Many people have tried to tell me that if you keep a second fridge running you should always have a couple cases of soda or beer in it because an empty refrigerator will run much more often than a full one.
I say this is nonsense.
Air, being less dense than any type of foodstuffs, will conduct heat slower. So a fridge full of air will stay cold longer that a fridge full of food.
I for one welcome our new insect overlords… - K. Brockman
the difference would be so small as to be negligible but since we are in search of pure knowledge we can theorize…
every time you open the door all the cold air rushes out and is replaced by warm air so, a full refrigerator would lose less heat. This is the reason for chest freezers and chest refrigerators.
but what if you do not open the door at all? In that case an empty refrigerater would have a substantial convection that would favor heat gain… my guess is that a full refrigerator with the stuff positioned so as to impede air flow would be best (but also the stuff would not be cooled as well)
that’s my guess
This was actually discussed here a while ago.
Full fridge use more electricity than an empty one?
Gypsy: Tom, I don’t get you.
Tom Servo: Nobody does. I’m the wind, baby.
I heard that about dryers too. A full load does better than a half load but I noticed in practice this is not so.
Alpha’s link starts off with the asumption that the 2 refrigerators have reached their operating temps. That’s important because it is gonna take more energy to cool a box full of beer than an empty one. But once all that beer is cold,every can is gonna act as a "cold storage " battery. ( yeh yeh I know there is no such thing as ‘cold’) Air is a terrible storage place. It is just gonna take longer for the ‘battery’ t6o warm up than the air even if all the cold air didn’t flow out the bottom every time you opened it.The solar heaters I build use fist sized irregular rocks as a battery,in dry cool night summer climates they can be used as coolers.There is also some blackbody radiation involved. Blow cool air thru it at night and the rocks absorb heat during the day.The same volume of air would cool off faster at night but wouldn’t “store enuff cold” to last an hour.) The fan helps move cool air and helps speed up the cooling. Has a minor effect on KEEPING it cool.If you are short term storing a reefer it is best to keep it running just to combat the stale air smell buid up. Turn it to its lowest temp, put milk jugs of water in the freezer, ( open until it freezes) Some boxes of soda and charcoal briquettes in the freezer.( doesn’t have to be “activated” charcoal,that is basically just charcoal that has been dried out. You can reactvate charcoal by putting it in an oven for a while.)Put stuff in the reefer, cans of beer is good, a case or two on each shelf,or just some bricks ( masons bricks!though some do store reefer in the icebox)more soda and charcoal, just a bag of charcoal with the top open. don’t worry about blocking air flow you cant really, just don’t cover the inlet and outlet. If you are storing one for a longer period of time ( at the cabin, say) empty and clean it good, wash it with a soda solution.Put soda and charcoal in it .Be sure and clean the drip pan underneath. Prop the doors open . SECURLY open. you don’t wanta come back and find a racoon has climbed in there and expired. Now there is a smell that Armand Hammer hiself couldn’t get rid of.Oh yeh there is beer stored in that refer in temp storage. We had an old 1950’s Leonard down at the shop, the thick walled, round cornered kind with the little ice making box at the top inside. It was mostly longer term storage for beer, we wedged a piece of Formica across the front opening at the bottom ,came about halfway up, just to keep the air from dumping out. We opened it maybe once a week, if enough time went by the stuff at the bottom was frozen solid!
“Pardon me while I have a strange interlude.”-Marx
Ok, I read the replies and the other thread and I still think everyone’s missing something.
Refrigerators are (reasonably) airtight so the inside would heat up thru conduction, not convection. That is, heat transfer thru solid matter not thru the air.
So once both fridges stopped running (and assuming the door is not opened) the rate at which they would heat up would be determined by the heat conductivity (i.e. density) of the material inside. And since air is a good insulator a fridge full of air would cause slower heat transfer that one filled with solid material.
Or am I missing something?
I for one welcome our new insect overlords… - K. Brockman
What you are all missing is a lesson in thermodynamics. Air has a low heat capacity. It will not hold the temperature of the refrigerator. This means that it will take more energy to heat the “soda” one degree celcius (or farrenheit)
Assuming you were to never open the door to the refrigerator and unplug it. The full refrigerator will hold it’s temperature longer because more outside heat would be required to heat the “soda”.
It will take longer for a full refrigerator to reach it’s equalibrium temperature for the very same reason. The “soda” stores more heat.
Interestingly, none of these facts will change the rate at which energy flows from the outside into your refrigorator. So as long as you keep the refrigerator door closed, the same amount of energy will be required to maintain the internal temperature of the refrigerator full or empty.
In fact, unless the item filling the refrigerator takes up considerable volume, the same amount of air (and therefore the same amount of energy) will enter the refrigerator when you open the door.
So do whatever you like. It makes no difference.
You could put a voltage meter on it & run it full & empty & see what the reading is.
A voltage meter wont read anything except 120V since that is what what runs through the house. What you would nead to measure is the energy or watt-hours your refrigerator used over the course of a week.
Or you could just measure the amount of time that the refrigerator pump were on with a stop watch. Since the pump is either off or on there is no need to measure anything else.
Oh that would be like watching grass grow.
More fun is to make sure your frig is operating at 40 deg.
You folks are all getting distracted from the most important thing by silly stuff like thermodynamics. What I want to know is, where do you have room in your kitchen for a second fridge? Or are you going to put it in the basement? And if I had room in MY k. for a 2nd f., I sure wouldn’t waste it on beer. It would be for MY stuff, plus all the interesting leftovers. Dibs on the pumpkin pie. This is my yogurt, that is your yogurt. Etc.
Okay. Now the thing that everyone is forgetting is not only basic thermodynamics, but also the sources of energy. Okay first the sources of energy for this problem. We have already assumed the actual heating unit for the refridgerator. There is also the heat transfer through the insulation material of the fridge. There are two types of radiation energy. The first everyone is familiar with: radiation for the sun and other sources. The second is a bit different and has slightly been addressed: radiation from the biological and non-biological materials within the fridge. Heats of radiation are negligble for non-biological materials (actually about 100 to 10000 fold difference in magnitude) and therefor are excluded from further consideration. Now onto basic thermo. Heat transfer occurs due to the differnece in the temperature between the two systems. This is also called the temperature gradient. For energy considerations there are a few things that may be assumed. The two fridges have the same materials and dimensions. This eliminates the heat transfer from the outside (ignoring for now the radiation from the sun) as being a possible difference. Likewise for the radiation, assuming that they have similar dimensions, the air with in the fridge will be heated the same. The difference here is that the fridge with the food in it will act as a better “blocker” for the radiation, thus absorbing more energy and consequently heating the food in addition to the normal radiation from biological materials. Now. Assuming that 1)the door remains closed and 2) that the system has reached steady state: the following holds true.
A)The difference in heat transfer from the outside is only due to the radiation. As stated earlier, the fridge with the food will retain more radiative energy.
B)The source of heat from within the fridge is once again radiation this time from the biological matter.
C)Within the fridges themselves, the air may be considered a fluid. Thus means that convection is the primary heat transfer agent. While this does nothing for this problem, I wanted to state that convection is the dominant heat transfer devie in this problem.
D)The volume (or mass) of air is negligible is comparison to the mass otherwise within the fridge. In 22.4 Liters there is only 1 mole of air. This is roughly 28 grams. Compared to the weight of even one soda (o say about 355 grams) this is negligible.
E)The total heating difference shows that the full fridge has a larger heat source for heating the fridge.
Assuming the same temperature for both fridges, there is more energy in the full fridge that must be replaced. The increase in this heat removal causes a “proportional” increase in work required.
Thus the full fridge draws more power.
An engineer that has a thesis due in a day and there for must procrastinate until then.
Peter
Oh yes and I know that there will be someone confused by the use of the word heater for the fridge. It depends only upon the reference point, and as I was taught why use two different words for the same unit? Oh yes and Sailor is right in that all of this would be negligible assuming steady state. The significant difference is in unsteady state. However everything above still is applicable assuming that the food is already at steady state and the door is not left opn for very long (only long enough for the air to be replaced otherwise there are a whole lotta variables that have to be considered). The difference here is that there is a greater amount of convection in the full fridge, thus cooling the air faster.