The matrix - chilled

Mar 17, 2006

A Kettering researcher is developing a matrix to make commercial refrigeration units more energy efficient.

Keeping things cool while keeping energy costs down has almost been an oxymoron - that is until now. Dr. Homayun Navaz, a professor of Mechanical Engineering at Kettering University, is on the verge of reconciling the two.

Navaz and a team of researchers have developed a machine called the "Proof of Concept Air Curtain" (POCAC) to test different scenarios in terms of geometrical configuration and turbulence levels throughout the air curtain that cause infiltration of warm air into a display case. The experimental setup will be used in conjunction with simulation software to collect data for a matrix that will span all possible design specifications of interest to display case manufacturers.

"We have to correlate about 3,000 data sets," said Navaz, "so we have to be clever with how we are going to do it. Our overall approach is to combine computational methods with experimental methods and eventually feed everything into a neural network. This is a new approach to cold air curtain research, to the best of our knowledge we are the first to do this," he said.

Cold air curtain open refrigerated display cases, commonly found in grocery stores around the world, are popular because they keep food cool and make it easy for consumers to see the products and comparison shop. Mostly used for dairy and meat products, these display cases use a lot of energy trying to keep food cool in an environment constantly infiltrated with warmer air. It is known that 70 to 80 percent of the cooling load is caused by the infiltration of warm air.

The POCAC was created in modules to allow the research team to change up to 18 variables to affect infiltration and map the flow of the air curtain. "We can move the modules and change the configuration," said Navaz, "we can change the offset angle of the opening, move either the discharge vent or the return vent or change distances between components." The machine is built in layers so researchers can change the geometry and test all the variables.

The infiltration rate will be directly measured by using a tracer gas and the level of mixing and turbulence will be measured by a Digital Particle Image Velocimetry (DPIV) technique that will also be used to calibrate the computational model.

The ultimate goal is to minimize the infiltration of the outside air into the return. The basic design of cold air curtain refrigeration involves a fan that sucks the air in, passes it through a cooling system and then releasing or blowing cold air out of the discharge areas.

The cold air coming down gets mixed up with the warmer outside air, the amount of outside air that gets into the return duct is called infiltration. "We want to minimize that," Navaz said, "because the more outside air that gets in the return duct, the more cooling load you have, and the harder it has to work the more energy it uses."

The past year has been spent designing and building the POCAC. Working with Navaz were Dr. Dana Dabiri, assistant professor in the College of Aerospace Engineering at the University of Washington, Mazyar Amin, a Ph.D. candidate from the University of Washington who designed the POCAC, and Claude Pilger, a Kettering undergraduate student in Mechanical Engineering who worked with Amin to assemble it.

The project is being done in conjunction with the University of Washington at Seattle, with funding from the California Energy Commission and the U.S. Department of Energy. The Southern California Edison is the prime contractor that will perform independent testing of a prototype based on the specs provided by Kettering team.

The 3,000 tests will begin in July. "We are performing computational fluid dynamic analysis right now," Navaz said, "We will have the stats by next December and then we'll give those stats to Hill Phoenix to fabricate a prototype for us based on those stats," he said. Hill Phoenix is a manufacturer of cold air curtain display cases

"We are giving industry a tool to find out what their rate of infiltration is and predict the performance of their product," said Navaz. "The end product is going to be a software manufacturers will use to design refrigerated units," he said.

"This program is getting worldwide exposure," Navaz said, "everybody is looking at it. It is a big issue and nobody has solved this problem. The last time we made a presentation, people came from all over the world to see what the outcome of our research would be. The impact is just huge," he added.

"It's been a lot of work to get to this point. I've been working on this project since 1998," said Navaz. "It took a while to gradually understand the problem so we could come up with a plan to tackle it."

Written by Dawn Hibbard