Open-front refrigerated display cases, which make up roughly 60 percent of the refrigerated cases in grocery stores, provide quick access to chilled products – but they’re hardly energy-efficient. Engineers at the University of Washington and Kettering University are working to cut the amount of energy used by these coolers, while enhancing product safety and quality. They found that tweaking the physics can reduce the energy used for refrigeration by as much as 15 percent.
Researchers built a modular mock display case and an air curtain simulator to test various designs. They measured how much air was infiltrated for various air curtain speeds, angles, and other factors to minimize the amount of warm, moist air entering the chilled compartment of the case. Results show that the most important factors that affect the amount of warm air penetrating the air curtain are the angle between the case’s discharge and return air grilles, and the jet’s exit Reynolds number (a figure that depends on the air speed and density), and the jet’s turbulence intensity.
Combining experimental results and mathematical models, the team developed a tool that lets manufacturers optimize their particular design. Researchers collaborated with a leading display-case manufacturer to retrofit a proof-of-concept case. Tests showed the retrofit was a cost-effective way to get a 10 percent reduction in infiltration of warm air. (Calculations for other display designs show potential savings of up to 15 percent.)