- BuildingDesign News - Construction / Services News Archives

  • Connect With Us
  • Follow BuildingDesign on Twitter Connect with BuildingDesign on LinkedIn Become a fan on Facebook Subscribe to BuildingDesign's RSS Feed Follow BuildingDesign Media on Google+
Article Date: 25th November 2013

Breathing Buildings - Making Sense of BB93 & Cross Talk Attenuation

Natural Ventilation - Smoke Ventilation - Ventilation Systems - Comfort Control

Breathing Acoustic Data

Acoustics, its a black art but you can assume that most typical products achieve the BB93 criteria, right? WRONG!

As the natural ventilation experts, customers come to us from all sectors asking for advice on which product is suitable for a room. To answer that question we ensure the natural ventilation systems we provide integrate with the rest of the building. This in turn means that our engineering expertise extends beyond ventilation to:

  • control architecture
  • heating
  • cooling
  • Part L and Part F compliance
  • acoustics

The one that confuses everyone the most is acoustics. It is seen as a black art, or at least a foreign language. This presents a problem because when a designer or contractor is comparing prices of different suppliers of equipment, it is not always easy to assess whether alternative suppliers are offering the same level of performance. What is critical is to make sure you choose a product that complies with the regulations!

One of the products we provide to help with cross-flow ventilation is an acoustic attenuator. This product is often located in a bulkhead between a central circulation space and a classroom.

The regulations governing noise in education buildings are Building Bulletin 93 (BB93). The relevant table in that document is Table 1.3 which outlines the required level of attenuation (see below).

The total weighted element-normalized level difference required for spaces except music rooms is 39dB*. But what does that mean in English?

Careful reading of the table shows that there is a reference to Dn,e,w-10lgN in the column header. The 10lgN is critically important! N denotes the number of attenuators required.

If more ventilation area is needed then multiple attenuators may be required. This increases the number of routes the noise can take to get into the room i.e. there is then more than one noise source into the classroom from the atrium. Therefore, in order to achieve the same noise level inside the classroom with multiple attenuators as with one attenuator, more attenuation is needed in each unit. But most typical products achieve this BB93 criteria, right? WRONG!

Let's consider a case where say 0.4sqm of free area is required per room between the classroom and the atrium, a typical requirement to naturally ventilate a school classroom. Below we compare some typical air transfer units and assess how they perform.

The reason for this disparity is simply because "foam" used in many products is not as effective at absorbing sound as the acoustic baffles in the Breathing Buildings units. This is not just an issue about differences in quality; it is about ensuring a design meets the regulations. If you come to Breathing Buildings we will ensure our units are fit for purpose and meet the requirements of the regulations. You wouldn't expect anything else.

BuildingDesign Media © - BuildingDesign Directory | BuildingDesign Tenders | BuildingDesign Recruitment