3.5 The NAT Vent - Installation

The NAT Vent Attenuator is an attenuator specifically designed for low energy buildings. This product allows for cross ventilation through a partition without downgrading its acoustic performance. To meet the acoustic and ventilation requirements, MACH Acoustics designs and tests attenuator configurations using our in-house test facility, such to meet the individual needs of a building. Please see our website for further details: www.machproducts.co.uk

The NAT Vent Attenuator is constructed using foam blocks which tessellate together to form this product. A range of raw materials can be selected to acoustically adjust its performance. In addition, materials can be selected to the meet fire (Class O) requirements of recycled content. To control air flow and prevent the spread of fire, the NAT Vent Attenuator is often combined with volume control and fire dampers.

The installation of the NAT Vent Attenuator is exceptionally simple; the foam tiles are pushed into a bulkhead formed from timber or metal. Timber bulkheads can be lined with plasterboard. If the NAT Vent Attenuator is supplied in a metal duct, it can be simply supported on uni-struts to hold it in place.

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.

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

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.

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.

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.

1.1 Introduction

The NAT Vent Attenuator has been designed to overcome the clashes between natural ventilation and acoustics. The NAT Vent Attenuator allows the fl ow of air into and through a building, whilst preventing the passage of sound. This product can easily be incorporated into the facade of a building, allowing for natural ventilation on all sites, irrespective of environmental noise levels. The NAT Vent Attenuator can also be used to prevent cross talk issues when implementing cross ventilation to atriums/corridors. This product can be made to comply with BREEAM, BCO, HTM, BB93 and other standards. 

The concepts and design specifi cations for this product have come from MACH Acoustics consulting experience. Our experience has shown that current products have a limited acoustic performance, are exceptionally infl exible, costly, and are lacking in technical innovation. Through frustration, knowledge and insight, the NAT Vent Attenuator has been designed and produced by MACH Products. The NAT Vent Attenuator is formed from W shaped tiles manufactured from acoustic foam. These elements are then tessellated and stacked together 11, 12 to form the NAT Vent Attenuator 13. The result is a fl exible product which can be fitted into bulk heads to allow for cross ventilation, or incorporated into the facade of a building to prevent noise break-in. 

The key features of the NAT Vent Attenuator are its patented technology based around the honeycomb structure, its novel W shaped splitter arrangement and the materials from which it is made. A simple manufacturing process delivers a cost effective, lightweight product, which is exceptionally flexible and therefore can be made to fit into a wide range of spaces and locations. The NAT Vent Attenuator is designed and manufactured bespoke for each project and tested using MACH Acoustics in-house test facilities 14 meaning that the acoustic specifi cation of this product meets the exact project requirements.

Introduction

MACH Acoustics is a specialist acoustics consultancy providing acoustic design across all buildings types. Our aim is to become one of the leading acoustic consultants in the field of sustainable and creative acoustics. Our ethos is to constantly develop our understanding of acoustics and other disciplines, including architecture, building services and structures. Through consultation, research and imaginative thinking, we find creative acoustic solutions to the challenges we are presented with.

Each blog post will be an excerpt from the MACH Acoustics book – “Sustainable Acoustics – Sustainable Acoustic Scheme Designs from MACH Acoustics”. The posts will be categorised into the relevant chapters as they appear in the book. The purpose of this book is to highlight some of the unique designs employed by MACH Acoustics and teams we have worked with. Inspiring concepts, challenging schemes and fresh design approaches are presented across all aspects of building design. This book hopes to help design teams think greener and to achieve sustainable designs. This book also aims to act as a reference document, including performance standards, rules of thumb and standard forms of construction.

The book begins with an introduction into The NAT Vent Attenuator, a flexible product developed by MACH Acoustics on the back of extensive research. This product allows the flow of air whilst restricting the passage of sound, hence it can be used to achieve cross ventilation whilst complying with BB93, HTM, BREEAM and other privacy requirements. The flexibility of the NAT Vent Attenuator means it can also be used to enhance the performance of vented facades such to accommodate noisy sites.

Chapter 2 looks in detail at one of the most important and challenging aspects of low energy buildings; acoustic facade design to prevent noise break-in. Chapter 2 looks at three areas; attenuated facades to multi storey buildings, single storey buildings, and double and screened facades.

Since the introduction of stringent performance requirements, cross ventilation has become more difficult to implement. Cross ventilation is highly effective and more cost efficient than single sided ventilation. Chapter 3 therefore looks at design options for cross venting to atriums/corridors, as well as single ventilating stacks feeding multiple floors.

Sound insulation is an important aspect of any building’s design. Chapter 4 provides a range of performance requirements, standard acoustic details and sustainability methods of providing sound insulation.

Creative room finishes are an important part of building design. Chapter 5 therefore provides a complete range of alternatives to ceiling tiles and standard forms of room acoustic treatments. To supplement this information, a series of case studies and green practical solutions are presented.

Open plan is an important aspect to teaching and office accommodation. Valuable design roles, schemes and design concepts are therefore addressed within Chapter 6 of this book.