stuffing a refrigerator

[J Burns]

I keep reading that you should use things like water bottles and crumpled newspapers to take up space so less air flows in when you open a refrigerator door.

I calculate that if you changed the air in an empty 17cu ft refrigerator for air at 75 F with a dew point of 65 F, cooling it to 35 F with a dew point of 0 F would mean moving 15 joules, or 1 watt for 15 seconds,or

1/240,000 kwh.

There doesn't seem to be any point in using filler to reduce an occasional air change. How about thermal mass? Water bottles could reduce cycle times by increasing thermal mass. A compressor draws more watts early in the cycle, but don't you get that back when the compressor turns off?

Can filling a refrigerator really save energy?

[gfretwell]

I am not sure about saving energy but packing it with bottled water will hold it longer in a power failure. That is a common thing to do in hurricane country. .The bottled water will come in handy too,

[Zaky Waky]

J Burns wrote in news:lqufij$chu$ [e-mail]:

Check your calcs. They're wrong.

[Frank]

Doubt it. The heat capacity of anything you put in is bound to be greater than air. I think water has over 1,000 times the heat capacity of air. That means putting things in and cooling them down will probably use more energy than that gained by the air volume loss.

OTOH, things that you normally cool down before using like bottled water might best be stored in the refrigerator to take advantage of maintaining cooling during a power failure.

[trader_4]

The concept is that you only have to cool the water once. The air you have to cool every time you open the door and the cold air pours out and room temp air goes in.

[Ed Pawlowski]

You have a valid point about stuffing for the sake of stuffing, but if you have a case of juice or beer, better to put it in to fill the space rather than put a bottle at a time. You'll be using the same amount of energy to get it down to temperature anyway, but get less air loss each time the door is opened.

[trader_4]

Even if it's not something that you need to cool anyway, once it's cooled it can stay cooled for years. The air that would be there instead can get changed out for warm air every time the door is open. Not that I think it's worth worrying about. My fridge uses less than $100 a year in electricity. I can't imagine this fussing around saving more than a couple bucks a year, it's just not worth it. And who has free space in their fridge to begin with? I don't have to add anything, it's already full.

[J Burns]

I was seeing if you were awake. Why don't you tell the class the correct answer?

[Frank]

I've used this excuse when the wife asks me, "Why is there so much beer in the refrigerator?"

[gfretwell]

That is better than her asking "where did all that beer go"?

[nestork]

Well, I think it's true that the more cold air that spills out of an open refrigerator, the more warm air comes in to replace it, and you pay to cool that warm air.

But, even though I haven't read every post in this thread, something I haven't seen mentioned is the word "momentum" and any reference to the driving force that would cause that air to gain momentum and spill out of the fridge.

Air is actually a lot heavier and denser than most of us realize. It's only because our bodies are also pressurized to the same pressure that surrounds us that we don't feel the force of the air pressure acting on us. In fact, for most of recorded history, people believe air didn't weigh anything at all. In fact, it's both the mass of the air and the tiny density difference between warm air and cold air that determines the rate at which cold air would spill out of a fridge. The calculation at the beginning of this thread presume ALL of the cold air spills out to be replaced by warm air each time the fridge door is opened and I don't believe that to be true. In order for air to spill out of an open fridge, it has to move, and it takes time for that to happen given the small difference in density which is the only thing causing the cold air to gain momentum.

That is, cold air isn't going to pour out of a fridge like cold water would. The small difference in density is going to result in the cold air spilling out much more slowly than cold water would (for example). I suspect the difference would be similar to what would happen if you had a fridge full of cold water submerged in a warm swimming pool. Opening the door would result in some cold water spilling out, but nowhere near as much as would spill out if that fridge weren't submerged in warm water. The important difference being the fact that the driving force imparting momentum to the cold water is very much reduced.

[Pavel314]

When I managed an apartment building, one of my elderly tenants complained that her refrigerator wasn't keeping things cold enough although it was goi ng on frequently. I called the repairman and went to inspect the refrigerat or with him. He opened her refrigerator and, seeing only a quart of milk an d a stick of butter, said that the problem was that she didn't have enough in it to keep the interior cold. He suggested that she keep a gallon of wat er in there, which solved the problem. Sort of like a thermal flywheel.

[jimmyDahGeek]

You should always keep the beer in the fridge. It's better cold and you never know when you might want another cold one.

;)