FEDS is highly scalable and excels at modeling individual buildings as well as large campuses or installations. Groups of like buildings that share common characteristics can be modeled together as a single building model, while maintaining some individuality in terms of heating, cooling, and hot water fuels and equipment. FEDS is also highly flexible in terms of allowing users to get started with minimal data requirements. FEDS applies intelligent inferences to fill in building system details that have not been specified, but users can always override these as more data becomes available. Further, a variety of analyses can be performed, from high-level screening and comparison of the efficiency opportunity across multiple sites, to detailed identification of the optimal package of energy efficiency measures for a single site, to a nearly unlimited set of comparative analyses to estimate savings potential resulting from changes to occupancy, technology selection, controls, and more. When performing retrofit project optimization analyses, users have the ability to either restrict or force certain options, exclude specific buildings from consideration, and alter project cost components and assumptions in numerous ways. FEDS is scalable and flexible to meet a wide range of needs.

When estimating the savings from energy efficiency measures, FEDS accounts for interactive effects—both within each building and amongst buildings at a site (on the same billing meter). For example, a project to install more efficient interior lighting fixtures will increase the heating load and reduce the cooling load of the building. FEDS accounts for the impact of the new lights on the HVAC system and reports it with the project savings detail. Further, the impact on the billed electric demand can be significantly different depending upon the number and characteristics of other connected buildings. FEDS builds and tracks the electric demand profile for each building and the site as a whole to determine just how much impact a given project will have to the overall demand seen by the meter. This allows FEDS to properly value the savings resulting from each project.

FEDS uses the very same life-cycle costing algorithms as contained within the Building Life-Cycle Cost program. Retrofit analysis and selection is based on an iterative optimization approach focused on minimizing life-cycle cost, and weighs project capital costs against expected savings in energy and demand costs, operations and maintenance costs, and incremental/periodic component replacement costs. Project capital costs are estimated based on characteristics, such as technology type and size, equipment and materials cost, required labor hours, and a host of regional cost factors including labor rates, materials cost factors, sales tax rates, and project overheads. Energy and demand savings are calculated based on the specified prices and rate structures, with future savings estimated via energy escalation indices established by the National Institute of Standards and Technology each year. Net life-cycle cost savings and other economic figures of merit including simple payback and savings-to-investment ratio are reported for each selected efficiency project.

FEDS was designed to provide retrofit recommendations based on detailed life-cycle cost analysis, assuming the current building technology or component was in working order and did not have to be replaced. With replace-on-failure economics, users have the option to specify that a particular piece of equipment or component must be replaced, and therefore require that FEDS select the best, most life-cycle cost-effective replacement. Whether a furnace stops working or  windows must be replaced, FEDS can now perform the necessary analysis to determine the most cost-effective replacement. With a simple check of a box, the model can determine the best replacement, as well as the estimated cost of the project. This provides the option to force specific building technology or envelope retrofits, or the abandonment of specific thermal loops or entire central plants.

In addition to energy and dollar savings, FEDS tracks and reports the impact of efficiency measures on six different types of air emissions, including CO₂. Emissions factors are embedded for each fuel type and electricity is based on the source resource mix of generation assets supplying the state where the buildings are located. All are user-modifiable in order to allow for further site-specific resource characteristic variability. Emissions are reported at the technology, building, and total site levels.

FEDS enables relatively detailed specification and analysis of any number of central energy plants and their associated distribution loops, which deliver steam, hot water, or chilled water to meet building loads. FEDS can determine:

• The total load from all connected buildings and other central plant equipment, both at baseline and throughout the retrofit optimization process.
• The value of steam, hot water, or chilled water delivered to each building, considering central plant equipment types and efficiencies, source fuel costs, auxiliary power requirements, O&M costs, loop losses, and other parameters.
• The cost effectiveness of various decentralization options including:
  • which individual technologies served centrally should be replaced with distributed technologies;
  • which thermal loops of a central energy plant should be abandoned with all attached technologies becoming decentralized; and
  • which central energy plants should be abandoned with all attached loops becoming abandoned and all attached technologies becoming decentralized.

This central plant and thermal loop analysis occurs automatically in conjunction with optimization of building energy systems.

An advanced geometry option allows users to specify detailed building geometry parameters at the specific zone and/or orientation level. This enables more detailed and accurate modeling of unique and difficult to model buildings, such as those with non-uniform geometries (that may impact a zone's wall or roof area, or volume) or envelope characteristics (e.g., different window areas on each side of the building). Parameters that are available by zone for advanced specification include the following:

• exterior wall area
• exterior window area
• roof area
• floor area (both total and ground floor)
• exterior perimeter length
• conditioned air volume.

• building shell (roof, walls, floor, windows)
• lighting
• heating
• cooling
• ventilation
• hot water
• miscellaneous equipment
• motors