by Adrian Tuluca, R.A.

The constant movement of air through the spaces of a building affects its thermal environment and, thus, its energy performance, yet this invisible "breathing" has been difficult to understand or predict using traditional tools.

Now, computer-based air flow modeling techniques are more available to architects to help visualize and fine-tune their designs to improve natural ventilation and related energy performance.

Computational fluid dynamics (CFD) describes how a building breathes. CFD computer analysis models the complex movement of air molecules and temperatures within spaces. This was originally an expensive and complex process employed only in highly technical engineering realms, such as aeronautical design and nuclear energy plant design.

Later, CFD modeling was applied to special, large-scale spaces, such as airport terminals or multistory atria. These CFD models were expensive and could take weeks to build in the computer. Because of this, the few architects even aware of CFD seldom considered this technology for run-of-the-mill projects.

Today, however, because this kind of modeling can significantly improve a building's energy performance and comfort, CFD is being used for all kinds of buildings. Architecturally, CFD modeling can directly affect building design—the placement of fenestration, for example, or building orientation.

Most importantly, CFD is no longer the budget buster it was a few years ago. Smaller buildings can be modeled for $5,000 to $10,000; a 2D CFD simulation can be done for $2,000 to $4,000.

For an atrium space at Oberlin College, CFD analysis modeled the path of air streams that moved from the front door to windows above the mezzanine. Image: Steven Winter Associates The computer model of the atrium included only those geometric features needed to study ventilation strategies. Image: Steven Winter Associates   Click on thumbnail images to view full-size pictures.