Retrofitting the existing building stock represents the largest and fastest way to reduce energy consumption for Department of Defense (DoD). However, the current retrofit process is manually intensive, focused on equipment selection for initial cost and not energy performance, and not amenable to systems solutions with potential for substantially reducing energy consumption in buildings. Systems approaches have been demonstrated in a number of "one-off" new construction projects, but significant challenges exist in being able to reproduce the energy savings in a cost-effective, timely, and reliable manner, particularly for the constrained problem of retrofitting existing buildings. The systems approach is based on the observation that a building is a multi-scale, heterogeneous, complex dynamic system with considerable uncertainty. Existing modeling and simulation tools cannot accurately capture the dynamic coupling among building subsystems, especially as it relates to control, and therefore represent a barrier to robust and scalable deployment of technologies that require low levels of energy consumption.

The objective of this project was to develop the required systems methodology and building physics and dynamics-based analysis tool set to deliver significantly higher energy performance in existing buildings than is achievable by the current retrofit process.

Technical Approach

The project was executed in two phases: 1) assessment and classification and 2) retrofit design. The assessment and classification phase involved model- and data-based representations of DoD existing building stock energy performance, classified by different building usage types and climates. This was followed by evaluation of the energy use reduction potential of different combinations of low energy design principles (e.g. insulation, daylighting and ground source heat pumps), resulting in system configurations for a class or cluster of buildings (i.e. representative of a particular combination of building usage types and climates).

In the retrofit design phase of the project, building clusters with the largest potential for energy use reduction were then identified and full system (thermo-fluid) simulations were performed to establish baseline energy performance. Subsequent evaluations of energy use reductions achievable with the best available system solutions were performed. Analytical tools for sensitivity and uncertainty analysis were used to reveal system couplings and interactions that underlie the baseline building energy performance and isolate critical failures and opportunities for energy efficiency improvements. Reduced-order models were used to evaluate the robustness of the energy efficient system designs and for optimization. The use of reduced-order models and new analysis tools for concept synthesis enabled rapid progression from a baseline building to a ranked set of retrofittable alternatives with quantified energy performance gains within known bounds of uncertainty.


The results of this project are listed below.  The tool developed through this project is now being demonstrated in ESTCP project EW-201257.

  • New tool developed to rapidly identify and assess energy performance via deep retrofits at a portfolio, and individual building level and prototyped with several DoD building types and climates to identify system alternatives for >50% energy use reduction.
  • Advances in parameter sampling integrated into a process to rapidly quantify uncertainty in building energy performance assessments and identify critical parameters during retrofit design.
  • New process and tools developed to automate analysis of energy performance failures from whole building energy models during design.
  • Reduced-order models for control design with low energy Heating, Ventilation and Air Conditioning (HVAC) systems developed with state-of-the-art techniques for model reduction.
  • Entire toolchain exercised for two DoD use cases with deep retrofit system configurations.


The building systems methodology developed through this project includes tools for rapid survey, audit, retrofit option analysis, and selection to ensure robust design and operation of buildings. This methodology and its associated tools for retrofitting building systems with energy efficiency gains of 50% or more is projected to be applicable to major retrofits of medium- to large-sized buildings, representing a nominal portion of the DoD building stock. Once these designs are demonstrated at DoD sites and the process and tool set is standardized for broader dissemination, significant impact on the DoD building stock is anticipated. A 50% reduction in energy utilization across all DoD facilities would yield $1.75 billion in energy cost savings.