The assessment of a building's energy performance as a design factor in the early design stages is a very demanding and complex procedure. Over the last decades, a number of tools and methods have been developed to address performance-related design questions, mostly using Multi-Objective Optimization Algorithms. Parametric modelling offers dynamic control over geometry and components, allowing the designer to assess multiple variants at the same time. In this paper, a new design workflow methodology is proposed, integrating evolutionary algorithms and energy simulation through Grasshopper for Rhinoceros 3d, for a comprehensive exploration of performance-based design alternatives in the building scale.