ASHRAE Journal - April 2011 - 29

nar participants possessed. However, that software had the capability of exporting BIM data to a neutral-format Industry Foundation Classes (IFC) file. There has been significant effort on the part of BIM software vendors in recent years to develop interoperability between different BIM platforms. IFC files have been touted as the basis of that ability to exchange data. When importing the IFC file from the architect, hundreds of error messages occurred (477 in all). These were mostly the result of elements not being precisely joined. Since the project was a renovation, and no BIM model existed, the architects created the building shell model from old “asbuilt” prints. This process is laborious and imperfect, so elements (such as walls, windows, column surrounds, etc.) that appeared correct on plots were actually slightly disconnected in places. Each error had to be reviewed, in order, and direction given to the IFC import module. Once the error messages were resolved, the newly created BIM model “looked” Figure 1a: First floor plan from IFC file. Figure 1b: 3-D model from IFC file. The model “looks” good. We could rotate the good, but the BIM model required lots of additional cleanup. view in 3-D and see a good representation of the renovated Headquarters (Figures 1a and software assigns a “space” to every enclosed volume. So re1b) and produce 2-D floor plans that, on the surface, looked stroom plumbing chases were defined automatically as spaces like the construction documents. (Figure 2). Something as thin as a wall-mounted whiteboard Once the import of the IFC file was complete, spaces were in a conference room was identified as a space. The “sliver defined for the load calculation process. While touted as an au- tolerance” in the input had been set too low. By adjusting that tomated process, it was fraught with problems. The BIM model value up, the false spaces were eliminated. derived from the IFC required lots of additional cleanup to eliminate extraneous lines and to properly define intended enclosed Architectural Spaces Differ From Mechanical Spaces spaces. Likewise, objects from the IFC file, such as tables and Once the BIM software executes its automated space definichairs, were sometimes interpreted by the BIM software as spac- tions, further manual adjustment is required for heating and es instead of furniture. Those had to be manually deleted. cooling load calculations. In the new conference center wing of the headquarters, a large room is subdivisible by movable Sliver Tolerance partitions into three smaller training rooms. Since each of In the process of space definition, we learned a new term: those smaller rooms has different exterior exposures, the load “sliver tolerance.” Because BIM models are so precise, the must be calculated for each space, not as a single combined

April 2011

ASHRAE Journal

ASHRAE Journal - April 2011

Table of Contents for the Digital Edition of ASHRAE Journal - April 2011