Engineered Systems - January 2009 - (Page 65) Despite how the song goes, there actually is something like the real thing. Here, one consulting firm reports on its own use of CFD — when to deploy it, how to incorporate it in given situations, and what kinds of benefits it can yield. From identifying trouble spots in fume ventilation to making a school district more comfortable with committing to underfloor air, the advantages can add up. BY BARRY J. STAMP, P.E., LEED® AP AND STEVE T. MAXSON, P.E., LEED AP omputational fluid dynamics (CFD) modeling has, since 2000, been used to provide high-quality space airflow visualization. Indeed, a key component of CFD’s value has been its ability to significantly reduce the time and expense involved in the design, optimization, and troubleshooting of HVAC systems. Traditionally, physical models and prototypes, along with simple rules of thumb and empirical correlations, have been the engineer’s main tools. Using CFD, virtual models are built and analyzed at a fraction of the cost and effort required for physical testing. In addition, CFD can provide insights into flow problems that would be too costly or physically prohibitive to explore by experimental techniques alone. The insight and understanding gained from CFD simulations give added confidence to design proposals at reduced risk, avoiding the need to design by over-sizing and over-specification. With ever-increasing awareness and concern regarding indoor environmental quality and all aspects of indoor perceived comfort, the demands placed on the HVAC system design require the design input CFD modeling can provide. As CFD software continues to advance, the benefits of CFD modeling utilization become increasingly apparent. C CFD AT SBEC Shaffer • Baucom Engineering & Consulting (SBEC) engineers have used CFD modeling in a number of projects to generate airflow models that analyze critical and complex applications, including laboratory exhaust modeling and room ventilation effectiveness analysis for LEED® rating criteria documentation, hospital operating room airflow, atrium smoke-control systems, and building exhaust placement analysis. SBEC specifically used Airpak3.0, a CFD-based HVAC system design software program by Fluent, Inc. SBEC engineers have found that the software allows them to enhance documentation and communication between design professionals and customers, help minimize liability exposure, and deliver a superior product to the client. Airflow behavior in simple spaces with conventional diffuser placement is typically easy to predict, and air device performance data can be applied to conventional designs with a high degree of reliability. For complicated industrial applications and displacement ventilation applications where airflow is strongly affected by convection and other more subtle forces, computer-based airflow modeling becomes a very powerful design tool. The following material includes two case studies that illustrate the application of computer-based w w w. esmag a zin e. c o m 65 http://www.esmagazine.com
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