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Current Status of Software Interoperability and DOE Tools

The International Alliance for Interoperability (IAI) started the development of a universal object data model that describes buildings more than five years ago. LBNL has actively participated since the beginning of this effort . In the last two and a half years the organization has grown from six to nine international chapters (in North America, United Kingdom, Germany, France, the Nordic region of Europe, Japan, Korea, Singapore and the Austral-Asian region). The international membership has grown from 400 to over 650 companies and organizations. During this period the IAI has released two new versions of its Industry Foundation Classes (IFC), the object data model it is developing: IFC 1.5.1 and IFC 2.0 (the latter was released in April 1999).

The IFC 1.5.1 model enabled the exchange of building geometry among IFC 1.5.1-compatible software applications. This means that two or more software applications that have implemented interfaces between the IFC object data model and their own model structure can read and write *.ifc format files that can contain all the information about a building's geometry. In that way the information developed by one such application (for example, by a CAD tool used by the architect to design the building) can be seamlessly imported by another compatible software application (such as an energy performance simulation tool). This shortens the time and eliminates error in preparing the input for the receiving application, which substantially reduces the cost of its use.

The IFC 2.0 model expands on that and enables the exchange of some of the non-CAD data used by applications that primarily generate and manipulate non-geometric information. These include classes (object/attribute/relationship sets) that describe surface properties for architectural visualization and lighting simulation, and equipment performance metrics for tracking the performance of mechanical systems. Such classes are particularly important to simulation tools LBNL has been developing with funding from DOE.

A number of IFC-compatible software products have been released primarily on the European market in the last 18 months. These are all CAD-based applications that support one of the earlier IFC releases: IFC 1.0 or IFC 1.5 that have been of little use in North America. All major CAD vendors, including Autodesk, are now developing products that will be IFC 1.5.1-compatible. Autodesk already offers an IFC Input/Output Utility with its new Architectural Desktop 2 that is IFC 1.5-compatible. Its next release will include an IFC 1.5.1-compatible Utility. The only IFC 2.0-compatible CAD tool expected on the North American market in the near future is Visio 2000 Technical, which is now in beta testing. With this tool the user will be able to create a quasithree- dimensional representation of a building from two-dimensional drawings saved in *.dwg, *.dxf and other proprietary CAD file formats, and save the result as an *.ifc file. This tool will be able to "populate" *.ifc project files with geometry and some other types of data needed by "downstream" applications.

Graphic illustrating how new additions to the model will be in form of domain extensions to the core model and interoperability level

Figure. Architecture of the IFC object data model.

EnergyPlus will be the first LBNL IFC-compatible simulation tool. Work to map IFC geometry to the EnergyPlus data structure is in progress. The interface itself will be developed pending further funding from DOE. Once the interface is in place (and IFCcompatible CAD tools like Visio 2000 Technical are on the market) an EnergyPlus user will be able to import the entire building geometry directly from CAD files, interactively define thermal zoning and proceed with the simulation much sooner than without the interface. LBNL is also working towards making Bild-IT (an integrated HVAC design tool that will incorporate CFD and thermal analyses) IFC-compatible.

The IAI is currently "stabilizing" the structure of the IFC object data model: Classes that all participating software implementers agree upon now will be left unchanged for at least the next two years. During that period all new additions to the model will be in form of "domain extensions" (Figure 1) to the "core" model and "interoperability level." HVAC equipment and systems are only partially defined in the current Building Services schemata. That precludes the development of an interface that would allow seamless acquisition of other non-geometric data needed by a building energy performance simulation tool like EnergyPlus or Bild-IT. LBNL plans to complete the HVAC schemata within the IFC object data model and thus solve this problem.

— Vladimir Bazjanac

For more information, contact:

  • Vladimir Bazjanac
  • (510) 486-4092; fax (510) 486-4089

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