CFD INVESTIGATION OF JET FAN SYSTEMS FOR POLLUTION CONTROL AND SMOKE CLEARANCE IN UNDERGROUND CAR PARKS

Abstract

Land in urban areas has traditionally been used for housing and entertainment purposes. Due to the limited availability of usable land in such areas, most car parks have typically been built vertically underground. Recently, ventilation in underground car parks using the jet fan system is becoming more common as well as more challenging in design.

In the present study, a jet fan model was developed and validated with experimental measurements along with a comparison between CFD results and analytical correlations for the fire modeling. An underground car park was chosen for this investigation with a net area of 5290 m2 and 3.7 m height. Two ventilation modes were considered; normal pollution ventilation and smoke clearance. Four parameters were examined to study the ventilation efficiency in the car park; the effect of the jet fan numbers and configurations, the consideration of the smoke clearance, the consideration of the ventilation zones, and the consideration of the fire location with a fire source of 4 MW. The ANSYS FLUENT 14.0 software was used for all numerical results obtained.

This study shows the importance of using the concept of the Local Mean Age of air (LMA) in the design of such systems. Velocity contours at 1.7 m, the average adult human height, within the car park were maintained within an accepted range. The desired ACH was achieved. Results showed that dividing the car park into zones is highly recommended and should be taken in the design of the jet fan system, providing that each zone has a sufficient source of fresh air. When the fire location was considered, the temperature is limited in the zone, where the fire is detected, and it is within an accepted range. The CO2 mass fraction was presented and showed how the jet fans contribute in reducing the concentration of contaminants.