A lot of effort has been put into improving energy performance of buildings, and still a lot of problems are found with thermal performance of windows. Although its U values are constantly being improved, overheating problems can often occur in buildings with large areas of transparent surfaces. Besides the conventional shading products, some innovative solutions already exist on the market, but their efficiency and performance are still not examined thoroughly. Smart glazing, and especially electrochromic window devices, is one of the most promising products that are commercially available. Its implementation in simulation programs, as well as the results of the simulations, is tested and analyzed in this research. Simulation is performed by coupling lighting simulation program and energy simulation program through the third program – Building Control Virtual Test Bed. Cooling loads of a commercial building are calculated and the possibilities of energy saving by using electrochromic windows are found. Cooling loads are compared to conventional windows, where the effect of electrochromism is examined. Simulations have also been performed with windows with shades. The results demonstrate potential cooling loads reduction when smart glazing is used in oceanic climates.