Together, residential and commercial buildings account for a staggering 40 percent of energy use in the United States, according to the U.S. Department of Energy (DOE). However, DOE’s National Renewable Energy Laboratory (NREL) is developing a suite of tools to tame this energy beast - and it is free to anyone who wants to use it.

Whether retrofitting existing buildings or designing new buildings, energy modeling is a core component to changing a building from an energy guzzler to an energy sipper. “It’s much cheaper to run an energy model than it is to build the wrong building or do the wrong retrofit,” said Nicholas Long, NREL senior engineer.

DOE’s EnergyPlus is a simulation engine that provides comprehensive building energy modeling. NREL is working to add tools to EnergyPlus, via its OpenStudio Application Suite, to improve overall functionality and make EnergyPlus easier to use.

OpenStudio software developers Larry Brackney, David Goldwasser and Nicholas Long appear in one of the Open Studio computer visualizations that helped to design the Research Support Facility (RSF) building at NREL. (Credit: Dennis Schroeder and David Goldwasser) (Click on the image for an enlarged view.)


“The easiest way to describe OpenStudio is a wrapper on top of EnergyPlus,” Long said. “OpenStudio handles the building geometry, building envelope, plug loads, people, and daylighting, along with many other inputs. It adds all of that data into one big massive engine and spits out results. Industry professionals will find that OpenStudio will help them quickly and easily analyze the energy use in their buildings.”

The first version of OpenStudio was released in 2008 and is a plug-in that leverages Google SketchUp, a user-friendly 3D drawing program. “OpenStudio was originally developed so people could view and edit geometry for EnergyPlus models,” said David Goldwasser, NREL OpenStudio developer. “We’ve now expanded it to be able to view and edit a lot of the other attributes of EnergyPlus building models, for example putting in loads like lights, equipment, and simple HVAC systems.”

“OpenStudio goes a long way towards easing workflows for industry professionals,” said Larry Brackney, NREL manager for analysis tools in commercial buildings. “We’ve enhanced it and there are a slew of new features - some of which NREL has developed and some of which we are just leveraging from Google and their massive investment in SketchUp.”

The new suite of OpenStudio tools includes the SketchUp plug-in plus:

ModelEditor, which provides users with a simpler way to edit the building model. It includes a way to access components that don’t have a physical representation in a building, like a mechanical system.

ResultsViewer, a way to review EnergyPlus simulation data in a graphical format. It allows users to look at the data, draw conclusions, and compare results.

RunManager, an application to run simultaneous simulations. This powerful tool can be used to run simulations on a desktop, computer cluster, or even a super computer. Designers can compare results between differing models to see where the best energy savings can be achieved.

The OpenStudio plug-in also heavily leverages a feature in SketchUp called Match Photo which uses photographs of a building to create a 3D model. Once the 3D model is finished, users can use the plug-in to trace over windows and doors for EnergyPlus’ use in running an energy model. It’s a tool that developers believe fills a need, especially for crews planning a building retrofit. “I see Match Photo as a killer app because this is an area that’s not been well served in the market,” Brackney said.

“We really appreciate Google’s integration goals. We think that with a lot of the things they are connecting - like Google Earth and Building Maker and SketchUp - there is collaboration between all of these technologies. It is creating this rich set of building geometry models that we can use for energy modeling. There’s a great synergy there between what they are doing and what we are trying to do.”

OpenStudio leverages Google Sketch-up to create 3D building geometry. Designers used the program to create energy models for NREL’s Research Support Facility. (Credit: Roger Hedrick, Architectural Energy Corp., and David Goldwasser, NREL) (Click on the image for an enlarged view.)


Although collaboration with Google is important to the NREL development team, more important is collaboration with OpenStudio users.

“OpenStudio uses open source code so if someone wants a feature that we don’t have the time or the funds to write, there are two options,” Goldwasser said. “First, they can write that code and submit it to us. We look at it and decide if it gets accepted and works with what we want. Another option is for them is to use an API [application programming interface] and ‘plug-in’ to our software and write applications without changing our code.”

OpenStudio is made available to anyone under the GNU Lesser General Public License, which allows third-parties to easily integrate the functionality into their applications without requiring them to contribute their code back. “We’re not selling this product, it’s free. And, what’s nice about it being open source is that someone can integrate it into their workflow,” said Brackney.

For users, “our goal at NREL is to help people design buildings that are more efficient so that we use less energy,” added Brackney.

To show how easy it is to develop an API to “plug-in” to OpenStudio, NREL developed a simple API for HVAC modeling. “SystemOutliner is a graphical user interface for constructing HVAC systems, which has been one of EnergyPlus’ Achilles’ heels,” Brackney said. “It’s an awesome example of how quickly users can build a very deep, meaningful user interface to OpenStudio that meets a real need.

“The key is all about accessibility, making the notion of doing energy modeling more and more accessible and eliminating the excuse for not doing energy modeling.”

Another potential barrier to using any new software is training; but NREL has seen to the user’s needs here as well. “We have extensive online video tutorials on how to use the new OpenStudio tools to help get users up and running sooner,” Long said.

In fact, the OpenStudio website and YouTube Channel have nearly two hours of videos that walk users through differing workflow applications for the program. The website also has full documentation for the API and source code to browse, and it is continually being updated by NREL staff.

“What’s great is that if I get a lot of questions on a certain subject, I can add in documentation on the fly and I don’t have to wait for the next release,” Goldwasser said.

There is also a user’s forum moderated by NREL for people to post questions and ideas for OpenStudio.

“The user support we provide is incredible,” Goldwasser added. “We provide a quick response, and if it’s a valid question, it might result in a new training video.”

“I’m really pleased with the way NREL is approaching this software development,” Brackney said.” We’ve got a full-blown software development team using rigorous software development process to produce a quality product that people can use to see if there are any other energy savings they can squeeze out of their buildings.”

Reprinted with permission from the National Renewable Energy Laboratory, Golden, Colo. For more information on EnergyPlus, visit To access the OpenStudio website, go to To view the OpenStudio training videos, go to

Publication date:05/09/2011