The present disclosure describes a system, method, and computer program for modeling and predicting energy use by non-plug-load mechanical/electrical systems in a building, such as lighting systems or HVAC systems. The present disclosure also discloses methods for using such models and predictions to identify energy saving measures for a building. An energy-consumption model for a building is built from energy-consumption models for components within the mechanical-electrical systems. Inputs to the energy-consumption model (i.e., values of variables in the energy-consumption model) are measurable, and behavior models are created for each of the inputs primarily from sensor and/or other measurement-device data. Using the behavior models, weather data, and the energy-consumption model for the building, a predicted non-plug-load energy use for the building is calculated based on the current configurations of the mechanical/electrical systems. Potential energy saving measures are identified by modeling the energy-consumption of alternate physical configurations of the mechanical/electrical systems.