Want to build a better refrigerator? Put an icemaker in the refrigerator compartment. That's part of the idea behind a cooling system developed at Notre Dame that promises to make refrigerators that are cheaper to operate and last longer.
The system is the result of three years of research by Kwang-Tzu Yang, the Viola D. Hank Professor of Aerospace and Mechanical Engineering, and doctoral candidate Mithal Pankaj. They've received financial support from the world's largest manufacturer of refrigerators, Whirlpool Corporation, based in nearby Benton Harbor, Michigan.
The Notre Dame refrigerator capitalizes on cooling technology already being used to reduce the cost of air conditioning in large buildings. Instead of running air conditioners during the day, these buildings freeze huge quantities of ice at night then use it the next day to supply chilled water for cooling offices.
The ice system saves money partly because utilities offer cut-rate electricity to customers who are willing to shift demand to off-hours. Since a power company always needs enough capacity for the moment of peak power pull, it looks for ways to level demand -- such as offering rate incentives -- in hopes of forestalling the day it will have to build more power plants.
Yang says 15 percent of all electricity consumed in the United States is used to power refrigerators. Which is why federal authorities have ordered appliance manufacturers to develop more energy-efficient models and why a consortium of power companies has offered $30 million to the first appliance company to produce a model that cuts power consumption in half.
The ND design could cut power consumption and greatly extend the life of the compressor -- the part of a refrigerator that typically wears out first.
In a conventional refrigerator, the compressor circulates freon through a coil in the back of the freezer. A fan circulates air over the chilled coils and blows cold air down through a slit into the refrigerator compartment. Unfortunately, the slit also allows moisture from refrigerated food to rise into the freezer. There it turns to frost, which must be melted off with a heating wire. The melted frost drips into a pan under the refrigerator and evaporates into the kitchen air.
The Notre Dame design employs two smaller cooling coils. One cools the freezer conventionally. The other freezes a mixture of ice and propylene glycol (like antifreeze but not toxic) between sheets of aluminum. Keeping the ice sheet frozen to cool the space inside the refrigerator uses much less electricity than the conventional dual-compartment coil in the freezer, Yang says. Plus, because no air is exchanged between the refrigerator and freezer, no defrosting is necessary.
The system offers the additional benefits of using a smaller-capacity compressor and requires fewer compressor starts and stops, which should greatly extend compressor life, he says.
Whether this type of refrigerator ever finds its way into appliance stores is up to manufacturers like Whirlpool. But the industry is ripe for serious change. Current technology, Yang says, has long since passed the age when tweaking it can be expected to yield significant gains in energy efficiency.