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Posted by IT MACH

Case Study – Dartington School Environmental Noise Break-in

Architecture, BB101, BB93, Eco Buildings, NAT Vent Attenuator, Natural Ventilation, Noise Map, Vented Facades

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.

Case Study - Dartington School Environmental Noise Break-in

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.

Case Study - Dartington School Environmental Noise Break-inA 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.

Case Study - Dartington School Environmental Noise Break-in

Case Study - Dartington School Environmental Noise Break-in
Click the preview below to download the full case study on Dartington
Case Study - Dartington School Environmental Noise Break-in
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Posted by IT MACH

Natural Ventilation Feasibility

BB93, BREEAM, NAT Vent Attenuator, Natural Ventilation, Vented Facades
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 5th 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.
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.
Natural Ventilation Feasibility
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.

Natural Ventilation Feasibility

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.
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