AIR CONDITIONING 2 CAR PARKS
those required to operate in order to control the flow of smoke, will be switched off in order to avoid inducing smoke into otherwise uncontaminated areas.
Modelling Such system designs will often be required to be supported by a computational fluid dynamics (CFD) model demonstrating the efficacy of the system. CFD modelling can
Regulations: System design standards All car park ventilation systems are required to be designed to meet the performance requirements of the current Building Regulations. The relevant regulations and standards relating to car park ventilation are as follows:
With the increasing use of carbon monoxide (CO) monitoring within car parks, car park environmental control has become far more efficient, enabling the ventilation rate to be accurately linked to the level of vehicle exhaust pollution within the car park.
Approved Document F1: This document sets out the minimum requirements for the day-to-day ventilation of naturally and mechanically ventilated car parks. It specifies the maximum permissible carbon monoxide levels of 30 ppm averaged over eight hours, with levels not exceeding 90 ppm for 15 minutes.
44 CIBSE Journal July 2012
Approved Document B3: Covers the provision of natural ventilation under fire conditions for ‘open sided’ car parks, and mechanical ventilation for those car parks that are ‘not open sided’.
Naturally ventilated car parks require a minimum 2.5% of the net floor area of the car
be a particularly useful tool to support the design of a car park ventilation system and, potentially, to demonstrate to the regulatory authorities that the principle of a proposed design is viable. CFD modelling, particularly that undertaken to support enhanced jet fan (impulse fan) ventilation system designs, should follow the specifications and guidance within Smoke Control Association document and BS7346: Pt 7: 2006, clauses 15.2 CFD modelling and 15.3 Selection of Verification Method. However, such modelling can potentially
park in openings linked directly to atmosphere with at least 50% of the opening being split between two opposing walls. The minimum airflow rate for a mechanically ventilated car park is 10 air changes per hour under fire conditions.
BS7346: Part 7: 2006: Specifies the requirements for one of three design options: smoke clearance; aid to fire fighting; and means of escape.
The document further sets out standards for controls and powers supplies, the criteria for computational fluid dynamic modelling and for commissioning of systems.
hide a multitude of sins and could be based on misleading data. It is unlikely that the models can simulate all the ‘as built’ conditions, final fan locations, drainage pipe, containment and ducting littering the soffit in areas not originally envisaged, and other structures appearing all have an adverse effect on the accuracy of the model. In addition, the performance of the jet fan
should be verified, and the way it interacts with the conditions within which it is located will have a direct and significant bearing on its ultimate performance. Accurate modelling of the jet fan aerodynamic characteristics is fundamental to the resultant accuracy of the model itself, and the fan model should form part of the CFD report. It is accepted that cold smoke generation
cannot fully represent a real fire condition; however, the cold smoke generation together
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