In this paper, the optimization of a weather-predicted free cooling system combined with heat storage is shown. The method of incorporating weather forecasts into the control system is presented. The regime of operation was selected and optimized based on free cooling energy and the required temperature parameters of a building's indoor environment, using variable flow rate control through the heat storage. The savings achieved by optimal operation compared to steady state operation were analyzed. The parametric analysis of optimal system operation was done for different outdoor and indoor environment parameters and for different heat storage construction parameters. The results showed a significant influence of system operation control on system performance. (C) 2011 Elsevier Ltd. All rights reserved.