2.3 Locating Inlet Vents and Cross Vents as a Noise Control Measure

Locating Air Inlet Vents
The orientation of a building has a significant impact upon noise levels at the different facades of the building. It is often the case that facades on the opposite side of a building to a significant noise source will be considerably lower than those on the noisy side of the building.
By orientating the building and by placing non-critical spaces on the noisy side of a building, it is possible to form a good acoustic buffer. In these instances, cross vent can be used where the air intake is placed on the quiet side of the building. Cross ventilation to an atrium or circulation zone is then used to provide the air extract. Alternatively, single sided ventilation could be used for sensitive spaces on the quiet side of a building.
1 shows sound levels around a building in the form of a noise map. The classroom on the far side of building to the A40 are vented using openable windows.

1

Cross Vent to Assist with the Prevention of Noise Break-in
In instances where a building is located on an exceptionally noisy site, cross ventilation can improve the feasibility of natural ventilation. Cross ventilation has an important advantage over single sided ventilation, in that air inlet vents can be between 25% to 75% smaller than those required for single sided ventilation. This significant reduction in vent size helps considerably in preventing noise break-in, as smaller vents restrict the passage of sound into a building.

1.2 Acoustics and Vented Facades

When naturally ventilating a building on a noisy or moderately noisy site the acoustic design of the facade becomes fundamental. The ability to provide high levels of sound resistance within a limited depth is often a requirement for an attenuator in the facade of a building. Due to the honeycomb structure and the performance of the acoustic foam, the NAT Vent Attenuator provides an exceptionally slim line attenuator with an outstanding acoustic performance. The size and depth of the NAT Vent Attenuator is dependent upon two main factors;

1 The free/open area specified by the M&E consultant/engineer. This governs the required face area of the attenuator and its percentage free area. A large face area will transfer a greater level of sound into a room, hence the depth of the attenuator is required to be lengthened such to resist the increased level of sound power.

2 The second factor affecting the depth of the attenuator is the required level difference between the environmental noise and the required internal noise level. The greater the difference, the longer the attenuator. To design and test the NAT Vent Attenuator, MACH Products has an in-house calibrated test rig to BS EN ISO 7235:2003.  This test facility enables MACH Acoustics to design and test a range of options during Design Stages C, D and E of a project.  The NAT Vent Attenuator is then manufactured to fit into a given location, as well as meeting the buildings ventilation and acoustic requirements.

See Chapter 2 and our website, www.machproducts.co.uk for further details.