Based on the method we suggested in a previous paper [Int. J. Heat Mass Transfer 45 (2002) pp. 2373-2385], the present work is to investigate the mixed convection problem. A two-dimensional, steady, laminar displacement ventilation model is adopted here for the interaction between the buoyancy driven natural convection and the external forced convection is important to achieve the goal of ventilation effectiveness. The solution is determined by the nondimensional parameters Gr and Gr/Re-2, the influences of which on the resulting heat and fluid flow are discussed. To optimize the ventilation system, different outlet locations are investigated. Results and comparisons show that the displacement ventilation guarantees a high indoor air quality (IAQ) and is therefore a desired air-conditioning system.