Does it cost more to refrigerate a (relatively) empty refrigerator than a full one?
The reason I ask is because I was always taught that a full, stocked refrigerator uses less electricity than a relatively empty one. And now I’m trying to get my wife to load the refrigerator up with our sodas and stuff, instead of letting them sit under the kitchen sink. She seems to think that it makes no difference. What do you guys think?
Probably doesn’t make much difference. But I guess there could be second-order effects predicting a full refrigerator would be more efficient than an empty one. For example, a full refrigerator may present an obstacle to convection currents, which (I believe) would help reduce heat flowing into the refrigerator.
From what I’ve read the mass of the objects inside the fridge helps to store cold, so that the refridgerator isn’t always running to cool the air down inside the unit. I noticed that when I first moved into this place the 'fridge ran a lot more until I started putting food into it.
Yes.
If you fill a frig (including the freezer) and allow it to cool down everything inside before opening the frig, from that point on the efficiency will go up.
Why?
In effect, the “cold” will also be stored in each item. Your frig will really only be cooling down the air from every time you open it.
It might be related to the difference between cooling a box of air to x temp and cooling a box of water (ie food) to x temp. The water (in cooled liquid or frozen state) will be far more efficient at staying cool than air even though it is much more massive and would take longer to cool down initially.
As long as it remains closed there isn’t a lot of diference, but when the door is opened the cold air, being heavier, spills out. With the fridge full there is less air exchange and thus less energy needed to cool the new, warm air.
A slight hijack but I have found that KitchenAid refrigerators are designed to operate with a decent amount of food in them. I have had several clients call me the day after we install a KA fridge to tell me their water line wasn’t hooked up correctly. What really happened is that although they had the temp set to 35-37, without the thermal mass of the food, the temp slipped below 32 degrees. freezing the water line.
I haven’t heard of this with too many other fridges though, maybe their water lines are better insulated.
Another vote here for “no difference”.
Best avoid the word “efficiency” in this context also.
Once you have a steady-state situation with the door closed, it should take exactly the same amount of energy to keep a fridge full of sodas cool as a fridge full of air. The effect of any thermal mass inside is nil.
The heat you have to take out of the fridge compartment to keep it at a certain temperature is equal to the heat transferred in through the insulated walls from the environment. This will depend on the temperature difference between inside and outside, and not on whether the fridge has a lot of soda in it.
If anything, soda cans in direct contact with the fridge wall would enhance heat transfer (it is easier to transfer heat from a liquid than a gas), and you would have to use more power to keep the compartment cold.
Even if you do open the door, the amount of energy needed to cool a fridge-full of air is very small - air has a very low heat capacity.
One would think that you tend to look inside a full refrigerator more often, thus consuming more energy.
Virtually every source in a quick google search says that a full refrigerator is more efficient than an empty one.This site says what someone else here has already said: that food and water stored allows the frige to recover more quickly after the door has been opened.
I agree. I think these “thermal mass” arguments are nonsense. Sure, when you close the door the air temperature will recover quicker w/ a full refrigerator, but now the food (i.e. the “mass”) is at a higher temperature. What’s going to cool the mass?
But as mentioned in my first post, a full refrigerator would minimize convection currents, which (I believe) would help reduce heat flowing into the refrigerator…
Do a Google for – refrigerator effeciency full empty
You’ll get about 7k hits… Every damned one of them I’ve looked at so far (about 15) says a full regrigerator is more efficient. In fact, several reccommend something I never thought of - if your refrigerator is mostly empty, load in containers of water to fill up the volume.
Remember, even though the air that’s exchanged by opening the door is easier to cool than most solids or liquids, it IS around 40 degrees warmer than cooled air in the frige. Any way you cut it, that’s a lot of cooling to do.
It depends on the starting point and the time duration you measure over, but my estimates are a mostly empty fridge will end up requiring more energy (depending on the number of openings/day) after about 10 days.
No, I’m not going to put my math here. I did that for the thermostat thread, and not only did no one give a shit, but the same motherfucking question got asked the very next week, thus nullifying any effort on my part to fight ignorance, since many cannot figure out that tricky “Search” function.
I agree a full refrigerator will consume less energy, all else being equal. I’m just trying to figure out why.
I can think of two reasons:
A full refrigerator provides obstacles to convection current.
An empty refrigerator has a relatively short thermal time constant. This means the refrigerator will kick on more often; however, each time it kicks on it will run for a short amount of time. By contrast, a full refrigerator has a relatively long thermal time constant. This means the refrigerator will kick on less often; however, each time it kicks on it will run for a longer amount of time. Theoretically, the power used in either case should be the same. (At least I think this is true.) However, it is more efficient for a compressor to run for longer periods of time (and kick on less often) than for a compressor to run for shorter periods of time (and kick on more often). This is due to the energy vs. temperature characteristics of the compressor.
Thermal mass isn’t BS, keep in mind that the specific heat of a material dictates how much heat energy can be stored. The base is water, with a specific heat of 1. Of coure, if you don’t open the door, it doesn’t make a difference - the amount of heat that conducts through the outside insulation is the same whether the fridge is empty or full. But the air inside only has a specific heat of 0.2, so the stuff inside the fridge won’t warm up too much in cooling down the air after you close the door. Also, know that most fridges don’t have a “cold mechanism” (evaporator) in the fridge, it’s in the freezer only. All the cold air in the fridge comes from the freezer, usually drifting down in convective air currents through adjustable vents. (When you turn the 2 knobs inside the fridge, only one is an actual thermostat, the other just moves the vent)
Among my vast collection of professions, I was an appliance repair person for a while, and I got to see a lot of fridges. The problem I saw most, at least as far as things freezing or not getting cold enough, was blockage of airflow in the fridge. There has to be space around the food for the air to circulate. If you take care of your fridge by cleaning the condenser, it can last a LONG time without major work…maybe even 100 years.
Most residential refridgerators are very inefficient. You can get vastly better ones from suppliers of solar & wind equipment. (Sun Frost is one manufacturer…interestingly enough, AFAIK none of the really efficient models have the “Energy Star” rating…odd, that) I’ve seen homemade, sunken thermal mass fridges that use almost no power at all…but you can’t put one of those in your kitchen, unless the house is designed for it.
A full refrigerator is more efficient because less air exchange takes place when you open the door.If you never open the door there’s no difference.
After doing a little looking around, I found this link:
http://www.windsun.com/Misc_AE/Sunfrost.htm
It appears the info I had was a bit outdated & inaccurate, Sun Frost’s claims were exaggerated.
“A full refrigerator is more efficient because less air exchange takes place when you open the door.If you never open the door there’s no difference.”
Exactly.