In what seems a counter-intuitive maneuver, Dr. Homayun Navaz, professor of Mechanical Engineering at Kettering University in Flint, Mich., turned down the velocity of cold air and raised the temperature to 32 degrees to improve energy efficiency in a refrigerated display case.
Ironically, it worked, energy savings went up and the food got colder.
“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,” explained Navaz.
Using a machine called the "Proof of Concept Air Curtain" (POCAC), designed and built at Kettering, a matrix of tests were performed and the resulting 3,000 data was correlated through a computer program based on an Artificial Neural Network (ANN).
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 real 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 nationwide savings on open vertical display cases is estimated at $170-200 million/year with more than 500,000-ton reduction in carbon dioxide emission.
Manufacturers implementing changes based on the Kettering research are already seeing better than predicted results and so far it hasn't cost them anything to implement the recommended changes.
The Department of Energy and the California Energy Commission and Edison underwrote the research project that began 1998. The total cost of the project came in just under $500,000, Navaz said.
Partnering organizations for the project included: The Technology Test Center (TTC) at Edison; Public Interest Energy Research (PIER) at California Energy Commission.
“Imagine if we could save 10 to 15 percent in all refrigeration units, what an impact what would make on energy consumption world wide.” Navaz is currently attempting to form a consortium to expand the research and create jobs in Michigan by starting a center for Efficient Refrigeration Technology.