The most economic air conditioning of living and working places can be achieved by natural ventilation if sufficient. This provides not only the circulation of clear air, but also the decrease of indoor temperature, especially, during hot summer days, provided that the temperature of clear air is lower than that of indoor. From the geometric optimization point of view, both size and position of windows in buildings are important parameters to obtain a uniform indoor air velocity distribution. In this study, the potential use of natural ventilation as a passive cooling system in new building designs in Kayseri, a midsize city in Turkey located at 38.44 degrees N and 35.29 degrees W, was investigated by computational fluid dynamics (CFD). Using the FLUENT 6.2 program, which employs finite element methods, indoor air velocity distributions with respect to changing wind direction and magnitude were obtained in living places of different dimensions. The simulation results suggest that natural ventilation can be used to provide a thermally comfortable indoor environment during the summer season in the study area. The study presents useful design guidelines for natural ventilation at both site planning and individual building levels. (c) 2005 Elsevier B.V. All rights reserved.