Kettering U Researches Refrigeration Units To Reduce Energy Use

• By Dian Schaffhauser
• 05/12/09

A professor in Michigan has developed the means to know how to optimize the settings for refrigerated display cases to reduce their energy use by 13 percent. A team, led by Homayun Navaz, a professor of mechanical engineering at Kettering University in Flint, MI, built a machine they call the "Proof of Concept Air Curtain," that proves how the velocity of cold air being sent into the refrigerated case can be reduced and the temperature raised to keep food cooler and energy usage down.

"Our computer model is based on experimental technology," said Navaz. "We came up with software based on an artificial neural network that can accurately measure and minimize the infiltration of warm air into a display case. The optimal infiltration rate is a narrow bridge, but easy to hit."

Lower infiltration means the air is coming out at a lower velocity, said Navaz. "Previously, air came out of the upper vent (or grille) of a specific display case at 90 feet per minute. We calculated the optimal speed as 65 feet per minute as an optimal discharge air velocity to yield lower infiltration rate," he said. "You would think more air coming faster would work better, but the decreased velocity improved infiltration, which resulted in the food being one degree colder because the cold air was distributed more efficiently."

By reducing the velocity by 30 percent, infiltration was reduced by 12 percent, and the power required was reduced by 13 percent.

Infiltration represents 83 percent of the cooling load and is the biggest energy draw for refrigerated display cases. Less energy use equals cost savings of about $13 million for the state of California alone, according to Navaz, and less energy use also reduces CO₂ emissions that cause green house gases. The annual nationwide savings on open vertical display cases is estimated at between $170 million and $200 million with a 500,000-ton reduction in carbon dioxide emission.

Manufacturers implementing changes based on the Kettering research are already seeing better than predicted results, according to Navaz, and so far it hasn't cost them anything to implement the recommended changes.

In addition to energy savings, lowering the pressure on the compressor also extends the life of the compressor and creates more cost savings over the long term, he said. "This is not something we are promising. It is something we have done and proven."

The Department of Energy, the California Energy Commission, and Southern California Edison underwrote the research project that began 1998. The total cost of the project came in just under $500,000, Navaz said.

"Imagine if we could save 10 [percent] to 15 percent in all refrigeration units, what an impact that would make on energy consumption worldwide," said Navaz. Currently, he's attempting to form a consortium to expand the research and create jobs in Michigan by starting a center for efficient refrigeration technology.