Take two identical refrigerators, fill one with food and leave the other empty. (Make sure you properly leave an air gap around the food for proper ventilation.) Once they both cool their contents to the set temperature, they will both use the same amount of energy if you keep the doors closed. The only energy used by either will be to compensate for the heat energy transferred from the outside to the inside through the insulated enclosure. Since both refrigerators should be identical, the heat transfer rate should be the same.
If you open them equally (Let’s say 10 seconds every half hour.), the empty refrigerator will lose all of the cold air (the full volume of the refrigerator) as it flows out the bottom of the door opening and is replaced with room temperature air that flows in. The full refrigerator, on the other hand, will only lose the air that is surrounding the food. Once the doors are closed, the refrigerators have to cool the new, warmer air down to the set temperature. It will take more energy to cool the greater amount of air in the empty refrigerator than it will to cool the air in the full refrigerator.
A fuller refrigerator uses less electricity.
