Following on from our recent blog on attenuation, we have recently been working on a project that offers an excellent example of why attenuation should indeed not be an afterthought.
Colt designed, supplied, and commissioned a controllable natural ventilation system to the boiler and turbine halls. The system supplies fresh air, removes heat, and provides smoke clearance in the event of a fire.
Attenuation decreases the product Cv (co-efficient) which increases the amount of equipment required to achieve the correct AvCv (aerodynamic free area).
Our system design confirmed that with attenuation the boiler hall would need 13.3m2 AvCv at low level and 8.9m2 AvCv at high level.
Using the product Cv we calculated that 75m2 of equipment for inlet and 29.67m2 for extract would be necessary to meet the system design.
After further investigation into acoustic requirements it was decided that attenuation was now not necessary for the boiler hall. Removing the attenuation reduced the required inlet from 75m2 to 49m2 and reduced the extract from 29.67m2 to 22.25m2.
Quite a difference in cost, steel, wiring, and controls!
Attenuation can have a large effect on the size, weight, and cost of your natural ventilation system. Detailed noise data is not always available at early design stage; however we recommend including some form of attenuation in your design calculations because (as this example shows) it can be difficult and expensive to add it retrospectively.
Graeme Clark is a Senior Consultant for Colt UK and specialises in the design and product application of energy efficient HVAC and smoke control systems.