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 square chimney, which vented out through natural vent towers on the roof of the building.

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. Click the preview below to download the full case study:

Cross Ventilating into a Noisy Atrium with NAT Vent Attenuator

The video above aims to demonstrate the performance of the NAT Vent Attenuator, and its ability to naturally ventilate, even between noisey areas. For more information about using central atriums, have a look at our previous post on atriums and case studies: Archway Primary School and Winford Primary School

Case Study: Dartington Primary School Nat Vent Box

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 first step of any noise break-in assessment is to establish levels across the site. This was done by carrying out noise monitoring throughout the site, over the full operational hours of the school.

A noise map was then created and used to assess the required level of attenuation required by facades of the school. The results indicated that the noise levels at the facades to the classroom block were higher than desirable.

The solution to the high noise levels at the building facade was to naturally ventilate using an external ground floor bulkhead containing the NVA, with hot air flowing out through openable window vents also containing the NVA. This solution allows for natural ventilation when it would otherwise not be possible through an open window for example. In addition to this, an acoustic screen and a strategically placed earth bund were designed to reduce noise levels at the classroom facade. The bund was formed from recycled tires, adding to the sustainability credentials of the building. Dartington Primary School is an inspiring development because a solid timber construction system has been used. BB93 also sets room reverberation requirements and the exposed timber in combination with barn shaped classrooms required some form of room acoustic treatments. The solution used was several acoustic beams provided by MACH Products (below).

The school met all BB93 requirements and BB101 ventilation specifications. Not only this but the finished design was pleasing and added function to the facade besides ventilation. The build was featured in ‘BD Reviews’ sustainability issue, a bow to the innovative design by MACH Acoustics, White Design and Arup. The photo below features the wooden beams put in place to reduce the reverberation. Click the preview below to download the full case study.

Demonstration of Sound Level Difference through Window Opening

When testing the performance of the NAT Vent Attenuator at Winford Primary School, we performed a noise break in assessment whilst opening a window. The video above illustrates the sound level difference has a steep decay from a small opening.

Case Study: Ebbw Vale Learning Zone

The Learning Zone lies at the heart of the regeneration and redevelopment of the former steelworks at Ebbw Vale, the largest regeneration project in Wales. MACH Acoustics worked with Architects BDP to develop a natural ventilation strategy between classrooms.

MF tracks were used to hold the NVA - creating a cost effective bulkhead, with acoustic attenuation and building services able to coexist in the same space.

The case study is a prime example of the NVA's ease of install and space saving advantages. The render above demonstrates how the NVA installs onto the MF tracking system.Generally a 1100mm depth NVA is used to sit between the standard 1200mm width between MF supports. The foam is positioned within the MF track in layers to form the honeycomb arrangement, which allows air to flow whilst attenuating noise.

Click the preview below to download the full case study:

Finite-Difference Time-Domain Models of Open Windows

An important area of research for MACH Acoustics, below are a few examples of a FDTD model we have produced to demonstrate various open window conditions.

First a top swung window, notice the noise ingress into the room.



The above but as a bottom swing.



An open window representation.



The above but with a internal baffle.



If you find this content interesting, why not arrange a CPD with MACH Acoustics?

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.

Click the preview below to download the complete case study (pdf)

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.

Click the preview below to download the full case study (pdf)

Case Study - Windford Primary School

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.

For the design of this building cost was a primary factor. There was a desire to naturally ventilate but under the flight path of Bristol Airport and with cost limits it was a challenge acoustically.

A full natural ventilation strategy was designed in partnership with Stride Treglown Architects. Air would enter the building through openable windows and horizontal louvred ducts - controlled by a BMS - ventilate classrooms and exit through the roof of a central atrium known as the ‘heart’. Cross ventilators were designed between floors, discretely ducted within ground level benches - maximising building usage.

The horizontal facade included thermal dampers, actuated by the building management system (BMS) and featured a 900 bend; reducing the protrusion and increasing acoustic attenuation. 

The central ‘heart’ of the building includes a plenum, where the hot air will exit the building. The design included a NVA bulkhead, mounted with BMS controlled actuated windows.

Working with Strides, the flexibility and bespoke nature of the NVA allowed for this design and enabled the same space to include solar thermal panels.

The school was fully compliant with BB93, confirming exceptional acoustic design considering the potential clash between natural ventilation and the busy Bristol Airport flight path.

Importantly, the reception of the building has been extremely positive, with teachers, parents and pupils heaping praise for the spacious and pleasant working environment. Winford’s pupils, who, according to parents are now ‘excited’ to go to school, enjoy day lit, naturally ventilated internal spaces with glazed screens between them so that all activity is in view.

The build received a BREEAM ‘Very Good’ rating and will generate a minimum of 15% of predicted energy consumption, thanks in part to the well executed natural ventilation system.

Click the preview below to download the full case study (pdf).

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.

Click the preview below to download the full case study on Dartington

Natural Ventilation Feasibility

As per the introduction to this blog, MACH Acoustics aims to provide a useful blog providing ideas, details and knowledge, where people can discuss ideas and hopefully move forwards in a more suitable and low carbon way.

MACH Acoustics has recently published four conference papers on the acoustic design of low energy buildings. Subjects covered are the acoustic performance of open windows, the design of high performance natural air vents, the onsite performance of corridor walls and methods of achieving cross ventilation. We are currently working on a 5^th paper looking at acoustic treatments in combination with thermal mass cooling. 

The starting point for this blog will therefore be a description of these papers.  The titles of each of the papers are listed below. There is also a link to a PDF copy of these papers below.

Acoustic Scaled Models and Naturally Vented Facades
NAT Vent Cross Talk Attenuator
NAT Vent Attenuator and Facades
Acoustic Performance of Open Windows

Green acoustic consultants probably have the greatest effect on a buildings carbon emission when reviewing the design of vented facades. This element of design is also likely to have the most significant impact upon the level of energy used by a building.

The graph below provided by Brent Associates Architects presents key information with respect to the energy consumption of building types and their location. This information in turn demonstrates how best to reduce the energy consumption of buildings.

Figure 1 - Energy consumption for a range of building types and their location

This graph shows that the greenest buildings are those that incorporate three elements; natural ventilation, a town or city centre location and the reuse of a building in the form of a refurbishment.  This conclusion is made on the basis that natural ventilation is significantly more energy efficient than mechanical ventilation (1 to 2 Figure 1).  A city centre location for a building reduces a significant chunk of the buildings carbon emissions as a result of reduced transportation (2 to 3). The third significant reduction in energy is achieved through refurbishing a building.  Here, the embodied energy required to form a building is not needed and hence this is a significant design goal for low energy building design (3 to 4).   

With respect to acoustics, these requirements make things difficult.  It is always complex and more complicated to refurbish a building. The difficulties arise as a result of reduced levels of flexibility in terms of design, structural constraints, facade restraints, planning, historical limitations, as well as other factors. As consultants we therefore need to be more creative and have a wide range of products and/or designs to overcome these limitations.

Locating the building within a city or town centre will always bring issues with respect to noise break in. The figure below shows a noise map taken from www.noiserus.com. Table 1 shows the percentage of land where it is possible to comply with BREEAM and BB93 internal noise levels when a building is ventilated by means of opening windows. The sound reduction of an open window is assumed to be 10 dBA.

Figure 2 - Town centre noise map provided by www.noiserus.com.

Table 1 - Percentage of sites available within town centres, where simple openable windows provide adequate levels of acoustic resistance such to comply with BREEAM and BB93 requirements.

Space	Target Noise Level	Percentage of site suitable for  natural ventilation
BREEAM – single occupancy offices	<40 dBA	41%
BREEAM – multiple occupancy offices	40-50 dB LAeq,T	47%
BB93 – classroom	35 dBA	22%
BB93 – lab/workshop	40 dBA	41%

It is clear from the figure above that the development of green buildings within towns and city centre locations, will more often than not require acoustic solutions which provide high levels of acoustic attenuation to environmental noise break in.

My next entry will therefore look at methods of increasing the acoustics resistance of vented facades.