New Pluses for EnergyPlus

Crawley's work has recently focused on a program called EnergyPlus, which began beta testing on April 5. When commercially released, EnergyPlus will permit users greater flexibility in the types of building they can analyze, including buildings with superinsulation, high-mass walls, passive-solar design, and moisture transfer features. This is a broader gamut of built-in building science capabilities than previous tools could handle.

EnergyPlus builds on the best features and capabilities of BLAST and DOE-2. It will include innovative simulation capabilities using time steps of less than one hour, systems simulation modules that are integrated with a heat balance-based zone simulation, and input and output data structures tailored to facilitate third-party interface development. Highlights include:

• simultaneous zone loads and HVAC systems simulation;
• improved daylighting modeling (simple and more complex);
• simple input and output processing;
• simple building-description-editing capabilities;
• a translator from BLAST (.bin files) to EnergyPlus input files; and
• basic HVAC simulation.

One downside to EnergyPlus is that users need to be pretty familiar with energy efficiency technologies and understand whole-building energy efficiency analysis methods to be able to use the software. It isn't for beginners. You also need a fairly powerful PC (a Pentium II, 400 Mhz or faster with 64-128 MB of RAM or more) and a large (at least 17-inch) monitor to display the numerous screens that are made available during a run. (Like most energy design software, it is not available for Macintosh-based computers.) Furthermore, unlike REM-Design or Energy-10, which are somewhat more easily understood by beginners, EnergyPlus does not offer a single unifying screen or hub from which to select options.

Information flow through EnergyPlus analysis begins with a building description and is coordinated by the Simulation Manager.

EnergyPlus's simulation engine appears destined to become a standard core for other building energy design tools, like future versions of the popular Energy-10 program (see "Putting the Byte into Your Analysis Toolkit," HE Sept/ Oct '98, p. 25). Crawley described EnergyPlus's approach to simulating HVAC systems as "very flexible, with no fixed templates." This should allow users to configure real mechanical systems that reflect what is in the building plans, without having to select from cookie cutter menus. However, the software will also have defaults built in for basic building types. Other planned capabilities of EnergyPlus include solar-thermal systems, multizone air-flow analysis, and photovoltaic and fuel cells applications.

EnergyPlus is currently under final development, with the final version due out by early 2001. It will be useful for both residential and commercial buildings. Although it is not designed as a weatherization tool, it will be very useful for residential architecture and engineering purposes. Because software engineers want to increase the ability of energy analysis tools to interface with architectural computer aided design (CAD) programs, DOE is also seriously considering open release of EnergyPlus program source codes and is preparing a developer license procedure. This would allow CAD program creators to easily interface with energy analysis programs and would also benefit users who appreciate higher speed due to more efficient interface code.

--Bion Howard

Bion Howard is principal of Building Environmental Science & Technology (BEST), an environmental building consulting firm in the Washington, D.C., area.

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