M.Abo.Elazm.. Proceedings of ICFDP9: Ninth International Congress of Fluid Dynamics & Propulsion December 18-21, 2008, Alexandria, Egypt ICFDP9-EG-246 A CFD. STUDY FOR THE VENTILATION EFFICIENCIES OF DIFFERENT VENTILATION SYSTEMS IN UNDERGROUND GARAGES. M.M. Abo Elazm Arab Academy for science, Technology and Maritime Transport, POBox 1029 Miami, Alexandria, Egypt. A.F. Elsafty Arab Academy for science, Technology and Maritime Transport, POBox 1029 Miami, Alexandria, Egypt. A.A. El-Ehwany Faculty of Engineering, Ain Shams University, Cairo, Egypt. R.A. Hammouda Faculty of Engineering, Alexandria University, Alexandria, Egypt. ABSTRACT: Unsatisfactory design of mechanical ventilation systems in underground car parks would give a poor and unhealthy indoor environment. Carbon monoxide (CO) is recognized as one of the most important pollutants that need to be regulated in urban atmospheres due to its toxicity and implications for human health. This study draws attention to the effect of exhaust fan height on the carbon monoxide (CO) dispersion in enclosed parking facilities. A mathematical model is presented in a general computer code that can provide detailed information on CO concentrations as well as airflow fields prevailing in three- dimensional enclosed spaces of any geometrical complexity. This model involves the partial differential equations governing CO levels and airflow transfer in large enclosures. In this paper the performance of the two types of ventilation systems (Suction-only and Supply-Suction) with different positions of exhaust fan and different occupational percentage was studied and the CO concentrations in the breathing zone were compared in order to find the most appropriate position for the exhaust fan to be used in underground garages in both case. It was found that the carbon monoxide concentration in the breathing zone has a strong relation to the exhaust fan position. The simulation results could be used as a base for ventilation design for enclosed garages, aimed at a proper ventilation system selection for a more healthy and comfortable working microenvironment. KEYWORDS: cfd, simulation, ventilation efficiency, underground garage, car park, carbon monoxide, air quality. 1- INTRODUCTION: Carbon monoxide is colorless, odorless, and at much higher levels, a poisonous gas is formed when carbon in fuels is not burned completely. It is a product of motor vehicle exhaust fumes, which contributes almost 100% of all CO emissions in urban areas. The accumulation of CO results in a varied constellation of symptoms deriving from the compound’s affinity and combination with hemoglobin, forming carboxyl- hemoglobin (COHb) and inhibits oxygen transport as shown in figure (1). Several epidemiological studies in parking areas show evidence of a positive relationship between CO in the air atmosphere and hospital admissions [1,2]. Figure 1: formation of carboxyl-hemoglobin (COHb) There are two popular methods to predict airflow fields, the first is the experimental model, and the second is the numerical simulation. Predictions are often obtained by setting up the flow configuration in a model of full-scale room. Flow visualization and measurements are used to get a picture of the flow. Such