Case Study: Hertfordshire University

The Law Court at the University of Hertfordshire is a £10M advanced facility, 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. A BREEAM project, the building was to be naturally ventilated. MEP designers AECOM specified the Mach Acoustics NatVent Attenuator to provide a vented facade solution using weather louvres, connected to a raised, vented floor containing the Nat Vent Attenuator.

Installing the NVA under-floor is a veryeffective 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.

Image provided by Aecom

Situated on a busy campus and next to a busy bus route, the natural ventilation strategy needed to be acoustically attenuated. Adding to the challenge was the fact that the building had already be designed for air inflow through the flooring, with acoustic dampers, louvre and bird mesh limiting flow to an already small 1.5m2 face area. Only thanks to the adaptable NVA foam, MACH Products was able to design the attenuator around modulated Kingspan flooring, sitting on pedestals 360mm high, fully filling the void. The profile was designed to the same size as the 600x600mm grid created by the flooring, such that the NVA would be easy to install. By installing in segments like this, we were able to create the required length of attenuator for the noise level at the facade.

Due to the bespoke nature of the NVA, the attenuator could be simply installed in coordination with the modular grid based flooring. The NVA segments were slid into place between the pedestals (1/4 circle sections were added to the corner profile to account for the structure), followed by the matching 600x600mm floor sections. Building services often exist within the flooring void, including a heated element in this case. The NVA foam can be easily adapted on site to accommodate for these items, unlike a common pre-defined attenuators.

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Case Study - University of Hertfordshire Law Court

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.

Situated on a busy campus and next to a busy bus route, the natural ventilation strategy need to be acoustically attenuated. Adding to the challenge was the fact that the building had already be designed for air inflow through the flooring, with acoustic dampers, louvre and bird mesh limiting flow to an already small 1.5m2 face area.

Only thanks to the adaptable NVA foam, MACH was able to design the attenuator around modulated Kingspan flooring, sitting on pedestals 360mm high, fully filling the void. The profile was designed to the same size as the 600x600mm grid created by the flooring, such that the NVA would be easy to install. By installing in segments like this, we were able to create the required length of attenuator for the noise level at the facade.

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.

Due to the bespoke nature of the NVA, the attenuator could be simply installed in coordination with the modular grid based flooring. The NVA segments were slid into place between the pedestals (1/4 circle sections were added to the corner profile to account for the structure), followed by the matching 600x600mm floor sections

Building services often exist within the flooring void, including a heated element in this case. The NVA foam can be easily adapted on site to accommodate for these items, unlike a common pre-defined attenuators.

The build meet the BB93 and BB101 requirements as a teaching space whilst creating a dynamic and pleasant space for students. MACH Acoustics and it’s partners helped the centre become one of the most innovative law schools in the UK and was recently awarded ‘The Most Sustainable Construction Award 2011’ by Building Futures and has been short listed for several other awards.

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Case Study - Llwynderw Primary School

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.

An important stage in the acoustic design of a building is an environmental noise survey of the existing site, a service provided by MACH Acoustics.

Using the data collected, a dynamic noise map was constructed and used to access the noise levels at each facade and the resulting noise break-in within the teaching spaces. It was clear that the site was not particularly noisy and that an open window would provide enough attenuation at the facade facing away from the roads - simple and low cost.

A ventilation strategy was developed in close coordination with Stride Treglown Architects - using the sound map - which efficiently attenuated noise on each facade.

On the noisy road facing facades, a cedar shingles feature created a duct, with intake perpendicular to the ground and containing the NVA. A 90deg arrangement like this increases attenuation and minimises impact on building space - highlighting the bespoke design options that the NVA offers. The quieter rooms with central chimney simply used openable acoustic windows.

The central chimney shown above is the highlight of the natural ventilation project. Each stack of classrooms featured a small sqaure chimney, which vented out through natural vent towers on the roof of the building. Details of the this are shown on the right.

A testament to the NVAs versatility whilst maintaining class leading acoustic performance, the build was impressive architecturally whilst naturally ventilating and meeting both BB93 and BB101 requirements as a teaching space.

Thanks to a partnership between MACH Acoustics and Strides, the building received a BREEAM ‘Very Good’ rating and was well received by parents, pupils and residents of the area.

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Case Study - London and West London Acadamies

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.

The academies featured many different imaginative implementations of the NVA as a cross ventilator, all venting into a central atrium. Air passed though the facade via actuated windows through bulkheads at ceiling height containing the NVA.

The main principle was to add an attenuator with 25% free area and a face area of 1.5m², with small splitter sizes.  The attenuator was to be located above a cupboard spaces as shown below. A flap enable the vent to be opened and closed.

One of the main advantages of the NVA is the ease and simplicity of installation. Once the bulkhead has been constructed, 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.

With the window facade bulkhead, we were able to implement cost savings by negating the need for expensive weather louvres, using actuated windows instead. Not only was the cost significantly reduced but the installation was greatly simplified - both points highly valued by the contractor. 

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Lecture theatre design - Bath University - Part II

Maximising Loudness

Speech intelligibility is highly dependent upon the audience being able to differentiate speech from background noise. To enhance intelligibility, speech levels should be maximised and distributed evenly across the seating areas. This is achieved by a combination of methods. First, restricting space increases the amount of sound energy per seat. Secondly, consideration of the length of the hall, to respect distance losses and increase awareness of any visual gestures is advised. Finally increasing the number of early reflections to the audience will increase intelligibility.

Room Shape - Volume

The ideal room volume per seat for lecture theatres is:

Volume / seat 2 – 5 m3

The lecture theatre at Bath University holds 350 people and has a volume of 1400 m3, this equates to 4 m3/seat, thus meeting the above criteria.

Room Shape – Length

Visual gestures made by the speaker can greatly improve the recognition of what is said. Although the benefit is not easily quantifiable, it is generally thought that the maximum distance from source to receiver should be no more than 20m. Firstly because this is the maximum distance a typical person can identify these visual prompts, and secondly, it ensures a good direct sound pressure level; essential for localisation.

The Bath lecture theatre had been designed with a maximum distance of 15m, from source to receiver and, depending on the design of a building, this can limit the audience capacity. However, Bath adopted a fan shaped room to maximise the audience capacity yet maintain the source to receiver distance.

Enhancing early reflections

As has been described, reflected sound plays a critical role in maximising loudness levels to the audience. Ideally, it is important to focus these reflections to the rear of the auditorium, since the direct sound at this point will be reduced due to the decay of sound over distance and the grazing effect of the audience. The method by which to focus these reflections is to correctly angle the surfaces at the front of the auditorium so that sound is directed towards the rear of the audience.

Angling the side walls of a given auditorium is often difficult due to the inherent restraints imposed by the building. Similarly in this case, the layout of the Bath University building is fixed, and therefore the option of

adding angled side walls was not explored further. The angle and layout of the ceiling then became the critical factor affecting the acoustic performance of the theatre.

The initial design of the ceiling was not favourable, the sudden step in the bulkhead and the down stand created by a structural steel, created two acoustic shadows on the audience.

To overcome this, the ceiling height was dropped to make the ceiling flat across the structural steel (green line). An angled ceiling was then introduced (blue). The position was calculated using a geometric method such that the audience to the rear of the theatre would receive two separate early reflections, instead of one; greatly improving the speech intelligibility within the lecture theatre.

Case Study - Dartington School Environmental Noise Break-in

Environmental noise break-in can be a significant issue when naturally ventilating a building located on a noise site, even if the noise is only moderate.  Dartington school, previously reviewed within this blog with regard to the creative room acoustic treatment, also required creative forms of noise control measures to prevent noise break-in to noise sensitive teaching spaces.

The first stage of any noise break-in assessment is to establish noise levels across the site.  This was done by carrying out noise monitoring throughout the site, over the full operational hours of the school.  During the noise survey addition data was collect with respect to traffic flow levels and other data need to build a noise map of the site.  A noise map was used such to assess the effects of the new school and to establish noise levels across all facades.

The result of the original noise mapping exercise is shown above in the left hand image. The results of this assessment indicated that noise levels at the facades to the classroom block where higher than desirable. The solution was to use an acoustic screen and strategically placed earth bund to reduce noise levels at the classroom.  The tire wall is shown on the front cover of “BD Reviews” was used to form the required acoustics screen.  This design is highly sustainable since these used tires did not go to land fill.  Aesthetically there is a strong recycled image and additionally over time the vegetation shown in the image will cover the wall to form a green, live acoustics screen.

A second observation from the above noise mapping exercise was that noise levels at the sports hall were too high to allow for natural ventilation by means of simple openable vents.  The solution was to added attenuated vents using the NAT Vent Attenuator.  The photo below shows this vent and the diagram provides 3D view through the vent box.

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Welcome to MACH Acoustics Blog!

The aim of MACH Acoustics is to become one of the leading acoustic consultants in the field of sustainable building design. This aim means that we specifically focus on projects around sustainable architecture and Eco buildings. A considerable portion of our time is therefore spent looking to solve some of the conflicts between acoustics and low carbon, sustainable constructions.

Acoustics and sustainability are not often spoken about together. On the other hand, air conditioning systems are often used to overcome noise ingress issues. Thermal mass cooling; exposed concrete soffits for example, can make buildings sound loud, harsh and noisy. Cross ventilation, exhaust stacks and other air ventilation systems can compromise the acoustic cross talk between office buildings accommodation and teaching spaces within educational buildings. Vented facades in combination with ventilation louvers and other types of air ventilation systems within the fenestrations of a building are often used to prevent noise ingress. Buildings are often built using high mass structures to achieve acoustic requirements.

These factors clearly show the link between acoustics and sustainability. Acoustics can therefore have a significant impact upon the levels of carbon emissions, ventilation system and the level of embodied energy in the buildings frame and other factors affecting the sustainable architecture of a given building. With changes to Building Control Documents Part L and Part E, along with new client expectations, there is an increasing importance to ensure that building designs become more integrated and greener.

MACH Acoustics view is that the best way to overcome the limitations imposed by acoustics on sustainable buildings is to increase our knowledge base. This simple goal is therefore the aim of this blog. We aim to provide a point of reference where detailed information will be regularly uploaded relating to residential buildings and the code for sustainable homes. We will be looking at Eco buildings and acoustic materials which match requirements for sustainable building design. Ventilation systems including vented facades, acoustic ventilation louvers, attenuators within facades, passive house systems, heat recovery systems, exhaust stacks and other air ventilation system will be discussed over time.