Multi-Storey Car Park Ventilation

Introduction

The new multi-storey car park for the Princesshay development in Exeter is a multi-useage building incorporating a residential block and retail units in addition to conventional multi-storey parking.

A major design feature is the use of an architectural double mesh around much of the perimeter of the car park (see the figure to the left). Whilst the mesh will have an appealing visual impact, it will also impart some air flow resistance which will reduce the ventilation efficiency of the car park.

Extra ventilation slits and balconies have been incorporated in an attempt to avoid the use of mechanical ventilation. Flow Analysis has been commissioned to investigate the ventilation efficiency of the design.

Modelling Approach

Since the investigation concerned the effectiveness of the wind-driven ventilation strategy, it was necessary to model both the interior and the exterior of the car park.

In order to keep the size of the model manageable, a pragmatic 2-stage approach was adopted. The first stage was a large scale external investigation of the wind flows around the car park and the surrounding buildings. The second stage involved focussing on the car park itself, using the results from the first stage as boundary conditions.

In this way it was possible to examine the flows through the interior of the car park in some detail, for several wind conditions.

Air Flow Patterns

The model created by Flow Analysis predicted some very complex internal and external flowfields. These are a result of many factors, including the surrounding building topology and the level of internal detail included in the model. The figures above show some of the external features and the figures to the left show some internal features.

The air resistance of the mesh can be clearly seen from the internal flow figures to the left. The zones of fast moving and slow moving air are clearly distinguishable. The mesh plays a significant role in the ventilation efficiency of the car park, but its blockage effect was found to be less severe than initially speculated.

Fume Dispersal

Some differences in the fume dispersal efficiency depending on the direction of the prevailing wind were found. Not surprisingly, in general, the upper-levels fair better then the lower-levels, but overall the prognosis is good.

On the negative side, depending on the direction of the wind, it was found that the residential block may inhibit air movement. However, on the positive side, the extra ventilation slits and balconies play a significant role in countering this blockage, demonstrating that these are effectively located.

Since analysis predicted fume dispersal to be slower in a lower, enclosed region of the car park directly beneath the residential block, it was recommended that the ventilation openings be increased here.

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