3.1Introduction

Cross ventilation is a highly effective method of ventilating a building 2. This type of ventiliation can also provide cost savings as cross ventilation requires a lower floor to ceiling height than single sided ventilation 1. The drawback of this type of ventilation is often a reduction in floor area as a result of using multiple chimneys 3 and the risk of compromising the acoustic separation across corridor walls.

When ventilating through corridor walls, cross talk attenuators 2 are required to maintain the acoustic performance of partitions, whilst allowing the flow of air into a circulation zone. In these instances, bulkheads accommodating attenuators (600mm to 1200m deep) are required to maintain the acoustic resistance of the partitions. These figures are based upon the NAT Vent Attenuator being used.

Ventilation chimneys are an alternative. As mentioned previously, the drawback of these schemes is reduced floor area such to accommodate multiple chimneys 3. Considerable care is often required when detailing and constructing these chimneys, such to ensure that these details do not compromise the acoustic performance of separating walls and floors.

When ventilating more than one floor, independent chimneys are often used such to maintain acoustic privacy between vertically stacked spaces. On the other hand, NAT Vent Attenuators can be placed within the ventilation stack, therefore removing the need for multiple chimneys 4.

2.6 Window Systems and Curtain Walling

The thermal damper is one of the main factors affecting the cost and depth of the NAT Vent Box. Replacing the damper with an openable or motorised vent/window, eliminates both the thermal damper and weather louvre from the box make up. This typically reduces costs by ≈50% and can reduce its depth by ≈225mm.
Facade and window manufacturers can easily accommodate openable vents in curtain walling or window frames. Placing the NAT Vent Attenuator directly behind an open vent, provides a simple, cost effective design solution for preventing noise break-in.

High level air inlet
In the case where noise levels are exceptionally high, for example due to motorway noise, flight paths or inner city noise, the depth of the attenuator is required to be increased. The additional depth of the NAT Vent Box can be accommodated by using a high level bulkhead 11.

1.3 Acoustics and Cross Ventilation

It is generally accepted that cross ventilation is the most effective form of natural ventilation. Acoustics plays a key role in the design of a cross ventilated building as air must flow freely through the building whilst maintaining privacy across partitions. To allow cross ventilation and maintain privacy, cross talk attenuators are required within partitions adjacent to circulation spaces.

One of the key design benefits of the NAT Vent Attenuator is the simple implementation of cross ventilation through a corridor wall, while still maintaining the acoustic integrity of these partitions. Furthermore, this product enables cross ventilation to vertically stacked rooms, vented through a single stack. In other words, vertically stacked spaces no longer require independent chimneys to maintain the acoustic separation between rooms, resulting in a significant recovery of floor area and a considerable cost saving.

One of the drawbacks of ventilating through the corridor wall is the requirement for an exceptionally large bulk head, such to accommodate large, heavy attenuators. The NAT Vent has been designed to provide exceptional levels of cross talk separation. MACH Acoustics has undertaken extensive research to understand the required levels of acoustic separation across these partitions. Depending upon the air flow and the required level of acoustic separation, the NAT Vent can be as slim as 600mm deep. In some instances, this is required to be increased to 1200mm, depending on the required acoustic performance.