Optimization, of the Elimination of Dead Zones, and Air Quality Analysis at Local Mean Age of Air in an Underground Car Park with an Impulse Ventilation System

Abstract

It is important to provide efficient ventilation of harmful gases from car engines to meet set thresholds for international air quality in covered car parks. Efficient ventilation is also crucial in case of fire as it serves to dilute the released smoke; thus preventing suffocation. In trying to overcome these challenges of ductless systems, researchers have introduced the Impulse Ventilation System (IVS) which uses jet fans for mixing and dilution of toxic exhaust gases. Most researchers have assumed that car park soffits are entirely flat despite services such as beams, sprinklers among others, resulting in very low headroom making it impractical to run jet fans below the beams. The jet fans can only be installed in the flat soffit whereby the beams block easy airflow resulting in dead zones and failing to achieve the recommended car park air quality. Moreover, these causes resistance and turbulence hence stagnating the air making the required air velocity of local mean age (LMA) of 0.1 m/s and above the 1.7 m LMA height (average human height) not achievable. This research is aimed at addressing the above challenges by using computational fluid dynamics (CFD) techniques in designing an IVS for a covered car park. The study also sought to eliminate dead zones and ensure desirable velocity of 0.1 m/s or greater at LMA at 1.7 m plane hence better air quality by optimally positioning economical jet fans for efficient operation for both the normal pollution ventilation (NPV) and emergency Mode (EM). A case study used in this study is Konza Technopolis, in Kenya (1.689°S 37.185°E ). The optimal placement of jet fans had 20% reduction on the number of jet fans from 26 to 21 hence a potential of monetary savings compared to the conventional method. The research results showed that there was an effect on the velocity obstruction on the jet fans that are in close proximity to the down stand beams. Three validation experiments were done; dead zones elimination was done by conducting experimental measurement points after driving a group of cars. Other validation experiments were conducted on analysis of airflow of entire car park and velocity at LMA at 1.7 m plane results analysis. The methodology used has the potential to reduce dead zones and increase air quality by 99%. From validation experiments, it was conclusive that the research was successful as all stagnant air were eliminated and desirable velocity range of 0.1 m/s and above achieved LMA at 1.7 m plane achieved. This research can be used to improve the design of ventilation systems while cutting down on time, cost and increasing efficiency while working with design standards