Before a dynamic, whole-building energy model (BEM) can be used to evaluate proposed energy conservation measures (ECMs) with reasonable certainty, it must be constructed and calibrated with metered site data to a predetermined level of fidelity using the existing building's actual operation conditions. In practice, ASHRAE level I or II energy audits are used to initiate a building retrofit project. Recorded variables and building operation measurements, particularly energy use associated with specific end use functionalities that are subsequently used as BEM inputs, can significantly impact the model's accuracy. Therefore, to efficiently establish a precise model, it is necessary to identify the minimum instrumentation and measurements needed to calibrate the BEM to the level of fidelity required for significant ECM to be specified, prioritized and implemented. This paper describes case studies of constructing and well-tuning EnergyPlus BEMs to as-operated conditions for two medium size office buildings located in Mid-Atlantic region (Climate Zone 4A). Guided by a prioritized, key parameter list generated through an EnergyPlus BEM sensitivity study, information collected from the buildings as-built drawings, the building automation system (BAS) sequence of operation documents, screenshots of the BAS interfaces, together with hourly sub-metering data and a short two-hour site visit are used to develop the as-operated BEMs. The actual meteorological year (AMY) weather file is used to perform real-time simulations and the simulated building energy use is then compared to the actual building monthly utility bills and sub-metered hourly energy data.