Engineering Firm Proves Its Point With Upfront Computational Fluid Dynamics

Nov. 1, 2009
Contaminant control improved despite nearly half the air

As part of a plan to reduce the energy consumption of the Yale School of Medicine in New Haven, Conn., to 25 to 30 percent below the criteria set forth in ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings, Genesys Engineering was hired to conduct an energy audit.

Initial work focused on a typical 1,800-sq-ft laboratory in The Anlyan Center. Comprising 475,000 sq ft of research laboratories, a magnetic-resonance-imaging suite, classrooms, offices, and support space, the eight-story building is the campus' largest structure, representing 25 percent of the school's total energy consumption. It was only 8 years old at the time.

Genesys started by studying the original drawings of the building, examining test-and-balance reports, and reviewing control-system schematics. The research was supplemented by hours of interviews with the school's operating staff and hundreds of hours of site examinations.

“We could see that current flow patterns were not enabling effective ventilation,” Marty Wallace, a senior associate for Genesys, said. “The Yale School of Medicine staff agreed and supported the idea of using upfront CFD (computational fluid dynamics) to help illustrate the problem and proposed solutions.”

Genesys worked with engineers from Blue Ridge Numerics Inc., maker of CFdesign software.

Parker Wright and Jason Pfeiffer of Blue Ridge Numerics began the analysis part of the project by taking detailed measurements of the laboratory.

Using the measurements and information on airflow rates and diffuser deflection angles, Wright built a computer-aided-design (CAD) model of the room in Autodesk Inventor. The model, containing only the features that impact airflow and contamination removal, was meshed automatically by CFdesign for simulation.

“The CFdesign simulations proved beyond a reasonable doubt that the patterns were turbulent and not conducive to moving contaminants out of the room very effectively,” Wallace said. “They also validated many of the occupants' complaints about uncomfortable drafts in certain parts of the room.”

Wallace produced a modified diffuser layout providing more uniform flow from the windows, down the bench aisles, and to the fume hood and general exhausts. Although an improvement, the revised design still resulted in too many drafts in the room when simulated in CFdesign. Two more diffuser locations were designed and tested before Wallace and Wright settled on the best option.

Moving from CAD to CFD and back to CAD was made quicker and easier by integrating CAD within CFdesign. Geometry from the CAD system was read directly into CFdesign, and all CFdesign parameters were preserved when geometry within the CAD system was changed.

Wright modeled the best option in CAD. He then brought the model into CFdesign for testing with several air-change rates, simulating heating, peak cooling, and emergency flush modes. He also ran several chemical-spill simulations.

“Diffuser placements and throws have to be designed in concert with hood flows from support equipment and exhaust outlets,” Wright said. “Complex interaction among different elements couldn't be fully understood until we ran the CFdesign simulations.

“The final arrangement promotes laminar (smooth) flow from diffuser (inlet) to exhaust grilles, clearing chemicals, reducing drafts, and resulting in a more sustainable design,” Wright concluded.

The design promised not only to eliminate contaminants more effectively, but to do so with nearly half of the airflow of the existing configuration.

“Typical guidelines say that more air means fewer contaminants lingering in a room,” Wallace said. “But high ventilation rates cost large sums of money and are not always necessary to control contaminant levels.”

According to Wallace, the changes have been successful. Room temperature is even, hot spots are gone, and occupant satisfaction has never been higher.

Information and image courtesy of Genesys Engineering.
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