Energy efficiency

An auto-defrost unit uses a blower fan to keep moisture out of the unit. It also has a heating coil beneath the evaporator that periodically heats the freezer compartment and melts any ice buildup. Some units also have heaters in the side of the door to keep the unit from "weeping." Manual defrost units are available in used-appliance shops or by special order.
Refrigerators used to consume more energy than any other home appliance, but in the last twenty years great strides have been made to make refrigerators more energy efficient. In the early 1990s a competition was held among the major manufacturers to encourage energy efficiency. Current models that are Energy Star qualified use 50 percent less energy than models made before 1993.[11] The most energy-efficient unit made in the US is designed to run on 120 or 110 volts, and consumes about half a kilowatt-hour per day.[12] But even ordinary units are quite efficient; some smaller units use less than 0.5 kilowatt-hour per day. Larger units, especially those with large freezers and icemakers, may use as much as 4 kWh per day.
Among the different styles of refrigerators, top-freezer models are more efficient than bottom-freezer models of the same capacity, which are in turn more efficient than side-freezer models. Models with through-the-door ice units are less efficient than those without.[13] Dr. Tom Chalko in Australia has developed an external thermostat to convert any chest freezer into a chest fridge using only about 0.1kWh per day—the amount of energy used by a 100 watt light bulb in one hour.[14] A similar device is manufactured by Johnson Controls.[15] Scientists at Oxford University have reconstructed a refrigerator invented in 1930 by Albert Einstein in their efforts to replace current technologies with energy efficient green technology. The Einstein refrigerator operates without electricity and uses no moving parts or greenhouse gases.[16]