Refrigerator and power used, full or empty?

Question

Everyone claims that a full refrigerator uses more power than an empty one. I never understood that, to me it should be the same. My reasoning follows, please point out any holes in my logic.

Consider two identical fridges, one almost full of various shaped food containers, and one empty. Let them sit for a few hours.

First take equilibrium. Everything inside is at the set temperature. The only losses are due to heat flow through the insulation. The two should have equal loses, so the energy input is equal.

Now open the door of each for a minute then close it. Almost all of the heat loss is due to cold air falling out and replaced by warm air. The full fridge has less air, so it losses less heat.

Now add a room temp container to each. Each fridge has to remove the same amount of energy from the container, so equal energy use.

So overall, the full fridge uses about the same, or a little less power as does the empty one, once the food has been cooled to the operating temperature.

Answer 1

I agree with your logic.  I have heard in the past that the full ones actually use less electricity than empty ones because all the stuff that's inside helps to keep the cool temperature more constant (kind of like throwing cold drinks into a cooler, the drinks themselves help to insulate each of the other drinks).

Answer 2

I think it would use more power to reach the set temperature than the empty fridge,but,as you say,it would reach room temperature more slowly once the door is opened.

Answer 3

Your logic is pretty much right and a full refridgerator uses less energy but there is one extra very important piece to the puzzle. I think you know it but didn't exactly mention it. When you open the door (more so on a vertical standing fridge or freezer) warm air rushes in to replace the cold air that left it. Getting rid of that warm air is where a lot of energy is used but there is less of it if the fridge is full.

So if your fridge is full and you have a power outage, keep the door shut. But if your fridge only has one rack of spare ribs and a 6 pack of beer in it you might as well take them out and light up the charcoal grill :)