EnergyPlus is DOE’s whole-building energy simulation engine. EnergyPlus includes advanced simulation features including sub-hourly time steps, simultaneous solution of zone conditions and HVAC system actions, a modular HVAC structure that accommodates a wide range of system configurations, and a runtime scripting language for user-defined control strategies. Originally released in 2001, EnergyPlus is continually updated—major updates are released twice a year—and fully documented and supported. EnergyPlus is open source software. It forms the analytical basis for energy-efficiency standards such as ASHRAE 90.1 and for both free and commercial energy analysis products. Version 8.4.0 was released 9/30/2015. Learn more at energyplus.net.

External Link to Product Page:
United States
Major Capabilities:
Whole Building Energy Simulation, Load Calculations, HVAC System Selection and Sizing, Lighting Simulation, Air Flow Simulation
Building Type:
Commercial, Residential, Multi Family
Linux, Windows, Mac OS X
Free, Open Source
Help And Support:
Free Email Support, Third Party Support
Last Software Update:
September 30, 2017
Building physics or mechanical engineering background is helpful.
Mechanical, energy, architectural, and control engineers, building auditors and operators, building product designers, energy-efficiency program administrators and portfolio managers, energy-efficiency policy analysts, researchers.
EnergyPlus is a console-based program that takes inputs—both building description and weather—as structured ASCII text files. EnergyPlus comes with IDF-Editor, a grid-based wizard that facilitates the creation of simple models and performs input-consistency checks. A number of comprehensive graphical user interfaces are also available (http://energyplus.net/interfaces/). Note: EnergyPlus building descriptions use a custom object-oriented format. DOE is currently developing a complementary format that uses the standard object-oriented JSON language. This new format will hopefully be available in the Fall 2016 release.
EnergyPlus produces both summary and detailed output in unstructured text, CSV, HTML, and SQLite formats. As is the case with input, EnergyPlus comes with a simple output visualization utility, EP-Compare. The above mentioned user interfaces also graphically display EnergyPlus output. Note: DOE is also currently developing a JSON-based output format that references the JSON-based input. This output option will hopefully be available in the Fall 2016 release.
EnergyPlus implements detailed building physics algorithms for heat transfer—radiation, convection, and conduction—air and moisture transfer, light distribution, and water flows. These allow EnergyPlus to model a broad range of of building and mechanical system configurations and conditions. EnergyPlus’ list of advanced features includes: * Integrated simultaneous solution of thermal zone conditions and HVAC system response that does not assume that the HVAC system can meet zone loads. * Automatically varied time steps for interactions between thermal zones and HVAC systems that can model systems with fast dynamics. * Heat balance-based solution of radiant and convective effects that produce accurate surface temperatures for calculating condensation and thermal comfort. * Combined heat and mass transfer model that accounts for air movement between zones.. * Illuminance and glare calculations for reporting visual comfort and driving lighting controls. * Component-based HVAC that flexibly supports both standard and novel system configurations. * A large number of built-in HVAC and lighting control strategies and an extensible runtime scripting system for user-defined control. * Functional Mockup Interface import and export for co-simulation with other engines. Other strengths include an open-source license and committed support from DOE.