CBS Newsletter
Summer 1998
pg. 6

EnergyPlus: The Merger of BLAST and DOE-2

EnergyPlus is a new Department of Energy-supported project that will merge two major building energy simulation programs, DOE-2 and Building Loads Analysis and System Thermodynamics (BLAST). Development of both software tools began in the 1970s, when the U.S. Department of Defense began funding the software that became BLAST and the Department of Energy began funding the DOE-2 program. At the time, it was not clear which effort, if either, would produce a usable building energy analysis program. Each has hundreds of subroutines designed to solve specific building-design problems, and each has been used successfully by building designers. The goal of EnergyPlus is to take the best features of DOE-2 and BLAST and unite them in a single program. EnergyPlus will also offer new analysis tools for building technologies that are too new to have been incorporated in the older software. The table below shows which elements of BLAST and DOE-2 will be present in EnergyPlus.

Program Structure

EnergyPlus will be structured using an input file containing the complete object-based description of the building and its HVAC system. The input file will be in a form that can be produced from the DOE-2 Building Description Language (BDL) file, the BLAST file, or user interfaces that may be developed in the future.

The building simulation will be based on the heat balance engine from IBLAST, a research version of BLAST with HVAC systems integrated into the building loads simulation. For maximum flexibility, the development team will write an HVAC simulation manager to handle communication between the heat-balance engine and the various HVAC modules, including DOE-2 and BLAST template systems, and, for custom systems simulation, the SPARK and HVACSIM+ programs. The HVAC manager will handle data communications between the HVAC modules and the input and output data structures.

The calculation engine will write results into an output data structure accessible to output postprocessing agents. The output data structures are designed to allow users access to the results of the simulation without the need for the software's developers to modify the calculation engine.

Integrated Simulation

The design community has told EnergyPlus developers that the new software will need additional modeling capabilities beyond those available in DOE-2 and BLAST. One of the improvements will be an integrated loads/HVAC technique that corrects a deficiency of both precursor programs: inaccurate prediction of indoor temperatures for undersized HVAC systems.

Integrated simulation will allow users to evaluate a number of energy-saving measures that DOE-2 and BLAST do not currently simulate accurately enough, including free cooling using outside air, realistic system controls, moisture adsorption and desorption in building elements and radiant heating and cooling systems.

To facilitate continuity with existing programs, the development teams at LBNL, the University of Illinois, the U.S. Army Construction Engineering Research Laboratories have combined efforts. The team will emphasize an input structure and format that eases the user transition to the new software. EnergyPlus computational techniques and program structures will represent a significant step toward a new generation of building simulation programs. The program's development process is structured to encourage broad participation (such as writing new modules and development of interfaces) by third parties. A beta version for interface developers will be available in December 1999; a version for testing will be available in Spring 1999. The program will be released in late 1999 or early 2000.

—Dru Crawley

[Excerpted from an article in the Building Energy Simulation User News, Vol. 18 No. 4 by C. Pedersen, D. Fisher, R. Liesen, R. Strand, and R. Taylor of the University of Illinois; W. Buhl and F. Winkelmann, LBNL; L. Lawrie, U.S. Army Construction Engineering Research Laboratories; and D. Crawley, U.S. Department of Energy.]

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BLAST Support Office, University of Illinois
(217) 333-3977; (217) 244-6534 fax

Visit the BLAST Support Office web site.

Kathy Ellington
Building Technologies Department
(510) 486-5711; (510) 486-4089 fax

Visit the Simulation Research Group web site.

This research is supported by the Department of Energy's Office of Building Technology, State and Community Programs, Office of Building Systems.

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