by Eddy Krygiel

In the process of sustainable design, at one point or another during the design or documentation process, there comes a need to quantify the energy savings, the daylighting, or the recycled content in your building materials. This is done by using other applications to run analysis on the building design and deliver these metrics.

In the days before BIM, this was done by remodeling the building in another application, typically one for each thing you wanted to measure — one model for energy, one for daylighting, and so on. This can not only be costly because of the time it takes, but it is open to opportunities for error, either through laboriously recreating the design intent from the design documents, or from later design changes not getting added to the recreated model.

With the use of BIM, we have the ability to take the building model geometry and move that directly into energy analysis or daylighting applications to calculate these metrics. This can help save time as well as eliminate geometric errors in the transition.

Energy Modeling

In the case of energy modeling and its relationship to BIM, there are three primary steps involved: modeling the building geometry, adding building loads, and performing the analysis.

If you compare the time it takes to perform each of these steps for the same building type across a variety of analysis packages, you will see very similar results. During years of integrated practice, I have found that more than 50 percent of the overall time needed to perform an energy analysis is consumed by modeling building geometry.

Adding building loads accounts for about 35 percent, followed by less than 15 percent to perform the actual analysis. By simply being able to reuse the model geometry and transfer the building design from the BIM model to the energy model, we can reduce the time needed to run an energy model by almost half.   >>>

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SUBSCRIPTION SAMPLE Comparing energy use in two variations on a building design, with and without a shade structure. Image: Eddy Krygiel/ Courtesy Sybex Extra Large Image SUBSCRIPTION SAMPLE A single source of model geometry leads to multiple analyses. Image: Eddy Krygiel Extra Large Image   Click on thumbnail images to view full-size pictures.