ASHRAE Standard 209-2018: Energy Simulation Aided Design for Buildings except Low-Rise Residential Buildings
About this book
ASHRAE Standard 209, "Energy Simulation Aided Design for Buildings Except Low-Rise Residential Buildings," establishes requirements for using whole-building energy simulation as an integrated part of the building design process. Unlike standards that specify minimum efficiency values, Standard 209 addresses the process of energy analysis — when simulations must be performed, what they must include, how they must be documented, and how simulation results must influence design decisions. The standard was developed in recognition of a fundamental gap in practice: while whole-building energy simulation software is widely available and used, the quality and completeness of simulations varied enormously, and simulation results were often applied too late in the design process to inform fundamental design decisions.
Standard 209 establishes a simulation-aided design process that runs in parallel with the design process from the earliest conceptual stages. The standard defines a phased simulation process corresponding to the major stages of building design: predesign (energy targets and climate analysis), schematic design (testing of passive design strategies including orientation, massing, and envelope), design development (system selection and sizing), and construction documents (compliance verification). Each phase has specific requirements for the minimum scope and completeness of simulation models.
A key innovation is the requirement for "integrated design analysis" — the evaluation of the interactions between building systems, rather than the isolated analysis of each system independently. For example, a simulation that evaluates lighting power density in isolation from its heat gain impact on the cooling system would not satisfy Standard 209's requirements. The standard also establishes requirements for simulation model documentation, uncertainty analysis, and the minimum credentials required for the energy analysts performing the simulations.
This addresses quality assurance concerns that had emerged from studies showing significant variability in simulation results produced by analysts of different skill levels. Standard 209 is referenced in several high-performance building programs and is increasingly specified by sophisticated building owners and developers who recognize that process requirements are as important as outcome requirements for achieving genuinely high-performance buildings. Sources: ASHRAE (ashrae.org); ASHRAE Standard 209-2018 official publication; ASHRAE Journal technical articles.