Inefficiencies in HVAC control and poorly designed glass façades can significantly impact energy demand and thermal comfort in buildings with extensive glass façades. Two potential solutions are the implementation of smart systems and retrofitting the glass façade. However, when considering these options in building design, it is often unclear which strategy is more effective. This thesis investigates the performance of smart systems using grey-box model predictive control (MPC) and the effectiveness of glass façade retrofitting strategies concerning energy savings and occupant thermal comfort. The case study for this research is an educational building with a vast glass façade. The study commenced with a review of relevant literature, followed by the development of the MPC system and an evaluation of its performance against various retrofitting strategies. The MPC system utilized a grey-box model for predictions and local optimization algorithms for control. The retrofitting strategies included the addition of films and curtains on the interior side of the glass façade. Results indicated a trade-off regarding the energy saving and thermal comfort between the two approaches. Compared to MPC, curtains did not reduce energy demand as significantly, but they provided better indoor thermal comfort. The study also found that the lumped model used in the MPC system had limitations for summer calculations and that some algorithms tended to be aggressive. In terms of retrofitting strategies, the application of curtains enhanced thermal comfort more effectively than adding films to the glass.