Investigation and elimination of dead zones in an underground car park with an impulse ventilation system

Abstract

It is important to provide efficient ventilation of harmful gases from car engines so as to meet set thresholds for international air quality in covered car parks. Efficient ventilation is crucial in case of fire as it serves to dilute the released smoke; thus, preventing suffocation. Globally, ducted ventilation systems have been used for years in covered car parks but have faced numerous challenges including the need to keep air flow low in order to prevent pressure loss, complex designs, high capital, and operational costs. Overcoming these challenges, researchers have introduced the Impulse Ventilation System (IVS) which uses jet fans for mixing and dilution of toxic exhaust gases where air is pushed towards extraction points instead of being pulled towards multiple points as in the ducted system. Most researchers have assumed that car park soffits are entirely flat despite services such as beams, sprinklers among others, resulting to very low headroom making it impractical to run jet fans below the beams. The beams block easy air flow resulting in dead zones thus failing to achieve the recommended car park air quality which is a major challenge in the design of efficient IVS. This paper aims at addressing the above challenges by using computational fluid dynamics (CFD) techniques in designing an IVS for a covered car park. A model with geometric characteristics was developed, computational domain and sub domains were assigned including fluid properties, boundary conditions, and finally meshing. The study also seeks to optimize positioning jet fans for efficient operation of the different pollution modes. A case study used is Konza Technopolis in Kenya (1.689°S 37.185°E ). The car park under study has a headroom of 3.6 m and down-stand beam of 750 mm hence a clear height of 2.85 m. This means that no fan installation can be done below the clear headroom at the drive ways. The recommended minimum height of clear headroom of 2.6 m is required and therefore the jet fans cannot be installed on the down stand beams as the remaining clear headroom would be less than 2.6 m. 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. The methodology used has a potential to reduce dead zones by 99%. Experiments were conducted to validate the results on the most probable dead zones areas and air flows rates in the actual car park. The optimal methodology of jet placement has a potential of saving $8, 500 compared to the conventional method. This research will help to improve on the design of ventilation systems, while cutting down on time, cost and increasing efficiency while working with design standards.