In the UK, enclosed car parks have to be provided with a smoke clearance system to achieve 10 air changes an hour (in fire condition) and a daily air ventilation system to achieve 6 air changes an hour (ach). This can be achieved by one ventilation system operating at different loads. Although the standard guidance recommends a mechanical system consisting of a large quantity of air ducts, there is an alternative solution to this costly option; impulse/jet fan systems.
There are three major advantages of these systems. Firstly, the floor to ceiling height of the car park can be minimised, thus reducing construction costs. Secondly, the impulse/jet fans can assist in the justification of design deviations (from standard guidance) and can also help to resolve non-compliant issues. Finally, as the air ducts are not required, there are cost savings on the ventilation system.
Sounds good? The design of the impulse/jet fan ventilation system requires the aid of CFD simulations. Innovation Fire Engineering are extremely experienced in utilising CFD to ensure design integrity and to deliver cost savings to our clients. Traditional CFD methods adopt the so called ‘mean air age’ concept which is deemed to be out of date. We adopt the state of the art CFD technology to analyse the air flow within the car park.
Illustrated below are images of the flow of air inside a car park. Transient velocity vectors (Table 1) and soot distributions can be obtained to best visualise the air and smoke flow in the car park. Smoke clearance can be seen directly (Table 2) and any stagnant areas can be easily identified using the velocity vectors, which can be used to help improve the design.