I have heard that it is better to leave your fridge open while, say, pouring a glass of juice or some other short task, rather than opening it, getting out the juice, closing it, pouring the juice, and then opening it back again to put the juice away. The reason I was told was that the suction created by opening the door pulls more cold air out than would flow out if it just sat open.
It makes sense, but then… air moves around pretty easily and it seems like it wouldn’t take being open very long at all before you would have lost that much air and more.
So which is more efficient? (I have also heard that storing your empty tupperware, sealed, in the fridge saves energy, because it traps the cold air in…
I’m suspicious of anyone who claims they can actually find a real-life effect in something this small compared to the number of times and length of time a real-life refrigerator is opened over the course of, say, a month.
Air is an insulator, one of the best. Having to cool air requires energy, more so than cooling a solid object once and keeping it cold. So the less volume of air to be cooled, the better. I’m not sure whether this effect is meaningful in a refrigerator, though. I’ve always heard it applied to a freezer compartment. The idea is to fill your freezer as much as possible with items you want to keep cold, rather than having one or two small items and a lot of empty space.