More than 90 percent of our time is spent in buildings i.e. either in the office or at home. All of the building energy consum ption occurs during the operational phase. As such, the operation of buildings contributes to 30-40% of total global energy use and associated CO2 emissions. Considering the building type and the local climate conditions, the major sources of energy consumption are cooling, heating, lighting, and the power consumed by the systems that support the building operation. The expected operational energy consumption is determined, mostly during the design phase, however, the energy efficiency can still be optimized during operations of the building through efficient facility management, retrofits/refurbishment and responsible occupant behavior.