Design communication is critical for the interaction between digital design models and human cognitive capacities in architectural design. Virtual environments, particularly mixed reality (MR) technologies, can improve spatial cognition, improve the space and effectiveness of space conflicts and support design collaboration . The focus of this study is design processes that incorporate building performance simulations and visualize results to inform the designers of daylighting performance. We present an MR design environment that supports architectural design integrated with design simulations. This environment seamlessly integrates Building information modelling (BIM) and building energy simulation tools with the proposed MR environment. The environment aims for improved efficiency in design processes that support the designer in context-aware and well-informed decision-making for sustainable building design. The evaluation of the environment was carried out through a 2.5-day design workshop. The results indicate that simulation results' visualization in mixed-reality has the potential to provide insight into one's design towards better-informed decision making in architecture.