One of the most important lessons of the RSF modeling effort is the degree to which unregulated plug and process loads can dominate energy use, and the degree to which these loads must be understood and controlled to meet a stringent absolute whole-building energy use target. Energy modeling typically focuses on envelope properties, mechanical systems, and regulated internal loads, but for the RSF great attention was paid to details such as schedules and the energy use of individual items ranging from telephones and task lights to lighting control systems (a constant 728 Watts in the case of the latter), distribution transformer losses, white noise generators, and sump pumps. Architectural details such as thermal bridging in window mullions (which might typically be ignored) were also important considerations. When detailed calculations of window performance were done instead of taking overall U-values from ASHRAE Fundamentals, expected U-values were found to be 30% greater.

With a whole-building absolute energy use goal, plug and process loads cannot be assumed to be the same between baseline and low-energy models and therefore "fall out" of the analysis when the two models are compared. They must be carefully modeled before construction and measured when the building is occupied. A corollary to this lesson is that the building owner, who controls the building program, must be committed to the energy goals and monitor end use energy consumption over time to make building performance match design and to sustain those energy savings. A design team cannot deliver a building that automatically reaches aggressive whole-building energy use targets; the building must emerge from an integrated design team that places energy use intensity at the top of the checklist throughout and uses rigorous simulation to verify the design's performance at every milestone.

The energy modeling process required close coordination between the engineering and design teams because of the expedited design-build process and the RFP's strict substantiation requirements. There was a constant tension between the model detail required for accuracy and the compressed design-build schedule. In retrospect, the energy modeling process should have been included as significant constraint instead of being squeezed into a schedule that was based primarily on design documentation and construction. This would likely have resulted in fewer design changes, a more streamlined decision making process, and a more integrated building. The workaround calculations, such as the heat budget of the labyrinth, were critical to the energy modeling process, but were significantly more time consuming than originally anticipated. When approaching these types of calculations in the future, the team would be much more likely to model these in an existing energy model with detailed heat transfer simulation capabilities rather than completely from scratch. Modeling uncertainties led the team to build an energy-use contingency into its design to provide a cushion should some assumptions fail. The RSF closeout energy modeling report cites a final energy use of 33.3 kBtu/(ft2·yr), 5.9% better than NREL's goal of 35.1 kBtu/(ft2·yr).

Energy modeling played a dramatically different role in this project versus a project where energy modeling is required only for code compliance or voluntary certification programs. The team had to model early and often at a high level of detail, to gain confidence that the building as constructed would meet its energy use goals. Energy modeling fundamentally influenced the design of the building, including the narrow floor plate; the size and performance of windows; architectural detailing to avoid thermal bridging; the data center cooling approach; and office equipment.