road, Richmond-upon-Thames, Surrey TW9 2EP

2 | MACH Products: NAT Vent Attenuator | www.machproducts.

What. The NAT Vent Attenuator (NVA) is a highly flexible but specifically designed product to overcome the clashes between natural ventilation and acoustics.

The NVA can be incorporated into the facade of a building or built into partitions for cross-ventilation, to allow a building to naturally ventilate whilst meeting the acoustic requirements.

Simple. Cost effective. Flexible. Customisable. Designed for low energy buildings, the result is exceptional performance and small size, while complying criteria associated with BREEAM, BB101 BB93, HTM and other standards.

We form the NVA by tessellating the iconic shape into our unique acoustic-grade foam.

Each project is laser cut to order, allowing for truly bespoke design to your requirement.

Patented technology, based around the honeycomb structure; the novel, W-shaped arrangement; and the materials used to make it.Thanks to the tessellating and lightweight design,

the NVA is a energy conscious before even being installed.

The honeycomb structure is easily formed on-site by simply alternating orientation of each layer.

Constructed in-situ and made of soft foam, installation is trouble free and can adapt to building services within a bulkhead.

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Why.

MACH Acoustics. What We Do.

One of the main difficulties in designing low energy buildings is the prevention of noise break-in from the many noisy sources affecting modern buildings, including motorways, dual carriageways, trains, airplanes and inner city noise. Secondly, whilst cross ventilation is one of the most effective forms of natural ventilation, maintaining privacy and standards across partitions presents an acoustic challenge.

The NVA was designed to form a unison between natural ventilation and acoustics, without having to design your building around large bulkheads accommodating big heavy attenuators.

MACH Products is part of MACH Acoustics, a specialist acoustics consultancy providing acoustic design for all building types.

We are proud of our design and performance, and are among the fastest growing acoustics product and consultancy companies in the UK.

Having previously worked with names such as JBL, James Dyson and Buro Happold for a number of years, Ze Nunes and the rest of the MACH Products team understand the importance of effective design and consistent delivery.

The Buildings we work on are complex and we spend a considerable length of time understand what a project needs, then The NAT Vent Attenuator is designed and manufactured specifically for each project and tested using MACH Acoustics in-house test facilities.

We can oversee the complete acoustic design process; from initial sound surveys and consultancy to design and product integration, and finally to BB93 and BREEAM pre-completion testing.


Application. Thanks to the excellent performance and versatility of the NVA, application is wide and extremely varied. The next couple

Facade Details.

Vertical Louvre.

Horizontal Louvre.

Discrete Installation.

The simplest method of enhancing the acoustics of a vented facade is to place the NVA behind an open-able vent/window. In this instance, the vent/window is used to control the air flow into the building, maintaining the thermal performance of the facade as well as keeping the weather out.

A small bulkhead is typically mounted behind the facade opening. The NVA may simply be supported by MF tracks or may be enclosed by purpose built ducting (plasterboard, timber etc.).

The flexibility of the NVA means that actuators to operate the vent/window can easily be accommodated for, including service hatches. The window vent can be at low level, high level or incorporated into curtain walling. Below are a few additional example facade installations.

A vertical louvre is ideal on windowless facades or where window space is at a premium.

The facade can either feature a standard weather lourve or a bespoke solution can be designed into the facade face - see the inspiration section. Using a vertical vent, a simple door can be used to control the internal flow of air.

Rather than mount the vent along the vertical plane of a facade, a horizontal installation is ideal below a window sill.

The vent can also be mounted at ground height with an external extruded bulkhead containing the NVA, saving internal space and creating a box that can be used for landscaping features.

As forward thinking acoustic consultants, we have done many alternative and discrete facade installations.

The NVA’s unique flexibility means that it can be installed under bench seating, in flower boxes, play boxes or small steps within the facade. View the inspiration section for more examples.

of pages feature a selection of common applications, frequently used in MACH Acoustics’ designs.


Cross Ventilation.

Bulkhead. Dog Leg. Under Floor.

Cross ventilation is one of the most effective forms of natural ventilation. One of the key benefits of the NAT Vent Attenuator is its simple implementation of cross ventilation through a corridor wall, whilst still maintaining acoustic integrity. It also enables cross ventilation to vertically stacked rooms, vented through a single stack.

The result is that vertically stacked spaces no longer require independent chimneys to maintain the acoustic separation between rooms, resulting in a significant recovery of floor area and considerable cost savings.

The number of applications using the NVA to cross ventilate is near limitless. Below are a number of common uses.

A simple, clean bulkhead containing the Nat Vent Attenuator is the most common way to install and achieve BB93 performance requirements.

Its lightweight design allows the MF system to be the supporting structure but equally, a purpose built bulkhead can be used; plasterboard, timber, metal ducting, etc. Please see the inspiration section for examples of how the NVA bulkhead can be used.

A dog leg attenuator is one way to minimise the presence of the attenuator and maximise building space. Experience has shown that it may even be the only feasible method for it to fit into a building’s design.

The 90 degree bend has the added benefit of increasing the acoustic performance, allowing for an even smaller unit.

Installing the NVA under-floor is a very effective method when dealing with high noise levels.

The vent openings are made within the spandrel panel between transoms. Air passes into the cellular space by passing through a external vent opening, through the NAT Vent Attenuator. The floor void is used as plenum - air enters the rooms above by means of floor diffusers.


Installation.Quick, simple and adaptable Installation is one of the key benefits of the NVA. The process is broadly the same for most applications. The tessellating foam is arranged into honeycomb pairs by alternating orientation, then simply slid into the duct. Since the foam is malleable and can be cut, fitting around building services or any on-site alternations can be easily achieved. Installation generally takes under one hour - saving money and construction time.

Facade Installation.The tessellating foam forms a honeycomb by alternating orientation of layers.

The assembled duct, which we call the ‘NAT Vent Box’.

Installed in the horizontal louvre arrangement under a window sill.

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3.

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4.

The honeycomb is then arranged either horizontally or vertically within the duct.

Architectural Grill

Thermal Damper

Weather Louvre

Vent Box Section.


Bulkhead Installation.

The tessellating foam is horizontally arranged in the bulkhead, forming the honeycomb formation. The process is the same whether installing to MF tracks or a pre-fabricated bulkhead.

The assembled NVA bulkhead. The finished bulkhead on the MF5 Tracking System.

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Once the NVA is in place, architectural grills are installed. It is important that the bulkhead is well finished, with no voids.

MF Track Section.


Performance.As a result of its honeycomb structure and the performance of its acoustic foam, the NAT Vent Attenuator is an exceptionally slim line attenuator with outstanding acoustic performance. It is capable of attenuating exceptionally high levels of noise, whilst maintaining adequate air flow.

Once placement method has been decided, the performance requirement is achieved by simply extending the length of the attenuator (the manufacturing process does not restrict the size of the product). This means the NAT Vent Attenuator can achieve performance levels from 20 dB Dne,w to 40+ dB Dne,w.

MACH Acoustics produce Dne,w calculations based on procedures described in BS EN 10140-1:vv2010, BS EN 10140-2:2010 and BS EN 10140-5:2010. The NVA is tested using our in house testing rig calibrated to BS 7251.

The NVA frequently performs better on-site. Attenuators are usually tested in accordance to BS EN ISO 10140-1:2010; however this is limited to attenuators with an opening of less than 1m2; much smaller than typically installed. Additionally, with all building elements place, the real-world is more forgiving than lab conditions.

The graph on the right illustrates the correlation between depth, free area and Dne,w.

Acoustic Performance.

Depth: Increase to improve acoustic performance once face area is defined.

Face Area: Selected based on size of vent, acoustic requirement and required free area.

Free Area: Defined by the percentage free area NVA used and denotes the equivelent open duct area.


Designed specifically for low energy buildings, the NVA offers extremely low resistance to air flow.

The marginal face velocities associated with natural ventilation makes accurate measurement of pressure drop difficult and prone to errors. For this reason, MACH Products used CFD to model the pressure drop of the NVA.

For typical natural ventilation and BB101 requirement flow rates, pressure drop is < 1Pa.

Air Flow Performance.

Pressure Drop.

0

5

10

15

20

25Pressure Drop 25% FA

Pressure Drop 50% FA

Pre

ssur

e D

rop

Pa

Velocity m/s0.5 1.0 1.5 2.0 2.5

Cd ≈ 0.42


Inspiration. MACH Acoustics are passionate about all aspects of acoustic design. Every job is unique and presents new challenges.

We have incorporated the NVA into many builds using many different techniques, all performing to their required specification and beyond.

It is impossible to cover all the possibilities in this document. Within his section are brief introductions to complete case studies, covering the design, installation and result, to inspire and inform you further for your own build. Follow the download link to read a case study in full.

Cross Ventilation.

1 MF Track bulkhead prior to

architectural grill being installed.

2 Alphabet CAD grill at Rogiet Primary

School.

3 Small letterbox style ceiling duct.

4 Cross talk attenuators above corridor

windows at Bath University.

5 Example of under-floor installation.

6 Discrete bench cross-vent at Winford

Primary School.

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2 3

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6


MACH Acoustics, in collaboration with Capita Architects have been involved in the design of Bristol University’s Graduate School refurbishment. The need for sustainable and low-energy buildings has led to a natural ventilation scheme being carefully implemented into the design.

The scheme involves air being brought into the classrooms through open-able windows and discharged into the main corridor via cross-talk attenuators.

Rogiet Primary School is a timber frame building, located between the M4, M48 and in close proximity to the intercity train between Swansea and London. Such a site is acoustically challenging before even considering natural ventilation. By performing an environmental survey of the site, MACH Acoustics successfully implemented natural ventilation though careful consideration of building placement and well executed cross ventilation.

Llwynderw Primary School is a project in Abergaveny that MACH Acoustics worked on in partnership with Stride Treglown Architects and Willmott Dixon.

The school incorporates natural ventilation through a vented facade and openable windows, which cross ventilate classrooms via a central chimney - saving money, building space and simplifying the construction.

London and West London Academies, two large £30M+ Academy are both designed around a natural ventilation, incorporating cross ventilation. Both schools were required to meet BB93 and BB101 ‘Ventilation of School Buildings’. MACH Acoustics worked with Fosters and Partners to develop a practical solution. Our findings were that the cost of conventional attenuators along with their size and short falls in performance prohibited the use of these devices but allowed for the NVA.

Bristol Graduate Centre.

Rogiet Primary School.

Llwyndrew School.

London Academies.

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Cross Ventilation.


1 Bespoke horizontal facade for Rogiet

Sports Hall.

2 Bespoke vertical facade for Rogiet.

3 Window vent (top) on facade.

4 Ground level external bulkhead at

Darlington School.

5 The external window bulkhead at

Winford Primary School.

6 Horizontal ducts positioned 900 to

the facade at Winford Primary School.

7 Discrete bench vented facade at St

Peter’s School.

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Facade Details.


St Peters school is located in relatively close proximity to the M5 and as such, environmental noise levels are too high to allow for natural ventilation through openable windows.

MACH Acoustics was employed by South Gloucestershire Council to provide a range of design options to prevent noise ingress into this classroom. A unique discrete facade vent, contained within a bench seat was employed.

Dartington Primary School is located in close proximity to the A384; a large busy road. A number of natural ventilation strategies were developed in cooperation with Arup, including the use of landscaping as a barrier.

This inspiring solid timber project presented challenges internally and externally. Natural ventilation is achieved through an external bulkhead cross-venting through the roof.

The Law Court at the University of Hertfordshire is a £10M building with advanced facilities, including a full-scale courtroom with public gallery, a working law clinic, a purpose built mediation centre and a dedicated CPD suite, as well as a large number of offices and classrooms. Aiming for BREEAM status, the building was to be naturally ventilated. MACH Acoustics provided a vented facade solution using weather louvres, connected to a raised, vented floor containing the NVA.

Winford school is located directly under the flight path of Bristol Airport, as such noise ingress is a significant issue. During the design stage of this building several design options where reviewed.

The school is a prime example of the versatility of the NVA and MACH Acoustics. Facade ventilation is incorporated through window and horizontal louvres. Cross ventilation is applied through internal benches and exhausted through atrium vents.

St Peter’s Primary School.

Dartington School.

Law Court Hertfordshire.

Winford Primary School.

Facade Details.

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Tel 0117 944 1388Email [email protected]

www.machacoustics.comwww.machproducts.comwww.machtesting.com

MACH Products, Trelawney House, Surrey Street, Bristol, BS2 8PS

Thanks for reading and your interest in MACH Products’ NAT Vent Attenuator. If you have any further questions, please contact MACH Products via any of the methods below.

For further information on our products and services follow us on various social media channels and have a look on our blog: http://blog.machacoustics.com

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NAT Vent Attenuator · intercity train between Swansea and London. Such a site is acoustically challenging before even considering natural ventilation. By performing an environmental