CAR PARKING VENTILATION
Types of Car Parking Ventilation
1.Open Sided car parks.
Image source: yourparkingspace.co.uk
These car parks are generally above ground level, where permanent natural ventilation is available. They should have permanent wall openings on each level, equal to at least 5% of the plan area, arranged to provide cross ventilation. At least half of this should be equally arranged between two opposing walls. These openings are considered to provide sufficient ventilation for clearance of both smoke and vehicle exhaust fumes. 2.Naturally Vented Car Parks.
These car parks are generally above ground level but do not have sufficient ventilation opening to class as "open sided. They should have permanent wall openings on each level equal to at least 2.5% of the plan area, arrange to provide cross ventilation at least half of this should be equally arranged between two opposing walls. These opening are deemed to provide sufficient ventilation for smoke clearance. However in addition mechanical extract providing three ar changes per hour should be provided for day to day usage to remove exhaust fumes. Note: The 5% and 2.5% areas re defined in approved Approved Document F as "aggregate Equivalent areas". They do not refer to the geometric areas. An equivalent area has an airflow performance equal to a square edged orifice of the required area. For openings that are obstructed in any way , by louvers, screens, etc, the aerodynamic coefficient of the obstruction is needed for calculation of the equivalent area.
3.Mechanically vented Car Parks.
When natural ventilation is not possible, such as where the car park is in a basement or fully enclosed, a mechanical extract system should be provided. The recommendation are that the system provide 6 air changes per hour(ACH) for day-to-day ventilation on all levels nd 10ACH on the fire floor in the event of a fire. The system should be capable of operating at temperatures of up to 300 degree Celsius for 60 minutes, and ductwork and fixing =s should be made from materials that have a melting point above 800 degree Celsius. The system should have at least 2 extract fans, each providing 50% of the duty, with a secondary power supply to operate in the event of a mains power failure. Extract points should be designed with 50% of the extract at high level and 50% at low level.
The following are the different type of mechanical ventilations:
*Ducted mechanical extract systems
Mechanical Extract systems are permitted by regulations but are rarely used nowadays due to the benefits provided by impulsive systems. They tend to used only where the car park size and geometry allows good distribution of air to be achieved without needing extensive ductwork.
The main issues relating to ducted mechanical extract systems which often cause problems for designers are :
*The ductwork runs underneath the celling, reducing the already restricted height normally available.
*Down stand beams require the ducting to be set down below them, thus diminishing the height even further.
*Low level extract points are required, often needing protective barriers to surround them, and these take up valuable floor space.
*The duct work gives the car par cluttered look and can interfere with CCTV coverage and lighting.
*Impulse ventilation systems.
*Induction Ventilation systems
*Induction ventilation systems further enhance the impulsive ventilation concept.
*Using the same principles s impulsive ventilators, induction fans are slimmer and potentially more powerful, thus reducing the number of units required.
*Impulsive fans are generally limited to a thrust of around 50N as they otherwise become physically too large for considered space available in a car park.
*Induction fan thrusts up to around 100N. The floor area ventilated per fan is thus significantly greater, equating to a requirement for fewer units. However , in contrast to impulse fans, induction fans cannot generally be made reversible.
*Induction fans are shorter and slimmer than impulsive fans, allowing a reduced excavation cost and lower car park height. They are particularly suited for effective ventilation where downs and beams are close together as they can more easily be located between them without compromising the performance.
*Fewer units means lower cabling and control requirements and lower installation and maintenance costs.
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