EnergyPlus is a whole building energy simulation program that engineers, architects, and researchers use to model both energy consumption—for heating, cooling, ventilation, lighting and plug and process loads—and water use in buildings. EnergyPlus is the core simulation engine used in BEND, AutoBEM, CityBES and other urban scale building performance simulation platforms.

EnergyPlus does detailed heat and mass balance calculations for each thermal zone of a building at sub-hourly timestep considering heat transfer through building envelope, air infiltration, solar heat gains, internal heat gains from occupants, lights and plug-in equipment, as well as supplied energy to the zone from HVAC (heating, ventilation, air-conditioning) systems. For the IM3 project, EnergyPlus is used to calculate (usually at 10 or 15 minutes time interval) building energy use as well as heat emissions from buildings to the ambient environment. EnergyPlus can be used to simulate and evaluate technologies that reduce building energy use, carbon emissions, peak demand, and anthropogenic heat from buildings.

EnergyPlus takes inputs of hourly weather data (a dozen variables), building and system description, indoor environmental quality requirements (scheduled setpoints of indoor air temperature, humidity, CO2), and building operation and control strategies to simulate building dynamics. Key outputs from EnergyPlus include detailed energy use (load profiles) at whole building and zone levels as well as breakdown into major end uses including lighting, HVAC, plug-loads, water heating, renewable energy generation from on-site PV etc. Time step indoor air conditions and heat emissions from buildings can be produced as well as thousands of variables characterizing building and system operational performance.