Energy consumption and performance investigations of environment-dependent systems such as building HVAC and refrigeration systems, solar collectors, cooling towers, usually require weather information. This introduces a problem because there may be significant variances between the recurrent days or years. In this work, typical hourly weather data for the selected 23 provinces that represent demographic and climatic conditions of Turkey are obtained by using actual recordings. The results are stored as computer files ready to be used by simulation programs. By using these typical meteorological years, heating and cooling degree-days, dry-bulb temperature bins and winter and summer design dry-bulb temperatures are calculated. Sample typical-year simulations show for example that energy savings of about 11 and 16 per cent could be expected in Ankara by 3 and 5 K night-setback, respectively. Copyright (C) 2000 John Wiley & Sons, Ltd.