Energy Efficiency Measures (EEM) are increasing to bridge the gap between energy supply and demand scenarios. About 70% of the electricity generated in the US is consumed by buildings alone. HVAC and lighting consume about 74% of electric load demand in a commercial office building. People, -equipment and lighting- load contribute major portion of internal load in office buildings. Building envelope of typical office building consisting of 40% window to wall ratio and meeting the minimum ASHRAE design guidelines contribute to around 33-35% thermal load except topmost floor which may be higher due to exposed roof. Except roof, windows contribute 70% of thermal load due to building envelope. Hence, need for energy efficient windows which have good thermal property for all environmental condition yet allow enough daylight in the space is important. Two types of smart windows, electrochromic glass and transparent solar glass, when used in optimum combination has potential of both, energy saving and energy generation with help of renewable energy source. The thesis focuses on reducing thermal load of the building by optimizing the window selection for building envelope based on building orientation and providing a stepping stone to smart plugin for integration of smart windows in existing energy simulation software.