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
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?
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,
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.
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.
On Saturday, July 26, 2014 9:46:03 AM UTC-4, Ed Pawlowski wrote:
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
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.
On Friday, July 25, 2014 4:44:02 PM UTC-4, J Burns wrote:
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.
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