Energy modeling helped the RSF design-build team to assess from the outset whether the design would be able to accomplish NREL's ambitious energy efficiency goals. The modeling process pushed the team's available energy modeling toolkit to, and perhaps past, the limit of its capabilities. Separate models were required for daylighting, natural ventilation, data center energy use, crawlspace heat recovery and storage, and renewable energy generation. The team successfully knit these outputs together; ultimately, however, a tool that could simulate the RSF from start to finish more seamlessly and with a reasonable learning curve would have been advantageous. Detailed monitoring of the RSF operational energy use has begun and the building is now partially occupied. These data will be used to verify model assumptions, calibrate a more detailed EnergyPlus model, and quantify operational energy use across days, seasons, and years.