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The system will need to perform a minimum of 6 air changes per hour (ACH) in environmental mode, and a minimum of 10 air changes per hour (ACH) in the event of a fire. (Approved Document B:2019 volume 1 16.12).
Flow rates can be estimated by taking into account the volume of the car park and the required air changes per hour. The exact flow rates will need to be proved with a CFD (Computational Fluid Dynamic) prior to installation of the system to ensure that the system performs.
CFD stands for Computational Fluid Dynamics. Sertus use in-house CFD and other design tools to simulate airflows and heat transfer within buildings. CFDs are required to prove that a mechanical smoke ventilation system will perform.
A mechanical smoke ventilation system must be used if the requirements for a natural ventilation system cannot be met.
A natural ventilation system can be used if there are permanent openings of which the aggregate free vent area is ‘a minimum of 1/40 of that levels floor area, at least half of which should be provided equally by two opposite walls (1/160 on each side)’. (Approved Document B Volume 2 2019 11.4)