We compared the energy simulations of a Net Zero Energy office building at the design stage to its energy consumption during operation. The office building was located near San Francisco, California. This comparison was difficult because the simulations used different classifications than were used to for collection through sub-metering. Overall, actual net energy use was 47% higher than simulations, while actual HVAC and lighting energy uses were lower than simulation by 91% and 66% respectively. Actual plug energy use was more than 1800% higher than simulations because part of the HVAC was included in plug energy measurements and the predicted value of the plug energy in the simulations was relatively low. Water heating energy disappeared as a separate, measurable end use and was subsumed within plug energy because decentralized, plug-in units replaced a single, central unit.