BEM predicts a building’s anticipated energy use and corresponding energy savings, as compared to a standard baseline. In so doing, it demonstrates project compliance with local, regional or national energy codes. BEM predicts energy performance based on Typical Meteorological Year (TMY) data, as well as assumptions about building operation and maintenance.
Accordingly, the prediction is only as accurate as the assumptions, which should be documented and understood by the project team, as well as the client, the building operator, and the end users. Changes made during the design and construction process should be used to update the BEM, to increase its utility and predictive accuracy.
Source: An Architect’s Guide to Integrating Energy Modeling in the Design Process. 2012. The American Institute of Architects.