Continuous commissioning on existing buildings aims at resolving building mechanical system operation problems, improving system reliability, improving occupants’ thermal comfort, increasing building energy efficiency, minimizing retrofit cost, and achieving energy savings at the same time. Dr. Lin will present the implementation of energy efficiency measures on two high-tech buildings in Silicon Valley, California. A total saving of 16,000,000kWh/yr in electricity was achieved and confirmed by measurements from 23 power meters throughout the two buildings. Saving of over 34,000MMBtu/yr in gas was also obtained based on the gas meter readings. The building owner was awarded a total rebate of $2,200,000 from PG & E upon completion of the energy efficiency project. The building HVAC system description and challenge, energy efficiency measures and energy saving results will be presented.