This paper proposes and validates a Discrete Event Simulation (DES) engine for the Smart-Building (SB). It strives to virtualize the common elements found within it and integrates them transparently to an existing Building Management System (BMS), along with existing infrastructure. Thanks to this integration layer, the building management and its control intelligence are completely agnostic to the operations of that virtualization engine. A unique feature of this engine is its micro-treading based core. The latter permits a highly optimized, pseudo-concurrent simulation of hundreds building elements (e.g. loads, sensors, storage, generation, user, etc) in a lean, commodity hardware. Primary virtualization aim is the real-time power data of a SB for the purpose of energy management and Smart Grid connectivity. Moreover, energy optimization and financial studies can be conducted proactively, before committing to costly physical infrastructure investments.