Keeping food cold in open store display cases is an ongoing challenge for designers.

A mechanical engineering professor at Flint's Kettering University says he's learned a lot in the years he's spent searching for ways to cut the energy that open refrigerators gobble up.

Early on, Homayun Navaz discovered that one key is slowing down the air circulating in the unit.

"By reducing the velocity by 30 percent, infiltration was reduced by 12 percent and the power required was reduced by 13 percent," Kettering spokeswoman Dawn Hibbard wrote on the school's Web site.

Previously, many people assumed faster air flow meant better refrigeration, Navaz said.

"You would think more air coming faster would work better, but interestingly, the decreased velocity improved infiltration, which resulted in the food being one degree colder than before," he said in a statement.

Air infiltration causes 83 percent of the cooling load for display cases, Navaz said.

Navaz worked with doctoral student Mazyar Amin and University of Washington professor Dana Dabiri to make a 15-foot-tall air circulation simulator and analyzed about 3,000 sets of tests.

The U.S. Department of Energy, California Energy Commission and California Edison underwrote the work, which started in 1998.

Manufacturers have made changes based on the research and are seeing better-than-expected results, Navaz said. He said the next challenge is controlling the turbulence of cold air in the units.

If successful, he said, "we can achieve another 10 to 15 percent improvement in energy efficiency."

"There is a potential for huge payoff," Navaz said. "Just multiply our results by the number of display cases used statewide, nationwide, and worldwide."